Effect of cyclic loading and retightening on reverse torque value in external and internal implants

PubMed Central

Cho, Woong-Rae; Huh, Yoon-Hyuk; Park, Chan-Jin

2015-01-01

PURPOSE The aim of this study was to evaluate the effect of cyclic loading and screw retightening on reverse torque value (RTV) in external and internal type implants. MATERIALS AND METHODS Cement-retained abutments were connected with 30 Ncm torque to external and internal type implants. Experimental groups were classified according to implant connection type and retightening/loading protocol. In groups with no retightening, RTV was evaluated after cyclic loading for 100,000 cycles. In groups with retightening, RTV was measured after 3, 10, 100 cycles as well as every 20,000 cycles until 100,000 cycles of loading. RESULTS Every group showed decreased RTV after cyclic loading. Before and after cyclic loading, external type implants had significantly higher RTVs than internal type implants. In external type implants, retightening did not affect the decrease in RTV. In contrast, retightening 5 times and retightening after 10 cycles of dynamic loading was effective for maintaining RTV in internal type implants. CONCLUSION Retightening of screws is more effective in internal type implants than external type implants. Retightening of screws is recommended in the early stage of functional loading. PMID:26330975

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 of fatigue-related failures in these elevated load and high cycle test scenarios are promising, as are the relatively low displacements given the extreme nature of each test. This cyclic loading method is intended to supplement the ASTM F2028-14 standard that adequately simulates the rocking horse loading mechanism but may not adequately simulate the fatigue-related failure modes.

A New High-Speed, High-Cycle, Gear-Tooth Bending Fatigue Test Capability

NASA Technical Reports Server (NTRS)

Stringer, David B.; Dykas, Brian D.; LaBerge, Kelsen E.; Zakrajsek, Andrew J.; Handschuh, Robert F.

2011-01-01

A new high-speed test capability for determining the high cycle bending-fatigue characteristics of gear teeth has been developed. Experiments were performed in the test facility using a standard spur gear test specimens designed for use in NASA Glenn s drive system test facilities. These tests varied in load condition and cycle-rate. The cycle-rate varied from 50 to 1000 Hz. The loads varied from high-stress, low-cycle loads to near infinite life conditions. Over 100 tests were conducted using AISI 9310 steel spur gear specimen. These results were then compared to previous data in the literature for correlation. Additionally, a cycle-rate sensitivity analysis was conducted by grouping the results according to cycle-rate and comparing the data sets. Methods used to study and verify load-path and facility dynamics are also discussed.

A Mechanism for the Loading-Unloading Substorm Cycle Missing in MHD Global Magnetospheric Simulation Models

NASA Technical Reports Server (NTRS)

Klimas, A. J.; Uritsky, V.; Vassiliadis, D.; Baker, D. N.

2005-01-01

Loading and consequent unloading of magnetic flux is an essential element of the substorm cycle in Earth's magnetotail. We are unaware of an available global MHD magnetospheric simulation model that includes a loading- unloading cycle in its behavior. Given the central role that MHD models presently play in the development of our understanding of magnetospheric dynamics, and given the present plans for the central role that these models will play in ongoing space weather prediction programs, it is clear that this failure must be corrected. A 2-dimensional numerical driven current-sheet model has been developed that incorporates an idealized current- driven instability with a resistive MHD system. Under steady loading, the model exhibits a global loading- unloading cycle. The specific mechanism for producing the loading-unloading cycle will be discussed. It will be shown that scale-free avalanching of electromagnetic energy through the model, from loading to unloading, is carried by repetitive bursts of localized reconnection. Each burst leads, somewhat later, to a field configuration that is capable of exciting a reconnection burst again. This process repeats itself in an intermittent manner while the total field energy in the system falls. At the end of an unloading interval, the total field energy is reduced to well below that necessary to initiate the next unloading event and, thus, a loading-unloading cycle results. It will be shown that, in this model, it is the topology of bursty localized reconnection that is responsible for the appearance of the loading-unloading cycle.

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-01-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-03-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

Fuel and Core Design Options to Overcome the Heavy Metal Loading Limit and Improve Performance and Safety of Liquid Salt Cooled Reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrovic, Bojan; Maldonado, Ivan

2016-04-14

The research performed in this project addressed the issue of low heavy metal loading and the resulting reduced cycle length with increased refueling frequency, inherent to all FHR designs with solid, non-movable fuel based on TRISO particles. Studies performed here focused on AHTR type of reactor design with plate (“plank”) fuel. Proposal to FY12 NEUP entitled “Fuel and Core Design Options to Overcome the Heavy Metal Loading Limit and Improve Performance and Safety of Liquid Salt Cooled Reactors” was selected for award, and the 3-year project started in August 2012. A 4-month NCE was granted and the project completed onmore » December 31, 2015. The project was performed by Georgia Tech (Prof. Bojan Petrovic, PI) and University of Tennessee (Prof. Ivan Maldonado, Co-PI), with a total funding of $758,000 over 3 years. In addition to two Co-PIs, the project directly engaged 6 graduate students (at doctoral or MS level) and 2 postdoctoral researchers. Additionally, through senior design projects and graduate advanced design projects, another 23 undergraduate and 12 graduate students were exposed to and trained in the salt reactor technology. We see this as one of the important indicators of the project’s success and effectiveness. In the process, 1 journal article was published (with 3 journal articles in preparation), together with 8 peer-reviewed full conference papers, 8 peer-reviewed extended abstracts, as well as 1 doctoral dissertation and 2 master theses. The work included both development of models and methodologies needed to adequately analyze this type of reactor, fuel, and its fuel cycle, as well as extensive analyses and optimization of the fuel and core design.« less

Acoustic and Electrical Signal Emission recordings when marble specimens are subjected to compressional mechanical stress

NASA Astrophysics Data System (ADS)

Triantis, Dimos; Stavrakas, Ilias; Hloupis, George; Ninos, Konstantinos; Vallianatos, Filippos

2013-04-01

The detection of Acoustic Emissions (AE) and Electrical Signals (ES) has been proved as a valuable experimental method to characterize the mechanical status of marble specimens when subjected to mechanical stress. In this work, marble specimens with dimensions 10cm x 4cm x 4cm where subjected to sequential loading cycles. The maximum stress of each loading was near the vicinity of fracture and was maintained for a relatively long time (th=200s). Concurrently to the mechanical tests, AE and ES were recorded. Specifically, two AE sensors and five ES sensors were installed on the surface of the specimens and the detected emissions were stored on a PC. The recordings show that AE and ES provide information regarding the damage spreading and location in the bulk of the specimen. Specifically, when the mechanical stress was maintained constant at the high stress value during each loading cycle the cumulative number of the AE hits become gradually less reaching a minimum after the first three loading cycles, indicating the existence of the Kaiser effect. During the eighth loading cycle the AE hits show a significant increase that became maximum at the ninth cycle before where failure occured. A similar behavior was observed for the cumulative energy. A b-value analysis was conducted following both Aki's and Gutenberg-Richter relations on the amplitudes of the AE hits. The b-values were found to increase during the three first loading cycles while consequently they were practically constant until reaching the two final loading cycles where they became gradually lower. The ES significantly increases during the stress increase of each cycle and gradually restores at a background level when the applied stress is maintained constant near the vicinity of fracture. It was observed that the background restoration level becomes gradually higher during the first four loading cycles. Consequently, during the next three loading cycles the background level is maintained practically constant. During the two final loading cycles the background restoration level significantly increases indicating the upcoming fracture. Acknowledgments. This work was supported by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non extensive statistical physics - Application to the geodynamic system of the Hellenic Arc. SEISMO FEAR HELLARC".

Inspection and monitoring of wind turbine blade-embedded wave defects during fatigue testing

DOE PAGES

Niezrecki, Christopher; Avitabile, Peter; Chen, Julie; ...

2014-05-20

The research we present in this article focuses on a 9-m CX-100 wind turbine blade, designed by a team led by Sandia National Laboratories and manufactured by TPI Composites Inc. The key difference between the 9-m blade and baseline CX-100 blades is that this blade contains fabric wave defects of controlled geometry inserted at specified locations along the blade length. The defect blade was tested at the National Wind Technology Center at the National Renewable Energy Laboratory using a schedule of cycles at increasing load level until failure was detected. Our researchers used digital image correlation, shearography, acoustic emission, fiber-opticmore » strain sensing, thermal imaging, and piezoelectric sensing as structural health monitoring techniques. Furthermore, this article provides a comparison of the sensing results of these different structural health monitoring approaches to detect the defects and track the resultant damage from the initial fatigue cycle to final failure.« less

Misfit of Three Different Implant-Abutment Connections Before and After Cyclic Load Application: An In Vitro Study.

