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Sample records for cyclic compressive loading

  1. Cyclic Compressive Loading Facilitates Recovery after Eccentric Exercise

    PubMed Central

    BUTTERFIELD, TIMOTHY A.; ZHAO, YI; AGARWAL, SUDHA; HAQ, FURQAN; BEST, THOMAS M.

    2016-01-01

    Purpose To assess the biologic basis of massage therapies, we developed an experimental approach to mimic Swedish massage and evaluate this approach on recovery from eccentric exercise-induced muscle damage using a well-controlled animal model. Methods Tibialis anterior muscles of six New Zealand White rabbits were subjected to one bout of damaging, eccentric contractions. One muscle was immediately subjected to cyclic compressive loads, and the contralateral served as the exercised control. Results We found that commencing 30 min of cyclic compressive loading to the muscle, immediately after a bout of eccentric exercise, facilitated recovery of function and attenuated leukocyte infiltration. In addition, fiber necrosis and wet weight of the tissue were also reduced by compressive loading. Conclusion We conclude that subjecting muscle to compressive loads immediately after exercise leads to an enhanced recovery of muscle function and attenuation of the damaging effects of inflammation in the rabbit model. Although these observations suggest that skeletal muscle responds to cyclic compressive forces similar to those generated by clinical approaches, such as therapeutic massage, further research is needed to assess the translational efficacy of these findings. PMID:18580410

  2. Investigation of Cyclic Deformation and Fatigue of Polycrystalline Cu under Pure Compression Cyclic Loading Conditions

    NASA Astrophysics Data System (ADS)

    Hsu, Tzu-Yin Jean

    It is commonly accepted that fatigue crack is initiated under tensile fatigue stresses. However, practical examples demonstrate that cracks may also initiate under pure compressive fluctuating loads such as the failures observed in aircraft landing gear frames. However, the mechanism of such failures is rarely investigated. Furthermore, knowledge on cyclic deformation response under pure compressive fatigue condition is also very limited or non-existent. Our recent work already verified that fatigue cracks may nucleate from stress concentration sites under pure compression fatigue, but whether or not a form of stress concentration is always needed to initiate a crack under pure compression fatigue remains uncertain. In this study, compression fatigue tests under different peak stresses were carried out on smooth bars of fully annealed OFHC Copper. The purpose of these tests is to investigate not only the cyclic deformation response but also the possibility of crack nucleation without the stress concentrator. Results showed that overall the cyclic stress-strain response and microstructural evolution of OFHC Copper under pure compression fatigue exhibits rather dissimilar behaviour compared to those under symmetrical fatigue. The specimens hardened rapidly within 10 cycles under pure compression fatigue unlike the gradual cyclic hardening behaviour in symmetrical fatigue with the same peak stress amplitude. Compressive cyclic creep behaviour was also observed under the same testing conditions. Moreover, unlike conventional tension-compression fatigue, only moderate slip activity was detectable on the surface instead of typical PSB features detected from TEM observations. The surface observations has revealed that surface slip bands did not increase in number nor did they become more pronounced in height with increasing number of cycles. In addition, surface roughening by grain boundary extrusion was detected to become more severe as the cycling progressed. Therefore

  3. Investigation of Cyclic Deformation and Fatigue of Polycrystalline Cu under Pure Compression Cyclic Loading Conditions

    NASA Astrophysics Data System (ADS)

    Hsu, Tzu-Yin Jean

    It is commonly accepted that fatigue crack is initiated under tensile fatigue stresses. However, practical examples demonstrate that cracks may initiate under pure compressive fluctuating loads, e.g. the failures observed in aircraft landing gear frames. As the mechanism of such failures is rarely investigated, there is very limited or non-existent knowledge pool on cyclic deformation response under pure compressive fatigue condition. Our recent work verified that fatigue cracks may nucleate from stress concentration sites under pure compression fatigue, but whether or not a form of stress concentration is always needed to initiate a crack remains uncertain. In this study, compression fatigue tests under different peak stresses were carried out on smooth bars of fully annealed OFHC Copper. The purpose of these tests is to investigate not only the cyclic deformation response but also the possibility of crack nucleation without the stress concentrator. Results showed that overall the cyclic stress-strain response and microstructural evolution of OFHC Copper under pure compression fatigue exhibits rather dissimilar behaviour compared to those under symmetrical fatigue. The specimens hardened rapidly within 10 cycles under pure compression fatigue unlike the gradual cyclic hardening behaviour in symmetrical fatigue with the same peak stress amplitude. Compressive cyclic creep behaviour was also observed. Moreover, TEM observation showed that only moderate slip activity was detectable on the surface instead of typical PSB features. The surface observations revealed that surface slip bands did not increase in number nor height as cycling progressed. In addition, surface roughening by grain boundary extrusion was detected to become more severe with further cycling. Therefore, the plastic strain accommodated within the samples was not mainly related to dislocation activities. Instead, the mechanism of cyclic creep response for pure compression fatigue was correlated and

  4. The impact of posture and prolonged cyclic compressive loading on vertebral joint mechanics.

    PubMed

    Gooyers, Chad E; McMillan, Robert D; Howarth, Samuel J; Callaghan, Jack P

    2012-08-01

    An in vitro biomechanics investigation exposing porcine functional spinal units (FSUs) to submaximal cyclic or static compressive forces while in a flexed, neutral, or extended posture. To investigate the combined effect of cyclically applied compressive force (e.g., vibration) and postural deviation on intervertebral joint mechanics. Independently, prolonged vibration exposure and non-neutral postures are known risk factors for development of low back pain and injury. However, there is limited basic scientific evidence to explain how the risk of low back injury from vibration exposure is modified by other mechanical factors. This work examined the influence of static postural deviation on vertebral joint height loss and compressive stiffness under cyclically applied compressive force. Forty-eight FSUs, consisting of 2 adjacent vertebrae, ligaments, and the intervening intervertebral disc were included in the study. Each specimen was randomized to 1 of 3 experimental posture conditions (neutral, flexed, or extended) and assigned to 1 of 2 loading protocols, consisting of (1) cyclic (1500 ± 1200 N applied at 5 Hz using a sinusoidal waveform, resulting in 0.2 g rms acceleration) or (2) 1500 N of static compressive force. RESULTS.: As expected, FSU height loss followed a typical first-order response in both the static and cyclic loading protocols, with the majority (~50%) of the loss occurring in the first 20 minutes of testing. A significant interaction between posture and loading protocol (P < 0.001) was noted in the magnitude of FSU height loss. Subsequent analysis of simple effects revealed significant differences between cyclic and static loading protocols in both a neutral (P = 0.016) and a flexed posture (P < 0.0001). No significant differences (P = 0.320) were noted between pre/postmeasurements of FSU compressive stiffness. Posture is an important mechanical factor to consider when assessing the risk of injury from cyclic loading to the lumbar spine.

  5. Analysis of the mechanical behavior of chondrocytes in unconfined compression tests for cyclic loading.

    PubMed

    Wu, John Z; Herzog, Walter

    2006-01-01

    Experimental evidence indicates that the biosynthetic activity of chondrocytes is associated with the mechanical environment. For example, excessive, repetitive loading has been found to induce cell death, morphological and cellular damage, as seen in degenerative joint disease, while cyclic, physiological-like loading has been found to trigger a partial recovery of morphological and ultrastructural aspects in osteoarthritic human articular chondrocytes. Mechanical stimuli are believed to influence the biosynthetic activity via the deformation of cells. However, the in situ deformation of chondrocytes for cyclic loading conditions has not been investigated experimentally or theoretically. The purpose of the present study was to simulate the mechanical response of chondrocytes to cyclic loading in unconfined compression tests using a finite element model. The material properties of chondrocytes and extracellular matrix were considered to be biphasic. The time-histories of the shape and volume variations of chondrocytes at three locations (i.e., surface, center, and bottom) within the cartilage were predicted for static and cyclic loading conditions at two frequencies (0.02 and 0.1 Hz) and two amplitudes (0.1 and 0.2 MPa). Our results show that cells at different depths within the cartilage deform differently during cyclic loading, and that the depth dependence of cell deformation is influenced by the amplitude of the cyclic loading. Cell deformations under cyclic loading of 0.02 Hz were found to be similar to those at 0.1 Hz. We conclude from the simulation results that, in homogeneous cartilage layers, cell deformations are location-dependent, and further are affected by load magnitude. In physiological conditions, the mechanical environment of cells are even more complex due to the anisotropy, depth-dependent inhomogeneity, and tension-compression non-linearity of the cartilage matrix. Therefore, it is feasible to speculate that biosynthetic responses of

  6. Compressive residual stress relaxation in hardened steel during cyclic and static load

    NASA Astrophysics Data System (ADS)

    Cseh, D.; Mertinger, V.

    2017-05-01

    The benefits of applied compressive residual stress on fatigue properties of materials is a well-known phenomenon, but not well described in all respects. The fatigue life and the fatigue limit could be improved by targeted created compressive residual stress in the surface layers therefore, diversified surface compressing methods are developed and used in the engineering industry. The relaxation of the compressive residual stress state during a cyclic and static load is determinative for the life time of a componenet. Compressive stress relaxation was experimentally determined during the cyclic and static load. The compressive residual stress was induced by shot penning on the surface of stainless steel, micro alloyed high strength steel and hardened steel specimens. The residual stress state was investigated nondestructively by X-ray diffraction method then these specimens were load. After a certain number of cycles the fatigue load was stopped and the residual stress state was recorded again and again until fracture. To investigate the relaxation process during static load a four-point bending bench was used. The compressive residual stress relaxation was correlated to the applied fatigue stress level, the cycle number the quality of alloys.

  7. The Effect of Cyclic Loading on the Compressive Strength of Core Build-Up Materials.

    PubMed

    Zankuli, Muayed A; Silikas, Nick; Devlin, Hugh

    2015-01-15

    To evaluate the effect of cyclic loading on compressive strength of core build-up materials. Four dual-cured composites (Core.X Flow, Grandio Core, Bright Flow Core, Spee-Dee) and one light-cured reinforced resin-modified glass ionomer (Fuji II LC) were tested. One hundred cylindrical specimens (4 mm × 6 mm) were prepared. Each material had two groups (ten specimens to be tested under static loading and ten specimens to be tested after cyclic loading). The specimens were stored wet, and after 30 days, one group of each material was cyclically loaded (for 250,000 cycles with a frequency of 1.6 Hz under stress load of 68.6 N) in a chewing simulator CS-4.2. Then specimens were subjected to static compressive loading until failure in a universal testing machine. Mean compressive strength values before cycling ranged from 144 MPa (15.8) for Fuji II LC to 277 MPa (23.2) for Grandio Core. Independent t-test showed no statistically significant difference (p > 0.05) in the compressive strength of each material before and after cycling (p = 0.7 Grandio Core, p = 0.3 Core.X Flow, p = 0.6 Bright Flow Core, p = 0.2 Spee-Dee, p = 0.6 Fuji II LC); however, there was a statistically significant difference between the materials when comparing before and after cycling. All tested materials showed no reduction in the compressive strength after cycling. Therefore, the tested materials can survive 1 year in service without a reduction in compressive strength. © 2015 by the American College of Prosthodontists.

  8. Fatigue response of notched laminates subjected to tension-compression cyclic loads

    NASA Technical Reports Server (NTRS)

    Bakis, C. E.; Stinchcomb, W. W.

    1986-01-01

    The fatigue response of a ((0/45/90/-45)(sub s))(sub 4) T300-5208 graphite-epoxy laminate with a drilled center-hole subjected to various components of tensile and compressive cyclic loads was investigated. Damage evaluation techniques such as stiffness monitoring, penetrant-enhanced X-ray radiography, C-scan, laminate deply and residual strength measurement were used to establish the mechanisms of damage development as well as the effect of such damage on the laminate strength, stiffness and life. Damage modes consisted of transverse matrix cracks, initiating at the hole, in all plies, followed by delamination between plies of different orientation. A characteristic stiffness repsonse during cyclic loading at two load levels was identified and utilized a more reliable indicator of material and residual properties than accumulated cycles. For the load ratios of tension-compression loading, residual tensile strength increased significantly above the virgin strength early in the fatigue life and remained approximately constant to near the end of life. A technique developed for predicting delamination initiation sites along the hole boundary correlated well with experimental evidence.

  9. Retention Strength after Compressive Cyclic Loading of Five Luting Agents Used in Implant-Supported Prostheses

    PubMed Central

    Alvarez-Arenal, Angel; Gonzalez-Gonzalez, Ignacio; deLlanos-Lanchares, Hector; Pinés-Hueso, Javier; Ellakuria-Echebarria, Joseba

    2016-01-01

    The purpose of this study was to evaluate and compare the retention strength of five cement types commonly used in implant-retained fixed partial dentures, before and after compressive cyclic loading. In five solid abutments screwed to 5 implant analogs, 50 metal Cr-Ni alloy copings were cemented with five luting agents: resin-modified glass ionomer (RmGI), resin composite (RC), glass ionomer (GI), resin urethane-based (RUB), and compomer cement (CC). Two tensile tests were conducted with a universal testing machine, one after the first luting of the copings and the other after 100,000 cycles of 100 N loading at 0.72 Hz. The one way ANOVA test was applied for the statistical analysis using the post hoc Tukey test when required. Before and after applying the compressive load, RmGI and RC cement types showed the greatest retention strength. After compressive loading, RUB cement showed the highest percentage loss of retention (64.45%). GI cement recorded the lowest retention strength (50.35 N) and the resin composite cement recorded the highest (352.02 N). The type of cement influences the retention loss. The clinician should give preference to lower retention strength cement (RUB, CC, and GI) if he envisages any complications and a high retention strength one (RmGI, RC) for a specific clinical situation. PMID:27822468

  10. A mathematical model of tissue-engineered cartilage development under cyclic compressive loading.

    PubMed

    Bandeiras, Cátia; Completo, António

    2016-11-05

    In this work a coupled model of solute transport and uptake, cell proliferation, extracellular matrix synthesis and remodeling of mechanical properties accounting for the impact of mechanical loading is presented as an advancement of a previously validated coupled model for free-swelling tissue-engineered cartilage cultures. Tissue-engineering constructs were modeled as biphasic with a linear elastic solid, and relevant intrinsic mechanical stimuli in the constructs were determined by numerical simulation for use as inputs of the coupled model. The mechanical dependent formulations were derived from a calibration and parametrization dataset and validated by comparison of normalized ratios of cell counts, total glycosaminoglycans and collagen after 24-h continuous cyclic unconfined compression from another dataset. The model successfully fit the calibration dataset and predicted the results from the validation dataset with good agreement, with average relative errors up to 3.1 and 4.3 %, respectively. Temporal and spatial patterns determined for other model outputs were consistent with reported studies. The results suggest that the model describes the interaction between the simultaneous factors involved in in vitro tissue-engineered cartilage culture under dynamic loading. This approach could also be attractive for optimization of culture protocols, namely through the application to longer culture times and other types of mechanical stimuli.

  11. Time of flight measurements of unirradiated and irradiated nuclear graphite under cyclic compressive load

    NASA Astrophysics Data System (ADS)

    Bodel, W.; Atkin, C.; Marsden, B. J.

    2017-04-01

    The time-of-flight technique has been used to investigate the stiffness of nuclear graphite with respect to the grade and grain direction. A loading rig was developed to collect time-of-flight measurements during cycled compressive loading up to 80% of the material's compressive strength and subsequent unloading of specimens along the axis of the applied stress. The transmission velocity (related to Young's modulus), decreased with increasing applied stress; and depending on the graphite grade and orientation, the modulus then increased, decreased or remained constant upon unloading. These tests were repeated while observing the microstructure during the load/unload cycles. Initial decreases in transmission velocity with compressive load are attributed to microcrack formation within filler and binder phases. Three distinct types of behaviour occur on unloading, depending on the grade, irradiation, and loading direction. These different behaviours can be explained in terms of the material microstructure observed from the microscopy performed during loading.

  12. Effects of Acoustic Emission and Energy Evolution of Rock Specimens Under the Uniaxial Cyclic Loading and Unloading Compression

    NASA Astrophysics Data System (ADS)

    Meng, Qingbin; Zhang, Mingwei; Han, Lijun; Pu, Hai; Nie, Taoyi

    2016-10-01

    Characteristics of energy accumulation, evolution, and dissipation in uniaxial cyclic loading and unloading compression of 30 sandstone rock specimens under six different loading rates were explored. Stress-strain relations and acoustic emission characteristics of the deformation and failure of rock specimens were analyzed. The densities and rates of stored energy, elastic energy, and dissipated energy under different loading rates were confirmed, and an effective approach for the equivalent energy surface was presented. The energy evolution of rock deformation and failure were revealed. It turns out that the rock deformation behavior under uniaxial cyclic loading and unloading compression remained almost unchanged compared with that of uniaxial compression. The degree of match between reloading stress-strain curves and previous unloading curves was high, thereby demonstrating the memory function of rock masses. The intensity of acoustic emission fluctuated continually during the entire cyclic process. Emissions significantly increased as the stress exceeded the unloading level. The peak of acoustic emission increased with increasing loading stress level. Relationships between energy density and axial load indicate that the rock mass possesses a certain energy storage limitation. The energy evolution of rock masses is closely related to the axial loading stress, rather than to the axial loading rate. With increasing axial loading stress, stored energy varied most rapidly, followed by that of the elastic energy, then dissipated energy. Energy accumulation dominates prior to the axial load reaching peak strength; thereafter, energy dissipation becomes dominant. The input energy causes the irreversible initiation and extension of microcracks in the rock body. Elastic energy release leads to sudden instability of rock bodies and drives rock damage.

  13. Cyclic impulsive compression loading along the radial and tangential wood directions causes localized fatigue

    NASA Astrophysics Data System (ADS)

    Salmi, Ari; Montonen, Risto; Salminen, Lauri I.; Suuronen, Jussi-Petteri; Serimaa, Ritva; Hæggström, Edward

    2012-12-01

    We report for the first time on the existence of a localized reduction in elasticity caused by repeated compression impaction applied along the tangential wood direction. Previous research indicates that localized strain profiles are generated by such cyclic impacting on wood along its radial direction. This finding is significant for the paper/board-making industry where wood is exposed to cyclic unipolar compression during grinding. However, the effect of the impacting direction, with respect to the orientation of the annual rings, on the localization phenomenon is unknown. In addition, the shape of the developing fatigue layer is unclear. We revisit the localization phenomenon with a focus on tangential impacting. We employed ultrasonics and x-ray tomography to quantify the induced fatigue. An interlacing technique increased the precision of the ultrasonic stiffness depth profiling technique. We studied both radial and tangential wood annual ring geometries. We used ultrasound to quantify the drop in shear modulus resulting from impacting. Both radial and tangential geometries featured strain localization, but the shape of the fatigued layer was different in the radial and tangential wood geometries (steeper profile in the radial geometry). The fatiguing reduced the shear modulus. These results tell us about the ratio of the number of hits that need to be delivered along the radial and tangential direction of the ground wood, respectively. This insight may translate into a design pattern for an energy saving grind stone surface.

  14. Fatigue damage prognosis of internal delamination in composite plates under cyclic compression loadings using affine arithmetic as uncertainty propagation tool

    NASA Astrophysics Data System (ADS)

    Gbaguidi, Audrey J.-M.

    Structural health monitoring (SHM) has become indispensable for reducing maintenance costs and increasing the in-service capacity of a structure. The increased use of lightweight composite materials in aircraft structures drastically increased the effects of fatigue induced damage on their critical structural components and thus the necessity to predict the remaining life of those components. Damage prognosis, one of the least investigated fields in SHM, uses the current damage state of the system to forecast its future performance by estimating the expected loading environments. A successful damage prediction model requires the integration of technologies in areas like measurements, materials science, mechanics of materials, and probability theories, but most importantly the quantification of uncertainty in all these areas. In this study, Affine Arithmetic is used as a method for incorporating the uncertainties due to the material properties into the fatigue life prognosis of composite plates subjected to cyclic compressive loadings. When loadings are compressive in nature, the composite plates undergo repeated buckling-unloading of the delaminated layer which induces mixed modes I and II states of stress at the tip of the delamination in the plates. The Kardomateas model-based prediction law is used to predict the growth of the delamination, while the integration of the effects of the uncertainties for modes I and II coefficients in the fatigue life prediction model is handled using Affine arithmetic. The Mode I and Mode II interlaminar fracture toughness and fatigue characterization of the composite plates are first experimentally studied to obtain the material coefficients and fracture toughness, respectively. Next, these obtained coefficients are used in the Kardomateas law to predict the delamination lengths in the composite plates while using Affine Arithmetic to handle their uncertainties. At last, the fatigue characterization of the composite plates during

  15. Delamination growth behavior in cross-ply composites under compressive cyclic (fatigue) loading

    NASA Astrophysics Data System (ADS)

    Pelegri, Assimina A.

    A mode dependent fatigue delamination growth law for anisotropic composite plates is presented in this thesis. The novelty of the presented law lies in the mode dependency of the material and laminate constants m(Psi) and C(Psi). The model describing the mode dependent delamination growth law consists of an initial postbuckling solution accounting for general delaminated composites, i.e. with no restrictive assumptions on the delamination dimensions, and a fracture mechanics solution. A numerical code was developed for the implementation of the closed form solution which gives the loading and geometrical quantities as well as the energy release rates and the mode mixities. The computer code was especially designed for parametric studies. Parameters assigned in this particular investigation were: end conditions, delamination position (h/T), and applied strain. The effect of the end conditions, i.e. clamped-clamped versus simply-supported ends on the initial postbuckling and growth behavior of delaminated plates was also investigated. In conjunction with the previous analysis, a detailed experimental study was designed and carried out in order to validate the proposed model. The tests were designed so that the effect of certain parameters on the delamination growth behavior could be evaluated. The parameters included in the investigation were: initial delamination length, applied strain and delamination position (h/T). Compressive static, compressive fatigue (constant displacement amplitude), and double cantilever beam (DCB) tests were conducted. Data acquisition and analysis for these tests were performed. By comparing analytical and experimental results it is shown that a very good correlation exists, and the presented mode dependent fatigue delamination growth law can accurately predict fatigue lives of delaminated composite structures.

  16. The relationship of the compressive modulus of articular cartilage with its deformation response to cyclic loading: does cartilage optimize its modulus so as to minimize the strains arising in it due to the prevalent loading regime?

    PubMed

    Barker, M K; Seedhom, B B

    2001-03-01

    To investigate the relationship of the instantaneous compressive modulus with its deformation response to cyclic loading typical of that encountered at the knee joint during level walking. The study was performed on 24 osteochondral plugs taken from three unembalmed cadaveric knees. As the compressive modulus of cartilage has been shown to vary topographically across the knee in an established manner, the specimens were taken from specific sites on the femur and tibia of each knee. All the cartilage specimens were immersed in Hanks' salt solution at 37 degrees C and were subjected to the same cyclic loading regimen that was representative of a typical walking cycle in a specialized indentation apparatus, for over 1 h. The viscous and elastic components of matrix strain, the creep rate and the cartilage compressive modulus were measured. The latter was found to be significantly related to the strain response of cartilage to cyclic loading. Elastic strain varied exponentially with the compressive modulus; specimens with a modulus less than 4 MPa experienced elastic strains in the range 0.18-0.36, whereas stiffer specimens experienced strains between 0.05 and 0.13. Viscous strain varied linearly with cartilage stiffness and was as low as 0.02 at the lower values of the compressive modulus but increased to 0.22 for a compressive modulus of 18 MN/m(2). The rate of creep under cyclic load was inversely linearly related to cartilage stiffness. The strain response of soft specimens approached steady state by 200 cycles but that of stiff specimens did not approach it until 1300 cycles. It was hypothesized that the viscous strain response of cartilage can be explained in terms of differences in permeability between specimens of different compressive modulus, stiffer cartilage having a lower permeability than soft cartilage.

  17. Thermal conductivity of a graphite bipolar plate (BPP) and its thermal contact resistance with fuel cell gas diffusion layers: Effect of compression, PTFE, micro porous layer (MPL), BPP out-of-flatness and cyclic load

    NASA Astrophysics Data System (ADS)

    Sadeghifar, Hamidreza; Djilali, Ned; Bahrami, Majid

    2015-01-01

    This paper reports on measurements of thermal conductivity of a graphite bipolar plate (BPP) as a function of temperature and its thermal contact resistance (TCR) with treated and untreated gas diffusion layers (GDLs). The thermal conductivity of the BPP decreases with temperature and its thermal contact resistance with GDLs, which has been overlooked in the literature, is found to be dominant over a relatively wide range of compression. The effects of PTFE loading, micro porous layer (MPL), compression, and BPP out-of-flatness are also investigated experimentally. It is found that high PTFE loadings, MPL and even small BPP out-of-flatness increase the BPP-GDL thermal contact resistance dramatically. The paper also presents the effect of cyclic load on the total resistance of a GDL-BPP assembly, which sheds light on the behavior of these materials under operating conditions in polymer electrolyte membrane fuel cells.

  18. Progressive cell-mediated changes in articular cartilage and bone in mice are initiated by a single session of controlled cyclic compressive loading.

    PubMed

    Ko, Frank C; Dragomir, Cecilia L; Plumb, Darren A; Hsia, Allison W; Adebayo, Olufunmilayo O; Goldring, Steven R; Wright, Timothy M; Goldring, Mary B; van der Meulen, Marjolein C H

    2016-11-01

    We previously showed that repetitive cyclic loading of the mouse knee joint causes changes that recapitulate the features of osteoarthritis (OA) in humans. By applying a single loading session, we characterized the temporal progression of the structural and compositional changes in subchondral bone and articular cartilage. We applied loading during a single 5-minute session to the left tibia of adult (26-week-old) C57Bl/6 male mice at a peak load of 9.0N for 1,200 cycles. Knee joints were collected at times 0, 1, and 2 weeks after loading. The changes in articular cartilage and subchondral bone were analyzed by histology, immunohistochemistry (caspase-3 and cathepsin K), and microcomputed tomography. At time 0, no change was evident in chondrocyte viability or cartilage or subchondral bone integrity. However, cartilage pathology demonstrated by localized thinning and proteoglycan loss occurred at 1 and 2 weeks after the single session of loading. Transient cancellous bone loss was evident at 1 week, associated with increased osteoclast number. Bone loss was reversed to control levels at 2 weeks. We observed formation of fibrous and cartilaginous tissues at the joint margins at 1 and 2 weeks. Our findings demonstrate that a single session of noninvasive loading leads to the development of OA-like morphological and cellular alterations in articular cartilage and subchondral bone. The loss in subchondral trabecular bone mass and thickness returns to control levels at 2 weeks, whereas the cartilage thinning and proteoglycan loss persist. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1941-1949, 2016.

  19. Exploring interactions between force, repetition and posture on intervertebral disc height loss and bulging in isolated porcine cervical functional spinal units from sub-acute-failure magnitudes of cyclic compressive loading.

    PubMed

    Gooyers, Chad E; Callaghan, Jack P

    2015-10-15

    Most in vitro studies are limited in the ability to partition intervertebral disc (IVD) height loss from total specimen height loss since the net changes in the actuator position of the materials testing system simply reflect net changes to functional spinal units (FSUs) used for testing. Three levels of peak compressive force, three cycle rates and two dynamic postural conditions were examined using a full-factorial design. Cyclic compressive force was applied using a time-varying waveform with synchronous flexion/extension for 5000 cycles. Surface scans from the anterior aspect of the IVD were recorded in a neutral and flexed posture before and after the cyclic loading protocol using a 3D laser scanner to characterise changes in IVD height loss and bulging. A significant three-way interaction (p=0.0092) between the magnitude of peak compressive force, cycle rate and degree of postural deviation was observed in cycle-varying specimen height loss data. A significant main effect of peak compressive force (p=0.0003) was also observed in IVD height loss calculated from the surface profiles of the IVD. The relative contribution of IVD height loss (measured on the anterior surface) to total specimen height loss across experimental conditions varied considerably, ranging from 19% to 58%. Postural deviation was the only factor that significantly affected the magnitude of peak AF bulge (p=0.0016). This investigation provides evidence that total specimen height loss is not an accurate depiction of cycle-varying changes in the IVD across a range of in vivo scenarios that were replicated with in vitro testing.

  20. Mechanics Model for Simulating RC Hinges under Reversed Cyclic Loading

    PubMed Central

    Shukri, Ahmad Azim; Visintin, Phillip; Oehlers, Deric J.; Jumaat, Mohd Zamin

    2016-01-01

    Describing the moment rotation (M/θ) behavior of reinforced concrete (RC) hinges is essential in predicting the behavior of RC structures under severe loadings, such as under cyclic earthquake motions and blast loading. The behavior of RC hinges is defined by localized slip or partial interaction (PI) behaviors in both the tension and compression region. In the tension region, slip between the reinforcement and the concrete defines crack spacing, crack opening and closing, and tension stiffening. While in the compression region, slip along concrete to concrete interfaces defines the formation and failure of concrete softening wedges. Being strain-based, commonly-applied analysis techniques, such as the moment curvature approach, cannot directly simulate these PI behaviors because they are localized and displacement based. Therefore, strain-based approaches must resort to empirical factors to define behaviors, such as tension stiffening and concrete softening hinge lengths. In this paper, a displacement-based segmental moment rotation approach, which directly simulates the partial interaction behaviors in both compression and tension, is developed for predicting the M/θ response of an RC beam hinge under cyclic loading. Significantly, in order to develop the segmental approach, a partial interaction model to predict the tension stiffening load slip relationship between the reinforcement and the concrete is developed. PMID:28773430

  1. Cyclic Loading Effects on the Creep and Dilation of Salt Rock

    NASA Astrophysics Data System (ADS)

    Roberts, Lance A.; Buchholz, Stuart A.; Mellegard, Kirby D.; Düsterloh, Uwe

    2015-11-01

    The Solution Mining Research Institute (SMRI) has embarked on inquiries into the effect cyclic loading might have on salt. This interest stems from the concept of using salt caverns as a storage medium for renewable energy projects such as compressed air energy storage where daily pressure cycles in the cavern are conceivable as opposed to the seasonal cycles that are typical for natural gas storage projects. RESPEC and the Institut für Aufbereitung und Deponietechnik at Clausthal University of Technology jointly executed a rock mechanics laboratory study using both facilities for performing triaxial cyclic loading creep tests on rock salt recovered from the Avery Island Mine in Louisiana, USA. The cyclic triaxial creep tests were performed under various load paths including compression, extension, and compression/extension. The tests were performed under both dilative and nondilative stress regimes. The cyclic compression creep data were compared to static creep tests performed under similar conditions to assess the effect of cycling of the applied stress. Furthermore, the cyclic compression tests were compared to a numerically simulated static creep test at the same stress and temperature conditions to determine if the creep behavior was similar under cyclic loading.

  2. Truss-core corrugation for compressive loads

    NASA Technical Reports Server (NTRS)

    Davis, Randall C. (Inventor); Jackson, Robert (Inventor)

    1988-01-01

    A corrugated panel structure for supporting compressive loads is described which includes curved cap strips separated by truss-core web segments. The truss-core web segments are formed from first and second flat panels with a corrugated filler in between them. The corrugated filler extends in the direction of the compressive load. As a result, all components of the panel structure have a compressive load carrying capability resulting in a high strength-to-weight ratio when the compressive load is limiting. Application to rocket and aircraft structures is suggested.

  3. Truss-core corrugation for compressive loads

    NASA Astrophysics Data System (ADS)

    Davis, Randall C.; Jackson, Robert

    1988-09-01

    A corrugated panel structure for supporting compressive loads is described which includes curved cap strips separated by truss-core web segments. The truss-core web segments are formed from first and second flat panels with a corrugated filler in between them. The corrugated filler extends in the direction of the compressive load. As a result, all components of the panel structure have a compressive load carrying capability resulting in a high strength-to-weight ratio when the compressive load is limiting. Application to rocket and aircraft structures is suggested.

  4. Intervertebral disc response to cyclic loading--an animal model.

    PubMed

    Ekström, L; Kaigle, A; Hult, E; Holm, S; Rostedt, M; Hansson, T

    1996-01-01

    The viscoelastic response of a lumbar motion segment loaded in cyclic compression was studied in an in vivo porcine model (N = 7). Using surgical techniques, a miniaturized servohydraulic exciter was attached to the L2-L3 motion segment via pedicle fixation. A dynamic loading scheme was implemented, which consisted of one hour of sinusoidal vibration at 5 Hz, 50 N peak load, followed by one hour of restitution at zero load and one hour of sinusoidal vibration at 5 Hz, 100 N peak load. The force and displacement responses of the motion segment were sampled at 25 Hz. The experimental data were used for evaluating the parameters of two viscoelastic models: a standard linear solid model (three-parameter) and a linear Burger's fluid model (four-parameter). In this study, the creep behaviour under sinusoidal vibration at 5 Hz closely resembled the creep behaviour under static loading observed in previous studies. Expanding the three-parameter solid model into a four-parameter fluid model made it possible to separate out a progressive linear displacement term. This deformation was not fully recovered during restitution and is therefore an indication of a specific effect caused by the cyclic loading. High variability was observed in the parameters determined from the 50 N experimental data, particularly for the elastic modulus E1. However, at the 100 N load level, significant differences between the models were found. Both models accurately predicted the creep response under the first 800 s of 100 N loading, as displayed by mean absolute errors for the calculated deformation data from the experimental data of 1.26 and 0.97 percent for the solid and fluid models respectively. The linear Burger's fluid model, however, yielded superior predictions particularly for the initial elastic response.

  5. Effect of cyclic impact load on shear bond strength of zirconium dioxide ceramics.

    PubMed

    Kawai, Naoko; Shinya, Akikazu; Yokoyama, Daiichiro; Gomi, Harunori; Shinya, Akiyoshi

    2011-06-01

    To investigate the influence of cyclic impact load and the number of load cycles on compressive shear bond strength under the three different cements. The following materials were used: Super Bond C&B (SB) and Panavia Fluoro Cement (PF) as adhesive resin cements, Fuji Luting (FL) as a resin-modified glass-ionomer cement, and zirconium dioxide ceramics as adherend. Before the shear bond test, three different impact loading conditions (compressive direction, shear direction, and no impact) and the number of load cycles (1 to 106 cycles), were performed. A total of 189 specimens (n = 3/group) were randomly assigned to groups and tested. A cyclic impact test was performed by applying a load of 98N at a distance of 40 mm and a loading cycle frequency of 1 Hz. All results were statistically analyzed with two-way ANOVA and Tukey's multiple comparison test. Shear bond strengths of SB, PF, and FL subjected to no cyclic impact load were 21.6 to 53.8 MPa in SB, 27.0 to 63.6 MPa in PF, and 20.0 to 35.9 MPa in FL. The shear bond strength of SB and PF increased to a certain degree from one to 105 cycles, while FL did likewise from one to 104 cycles. The shear bond strengths of SB, PF, and FL were greatest without cyclic impact, followed by compressive and then shear cyclic impact.

  6. Collagen network strengthening following cyclic tensile loading.

    PubMed

    Susilo, Monica E; Paten, Jeffrey A; Sander, Edward A; Nguyen, Thao D; Ruberti, Jeffrey W

    2016-02-06

    The bulk mechanical properties of tissues are highly tuned to the physiological loads they experience and reflect the hierarchical structure and mechanical properties of their constituent parts. A thorough understanding of the processes involved in tissue adaptation is required to develop multi-scale computational models of tissue remodelling. While extracellular matrix (ECM) remodelling is partly due to the changing cellular metabolic activity, there may also be mechanically directed changes in ECM nano/microscale organization which lead to mechanical tuning. The thermal and enzymatic stability of collagen, which is the principal load-bearing biopolymer in vertebrates, have been shown to be enhanced by force suggesting that collagen has an active role in ECM mechanical properties. Here, we ask how changes in the mechanical properties of a collagen-based material are reflected by alterations in the micro/nanoscale collagen network following cyclic loading. Surprisingly, we observed significantly higher tensile stiffness and ultimate tensile strength, roughly analogous to the effect of work hardening, in the absence of network realignment and alterations to the fibril area fraction. The data suggest that mechanical loading induces stabilizing changes internal to the fibrils themselves or in the fibril-fibril interactions. If such a cell-independent strengthening effect is operational in vivo, then it would be an important consideration in any multiscale computational approach to ECM growth and remodelling.

  7. Changes in nuclear composition following cyclic compression of the intervertebral disc in an in vivo rat-tail model.

    PubMed

    Ching, Congo T S; Chow, Daniel H K; Yao, Fiona Y D; Holmes, Andrew D

    2004-09-01

    While in vitro studies have shown that mechanical loading can result in changes in the composition of intervertebral disc matrix, the effects of cyclic loading in vivo have not been considered. The objective of this study was to assess the effect of static and cyclic compression of different frequencies on the nuclear composition of the intervertebral disc. Thirty-six Sprague-Dawley rats were randomly divided into a control group (no pin insertion, no loading), a sham group (pins inserted in sixth and seventh caudal vertebrae, no loading), a static loading group (compression applied via pins) and cyclic loading groups (loading at 0.5, 1.5 or 2.5 Hz). Loading was applied for 1 h each day from the third to 17th day following pin insertion, and the caudal 5-6, 6-7 and 7-8 discs harvested to quantify proteoglycan content, collagen content and chondrocyte density in the nucleus pulposus. Static compression resulted in a significant reduction in total proteoglycan content as compared with the adjacent control disc, but this effect was not seen in any of the cyclic loading groups. However, comparison with the sham group appears to indicate an overall decrease in total proteoglycan content at the targeted and adjacent levels following cyclic loading. The 0.5 Hz loading group showed a significantly greater total proteoglycan content than all other compression groups, and also showed a lower total collagen content than the sham group. Results suggest that frequency dependent changes in composition occur in response to cyclic loading, but are not limited to the directly loaded disc alone. Further studies are required to verify this, but the choice of control appears to need careful consideration in all studies of this nature.

  8. Effect of Cyclic Thermo-Mechanical Loads on Fatigue Reliability in Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Shah, A. R.; Murthy, P. L. N.; Chamis, C. C.

    1996-01-01

    A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multi-factor interaction relationship developed at NASA Lewis Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability- based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)(sub s) graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

  9. Cyclic Load Effects on Long Term Behavior of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Shah, A. R.; Chamis, C. C.

    1996-01-01

    A methodology to compute the fatigue life for different ratios, r, of applied stress to the laminate strength based on first ply failure criteria combined with thermal cyclic loads has been developed and demonstrated. Degradation effects resulting from long term environmental exposure and thermo-mechanical cyclic loads are considered in the simulation process. A unified time-stress dependent multi-factor interaction equation model developed at NASA Lewis Research Center has been used to account for the degradation of material properties caused by cyclic and aging loads. Effect of variation in the thermal cyclic load amplitude on a quasi-symmetric graphite/epoxy laminate has been studied with respect to the impending failure modes. The results show that, for the laminate under consideration, the fatigue life under combined mechanical and low thermal amplitude cyclic loads is higher than that due to mechanical loads only. However, as the thermal amplitude increases, the life also decreases. The failure mode changes from tensile under mechanical loads only to the compressive and shear at high mechanical and thermal loads. Also, implementation of the developed methodology in the design process has been discussed.

  10. Compressive strength of axially loaded composite cylinders

    NASA Astrophysics Data System (ADS)

    Kollar, Laszlo P.; Springer, George C.; Spingarn, Jay; McColskey, J. D.

    1993-10-01

    Tests were performed to measure the failure loads of axially compressed glass-fiber-reinforced and graphite-fiber-reinforced composite cylinders. The data were compared with the results of a previous model, which was based on a three-dimensional stress analysis and the Tsai-Wu quadratic first-ply failure criterion. This model predicted the failure loads for glass-fiber-reinforced composites with good accuracy, but less accurately for failure loads of graphite-epoxy composites.

  11. Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes

    DOE PAGES

    Ghassemi-Armaki, Hassan; Leff, Asher C.; Taheri, Mitra L.; ...

    2017-06-22

    Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. Furthermore, the cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of -5 °C ismore » compared. The texture of the tube with the Af of -5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. Our observations lead to the conclusion that micropillar compression testing in a cyclic mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.« less

  12. Fatigue failure of dentin-composite disks subjected to cyclic diametral compression

    PubMed Central

    Li, Yuping; Carrera, Carola; Chen, Ruoqiong; Li, Jianying; Chen, Yungchung; Lenton, Patricia; Rudney, Joel. D.; Jones, Robert S.; Aparicio, Conrado; Fok, Alex

    2015-01-01

    Objective Our aim was to establish the relationship between cyclic loading and fatigue life of the dentin-composite interface using the newly developed disk in diametral compression tests. The results were then used to estimate the fatigue life of restored teeth under occlusal loading. Methods Disk specimens (5mm dia. × 2mm thick) were prepared using bovine incisors and restored with either a methacrylate-based composite Z100™ with Adper Single Bond Plus (Z100) or silorane-based composite Filtek ™ LS with LS System adhesive (LS). The dentin-composite disks were tested under cyclic diametral compression to determine the number of cycles to failure (Nf) at three load levels (n = 3 per group). Finite element analysis (FEA) was used to calculate the interfacial stresses (σ) within the specimen, to establish the σ vs. Nf curves, and those within a restored tooth under normal chewing forces (15N maximum). These were then used to estimate the lifetime of the restored tooth for the two restorative systems. Results The disks restored with LS had a higher fatigue resistance than those restored with Z100. The maximum interfacial stress in the restored tooth determined by FEA was ∼0.5MPa. Based on the estimate of 300,000 cycles of chewing per year, the predicted lifetime under occlusal loading for teeth restored with LS and Z100 was 33 and 10 years, respectively. Significance The disk in cyclic diametral compression has been used successfully to provide fatigue data which allows the lifetime of composite-restored teeth under occlusal loading to be predicted using numerical simulation. PMID:25958269

  13. Fuel cell stack compressive loading system

    DOEpatents

    Fahle, Ronald W.; Reiser, Carl A.

    1982-01-01

    A fuel cell module comprising a stack of fuel cells with reactant gas manifolds sealed against the external surfaces of the stack includes a constraint system for providing a compressive load on the stack wherein the constraint system maintains the stack at a constant height (after thermal expansion) and allows the compressive load to decrease with time as a result of the creep characteristics of the stack. Relative motion between the manifold sealing edges and the stack surface is virtually eliminated by this constraint system; however it can only be used with a stack having considerable resiliency and appropriate thermal expansion and creep characteristics.

  14. Specific Features of the Nucleation and Growth of Fatigue Cracks in Steel under Cyclic Dynamic Compression

    NASA Astrophysics Data System (ADS)

    Popelyukh, A. I.; Popelyukh, P. A.; Bataev, A. A.; Nikulina, A. A.; Smirnov, A. I.

    2016-03-01

    The processes of the fracture of 40Kh and U8 steels under cyclic dynamic compression are studied. It has been found that the main cause for the fracture of the cyclically compressed specimens is the propagation of cracks due to the effect of residual tensile stresses, which arise near the tips of the cracks at the stage of the unloading of the specimens. The growth rate of a crack has the maximum value at the initial stage of its propagation in the vicinity of the stress concentrator. As the crack propagates deep into the specimen, its growth rate decreases and depends only slightly on the real cross section of the specimen. The model of the process of the fatigue fracture of the steels under dynamic loading by a cyclically varied compressive force is proposed. It has been found that the high fatigue endurance is provided by tempering at 200°C for the 40Kh steel and at 300°C for the U8 steel.

  15. Viscoelastic properties of passive skeletal muscle in compression-cyclic behaviour.

    PubMed

    Van Loocke, M; Simms, C K; Lyons, C G

    2009-05-29

    Skeletal muscle relaxation behaviour in compression has been previously reported, but the anisotropic behaviour at higher loading rates remains poorly understood. In this paper, uniaxial unconfined cyclic compression tests were performed on fresh porcine muscle samples at various fibre orientations to determine muscle viscoelastic behaviour. Mean compression level of 25% was applied and cycles of 2% and 10% amplitude were performed at 0.2-80Hz. Under cycles of low frequency and amplitude, linear viscoelastic cyclic relaxation was observed. Fibre/cross-fibre results were qualitatively similar, but the cross-fibre direction was stiffer (ratio of 1.2). In higher amplitude tests nonlinear viscoelastic behaviour with a frequency dependent increase in the stress cycles amplitude was found (factor of 4.1 from 0.2 to 80Hz). The predictive capability of an anisotropic quasi-linear viscoelastic model previously fitted to stress-relaxation data from similar tissue samples was investigated. Good qualitative results were obtained for low amplitude cycles but differences were observed in the stress cycle amplitudes (errors of 7.5% and 31.8%, respectively, in the fibre/cross-fibre directions). At higher amplitudes significant qualitative and quantitative differences were evident. A nonlinear model formulation was therefore developed which provided a good fit and predictions to high amplitude low frequency cyclic tests performed in the fibre/cross-fibre directions. However, this model gave a poorer fit to high frequency cyclic tests and to relaxation tests. Neither model adequately predicts the stiffness increase observed at frequencies above 5Hz. Together with data previously presented, the experimental data presented here provide a unique dataset for validation of future constitutive models for skeletal muscle in compression.

  16. A comparison of fixation screws for the scaphoid during application of cyclical bending loads.

    PubMed

    Toby, E B; Butler, T E; McCormack, T J; Jayaraman, G

    1997-08-01

    Matched pairs of scaphoids from cadavera were stressed with ramped intensity cyclical bending loads after osteotomy and fixation of one scaphoid with a Herbert screw and fixation of the other with an AO 3.5-millimeter cannulated screw, a Herbert-Whipple screw, an Acutrak cannulated screw, or a Universal Compression screw. The AO screw, Acutrak screw, and Herbert-Whipple screw demonstrated superior resistance to cyclical bending loads compared with the Herbert screw. The Universal Compression screw did not provide better fixation than the Herbert screw because of fractures that occurred at the time of insertion. The AO screw and the Herbert screw were then tested in a separate setup in which a segment of volar cortex had been removed in addition to the simple osteotomy. The loss of volar cortex greatly diminished the quality of the fixation provided by both of the screws during application of ramped intensity cyclical bending loads. A fixation device in the scaphoid must be able to withstand the stresses that are placed on the scaphoid as a result of its position spanning the proximal and distal carpal rows. Also, because of the prolonged time required for healing of fractures or non-unions of the scaphoid, the device must be able to withstand many such cycles of stress. The present study demonstrates that commonly used screws for fixation of the scaphoid vary significantly (p < 0.005) in their ability to resist cyclical bending loads.

  17. Effect of cyclic loading on the nanoscale deformation of hydroxyapatite and collagen fibrils in bovine bone.

    PubMed

    Singhal, Anjali; Stock, Stuart R; Almer, Jonathan D; Dunand, David C

    2014-06-01

    Cyclic compressive loading tests were carried out on bovine femoral bones at body temperature (37 °C), with varying mean stresses (-55 to -80 MPa) and loading frequencies (0.5-5 Hz). At various times, the cyclic loading was interrupted to carry out high-energy X-ray scattering measurements of the internal strains developing in the hydroxyapatite (HAP) platelets and the collagen fibrils. The residual strains upon unloading were always tensile in the HAP and compressive in the fibrils, and each increases in magnitude with loading cycles, which can be explained from damage at the HAP–collagen interface and accumulation of plastic deformation within the collagen phase. The samples tested at a higher mean stress and stress amplitude, and at lower loading frequencies exhibit greater plastic deformation and damage accumulation, which is attributed to greater contribution of creep. Synchrotron microcomputed tomography of some of the specimens showed that cracks are produced during cyclic loading and that they mostly occur concentric with Haversian canals.

  18. Compressive cyclic ratcheting and fatigue of synthetic, soft biomedical polymers in solution.

    PubMed

    Miller, Andrew T; Safranski, David L; Smith, Kathryn E; Guldberg, Robert E; Gall, Ken

    2016-02-01

    The use of soft, synthetic materials for the replacement of soft, load-bearing tissues has been largely unsuccessful due to a lack of materials with sufficient fatigue and wear properties, as well as a lack of fundamental understanding on the relationship between material structure and behavior under cyclic loads. In this study, we investigated the response of several soft, biomedical polymers to cyclic compressive stresses under aqueous conditions and utilized dynamic mechanical analysis and differential scanning calorimetry to evaluate the role of thermo-mechanical transitions on such behavior. Studied materials include: polycarbonate urethane, polydimethylsiloxane, four acrylate copolymers with systematically varied thermo-mechanical transitions, as well as bovine meniscal tissue for comparison. Materials showed compressive moduli between 2.3 and 1900MPa, with polycarbonate urethane (27.3MPa) matching closest to meniscal tissue (37.0MPa), and also demonstrated a variety of thermo-mechanical transition behaviors. Cyclic testing resulted in distinct fatigue-life curves, with failure defined as either classic fatigue fracture or a defined increased in maximum strain due to ratcheting. Our study found that polymers with sufficient dissipation mechanisms at the testing temperature, as evidenced by tan delta values, were generally tougher than those with less dissipation and exhibited ratcheting rather than fatigue fracture much like meniscal tissue. Strain recovery tests indicated that, for some toughened polymers, the residual strain following our cyclic loading protocol could be fully recovered. The similarity in ratcheting behavior, and lack of fatigue fracture, between the meniscal tissue and toughened polymers indicates that such polymers may have potential as artificial soft tissue.

  19. Analysis of gene expression profile of periodontal ligament cells subjected to cyclic compressive force.

    PubMed

    Wu, Jiapei; Li, Yu; Fan, Xiaofeng; Zhang, Chaoliang; Wang, Yu; Zhao, Zhihe

    2011-11-01

    Cyclic compressive force is an important mechanical stimulus on periodontal ligament (PDL). The differential expression of genes in PDL cells is thought to be involved in the remodeling of periodontal tissues subjected to mechanical stress. However, little is known about differentially expressed genes in PDL cells under cyclic compressive force. In our study, human PDL cells were subjected to 4000 μ strain compressive stress loading at 0.5 Hz for 2 h. The effect of mechanical stress on PDL cells proliferation was observed by flow cytometry. Microarray analysis was used to investigate the mechano-induced differential gene profile in PDL cells. Differential expression was confirmed by quantitative real-time polymerase chain reaction (RT-PCR) analysis on genes of interest and explored at two more force loading times (6 h, 12 h). After mechanical loading, cell proliferation was repressed. The microarray data showed that 217 out of 35,000 genes were differentially expressed; among the 217 genes, 207 were up-regulated whereas 10 were down-regulated (p < 0.05). Gene ontology analysis suggested that majority of differentially expressed genes were located in the nucleus and functioned as transcription factors involved in a variety of biological processes. Five genes of interest (IL6, IL8, ETS1, KLF10, and DLC1) were found to be closely related to negative regulation of cell proliferation. The PCR results showed increased expression after 2 h loading, then a decline with extended loading time. The signaling pathways involved were also identified. These findings expand understanding of molecular regulation in the mechano-response of PDL cells.

  20. Energy-based analysis of permanent strain behaviour of cohesive soil under cyclic loading

    NASA Astrophysics Data System (ADS)

    Sas, Wojciech; Głuchowski, Andrzej; Bursa, Bartłomiej; Szymański, Alojzy

    2017-04-01

    In this paper the original results of uniaxial cyclic compression test on cohesive soil are presented. The shakedown phenomena in cohesive soil are described. Energy-based method highlights the change of soil material behaviour from plastic shakedown through plastic creep shakedown to incremental collapse. The samples were cyclically loaded under undrained conditions with the constant amplitude of stress in one-way test procedure. In this study the energy-based method was presented as a proper method to categorise response of cohesive soil to cyclic loading in uniaxial conditions. A shakedown criterion factor, S E, was introduced to help understand the shakedown phenomena in cohesive soil. In cohesive soils the absence of a limit between plastic shakedown and plastic creep shakedown was pointed out.

  1. Mechanical annealing under low-amplitude cyclic loading in micropillars

    NASA Astrophysics Data System (ADS)

    Cui, Yi-nan; Liu, Zhan-li; Wang, Zhang-jie; Zhuang, Zhuo

    2016-04-01

    Mechanical annealing has been demonstrated to be an effective method for decreasing the overall dislocation density in submicron single crystal. However, simultaneously significant shape change always unexpectedly happens under extremely high monotonic loading to drive the pre-existing dislocations out of the free surfaces. In the present work, through in situ TEM experiments it is found that cyclic loading with low stress amplitude can drive most dislocations out of the submicron sample with virtually little change of the shape. The underlying dislocation mechanism is revealed by carrying out discrete dislocation dynamic (DDD) simulations. The simulation results indicate that the dislocation density decreases within cycles, while the accumulated plastic strain is small. By comparing the evolution of dislocation junction under monotonic, cyclic and relaxation deformation, the cumulative irreversible slip is found to be the key factor of promoting junction destruction and dislocation annihilation at free surface under low-amplitude cyclic loading condition. By introducing this mechanics into dislocation density evolution equations, the critical conditions for mechanical annealing under cyclic and monotonic loadings are discussed. Low-amplitude cyclic loading which strengthens the single crystal without seriously disturbing the structure has the potential applications in the manufacture of defect-free nano-devices.

  2. Degradation forecast for PEMFC cathode-catalysts under cyclic loads

    NASA Astrophysics Data System (ADS)

    Moein-Jahromi, M.; Kermani, M. J.; Movahed, S.

    2017-08-01

    Degradation of Fuel Cell (FC) components under cyclic loads is one of the biggest bottlenecks in FC commercialization. In this paper, a novel experimental based algorithm is presented to predict the Catalyst Layer (CL) performance loss during cyclic load. The algorithm consists of two models namely Models 1 and 2. The Model 1 calculates the Electro-Chemical Surface Area (ECSA) and agglomerate size (e.g. agglomerate radius, rt,agg) for the catalyst layer under cyclic load. The Model 2 is the already-existing model from our earlier studies that computes catalyst performance with fixed structural parameters. Combinations of these two Models predict the CL performance under an arbitrary cyclic load. A set of parametric/sensitivity studies is performed to investigate the effects of operating parameters on the percentage of Voltage Degradation Rate (VDR%) with rank 1 for the most influential one. Amongst the considered parameters (such as: temperature, relative humidity, pressure, minimum and maximum voltage of the cyclic load), the results show that temperature and pressure have the most and the least influences on the VDR%, respectively. So that, increase of temperature from 60 °C to 80 °C leads to over 20% VDR intensification, the VDR will also reduce 1.41% by increasing pressure from 2 atm to 4 atm.

  3. Microstructure of NiTi shape memory alloy due to tension-compression cyclic deformation

    SciTech Connect

    Xie, Z.; Liu, Y.; Humbeeck, J. van

    1998-03-23

    Experimental results have shown that, during mechanical cycling under tension-compression load within {+-}4% strains, the NiTi shape memory alloy is cyclic strain-hardened. The maximum stresses under both tension and compression increase with increasing number of cycles and tend to stabilize with further cycling. The present work is focused on the martensite microstructure developed as a result of mechanical cycling. TEM observations show that, before cycling, the martensite variants are well self-accommodated to each other with the <011> type II twinning as the main lattice invariant shear. After mechanical cycling, the martensite plates are still self-accommodated and the (11{bar 1}) type I twinning is most frequently observed. In addition to the stress-induced re-orientation of martensite and twin boundary movement within the martensite plate, various lattice defects have been developed both in the junction plane areas of martensite plates and within the martensite twins.

  4. Performance of tubular members under cyclic axial loads

    SciTech Connect

    Shaker, R.E.; Murakawa, Hidekazu; Ueda, Yukio

    1995-12-31

    In this paper the behavior of pin-ended tubular steel members under cyclic axial loads is studied by using Finite Element Method (FEM) considering both geometrical and material non-linearities. The factors considered in this study are the cyclic loading characteristics (displacement amplitude and mean displacement), geometrical parameters (diameter-to-thickness ratio D/t and normalized slenderness ratio {lambda}) and inelastic characteristics of the material. The results of numerical analysis are closely examined with respect to both ultimate strength and energy dissipation capacity.

  5. Cyclic mechanical loading enables solute transport and oxygen supply in bone healing: an in vitro investigation.

    PubMed

    Witt, Florian; Duda, Georg N; Bergmann, Camilla; Petersen, Ansgar

    2014-02-01

    Bone healing is a complex process with an increased metabolic activity and consequently high demand for oxygen. In the hematoma phase, inflammatory cells and mesenchymal stromal cells (MSCs) are initially cut off from direct nutritional supply via blood vessels. Cyclic mechanical loading that occurs, for example, during walking is expected to have an impact on the biophysical environment of the cells but meaningful quantitative experimental data are still missing. In this study, the hypothesis that cyclic mechanical loading within a physiological range significantly contributes to oxygen transport into the fracture hematoma was investigated by an in vitro approach. MSCs were embedded in a fibrin matrix to mimic the hematoma phase during bone healing. Construct geometry, culture conditions, and parameters of mechanical loading in a bioreactor system were chosen to resemble the in vivo situation based on data from human studies and a well-characterized large animal model. Oxygen tension was measured before and after mechanical loading intervals by a chemical optical microsensor. The increase in oxygen tension at the center of the constructs was significant and depended on loading time with maximal values of 9.9%±5.1%, 14.8%±4.9%, and 25.3%±7.2% of normal atmospheric oxygen tension for 5, 15, and 30 min of cyclic loading respectively. Histological staining of hypoxic cells after 48 h of incubation confirmed sensor measurements by showing an increased number of normoxic cells with intermittent cyclic compression compared with unloaded controls. The present study demonstrates that moderate cyclic mechanical loading leads to an increased oxygen transport and thus to substantially enhanced supply conditions for cells entrapped in the hematoma. This link between mechanical conditions and nutrition supply in the early regenerative phases could be employed to improve the environmental conditions for cell metabolism and consequently prevent necrosis.

  6. Development of a viscoelastic continuum damage model for cyclic loading

    NASA Astrophysics Data System (ADS)

    Sullivan, R. W.

    2008-12-01

    A previously developed spectrum model for linear viscoelastic behavior of solids is used to describe the rate-dependent damage growth of a time dependent material under cyclic loading. Through the use of the iterative solution of a special Volterra integral equation, the cyclic strain history is described. The spectrum-based model is generalized for any strain rate and any uniaxial load history to formulate the damage function. Damage evolution in the body is described through the use of a rate-type evolution law which uses a pseudo strain to express the viscoelastic constitutive equation with damage. The resulting damage function is used to formulate a residual strength model. The methodology presented is demonstrated by comparing the peak values of the computed cyclic strain history as well as the residual strength model predictions to the experimental data of a polymer matrix composite.

  7. Undrained behaviour of volcanic soils under monotonic and cyclic loading

    NASA Astrophysics Data System (ADS)

    de Cristofaro, Martina; Brunzo, Antonia; Mottola, Luciano; Netti, Nadia; Olivares, Lucio; Orense, Rolando; Asadi, Sadeq

    2017-04-01

    Undrained behaviour of volcanic soils under monotonic and cyclic loading. In this study, we focus on the undrained behaviour of volcanic deposits under monotonic and cyclic loading in order to define the susceptibility to liquefaction of granular volcanic deposits. We assume that, in the case of saturated granular volcanic deposits susceptible to liquefaction, an undrained unstable behaviour can be responsible for both, the evolution of flowslide due to rainfall and liquefaction under seismic loading. Starting from these considerations we define a complex experimental program to analyze their undrained behaviour through laboratory testing on reconstituted specimens of cohesionless volcanic soils. The first part of the experimental program is devoted to the use of the steady state concept to evaluate the influence of void ratio and effective confining pressure on the undrained behaviour of Cervinara pyroclastic soils (Italy) under monotonic and cyclic loading. The second part of the experimental program is devoted to the analysis of the influence of particles crushing of pumice soils from Rangiriri (New Zeland) in both monotonic and cyclic undrained triaxial tests.

  8. Design for cyclic loading endurance of composites

    NASA Technical Reports Server (NTRS)

    Shiao, Michael C.; Murthy, Pappu L. N.; Chamis, Christos C.; Liaw, Leslie D. G.

    1993-01-01

    The application of the computer code IPACS (Integrated Probabilistic Assessment of Composite Structures) to aircraft wing type structures is described. The code performs a complete probabilistic analysis for composites taking into account the uncertainties in geometry, boundary conditions, material properties, laminate lay-ups, and loads. Results of the analysis are presented in terms of cumulative distribution functions (CDF) and probability density function (PDF) of the fatigue life of a wing type composite structure under different hygrothermal environments subjected to the random pressure. The sensitivity of the fatigue life to a number of critical structural/material variables is also computed from the analysis.

  9. Influences of cyclic loading on martensite transformation of TRIP steels

    NASA Astrophysics Data System (ADS)

    Dan, W. J.; Hu, Z. G.; Zhang, W. G.

    2013-03-01

    While austenite transformation into martensite induces increasing of the crack initiation life and restraining of the growth of fatigue cracks in cyclic-loading processes, TRIP-assisted steels have a better fatigue life than the AHSS (Advance High Strength Steels). As two key parameters in the cyclic loading process, strain amplitude and cyclic frequency are used in a kinetic transformation model to reasonably evaluate the phase transformation from austenite into martensite with the shear-band intersections theory, in which strain amplitude and cyclic frequency are related to the rate of shear-band intersection formation and the driving force of phase transformation. The results revealed that the martensite volume fraction increased and the rate of phase transformation decrease while the number of cycles increased, and the martensite volume fraction was almost constant after the number of cycles was more than 2000 times. Higher strain amplitude promotes martensite transformation and higher cyclic frequency impedes phase transformation, which are interpreted by temperature increment, the driving force of phase transformation and the rate of shearband intersection formation.

  10. Durability of Polymeric Coatings: Cyclic Loading and Free Volumes

    NASA Astrophysics Data System (ADS)

    Chen, Hongmin; Peng, Qinghua; Wu, Yichu; Li, Ying; Zhang, Junjie; Sandreczki, T. C.; Zhang, Renwu; Jean, Y. C.; Richardson, J. R.

    2002-03-01

    The mechanical durability of seven commercially polymeric coatings is investigated using slow positron beam techniques to monitor changes in sub nanometer defects during the cyclic loading process. Doppler broadened energy spectra and positron annihilation lifetime measurements were performed as a function of the slow positron energy at different periods of cycling loading. The positron annihilation dada show that both S-defect parameter and ortho-positronium intensity decrease as the loading cycles increase. The results indicate a loss of free volumes due to mechanical loading and cycling. A direct correlation between the loss of free-volume parameter and of loading cycle is observed. This is interpreted as that durability of polymeric coatings is controlled by the atomic level defects. It is shown that the slow positron beam is very successful probe in detecting the very early stages of coating degradation due to mechanical processes. Supported by NSF-CMS-9812717

  11. Cyclical loading of coracoclavicular ligament reconstructions: a comparative biomechanical study.

    PubMed

    Lee, Steven J; Keefer, Eric P; McHugh, Malachy P; Kremenic, Ian J; Orishimo, Karl F; Ben-Avi, Simon; Nicholas, Stephen J

    2008-10-01

    Reconstruction for injuries to the acromioclavicular joint remains controversial. A coracoclavicular ligament reconstruction with a semitendinosus tendon would have superior performance to the classic coracoacromial ligament transfer with or without augmentation. Controlled laboratory study. Five cadaveric shoulders were used to reconstruct the coracoclavicular ligaments with 3 methods: coracoacromial ligament transfer without augmentation, coracoacromial ligament transfer augmented with No. 5 Ethibond suture, and a semitendinosus tendon. Each reconstruction was cyclically loaded at 40 N to 80 N for 2500 cycles, then from 40 N to 210 N for 2500 cycles, followed by loading to failure. The number of cycles to 50% and 100% loss of acromioclavicular joint reduction were recorded. During the 40 N to 80 N-loading cycle, the coracoacromial transfer without augmentation failed (15 +/- 16 cycles). The augmented coracoacromial ligament transfer and the semitendinosus reconstruction did not fail (P = .008). During the 40 N to 210 N-loading cycle, the augmented coracoacromial ligament transfer failed (207 +/- 399 cycles). The semitendinosus reconstruction survived through both loading cycles (P < .01). Coracoclavicular ligament reconstruction with a semitendinosus graft is a biomechanically superior construct in a cyclically loaded setting to a coracoacromial ligament transfer augmented with a No. 5 Ethibond suture. The semitendinosus graft is a strong, biologic option for reconstruction of the coracoclavicular ligaments.

  12. Compressed magnetic flux amplifier with capacitive load

    SciTech Connect

    Stuetzer, O.M.

    1980-03-01

    A first-order analysis is presented for a compressed magnetic flux (CMF) current amplifier working into a load with a capacitive component. Since the purpose of the investigation was to gain a general understanding of the arrangement, a number of approximations and limitations were accepted. The inductance of the transducer varies with time; the inductance/resistance/capacitance (LRC) circuit therefore is parametric and solutions are different for the stable regime (high C), the oscillation regime (low C), and the transition case. Solutions and performance depend strongly on circuit boundary conditions, i.e., energization of the circuit by either an injected current or by an applied capacitor charge. The behavior of current and energy amplification for the various cases are discussed in detail. A number of experiments with small CMF devices showed that the first-order theory presented predicts transducer performance well in the linear regime.

  13. Matrix cracking in laminated composites under monotonic and cyclic loadings

    NASA Technical Reports Server (NTRS)

    Allen, David H.; Lee, Jong-Won

    1991-01-01

    An analytical model based on the internal state variable (ISV) concept and the strain energy method is proposed for characterizing the monotonic and cyclic response of laminated composites containing matrix cracks. A modified constitution is formulated for angle-ply laminates under general in-plane mechanical loading and constant temperature change. A monotonic matrix cracking criterion is developed for predicting the crack density in cross-ply laminates as a function of the applied laminate axial stress. An initial formulation for a cyclic matrix cracking criterion for cross-ply laminates is also discussed. For the monotonic loading case, a number of experimental data and well-known models are compared with the present study for validating the practical applicability of the ISV approach.

  14. Matrix cracking in laminated composites under monotonic and cyclic loadings

    NASA Technical Reports Server (NTRS)

    Allen, David H.; Lee, Jong-Won

    1991-01-01

    An analytical model based on the internal state variable (ISV) concept and the strain energy method is proposed for characterizing the monotonic and cyclic response of laminated composites containing matrix cracks. A modified constitution is formulated for angle-ply laminates under general in-plane mechanical loading and constant temperature change. A monotonic matrix cracking criterion is developed for predicting the crack density in cross-ply laminates as a function of the applied laminate axial stress. An initial formulation for a cyclic matrix cracking criterion for cross-ply laminates is also discussed. For the monotonic loading case, a number of experimental data and well-known models are compared with the present study for validating the practical applicability of the ISV approach.

  15. Analysis Of The Interface Behavior Under Cyclic Loading

    SciTech Connect

    Mortara, Giuseppe

    2008-07-08

    This paper analyses the frictional behavior between soil and structures under cyclic loading conditions. In particular, the attention is focused on the stress degradation occurring in sand-metal interface tests and on the relevant parameters playing a role in such kind of tests. Also, the paper reports the analysis of the experimental data from the constitutive point of view with a two-surface elastoplastic model.

  16. Plasticity model for metals under cyclic large-strain loading

    NASA Astrophysics Data System (ADS)

    Greshnov, V. M.; Puchkova, I. V.

    2010-03-01

    This paper deals with mathematical modeling of one of the effective technologies of plastic metal forming — multistep cold metal forging. Experimental results are given on the plastic behavior of metals under cyclic loading at large strains accumulated for one cycle. Based on the experimental data obtained, a plasticity model is developed and shown to be effective in testing and improving the technology of forging a nut blank by using a computer-aided engineering analysis system.

  17. Adjustable-Length Strut Withstands Large Cyclic Loads

    NASA Technical Reports Server (NTRS)

    Carner, Fred P.

    1995-01-01

    Adjustable-length strut designed for installation in structure subjected to large cyclic loads. Partly resembles large turnbuckle: includes oppositely threaded eyebolts engaging correspondingly threaded holes at opposite ends of shaft, and shaft turned to adjust length. However, unlike in turnbuckle, length setting not fixed by use of simple jam nuts: instead, length setting fixed by use of more complex threaded-end flanges partly resembling jam nuts but function somewhat differently.

  18. DEFORMATION CHARACTERISTICS OF CRUSHED-STONE LAYER UNDER CYCLIC IMPACT LOADING FROM MICRO-MECHANICAL VIEW

    NASA Astrophysics Data System (ADS)

    Kono, Akiko; Matsushima, Takashi

    'Hanging sleepers', which have gaps between sleepers and ballast layer are often found in the neighborhood of rail joints or rugged surface rails. This suggests that differential settlement of the ballast layer is due to impact loading generated by the contact between running wheel and rugged surface rail. Then cyclic loading tests were performed on crushed-stone layer with two loading patterns, the one is a cyclic impact loading and the other one is cyclic 'standard' loading controlled at 1/10 loading velocity of the impact loading. It was shown that the crashed-stone layer deforms with volumetric expansion during every off-loading processes under the cyclic impact loading. This phenomena prevents crushed stone layer from forming stable grain columns, then the residual settlement under the cyclic impact loading is larger than that under the cyclic 'standard' loading. A simple mass-spring model simulates that two masses move in the opposite direction with increased frequency of harmonic excitation.

  19. Bladder tissue passive response to monotonic and cyclic loading.

    PubMed

    Zanetti, Elisabetta M; Perrini, Michela; Bignardi, Cristina; Audenino, Alberto L

    2012-01-01

    The fundamental passive mechanical properties of the bladder need to be known in order to design the most appropriate long-term surgical repair procedures and develop materials for bladder reconstruction. This study has focused on the bladder tissue viscoelastic behavior, providing a comprehensive analysis of the effects of fibers orientation, strain rate and loading history. Whole bladders harvested from one year old fat pigs (160 kg approximate weight) were dissected along the apex-to-base direction and samples were isolated from the lateral region of the wall, as well as along apex-to-base and transverse directions. Uniaxial monotonic (stress relaxation) and cyclic tests at different frequencies have been performed with the Bose Electroforce(®) 3200. Normalized stress relaxation functions have been interpolated using a second-order exponential series and loading and unloading stress-strain curves have been interpolated with a non-linear elastic model. The passive mechanical behavior of bladder tissue was shown to be heavily influenced by frequency and loading history, both in monotonic and cyclic tests. The anisotropy of the tissue was evident in monotonic and in cyclic tests as well, especially in tests performed on an exercised tissue and at high frequencies. In contrast, transverse and apex-to-base samples demonstrated an analogous relaxation behavior.