PubMed

Gehrke, Sergio Alexandre; Delgado-Ruiz, Rafael Arcesio; Prados Frutos, Juan Carlos; Prados-Privado, María; Dedavid, Berenice Anina; Granero Marín, Jose Manuel; Calvo Guirado, José Luiz

This study aimed to evaluate the misfit of three different implant-abutment connections before and after cycling load. One hundred twenty dental implants and correspondent prefabricated titanium abutments were used. Three different implant-abutment connections were evaluated: Morse taper (MT group), external hexagon (EH group), and internal hexagon (IH group). Forty implants and 40 abutments were used per group. The parameters for the mechanical evaluation were set as: 360,000 cycles, load of 150 N, and frequency of 4 Hz. Samples were sectioned in their longitudinal and transversal axes, and the misfit of the implant-abutment connection was evaluated by scanning electron microscopy analysis. One-way analyses of variance, Tukey post hoc analyses (α = .05), and t test (P < .05) were used to determine differences between groups. At the longitudinal direction, all the groups showed the presence of microgaps before cycling load; after cycling load, microgaps were reduced in all groups (P > .05). Transversally, only the MT group showed full fitting after cycling load compared with the other groups (EH and IH) (P < .0001). The application of cycling load produces an accommodation of the implant-abutment connection in internal, external, and Morse taper connections. In the longitudinal direction, the accommodation decreases and/or eliminates the gap observed initially (before load). In the horizontal direction, Morse cone implant-abutment connections experience a complete accommodation with the elimination of the gap.

National Launch System cycle 1 loads and models data book

NASA Technical Reports Server (NTRS)

Bugg, F.; Brunty, J.; Ernsberger, G.; Mcghee, D.; Gagliano, L.; Harrington, F.; Meyer, D.; Blades, E.

1992-01-01

This document contains preliminary cycle 1 loads for the National Launch System (NLS) 1 and 2 vehicles. The loads provided and recommended as design loads represent the maximum load expected during prelaunch and flight regimes, i.e., limit loads, except that propellant tank ullage pressure has not been included. Ullage pressure should be added to the loads book values for cases where the addition results in higher loads. The loads must be multiplied by the appropriate factors of safety to determine the ultimate loads for which the structure must be capable.

Knotless anchors with sutures external to the anchor body may be at risk for suture cutting through osteopenic bone

PubMed Central

Ono, Y.; Woodmass, J. M.; Nelson, A. A.; Boorman, R. S.; Thornton, G. M.

2016-01-01

Objectives This study evaluated the mechanical performance, under low-load cyclic loading, of two different knotless suture anchor designs: sutures completely internal to the anchor body (SpeedScrew) and sutures external to the anchor body and adjacent to bone (MultiFIX P). Methods Using standard suture loops pulled in-line with the rotator cuff (approximately 60°), anchors were tested in cadaveric bone and foam blocks representing normal to osteopenic bone. Mechanical testing included preloading to 10 N and cyclic loading for 500 cycles from 10 N to 60 N at 60 mm/min. The parameters evaluated were initial displacement, cyclic displacement and number of cycles and load at 3 mm displacement relative to preload. Video recording throughout testing documented the predominant source of suture displacement and the distance of ‘suture cutting through bone’. Results In cadaveric bone and foam blocks, MultiFIX P anchors had significantly greater initial displacement, and lower number of cycles and lower load at 3 mm displacement than SpeedScrew anchors. Video analysis revealed ‘suture cutting through bone’ as the predominant source of suture displacement in cadaveric bone (qualitative) and greater ‘suture cutting through bone’ comparing MultiFIX P with SpeedScrew anchors in foam blocks (quantitative). The greater suture displacement in MultiFIX P anchors was predominantly from suture cutting through bone, which was enhanced in an osteopenic bone model. Conclusions Anchors with sutures external to the anchor body are at risk for suture cutting through bone since the suture eyelet is at the distal tip of the implant and the suture directly abrades against the bone edge during cyclic loading. Suture cutting through bone may be a significant source of fixation failure, particularly in osteopenic bone. Cite this article: Y. Ono, J. M. Woodmass, A. A. Nelson, R. S. Boorman, G. M. Thornton, I. K. Y. Lo. Knotless anchors with sutures external to the anchor body may be at risk for suture cutting through osteopenic bone. Bone Joint Res 2016;5:269–275. DOI: 10.1302/2046-3758.56.2000535. PMID:27357383

Knotless anchors with sutures external to the anchor body may be at risk for suture cutting through osteopenic bone.

PubMed

Ono, Y; Woodmass, J M; Nelson, A A; Boorman, R S; Thornton, G M; Lo, I K Y

2016-06-01

This study evaluated the mechanical performance, under low-load cyclic loading, of two different knotless suture anchor designs: sutures completely internal to the anchor body (SpeedScrew) and sutures external to the anchor body and adjacent to bone (MultiFIX P). Using standard suture loops pulled in-line with the rotator cuff (approximately 60°), anchors were tested in cadaveric bone and foam blocks representing normal to osteopenic bone. Mechanical testing included preloading to 10 N and cyclic loading for 500 cycles from 10 N to 60 N at 60 mm/min. The parameters evaluated were initial displacement, cyclic displacement and number of cycles and load at 3 mm displacement relative to preload. Video recording throughout testing documented the predominant source of suture displacement and the distance of 'suture cutting through bone'. In cadaveric bone and foam blocks, MultiFIX P anchors had significantly greater initial displacement, and lower number of cycles and lower load at 3 mm displacement than SpeedScrew anchors. Video analysis revealed 'suture cutting through bone' as the predominant source of suture displacement in cadaveric bone (qualitative) and greater 'suture cutting through bone' comparing MultiFIX P with SpeedScrew anchors in foam blocks (quantitative). The greater suture displacement in MultiFIX P anchors was predominantly from suture cutting through bone, which was enhanced in an osteopenic bone model. Anchors with sutures external to the anchor body are at risk for suture cutting through bone since the suture eyelet is at the distal tip of the implant and the suture directly abrades against the bone edge during cyclic loading. Suture cutting through bone may be a significant source of fixation failure, particularly in osteopenic bone.Cite this article: Y. Ono, J. M. Woodmass, A. A. Nelson, R. S. Boorman, G. M. Thornton, I. K. Y. Lo. Knotless anchors with sutures external to the anchor body may be at risk for suture cutting through osteopenic bone. Bone Joint Res 2016;5:269-275. DOI: 10.1302/2046-3758.56.2000535. © 2016 Lo et al.

Optical Fiber Distributed Sensing Structural Health Monitoring (SHM) Strain Measurements Taken During Cryotank Y-Joint Test Article Load Cycling at Liquid Helium Temperatures

NASA Technical Reports Server (NTRS)

Allison, Sidney G.; Prosser, William H.; Hare, David A.; Moore, Thomas C.; Kenner, Winfred S.

2007-01-01

This paper outlines cryogenic Y-joint testing at Langley Research Center (LaRC) to validate the performance of optical fiber Bragg grating strain sensors for measuring strain at liquid helium temperature (-240 C). This testing also verified survivability of fiber sensors after experiencing 10 thermal cool-down, warm-up cycles and 400 limit load cycles. Graphite composite skins bonded to a honeycomb substrate in a sandwich configuration comprised the Y-joint specimens. To enable SHM of composite cryotanks for consideration to future spacecraft, a light-weight, durable monitoring technology is needed. The fiber optic distributed Bragg grating strain sensing system developed at LaRC is a viable substitute for conventional strain gauges which are not practical for SHM. This distributed sensing technology uses an Optical Frequency Domain Reflectometer (OFDR). This measurement approach has the advantage that it can measure hundreds of Bragg grating sensors per fiber and the sensors are all written at one frequency, greatly simplifying fiber manufacturing. Fiber optic strain measurements compared well to conventional strain gauge measurements obtained during these tests. These results demonstrated a high potential for a successful implementation of a SHM system incorporating LaRC's fiber optic sensing system on the composite cryotank and other future cryogenic applications.

REVIEW ARTICLE: The physics of biological molecular motors

NASA Astrophysics Data System (ADS)

Thomas, N.; Thornhill, R. A.

1998-02-01

Molecular motors are the fundamental agents of movement in living organisms. A prime example is the actomyosin motor that powers muscle contraction. We illustrate the remarkable physics of this motor using a simplified three-state model, in which a myosin cross-bridge attaches to an actin filament, tilts over and then detaches. This `cross-bridge cycle', driven by ATP hydrolysis, is similar to a thermodynamic cycle, except that the molecular system is stochastic. Random transitions in the cycle therefore produce tension fluctuations, which have recently been observed in single-molecule experiments. Furthermore, since the rate constants for attachment and tilting depend on the elastic energy in the cross-bridge spring, the molecular motor is a highly nonlinear mechanical system. A bias tension `stretch activates' the motor, and it then develops the remarkable property of `negative viscosity', which allows it to perform as a self-sustained mechanical oscillator. However, when a series of attachment sites is available, the motor operates instead as a ratchet, pulling the actin filament rapidly forwards against a light load, whilst a heavy load pulls the filament only very slowly in the opposite direction. Similar ideas may apply to the dynein-tubulin motor that powers cilia and flagella and the kinesin-tubulin motor used in intracellular transport.

Matrix Fatigue Cracking Mechanisms of Alpha(2) TMC for Hypersonic Applications

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Gayda, John

1994-01-01

The objective of this work was to understand matrix cracking mechanisms in a unidirectional alpha(sub 2) TMC in possible hypersonic applications. A (0)(sub 8) SCS-6/Ti-24Al-11Nb (at. percent) TMC was first subjected to a variety of simple isothermal and nonisothermal fatigue cycles to evaluate the damage mechanisms in simple conditions. A modified ascent mission cycle test was then performed to evaluate the combined effects of loading modes. This cycle mixes mechanical cycling at 150 and 483 C, sustained loads, and a slow thermal cycle to 815 C. At low cyclic stresses and strains more common in hypersonic applications, environment-assisted surface cracking limited fatigue resistance. This damage mechanism was most acute for out-of-phase nonisothermal cycles having extended cycle periods and the ascent mission cycle. A simple linear fraction damage model was employed to help understand this damage mechanism. Time-dependent environmental damage was found to strongly influence out-of-phase and mission life, with mechanical cycling damage due to the combination of external loading and CTE mismatch stresses playing a smaller role. The mechanical cycling and sustained loads in the mission cycle also had a smaller role.

Effect of water temperature on cyclic fatigue properties of glass-fiber-reinforced hybrid composite resin and its fracture pattern after flexural testing.

PubMed

Kuroda, Soichi; Shinya, Akikazu; Vallittu, Pekka K; Nakasone, Yuji; Shinya, Akiyoshi

2013-02-01

To evaluate in vitro the influence of dynamic loading applied to a glass-fiber-reinforced hybrid composite resin on its flexural strength in a moist, simulated oral environment. Three-point flexural strength specimens were subjected to cyclic loading in water at 37°C and 55°C to investigate the influence of immersion temperature on impact fatigue properties. Specimens were subjected to cyclic impact loading at 1 Hz for up to 5 × 105 cycles to obtain the number of cycles to failure, the number of unbroken specimens after 5 × 105 cycles, and the residual flexural strength of unbroken specimens. Maximum loads of 100, 200, and 300 N were chosen for both the non-reinforced and the glass-fiber reinforced hybrid composite resins. The mean residual flexural strength for 100 N impact loading at temperatures of 37°C and 55°C was 634 and 636 MPa, respectively. All specimens fractured at fewer than 5 × 105 cycles for loads of 200 and 300 N. Reduced numbers of cycles to fracture and lower fatigue values were observed as both the maximum load and immersion temperature increased.

The effect of mechanical load cycling and polishing time on microleakage of class V glass-ionomer and composite restorations: A scanning electron microscopy evaluation

PubMed Central

Mirzaie, Mansoreh; Yasini, Esmail; Kermanshah, Hamid; Omidi, Baharan Ranjbar

2014-01-01

Background: Microleakage is one of the challenging concerns in direct filling restorations. Understanding of its related factors is important in clinical practice. The aim of this study was scanning electron microscopy (SEM) evaluation of marginal integrity in three types of tooth-colored restorative materials in class V cavity preparations and the effect of load cycling and polishing time on the microleakage. Materials and Methods: In this in vitro experimental study, class V cavity preparations were prepared on the buccal and lingual surfaces of 60 bovine incisors. The specimens were divided into three groups each containing 20 teeth: group 1: Filtek Z350, Group 2: Fuji IX/G Coat Plus, Group 3: Fuji II LC/GC varnish. In each group, 2 subgroups (n = 20) were established based on finishing time (immediate or delayed by 24 h). All specimens were thermocycled (×2,000, 5-50°C). In each sub groups, half of the teeth were load cycled. Epoxy resin replicas of 24 specimens were evaluated under field emission-SEM and interfacial gaps were measured. All teeth were then immersed in 0.5% basic fuchsin dye for 24 h, sectioned and observed under stereomicroscope. Data were analyzed with Kruskal-Wallis’ test and Mann-Whitney U test and a comparison between incisal and cervical microleakage was made with Wilcoxon test. P < 0.05 was considered as significant. Results: Load cycling and filling material had a significant effect on microleakage, but polishing time did not. Cervical microleakage in Z350/load cycle/immediate polish and Fuji IX/load cycle/immediate or delayed polish and Fuji IX/no load cycle/immediate polish were significantly higher than incisal microleakage. Conclusion: It was concluded that the cervical sealing ability of Fuji IX under load cycling was better than Fuji II LC. Under load cycling and immediate polishing Z350 showed better marginal integrity than both Fuji II LC and Fuji IX. The immediate polishing didn’t cause a statistically significant increase in microleakage of evaluated tooth-colored class V restorations. PMID:24688568

The effect of mechanical load cycling and polishing time on microleakage of class V glass-ionomer and composite restorations: A scanning electron microscopy evaluation.

PubMed

Mirzaie, Mansoreh; Yasini, Esmail; Kermanshah, Hamid; Omidi, Baharan Ranjbar

2014-01-01

Microleakage is one of the challenging concerns in direct filling restorations. Understanding of its related factors is important in clinical practice. The aim of this study was scanning electron microscopy (SEM) evaluation of marginal integrity in three types of tooth-colored restorative materials in class V cavity preparations and the effect of load cycling and polishing time on the microleakage. In this in vitro experimental study, class V cavity preparations were prepared on the buccal and lingual surfaces of 60 bovine incisors. The specimens were divided into three groups each containing 20 teeth: group 1: Filtek Z350, Group 2: Fuji IX/G Coat Plus, Group 3: Fuji II LC/GC varnish. In each group, 2 subgroups (n = 20) were established based on finishing time (immediate or delayed by 24 h). All specimens were thermocycled (×2,000, 5-50°C). In each sub groups, half of the teeth were load cycled. Epoxy resin replicas of 24 specimens were evaluated under field emission-SEM and interfacial gaps were measured. All teeth were then immersed in 0.5% basic fuchsin dye for 24 h, sectioned and observed under stereomicroscope. Data were analyzed with Kruskal-Wallis' test and Mann-Whitney U test and a comparison between incisal and cervical microleakage was made with Wilcoxon test. P < 0.05 was considered as significant. Load cycling and filling material had a significant effect on microleakage, but polishing time did not. Cervical microleakage in Z350/load cycle/immediate polish and Fuji IX/load cycle/immediate or delayed polish and Fuji IX/no load cycle/immediate polish were significantly higher than incisal microleakage. It was concluded that the cervical sealing ability of Fuji IX under load cycling was better than Fuji II LC. Under load cycling and immediate polishing Z350 showed better marginal integrity than both Fuji II LC and Fuji IX. The immediate polishing didn't cause a statistically significant increase in microleakage of evaluated tooth-colored class V restorations.