  20. Dual-phase steel sheets under cyclic tension-compression to large strains: Experiments and crystal plasticity modeling

    NASA Astrophysics Data System (ADS)

    Zecevic, Milovan; Korkolis, Yannis P.; Kuwabara, Toshihiko; Knezevic, Marko

    2016-11-01

    In this work, we develop a physically-based crystal plasticity model for the prediction of cyclic tension-compression deformation of multi-phase materials, specifically dual-phase (DP) steels. The model is elasto-plastic in nature and integrates a hardening law based on statistically stored dislocation density, localized hardening due to geometrically necessary dislocations (GNDs), slip-system-level kinematic backstresses, and annihilation of dislocations. The model further features a two level homogenization scheme where the first level is the overall response of a two-phase polycrystalline aggregate and the second level is the homogenized response of the martensite polycrystalline regions. The model is applied to simulate a cyclic tension-compression-tension deformation behavior of DP590 steel sheets. From experiments, we observe that the material exhibits a typical decreasing hardening rate during forward loading, followed by a linear and then a non-linear unloading upon the load reversal, the Bauschinger effect, and changes in hardening rate during strain reversals. To predict these effects, we identify the model parameters using a portion of the measured data and validate and verify them using the remaining data. The developed model is capable of predicting all the particular features of the cyclic deformation of DP590 steel, with great accuracy. From the predictions, we infer and discuss the effects of GNDs, the backstresses, dislocation annihilation, and the two-level homogenization scheme on capturing the cyclic deformation behavior of the material.

  1. Infrared thermographic analysis of shape memory polymer during cyclic loading

    NASA Astrophysics Data System (ADS)

    Staszczak, Maria; Pieczyska, Elżbieta A.; Maj, Michał; Kukla, Dominik; Tobushi, Hisaaki

    2016-12-01

    In this paper we present the effects of thermomechanical couplings occurring in polyurethane shape memory polymer subjected to cyclic tensile loadings conducted at various strain rates. Stress-strain characteristics were elaborated using a quasistatic testing machine, whereas the specimen temperature changes accompanying the deformation process were obtained with an infrared camera. We demonstrate a tight correlation between the mechanical and thermal results within the initial loading stage. The polymer thermomechanical behaviour in four subsequent loading-unloading cycles and the influence of the strain rate on the stress and the related temperature changes were also examined. In the range of elastic deformation the specimen temperature drops below the initial level due to thermoelastic effect whereas at the higher strains the temperature always increased, due to the dissipative deformation mechanisms. The difference in the characteristics of the specimen temperature has been applied to determine a limit of the polymer reversible deformation and analyzed for various strain rates. It was shown that at the higher strain rates higher values of the stress and temperature changes are obtained, which are related to higher values of the polymer yield points. During the cyclic loading a significant difference between the first and the second cycle was observed. The subsequent loading-unloading cycles demonstrated similar sharply shaped stress and temperature profiles and gradually decrease in values.

  2. Cyclic stretch and compression forces alter microRNA-29 expression of human periodontal ligament cells.

    PubMed

    Chen, Yinghua; Mohammed, Arshad; Oubaidin, Maysaa; Evans, Carla A; Zhou, Xiaofeng; Luan, Xianghong; Diekwisch, Thomas G H; Atsawasuwan, Phimon

    2015-07-15

    MicroRNAs (miRs) play an important role in the development and remodeling of tissues through the regulation of large cohorts of extracellular matrix (ECM) genes. The purpose of the present study was to determine the response of miR-29 family expression to loading forces and their effects on ECM gene expression in periodontal ligament cells, the key effector cell population during orthodontic tooth movement. In a comparison between miRs from human periodontal ligament cells (PDLCs) and alveolar bone cells (ABCs) from healthy human subjects, the ABC cohort of miRs was substantially greater than the corresponding PDLC cohort. Cyclic mechanical stretch forces at 12% deformation at 0.1Hz for 24h decreased expression of miR-29 family member miRs about 0.5 fold while 2g/cm(2) compression force for 24h increased miR-29 family member expression in PDLCs 1.8-4 folds. Cyclic stretch up-regulated major ECM genes in PDLCs, such as COL1A1, COL3A1 and COL5A1, while the compression force resulted in a down-regulation of these ECM genes. Direct interactions of miR-29 and Col1a1, Col3a1 and Col5a1 were confirmed using a dual luciferase reporter gene assay. In addition, transient transfection of a miR-29b mimic in mouse PDLCs down-regulated Col1a1, Col3a1 and Col5a1 while the transfection of miR-29b inhibitor up-regulated these genes compared to control transfection indicating that these target ECM genes directly responded to the altered level of miR-29b. These results provided a possible explanation for the effects of the miR-29 family on loaded PDLCS and their roles in extracellular matrix gene expression.

  3. Inverse Slip Accompanying Twinning and Detwinning during Cyclic Loading of Magnesium Single Crystal

    DOE PAGES

    Yu, Qin; Wang, Jian; Jiang, Yanyao

    2013-01-01

    In situ , observation of twinning and detwinning in magnesium single crystals during tension-compression cyclic loading was made using optical microscopy. A quantitative analysis of plastic strain indicates that twinning and detwinning experience two stages, low and high work hardening de-twinning, and pure re-twinning and fresh twinning combined with retwinning. Slip is always activated. For the first time, inverse slip accompanying with pure retwinning and high work hardening detwinning was experimentally identified, which provides insights in better understanding of the activity of twining, detwinning, and slips.

  4. Dynamic performance of angle-steel concrete columns under low cyclic loading-I: Experimental study

    NASA Astrophysics Data System (ADS)

    Zheng, Wenzhong; Ji, Jing

    2008-03-01

    This paper describes low cyclic loading testing of nine angle-steel concrete column (ASCC) specimens. In the tests, the influence of the shear-span ratio, axial compression ratio and shear steel plate ratio on the hysteretic behavior, energy dissipation, strength degradation, stiffness degradation, skeleton curve and ductility of the ASCCs is studied. Based on the test results, some conclusions are presented. The P- Δ and sectional M — ϕ hysteretic models for the ASCCs are presented in a companion paper (Zheng and Ji, 2008).

  5. Behavior of nonplastic silty soils under cyclic loading.

    PubMed

    Ural, Nazile; Gunduz, Zeki

    2014-01-01

    The engineering behavior of nonplastic silts is more difficult to characterize than is the behavior of clay or sand. Especially, behavior of silty soils is important in view of the seismicity of several regions of alluvial deposits in the world, such as the United States, China, and Turkey. In several hazards substantial ground deformation, reduced bearing capacity, and liquefaction of silty soils have been attributed to excess pore pressure generation during dynamic loading. In this paper, an experimental study of the pore water pressure generation of silty soils was conducted by cyclic triaxial tests on samples of reconstituted soils by the slurry deposition method. In all tests silty samples which have different clay percentages were studied under different cyclic stress ratios. The results have showed that in soils having clay content equal to and less than 10%, the excess pore pressure ratio buildup was quicker with an increase in different cyclic stress ratios. When fine and clay content increases, excess pore water pressure decreases constant cyclic stress ratio in nonplastic silty soils. In addition, the applicability of the used criteria for the assessment of liquefaction susceptibility of fine grained soils is examined using laboratory test results.

  6. Behavior of Nonplastic Silty Soils under Cyclic Loading

    PubMed Central

    Ural, Nazile; Gunduz, Zeki

    2014-01-01

    The engineering behavior of nonplastic silts is more difficult to characterize than is the behavior of clay or sand. Especially, behavior of silty soils is important in view of the seismicity of several regions of alluvial deposits in the world, such as the United States, China, and Turkey. In several hazards substantial ground deformation, reduced bearing capacity, and liquefaction of silty soils have been attributed to excess pore pressure generation during dynamic loading. In this paper, an experimental study of the pore water pressure generation of silty soils was conducted by cyclic triaxial tests on samples of reconstituted soils by the slurry deposition method. In all tests silty samples which have different clay percentages were studied under different cyclic stress ratios. The results have showed that in soils having clay content equal to and less than 10%, the excess pore pressure ratio buildup was quicker with an increase in different cyclic stress ratios. When fine and clay content increases, excess pore water pressure decreases constant cyclic stress ratio in nonplastic silty soils. In addition, the applicability of the used criteria for the assessment of liquefaction susceptibility of fine grained soils is examined using laboratory test results. PMID:24672343

  7. Micromechanics of intergranular creep failure under cyclic loading

    SciTech Connect

    Giessen, E. van der; Tvergaard, V.

    1996-07-01

    This paper is concerned with a micromechanical investigation of intergranular creep failure caused by grain boundary cavitation under strain-controlled cyclic loading conditions. Numerical unit cell analyses are carried out for a planar polycrystal model in which the grain material and the grain boundaries are modeled individually. The model incorporates power-law creep of the grains, viscous grain boundary sliding between grains as well as the nucleation and growth of grain boundary cavities until they coalesce and form microcracks. Study of a limiting case with a facet-size microcrack reveals a relatively simple phenomenology under either balanced loading, slow-fast loading or balanced loading with a hold period at constant tensile stress. Next, a (non-dimensionalized) parametric study is carried out which focuses on the effect of the diffusive cavity growth rate relative to the overall creep rate, and the effects of cavity nucleation and grain boundary sliding. The model takes account of the build up of residual stresses during cycling, and it turns out that this, in general, gives rise to a rather complex phenomenology, but some cases are identified which approach the simple microcrack behavior. The analyses provide some new understanding that helps to explain the sometimes peculiar behavior under balanced cyclic creep.

  8. An anisotropic damage model for concrete structures under cyclic loading-uniaxial modeling

    NASA Astrophysics Data System (ADS)

    Long, Yuchuan; He, Yuming

    2017-05-01

    An anisotropic damage model is developed based on conventional rotating crack approach. It uses nonlinear unloading/linear reloading branches to model the hysteretic behavior of concrete. Two damage variables, determined by the ratio of accumulated dissipating energy to fracture energy, are introduced to represent the stiffness degradation in tension and compression. Three cyclic tests are simulated by this model and sensitivity analyses are conducted as well. The numerical responses calculated by the damage model are consistent with those obtained from the experiments. The numerical results reflect the nonlinear behavior observed in those tests, such as the damage-induced stiffness degradation, accumulation of residual deformation, energy dissipation caused by hysteretic behavior and stiffness recovery effect due to crack closure. Sensitivity analyses show that the damage exponents have significant influence on the computational accuracy. It is concluded that the anisotropic damage model is applicable to the nonlinear analyses of concrete structures subjected to cyclic loading.

  9. Fatigue crack growth in ferroelectrics driven by cyclic electric loading

    NASA Astrophysics Data System (ADS)

    Zhu, Ting; Yang, Wei

    1998-12-01

    Fatigue crack growth has been observed recently in ferroelectrics under cyclic electric loading. Does the crack grow by electric breakdown, or by the stress field near the crack tip? The present paper provides a mechanistic explanation for the electric-field-induced fatigue crack growth. The non-uniform electric field near an insulated crack tip might cause domain switching which in turn produces a concentrated stress field characterized by a stress intensity factor. For ferroelectrics poled along a direction perpendicular to the crack, we are able to show quantitatively that: (1) the stress intensity factor under a negative electric field is nine times as large as the stress intensity factor under a positive electric field; (2) the crack starts to grow if the stress intensity factor is higher than the fracture toughness of the material, but the stress intensity factor decreases as the crack extends and eventually results in crack arrest; (3) by reversing the electric field, the stress intensity factor is increased and crack growth resumes; and (4) this model can predict the extent of fatigue crack growth. In contrast to the conventional perception of (mechanical) fatigue, the fatigue crack growth in ferroelectrics under cyclic electric loading is a step by step cleavage process caused by a domain switching sequence that generates a cyclic driving stress field near the crack tip.

  10. High load operation in a homogeneous charge compression ignition engine

    DOEpatents

    Duffy, Kevin P [Metamora, IL; Kieser, Andrew J [Morton, IL; Liechty, Michael P [Chillicothe, IL; Hardy, William L [Peoria, IL; Rodman, Anthony [Chillicothe, IL; Hergart, Carl-Anders [Peoria, IL

    2008-12-23

    A homogeneous charge compression ignition engine is set up by first identifying combinations of compression ratio and exhaust gas percentages for each speed and load across the engines operating range. These identified ratios and exhaust gas percentages can then be converted into geometric compression ratio controller settings and exhaust gas recirculation rate controller settings that are mapped against speed and load, and made available to the electronic

  11. Cyclic Plasticity under Shock Loading in an HCP Metal

    SciTech Connect

    Prime, Michael B.; Hunter, Abigail; Canfield, Thomas R.; Adams, Chris D.

    2012-06-08

    Plate impact experiments with pressures from 2 to 20 GPa, including one shock-partial release-reshock experiment, were performed on vacuum hot-pressed S-200F Beryllium. This hexagonal close-packed (HCP) metal shows significant plasticity effects in such conditions. The experiments were modeled in a Lagrangian hydrocode using an experimentally calibrated Preston-Tonks-Wallace (PTW) constitutive model. By using the shock data to constrain a high rate portion of PTW, the model was able to generally match plasticity effects on the measured wave profile (surface velocity) during the shock loading, but not unloading. A backstress-based cyclic plasticity model to capture the quasi-elastic release (Bauschinger-type effect) was explored in order to match the unloading and reloading portions of the measured wave profiles. A comparison is made with other approaches in the literature to capture the cyclic plasticity in shock conditions.

  12. Compressive Failure of Fiber Composites under Multi-Axial Loading

    NASA Technical Reports Server (NTRS)

    Basu, Shiladitya; Waas, Anthony M.; Ambur, Damodar R.

    2006-01-01

    This paper examines the compressive strength of a fiber reinforced lamina under multi-axial stress states. An equilibrium analysis is carried out in which a kinked band of rotated fibers, described by two angles, is sandwiched between two regions in which the fibers are nominally straight. Proportional multi-axial stress states are examined. The analysis includes the possibility of bifurcation from the current equilibrium state. The compressive strength of the lamina is contingent upon either attaining a load maximum in the equilibrium response or satisfaction of a bifurcation condition, whichever occurs first. The results show that for uniaxial loading a non-zero kink band angle beta produces the minimum limit load. For multi-axial loading, different proportional loading paths show regimes of bifurcation dominated and limit load dominated behavior. The present results are able to capture the beneficial effect of transverse compression in raising the composite compressive strength as observed in experiments.

  13. Compressive failure of fiber composites under multi-axial loading

    NASA Astrophysics Data System (ADS)

    Basu, Shiladitya; Waas, Anthony M.; Ambur, Damodar R.

    2006-03-01

    This paper examines the compressive strength of a fiber reinforced lamina under multi-axial stress states. An equilibrium analysis is carried out in which a kinked band of rotated fibers, described by two angles, is sandwiched between two regions in which the fibers are nominally straight. Proportional multi-axial stress states are examined. The analysis includes the possibility of bifurcation from the current equilibrium state. The compressive strength of the lamina is contingent upon either attaining a load maximum in the equilibrium response or satisfaction of a bifurcation condition, whichever occurs first. The results show that for uniaxial loading a non-zero kink band angle β produces the minimum limit load. For multi-axial loading, different proportional loading paths show regimes of bifurcation dominated and limit load dominated behavior. The present results are able to capture the beneficial effect of transverse compression in raising the composite compressive strength as observed in experiments.

  14. Compressive Failure of Fiber Composites under Multi-Axial Loading

    NASA Technical Reports Server (NTRS)

    Basu, Shiladitya; Waas, Anthony M.; Ambur, Damodar R.

    2006-01-01

    This paper examines the compressive strength of a fiber reinforced lamina under multi-axial stress states. An equilibrium analysis is carried out in which a kinked band of rotated fibers, described by two angles, is sandwiched between two regions in which the fibers are nominally straight. Proportional multi-axial stress states are examined. The analysis includes the possibility of bifurcation from the current equilibrium state. The compressive strength of the lamina is contingent upon either attaining a load maximum in the equilibrium response or satisfaction of a bifurcation condition, whichever occurs first. The results show that for uniaxial loading a non-zero kink band angle beta produces the minimum limit load. For multi-axial loading, different proportional loading paths show regimes of bifurcation dominated and limit load dominated behavior. The present results are able to capture the beneficial effect of transverse compression in raising the composite compressive strength as observed in experiments.

  15. Interactive evolution concept for analyzing a rock salt cavern under cyclic thermo-mechanical loading

    NASA Astrophysics Data System (ADS)

    König, Diethard; Mahmoudi, Elham; Khaledi, Kavan; von Blumenthal, Achim; Schanz, Tom

    2016-04-01

    The excess electricity produced by renewable energy sources available during off-peak periods of consumption can be used e.g. to produce and compress hydrogen or to compress air. Afterwards the pressurized gas is stored in the rock salt cavities. During this process, thermo-mechanical cyclic loading is applied to the rock salt surrounding the cavern. Compared to the operation of conventional storage caverns in rock salt the frequencies of filling and discharging cycles and therefore the thermo-mechanical loading cycles are much higher, e.g. daily or weekly compared to seasonally or yearly. The stress strain behavior of rock salt as well as the deformation behavior and the stability of caverns in rock salt under such loading conditions are unknown. To overcome this, existing experimental studies have to be supplemented by exploring the behavior of rock salt under combined thermo-mechanical cyclic loading. Existing constitutive relations have to be extended to cover degradation of rock salt under thermo-mechanical cyclic loading. At least the complex system of a cavern in rock salt under these loading conditions has to be analyzed by numerical modeling taking into account the uncertainties due to limited access in large depth to investigate material composition and properties. An interactive evolution concept is presented to link the different components of such a study - experimental modeling, constitutive modeling and numerical modeling. A triaxial experimental setup is designed to characterize the cyclic thermo-mechanical behavior of rock salt. The imposed boundary conditions in the experimental setup are assumed to be similar to the stress state obtained from a full-scale numerical simulation. The computational model relies primarily on the governing constitutive model for predicting the behavior of rock salt cavity. Hence, a sophisticated elasto-viscoplastic creep constitutive model is developed to take into account the dilatancy and damage progress, as well as

  16. Modeling of Anisotropic Rock Joints Under Cyclic Loading (Invited)

    NASA Astrophysics Data System (ADS)

    White, J. A.

    2013-12-01

    This work describes a constitutive framework for modeling the behavior of rough joints under cyclic loading. Particular attention is paid to the intrinsic links between dilatancy, surface degradation, and mobilized shear strength. The framework also accounts for the important effect of shear-induced anisotropy. Both the governing formulation and an algorithm for implicit numerical integration are presented. While the proposed methods are general, we also postulate a specific model that is compared with experimental data. It employs relatively few free parameters, but shows good agreement with laboratory tests.

  17. Mercury embrittlement of Cu-Al alloys under cyclic loading

    NASA Technical Reports Server (NTRS)

    Regan, T. M.; Stoloff, N. S.

    1977-01-01

    The effect of mercury on the room temperature, high cycle fatigue properties of three alloys: Cu-5.5 pct Al, Cu-7.3 pct Al, and Cu-6.3 pct Al-2.5 pct Fe has been determined. Severe embrittlement under cyclic loading in mercury is associated with rapid crack propagation in the presence of the liquid metal. A pronounced grain size effect is noted under mercury, while fatigue properties in air are insensitive to grain size. The fatigue results are discussed in relation to theories of adsorption-induced liquid metal embrittlement.

  18. Damage Evolution On Mechanical Parts Under Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Lestriez, P.; Bogard, F.; Shan, J. L.; Guo, Y. Q.

    2007-05-01

    This paper presents a fatigue damage model, based on the continuum damage mechanics and general thermodynamic theory, proposed by Lemaitre and Chaboche, for rolling bearings under very numerous loading cycles. A flow surface of fatigue using the Sines criterion is adopted. The coupling between the hardening plasticity and damage effects is considered in the constitutive equations. An explicit algorithm of weak coupling leads to a calculation very fast. This fatigue damage model is implemented into Abaqus/Explicit using a Vumat user's subroutine. Moreover, the damage variable in function of time is transformed into a function of number of cycles. An algorithm of cycle jump, with a criterion for choosing the number increment of cycles, is proposed, which allows to largely reduce the CPU time. The present damage simulation allows to determine the lifetime of mechanical parts under cyclic loading.

  19. Rat disc torsional mechanics: effect of lumbar and caudal levels and axial compression load.

    PubMed

    Espinoza Orías, Alejandro A; Malhotra, Neil R; Elliott, Dawn M

    2009-03-01

    Rat models with altered loading are used to study disc degeneration and mechano-transduction. Given the prominent role of mechanics in disc function and degeneration, it is critical to measure mechanical behavior to evaluate changes after model interventions. Axial compression mechanics of the rat disc are representative of the human disc when normalized by geometry, and differences between the lumbar and caudal disc have been quantified in axial compression. No study has quantified rat disc torsional mechanics. Compare the torsional mechanical behavior of rat lumbar and caudal discs, determine the contribution of combined axial load on torsional mechanics, and compare the torsional properties of rat discs to human lumbar discs. Cadaveric biomechanical study. Cyclic torsion without compressive load followed by cyclic torsion with a fixed compressive load was applied to rat lumbar and caudal disc levels. The apparent torsional modulus was higher in the lumbar region than in the caudal region: 0.081+/-0.026 (MPa/degrees, mean+/-SD) for lumbar axially loaded; 0.066+/-0.028 for caudal axially loaded; 0.091+/-0.033 for lumbar in pure torsion; and 0.056+/-0.035 for caudal in pure torsion. These values were similar to human disc properties reported in the literature ranging from 0.024 to 0.21 MPa/degrees. Use of the caudal disc as a model may be appropriate if the mechanical focus is within the linear region of the loading regime. These results provide support for use of this animal model in basic science studies with respect to torsional mechanics.

  20. Crack growth and closure effects under far-field cyclic compression in a SiC-whisker-reinforced 2124 aluminum composite

    SciTech Connect

    Dongil Kwon ); Younghwan Kim ); Sunghak Lee )

    1993-04-01

    In this study, cyclic compression fatigue tests were carried out on CT-type specimens of an aluminum matrix composite reinforced with SiC whiskers. The material used in this study was a 2124 Al-SiC[sub w] composite, manufactured by power metallurgy techniques and containing 15 v/o reinforcing SiC whisker. The crack closure induced by crack-face roughness in the wake region is found to be an important factor in limiting total fatigue crack growth distance in a 2124 Al-SiC[sub w] composite under cyclic compression. The critical saturation crack length in cyclic periodic compression loading can be controlled by compressive overload application, which decreases the crack-face roughness; here, a fatigue crack of 0.41 mm in length was obtained under cyclic compression. The tendency for the tension fatigue crack to bypass SiC whiskers microscopically and whisker-rich regions macroscopically leaves very rough features on fracture surfaces of the composite. However, most compression-fatigued fracture surfaces are found to be relatively flat, except around the crack tip region, which has an appearance (growth mechanism) similar to the tension-fatigued region.

  1. Loading and Boundary Condition Influences in a Poroelastic Finite Element Model of Cartilage Stresses in a Triaxial Compression Bioreactor

    PubMed Central

    Kallemeyn, Nicole A; Grosland, Nicole M; Pedersen, Doug R; Martin, James A; Brown, Thomas D

    2006-01-01

    Background: We developed a poroelastic finite element (FE) model of cartilage in dynamic triaxial compression to parametrically analyze the effects of loading and boundary conditions on a baseline model. Conventional mechanical tests on articular cartilage such as confined and unconfined compression, indentation, etc., do not fully allow for modulation of compression and shear at physiological levels whereas triaxial compression does. A Triaxial Compression Bioreactor, or TRIAX, has been developed to study chondrocyte responses to multi-axial stress conditions under cyclic loading. In the triaxial setting, however, a cartilage explant's physical testing environment departs from the ideal homogeneous stress state that would occur from strict linear superposition of the applied axial and transverse pressure. Method of Approach: An axisymmetric poroelastic FE model of a cartilage explant (4 mm diameter, 1.5 mm thick) in cyclic triaxial compression was created. Axial and transverse loads (2 MPa at 1 Hz.) were applied via a platen and containment sheath. Parameters of interest included the rise time and magnitude of the applied load, in addition to the containment sheath modulus and the friction coefficient at the cartilage/platen interfaces. Metrics of interest in addition to whole explant axial strain included axial (surface normal) stress, shear stress, pore pressure, and the fluid load carriage fraction within the explant. Results: Strain results were compared to experimental data from explants tested in the TRIAX under conditions similar to the baseline model. Explant biomechanics varied considerably over numbers of load cycles and parameter values. Cyclic loading caused an increase in accumulated strain for the various loading and boundary conditions. Conclusions: Unlike what would be expected from linear superposition of the homogeneous stresses from the applied axial and transverse pressure, we have shown that the stress state within the TRIAX is considerably

  2. Effects of Cyclic Loading on the Uniaxial Behavior of Nitinol

    NASA Astrophysics Data System (ADS)

    Schlun, M.; Zipse, A.; Dreher, G.; Rebelo, N.

    2011-07-01

    The widespread development and use of implants made from NiTi is accompanied by the publication of many NiTi material characterization studies. These publications have increased significantly the knowledge about the mechanical properties of NiTi. However, this knowledge also increased the complexity of the numerical simulation of NiTi implants or devices. This study is focused on the uniaxial behavior of NiTi tubing due to cyclic loading and had the goal to deliver both precise and application-oriented results. Single aspects of this study have already been published (Wagner in Ein Beitrag zur strukturellen und funktionalen Ermüdung von Drähten und Federn aus NiTi-Formgedaechtnislegierungen, Ph.D. Thesis, 2005; Eucken and Duerig in Acta Metall 37:2245-2252, 1989; Yawny et al. in Z Metallkd 96:608-618, 2005); however, there is no publication known that shows all the single effects combined in a "duty cycle case." It was of particular importance to summarize the main effects of pre-strain and subsequent small or large strain amplitudes on the material properties. The phenomena observed were captured in an extended Abaqus® Nitinol material model, presented by Rebelo et al. (A Material Model for the Cyclic Behavior of Nitinol, SMST Extended Abstracts 2010). The cyclic tensile tests were performed using a video extensometer to obtain accurate strain measurement on small electro-polished dog-bone specimen that were incorporated into a stent framework so that standard manufacturing methods could be used for the fabrication. This study indicates that a prestrain beyond 6% strain alters the transformation plateaus and if the cyclic displacement amplitude is large enough, additional permanent deformations are observed, the lower plateau and most notably the upper plateau change. The changes to the upper plateau are very interesting in the sense that an additional stress plateau develops: its "start stress" is lowered thereby creating a new plateau up to the highest level

  3. BEHAVIOR OF POST-INSTALLED ANCHORS TESTED BY STEPWISE INCREASING CYCLIC LOAD PROTOCOLS

    PubMed Central

    Mahrenholtz, Philipp; Eligehausen, Rolf; Hutchinson, Tara C.; Hoehler, Matthew S.

    2016-01-01

    Cyclic loads are a characteristic feature of actions acting on structures and anchorages during earthquakes. For this reason, seismic qualification of post-installed concrete anchors according to the internationally recognized American Concrete Institute (ACI) standard ACI 355 is based on cyclic load tests. The protocols for these tests, however, have limited scientific basis. Therefore, in the present paper newly-developed test protocols with stepwise-increasing load amplitudes are utilized to more realistically evaluate anchor seismic performance. The study focuses on the load-displacement behavior of common anchor types installed in cracked concrete and subjected to both cyclic tension and cyclic shear actions. The results confirmed robust behavior for anchors loaded in cyclic tension even in the presence of crack widths in the anchorage material larger than currently required by ACI 355. In addition, the critical influence of low cycle fatigue on the performance of anchors loaded in cyclic shear is demonstrated. PMID:27890969

  4. BEHAVIOR OF POST-INSTALLED ANCHORS TESTED BY STEPWISE INCREASING CYCLIC LOAD PROTOCOLS.

    PubMed

    Mahrenholtz, Philipp; Eligehausen, Rolf; Hutchinson, Tara C; Hoehler, Matthew S

    2016-09-01

    Cyclic loads are a characteristic feature of actions acting on structures and anchorages during earthquakes. For this reason, seismic qualification of post-installed concrete anchors according to the internationally recognized American Concrete Institute (ACI) standard ACI 355 is based on cyclic load tests. The protocols for these tests, however, have limited scientific basis. Therefore, in the present paper newly-developed test protocols with stepwise-increasing load amplitudes are utilized to more realistically evaluate anchor seismic performance. The study focuses on the load-displacement behavior of common anchor types installed in cracked concrete and subjected to both cyclic tension and cyclic shear actions. The results confirmed robust behavior for anchors loaded in cyclic tension even in the presence of crack widths in the anchorage material larger than currently required by ACI 355. In addition, the critical influence of low cycle fatigue on the performance of anchors loaded in cyclic shear is demonstrated.

  5. 78. PIPING CHANNEL FOR FUEL LOADING, FUEL TOPPING, COMPRESSED AIR, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    78. PIPING CHANNEL FOR FUEL LOADING, FUEL TOPPING, COMPRESSED AIR, GASEOUS NITROGEN, AND HELIUM - Vandenberg Air Force Base, Space Launch Complex 3, Launch Pad 3 East, Napa & Alden Roads, Lompoc, Santa Barbara County, CA

  6. Cyclic-loading Induced Lattice-Strain Asymmetry in Loading and Transverse Directions

    SciTech Connect

    Huang, E-Wen; Barabash, Rozaliya; Clausen, Bjorn; Liaw, Peter K

    2012-01-01

    Cyclic-loading effects on a nickel-based superalloy are investigated with in-situ neutron-diffraction measurements. The thermoelastic-temperature evolution subjected to cyclic loading is estimated based on the lattice-strain evolution. The atomic thermoelastic responses are compared with the measured bulk temperature evolution. Two transitions in the temperature-evolution are observed. The first transition, observed with the neutron-measurement results, is associated with the cyclic hardening/softening-structural transformation. The second transition is observed at larger number of fatigue cycles. It has a distinct origin and is related to the start of irreversible structural transformations during fatigue. A lattice-strain asymmetry behavior is observed. The lattice-strain asymmetry is quantified as a grain-orientation-dependent transverse/loading parameter (P-ratio). The P-ratio parameter evolution reveals the irreversible plastic deformation subjected to the fatigue. The irreversible fatigue phenomena might relate to the formation of the microcracks. At elevated temperatures the cyclic hardening/softening transition starts at lower fatigue cycles as compared to room temperature. A comparison between the room-temperature and the elevated-temperature fatigue experiments is performed. The P-ratio parameters show the same irreversible trends at both the room and the elevated temperatures.

  7. Chloride Permeability of Damaged High-Performance Fiber-Reinforced Cement Composite by Repeated Compressive Loads.

    PubMed

    Lee, Byung Jae; Hyun, Jung Hwan; Kim, Yun Yong; Shin, Kyung Joon

    2014-08-11

    The development of cracking in concrete structures leads to significant permeability and to durability problems as a result. Approaches to controlling crack development and crack width in concrete structures have been widely debated. Recently, it was recognized that a high-performance fiber-reinforced cement composite (HPFRCC) provides a possible solution to this inherent problem of cracking by smearing one or several dominant cracks into many distributed microcracks under tensile loading conditions. However, the chloride permeability of HPFRCC under compressive loading conditions is not yet fully understood. Therefore, the goal of the present study is to explore the chloride diffusion characteristics of HPFRCC damaged by compressive loads. The chloride diffusivity of HPFRCC is measured after being subjected to various repeated loads. The results show that the residual axial strain, lateral strain and specific crack area of HPFRCC specimens increase with an increase in the damage induced by repeated loads. However, the chloride diffusion coefficient increases only up to 1.5-times, whereas the specific crack area increases up to 3-times with an increase in damage. Although HPFRCC shows smeared distributed cracks in tensile loads, a significant reduction in the diffusion coefficient of HPFRCC is not obtained compared to plain concrete when the cyclic compressive load is applied below 85% of the strength.

  8. Assessment of Composite Delamination Self-Healing Under Cyclic Loading

    NASA Technical Reports Server (NTRS)

    O'Brien, T. Kevin

    2009-01-01

    Recently, the promise of self-healing materials for enhanced autonomous durability has been introduced using a micro-encapsulation technique where a polymer based healing agent is encapsulated in thin walled spheres and embedded into a base polymer along with a catalyst phase. For this study, composite skin-stiffener flange debonding specimens were manufactured from composite prepreg containing interleaf layers with a polymer based healing agent encapsulated in thin-walled spheres. Constant amplitude fatigue tests in three-point bending showed the effect of self-healing on the fatigue response of the skin-stiffener flange coupons. After the cycling that created debonding, fatigue tests were held at the mean load for 24 hours. For roughly half the specimens tested, when the cyclic loading was resumed a decrease in compliance (increase in stiffness) was observed, indicating that some healing had occurred. However, with continued cycling, the specimen compliance eventually increased to the original level before the hold, indicating that the damage had returned to its original state. As was noted in a prevoius study conducted with specimens tested under monotonically increasing loads to failure, healing achieved via the micro-encapsulation technique may be limited to the volume of healing agent available relative to the crack volume.

  9. Experimental Characteristics of Dry Stack Masonry under Compression and Shear Loading

    PubMed Central

    Lin, Kun; Totoev, Yuri Zarevich; Liu, Hongjun; Wei, Chunli

    2015-01-01

    The behavior of dry stack masonry (DSM) is influenced by the interaction of the infill with the frame (especially the joints between bricks), which requires further research. This study investigates the compression and shear behaviors of DSM. First, a series of compression tests were carried out on both masonry prism with mortar (MP_m) and DSM prism (MP_ds). The failure mode of each prism was determined. Different from the MP_m, the stress-strain relationship of the MP_ds was characterized by an upward concavity at the initial stage. The compression strength of the MP_ds was slightly reduced by 15%, while the elastic modulus was reduced by over 62%. In addition, 36 shear-compression tests were carried out under cyclic loads to emphasize the influence of various loads on the shear-compression behavior of DSM. The results showed that the Mohr-Coulomb friction law adequately represents the failure of dry joints at moderate stress levels, and the varying friction coefficients under different load amplitudes cannot be neglected. The experimental setup and results are valuable for further research. PMID:28793741

  10. Internal loading of an inhomogeneous compressible Earth with phase boundaries

    NASA Technical Reports Server (NTRS)

    Defraigne, P.; Dehant, V.; Wahr, J. M.

    1996-01-01

    The geoid and the boundary topography caused by mass loads inside the earth were estimated. It is shown that the estimates are affected by compressibility, by a radially varying density distribution, and by the presence of phase boundaries with density discontinuities. The geoid predicted in the chemical boundary case is 30 to 40 percent smaller than that predicted in the phase case. The effects of compressibility and radially varying density are likely to be small. The inner core-outer core topography for loading inside the mantle and for loading inside the inner core were computed.

  11. Internal loading of an inhomogeneous compressible Earth with phase boundaries

    NASA Technical Reports Server (NTRS)

    Defraigne, P.; Dehant, V.; Wahr, J. M.

    1996-01-01

    The geoid and the boundary topography caused by mass loads inside the earth were estimated. It is shown that the estimates are affected by compressibility, by a radially varying density distribution, and by the presence of phase boundaries with density discontinuities. The geoid predicted in the chemical boundary case is 30 to 40 percent smaller than that predicted in the phase case. The effects of compressibility and radially varying density are likely to be small. The inner core-outer core topography for loading inside the mantle and for loading inside the inner core were computed.

  12. Characterization of ultrafine-grained aluminum tubes processed by Tube Cyclic Extrusion–Compression (TCEC)

    SciTech Connect

    Babaei, A. Mashhadi, M.M.

    2014-09-15

    Tube Cyclic Extrusion–Compression as a novel severe plastic deformation technique for tubes was utilized for processing ultrafine grained 1050 aluminum alloy for the first time. In this method, aluminum tube is fully constrained and deformed between mandrel and chamber with a small neck zone. The material deformation during Tube Cyclic Extrusion–Compression processing analyzed and the grain refinement mechanism were described. The capability of Tube Cyclic Extrusion–Compression in grain refinement of the aluminum alloy was demonstrated by transmission electron microscopy observations and X-ray diffraction line profile analysis. The micrographs of the evolved microstructure show grain size of 850 nm and 550 nm after the first and second processing cycles of Tube Cyclic Extrusion–Compression, respectively. Mechanical properties of the initial and processed specimens were extracted from ring-hoop tensile tests. The documented results confirm grain refinement by showing remarkable increase in the yield and ultimate strengths. The main increase in strength and decrease in elongation take place after the first cycle. The microhardness assessments illustrate increase from the initial value of 29 Hv to 44 and 49 Hv respectively after the first and second cycles of Tube Cyclic Extrusion–Compression. There is a good homogeneity in peripheral microhardness and microhardness across the tube thickness. - Highlights: • Tubes of AA1050 for the first time were successfully SPD processed by TCEC. • The grain size was refined to 550 nm after two cycles of TCEC. • Notable increase in the strength and decrease in the elongation were documented. • The microhardness increased to 49 Hv from the initial value of 29 Hv. • Good homogeneity in the microhardness distribution was recorded.

  13. Behavior of tunnel form buildings under quasi-static cyclic lateral loading

    USGS Publications Warehouse

    Yuksel, S.B.; Kalkan, E.

    2007-01-01

    In this paper, experimental investigations on the inelastic seismic behavior of tunnel form buildings (i.e., box-type or panel systems) are presented. Two four-story scaled building specimens were tested under quasi-static cyclic lateral loading in longitudinal and transverse directions. The experimental results and supplemental finite element simulations collectively indicate that lightly reinforced structural walls of tunnel form buildings may exhibit brittle flexural failure under seismic action. The global tension/compression couple triggers this failure mechanism by creating pure axial tension in outermost shear-walls. This type of failure takes place due to rupturing of longitudinal reinforcement without crushing of concrete, therefore is of particular interest in emphasizing the mode of failure that is not routinely considered during seismic design of shear-wall dominant structural systems.

  14. Evaluation of an In Situ Gelable and Injectable Hydrogel Treatment to Preserve Human Disc Mechanical Function Undergoing Physiologic Cyclic Loading Followed by Hydrated Recovery.

    PubMed

    Showalter, Brent L; Elliott, Dawn M; Chen, Weiliam; Malhotra, Neil R

    2015-08-01

    Despite the prevalence of disc degeneration and its contributions to low back problems, many current treatments are palliative only and ultimately fail. To address this, nucleus pulposus replacements are under development. Previous work on an injectable hydrogel nucleus pulposus replacement composed of n-carboxyethyl chitosan, oxidized dextran, and teleostean has shown that it has properties similar to native nucleus pulposus, can restore compressive range of motion in ovine discs, is biocompatible, and promotes cell proliferation. The objective of this study was to determine if the hydrogel implant will be contained and if it will restore mechanics in human discs undergoing physiologic cyclic compressive loading. Fourteen human lumbar spine segments were tested using physiologic cyclic compressive loading while intact, following nucleotomy, and again following treatment of injecting either phosphate buffered saline (PBS) (sham, n = 7) or hydrogel (implant, n = 7). In each compressive test, mechanical parameters were measured immediately before and after 10,000 cycles of compressive loading and following a period of hydrated recovery. The hydrogel implant was not ejected from the disc during 10,000 cycles of physiological compression testing and appeared undamaged when discs were bisected following all mechanical tests. For sham samples, creep during cyclic loading increased (+15%) from creep during nucleotomy testing, while for implant samples creep strain decreased (-3%) toward normal. There was no difference in compressive modulus or compressive strains between implant and sham samples. These findings demonstrate that the implant interdigitates with the nucleus pulposus, preventing its expulsion during 10,000 cycles of compressive loading and preserves disc creep within human L5-S1 discs. This and previous studies provide a solid foundation for continuing to evaluate the efficacy of the hydrogel implant.

  15. Mechanical Behavior of AZ31B Mg Alloy Sheets under Monotonic and Cyclic Loadings at Room and Moderately Elevated Temperatures

    PubMed Central

    Nguyen, Ngoc-Trung; Seo, Oh Suk; Lee, Chung An; Lee, Myoung-Gyu; Kim, Ji-hoon; Kim, Heon Young

    2014-01-01

    Large-strain monotonic and cyclic loading tests of AZ31B magnesium alloy sheets were performed with a newly developed testing system, at different temperatures, ranging from room temperature to 250 °C. Behaviors showing significant twinning during initial in-plane compression and untwinning in subsequent tension at and slightly above room temperature were recorded. Strong yielding asymmetry and nonlinear hardening behavior were also revealed. Considerable Bauschinger effects, transient behavior, and variable permanent softening responses were observed near room temperature, but these were reduced and almost disappeared as the temperature increased. Different stress–strain responses were inherent to the activation of twinning at lower temperatures and non-basal slip systems at elevated temperatures. A critical temperature was identified to account for the transition between the twinning-dominant and slip-dominant deformation mechanisms. Accordingly, below the transition point, stress–strain curves of cyclic loading tests exhibited concave-up shapes for compression or compression following tension, and an unusual S-shape for tension following compression. This unusual shape disappeared when the temperature was above the transition point. Shrinkage of the elastic range and variation in Young’s modulus due to plastic strain deformation during stress reversals were also observed. The texture-induced anisotropy of both the elastic and plastic behaviors was characterized experimentally. PMID:28788514

  16. A loading system for creep testing under constant compressive stress

    NASA Technical Reports Server (NTRS)

    Dobes, F.; Zverina, O.; Cadek, J.

    1987-01-01

    A critical analysis is made of layouts assuring constant stress under creep, pointing out the difficulties of using these layouts for compressive testing. A new mechanical system to maintain stress during creep testing is proposed. Constant stress is achieved by a definite motion of the load. The proposed system can be used in tensile or compressive testing. Practical measurements reveal that the stress constancy error is not greater than plus or minus 1.5 percent up to relative deformation of 30 percent.

  17. Numerical Investigation of the Dynamic Properties of Intermittent Jointed Rock Models Subjected to Cyclic Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Dai, Feng; Zhao, Tao; Xu, Nu-wen

    2017-01-01

    Intermittent jointed rocks, which exist in a myriad of engineering projects, are extraordinarily susceptible to cyclic loadings. Understanding the dynamic fatigue properties of jointed rocks is necessary for evaluating the stability of rock engineering structures. This study numerically investigated the influences of cyclic loading conditions (i.e., frequency, maximum stress and amplitude) and joint geometric configurations (i.e., dip angle, persistency and interspace) on the dynamic fatigue mechanisms of jointed rock models. A reduction model of stiffness and strength was first proposed, and then, sixteen cyclic uniaxial loading tests with distinct loading parameters and joint geometries were simulated. Our results indicate that the reduction model can effectively reproduce the hysteresis loops and the accumulative plastic deformation of jointed rocks in the cyclic process. Both the loading parameters and the joint geometries significantly affect the dynamic properties, including the irreversible strain, damage evolution, dynamic residual strength and fatigue life. Three failure modes of jointed rocks, which are principally controlled by joint geometries, occur in the simulations: splitting failure through the entire rock sample, sliding failure along joint planes and mixed failure, which are principally controlled by joint geometries. Furthermore, the progressive failure processes of the jointed rock samples are numerically observed, and the different loading stages can be distinguished by the relationship between the number of broken bonds and the axial stress.

  18. Tensile Fracture Strength of Brisbane Tuff by Static and Cyclic Loading Tests

    NASA Astrophysics Data System (ADS)

    Erarslan, N.; Alehossein, H.; Williams, D. J.

    2014-07-01

    This research presents the results of laboratory experiments during the investigation of tensile strength-strain characteristics of Brisbane tuff disc specimens under static and diametral cyclic loading. Three different cyclic loading methods were used; namely, sinusoidal cyclic loading, type I and II increasing cyclic loading with various amplitude values. The first method applied the stress amplitude-cycle number (s-n) curve approach to the measurement of the indirect tensile strength (ITS) and fracture toughness ( K IC) values of rocks for the first time in the literature. The type I and II methods investigated the effect of increasing cyclic loading on the ITS and K IC of rocks. For Brisbane tuff, the reduction in ITS was found to be 30 % under sinusoidal loading, whereas type I and II increasing cyclic loading caused a maximum reduction in ITS of 36 %. The maximum reduction of the static K IC of 46 % was obtained for the highest amplitude type I cyclic loading tested. For sinusoidal cyclic loading, a maximum reduction of the static K IC of 30 % was obtained. A continuous irreversible accumulation of damage was observed in dynamic cyclic tests conducted at different amplitudes and mean stress levels. Scanning electron microscope images showed that fatigue damage in Brisbane tuff is strongly influenced by the failure of the matrix because of both inter-granular fracturing and trans-granular fracturing. The main characteristic was grain breakage under cyclic loading, which probably starts at points of contact between grains and is accompanied by the production of very small fragments, probably due to frictional sliding within the weak matrix.

  19. Structural strength of cancellous specimens from bovine femur under cyclic compression

    PubMed Central

    Endo, Kaori; Yamada, Satoshi; Todoh, Masahiro; Takahata, Masahiko; Iwasaki, Norimasa

    2016-01-01

    The incidence of osteoporotic fractures was estimated as nine million worldwide in 2000, with particular occurrence at the proximity of joints rich in cancellous bone. Although most of these fractures spontaneously heal, some fractures progressively collapse during the early post-fracture period. Prediction of bone fragility during progressive collapse following initial fracture is clinically important. However, the mechanism of collapse, especially the gradual loss of the height in the cancellous bone region, is not clearly proved. The strength of cancellous bone after yield stress is difficult to predict since structural and mechanical strength cannot be determined a priori. The purpose of this study was to identify whether the baseline structure and volume of cancellous bone contributed to the change in cancellous bone strength under cyclic loading. A total of fifteen cubic cancellous bone specimens were obtained from two 2-year-old bovines and divided into three groups by collection regions: femoral head, neck, and proximal metaphysis. Structural indices of each 5-mm cubic specimen were determined using micro-computed tomography. Specimens were then subjected to five cycles of uniaxial compressive loading at 0.05 mm/min with initial 20 N loading, 0.3 mm displacement, and then unloading to 0.2 mm with 0.1 mm displacement for five successive cycles. Elastic modulus and yield stress of cancellous bone decreased exponentially during five loading cycles. The decrease ratio of yield stress from baseline to fifth cycle was strongly correlated with bone volume fraction (BV/TV, r = 0.96, p < 0.01) and structural model index (SMI, r = − 0.81, p < 0.01). The decrease ratio of elastic modulus from baseline to fifth cycle was also correlated with BV/TV (r = 0.80, p < 0.01) and SMI (r = − 0.78, p < 0.01). These data indicate that structural deterioration of cancellous bone is associated with bone strength after yield stress. This study suggests that baseline cancellous

  20. Elevated Temperature Slow Crack Growth of Silicon Nitride Under Dynamic, Static and Cyclic Flexural Loading

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Salem, Jonathan A.; Nemeth, Noel; Gyekenyesi, John P.

    1994-01-01

    The slow crack growth parameters of a hot-pressed silicon nitride were determined at 1200 and 1300 C in air by statically, dynamically and cyclicly loading bend specimens. The fatigue parameters were estimated using the recently developed CARES/Life computer code. Good agreement exists between the flexural results. However, fatigue susceptibility under static uniaxial tensile loading, reported elsewhere, was greater than in flexure. Cyclic flexural loading resulted in the lowest apparent flexural fatigue susceptibility.

  1. Experimental investigation on mechanical damage characteristics of sandstone under triaxial cyclic loading

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Qi; Ranjith, P. G.; Huang, Yan-Hua; Yin, Peng-Fei; Jing, Hong-Wen; Gui, Yi-Lin; Yu, Qing-Lei

    2015-05-01

    The mechanical damage characteristics of sandstone subjected to cyclic loading is very significant to evaluate the stability and safety of deep excavation damage zones. However to date, there are very few triaxial experimental studies of sandstone under cyclic loading. Moreover, few X-ray micro-computed tomography (micro-CT) observations have been adopted to reveal the damage mechanism of sandstone under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic loading tests and X-ray micro-CT observations were conducted to analyse the mechanical damage characteristics of sandstone with respect to different confining pressures. The results indicated that at lower confining pressures, the triaxial strength of sandstone specimens under cyclic loading is higher than that under monotonic loading; whereas at confining pressures above 20 MPa, the triaxial strength of sandstone under cyclic loading is approximately equal to that under monotonic loading. With the increase of cycle number, the crack damage threshold of sandstone first increases, and then significantly decreases and finally remains constant. Based on the damage evolution of irreversible deformation, it appears that the axial damage value of sandstone is all higher than the radial damage value before the peak strength; whereas the radial damage value is higher than the axial damage value after the peak strength. The evolution of Young's modulus and Poisson's ratio of sandstone can be characterized as having four stages: (i) Stage I: material strengthening; (ii) Stage II: material degradation; (iii) Stage III: material failure and (iv) Stage IV: structure slippage. X-ray micro-CT observations demonstrated that the CT scanning surface images of sandstone specimens are consistent with actual surface crack photographs. The analysis of the cross-sections of sandstone supports that the system of crack planes under triaxial cyclic loading is much more complicated than that under triaxial

  2. Analysis of Glenoid Fixation with Anatomic Total Shoulder Arthroplasty in an Extreme Cyclic Loading Scenario.

    PubMed

    Roche, Christopher P; Staunch, Cameron; Hahn, William; Grey, Sean G; Flurin, Pierre-Henri; Wright, Thomas W; Zuckerman, Joseph D

    2015-12-01

    ASTM F2028-14 was adopted to recom mend a cyclic eccentric glenoid edge loading test that simulates the rocking horse loading mechanism beleived to cause aTSA glenoid loosening. While this method accurately simulates that failure mechanism, the recommended 750 N load may not be sufficient to simulate worst-case loading magnitudes, and the recommended 100,000 cycles may not be sufficient to simulate device fatigue-related failure modes. Finally, if greater loading magnitude or a larger number of cycles is performed, the recommended substrate density may not be sufficiently strong to support the elevated loads and cycles. To this end, a new test method is proposed to supplement ASTM F2028-14. A series of cyclic tests were performed to evaluate the long-term fixation strength of two different hybrid glenoid designs in both low (15 pcf) and high (30 pcf) density polyurethane blocks at elevated loads relative to ASTM F2028-14. To simulate a worst case clinical condition in which the humeral head is superiorly migrated, a cyclic load was applied to the superior glenoid rim to induce a maximum torque on the fixation pegs for three different cyclic loading tests: 1. 1,250 N load for 0.75 M cycles in a 15 pcf block, 2. 1,250 N load for 1.5 M cycles in a 30 pcf block, and 3. 2,000 N load for 0.65 M cycles in a 30 pcf block. All devices completed cyclic loading without failure, fracture, or loss of fixation regardless of glenoid design, polyurethane density, loading magnitude, or cycle length. No significant difference in post-cyclic displacement was noted between designs in any of the three tests. Post-cyclic radiographs demonstrated that each device maintained fixa - tion with the metal pegs within the bone-substitute blocks with no fatigue related failures. These results demonstrate that both cemented hybrid glenoids maintained fixation when tested according to each cyclic loading scenario, with no difference in post-cyclic displacement observed between designs. The lack

  3. Composite lamina compressive properties using the Wyoming combined loading compression test method

    NASA Astrophysics Data System (ADS)

    Wegner, Peter Mark

    The determination of lamina compressive strength and modulus using the Wyoming Combined Loading Compression (CLC) test method was investigated. In this test method an untabbed [90/0]ns cross-ply test coupon is tested in uniaxial compression using the CLC test fixture. The longitudinal modulus and strength of the 0°-plies are determined by applying a back-out factor, calculated using Classical Lamination Theory, to the measured longitudinal laminate modulus and strength. A parametric study revealed that specimen quality, load train alignment, and fixture dimensional tolerances have a large impact on the measured compressive properties. Thus, a significant amount of time was dedicated to developing specimen fabrication and testing procedures to minimize variations in the measured compressive properties. A comparative study of the CLC and IITRI test fixtures showed that the CLC test fixture is superior to the IITRI fixture in many ways. Although the compressive properties measured using these two fixtures are often statistically equivalent, the CLC test fixture is easier to use, less expensive to fabricate, and much less massive than the IITRI fixture. In a second portion of the comparative study, the 0°-ply compressive strength obtained using [90/0]ns cross-ply test specimens was compared to the 0°-ply compressive strength obtained using quasi-isotropic test specimens. This revealed that the 0°-ply compressive strength was independent of the laminate orientation. This "backed-out" 0°-ply compressive strength is then by definition the "design value" for the strength of the composite material in compression. The present study showed that valid "design values" for the compressive strength of laminated composite materials can be obtained using the CLC test method. This was verified by testing two classes of structural components in compression, filament-wound cylinders, and honeycomb sandwich beams. The compressive strength of the 0°-plies at failure in the

  4. Mechanical instabilities of individual multiwalled carbon nanotubes under cyclic axial compression.

    PubMed

    Yap, Hsao W; Lakes, Roderic S; Carpick, Robert W

    2007-05-01

    Individual multiwalled carbon nanotubes with a range of aspect ratios are subjected to cyclic axial compression to large strains using atomic force microscopy. Distinct elastic buckling and post-buckling phenomena are observed reproducibly and are ascribed to Euler, asymmetric shell buckling (i.e., kinking), and symmetric shell buckling. These show agreement with continuum theories that range from approximate to remarkable. Shell buckling yields reproducible incremental negative stiffness in the initial post-buckled regime.

  5. Removal torque evaluation of three different abutment screws for single implant restorations after mechanical cyclic loading

    PubMed Central

    PAEPOEMSIN, T.; REICHART, P. A.; CHAIJAREENONT, P.; STRIETZEL, F. P.; KHONGKHUNTHIAN, P.

    2016-01-01

    SUMMARY Purpose The aim of this study was to evaluate the removal torque of three different abutment screws and pull out strength of implant-abutment connection for single implant restorations after mechanical cyclic loading. Methods The study was performed in accordance with ISO 14801:2007. Three implant groups (n=15) were used: group A, PW Plus® with flat head screw; group B, PW Plus® with tapered screw; and group C, Conelog® with flat head screw. All groups had the same implant-abutment connection feature: cone with mandatory index. All screws were tightened with manufacturer’s recommended torque. Ten specimens in each group underwent cyclic loading (1×106 cycles, 10 Hz, and 250 N). Then, all specimens were un-tightened, measured for the removal torque, and underwent a tensile test. The force that dislodged abutment from implant fixture was recorded. The data were analysed using independent sample t-test, ANOVA and Tukey HSD test. Results Before cyclic loading, removal torque in groups A, B and C were significantly different (B> A> C, P<.05). After cyclic loading, removal torque in all groups decreased significantly (P<.05). Group C revealed significantly less removal torque than groups A and B (P<.005). Tensile force in all groups significantly increased after cyclic loading (P<.05), group A had significantly less tensile force than groups B and C (P<.005). Conclusions Removal torque reduced significantly after cyclic loading. Before cyclic loading, tapered screws maintained more preload than did flat head screws. After cyclic loading, tapered and flat head screws maintained even amounts of preload. The tensile force that dislodged abutment from implant fixture increased immensely after cyclic loading. PMID:28042450

  6. Embedded trilayer graphene flakes under tensile and compressive loading

    NASA Astrophysics Data System (ADS)

    Tsoukleri, G.; Parthenios, J.; Galiotis, C.; Papagelis, K.

    2015-06-01

    The mechanical response of embedded ABA trilayer graphene flakes loaded in tension and compression on polymer beams is monitored by simultaneous Raman measurements through the strain sensitivity of the G or 2D peaks. A characteristic peculiarity of the investigated flake is that it contains a trilayer and bilayer part. The Bernal stacked bilayer was used as a strain sensor aiming to assess the efficiency of the load transfer from the polymer matrix through shear to the individual graphene layers. For the trilayer graphene in tension, both peaks are redshifted and splitting of the G peak is reported for the first time. In compression, the studied sample was an almost isolated trilayer, in which both peaks are blue-shifted up to a critical compressive strain. This critical strain is found to be one fourth of the value found in the case of single layer graphene despite the higher bending rigidity that trilayer exhibits over the much thinner monolayer.

  7. Frozen storage increases the ultimate compressive load of porcine vertebrae.

    PubMed

    Callaghan, J P; McGill, S M

    1995-09-01

    The use of freezing as a method of storage is commonplace in mechanical testing of biological tissues. The effects of freezing on tissues that comprise spinal segments have been examined separately, but little work has been done on intact specimens. We examined the effect of freezing on the structural properties of porcine cervical spines. The intact cervical spines of seven pigs (a total of 14 specimens--seven of C2-C4 and seven of C5-C7) were stored frozen (-20 degrees C) for 1 month. The ultimate compressive load, displacement, stiffness, and energy absorbed were obtained using a monotonic compressive load applied at 3,000 N/sec. The structural properties were compared with those of another 14 porcine cervical specimens (control group, matched for age and weight) that were tested in a fresh state. The frozen storage of the vertebral specimens significantly increased the ultimate compressive load (24%) and energy absorbed to failure (33%). The stiffness and displacement at failure were not affected. We concluded that the use of freezing as a storage medium should be of concern when the resulting measures are used to quantify the ultimate compressive load of the spinal motion segments.

  8. Loading rate sensitivity of open hole composites in compression

    NASA Technical Reports Server (NTRS)

    Lubowinski, Steve J.; Guynn, E. G.; Elber, Wolf; Whitcomb, J. D.

    1988-01-01

    The results are reported of an experimental study on the compressive, time-dependent behavior of graphite fiber reinforced polymer composite laminates with open holes. The effect of loading rate on compressive strength was determined for six material systems ranging from brittle epoxies to thermoplastics at both 75 F and 220 F. Specimens were loaded to failure using different loading rates. The slope of the strength versus elapsed time-to-failure curve was used to rank the materials' loading rate sensitivity. All of the materials had greater strength at 75 F than at 220 F. All the materials showed loading rate effects in the form of reduced failure strength for longer elapsed-time-to-failure. Loading rate sensitivity was less at 220 F than the same material at 70 F. However, C12000/ULTEM and IM7/8551-7 were more sensitive to loading rate than the other materials at 220 F. AS4/APC2 laminates with 24, 32, and 48 plies and 1/16 and 1/4 inch diameter holes were tested. The sensitivity to loading rate was less for either increasing number of plies or larger hole size. The failure of the specimens made from brittle resins was accompanied by extensive delaminations while the failure of the roughened systems was predominantly by shear crippling. Fewer delamination failures were observed at the higher temperature.

  9. Effect of cyclic loading and temper condition on the tensile behavior of boron-aluminum

    NASA Technical Reports Server (NTRS)

    Herakovich, C. T.; Kennedy, J. M.; Tenney, D. R.

    1978-01-01

    Experimental results from monotonic and cyclic tension tests on six different 6061 boron-aluminum laminates show that the strength of fiber dominated laminates is decreased and the strength of matrix dominated laminates is increased by T6 heat treatment. Cyrogenic exposure and cyclic loading are shown to have little influence on strength. Cyclic loading is also shown to produce small reductions in modulus for some laminates and some temper conditions. The results are discussed in light of expected metallurgical and residual stress changes due to temperature excursions and loading cycles.

  10. Flexor tenorrhaphy tensile strength: reduction by cyclic loading: in vitro and ex vivo porcine study.

    PubMed

    Gibbons, C E R; Thompson, D; Sandow, M J

    2009-06-01

    The integrity of the repair is critical to maintain coaptation of the severed flexor tendon end until healing has advanced sufficiently. In our hospital, we use a modified Savage repair (four-strand Adelaide technique) using 3-0 Ethibond (Ethicon, Somerville, NJ, USA) for acute flexor tenorrhaphy and an active postrepair mobilization protocol. To explain the apparent differences between the theoretical and actual repair strength of a multistrand repair in a single tension test and the reduced strength of a repair subjected to cyclic loading, we compared single and cyclical tensile loading with different suture in vitro configurations of 3-0 Ethibond (Ethicon, Somerville, NJ, USA; one, two, and four strands) and an ex vivo four-strand repair of freshly divided porcine tendon to calculate the ultimate tensile strength (UTS). Mechanical testing was repeated 15 times with both single tensile and cyclical loading for each suture configuration and porcine repair. In the in vitro model, the presence of a knot in a single strand reduced the UTS by 50%. The stiffness of a knotted strand was substantially less than the unknotted strand but became identical after cyclical loading. There was no statistical significance of the UTS between single and cyclical loading with different numbers of strands in this model. In the ex vivo four-strand porcine repair model, there was a significant reduction in UTS with cyclical loading, which equated to the number of strands times the strength of the knotted strand. This discrepancy can be explained by the change in stiffness of the knotted strand after cyclical loading and has important implications for previous studies of suture tendon repair using single tensile loading where the UTS may have been overestimated. We believe that cyclical loading is more representative of physiological loading after acute flexor tendon repair and should be the testing model of choice in suture tenorrhaphy studies.

  11. Monotonic and cyclic loading behavior of porous scaffolds made from poly(para-phenylene) for orthopedic applications.

    PubMed

    Hoyt, Anthony J; Yakacki, Christopher M; Fertig, Ray S; Dana Carpenter, R; Frick, Carl P

    2015-01-01

    Porous poly(para-phenylene) (PPP) scaffolds have tremendous potential as an orthopedic biomaterial; however, the underlying mechanisms controlling the monotonic and cyclic behavior are poorly understood. The purpose of this study was to develop a method to integrate micro-computed tomography (μCT), finite-element analysis (FEA), and experimental results to uncover the relationships between the porous structure and mechanical behavior. The μCT images were taken from porous PPP scaffolds with a porosity of 75vol% and pore size distribution between 420 and 500µm. Representative sections of the image were segmented and converted into finite-element meshes. It was shown through FEA that localized stresses within the microstructure were approximately 100 times higher than the applied global stress during the linear loading regime. Experimental analysis revealed the S-N fatigue curves for fully dense and porous PPP samples were parallel on log-log plots, with the endurance limit for porous samples in tension being approximately 100 times lower than their solid PPP counterparts (0.3-35MPa) due to the extreme stress concentrations caused by the porous microarchitecture. The endurance limit for porous samples in compression was much higher than in tension (1.60MPa). Through optical, laser-scanning, and scanning-electron microscopy it was found that porous tensile samples failed under Mode I fracture in both monotonic and cyclic loading. By comparison, porous compressive samples failed via strut buckling/pore collapse monotonically and by shearing fracture during cyclic loading. Monotonic loading showed that deformation behavior was strongly correlated with pore volume fraction, matching foam theory well; however, fatigue behavior was much more sensitive to local stresses believed to cause crack nucleation.

  12. Analysis of delamination growth in compressively loaded composite laminates

    NASA Astrophysics Data System (ADS)

    Tratt, Matthew D.

    The present analytical and empirical study of composite structure delamination has attempted to predict the threshold stress for the initiation of delamination growth in compressively loaded composite laminates. The strain-energy release-rate distributions around circular delaminations are computed via MSC/NASTRAN analysis in conjunction with a virtual crack-opening technique. Static compression tests were conducted on specimens of graphite fiber-reinforced epoxy having circular delaminations of various sizes. Computed delamination growth threshold-stress prediction results were at substantial variance with the test data, but confirmed trends and gave qualitative insight into quasi-static delamination growth.

  13. Insentropic compression of solid using pulsed magnetic loading

    SciTech Connect

    HALL,CLINT A.; ASAY,JAMES R.; STYGAR,WILLIAM A.; SPIELMAN,RICK B.; ROSENTHAL,STEPHEN E.; KNUDSON,MARCUS D.; REISMAN,D.; TOOR,A.; CAUBLE,R.; HAYES,D.B.

    2000-04-18

    Shock loading techniques are often used to determine material response along a specific pressure loading curve referred to as the Hugoniot. However, many technological and scientific applications require accurate determination of dynamic material response that is off-Hugoniot, covering large regions of the equation-of-state surface. Unloading measurements from the shocked state provide off-Hugoniot information, but experimental techniques for measuring compressive off-Hugoniot response have been limited. A new pulsed magnetic loading technique is presented which provides previously unavailable information on isentropic loading of materials to pressures of several hundred kbar. This smoothly increasing pressure loading provides a good approximation to the high-pressure material isentrope centered at ambient conditions. The approach uses high current densities to create ramped magnetic loading to a few hundred kbar over time intervals of 100--200 ns. The method has successfully determined the isentropic mechanical response of copper to about 200 kbar and has been used to evaluate the kinetics of the alpha-epsilon phase transition occurring in iron at 130 kbar. With refinements in progress, the method shows promise for performing isentropic compression experiments to multi-Mbar pressures.

  14. Physical properties and compression loading behaviour of corn seed

    NASA Astrophysics Data System (ADS)

    Babić, Lj.; Radojèin, M.; Pavkov, I.; Babić, M.; Turan, J.; Zoranović, M.; Stanišić, S.

    2013-03-01

    The aim of this study was to acquire data on the physical properties and compression loading behaviour of seed of six corn hybrid varieties. The mean values of length, width, thickness, geometric diameter, surface area, porosity, single kernel mass, sphericity, bulk and true density, 1 000 kernelmass and coefficient of friction were studied at single level of corn seed moisture content. The calculated secant modulus of elasticity during compressive loading for dent corn was 0.995 times that of the semi-flint type; there were no significant differences in the value of this mechanical property between semi-flint and dent corn varieties. The linear model showed a decreasing tendency of secant modulus of elasticity for all hybrids as the moisture content of seeds increased.

  15. Compression loading behaviour of sunflower seeds and kernels

    NASA Astrophysics Data System (ADS)

    Selvam, Thasaiya A.; Manikantan, Musuvadi R.; Chand, Tarsem; Sharma, Rajiv; Seerangurayar, Thirupathi

    2014-10-01

    The present study was carried out to investigate the compression loading behaviour of five Indian sunflower varieties (NIRMAL-196, NIRMAL-303, CO-2, KBSH-41, and PSH- 996) under four different moisture levels (6-18% d.b). The initial cracking force, mean rupture force, and rupture energy were measured as a function of moisture content. The observed results showed that the initial cracking force decreased linearly with an increase in moisture content for all varieties. The mean rupture force also decreased linearly with an increase in moisture content. However, the rupture energy was found to be increasing linearly for seed and kernel with moisture content. NIRMAL-196 and PSH-996 had maximum and minimum values of all the attributes studied for both seed and kernel, respectively. The values of all the studied attributes were higher for seed than kernel of all the varieties at all moisture levels. There was a significant effect of moisture and variety on compression loading behaviour.

  16. Ultrasonic Measurement of Strain Distribution Inside Object Cyclically Compressed by Dual Acoustic Radiation Force

    NASA Astrophysics Data System (ADS)

    Odagiri, Yoshitaka; Hasegawa, Hideyuki; Kanai, Hiroshi

    2008-05-01

    One possible way to evaluate acupuncture therapy quantitatively is to measure the change in the elastic property of muscle after application of the therapy. Many studies have been conducted to measure mechanical properties of tissues using ultrasound-induced acoustic radiation force. To assess mechanical properties, strain must be generated in an object. However, a single radiation force is not effective because it mainly generates translational motion when the object is much harder than the surrounding medium. In this study, two cyclic radiation forces are simultaneously applied to a muscle phantom from two opposite horizontal directions so that the object is cyclically compressed in the horizontal direction. By the horizontal compression, the object is expanded vertically based on its incompressibility. The resultant vertical displacement is measured using another ultrasound pulse. Two ultrasonic transducers for actuation were both driven by the sum of two continuous sinusoidal signals at two slightly different frequencies [1 MHz and (1 M + 5) Hz]. The displacement of several micrometers in amplitude, which fluctuated at 5 Hz, was measured by the ultrasonic phased tracking method. Increase in thickness inside the object was observed just when acoustic radiation forces increased. Such changes in thickness correspond to vertical expansion due to horizontal compression.

  17. A Study of Polymer Materials Subjected to Isentropic Compression Loading

    NASA Astrophysics Data System (ADS)

    Hall, C. A.; Baer, M. R.; Gustavsen, R. L.; Hooks, D. E.; Orler, E. Bruce; Dattelbaum, D. M.; Sheffield, S. A.; Sutherland, G. T.

    2006-07-01

    This work applies a ramped, quasi-isentropic compression loading technique (ICE) to investigate the mechanical behavior of polymers that are often used in energetic composites. The focus of this effort is the determination of appropriate constitutive and EOS property data at high stress states and moderate strain rates that is needed for detailed mesoscale modeling. Several thicknesses of samples were subjected to a ramp load of ˜45 Kbar over 500 ns duration using the Sandia Z-machine. Profiles of transmitted ramp waves were measured at window interfaces using conventional VISAR. Shock physics analysis is then used to determine the nonlinear material response of the binder materials.

  18. Effects of Cyclic Loading Performance on Grain Boundary Motion of Nanocrystalline Ni

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Yang, Xinhua; Peng, Di

    2017-10-01

    Structural transformations and grain boundary (GB) motion in nanocrystalline Ni under cyclic loading were studied by molecular dynamics simulations, in particular the effects of maximum strain and cyclic strain amplitude. At a fixed cyclic strain amplitude, increases of the maximum strain increased the length of disordered segments at both ends of the GB and removed the GB migration hysteresis. Conversely, the cyclic strain amplitude shows different effects on the GB migration hysteresis at different maximum strains. The nucleation and motion of GB disconnections were not strongly affected by dislocations at a maximum strain of 4 pct. The cyclic strain amplitude slightly influenced GB migration hysteresis, such that the hysteresis was maintained over six cycles. Nevertheless, at a maximum strain of 6 pct, disordered GB segments at both ends of the GB shortened the distance between the two pinning points of GB motion. Thus, the cyclic strain amplitude has a marked effect on the GB migration hysteresis.