High Fidelity Simulations for Unsteady Flow Through the Orbiter LH2 Feedline Flowliner

NASA Technical Reports Server (NTRS)

Kiris, Cetin C.; Kwak, Dochan; Chan, William; Housman, Jeffrey

2005-01-01

High fidelity computations were carried out to analyze the orbiter M2 feedline flowliner. Various computational models were used to characterize the unsteady flow features in the turbopump, including the orbiter Low-Pressure-Fuel-Turbopump (LPFTP) inducer, the orbiter manifold and a test article used to represent the manifold. Unsteady flow originating from the orbiter LPFTP inducer is one of the major contributors to the high frequency cyclic loading that results in high cycle fatigue damage to the gimbal flowliners just upstream of the LPFTP. The flow fields for the orbiter manifold and representative test article are computed and analyzed for similarities and differences. An incompressible Navier-Stokes flow solver INS3D, based on the artificial compressibility method, was used to compute the flow of liquid hydrogen in each test article.

Influence of Endodontic Treatment and Retreatment on the Fatigue Failure Load, Numbers of Cycles for Failure, and Survival Rates of Human Canine Teeth.

PubMed

Missau, Taiane; De Carlo Bello, Mariana; Michelon, Carina; Mastella Lang, Pauline; Kalil Pereira, Gabriel; Baldissara, Paolo; Valandro, Luiz Felipe; Souza Bier, Carlos Alexandre; Pivetta Rippe, Marília

2017-12-01

This study evaluated the effects of endodontic treatment and retreatment on the fatigue failure load, numbers of cycles for failure, and survival rates of canine teeth. Sixty extracted canine teeth, each with a single root canal, were selected and randomly divided into 4 groups (n = 15): untreated, teeth without endodontic intervention; prepared, teeth subjected only to rotary instrumentation; filled, teeth receiving complete endodontic treatment; and retreated, teeth retreated endodontically. After the different endodontic interventions, the specimens were subjected to fatigue testing by the stepwise method: 200 N (× 5000 load pulses), 300 N, 400 N, 500 N, 600 N, 800 N, and 900 N at a maximum of 30,000 load pulses each or the occurrence of fracture. Data from load to failure and numbers of cycles for fracture were recorded and subjected to Kaplan-Meier and Log Rank tests (P < .05), in addition to Weibull analysis. The fractures of the specimens were classified as repairable or catastrophic. The retreated, filled, and untreated groups presented statistically significantly higher fatigue failure loads and numbers of cycles for failure than did the prepared group. Weibull analysis showed no statistically significant difference among the treatments for characteristic load to failure and characteristic number of cycles for failure, although, for number of cycles, a higher Weibull modulus was observed in filled and retreated conditions. The predominant mode of failure was catastrophic. Teeth subjected to complete endodontic treatment and retreatment behaved similarly in terms of fatigue failure load and number of cycles to failure when compared with untreated teeth. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Strength degradation and lifetime prediction of dental zirconia ceramics under cyclic normal loading.

PubMed

Li, Wanzhong; Xu, Yingqiang; He, Huiming; Zhao, Haidan; Sun, Jian; Hou, Yue

2015-01-01

Clinical cases show that zirconia restoration could happen fracture by accident under overloading after using a period of time. The purpose of this study is to research mechanical behavior and predict lifetime of dental zirconia ceramics under cyclic normal contact loading with experiments. Cyclic normal contact loading test and three point bending test are carried on specimens made of two brands of dental zirconia ceramic to obtain flexure strength and damage degree after different number of loading cycles. By means of damage mechanics model, damage degree under different number of contact loading cycles are calculated according to flexure strength, and verified by SEM photographs of cross section morphology of zirconia ceramics specimen phenomenologically. Relation curve of damage degree and number of cycles is fitted by polynomial fitting, then the number of loading cycles can be concluded when the specimen is complete damage. Strength degradation of two brands dental zirconia ceramics are researched in vitro, and prediction method of contact fatigue lifetime is established.

The Fatigue Behavior of Built-Up Welded Beams of Commercially Pure Titanium

NASA Astrophysics Data System (ADS)

Patnaik, Anil; Poondla, Narendra; Bathini, Udaykar; Srivatsan, T. S.

2011-10-01

In this article, the results of a recent study aimed at evaluating, understanding, and rationalizing the extrinsic influence of fatigue loading on the response characteristics of built-up welded beams made from commercially pure titanium (Grade 2) are presented and discussed. The beams were made from welding plates and sheets of titanium using the pulsed gas metal arc welding technique to form a structural beam having an I-shaped cross section. The welds made for the test beams of the chosen metal were fillet welds using a matching titanium filler metal wire. The maximum and minimum load values at which the built-up beams were cyclically deformed were chosen to be within the range of 22-45% of the maximum predicted flexural static load. The beams were deformed in fatigue at a stress ratio of 0.1 and constant frequency of 5 Hz. The influence of the ratio of maximum load with respect to the ultimate failure load on fatigue performance, quantified in terms of fatigue life, was examined. The percentage of maximum load to ultimate load that resulted in run-out of one million cycles was established. The overall fracture behavior of the failed beam sample was characterized by scanning electron microscopy observations to establish the conjoint influence of load severity, intrinsic microstructural effects, and intrinsic fracture surface features in governing failure by fracture.

Lamination residual stresses in fiber composites

NASA Technical Reports Server (NTRS)

Daniel, I. M.; Liber, T.

1975-01-01

An experimental investigation was conducted to determine the magnitude of lamination residual stresses in angle-ply composites and to evaluate their effects on composite structural integrity. The materials investigated were boron/epoxy, boron/polyimide, graphite/low modulus epoxy, graphite/high modulus epoxy, graphite/polyimide and s-glass/epoxy. These materials were fully characterized. Static properties of laminates were also determined. Experimental techniques using embedded strain gages were developed and used to measure residual strains during curing. The extent of relaxation of lamination residual stresses was investigated. It was concluded that the degree of such relaxation is low. The behavior of angle-ply laminates subjected to thermal cycling, tensile load cycling, and combined thermal cycling with tensile load was investigated. In most cases these cycling programs did not have any measurable influence on residual strength and stiffness of the laminates. In the tensile load cycling tests, the graphite/polyimide shows the highest endurance with 10 million cycle runouts at loads up to 90 percent of the static strength.

Feasibility of a nickel-metal hydride battery for totally implantable artificial hearts.

PubMed

Okamoto, E; Yoshida, T; Fujiyoshi, M; Shimanaka, M; Takeuchi, A; Mitamura, Y; Mikami, T

1996-01-01

An implantable rechargeable battery is one of the key technologies for totally implantable artificial hearts. The nickel-metal hydride (Ni-MH) battery is promising for its high energy density of 1.5-2.0 times that of a nickel-cadmium battery. In this study, the effects of pulsatile discharge loads on the operating time and cycle life of Ni-MH batteries at 39 degrees C were studied. Two battery cells (TH-3M, 1,200 mAh, phi 14.5 x 49 mm; Toshiba, Tokyo, Japan) in series were charge/discharge cycled at 39 degrees C using a charge current of 1CA (1,200 mA) and then were fully discharged to 1.0 V/cell under either pulsatile discharge loads, which mimicked a systole (1 A for 0.3 sec) and a diastole (0.4 A for 0.3 sec), or a non pulsatile discharge load equivalent to the average of the pulsatile loads (0.7 A). Each cycle life test was interrupted on the 482nd cycle under pulsatile load, and on the 423rd cycle under non pulsatile load, because of malfunction of each battery charger. The tests showed that the pulsatile discharge cells had significantly (p < 0.001) less operating time (74.0 +/- 7.15 min) throughout the test period (up to 482 days) compared to the cells under equivalent non pulsatile discharge loads (93.7 +/- 7.74 min). The pulsatile-discharged Ni-MH cells provide significantly less operating time than the constantly discharged cells; the Ni-MH battery has an operating time of over 78 min and a cycle life of almost 500 cycles at 39 degrees C. In conclusion, the Ni-MH battery is feasible as an implantable back-up battery for a totally implantable artificial heart system.

The Contact Ageing Effect on Fretting Damage of an Electro-Deposited Coating against an AISI52100 Steel Ball

PubMed Central

Kim, Kyungmok; Ko, Joon Soo

2016-01-01

This article investigates the effect of contact ageing on fretting damage of an epoxy-based cathodic electro-deposited coating for use on automotive seat slide tracks (made of cold-rolled high strength steel). Static normal load was induced at the contact between the coating and an AISI52100 ball for a certain duration. It was identified that plastically deformed contact area increased logarithmically as a function of time when the contact was under static normal load. Fretting tests after various durations of static contact were conducted using a ball-on-flat plate apparatus. All fretting tests were halted when the friction coefficient reached a critical value of 0.5, indicating complete coating failure. The total number of fretting cycles to the critical friction coefficient was found to vary with the duration of static contact before fretting. It was identified that the number of cycles to the critical friction coefficient decreased with the increased duration of static contact. Meanwhile, the friction coefficient at steady-state sliding was not greatly affected by the duration of static contact before fretting. Finally, the relation between coating thickness after indentation creep and the number of cycles to the critical friction coefficient was found to be linear. Obtained results show that the duration of static contact before fretting has an influence on the fretting lifetime of an electro-deposited coating. PMID:28773873

The Contact Ageing Effect on Fretting Damage of an Electro-Deposited Coating against an AISI52100 Steel Ball.

PubMed

Kim, Kyungmok; Ko, Joon Soo

2016-09-03

This article investigates the effect of contact ageing on fretting damage of an epoxy-based cathodic electro-deposited coating for use on automotive seat slide tracks (made of cold-rolled high strength steel). Static normal load was induced at the contact between the coating and an AISI52100 ball for a certain duration. It was identified that plastically deformed contact area increased logarithmically as a function of time when the contact was under static normal load. Fretting tests after various durations of static contact were conducted using a ball-on-flat plate apparatus. All fretting tests were halted when the friction coefficient reached a critical value of 0.5, indicating complete coating failure. The total number of fretting cycles to the critical friction coefficient was found to vary with the duration of static contact before fretting. It was identified that the number of cycles to the critical friction coefficient decreased with the increased duration of static contact. Meanwhile, the friction coefficient at steady-state sliding was not greatly affected by the duration of static contact before fretting. Finally, the relation between coating thickness after indentation creep and the number of cycles to the critical friction coefficient was found to be linear. Obtained results show that the duration of static contact before fretting has an influence on the fretting lifetime of an electro-deposited coating.

High Fidelity Simulations of Unsteady Flow through Turbopumps and Flowliners

NASA Technical Reports Server (NTRS)

Kiris, Cetin C.; Kwak, dochan; Chan, William; Housman, Jeff

2006-01-01

High fidelity computations were carried out to analyze the orbiter LH2 feedline flowliner. Computations were performed on the Columbia platform which is a 10,240-processor supercluster consisting of 20 Altix nodes with 512 processor each. Various computational models were used to characterize the unsteady flow features in the turbopump, including the orbiter Low-Pressure-Fuel-Turbopump (LPFTP) inducer, the orbiter manifold and a test article used to represent the manifold. Unsteady flow originating from the orbiter LPFTP inducer is one of the major contributors to the high frequency cyclic loading that results in high cycle fatigue damage to the gimbal flowliners just upstream of the LPFTP. The flow fields for the orbiter manifold and representative test article are computed and analyzed for similarities and differences. The incompressible Navier-Stokes flow solver INS3D, based on the artificial compressibility method, was used to compute the flow of liquid hydrogen in each test article.

Analysis of the workload imposed on the workers of the imprint and cutting/welding sectors of a flexible packaging manufacturer.

PubMed

de M Guimarães, L B; Pessa, S L R; Biguelini, C

2012-01-01

This article presents a study on the evaluation of the workload imposed to workers of two sectors of a flexible packaging manufacturer that operates in three shifts. The workers are allocated in one of the shifts (morning, evening and night shifts) without evaluation of their chronotype and/or social needs. The Imprint sector has a more dynamic work, which is done only by man due to the effort demanded by handling loads. The work in the Cutting/Welding sector is static, done mainly by women. The results showed that the overall workload was the same in the Imprint and Cutting/Welding sectors, because physical effort for load handling is higher in the former but the latter involves high static load. The levels of urinary catecholamines and salivary cortisol were consistent with the workers biological clock showing that none of the workers changed his/her biological cycle to accommodate to the time of the shift schedule.

Crank inertial load has little effect on steady-state pedaling coordination.

PubMed

Fregly, B J; Zajac, F E; Dairaghi, C A

1996-12-01

Inertial load can affect the control of a dynamic system whenever parts of the system are accelerated or decelerated. During steady-state pedaling, because within-cycle variations in crank angular acceleration still exist, the amount of crank inertia present (which varies widely with road-riding gear ratio) may affect the within-cycle coordination of muscles. However, the effect of inertial load on steady-state pedaling coordination is almost always assumed to be negligible, since the net mechanical energy per cycle developed by muscles only depends on the constant cadence and workload. This study test the hypothesis that under steady-state conditions, the net joint torques produced by muscles at the hip, knee, and ankle are unaffected by crank inertial load. To perform the investigation, we constructed a pedaling apparatus which could emulate the low inertial load of a standard ergometer or the high inertial load of a road bicycle in high gear. Crank angle and bilateral pedal force and angle data were collected from ten subjects instructed to pedal steadily (i.e., constant speed across cycles) and smoothly (i.e., constant speed within a cycle) against both inertias at a constant workload. Virtually no statistically significant changes were found in the net hip and knee muscle joint torques calculated from an inverse dynamics analysis. Though the net ankle muscle joint torque, as well as the one- and two-legged crank torque, showed statistically significant increases at the higher inertia, the changes were small. In contrast, large statistically significant reductions were found in crank kinematic variability both within a cycle and between cycles (i.e., cadence), primarily because a larger inertial load means a slower crank dynamic response. Nonetheless, the reduction in cadence variability was somewhat attenuated by a large statistically significant increase in one-legged crank torque variability. We suggest, therefore, that muscle coordination during steady-state pedaling is largely unaffected, though less well regulated, when crank inertial load is increased.

Resin-dentin bonds to EDTA-treated vs. acid-etched dentin using ethanol wet-bonding. Part II: Effects of mechanical cycling load on microtensile bond strengths.

PubMed

Sauro, Salvatore; Toledano, Manuel; Aguilera, Fatima Sánchez; Mannocci, Francesco; Pashley, David H; Tay, Franklin R; Watson, Timothy F; Osorio, Raquel

2011-06-01

To compare microtensile bond strengths (MTBS) subsequent to load cycling of resin bonded acid-etched or EDTA-treated dentin using a modified ethanol wet-bonding technique. Flat dentin surfaces were obtained from extracted human molars and conditioned using 37% H(3)PO(4) (PA) (15s) or 0.1M EDTA (60s). Five experimental adhesives and one commercial bonding agent were applied to the dentin and light-cured. Solvated experimental resins (50% ethanol/50% comonomers) were used as primers and their respective neat resins were used as the adhesives. The resin-bonded teeth were stored in distilled water (24h) or submitted to 5000 loading cycles of 90N. The bonded teeth were then sectioned in beams for MTBS. Modes of failure were examined by scanning electron microscopy. The most hydrophobic resin 1 gave the lowest bond strength values to both acid and EDTA-treated dentin. The hydrophobic resin 2 applied to EDTA-treated dentin showed lower bond strengths after cycling load but this did not occur when it was bonded to PA-etched dentin. Resins 3 and 4, which contained hydrophilic monomers, gave higher bond strengths to both EDTA-treated or acid-etched dentin and showed no significant difference after load cycling. The most hydrophilic resin 5 showed no significant difference in bond strengths after cycling loading when bonded to EDTA or phosphoric acid treated dentin but exhibited low bond strengths. The presence of different functional monomers influences the MTBS of the adhesive systems when submitted to cyclic loads. Adhesives containing hydrophilic comonomers are not affected by cycling load challenge especially when applied on EDTA-treated dentin followed by ethanol wet bonding. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Inelastic compaction, dilation and hysteresis of sandstones under hydrostatic conditions

NASA Astrophysics Data System (ADS)

Shalev, Eyal; Lyakhovsky, Vladimir; Ougier-Simonin, Audrey; Hamiel, Yariv; Zhu, Wenlu

2014-05-01

Sandstones display non-linear and inelastic behaviour such as hysteresis when subjected to cyclic loading. We present three hydrostatic compaction experiments with multiple loading-unloading cycles on Berea and Darley Dale sandstones and explain their hysteretic behaviour using non-linear inelastic compaction and dilation. Each experiment included eight to nine loading-unloading cycles with increasing maximum pressure in each subsequent cycle. Different pressure-volumetric strain relations during loading and unloading were observed. During the first cycles, under relatively low pressures, not all of the volumetric strain is recovered at the end of each cycle whereas at the last cycles, under relatively high pressures, the strain is recovered and the pressure-volumetric strain hysteresis loops are closed. The observed pressure-volumetric strain relations are non-linear and the effective bulk modulus of the sandstones changes between cycles. Observations are modelled with two inelastic deformation processes: irreversible compaction caused by changes in grain packing and recoverable compaction associated with grain contact adhesion, frictional sliding on grains or frictional sliding on cracks. The irreversible compaction is suggested to reflect rearrangement of grains into a more compact mode as the maximum pressure increases. Our model describes the `inelastic compaction envelope' in which sandstone sample will follow during hydrostatic loading. Irreversible compaction occurs when pressure is greater than a threshold value defined by the `inelastic compaction envelope'.