  19. Concrete Behavior under Dynamic Tensile-Compressive Load.

    DTIC Science & Technology

    1984-01-01

    be reviewed as well. Although structural concrete does not possess the thermal cracking problems during curing to the extent that mass concrete does...3 Hil H1 2 H13 H0 - OUTSIDE SURFACE OF CONCRETE CYLINDER Hl - INSIDE SURFACE OF CONCRETE CYLINDER Figure 2.4 Location of strain gages. CHAPTER 3...34 Fatigue Failure of Concrete Under Periodic Compressive Load," Trans Japanese Soc Civil Engrs, Vol 3, Part 1, pp 106-107. Kirillov, A. P. 1977. "Strength

  20. Evaluation of load transfer characteristics of a dynamic stabilization device on disc loading under compression.

    PubMed

    Zhang, Qing Hang; Zhou, Yuan Li; Petit, Dominique; Teo, Ee Chon

    2009-06-01

    In the current study, finite element analyses were conducted to examine the biomechanical capability of a newly design dynamic stabilization system, FlexPLUS, to restore the load transmission of degenerated intervertebral L4-L5 lumbar motion segment spine under compression. Detailed three-dimensional FE models of L4-L5 motion segment and the FlexPLUS were developed. Compressive loading up to 1000N was applied to the intact L4-L5 model, the L4-L5 models with slight and moderate degenerated disc, and the implanted L4-L5 model. Further more, the load transmission characteristics of Dynesys and a rigid rod was also simulated for comparison. The resultant load-displacement curves and the load transferred through annulus under various conditions were compared. The predicted axial displacement of L4 top surface against applied compressive force of the intact L4-L5 model agreed well with experimental data. The predicted results showed that degenerated disc has significant effect on the lumbar segment load bearing capacity. Not only the stiffness of the segment was greatly increased, the uniform nature of the disc stress distribution was also altered. The FlexPLUS can effectively reduce the disc loading of degenerated model. Although the non-uniform load distribution pattern through annulus was not improved, the overall stress magnitude was greatly reduced to the level of intact model for grade II degeneration.

  1. Behaviour and Analysis of Steel and Macro-Synthetic Fibre Reinforced Concrete Subjected to Reversed Cyclic Loading: A Pilot Investigation

    NASA Astrophysics Data System (ADS)

    Carnovale, David Joseph

    The benefits of fibre reinforced concrete (FRC) have been thoroughly investigated. Much of this work has focussed on steel FRC subjected to monotonic loads. Data on the structural behaviour of macro-synthetic FRC or FRC under cyclic loads is scarce. A pilot investigation on the shear behaviour of macro-synthetic FRC and on the behaviour of FRC under reversed cyclic in-plane shear loading was carried out. Five in-plane shear panel tests were performed. The parameters under study were the fibre material type (steel or macrosynthetic) and loading protocol. Additionally, a number of compression, direct tension, and flexural tests were performed to determine the material properties of the concretes for comparison. The material response of 2.0% by volume of macro-synthetic FRC matched closely with 1.0% steel FRC. Finally, building upon an existing steel FRC model, a model for macro-synthetic FRC in tension was proposed and a short verification study was undertaken.

  2. A testing technique allowing cyclic application of axial, bending, and torque loads to fracture plates to examine screw loosening.

    PubMed

    Szivek, J A; Yapp, R A

    1989-04-01

    Orthopaedic internal fracture fixation plates are subjected to combined axial, bending, and torsional loads in vivo which can cause screw loosening and implant failure. This paper outlines a relatively simple technique which allows controlled application of combined axial, bending, and torsional loading to examine the loosening rate of cortical screws used to attach these plates. Fiber reinforced polycarbonate rods with a tensile strength similar to that of cortical bone were cut at half their length to simulate fractured tibii. These were compression plated using a standardized technique and placed in a loading fixture. Joint loads at the knee determined from force plate analysis and statics were applied to a plated fixture during testing. The design of the fixture allowed adjustment of the proportion of bending and torsional loads applied to the test samples. It also allowed a reproducible means of applying a predetermined axial, bending, and torsional load. Screw loosening following cyclical loading was evaluated by measuring the amount of angular displacement required to retighten screws to a prescribed torque value. A torque wrench was modified to allow the measurement of these displacements.

  3. A study of binder materials subjected to isentropic compression loading.

    SciTech Connect

    Hall, Clint Allen; Orler, E. Bruce; Sheffield, Steve A; Gustavsen, Rick L.; Sutherland, Gerrit; Baer, Melvin R.; Hooks, D.E.

    2005-07-01

    Binders such as Estane, Teflon, Kel F and HTPB are typically used in heterogeneous explosives to bond polycrystalline constituents together as an energetic composite. Combined theoretical and experimental studies are underway to unravel the mechanical response of these materials when subjected to isentropic compression loading. Key to this effort is the determination of appropriate constitutive and EOS property data at extremely high stress-strain states as required for detailed mesoscale modeling. The Sandia Z accelerator and associated diagnostics provides new insights into mechanical response of these nonreactive constituents via isentropic ramp-wave compression loading. Several thicknesses of samples, varied from 0.3 to 1.2 mm, were subjected to a ramp load of {approx}42 Kbar over 500 ns duration using the Sandia Z-machine. Profiles of transmitted ramp waves were measured at window interfaces using conventional VISAR. Shock physics analysis is then used to determine the nonlinear material response of the binder materials. In this presentation we discuss experimental and modeling details of the ramp wave loading ICE experiments designed specifically for binder materials.

  4. Elastic-plastic analysis of a propagating crack under cyclic loading

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.; Armen, H., Jr.

    1974-01-01

    Development and application of a two-dimensional finite-element analysis to predict crack-closure and crack-opening stresses during specified histories of cyclic loading. An existing finite-element computer program which accounts for elastic-plastic material behavior under cyclic loading was modified to account for changing boundary conditions - crack growth and intermittent contact of crack surfaces. This program was subsequently used to study the crack-closure behavior under constant-amplitude and simple block-program loading.

  5. Elastic-plastic analysis of a propagating crack under cyclic loading

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.; Armen, H., Jr.

    1974-01-01

    Development and application of a two-dimensional finite-element analysis to predict crack-closure and crack-opening stresses during specified histories of cyclic loading. An existing finite-element computer program which accounts for elastic-plastic material behavior under cyclic loading was modified to account for changing boundary conditions - crack growth and intermittent contact of crack surfaces. This program was subsequently used to study the crack-closure behavior under constant-amplitude and simple block-program loading.

  6. Estimation of the Residual Fatigue Life of Laminated Composites Under a Multistage Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Strizhius, V.

    2016-11-01

    Problems on estimation of the residual fatigue life of laminated composites under a multistage regular cyclic loading (with a constant amplitude at each loading stage) are among the most frequently ones encountered in the practice of fatigue life estimations of laminated composites. There are several methods for solving these problems, but their use not always gives results of acceptable accuracy. To improve the accuracy of such estimations for the type of cyclic loading mentioned, a special model of nonlinear accumulation of fatigue damage is proposed.

  7. Modelling of Stress-Strain Relationship of Toyoura Sand in Large Cyclic Torsional Loading

    NASA Astrophysics Data System (ADS)

    Hong Nam, Nguyen; Koseki, Junichi

    The relationships between normalized shear stress and plastic shear strain of air-dried, dense Toyoura sand measured during large amplitude cyclic torsional loading with using local strain measurement could be well simulated numerically by the proportional rule combined with the drag rule. The proportional rule is an extended version of the Masing's second rule and can account for unsymmetrical stress strain behavior about neutral axis. The drag rule can account for strain hardening in cyclic loadings. Use of the newly proposed hypoelastic model for the quasi-elastic properties, the backbone curve using general hyperbolic equation or newly proposed lognormal equation for monotonic loading behavior, and the combination of the proportional rule and the drag rule for cyclic loading behavior would enable more precise simulation of deformation properties than before.

  8. The Mechanism of Orientation Dependence of Cyclic Stability of Superelesticity in NiFeGaCo Single Crystals Under Compression

    NASA Astrophysics Data System (ADS)

    Timofeeva, E. E.; Panchenko, E. Yu.; Vetoshkina, N. G.; Chumlyakov, Yu. I.; Tagiltsev, A. I.; Eftifeeva, A. S.; Maier, H.

    2016-12-01

    Using single crystals of the Ni49Fe18Ga27Co6 (at.%) alloy, oriented along [001]- and [123]-directions, cyclic stability of superelasticity is investigated in isothermal loading/unloading cycles at T = Af +(12-15) K (100 cycles) under compressive stress as a function of given strain per cycle, presence of disperse γ-phase particles measuring 5-10 μm, austenitic (B2 or L21) and stress-induced martensitic crystal structure (14M or L10). It is shown that single-phase L21-crystals demonstrate high cyclic stability during L21-14M-transitions with narrow hysteresises Δσ < 50 MPa in the absence of detwinning of the martensite. During the development of L21-14M stress-induced transformation, the reversible energy ΔGrev for these crystals exceeds the dissipated energy ΔGirr, and ΔGrev/ΔGirr = 1.7-1.8. A significant degradation of superelasticity is observed in [123]-oriented crystals during the development of L21-14M-L10-transformations followed by detwinning of the L10-martensite crystals and heterophase (B2+γ) single crystals, irrespective of their orientation during the B2-L10-transition. In the latter case, martensitic transformations are characterized by a wide stress hysteresis Δσ ≥ 80 MPa and the dissipated energy exceeds the reversible energy ΔGrev/ΔGirr = 0.5. The empirical criterion, relying on the analysis of the reversible-to-irreversible energy ratio, ΔGrev/ΔGirr, during stressinduced martensitic transformations, can be used to predict the cyclic stability of superelasticity in NiFeGaCo alloys subjected to different types of heat treatment.

  9. CYCLIC-LOADING TESTS OF TWO GLASSREINFORCED PLASTIC CYLINDERS,

    DTIC Science & Technology

    SUBMARINE HULLS, *LAMINATED PLASTICS , COMPOSITE MATERIALS, GLASS TEXTILES, PRESSURE VESSELS, HYDROSTATIC PRESSURE, FATIGUE(MECHANICS), MODEL TESTS, LOADS(FORCES), RINGS, TAPES, CREEP, SHELLS(STRUCTURAL FORMS).

  10. Finite Element Analysis of Sacroiliac Joint Fixation under Compression Loads

    PubMed Central

    Bruna-Rosso, Claire; Arnoux, Pierre-Jean; Bianco, Rohan-Jean; Godio-Raboutet, Yves; Fradet, Léo

    2016-01-01

    Background Sacroiliac joint (SIJ) is a known chronic pain-generator. The last resort of treatment is the arthrodesis. Different implants allow fixation of the joint, but to date there is no tool to analyze their influence on the SIJ biomechanics under physiological loads. The objective was to develop a computational model to biomechanically analyze different parameters of the stable SIJ fixation instrumentation. Methods A comprehensive finite element model (FEM) of the pelvis was built with detailed SIJ representation. Bone and sacroiliac joint ligament material properties were calibrated against experimentally acquired load-displacement data of the SIJ. Model evaluation was performed with experimental load-displacement measurements of instrumented cadaveric SIJ. Then six fixation scenarios with one or two implants on one side with two different trajectories (proximal, distal) were simulated and assessed with the FEM under vertical compression loads. Results The simulated S1 endplate displacement reduction achieved with the fixation devices was within 3% of the experimentally measured data. Under compression loads, the uninstrumented sacrum exhibited mainly a rotation motion (nutation) of 1.38° and 2.80° respectively at 600 N and 1000 N, with a combined relative translation (0.3 mm). The instrumentation with one screw reduced the local displacement within the SIJ by up to 62.5% for the proximal trajectory vs. 15.6% for the distal trajectory. Adding a second implant had no significant additional effect. Conclusion A comprehensive finite element model was developed to assess the biomechanics of SIJ fixation. SIJ devices enable to reduce the motion, mainly rotational, between the sacrum and ilium. Positioning the implant farther from the SIJ instantaneous rotation center was an important factor to reduce the intra-articular displacement. Clinical relevance Knowledge provided by this biomechanical study enables improvement of SIJ fixation through optimal implant

  11. Effects of shear stress component and loading path on fatigue strength under tension/torsion biaxial cyclic loading

    SciTech Connect

    Morita, Y.; Fujii, T.

    1994-12-31

    The material degradation and its mechanism of a plain woven glass fabric under tension/torsion biaxial cyclic loading were investigated. Thin-walled tubular specimens were used. Different types of loading sequence were applied to the specimens in order to estimate the effect of shear stress component on fatigue degradation of the composite under biaxial cyclic loading. All biaxial loads were proportionally applied to the specimens, but the number of torsion loading cycles and its direction (pulsating or alternate) were changed. Various wave forms were also used to estimate the effect of loading path. Loading path was changed but the final stress state (tensile and shear stresses) was the same. Stress-strain relation and stiffness reduction were observed to evaluate the degree of fatigue damage. The experimental results show that the role of shear stress is important when the material degradation is dominated by the shear stress component although the effect of shear stress component on fatigue strength decreases with an increase of tensile stress component under tension/torsion biaxial loading. Loading sequence also affects more or less on the fatigue life. On the other hand, it is well estimated that the fatigue life is little dependent on loading path in the case of high cycle fatigue.

  12. Behavior of sandwich panels subjected to bending fatigue, axial compression loading and in-plane bending

    NASA Astrophysics Data System (ADS)

    Mathieson, Haley Aaron

    This thesis investigates experimentally and analytically the structural performance of sandwich panels composed of glass fibre reinforced polymer (GFRP) skins and a soft polyurethane foam core, with or without thin GFRP ribs connecting skins. The study includes three main components: (a) out-of-plane bending fatigue, (b) axial compression loading, and (c) in-plane bending of sandwich beams. Fatigue studies included 28 specimens and looked into establishing service life (S-N) curves of sandwich panels without ribs, governed by soft core shear failure and also ribbed panels governed by failure at the rib-skin junction. Additionally, the study compared fatigue life curves of sandwich panels loaded under fully reversed bending conditions (R=-1) with panels cyclically loaded in one direction only (R=0) and established the stiffness degradation characteristics throughout their fatigue life. Mathematical models expressing fatigue life and stiffness degradation curves were calibrated and expanded forms for various loading ratios were developed. Approximate fatigue thresholds of 37% and 23% were determined for non-ribbed panels loaded at R=0 and -1, respectively. Digital imaging techniques showed significant shear contribution significantly (90%) to deflections if no ribs used. Axial loading work included 51 specimens and examined the behavior of panels of various lengths (slenderness ratios), skin thicknesses, and also panels of similar length with various rib configurations. Observed failure modes governing were global buckling, skin wrinkling or skin crushing. In-plane bending involved testing 18 sandwich beams of various shear span-to-depth ratios and skin thicknesses, which failed by skin wrinkling at the compression side. The analytical modeling components of axially loaded panels include; a simple design-oriented analytical failure model and a robust non-linear model capable of predicting the full load-displacement response of axially loaded slender sandwich panels

  13. The mechanical behaviour of NBR/FEF under compressive cyclic stress strain

    NASA Astrophysics Data System (ADS)

    Mahmoud, W. E.; El-Eraki, M. H. I.; El-Lawindy, A. M. Y.; Hassan, H. H.

    2006-06-01

    Acrylonitrile butadiene rubber compounds filled with different concentrations of fast extrusion furnace (FEF) carbon black were experimentally investigated. The stress-strain curves of the composites were studied, which suggest good filler-matrix adhesion. The large reinforcement effect of the filler followed the Guth model for non-spherical particles. The effect of FEF carbon black on the cyclic fatigue and hysteresis was also examined. The loading and unloading stress-strain relationships for any cycle were described by applying Ogden's model for rubber samples. The dissipation energy that indicates the vibration damping capacity for all samples was determined. A simple model was proposed, to investigate the relation between maximum stress and the number of cyclic fatigue.

  14. Instantaneous angular speed monitoring of gearboxes under non-cyclic stationary load conditions

    NASA Astrophysics Data System (ADS)

    Stander, C. J.; Heyns, P. S.

    2005-07-01

    Recent developments in the condition monitoring and asset management market have led to the commercialisation of online vibration-monitoring systems. These systems are primarily utilised to monitor large mineral mining equipment such as draglines, continuous miners and hydraulic shovels. Online monitoring systems make diagnostic information continuously available for asset management, production outsourcing and maintenance alliances with equipment manufacturers. However, most online vibration-monitoring systems are based on conventional vibration-monitoring technologies, which are prone to giving false equipment deterioration warnings on gears that operate under fluctuating load conditions. A simplified mathematical model of a gear system was developed to illustrate the feasibility of monitoring the instantaneous angular speed (IAS) as a means of monitoring the condition of gears that are subjected to fluctuating load conditions. A distinction is made between cyclic stationary load modulation and non-cyclic stationary load modulation. It is shown that rotation domain averaging will suppress the modulation caused by non-cyclic stationary load conditions but will not suppress the modulation caused by cyclic stationary load conditions. An experimental investigation on a test rig indicated that the IAS of a gear shaft could be monitored with a conventional shaft encoder to indicate a deteriorating gear fault condition.

  15. Fatigue degradation in compressively loaded composite laminates. [graphite-epoxy composites

    NASA Technical Reports Server (NTRS)

    Ramkumar, R. L.

    1981-01-01

    The effect of imbedded delaminations on the compression fatigue behavior of quasi-isotropic, T300/5208, graphite/epoxy laminates was investigated. Teflon imbedments were introduced during panel layup to create delaminations. Static and constant amplitude (R=10, omega = 10 Hz) fatigue tests were conducted. S-N data and half life residual strength data were obtained. During static compression loading, the maximum deflection of the buckled delaminated region was recorded. Under compression fatigue, growth of the imbedded delamination was identified as the predominant failure mode in most of the test cases. Specimens that exhibited others failures had a single low stiffness ply above the Teflon imbedment. Delamination growth during fatigue was monitored using DIB enhanced radiography. In specimens with buried delaminations, the dye penetrant (DIB) was introduced into the delaminated region through a minute laser drilled hole, using a hypodermic needle. A low kV, microfocus, X-ray unit was mounted near the test equipment to efficiently record the cyclic growth of buried delaminations on Polaroid film.

  16. Cyclic mechanical loading promotes bacterial penetration along composite restoration marginal gaps

    PubMed Central

    Khvostenko, D.; Salehi, S.; Naleway, S. E.; Hilton, T. J.; Ferracane, J. L.; Mitchell, J. C.; Kruzic, J. J.

    2015-01-01

    Objectives Secondary caries is the most common reason for composite restoration replacement and usually forms between dentin and the filling. The objective of this study was to investigate the combined effect of cyclic loading and bacterial exposure on bacterial penetration into gaps at the interface between dentin and resin composite restorative material using a novel bioreactor system and test specimen design. Methods Human molars were machined into 3 mm thick disks with 2 mm deep × 5 mm diameter cavity preparations into which composite restorations were placed. A ∼15-30 micrometer (small) or ∼300 micrometer wide (large) dentin-restoration gap was introduced along half of the interface between the dentin and restoration. Streptococcus mutans UA 159 biofilms were grown on each sample prior to testing in a bioreactor both with and without cyclic loading. Both groups of samples were tested for 2 weeks and post-test biofilm viability was confirmed with a live-dead assay. Samples were fixed, mounted and cross-sectioned to reveal the gaps and observe the depth of bacterial penetration. Results It was shown that for large gap samples the bacteria easily penetrated to the full depth of the gap independent of loading or non-loading conditions. The results for all cyclically loaded small gap samples show a consistently deep bacterial penetration down 100% of the gap while the average penetration depth was only 67% for the non-loaded samples with only two of six samples reaching 100%. Significance A new bioreactor was developed that allows combining cyclic mechanical loading and bacterial exposure of restored teeth for bacterial biofilm and demineralization studies. Cyclic loading was shown to aid bacterial penetration into narrow marginal gaps, which could ultimately promote secondary caries formation. PMID:25900624

  17. Mechanical Behavior and Microcrack Development in Nominally Dry Synthetic Salt-rock During Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Ding, J.; Chester, F. M.; Chester, J. S.; Zhu, C.; Shen, X.; Arson, C. F.

    2016-12-01

    Synthetic salt-rock is produced through uniaxial consolidation of sieved granular salt (0.3-0.355 mm grain diam.) at 75-107 MPa pressure and 100-200 0 C for 15 min duration, to produce low porosity (3%-6%) aggregates. Based on microstructural observations, consolidation mechanisms are grain rearrangement, intragranular plastic flow, and minor microfracture and recrystallization. Following consolidation, the salt-rock is deformed by cyclic, triaxial loading at room temperature and 4 MPa confining pressure to investigate microfracture development, closure and healing effects on elastic properties and flow strength. Load cycles are performed within the elastic regime, up to yielding, and during steady ductile flow. The mechanical properties are determined using an internal load cell and strain gages bonded to the samples. Elastic properties vary systematically during deformation reflecting cracking and pore and grain shape changes. Between triaxial load cycles, samples are held at isostatic loads for durations up to one day to determine healing rates and strength recovery; a change in mechanical behavior is observed when significant healing is induced. The microstructures of all samples are characterized before and after cyclic loading using optical microscopy. The consolidation and cyclic triaxial tests, and optical microscopy investigations, are conducted in a controlled low-humidity environment to ensure nominally dry conditions. The microstructures of samples from different stages of cyclic triaxial deformation indicate that intracrystalline plasticity, accompanied by minor recovery by recrystallization, is dominant; but, grain-boundary crack opening also becomes significant. Grain-boundary microcracks have preferred orientations that are sub-parallel to the load axis. The stress-strain behavior correlates with microcrack fabrics and densities during cyclic loading. These experiments are used to both inform and test continuum damage mechanics models of salt

  18. Cyclic mechanical loading promotes bacterial penetration along composite restoration marginal gaps.

    PubMed

    Khvostenko, D; Salehi, S; Naleway, S E; Hilton, T J; Ferracane, J L; Mitchell, J C; Kruzic, J J

    2015-06-01

    Secondary caries is the most common reason for composite restoration replacement and usually forms between dentin and the filling. The objective of this study was to investigate the combined effect of cyclic loading and bacterial exposure on bacterial penetration into gaps at the interface between dentin and resin composite restorative material using a novel bioreactor system and test specimen design. Human molars were machined into 3mm thick disks with 2mm deep × 5 mm diameter cavity preparations into which composite restorations were placed. A ∼ 15-30 μm (small) or ∼ 300 μm wide (large) marginal gap was introduced along half of the interface between the dentin and restoration. Streptococcus mutans UA 159 biofilms were grown on each sample prior to testing each in a bioreactor both with and without cyclic loading. Both groups of samples were tested for 2 weeks and post-test biofilm viability was confirmed with a live-dead assay. Samples were fixed, mounted and cross-sectioned to reveal the gaps and observe the depth of bacterial penetration. It was shown that for large gap samples the bacteria easily penetrated to the full depth of the gap independent of loading or non-loading conditions. The results for all cyclically loaded small gap samples show a consistently deep bacterial penetration down 100% of the gap while the average penetration depth was only 67% for the non-loaded samples with only two of six samples reaching 100%. A new bioreactor was developed that allows combining cyclic mechanical loading and bacterial exposure of restored teeth for bacterial biofilm and demineralization studies. Cyclic loading was shown to aid bacterial penetration into narrow marginal gaps, which could ultimately promote secondary caries formation. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  19. Dislocation substructures and nonproportional hardening. [TEM observations under tension-torsion cyclic loading

    SciTech Connect

    Shiinghwa Doong; Socie, D.F.; Robertson, I.M. )

    1990-10-01

    The dislocation substructures created in 1100 aluminum, OFHC copper, and type 304 and 310 stainless steels by in-phase (proportional) and 90 deg out-of-phase (nonproportional) tension-torsion cyclic loading were examined with a transmission-electron microscope. Multislip structures (cells and subgrains) are observed in aluminum under both in-phase and 90 deg out-of-phase tension-torsion loading. For copper and stainless steel, single-slip structures (planar dislocations, matrix veins, and ladders) are observed after proportional loading, whereas multislip structures (cells and labyrinths) are observed after nonproportional loading. The increased cyclic hardening of copper and stainless steels under nonproportional loading is attributed to the change of dislocation substructures. Based on these observations, formulation of a nonproportionality parameter for constitutive modeling is discussed.

  20. Inelastic Behavior of Randomly Reinforced Polymeric Composites under Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Smith, L. V.; Weitsman, Y. J.

    1997-09-01

    This study examines the development of damage in randomly reinforced polymeric composite materials. The material under consideration was made in a structural reaction injection molding process (SRIM) involving a continuous strand swirl mat of E-glass fibers and a urethane matrix. Theobjective of this work is to establish a predictive deformation model based on principles of viscoelasticity, damage mechanics and plasticity which maybe experimentally verified. Tests involving creep above a threshold stress level and recovery after load removal showed evidence of damage that was uniformly distributed throughout the coupon in the form of multitudes of matrix micro-cracks. Previous studies have shown that the material possesses a void content of about 5% and exhibits material property scatter of about 20%. The effects of damage could be assessed only when the scatter was separated by normalizing the data with individual coupon stiffness. Damage was measured through an increase in compliance and resulted in a permanent strain after load removel. The current study involves repeated loading. Compliance has been observed to increase with load cycle, while the permanent strain remains small and is neglected.Damage, as a function of load cycle, is incorporated into the non-linear viscoelastic model developed previously for creep/recovery response.Comparisons of the predictive model with experimental data are presented and show good agreement.

  1. Inhomogeneous deformation in INCONEL 718 during monotonic and cyclic loadings

    NASA Technical Reports Server (NTRS)

    Worthem, D. W.; Robertson, I. M.; Socie, D. F.; Altstetter, C. J.; Leckie, F. A.

    1990-01-01

    The paper concentrates on the relation between microstructural observations of the dislocation structures and the macroscopic deformation responses of both aged and homogenized precipitate-hardened alloys at room temperature. The deformation responses are compared to the cyclic deformation response of an aged precipitate-hardened alloy. Early in the deformation, one deformation band per grain and little evidence of work hardening are observed; with increased deformation, work hardening begins, more bands nucleate, and their spacing becomes similar to that in the aged material. It is pointed out that the degree of coarseness of inhomogeneous deformation is not a result of a softening process within the bands due to precipitate shearing, but it is a function of the amount of work hardening within the bands.

  2. Fatigue Damage in Notched Composite Laminates Under Tension-Tension Cyclic Loads

    NASA Technical Reports Server (NTRS)

    Stinchcomb, W. W.; Henneke, E. G.; Reifsnider, K. L.; Kress, G. R.

    1985-01-01

    The results are given of an investigation to determine the damage states which develop in graphite epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Two quasi-isotropic laminates were selected to give different distributions of interlaminar stresses around the hole. The laminates were tested under cyclic loads (R=0.1, 10 Hz) at maximum stresses ranging between 60 and 95 percent of the notched tensile strength.

  3. An in-situ neutron diffraction study of a multi-phase transformation and twinning-induced plasticity steel during cyclic loading

    SciTech Connect

    Saleh, Ahmed A.; Brown, Donald W.; Clausen, Bjørn; Tomé, Carlos N.; Pereloma, Elena V.; Davies, Christopher H. J.; Gazder, Azdiar A.

    2015-04-27

    In-situ neutron diffraction during cyclic tension-compression loading (∼+3.5% to −2.8%) of a 17Mn-3Al-2Si-1Ni-0.06C steel that exhibits concurrent transformation and twinning -induced plasticity effects indicated a significant contribution of intragranular back stresses to the observed Bauschinger effect. Rietveld analysis revealed a higher rate of martensitic transformation during tension compared to compression. Throughout cycling, α′-martensite exhibited the highest phase strains such that it bears an increasing portion of the macroscopic load as its weight fraction evolves. On the other hand, the ε-martensite strain remained compressive as it accommodated most of the internal strains caused by the shape misfit associated with the γ→ε and/or ε→α′ transformations.

  4. Active stabilization of thin-wall structures under compressive loading

    NASA Astrophysics Data System (ADS)

    Welham, Jared; Calius, Emilio P.; Chase, J. Geoffrey

    2003-08-01

    The active suppression of elastic buckling instability has the potential to significantly increase the effective strength of thin-wall structures. Despite all the interest in smart structures, the active suppression of buckling has received comparatively little attention. This paper addresses the effects of embedded actuation on the compression buckling strength of laminated composite plates through analysis and simulation. Numerical models are formulated that include the influence of essential features such as sensor uncertainty and noise, actuator saturation and control architecture on the buckling process. Silicon-based strain sensors and diffuse laser distance sensors are both considered for use in the detection of incipient buckling behavior due to their increased sensitivity. Actuation is provided by paired distributions of piezo-electric material incorporated into both sides of the laminate. Optimal controllers are designed to command the structure to deform in ways that interfere with the development of buckling mode shapes. Commercial software packages are used to solve the resulting non-linear equations, and some of the tradeoffs are enumerated. Overall, the results show that active buckling control can considerably enhance resistance to instability under compressive loads. These buckling load predictions demonstrate the viability of optimal control and piezo-electric actuation for implementing active buckling control. Due to the importance of early detection, the relative effectiveness of active buckling control is shown to be strongly dependent on the performance of the sensing scheme, as well as on the characteristics of the structure.

  5. FEM modelling of soil behaviour under compressive loads

    NASA Astrophysics Data System (ADS)

    Ungureanu, N.; Vlăduţ, V.; Biriş, S. Şt

    2017-01-01

    Artificial compaction is one of the most dangerous forms of degradation of agricultural soil. Recognized as a phenomenon with multiple negative effects in terms of environment and agricultural production, soil compaction is strongly influenced by the size of external load, soil moisture, size and shape of footprint area, soil type and number of passes. Knowledge of soil behavior under compressive loads is important in order to prevent or minimize soil compaction. In this paper were developed, by means of the Finite Element Method, various models of soil behavior during the artificial compaction produced by the wheel of an agricultural trailer. Simulations were performed on two types of soil (cohesive and non-cohesive) with known characteristics. By applying two loads (4.5 kN and 21 kN) in footprints of different sizes, were obtained the models of the distributions of stresses occuring in the two types of soil. Simulation results showed that soil stresses increase with increasing wheel load and vary with soil type.

  6. Effect of cyclic loading on the bond strength of class II restorations with different composite materials.

    PubMed

    Cavalcanti, Andrea Nóbrega; Mitsui, Fabio Hiroyuki Ogata; Silva, Flávia; Peris, Alessandra Rezende; Bedran-Russo, Ana; Marchi, Giselle Maria

    2008-01-01

    This study evaluated the effect of cyclic loading on the bond strength of Class II restorations using different composite materials. Class II preparations with gingival margins located in dentin were performed on the mesial surface of 80 bovine incisors. The teeth were randomly allocated to eight groups (n=10) according to resin composite (Filtek Z250, Filtek Supreme, Tetric Ceram HB and Esthet-X) and use of cyclic loading. The restorations were bonded with the Single Bond adhesive system. Simulated aging groups were cyclic loaded for 200,000 cycles with 80N load (2Hz). The specimens were vertically sectioned (two slabs per restoration) and further trimmed into an hour-glass shape at the adhesive interface to obtain a final bonded area 1 mm2. Samples were placed in an apparatus and tested under tension using a universal testing machine. The data were analyzed using two-way ANOVA and Tukey test with a 95% confidence level. Aged groups presented significantly lower means when compared to the groups that were not aged (p=0.03). However, significant differences among composite materials were not observed (p=0.17). Regardless of the restorative composite material used, it could be concluded that the bond strength of Class II restorations at the gingival wall was affected by simulated cyclic loading.

  7. Molecular dynamics investigation of the grain boundary migration hysteresis of nanocrystalline Ni under cyclic shear loading

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Yang, Xinhua; Peng, Di

    2017-02-01

    The deformation behavior and grain boundary (GB) response of nanocrystalline Ni under cyclic shear loading are investigated by molecular dynamics simulations. The GB migration hysteresis phenomenon, in which the GB migration displacement lags behind the change in nominal shear strain, is observed in the symmetric tilt GBs for the first time. The elementary structure transformation occurring at the two end segments of the observed GB during GB migration produces a disordered and irreversible state, while the transformation in the middle segment is reversible. Both dislocation retraction and nucleation occur during unloading. Relatively large cyclic strain amplitudes lead to disordered GB segments of greater length, such that the residual GB migration displacement increases with increasing cyclic amplitude. GB migration hysteresis vanishes after the GB becomes immobile owing to a cyclic shear induced transition to a disordered state along its entire length.

  8. Biomechanical properties under cyclic loading of seven meniscus repair techniques.

    PubMed

    Becker, Roland; Stärke, Christian; Heymann, Marlen; Nebelung, Wolfgang

    2002-07-01

    The purpose of the current study was to obtain additional information about the biomechanical behavior of different fixation techniques for meniscus repair using recently developed biodegradable implants and suture repair techniques. The posterior horns of human menisci were used to investigate the meniscus repair construct of the Arrow, Screw, Stinger, Fastener, T-fix, and horizontal and vertical mattress suture. A 20 mm-longitudinal incision was made in the meniscus, similar to a bucket handle lesion, 3 mm from the meniscosynovial rim and was repaired. One hundred cycles between 5 N and 15 N were done using a tension load machine with a loading rate of 10 N/second. The stiffness, displacement, and pullout strength were examined. The significantly highest stiffness was found for the vertical mattress suture (17.1 N/mm) and Stinger (15 N/mm) followed by the Arrow (13.7 N/mm), T-fix (10.5 N/mm), and horizontal mattress suture (10 N/mm). Superior load to failure was obtained for the suture repair in comparison with the biodegradable implants. Despite the lower pullout strength of biodegradable implants, similar stiffnesses were found for the Stinger and Arrow in comparison with the mattress suture technique. These techniques provide the most rigid fixation that is essential for tissue healing.

  9. Cyclic tension compression testing of AHSS flat specimens with digital image correlation system

    NASA Astrophysics Data System (ADS)

    Knoerr, Lay; Sever, Nimet; McKune, Paul; Faath, Timo

    2013-12-01

    A cyclic tension-compression testing program was conducted on flat specimens of TPN-W®780 (Three Phase Nano) and DP980 (Dual Phase) Advanced High Strength Steels (AHSS). This experimental method was enabled utilizing an anti-buckling clamping device performed in a test machine, and the surface strains along the thickness edge are measured with a three-dimensional Digital Image Correlation (DIC) system. The in-plane pre-strain and reversed strain values, at specified strain rates, are investigated to observe the potential plastic flow and the nonlinear strain hardening behavior of the materials. The validity of the test results is established with the monotonic tension tests, to substantiate the true stress-strain curves corrected for the frictional and biaxial stresses induced by the clamping device. A process method for analyzing the correction using a macro script is shown to simplify the output of the true stress-strain results for material model calibration. An in progress study to validate the forming and spring-back predictive capabilities of a calibrated TPN-W®780 complex material model to an actual stamping of an automotive component will demonstrate the usefulness of the experimental cyclic test method. Suggestions to improve the testing, strain analysis and calibration of the model parameters are proposed for augmented use of this test method.

  10. Modeling of Rock Joints Under Cyclic Loading Conditions Using Discontinuous Deformation Analysis

    NASA Astrophysics Data System (ADS)

    Ma, Shuqi; He, Chuan; Zhao, Zhiye; Nie, Wen; Zhu, Xing; Zhang, Zhenyu

    2017-05-01

    The shear strength of rock joints is an important factor to be considered when analyzing the stability of jointed rock mass. Rock joints tend to have smaller shear resistances in the reverse shearing than that of the forward shearing. A conceptual model describing the general shear behavior of rock joints under cyclic loading and the Barton-Bandis joint model considering the surface roughness degradation are implemented into the two-dimensional discontinuous deformation analysis (DDA) model. The modified DDA model is empirically validated by cyclic shear tests on two types of rock joints. Numerical simulations agree well with the experimental results, indicating that the DDA model is capable of describing the varying shear behaviors of rock joints subjected to cyclic loading conditions.

  11. Quantitative tracking of grain structure evolution in a nanocrystalline metal during cyclic loading

    NASA Astrophysics Data System (ADS)

    Panzarino, Jason F.; Ramos, Jesus J.; Rupert, Timothy J.

    2015-02-01

    Molecular dynamics simulations were used to quantify mechanically induced structural evolution in nanocrystalline Al with an average grain size of 5 nm. A polycrystalline sample was cyclically strained at different temperatures, while a recently developed grain tracking algorithm was used to measure the relative contributions of novel deformation mechanisms such as grain rotation and grain sliding. Sample texture and grain size were also tracked during cycling, to show how nanocrystalline plasticity rearranges overall grain structure and alters the grain boundary network. While no obvious texture is developing during cycling, the processes responsible for plasticity act collectively to alter the interfacial network. Cyclic loading led to the formation of many twin boundaries throughout the sample as well as the occasional coalescence of neighboring grains, with higher temperatures causing more evolution. A temperature-dependent cyclic strengthening effect was observed, demonstrating that both the structure and properties of nanocrystalline metals can be dynamic during loading.

  12. Influence of cyclic loading on the fracture toughness and load bearing capacities of all-ceramic crowns

    PubMed Central

    Wang, Rao-Rao; Lu, Cheng-Lin; Wang, Gang; Zhang, Dong-Sheng

    2014-01-01

    The purpose of this study was to investigate how cyclic loading influenced the fracture toughness of hot-press lithium disilicate and zirconia core materials and whether there was an increase in the propensity for crown failure. Two types of all-ceramic crowns including the IPS e.max Press system (n=24) and the Lava zirconia system (n=24), were selected. Sectioned specimens were subjected to cyclic loading with the maximum magnitude of 200 N (R=0.1) until two million cycles. The material properties including Young's modulus (E) and hardness (H) and the fracture toughness (KIC) of the core materials were evaluated using indentation methods (n=12 each). The load-bearing capacities of the specimens were examined by means of monotonic load to fracture (n=12 each). It was found that the material properties, including E, H and KIC, of the two types of dental ceramics, were reduced. Statistical analysis indicated that there were no significant influences of fatigue loading on material properties E and H for both types of dental ceramics or KIC for zirconia, while for the IPS e.max Press core, KIC, which was parallel to the direction of the lithium disilicate crystals, was significantly reduced (P=0.001). A conclusion was drawn that zirconia possesses high mechanical reliability and sustainable capacity to resist fatigue loading, while fatigue loading remarkably degraded the anisotropic mechanical behaviour of hot-press lithium disilicate ceramics. PMID:24335786

  13. Behavior of prestressed concrete subjected to low temperatures and cyclic loading

    SciTech Connect

    Berner, D.E.

    1984-01-01

    Concrete has exhibited excellent behavior in cryogenic containment vessels for several decades under essentially static conditions. Tests were conducted to determine the response of prestressed lightweight concrete subjected to high-intensity cyclic loading and simultaneous cryogenic thermal shock, simulating the relatively dynamic conditions encountered offshore or in seismic areas. Lightweight concrete has several attractive properties for cryogenic service including: (1) very low permeability, (2) good strain capacity, (3) relatively low thermal conductivity, and (4) a low modulus of elasticity. Experimental results indicated that the mechanical properties of plain lightweight concrete significantly increase with moisture content at low temperatures, while cyclic loading fatigue effects are reduced at low temperatures. Also, tests on uniaxially and on biaxially prestressed lightweight concrete both indicate that the test specimens performed well under severe cyclic loading and cryogenic thermal shock with only moderate reduction in flexural stiffness. Supplementary tests conducted in this study indicate that conventionally reinforced concrete degrades significantly faster than prestressed concrete when subjected to cyclic loading and thermal shock.

  14. Life prediction of materials exposed to monotonic and cyclic loading: A technology survey and bibliography

    NASA Technical Reports Server (NTRS)

    Stuhrke, W. F.; Carpenter, J. L., Jr.; Moya, N.; Mandel, G.

    1975-01-01

    Announced survey directs attention toward low cycle fatigue and thermal fatigue experienced at elevated temperatures equivalent to those found in hot end of gas turbine engine. Majority of bibliographic references are on life prediction for materials exposed to monotonic and cyclic loading in high temperature environments.

  15. Undisturbed Sampling and Cyclic Load Testing of Sands,

    DTIC Science & Technology

    1979-12-01

    description of the apparatus including the MTS and the Sanborn recording systems, the reader is referred to Wong’s thesis . For the present...to take place soon after; and the confining 93 -0 o V)I CL)L 00 i -0 U- Lii C’, - -0 cm oo00 c, 00 41(f L.> 0 3 efl "~ L IN 0 * U- 944 0 I U - LL) a...is referred to Wong’s thesis . Major modifications were, however, made in relocation of the load cell and in the cap to permit freezing of the sample

  16. Shear Performance of Horizontal Joints in Short Precast Concrete Columns with Sleeve Grouted Connections under Cyclic Loading.

    PubMed

    Feng, Bo; Xiong, Feng; Liu, Bingyu; Chen, Jiang; Zhang, Yiping

    2016-01-01

    In this study, two short precast concrete columns and two cast-in-situ concrete columns were tested under cyclic loads. It was shown that the sleeve grouted connection was equivalent to the cast-in-situ connections for short columns when the axial compression ratio was 0.6. In order to determine the influence of the axial compression ratio and the shear-span ratio on the shear capacity of the horizontal joint, a FE model was established and verified. The analysis showed that the axial compression ratio is advantageous to the joint and the shear capacity of the horizontal joint increases with increase of the shear-span ratio. Based on the results, the methods used to estimate the shear capacity of horizontal joints in the Chinese Specification and the Japanese Guidelines are discussed and it was found that both overestimated the shear capacity of the horizontal joint. In addition, the Chinese Specification failed to consider the influence of the shear-span ratio.

  17. Shear Performance of Horizontal Joints in Short Precast Concrete Columns with Sleeve Grouted Connections under Cyclic Loading

    PubMed Central

    Liu, Bingyu; Chen, Jiang; Zhang, Yiping

    2016-01-01

    In this study, two short precast concrete columns and two cast-in-situ concrete columns were tested under cyclic loads. It was shown that the sleeve grouted connection was equivalent to the cast-in-situ connections for short columns when the axial compression ratio was 0.6. In order to determine the influence of the axial compression ratio and the shear-span ratio on the shear capacity of the horizontal joint, a FE model was established and verified. The analysis showed that the axial compression ratio is advantageous to the joint and the shear capacity of the horizontal joint increases with increase of the shear-span ratio. Based on the results, the methods used to estimate the shear capacity of horizontal joints in the Chinese Specification and the Japanese Guidelines are discussed and it was found that both overestimated the shear capacity of the horizontal joint. In addition, the Chinese Specification failed to consider the influence of the shear-span ratio. PMID:27861493

  18. One-dimensional consolidation in unsaturated soils under cyclic loading

    NASA Astrophysics Data System (ADS)

    Lo, Wei-Cheng; Sposito, Garrison; Lee, Jhe-Wei; Chu, Hsiuhua

    2016-05-01

    The one-dimensional consolidation model of poroelasticity of Lo et al. (2014) for an unsaturated soil under constant loading is generalized to include an arbitrary time-dependent loading. A closed-form solution for the pore water and air pressures along with the total settlement is derived by employing a Fourier series representation in the spatial domain and a Laplace transformation in the time domain. This solution is illustrated for the important example of a fully-permeable soil cylinder with an undrained initial condition acted upon by a periodic stress. Our results indicate that, in terms of a dimensionless time scale, the transient solution decays to zero most slowly in a water-saturated soil, whereas for an unsaturated soil, the time for the transient solution to die out is inversely proportional to the initial water saturation. The generalization presented here shows that the diffusion time scale for pore water in an unsaturated soil is orders of magnitude greater than that in a water-saturated soil, mainly because of the much smaller hydraulic conductivity of the former.

  19. Comparison of 2-Dimensional and 3-Dimensional Metacarpal Fracture Plating Constructs Under Cyclic Loading.

    PubMed

    Tannenbaum, Eric P; Burns, Geoffrey T; Oak, Nikhil R; Lawton, Jeffrey N

    2017-03-01

    Metacarpal fractures are commonly treated by a variety of means including casting or open reduction internal fixation when unacceptable alignment is present following attempted closed reduction. Dorsal plating with either single-row 2-dimensional or double-row 3-dimensional plates has been proposed. This study's purpose was to determine if there are any differences in fixation construct stability under cyclic loading and subsequent load to failure between the lower profile 3-dimensional and the larger 2-dimensional plates in a metacarpal fracture gap sawbone model. Thirty metacarpal cortico-cancellous synthetic bones were cut with a 1.75-mm gap between the 2 fragments simulating mid-diaphyseal fracture comminution. Half of the metacarpals were plated with 2.0-mm locking 2-dimensional plates and half with 1.5-mm locking 3-dimensional plates. The plated metacarpals were mounted into a materials testing apparatus and cyclically loaded under cantilever bending for 2,000 cycles at 70 N, then 2,000 cycles at 120 N, and finally monotonically loaded to failure. Throughout testing, fracture gap sizes were measured, failure modes were recorded, and construct strength and stiffness values were calculated. All 3-dimensional constructs survived both cyclic loading conditions. Ten (67%) 2-dimensional constructs survived both loading conditions, whereas 5 (33%) failed the 120-N loading at 1377 ± 363 cycles. When loaded to failure, the 3-dimensional constructs failed at 265 N ± 21 N, whereas the 2-dimensional constructs surviving cyclic loading failed at 190 N ± 17 N. The shorter, thinner 3-dimensional metacarpal plates demonstrated increased resistance to failure in a cyclic loading model and increased load to failure compared with the relatively longer, thicker 2-dimensional metacarpal plates. The lower-profile 3-dimensional metacarpal plate fixation demonstrated greater stability for early postoperative resistance than the thicker 2-dimensional fixation, whereas the smaller

  20. Life Prediction for a Structural Material under Cyclic Loads with Hold Times Using a Viscoplastic Constitutive Model.

    DTIC Science & Technology

    1984-12-31

    times. The six material parameters of the viscoplastic theory were S evaluated from a series of strain - controlled stabilized cyclic loading tests, and...fatigue. Two sets of low cycle :ati;ue life predictions were carried out and compared with experimental data. One in- Valved strain - controlled cyclic... strain for a strain -time 0e input that produces stress relaxation. Figures 2.22-2.30 illustrate the effects of strain controlled cyclic loading. For

  1. Characterization of focal muscle compression under impact loading

    NASA Astrophysics Data System (ADS)

    Butler, B. J.; Sory, D. R.; Nguyen, T.-T. N.; Proud, W. G.; Williams, A.; Brown, K. A.

    2017-01-01

    In modern wars over 70% of combat wounds are to the extremities. These injuries are characterized by disruption and contamination of the limb soft tissue envelope. The extent of this tissue trauma and contamination determine the outcome of the extremity injury. In military injury, common post-traumatic complications at amputation sites include heterotopic ossification (formation of bone in soft tissue), and severe soft tissue and bone infections. We are currently developing a model of soft tissue injury that recreates pathologies observed in combat injuries. Here we present characterization of a controlled focal compression of the rabbit flexor carpi ulnaris (FCU) muscle group. The FCU was previously identified as a suitable site for studying impact injury because its muscle belly can easily be mobilized from the underlying bone without disturbing anatomical alignment in the limb. We show how macroscopic changes in tissue organization, as visualized using optical microscopy, can be correlated with data from temporally resolved traces of loading conditions.

  2. Case study of preliminary cyclic load evaluation and triaxial soil testing in offshore wind farm planning

    NASA Astrophysics Data System (ADS)

    Otto, Daniel; Ossig, Benjamin; Kreiter, Stefan; Kouery, Saed; Moerz, Tobias

    2010-05-01

    In 2020 Germany aims to produce 20% of its electrical power trough renewable energy sources. Assigned Offshore Wind farms in the German exclusive economic zone of the North- and the Baltic Sea are important step toward a fulfilment of this goal. However the save erecting of 5-6 MW wind power plants (total construction size: > 200m) in water depth of around 40 m is related to unprecedented technical, logistical and financial challenges. With an intended lifetime expectation of 50 years for the foundations, construction materials and the soils around the foundation are subject to high and continued stresses from self-weight, waves, wind and current. These stresses are not only static, but have also a significant cyclic component. An estimated 250 million cyclic load changes may lead to an accumulation of plastic deformation in the soil that potentially may affect operability or lifespan of the plant. During a preliminary geotechnical site survey of one of the largest (~150 km2) offshore wind project sites within the German Bight (~45 km North off the island Juist) a total of 16 drill cores with in situ cone penetration data and a total sample length of ~800 m where recovered. Preliminary foundation designs and static self weight and lateral load calculations were used to design a cycling triaxial lab testing program on discrete natural soil samples. Individual tests were performed by foundation type and at vertical and lateral load maxima to evaluate the long-term soil behaviour under cyclic load. Tests have been performed on granular, cohesive and intermediate natural soils. Following an introduction to the unique MARUM triaxial apparatus and testing conditions, the cyclic triaxial test results are shown and explained. Furthermore cyclic shear strength and stiffness are compared to their static counterparts. Unique soil behaviour like abrupt partial failure, pore pressure response and unexpected in part load independent cyclic deformation behaviour is discussed and

  3. Tensile and compressive failure modes of laminated composites loaded by fatigue with different mean stress

    NASA Technical Reports Server (NTRS)

    Rotem, Assa

    1990-01-01

    Laminated composite materials tend to fail differently under tensile or compressive load. Under tension, the material accumulates cracks and fiber fractures, while under compression, the material delaminates and buckles. Tensile-compressive fatigue may cause either of these failure modes depending on the specific damage occurring in the laminate. This damage depends on the stress ratio of the fatigue loading. Analysis of the fatigue behavior of the composite laminate under tension-tension, compression-compression, and tension-compression had led to the development of a fatigue envelope presentation of the failure behavior. This envelope indicates the specific failure mode for any stress ratio and number of loading cycles. The construction of the fatigue envelope is based on the applied stress-cycles to failure (S-N) curves of both tensile-tensile and compressive-compressive fatigue. Test results are presented to verify the theoretical analysis.

  4. Thermomechanical characterization of Hastelloy-X under uniaxial cyclic loading

    NASA Technical Reports Server (NTRS)

    Ellis, J. R.; Bartolotta, P. A.; Allen, G. P.; Robinson, D. N.

    1986-01-01

    In most high-temperature engineering applications, components are subjected to complex combinations of thermal and mechanical loading during service. A number of viscoplastic constitutive models were proposed which potentially can provide mathematical descriptions of material response under such conditions. Implementation of these models into large finite element codes such as MARC has already resulted in much improved inelastic analysis capability for hot-section aircraft engine components. However, a number of questions remain regarding the validity of methods adopted in characterizing these constitutive models for particular high-temperature materials. One area of concern is that the majority of experimental data available for this purpose are determined under isothermal conditions. This is in contrast to service conditions which, as noted above, almost always involve some form of thermal cycling. The obvious question arises as to whether a constitutive model characterized using an isothermal data base can adequately predict material response under thermomechanical conditions. An experimental program was initiated within the HOST program to address this particular concern. The results of the most recent isothermal and thermomechanical experiments are described.

  5. Behavior of pile group with elevated cap subjected to cyclic lateral loads

    NASA Astrophysics Data System (ADS)

    Chen, Yun-min; Gu, Ming; Chen, Ren-peng; Kong, Ling-gang; Zhang, Zhe-hang; Bian, Xue-cheng

    2015-06-01

    The pile group with elevated cap is widely used as foundation of offshore structures such as turbines, power transmission towers and bridge piers, and understanding its behavior under cyclic lateral loads induced by waves, tide water and winds, is of great importance to designing. A large-scale model test on 3×3 pile group with elevated cap subjected to cyclic lateral loads was performed in saturated silts. The preparation and implementation of the test is presented. Steel pipes with the outer diameter of 114 mm, thickness of 4.5 mm, and length of 6 m were employed as model piles. The pile group was cyclic loaded in a multi-stage sequence with the lateral displacement controlled. In addition, a single pile test was also conducted at the same site for comparison. The displacement of the pile cap, the internal forces of individual piles, and the horizontal stiffness of the pile group are presented and discussed in detail. The results indicate that the lateral cyclic loads have a greater impact on pile group than that on a single pile, and give rise to the significant plastic strain in the soil around piles. The lateral loads carried by each row of piles within the group would be redistributed with loading cycles. The lateral stiffness of the pile group decreases gradually with cycles and broadly presents three different degradation patterns in the test. Significant axial forces were measured out in some piles within the group, owing to the strong restraint provided by the cap, and finally lead to a large settlement of the pile group. These findings can be referred for foundation designing of offshore structures.

  6. Determination of shear stress-strain curve from torsion tests for loading-unloading and cyclic loading

    SciTech Connect

    Wu, H.C.; Xu, Z.; Wang, P.T.

    1997-01-01

    This paper discusses a method, based on Nadai`s solution, which can be used to determine the true (Cauchy) shear stress-strain curve of a material by means of torsion test of a solid shaft. The method is shown to be applicable to loading, unloading and cyclic loading. It is also applicable to fixed-end torsion of a solid shaft in the large shear strain range. A modified method has also been derived for the case of free-end torsion of a tubular specimen in the large strain range.

  7. Cyclic loading increases friction and changes cartilage surface integrity in lubricin-mutant mouse knees

    PubMed Central

    Drewniak, Elizabeth I; Jay, Gregory D; Fleming, Braden C; Zhang, Ling; Warman, Matthew L; Crisco, Joseph J

    2012-01-01

    Objective To investigate the effects of lubricin gene dosage and cyclic loading on whole joint coefficient of friction and articular cartilage surface integrity in mouse knee joints. Methods Joints from mice with 2 (Prg4+/+), 1 (Prg4+/−), or no (Prg4−/−) functioning lubricin alleles were subjected to 26 hours of cyclic loading using a custom-built pendulum. Coefficient of friction values were measured at multiple time points. Contralateral control joints were left unloaded. Following testing, joints were examined for histologic evidence of damage and cell viability. Results At baseline, the coefficient of friction values in Prg4−/− mice were significantly higher than those in Prg4+/+ and Prg4+/− mice (P < 0.001). Cyclic loading continuously increased the coefficient of friction in Prg4−/− mouse joints. In contrast, Prg4+/− and Prg4+/+ mouse joints had no coefficient of friction increases during the first 4 hours of loading. After 26 hours of loading, joints from all genotypes had increased coefficient of friction values compared to baseline and unloaded controls. Significantly greater increases occurred in Prg4−/− and Prg4+/− mouse joints compared to Prg4+/+ mouse joints. The coefficient of friction values were not significantly associated with histologic evidence of damage or loss of cell viability. Conclusion Our findings indicate that mice lacking lubricin have increased baseline coefficient of friction values and are not protected against further increases caused by loading. Prg4+/− mice are indistinguishable from Prg4+/+ mice at baseline, but have significantly greater coefficient of friction values following 26 hours of loading. Lubricin dosage affects joint properties during loading, and may have clinical implications in patients for whom injury or illness alters lubricin abundance. PMID:21905020

  8. Cyclic loading increases friction and changes cartilage surface integrity in lubricin-mutant mouse knees.

    PubMed

    Drewniak, Elizabeth I; Jay, Gregory D; Fleming, Braden C; Zhang, Ling; Warman, Matthew L; Crisco, Joseph J

    2012-02-01

    To investigate the effects of lubricin gene dosage and cyclic loading on whole joint coefficient of friction and articular cartilage surface integrity in mouse knee joints. Joints from mice with 2 (Prg4(+/+)), 1 (Prg4(+/-)), or no (Prg4(-/-)) functioning lubricin alleles were subjected to 26 hours of cyclic loading using a custom-built pendulum. Coefficient of friction values were measured at multiple time points. Contralateral control joints were left unloaded. Following testing, joints were examined for histologic evidence of damage and cell viability. At baseline, the coefficient of friction values in Prg4(-/-) mice were significantly higher than those in Prg4(+/+) and Prg4(+/-) mice (P < 0.001). Cyclic loading continuously increased the coefficient of friction in Prg4(-/-) mouse joints. In contrast, Prg4(+/-) and Prg4(+/+) mouse joints had no coefficient of friction increases during the first 4 hours of loading. After 26 hours of loading, joints from all genotypes had increased coefficient of friction values compared to baseline and unloaded controls. Significantly greater increases occurred in Prg4(-/-) and Prg4(+/-) mouse joints compared to Prg4(+/+) mouse joints. The coefficient of friction values were not significantly associated with histologic evidence of damage or loss of cell viability. Our findings indicate that mice lacking lubricin have increased baseline coefficient of friction values and are not protected against further increases caused by loading. Prg4(+/-) mice are indistinguishable from Prg4(+/+) mice at baseline, but have significantly greater coefficient of friction values following 26 hours of loading. Lubricin dosage affects joint properties during loading, and may have clinical implications in patients for whom injury or illness alters lubricin abundance. Copyright © 2012 by the American College of Rheumatology.

  9. Alumina reinforced zirconia implants: effects of cyclic loading and abutment modification on fracture resistance.

    PubMed

    Spies, Benedikt Christopher; Sauter, Carmen; Wolkewitz, Martin; Kohal, Ralf-Joachim

    2015-03-01

    The aim of the study was to evaluate the thermomechanical behavior of alumina-toughened zirconia (ATZ) oral implants in the artificial mouth and the fracture resistance (fracture load and bending moment) in a subsequent static fracture load test. The effects of abutment modification and different cyclic loadings were evaluated. A total of 48 implants were used. 24 implants were left as machined (Group A), and 24 implants were shape modified at the abutment (Group B). Groups were divided into three subgroups composed of 8 samples each (A1/B1: no cyclic loading; A2/B2: 1.2 million cycles; A3/B3: 5 million cycles). Subsequently, all implants were statically loaded to the point of fracture. The implants showed the following survival rates after the artificial mouth: A2 and B2 100%; A3 and B3 87.5%. The following average fracture resistance values were found (fracture load [N]/bending moment [Nmm]): A1 (583/2907), B1 (516/2825), A2 (618/2737), B2 (550/3150), A3 (802/3784) and B3 (722/3809). After 5 million loading cycles a significant increase in fracture load and bending moment was found. Modification of the abutment significantly decreased the fracture load of implants without foregoing dynamic loading. However, the shape modification altered the lever arm. For that reason, a smaller load resulted in the same bending moment. Therefore, abutment modification had no significant influence on the fracture resistance of ATZ. Neither thermomechanical cycling in an aqueous environment nor modification of the abutment had a negative effect on the fracture resistance of ATZ. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  10. Multiple spatio-temporal scale modeling of composites subjected to cyclic loading

    NASA Astrophysics Data System (ADS)

    Crouch, Robert; Oskay, Caglar; Clay, Stephen

    2013-01-01

    This manuscript presents a multiscale modeling methodology for failure analysis of composites subjected to cyclic loading conditions. Computational homogenization theory with multiple spatial and temporal scales is employed to devise the proposed methodology. Multiple spatial scales address the disparity between the length scale of material heterogeneities and the overall structure, whereas multiple temporal scales with almost periodic fields address the disparity between the load period and overall life under cyclic loading. The computational complexity of the multiscale modeling approach is reduced by employing a meso-mechanical model based on eigendeformation based homogenization with symmetric coefficients in the space domain, and an adaptive time stepping strategy based on a quadratic multistep method with error control in the time domain. The proposed methodology is employed to simulate the response of graphite fiber-reinforced epoxy composites. Model parameters are calibrated using a suite of experiments conducted on unidirectionally reinforced specimens subjected to monotonic and cyclic loading. The calibrated model is employed to predict damage progression in quasi-isotropic specimens. The capabilities of the model are validated using acoustic emission testing.

  11. Mechanical strength and subcritical crack growth under wet cyclic loading of glass-infiltrated dental ceramics.

    PubMed

    Salazar Marocho, Susana M; Studart, André R; Bottino, Marco A; Bona, Alvaro Della

    2010-05-01

    Evaluate the flexural strength (sigma) and subcritical crack growth (SCG) under cyclic loading of glass-infiltrated alumina-based (IA, In-Ceram Alumina) and zirconia-reinforced (IZ, In-Ceram Zirconia) ceramics, testing the hypothesis that wet environment influences the SCG of both ceramics when submitted to cyclic loading. Bar-shaped specimens of IA (n=45) and IZ (n=45) were fabricated and loaded in three-point bending (3P) in 37 degrees C artificial saliva (IA(3P) and IZ(3P)) and cyclic fatigued (F) in dry (D) and wet (W) conditions (IA(FD), IA(FW), IZ(FD), IZ(FW)). The initial sigma and the number of cycles to fracture were obtained from 3P and F tests, respectively. Data was examined using Weibull statistics. The SCG behavior was described in terms of crack velocity as a function of maximum stress intensity factor (K(Imax)). The Weibull moduli (m=8) were similar for both ceramics. The characteristic strength (sigma(0)) of IA and IZ was and 466MPa 550MPa, respectively. The wet environment significantly increased the SCG of IZ, whereas a less evident effect was observed for IA. In general, both ceramics were prone to SCG, with crack propagation occurring at K(I) as low as 43-48% of their critical K(I). The highest sigma of IZ should lead to longer lifetimes for similar loading conditions. Water combined with cyclic loading causes pronounced SCG in IZ and IA materials. The lifetime of dental restorations based on these ceramics is expected to increase by reducing their direct exposure to wet conditions and/or by using high content zirconia ceramics with higher strength. 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  12. Fracture Modes in Curved Brittle Layers Subject to Concentrated Cyclic Loading in Liquid Environments.

    PubMed

    Kim, Jae-Won; Thompson, Van P; Rekow, E Dianne; Jung, Yeon-Gil; Zhang, Yu

    2009-03-01

    Damage response of brittle curved structures subject to cyclic Hertzian indentation was investigated. Specimens were fabricated by bisecting cylindrical quartz glass hollow tubes. The resulting hemi-cylindrical glass shells were bonded internally and at the edges to polymeric supporting structures and loaded axially in water on the outer circumference with a spherical tungsten carbide indenter. Critical loads and number of cycles to initiate and propagate near-contact cone cracks and far-field flexure radial cracks to failure were recorded. Flat quartz glass plates on polymer substrates were tested as a control group. Our findings showed that cone cracks form at lower loads, and can propagate through the quartz layer to the quartz/polymer interface at lower number of cycles, in the curved specimens relative to their flat counterparts. Flexural radial cracks require a higher load to initiate in the curved specimens relative to flat structures. These radial cracks can propagate rapidly to the margins, the flat edges of the bisecting plane, under cyclic loading at relatively low loads, owing to mechanical fatigue and a greater spatial range of tensile stresses in curved structures.

  13. Biaxial ratcheting and cyclic plasticity for Bree-type loading. Part 1: Finite element analysis

    SciTech Connect

    Ng, H.W.; Nadarajah, C.

    1996-05-01

    The Bree diagram has been incorporated in the ASME B and PV Code in the elevated temperature Code Case N47 as a design approach for limiting strain accumulation in cylinders subjected to cyclic thermal loadings under sustained primary stress. Since the Bree diagram is based upon uniaxial-stress model, it is pertinent to examine the influence of biaxial stresses on strain growth and cyclic stress-strain hysteresis response. The results of inelastic analyses presented in this paper showed that ratcheting and hysteresis behavior may also occur in the axial direction in addition to the hoop direction. Results of almost 100 load cases were presented to clarify the influence of biaxial membrane and thermal bending stresses on the structural behavior. A design approach for the assessment of this type of problem was suggested which utilizes these results.

  14. Crack density and electrical resistance in indium-tin-oxide/polymer thin films under cyclic loading

    NASA Astrophysics Data System (ADS)

    Mora, Angel; Khan, Kamran A.; El Sayed, Tamer

    2014-11-01

    Here, we propose a damage model that describes the degradation of the material properties of indium-tin-oxide (ITO) thin films deposited on polymer substrates under cyclic loading. We base this model on our earlier tensile test model and show that the new model is suitable for cyclic loading. After calibration with experimental data, we are able to capture the stress-strain behavior and changes in electrical resistance of ITO thin films. We are also able to predict the crack density using calibrations from our previous model. Finally, we demonstrate the capabilities of our model based on simulations using material properties reported in the literature. Our model is implemented in the commercially available finite element software ABAQUS using a user subroutine UMAT. [Figure not available: see fulltext.

  15. Subcritical crack growth in glasses under cyclic loads: Effect of hydrodynamic pressure in aqueous environments

    SciTech Connect

    Yi, K.S.; Dill, S.J.; Dauskardt, R.H.

    1997-07-01

    The effect of hydrodynamic pressure developed in the wake of a crack growing in a brittle material under cyclic loads in an aqueous environment is considered. The pressure acts in opposition to the movement of the crack faces, thus shielding the crack up from the applied loads. A general hydrodynamic fluid pressure relation based on a one-dimensional Reynolds equation, which applicable to a crack with an arbitrary crack opening profile, is developed. The model is modified to account for side flow through the thickness of the sample and cavitation near the crack tip. Both effects significantly modify the hydrodynamic pressure distribution. Finally, the resulting hydrodynamic pressure relations are combined with a fracture mechanics model to account for the change in the near-tip stress intensity. Resulting predictions of the cyclic crack-growth rate are found to be in good agreement with measured values for a borosilicate glass tested at various frequencies in a water environment.

  16. Life prediction of materials exposed to monotonic and cyclic loading: Bibliography

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.; Moya, N.; Stuhrke, W. F.

    1975-01-01

    This bibliography is comprised of approximately 1200 reference citations related to the mechanics of failure in aerospace structures. Most of the references are for information on life prediction for materials exposed to monotonic and cyclic loading in elevated temperature environments such as that in the hot end of a gas turbine engine. Additional citations listed are for documents on the thermal and mechanical effects on solar cells in the cryogenic vacuum environment; radiation effects on high temperature mechanical properties; and high cycle fatigue technology as applicable to gas turbine engine bearings. The bibliography represents a search of the literature published in the period April 1962 through April 1974 and is largely limited to documents published in the United States. It is a companion volume to NASA CR-134750, Life Prediction of Materials Exposed to Monotonic and cyclic Loading - A Technology Survey.

  17. Nonlinear finite element analysis of PVA fiber reinforced high strength concrete columns under low cyclic loading

    NASA Astrophysics Data System (ADS)

    Su, Jun; Hu, Qiang; Liu, Jianping

    2017-04-01

    In this paper, four PVA fiber reinforced super-high-strength concrete columns under the low cyclic reciprocating load were studied by using the finite element analysis software OpenSEES and their hysteretic curves and skeleton curves were studied. The energy dissipation capacity of PVA fiber were analyzed to evaluate the effect of PVA fiber on the seismic performance of concrete columns. The results show that the restoring force curve of the finite element analysis software OpenSEES simulation agrees well with the experimental curve, which can fully reflect the hysteretic behavior of fiber reinforced concrete columns under low cyclic loading. The incorporation of PVA fiber can obviously improve the energy dissipation capacity of ordinary concrete columns.

  18. Calcium regulates cyclic compression-induced early changes in chondrocytes during in vitro cartilage tissue formation.

    PubMed

    Raizman, Igal; De Croos, J N Amritha; Pilliar, Robert; Kandel, Rita A

    2010-10-01

    A single application of cyclic compression (1kPa, 1Hz, 30min) to bioengineered cartilage results in improved tissue formation through sequential catabolic and anabolic changes mediated via cell shape changes that are regulated by α5β1 integrin and membrane-type metalloprotease (MT1-MMP). To determine if calcium was involved in this process, the role of calcium in regulating cell shape changes, MT1-MMP expression and integrin activity in response to mechanical stimulation was examined. Stimulation-induced changes in cell shape and MT1-MMP expression were abolished by chelation of extracellular calcium, and this effect was reversed by re-introduction of calcium. Spreading was inhibited by blocking stretch-activated channels (with gadolinium), while retraction was prevented by blocking the L-Type voltage-gated channel (with nifedipine); both compounds inhibited MT1-MMP upregulation. Calcium A23187 ionophore restored cellular response further supporting a role for these channels. Calcium regulated the integrin-mediated signalling pathway, which was facilitated through Src kinase. Both calcium- and integrin-mediated pathways converged on ERK-MAPK in response to stimulation. While both integrins and calcium signalling mediate chondrocyte mechanotransduction, calcium appears to play the major regulatory role. Understanding the underlying molecular mechanisms involved in chondrocyte mechanotransduction may lead to the development of improved bioengineered cartilage.

  19. Electrical Conductivity, Thermal Stability, and Lattice Defect Evolution During Cyclic Channel Die Compression of OFHC Copper

    NASA Astrophysics Data System (ADS)

    Satheesh Kumar, S. S.; Raghu, T.

    2015-02-01

    Oxygen-free high-conductivity (OFHC) copper samples are severe plastically deformed by cyclic channel die compression (CCDC) technique at room temperature up to an effective plastic strain of 7.2. Effect of straining on variation in electrical conductivity, evolution of deformation stored energy, and recrystallization onset temperatures are studied. Deformation-induced lattice defects are quantified using three different methodologies including x-ray diffraction profile analysis employing Williamson-Hall technique, stored energy based method, and electrical resistivity-based techniques. Compared to other severe plastic deformation techniques, electrical conductivity degrades marginally from 100.6% to 96.6% IACS after three cycles of CCDC. Decrease in recrystallization onset and peak temperatures is noticed, whereas stored energy increases and saturates at around 0.95-1.1J/g after three cycles of CCDC. Although drop in recrystallization activation energy is observed with the increasing strain, superior thermal stability is revealed, which is attributed to CCDC process mechanics. Low activation energy observed in CCDC-processed OFHC copper is corroborated to synergistic influence of grain boundary characteristics and lattice defects distribution. Estimated defects concentration indicated continuous increase in dislocation density and vacancy with strain. Deformation-induced vacancy concentration is found to be significantly higher than equilibrium vacancy concentration ascribed to hydrostatic stress states experienced during CCDC.