Effects of sulfur loading on the corrosion behaviors of metal lithium anode in lithium–sulfur batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Yamiao; Duan, Xiaobo; Li, Yanbing

2015-08-15

Highlights: • The effects of sulfur loading on the corrosion behaviors were investigated systematically. • The corrosion became severer with increasing sulfur loading or cycle times. • The corrosion films are porous and loose and cannot prevent further reaction between lithium and polysulfides. - Abstract: The corrosion behaviors in rechargeable lithium–sulfur batteries come from the reactions between polysulfides and metal lithium anode, and they are significantly influenced by the sulfur loading. While there are limited papers reported on the effects of sulfur loading on the corrosion behaviors. In this paper, the effects have been investigated systematically. The corrosion films consistedmore » of insulating lithium ion conductors are loose and porous, so that the corrosive reactions cannot be hindered. The thickness of the corrosion layers, consequently, increased along with increasing sulfur loading or cycle times. For instance, the thickness of corrosion layers after 50 cycles was 98 μm in the cell with 5 mg sulfur while it reached up to 518 μm when the loading increased to 15 mg. The continuous deposition of corrosion products gave rise to low active materials utilization and poor cycling performance.« less

A comparison of the fracture resistance of three machinable ceramics after thermal and mechanical fatigue.

PubMed

Yang, Rui; Arola, Dwayne; Han, Zhihui; Zhang, Xiuyin

2014-10-01

Mechanical and thermal fatigue may affect ceramic restorations in the oral environment. The purpose of this study was to determine the influence of thermal and mechanical cycling on the fracture load and fracture patterns of 3 machinable ceramics. Seventy-two human third molar teeth were prepared for bonding ceramic specimens of Sirona CEREC Blocs, IPS e.maxCAD, or inCoris ZI meso blocks. The 24 specimens of each ceramic were divided into 4 groups (n=6), which underwent no preloading (control), thermocycling (5°C-55°C, 2000 cycles), mechanical cycling (10(5) cycles, 100 N), and thermocycling (5°C-55°C, 2000 cycles) plus mechanical cycling (10(5) cycles, 100 N). The specimens were subsequently loaded to failure, and both stereomicroscopy and scanning electron microscopy were used to investigate the fracture patterns. The data were analyzed with 2-way ANOVA and the Fisher exact probability test (α=.05). Mechanical and thermal cycling had a significant influence on the critical load to failure of the 3 ceramics. No significant difference was found between mechanical cycling for 10(5) times and thermocycling for 2000 times within the same ceramic. The specimens of inCoris ZI experienced significantly higher fracture loads for all the groups. The fracture patterns of the 3 machinable ceramics showed that failure mainly occurred at the cement-dentin interface. The effects of combined thermal and mechanical cycling on the fracture load of ceramics were more significant than any individual mode of cyclic fatigue. Overall, the inCoris ZI resisted thermal and mechanical fatigue better than the Sirona CEREC and IPS e.maxCAD. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

A comparison of single-cycle versus multiple-cycle proof testing strategies

NASA Technical Reports Server (NTRS)

Hudak, S. J., Jr.; Mcclung, R. C.; Bartlett, M. L.; Fitzgerald, J. H.; Russell, D. A.

1990-01-01

An evaluation of single-cycle and multiple-cycle proof testing (MCPT) strategies for SSME components is described. Data for initial sizes and shapes of actual SSME hardware defects are analyzed statistically. Closed-form estimates of the J-integral for surface flaws are derived with a modified reference stress method. The results of load- and displacement-controlled stable crack growth tests on thin IN-718 plates with deep surface flaws are summarized. A J-resistance curve for the surface-cracked configuration is developed and compared with data from thick compact tension specimens. The potential for further crack growth during large unload/reload cycles is discussed, highlighting conflicting data in the literature. A simple model for ductile crack growth during MCPT based on the J-resistance curve is used to study the potential effects of key variables. The projected changes in the crack size distribution during MCPT depend on the interactions between several key parameters, including the number of proof cycles, the nature of the resistance curve, the initial crack size distribution, the component boundary conditions (load vs. displacement control), and the magnitude of the applied load or displacement. The relative advantages of single-cycle and multiple-cycle proof testing appear to be specific, therefore, to individual component geometry, material, and loading.

Resistance Spot Welding Characteristics and High Cycle Fatigue Behavior of DP 780 Steel Sheet

NASA Astrophysics Data System (ADS)

Pal, Tapan Kumar; Bhowmick, Kaushik

2012-02-01

Resistance spot welding characteristics of DP 780 steel was investigated using peel test, microhardness test, tensile shear test, and fatigue test. Tensile shear test provides better spot weld quality than conventional peel test and hardness is not a good indicator of the susceptibility to interfacial fracture. The results of high-cycle fatigue behavior of spot welded DP 780 steel under two different parameters show that at high load low cycle range a significant difference in the S- N curve and almost similar fatigue behavior of spot welds at low load high cycle range are obtained. However, when applied load was converted to stress intensity factor, the difference in the fatigue behavior between welds diminished. Furthermore, a transition in fracture mode, i.e., interfacial and plug and hole-type at about 50% of yield load is observed.

Use of Guided Acoustic Waves to Assess the Effects of Thermal-Mechanical Cycling on Composite Stiffness

NASA Technical Reports Server (NTRS)

Seale, Michael D.; Madaras, Eric I.

2000-01-01

The introduction of new, advanced composite materials into aviation systems requires it thorough understanding of the long-term effects of combined thermal and mechanical loading. As part of a study to evaluate the effects of thermal-mechanical cycling, it guided acoustic (Lamb) wave measurement system was used to measure the bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system uses a pulse/receive technique that excites an antisymmetric Lamb mode and measures the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the velocity dispersion curve. A series of 16 and 32-ply composite laminates were subjected to it thermal-mechanical loading profile in load frames equipped with special environmental chambers. The composite systems studied were it graphite fiber reinforced amorphous thermoplastic polyimide and it graphite fiber reinforced bismaleimide thermoset. The samples were exposed to both high and low temperature extremes its well as high and low strain profiles. The bending and out-of-plane stiffnesses for composite sample that have undergone over 6,000 cycles of thermal-mechanical loading are reported. The Lamb wave generated elastic stiffness results have shown decreases of up to 20% at 4,936 loading cycles for the graphite/thermoplastic samples and up to 64% at 4,706 loading cycles for the graphite/thermoset samples.

Open Screw Placement in a 1.5 mm LCP Over a Fracture Gap Decreases Fatigue Life

PubMed Central

Alwen, Sarah G. J.; Kapatkin, Amy S.; Garcia, Tanya C.; Milgram, Joshua; Stover, Susan M.

2018-01-01

Objective To investigate the influence of plate and screw hole position on the stability of simulated radial fractures stabilized with a 1.5 mm condylar locking compression plate (LCP). Study Design In vitro mechanical testing of paired cadaveric limbs. Sample Population Paired radii (n = 7) stabilized with a 1.5 mm condylar LCP with an open screw hole positioned either proximal to (PG), or over (OG), a simulated small fracture gap. Methods Constructs were cycled in axial compression at a simulated trot load until failure or a maximum of 200,000 cycles. Specimens that sustained 200,000 cycles without failure were then loaded in axial compression in a single cycle to failure. Construct cyclic axial stiffness and gap strain, fatigue life, and residual strength were evaluated and compared between constructs using analysis of variance. Results Of pairs that had a failure during cyclic loading, OG constructs survived fewer cycles (54,700 ± 60,600) than PG (116,800 ± 49,300). OG constructs had significantly lower initial stiffness throughout cyclic loading and higher gap strain range within the first 1,000 cycles than PG constructs. Residual strength variables were not significantly different between constructs, however yield loads occurred at loads only marginally higher than approximated trot loads. Fatigue life decreased with increasing body weight. Conclusion Fracture fixation stability is compromised by an open screw hole directly over a fracture gap compared to the open screw hole being buttressed by bone in the model studied. The 1.5 mm condylar LCP may be insufficient stabilization in dogs with appropriate radial geometry but high body weights. PMID:29876361

Long life nickel electrodes for a nickel-hydrogen cell: Cycle life tests

NASA Technical Reports Server (NTRS)

Lim, H. S.; Verzwyvelt, S. A.

1985-01-01

In order to develop a long life nickel electrode for a Ni/H2 cell, the cycle life of nickel electrodes was tested in Ni/H2 boiler plate cells. A 19 test cell matrix was made of various nickel electrode designs including three levels each of plaque mechanical strength, median pore size of the plaque, and active material loading. Test cells were cycled to the end of their life (0.5v) in a 45 minute low Earth orbit cycle regime at 80% depth-of-discharge. It is shown that the active material loading level affects the cycle life the most with the optimum loading at 1.6 g/cc void. Mechanical strength does not affect the cycle life noticeably in the bend strength range of 400 to 700 psi. It is found that the best plaque is made of INCO nickel powder type 287 and has median pore size of 13 micron.

A LATIN-based model reduction approach for the simulation of cycling damage

NASA Astrophysics Data System (ADS)

Bhattacharyya, Mainak; Fau, Amelie; Nackenhorst, Udo; Néron, David; Ladevèze, Pierre

2017-11-01

The objective of this article is to introduce a new method including model order reduction for the life prediction of structures subjected to cycling damage. Contrary to classical incremental schemes for damage computation, a non-incremental technique, the LATIN method, is used herein as a solution framework. This approach allows to introduce a PGD model reduction technique which leads to a drastic reduction of the computational cost. The proposed framework is exemplified for structures subjected to cyclic loading, where damage is considered to be isotropic and micro-defect closure effects are taken into account. A difficulty herein for the use of the LATIN method comes from the state laws which can not be transformed into linear relations through an internal variable transformation. A specific treatment of this issue is introduced in this work.

Microstructure Evolution from X-CT Measurements for Concrete/mortar under Multi-actions of Composite Salts Dry-wet Cycles and Loading

NASA Astrophysics Data System (ADS)

Chen, Yanjuan; Gao, Jianming; Shen, Daman

2017-08-01

Inthis research, microstructure evolution forconcrete/mortar under multi-actions of composite salts dry-wet cycles and loading was investigated through X-CT measurements. The evolution process of pores and micro-cracking with the erosion time were tracked. Compared the different erosion actions, it was found that dry-wet cycles promoted the pores become connected gradually. Besides, the dry-wet cycles accelerated the damage seriously on interface area between concrete and aggregate, whistle, loading contributes to the cracking propagation toward the internal. Moreover, fly ash played a positive role in the increasing of the number of harmless holes again and contributed to the durability of concrete.

Low cycle fatigue

NASA Technical Reports Server (NTRS)

Solomon, H. D. (Editor); Kaisand, L. R. (Editor); Halford, G. R. (Editor); Leis, B. N. (Editor)

1988-01-01

The papers contained in this volume focus on various aspects of low cycle fatigue, including cyclic deformation, crack propagation, high-temperature low cycle fatigue, microstructural defects, multiaxial and variable amplitude loading, and life prediction. Papers are presented on the low cycle fatigue of some aluminum alloys, prediction of crack growth under creep-fatigue loading conditions, high-temperature low cycle fatigue behavior and lifetime prediction of a nickel-base ODS alloy, and an integrated approach to creep-fatigue life prediction. Other topics discussed include thermal fatigue testing of coated monocrystalline superalloys, low cycle fatigue of Al-Mg-Si alloys, and the effect of superimposed stresses at high frequency on low cycle fatigue.

Modeling and Depletion Simulations for a High Flux Isotope Reactor Cycle with a Representative Experiment Loading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chandler, David; Betzler, Ben; Hirtz, Gregory John

2016-09-01

The purpose of this report is to document a high-fidelity VESTA/MCNP High Flux Isotope Reactor (HFIR) core model that features a new, representative experiment loading. This model, which represents the current, high-enriched uranium fuel core, will serve as a reference for low-enriched uranium conversion studies, safety-basis calculations, and other research activities. A new experiment loading model was developed to better represent current, typical experiment loadings, in comparison to the experiment loading included in the model for Cycle 400 (operated in 2004). The new experiment loading model for the flux trap target region includes full length 252Cf production targets, 75Se productionmore » capsules, 63Ni production capsules, a 188W production capsule, and various materials irradiation targets. Fully loaded 238Pu production targets are modeled in eleven vertical experiment facilities located in the beryllium reflector. Other changes compared to the Cycle 400 model are the high-fidelity modeling of the fuel element side plates and the material composition of the control elements. Results obtained from the depletion simulations with the new model are presented, with a focus on time-dependent isotopic composition of irradiated fuel and single cycle isotope production metrics.« less

Analysis of a Temperature-Controlled Exhaust Thermoelectric Generator During a Driving Cycle

NASA Astrophysics Data System (ADS)

Brito, F. P.; Alves, A.; Pires, J. M.; Martins, L. B.; Martins, J.; Oliveira, J.; Teixeira, J.; Goncalves, L. M.; Hall, M. J.

2016-03-01

Thermoelectric generators can be used in automotive exhaust energy recovery. As car engines operate under wide variable loads, it is a challenge to design a system for operating efficiently under these variable conditions. This means being able to avoid excessive thermal dilution under low engine loads and being able to operate under high load, high temperature events without the need to deflect the exhaust gases with bypass systems. The authors have previously proposed a thermoelectric generator (TEG) concept with temperature control based on the operating principle of the variable conductance heat pipe/thermosiphon. This strategy allows the TEG modules’ hot face to work under constant, optimized temperature. The variable engine load will only affect the number of modules exposed to the heat source, not the heat transfer temperature. This prevents module overheating under high engine loads and avoids thermal dilution under low engine loads. The present work assesses the merit of the aforementioned approach by analysing the generator output during driving cycles simulated with an energy model of a light vehicle. For the baseline evaporator and condenser configuration, the driving cycle averaged electrical power outputs were approximately 320 W and 550 W for the type-approval Worldwide harmonized light vehicles test procedure Class 3 driving cycle and for a real-world highway driving cycle, respectively.

The effect of cycling deflection on the injection-molded thermoplastic denture base resins.

PubMed

Hamanaka, Ippei; Iwamoto, Misa; Lassila, Lippo Vj; Vallittu, Pekka K; Shimizu, Hiroshi; Takahashi, Yutaka

2016-01-01

The aim of this study was to evaluate the effect of cycling deflection on the flexural behavior of injection-molded thermoplastic resins. Six injection-molded thermoplastic resins (two polyamides, two polyesters, one polycarbonate, one polymethyl methacrylate) and, as a control, a conventional heat-polymerized denture based polymer of polymethyl methacrylate (PMMA) were used in this study. The cyclic constant magnitude (1.0 mm) of 5000 cycles was applied using a universal testing machine to demonstrate plasticization of the polymer. Loading was carried out in water at 23ºC with eight specimens per group (n = 8). Cycling load (N) and deformation (mm) were measured. Force required to deflect the specimens during the first loading cycle and final loading cycle was statistically significantly different (p < 0.05) with one polyamide based polymer (Valplast) and PMMA based polymers (Acrytone and Acron). The other polyamide based polymer (LucitoneFRS), polyester based polymers (EstheShot and EstheShotBright) and polycarbonate based polymer (ReigningN) did not show significant differences (p > 0.05). None of the materials fractured during the loading test. One polyamide based polymer (Valplast) displayed the highest deformation and PMMA based polymers (Acrytone and Acron) exhibited the second highest deformation among the denture base materials. It can be concluded that there were considerable differences in the flexural behavior of denture base polymers. This may contribute to the fatigue resistance of the materials.

Single-Cycle Versus Multicycle Proof Testing

NASA Technical Reports Server (NTRS)

Hudak, S. J., Jr.; Mcclung, R. C.; Bartlett, M. L.; Fitzgerald, J. H.; Russell, D. A.