  20. Does Abutment Collar Length Affect Abutment Screw Loosening After Cyclic Loading?

    PubMed

    Siadat, Hakimeh; Pirmoazen, Salma; Beyabanaki, Elaheh; Alikhasi, Marzieh

    2015-07-01

    A significant vertical space that is corrected with vertical ridge augmentation may necessitate selection of longer abutments, which would lead to an increased vertical cantilever. This study investigated the influence of different abutment collar heights on single-unit dental implant screw-loosening after cyclic loading. Fifteen implant-abutment assemblies each consisted of an internal hexagonal implant were randomly assigned to 3 groups: Group1, consisting of 5 abutments with 1.5 mm gingival height (GH); Group2, 5 abutments with 3.5 mm GH; and Group3, 5 abutments with 5.5 mm GH. Each specimen was mounted in transparent auto-polymerizing acrylic resin block, and the abutment screw was tightened to 35 Ncm with an electric torque wrench. After 5 minutes, initial torque loss (ITL) was recorded for all specimens. Metal crowns were fabricated with 45° occlusal surface and were placed on the abutments. A cyclic load of 75 N and frequency of 1 Hz were applied perpendicular to the long axis of each specimen. After 500 000 cycles, secondary torque loss (STL) was recorded. One-way ANOVA analysis was used to evaluate the effects of abutment collar height before and after cyclic loading. One-way ANOVA showed that ITL among the groups was not significantly different (P = .52), while STL was significantly different among the groups (P = .008). Post-hoc Tukey HSD tests showed that STL values were significantly different between the abutments with 1.5 mm GH (Group1) and with 5.5 mm GH (Group3) (P = .007). A paired comparison t-test showed that cyclic loading significantly influenced the STL in comparison with the ITL in each group. Within the limitations of this study, it can be concluded that increase in height of the abutment collar could adversely affect the torque loss of the abutment screw.

  1. Experimental Research into the Behavior of Piles and Pile Groups Subjected to Cyclic Lateral Loading

    DTIC Science & Technology

    1988-06-01

    FI LE CoP, MISCELLANECUS PAPER GL 88 10 EXPERIMENTAL RESEARCH INTO THE of EngnBEHAVIOR OF PILES AND PILE GROUPS SUBJECTED TO CYCLIC LATERAL LOADING...1988 Final Report "- n, .... "/ Minerals Management Service US Department of Interior, Reston, Virginia 22090 and Department of Research . Federal Highway...PROJECT TASK WORK UNIT ELEMENT NO NO NO ACCESSION NO See reverse 11 TITLE (Include Security Classification) 0 Experimental Research Into the Behavior of

  2. A Unified Approach for Modeling Inelastic Behavior of Structural Metals under Complex Cyclic Loadings.

    DTIC Science & Technology

    1977-05-01

    STRUCTURA——ETC (U) - UNCLASSIFIED MAY CERL—TR—M—214 NL construction engineering TECHNICAL REPORT M.214 research Respon~ to Cyclic Loading...this report are not to be used for advertising, publication, or promotional purposes. Citat ion of trade names does not constitute an off icial...indorsement or approval of the use of such commercial products. The findings of this report are not to be construed as an official Department of the Army

  3. Life prediction of materials exposed to monotonic and cyclic loading: A new technology survey

    NASA Technical Reports Server (NTRS)

    Stuhrke, W. F.; Carpenter, J. L., Jr.

    1975-01-01

    Reviewed and evaluated technical abstracts for about 100 significant documents are reported relating primarily to life prediction for structural materials exposed to monotonic and cyclic loading, particularly in elevated temperature environments. The abstracts in the report are mostly for publications in the period April 1962 through April 1974. The purpose of this report is to provide, in quick reference form, a dependable source for current information

  4. Characterization of Focal Muscle Compression Under Impact Loading

    NASA Astrophysics Data System (ADS)

    Butler, Ben; Sory, David; Nguyen, Thuy-Tien; Curry, Richard; Clasper, Jon; Proud, William; Williams, Alun; Brown, Kate

    2015-06-01

    The pattern of battle injuries sustained in modern wars shows that over 70% of combat wounds are to the extremities. These injuries are characterized by disruption and contamination of the limb soft tissue envelope. The extent of this tissue trauma and contamination determine the outcome in extremity injury. In military injury, common post-traumatic complications at amputation sites include heterotopic ossification (formation of bone in soft tissue), and severe soft tissue and bone infections. We are currently developing a model of soft tissue injury that recreates pathologies observed in combat injuries. Here we present characterization of a controlled focal compression of the rabbit flexor carpi ulnaris (FCU) muscle group. The FCU was previously identified as a suitable site for studying impact injury because its muscle belly can easily be mobilized from the underlying bone without disturbing anatomical alignment in the limb. We show how macroscopic changes in tissue organization, as visualized using optical microscopy, can be correlated with data from temporally resolved traces of loading conditions. Funding provided by the Royal British Legion.

  5. Investigation on hardening behavior of metallic glass under cyclic indentation loading via molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zhao, Dan; Zhao, Hongwei; Zhu, Bo; Wang, Shunbo

    2017-09-01

    Mechanical behavior of a Cu-Zr metallic glass (MG) under cyclic indentation loading is investigated via molecular dynamics simulation. A large-depth indentation after cycling is conducted, and the indentation curves show that hardening behavior occurs with cyclic indentation amplitudes exceeding elastic range. The atomic Von Mises shear strain distributions during the large-depth indentation are investigated, and the pre-existing plastic deformation induced by cyclic indentation is found to be the main contributor to the hardening behavior. By monitoring the atom trajectories and Voronoi atom volume, structure densification and free volume reduction phenomenon are found in the area beneath indenter after cycles. The accumulations of irreversible shear strain during cycling induce the area beneath indenter experience atom structure transition and become densified, thus the sample becomes more resistant to further deformation. In addition, the effects of temperatures and loading rates on the hardening behavior are studied. With higher temperature, more homogenous deformation and plasticity are produced, and then inducing more severe hardening in the MG. While with lower loading rate, the hardening phenomenon is found to be less severe because of the localization of shear strain during cycling.

  6. Acoustic emission monitoring of fracture process of SiC/Al composites under cyclic loading

    NASA Astrophysics Data System (ADS)

    Lee, Joon-Hyun; Kim, Jong-Hwan; Yoon, Dong-Jin; Kwon, Oh-Yang

    Acoustic emission was used to clarify fatigue failure mechanisms of aliminum alloys reinforced with SiC particulate (SiCp/A356) or whisker (SiCw/Al2009). For this purpose, special attention was given to AE characteristics including AE event, energy and peak amplitude distribution which were associated with micro-fracture processes of metal matrix composites under the cyclic loading. The effects of form of reinforcements, heat treatment, orientation of whisker and loading condition on AE characteristics were discussed based on SEM fractographic results.

  7. The Characterization of Mechanical Properties of a Rabbit Femur-Anterior Cruciate Ligament-Tibia Complex During Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Hidetaka; Han, Jungsoo; Ryu, Jaiyoung; Han, Changsoo

    The purpose of this study was to investigate the effect of cyclic loading, which produced the condition of ACLs during sports activities, on tensile properties of femur-ACL-tibia complexes (FATCs). Paired FATCs of 40 New Zealand white rabbits were tested on a materials testing machine. One specimen of each pair was designated as a control and loaded until failure. The contralateral specimen was loaded cyclically (1.4 Hz, 1 hr.) with 20%, 30%, 40%, or 50% of ultimate tensile strength (UTS) of the control and then loaded until failure. The UTS and mode of failure were recorded after each test. Five specimens ruptured during cyclic loading in the 50% group. In the 40% group, the mean value of UTS of cycled specimens was significantly lower than that of controls. There was no statistically significant difference in UTS values between control and cycled specimens in the 20% and 30% groups. Cycled specimens had a significantly higher incidence of substance failure than controls. Our results demonstrated that FATCs have the strength to withstand cyclic loading within normal sports activity levels. However, FACTs can be damaged by cyclic loading under strenuous sports activity levels. We speculate that cyclic loading makes the ACL substance weaker than the insertion site.

  8. Influence of cementation technique on fracture strength and leakage of alumina all-ceramic crowns after cyclic loading.

    PubMed

    Blatz, Markus B; Oppes, Steven; Chiche, Gerard; Holst, Stefan; Sadan, Avishai

    2008-01-01

    To compare in vitro the influence of 3 cementation techniques on leakage and fracture strength of alumina all-ceramic crowns after cyclic loading in an artificial chewing simulator. Forty-eight extracted molars were mounted in a way that simulates natural tooth mobility. Crowns (Procera Alumina, Nobel Biocare) were fabricated and inserted with either conventional cementation with zinc phosphate cement without pretreatment (group ZOP); cementation with a universal adhesive resin cement without pretreatment (group HYB); or adhesive bonding with composite resin after pretreatment of the tooth (dentin bonding agent) and the crown (airborne-particle abrasion and a special ceramic priming agent containing adhesive monomers that bond to metal-oxide ceramics) (group ADH). All specimens were stored in artificial saliva and subjected to 1.2 million load cycles in a dual-axis chewing simulator (Willytec). Eight specimens per group were subjected to compressive load until failure, while the remaining 8 specimens were stained and sectioned for measuring of dye penetration. One-way ANOVA and Tukey HSD were used for statistical analyses (alpha = .05). Cementation techniques were significantly different (P = .009) in regard to mean load at failure. Fracture strength was significantly greater for ADH (mean load at fracture, 2,782 +/- 419 N) as compared to HYB (1,980 +/- 270 N) or ZOP (1,788 +/- 242 N). All groups differed significantly for leakage values (P < .001), with ADH showing the lowest mean leakage (0.04 +/- 0.07 mm), followed by HYB (0.96 +/- 0.16 mm) and ZOP (2.44 +/- 0.19 mm). Cementation technique affects fracture strength and leakage of all-ceramic molar crowns. Fracture strengths were well above natural chewing forces for all cementation methods. However, adhesive bonding significantly increased fracture strength and improved marginal seal of alumina crowns.

  9. Modelling of Fiber/Matrix Debonding of Composites Under Cyclic Loading

    NASA Technical Reports Server (NTRS)

    Naghipour, Paria; Pineda, Evan J.; Bednarcyk, Brett A.; Arnold, Steven M.

    2013-01-01

    The micromechanics theory, generalized method of cells (GMC), was employed to simulate the debonding of fiber/matrix interfaces, within a repeating unit cell subjected to global, cyclic loading, utilizing a cyclic crack growth law. Cycle dependent, interfacial debonding was implemented as a new module to the available GMC formulation. The degradation of interfacial stresses, with applied load cycles, was achieved via progressive evolution of the interfacial compliance. A periodic repeating unit cell, representing the fiber/matrix architecture of a composite, was subjected to combined normal and shear loadings, and degradation of the global transverse stress in successive cycles was monitored. The obtained results were compared to values from a corresponding finite element model. Reasonable agreement was achieved for combined normal and shear loading conditions, with minimal variation for pure loading cases. The local effects of interfacial debonding, and fatigue damage will later be combined as sub-models to predict the experimentally obtained fatigue life of Ti-15-3/Sic composites at the laminate level.

  10. Load/Strain Distribution between Ulna and Radius in the Mouse Forearm Compression Loading Model

    PubMed Central

    Lu, Yunkai; Thiagarajan, Ganesh; Nicolella, Daniel P.; Johnson, Mark L.

    2011-01-01

    Finite element analysis (FEA) of the mouse forearm compression loading model is used to relate strain distributions with downstream changes in bone formation and responses of bone cells. The objective of this study was to develop two FEA models – the first one with the traditional ulna only and the second one in which both the ulna and radius are included, in order to examine the effect of the inclusion of the radius on the strain distributions in the ulna. The entire mouse forearm was scanned using microCT and images were converted into FEA tetrahedral meshes using a suite of software programs. The performance of both linear and quadratic tetrahedral elements and coarse and fine meshes were studied. A load of 2 N was applied to the ulna/radius model and a 1.3 N load (based on previous investigations of load sharing between the ulna and radius in rats) was applied to the ulna only model for subsequent simulations. The results showed differences in the cross sectional strain distributions and magnitude within the ulna for the combined ulna/radius model versus the ulna only model. The maximal strain in the combined model occurred about 4 mm towards the distal end from the ulna mid-shaft in both models. Results from the FEA model simulations were also compared to experimentally determined strain values. We conclude that inclusion of the radius in FE models to predict strains during in vivo forearm loading increases the magnitude of the estimated ulna strains compared to those predicted from a model of the ulna alone but the distribution was similar. This has important ramifications for future studies to understand strain thresholds needed to activate bone cell responses to mechanical loading. PMID:21903442

  11. Mechanical behavior of zirconia and titanium abutments before and after cyclic load application.

    PubMed

    Gehrke, Sergio Alexandre; Poncio da Silva, Pablo Mateus; Calvo Guirado, José Luiz; Delgado-Ruiz, Rafael Arcesio; Dedavid, Berenice Anina; Aline Nagasawa, Magda; Shibli, Jamil Awad

    2016-10-01

    Esthetic factors influence the decision to use titanium or zirconia abutments in anterior regions. Clinicians may have concerns about the durability and behavior of these zirconia abutments. The purpose of this in vitro study was to evaluate the longitudinal and transverse long axes of the implant-abutment interface before and after the cyclic loading of titanium and zirconia abutments with an external hexagon. Forty dental implants with an external hexagon and 40 corresponding abutments made of titanium (Ti) and zirconia (Zr) were subjected to cyclic load (c1) versus no load (c2). The longitudinal and transverse axes of 4 experimental groups (Tic1, Tic2, Zrc1, and Zrc2) were analyzed (vertical/horizontal adjustment) using a scanning electron microscope at ×1000 magnification. The differences among the groups were determined by 1-way analysis of variance (ANOVA) and post hoc Tukey tests (α=.05). T tests were used to identify the statistically significant differences between each group and each condition (α=.05). Significant differences were found among the groups with respect to the misfits analyzed in the 2 sections (longitudinal and transverse) before and after load application (P<.05). The behaviors of the groups differed particularly with regard to the accommodation of sets (abutment/implant) after the application of cyclic loads (P<.05). The use of zirconia abutments in titanium implants can cause changes to and/or permanent deformation of the implant hexagon. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  12. Fracture mode during cyclic loading of implant-supported single-tooth restorations.

    PubMed

    Hosseini, Mandana; Kleven, Erik; Gotfredsen, Klaus

    2012-08-01

    Fracture of veneering ceramics in zirconia-based restorations has frequently been reported. Investigation of the fracture mode of implant-supported ceramic restorations by using clinically relevant laboratory protocols is needed. This study compared the mode of fracture and number of cyclic loads until veneering fracture when ceramic and metal ceramic restorations with different veneering ceramics were supported by implants. Thirty-two implant-supported single-tooth restorations were fabricated. The test group was composed of 16 ceramic restorations of zirconia abutment-retained crowns with zirconia copings veneered with glass-ceramics (n=8) and feldspathic ceramics (n=8). The control group was composed of 16 metal ceramic restorations of titanium abutment-retained crowns with gold alloy copings veneered with glass (n=8) and feldspathic ceramics (n=8). The palatal surfaces of the crowns were exposed to cyclic loading of 800 N with a frequency of 2 Hz, which continued to 4.2 million cycles or until fracture of the copings, abutments, or implants. The number of cycles and the fracture modes were recorded. The fracture modes were analyzed by descriptive analysis and the Mann-Whitney test (α=.05). The differences in loading cycles until veneering fracture were estimated with the Cox proportional hazards analysis. Veneering fracture was the most frequently observed fracture mode. The severity of fractures was significantly more in ceramic restorations than in metal ceramic restorations. Significantly more loading cycles until veneering fracture were estimated with metal ceramic restorations veneered with glass-ceramics than with other restorations. The metal ceramic restorations demonstrated fewer and less severe fractures and resisted more cyclic loads than the ceramic restorations, particularly when the metal ceramic crowns were veneered with glass-ceramics. Copyright © 2012 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All

  13. Strain Amplification Analysis of an Osteocyte under Static and Cyclic Loading: A Finite Element Study

    PubMed Central

    Xian, Cory J.

    2015-01-01

    Osteocytes, the major type of bone cells which reside in their lacunar and canalicular system within the bone matrix, function as biomechanosensors and biomechanotransducers of the bone. Although biomechanical behaviour of the osteocyte-lacunar-canalicular system has been investigated in previous studies mostly using computational 2-dimensional (2D) geometric models, only a few studies have used the 3-dimensional (3D) finite element (FE) model. In the current study, a 3D FE model was used to predict the responses of strain distributions of osteocyte-lacunar-canalicular system analyzed under static and cyclic loads. The strain amplification factor was calculated for all simulations. Effects on the strain of the osteocyte system were investigated under 500, 1500, 2000, and 3000 microstrain loading magnitudes and 1, 5, 10, 40, and 100 Hz loading frequencies. The maximum strain was found to change with loading magnitude and frequency. It was observed that maximum strain under 3000-microstrain loading was higher than those under 500, 1500, and 2000 microstrains. When the loading strain reached the maximum magnitude, the strain amplification factor of 100 Hz was higher than those of the other frequencies. Data from this 3D FE model study suggests that the strain amplification factor of the osteocyte-lacunar-canalicular system increases with loading frequency and loading strain increasing. PMID:25664319

  14. Effect of dynamic monotonic and cyclic loading on fracture behavior for Japanese carbon steel pipe STS410

    SciTech Connect

    Kinoshita, Kanji; Murayama, Kouichi; Ogata, Hiroyuki

    1997-04-01

    The fracture behavior for Japanese carbon steel pipe STS410 was examined under dynamic monotonic and cyclic loading through a research program of International Piping Integrity Research Group (EPIRG-2), in order to evaluate the strength of pipe during the seismic event The tensile test and the fracture toughness test were conducted for base metal and TIG weld metal. Three base metal pipe specimens, 1,500mm in length and 6-inch diameter sch.120, were employed for a quasi-static monotonic, a dynamic monotonic and a dynamic cyclic loading pipe fracture tests. One weld joint pipe specimen was also employed for a dynamic cyclic loading test In the dynamic cyclic loading test, the displacement was controlled as applying the fully reversed load (R=-1). The pipe specimens with a circumferential through-wall crack were subjected four point bending load at 300C in air. Japanese STS410 carbon steel pipe material was found to have high toughness under dynamic loading condition through the CT fracture toughness test. As the results of pipe fracture tests, the maximum moment to pipe fracture under dynamic monotonic and cyclic loading condition, could be estimated by plastic collapse criterion and the effect of dynamic monotonic loading and cyclic loading was a little on the maximum moment to pipe fracture of the STS410 carbon steel pipe. The STS410 carbon steel pipe seemed to be less sensitive to dynamic and cyclic loading effects than the A106Gr.B carbon steel pipe evaluated in IPIRG-1 program.

  15. Damage and performance characterization of ARALL laminates subjected to tensile cyclic loading

    NASA Astrophysics Data System (ADS)

    Osiroff, Ricardo; Stinchcomb, Wayne W.; Reifsnider, Kenneth L.

    The behavior of ARALL (ARamid ALuminum Laminates) subjected to tension-tension cyclic loading was experimentally investigated as a first step toward the understanding of the long-term bahavior of ARALL laminates. Specifically, this work addresses fatigue damage mechanisms and relationships between damage and stiffness change, remaining strength, and life. The quasi-static and dynamic material response of unnotched ARALL-2 coupons were measured at normalized maximum stress levels (S) ranging from 0.4 to 0.9 of the ultimate tensile strength. The damage mechanisms and failure modes changed over this range of cyclic stresses. While at low cyclic stress levels, the fatigue properties of the fiber-reinforced plies are key factors; at high cyclic stress levels, the laminate's response is governed by the aluminum plies. Five distinct stages were recognized in the damage sequence. A shear lag analysis is presented to model the regular spacing of cracks called the characteristic damage state. Appropriate modifications were made to accommodate for the hybrid nature of the laminate.

  16. Analytical basis for the determination of the lacunar-canalicular permeability of bone using cyclic loading.

    PubMed

    Benalla, M; Cardoso, L; Cowin, S C

    2012-07-01

    An analytical model for the determination of the permeability in the lacunar-canalicular porosity of bone using cyclic loading is described in this contribution. The objective of the analysis presented is to relate the lacunar-canalicular permeability to a particular phase angle that is measurable when the bone is subjected to infinitesimal cyclic strain. The phase angle of interest is the lag angle between the applied strain and the resultant stress. Cyclic strain causes the interstitial fluid to move. This movement is essential for the viability of osteocytes and is believed to play a major role in the bone mechanotransduction mechanism. However, certain bone fluid flow properties, notably the permeability of the lacunar-canalicular porosity, are still not accurately determined. In this paper, formulas for the phase angle as a function of permeability for infinitesimal cyclic strain are presented and mathematical expressions for the storage modulus, loss modulus, and loss tangent are obtained. An accurate determination of the PLC permeability will improve our ability to understand mechanotransduction and mechanosensory mechanisms, which are fundamental to the understanding of how to treat osteoporosis, how to cope with microgravity in long-term manned space flights, and how to increase the longevity of prostheses that are implanted in bone tissue.

  17. Buckling behavior of long symmetrically laminated plates subjected to compression, shear, and inplane bending loads

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1992-01-01

    A parametric study of the buckling behavior of infinitely long symmetrically laminated anisotropic plates subjected to combined loadings are presented. The loading conditions considered are pure inplane bending, transverse tension and compression, and shear. Results obtained using a special purpose analysis are presented for clamped and simply supported plates. An important finding of the study is that the effects of anisotropy are much more pronounced in shear-loaded plates than in axial compression-loaded plates and plates loaded by pure inplane bending.

  18. An extended thermomechanically coupled 3D rate-dependent model for pseudoelastic SMAs under cyclic loading

    NASA Astrophysics Data System (ADS)

    Gu, Xiaojun; Zhang, Weihong; Zaki, Wael; Moumni, Ziad

    2017-09-01

    The model presented in this paper was shown to successfully account for cyclic loading effects and thermomechanical coupling in SMAs, including the influence of load rate and temperature on both the rate and value at saturation of the residual strain. It is the first such comprehensive model to be successfully utilized for relatively complex simulations involving SMAs subjected to multiaxial nonproportional loading, which possibly result in strong stress gradients such as fracture mechanics. In fact, it is known that the high stress concentration at the tip of a crack in SMAs results in increased martensite transformation and reorientation, which influence the growth of the crack. The derivation of the constitutive equations as well as the time integration and relevant algorithmic considerations are presented in detail. The model was shown to allow reasonable agreement with several sets of reference experimental and simulation data taken from the literature.

  19. Microscopic observations during longitudinal compression loading of single pulp fibers

    Treesearch

    Irving B. Sachs

    1986-01-01

    Paperboard components (linerboard adn corrugating medium) fail in edgewise compression because of failure of single fibers, as well as fiber-to-fiber bonds. While fiber-to-fiber-bond failure has been studied extensively, little is known about the longitudinal compression failure of a single fiber. In this study, surface alterations on single loblolly pine kraft pulp...

  20. The tolerance of the femoral shaft in combined axial compression and bending loading.

    PubMed

    Ivarsson, B Johan; Genovese, Daniel; Crandall, Jeff R; Bolton, James R; Untaroiu, Costin D; Bose, Dipan

    2009-11-01

    The likelihood of a front seat occupant sustaining a femoral shaft fracture in a frontal crash has traditionally been assessed by an injury criterion relying solely on the axial force in the femur. However, recently published analyses of real world data indicate that femoral shaft fracture occurs at axial loads levels below those found experimentally. One hypothesis attempting to explain this discrepancy suggests that femoral shaft fracture tends to occur as a result of combined axial compression and applied bending. The current study aims to evaluate this hypothesis by investigating how these two loading components interact. Femoral shafts harvested from human cadavers were loaded to failure in axial compression, sagittal plane bending, and combined axial compression and sagittal plane bending. All specimens subjected to bending and combined loading fractured midshaft, whereas the specimens loaded in axial compression demonstrated a variety of failure locations including midshaft and distal end. The interaction between the recorded levels of applied moment and axial compression force at fracture were evaluated using two different analysis methods: fitting of an analytical model to the experimental data and multiple regression analysis. The two analysis methods yielded very similar relationships between applied moment and axial compression force at midshaft fracture. The results indicate that posteroanterior bending reduces the tolerance of the femoral shaft to axial compression and that that this type of combined loading therefore may contribute to the high prevalence of femoral shaft fracture in frontal crashes.

  1. In vivo dynamic stiffness of the porcine lumbar spine exposed to cyclic loading: influence of load and degeneration.

    PubMed

    Kaigle, A; Ekström, L; Holm, S; Rostedt, M; Hansson, T

    1998-02-01

    The dynamic axial stiffness of the L2-3 motion segment subjected to vibratory loading under intact and injured states of the intervertebral disc was studied using an in vivo porcine model. Three groups of animals with the following states of the intervertebral discs were studied: intact disc, acutely injured disc, and degenerated disc. A miniaturized servo-hydraulic exciter was used to sinusoidally vibrate the motion segment from 0.05 to 25 Hz under a compressive load with a peak value of either 100 or 200 N. The dynamic axial stiffness of the intervertebral disc was calculated at 1-Hz intervals over the frequency range. The results showed that the dynamic axial stiffness was frequency dependent. A positive relationship was found between an increase in mean dynamic stiffness and load magnitude. An increase in mean stiffness with successive exposures at the same load magnitude was observed, despite the allowance of a recovery period between loading. The greatest difference was noted between the first and second load sets. No significant change in stiffness was found due to an acute disc injury, whereas a significant increase in mean stiffness was found for the degenerated disc group as compared with the intact group. The form of the frequency response curve, however, remained relatively unaltered regardless of the degenerated state of the disc. With heavier loads, repeated loading, and/or disc degeneration, the stiffness of the intervertebral disc increases. An increase in stiffness can mean a reduction in the amount of allowable motion within the motion segment or a potentially harmful increase in force to obtain the desired motion. This may locally result in greater stresses due to an altered ability of the disc to distribute loads.

  2. Field testing of stiffened deep cement mixing piles under lateral cyclic loading

    NASA Astrophysics Data System (ADS)

    Raongjant, Werasak; Jing, Meng

    2013-06-01

    Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns (SDCM). This research investigates methods used to improve the level of bearing capacity of these SDCM when subjected to cyclic lateral loading via various types of stiffer cores. Eight piles, two deep cement mixed piles and six stiffened deep cement mixing piles with three different types of cores, H shape cross section prestressed concrete, steel pipe, and H-beam steel, were embedded though soft clay into medium-hard clay on site in Thailand. Cyclic horizontal loading was gradually applied until pile failure and the hysteresis loops of lateral load vs. lateral deformation were recorded. The lateral carrying capacities of the SDCM piles with an H-beam steel core increased by 3-4 times that of the DCM piles. This field research clearly shows that using H-beam steel as a stiffer core for SDCM piles is the best method to improve its lateral carrying capacity, ductility and energy dissipation capacity.

  3. Crack classification and evolution in anisotropic shale during cyclic loading tests by acoustic emission

    NASA Astrophysics Data System (ADS)

    Wang, Miaomiao; Tan, Chengxuan; Meng, Jing; Yang, Baicun; Li, Yuan

    2017-08-01

    Characterization and evolution of the cracking mode in shale formation is significant, as fracture networks are an important element in shale gas exploitation. In this study we determine the crack modes and evolution in anisotropic shale under cyclic loading using the acoustic emission (AE) parameter-analysis method based on the average frequency and RA (rise-time/amplitude) value. Shale specimens with bedding-plane orientations parallel and perpendicular to the axial loading direction were subjected to loading cycles with increasing peak values until failure occurred. When the loading was parallel to the bedding plane, most of the cracks at failure were shear cracks, while tensile cracks were dominant in the specimens that were loaded normal to the bedding direction. The evolution of the crack mode in the shale specimens observed in the loading-unloading sequence except for the first cycle can be divided into three stages: (I) no or several cracks (AE events) form as a result of the Kaiser effect, (II) tensile and shear cracks increase steadily at nearly equal proportions, (III) tensile cracks and shear cracks increase abruptly, with more cracks forming in one mode than in the other. As the dominant crack motion is influenced by the bedding, the failure mechanism is discussed based on the evolution of the different crack modes. Our conclusions can increase our understanding of the formation mechanism of fracture networks in the field.

  4. Damage & fracture of high-explosive mock subject to cyclic loading

    SciTech Connect

    Liu, Cheng; Rae, Philip J; Cady, Carl M; Lovato, Manuel L

    2011-01-11

    We use four-point bend specimen with a single shallow edge notch to study the fracture process in Mock 900-21, a PBX 9501 high explosive simulant mock. Subject to monotonic loading we determine quantitatively the threshold load for macroscopic crack initiation from the notch tip. The four-point bend specimen is then subject to cyclic loading in such a way that during the first cycle, the applied force approaches but does not exceed the threshold load determined from the monotonic loading test and in the subsequent cycles, the overall maximum deformation is maintained to be equal to that of the first cycle. It is expected and is also confirmed that no macroscopic damage and cracking occur during the first cycle. However, we observe that sizable macroscopic crack is generated and enlarged during the subsequent cycles, even though the applied force never exceeds the threshold load. Details of the process of damage fonnation, accumulation, and crack extension are presented and the mechanical mechanism responsible for such failure process is postulated and discussed.

  5. Biomechanical properties of abdominal organs in vivo and postmortem under compression loads.

    PubMed

    Rosen, Jacob; Brown, Jeffrey D; De, Smita; Sinanan, Mika; Hannaford, Blake

    2008-04-01

    Accurate knowledge of biomechanical characteristics of tissues is essential for developing realistic computer-based surgical simulators incorporating haptic feedback, as well as for the design of surgical robots and tools. As simulation technologies continue to be capable of modeling more complex behavior, an in vivo tissue property database is needed. Most past and current biomechanical research is focused on soft and hard anatomical structures that are subject to physiological loading, testing the organs in situ. Internal organs are different in that respect since they are not subject to extensive loads as part of their regular physiological function. However, during surgery, a different set of loading conditions are imposed on these organs as a result of the interaction with the surgical tools. Following previous research studying the kinematics and dynamics of tool/tissue interaction in real surgical procedures, the focus of the current study was to obtain the structural biomechanical properties (engineering stress-strain and stress relaxation) of seven abdominal organs, including bladder, gallbladder, large and small intestines, liver, spleen, and stomach, using a porcine animal model. The organs were tested in vivo, in situ, and ex corpus (the latter two conditions being postmortem) under cyclical and step strain compressions using a motorized endoscopic grasper and a universal-testing machine. The tissues were tested with the same loading conditions commonly applied by surgeons during minimally invasive surgical procedures. Phenomenological models were developed for the various organs, testing conditions, and experimental devices. A property database-unique to the literature-has been created that contains the average elastic and relaxation model parameters measured for these tissues in vivo and postmortem. The results quantitatively indicate the significant differences between tissue properties measured in vivo and postmortem. A quantitative understanding of

  6. Fabric Evolution in Granular Materials Subject to Drained, Strain Controlled Cyclic Loading

    NASA Astrophysics Data System (ADS)

    O'Sullivan, C.; Cui, L.

    2009-06-01

    While there have been many discrete element method (DEM) publications considering the micromechanics of granular materials subject to monotonic loading, studies of the particle-scale material response to cyclic or repeated loading have been comparatively rare. From a geotechnical perspective soil is subjected to repeated loading in a variety of situations. Examples include foundations to railways and roads, foundations to wind turbines, soil adjacent to integral bridges, etc. The work described in this paper extends an earlier study by O'Sullivan et al.. [1]. In this earlier study, DEM simulations of strain controlled cyclic triaxial tests were coupled with laboratory experiments to validate a DEM model. The simulations were performed using the axi-symmetric DEM formulation proposed by [2] and a stress controlled membrane algorithm was used to apply forces to balls along the outer vertical boundaries to model the latex membrane used in the laboratory tests. Specimens of uniform spheres and mixtures of sphere sizes were considered in the validation stage of this research. The earlier study considered strain amplitudes of 1%, 0.5% and 0.1%. In the current study the response is extended to consider the smaller strain amplitude of 0.01%. All of the simulations were carried out in a quasi-static mode and in all cases the maximum stress level mobilized was significantly lower than the peak stress measured in equivalent monotonic physical tests and DEM simulations [2]. In examining the response of the material to the smaller strain amplitude, the macro scale analyses considered the stress strain response and specimen stiffness. At the particle scale, the variation in coordination number and deviator fabric are considered as well as the distribution of the contact forces orientations. The findings may provide insight to the development of continuum constitutive models for cyclic soil response that include fabric parameters [3].

  7. Finite Element Modeling of Metal Foam Structures Subject to Compressive Loading

    DTIC Science & Technology

    2001-12-01

    TERMS aluminum metal foam, composite metal foam, metal foam compressive loading, metal foam stiffness, metal foam strength 16. PRICE CODE 17...EXPERIMENTS........................................................................................................ 23 A. OPEN CELL ALUMINUM METAL FOAM...23 B. ALUMINUM METAL FOAM FILLED WITH ELASTO-PLASTIC MATERIAL

  8. High Temperature Environmental Test Facility for Uniaxial Testing under Cyclic Loading

    DTIC Science & Technology

    2007-11-02

    20503. 1. AGENCY USE ONLY ( Leave Blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED March 23, 1998 Final Report (1 Aug 95 to 31 Jul 97) 4 . TITLE...AND SUBTITLE 5. FUNDING NUMBERS High Temperature Environmental Test Facility For Uniaxial F49620-95- 1-04 70 Testing Under Cyclic Loading 6 . AUTHOR(S...extensometer is rated for 1200 ’C. The system is capable of fatigue testing conventional aluminum and titanium materials and high temperature or single crystal

  9. Damage accumulation in cyclically-loaded glass-ceramic matrix composites monitored by acoustic emission.

    PubMed

    Aggelis, D G; Dassios, K G; Kordatos, E Z; Matikas, T E

    2013-01-01

    Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested in a cyclic loading protocol. Broadband acoustic emission (AE) sensors are used for monitoring the occurrence of different possible damage mechanisms. Improved use of AE indices is proposed by excluding low-severity signals based on waveform parameters, rather than only threshold criteria. The application of such improvements enhances the accuracy of the indices as accumulated damage descriptors. RA-value, duration, and signal energy follow the extension cycles indicating moments of maximum or minimum strain, while the frequency content of the AE signals proves very sensitive to the pull-out mechanism.

  10. Damage Accumulation in Cyclically-Loaded Glass-Ceramic Matrix Composites Monitored by Acoustic Emission

    PubMed Central

    Aggelis, D. G.; Dassios, K. G.; Kordatos, E. Z.; Matikas, T. E.

    2013-01-01

    Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested in a cyclic loading protocol. Broadband acoustic emission (AE) sensors are used for monitoring the occurrence of different possible damage mechanisms. Improved use of AE indices is proposed by excluding low-severity signals based on waveform parameters, rather than only threshold criteria. The application of such improvements enhances the accuracy of the indices as accumulated damage descriptors. RA-value, duration, and signal energy follow the extension cycles indicating moments of maximum or minimum strain, while the frequency content of the AE signals proves very sensitive to the pull-out mechanism. PMID:24381524

  11. Methodology to Calibrate Disc Degeneration in the Cervical Spine During Cyclic Fatigue Loading.

    PubMed

    Masoudi, Aidin; Fama, Daniel; Yoganandan, Narayan; Snyder, Brian

    2015-01-01

    Prolonged exposure to vibrational working conditions can cause neck, back, and shoulder pain. Mechanical degradation of soft tissues resulting from this type of fatigue was experimentally shown to contribute to endplate and compression fractures. However, effects of repetitive subfailure loading on intervertebral disc (IVD) behavior have not been well defined. This manuscript describes a methodology to experimentally characterize changes in cervical spine IVD material properties under fatigue. Bone-disc-bone spinal units with intact ligaments obtained from human cervical spines were obtained and a lack of bony or soft tissue degeneration was confirmed using X-ray and MRI scans. Cranial and caudal specimen extents were fixed in PMMA to facilitate attachment to testing devices. Baseline response was quantified using flexion/extension pure moment protocols. Specimens were immersed in a 34-deg-C saline bath and allowed to acclimate for one hour. A stress-relaxation test was then performed and viscoelasticity quantified using a quasi linear viscoelastic (QLV) material model. Fatigue testing was performed for up to 50,000 cycles with intermittent viscoelasticity, pure moment testing, and imaging scans performed to quantify cycle-dependent changes in disc properties. Preliminary results demonstrated progressive changes in viscoelasticity and bending response of cervical spine segments with increasing number of load cycles. This procedure will be used to quantify degradation of the IVD under repetitive compressive loads, focusing on effects of loading magnitude and frequency.

  12. Self-Sensing of Damage Progression in Unidirectional Multiscale Hierarchical Composites Subjected to Cyclic Tensile Loading

    PubMed Central

    Ku-Herrera, J. J.; Pacheco-Salazar, O. F.; Ríos-Soberanis, C. R.; Domínguez-Rodríguez, G.; Avilés, F.

    2016-01-01

    The electrical sensitivity of glass fiber/multiwall carbon nanotube/vinyl ester hierarchical composites containing a tailored electrically-percolated network to self-sense accumulation of structural damage when subjected to cyclic tensile loading-unloading is investigated. The hierarchical composites were designed to contain two architectures differentiated by the location of the multiwall carbon nanotubes (MWCNTs), viz. MWCNTs deposited on the fibers and MWCNTs dispersed within the matrix. The changes in electrical resistance of the hierarchical composites are associated to their structural damage and correlated to acoustic emissions. The results show that such tailored hierarchical composites are able to self-sense damage onset and accumulation upon tensile loading-unloading cycles by means of their electrical response, and that the electrical response depends on the MWCNT location. PMID:26999158

  13. Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

    NASA Astrophysics Data System (ADS)

    Gu, Linlin; Ye, Guanlin; Wang, Zhen; Ling, Xianzhang; Zhang, Feng

    2017-07-01

    In this paper, numerical simulation with soil-water coupling finite element-finite difference (FE-FD) analysis is conducted to investigate the settlement and the excess pore water pressure (EPWP) of a piled-raft foundation due to cyclic high-speed (speed: 300km/h) train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer (No-9 layer) has better effect on reducing the settlement.

  14. Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material

    NASA Technical Reports Server (NTRS)

    Vandermey, Nancy E.; Morris, Don H.; Masters, John E.

    1991-01-01

    Damage initiation and growth under compression-compression fatigue loading were investigated for a stitched uniweave material system with an underlying AS4/3501-6 quasi-isotropic layup. Performance of unnotched specimens having stitch rows at either 0 degree or 90 degrees to the loading direction was compared. Special attention was given to the effects of stitching related manufacturing defects. Damage evaluation techniques included edge replication, stiffness monitoring, x-ray radiography, residual compressive strength, and laminate sectioning. It was found that the manufacturing defect of inclined stitches had the greatest adverse effect on material performance. Zero degree and 90 degree specimen performances were generally the same. While the stitches were the source of damage initiation, they also slowed damage propagation both along the length and across the width and affected through-the-thickness damage growth. A pinched layer zone formed by the stitches particularly affected damage initiation and growth. The compressive failure mode was transverse shear for all specimens, both in static compression and fatigue cycling effects.

  15. The Critical Compression Load for a Universal Testing Machine When the Specimen Is Loaded Through Knife Edges

    NASA Technical Reports Server (NTRS)

    Lundquist, Eugene E; Schwartz, Edward B

    1942-01-01

    The results of a theoretical and experimental investigation to determine the critical compression load for a universal testing machine are presented for specimens loaded through knife edges. The critical load for the testing machine is the load at which one of the loading heads becomes laterally instable in relation to the other. For very short specimens the critical load was found to be less than the rated capacity given by the manufacturer for the machine. A load-length diagram is proposed for defining the safe limits of the test region for the machine. Although this report is particularly concerned with a universal testing machine of a certain type, the basic theory which led to the derivation of the general equation for the critical load, P (sub cr) = alpha L can be applied to any testing machine operated in compression where the specimen is loaded through knife edges. In this equation, L is the length of the specimen between knife edges and alpha is the force necessary to displace the upper end of the specimen unit horizontal distance relative to the lower end of the specimen in a direction normal to the knife edges through which the specimen is loaded.

  16. Effects of Cyclic Loading on the Shear Behaviour of Infilled Rock Joints Under Constant Normal Stiffness Conditions

    NASA Astrophysics Data System (ADS)

    Mirzaghorbanali, Ali; Nemcik, Jan; Aziz, Naj

    2014-07-01

    The variation of the shear strength of infilled rock joints under cyclic loading and constant normal stiffness conditions is studied. To simulate the joints, triangular asperities inclined at angles of 9.5° and 18.5° to the shear movement were cast using high-strength gypsum plaster and infilled with clayey sand. These joints were sheared cyclically under constant normal stiffness conditions. It was found that, for a particular normal stiffness, the shear strength is a function of the initial normal stress, initial asperity angle, joint surface friction angle, infill thickness, infill friction angle, loading direction and number of loading cycles. Based on the experimental results, a mathematical model is proposed to evaluate the shear strength of infilled rock joints in cyclic loading conditions. The proposed model takes into consideration different initial asperity angles, initial normal stresses and ratios of infill thickness to asperity height.

  17. Dynamic Behavior of Single-Stage Bellows of Titanium-Nickel Shape Memory Alloy Under Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Semba, Hiromasa; Okabe, Nagatoshi; Yamaji, Toru; Okita, Keisuke; Yamauchi, Kiyoshi

    The dynamic behavior of TiNi shape memory alloy (SMA) bellows is examined in light of its potential use as elements in seismic protection devices. Dynamic property results obtained from cyclic tests under tension-compression loading of TiNi SMA single-stage bellows, with different shapes and with different heat treatments, are reported as a function of displacement amplitude and frequency. It was found that the displacement-force loops were almost symmetric with respect to the central point for almost all specimens. The normalized secant stiffness diminishes significantly with increasing bulge height as well as displacement amplitude. From hysteretic cycles, an equivalent damping of about 15% was recognized for longtime-aged bellows with relatively high bulge height. Frequencies, in the range of interest for seismic applications, had a small influence on damping values. Under the conditions studied in this research, the bellows had better damping performance in a martensite phase than in a rhombohedral phase. SMA bellows in martensite phase subjected to the longtime-ageing have great potential as an element in seismic devices.

  18. FEA Based Tool Life Quantity Estimation of Hot Forging Dies Under Cyclic Thermo-Mechanical Loads

    NASA Astrophysics Data System (ADS)

    Behrens, B.-A.; Bouguecha, A.; Schäfer, F.; Hadifi, T.

    2011-01-01

    Hot forging dies are exposed during service to a combination of cyclic thermo-mechanical, tribological and chemical loads. Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most frequent causes of failure. In order to extend the tool life, the finite element analysis (FEA) may serve as a means for process design and process optimisation. So far the FEA based estimation of the production cycles until initial cracking is limited as tool material behaviour due to repeated loading is not captured with the required accuracy. Material models which are able to account for cyclic effects are not verified for the fatigue life predictions of forging dies. Furthermore fatigue properties from strain controlled fatigue tests of relevant hot work steels are to date not available to allow for a close-to-reality fatigue life prediction. Two industrial forging processes, where clear fatigue crack initiation has been observed are considered for a fatigue analysis. For this purpose the relevant tool components are modelled with elasto-plastic material behaviour. The predicted sites, where crack initiation occurs, agree with the ones observed on the real die component.

  19. A crystal plasticity model incorporating the effects of precipitates in superalloys: Application to tensile, compressive, and cyclic deformation of Inconel 718

    DOE PAGES

    Ghorbanpour, Saeede; Zecevic, Milovan; Kumar, Anil; ...

    2017-09-14

    An elasto-plastic polycrystal plasticity model is developed and applied to an Inconel 718 (IN718) superalloy that was produced by additive manufacturing (AM). The model takes into account the contributions of solid solution, precipitates shearing, and grain size and shape effects into the initial slip resistance. Non-Schmid effects and backstress are also included in the crystal plasticity model for activating slip. The hardening law for the critical resolved shear stress is based on the evolution of dislocation density. In using the same set of material and physical parameters, the model is compared against a suite of compression, tension, and large-strain cyclicmore » mechanical test data applied in different AM build directions. We demonstrate that the model is capable of predicting the particularities of both monotonic and cyclic deformation to large strains of the alloy, including decreasing hardening rate during monotonic loading, the non-linear unloading upon the load reversal, the Bauschinger effect, the hardening rate change during loading in the reverse direction as well as plastic anisotropy and the concomitant microstructure evolution. It is anticipated that the general model developed here can be applied to other multiphase alloys containing precipitates.« less

  20. Compressive Loading and Modeling of Stitched Composite Stiffeners

    NASA Technical Reports Server (NTRS)

    Leone, Frank A., Jr.; Jegley, Dawn C.; Linton, Kim A.

    2016-01-01

    A series of single-frame and single-stringer compression tests were conducted at NASA Langley Research Center on specimens harvested from a large panel built using the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept. Different frame and stringer designs were used in fabrication of the PRSEUS panel. In this paper, the details of the experimental testing of single-frame and single-stringer compression specimens are presented, as well as discussions on the performance of the various structural configurations included in the panel. Nonlinear finite element models were developed to further understand the failure processes observed during the experimental campaign.

  1. Automatic Modulation Classification of Common Communication and Pulse Compression Radar Waveforms using Cyclic Features

    DTIC Science & Technology

    2013-03-01

    from estimated duty cycle, cyclic spectral correlation, and cyclic cumulants. The modulations considered in this research are BPSK, QPSK, 16- QAM , 64- QAM ...spectral density PSK phase shift keying QAM quadrature amplitude modulation QPSK quadrature phase shift keying RADAR radio detection and ranging RF radio...spectrum sensing research, automatic modulation recognition has emerged as an important process in cognitive spectrum management and EW applications

  2. Crystal Plasticity Analysis on Compressive Loading of Magnesium with Suppression of Twinning

    NASA Astrophysics Data System (ADS)

    Mayama, Tsuyoshi; Ohashi, Tetsuya; Higashida, Kenji; Kawamura, Yoshihito

    The compressive loading behavior of single crystals and bicrystals of magnesium without consideration of deformation twinning has been investigated by crystal plasticity finite element analysis with the aim of fundamental understanding of kink band formation in magnesium alloys with long period stacking ordered structure (LPSO) phase. The basal plane of the single crystal model is set to be parallel to the compressive direction. The result of the compressive loading analysis of single crystals indicates the significant influence of suppression of twinning on the activation of nonbasal slip systems and stress-strain behavior. The compressive analysis of symmetric bicrystal is also performed to clarify the influence of the angle between basal plane and the loading axis. The influence of the introduction of grain boundary and the slight change of crystal orientation is discussed in terms of activated deformation modes.

  3. Acoustics and temperature based NDT for damage assessment of concrete masonry system subjected to cyclic loading

    NASA Astrophysics Data System (ADS)

    Khan, Fuad; Bartoli, Ivan; Rajaram, Satish; Vanniamparambil, Prashanth A.; Kontsos, Antonios; Bolhassani, Mohammad; Hamid, Ahmad

    2014-04-01

    This paper represents a hybrid non-destructive testing (HNDT) approach based on infrared thermography (IRT), acoustic emission (AE) and ultrasonic (UT) techniques for effective damage quantification of partially grouted concrete masonry walls (CMW). This integrated approach has the potential to be implemented for the health monitoring of concrete masonry systems. The implementation of this hybrid approach assists the cross validation of in situ recorded information for structural damage assessment. In this context, NDT was performed on a set of partially grouted CMW subjected to cyclic loading. Acoustic emission (AE) signals and Infrared thermography (IRT) images were recorded during each cycle of loading while the ultrasonic (UT) tests were performed in between each loading cycle. Four accelerometers, bonded at the toe of the wall, were used for recording waveforms for both passive (AE) and active (UT) acoustics. For the active approach, high frequency stress waves were generated by an instrumented hammer and the corresponding waveforms were recorded by the accelerometers. The obtained AE, IRT, and UT results were correlated to visually confirm accumulated progressive damage throughout the loading history. Detailed post-processing of these results was performed to characterize the defects at the region of interest. The obtained experimental results demonstrated the potential of the methods to detect flaws on monitored specimens; further experimental investigations are planned towards the quantitative use of these NDT methods.

  4. High temperature fatigue behaviour of TZM molybdenum alloy under mechanical and thermomechanical cyclic loads

    NASA Astrophysics Data System (ADS)

    Shi, H. J.; Niu, L. S.; Korn, C.; Pluvinage, G.

    2000-02-01

    High temperature isothermal mechanical fatigue and in-phase thermomechanical fatigue (TMF) tests in load control were carried out on a molybdenum-based alloy, one of the best known of the refractory alloys, TZM. The stress-strain response and the cyclic life of the material were measured during the tests. The fatigue lives obtained in the in-phase TMF tests are lower than those obtained in the isothermal mechanical tests at the same load amplitude. It appears that an additional damage is produced by the reaction of mechanical stress cycles and temperature cycles in TMF situation. Ratcheting phenomenon occurred during the tests with an increasing creep rate and it was dependent on temperature and load amplitude. A model of lifetime prediction, based on the Woehler-Miner law, was discussed. Damage coefficients that are functions of the maximum temperature and the variation of temperature are introduced in the model so as to evaluate TMF lives in load control. With this method the lifetime prediction gives results corresponding well to experimental data.

  5. Fixture for environmental exposure of structural materials under compression load

    NASA Technical Reports Server (NTRS)

    Clark, R. K.; Lisagor, W. B. (Inventor)

    1983-01-01

    A device for stressing a deformable material specimen consists of top plate and a bottom plate sandwiching a guide cylinder. The specimen is positioned on the bottom plate and attached to a load piston. Force is applied through the top plate into the guide cylinder. Once the specimen is loaded, the stress is maintained by tightening tie bolt nuts.

  6. Apparatus for measuring static coefficient of friction under compressive loads

    NASA Technical Reports Server (NTRS)

    Haehner, C. L.; Tarpley, J. L.

    1975-01-01

    Device includes load cell attached to rigid structure. Crosshead directly beneath cell is connected to constant-speed electrical motor. Crossarm supported by crosshead serves as platform on which bodies are tested. Test data are recorded on X-Y recorder which is connected to load cell and motor.

  7. Development of a new connection for precast concrete walls subjected to cyclic loading

    NASA Astrophysics Data System (ADS)

    Vaghei, Ramin; Hejazi, Farzad; Taheri, Hafez; Jaafar, Mohd Saleh; Aziz, Farah Nora Aznieta Abdul

    2017-01-01

    The Industrialized Building System (IBS) was recently introduced to minimize the time and cost of project construction. Accordingly, ensuring the integration of the connection of precast components in IBS structures is an important factor that ensures stability of buildings subjected to dynamic loads from earthquakes, vehicles, and machineries. However, structural engineers still lack knowledge on the proper connection and detailed joints of IBS structure construction. Therefore, this study proposes a special precast concrete wall-to-wall connection system for dynamic loads that resists multidirectional imposed loads and reduces vibration effects (PI2014701723). This system is designed to connect two adjacent precast wall panels by using two steel U-shaped channels (i.e., male and female joints). During casting, each joint is adapted for incorporation into a respective wall panel after considering the following conditions: one side of the steel channel opens into the thickness face of the panel; a U-shaped rubber is implemented between the two channels to dissipate the vibration effect; and bolts and nuts are used to create an extension between the two U-shaped male and female steel channels. The developed finite element model of the precast wall is subjected to cyclic loads to evaluate the performance of the proposed connection during an imposed dynamic load. Connection performance is then compared with conventional connections based on the energy dissipation, stress, deformation, and concrete damage in the plastic range. The proposed precast connection is capable of exceeding the energy absorption of precast walls subjected to dynamic load, thereby improving its resistance behavior in all principal directions.

  8. Fatigue strength of bilayered ceramics under cyclic loading as a function of core veneer thickness ratios.

    PubMed

    Dibner, Aurora Clark; Kelly, J Robert

    2016-03-01

    Minimal evidence is available concerning the appropriate thickness of each layer in bilayered ceramic systems. The purpose of this in vitro study was to examine the effect of core-veneer thickness ratios on the fatigue strength of a bonded bilayered ceramic system. Specimens of Ivoclar Porcelain System (IPS) e.max lithium disilicate were fabricated with core/veneer thicknesses of 0.5/1.0 mm, 0.75/0.75 mm, 1.0/0.5 mm, and 1.5/0.0 mm. All specimens were cemented to bases of a dentin-like material. Each specimen was cyclically loaded by a 2-mm-diameter G10 piston in water. Loads ranging from 10 N to the target load were applied at a frequency of 20 Hertz for 500,000 cycles. If cracked, the next specimen was cycled at a lower load; if not cracked, at a higher load (step size of 25 N). Mean and standard deviations of fatigue loads for the different core thicknesses were 0.5-mm core 610.94 N ±130.11; 0.75-mm core 600.0 N ±132.80; 1.0-mm core 537.50 N ±41.67; a Nd 1.5-mm core 501.14 N ±70.12. All veneered groups were significantly stronger than the full thickness group (ANOVA, P<.001; 95% post hoc). Cone cracking was observed only in the 2 thinner core groups (χ(2) test, P<.05), possibly indicating residual stresses. Results indicate that the addition of veneering porcelain to lithium disilicate cores increases the fatigue strength of the biceramic system. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  9. Buckling Behavior of Compression-Loaded Quasi-Isotropic Curved Panels with a Circular Cutout

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Britt, Vicki O.; Nemeth, Michael P.

    1999-01-01

    Results from a numerical and experimental study of the response of compression-loaded quasi-isotropic curved panels with a centrally located circular cutout are presented. The numerical results were obtained by using a geometrically nonlinear finite element analysis code. The effects of cutout size, panel curvature and initial geo- metric imperfections on the overall response of compression-loaded panels are described. In addition, results are presented from a numerical parametric study that indicate the effects of elastic circumferential edge restraints on the prebuckling and buckling response of a selected panel and these numerical results are compared to experimentally measured results. These restraints are used to identify the effects of circumferential edge restraints that are introduced by the test fixture that was used in the present study. It is shown that circumferential edge restraints can introduce substantial nonlinear prebuckling deformations into shallow compression-loaded curved panels that can results in a significant increase in buckling load.

  10. Buckling and Failure of Compression-loaded Composite Cylindrical Shells with Reinforced Cutouts

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Nemeth, Michael P.

    2005-01-01

    Results from a numerical and experimental study that illustrate the effects of selected cutout reinforcement configurations on the buckling and failure response of compression-loaded composite cylindrical shells with a cutout are presented. The effects of reinforcement size, thickness, and orthotropy on the overall response of compression-loaded shells are described. In general, reinforcement around a cutout in a compression-loaded shell can retard or eliminate the local buckling response and material failure near the cutout and increase the buckling load of the shell. However, some results show that certain reinforcement configurations can cause a significant increase in the local interlaminar failures that can accumulate near the free edges of a cutout during a local buckling event.

  11. Unfolding of membrane ruffles of in situ chondrocytes under compressive loads.

    PubMed

    Moo, Eng Kuan; Herzog, Walter

    2017-02-01

    Impact loading results in chondrocyte death. Previous studies implicated high tensile strain rates in chondrocyte membranes as the cause of impact-induced cell deaths. However, this hypothesis relies on the untested assumption that chondrocyte membranes unfold in vivo during physiological tissue compression, but do not unfold during impact loading. Although membrane unfolding has been observed in isolated chondrocytes during osmotically induced swelling and mechanical compression, it is not known if membrane unfolding also occurs in chondrocytes embedded in their natural extracellular matrix. This study was aimed at quantifying changes in membrane morphology of in situ superficial zone chondrocytes during slow physiological cartilage compression. Bovine cartilage-bone explants were loaded at 5 μm/s to nominal compressive strains ranging from 0% to 50%. After holding the final strains for 45 min, the loaded cartilage was chemically pre-fixed for 12 h. The cartilage layer was post-processed for visualization of cell ultrastructure using electron microscopy. The changes in membrane morphology in superficial zone cells were quantified from planar electron micrographs by measuring the roughness and the complexity of the cell surfaces. Qualitatively, the cell surface ruffles that existed before loading disappeared when cartilage was loaded. Quantitatively, the roughness and complexity of cell surfaces decreased with increasing load magnitudes, suggesting a load-dependent use of membrane reservoirs. Chondrocyte membranes unfold in a load-dependent manner when cartilage is compressed. Under physiologically meaningful loading conditions, the cells likely expand their surface through unfolding of the membrane ruffles, and therefore avoid direct stretch of the cell membrane. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:304-310, 2017. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

  12. Validation of Lower-Bound Estimates for Compression-Loaded Cylindrical Shells

    NASA Technical Reports Server (NTRS)

    Haynie, Waddy T.; Hilburger, Mark W.; Bogge, Massimiliano; Kriegesmann, Benedikt

    2012-01-01

    The traditional approach used in the design of stability critical thin-walled circular cylin- ders, is to reduce unconservative buckling load predictions with an empirical knockdown factor. An alternative analysis-based approach to determine a lower bound buckling load for cylinders under axial compression is to use a lateral perturbation load to create an initial imperfection and determine the buckling load while that load is applied. This paper describes a preliminary e ort to develop a test capability to verify this approach. Results from tests of three aluminum alloy cylinders are described and compared to nite element predictions.

  13. Ultrasound-assisted preparation of novel ibuprofen-loaded excipient with improved compression and dissolution properties.

    PubMed

    Gandhi, Paras; Patil, Sharvil; Aher, Suyog; Paradkar, Anant

    2016-10-01

    Most of the active pharmaceutical ingredients (APIs) suffer from a drawback of poor aqueous solubility. In addition to the same, some APIs show poor tabletting behavior creating problems in formulation development. Crystal engineering can be an efficient tool in rectification of such problems associated with the APIs. Thus present work deals with crystallization of ibuprofen (a model drug) onto the surface of dicalcium phosphate (DCP) particles using different techniques. The objective of the present work was to prepare ibuprofen-loaded DCP particles and further to analyze them for compressibility and dissolution behavior. Various crystallization techniques such as solvent evaporation (SE), melt crystallization (MC), melt sonocrystallization (MSC), antisolvent crystallization (AC), and antisolvent sonocrystallization (ASC) were screened for the preparation of ibuprofen-loaded DCP. Products obtained from different techniques were analyzed for physicochemical, micromeritic and compression properties. ASC technique was found to be suitable for preparing directly compressible ibuprofen-loaded DCP particles. The change in the crystal habit (needle to plate shape) of ibuprofen and its crystallization in miniscular form onto the surface of DCP particles showed significant improvement in the dissolution rate and compression properties of ibuprofen due to an increase in specific surface area when compared with ibuprofen crystallized by other techniques. Additionally, the tablets prepared from ASC powder did not require binder since ibuprofen acted as melt binder during compression. Directly compressible ibuprofen-loaded DCP particles can serve as an alternative for conventional ibuprofen tablets prepared by wet granulation technique.

  14. The influence of cyclic concentric and eccentric submaximal muscle loading on cell viability in the rabbit knee joint.

    PubMed

    Horisberger, Monika; Fortuna, Rafael; Leonard, Timothy R; Valderrabano, Victor; Herzog, Walter

    2012-03-01

    Cartilage loading is associated with the onset and progression of osteoarthritis and cell death may play an important role in these processes. Although much is known about cell death in joint impact loading, there is no information on joints loaded by muscular contractions. The aim of this study was to evaluate the influence of muscle generated eccentric and concentric submaximal joint loading on chondrocyte viability. We hypothesised that eccentric muscle activation leads to increased cell death rates compared to concentric loading and to controls. 16 rabbits received either 50 min of uni-lateral, cyclic eccentric (n=8) or concentric (n=8) knee loading. Muscle activation for these dynamic conditions was equivalent to an activation level that produced 20% of maximum isometric force. Contralateral joints served as unloaded controls. Cell viability was assessed using confocal microscopy. Eccentric contractions produced greater knee loading than concentric contractions. Sub-maximal contractions caused a significant increase in cell death in the loaded knees compared to the unloaded controls, and eccentric loading caused significantly more cell death than concentric loading. Cyclic sub-maximal muscle loading of the knee caused increased chondrocyte death in rabbits. These findings suggest that low levels of joint loading for prolonged periods, as occurs in endurance exercise or physical labour, may cause chondrocyte death, thereby predisposing joints to degeneration. Copyright © 2011 Elsevier Ltd. All rights reserved.

  15. Spinal muscles can create compressive follower loads in the lumbar spine in a neutral standing posture.

    PubMed

    Han, Kap-Soo; Rohlmann, Antonius; Yang, Seok-Jo; Kim, Byeong Sam; Lim, Tae-Hong

    2011-05-01

    The ligamentous spinal column buckles under compressive loads of even less than 100N. Experimental results showed that under the follower load constraint, the ligamentous lumbar spine can sustain large compressive loads without buckling, while at the same time maintaining its flexibility reasonably well. The purpose of this study was to investigate the feasibility of follower loads produced by spinal muscles in the lumbar spine in a quiet standing posture. A three-dimensional static model of the lumbar spine incorporating 232 back muscles was developed and utilized to perform the optimization analysis in order to find the muscle forces, and compressive follower loads (CFLs) along optimum follower load paths (FLPs). The effect of increasing external loads on CFLs was also investigated. An optimum solution was found which is feasible for muscle forces producing minimum CFLs along the FLP located 11 mm posterior to the curve connecting the geometrical centers of the vertebral bodies. Activation of 30 muscles was found to create CFLs with zero joint moments in all intervertebral joints. CFLs increased with increasing external loads including FLP deviations from the optimum location. Our results demonstrate that spinal muscles can create CFLs in the lumbar spine in a neutral standing posture in vivo to sustain stability. Therefore, its application in experimental and numerical studies concerning loading conditions seems to be suitable for the attainment of realistic results. Published by Elsevier Ltd.

  16. Mechanical durability of polymeric coatings studied by positron annihilation spectroscopy: correlation between cyclic loading and free volumes

    NASA Astrophysics Data System (ADS)

    Chen, H.; Peng, Q.; Huang, Y. Y.; Zhang, R.; Mallon, P. E.; Zhang, J.; Li, Y.; Wu, Y.; Richardson, J. R.; Sandreczki, T. C.; Jean, Y. C.; Suzuki, R.; Ohdaira, T.

    2002-06-01

    The mechanical durability of seven commercially polymeric coatings is investigated using slow positron beam techniques to monitor changes in sub-nanometer defects during the process of cyclic loading. Doppler broadened energy spectra and positron annihilation lifetime (PAL) measurements were performed as a function of the slow positron energy at different periods of cycling loading. The positron annihilation dada show that both S-defect parameter and o-positronium (Ps) lifetime decrease as the loading cycle increases. The results indicate a loss of free volumes due to the loss of mechanical durability by cyclic loading. A direct correlation between the loss of S-defect parameter and the period of loading cycle is observed. This is interpreted as that durability of polymeric coatings is controlled by the atomic level free volumes. It is shown that the slow positron beam is a very successful probe in detecting the very early stages of coating degradation due to mechanical processes.

  17. Cortical and trabecular bone adaptation to incremental load magnitudes using the mouse tibial axial compression loading model.

    PubMed

    Weatherholt, Alyssa M; Fuchs, Robyn K; Warden, Stuart J

    2013-01-01

    The mouse tibial axial compression loading model has recently been described to allow simultaneous exploration of cortical and trabecular bone adaptation within the same loaded element. However, the model frequently induces cortical woven bone formation and has produced inconsistent results with regards to trabecular bone adaptation. The aim of this study was to investigate bone adaptation to incremental load magnitudes using the mouse tibial axial compression loading model, with the ultimate goal of revealing a load that simultaneously induced lamellar cortical and trabecular bone adaptation. Adult (16 weeks old) female C57BL/6 mice were randomly divided into three load magnitude groups (5, 7 and 9N), and had their right tibia axially loaded using a continuous 2-Hz haversine waveform for 360 cycles/day, 3 days/week for 4 consecutive weeks. In vivo peripheral quantitative computed tomography was used to longitudinally assess midshaft tibia cortical bone adaptation, while ex vivo micro-computed tomography and histomorphometry were used to assess both midshaft tibia cortical and proximal tibia trabecular bone adaptation. A dose response to loading magnitude was observed within cortical bone, with increasing load magnitude inducing increasing levels of lamellar cortical bone adaptation within the upper two thirds of the tibial diaphysis. Greatest cortical bone adaptation was observed at the midshaft where there was a 42% increase in estimated mechanical properties (polar moment of inertia) in the highest (9N) load group. A dose response to load magnitude was not clearly evident within trabecular bone, with only the highest load (9N) being able to induce measureable adaptation (31% increase in trabecular bone volume fraction at the proximal tibia). The ultimate finding was that a load of 9N (engendering a tensile strain of 1833 με on medial surface of the midshaft tibia) was able to simultaneously induce measurable lamellar cortical and trabecular bone adaptation

  18. Effect of Cyclic Loading on Bond Strength of Fiber Posts to Root Canal Dentin

    PubMed Central

    Khamverdi, Zahra; Damavandi, Leila Yazdani; Kasraei, Shahin

    2014-01-01

    Objective: The aim of this study was to evaluate the effect of cyclic loading on the bond strength of quartz fiber posts to root canal dentin after different surface treatments of different regions of root canal dentin. Materials and Methods: Forty-eight single-rooted human teeth were selected. Post spaces were prepared and then the teeth were divided into four groups: G1: no treatment (control); G2: irrigation with a chemical solvent; G3: etching with 37% phosphoric acid; G4: treatment with ultrasonic file. The fiber posts were cemented using dual-cured resin cement. Half of the specimens were load-cycled (10000 cycles, 3 cycles/s) and the others did not undergo any load cycling. From each root, two slides measuring 1 mm in thickness were obtained from the apical and cervical regions. The push-out bond strength test was performed for each slice. Data were analyzed by using 3-way ANOVA and Tukey HSD tests. The fracture modes were evaluated under a stereomicroscope at ×20. Results: The effect of load cycling and surface treatment as the main factors and the interaction of main factors were not significant (P=0.734, P=0.180, and P=0.539, respectively). The most frequent failure mode under the stereomicroscope was adhesive. Conclusion: It appears that load cycling and surface treatment methods had no effect on the bond strength of fiber posts to root canal dentin, but it depended on the region of the root canal dentin. PMID:24910680

  19. Damage mechanisms in PBT-GF30 under thermo-mechanical cyclic loading

    SciTech Connect

    Schaaf, A. De Monte, M. Hoffmann, C.; Vormwald, M.; Quaresimin, M.

    2014-05-15

    The scope of this paper is the investigation of damage mechanisms at microscopic scale on a short glass fiber reinforced polybutylene terephthalate (PBT-GF30) under thermo-mechanical cyclic loading. In addition the principal mechanisms are verified through micro mechanical FE models. In order to investigate the fatigue behavior of the material both isothermal strain controlled fatigue (ISCF) tests at three different temperatures and thermo-mechanical fatigue (TMF) tests were conducted on plain and notched specimens, manufactured by injection molding. The goal of the work is to determine the damage mechanisms occurring under TMF conditions and to compare them with the mechanisms occurring under ISCF. For this reason fracture surfaces of TMF and ISCF samples loaded at different temperature levels were analyzed using scanning electron microscopy. Furthermore, specimens that failed under TMF were examined on microsections revealing insight into both crack initiation and crack propagation. The findings of this investigation give valuable information about the main damage mechanisms of PBT-GF30 under TMF loading and serve as basis for the development of a TMF life estimation methodology.

  20. Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction

    NASA Technical Reports Server (NTRS)

    Jones, David J.; Kurath, Peter

    1988-01-01

    Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions.

  1. A new method for assessing relative dynamic motion of vertebral bodies during cyclic loading in vitro.

    PubMed

    Dean, J C; Wilcox, C H; Daniels, A U; Goodwin, R R; Van Wagoner, E; Dunn, H K

    1991-01-01

    A new experimental technique for measuring generalized three-dimensional motion of vertebral bodies during cyclic loading in vitro is presented. The system consists of an orthogonal array of three lasers mounted rigidly to one vertebra, and a set of three mutually orthogonal charge-coupled devices mounted rigidly to an adjacent vertebra. Each laser strikes a corresponding charge-coupled device screen. The mathematical model of the system is reduced to a linear set of equations with consequent matrix algebra allowing fast real-time data reduction during cyclic movements of the spine. The range and accuracy of the system is well suited for studying thoracolumbar motion segments. Distinct advantages of the system include miniaturization of the components, the elimination of the need for mechanical linkages between the bodies, and a high degree of accuracy which is not dependent on viewing volume as found in photogrammetric systems. More generally, the spectrum of potential applications of systems of this type to the real-time measurement of the relative motion of two bodies is extremely broad.

  2. Numerical Modeling of Multimaterial Thermoelectric Devices Under Static and Cyclic Thermal Loading

    NASA Astrophysics Data System (ADS)

    Fergus, Jeffrey W.; Yerkes, Kirk; Yost, Kevin

    2014-02-01

    Selection of materials for thermoelectric devices is generally based on a figure of merit that is a function of the Seebeck coefficient, electrical conductivity, and thermal conductivity. While this figure of merit is a useful metric for comparing materials, the relative importance of the constituent properties depends on the particular application and conditions. In addition, multiple materials can be used together to improve the performance or extend the operating range, and determining the performance of such multimaterial combinations requires analysis beyond simply averaging the properties of the constituent materials. In this paper, finite-element numerical simulations under static and cyclic thermal loadings are used to investigate how device performance can be improved by judicious location of the different materials within the device. The results show that the performance of a device with two different materials can be better than that of either of the individual materials. The greatest improvement in performance occurs with cyclic heating, where the overall performance is strongly influenced by the behavior under transient conditions during heating and cooling.

  3. Numerical simulation of the low-cyclic loading of new-type assembled integral beam-column joints

    NASA Astrophysics Data System (ADS)

    Wu, Jiangchuan; Zhang, Jiwen; Yin, Wanyun; Jin, Rencai

    2017-04-01

    In this paper, the low-cycle cyclic loading test and the elasto-plastic numerical simulation by OpenSEES of assembled integral beam-column joints of the three new prefabricated prestressed concrete beams are carried out. The key technologies such as unit selection, material model selection and prestressing in the numerical simulation of the new assembly-type beam-column joint is studied deeply. The results show that the relative model and parameters of the OpenSEES software can be used to simulate the hysteresis performance of the low-cycle cyclic loading of the new-type assembled integral beam-column joints.

  4. Results of a Cyclic Load Test of an RB-47E Airplane

    NASA Technical Reports Server (NTRS)

    Huston, Wilber B.

    1959-01-01

    Results of a cyclic load test made by NASA on an EB-47E airplane are given. The test reported on is for one of three B-47 airplanes in a test program set up by the U. S. Air Force to evaluate the effect of wing structural reinforcements on fatigue life. As a result of crack development in the upper fuselage longerons of the other two airplanes in the program, a longeron and fuselage skin modification was incorporated early in the test. Fuselage strain-gage measurements made before and after the longeron modification and wing strain-gage measurements made only after wing reinforcement are summarized. The history of crack development and repair is given in detail. Testing was terminated one sequence short of the planned end of the program with the occurrence of a major crack in the lower right wing skin.

  5. Electrochemical Behavior of Novel Superelastic Biomedical Alloys in Simulated Physiological Media Under Cyclic Load

    NASA Astrophysics Data System (ADS)

    Zhukova, Yu. S.; Pustov, Yu. A.; Konopatsky, A. S.; Filonov, M. R.; Prokoshkin, S. D.

    2014-07-01

    The aim of the present work was to study corrosion and electrochemical behavior of Ti-22Nb-6Ta and Ti-22Nb-6Zr (at.%) superelastic alloys under conditions which imitate the performance mode of target devices (bone implants), i.e., under cyclic load in simulated physiological solutions. Open circuit potential (OCP) measurements were carried out on wire specimens in Hank's solution and artificial saliva at 37 °C with various strain values up to 1.5%. It is shown that at clinically relevant strain values (about 0.2%) the alloys exhibit OCP growth indicating their high stability and resistance to corrosion fatigue under these cycling conditions. At much higher strains (about 1%), fatigue crack initiation and propagation take place, however, the corresponding OCP variation indicates that the fracture process is significantly restrained by reversible martensitic transformation during cycling.

  6. Models for predicting damage evolution in metal matrix composites subjected to cyclic loading

    SciTech Connect

    Allen, D.H.; Hurtado, L.D.; Helms, K.L.E.

    1995-03-01

    A thermomechanical analysis of a continuous fiber metal matrix composite (MMC) subjected to cyclic loading is performed herein. The analysis includes the effects of processing induced residual thermal stresses, matrix inelasticity, and interface cracking. Due to these complexities, the analysis is performed computationally using the finite element method. Matrix inelasticity is modelled with a rate dependent viscoplasticity model. Interface fracture is modelled by the use of a nonlinear interface constitutive model. The problem formulation is summarized, and results are given for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue. Results indicate rate dependent viscoplasticity can be a significant mechanism for dissipating the energy available for damage propagation, thus contributing to improved ductility of the composite. Results also indicate that the model may be useful for inclusion in life prediction methodologies for MMC`s.

  7. Self-sensing of carbon nanofiber concrete columns subjected to reversed cyclic loading

    NASA Astrophysics Data System (ADS)

    Howser, R. N.; Dhonde, H. B.; Mo, Y. L.

    2011-08-01

    Civil infrastructures are generally a country's most expensive investment, and concrete is the most widely used material in the construction of civil infrastructures. During a structure's service life, concrete ages and deteriorates, leading to substantial loss of structural integrity and potentially resulting in catastrophic disasters such as highway bridge collapses. A solution for preventing such occurrences is the use of structural health monitoring (SHM) technology for concrete structures containing carbon nanofibers (CNF). CNF concrete has many structural benefits. CNF restricts the growth of nanocracks in addition to yielding higher strength and ductility. Additionally, test results indicate a relationship between electrical resistance and concrete strain, which can be well utilized for SHM. A series of reinforced concrete (RC) columns were built and tested under a reversed cyclic loading using CNF as a SHM device. The SHM device detected and assessed the level of damage in the RC columns, providing a real-time health monitoring system for the structure's overall integrity.

  8. Mechanical behaviors of multi-filament twist superconducting strand under tensile and cyclic loading

    NASA Astrophysics Data System (ADS)

    Wang, Xu; Li, Yingxu; Gao, Yuanwen

    2016-01-01

    The superconducting strand, serving as the basic unit cell of the cable-in-conduit-conductors (CICCs), is a typical multi-filament twist composite which is always subjected to a cyclic loading under the operating condition. Meanwhile, the superconducting material Nb3Sn in the strand is sensitive to strain frequently relating to the performance degradation of the superconductivity. Therefore, a comprehensive study on the mechanical behavior of the strand helps understanding the superconducting performance of the strained Nb3Sn strands. To address this issue, taking the LMI (internal tin) strand as an example, a three-dimensional structural finite element model, named as the Multi-filament twist model, of the strand with the real configuration of the LMI strand is built to study the influences of the plasticity of the component materials, the twist of the filament bundle, the initial thermal residual stress and the breakage and its evolution of the filaments on the mechanical behaviors of the strand. The effective properties of superconducting filament bundle with random filament breakage and its evolution versus strain are obtained based on the damage theory of fiber-reinforced composite materials proposed by Curtin and Zhou. From the calculation results of this model, we find that the occurrence of the hysteresis loop in the cyclic loading curve is determined by the reverse yielding of the elastic-plastic materials in the strand. Both the initial thermal residual stress in the strand and the pitch length of the filaments have significant impacts on the axial and hysteretic behaviors of the strand. The damage of the filaments also affects the axial mechanical behavior of the strand remarkably at large axial strain. The critical current of the strand is calculated by the scaling law with the results of the Multi-filament twist model. The predicted results of the Multi-filament twist model show an acceptable agreement with the experiment.

  9. Buckling behavior of composite cylinders subjected to compressive loading

    NASA Technical Reports Server (NTRS)

    Carri, R. L.

    1973-01-01

    Room temperature compressive buckling strengths of eight cylinders, four boron-epoxy and four boron-epoxy reinforced-titanium, with diameter to thickness ratios ranging between 40 and 67 are determined experimentally and compared with analytical predictions. Numerical buckling strengths are presented for Donnell's, Flugge's and Sanders' shell theories for anisotropic and orthotropic material cases. Comparison of analytical predictions with experimental results indicates good agreement and the recommended correlation factor suggested in the literature is applicable for design. For the cylinders tested, the correlation between experiment and theory ranged from 0.73 to 0.97.

  10. Influence of compressive load on microstructure of micro-scaled DLC structures produced by FIB-CVD

    NASA Astrophysics Data System (ADS)

    Sakamoto, N.; Kogo, Y.; Yasuno, T.

    2008-03-01

    Influence of compressive load on microstructure of micro-scaled diamond-like carbon (DLC) structures was investigated by high-resolution electron transmission microscopy (HRTEM) analyses. The micro-scaled structures were produced by the focused ion-beam chemical vapor deposition method. The compressive loads were applied by a dynamic ultra micro hardness tester equipped with a flat-tip diamond indenter. Microgrid images in HRTEM observation and selected area diffraction patterns were varied by the compressive loads. The variations revealed that constituent atoms arranged disorderly in DLC were clustered by compressive loads. Electron energy loss spectroscopy measurements indicated that sp3 fraction in DLC was decreased by the compressive load. Consequently, it was suggested that graphitic clusters were formed in the microstructure of DLC by the compressive loads.

  11. Dynamic Crush Behaviors Of Aluminum Honeycomb Specimens Under Compression Dominant Inclined Loads

    SciTech Connect

    Hong, Sung-tae; Pan, Jwo; Tyan, Tau; Prasad, Priya

    2008-01-01

    The quasi-static and dynamic crush behaviors of aluminum 5052-H38 honeycomb specimens under out-of-plane inclined loads are investigated by experiments. Different types of honeycomb specimens were designed for crush tests under pure compressive and inclined loads with respect to the out-of-plane direction. A test fixture was designed for both quasi-static and dynamic crush tests under inclined loads. The results of the quasi-static crush tests indicate that the normal crush and shear strengths under inclined loads are consistent with the corresponding results under combined loads. The results of the dynamic crush tests indicate that as the impact velocity increases, the normal crush strength increases and the shear strength remains nearly the same. The trends of the normalized normal crush strengths under inclined loads for specimens with different in-plane orientation angles as functions of the impact velocity are very similar to each other. Based on the experimental results, a macroscopic yield criterion as a function of the impact velocity is proposed. The experimental results suggest that as the impact velocity increases, the shape of the macroscopic yield surface changes, or more specifically, the curvature of the yield surface increases near the pure compression state. The experimental results also show similar microscopic progressive folding mechanisms in honeycomb specimens under pure compressive and inclined loads. However, honeycomb specimens under inclined loads show inclined stacking patterns of folds due to the asymmetric location of horizontal plastic hinge lines.

  12. The dynamic conductance response and mechanics-modulated memristive behavior of the Azurin monolayer under cyclic loads.

    PubMed

    Zhang, Xiaoyue; Shao, Jian; Chen, Yun; Chen, Weijin; Yu, Jing; Wang, Biao; Zheng, Yue

    2017-03-01

    Azurin (Az) has been considered as the research hotspot in molecular electronics, as well as a promising material for building functional devices on the molecular scale because of its special electrical properties and force-dependent conductance effects. Here we carry out an in-depth investigation combined with molecular scale experiments, molecular dynamics simulations, first-principles calculations and theoretical models to reveal the dynamic conductance response of the Az monolayer under cyclic mechanical loading. Experimentally, the conductance of the Az monolayer under continuous cyclic loads was recorded using a conductive atomic force microscope. Our results demonstrate the strong nonlinear force-dependence and significant time-delayed characteristics, which distinctly differ from the results obtained under stepwise loading. It is also found that the period and amplitude of cyclic loads have a great impact on the magnitude, peak value and change rate of the current. The regular dynamic response of the Az conductance under mechanical force looks like a type of memristive behavior, which is defined as mechanics-modulated memristive behavior in this work. In order to verify these peculiar experimental results, we employed both molecular dynamics simulations and first-principles calculations to analyze the structural deformation and molecular orbitals of Az under cyclic loads. A phenomenological model is also established to explain experimental findings and further illustrate mechanics-modulated memristive behavior.

  13. Mechanical behaviour of selected bulk oilseeds under compression loading

    NASA Astrophysics Data System (ADS)

    Mizera, Č.; Herák, D.; Hrabě, P.; Aleš, Z.; Pavlů, J.

    2017-09-01

    Pressing of vegetable oils plays an important role in modern agriculture. This study was focused on the linear pressing of soybean seeds (Glycine max L.), Jatropha seeds (Jatropha curcas L.) and palm kernel (Elaeisguineensis). For pressing test the compressive device (ZDM, model 50, Germany) was used. The maximum pressing force of 100 kN with a compression speed of 1 mm s-1 was used to record the force-deformation characteristics. The pressing vessel with diameter 60 mm and initial height of seeds 80 mm were used. The specific energy per gram of oil of soybean, palm kernel and Jatropha was 158.92 ± 7.21, 128.78 ± 8.36 and 68.26 ± 5.94 J.goil-1, respectively. The oil content of soybean, palm kernel and Jatropha was 20.4 ± 1.23, 44.7 ± 2.27 and 34.2 ± 1.75 %, respectively. Water concentration, dynamic and kinematic viscosity of obtained oils was also determined.

  14. Effect of the loading rate on compressive properties of goose eggs.

    PubMed

    Nedomová, Š; Kumbár, V; Trnka, J; Buchar, J

    2016-03-01

    The resistance of goose (Anser anser f. domestica) eggs to damage was determined by measuring the average rupture force, specific deformation and rupture energy during their compression at different compression speeds (0.0167, 0.167, 0.334, 1.67, 6.68 and 13.36 mm/s). Eggs have been loaded between their poles (along X axis) and in the equator plane (Z axis). The greatest amount of force required to break the eggs was required when eggs were loaded along the X axis and the least compression force was required along the Z axis. This effect of the loading orientation can be described in terms of the eggshell contour curvature. The rate sensitivity of the eggshell rupture force is higher than that observed for the Japanese quail's eggs.

  15. A novel ex vivo model of compressive immature rib fractures at pathophysiological rates of loading.

    PubMed

    Beadle, Nicola; Burnett, Timothy L; Hoyland, Judith A; Sherratt, Michael J; Freemont, Anthony J

    2015-11-01

    Compressive rib fractures are considered to be indicative of non-accidental injury (NAI) in infants, which is a significant and growing issue worldwide. The diagnosis of NAI is often disputed in a legal setting, and as a consequence there is a need to model such injuries ex vivo in order to characterise the forces required to produce non-accidental rib fractures. However, current models are limited by type of sample, loading method and rate of loading. Here, we aimed to: i) develop a loading system for inducing compressive fractures in whole immature ribs that is more representative of the physiological conditions and mechanism of injury employed in NAI and ii) assess the influence of loading rate and rib geometry on the mechanical performance of the tissue. Porcine ribs (5-6 weeks of age) from 12 animals (n=8 ribs/animal) were subjected to axial compressive load directed through the anterior-posterior rib axis at loading rates of 1, 30, 60 or 90 mm/s. Key mechanical parameters (including peak load, load and percentage deformation to failure and effective stiffness) were quantified from the load-displacement curves. Measurements of the rib length, thickness at midpoint, distance between anterior and posterior extremities, rib curvature and fracture location were determined from radiographs. This loading method typically produced incomplete fractures around the midpoint of the ribs, with 87% failing in this manner; higher loads and less deformation were required for ribs to completely fracture through both cortices. Loading rate, within the range of 1-90 mm/s, did not significantly affect any key mechanical parameters of the ribs. Load-displacement curves displaying characteristic and quantifiable features were produced for 90% of the ribs tested, and multiple regression analyses indicate that, in addition to the geometrical variables, there are other factors such as the micro- and nano-structure that influence the measured mechanical data. A reproducible method of

  16. Laser driven quasi-isentropic compression experiments (ICE) for dynamically loading materials at high strain rates

    SciTech Connect

    Smith, R; Eggert, J; Celliers, P; Jankowski, A; Lorenz, T; Moon, S; Edwards, M J; Collins, G

    2006-03-30

    We demonstrate the recently developed technique of laser driven isentropic compression (ICE) for dynamically compressing Al samples at high loading rates close to the room temperature isentrope and up to peak stresses above 100GPa. Upon analysis of the unloading profiles from a multi-stepped Al/LiF target a continuous path through Stress-Density space may be calculated. For materials with phase transformations ramp compression techniques reveals the location of equilibrium phase boundaries and provide information on the kinetics of the lattice re-ordering.

  17. Calibration of hyperelastic material properties of the human lumbar intervertebral disc under fast dynamic compressive loads.

    PubMed

    Wagnac, Eric; Arnoux, Pierre-Jean; Garo, Anaïs; El-Rich, Marwan; Aubin, Carl-Eric

    2011-10-01

    Under fast dynamic loading conditions (e.g. high-energy impact), the load rate dependency of the intervertebral disc (IVD) material properties may play a crucial role in the biomechanics of spinal trauma. However, most finite element models (FEM) of dynamic spinal trauma uses material properties derived from quasi-static experiments, thus neglecting this load rate dependency. The aim of this study was to identify hyperelastic material properties that ensure a more biofidelic simulation of the IVD under a fast dynamic compressive load. A hyperelastic material law based on a first-order Mooney-Rivlin formulation was implemented in a detailed FEM of a L2-L3 functional spinal unit (FSU) to represent the mechanical behavior of the IVD. Bony structures were modeled using an elasto-plastic Johnson-Cook material law that simulates bone fracture while ligaments were governed by a viscoelastic material law. To mimic experimental studies performed in fast dynamic compression, a compressive loading velocity of 1 m/s was applied to the superior half of L2, while the inferior half of L3 was fixed. An exploratory technique was used to simulate dynamic compression of the FSU using 34 sets of hyperelastic material constants randomly selected using an optimal Latin hypercube algorithm and a set of material constants derived from quasi-static experiments. Selection or rejection of the sets of material constants was based on compressive stiffness and failure parameters criteria measured experimentally. The two simulations performed with calibrated hyperelastic constants resulted in nonlinear load-displacement curves with compressive stiffness (7335 and 7079 N/mm), load (12,488 and 12,473 N), displacement (1.95 and 2.09 mm) and energy at failure (13.5 and 14.7 J) in agreement with experimental results (6551 ± 2017 N/mm, 12,411 ± 829 N, 2.1 ± 0.2 mm and 13.0 ± 1.5 J respectively). The fracture pattern and location also agreed with experimental results. The simulation performed with

  18. Experimental investigation on yield behavior of PMMA under combined shear-compression loading

    NASA Astrophysics Data System (ADS)

    Zhang, Jianjun; Jin, Tao; Wang, Zhihua; Zhao, Longmao

    The work experimentally studies the yielding behavior of polymethyl methacrylate (PMMA) at three different loading rates through a developed combined shear-compression test technique which contains a universal materials testing machine, mental blocks with double beveled ends (combined shear-compression loading setup) and a column sleeve made of Teflon. The results show that the failure loci agree well with theoretical predictions involving the strain rate dependence, which indicates the validity of this test method. Additionally, the experimental data enrich the previous experimental work about polymer yielding surface in the principle stress space.

  19. Subcritical crack-growth behavior of borosilicate glass under cyclic loads: Evidence of a mechanical fatigue effect

    SciTech Connect

    Dill, S.J.; Dauskardt, R.H.; Bennison, S.J.

    1997-03-01

    Amorphous glasses are generally considered immune to mechanical fatigue effects associated with cyclic loading. In this study surprising new evidence is presented for a mechanical fatigue effect in borosilicate glass, in both moist air and dry nitrogen environments. The fatigue effect occurs at near threshold subcritical crack-growth rates (da/dt < 3 {times} 10{sup {minus}8} m/s) as the crack extension per cycle approaches the dimensions of the borosilicate glass network. While subcritical crack growth under cyclic loads at higher load levels is entirely consistent with environmentally assisted crack growth, lower growth rates actually exceed those measured under monotonic loads. This suggests a mechanical fatigue effect which accelerates subcritical crack-growth rates. Likely mechanisms for the mechanical fatigue effect are presented.

  20. Longitudinal Weld Land Buckling in Compression-Loaded Orthogrid Cylinders

    NASA Technical Reports Server (NTRS)

    Thornburgh, Robert P.; Hilburger, Mark W.

    2010-01-01

    Large stiffened cylinders used in launch vehicles (LV), such as the Space Shuttle External Tank, are manufactured by welding multiple curved panel sections into complete cylinders. The effects of the axial weld lands between the panel sections on the buckling load were studied, along with the interaction between the acreage stiffener arrangement and the weld land geometry. This document contains the results of the studies.

  1. [Biomechanical properties (compressive strength and compressive pressure at break) of hyaline cartilage under axial load].

    PubMed

    Spahn, G; Wittig, R

    2003-01-01

    Explanations concerning the physical properties of hyaline cartilage are different. It was the intention of this study to determine the material parameters of hyaline cartilage under axial load (elasticity, plasticity, elasticity and module pressure stress to break). Specimens from the medial femoral condyle (chondro-cortical ships) from adult female domestic pigs (n=28) were used for the experiments. The specimens were completely embedded in plaster to minimize shearing. Axial load was carried out by an universal mechanical testing machine (Zwick Z2.5/TS1S, Ulm, Germany) to determine elastic and plastic deformation and pressure stress to break. Axial load up to 5 MPa produces an almost elastic deformation, an increasing axial load results in a plastic deformation. In the range of 3 to 5 MPa the principle of Hooke is valid. The elasticity module amounted to 39.2 +/- 11.9 N/mm(2), determined under 3.8 MPa axial load. An axial load of 25.8 +/- 5.2 MPa (sigma max ) causes a break of cartilage. A strong correlation between break resistance and thickness of the chondral slice (r=0.71; p < 0.05) was observed. The low module of chondral elasticity characterizes this tissue as "soft". Moderate axial load causes an ideal elastic, higher axial load a plastic deformation. The medium pressure to break to amounted 25.8 MPa. The medium pressure to break of 25.8 MPa is comparable with the forces produced by an unrestrained limited downfall from a height of 4.3 m. It must be concluded that isolated chondral fractures are rare consequences of a trauma as long as accompanying ligamentous or osseous damages are not found.

  2. Buckling Behavior of Compression-Loaded Composite Cylindrical Shells with Reinforced Cutouts

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Starnes, James H., Jr.

    2002-01-01

    Results from a numerical study of the response of thin-wall compression-loaded quasi-isotropic laminated composite cylindrical shells with reinforced and unreinforced square cutouts are presented. The effects of cutout reinforcement orthotropy, size, and thickness on the nonlinear response of the shells are described. A high-fidelity nonlinear analysis procedure has been used to predict the nonlinear response of the shells. The analysis procedure includes a nonlinear static analysis that predicts stable response characteristics of the shells and a nonlinear transient analysis that predicts unstable dynamic buckling response characteristics. The results illustrate how a compression-loaded shell with an unreinforced cutout can exhibit a complex nonlinear response. In particular, a local buckling response occurs in the shell near the cutout and is caused by a complex nonlinear coupling between local shell-wall deformations and in-plane destabilizing compression stresses near the cutout. In general, the addition of reinforcement around a cutout in a compression-loaded shell can retard or eliminate the local buckling response near the cutout and increase the buckling load of the shell, as expected. However, results are presented that show how certain reinforcement configurations can actually cause an unexpected increase in the magnitude of local deformations and stresses in the shell and cause a reduction in the buckling load. Specific cases are presented that suggest that the orthotropy, thickness, and size of a cutout reinforcement in a shell can be tailored to achieve improved response characteristics.

  3. MEMS measurements of single cell stiffness decay due to cyclic mechanical loading.

    PubMed

    Barazani, Bruno; Warnat, Stephan; MacIntosh, Andrew J; Hubbard, Ted

    2017-08-25

    The goal of this study was to measure the mechanical stiffness of individual cells and to observe changes due to the application of repeated cell mechanical loads. 28 single baker's yeast cells (Saccharomyces cerevisiae) were fatigue tested and had their stiffness measured during repetitive loading cycles performed by a MEMS squeezer in aqueous media. Electrothermal micro-actuators compressed individual cells against a reference back spring; cell and spring motions were measured using a FFT image analysis technique with ~10 nm resolution. Cell stiffness was calculated based on measurements of cell elongation vs. applied force which resulted in stiffness values in the 2-10 N/m range. The effect of increased force was studied for cells mechanically cycled 37 times. Cell stiffness decreased as the force and the cycle number increased. After 37 loading cycles (~4 min), forces of 0.24, 0.29, 0.31, and 0.33 μN caused stiffness drops of 5%, 13%, 31% and 41% respectively. Cells force was then set to 0.29 μN and cells were tested over longer runs of 118 and 268 cycles. After 118 cycles (~12 min) cells experienced an average stiffness drop of 68%. After 268 cycles (~25 min) cells had a stiffness drop of 77%, and appeared to reach a stiffness plateau of 20-25% of the initial stiffness after approximately 200 cycles.

  4. Off-loading of cyclic hydrostatic pressure promotes production of extracellular matrix by chondrocytes.

    PubMed

    Tatsumura, Masaki; Sakane, Masataka; Ochiai, Naoyuki; Mizuno, Shuichi

    2013-01-01

    The addition of cyclic hydrostatic pressure (cHP) to cell culture medium has been used to promote extracellular matrix (ECM) production by articular chondrocytes. Though a combination of cHP followed by atmospheric pressure (AP) has been examined previously, the rationale of such a combination was unclear. We compared the effects of loading once versus twice (combinations of cHP followed by AP) regarding both gene expression and biochemical and histological phenotypes of chondrocytes. Isolated bovine articular chondrocytes were embedded in a collagen gel and incubated for 14 days under conditions combining cHP and AP. The gene expression of aggrecan core protein and collagen type II were upregulated in response to cHP, and those levels were maintained for at least 4 days after cHP treatment. Accumulation of cartilage-specific sulfated glycosaminoglycans following cHP for 7 days and subsequent AP for 7 days was significantly greater than that of the AP control (p < 0.05). Therefore, incubation at AP after loading with cHP was found to beneficially affect ECM accumulation. Manipulating algorithms of cHP combined with AP will be useful in producing autologous chondrocyte-based cell constructs for implantation. © 2014 S. Karger AG, Basel.

  5. Portevin-Le Chatelier effect under cyclic loading: experimental and numerical investigations

    NASA Astrophysics Data System (ADS)

    Mazière, M.; Pujol d'Andrebo, Q.

    2015-10-01

    The Portevin-Le Chatelier (PLC) effect is generally evidenced by the apparition of serrated yielding under monotonic tensile loading conditions. It appears at room temperature in some aluminium alloys, around ? in some steels and in many other metallic materials. This effect is associated with the propagation of bands of plastic deformation in tensile specimens and can in some cases lead to unexpected failures. The PLC effect has been widely simulated under monotonic conditions using finite elements and an appropriate mechanical model able to reproduce serrations and strain localization. The occurrence of serrations can be predicted using an analytical stability analysis. Recently, this serrated yielding has also been observed in specimens made of Cobalt-based superalloy under cyclic loading, after a large number of cycles. The mechanical model has been identified in this case to accurately reproduce this critical number of cycle where serrations appear. The associated apparition of localized bands of deformation in specimens and their influence on its failure has also been investigated using finite element simulations.

  6. Fascicles from energy-storing tendons show an age-specific response to cyclic fatigue loading

    PubMed Central

    Thorpe, Chavaunne T.; Riley, Graham P.; Birch, Helen L.; Clegg, Peter D.; Screen, Hazel R. C.

    2014-01-01

    Some tendons, such as the human Achilles and equine superficial digital flexor tendon (SDFT), act as energy stores, stretching and recoiling to increase efficiency during locomotion. Our previous observations of rotation in response to applied strain in SDFT fascicles suggest a helical structure, which may provide energy-storing tendons with a greater ability to extend and recoil efficiently. Despite this specialization, energy-storing tendons are prone to age-related tendinopathy. The aim of this study was to assess the effect of cyclic fatigue loading (FL) on the microstructural strain response of SDFT fascicles from young and old horses. The data demonstrate two independent age-related mechanisms of fatigue failure; in young horses, FL caused low levels of matrix damage and decreased rotation. This suggests that loading causes alterations to the helix substructure, which may reduce their ability to recoil and recover. By contrast, fascicles from old horses, in which the helix is already compromised, showed greater evidence of matrix damage and suffer increased fibre sliding after FL, which may partially explain the age-related increase in tendinopathy. Elucidation of helix structure and the precise alterations occurring owing to both ageing and FL will help to develop appropriate preventative and repair strategies for tendinopathy. PMID:24402919

  7. A coupled damage-plasticity model for the cyclic behavior of shear-loaded interfaces

    NASA Astrophysics Data System (ADS)

    Carrara, P.; De Lorenzis, L.

    2015-12-01

    The present work proposes a novel thermodynamically consistent model for the behavior of interfaces under shear (i.e. mode-II) cyclic loading conditions. The interface behavior is defined coupling damage and plasticity. The admissible states' domain is formulated restricting the tangential interface stress to non-negative values, which makes the model suitable e.g. for interfaces with thin adherends. Linear softening is assumed so as to reproduce, under monotonic conditions, a bilinear mode-II interface law. Two damage variables govern respectively the loss of strength and of stiffness of the interface. The proposed model needs the evaluation of only four independent parameters, i.e. three defining the monotonic mode-II interface law, and one ruling the fatigue behavior. This limited number of parameters and their clear physical meaning facilitate experimental calibration. Model predictions are compared with experimental results on fiber reinforced polymer sheets externally bonded to concrete involving different load histories, and an excellent agreement is obtained.

  8. Inelastic behavior of cold-formed braced walls under monotonic and cyclic loading

    NASA Astrophysics Data System (ADS)

    Gerami, Mohsen; Lotfi, Mohsen; Nejat, Roya

    2015-06-01

    The ever-increasing need for housing generated the search for new and innovative building methods to increase speed and efficiency and enhance quality. One method is the use of light thin steel profiles as load-bearing elements having different solutions for interior and exterior cladding. Due to the increase in CFS construction in low-rise residential structures in the modern construction industry, there is an increased demand for performance inelastic analysis of CFS walls. In this study, the nonlinear behavior of cold-formed steel frames with various bracing arrangements including cross, chevron and k-shape straps was evaluated under cyclic and monotonic loading and using nonlinear finite element analysis methods. In total, 68 frames with different bracing arrangements and different ratios of dimensions were studied. Also, seismic parameters including resistance reduction factor, ductility and force reduction factor due to ductility were evaluated for all samples. On the other hand, the seismic response modification factor was calculated for these systems. It was concluded that the highest response modification factor would be obtained for walls with bilateral cross bracing systems with a value of 3.14. In all samples, on increasing the distance of straps from each other, shear strength increased and shear strength of the wall with bilateral bracing system was 60 % greater than that with lateral bracing system.

  9. Residual interface tensile strength of ceramic bonded to dentin after cyclic loading and aging.

    PubMed

    Hernandez, Alfredo I; Roongruangphol, Thasanai; Katsube, Noriko; Seghi, Robert R

    2008-03-01

    To guard against the potential risk of cusp fracture, esthetic onlay restorations have been advocated for teeth with large restorations. The influence of the adhesive resin cement is believed to play a role in strengthening these restorations. The durability of this tooth/adhesive/ceramic interface is critical to ensure clinical longevity. The purpose of this study was to assess the effects of cyclic loading and environmental aging on the residual interface strength of a ceramic bonded to dentin structure. Eighteen simple trilayer specimens were fabricated, consisting of a 1.5-mm-thick ceramic plate (ProCAD) bonded to a flattened human molar tooth with exposed coronal dentin. The ceramic plates were bonded using resin cement (Nexus 2) and manufacturer-recommended bonding techniques. The specimens were divided into 3 equal groups and were stored in water at 37 degrees C for 10 weeks as a control group (CT), 9 months as an aging group (AG), or placed in water at 37 degrees C while being subjected to 10 million vertical loading cycles between 20 N to 200 N, as a fatigue group (FG). After the specimens were subjected to the experimental conditions, they were sectioned perpendicular to the flat ceramic surface into 1 x 1-mm sticks. The mean residual interface microtensile bond (MTB) strength was determined for each specimen using only those sticks which contained ceramic bonded to dentin. The MTB strength data were analyzed using Weibull analysis methods to determine differences between groups. All subsequent failed specimen surfaces were evaluated under a stereomicroscope at x10 magnification to determine the apparent failure modes. Some specimens were selected from each failure mode category for surface evaluation under a scanning electron microscope (SEM). The characteristic Weibull means for the 3 groups were CT, 19.2, FG, 14.7, and AG, 11.7. The bond strength of group CT was significantly greater than both AG (P=.007) and FG (P=.014). Light microscopic

  10. Modeling the response of exogenously crosslinked tissue to cyclic loading: The effects of permanent set.

    PubMed

    Zhang, Will; Sacks, Michael S

    2017-07-11

    Bioprosthetic heart valves (BHVs), fabricated from exogenously crosslinked collagenous tissues, remain the most popular heart valve replacement design. However, the life span of BHVs remains limited to 10-15 years, in part because the mechanisms that underlie BHV failure remain poorly understood. Experimental evidence indicates that BHVs undergo significant changes in geometry with in vivo operation, which lead to stress concentrations that can have significant impact on structural damage. These changes do not appear to be due to plastic deformation, as the leaflets only deform in the elastic regime. Moreover, structural damage was not detected by the 65 million cycle time point. Instead, we found that this nonrecoverable deformation is similar to the permanent set effect observed in elastomers, which allows the reference configuration of the material to evolve over time. We hypothesize that the scission-healing reaction of glutaraldehyde is the underlying mechanism responsible for permanent set in exogenously crosslinked soft tissues. The continuous scission-healing process of glutaraldehyde allows a portion of the exogenously crosslinked matrix, which is considered to be the non-fibrous part of the extra-cellular matrix, to be re-crosslinked in the loaded state. Thus, this mechanism for permanent set can be used to explain the time evolving mechanical response and geometry of BHVs in the early stage. To model the permanent set effect, we assume that the exogenously crosslinked matrix undergoes changes in reference configurations over time. The changes in the collagen fiber architecture due to dimensional changes allow us to predict subsequent changes in mechanical response. Results show that permanent set alone can explain and, more importantly, predict how the mechanical response of the biomaterial change with time. Furthermore, we found is no difference in permanent set rate constants between the strain controlled and the stress controlled cyclic loading

  11. The resistance of cortical bone tissue to failure under cyclic loading is reduced with alendronate.

    PubMed

    Bajaj, Devendra; Geissler, Joseph R; Allen, Matthew R; Burr, David B; Fritton, J C

    2014-07-01

    Bisphosphonates are the most prescribed preventative treatment for osteoporosis. However, their long-term use has recently been associated with atypical fractures of cortical bone in patients who present with low-energy induced breaks of unclear pathophysiology. The effects of bisphosphonates on the mechanical properties of cortical bone have been exclusively studied under simple, monotonic, quasi-static loading. This study examined the cyclic fatigue properties of bisphosphonate-treated cortical bone at a level in which tissue damage initiates and is accumulated prior to frank fracture in low-energy situations. Physiologically relevant, dynamic, 4-point bending applied to beams (1.5 mm × 0.5 mm × 10 mm) machined from dog rib (n=12/group) demonstrated mechanical failure and micro-architectural features that were dependent on drug dose (3 groups: 0, 0.2, 1.0mg/kg/day; alendronate [ALN] for 3 years) with cortical bone tissue elastic modulus (initial cycles of loading) reduced by 21% (p<0.001) and fatigue life (number of cycles to failure) reduced in a stress-life approach by greater than 3-fold with ALN1.0 (p<0.05). While not affecting the number of osteons, ALN treatment reduced other features associated with bone remodeling, such as the size of osteons (-14%; ALN1.0: 10.5±1.8, VEH: 12.2±1.6, ×10(3) μm2; p<0.01) and the density of osteocyte lacunae (-20%; ALN1.0: 11.4±3.3, VEH: 14.3±3.6, ×10(2) #/mm2; p<0.05). Furthermore, the osteocyte lacunar density was directly proportional to initial elastic modulus when the groups were pooled (R=0.54, p<0.01). These findings suggest that the structural components normally contributing to healthy cortical bone tissue are altered by high-dose ALN treatment and contribute to reduced mechanical properties under cyclic loading conditions. Copyright © 2014 Elsevier Inc. All rights reserved.

  12. Reversible-strain criteria of ferromagnetic shape memory alloys under cyclic 3D magneto-mechanical loadings

    NASA Astrophysics Data System (ADS)

    He, Y. J.; Chen, X.; Moumni, Z.

    2012-08-01

    Recent researches revealed that ferromagnetic shape memory alloys (FSMA) in 2D/3D configurations (with multi-axial stresses) had much more advantages (e.g., higher working stress and more application flexibility) than that in 1D configuration (with uniaxial stress). In literature, however, there is no simple criterion to judge whether a cyclic 3D magneto-mechanical loading can induce a large reversible strain (via martensite reorientation in FSMA). In this paper, a 3D magneto-mechanical energy analysis is proposed and incorporated into a phase diagram in terms of deviatoric stresses (including mechanical and magneto-stresses) to study the path-dependent (hysteretic) martensite reorientation in FSMA under 3D cyclic loadings. Based on the phase diagram (a plane graph), general criteria for obtaining reversible strain under cyclic magneto-mechanical loadings are derived, which provide basic guidelines for FSMA's applications under multi-axial loadings. Particularly for FSMA actuators driven by cyclic magnetic fields, the criteria of setting the 3D mechanical stresses to allow field-induced reversible strain are formulated. The 3D criteria can be reduced to 1D and 2D criteria which agree with the existing 1D/2D theoretical and experimental studies.

  13. Load-bearing capacity of screw-retained CAD/CAM-produced titanium implant frameworks (I-Bridge®2) before and after cyclic mechanical loading

    PubMed Central

    DITTMER, Marc Philipp; NENSA, Moritz; STIESCH, Meike; KOHORST, Philipp

    2013-01-01

    Implant-supported screw-retained fixed dental prostheses (FDPs) produced by CAD/ CAM have been introduced in recent years for the rehabilitation of partial or total endentulous jaws. However, there is a lack of data about the long-term mechanical characteristics. Objective The aim of this study was to investigate the failure mode and the influence of extended cyclic mechanical loading on the load-bearing capacity of these frameworks. Material and Methods Ten five-unit FDP frameworks simulating a free-end situation in the mandibular jaw were manufactured according to the I-Bridge®2-concept (I-Bridge®2, Biomain AB, Helsingborg, Sweden) and each was screw-retained on three differently angulated Astra Tech implants (30º buccal angulation/0º angulation/30º lingual angulation). One half of the specimens was tested for static load-bearing capacity without any further treatment (control), whereas the other half underwent five million cycles of mechanical loading with 100 N as the upper load limit (test). All specimens were loaded until failure in a universal testing machine with an occlusal force applied at the pontics. Load-displacement curves were recorded and the failure mode was macro- and microscopically analyzed. The statistical analysis was performed using a t-test (p=0.05). Results All the specimens survived cyclic mechanical loading and no obvious failure could be observed. Due to the cyclic mechanical loading, the load-bearing capacity decreased from 8,496 N±196 N (control) to 7,592 N±901 N (test). The cyclic mechanical loading did not significantly influence the load-bearing capacity (p=0.060). The failure mode was almost identical in all specimens: large deformations of the framework at the implant connection area were obvious. Conclusion The load-bearing capacity of the I-Bridge®2 frameworks is much higher than the clinically relevant occlusal forces, even with considerably angulated implants. However, the performance under functional loading in vivo

  14. Diagnostics for piezoelectric transducers under cyclic loads deployed for structural health monitoring applications

    NASA Astrophysics Data System (ADS)

    Taylor, Stuart G.; Park, Gyuhae; Farinholt, Kevin M.; Todd, Michael D.

    2013-02-01

    Accurate sensor self-diagnostics are a key component of successful structural health monitoring (SHM) systems. Transducer failure can be a significant source of failure in SHM systems, and neglecting to incorporate an adequate sensor diagnostics capability can lead to false positives in damage detection. Any permanently installed SHM system will thus require the ability to accurately monitor the health of the sensors themselves, so that when deviations in baseline measurements are observed, one can clearly distinguish between structural changes and sensor malfunction. This paper presents an overview of sensor diagnostics for active-sensing SHM systems employing piezoelectric transducers, and it reviews the sensor diagnostics results from an experimental case study in which a 9 m wind turbine rotor blade was dynamically loaded in a fatigue test until reaching catastrophic failure. The fatigue test for this rotor blade was unexpectedly long, requiring more than 8 million fatigue cycles before failure. Based on previous experiments, it was expected that the rotor blade would reach failure near 2 million fatigue cycles. Several sensors failed in the course of this much longer than expected test, although 48 out of 49 installed piezoelectric transducers survived beyond the anticipated 2 million fatigue cycles. Of the transducers that did fail in the course of the test, the sensor diagnostics methods presented here were effective in identifying them for replacement and/or data cleansing. Finally, while most sensor diagnostics studies have been performed in a controlled, static environment, some data in this study were collected as the rotor blade underwent cyclic loading, resulting in nonstationary structural impedance. This loading condition motivated the implementation of a new, additional data normalization step for sensor diagnostics with piezoelectric transducers in operational environments.

  15. Monotonic and fatigue properties of kenaf /glass hybrid composites under fully reversed cyclic loading

    NASA Astrophysics Data System (ADS)

    Sharba, M. J.; Leman, Z.; Sultan, M. T. H.; Ishak, M. R.; Hanim, M. A. A.

    2015-12-01

    The aim of this work is to investigate the effect of hybridization of kenaf-glass fibers reinforced unsaturated polyester on fatigue life. Three types of composites were fabricated using hands lay-up method, namely, kenaf, glass, and hybrid composites with 30% of weight fraction, the hybrid was mixed with a ratio of kenaf: glass 10:20. Monotonic tests were achieved (Tensile and compression) to determine the fatigue stress levels. Fully reversed fatigue loading was conducted with a stress ratio of -1 and stress levels 55-85% of the ultimate static stresses, all tests were conducted at 10 Hz of frequency. The results proof a positive hybrid composite; also agree with the rule of mixture that can predict the final composite properties. Moreover, it's been observed an improvement in overall mechanical properties of hybrid compared to individual ones.

  16. Effects of Nesting on Compression-Loaded 2-D Woven Textile Composites

    NASA Technical Reports Server (NTRS)

    Adams, Daniel OHare; Breiling, Kurtis B.; Verhulst, Mark A.

    1995-01-01

    Layer nesting was investigated in five harness satin weave textile composite laminates under static compression loading. Two carbon/epoxy material systems, AS4/3501-6 and IM7/8551-7A were considered. Laminates were fabricated with three idealized nesting cases: stacked, split-span and diagonal. Similar compression strength reductions due to the effects of idealized nesting were identified for each material. The diagonal nesting geometry produced the largest reduction in static strength when compared to the compression strength of a conventional textile composite. All three nesting cases produced reductions in strength and ultimate strain due to the effects of idealized nesting. Finite element results showed consistent strength reduction trends for the idealized nesting cases, however the magnitudes of compressive strengths were overpredicted.

  17. Crack propagation in SiC f/SiC ceramic matrix composite under static and cyclic loading conditions

    NASA Astrophysics Data System (ADS)

    Raghuraman, S.; Stubbins, J. F.; Ferber, M. K.; Wereszczak, A. A.

    1994-09-01

    {SiC f}/{SiC} ceramic matrix composite material is of high interest for potential application as a structural and barrier material in fusion systems. It possesses reasonable fracture toughness over a range of temperatures and, due to the low atomic number of its constituents, is appealing for low activation reasons. This study examines the mechanical durability of a Nicalon fiber-SiC composite which has been tested at temperatures up to 1400°C to determine its resistance to crack propagation under static and cyclic loading conditions. The crack growth characteristics are governed by the fiber and interface failure modes. These, in turn are affected by loading parameters, temperature and environmental effects. The material shows R-curve behavior, due to fiber bridging of the crack wake. The material also shows time dependent crack growth at elevated temperature, but not at room temperature. However, cyclic loading does induce crack extension at room temperature.

  18. Water diffusion pathway, swelling pressure, and biomechanical properties of the intervertebral disc during compression load

    SciTech Connect

    Ohshima, H.; Tsuji, H.; Hirano, N.; Ishihara, H.; Katoh, Y.; Yamada, H. )

    1989-11-01

    The behavior of water in the intervertebral disc of pig tail and its physiologic and biomechanical properties were investigated in relation to compression load. The water content, chemical composition, and swelling pressure in the intervertebral disc were measured, and the mechanism of the generation of the swelling pressure in relation to compression load stress was studied. The swelling pressure, through regulation of the water content of the disc and the resistance of the external load, differs with the region of the intervertebral disc. In the nucleus pulposus and the inner layer of the anulus fibrosus, the swelling pressure rises in proportion to the load, but few changes occur in the outer layer of the anulus fibrosus, and the constant pressure environment is thus maintained. The tritiated water (3H2O) uptake of the disc under various loads was measured. The molar partition coefficient of tritiated water is almost equal to 1 even under a compression load, which suggests that water is freely exchangeable. The diffusion of 3H2O in the intervertebral disc was traced using two pathway models: the perianular route and the end-plate route. The diffusion of water in the unloaded disc for both uptake and washout was about 2 to 3 times larger in the perianular route than in the end-plate route. Under load, the water diffusion was inhibited in both pathways. The relation between the load and displacement revealed viscoelastic properties indicating creep and stress relaxation. Young's modulus and the stiffness increased with a rise in load speed.

  19. Effect of cyclic loading on microleakage of silorane based composite compared with low shrinkage methacrylate-based composites

    PubMed Central

    Kermanshah, Hamid; Yasini, Esmail; Hoseinifar, Razieh

    2016-01-01

    Background: There are many concerns regarding the marginal seal of composite restorations, especially when composite restorations are subjected to cyclic loading. The aim of this study was to evaluate the effect of cyclic loading on the microleakage of silorane based composite compared with low shrinkage methacrylate-based composites in class V cavities. Materials and Methods: In this in vitro study, class V cavities were prepared on the facial and lingual surfaces of 48 human premolars (96 cavities). The teeth were randomly divided into four groups of 12 teeth (24 cavities) each and restored as follows: Group 1 (Siloran System Adhesive + Filtek P90), Group 2 (All Bond SE + Aelite LS Posterior), Group 3 (Futurabond NR + Grandio), and Group 4 (G-Bond + Kalore-GC). All the specimens were thermocycled for 2000 cycles (5-55°C) and then half of the specimens from each group, were Load cycled. All teeth were immersed in 0.5% basic fuchsine dye, sectioned, and observed under a stereomicroscope. Data were analyzed using Wilcoxon test, Kruskal–Wallis, and Mann–Whitney U-tests. P < 0.05 was considered as significant. Results: In both unloaded and loaded groups, no statistically significant differences were observed among four composites at the occlusal margin, but a significant difference in gingival microleakage was found between Aelite and silorane. Occlusal and gingival microleakage was not affected by cyclic loading in none of the four restorative materials. Conclusion: Silorane did not provide better marginal seal than the low shrinkage methacrylate-based composites (except Aelite). In addition, cyclic loading did not affect the marginal microleakage of evaluated composite restorations. PMID:27274348

  20. Experimental and Numerical Studies on Development of Fracture Process Zone (FPZ) in Rocks under Cyclic and Static Loadings

    NASA Astrophysics Data System (ADS)

    Ghamgosar, M.; Erarslan, N.

    2016-03-01

    The development of fracture process zones (FPZ) in the Cracked Chevron Notched Brazilian Disc (CCNBD) monsonite and Brisbane tuff specimens was investigated to evaluate the mechanical behaviour of brittle rocks under static and various cyclic loadings. An FPZ is a region that involves different types of damage around the pre-existing and/or stress-induced crack tips in engineering materials. This highly damaged area includes micro- and meso-cracks, which emerge prior to the main fracture growth or extension and ultimately coalescence to macrofractures, leading to the failure. The experiments and numerical simulations were designed for this study to investigate the following features of FPZ in rocks: (1) ligament connections and (2) microcracking and its coalescence in FPZ. A Computed Tomography (CT) scan technique was also used to investigate the FPZ behaviour in selected rock specimens. The CT scan results showed that the fracturing velocity is entirely dependent on the appropriate amount of fracture energy absorbed in rock specimens due to the change of frequency and amplitudes of the dynamic loading. Extended Finite Element Method (XFEM) was used to compute the displacements, tensile stress distribution and plastic energy dissipation around the propagating crack tip in FPZ. One of the most important observations, the shape of FPZ and its extension around the crack tip, was made using numerical and experimental results, which supported the CT scan results. When the static rupture and the cyclic rupture were compared, the main differences are twofold: (1) the number of fragments produced is much greater under cyclic loading than under static loading, and (2) intergranular cracks are formed due to particle breakage under cyclic loading compared with smooth and bright cracks along cleavage planes under static loading.

  1. Optimization of composite sandwich cover panels subjected to compressive loadings

    NASA Technical Reports Server (NTRS)

    Cruz, Juan R.

    1991-01-01

    An analysis and design method is presented for the design of composite sandwich cover panels that include the transverse shear effects and damage tolerance considerations. This method is incorporated into a sandwich optimization computer program entitled SANDOP. As a demonstration of its capabilities, SANDOP is used in the present study to design optimized composite sandwich cover panels for for transport aircraft wing applications. The results of this design study indicate that optimized composite sandwich cover panels have approximately the same structural efficiency as stiffened composite cover panels designed to satisfy individual constraints. The results also indicate that inplane stiffness requirements have a large effect on the weight of these composite sandwich cover panels at higher load levels. Increasing the maximum allowable strain and the upper percentage limit of the 0 degree and +/- 45 degree plies can yield significant weight savings. The results show that the structural efficiency of these optimized composite sandwich cover panels is relatively insensitive to changes in core density. Thus, core density should be chosen by criteria other than minimum weight (e.g., damage tolerance, ease of manufacture, etc.).

  2. Contact mechanics of the human finger pad under compressive loads.

    PubMed

    Dzidek, Brygida M; Adams, Michael J; Andrews, James W; Zhang, Zhibing; Johnson, Simon A

    2017-02-01

    The coefficient of friction of most solid objects is independent of the applied normal force because of surface roughness. This behaviour is observed for a finger pad except at long contact times (greater than 10 s) against smooth impermeable surfaces such as glass when the coefficient increases with decreasing normal force by about a factor of five for the load range investigated here. This is clearly an advantage for some precision manipulation and grip tasks. Such normal force dependence is characteristic of smooth curved elastic bodies. It has been argued that the occlusion of moisture in the form of sweat plasticises the surface topographical features and their increased compliance allows flattening under an applied normal force, so that the surfaces of the fingerprint ridges are effectively smooth. While the normal force dependence of the friction is consistent with the theory of elastic frictional contacts, the gross deformation behaviour is not and, for commonly reported values of the Young's modulus of stratum corneum, the deformation of the ridges should be negligible compared with the gross deformation of the finger pad even when fully occluded. This paper describes the development of a contact mechanics model that resolves these inconsistencies and is validated against experimental data.

  3. Importance of anisotropy on design of compression-loaded composite corrugated panels

    NASA Technical Reports Server (NTRS)

    Gurdal, Zafer; Young, Richard D.

    1990-01-01

    An investigation is conducted of the importance of anisotropic terms in the design of composite corrugated panels, for a range of axial compressive load intensities. The two panel configurations treated were panels with tailored laminates and panels with a continuous laminate; both are of interest to aircraft designers and prone to anisotropic effects which are of as-yet undetermined extent. The importance of the anisotropic terms is measured by the difference between the design load and the buckling load obtained from the ultimate structural analysis.

  4. Behavior of Compression-Loaded Composite Panels with Stringer Terminations and Impact Damage

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1998-01-01

    The results of an analytical and experimental study of graphite-epoxy stiffened panels with impact-damaged stringer terminations are presented. Five stitched graphite-epoxy panels with stiffeners with a gradual reduction in either thickness or height were examined. Panels were analyzed using finite element analysis and tested by loading them in axial compression to a predetermined load. The panels were then subjected to impact damage and loaded to failure. Axial midplane strains, surface strains, interlaminar strains and failure results are discussed.

  5. Recent developments in reassessment of jacket structures under extreme storm cyclic loading. Part 2: Cyclic capacity of tubular members

    SciTech Connect

    Amdahl, J.; Skallerud, B.H.; Eide, O.I.; Johansen, A.

    1995-12-31

    Tubular members with D/t ratio 35, 45, 60 and 80 were tested under controlled axial displacement described by an amplitude and a mean level. The material was structural steel to St. 52-3N, with minimum yield stress 345 MPa. The slenderness ratio of the specimens were in the range 50--70. During testing, the specimens were instrumented for measurements of longitudinal and transversal deflections, ovalization, and extreme fiber strains. Number of cycles to local buckling and through thickness cracking was recorded. Selected tests were simulated by use of the nonlinear beam-column FE program USFOS and the shell FE program ABAQUS. Comparisons were made to the corresponding test results. Monotonic and cyclic capacity criteria of tubular members are discussed on the basis of the results obtained.

  6. A Numerical and Experimental Study of Compression-Loaded Composite Panels With Cutouts

    NASA Technical Reports Server (NTRS)

    Thornburgh, Robert P.; Hilburger, Mark W.

    2006-01-01

    Results from a numerical and experimental study on the effects of laminate orthotropy and circular cutout size on the response of compression-loaded composite curved panels are presented. Several 60-in-radius composite panels with four different laminate configurations were tested with cutout diameters that range from 10% to 60% of the panel width. Finite-element analyses were performed for each panel in order to identify the effects boundary conditions, measured initial geometric imperfections and thickness variations had on the nonlinear and buckling behavior of the panels. The compression-loaded panels considered herein exhibited two separate types of behavior depending on the laminate stacking sequence and cutout size. More specifically, some of the panels exhibited the classical snap-through type buckling response; however, some of the panels exhibited a monotonically increasing stable response and achieved compressive loads in excess of twice the predicted linear bifurcation buckling load. In general, the finite-element analyses were able to predict accurately the nonlinear response and buckling loads of the panels and the prebuckling and postbuckling out-of-plane deformations and strains.

  7. Buckling Behavior of Compression-Loaded Composite Cylindrical Shells With Reinforced Cutouts

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Sarnes, James H., Jr.

    2004-01-01

    Results from a numerical study of the response of thin-walled compression-loaded quasi-isotropic laminated composite cylindrical shells with unreinforced and reinforced square cutouts are presented. The effects of cutout reinforcement orthotropy, size, and thickness on the nonlinear response of the shells are described. A nonlinear analysis procedure has been used to predict the nonlinear response of the shells. The results indicate that a local buckling response occurs in the shell near the cutout when subjected to load and is caused by a nonlinear coupling between local shell-wall deformations and in-plane destabilizing compression stresses near the cutout. In general, reinforcement around a cutout in a compression-loaded shell is shown to retard or eliminate the local buckling response near the cutout and increase the buckling load of the shell. However, some results show that certain reinforcement configurations can cause an unexpected increase in the magnitude of local deformations and stresses in the shell and cause a reduction in the buckling load. Specific cases are presented that suggest that the orthotropy, thickness, and size of a cutout reinforcement in a shell can be tailored to achieve improved buckling response characteristics.

  8. Cartilage interstitial fluid load support in unconfined compression following enzymatic digestion.

    PubMed

    Basalo, Ines M; Mauck, Robert L; Kelly, Terri-Ann N; Nicoll, Steven B; Chen, Faye H; Hung, Clark T; Ateshian, Gerard A

    2004-12-01

    Interstitial fluid pressurization plays an important role in cartilage biomechanics and is believed to be a primary mechanism of load support in synovial joints. The objective of this study was to investigate the effects of enzymatic degradation on the interstitial fluid load support mechanism of articular cartilage in unconfined compression. Thirty-seven immature bovine cartilage plugs were tested in unconfined compression before and after enzymatic digestion. The peak fluid load support decreased significantly (p < 0.0001) from 84 +/- 10% to 53 +/- 19% and from 80 +/- 10% to 46 +/- 21% after 18-hours digestion with 1.0 u/mg-wet-weight and 0.7 u/mg-wet-weight of collagenase, respectively. Treatment with 0.1 u/ml of chondroitinase ABC for 24 hours also significantly reduced the peak fluid load support from 83 +/- 12% to 48 +/- 16% (p < 0.0001). The drop in interstitial fluid load support following enzymatic treatment is believed to result from a decrease in the ratio of tensile to compressive moduli of the solid matrix.

  9. Intraocular pressure effects of water loading and venous compression tests in normal and denervated pigmented rabbits.

    PubMed

    Gual, A; Mintenig, G M; Belmonte, C

    1989-03-01

    We have compared IOP elevations induced by water-loading and by increased cephalic venous pressure in normal and denervated pigmented rabbits. Denervations were performed by sympathetic ganglionectomy and/or blockade of the sensory and autonomic innervation of the eye through retrobulbar anesthesia; retrobulbar anesthesia induced significant decreases of the basal IOP in control but not in ganglionectomized eyes. The water-loading test induced a peak pressure elevation approximately 30 min after water administration that could be counteracted by retrobulbar anesthesia. Ganglionectomized rabbits exhibited steeper IOP rises and greater IOP increases following water-loading than the control eyes; retrobulbar anesthesia in ganglionectomized eyes delayed the IOP response to water-loading. Compressions of the neck lasting 30 min elicited significant IOP elevations that were more pronounced in ganglionectomized eyes. In these eyes, retrobulbar anesthesia further increased the IOP rise elicited by neck compression. An IOP decrease below control values was observed at the end of the venous compression. The results indicate that an intact efferent innervation of the eye contributes to buffer IOP elevations induced by water-loading or cephalic venous stasis, presumably through the vascular effects of the ocular autonomic nerves.

  10. Engineering the periodontal ligament in hyaluronan-gelatin-type I collagen constructs: upregulation of apoptosis and alterations in gene expression by cyclic compressive strain.

    PubMed

    Saminathan, Aarthi; Sriram, Gopu; Vinoth, Jayasaleen Kumar; Cao, Tong; Meikle, Murray C

    2015-02-01

    To engineer constructs of the periodontal ligament (PDL), human PDL cells were incorporated into a matrix of hyaluronan, gelatin, and type I collagen (COLI) in sample holders (13×1 mm) of six-well Biopress culture plates. The loading dynamics of the PDL were mimicked by applying a cyclic compressive strain of 33.4 kPa (340.6 gm/cm(2)) to the constructs for 1.0 s every 60 s, for 6, 12, and 24 h in a Flexercell FX-4000C Strain Unit. Compression significantly increased the number of nonviable cells and increased the expression of several apoptosis-related genes, including initiator and executioner caspases. Of the 15 extracellular matrix genes screened, most were upregulated at some point after 6-12 h deformation, but all were downregulated at 24 h, except for MMPs1-3 and CTGF. In culture supernatants, matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of metalloproteinases-1 (TIMP-1) protein levels were upregulated at 24 h; receptor activator of nuclear kappa factor B (RANKL), osteoprotegerin (OPG) and fibroblast growth factor-2 (FGF-2) were unchanged; and connective tissue growth factor (CTGF) not detected. The low modulus of elasticity of the constructs was a disadvantage-future mechanobiology studies and tissue engineering applications will require constructs with much higher stiffness. Since the major structural protein of the PDL is COLI, a more rational approach would be to permeabilize preformed COLI scaffolds with PDL-populated matrices.

  11. Creep-fatigue of High Temperature Materials for VHTR: Effect of Cyclic Loading and Environment

    SciTech Connect

    Celine Cabet; L. Carroll; R. Wright; R. Madland

    2011-05-01

    Alloy 617 is the one of the leading candidate materials for Intermediate Heat eXchangers (IHX) of a Very High Temperature Reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Furthermore, the anticipated IHX operating temperature, up to 950°C, is in the range of creep so that creep-fatigue interaction, which can significantly increase the fatigue crack growth, may be one of the primary IHX damage modes. To address the needs for Alloy 617 codification and licensing, a significant creep-fatigue testing program is underway at Idaho National Laboratory. Strain controlled LCF tests including hold times up to 1800s at maximum tensile strain were conducted at total strain range of 0.3% and 0.6% in air at 950°C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The creep-fatigue tests resulted in failure times up to 1000 hrs. Fatigue resistance was significantly decreased when a hold time was added at peak stress and when the total strain was increased. The fracture mode also changed from transgranular to intergranular with introduction of a tensile hold. Changes in the microstructure were methodically characterized. A combined effect of temperature, cyclic and static loading and environment was evidenced in the targeted operating conditions of the IHX. This paper This paper reviews the data previously published by Carroll and co-workers in references 10 and 11 focusing on the role of inelastic strain accumulation and of oxidation in the initiation and propagation of surface fatigue cracks.

  12. Influence of plate-bone contact on cyclically loaded conically coupled locking plate failure.

    PubMed

    Rotne, Randi; Bertollo, Nicky; Walsh, William; Dhand, Navneet K; Voss, Katja; Johnson, Kenneth A

    2014-03-01

    The maintenance of friction between locking plates and bone is not essential, so that they can be applied with a gap between the plate and underlying bone. We hypothesised that the presence of a gap under a locking plate with a conical coupling mechanism would reduce fixation stability or allow uncoupling of the locking screws from the plate. Locking plates with two conically coupled locking screws were applied to 6 pairs of adult canine femora. One of each pair had plate to bone contact and the contralateral construct had a 2 mm plate to bone gap. Constructs were cyclically loaded in cantilever bending with 10 percent incremental increases every 1000 cycles at 2 Hz, starting at 250 N. The constructs were fatigued to failure. To evaluate fatigue life of the conical coupling, testing was repeated with aluminium tubing replacing the bone, to eliminate screw-bone cutout failure. The mean sustained loads and cycles to failure in the contact group (420.80, standard error [SE] 14.97 N; 7612.00, SE 574.70 cycles) were significantly greater than in the gap group (337.50, SE 14.97 N; 4252.00, SE 574.70 cycles), (p<0.001). Failure mode of all bone constructs was via screw cutout from the bone. Aluminium tubing constructs failed via screw or plate fatigue and breaking, with one construct having elevation of the plate over the screw head. Elevation of locking plates with a conical coupling system by 2 mm from the bone reduced construct fatigue life but did not result in screw head uncoupling from the plate. Copyright © 2013 Elsevier Ltd. All rights reserved.

  13. Experimental study of hollow rectangular bridge column performance under vertical and cyclically bilateral loads

    NASA Astrophysics Data System (ADS)

    Han, Qiang; Du, Xiuli; Zhou, Yihui; Lee, George C.

    2013-09-01

    To investigate the seismic performance of hollow reinforced concrete (RC) bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges (JTG/T B02-01-2008). The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.

  14. Investigation of changes in the electrical properties of novel knitted conductive textiles during cyclic loading.

    PubMed

    Isaia, Cristina; McNally, Donal; McMaster, Simon A; Branson, David T

    2016-08-01

    Combining stainless steel with polyester fibres adds an attractive conductive behaviour to the yarn. Once knitted in such a manner, fabrics develop sensing properties that make the textiles, also known as e-textiles, suitable for smart/wearable applications. Structural deformations of the fibres (e.g. stretching) will cause changes in the conductivity of the fabric. This work investigates changes in the electrical properties exhibited by four knitted conductive textiles made of 20% stainless steel and 80% polyester fibres during cyclic loading. The samples were preconditioned first with 500 hundred cycles of unidirectional elongation and, after a rest interval, tested again for repeatability at the same conditions. In both cases the electrical behaviour stabilises after a few tens of cycles. In particular the repeatability test exhibited a considerably smaller settling time and a larger resistance due to the mechanical stabilisation and the loosening of the fabrics, respectively. It was found that the current provided to the fabrics affects the resistance measurements by decreasing the resistance value at which the samples become electrically stable. The reported findings present a valid method for the electrical characterisation of conductive textiles for use in further studies as a wearable technology.

  15. Performance of extrinsic Fabry-Perot optical fiber strain sensors in the presence of cyclic loads

    NASA Astrophysics Data System (ADS)

    Shyprykevich, Peter; Fogg, Brian R.; Murphy, Kent A.; Claus, Richard O.

    1993-07-01

    An experimental study was conducted to determine the utility of in-line optical fiber-based extrinsic Fabry-Perot interferometers (EFPIs), in a fatigue environment typical of aircraft structures. Metallic and composite coupons with EFPIs attached to and embedded within were tested in constant amplitude cyclic fatigue at room temperature. An additional composite coupon was tested similarly at an elevated temperature. For the consideration of composite material applications the objectives were to determine the durability of the sensor and its ability to measure strains accurately, even when the EFPI sensor was embedded at an angle with respect to the principal adjacent reinforcing fibers of the composite. For metals, in addition to durability considerations, research was conducted as to how the EFPI sensor may be used to detect crack initiation and growth. The results of the test program have established the excellent durability of the EFPI sensor element for fatigue loading up to 50,000 cycles at R equals 0.1 (tension-tension fatigue) with a maximum strain level of 3,500 microinch/inch, for both attached and embedded sensors, once the optical fiber and sensor survived the composite laminate panel curing process.

  16. Design maps for failure of all-ceramic layer structures in concentrated cyclic loading

    PubMed Central

    Bhowmick, Sanjit; Meléndez-Martínez, Juan José; Zhang, Yu; Lawn, Brian R.

    2009-01-01

    A study is made of the competition between failure modes in ceramic-based bilayer structures joined to polymer-based substrates, in simulation of dental crown-like structures with a functional but weak “veneer” layer bonded onto a strong “core” layer. Cyclic contact fatigue tests are conducted in water on model flat systems consisting of glass plates joined to glass, sapphire, alumina or zirconia support layers glued onto polycarbonate bases. Critical numbers of cycles to take each crack mode to failure are plotted as a function of peak contact load on failure maps showing regions in which each fracture mode dominates. In low-cycle conditions, radial and outer cone cracks are competitive in specimens with alumina cores, and outer cone cracks prevail in specimens with zirconia cores; in high-cycle conditions, inner cone cracks prevail in all cases. The roles of other factors, e.g. substrate modulus, layer thickness, indenter radius and residual stresses from specimen preparation, are briefly considered. PMID:19562095

  17. Poroelastic analysis of interstitial fluid flow in a single lamellar trabecula subjected to cyclic loading.

    PubMed

    Kameo, Yoshitaka; Ootao, Yoshihiro; Ishihara, Masayuki

    2016-04-01

    Trabecula, an anatomical unit of the cancellous bone, is a porous material that consists of a lamellar bone matrix and interstitial fluid in a lacuno-canalicular porosity. The flow of interstitial fluid caused by deformation of the bone matrix is believed to initiate a mechanical response in osteocytes for bone remodeling. In order to clarify the effect of the lamellar structure of the bone matrix--i.e., variations in material properties--on the fluid flow stimuli to osteocytes embedded in trabeculae, we investigated the mechanical behavior of an individual trabecula subjected to cyclic loading based on poroelasticity. We focused on variations in the trabecular permeability and developed an analytical solution containing both transient and steady-state responses for interstitial fluid pressure in a single trabecular model represented by a multilayered two-dimensional poroelastic slab. Based on the obtained solution, we calculated the pressure and seepage velocity of the interstitial fluid in lacuno-canalicular porosity, within the single trabecula, under various permeability distributions. Poroelastic analysis showed that a heterogeneous distribution of permeability produces remarkable variations in the fluid pressure and seepage velocity in the cross section of the individual trabecula, and suggests that fluid flow stimuli to osteocytes are mostly governed by the value of permeability in the neighborhood of the trabecular surfaces if there is no difference in the average permeability in a single trabecula.

  18. Fatigue Modeling for Superelastic NiTi Considering Cyclic Deformation and Load Ratio Effects

    NASA Astrophysics Data System (ADS)

    Mahtabi, Mohammad J.; Shamsaei, Nima

    2017-08-01

    A cumulative energy-based damage model, called total fatigue toughness, is proposed for fatigue life prediction of superelastic NiTi alloys with various deformation responses (i.e., transformation stresses), which also accounts for the effects of mean strain and stress. Mechanical response of superelastic NiTi is highly sensitive to chemical composition, material processing, as well as operating temperature; therefore, significantly different deformation responses may be obtained for seemingly identical NiTi specimens. In this paper, a fatigue damage parameter is proposed that can be used for fatigue life prediction of superelastic NiTi alloys with different mechanical properties such as loading and unloading transformation stresses, modulus of elasticity, and austenite-to-martensite start and finish strains. Moreover, the model is capable of capturing the effects of tensile mean strain and stress on the fatigue behavior. Fatigue life predictions using the proposed damage parameter for specimens with different cyclic stress responses, tested at various strain ratios (R ɛ = ɛ min /ɛ max) are shown to be in very good agreement with the experimentally observed fatigue lives.

  19. Numerical analyses of caisson breakwaters on soft foundations under wave cyclic loading

    NASA Astrophysics Data System (ADS)

    Wang, Yuan-zhan; Yan, Zhen; Wang, Yu-chi

    2016-03-01

    A caisson breakwater is built on soft foundations after replacing the upper soft layer with sand. This paper presents a dynamic finite element method to investigate the strength degradation and associated pore pressure development of the intercalated soft layer under wave cyclic loading. By combining the undrained shear strength with the empirical formula of overconsolidation clay produced by unloading and the development model of pore pressure, the dynamic degradation law that describes the undrained shear strength as a function of cycle number and stress level is derived. Based on the proposed dynamic degradation law and M-C yield criterion, a dynamic finite element method is numerically implemented to predict changes in undrained shear strength of the intercalated soft layer by using the general-purpose FEM software ABAQUS, and the accuracy of the method is verified. The effects of cycle number and amplitude of the wave force on the degradation of the undrained shear strength of the intercalated soft layer and the associated excess pore pressure response are investigated by analyzing an overall distribution and three typical sections underneath the breakwater. By comparing the undrained shear strength distributions obtained by the static method and the quasi-static method with the undrained shear strength distributions obtained by the dynamic finite element method in the three typical sections, the superiority of the dynamic finite element method in predicting changes in undrained shear strength is demonstrated.

  20. Tooth-PDL-bone complex: response to compressive loads encountered during mastication - a review.

    PubMed

    Naveh, Gili R S; Lev-Tov Chattah, Netta; Zaslansky, Paul; Shahar, Ron; Weiner, Steve

    2012-12-01

    The components of the tooth-periodontal ligament (PDL)-alveolar bone complex act in a synergistic manner to dissipate the loads incurred during mastication. The complex incorporates a diverse array of structural features for this purpose. These include the non-mineralized and hence soft PDL that absorbs much of the initial loads. The internal structure of the tooth also includes soft interphases that essentially surround the dentine core. These interphases, although stiffer than the PDL, still are more compliant than the dentine core, and are thus key components that allow the tooth itself to deform and hence help dissipate the compressive loads. There is also direct evidence that even under moderate compressive loads, when the tooth moves in the alveolar bone socket, this movement is guided by specific locations where the tooth comes into contact with the bone surface. The combination of all these responses to load is that each tooth type appears to move and deform in a specific manner when loaded. Much, however, still remains to be learned about these three-dimensional responses to load and the factors that control them. Such an understanding will have major implications for dentistry, that include a better understanding of phenomena such as abfraction, the manner in which tooth implants function even in the absence of a PDL-like tissue and the implications to bone remodelling of the movements imposed during orthodontic interventions.

  1. The effect of thoracic kyphosis and sagittal plane alignment on vertebral compressive loading

    PubMed Central

    Bruno, Alexander G.; Anderson, Dennis E.; D’Agostino, John; Bouxsein, Mary L.

    2012-01-01

    To better understand the biomechanical mechanisms underlying the association between hyperkyphosis of the thoracic spine and risk of vertebral fracture and other degenerative spinal pathology, we used a previously validated musculoskeletal model of the spine to determine how thoracic kyphosis angle and spinal posture affect vertebral compressive loading. We simulated an age-related increase in thoracic kyphosis (T1-T12 Cobb angle 50° to 75°) during two different activities (relaxed standing and standing with 5 kg weights in the hands) and three different posture conditions: 1) an increase in thoracic kyphosis with no postural adjustment (uncompensated posture), 2) an increase in thoracic kyphosis with a concomitant increase in pelvic tilt that maintains a stable center of mass and horizontal eye gaze (compensated posture), and 3) an increase in thoracic kyphosis with a concomitant increase in lumbar lordosis that also maintains a stable center of mass and horizontal eye gaze (congruent posture). For all posture conditions, compressive loading increased with increasing thoracic kyphosis, with loading increasing more in the thoracolumbar and lumbar regions than in the mid-thoracic region. Loading increased the most for the uncompensated posture, followed by the compensated posture, with the congruent posture almost completely mitigating any increases in loading with increased thoracic kyphosis. These findings indicate that thoracic kyphosis and spinal posture both influence vertebral loading during daily activities, implying that thoracic kyphosis measurements alone are not sufficient to characterize the impact of spinal curvature on vertebral loading. PMID:22589006

  2. The effects of cyclic loading and preparation on the fracture strength of zirconium-dioxide implants: an in vitro investigation.

    PubMed

    Kohal, Ralf J; Wolkewitz, Martin; Tsakona, Anastasia

    2011-08-01

    Zirconia is a potential material for the fabrication of oral implants. The aim of this study was to evaluate the effects of cyclic loading and preparation on the fracture strength of a zirconia implant system. Forty-eight one-piece implants were divided into two groups of 24 implants: group A (without modification) and group B (1 mm chamfer preparation). Groups A and B were divided into three subgroups of eight implants each (1 = no artificial load, 2 = artificial load [98 N; 1.2 million loading cycles], and 3 = artificial load [98 N; 5 million loading cycles]). After completion of the loading, the fracture strength of each implant was determined in a universal testing machine. A two-way analysis of variance was used, the continuous response variable (fracture strength in Newtons) is modeled as a function of preparation, cycles, and the corresponding interaction as explanatory variables. The mean fracture strength values obtained for the groups were: A1 (no preparation, no load) = 1928.73 N, A2 (no preparation, 1.2 million cycles) = 2044.84 N, A3 (no preparation, 5 million cycles) = 1364.50 N, B1 (preparation, no load) = 1221.66 N, B2 (preparation, 1.2 million cycles) = 967.11 N, and B3 (preparation, 5 million cycles) = 884.89 N. Fracture values were significantly different between subgroups A1 vs. A3 and B1 vs. B3. There was no significant difference between subgroups A1 vs. A2 and B1 vs. B2. Preparation as well as cyclic loading can decrease the fracture strength resistance of zirconia implants. Nevertheless, even the lowest values of mean fracture strength of the implants used in our study seem to withstand average occlusal forces even after an extended interval of artificial loading. © 2011 John Wiley & Sons A/S.

  3. Impact of constrained dual-screw anchorage on holding strength and the resistance to cyclic loading in anterior spinal deformity surgery: a comparative biomechanical study.

    PubMed

    Koller, Heiko; Fierlbeck, Johann; Auffarth, Alexander; Niederberger, Alfred; Stephan, Daniel; Hitzl, Wolfgang; Augat, Peter; Zenner, Juliane; Blocher, Martina; Blocher, Martina; Resch, Herbert; Mayer, Michael

    2014-03-15

    Biomechanical in vitro laboratory study. To compare the biomechanical performance of 3 fixation concepts used for anterior instrumented scoliosis correction and fusion (AISF). AISF is an ideal estimate for selective fusion in adolescent idiopathic scoliosis. Correction is mediated using rods and screws anchored in the vertebral bodies. Application of large correction forces can promote early weakening of the implant-vertebra interfaces, with potential postoperative loss of correction, implant dislodgment, and nonunion. Therefore, improvement of screw-rod anchorage characteristics with AISF is valuable. A total of 111 thoracolumbar vertebrae harvested from 7 human spines completed a testing protocol. Age of specimens was 62.9 ± 8.2 years. Vertebrae were potted in polymethylmethacrylate and instrumented using 3 different devices with identical screw length and unicortical fixation: single constrained screw fixation (SC fixation), nonconstrained dual-screw fixation (DNS fixation), and constrained dual-screw fixation (DC fixation) resembling a novel implant type. Mechanical testing of each implant-vertebra unit using cyclic loading and pullout tests were performed after stress tests were applied mimicking surgical maneuvers during AISF. Test order was as follows: (1) preload test 1 simulating screw-rod locking and cantilever forces; (2) preload test 2 simulating compression/distraction maneuver; (3) cyclic loading tests with implant-vertebra unit subjected to stepwise increased cyclic loading (maximum: 200 N) protocol with 1000 cycles at 2 Hz, tests were aborted if displacement greater than 2 mm occurred before reaching 1000 cycles; and (4) coaxial pullout tests at a pullout rate of 5 mm/min. With each test, the mode of failure, that is, shear versus fracture, was noted as well as the ultimate load to failure (N), number of implant-vertebra units surpassing 1000 cycles, and number of cycles and related loads applied. Thirty-three percent of vertebrae surpassed 1000

  4. Analysis of the complex stress state during early loading in cylindrical compression-shear specimens

    NASA Astrophysics Data System (ADS)

    Pfeiffer, S.; Frint, P.; F-X Wagner, M.

    2017-03-01

    In most engineering applications, materials are subjected to complex load cases rather than the simple uniaxial ones typically used for material characterization. To experimentally study the material behavior under a combination of compression and shear, an inclined compression specimen can be used. This specimen has been applied in various earlier experimental studies, typically to investigate shear localization under quasi-static or impact loading. In this contribution, we analyze the stress state in a compression-shear specimen in detail using an elastic-ideal plastic finite element simulation. The effects of specimen aspect ratio (height/diameter), inclination angle, and friction conditions between specimen and tool plates are investigated using the material parameters of different conventional steels as input. Shear stress distributions in characteristic shear directions on specific planes in the specimen that control the subsequent plastic deformation behavior are evaluated. Our results show that, even in the absence of friction, shear stresses are distributed heterogeneously in the inclined specimen, which differs from the stress distribution in a conventional compression specimen. Moreover, the highest shear and equivalent stresses always occur at the edges of the short diagonal plane of the specimen, independent of the investigated parameters. This study contributes to a more detailed understanding of the elasto-plastic mechanics in compression-shear specimens, and it specifically provides information for the analysis of the onset of early plastic deformation.

  5. THE EFFECT OF REPEATED COMPRESSIVE DYNAMIC LOADING ON THE STRESS-INDUCED MARTENSITIC TRANSFORMATION IN NiTi SHAPE MEMORY ALLOYS

    SciTech Connect

    D. MILLER; W. THISSELL; ET AL

    2000-08-01

    It has been shown that quasi-static, cyclic, isothermal mechanical loading influences the mechanical response of the stress-induced martensitic transformation in fully annealed NiTi Shape Memory Alloys (SMAs). As the cycle number increases, hardening of the stress-strain response during the martensitic phase transformation is seen along with a decrease in the threshold stress for initiation of stress-induced martensite. Also, the amount of plastic strain and detwinned martensitic strain decreases as the cycle number increases. However, NiTi SMAs have not been experimentally explored under high compressive strain rates. This research explores the cyclic near-adiabatic stress-induced martensitic loading using a Split Hopkinskin Pressure Bar (SHPB). The results of the dynamic loading tests are presented with emphasis on the loading rate, stress-strain response, specimen temperature and post-test microstructural evaluation. The results from the high strain rate tests show similarities with the quasi-static results in the hardening of the stress-strain response and shifting of the threshold stress for initiation of stress-induced martensite.

  6. Design of a miniature hydraulic compression load frame for microdiffraction tests at the Advanced Photon Source.

    SciTech Connect

    Shu, D.; Varma, R.; Krasnicki, S.; Sinha, S.

    1999-10-11

    In support of the x-ray synchrotrons radiation multidiffraction project of Los Alamos National Laboratory at the Advanced Photon Source (APS), we have designed and fabricated a miniature hydraulic compression load frame with 20000 N load capacity for metal specimen tests at the APS. The compact design allows the load frame to sit on the center of a 6-circle goniometer with six degrees of freedom and maximum solid angle accessibility for the incoming x-ray beam and diffraction beam detectors. A set of compact precision stages with submicron resolution has been designed for the load frame positioning to compensate the sample internal elastic and/or plastic deformation during the loading process. The system design, specifications, and test results are presented.

  7. Cyclic-loading-induced accumulation of geometrically necessary dislocations near grain boundaries in a an ni-based superalloy.

    SciTech Connect

    Huang, E. W.; Barabash, R. I.; Ice, G. I.; Liu, W.; Liu, Y. L.; Kai, J. J.; Liaw, P. K.; Univ.of Tennessee; ORNL; Tsing-Hua Univ.

    2009-01-01

    In this study, the fatigue-induced microstructure produced in a nickel-based polycrystalline superalloy that was subjected to cyclic loading was characterized by polychromatic x-ray microdiffraction (PXM) together with in-situ neutron diffraction and transmission-electron microscopy (TEM). In-situ neutron-diffraction measurements reveal two distinct stages of the fatigue damage: cyclic hardening followed by cyclic softening. Three-dimensional spatially resolved PXM micro-Laue measurements find an increase in the density of geometrically necessary dislocations near the grain boundaries, which is accompanied by lattice rotations and grain subdivisions. The PXM results are in agreement with the in-situ neutron-diffraction and TEM results.

  8. Investigation of the failure behaviour of vertebral trabecular architectures under uni-axial compression and wedge action loading conditions.

    PubMed

    McDonnell, P; Harrison, N; McHugh, P E

    2010-07-01

    Vertebral wedge fractures are associated with combined compression and flexure loading and are the most common fracture type for human vertebrae. In this study, rapid prototype (RP) biomodels of human vertebral trabecular bone were mechanically tested under uni-axial compression loading and also under wedge action loading (combination of compression and flexure loading) to investigate the mode of failure and the ultimate loads that could be sustained under these different loading conditions. Two types of trabecular bone models were manufactured and tested: baseline models which were directly derived from microCT scans of human thoracic vertebrae, and osteoporotic models which were generated from the baseline models using a custom-developed bone loss algorithm. The ultimate load for each model under compression and wedge action loading was determined and a video was recorded of each test so that failure mechanisms could be evaluated. The results of the RP model mechanical tests showed that the ultimate loads that could be supported by vertebral trabecular architectures under wedge action loading were less than those that could be supported under uni-axial compression loading by up to 26%. Also, the percentage reduction in strength from the baseline value due to osteoporotic bone loss was slightly less for the wedge action loading compared to uni-axial compression loading. Analysis of the videos for each test revealed that failure occurred in localised regions of the trabecular structure due to bending and buckling of thin vertical struts. These results suggest that vertebral trabecular bone is more susceptible to failure from wedge action loading compared to uni-axial compression loading, although this effect is not exacerbated by osteoporotic bone loss.

  9. Effect of static and cyclic loading on ceramic laminate veneers adhered to teeth with and without aged composite restorations.

    PubMed

    Gresnigt, Marco M; Ozcan, Mutlu; Kalk, Warner; Galhano, Graziela

    2011-12-01

    Existing composite restorations on teeth are often remade prior to the cementation of fixed dental prostheses. The aim of this study was to evaluate the effect of static and cyclic loading on ceramic laminate veneers adhered to aged resin composite restorations. Eighty sound maxillary incisors were collected and randomly divided into four groups: group 1: control group, no restorations; group 2: two Class III restorations; group 3: two Class IV restorations; group 4: complete composite substrate. Standard composite restorations were made using a microhybrid resin composite (Anterior Shine). Restored teeth were subjected to thermocycling (6000 cycles). Window preparations were made on the labial surface of the teeth for ceramic laminate fabrication (Empress II). Teeth were conditioned using an etch-and-rinse system. Existing composite restorations representing the aged composites were silica coated (CoJet) and silanized (ESPE-Sil). Ceramic laminates were cemented using a bis-GMA-based cement (Variolink Veneer). The specimens were randomly divided into two groups and were subjected to either static (groups 1a, 2a, 3a, 4a) or cyclic loading (groups 1b, 2b, 3b, 4b). Failure type and location after loading were classified. Data were analyzed using one-way ANOVA and Tukey's test. Significantly higher fracture strength was obtained in group 4 (330 ± 81 N) compared to the controls in group 1 (179 ± 120 N) (one-way ANOVA, p < 0.05). Group 1b survived a lower mean number of cyclic loads (672,820 cycles) than teeth of groups 2b to 4b (846x103 to 873x103 cycles). Failure type evaluation after the fracture test showed predominantly adhesive failures between dentin and cement, but after cyclic loading, more cohesive fractures in the ceramic were seen. Ceramic laminate veneers bonded to conditioned aged composite restorations provided favorable results. Surface conditioning of existing restorations may eliminate the necessity of removing aged composite restorations.

  10. Effectiveness of a Load-Imposing Device for Cyclic Stretching of Isolated Human Bronchi: A Validation Study

    PubMed Central

    Le Guen, Morgan; Naline, Emmanuel; Grassin-Delyle, Stanislas; Devillier, Philippe; Faisy, Christophe

    2015-01-01

    Background Mechanical ventilation may induce harmful effects in the airways of critically ill patients. Nevertheless, the effects of cyclic stretching caused by repetitive inflation-deflation of the bronchial compartment have not been well characterized in humans. The objective of the present study was to assess the effectiveness of a load-imposing device for the cyclic stretching of human bronchi. Methods Intact bronchial segments were removed from 128 thoracic surgery patients. After preparation and equilibration in an organ bath, bronchi were stretched repetitively and cyclically with a motorized transducer. The peak force imposed on the bronchi was set to 80% of each individual maximum contraction in response to acetylcholine and the minimal force corresponded to the initial basal tone before stretching. A 1-min cycle (stretching for 15 sec, relaxing for 15 sec and resting for 30 sec) was applied over a time period ranging from 5 to 60 min. The device's performance level was assessed and the properties of the stretched bronchi were compared with those of paired, non-stretched bronchi. Results Despite the intrinsic capacities of the device, the targets of the tension adjustments remained variable for minimal tension (156–178%) while the peak force set point was unchanged (87–115%). In the stretched bronchi, a time-dependent rise in basal tone (P <.05 vs. non-stretched) was apparent after as little as 5 min of cyclic stretching. The stretch-induced rise in basal tone continued to increase (P <.01) after the stretching had ended. Only 60 min of cyclic stretching was associated with a significant (P <.05) increase in responsiveness to acetylcholine, relative to non-stretched bronchi. Conclusions Low-frequency, low-force, cyclic loading of human bronchi is associated with elevated basal tone and acetylcholine responsiveness. The present experimental model is likely to be a useful tool for future investigations of the bronchial response to repetitive stress

  11. Failure mechanisms of uni-ply composite plates with a circular hole under static compressive loading

    NASA Technical Reports Server (NTRS)

    Khamseh, A. R.; Waas, A. M.

    1992-01-01

    The objective of the study was to identify and study the failure mechanisms associated with compressive-loaded uniply graphite/epoxy square plates with a central circular hole. It is found that the type of compressive failure depends on the hole size. For large holes with the diameter/width ratio exceeding 0.062, fiber buckling/kinking initiated at the hole is found to be the dominant failure mechanism. In plates with smaller hole sizes, failure initiates away from the hole edge or complete global failure occurs. Critical buckle wavelengths at failure are presented as a function of the normalized hole diameter.

  12. Failure mechanisms of composite plates with a circular hole under remote biaxial planar compressive loads

    SciTech Connect

    Khamseh, A.R.; Waas, A.M.

    1997-01-01

    The authors report the results of an experimental investigation carried out for the analysis of failure mechanisms in fibrous laminated composite plates containing stress raisers, in the form of circular cutouts, under static biaxial planar compressive loading (i.e., compression in the two inplane orthogonal directions). A series of biaxial tests were carried out with 48 ply graphite/epoxy composites of varying fiber orientation. In all cases, the hole diameter to plate with aspect ratio remained in a range suitable for infinite plate assumptions. Fiber microbuckling, fiber kink banding, and fiber/matrix debonding are identified as the dominant failure mechanisms.

  13. The influence of low-temperature degradation and cyclic loading on the fracture resistance of monolithic zirconia molar crowns.

    PubMed

    Nakamura, K; Harada, A; Kanno, T; Inagaki, R; Niwano, Y; Milleding, P; Örtengren, U

    2015-07-01

    The present study analyzed the kinetics of low-temperature degradation (LTD) in zirconia, and evaluated the influence of LTD and cyclic loading on the fracture resistance of monolithic zirconia molar crowns. Bar-shaped zirconia specimens were divided into nine groups and autoclaved at 134°C for 0-200h to induce LTD. The surface fraction and penetration depth of the monoclinic phase were examined using X-ray diffraction and scanning electron microscopy. Monolithic zirconia molar crowns were prepared for crown fracture testing. The crowns were autoclaved for 0-100h (n=6) and cemented to dies. Six crown-die samples that were not autoclaved and six samples that were autoclaved for 100h were subjected to cyclic loading with a load of 300N for 240,000 cycles. All samples were tested in a load-to-failure test. The monoclinic fraction on the surface increased with autoclaving time and reached a plateau after 50h. The depth of the monoclinic phase increased without reaching a plateau. The fracture load of the crowns significantly decreased from 5683N (SD: 342) to 3975N (SD: 194) after 100h of autoclaving. Cyclic loading did not significantly affect the fracture resistance of the crowns in all cases. Kinetic analysis showed no linear correlation between the surface fraction and depth of the monoclinic phase after 50h of autoclaving. Even though LTD increased the monoclinic phase, resulting in lower strength, the fracture resistance of the monolithic zirconia crowns was still sufficient to withstand the loading conditions in the molar regions.

  14. Evaluation of a Compression-Loaded-Stitched-Multi-Bay Fuselage Panel With Barely Visible Impact Damage

    NASA Technical Reports Server (NTRS)

    Baker, Donald J.; Li, Ji-An

    2005-01-01

    The experimental results from a stitched VaRTM carbon-epoxy composite panel tested under uni-axial compression loading are presented along with nonlinear finite element analysis prediction of the response. The curved panel is divided by frames and stringers into six bays with a column of three bays along the compressive loading direction. The frames are supported at the frame ends to resist out-of-plane translation. Back-to-back strain gages are used to record the strain and displacement transducers were used to record the out-of-plane displacements. In addition a full-field-displacement measurement technique that utilizes a camera-based-stereo-vision system was used to record the displacements. The panel was loaded to 1.5 times the predicted initial buckling load (1st bay buckling load, P(sub er) from the nonlinear finite element analysis and then was removed from the test machine for impact testing. After impacting with 20 ft-lbs of energy using a spherical impactor to produce barely visible damage the panel was loaded in compression until failure. The buckling load of the first bay to buckle was 97% of the buckling load before impact. The stitching constrained the impact damage from growing during the loading to failure. Impact damage had very little overall effect on panel stiffness. Panel stiffness measured by the full-field-displacement technique indicated a 13% loss in stiffness after impact. The panel failed at 1.64 times the first panel buckling load. The barely visible impact damage did not grow noticeably as the panel failed by global instability due to stringer-web terminations at the frame locations. The predictions from the nonlinear analysis of the finite element modeling of the entire specimen were very effective in the capture of the initial buckling and global behavior of the panel. In addition, the prediction highlighted the weakness of the panel under compression due to stringer web terminations. Both the test results and the nonlinear

  15. Pro-inflammatory cytokines expression increases following low- and high-magnitude cyclic loading of lumbar ligaments

    PubMed Central

    D’Ambrosia, Peter; King, Karen; Davidson, Bradley; Zhou, Bing He; Lu, Yun

    2010-01-01

    Repetitive or overuse disorders of the lumbar spine affect the lives of workers and athletes. We hypothesize that repetitive anterior lumbar flexion–extension under low or high load will result in significantly elevated pro-inflammatory cytokines expression several hours post-activity. High loads will exhibit significantly higher expression than low loads. Lumbar spine of in vivo feline was subjected to cyclic loading at 0.25 Hz for six 10-min periods with 10 min of rest in between. One group was subjected to a low peak load of 20 N, whereas the second group to a high peak load of 60 N. Following a 7-h post-loading rest, the supraspinous ligaments of L-3/4, L-4/5 and L-5/6 and the unstimulated T-10/11 were excised for mRNA analysis and IL-1β, IL-6, IL-8, TNFα and TGFβ1 pro-inflammatory cytokines expression. Creep (laxity) developed in the lumbar spine during the loading and the subsequent 7 h of rest was calculated. A two-way mixed model ANOVA was used to assess difference in each cytokines expression between the two groups and control. Tukey HSD post hoc analysis delineated specific significant effects. Significance was set at 0.05. Low and high-load groups exhibited development of creep throughout the cyclic loading period and gradual recovery throughout the 7-h rest period. Residual creep of 24.8 and 30.2% were present in the low and high-load groups, respectively, 7-h post-loading. Significant increases in expression of all cytokines measured relative to control were obtained for supraspinous ligaments from both low and high-load magnitudes. IL-6, IL-8 and TGFβ1 expression in the high-load group were significantly higher relative to the low-load group. Significant increases in cytokines expression indicating tissue inflammation are observed several hours post-repetitive lumbar flexion–extension regardless of the load magnitude applied. Repetitive occupational and athletic activity, regardless of the load applied, may be associated with the

  16. Intervertebral disc responses during spinal loading with MRI-compatible spinal compression apparatus

    NASA Astrophysics Data System (ADS)

    Mitsui, Iwane; Yamada, Yoshiya

    2004-07-01

    This study addresses the development of an MRI-compatible spinal compression harness for use as a research and diagnostic tool. This apparatus adds valuable information to MRI imaging regarding the physiology/biomechanics of intervertebral discs and pathophysiology of back pain in patients and astronauts in space. All materials of the spinal compression apparatus are non-metallic for MRI compatibility. The compact design fits into standard MRI or CT scanners and loading is adjusted to specific percentages of BW with elastic cords. Previously this capability has not been available. Three healthy male subjects were fitted with a spinal compression harness and placed supine in a MRI scanner. Longitudinal distance between T7/8 and L5/S1 discs decreased 5.6 mm with 50% BW compression. Lumbosacral angle increased 17.2 degrees. T2 values of nucleus pulposus from L1/2 to L5/S1 discs increased 18.2+/-6.1% (+/-SD) during 50% BW compression and 25.3+/-7.4% (+/-SD) during 75% BW compression.

  17. Failure of woven carbon-polyimide laminates under off-axis compression loading

    SciTech Connect

    Gupta, V.; Anand, K.; Grape, J.

    1998-01-05

    This paper reports the failure mechanisms in a woven 0/90 carbon-polyimide laminate under 45{degree} off-axis compression loading. The stress carried by the composite increased linearly with increasing levels of applied displacements and, at about 188 MPa, the load dropped suddenly to 172 MPa and remained constant thereafter till about 8.9% strain, at which point the load reduced drastically and resulted in the ultimate failure of the sample. The damage started with the nucleation of several in-plane cracks which split both the wrap and fill yarns completely, and ran diagonally across the sample`s entire width. Upon further loading, the cracking progressed in bundles towards the sample`s interior, and eventually, at a strain of about 5%, a saturation cracking state was reached with each bundle split by at least three-to-four longitudinal cracks. The sample was able to accommodate further strain via nucleation of additional cracks formed at the edges of the longitudinal cracks with their planes parallel to the loading axis and orthogonal to those occupied by the longitudinal cracks. Essentially, these new cracks separated the longitudinally-split bundles in the sample`s thickness direction and resulted in the creation of three-to-four independent bundles from the original well-bonded warp or fill bundle. At this stage, the compressive load carrying capacity of the original bundle was largely compromised and the sample failed through gross delaminations, resulting in the bulging of the sample normal to its largest faces. The above deformation was remarkably different from that observed under bundle-aligned compression loading where the samples failed at an average stress of 588 MPa in more or less brittle catastrophic manner after undergoing only 1.5% strain.

  18. a Study of the Shock Sensitivity of PBX 9501 Damaged by Compressive Loading

    NASA Astrophysics Data System (ADS)

    Thompson, D. G.; Gustavsen, R. L.; Hooks, D. E.; Peterson, P. D.; DeLuca, R.; Stahl, D. B.; Hagelberg, S. I.; Alcon, R. R.

    2007-12-01

    We have studied the effects of damage caused by compressive loading on the shock sensitivity of the plastic bonded explosive PBX 9501. PBX 9501 consists of 95 wt. % HMX and 5 wt. % nitroplasticized Estane binder. The binder is a mixture of 49 wt. % Estane® 5703 (BF Goodrich), 49 wt. % Nitroplasticizer (a eutectic mixture of bis(2,2-dinitropropyl)formal and bis(2,2 dinitropropyl)acetal), and 2 wt. % Irganox® 1010 stabilizer. PBX 9501 cubes, 25.4 mm on a side, were compressed to various uniaxial loads in an Instron machine. After loading, 10×10 mm cross-sections, 3.5 mm thick, were taken from the center of each cube. These slices were then subjected to nearly identical 35 kbar shocks. Transmitted shock wave profiles were measured using interface velocimetry (VISAR). Comparison of shock wave growth is a measure of shock sensitivity. Results on four samples indicate little change in sensitivity caused by compressive loading.

  19. Experimental research on behavior of 460 MPa high strength steel I-section columns under cyclic loading

    NASA Astrophysics Data System (ADS)

    Wang, Jiaojiao; Shi, Gang; Shi, Yongjiu

    2014-12-01

    To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel (HSS), six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.

  20. Effects of saline loading during head down tilt on ANP and cyclic GMP levels and on urinary fluid excretion

    NASA Astrophysics Data System (ADS)

    Drummer, C.; Lang, R. E.; Baisch, F.; Blomqvist, G.; Heer, M.; Gerzer, R.

    In the present study the renal and humoral effects of acute saline infusions were investigated in six healthy male volunteers before, during and after a ten day period of -6° head-down-tilt (HDT). During the whole 23-day study period the subjects received a standardized diet including 40 ml water and 125 mg NaCl per kg body weight per day. After the infusion of 0.9% saline (22 ml/kg within 20 minutes) plasma atrial natriuretic peptide (ANP) levels were only slightly increased (not significant) at the end of the infusion, while plasma cyclic GMP levels were significantly increased by about 40% (p<0.05) one hour later. No difference was observed in the plasma ANP and cyclic GMP changes between the pre-HDT, the HDT and the post-HDT infusion experiment. Urine flow, sodium excretion and urinary cyclic GMP excretion were significantly increased (p<0.05 and below) by 100 to 300% during the second and third hour after each saline infusion. However, during these short-term periods only 20% of the infused water and less than 20% of the infused sodium were excreted. Furthermore, a significantly increased volume, sodium and cyclic GMP excretion was observed for over 48 hours after each fluid load experiment. These data suggest that HDT does not induce major alterations in the regulation of an acute saline infusion and plasma ANP does not play a major role in the diuretic/natriuretic effects of volume loading.

  1. Polycrystal plasticity modeling of nickel-based superalloy IN 617 subjected to cyclic loading at high temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang; Oskay, Caglar

    2016-06-01

    A crystal plasticity finite element (CPFE) model considering isothermal, large deformation and cyclic loading conditions has been formulated and employed to investigate the mechanical response of a nickel-based alloy at high temperature. The investigations focus on fatigue and creep-fatigue hysteresis response of IN 617 subjected to fatigue and creep-fatigue cycles. A new slip resistance evolution equation is proposed to account for cyclic transient features induced by solute drag creep that occur in IN 617 at 950 °C. The crystal plasticity model parameters are calibrated against the experimental fatigue and creep-fatigue data based on an optimization procedure that relies on a surrogate modeling (i.e. Gaussian process) technique to accelerate multi-parameter optimizations. The model predictions are validated against experimental data, which demonstrates the capability of the proposed model in capturing the hysteresis behavior for various hold times and strain ranges in the context of fatigue and creep-fatigue loading.

  2. The Effects of Geometric and Loading Imperfections on the Response and Lower-Bound Buckling Load of a Compression-Loaded Cylindrical Shell

    NASA Technical Reports Server (NTRS)

    Kriegesmann, Benedikt; Hilburger, Mark W.; Rolfes, Raimund

    2012-01-01

    Results from a numerical study of the buckling response of a thin-walled compressionloaded isotropic circular cylindrical shell with initial geometric and loading imperfections are used to determine a lower bound buckling load estimate suitable for preliminary design. The lower bound prediction techniques presented herein include an imperfection caused by a lateral perturbation load, an imperfection in the shape of a single stress-free dimple (similar to the lateral pertubation imperfection), and a distributed load imperfection that induces a nonuniform load in the shell. The ABAQUS finite element code is used for the analyses. Responses of the cylinders for selected imperfection amplitudes and imperfection types are considered, and the effect of each imperfection is compared to the response of a geometrically perfect cylinder. The results indicate that compression-loaded shells subjected to a lateral perturbation load or a single dimple imperfection, and a nonuniform load imperfection, exhibit similar buckling behavior and lower bound trends and the predicted lower bounds are much less conservative than the corresponding design recommendation NASA SP-8007 for the design of buckling-critical shells. In addition, the lateral perturbation technique and the distributed load imperfection produce response characteristics that are physically meaningful and can be validated via laboratory testing.

  3. Relined Fiberglass Post: Effect of Luting Length, Resin Cement, and Cyclic Loading on the Bond to Weakened Root Dentin.

    PubMed

    de Souza, N C; Marcondes, M L; da Silva, Dff; Borges, G A; Júnior, Lh Burnett; Spohr, A M

    This study evaluated the effects of luting length of the post, the resin cement, and cyclic loading on pull-out bond strength of fiberglass posts relined with composite resin in weakened roots. The canals of 80 bovine incisors were endodontically treated and weakened with diamond burs. The teeth were randomly divided into eight groups (n=10) according to the luting procedures of the relined fiberglass post (RFP): In groups 1, 2, 3, and 4, the RFPs were luted with RelyX ARC, and in groups 5, 6, 7, and 8 they were luted with RelyX U200. In groups 1, 3, 5, and 7, the RFPs were luted at a length of 5 mm, and in groups 2, 4, 6, and 8 they were luted at a length of 10 mm. Specimens from groups 3, 4, 7, and 8 were submitted to cyclic loading. Specimens were subjected to a pull-out bond strength test in a universal testing machine. The results (MPa) were analyzed by three-way analysis of variance and the Tukey post hoc test (α=0.05). Six human upper anterior teeth were used to analyze the bond interface by confocal laser scanning microscopy (CLSM). The pull-out bond strength of RFPs luted with RelyX U200 was statistically higher than that of RelyX ARC. Cyclic loading influenced the bond strength only for the luting length of 5 mm. CLSM analysis revealed the formation of resin cement tags for both materials. Luting length is an important factor in retaining RFPs in weakened roots when they are subjected to cyclic loading, and RelyX U200 resulted in greater bond strengths to the root canal in comparison with RelyX ARC.

  4. Damage Characteristics and Residual Strength of Composite Sandwich Panels Impacted with and Without Compression Loading

    NASA Technical Reports Server (NTRS)

    McGowan, David M.; Ambur, Damodar R.

    1998-01-01

    The results of an experimental study of the impact damage characteristics and residual strength of composite sandwich panels impacted with and without a compression loading are presented. Results of impact damage screening tests conducted to identify the impact-energy levels at which damage initiates and at which barely visible impact damage occurs in the impacted facesheet are discussed. Parametric effects studied in these tests include the impactor diameter, dropped-weight versus airgun-launched impactors, and the effect of the location of the impact site with respect to the panel boundaries. Residual strength results of panels tested in compression after impact are presented and compared with results of panels that are subjected to a compressive preload prior to being impacted.

  5. Fibrocartilage in tendons and ligaments — an adaptation to compressive load

    PubMed Central

    BENJAMIN, M.; RALPHS, J. R.

    1998-01-01

    Where tendons and ligaments are subject to compression, they are frequently fibrocartilaginous. This occurs at 2 principal sites: where tendons (and sometimes ligaments) wrap around bony or fibrous pulleys, and in the region where they attach to bone, i.e. at their entheses. Wrap-around tendons are most characteristic of the limbs and are commonly wider at their point of bony contact so that the pressure is reduced. The most fibrocartilaginous tendons are heavily loaded and permanently bent around their pulleys. There is often pronounced interweaving of collagen fibres that prevents the tendons from splaying apart under compression. The fibrocartilage can be located within fascicles, or in endo- or epitenon (where it may protect blood vessels from compression or allow fascicles to slide). Fibrocartilage cells are commonly packed with intermediate filaments which could be involved in transducing mechanical load. The ECM often contains aggrecan which allows the tendon to imbibe water and withstand compression. Type II collagen may also be present, particularly in tendons that are heavily loaded. Fibrocartilage is a dynamic tissue that disappears when the tendons are rerouted surgically and can be maintained in vitro when discs of tendon are compressed. Finite element analyses provide a good correlation between its distribution and levels of compressive stress, but at some locations fibrocartilage is a sign of pathology. Enthesis fibrocartilage is most typical of tendons or ligaments that attach to the epiphyses of long bones where it may also be accompanied by sesamoid and periosteal fibrocartilages. It is characteristic of sites where the angle of attachment changes throughout the range of joint movement and it reduces wear and tear by dissipating stress concentration at the bony interface. There is a good correlation between the distribution of fibrocartilage within an enthesis and the levels of compressive stress. The complex interlocking between calcified

  6. Force response of the fingertip pulp to repeated compression--effects of loading rate, loading angle and anthropometry.

    PubMed

    Serina, E R; Mote, C D; Rempel, D

    1997-10-01

    Repeated loading of the fingertips has been postulated to contribute to tendon and nerve disorders at the wrist during activities associated with prolonged fingertip loading such as typing. To fully understand the pathomechanics of these soft tissue disorders, the role of the fingertip pulp in attenuating the applied dynamic forces must be known. An experiment was conducted to characterize the response of the in vivo fingertip pulp under repeated, dynamic, compressive loadings, to identify factors that influence pulp dynamics, and to better understand the force modulation by the pulp. Twenty subjects tapped repeatedly on a flat plate with their left index finger, while the contact force and pulp displacement were measured simultaneously. Tapping trials were conducted at three fingertip contact angles from the horizontal plane (0 degree, 45 degrees, and 90 degrees) and five tapping rates (0.25, 0.5, 1, 2, and 3 Hz). The fingertip pulp responds as a viscoelastic material, exhibiting rate-dependence, hysteresis, and a nonlinear force-displacement relationship. The pulp was relatively compliant at forces less than 1 N, but stiffened rapidly with displacement at higher forces for all loading conditions. This suggests that high-frequency forces of a small magnitude (< 1 N) are attenuated by the nonlinearly stiffening pulp while these forces of larger magnitude are transmitted to the bone. Pulp response was significantly influenced by the angle of loading. Fingertip dimensions, gender, and subject age had little to no influence on pulp parameters.

  7. Effect of chlorhexidine and ethanol on push-out bond strength of fiber posts under cyclic loading.

    PubMed

    Cecchin, Doglas; Giacomin, Mateus; Farina, Ana Paula; Bhering, Cláudia Lopes; Mesquita, Marcelo Ferraz; Ferraz, Caio Cezar

    2014-02-01

    To investigate the effects of pretreatment with 2% chlorhexidine in a gel base (CHX) and 100% ethanol (EtOH) on the bond strength between fiber posts relined with resin composite and root dentin under cyclic loading. Forty bovine incisor roots were divided into four groups after phosphoric acid etching: group 1 (control), irrigation with physiological saline solution; group 2, 5 min pretreatment with CHX; group 3, 1 min pretreatment with EtOH; group 4, 5 min pretreatment with CHX followed by 1 min with EtOH. Fiber posts relined with resin composite were cemented with RelyX ARC and the etch-and-rinse adhesive system Scotchbond Multi-Purpose. Each group was randomly divided into two subgroups: 24 h of storage (immediate groups) and cyclic loading (loading groups) with 250,000 cycles in a controlled chewing simulator. All roots were sectioned transversely and push-out tests were performed. Failure modes were observed and the bond strength means were analyzed using ANOVA and Tukey's test (a = 0.05). The mean values for the bond strength test (MPa) in immediate groups were: group 1, 5.44 ± 1.48; group 2, 5.57 ± 1.41; group 3, 5.49 ± 1.48; group 4, 5.57 ± 1.42. Immediate groups showed similar bond strength values (p > 0.05). In the cyclic loading groups, the bond strength values were: group 1, 2.80 ± 0.79; group 2, 4.02 (1.30); group 3, 4.50 ± 1.67; group 4, 4.97 ± 2.00. After cyclic loading, a significant decrease in the control group was observed (p < 0.05), while CHX pretreatment resulted in intermediate values (p < 0.05) and EtOH alone or associated with CHX preserved the bond strength values (p > 0.05). Chlorhexidine and/or ethanol pretreatment preserved the bond strength of the fiber post after cyclic loading.

  8. Bonding of flowable resin composite restorations to class 1 occlusal cavities with and without cyclic load stress.

    PubMed

    Kawai, Takatoshi; Maseki, Toshio; Nara, Yoichiro

    2016-01-01

    To examine the bonding of flowable resin composite restorations (F-restoration) to class 1 occlusal cavities with and without cyclic load stress, compared with that of a universal resin composite restoration (U-restoration). Two flowable composites and one universal composite (control) were applied with an adhesive system to 42 standardized class 1 occlusal cavities. The restored specimens were subjected to cyclic load stress and no stress modes. The microtensile bond strength (μ-TBS) of the dentin floor was measured. The U-restoration did not show pretesting failure. The F-restorations exhibited pretesting failure, regardless of the stress mode. The μ-TBS was not significantly different among the three restorations, regardless of the stress mode. The cyclic load stress did not influence the μ-TBS of the F-restorations; however, it significantly reduced μ-TBS in the U-restoration. The bonding reliability of the F-restorations was inferior to that of the U-restoration, for both stress modes.

  9. Uniaxial and triaxial compression tests of silicon carbide ceramics under quasi-static loading condition.

    SciTech Connect

    Brannon, Rebecca Moss; Lee, Moo Yul; Bronowski, David R.

    2005-02-01

    To establish mechanical properties and failure criteria of silicon carbide (SiC-N) ceramics, a series of quasi-static compression tests has been completed using a high-pressure vessel and a unique sample alignment jig. This report summarizes the test methods, set-up, relevant observations, and results from the constitutive experimental efforts. Results from the uniaxial and triaxial compression tests established the failure threshold for the SiC-N ceramics in terms of stress invariants (I{sub 1} and J{sub 2}) over the range 1246 < I{sub 1} < 2405. In this range, results are fitted to the following limit function (Fossum and Brannon, 2004) {radical}J{sub 2}(MPa) = a{sub 1} - a{sub 3}e -a{sub 2}(I{sub 1}/3) + a{sub 4} I{sub 1}/3, where a{sub 1} = 10181 MPa, a{sub 2} = 4.2 x 10{sup -4}, a{sub 3} = 11372 MPa, and a{sub 4} = 1.046. Combining these quasistatic triaxial compression strength measurements with existing data at higher pressures naturally results in different values for the least-squares fit to this function, appropriate over a broader pressure range. These triaxial compression tests are significant because they constitute the first successful measurements of SiC-N compressive strength under quasistatic conditions. Having an unconfined compressive strength of {approx}3800 MPa, SiC-N has been heretofore tested only under dynamic conditions to achieve a sufficiently large load to induce failure. Obtaining reliable quasi-static strength measurements has required design of a special alignment jig and load-spreader assembly, as well as redundant gages to ensure alignment. When considered in combination with existing dynamic strength measurements, these data significantly advance the characterization of pressure-dependence of strength, which is important for penetration simulations where failed regions are often at lower pressures than intact regions.

  10. Buckling and Failure of Compression-Loaded Composite Laminated Shells With Cutouts

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.

    2007-01-01

    Results from a numerical and experimental study that illustrate the effects of laminate orthotropy on the buckling and failure response of compression-loaded composite cylindrical shells with a cutout are presented. The effects of orthotropy on the overall response of compression-loaded shells is described. In general, preliminary numerical results appear to accurately predict the buckling and failure characteristics of the shell considered herein. In particular, some of the shells exhibit stable post-local-buckling behavior accompanied by interlaminar material failures near the free edges of the cutout. In contrast another shell with a different laminate stacking sequence appears to exhibit catastrophic interlaminar material failure at the onset of local buckling near the cutout and this behavior correlates well with corresponding experimental results.

  11. Damage Progression in Buckle-Resistant Notched Composite Plates Loaded in Uniaxial Compression

    NASA Technical Reports Server (NTRS)

    McGowan, David M.; Davila, Carlos G.; Ambur, Damodar R.

    2001-01-01

    Results of an experimental and analytical evaluation of damage progression in three stitched composite plates containing an angled central notch and subjected to compression loading are presented. Parametric studies were conducted systematically to identify the relative effects of the material strength parameters on damage initiation and growth. Comparisons with experiments were conducted to determine the appropriate in situ values of strengths for progressive failure analysis. These parametric studies indicated that the in situ value of the fiber buckling strength is the most important parameter in the prediction of damage initiation and growth in these notched composite plates. Analyses of the damage progression in the notched, compression-loaded plates were conducted using in situ material strengths. Comparisons of results obtained from these analyses with experimental results for displacements and axial strains show good agreement.

  12. Origin of compression-induced failure in brittle solids under shock loading

    NASA Astrophysics Data System (ADS)

    Huang, J. Y.; Li, Y.; Liu, Q. C.; Zhou, X. M.; Liu, L. W.; Liu, C. L.; Zhu, M. H.; Luo, S. N.

    2015-10-01

    The origin of compression-induced failure in brittle solids has been a subject of debate. Using in situ, high-speed, strain field mapping of a representative material, polymethylmethacrylate, we reveal that shock loading leads to heterogeneity in a compressive strain field, which in turn gives rise to localized lateral tension and shear through Poisson's effects, and, subsequently, localized microdamage. A failure wave nucleates from the impact surface and its propagation into the microdamage zone is self-sustained, triggering interior failure. Its velocity increases with increasing shock strength and eventually approaches the shock velocity. The seemingly puzzling phenomena observed in previous experiments, including incubation time, failure wave velocity variations, and surface roughness effects, can all be explained consistently with the nucleation and growth of the microdamage, and the effects of loading strength and preexisting defects.

  13. Closed-form solution of the Ogden-Hill's compressible hyperelastic model for ramp loading

    NASA Astrophysics Data System (ADS)

    Berezvai, Szabolcs; Kossa, Attila

    2017-05-01

    This article deals with the visco-hyperelastic modelling approach for compressible polymer foam materials. Polymer foams can exhibit large elastic strains and displacements in case of volumetric compression. In addition, they often show significant rate-dependent properties. This material behaviour can be accurately modelled using the visco-hyperelastic approach, in which the large strain viscoelastic description is combined with the rate-independent hyperelastic material model. In case of polymer foams, the most widely used compressible hyperelastic material model, the so-called Ogden-Hill's model, was applied, which is implemented in the commercial finite element (FE) software Abaqus. The visco-hyperelastic model is defined in hereditary integral form, therefore, obtaining a closed-form solution for the stress is not a trivial task. However, the parameter-fitting procedure could be much faster and accurate if closed-form solution exists. In this contribution, exact stress solutions are derived in case of uniaxial, biaxial and volumetric compression loading cases using ramp-loading history. The analytical stress solutions are compared with the stress results in Abaqus using FE analysis. In order to highlight the benefits of the analytical closed-form solution during the parameter-fitting process experimental work has been carried out on a particular open-cell memory foam material. The results of the material identification process shows significant accuracy improvement in the fitting procedure by applying the derived analytical solutions compared to the so-called separated approach applied in the engineering practice.

  14. Buckling and postbuckling behavior of square compression-loaded graphite-epoxy plates with circular cutouts

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1989-01-01

    The postbuckling behavior of square compression-loaded graphite-epoxy plates and isotropic plates with a central circular cutout is studied. The results suggest that the change in the plate's axial stiffness is strongly dependent on cutout size and plate orthotropy. It is found that the cutout size and stacking sequence of a composite plate may be tailored to optimize postbuckling stiffness. Also, it is suggested that a cutout may influence model interaction in a plate. The effects of load-path eccentricity on buckling behavior are examined.

  15. Prediction of the critical buckling load of multi-walled carbon nanotubes under axial compression

    NASA Astrophysics Data System (ADS)

    Timesli, Abdelaziz; Braikat, Bouazza; Jamal, Mohammad; Damil, Noureddine

    2017-02-01

    In this paper, we propose a new explicit analytical formula of the critical buckling load of double-walled carbon nanotubes (DWCNT) under axial compression. This formula takes into account van der Waals interactions between adjacent tubes and the effect of terms involving tube radii differences generally neglected in the derived expressions of the critical buckling load published in the literature. The elastic multiple Donnell shells continuum approach is employed for modelling the multi-walled carbon nanotubes. The validation of the proposed formula is made by comparison with a numerical solution. The influence of the neglected terms is also studied.

  16. Evaluation of Composite Honeycomb Sandwich Panels Under Compressive Loads at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Walker, Sandra P.

    1998-01-01

    Fourteen composite honeycomb sandwich panels were tested to failure under compressive loading. The test specimens included panels with both 8 and 24-ply graphite-bismaleimide composite facesheets and both titanium and graphite-polyimide core materials. The panels were designed to have the load introduced through fasteners attached to pairs of steel angles on the ends of the panels to simulate double shear splice joints. The unloaded edges were unconstrained. Test temperatures included room temperature, 250F, and 300F. For the room and 250F temperature tests, the 24-ply specimen failure strains were close to the unnotched allowable strain values and failure loads were well above the design loads. However, failure strains much lower than the unnotched allowable strain values, and failure loads below the design loads were observed with several of the 8-ply specimens. For each individual test temperature, large variations in the failure strains and loads were observed for the 8-ply specimens. Dramatic decreases in the failure strains and loads were observed for the 24-ply specimens as the test temperature was increased from 250F to 300F. All 8-ply specimens appeared to have failed in a facesheet strength failure mode for all test temperatures. The 24-ply specimens displayed appreciably greater amounts of bending prior to failure than the 8-ply specimens, and panel buckling occurred prior to facesheet strength failure for the 24-ply room and 250F temperature tests.

  17. Isentropic Compression Loading of HMX and the Pressure-induced Phase Transition at 27 GPa

    SciTech Connect

    Hare, D E; Reisman, D B; Dick, J J; Forbes, J W

    2004-02-25

    The 27 GPa pressure-induced epsilon-phi phase transition in HMX is explored using the Isentropic Compression Experiment (ICE) technique at the Sandia National Laboratories Z-machine facility. Our data indicate that this phase transition is sluggish and if it does occur to any extent under the time scales (200-500 ns) and strain rates (5 x 10{sup 5}) typical of ICE loading conditions, the amount of conversion is small.

  18. Effects of specimen size on limiting compressive loading for silicate, ceramic, and other materials

    SciTech Connect

    Okhrimenko, G.M.

    1995-06-01

    Published data are examined on the ultimate strength in uniaxial compression for glass, glass ceramics, porcelain, crystalline silicon, periclase - spinel - chromite material PSCM, and ferrite in relation to the specimen dimensions. Two methods are proposed for combined experimental and computational estimation of the effects from the volume on the limiting load, which are based only on the data obtained from testing specimens with one or two standard dimensions.

  19. Dry plant extracts loaded on fumed silica for direct compression: preparation and preformulation.

    PubMed

    Palma, S D; Manzo, R H; Allemandi, D A

    1999-01-01

    This paper describes the development of a method to load fumed silica with vegetal material (solid residue) from a liquid extract to obtain a solid loaded silica product (LSP) with satisfactory flow properties and compressibility to be processed by direct-compression technology. Extracts of Melissa officinalis L. (M.o.), Cardus marianus L. (C.m.), and Peumus boldus L. (P.b.) were used to load silica support. The release of boldine from LSP (P.b.) reached 100% in HCl 0.1 N solution and only approximately 70% in water. Some physical-mechanical properties of LSP (M.o. and C.m.) alone and LSP-excipient mixtures were determined. The densities (bulk and tap) of LSP were higher than those of fumed silica alone. Consequently, good flow properties of LSP products were observed. On the other hand, flowability, densities, and compactibility of directly compressible excipients (lactose, dicalcium phosphate dihydrate, and microcrystalline cellulose) were not adversely affected when mixed with LSP.

  20. Cyclic Compressive Stress Regulates Apoptosis in Rat Osteoblasts: Involvement of PI3K/Akt and JNK MAPK Signaling Pathways

    PubMed Central

    Jiang, Dawei; Wang, Tianchen; Zhang, Yinquan; Ma, Hui

    2016-01-01

    It is widely accepted that physiological mechanical stimulation suppresses apoptosis and induces synthesis of extracellular matrix by osteoblasts; however, the effect of stress overloading on osteoblasts has not been fully illustrated. In the present study, we investigated the effect of cyclic compressive stress on rat osteoblasts apoptosis, using a novel liquid drop method to generate mechanical stress on osteoblast monolayers. After treatment with different levels of mechanical stress, apoptosis of osteoblasts and activations of mitogen-activated protein kinases (MAPKs) and PI3-kinase (PI3K)/Akt signaling pathways were investigated. Osteoblasts apoptosis was observed after treated with specific inhibitors prior to mechanical stimulation. Protein levels of Bax/Bcl-2/caspase-3 signaling were determined using western blot with or without inhibitors of PI3K/Akt and phosphorylation of c-jun N-terminal kinase (JNK) MAPK. Results showed that mechanical stimulation led to osteoblasts apoptosis in a dose-dependent manner and a remarkable activation of MAPKs and PI3K/Akt signaling pathways. Activation of PI3K/Akt protected against apoptosis, whereas JNK MAPK increased apoptosis via regulation of Bax/Bcl-2/caspase-3 activation. In summary, the PI3K/Akt and JNK MAPK signaling pathways played opposing roles in osteoblasts apoptosis, resulting in inhibition of apoptosis upon small-magnitude stress and increased apoptosis upon large-magnitude stress. PMID:27806136

  1. Cyclical compressive stress induces differentiation of rat primary mandibular condylar chondrocytes through phosphorylated myosin light chain II.

    PubMed

    Liu, Limin; Chen, Lin; Mai, Zhihui; Peng, Zhuli; Yu, Kafung; Liu, Guanqi; Ai, Hong

    2016-11-01

    The role of myosin light chain II (MLC‑II) in cellular differentiation of rat mandibular condylar chondrocytes (MCCs) induced by cyclical uniaxial compressive stress (CUCS) remains unclear. In the current study, a four‑point bending system was used to apply CUCS to primary cultured MCCs from rats. It was identified that CUCS stimulated features of cellular differentiation including morphological alterations, cytoskeleton rearrangement and overproduction of proteoglycans. Furthermore, CUCS promoted runt‑related transcription factor‑2 (RUNX2) expression at mRNA (P<0.01) and protein levels (P<0.05) and elevated alkaline phosphatase (ALP) activity (P<0.01), which are both markers of osteogenic differentiation. Under conditions of stress, western blotting indicated that the ratio of phosphorylated MLC‑II to total MLC‑II was increased significantly (P<0.05). Silencing MLC‑II by RNA interference reduced ALP activity (P<0.01), and eliminated RUNX2 mRNA expression (P<0.01). Addition of the MLC kinase inhibitor, ML‑7, reduced the CUCS‑associated upregulation of RUNX2 expression (P<0.01) and ALP activity (P<0.01). The data indicated that CUCS promoted cellular differentiation of rat primary MCCs, and this was suggested to be via the phosphorylation of MLC‑II.

  2. Measurements of the stress supported by the crush zone in open hole composite laminates loaded in compression

    NASA Technical Reports Server (NTRS)

    Guynn, E. Gail; Bradley, Walter L.

    1989-01-01

    Measurements of the stress supported by the crush zone in open hole specimens loaded in compression were carried out on two composite laminates, AS4/PEEK and IM6/HST-7, containing circular holes of three different diameters. Compression tests were conducted in a specially designed high-axial-alignment material test system machine. Results indicated that the local stress supported in the crush zone is much less than the stress required to initiate the crush, providing the reason for the finding of Guynn et al. (1987) that the Dugdale model does not accurately predict the load-damage size relationship of open hole composite specimens loaded in compression.

  3. The influence of veneering porcelain thickness of all-ceramic and metal ceramic crowns on failure resistance after cyclic loading.

    PubMed

    Shirakura, Akihiko; Lee, Heeje; Geminiani, Alessandro; Ercoli, Carlo; Feng, Changyong

    2009-02-01

    In some clinical situations, the length of either a prepared tooth or an implant abutment is shorter than ideal, and the thickness of a porcelain crown must be increased. Thickness of the coping and the veneering porcelain should be considered to prevent mechanical failure of the crown. The purpose of this study was to investigate the influence of veneering porcelain thickness for all-ceramic and metal ceramic crowns on failure resistance after cyclic loading. All-ceramic and metal ceramic crowns (n=20) were fabricated on an implant abutment (RN Solid Abutment) for the study. Two different framework designs with 2 different incisal thicknesses of veneering porcelain (2 mm and 4 mm) were used for each all-ceramic and metal ceramic crown system, resulting in 4 experimental groups (n=10) with identically shaped crowns. The all-ceramic crown consisted of alumina (Procera AllCeram) frameworks and veneering porcelain (Cerabien), while metal ceramic crowns were made of high noble metal (Leo) frameworks and veneering porcelain (IPS Classic). All crowns were cemented on the corresponding abutments using a resin cement (Panavia 21). They were subjected to 1000 cycles of thermal cycling (5 degrees C and 55 degrees C; 5-second dwell time). The crowns were tested with a custom-designed cyclic loading apparatus which delivered simultaneous unidirectional cyclic loading at 135 degrees, vertically, at an rpm of 250, with a load of 49 N. Each specimen was loaded for 1.2 x 106 cycles or until it failed. The specimens were thoroughly evaluated for cracks and/or bulk fracture with an optical stereomicroscope (x10) and assigned a score of success, survival, or failure. The specimens without bulk fracture after cyclic loading were loaded along the long axis of the tooth, on the incisal edge, in a universal testing machine at a crosshead speed of 1.5 mm/min, until fracture. Fisher's exact test was used to compare the success and survival rate between the 2 different materials (alpha=.05

  4. [Effect of rolling compression loading bioreactor on chondrogenesis of rabbit bone marrow mesenchymal stem cells with different loading parameters].

    PubMed

    Sun, Minglin; Zhu, Lei; Lü, Dan; Zhang, Chunqiu

    2013-01-01

    To explore the effect of rolling compression loading bioreactor on chondrogenesis of rabbit bone marrow mesenchymal stem cells (BMSCs) with different loading parameters. BMSCs were isolated from New Zealand rabbits, aged 2.5 months. BMSCs at passage 3 were used to prepare BMSCs-agarose gels (4 mm in diameter and height, respectively). Samples were divided into 8 groups: 10% (group A1), 20% (group A2), and 30% (group A3) compression groups (0.4 Hz, 3 h/d) and 20 minutes (group B1), 3 hours (group B2), and 12 hours (group B3) rolling time groups and static culture (control groups). The living cell rate, the collagen type II and Aggrecan gene expressions, and glycosaminoglycan (GAG) content were determined, and histological staining was done at 24 hours, 7 days, 14 days, and 21 days after culture. At 14 and 21 days, the living cell rates of groups A1 and A2 were significantly higher than that of group A3 (P < 0.05), groups B1 and B2 were significantly higher than group B3 (P < 0.05). Collagen type II and Aggrecan gene expressions of the experimental groups at each time point were significantly higher than those of the control groups (P < 0.05); at 14 and 21 days, collagen type II and Aggrecan gene expressions of groups A1 and A2 were significantly higher than those of group A3, and groups B1 and B2 were also significantly higher than group B3 (P < 0.05). At 14 and 21 days, the GAG contents of groups A1 and A2 were significantly higher than those of group A3 (P < 0.05); groups B1 and B2 were also significantly higher than group B3 (P < 0.05). At 21 days, toluidine blue staining showed that obvious blue-staining and even cartilage lacunae were seen in groups A2 and B2, but light and quite rare blue-staining in groups A1, A3, B1, and B3. The rolling compression loading bioreactor has great promotion effect on chondrogenesis of rabbit BMSCs with rolling parameters of 0.4 Hz, 3 hours, and 20% compression.

  5. MRI Evaluation of Spinal Length and Vertebral Body Angle During Loading with a Spinal Compression Harness

    NASA Technical Reports Server (NTRS)

    Campbell, James A.; Hargens, Alan R.; Murthy, G.; Ballard, R. E.; Watenpaugh, D. E.; Hargens, Alan, R.; Sanchez, E.; Yang, C.; Mitsui, I.; Schwandt, D.; Fechner, K. P.; Holton, Emily M. (Technical Monitor)

    1998-01-01

    Weight bearing by the spinal column during upright posture often plays a role in the common problem of low back pain. Therefore, we developed a non-ferromagnetic spinal compression harness to enable MRI investigations of the spinal column during axial loading. Human subjects were fitted with a Nest and a footplate which were connected by adjustable straps to an analog load cell. MRI scans of human subjects (5 males and 1 female with age range of 27-53 yrs) during loaded and unloaded conditions were accomplished with a 1.5 Tesla GE Signa scanner. Studies of two subjects undergoing sequentially increasing spinal loads revealed significant decreases (r(sup 2) = 0.852) in spinal length between T4 and L5 culminating in a 1.5 to 2% length decrease during loading with 75% body weight. Sagittal vertebral body angles of four subjects placed under a constant 50% body weight load for one hour demonstrated increased lordotic and kyphotic curvatures. In the lumbar spine, the L2 vertebral body experienced the greatest angular change (-3 deg. to -5 deg.) in most subjects while in the thoracic spine, T4 angles increased from the unloaded state by +2 deg. to +9 deg. Overall, our studies demonstrate: 1) a progressive, although surprisingly small, decrease in spinal length with increasing load and 2) relatively large changes in spinal column angulation with 50% body weight.

  6. MRI Evaluation of Spinal Length and Vertebral Body Angle During Loading with a Spinal Compression Harness

    NASA Technical Reports Server (NTRS)

    Campbell, James A.; Hargens, Alan R.; Murthy, G.; Ballard, R. E.; Watenpaugh, D. E.; Hargens, Alan, R.; Sanchez, E.; Yang, C.; Mitsui, I.; Schwandt, D.; hide

    1998-01-01

    Weight bearing by the spinal column during upright posture often plays a role in the common problem of low back pain. Therefore, we developed a non-ferromagnetic spinal compression harness to enable MRI investigations of the spinal column during axial loading. Human subjects were fitted with a Nest and a footplate which were connected by adjustable straps to an analog load cell. MRI scans of human subjects (5 males and 1 female with age range of 27-53 yrs) during loaded and unloaded conditions were accomplished with a 1.5 Tesla GE Signa scanner. Studies of two subjects undergoing sequentially increasing spinal loads revealed significant decreases (r(sup 2) = 0.852) in spinal length between T4 and L5 culminating in a 1.5 to 2% length decrease during loading with 75% body weight. Sagittal vertebral body angles of four subjects placed under a constant 50% body weight load for one hour demonstrated increased lordotic and kyphotic curvatures. In the lumbar spine, the L2 vertebral body experienced the greatest angular change (-3 deg. to -5 deg.) in most subjects while in the thoracic spine, T4 angles increased from the unloaded state by +2 deg. to +9 deg. Overall, our studies demonstrate: 1) a progressive, although surprisingly small, decrease in spinal length with increasing load and 2) relatively large changes in spinal column angulation with 50% body weight.

  7. Life prediction for a structural material under cyclic loads with hold times using a viscoplastic constitutive model. Final report, 1 February 1983-31 January 1984

    SciTech Connect

    Eftis, J.; Jones, D.L.

    1984-12-31

    This investigation demonstrates the ability of the Chaboche viscoplastic constitutive theory to model the behavior of Ti-6Al-4V alloy at non-elevated temperature. The range of material behavior considered includes uniaxial monotonic stress-strain primary creep, stress relaxation, kinematic and isotropic hardening (and softening) under cyclic loading with and without hold times. The six materials parameters of the viscoplastic theory were evaluated from a series of strain-controlled stabilized cyclic loading tests, and room temperature primary creep tests. The viscoplastic strain calculations were integrated into a fatigue life prediction methodology for low cycle fatigue. Two sets of low cycle fatigue life predictions were carried out and compared with experimental data. One involved strain-controlled cyclic loading without hold times, and the other stress-controlled cyclic loading with hold times. Good agreement was found between predicted and actual results.

  8. Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants

    PubMed Central

    Mohammed, Hnd Hadi; Lee, Jin-Han; Bae, Ji-Myung

    2016-01-01

    PURPOSE The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants. MATERIALS AND METHODS Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests. RESULTS The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05). CONCLUSION Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading. PMID:26949489

  9. Investigation of Anomalous Behavior in Metallic-Based Materials Under Compressive Loading

    NASA Technical Reports Server (NTRS)

    Gil, Christopher M.; Lissenden, Cliff J.; Lerch, Bradley A.

    1998-01-01

    An anomalous material response has been observed under the action of applied compressive loads in fibrous SiC/Ti (both Ti-6242 and Ti-15-3 alloys) and the monolithic nickel-base alloy IN-718 in the aged condition. The observed behavior is an increase, rather than a decrease, in the instantaneous Young's modulus with increasing load. This increase is small, but can be significant in yield surface determination tests, where an equivalent offset strain on the order of 10 micron(1 x 10(exp -6) m/m) is being used. Stiffening has been quantified by calculating offset strains from the linear elastic loading line. The offset strains associated with stiffening during compressive loading are positive and of the same order as the target offset strains in yield surface determination tests. At this time we do not have a reasonable explanation for this response nor can we identify a deformation mechanism that might cause it. On the other hand, we are not convinced that it is an artifact of the experimental procedure because a number of issues have been identified and seemingly ruled out. In fact, stiffening appears to be temperature dependent, since it decreases as the temperature increases.

  10. Effect of a circular hole on the buckling of cylindrical shells loaded by axial compression.

    NASA Technical Reports Server (NTRS)

    Starnes, J. H., Jr.

    1972-01-01

    An experimental and analytical investigation of the effect of a circular hole on the buckling of thin cylindrical shells under axial compression was carried out. The experimental results were obtained from tests performed on seamless electroformed copper shells and Mylar shells with a lap joint seam. These results indicated that the character of the shell buckling was dependent on a parameter which is proportional to the hole radius divided by the square root of the product of the shell radius and thickness. For small values of this parameter, there was no apparent effect of the hole on the buckling load. For slightly larger values of the parameter, the shells still buckled into a general collapse configuration, but the buckling loads were sharply reduced as the parameter increased. For still larger values of the parameter, the buckling loads were further reduced, and the shells buckled into a stable local buckling configuration.

  11. Design, fabrication and test of lightweight shell structure. [axial compression loads and torsion stress

    NASA Technical Reports Server (NTRS)

    Lager, J. R.

    1975-01-01

    A cylindrical shell structure 3.66 m (144 in.) high by 4.57 m (180 in.) diameter was designed using a wide variety of materials and structural concepts to withstand design ultimate combined loading 1225.8 N/cm (700 lb/in.) axial compression and 245.2 N/cm (140 lb/in.) torsion. The overall cylinder geometry and design loading are representative of that expected on a high performance space tug vehicle. The relatively low design load level results in designs that use thin gage metals and fibrous-composite laminates. Fabrication and structural tests of small panels and components representative of many of the candidate designs served to demonstrate proposed fabrication techniques and to verify design and analysis methods. Three of the designs evaluated, honeycomb sandwich with aluminum faceskins, honeycomb sandwich with graphite/epoxy faceskins, and aluminum truss with fiber-glass meteoroid protection layers, were selected for further evaluation.

  12. Observation of the initiation and progression of damage in compressively loaded composite plates containing a cutout

    NASA Technical Reports Server (NTRS)

    Waas, A.; Babcock, C., Jr.

    1986-01-01

    A series of experiments was carried out to determine the mechanism of failure in compressively loaded laminated plates with a circular cutout. Real time holographic interferometry and photomicrography are used to observe the progression of failure. These observations together with post experiment plate sectioning and deplying for interior damage observation provide useful information for modelling the failure process. It is revealed that the failure is initiated as a localised instability in the zero layers, at the hole surface. With increasing load extensive delamination cracking is observed. The progression of failure is by growth of these delaminations induced by delamination buckling. Upon reaching a critical state, catastrophic failure of the plate is observed. The levels of applied load and the rate at which these events occur depend on the plate stacking sequence.

  13. Buckling and Failure of Compression-Loaded Composite Cylindrical Shells With Geometric and Material Imperfections

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Starnes, James H., Jr.

    2004-01-01

    The results of an experimental and numerical study of the effects of initial imperfections on the buckling response and failure of unstiffened thin-walled compression-loaded graphite-epoxy cylindrical shells are presented. The shells considered in the study have six different orthotropic or quasi-isotropic shell-wall laminates and two different shell-radius-to-thickness ratios. The numerical results include the effects of geometric shell-wall mid-surface imperfections, shell-wall thickness variations, local shell-wall ply-gaps associated with the fabrication process, shell-end geometric imperfections, nonuniform end loads, and the effects of elastic boundary conditions. Selected cylinder parameter uncertainties were also considered. Results that illustrate the effects of imperfections and uncertainties on the nonlinear response characteristics, buckling loads and failure the shells are presented. In addition, a common failure analysis is used to predict material failures in the shells.

  14. Parametric Study on the Response of Compression-Loaded Composite Shells With Geometric and Material Imperfections

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Starnes, James H., Jr.

    2004-01-01

    The results of a parametric study of the effects of initial imperfections on the buckling and postbuckling response of three unstiffened thinwalled compression-loaded graphite-epoxy cylindrical shells with different orthotropic and quasi-isotropic shell-wall laminates are presented. The imperfections considered include initial geometric shell-wall midsurface imperfections, shell-wall thickness variations, local shell-wall ply-gaps associated with the fabrication process, shell-end geometric imperfections, nonuniform applied end loads, and variations in the boundary conditions including the effects of elastic boundary conditions. A high-fidelity nonlinear shell analysis procedure that accurately accounts for the effects of these imperfections on the nonlinear responses and buckling loads of the shells is described. The analysis procedure includes a nonlinear static analysis that predicts stable response characteristics of the shells and a nonlinear transient analysis that predicts unstable response characteristics.

  15. Characterization of light emission from mechanoluminescent composites subjected to high-rate compressive loading (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Ryu, Donghyeon; Castaño, Nicolas; Bhakta, Raj; Romero, Michael; Kimberley, Jamie

    2016-04-01

    This study aims to devise multifunctional composites using fracto-mechanoluminescent (FML) materials and photoactive sensing thin films for autonomous and self-powered impact damage detection. In previous studies, multifunctional photoactive thin films were suggested as a strain sensor that does not require any external electrical source. Instead, the photoactive thin films generated direct current (DC) (or photocurrent) under ambient light, whose magnitude varied linearly with applied strain. In this study, multifunctional FML materials-photoactive thin film composites will be devised for autonomously sensing high-speed compressive strains without supplying any external photonic or electrical energy. FML materials exhibit transformative properties that emit light when its crystalline structures are fractured. The developed photoactive strain sensing thin film will be integrated with the FML materials. Thus, it is envisioned that the FML materials will emit light, which will be supplied to the photoactive sensing thin films when the high-speed compressive loadings break FML materials' crystalline structures. First, synthesized europium tetrakit(dibenzoylmethide) triethylammonium (EuD4TEA) crystals will be embedded in the elastomeric and transparent polydimethylsiloxane (PDMS) matrix to prepare test specimens. Second, the FML properties of the EuD4TEA-PDMS composites will be characterized at various compressive strains, which will be applied by Kolsky bar testing setup. Light emission from the EuD4TEA-PDMS test specimens will be recorded using a high-speed camera. Intensity of the light emissions will be quantified via image processing techniques by taking into account pixel profiles of the high-speed camera captured images (e.g., pixel values, counts of pixels, and RGB values) at various levels of compressive strains. Lastly, the autonomous high-speed compressive sensor modules will be fabricated by integrating the EuD4TEA-PDMS composites with the photoactive thin

  16. Mechanical properties of the human spinal cord under the compressive loading.

    PubMed

    Karimi, Alireza; Shojaei, Ahmad; Tehrani, Pedram

    2017-07-15

    The spinal cord as the most complex and critical part of the human body is responsible for the transmission of both motor and sensory impulses between the body and the brain. Due to its pivotal role any types of physical injury in that disrupts its function following by shortfalls, including the minor motor and sensory malfunctions as well as complicate quadriplegia and lifelong ventilator dependency. In order to shed light on the injuries to the spinal cord, the application of the computational models to simulate the trauma impact loading to that are deemed required. Nonetheless, it has not been fulfilled since there is a paucity of knowledge about the mechanical properties of the spinal cord, especially the cervical one, under the compressive loading on the grounds of the difficulty in obtaining this tissue from the human body. This study was aimed at experimentally measuring the mechanical properties of the human cervical spinal cord of 24 isolated fresh samples under the unconfined compressive loading at a relatively low strain rate. The stress-strain data revealed the elastic modulus and maximum/failure stress of 40.12±6.90 and 62.26±5.02kPa, respectively. Owing to the nonlinear response of the spinal cord, the Yeoh, Ogden, and Mooney-Rivlin hyperelastic material models have also been employed. The results may have implications not only for understanding the linear elastic and nonlinear hyperelastic mechanical properties of the cervical spinal cord under the compressive loading, but also for providing a raw data for investigating the injury as a result of the trauma thru the numerical simulations. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. The Instructional Effects of Diagrams and Time-Compressed Instruction on Student Achievement and Learners' Perceptions of Cognitive Load

    ERIC Educational Resources Information Center

    Pastore, Raymond S.

    2009-01-01

    The purpose of this study was to examine the effects of visual representations and time-compressed instruction on learning and learners' perceptions of cognitive load. Time-compressed instruction refers to instruction that has been increased in speed without sacrificing quality. It was anticipated that learners would be able to gain a conceptual…

  18. The Instructional Effects of Diagrams and Time-Compressed Instruction on Student Achievement and Learners' Perceptions of Cognitive Load

    ERIC Educational Resources Information Center

    Pastore, Raymond S.

    2009-01-01

    The purpose of this study was to examine the effects of visual representations and time-compressed instruction on learning and learners' perceptions of cognitive load. Time-compressed instruction refers to instruction that has been increased in speed without sacrificing quality. It was anticipated that learners would be able to gain a conceptual…

  19. The Effects of Diagrams and Time-Compressed Instruction on Learning and Learners' Perceptions of Cognitive Load

    ERIC Educational Resources Information Center

    Pastore, Raymond S.

    2010-01-01

    The purpose of this study was to examine the effects of diagrams and time-compressed instruction on learning and learners' perceptions of cognitive load. The following design factors, visuals (visuals and non-visuals) and time-compressed instruction (0%-normal paced, 25, and 50%) were presented to 216 university students to analyze learning in a…

  20. Deformation of PEM fuel cell gas diffusion layers under compressive loading: An analytical approach

    NASA Astrophysics Data System (ADS)

    Norouzifard, Vahid; Bahrami, Majid

    2014-10-01

    In the PEM fuel cell stack, the fibrous porous gas diffusion layer (GDL) provides mechanical support for the membrane assembly against the compressive loads imposed by bipolar plates. In this study, a new mechanistic model is developed using fundamental beam theory that can accurately predict the mechanical deflection of GDL under compressive loads. The present analytical model is built on a unit cell approach, which assumes a simplified geometry for the complex and random GDL microstructure. The model includes salient microstructural parameters and properties of the fibrous porous medium including: carbon fiber diameter, fiber elastic modulus, pore size distribution, and porosity. Carbon fiber bending is proved to be the main deformation mechanism at the unit cell level. A comprehensive optical measurement study with statistical analysis is performed to determine the geometrical parameters of the model for a number of commercially available GDL samples. A comparison between the present model and our experimental stress-strain data shows a good agreement for the linear deformation region, where the compressive pressure is higher than 1 MPa.

  1. Compression-Loaded Composite Panels With Elastic Edge Restraints and Initial Prestress

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Nemeth, Michael P.; Riddick, Jaret C.; Thornburgh, Robert P.

    2005-01-01

    A parametric study of the effects of test-fixture-induced initial prestress and elastic edge restraints on the prebuckling and buckling responses of a compression-loaded, quasi-isotropic curved panel is presented. The numerical results were obtained by using a geometrically nonlinear finite element analysis code with high-fidelity models. The results presented show that a wide range of prebuckling and buckling behavior can be obtained by varying parameters that represent circumferential loaded-edge restraint and rotational unloaded-edge restraint provided by a test fixture and that represent the mismatch in specimen and test-fixture radii of curvature. For a certain range of parameters, the panels exhibit substantial nonlinear prebuckling deformations that yield buckling loads nearly twice the corresponding buckling load predicted by a traditional linear bifurcation buckling analysis for shallow curved panels. In contrast, the results show another range of parameters exist for which the nonlinear prebuckling deformations either do not exist or are relatively benign, and the panels exhibit buckling loads that are nearly equal to the corresponding linear bifurcation buckling load. Overall, the results should be of particular interest to scientists, engineers, and designers involved in simulating flight-hardware boundary conditions in structural verification and certification tests, involved in validating structural analysis tools, and interested in tailoring buckling performance.

  2. A nonlinear CDM model for ductile failure analysis of steel bridge columns under cyclic loading

    NASA Astrophysics Data System (ADS)

    Nguyen Van Do, Vuong; Lee, Chin-Hyung; Chang, Kyong-Ho

    2014-06-01

    A nonlinear cyclic plasticity damage model for ductile metals, which is able to take large deformation effects into consideration, has been developed using a new damage dissipation potential formulation in order to predict the cyclic inelastic behavior of steel bridge piers. The cyclic constitutive equations that employ the combined isotropic-kinematic hardening rule for plastic deformation is incorporated into the damage mechanics in conjunction with the large strain formulation. The damage growth law is based on the experimental observations that the evolution of microvoids results in nonlinear damage accumulation with plastic deformation. The damage model parameters and the procedure for their identification are presented. The proposed model has been validated and successfully applied to thin-walled steel bridge tubular columns subjected to alternating lateral displacements to evaluate the seismic performance.

  3. The high temperature deformation in cyclic loading of a single crystal nickel-base superalloy

    NASA Technical Reports Server (NTRS)

    Gabb, T. P.; Welsch, G.

    1989-01-01

    The high temperature cyclic stress softening response of the single crystal nickel-base superalloy PWA 1480 was investigated. Specimens oriented near the 001- and 111-lines were tested at 1050 C in low-cycle fatigue and then microstructurally evaluated. The 001- and 111-line specimens had dissimilar flow behavior in monotonic tensile tests, but comparable softening in low-cycle fatigue. This softening was accompanied by rapid generation of dislocation networks at the gamma-gamma-prime interfaces and by a slower time-dependent coarsening of gamma-prime precipitates. Due to the rapid formation of a dislocation substructure at the gamma-gamma-prime interfaces, the cyclic stress softening could be modeled with an existing theory which related cyclic stress to the evolving microstructure and dislocation structure.

  4. Study on the Aging Behaviors of Rubber Materials in Tension and Compression Loads

    NASA Astrophysics Data System (ADS)

    Jiang, Can; Wang, Hongyu; Ma, Xiaobing

    Rubber materials are widely used in aviation, aerospace, shipbuilding, automobile and other military field. However, rubber materials are easy to aging, which largely restricts its using life. In working environment, due to the combined effect of heat and oxygen, vulcanized rubber will undergo degradation and crosslinking reaction which will cause elasticity decease and permanent deformation, so mostly rubber products are used under stress state. Due to the asymmetric structure and asymmetric stress distribution, mechanical stress may cause serious damage to molecular structure; therefore, this paper is aimed to analyze the aging behavior of rubber materials under tensile and compressive loadings, through analyzing experiment data, and adopting Gauss function to describe stress relaxation coefficient, to build an aging equation containing compression ratio parameter and aging time.

  5. Residual strength of composite laminates subjected to tensile-compressive fatigue loading

    NASA Technical Reports Server (NTRS)

    Rotem, Assa; Nelson, H. G.

    1990-01-01

    Results are presented on the measurements of the residual strengths of T300/934 graphite epoxy laminates, in tension and in compression, after the samples were exposed to tension-compression fatigue loading (R = -1). Four laminate ocnfigurations were tested: unidirectional, cross-ply, angle-ply, and quasi-isotropic. It was found that the fatigue behavior of laminates was dependent on the quasi-static strengths and the specific structure of the laminate. No direct correlation was found between remaining residual strengths and the percentage of average fatigue life. However, a correlation scheme was developed for the individual specimen under test, based on a cumulative damage model and a stiffness change of the material.

  6. A potential means of using acoustic emission for crack detection under cyclic-load conditions.

    NASA Technical Reports Server (NTRS)

    Vary, A.; Klima, S. J.

    1973-01-01

    A preliminary investigation was conducted to assess the feasibility of monitoring acoustic emission signals from fatigue cracks during cyclic bend tests. Plate specimens of 6Al-4V titanium, 2219-T87 aluminum, and 18-Ni maraging steel were tested with and without crack starter notches. It was found that significant acoustic emission signals could be detected in the frequency range from 100 to 400 kHz. Cracks emanating from starter notches were monitored by the ultrasonic pulse-echo technique and periodically measured by micro-optical examination. The investigation indicated that it was possible to extract meaningful acoustic emission signals in a cyclic bend machine environment.

  7. A potential means of using acoustic emission for crack detection under cyclic-load conditions.

    NASA Technical Reports Server (NTRS)

    Vary, A.; Klima, S. J.

    1973-01-01

    A preliminary investigation was conducted to assess the feasibility of monitoring acoustic emission signals from fatigue cracks during cyclic bend tests. Plate specimens of 6Al-4V titanium, 2219-T87 aluminum, and 18-Ni maraging steel were tested with and without crack starter notches. It was found that significant acoustic emission signals could be detected in the frequency range from 100 to 400 kHz. Cracks emanating from starter notches were monitored by the ultrasonic pulse-echo technique and periodically measured by micro-optical examination. The investigation indicated that it was possible to extract meaningful acoustic emission signals in a cyclic bend machine environment.

  8. A Strip-Yield Model for Predicting the Growth of Part-Through Cracks Under Cyclic Loading

    NASA Technical Reports Server (NTRS)

    Daniewicz, S. R.; Newman, J. C., Jr. (Technical Monitor)

    2000-01-01

    Flaws exist in aircraft structures due to manufacturing operations and material defects. Under variable amplitude cyclic loading, these flaws grow as part-through cracks reducing the residual strength of structural components. To meet damage tolerant design requirements, accurate flaw growth predictions are needed which account for continual changes in crack shape as well as crack growth retardation and acceleration. Predicting the growth of part-through cracks under cyclic loading using an innovative and computationally efficient model is the focus of the research summarized in this report. In this research effort, a slice synthesis methodology was developed and used to construct a modified strip-yield model for the part-through semi-elliptical surface flaw, enabling prediction of plasticity-induced closure along the crack front and subsequent fatigue crack growth under constant amplitude and variable amplitude loading. While modeling the plasticity-induced closure in a part-through flaw may be performed using three dimensional elastic-plastic finite element analysis, this type of effort is impractical from an engineering perspective. A modified strip-yield model similar to that used in FASTRAN for part-through flaws is a much needed engineering design tool, particularly when computational resources are limited.

  9. A Study of the Shock Sensitivity of PBX 9501 Damaged by Compressive Loading

    NASA Astrophysics Data System (ADS)

    Thompson, Darla; Gustavsen, Richard; Hooks, Daniel; Peterson, Paul; Deluca, Racci; Stahl, David; Hagelberg, Stephanie; Alcon, Robert

    2007-06-01

    We have studied the effects of damage caused by compressive loading on the shock sensitivity of the plastic bonded explosive PBX 9501. PBX 9501 consists of 95 wt. % HMX (C4H8N8O8) and 5 wt. % Nitroplasticized Estane binder. The binder is a mixture of 49 wt. % Estane^5703 (BF Goodrich), 49 wt. % Nitroplasticizer (a 50/50 eutectic mixture of bis(2,2-dinitropropyl)formal and bis(2,2 dinitropropyl)acetal), and 2 wt. % Irganox^ 1010 stabilizer. PBX 9501 cubes, 25.4 mm on a side, were subjected to various uniaxial compressive loads in an Instron machine. After loading, 3.5 mm thick slices were taken from the center of each cube. These slices were then subjected to nearly identical 35 kbar shocks. Transmitted shock wave profiles were measured using interface velocimetry (VISAR). Comparison of shock wave growth is a measure of shock sensitivity. Results on four specimens are being analyzed relative to previous baseline data on PBX 9501 at various pressed densities, to determine if the response of damaged material is due to factors other than simple density changes. (LA-UR 07-1206)

  10. Static and dynamic moduli of posterior dental resin composites under compressive loading.

    PubMed

    Tanimoto, Yasuhiro; Hirayama, Satoshi; Yamaguchi, Masaru; Nishiwaki, Tsuyoshi

    2011-10-01

    Dental resin composites are commonly used as restorative materials for dental treatment. To comprehend the static and dynamic moduli of dental resin composites, we investigated the mechanical behaviors of resin composites under static and dynamic loading conditions. Four commercially available resin composites for posterior restorations were evaluated. The percentages, by weight, of inorganic fillers of resin composites were examined by the ashing technique. The static compressive tests were undertaken with a constant loading speed of 1.0 mm/min using a computer-controlled INSTRON testing machine. The dynamic properties of composites were determined using the split Hopkinson pressure bar (SHPB) technique. When inorganic filler content was increased, a remarkable increase in the static modulus and dynamic modulus were observed. Furthermore, there was a strong relationship between the static modulus and dynamic modulus (r(2) = 0.947). The SHPB technique clearly demonstrated the dynamic properties of composites, and was a useful technique for determining the mechanical behavior of composites under dynamic compressive loading. Copyright © 2011 Elsevier Ltd. All rights reserved.

  11. The Behaviour of Palm Oil Fibre Block Masonry Prism under Eccentric Compressive Loading

    NASA Astrophysics Data System (ADS)

    Mokhtar, Mardiha; Kolop, Roslan; Baizura Hamid, Nor; Kaamin, Masiri; Farhan Rosdi, Mohd; Ngadiman, Norhayati; Sahat, Suhaila

    2017-08-01

    Dry-stacked masonry offers great benefits in constructing masonry buildings. Several examples from previous research show that dry masonry is reasonable alternative to the traditional building system. By addition of fibre, the ductility and the propagation of cracking will be improved. This study investigates the dry stack oil palm fibre block prisms which were subjected to eccentricity compression loads. These concrete blocks were cast using a single mould with suitable fibre-cement composition namely 1:4 (cement: sand) and 0.40 water to the cement ratio based on cement weight. Prisms test using 400 (length) × 150 (width) × 510 (height) mm specimen was carried under eccentric load. There were forty eight (48) prisms built with different configurations based on their volume of fibre. In this study, one types of grout were used namely the fine grout of mix 1:3:2 (cement: sand: aggregate (5mm maximum). Based on the test performed, the failure mechanism and influencing parameters were discussed. From compressive strength test result, it shows that the strength of concrete block decreased with the increase of fibre used. Although the control sample has the higher strength compared to concrete with EFB, it can be seen from mode failure of masonry prism that fibre could extend the cracking time. These results show that the oil palm fibre blocks can improve the failure behaviour and suitable to be used as load bearing wall construction in Malaysia.

  12. Closed-form solution of the Ogden-Hill's compressible hyperelastic model for ramp loading

    NASA Astrophysics Data System (ADS)

    Berezvai, Szabolcs; Kossa, Attila

    2016-09-01

    This article deals with the visco-hyperelastic modelling approach for compressible polymer foam materials. Polymer foams can exhibit large elastic strains and displacements in case of volumetric compression. In addition, they often show significant rate-dependent properties. This material behaviour can be accurately modelled using the visco-hyperelastic approach, in which the large strain viscoelastic description is combined with the rate-independent hyperelastic material model. In case of polymer foams, the most widely used compressible hyperelastic material model, the so-called Ogden-Hill's model, was applied, which is implemented in the commercial finite element (FE) software uc(Abaqus). The visco-hyperelastic model is defined in hereditary integral form, therefore, obtaining a closed-form solution for the stress is not a trivial task. However, the parameter-fitting procedure could be much faster and accurate if closed-form solution exists. In this contribution, exact stress solutions are derived in case of uniaxial, biaxial and volumetric compression loading cases using ramp-loading history. The analytical stress solutions are compared with the stress results in uc(Abaqus) using FE analysis. In order to highlight the benefits of the analytical closed-form solution during the parameter-fitting process experimental work has been carried out on a particular open-cell memory foam material. The results of the material identification process shows significant accuracy improvement in the fitting procedure by applying the derived analytical solutions compared to the so-called separated approach applied in the engineering practice.

  13. Failure mechanisms in SiC-fiber reinforced 6061 aluminum alloy composites under monotonic and cyclic loading

    NASA Astrophysics Data System (ADS)

    Rao, K. T. Venkateswara; Siu, S. C.; Ritchie, R. O.

    1993-03-01

    Micromechanisms influencing crack propagation in a unidirectional SiC-fiber (SCS-8) continuously reinforced Al-Mg-Si 6061 alloy metal-matrix composite (SiCf/Al-6061) during monotonie and cyclic loading are examined at room temperature, both for the longitudinal (0 deg or L-T) and transverse (90 deg or T-L) orientations. It is found that the composite is insensitive to the presence of notches in the L-T orientation under pure tension loading due to the weak fiber/matrix interface; notched failure strengths are ˜1500 MPa compared to 124 MPa for unreinforced 6061. However, behavior is strongly dependent on loading configuration, specimen geometry, and orientation. Specifically, properties in SiCf/Al in the T-L orientation are inferior to unreinforced 6061, although the composite does exhibit increasing crack-growth resistance with crack extension (resistance-curve behavior) under monotonie loading; peak toughnesses of ˜16 MPa√m are achieved due to crack bridging by the continuous metal phase between fibers and residual plastic deformation in the crack wake. In contrast, such bridging is minimal under cyclic loading, as the ductile phase fails subcritically by fatigue such that the transverse fatigue crack-growth resistance is superior in the unreinforced alloy, particularly at high stress-intensity levels. Conversely, fatigue cracks are bridged by unbroken SiC fibers in the L-T orientation and exhibit marked crack deflection and branching; the fatigue crack-growth resistance in this orientation is clearly superior in the composite.

  14. Compressive sampling based approach for identification of moving loads distribution on cable-stayed bridges

    NASA Astrophysics Data System (ADS)

    Bao, Yuequan; Li, Hui; Zhang, Fujian; Ou, Jinping

    2013-04-01

    A moving loads distribution identification method for cable-stayed bridges based on compressive sampling (CS) technique is proposed. CS is a technique for obtaining sparse signal representations to underdetermined linear measurement equations. In this paper, CS is employed to localize moving loads of cable-stayed bridges by limit cable force measurements. First, a vehicle-bridge model for cable-stayed bridges is presented. Then the relationship between the cable force and moving loads is constructed based on the influence lines. With the hypothesis of sparsity distribution of vehicles on bridge deck (which is practical for long-span bridges), the moving loads are identified by minimizing the `l2-norm of the difference between the observed and simulated cable forces caused by moving vehicles penalized by the `l1-norm' of the moving load vector. The resultant minimization problem is convex and can be solved efficiently. A numerical example of a real cable-stayed bridge is carried out to verify the proposed method. The robustness and accuracy of the identification approach with limit cable force measurement for multi-vehicle spatial localization are validated.

  15. Buckling Of Long Compression-Loaded Anisotropic Plates Restrained Against Inplane Lateral and Shear Deformations

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    2003-01-01

    An approach for synthesizing buckling results and behavior for thin balanced and unbalanced symmetric laminates that are subjected to uniform axial compression loads and elastically restrained against inplane expansion, contraction, and shear deformation is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates (coupling between bending and twisting) that are subjected to combined mechanical loads and is based on nondimensional parameters. In addition, nondimensional loading parameters are derived that account for the effects of the elastic inplane deformation restraints, membrane orthotropy, and membrane anisotropy on the induced prebuckling stress state. The loading parameters are used to determine buckling coefficients that include the effects of flexural orthotropy and flexural anisotropy. Many results are presented, for some selected laminates, that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented and discussed in the paper. Several buckling response curves are presented that provide physical insight into the behavior for combined loads, in addition to providing useful design data. An example is presented that demonstrates the use of the generic design curves, which are applicable to a wide range of laminate constructions. The analysis approach and generic results indicate the effects and characteristics of laminate orthotropy and anisotropy in a very general and unifying manner.

  16. Influence of high pressure hydrogen on cyclic load crack growth in metals

    NASA Technical Reports Server (NTRS)

    Jewett, R. P.; Walter, R. J.; Chandler, W. T.

    1978-01-01

    The effect of high pressure hydrogen on the crack growth rate of various nickel-base alloys was studied at ambient temperature. Considerable enhancement of the cyclic flaw growth rate was observed for Inconel 718, wrought and cast, and Waspaloy, a nickel-base alloy similar to Inconel 718. Only slight enhancement of the flaw growth rate for Alloy 903 was observed.

  17. Effect of cyclic loading on the creep performance of silicon nitride

    SciTech Connect

    Wereszczak, A.A.; Ferber, M.K.; Kirkland, T.P.; Lin, C.K.J.

    1995-04-01

    Tension-tension cyclic fatigue tests (triangular waveform, {sigma}{sub max} = 100 MPa, R = 0.1) were conducted on hot isostatically pressed (HIPed) silicon nitride at frequencies spanning several orders of magnitude (5.6 {times} 10{sup {minus}6} to 0.1 Hz or 10{sup {minus}3} MPa/s to 18 MPa/s) at 1,370 C in air. The amount of cyclic creep strain was found to be a function of the frequency or stressing rate with greater strains to failure observed as the frequency or stressing rate decreased. The total strain was viewed as the sum of elastic, anelastic (or transient recoverable), and plastic (viscous or non-recoverable) strain contributions, after the empirical Pao and Marin model. The plastic strain was found to be the dominant component of the total creep and was unsatisfactorily represented by the Pao and Marin model. To circumvent this, a time exponent was introduced in the plastic strain term in the Pao and Marin model. This modification resulted in good correlation between model and experiment at the slower frequencies examined but over-predicted the cyclic creep strain at the faster frequencies. The utility of using the modified Pao and Marin model to predict cyclic creep response from static creep and strain relaxation tests is described.

  18. Can human mesenchymal stem cells survive on a NiTi implant material subjected to cyclic loading?

    PubMed

    Habijan, T; Glogowski, T; Kühn, S; Pohl, M; Wittsiepe, J; Greulich, C; Eggeler, G; Schildhauer, T A; Köller, M

    2011-06-01

    Nickel-titanium shape memory alloys (NiTi-SMAs) exhibit mechanical and chemical properties which make them attractive candidate materials for various types of biomedical applications. However, the high nickel content of NiTi-SMAs may result in adverse tissue reactions, especially when they are considered for load-bearing implants. It is generally assumed that a protective titanium oxide layer separates the metallic alloy from its environment and that this explains the good biocompatibility of NiTi. Cyclic loading may result in failure of the protective oxide layer. The scientific objective of this work was to find out whether cyclic dynamic strain, in a range relevant for orthopedic implants, diminishes the biocompatibility of NiTi-SMAs. In order to analyze the biocompatibility of NiTi-SMA surfaces subjected to cyclic loading, NiTi-SMA tensile specimens were preloaded with mesenchymal stem cells, transferred to a sterile cell culture system and fixed to the pull rods of a tensile testing machine. Eighty-six thousand and four hundred strain cycles at 2% pseudoelastic strain were performed for a period of 24 h or 7 days. Cytokines (IL-6, IL-8 and VEGF) and nickel ion release were determined within the cell culture medium. Adherent cells on the tensile specimens were stained with calcein-AM and propidium iodide to determine cell viability. Dynamic loading of the tensile specimens did not influence the viability of adherent human mesenchymal stem cells (hMSCs) after 24 h or 7 days compared with the non-strained control. Dynamic cycles of loading and unloading did not affect nickel ion release from the tensile specimens. The release of IL-6 from hMSCs cultured under dynamic conditions was significantly higher after mechanical load (873 pg ml(-1)) compared with static conditions (323 pg ml(-1)). The present work demonstrates that a new type of mechanical in vitro cell culture experiment can provide information which previously could only be obtained in large animal

  19. Effects of method of loading and specimen configuration on compressive strength of graphite/epoxy composite materials

    NASA Technical Reports Server (NTRS)

    Clark, R. K.; Lisagor, W. B.

    1980-01-01

    Three test schemes were examined for testing graphite/epoxy (Narmco T300/5208) composite material specimens to failure in compression, including an adaptation of the IITRI "wedge grip" compression fixture, a face-supported-compression fixture, and an end-loaded-coupon fixture. The effects of specimen size, specimen support arrangement and method of load transfer on compressive behavior of graphite/epoxy were investigated. Compressive stress strain, strength, and modulus data obtained with the three fixtures are presented with evaluations showing the effects of all test parameters, including fiber orientation. The IITRI fixture has the potential to provide good stress/strain data to failure for unidirectional and quasi-isotropic laminates. The face supported fixture was found to be the most desirable for testing + or - 45 s laminates.

  20. Effect of tear location on propagation of isolated supraspinatus tendon tears during increasing levels of cyclic loading.

    PubMed

    Araki, Daisuke; Miller, R Matthew; Fujimaki, Yoshimasa; Hoshino, Yuichi; Musahl, Volker; Debski, Richard E

    2015-02-18

    The morphology of the supraspinatus tendon may affect tear propagation. It was hypothesized that tears located in the anterior third of the supraspinatus tendon would propagate more readily and would require lower loads to reach critical amounts of tear propagation than those located in the middle third of the supraspinatus tendon. Twenty-three fresh-frozen human cadaveric shoulders were tested under increasing levels of cyclic loading. Tears were created in the anterior third (Group A, n=10) or the middle third (Group M, n=13) of the supraspinatus tendon. The maximum load at which a critical tear retraction was reached and the tear area for the final loading set were compared between groups. A correlation analysis was also performed for age compared with maximum load. No significant differences were found between the anterior-third tear group (Group A) and the middle-third tear group (Group M) in maximum load (p=0.09) or tear area (p=0.6). However, Group A first reached a 100% increase in tear size at a significantly lower load than Group M (p=0.03). Strong negative correlations were detected between age and maximum load in Group A (τ=-0.82) and Group M (r=-0.63). Other factors being equal, tears in the anterior supraspinatus tendon may propagate more readily than tears in the tendon's middle part. Age may be a factor for tear propagation. Older patients and patients with tears in the anterior supraspinatus should be followed especially carefully. Copyright © 2015 by The Journal of Bone and Joint Surgery, Incorporated.

  1. Identifying and Characterizing Discrepancies Between Test and Analysis Results of Compression-Loaded Panels

    NASA Technical Reports Server (NTRS)

    Thornburgh, Robert P.; Hilburger, Mark W.

    2005-01-01

    Results from a study to identify and characterize discrepancies between validation tests and high-fidelity analyses of compression-loaded panels are presented. First, potential sources of the discrepancies in both the experimental method and corresponding high-fidelity analysis models were identified. Then, a series of laboratory tests and numerical simulations were conducted to quantify the discrepancies and develop test and analysis methods to account for the discrepancies. The results indicate that the discrepancies between the validation tests and high-fidelity analyses can be attributed to imperfections in the test fixture and specimen geometry; test-fixture-induced changes in specimen geometry; and test-fixture-induced friction on the loaded edges of the test specimen. The results also show that accurate predictions of the panel response can be obtained when these specimen imperfections and edge conditions are accounted for in the analysis. The errors in the tests and analyses, and the methods used to characterize these errors are presented.

  2. Evaluation of flawed composite structural components under static and cyclic loading. [fatigue life of graphite-epoxy composite materials

    NASA Technical Reports Server (NTRS)

    Porter, T. R.

    1979-01-01

    The effects of initial defects on the fatigue and fracture response of graphite-epoxy composite laminates are presented. The structural laminates investigated were a typical angle ply laminate, a polar/hoop wound pressure vessel laminate, and a typical engine fan blade laminate. Defects investigated were full and half penetration circular holes, full and half penetration slits, and countersink holes. The effects of the defect size and type on the static fracture strength, fatigue performance, and residual static strength are shown as well as the results of loadings on damage propagation in composite laminates. The data obtained were used to define proof test levels as a qualification procedure in composite structure subjected to cyclic loading.

  3. REVERSAL CYCLIC LOADING TEST OF REINFORCED CONCRETE COLUMN WITH HIGH DENSITY LONGITUDINAL REINFORCEMENT CONFINED BY SPIRAL REINFORCEMENT

    NASA Astrophysics Data System (ADS)

    Ohba, Mitsuaki; Sato, Akiko; Ishibashi, Tadayoshi

    In case of that column diameter is restricted by the narrow construction space, Concrete filled steel tube column is used. Authors developed new arrangement of bars that the range of longitudinal reinforcement ratio is from 14.8% to 24.7% and the longitudinal reinforcements are reinforced by spiral reinforcement. For the confirmation of the damage form and the deformation performance of the column with new bar arrangement at the earthquake, static reversal cyclic loading test was carried out. The parameters are longitudinal reinforcement ratio, shear span ratio and strength ratio. As the result, the damage form showed different trends due to longitudinal reinforcement ratio, shear span ratio and flexural strength and shear strength ratio. And specimens with the new bar arrangement had a good ductility with rotation angle of the column more than 1/10 and no rapid decline of strength. And, it is possible to evaluate ultimate bending capacity by considering the damage situation at maximum load.

  4. Constitutive modeling of the rate, temperature, and hydration dependent deformation response of Nafion to monotonic and cyclic loading

    NASA Astrophysics Data System (ADS)

    Silberstein, Meredith N.; Boyce, Mary C.

    The elastic-plastic behavior of the polymer electrolyte membrane (PEM) Nafion is characterized via monotonic and cyclic uniaxial tension testing as a function of strain rate, temperature, and hydration. Dynamic mechanical analysis shows that, under dry (30%RH) conditions, the material begins to transition from the glassy to the rubbery state at 75 ° C, with a glass transition of 105 ° C. DMA reveals the fully hydrated state to be significantly more compliant than the dry state, with a glass transition beginning at 40 ° C. Large strain monotonic tensile tests find the rate-dependent stress-strain behavior to be highly dependent on temperature and hydration. The dry state transitions from an elastic-plastic behavior at 25 ° C to an increasingly more compliant behavior and lower yield stress as temperature is increased through the glass transition, until exhibiting a rubbery-like behavior at 100 ° C. At 25 ° C, the stress-strain behavior remains elastic-plastic for all hydrated states with the stiffness and yield stress decreasing with increasing hydration. Increasing hydration at all temperatures acts to decrease the initial elastic stiffness and yield stress. Unloading from different strains reveals the elastic-plastic nature of the behavior even for the elevated temperature and hydrated states. Cyclic loading-unloading-reloading excursions to different strains show significant nonlinear recovery at all strains past yield with a highly nonlinear reloading behavior which rejoins the initial loading path. A micromechanically motivated constitutive model consisting of an intermolecular resistance in parallel with an elastic network resistance is shown to be capable of capturing the rate, temperature, and hydration dependence of the monotonic stress-strain behavior. The intermolecular resistance captures the local intermolecular barriers to initial elastic deformation and also captures the thermally activated nature of yield; these intermolecular barriers are

  5. Effect of local buckling and work-hardening properties of the material on the hysteretic behavior of cantilever I-beam subjected to lateral cyclic load

    SciTech Connect

    Shaker, R.E.; Murakawa, Hidekazu; Ueda, Yukio

    1993-12-31

    The hysteretic behavior of cantilever I-beam subjected to cyclic lateral loads is investigated in this paper. Finite Element Method (FEM) considering the geometrical and material non-linearities is utilized in this study. Special attention is paid to the effects of local buckling occurring in the flanges and the web, and the material work-hardening properties on the performance of I-beam in view of a seismic design considerations. The behavior of I-beam subjected to cyclic lateral loads is closely examined with respect to the ductility, strength and absorbed energy. From this study, it is found that smaller slenderness ratios of the flange and web are recommended for improving the ductility, strength and absorbed energy. Also, the material having lower yield-to-tensile strength improves the ductility of I-beam under cyclic lateral loads as well as monotonically increasing load.

  6. Angiopoietin-like 4 promotes angiogenesis in the tendon and is increased in cyclically loaded tendon fibroblasts.

    PubMed

    Mousavizadeh, Rouhollah; Scott, Alex; Lu, Alex; Ardekani, Gholamreza S; Behzad, Hayedeh; Lundgreen, Kirsten; Ghaffari, Mazyar; McCormack, Robert G; Duronio, Vincent

    2016-06-01

    Angiopoietin-like 4 (ANGPTL4) modulates tendon neovascularization. Cyclic loading stimulates the activity of transforming growth factor-β and hypoxia-inducible factor 1α and thereby increases the expression and release of ANGPTL4 from human tendon cells. Targeting ANGPTL4 and its regulatory pathways is a potential avenue for regulating tendon vascularization to improve tendon healing or adaptation. The mechanisms that regulate angiogenic activity in injured or mechanically loaded tendons are poorly understood. The present study examined the potential role of angiopoietin-like 4 (ANGPTL4) in the angiogenic response of tendons subjected to repetitive mechanical loading or injury. Cyclic stretching of human tendon fibroblasts stimulated the expression and release of ANGPTL4 protein via transforming growth factor-β (TGF-β) and hypoxia-inducible factor 1α (HIF-1α) signalling, and the released ANGPTL4 was pro-angiogenic. Angiogenic activity was increased following ANGPTL4 injection into mouse patellar tendons, whereas the patellar tendons of ANGPTL4 knockout mice displayed reduced angiogenesis following injury. In human rotator cuff tendons, the expression of ANGPTL4 was correlated with the density of tendon endothelial cells. To our knowledge, this is the first study characterizing a role of ANGPTL4 in the tendon. ANGPTL4 may assist in the regulation of vascularity in the injured or mechanically loaded tendon. TGF-β and HIF-1α comprise two signalling pathways that modulate the expression of ANGPTL4 by mechanically stimulated tendon fibroblasts and, in the future, these could be manipulated to influence tendon healing or adaptation. © 2015 The Authors. The Journal of Physiology © 2015 The Physiological Society.

  7. Cyclic fatigue resistance tests of Nickel-Titanium rotary files using simulated canal and weight loading conditions

    PubMed Central

    Cho, Ok-In; Versluis, Antheunis; Cheung, Gary SP; Ha, Jung-Hong; Hur, Bock

    2013-01-01

    Objectives This study compared the cyclic fatigue resistance of nickel-titanium (NiTi) files obtained in a conventional test using a simulated canal with a newly developed method that allows the application of constant fatigue load conditions. Materials and Methods ProFile and K3 files of #25/.06, #30/.06, and #40/.04 were selected. Two types of testing devices were built to test their fatigue performance. The first (conventional) device prescribed curvature inside a simulated canal (C-test), the second new device exerted a constant load (L-test) whilst allowing any resulting curvature. Ten new instruments of each size and brand were tested with each device. The files were rotated until fracture and the number of cycles to failure (NCF) was determined. The NCF were subjected to one-way ANOVA and Duncan's post-hoc test for each method. Spearman's rank correlation coefficient was computed to examine any association between methods. Results Spearman's rank correlation coefficient (ρ = -0.905) showed a significant negative correlation between methods. Groups with significant difference after the L-test divided into 4 clusters, whilst the C-test gave just 2 clusters. From the L-test, considering the negative correlation of NCF, K3 gave a significantly lower fatigue resistance than ProFile as in the C-test. K3 #30/.06 showed a lower fatigue resistance than K3 #25/.06, which was not found by the C-test. Variation in fatigue test methodology resulted in different cyclic fatigue resistance rankings for various NiTi files. Conclusions The new methodology standardized the load during fatigue testing, allowing determination fatigue behavior under constant load conditions. PMID:23493583

  8. A potential means of using acoustic emission for crack detection under cyclic-load conditions

    NASA Technical Reports Server (NTRS)

    Vary, A.; Klima, S. J.

    1973-01-01

    A preliminary investigation was conducted to assess the feasibility of monitoring acoustic emission signals from fatigue cracks during cyclic bend tests. Plate specimens of 6A1-4V titanium, 2219-T87 aluminum, and 18-Ni maraging steel were tested with and without crack starter notches. It was found that significant acoustic emission signals could be detected in the frequency range from 100 kHz to 400 kHz. Cracks emanating from starter notches were monitored by the ultrasonic pulse-echo technique and periodically measured by micro-optical examination. Methods used to reduce the effects of extraneous noises (i.e., machine noises, fretting) are described. A frequency spectrum analyzer was used to characterize the emissions and to evaluate methods used to acquire the signals (i.e., transducer location, bandwidth selection). The investigation indicated that it was possible to extract meaningful acoustic emission signals in a cyclic bend machine environment.

  9. A Users manual for the nonlinear kinematic hardening model for cyclic loading

    SciTech Connect

    Puso, M

    2000-09-15

    This report describes the implementation of the Chaboche type Nonlinear Kinematic Hardening Model developed for the PNGV SPP (Partnership for the Next Generation Vehicle, Spring-back Predictability Project). The material model includes a nonlinear kinematic and isotropic hardening law, transverse anisotropy, strain range memorization for cyclic hardening/softening and viscoplasticity. This report is a companion to the report: ''A Return Mapping Algorithm for Cyclic Viscoplastic Constitutive Models'' which concentrates on the theoretical aspects of the model. This report summarizes the necessary parameters for the model, briefly discusses their interpretation and shows some numerical simulations. The report also specifies the data structure requirements for linking the material model software by explicitly referencing the source code delivered to the SPP collaborators.

  10. Crack Growth in Mercury Embrittled Aluminum Alloys under Cyclic and Static Loading Conditions

    DTIC Science & Technology

    1983-03-01

    argument is given further credence by the unpublished work of Lynn and Warke reported by Stoloff.3 In that study, static fatigue of 4140 steel plated...Continue on reverae aide If neceaaary and Identify by block number) Fracture Fatigue Fracture Mechanics Adsorption Liquid Metal Embrittlement Mercury...Behavior for 79 the 11g-Si Aluminum Alloy 6061-T651 4.2.1 Static Fatigue 79 4.2.2 Cyclic Fatigue 84 5. ANALYSIS AND DISCUSSION 88 6. CONCLUSIONS

  11. Short-period cyclic loading system for in situ X-ray observation of anelastic properties at high pressure

    NASA Astrophysics Data System (ADS)

    Yoshino, Takashi; Yamazaki, Daisuke; Tange, Yoshinori; Higo, Yuji

    2016-10-01

    To determine the anelastic properties of materials of the Earth's interior, a short-period cyclic loading system was installed for in situ X-ray radiographic observation under high pressure to the multi-anvil deformation DIA press at the bending magnet beam line BL04B1 at SPring-8. The hydraulic system equipped with a piston controlled by a solenoid was designed so as to enable producing smooth sinusoidal stress in a wide range of oscillation period from 0.2 to 100 s and generating variable amplitudes. Time resolved X-ray radiography imaging of the sample and reference material provides their strain as a function of time during cyclic loading. A synchrotron X-ray radiation source allows us to resolve their strain variation with time even at the short period (<1 s). The minimum resolved strain is as small as 10-4, and the shortest oscillation period to detect small strain is 0.5 s. Preliminary experimental results exhibited that the new system can resolve attenuation factor Q-1 at upper mantle conditions. These results are in quantitative agreement with previously reported data obtained at lower pressures.

  12. Bonding state of metal-free CAD/CAM onlay restoration after cyclic loading with and without immediate dentin sealing.

    PubMed

    Ishii, Noriko; Maseki, Toshio; Nara, Yoichiro

    2017-05-31

    To examine the bonding state of metal-free CAD/CAM onlay restorations made from two popular resin composite blocks and a typical glass-ceramic block after cyclic loading, with and without immediate dentin sealing (IDS). Standardized mesial-distal-occlusalbuccal (MODB) cavities in 24 extracted human molars were prepared. The intra-cavity dentin surfaces of half of the cavities were immediately sealed with all-in-one adhesive and flowable composite, while those of the other half were not. All cavities were scanned, from which CAD/CAM onlays were fabricated from three types of block and cemented with an adhesive resin cement system. The restored specimens were subjected to cyclic loading and the intra-cavity microtensile bond strength was measured. IDS improves not only the internal bond strength, but also the bond reliability of metal-free CAD/CAM onlay restorations. The resin composite block seems to be more effective than a typical glass-ceramic block for achieving both high bond strength and excellent bond reliability.

  13. Crack Initiation Life of Materials Under Combined Pitting Corrosion and Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Sriraman, M. R.; Pidaparti, R. M.

    2010-02-01

    Pitting corrosion triggered damage is responsible for the degradation of many metallic materials affecting structural integrity. As pitting and crack initiation processes govern the overall life of such structures and components, particularly at nominal cyclic stresses, there is a need to develop simple models to estimate crack initiation life of materials. This paper presents a simple deterministic model that considers the effect of cyclic stressing under pitting corrosion conditions. The developed model is validated on an aluminum alloy 2024-T3, and 12% Cr stainless steel used in aircraft and steam turbines, respectively. The predicted critical pit depth values are in fair agreement with the limited experimental data available in the literature. The model indicates that at high stresses, the crack initiation can occur very rapidly even from relatively small pits. The crack initiation life predictions when compared with the available experimental data, suggest a probable stress-level dependency with regard to the form and extent of the influence of cyclic stresses on pit growth and subsequent crack formation.

  14. Structural Response of Compression-Loaded, Tow-Placed, Variable Stiffness Panels

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey; Guerdal, Zafer; Starnes, James H., Jr.

    2002-01-01

    Results of an analytical and experimental study to characterize the structural response of two compression-loaded variable stiffness composite panels are presented and discussed. These variable stiffness panels are advanced composite structures, in which tows are laid down along precise curvilinear paths within each ply and the fiber orientation angle varies continuously throughout each ply. The panels are manufactured from AS4/977-3 graphite-epoxy pre-preg material using an advanced tow placement system. Both variable stiffness panels have the same layup, but one panel has overlapping tow bands and the other panel has a constant-thickness laminate. A baseline cross-ply panel is also analyzed and tested for comparative purposes. Tests performed on the variable stiffness panels show a linear prebuckling load-deflection response, followed by a nonlinear response to failure at loads between 4 and 53 percent greater than the baseline panel failure load. The structural response of the variable stiffness panels is also evaluated using finite element analyses. Nonlinear analyses of the variable stiffness panels are performed which include mechanical and thermal prestresses. Results from analyses that include thermal prestress conditions correlate well with measured variable stiffness panel results. The predicted response of the baseline panel also correlates well with measured results.

  15. Use of loading-unloading compression curves in medical device design

    NASA Astrophysics Data System (ADS)

    Ciornei, M. C.; Alaci, S.; Ciornei, F. C.; Romanu, I. C.

    2017-08-01

    The paper presents a method and experimental results regarding mechanical testing of soft materials. In order to characterize the mechanical behaviour of technological materials used in prosthesis, a large number of material constants are required, as well as the comparison to the original. The present paper proposes as methodology the comparison between compression loading-unloading curves corresponding to a soft biological tissue and to a synthetic material. To this purpose, a device was designed based on the principle of the dynamic harness test. A moving load is considered and the force upon the indenter is controlled for loading-unloading phases. The load and specimen deformation are simultaneously recorded. A significant contribution of this paper is the interpolation of experimental data by power law functions, a difficult task because of the instability of the system of equations to be optimized. Finding the interpolation function was simplified, from solving a system of transcendental equations to solving a unique equation. The characteristic parameters of the experimentally curves must be compared to the ones corresponding to actual tissue. The tests were performed for two cases: first, using a spherical punch, and second, for a flat-ended cylindrical punch.

  16. Effects of Imperfections on the Buckling Response of Compression-Loaded Composite Shells

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Starnes, James H., Jr.

    2002-01-01

    The results of an experimental and analytical study of the effects of initial imperfections on the buckling and postbuckling response of three unstiffened thin-walled compression-loaded graphite-epoxy cylindrical shells with different orthotropic and quasi-isotropic shell-wall laminates are presented. The results identify the effects of traditional and non-traditional initial imperfections on the non-linear response and buckling loads of the shells. The traditional imperfections include the geometric shell-wall mid-surface imperfect ions that are commonly discussed in the literature on thin shell buckling. The non-traditional imperfections include shell-wall thickness variations local shell-wall ply-gaps associated with the fabrication process, sheltered geometric imperfections, non-uniform applied end loads, and variations in the boundary conditions including the effects of elastic boundary conditions. A high-fidelity non-linear shell analysis procedure that accurately accounts for the effects of these traditional and non-traditional imperfections on the nonlinear response, and buckling loads of the shells is described. The analysis procedure includes a non-linear static analysis that predicts stable response characteristics of the shells and a non-linear transient analysis that predicts unstable response characteristics.

  17. Cyclic hardening in copper described in terms of combined monotonic and cyclic stress-strain curves

    SciTech Connect

    Chandler, H.D. . School of Mechanical Engineering)

    1995-01-01

    Hardening of polycrystalline copper subjected to tension-compression loading cycles in the plastic region is discussed with reference to changes in flow stress determined from equations describing dislocation glide. It is suggested that hardening is as a result of the accumulation of strain on a monotonic stress-strain curve. On initial loading, the behavior is monotonic. On stress reversal, a characteristic cyclic stress-strain curve is followed until the stress reaches a value in reverse loading corresponding to the maximum attained during the preceding half cycle. Thereafter, the monotonic path is followed until strain reversal occurs at completion of the half cycle. Repetition of the process results in cyclic hardening. Steady state cyclic behavior is reached when a stress associated with the monotonic stress-strain curve is reached which is equal to the stress associated with the cyclic stress-strain curve corresponding to the imposed strain amplitude.

  18. Performance of HESCO Bastion Units Under Combined Normal and Cyclic Lateral Loading

    DTIC Science & Technology

    2017-02-01

    displacement ............................................................................................19 4.3 Investigation of accidental torsion ...and lateral loads to ensure that the laboratory environment best models the field envi- ronment. At each displacement level the normal load was...4.3 Investigation of accidental torsion To prevent torsion of the entire specimen, string potentiometers were at- tached on both sides of the

  19. Performance of HESCO Bastion Units Under Combined Normal and Cyclic Lateral Loading

    DTIC Science & Technology

    2017-02-01

    Army investigates construction methods that use indigenous materials in place of commercial materials manufactured far away. An established...reduce costs and logisti- cal burdens for Class 4 construction materials . Before developing such ap- plications, however, the load-resisting...2 2 Material Properties and Design Loads .......................................................................... 3 2.1 HESCO steel mesh and

  20. Study the Cyclic Plasticity Behavior of 508 LAS under Constant, Variable and Grid-Load-Following Loading Cycles for Fatigue Evaluation of PWR Components

    SciTech Connect

    Mohanty, Subhasish; Barua, Bipul; Soppet, William K.; Majumdar, Saurin; Natesan, Ken

    2016-09-01

    This report provides an update of an earlier assessment of environmentally assisted fatigue for components in light water reactors. This report is a deliverable in September 2016 under the work package for environmentally assisted fatigue under DOE’s Light Water Reactor Sustainability program. In an April 2016 report, we presented a detailed thermal-mechanical stress analysis model for simulating the stress-strain state of a reactor pressure vessel and its nozzles under grid-load-following conditions. In this report, we provide stress-controlled fatigue test data for 508 LAS base metal alloy under different loading amplitudes (constant, variable, and random grid-load-following) and environmental conditions (in air or pressurized water reactor coolant water at 300°C). Also presented is a cyclic plasticity-based analytical model that can simultaneously capture the amplitude and time dependency of the component behavior under fatigue loading. Results related to both amplitude-dependent and amplitude-independent parameters are presented. The validation results for the analytical/mechanistic model are discussed. This report provides guidance for estimating time-dependent, amplitude-independent parameters related to material behavior under different service conditions. The developed mechanistic models and the reported material parameters can be used to conduct more accurate fatigue and ratcheting evaluation of reactor components.

  1. Effect of plate working length on plate stiffness and cyclic fatigue life in a cadaveric femoral fracture gap model stabilized with a 12-hole 2.4 mm locking compression plate

    PubMed Central

    2013-01-01

    Background There are several factors that can affect the fatigue life of a bone plate, including the mechanical properties of the plate and the complexity of the fracture. The position of the screws can influence construct stiffness, plate strain and cyclic fatigue of the implants. Studies have not investigated these variables in implants utilized for long bone fracture fixation in dogs and cats. The purpose of the present study was to evaluate the effect of plate working length on construct stiffness, gap motion and resistance to cyclic fatigue of dog femora with a simulated fracture gap stabilized using a 12-hole 2.4 mm locking compression plates (LCP). Femora were plated with 12-hole 2.4 mm LCP using 2 screws per fracture segment (long working length group) or with 12-hole 2.4 mm LCP using 5 screws per fracture segment (a short working length group). Results Construct stiffness did not differ significantly between stabilization techniques. Implant failure did not occur in any of the plated femora during cycling. Mean ± SD yield load at failure in the short plate working length group was significantly higher than in the long plate working length group. Conclusion In a femoral fracture gap model stabilized with a 2.4 mm LCP applied in contact with the bone, plate working length had no effect on stiffness, gap motion and resistance to fatigue. The short plate working length constructs failed at higher loads; however, yield loads for both the short and long plate working length constructs were within physiologic range. PMID:23800317

  2. Effects of serum and compressive loading on the cartilage matrix synthesis and spatiotemporal deposition around chondrocytes in 3D culture.

    PubMed

    Wu, Peihui; DeLassus, Elizabeth; Patra, Debabrata; Liao, Weiming; Sandell, Linda J

    2013-05-01

    The aim of this study was to investigate the effects of serum and compressive dynamic loading on the cartilaginous matrix spatiotemporal distribution around chondrocytes in vitro. Murine chondrocytes suspended in agarose were cultured in serum-free media or in varying concentrations of serum with or without compressive dynamic loading. Gene expression was assayed by quantitative polymerase chain reaction. Immunohistochemistry was performed for type II collagen and type VI collagen, aggrecan, or cartilage oligomeric matrix protein (COMP) to study the effect of serum and dynamic loading on the spatiotemporal distribution of cartilage matrix components. Chondrocytes in serum-free culture exhibited negligible differences in type II collagen, aggrecan, and COMP mRNA expression levels over 15 days of cultivation. However, higher serum concentrations decreased matrix gene expression. Expression of the matrix metalloproteinases (MMP)-3 and MMP-13 mRNA increased over time in serum-free or reduced serum levels, but was significantly suppressed in 10% fetal bovine serum (FBS). Compressive loading significantly stimulated MMP-3 expression on days 7 and 15. Immunohistochemical analysis demonstrated that maximum pericellular matrix deposition was achieved in 10% FBS culture in the absence of compressive loading. The pericellular distribution of type II and VI collagens, aggrecan, and COMP proteins tended to be more co-localized in the pericellular region from day 9 to day 21; compressive loading helped promote this co-localization of matrix proteins. The results of this study suggest that the quantity, quality, and spatial distribution of cartilaginous matrix can be altered by serum concentrations and compressive loading.

  3. In situ AE records in cyclically loaded rock salt - The stress memory effect and spatio-temporal characteristics

    NASA Astrophysics Data System (ADS)

    Becker, D.; Cailleau, B.; Dahm, T.; Shapiro, S.; Kaiser, D.

    2009-04-01

    We study acoustic emission (AE) activity caused by cyclic thermal loading due to the backfilling of a cavity in an abandoned salt mine to answer questions regarding the stress memory effect of rock (Kaiser effect), the dependence of AE rates and b-value on the stress state as well as the stress rate and the spatio-temporal evolution of the AE activity. Event rates and b-values of the frequency magnitude relation are calculated for a region well covered by a network of piezo-electric receivers from an event catalog corrected for incomplete recording times. Results are compared and correlated with the output of a 2D thermo-elastic stress modelling performed with an FE program. The high quality of the AE dataset as well as the good control of the input parameters of the FE program allows us to study the in situ activity in the mining environment with exceptionally high precision and temporal resolution. The backfilling period can be subdivided into two AE activity regimes. The first one exhibits a clear and pronounced Kaiser effect as well as an upward migration of the AE event front away from the ceiling of the cavity which correlates with the calculated stress field. This observation of the Kaiser effect implies that no healing effect is observed for these first few loading cycles. The maximum event rate observed during a loading cycle scales with the absolute stress increase of this cycle with respect to the former maximum. This behavior is also observed for later loading cycles which show a deteriorated Kaiser effect with an onset of AE activity well before the former maximum stress and a smaller slope of the relation between maximum event rate and absolute stress increase. During later loading cycles also time periods showing a pronounced anti-correlation between event rate and Coulomb stress with event rate maxima during minima of the Coulomb stress are observed. These time periods are generally characterized by a b-value of the frequency magnitude relation much

  4. Experimental Investigation of the Influence of Joint Geometric Configurations on the Mechanical Properties of Intermittent Jointed Rock Models Under Cyclic Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Dai, Feng; Fan, Pengxian; Xu, Nuwen; Dong, Lu

    2017-06-01

    Intermittent joints in rock mass are quite sensitive to cyclic loading conditions. Understanding the fatigue mechanical properties of jointed rocks is beneficial for rational design and stability analysis of rock engineering projects. This study experimentally investigated the influences of joint geometry (i.e., dip angle, persistency, density and spacing) on the fatigue mechanism of synthetic jointed rock models. Our results revealed that the stress-strain curve of jointed rock under cyclic loadings is dominated by its curve under monotonic uniaxial loadings; the terminal strain in fatigue curve is equal to the post-peak strain corresponding to the maximum cyclic stress in the monotonic stress-strain curve. The four joint geometrical parameters studied significantly affect the fatigue properties of jointed rocks, including the irreversible strains, the fatigue deformation modulus, the energy evolution, the damage variable and the crack coalescence patterns. The higher the values of the geometrical parameters, the lower the elastic energy stores in this jointed rock, the higher the fatigue damage accumulates in the first few cycles, and the lower the fatigue life. The elastic energy has certain storage limitation, at which the fatigue failure occurs. Two basic micro-cracks, i.e., tensile wing crack and shear crack, are observed in cyclic loading and unloading tests, which are controlled principally by joint dip angle and persistency. In general, shear cracks only occur in the jointed rock with higher dip angle or higher persistency, and the jointed rock is characterized by lower fatigue strength, larger damage variable and lower fatigue life.

  5. Effects of applied stress ratio on the fatigue behavior of additively manufactured porous biomaterials under compressive loading.

    PubMed

    de Krijger, Joep; Rans, Calvin; Van Hooreweder, Brecht; Lietaert, Karel; Pouran, Behdad; Zadpoor, Amir A

    2016-12-07

    Additively manufactured (AM) porous metallic biomaterials are considered promising candidates for bone substitution. In particular, AM porous titanium can be designed to exhibit mechanical properties similar to bone. There is some experimental data available in the literature regarding the fatigue behavior of AM porous titanium, but the effect of stress ratio on the fatigue behavior of those materials has not been studied before. In this paper, we study the effect of applied stress ratio on the compression-compression fatigue behavior of selective laser melted porous titanium (Ti-6Al-4V) based on the diamond unit cell. The porous titanium biomaterial is treated as a meta-material in the context of this work, meaning that R-ratios are calculated based on the applied stresses acting on a homogenized volume. After morphological characterization using micro computed tomography and quasi-static mechanical testing, the porous structures were tested under cyclic loading using five different stress ratios, i.e. R = 0.1, 0.3, 0.5, 0.7 and 0.8, to determine their S-N curves. Feature tracking algorithms were used for full-field deformation measurements during the fatigue tests. It was observed that the S-N curves of the porous structures shift upwards as the stress ratio increases. The stress amplitude was the most important factor determining the fatigue life. Constant fatigue life diagrams were constructed and compared with similar diagrams for bulk Ti-6Al-4V. Contrary to the bulk material, there was limited dependency of the constant life diagrams to mean stress. The notches present in the AM biomaterials were the sites of crack initiation. This observation and other evidence suggest that the notches created by the AM process cause the insensitivity of the fatigue life diagrams to mean stress. Feature tracking algorithms visualized the deformation during fatigue tests and demonstrated the root cause of inclined (45°) planes of specimen failure. In conclusion, the R

  6. Permeability Evolution in Natural Fractures Subject to Cyclic Loading and Gouge Formation

    NASA Astrophysics Data System (ADS)

    Vogler, Daniel; Amann, Florian; Bayer, Peter; Elsworth, Derek

    2016-09-01

    Increasing fracture aperture by lowering effective normal stress and by inducing dilatant shearing and thermo-elastic effects is essential for transmissivity increase in enhanced geothermal systems. This study investigates transmissivity evolution for fluid flow through natural fractures in granodiorite at the laboratory scale. Processes that influence transmissivity are changing normal loads, surface deformation, the formation of gouge and fracture offset. Normal loads were varied in cycles between 1 and 68 MPa and cause transmissivity changes of up to three orders of magnitude. Similarly, small offsets of fracture surfaces of the order of millimeters induced changes in transmissivity of up to three orders of magnitude. During normal load cycling, the fractures experienced significant surface deformation, which did not lead to increased matedness for most experiments, especially for offset fractures. The resulting gouge material production may have caused clogging of the main fluid flow channels with progressing loading cycles, resulting in reductions of transmissivity by up to one order of magnitude. During one load cycle, from low to high normal loads, the majority of tests show hysteretic behavior of the transmissivity. This effect is stronger for early load cycles, most likely when surface deformation occurs, and becomes less pronounced in later cycles when asperities with low asperity strength failed. The influence of repeated load cycling on surface deformation is investigated by scanning the specimen surfaces before and after testing. This allows one to study asperity height distribution and surface deformation by evaluating the changes of the standard deviation of the height, distribution of asperities and matedness of the fractures. Surface roughness, as expressed by the standard deviation of the asperity height distribution, increased during testing. Specimen surfaces that were tested in a mated configuration were better mated after testing, than

  7. Dose-Dependent Response of Tissue-Engineered Intervertebral Discs to Dynamic Unconfined Compressive Loading

    PubMed Central

    Hudson, Katherine D.; Mozia, Robert I.

    2015-01-01

    Because of the limitations of current surgical methods in the treatment of degenerative disc disease, tissue-engineered intervertebral discs (TE-IVDs) have become an important target. This study investigated the biochemical and mechanical responses of composite TE-IVDs to dynamic unconfined compression. TE-IVDs were manufactured by floating an injection molded alginate nucleus pulposus (NP) in a type I collagen annulus fibrosus (AF) that was allowed to contract for 2 weeks before loading. The discs were mechanically stimulated at a range of strain amplitude (1–10%) for 2 weeks with a duty cycle of 1 h on–1 h off–1 h on before being evaluated for their biochemical and mechanical properties. Mechanical loading increased all properties in a dose-dependent manner. Glycosaminoglycans (GAGs) increased between 2.8 and 2.2 fold in the AF and NP regions, respectively, whereas the hydroxyproline content increased between 1.2 and 1.8 fold. The discs also experienced a 2-fold increase in the equilibrium modulus and a 4.3-fold increase in the instantaneous modulus. Full effects for all properties were seen by 5% strain amplitude. These data suggest that dynamic loading increases the functionality of our TE-IVDs with region-dependent responses using a method that may be scaled up to larger disc models to expedite maturation for implantation. PMID:25277703

  8. Tow-Steered Panels With Holes Subjected to Compression or Shear Loads

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.; Tatting, Brian F.; Guerdal, Zafer

    2005-01-01

    Tailoring composite laminates to vary the fiber orientations within a fiber layer of a laminate to address non-uniform stress states and provide structural advantages such as the alteration of principal load paths has potential application to future low-cost, light-weight structures for commercial transport aircraft. Evaluation of this approach requires the determination of the effectiveness of stiffness tailoring through the use of curvilinear fiber paths in flat panels including the reduction of stress concentrations around the holes and the increase in load carrying capability. Panels were designed through the use of an optimization code using a genetic algorithm and fabricated using a tow-steering approach. Manufacturing limitations, such as the radius of curvature of tows the machine could support, avoidance of wrinkling of fibers and minimization of gaps between fibers were considered in the design process. Variable stiffness tow-steered panels constructed with curvilinear fiber paths were fabricated so that the design methodology could be verified through experimentation. Finite element analysis where each element s stacking sequence was accurately defined is used to verify the behavior predicted based on the design code. Experiments on variable stiffness flat panels with central circular holes were conducted with the panels loaded in axial compression or shear. Tape and tow-steered panels are used to demonstrate the buckling, post-buckling and failure behavior of elastically tailored panels. The experimental results presented establish the buckling performance improvements attainable by elastic tailoring of composite laminates.

  9. Comparison of Methods to Predict Lower Bound Buckling Loads of Cylinders Under Axial Compression

    NASA Technical Reports Server (NTRS)

    Haynie, Waddy T.; Hilburger, Mark W.

    2010-01-01

    Results from a numerical study of the buckling response of two different orthogrid stiffened circular cylindrical shells with initial imperfections and subjected to axial compression are used to compare three different lower bound buckling load prediction techniques. These lower bound prediction techniques assume different imperfection types and include an imperfection based on a mode shape from an eigenvalue analysis, an imperfection caused by a lateral perturbation load, and an imperfection in the shape of a single stress-free dimple. The STAGS finite element code is used for the analyses. Responses of the cylinders for ranges of imperfection amplitudes are considered, and the effect of each imperfection is compared to the response of a geometrically perfect cylinder. Similar behavior was observed for shells that include a lateral perturbation load and a single dimple imperfection, and the results indicate that the predicted lower bounds are much less conservative than the corresponding results for the cylinders with the mode shape imperfection considered herein. In addition, the lateral perturbation technique and the single dimple imperfection produce response characteristics that are physically meaningful and can be validated via testing.

  10. Effects of Imperfections on the Buckling Response of Compression-Loaded Composite Shells

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Starnes, James H., Jr.

    2000-01-01

    The results of an experimental and numerical study of the effects of imperfections on the buckling response of unstiffened thin-walled composite cylindrical shells are presented. Results that identify the individual and combined effects of traditional initial geometric shell-wall imperfections and non-traditional shell-wall thickness variations, shell-end geometric imperfections and variations in loads applied to the ends of the shells on the shell buckling response are included. In addition, results illustrating the effects of manufacturing flaws in the form of gaps between adjacent pieces of graphite-epoxy tape in some of the laminate plies are presented in detail. The shells have been analyzed with a nonlinear finite-element analysis code that accurately accounts for these effects on the buckling and nonlinear responses of the shells. The numerical results indicate that traditional and nontraditional initial imperfections can cause a significant reduction in the buckling load of a compression-loaded composite shell. Furthermore, the results indicate that the imperfections couple in a nonlinear manner. The numerical results correlate well with the experimental results. The nonlinear analysis results are also compared to the results from a traditional linear bifurcation buckling analysis. The results suggest that the nonlinear analysis procedure can be used for determining accurate, high-fidelity design knockdown factors for shell buckling and collapse. The results can also be used to determine the effects of manufacturing tolerances on the buckling response of composite shells.

  11. Dynamic mechanical response of magnesium single crystal under compression loading: Experiments, model, and simulations

    NASA Astrophysics Data System (ADS)

    Li, Qizhen

    2011-05-01

    Magnesium single crystal samples are compressed at room temperature under quasistatic (˜0.001 s-1) loading in a universal testing machine and dynamic (430, 1000, and 1200 s-1) loading in a split Hopkinson pressure bar system. Stress-strain curves show that (a) the fracture strain slightly increases with the strain rate; and (b) the maximum strength and strain hardening rate increase significantly when the testing changes from quasistatic to dynamic, although they do not vary much when the strain rate for dynamic testing varies in the range of 430-1200 s-1. The operation of the secondary pyramidal slip system is the dominating deformation mechanism, which leads to a fracture surface with an angle of ˜42° with respect to the loading axial direction. A theoretical material model based on Johnson-Cook law is also derived. The model includes the strain hardening and strain rate hardening terms, and provides the stress-strain relations matching with the experimental results. Finite element simulations for the strain rates used in the experiments predict the mechanical responses of the material that agree well with the experimental data.

  12. Axially compressed buckling of an embedded boron nitride nanotube subjected to thermo-electro-mechanical loadings

    NASA Astrophysics Data System (ADS)

    Salehi-Khojin, Amin; Jalili, Nader

    2007-04-01

    Unlike widely-used carbon nanotubes, boron nitride nanotubes (BNNTs) have shown to possess stable semiconducting behavior and strong piezoelectricity. Such properties along with their outstanding mechanical properties and thermal conductivity, make BNNTs promising candidate reinforcement materials for a verity of applications especially nanoelectronic and nanophotonic devices. Motivated by these abilities, we aim to study the buckling behavior of BNNT-reinforced piezoelectric polymeric composites when subjected to combined electro-thermo-mechanical loadings. For this, the multi-walled structure of BNNT is considered as elastic media and a set of concentric cylindrical shell with van der Waals interaction between them. Using three-dimensional equilibrium equations, Donnell shell theory is utilized to show that the axially compressive resistance of BNNT varies with applying thermal and electrical loads. The effect of BNNT piezoelectric property on the buckling behavior of the composites is demonstrated. More specifically, it is shown that applying direct and reverse voltages to BNNT changes the buckling loads for any axial and circumferential wavenumbers. Such capability could be uniquely utilized when designing BNNT-reinforced composites.

  13. Ambient Compression-Compression Fatigue Behavior of Magnesium Single Crystal

    NASA Astrophysics Data System (ADS)

    Li, Qizhen

    2014-01-01

    A magnesium single crystal sample with a near orientation was tested at room temperature under compression-compression cyclic loading, and the microstructure was characterized to disclose the involved deformation mechanisms. No plastic deformation region appeared on the stress-strain curve during the cyclic loading. The stress-strain curve stabilized at the first cycle, the strain range for each cycle fluctuated slightly around a constant value, and the mean strain for each cycle was in a narrow range from 0.0846 to 0.0863 during the whole test. The ratcheting strain rate decreased exponentially from ~0.0003, and reached a relatively small and stable value of about zero. The observed deformation mechanisms were prismatic slip, compression twinning, and tension twinning. The prismatic dislocation slip roughened the cylindrical sample surface by forming extrusions and intrusions, and small cracks were also observed on the surface.

  14. Compression and compression fatigue testing of composite laminates

    NASA Technical Reports Server (NTRS)

    Porter, T. R.

    1982-01-01

    The effects of moisture and temperature on the fatigue and fracture response of composite laminates under compression loads were investigated. The structural laminates studied were an intermediate stiffness graphite-epoxy composite (a typical angle ply laimna liminate had a typical fan blade laminate). Full and half penetration slits and impact delaminations were the defects examined. Results are presented which show the effects of moisture on the fracture and fatigue strength at room temperature, 394 K (250 F), and 422 K (300 F). Static tests results show the effects of defect size and type on the compression-fracture strength under moisture and thermal environments. The cyclic tests results compare the fatigue lives and residual compression strength under compression only and under tension-compression fatigue loading.

  15. Static and Cyclic Load-Deflection Characteristics of NiTi Orthodontic Archwires Using Modified Bending Tests

    NASA Astrophysics Data System (ADS)

    Nili Ahmadabadi, Mahmoud; Shahhoseini, Tahereh; Habibi-Parsa, Mohamad; Haj-Fathalian, Maryam; Hoseinzadeh-Nik, Tahereh; Ghadirian, Hananeh

    2009-08-01

    Near-equiatomic nickel-titanium (nitinol) has the ability to return to a former shape when subjected to an appropriate thermomechanical procedure. One of the most successful applications of nitinol is orthodontic archwire. One of the suitable characteristics of these wires is superelasticity, a phenomenon that allows better-tolerated loading conditions during clinical therapy. Superelastic nitinol wires deliver clinically desired light continuous force enabling effective tooth movement with minimal damage for periodontal tissues. In this research, a special three-point bending fixture was invented and designed to determine the superelastic property in simulated clinical conditions, where the wire samples were held in the fixture similar to an oral cavity. In this experimental study, the load-deflection characteristics of superelastic NiTi commercial wires were studied through three-point bending test. The superelastic behavior was investigated by focusing on bending time, temperature, and number of cycles which affects the energy dissipating capacity. Experimental results show that the NiTi archwires are well suited for cyclic load-unload dental applications. Results show reduction in superelastic property for used archwires after long-time static bending.

  16. An investigation of the self-heating phenomenon in viscoelastic materials subjected to cyclic loadings accounting for prestress

    NASA Astrophysics Data System (ADS)

    de Lima, A. M. G.; Rade, D. A.; Lacerda, H. B.; Araújo, C. A.

    2015-06-01

    It has been demonstrated by many authors that the internal damping mechanism of the viscoelastic materials offers many possibilities for practical engineering applications. However, in traditional procedures of analysis and design of viscoelastic dampers subjected to cyclic loadings, uniform, constant temperature is generally assumed and do not take into account the self-heating phenomenon. Moreover, for viscoelastic materials subjected to dynamic loadings superimposed on static preloads, such as engine mounts, these procedures can lead to poor designs or even severe failures since the energy dissipated within the volume of the material leads to temperature rises. In this paper, a hybrid numerical-experimental investigation of effects of the static preloads on the self-heating phenomenon in viscoelastic dampers subjected to harmonic loadings is reported. After presenting the theoretical foundations, the numerical and experimental results obtained in terms of the temperature evolutions at different points within the volume of the viscoelastic material for various static preloads are compared, and the main features of the methodology are discussed.

  17. Microleakage along glass-fibre posts cemented with three different materials after cyclic loading: a pilot study.

    PubMed

    Barbić, Marija Rogić; Segović, Sanja; Baraba, Anja; Ribarić, Sonja Pezelj; Katunarić, Marina; Anić, Ivica

    2013-06-01

    The purpose of this in vitro study was to evaluate microleakage along glass-fibre posts cemented with three different cements after cyclic loading. After post-space preparation, fifty obturated root canals were randomly divided into three experimental groups and two control groups. In group 1, Glassix posts were cemented using Harvard cement, in group 2, Fuji PLUS cement was used and in group 3, Variolink II was used for post cementation. The specimens were artificially aged by loading in a special testing machine. Coronal leakage was evaluated using a fluid transport system. Posts cemented with Variolink II, showed significantly higher failure rate after loading, compared to group 1 and 2 (p = 0.009). Comparing microleakage in samples that have not failed, specimens cemented with Variolink II showed significantly less fluid transport than specimens cemented with zinc phosphate and glass ionomer cements (p = 0.04 and p = 0.006, respectively). Variolink II cement exibited significantly less fluid movement compared with Harvard and Fuji PLUS cement.

  18. Sulfur loaded in micropore-rich carbon aerogel as cathode of lithium-sulfur battery with improved cyclic stability

    NASA Astrophysics Data System (ADS)

    Li, Zihao; Li, Xiaogang; Liao, Youhao; Li, Xiaoping; Li, Weishan

    2016-12-01

    We report a novel composite of sulfur loaded in micropore-rich carbon aerogel (CA-S), as cathode of lithium-sulfur battery. Carbon aerogel (CA) is synthesized through phenol-formaldehyde reaction with a low catalyst concentration and carbonization under high temperature, and loaded with sulfur via chemical deposition and heat treatment. The physical properties of the resulting CA and the electrochemical performances of the resulting CA-S are investigated by scanning electron microscopy, thermal gravimetric analysis, Brunauer-Emmett-Teller characterization, electrochemical impedance spectroscopy, and galvanostatic discharge/charge test, with a comparison of a common carbon material, acetylene black (AB), and sulfur loaded in AB (AB-S). It is found that the CA is micropore-rich with micropore volume over 66% of total pore volume, and the CA-S exhibits significantly improved cyclic stability compared with AB-S. The improved performance of CA-S is attributed to the confinement of the micropores in CA to small sulfur allotropes and corresponding lithium sulfides.

  19. Compressive Properties of PTFE/Al/Ni Composite Under Uniaxial Loading

    NASA Astrophysics Data System (ADS)

    Wang, Huai-xi; Li, Yu-chun; Feng, Bin; Huang, Jun-yi; Zhang, Sheng; Fang, Xiang

    2017-05-01

    To investigate the mechanical properties of pressed and sintered PTFE/Al/Ni (polytetrafluoroethylene/aluminum/nickel) composite, uniaxial quasi-static and dynamic compression experiments were conducted at strain rates from 10-2 to 3 × 103/s. The prepared samples were tested by an electrohydraulic press with 300 kN loading capacity and a split Hopkinson pressure bar (SHPB) device at room temperature. Experimental results show that PTFE/Al/Ni composite exhibits evident strain hardening and strain rate hardening. Additionally, a bilinear relationship between stress and {{log(}}\\dot{ɛ} ) is observed. The experimental data were fit to Johnson-Cook constitutive model, and the results are in well agreement with measured data.

  20. Buckling and postbuckling behavior of compression-loaded isotropic plates with cutouts

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1990-01-01

    An experimental study of buckling and postbuckling behavior of square and rectangular compression-loaded aluminum plates with centrally located circular, square, and elliptical cutouts is presented. Experimental results indicate that the plates exhibit overall trends of increasing buckling strain and decreasing initial postbuckling stiffness with increasing cutout width. Corresponding plates with circular and square cutouts of the same width buckle at approximately the same strain level, and exhibit approximately the same initial postbuckling stiffness. Results show that the reduction in initial postbuckling stiffness due to a cutout generally decreases as the plate aspect ratio increases. Other results presented in this paper indicate that square plates with elliptical cutouts having a large cutout-width-to-plate-width ratio generally lose prebuckling and initial postbuckling stiffness as the cutout height increases. However, the plates buckle at essentially the same strain level. Results also indicate that postbuckling stiffness is more sensitive to changes in elliptical cutout height than are prebuckling stiffness and buckling strain.

  1. Analytical Prediction of Damage Growth in Notched Composite Panels Loaded in Axial Compression

    NASA Technical Reports Server (NTRS)

    Ambur, Damodar R.; McGowan, David M.; Davila, Carlos G.

    1999-01-01

    A progressive failure analysis method based on shell elements is developed for the computation of damage initiation and growth in stiffened thick-skin stitched graphite-epoxy panels loaded in axial compression. The analysis method involves a step-by-step simulation of material degradation based on ply-level failure mechanisms. High computational efficiency is derived from the use of superposed layers of shell elements to model each ply orientation in the laminate. Multiple integration points through the thickness are used to obtain the correct bending effects through the thickness without the need for ply-by-ply evaluations of the state of the material. The analysis results are compared with experimental results for three stiffened panels with notches oriented at 0, 15 and 30 degrees to the panel width dimension. A parametric study is performed to investigate the damage growth retardation characteristics of the Kevlar stitch lines in the pan

  2. Loading and compressing cesium atoms in a very far-off- resonant light trap

    NASA Astrophysics Data System (ADS)

    Depue, Marshall Thomas

    An experiment is described in which 3 × 107 Cs atoms are loaded into a 400 μm crossed beam far-off-resonant trap (FORT) that is only 2.5 μK deep. A high density sample is prepared in a magneto-optic trap (MOT), cooled in a 3D far-off-resonant lattice (FORL), optically pumped into the lowest energy state, adiabatically released from the FORL, magnetically levitated, and transferred to the final FORT trap with a phase space density of 10-3. Spontaneous emission in the FORT is negligible, and the atoms can be compressed in the FORT to a spatial density of higher than 1014 cm-3. Evaporative cooling under these conditions can proceed rapidly. The atoms are monitored with a high intensity fluorescent imaging technique that is well suited to providing accurate number and density measurements for optically thick samples.

  3. Triple Guest Occupancy and Negative Compressibility in Hydrogen-Loaded β-Hydroquinone Clathrate.

    PubMed

    Rozsa, Viktor F; Strobel, Timothy A

    2014-06-05

    The molecular interactions and structural behavior of a previously unexplored clathrate system, hydrogen-loaded β-hydroquinone (β-HQ+H2), were investigated under high pressure with synchrotron X-ray diffraction and Raman/infrared spectroscopies. The β-HQ+H2 system exhibits coupling of two independently rare phenomena: multiple occupancy and negative compressibility. The number of H2 molecules per cavity increases from one to three, causing unit cell volume increase by way of unique crystallographic interstitial guest positioning. We anticipate these occupancy-derived trends may be general to a range of inclusion compounds and may aid the chemical and crystallographic design of both high-occupancy hydrogen storage clathrates and novel, variable-composition materials with tunable mechanical properties.

  4. Experimental behavior of graphite-epoxy Y-stiffened specimens loaded in compression

    NASA Technical Reports Server (NTRS)

    Sydow, P. Daniel; Shuart, Mark J.

    1992-01-01

    An experimental investigation of the behavior of graphite-epoxy Y-stiffened specimens loaded in compression is presented. Experimental results are presented for element specimens with a single stiffener and for panel specimens with three stiffeners. Response and failure characteristics of the specimens are described. Effects of impact damage on structural response for both specimen configurations are also presented. Experimental results indicate that impact location may significantly affect the residual strength of the Y-stiffened specimens. The failure results indicate that the critical failure mode is buckling of the stiffener webs for Y-stiffened element specimens and buckling of the stiffener webs and other stiffener blades for the Y-stiffened panel specimens.

  5. Buckling and postbuckling behavior of compression-loaded isotropic plates with cutouts

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1990-01-01

    An experimental study of the buckling and postbuckling behavior of square and rectangular compression loaded aluminum plates with centrally located circular, square, and elliptical cutouts is presented. Experimental results indicate that the plates exhibit overall trends of increasing buckling strain and decreasing initial postbuckling stiffness with increasing cutout width. Corresponding plates with circular and square cutouts of the same width buckle at approximately the same strain level, and exhibit approximately the same initial postbuckling stiffness. Results show that the reduction in initial postbuckling stiffness due to a cutout generally decreases as the plate aspect ratio increases. Other results presented indicate that square plates with elliptical cutouts having a large cutout-width-to-plate-width ratio generally lose prebuckling and initial postbuckling stiffness as the cutout height increases. However, the plates buckle at essentially the same strain level. Results also indicate that postbuckling stiffness is more sensitive to changes in elliptical cutout height than are prebuckling stiffness and buckling strain.

  6. SHS and RHS stainless steel slender members loaded by compression and bending interaction

    NASA Astrophysics Data System (ADS)

    Židlický, Břetislav; Jandera, Michal

    2017-09-01

    Behaviour of stainless steel slender members loaded by interaction of axial compressive force and bending moment is investigated in this research. Square hollow sections (SHS) made of austenitic stainless steel grade are considered. An initial numerical parametric study in FE software Abaqus is given and its results are compared to the existing design procedures and design standard rules. The investigated parameters are mainly the column slenderness, section slenderness, ratio between the applied bending moment and axial compressive force and the moment distribution along the member. The necessity of having additional design rules for stainless steels is firstly demonstrated on the values of interaction factors ky which are significantly higher for stainless steel members due to the material nonlinearity with decreased stiffness even at lower stress levels. As an alternative, the General Method is used for comparison to the Abaqus GMNIA model results. The limitation of the method when used for members of non-linear material behaviour is shown and a safe modification of design procedure is suggested.

  7. Postbuckling response of long thick isotropic plates loaded in compression including higher order transverse shearing effects

    NASA Technical Reports Server (NTRS)

    Stein, Manuel; Sydow, P. Daniel; Librescu, Liviu

    1990-01-01

    Buckling and postbuckling results for aluminum plates loaded in compression are presented. The buckling results were plotted to show the effects of thickness on the stress coefficient. Buckling results are given for various length-to-width ratios. Postbuckling results for plates with transverse shearing flexibility are compared to results from classical theory for various width-to-thickness ratios. The plates are considered to be long with side edges simply supported, with edges free of stress and the plates are subjected to longitudinal compressive displacement. Characteristic curves indicating the average longitudinal direct stress resultant as a function of the applied displacements are calculated based on four different theories: Classical von Karman, first-order shear deformation, higher-order shear deformation, and three-dimensional flexibility. Present results indicate that the three-dimensional flexibility theory gives the lowest and therefore, most accurate results. The higher-order shear deformation theory has fewer unknowns than the three-dimensional flexibility but is not as accurate. The figures presented show that small differences occur in the maximum stress resultants and the transverse displacements calculated when the effects of transverse shear are included.

  8. Crack growth of 10M Ni-Mn-Ga material in cyclic mechanical loading

    NASA Astrophysics Data System (ADS)

    Aaltio, I.; Ge, Y.; Pulkkinen, H.; Sjöberg, A.; Söderberg, O.; Liu, X. W.; Hannula, S.-P.

    The 10M martensitic Ni-Mn-Ga single crystal materials are usually applied in the magneto-mechanical actuators. Therefore, it is important to know the possible effect of the long-term cyclic shape changes on their structure and behavior. This can be evaluated with the mechanical fatigue testing. In the present study, the single crystal 10M Ni-Mn-Ga samples of different compositions were applied to strain-controlled uniaxial mechanical cycling in the multivariant state at ambient temperature. The experiments revealed distinctive changes of the twin variant structure, especially in the mobile twin area, density of twin boundaries, and in the tendency for fatigue crack growth. Characterization of the crack surface showed that the cracks in the microscale grow in a step-wise manner on specific crystallographic planes, i.e, twin boundary planes, but that the macroscopic crack does not occur only along crystallographic directions.

  9. The transition from stress softening to stress hardening under cyclic loading induced by magnetic field for magneto-sensitive polymer gels

    NASA Astrophysics Data System (ADS)

    Xu, Yangguang; Liao, Guojiang; Zhang, Canyang; Wan, Qiang; Liu, Taixiang

    2016-04-01

    Magneto-sensitive polymer gel (MSPG) is a kind of ferromagnetic particle filled smart polymer composite, whose magneto-mechanical coupling mechanism has attracted increasing attention in recent years. In this work, the magneto-induced rheological response of MSPG under cyclic shear loading was investigated. It was found that magnetic field is the critical reason for the transition from stress softening to stress hardening under cyclic loading. Besides, the particle concentration and temperature are the controlling factors in the structure optimization of MSPG in the presence of magnetic field. The magneto-induced hardening mechanism was further proposed based on the related experimental results.

  10. An experimentally validated micromechanical model of a rat vertebra under compressive loading.

    PubMed

    Tsafnat, Naomi; Wroe, Stephen

    2011-01-01

    In recent years, finite element analysis (FEA) has been increasingly applied to examine and predict the mechanical behaviour of craniofacial and other bony structures. Traditional methods used to determine material properties and validate finite element models (FEMs) have met with variable success, and can be time-consuming. An implicit assumption underlying many FE studies is that relatively high localized stress/strain magnitudes identified in FEMs are likely to predict material failure. Here we present a new approach that may offer some advantages over previous approaches. Recently developed technology now allows us to both image and conduct mechanical tests on samples in situ using a materials testing stage (MTS) fitted inside the microCT scanner. Thus, micro-finite element models can be created and validated using both quantitative and qualitative means. In this study, a rat vertebra was tested under compressive loading until failure using an MTS. MicroCT imaging of the vertebra before mechanical testing was used to create a high resolution finite element model of the vertebra. Load-displacement data recorded during the test were used to calculate the effective Young's modulus of the bone (found to be 128 MPa). The microCT image of the compressed vertebra was used to assess the predictive qualities of the FE model. The model showed the highest stress concentrations in the areas that failed during the test. Clearly, our analyses do not directly address biomechanics of the craniofacial region; however, the methodology adopted here could easily be applied to examine the properties and behaviour of specific craniofacial structures, or whole craniofacial regions of small vertebrates. Experimentally validated micro-FE analyses are a powerful method in the study of materials with complex microstructures such as bone. © 2010 The Authors. Journal of Anatomy © 2010 Anatomical Society of Great Britain and Ireland.

  11. Innovative design of composite structures: Axisymmetric deformations of unsymmetrically laminated cylinders loaded in axial compression

    NASA Technical Reports Server (NTRS)

    Hyer, M. W.; Paraska, P. J.

    1990-01-01

    The study focuses on the axisymmetric deformation response of unsymmetrically laminate cylinders loaded in axial compression by known loads. A geometrically nonlinear analysis is used. Though buckling is not studied, the deformations can be considered to be the prebuckling response. Attention is directed at three 16 layer laminates: a (90 sub 8/0 sub 8) sub T; a (0 sub 8/90 sub 8) sub T and a (0/90) sub 4s. The symmetric laminate is used as a basis for comparison, while the two unsymmetric laminates were chosen because they have equal but opposite bending-stretching effects. Particular attention is given to the influence of the thermally-induced preloading deformations that accompany the cool-down of any unsymmetric laminate from the consolidation temperature. Simple support and clamped boundary conditions are considered. It is concluded that: (1) The radial deformations of an unsymmetric laminate are significantly larger than the radial deformations of a symmetric laminate, although for both symmetric and unsymmetric laminates the large deformations are confined to a boundary layer near the ends of the cylinder; (2) For this nonlinear problem the length of the boundary layer is a function of the applied load; (3) The sign of the radial deformations near the supported end of the cylinder depends strongly on the sense (sign) of the laminate asymmetry; (4) For unsymmetric laminates, ignoring the thermally-induced preloading deformations that accompany cool-down results in load-induced deformations that are under predicted; and (5) The support conditions strongly influence the response but the influence of the sense of asymmetry and the influence of the thermally-induced preloading deformations are independent of the support conditions.

  12. High-Fidelity Nonlinear Analysis of Compression-Loaded Composite Shells

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Starnes, James H., Jr.

    2001-01-01

    The results of an experimental and analytical study of the effects of initial imperfections on the buckling and postbuckling response of unstiffened thin-walled compression-loaded graphite-epoxy cylindrical shells are presented. The shells considered in the study have four different shell-wall laminates and two different shell-radius-to-thickness ratios. The shell-wall laminates include two different orthotropic laminates and two different quasi-isotropic laminates. The shell-radius-to-thickness ratios include shell-radius-to-thickness ratios equal to 100 and 200. The results identify the effects of traditional and nontraditional initial imperfections on the nonlinear response characteristics and buckling loads of the shells. The traditional imperfections include the geometric shell-wall mid-surface imperfections that are commonly discussed in the literature on thin shell buckling. The nontraditional imperfections include shell-wall thickness variations, local shell-wall ply-gaps associated with the fabrication process, shell-end geometric imperfections, nonuniform applied end loads, and variations in the boundary conditions including the effects of elastic boundary conditions. A high-fidelity nonlinear shell analysis procedure that accurately accounts for the effects of these traditional and nontraditional imperfections on the nonlinear response characteristics and buckling loads of the shells is described. The analysis procedure includes a nonlinear static analysis that predicts the stable response characteristics of the shells, and a nonlinear transient analysis that predicts the unstable response characteristics. The results of a local shell-wall stress analysis used to estimate failure stresses are also described.

  13. Mechanical strength of the silicon carbide-bearing materials under cyclic loading

    SciTech Connect

    Babaev, E.I.; Berdichevskii, I.M.; Kozlovskii, L.V.; Mei, E.P.; Rozhkova, R.A.

    1987-03-01

    The authors seek to optimize the firing process for porcelain both for the resulting properties of the porcelain and for the thermal efficiency of the furnace by finding a structural furnace material which will withstand the designated optimal firing regime. To this end they select and test a silicon carbide refractory for its ultimate flexural and compression strength and its resistance to fracture under thermal cycling and stress conditions.In actual service the refractory is found to increase the service life and reduce the frequency of maintenance of the furnace.

  14. Cyclic-load crack growth in ASME SA-105 grade II steel in high-pressure hydrogen at ambient temperature

    NASA Technical Reports Server (NTRS)

    Walter, R. J.; Chandler, W. T.

    1976-01-01

    ASME SA-105 Grade II steel, which is used in high-pressure hydrogen compressor systems, is similar to steels used or considered for use in high-pressure hydrogen storage vessels and pipelines. This paper summarizes the results of a program conducted to provide cyclic-load crack growth rate (da/dN) data for a fracture mechanics analysis of a 15,000 psi hydrogen compressor facility which contains pulse quieter and after-cooler separator vessels constructed of the ASME SA-105 Grade II steel. Included in the program were tests performed to assist in establishing operating procedures that could minimize the effect of hydrogen on crack growth rates during operation.

  15. Mixed-mode hydrogen-assisted cracking of high-strength steel: The role of cyclic load history

    SciTech Connect

    Toribio, J.; Ovejero, E.; Kharin, V.

    1999-07-01

    Prestressing steel wires are manufactured from a hot-rolled bar, which is heavily cold drawn to produce a highly resistant material. This manufacturing process generates very intense plastic deformations in the material and causes severe changes in its pearlitic microstructure, thus leading to anisotropic stress corrosion behavior in the form of environmentally assisted longitudinal splitting and, thus, mixed-mode stress corrosion cracking. This work describes experimental evidence of mixed-mode hydrogen-assisted cracking of high-strength steel and discusses the role of cyclic load history, because fatigue precracking is a fundamental technique of crack generation for posterior stress corrosion testing, and it has been reported that fatigue preloading may substantially alter the results from stress corrosion cracking tests, especially in the case of hydrogen-assisted cracking.

  16. An in vitro evaluation of effect of ionizing radiotherapy on push-out strength of fiber posts under cyclic loading.

    PubMed

    Aggarwal, Vivek

    2009-05-01

    Ionizing radiotherapy has a deleterious effect on all vital cells and thus might affect the collagen fibril network of dentin and formation of hybrid layer of composite resins. The present study evaluated the effect of ionizing x-ray radiotherapy on push-out bond strength of fiber posts. Sixty mandibular premolar roots were divided into 4 groups: group I, control group with no irradiation, restored with a quartz fiber post system with cyclic loading; group II, samples were exposed to 60 Gy radiation dosage and than restored; group III, samples were restored and then irradiated; and group IV, samples were restored during irradiation. A push-out bond strength test was done. Radiotherapy significantly reduced the push-out bond strength of fiber posts. Patients undergoing ionizing radiotherapy might have a less than ideal prognosis of fiber posts luted with dual cure resin cement with total etch bonding system, if restorations are done after radiotherapy.

  17. A study in vivo of the effects of a static compressive load on the proximal tibial physis in rabbits.

    PubMed

    Bries, Andrew D; Weiner, Dennis S; Jacquet, Robin; Adamczyk, Mark J; Morscher, Melanie A; Lowder, Elizabeth; Askew, Michael J; Steiner, Richard P; Horne, Walter I; Landis, William J

    2012-08-01

    The effect of compression on the physis is generally defined by the Hueter-Volkmann principle, in which decreased linear growth of the physis results from increased compression. This investigation examined whether mechanically induced compression of rabbit physes causes changes in gene expression, cells, and extracellular components that promote physeal resilience and strength (type-II collagen and aggrecan) and cartilage hypertrophy (type-X collagen and matrix metalloprotease-13). Static compressive loads (10 N or 30 N) were applied for two or six weeks across one hind limb proximal tibial physis of thirteen-week-old female New Zealand White rabbits (n = 18). The contralateral hind limb in all rabbits underwent sham surgery with no load to serve as an internal control. Harvested physes were divided into portions for histological, immunohistochemical, and quantitative reverse transcription-polymerase chain reaction analysis. Gene expression was statistically analyzed by means of comparisons between loaded samples and unloaded shams with use of analysis of variance and a Tukey post hoc test. Compared with unloaded shams, physes loaded at 10 N or 30 N for two weeks and at 10 N for six weeks showed histological changes in cells and matrices. Physes loaded at 30 N for six weeks were decreased in thickness and had structurally disorganized chondrocyte columns, a decreased extracellular matrix, and less intense type-II and X collagen immunohistochemical staining. Quantitative reverse transcription-polymerase chain reaction analysis of loaded samples compared with unloaded shams yielded a significantly (p ≤ 0.05) decreased gene expression of aggrecan and type-II and X collagen and no significant (p > 0.05) changes in the matrix metalloprotease-13 gene expression with increasing load. Compressed rabbit physes generate biochemical changes in collagens, proteoglycan, and cellular and tissue matrix architecture. Changes potentially weaken overall physeal strength

  18. Particle loading time and humidity effects on the efficiency of an N95 filtering facepiece respirator model under constant and inhalation cyclic flows.

    PubMed

    Mahdavi, Alireza; Haghighat, Fariborz; Bahloul, Ali; Brochot, Clothilde; Ostiguy, Claude

    2015-06-01

    It is necessary to investigate the efficiencies of filtering facepiece respirators (FFRs) exposed to ultrafine particles (UFPs) for long periods of time, since the particle loading time may potentially affect the efficiency of FFRs. This article aims to investigate the filtration efficiency for a model of electrostatic N95 FFRs with constant and 'inhalation-only' cyclic flows, in terms of particle loading time effect, using different humidity conditions. Filters were exposed to generated polydisperse NaCl particles. Experiments were performed mimicking an 'inhalation-only' scenario with a cyclic flow of 85 l min(-1) as the minute volume [or 170 l min(-1) as mean inhalation flow (MIF)] and for two constant flows of 85 and 170 l min(-1), under three relative humidity (RH) levels of 10, 50, and 80%. Each test was performed for loading time periods of 6h and the particle penetration (10-205.4nm in electrical mobility diameter) was measured once every 2h. For a 10% RH, the penetration of smaller size particles (<80nm), including the most penetrating particle size (MPPS), decreased over time for both constant and cyclic flows. For 50 and 80% RH levels, the changes in penetration were typically observed in an opposite direction with less magnitude. The penetrations at MPPS increased with respect to loading time under constant flow conditions (85 and 170 l min(-1)): it did not substantially increase under cyclic flows. The comparison of the cyclic flow (85 l min(-1) as minute volume) and constant flow equal to the cyclic flow minute volume indicated that, for all conditions the penetration was significantly less for the constant flow than that of cyclic flow. The comparison between the cyclic (170 l min(-1) as MIF) and constant flow equal to cyclic flow MIF indicated that, for the initial stage of loading, the penetrations were almost equal, but they were different for the final stages of the loading time. For a 10% RH, the penetration of a wide range of sizes was observed

  19. Loading-path dependent deformation of nanocrystalline Ta under single- and double-shock, and quasi-isentropic compression

    NASA Astrophysics Data System (ADS)

    Tang, M. X.; E, J. C.; Wang, L.; Luo, S. N.

    2017-03-01

    We investigate dynamic deformation of nanocrystalline Ta under single- and double-shock, and quasi-isentropic compression, with large-scale molecular dynamics simulations. Orientation mapping, selected area electron diffraction, and x-ray diffraction are implemented for microstructure analysis. Different deformation modes are found for different loading paths, and are attributed to the differences in temperature rise induced by dynamic compression. For sufficiently strong shocks, catastrophic activation of slip systems and their growth in single-shock loading with the largest temperature rise lead to amorphization and recrystallization, while stacking faults and dislocation slip dominate deformation in double-shock loading with intermediate temperature rise, and deformation twinning is the principal mode in quasi-isentropic loading with the least temperature rise.

  20. Effect of Initial Geometrical Imperfection on the Buckling Load of Cylindrical Sandwich Shells Under Axial Compression

    NASA Astrophysics Data System (ADS)

    Casado, Victor M.; Hinsch, Svend; Garcia, Jesus Gomez; Castro, Saullo G. P.

    2014-06-01

    The impact of geometrical imperfections on the general instability of laminated cylindrical sandwich shells was assessed by means of a numerical investigation. Five forms of 'ideal' initial geometrical imperfection patterns were studied: eigen-mode shaped, axisymmetric dimple, geometric dimple, single perturbation load and single stress-free dimple. Implementation of such imperfections, despite their simplicity, can provide a method for predicting lower-bound buckling loads during the preliminary design phase, when the structural defects of the real hardware are unknown. Numerical prediction of the non- linear instability of the cylinders under axial compression was performed using the finite element method. A typical launcher Inter Stage Skirt (ISS) structure is used as the basis for the chosen geometry and materials. In order to make design and qualification tests more affordable, it is common to use representative sub-scaled hardware. This paper verifies the validity of the chosen sub-scaling method of an ISS cylindrical shell. Buckling mechanisms are described and the different lower-bound methods are discussed.

  1. Postbuckling response of long thick plates loaded in compression including higher order transverse shearing effects

    NASA Technical Reports Server (NTRS)

    Stein, Manuel; Sydow, P. Daniel; Librescu, Liviu

    1990-01-01

    Buckling and postbuckling results are presented for compression-loaded simply-supported aluminum plates and composite plates with a symmetric lay-up of thin + or - 45 deg plies composed of many layers. Buckling results for aluminum plates of finite length are given for various length-to-width ratios. Asymptotes to the curves based on buckling results give N(sub xcr) for plates of infinite length. Postbuckling results for plates with transverse shearing flexibility are compared to results from classical theory for various width-to-thickness ratios. Characteristic curves indicating the average longitudinal direct stress resultant as a function of the applied displacements are calculated based on four different theories: Classical von Karman theory using the Kirchoff assumptions, first-order shear deformation theory, higher-order shear deformation theory, and 3-D flexibility theory. Present results indicate that the 3-D flexibility theory gives the lowest buckling loads. The higher-order shear deformation theory has fewer unknowns than the 3-D flexibility theory but does not take into account through-the-thickness effects. The figures presented show that small differences occur in the average longitudinal direct stress resultants from the four theories that are functions of applied end-shortening displacement.

  2. Numerical Modeling of Jointed Rock Under Compressive Loading Using X-ray Computerized Tomography

    NASA Astrophysics Data System (ADS)

    Yu, Qinglei; Yang, Shengqi; Ranjith, P. G.; Zhu, Wancheng; Yang, Tianhong

    2016-03-01

    As jointed rocks consist of joints embedded within intact rock blocks, the presence and geometrical fabric of joints have a great influence on the mechanical behavior of rock. With consideration of the actual spatial shape of joints, a numerical model is proposed to investigate the fracture evolution mechanism of jointed rocks. In the proposed model, computerized tomography (CT) scanning is first used to capture the microstructure of a jointed sandstone specimen, which is artificially fabricated by loading the intact sample until the residual strength, and then digital image processing (DIP) techniques are applied to characterize the geometrical fabric of joints from the CT images. A simple vectorization method is used to convert the microstructure based on a cross-sectional image into a layer of 3-D vectorized microstructure and the overall 3-D model of the jointed sandstone including the real spatial shape of the joints is established by stacking the layers in a specific sequence. The 3-D model is then integrated into a well-established code [three-dimensional Rock Failure Process Analysis, (RFPA3D)]. Using the proposed model, a uniaxial compression test of the jointed sandstone is simulated. The results show that the presence of joints can produce tensile stress zones surrounding them, which result in the fracture of jointed rocks under a relatively small external load. In addition, the spatial shape of the joints has a great influence on the fracture process of jointed rocks.

  3. Buckling and postbuckling behavior of square compression-loaded graphite-epoxy plates with circular cutouts

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1990-01-01

    An experimental study of the postbuckling behavior of square compression-loaded graphite-epoxy plates and isotropic plates with a central circular cutout is presented. Results are presented for unidirectional (0 sub 10)s and (90 sub 10)s plates, (0/90 sub 5)s plates, and for aluminum plates. Results are also presented for (+ or - O sub 6)s angle-ply plates for values of O = 30, 46, and 60 degrees. The experimental results indicate that the change in axial stiffness of a plate at buckling is strongly dependent upon cutout size and plate orthotropy. The presence of a cutout gives rise to an internal load distribution that changes, sometimes dramtically, as a function of cutout size coupled with the plate orthotropy. In the buckled state, the role of orthotropy becomes more significant since bending in addition to membrane orthotropy is present. Most of the plates with cutouts exhibited less postbuckling stiffness than the corresponding plate without a cutout, and the postbuckling stiffness decreased with increasing cutout size. However, some of the highly orthotropic plates with cutouts exhibited more postbuckling stiffness than the corresponding plate without a cutout.

  4. Effects of Carbon Nanomaterial Reinforcement on Composite Joints Under Cyclic and Impact Loading

    DTIC Science & Technology

    2012-03-01

    Molding ( VARTM ) technique with 7.5g/m2 of MWCNTs or CNFs dispersed at the joint interface ahead of the crack tip. The test coupons were loaded in 3...fabricated via Vacuum Assisted Resin Transfer Molding ( VARTM ) technique with 7.5g/m 2 of MWCNTs or CNFs dispersed at the joint interface ahead of... VARTM setup in the laboratory ........................................................................9 Figure 7. Arrangement of the various layers

  5. Capacity fade modelling of lithium-ion battery under cyclic loading conditions

    NASA Astrophysics Data System (ADS)

    Ashwin, T. R.; Chung, Yongmann M.; Wang, Jihong

    2016-10-01

    A pseudo two-dimensional (P2D) electro-chemical lithium-ion battery model is presented in this paper to study the capacity fade under cyclic charge-discharge conditions. The Newman model [1,2] has been modified to include a continuous solvent reduction reaction responsible for the capacity fade and power fade. The temperature variation inside the cell is accurately predicted using a distributed thermal model coupled with the internal chemical heat generation. The model is further improved by linking the porosity variation with the electrolyte partial molar concentration, thereby proving a stronger coupling between the battery performance and the chemical properties of electrolyte. The solid electrolyte interface (SEI) layer growth is estimated for different cut-off voltages and charging current rates. The results show that the convective heat transfer coefficient as well as the porosity variation influences the SEI layer growth and the battery life significantly. The choice of an electrolyte decides the conductivity and partial molar concentration, which is found to have a strong influence on the capacity fade of the battery. The present battery model integrates all essential electro-chemical processes inside a lithium-ion battery under a strong implicit algorithm, proving a useful tool for computationally fast battery monitoring system.

  6. Distinct cyclosporin a doses are required to enhance bone formation induced by cyclic and rest-inserted loading in the senescent skeleton.

    PubMed

    Srinivasan, Sundar; Threet, Dewayne; Worton, Leah E; Ausk, Brandon J; Bain, Steven D; Gardiner, Edith M; Kwon, Ronald Y; Gross, Ted S

    2014-01-01

    Age-related decline in periosteal adaptation negatively impacts the ability to utilize exercise to enhance bone mass and strength in the elderly. We recently observed that in senescent animals subject to cyclically applied loading, supplementation with Cyclosporin A (CsA) substantially enhanced the periosteal bone formation rates to levels observed in young animals. We therefore speculated that if the CsA supplement could enhance bone response to a variety of types of mechanical stimuli, this approach could readily provide the means to expand the range of mild stimuli that are robustly osteogenic at senescence. Here, we specifically hypothesized that a given CsA supplement would enhance bone formation induced in the senescent skeleton by both cyclic (1-Hz) and rest-inserted loading (wherein a 10-s unloaded rest interval is inserted between each load cycle). To examine this hypothesis, the right tibiae of senescent female C57BL/6 mice (22 Mo) were subjected to cyclic or rest-inserted loading supplemented with CsA at 3.0 mg/kg. As previously, we initially found that while the periosteal bone formation rate (p.BFR) induced by cyclic loading was enhanced when supplemented with 3.0 mg/kg CsA (by 140%), the response to rest-inserted loading was not augmented at this CsA dosage. In follow-up experiments, we observed that while a 30-fold lower CsA dosage (0.1 mg/kg) significantly enhanced p.BFR induced by rest-inserted loading (by 102%), it was ineffective as a supplement with cyclic loading. Additional experiments and statistical analysis confirmed that the dose-response relations were significantly different for cyclic versus rest-inserted loading, only because the two stimuli required distinct CsA dosages for efficacy. While not anticipated a priori, clarifying the complexity underlying the observed interaction between CsA dosage and loading type holds potential for insight into how bone response to a broad range of mechanical stimuli may be substantially enhanced in

  7. Thermally Stratified Compression Ignition: A new advanced low temperature combustion mode with load flexibility

    DOE PAGES

    Lawler, Benjamin; Splitter, Derek; Szybist, James; ...

    2017-03-01

    We introduce a new advanced combustion mode, called Thermally Stratified Compression Ignition (TSCI), which uses direct water injection to control both the average temperature and the temperature distribution prior to ignition, thereby providing cycle-to-cycle control over the start and rate of heat release in Low Temperature Combustion (LTC). Experiments were conducted to fundamentally understand the effects of water injection on heat release in LTC. Our results show that water injection retards the start of combustion due to the latent heat of vaporization of the injected water. Furthermore, for start of water injection timings between 20 and 70 degrees before topmore » dead center, combustion is significantly elongated compared to without water injection. The 10–90% burn duration with 6.6 and 9.0 mg of water per cycle was 77% and 146% longer than without water injection, respectively. Forced thermal stratification result from a direct water injection which reduces the heat release rate by local evaporative cooling. Finally, the load limits with and without water injection were determined experimentally. Without water injection, the load range was 2.3–3.6 bar gross IMEP. By using water injection to control heat release, the load range in TSCI was 2.3–8.4 bar gross IMEP, which is a range expansion of over 350%. These results demonstrate that direct water injection can provide significant improvements to both controllability and the range of operability of LTC, thereby resolving the major challenges associated with HCCI.« less

  8. Index of Unconfined Compressive Strength of SAFOD Core by Means of Point-Load Penetrometer Tests

    NASA Astrophysics Data System (ADS)

    Enderlin, M. B.; Weymer, B.; D'Onfro, P. S.; Ramos, R.; Morgan, K.

    2010-12-01

    The San Andreas Fault Observatory at Depth (SAFOD) project is motivated by the need to answer fundamental questions on the physical and chemical processes controlling faulting and earthquake generation within major plate-boundaries. In 2007, approximately 135 ft (41.1 m) of 4 inch (10.61 cm) diameter rock cores was recovered from two actively deforming traces of the San Andreas Fault. 97 evenly (more or less) distributed index tests for Unconfined Compressive Strength (UCS) where performed on the cores using a modified point-load penetrometer. The point-load penetrometer used was a handheld micro-conical point indenter referred to as the Dimpler, in reference to the small conical depression that it creates. The core surface was first covered with compliant tape that is about a square inch in size. The conical tip of the indenter is coated with a (red) dye and then forced, at a constant axial load, through the tape and into the sample creating a conical red depression (dimple) on the tape. The combination of red dye and tape preserves a record of the dimple geometrical attributes. The geometrical attributes (e.g. diameter and depth) depend on the rock UCS. The diameter of a dimple is measured with a surface measuring magnifier. Correlation between dimple diameter and UCS has been previously established with triaxial testing. The SAFOD core gave Dimpler UCS values in the range of 10 psi (68.9 KPa) to 15,000 psi (103.4 MPa). The UCS index also allows correlations between geomechanical properties and well log-derived petrophysical properties.

  9. Synergistic Effects of Stress-Rupture and Cyclic Loading on Strain Response of Fiber-Reinforced Ceramic-Matrix Composites at Elevated Temperature in Oxidizing Atmosphere

    PubMed Central

    Li, Longbiao

    2017-01-01

    In this paper, the synergistic effects of stress rupture and cyclic loading on the strain response of fiber-reinforced ceramic-matrix composites (CMCs) at elevated temperature in air have been investigated. The stress-strain relationships considering interface wear and interface oxidation in the interface debonded region under stress rupture and cyclic loading have been developed to establish the relationship between the peak strain, the interface debonded length, the interface oxidation length and the interface slip lengths. The effects of the stress rupture time, stress levels, matrix crack spacing, fiber volume fraction and oxidation temperature on the peak strain and the interface slip lengths have been investigated. The experimental fatigue hysteresis loops, interface slip lengths, peak strain and interface oxidation length of cross-ply SiC/MAS (magnesium alumino-silicate, MAS) composite under cyclic fatigue and stress rupture at 566 and 1093 °C in air have been predicted. PMID:28772544

  10. The Effects of Time-Compressed Instruction and Redundancy on Learning and Learners' Perceptions of Cognitive Load

    ERIC Educational Resources Information Center

    Pastore, Ray

    2012-01-01

    Can increasing the speed of audio narration in multimedia instruction decrease training time and still maintain learning? The purpose of this study was to examine the effects of time-compressed instruction and redundancy on learning and learners' perceptions of cognitive load. 154 university students were placed into conditions that consisted of…

  11. The Effects of Time-Compressed Instruction and Redundancy on Learning and Learners' Perceptions of Cognitive Load

    ERIC Educational Resources Information Center

    Pastore, Ray

    2012-01-01

    Can increasing the speed of audio narration in multimedia instruction decrease training time and still maintain learning? The purpose of this study was to examine the effects of time-compressed instruction and redundancy on learning and learners' perceptions of cognitive load. 154 university students were placed into conditions that consisted of…

  12. A Splitting Scheme for Solving Reaction-Diffusion Equations Modeling Dislocation Dynamics in Materials Subjected to Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Pontes, J.; Walgraef, D.; Christov, C. I.

    2010-11-01

    Strain localization and dislocation pattern formation are typical features of plastic deformation in metals and alloys. Glide and climb dislocation motion along with accompanying production/annihilation processes of dislocations lead to the occurrence of instabilities of initially uniform dislocation distributions. These instabilities result into the development of various types of dislocation micro-structures, such as dislocation cells, slip and kink bands, persistent slip bands, labyrinth structures, etc., depending on the externally applied loading and the intrinsic lattice constraints. The Walgraef-Aifantis (WA) (Walgraef and Aifanits, J. Appl. Phys., 58, 668, 1985) model is an example of a reaction-diffusion model of coupled nonlinear equations which describe 0 formation of forest (immobile) and gliding (mobile) dislocation densities in the presence of cyclic loading. This paper discuss two versions of the WA model and focus on a finite difference, second order in time 1-Nicolson semi-implicit scheme, with internal iterations at each time step and a spatial splitting using the Stabilizing, Correction (Christov and Pontes, Mathematical and Computer Modelling, 35, 87, 2002) for solving the model evolution equations in two dimensions. The results of two simulations are presented. More complete results will appear in a forthcoming paper.

  13. Effect of Air Abrasion Preconditioning on Microleakage in Class V Restorations Under Cyclic Loading: An In-vitro Study

    PubMed Central

    Dharmani, Charan Kamal Kaur; Singh, Shamsher; Logani, Ajay; Shah, Naseem

    2014-01-01

    Background: Microleakage in class V Glass Ionomer Cement(GIC) or composite restorations at enamel or cementum margins has been cited as a reason for their failure. Air abrasion has been used to precondition tooth surface for increasing retention of such restorations. This study is done to evaluate the effect of preconditioning with air abrasion on microleakage in class V GIC and composite restorations. Materials and Methods: Class V cavities were prepared in 40 freshly extracted teeth. They were categorised into following four groups (n=10) depending on cavity preconditioning and restoration. Group I: 10% polyacrylic acid and GI (Ketac molar TM 3M ESPE); Group II: AA and GI; Group III: 35% Phosphoric acid and micro filled composite (MC) (Heliomolar, Ivoclar Vivadent); Group IV: AA and MC. Each group was further divided into subgroups A (no loading) & B (cyclic loading). Microleakage at occlusal and gingival margins was evaluated using methylene blue dye penetration method. Statistical analysis was done using Kruskal-wallis test and Mann-Whitney U test. Results: Microleakage at cementum margins was higher than at enamel margins in all the groups. Preconditioning with AA resulted in increased micro leakage. Conclusion: AA as a preconditioning agent was ineffective in producing superior tooth-restoration bonding. PMID:24995240

  14. Crack Growth Behavior in the Threshold Region for High Cyclic Loading

    NASA Technical Reports Server (NTRS)

    Forman, R.; Figert, J.; Beek, J.; Ventura, J.; Martinez, J.; Samonski, F.

    2011-01-01

    The present studies show that fanning in the threshold regime is likely caused by other factors than a plastic wake developed during load shedding. The cause of fanning at low R-values is a result of localized roughness, mainly formation of a faceted crack surface morphology , plus crack bifurcations which alters the crack closure at low R-values. The crack growth behavior in the threshold regime involves both crack closure theory and the dislocation theory of metals. Research will continue in studying numerous other metal alloys and performing more extensive analysis, such as the variation in dislocation properties (e.g., stacking fault energy) and its effects in different materials.

  15. Compressive neuropathy of long thoracic nerve and accessory nerve secondary to heavy load bearing. A case report.

    PubMed

    Sahin, F; Yilmaz, F; Esit, N; Aysal, F; Kuran, B

    2007-03-01

    Carrying heavy loads that compress the shoulders is a possible etiological factor for both accessory and long thoracic nerve entrapment. In our patient, shouldering heavy loads damaged both nerves. A 27-year-old right-hand-dominant man was referred because of difficulty in raising his arms after a brief period of painful episodes due to heavy load bearing on both shoulders. Atrophic muscles around the shoulders, depressed and winged scapula were noted. An EMG confirmed entrapment of long thoracic and accessory nerves. An exercise program was instituted; 16 months after initial referral, though winged scapula was still noted, manual muscular strength had returned without functional limitation.

  16. Effect of Short-Duration Low-Magnitude Cyclic Loading Versus Immobilization on Tendon-Bone Healing After ACL Reconstruction in a Rat Model

    PubMed Central

    Brophy, Robert H.; Kovacevic, David; Imhauser, Carl W.; Stasiak, Mark; Bedi, Asheesh; Fox, Alice J.S.; Deng, Xiang-Hua; Rodeo, Scott A.

    2011-01-01

    Background: Successful anterior cruciate ligament reconstruction with use of soft-tissue grafts requires healing between tendon and bone. Little is known about the effect of mechanical load on the cellular and molecular cascade of tendon-to-bone healing. Understanding these mechanical influences has critical implications for postoperative rehabilitation following anterior cruciate ligament reconstruction. The purpose of this study was to test the hypothesis that, compared with perioperative immobilization, short-duration low-magnitude cyclic axial loading would result in impaired tendon-to-bone healing after anterior cruciate ligament reconstruction in a rat model. Methods: Fifty-two male Sprague-Dawley rats underwent anterior cruciate ligament reconstruction with use of a flexor digitorum longus autograft. The patellar tendon, capsule, and ligamentous structures were circumferentially released, and an external fixator parallel to the anterior cruciate ligament graft was placed across the knee. Mechanical loading, consisting of cyclic displacement of the femur and tibia constrained to axial translation parallel to the graft, was applied daily. The rats were randomly assigned to immobilization or daily loading, for fourteen or twenty-eight days. Biomechanical, micro-computed tomographic, and histomorphometric analysis was performed on the bone-tendon-bone complexes. Results: The load measured across the knees during cyclic displacement increased over time (p < 0.05). Load-to-failure testing of the isolated femur-anterior cruciate ligament graft-tibia specimens revealed no significant differences between groups at two or four weeks. By two weeks postoperatively, a greater number of ED1+ inflammatory macrophages (phagocytic cells involved in the initial injury response) were seen at the tendon-bone interface after loading in the cyclically loaded group than in the immobilized group (p = 0.01). Compared with the baseline values, the number of trabeculae was

  17. Effect of cyclic high loading rates on the fatigue strength of aluminum-based composites

    NASA Astrophysics Data System (ADS)

    Calderon Arteaga, Hermes Eskander

    The study of fatigue under high loading rates is of great interest in the complete characterization of a new series of composites with Al-Cu-Mg matrix reinforced with AlB2 dispersoids. Homogeneous and functionally graded composites were prepared via gravity and centrifugal casting, respectively. Through centrifugal casting a gradual variation of the volume fraction of reinforcing particles along the cross section was obtained. In specific fabrication conditions, even complete segregation of the reinforcement particles was achieved. Charpy impact tests as well as hardness tests were conducted to assess the composite strength as a function of the weight percent of boron. The tensile properties of gravity cast samples were obtained. Then for both casting conditions, simple edge-notched bend SE(B) specimens were tested under fatigue conditions (three-point bending). The results from impact and hardness tests allowed identifying an interaction between the Mg dissolved in the matrix and the diborides. This interaction, which has never been reported before, was responsible for the strength reduction observed. It was assumed that a substitutional diffusion of Al by Mg atoms in the hp3 structure of diboride was causing the strength reduction, and three approaches were developed to estimate the amount of Mg depleted from the matrix by the diborides during the composite processing. Gravity cast samples were more sensitive to monotonic damage due to fatigue loads where compared with functionally-graded composites. Contrary to the centrifugal cast samples, gravity samples were also affected by the loading rate. The Mg-AlB2 interaction was also responsible for the reduction in the fatigue resistance as the weight percent of boron increased in both types of composites; regression models were obtained to predict the crack growth curve slope change as function of the boron level. The particle distribution showed to affect the crack growth behavior of the FGMs, decreasing the

  18. Effect of Cyclic Thermal Loads on Fatigue Reliability in Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.

    1997-01-01

    Technological solutions that will ensure the economic viability and environmental compatibility of a future High Speed Civil Transport plane are currently being sought. Lighter structural materials for both airframe primary structures and engine structure components are being investigated. We believe that such objectives can be achieved through the use of high-temperature composites as well as other conventional, lighter weight alloys. One of the prime issues for these structural components is assured long-term behavior with a specified reliability. An investigation was conducted to describe a computational simulation methodology for predicting fatigue life, reliability, and probabilistic long-term behavior of polymer matrix composites. A unified time-, stress-, and load-dependent Multi- Factor Interaction Equation (MFIE) model developed at the NASA Lewis Research Center was used to simulate the long-term behavior of polymer matrix composites.

  19. Relation of cyclic loading pattern to microstructural fracture in creep fatigue

    NASA Technical Reports Server (NTRS)

    Manson, S. S.; Halford, G. R.; Oldrieve, R. E.

    1983-01-01

    Creep-fatigue-environment interaction is discussed using the 'strainrange partitioning' (SRP) framework as a basis. The four generic SRP strainrange types are studied with a view of revealing differences in micromechanisms of deformation and fatigue degradation. Each combines in a different manner the degradation associated with slip-plane sliding, grain-boundary sliding, migration, cavitation, void development and environmental interaction; hence the approch is useful in delineating the relative importance of these mechanisms in the different loadings. Micromechanistic results are shown for a number of materials, including 316 SS, wrought heat resistant alloys, several nickel-base superalloys, and a tantalum base alloy, T-111. Although there is a commonality of basic behavior, the differences are useful in delineation several important principles of interpretation. Some quantitative results are presented for 316 SS, involving crack initiation and early crack growth, as well as the interaction of low-cycle fatigue with high-cycle fatigue.

  20. Effect of various endodontic solutions on punch out strength of Resilon under cyclic loading

    PubMed Central

    Kumar, Narender; Aggarwal, Vivek; Singla, Mamta; Gupta, Ridhima

    2011-01-01

    Background: Before obturation, various endodontic solutions are used as a final rinse. These solutions might affect the bond strength of Resilon-Epiphany system. The aim of this study was to evaluate the effect of NaOCl (5.25%), chlorhexidine CHX (2%), EDTA solution (17%), and BioPure MTAD on push out bond strength of Resilon-Epiphany system. Materials and Methods: Seventy-five human premolar roots were prepared and divided on the basis of final endodontic solution rinse. The canals were obturated with Resilon-Epiphany system. All samples were restored using a fiber post system and indirect composite crown. The samples received 150 000 cycles of mechanical loading. Push out bond strength was performed in the apical third of root having Resilon obturation. Results and Conclusions: Different endodontic solutions tested, did not affected the push out bond strength of Resilon-Epiphany obturation system. PMID:22144804

  1. Technical and economic assessment of fluidized-bed-augmented compressed-air energy-storage system: system load following capability

    SciTech Connect

    Lessard, R.D.; Blecher, W.A.; Merrick, D.

    1981-09-01

    The load-following capability of fluidized bed combustion-augmented compressed air energy storage systems was evaluated. The results are presented in two parts. The first part is an Executive Summary which provides a concise overview of all major elements of the study including the conclusions, and, second, a detailed technical report describing the part-load and load following capability of both the pressurized fluid bed combustor and the entire pressurized fluid bed combustor/compressed air energy storage system. The specific tasks in this investigation were to: define the steady-state, part-load operation of the CAES open-bed PFBC; estimate the steady-state, part-load performance of the PFBC/CAES system and evaluate any possible operational constraints; simulate the performance of the PFBC/CAES system during transient operation and assess the load following capability of the system; and establish a start-up procedure for the open-bed PFBC and evaluate the impact of this procedure. The conclusions are encouraging and indicate that the open-bed PFBC/CAES power plant should provide good part-load and transient performance, and should have no major equipment-related constraints, specifically, no major problems associated with the performance or design of either the open-end PFBC or the PFBC/CAES power plant in steady-state, part-load operation are envisioned. The open-bed PFBC/CAES power plant would have a load following capability which would be responsive to electric utility requirements for a peak-load power plant. The open-bed PFBC could be brought to full operating conditions within 15 min after routine shutdown, by employing a hot-start mode of operation. The PFBC/CAES system would be capable of rapid changes in output power (12% of design load per minute) over a wide output power range (25% to 100% of design output). (LCL)

  2. Cyclic Deformation in Metallic Glasses.

    PubMed

    Sha, Z D; Qu, S X; Liu, Z S; Wang, T J; Gao, H

    2015-10-14

    Despite the utmost importance and decades of experimental studies on fatigue in metallic glasses (MGs), there has been so far little or no atomic-level understanding of the mechanisms involved. Here we perform molecular dynamics simulations of tension-compression fatigue in Cu50Zr50 MGs under strain-controlled cyclic loading. It is shown that the shear band (SB) initiation under cyclic loading is distinctly different from that under monotonic loading. Under cyclic loading, SB initiation takes place when aggregates of shear transformation zones (STZs) accumulating at the MG surface reach a critical size comparable to the SB width, and the accumulation of STZs follows a power law with rate depending on the applied strain. It is further shown that almost the entire fatigue life of nanoscale MGs under low cycle fatigue is spent in the SB-initiation stage, similar to that of crystalline materials. Furthermore, a qualitative investigation of the effect of cycling frequency on the fatigue behavior of MGs suggests that higher cycling frequency leads to more cycles to failure. The present study sheds light on the fundamental fatigue mechanisms of MGs that could be useful in developing strategies for their engineering applications.

  3. Processing-induced-transformations (PITs) during direct compression: Impact of tablet composition and compression load on phase transition of caffeine.

    PubMed

    Juban, Audrey; Briançon, Stéphanie; Puel, François

    2016-03-30

    In the pharmaceutical field, solid-state transitions that may occur during manufacturing of pharmaceuticals are of great importance. The phase transition of a model API, caffeine Form I (CFI), was studied during direct compression process by analysing the impacts of the operating conditions (process and formulation). This work is focused on two formulation parameters: nature of the diluent and impact of the caffeine dilution, and one process parameter: the compression pressure that may impact the phase transition of CFI. Tablets were made from pure CFI and from binary mixture of CFI/diluent (microcrystalline cellulose or anhydrous dicalcium phosphate). A kinetic study performed during six months helped to highlight the influence of these parameters on the CFI transition degree. Results showed a triggering effect of the direct compression process, transformation was higher in tablets than in uncompressed powders. Whatever the pressure applied, CFI transition degree was almost constant and uniformly occurring throughout the tablet volume. Nevertheless, several differences on the evolution of the CFI transition degree were observed between binary mixtures of CFI/diluent. An analysis of the transition mechanism with a stretched exponential law of the Johnson-Mehl-Avrami model shows that tableting accelerates the polymorphic transition without modifying its mechanism controlled by nucleation only. Copyright © 2016 Elsevier B.V. All rights reserved.

  4. A method for the geometrically nonlinear analysis of compressively loaded prismatic composite structures

    NASA Technical Reports Server (NTRS)

    Stoll, Frederick; Gurdal, Zafer; Starnes, James H., Jr.

    1991-01-01

    A method was developed for the geometrically nonlinear analysis of the static response of thin-walled stiffened composite structures loaded in uniaxial or biaxial compression. The method is applicable to arbitrary prismatic configurations composed of linked plate strips, such as stiffened panels and thin-walled columns. The longitudinal ends of the structure are assumed to be simply supported, and geometric shape imperfections can be modeled. The method can predict the nonlinear phenomena of postbuckling strength and imperfection sensitivity which are exhibited by some buckling-dominated structures. The method is computer-based and is semi-analytic in nature, making it computationally economical in comparison to finite element methods. The method uses a perturbation approach based on the use of a series of buckling mode shapes to represent displacement contributions associated with nonlinear response. Displacement contributions which are of second order in the model amplitudes are incorported in addition to the buckling mode shapes. The principle of virtual work is applied using a finite basis of buckling modes, and terms through the third order in the model amplitudes are retained. A set of cubic nonlinear algebraic equations are obtained, from which approximate equilibrium solutions are determined. Buckling mode shapes for the general class of structure are obtained using the VIPASA analysis code within the PASCO stiffened-panel design code. Thus, subject to some additional restrictions in loading and plate anisotropy, structures which can be modeled with respect to buckling behavior by VIPASA can be analyzed with respect to nonlinear response using the new method. Results obtained using the method are compared with both experimental and analytical results in the literature. The configurations investigated include several different unstiffened and blade-stiffening panel configurations, featuring both homogeneous, isotropic materials, and laminated composite

  5. Two-way Shape Memory Effect of NiTi under Compressive Loading Cycles

    NASA Astrophysics Data System (ADS)

    Yoo, Young Ik; Lee, Jung Ju

    In this study, the two-way shape memory effect (TWSME) of a Ni-54.5 at.% Ti alloy was investigated experimentally to develop a NiTi linear actuator. The two-way shape memory effect was induced through a compressive shape memory cycle composed of four steps: (1) loading to maximum deformation; (2) unloading; (3) heating; (4) and cooling. Six types of specimens (one solid cylindrical and five tubular) were used to obtain the twoway shape memory strain and two-way recovery stress and to evaluate the actuating capacity. The two-way actuating strain showed a convergent tendency after several training cycles for the same maximum deformation. A maximum value of the two-way strain was obtained for 7% of maximum deformation, independently of the geometry of the tubular specimens. The two-way strains obtained by the shape memory cycles and two-way recovery stress linearly increase as a function of the maximum deformation and the two-way strain, respectively, and the geometry of specimen affects the two-way recovery stress. Although the results show that sufficient recovery stress can be generated by either the two-way shape memory process or by the one-way shape memory process, the two-way shape memory process can be applied more conveniently to actuating applications.

  6. Characterization of Aortic Tissue Fracture Toughness and Stiffness under Cyclical Fatigue Loading

    NASA Astrophysics Data System (ADS)

    Chu, Boby

    An ascending aortic aneurysm is an asymptomatic disease that, if left untreated, could lead to death through its eventual rupture. Current clinical management practices are based primarily on the monitoring of an aneurysm's growth, followed by surgical resection of the affected aortic segment when its diameter reaches 5 to 5.5 centimetres. Unfortunately, this method is based solely on clinical observations and is frequently inaccurate in predicting the risk of an imminent rupture. More sophisticated tools have been developed and do not depend on aneurysm size alone, but these have focused mostly on the distribution of stresses within an aneurismal aortic wall and do not give clinicians an estimate of the time to failure. This present work incorporates the temporal aspect by examining the effects of fatigue on aortic wall properties, and adopts an energetics approach to evaluating the aorta's resistance to rupture. Tissue samples from porcine aortas were fatigued and were subjected to both biaxial and guillotine tests to assess stiffness and fracture toughness. The experiments indicate that both properties decreased according to a power function. After 1 000 000 loading cycles, the final/initial stiffness ratio dropped to 0.85, while its toughness counterpart fell to 0.80. This work constitutes the first tentative steps towards the development of a clinical tool that can evaluate the fracture toughness of aneurismal aortic tissues and predict the temporal likelihood of aneurismal rupture.

  7. Evaluating the capability of time-of-flight cameras for accurately imaging a cyclically loaded beam

    NASA Astrophysics Data System (ADS)

    Lahamy, Hervé; Lichti, Derek; El-Badry, Mamdouh; Qi, Xiaojuan; Detchev, Ivan; Steward, Jeremy; Moravvej, Mohammad

    2015-05-01

    Time-of-flight cameras are used for diverse applications ranging from human-machine interfaces and gaming to robotics and earth topography. This paper aims at evaluating the capability of the Mesa Imaging SR4000 and the Microsoft Kinect 2.0 time-of-flight cameras for accurately imaging the top surface of a concrete beam subjected to fatigue loading in laboratory conditions. Whereas previous work has demonstrated the success of such sensors for measuring the response at point locations, the aim here is to measure the entire beam surface in support of the overall objective of evaluating the effectiveness of concrete beam reinforcement with steel fibre reinforced polymer sheets. After applying corrections for lens distortions to the data and differencing images over time to remove systematic errors due to internal scattering, the periodic deflections experienced by the beam have been estimated for the entire top surface of the beam and at witness plates attached. The results have been assessed by comparison with measurements from highly-accurate laser displacement transducers. This study concludes that both the Microsoft Kinect 2.0 and the Mesa Imaging SR4000s are capable of sensing a moving surface with sub-millimeter accuracy once the image distortions have been modeled and removed.

  8. An Investigation of SiC/SiC Woven Composite Under Monotonic and Cyclic Loading

    NASA Technical Reports Server (NTRS)

    Lang, J.; Sankar, J.; Kelkar, A. D.; Bhatt, R. T.; Singh, M.; Lua, J.

    1997-01-01

    The desirable properties in ceramic matrix composites (CMCs), such as high temperature strength, corrosion resistance, high toughness, low density, or good creep resistance have led to increased use of CMCs in high-speed engine structural components and structures that operate in extreme temperature and hostile aero-thermo-chemical environments. Ceramic matrix composites have been chosen for turbine material in the design of 21 st-century civil propulsion systems to achieve high fuel economy, improved reliability, extended life, and reduced cost. Most commercial CMCs are manufactured using a chemical vapor infiltration (CVI) process. However, a lower cost fabrication known as melt-infiltration process is also providing CMCs marked for use in hot sections of high-speed civil transports. The scope of this paper is to report on the material and mechanical characterization of the CMCs subjected to this process and to predict the behavior through an analytical model. An investigation of the SiC/SiC 8-harness woven composite is ongoing and its tensile strength and fatigue behavior is being characterized for room and elevated temperatures. The investigation is being conducted at below and above the matrix cracking stress once these parameters are identified. Fractography and light microscopy results are being studied to characterize the failure modes resulting from pure uniaxial loading. A numerical model is also being developed to predict the laminate properties by using the constituent material properties and tow undulation.

  9. A scanning electron-microscopic study of in vitro abrasion of mammalian tooth enamel under compressive loads.

    PubMed

    Maas, M C

    1994-01-01

    Microscopic tooth-wear (microwear) patterns can be an important tool for assessing modes and rates of abrasive tooth wear, but their analysis and interpretation is complicated by the fact that microwear is influenced by many factors. Three of these factors were here tested under conditions of compressive loading: (1) species differences in enamel structure, (2) abrasive particle size and (3) magnitude of force. Teeth of four species (Homo sapiens, Lemur fulvus, Ovis aries and Crocodylus rhombifer) were abraded in vitro using three sizes of abrasive silicon-carbide grit (average diameters 73, 23 and 14 microns), at two loads (50 and 100 kg). Microwear features were assessed by scanning electron microscopy of lightly etched enamel surfaces and epoxy replicas. Microwear pits (length:width < 4:1) were the predominant feature type. Factorial analysis of variance of rank-transformed, feature-area measurements demonstrated that, under conditions of compressive loading, the size of abrasive particles was the primary determinant of microwear size. These results contrast with previous experimental tests of abrasion by predominantly shearing loads, where feature size was influenced by interaction among experimental factors, including the microscopic orientation of enamel crystallites. Although magnitude of compressive force was not a factor in microwear size variation, it may be a critical factor in explaining the presence or absence of microwear on tooth surfaces. The relatively small compressive bite force generated during typical chewing may not consistently produce abrasive pitting. These experiments demonstrate that, as the same abrasive regime can produce both large and small pits, the mechanism by which wear features are formed (i.e. compression or adhesion) cannot be determined from the size of features alone. Nevertheless, the dependence of pit size on abrasive particle size demonstrates that metrical variation in wear features can elucidate important attributes of

  10. Effect of Degeneration on Fluid–Solid Interaction within Intervertebral Disk Under Cyclic Loading – A Meta-Model Analysis of Finite Element Simulations

    PubMed Central

    Nikkhoo, Mohammad; Khalaf, Kinda; Kuo, Ya-Wen; Hsu, Yu-Chun; Haghpanahi, Mohammad; Parnianpour, Mohamad; Wang, Jaw-Lin

    2015-01-01

    The risk of low back pain resulted from cyclic loadings is greater than that resulted from prolonged static postures. Disk degeneration results in degradation of disk solid structures and decrease of water contents, which is caused by activation of matrix digestive enzymes. The mechanical responses resulted from internal solid–fluid interactions of degenerative disks to cyclic loadings are not well studied yet. The fluid–solid interactions in disks can be evaluated by mathematical models, especially the poroelastic finite element (FE) models. We developed a robust disk poroelastic FE model to analyze the effect of degeneration on solid–fluid interactions within disk subjected to cyclic loadings at different loading frequencies. A backward analysis combined with in vitro experiments was used to find the elastic modulus and hydraulic permeability of intact and enzyme-induced degenerated porcine disks. The results showed that the averaged peak-to-peak disk deformations during the in vitro cyclic tests were well fitted with limited FE simulations and a quadratic response surface regression for both disk groups. The results showed that higher loading frequency increased the intradiscal pressure, decreased the total fluid loss, and slightly increased the maximum axial stress within solid matrix. Enzyme-induced degeneration decreased the intradiscal pressure and total fluid loss, and barely changed the maximum axial stress within solid matrix. The increase of intradiscal pressure and total fluid loss with loading frequency was less sensitive after the frequency elevated to 0.1 Hz for the enzyme-induced degenerated disk. Based on this study, it is found that enzyme-induced degeneration decreases energy attenuation capability of disk, but less change the strength of disk. PMID:25674562

  11. Anelastic Response of Ice-I/Magnesium Sulfate Hydrate Eutectic Aggregates Obtained from Creep and Cyclic-Loading Experiments

    NASA Astrophysics Data System (ADS)

    McCarthy, C.; Goldsby, D. L.; Cooper, R. F.

    2007-12-01

    The large icy satellites of the giant planets are subjected to periodic stress due to their resonance-effected orbital eccentricity. The dissipation of this tidal elastic energy represents a potentially significant internal energy source, the magnitude of which depends on the anelastic properties of the various material layers (ice, rock, etc.). In an icy satellite incorporating an internal ocean, as is suggested for Europa, most of the tidal dissipation (attenuation) occurs in the outer ice layer. Current models for attenuation in the icy shell rely on the inversion of a Maxwell model of steady-state rheology because, to date, no direct dynamic measurements of energy absorption in polycrystalline ice at low-stress/low-frequency planetary conditions have been reported. We are pursuing transient and steady-state creep as well as direct attenuation measurements on polycrystalline ice-I and on eutectic aggregates of ice-I and salt hydrates, such as those suggested to be present on the surface of Europa by the near-infrared spectral data. We focus primarily on system H2O-MgSO4 because it represents the best (binary-system) fit to the spectral data. Samples are fabricated using a misting/sifting technique in order to obtain fine grain-size, or, more accurately, eutectic colony-size (< 25 μm). Transformation of the time- domain data suggest the Maxwell model of steady state is inappropriate for understanding attenuation in pure ice, and wildly inappropriate for a ice-I/magnesium sulfate hydrate eutectic material, which demonstrates far higher attenuation (e.g., a factor of 102 at 1 Hz) than that predicted from the model. The absorption behavior of solid-state heterophase boundaries are argued as crucial in this behavior. Attenuation (cyclic compression- compression) experiments have commenced; we will report initial results, comparing these to earlier studies of the static response. Information gleaned from these experiment can help constrain models of crustal thickness

  12. Cyclic loading experiments to measure material response over a broad frequency range: from tickling of rocks to squeezing of moons

    NASA Astrophysics Data System (ADS)

    McCarthy, C.; Takei, Y.; Cooper, R. F.; Savage, H. M.

    2014-12-01

    Seismology provides powerful methods for imaging the interior of the Earth, not only through differences in seismic velocities, but also through attenuation contrasts. As seismic waves travel through the Earth they are attenuated in accordance with the viscoelastic properties of the material through which they pass. With proper constraints, we will someday be able to use seismic attenuation data as a prospecting tool to determine the grain size, temperature, pressure, melt content, and water content of the material along the ray path. Furthermore, it should be possible to determine active deformation structure, such as crystallographic preferred orientations that form in response to far-field natural tectonic loading. Laboratory studies are striving to provide these needed constraints. Using analogues to mantle rock, we isolate and scrutinize the physics of how microstructural elements affect macroscopic properties of attenuation and steady-state viscosity. An organic analogue, borneol, was used to measure the effects of grain size, temperature, and melt content over a broad frequency range. In these experiments, grain boundary processes were found to play a major role. Polycrystalline ice, which can be considered a rock analogue, has been used to explore the effect of accumulated strain on attenuation, particularly in material that is actively deforming via dislocation creep. Here, defect concentration and substructure are important. I will discuss the use of cyclic loading experiments on borneol and on polycrystalline ice to probe material response from seismic to tidal frequencies, from 10 Hz to 10-4 Hz respectively. These experiments, then, inform our knowledge of viscoelastic behavior of geologic materials at not only seismic frequencies, but also the tidal forcing frequencies experienced by tidewater glaciers and icy satellites.

  13. Fatigue Damage and Lifetime of SiC/SiC Ceramic-Matrix Composite under Cyclic Loading at Elevated Temperatures.

    PubMed

    Li, Longbiao

    2017-03-31

    In this paper, the fatigue damage and lifetime of 2D SiC/SiC ceramic-matrix composites (CMCs) under cyclic fatigue loading at 750, 1000, 1100, 1200 and 1300 °C in air and in steam atmosphere have been investigated. The damage evolution versus applied cycles of 2D SiC/SiC composites were analyzed using fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain and interface shear stress. The presence of steam accelerated the damage development inside of SiC/SiC composites, which increased the increasing rate of the fatigue hysteresis dissipated energy and the fatigue peak strain, and the decreasing rate of the fatigue hysteresis modulus and the interface shear stress. The fatigue life stress-cycle (S-N) curves and fatigue limit stresses of 2D SiC/SiC composites at different temperatures in air and in steam condition have been predicted. The fatigue limit stresses approach 67%, 28%, 39% 17% and 28% tensile strength at 750, 1000, 1100, 1200 and 1300 °C in air, and 49%, 10%, 9% and 19% tensile strength at 750, 1000, 1200 and 1300 °C in steam conditions, respectively.

  14. Fatigue Damage and Lifetime of SiC/SiC Ceramic-Matrix Composite under Cyclic Loading at Elevated Temperatures

    PubMed Central

    Li, Longbiao

    2017-01-01

    In this paper, the fatigue damage and lifetime of 2D SiC/SiC ceramic-matrix composites (CMCs) under cyclic fatigue loading at 750, 1000, 1100, 1200 and 1300 °C in air and in steam atmosphere have been investigated. The damage evolution versus applied cycles of 2D SiC/SiC composites were analyzed using fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain and interface shear stress. The presence of steam accelerated the damage development inside of SiC/SiC composites, which increased the increasing rate of the fatigue hysteresis dissipated energy and the fatigue peak strain, and the decreasing rate of the fatigue hysteresis modulus and the interface shear stress. The fatigue life stress-cycle (S-N) curves and fatigue limit stresses of 2D SiC/SiC composites at different temperatures in air and in steam condition have been predicted. The fatigue limit stresses approach 67%, 28%, 39% 17% and 28% tensile strength at 750, 1000, 1100, 1200 and 1300 °C in air, and 49%, 10%, 9% and 19% tensile strength at 750, 1000, 1200 and 1300 °C in steam conditions, respectively. PMID:28772736

  15. Relationship Between Hysteresis Dissipated Energy and Temperature Rising in Fiber-Reinforced Ceramic-Matrix Composites Under Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2016-06-01

    In this paper, the relationship between hysteresis dissipated energy and temperature rising of the external surface in fiber-reinforced ceramic-matrix composites (CMCs) during the application of cyclic loading has been analyzed. The temperature rise, which is caused by frictional slip of fibers within the composite, is related to the hysteresis dissipated energy. Based on the fatigue hysteresis theories considering fibers failure, the hysteresis dissipated energy and a hysteresis dissipated energy-based damage parameter changing with the increase of cycle number have been investigated. The relationship between the hysteresis dissipated energy, a hysteresis dissipated energy-based damage parameter and a temperature rise-based damage parameter have been established. The experimental temperature rise-based damage parameter of unidirectional, cross-ply and 2D woven CMCs corresponding to different fatigue peak stresses and cycle numbers have been predicted. It was found that the temperature rise-based parameter can be used to monitor the fatigue damage evolution and predict the fatigue life of fiber-reinforced CMCs.

  16. Analysis of Plasma-Sprayed Thermal Barrier Coatings With Homogeneous and Heterogeneous Bond Coats Under Spatially Uniform Cyclic Thermal Loading

    NASA Technical Reports Server (NTRS)

    Arnold, Steven M.; Pindera, Marek-Jerzy; Aboudi, Jacob

    2003-01-01

    This report summarizes the results of a numerical investigation into the spallation mechanism in plasma-sprayed thermal barrier coatings observed under spatially-uniform cyclic thermal loading. The analysis focuses on the evolution of local stress and inelastic strain fields in the vicinity of the rough top/bond coat interface during thermal cycling, and how these fields are influenced by the presence of an oxide film and spatially uniform and graded distributions of alumina particles in the metallic bond coat aimed at reducing the top/bond coat thermal expansion mismatch. The impact of these factors on the potential growth of a local horizontal delamination at the rough interface's crest is included. The analysis is conducted using the Higher-Order Theory for Functionally Graded Materials with creep/relaxation constituent modeling capabilities. For two-phase bond coat microstructures, both the actual and homogenized properties are employed in the analysis. The results reveal the important contributions of both the normal and shear stress components to the delamination growth potential in the presence of an oxide film, and suggest mixed-mode crack propagation. The use of bond coats with uniform or graded microstructures is shown to increase the potential for delamination growth by increasing the magnitude of the crack-tip shear stress component.

  17. Liposomes loaded with a STING pathway ligand, cyclic di-GMP, enhance cancer immunotherapy against metastatic melanoma.

    PubMed

    Nakamura, Takashi; Miyabe, Hiroko; Hyodo, Mamoru; Sato, Yusuke; Hayakawa, Yoshihiro; Harashima, Hideyoshi

    2015-10-28

    Malignant melanomas escape immunosurveillance via the loss/down-regulation of MHC-I expression. Natural killer (NK) cells have the potential to function as essential effector cells for eliminating melanomas. Cyclic di-GMP (c-di-GMP), a ligand of the stimulator of interferon genes (STING) signal pathway, can be thought of as a new class of adjuvant against cancer. However, it is yet to be tested, because technologies for delivering c-di-GMP to the cytosol are required. Herein, we report that c-di-GMP efficiently activates NK cells and induces antitumor effects against malignant melanomas when loaded in YSK05 lipid containing liposomes, by assisting in the efficient delivery of c-di-GMP to the cytosol. The intravenous administration of c-di-GMP encapsulated within YSK05-liposomes (c-di-GMP/YSK05-Lip) into mice efficiently induced the production