1992-01-01

Report compares single-cycle with multiple-cycle mechanical-stress tests of parts under mechanical stresses. Objective of proof testing: to screen out gross manufacturing or material deficiencies and provide additional assurance of quality. Report concludes that changes in distribution of crack sizes during multicycle proof testing depend on initial distribution, number of cycles, relationship between resistance of material and elastic/plastic fracture-mechanics parameter, relationship between load control and displacement control, and magnitude of applied load or displacement. Whether single-cycle or multicycle testing used depends on shape, material, and technique of fabrication of components tested.

Comparison of Two Parametric Methods to Estimate Pesticide Mass Loads in California's Central Valley

USGS Publications Warehouse

Saleh, D.K.; Lorenz, D.L.; Domagalski, Joseph L.

2011-01-01

Mass loadings were calculated for four pesticides in two watersheds with different land uses in the Central Valley, California, by using two parametric models: (1) the Seasonal Wave model (SeaWave), in which a pulse signal is used to describe the annual cycle of pesticide occurrence in a stream, and (2) the Sine Wave model, in which first-order Fourier series sine and cosine terms are used to simulate seasonal mass loading patterns. The models were applied to data collected during water years 1997 through 2005. The pesticides modeled were carbaryl, diazinon, metolachlor, and molinate. Results from the two models show that the ability to capture seasonal variations in pesticide concentrations was affected by pesticide use patterns and the methods by which pesticides are transported to streams. Estimated seasonal loads compared well with results from previous studies for both models. Loads estimated by the two models did not differ significantly from each other, with the exceptions of carbaryl and molinate during the precipitation season, where loads were affected by application patterns and rainfall. However, in watersheds with variable and intermittent pesticide applications, the SeaWave model is more suitable for use on the basis of its robust capability of describing seasonal variation of pesticide concentrations. ?? 2010 American Water Resources Association. This article is a US Government work and is in the public domain in the USA.

Development of a clinically validated bulk failure test for ceramic crowns.

PubMed

Kelly, J Robert; Rungruanganunt, Patchnee; Hunter, Ben; Vailati, Francesca

2010-10-01

Traditional testing of ceramic crowns creates a stress state and damage modes that differ greatly from those seen clinically. There is a need to develop and communicate an in vitro testing protocol that is clinically valid. The purpose of this study was to develop an in vitro failure test for ceramic single-unit prostheses that duplicates the failure mechanism and stress state observed in clinically failed prostheses. This article first compares characteristics of traditional load-to-failure tests of ceramic crowns with the growing body of evidence regarding failure origins and stress states at failure from the examination of clinically failed crowns, finite element analysis (FEA), and data from clinical studies. Based on this analysis, an experimental technique was systematically developed and test materials were identified to recreate key aspects of clinical failure in vitro. One potential dentin analog material (an epoxy filled with woven glass fibers; NEMA grade G10) was evaluated for elastic modulus in blunt contact and for bond strength to resin cement as compared to hydrated dentin. Two bases with different elastic moduli (nickel chrome and resin-based composite) were tested for influence on failure loads. The influence of water during storage and loading (both monotonic and cyclic) was examined. Loading piston materials (G10, aluminum, stainless steel) and piston designs were varied to eliminate Hertzian cracking and to improve performance. Testing was extended from a monolayer ceramic (leucite-filled glass) to a bilayer ceramic system (glass-infiltrated alumina). The influence of cyclic rate on mean failure loads was examined (2 Hz, 10 Hz, 20 Hz) with the extremes compared statistically (t test; α=.05). Failure loads were highly influenced by base elastic modulus (t test; P<.001). Cyclic loading while in water significantly decreased mean failure loads (1-way ANOVA; P=.003) versus wet storage/dry cycling (350 N vs. 1270 N). G10 was not significantly different from hydrated dentin in terms of blunt contact elastic behavior or resin cement bond strength. Testing was successful with the bilayered ceramic, and the cycling rate altered mean failure loads only slightly (approximately 5%). Test methods and materials were developed to validly simulate many aspects of clinical failure. Copyright © 2010 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

Texture evolution during isothermal, isostrain, and isobaric loading of polycrystalline shape memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Padula, S. A.; Benafan, O.; Vaidyanathan, R.

2017-06-01

In situ neutron diffraction was used to provide insights into martensite variant microstructures during isothermal, isobaric, and isostrain loading in shape memory NiTi. The results show that variant microstructures were equivalent for the corresponding strain, and more importantly, the reversibility and equivalency were immediately evident in variant microstructures that were first formed isobarically but then reoriented to near random self-accommodated microstructures following isothermal deformation. Variant microstructures formed isothermally were not significantly affected by a subsequent thermal cycle under constant strain. In all loading cases considered, the resulting variant microstructure correlated with strain and did not correlate with stress. Based on the ability to select a variant microstructure for a given strain despite thermomechanical loading history, the results demonstrated here can be obtained by following any sequence of thermomechanical loading paths over multiple cycles. Thus, for training shape memory alloys (repeating thermomechanical cycling to obtain the desired variant microstructure), optimal paths can be selected so as to minimize the number of training cycles required, thereby increasing the overall stability and fatigue life of these alloys in actuator or medical applications.

Constant and variable amplitude ultrasonic fatigue of 2024-T351 aluminium alloy at different load ratios.

PubMed

Mayer, H; Fitzka, M; Schuller, R

2013-12-01

Ultrasonic fatigue testing equipment is presented that is capable of performing constant amplitude (CA) and variable amplitude (VA) experiments at different constant load ratios. This equipment is used to study cyclic properties of aluminium alloy 2024-T351 in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime at load ratios R=-1 and R=0.5. CA loading does not reveal a fatigue limit below 10¹⁰ cycles. Cracks leading to VHCF failure start at broken constituent particles. Specimens that survived more than 10¹⁰ cycles at R=-1 contain non-propagating cracks of lengths below grain size. Resonance frequency and nonlinearity parameter β(rel) show changes of vibration properties of specimens at low fractions of their VHCF lifetime. VA lifetimes are measured in the HCF and VHCF regime and compared with Miner calculations. Damage sums decrease with decreasing load (and increasing mean lifetimes) and are lower for R=0.5 than R=-1. Copyright © 2013 Elsevier B.V. All rights reserved.

Internal cycling, not external loading, decides the nutrient limitation in eutrophic lake: A dynamic model with temporal Bayesian hierarchical inference.

PubMed

Wu, Zhen; Liu, Yong; Liang, Zhongyao; Wu, Sifeng; Guo, Huaicheng

2017-06-01

Lake eutrophication is associated with excessive anthropogenic nutrients (mainly nitrogen (N) and phosphorus (P)) and unobserved internal nutrient cycling. Despite the advances in understanding the role of external loadings, the contribution of internal nutrient cycling is still an open question. A dynamic mass-balance model was developed to simulate and measure the contributions of internal cycling and external loading. It was based on the temporal Bayesian Hierarchical Framework (BHM), where we explored the seasonal patterns in the dynamics of nutrient cycling processes and the limitation of N and P on phytoplankton growth in hyper-eutrophic Lake Dianchi, China. The dynamic patterns of the five state variables (Chla, TP, ammonia, nitrate and organic N) were simulated based on the model. Five parameters (algae growth rate, sediment exchange rate of N and P, nitrification rate and denitrification rate) were estimated based on BHM. The model provided a good fit to observations. Our model results highlighted the role of internal cycling of N and P in Lake Dianchi. The internal cycling processes contributed more than external loading to the N and P changes in the water column. Further insights into the nutrient limitation analysis indicated that the sediment exchange of P determined the P limitation. Allowing for the contribution of denitrification to N removal, N was the more limiting nutrient in most of the time, however, P was the more important nutrient for eutrophication management. For Lake Dianchi, it would not be possible to recover solely by reducing the external watershed nutrient load; the mechanisms of internal cycling should also be considered as an approach to inhibit the release of sediments and to enhance denitrification. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effect of afferent feedback and central motor commands on soleus H-reflex suppression during arm cycling.

PubMed

Hundza, S R; de Ruiter, Geoff C; Klimstra, M; Zehr, E Paul

2012-12-01

Suppression of soleus H-reflex amplitude in stationary legs is seen during rhythmic arm cycling. We examined the influence of various arm-cycling parameters on this interlimb reflex modulation to determine the origin of the effect. We previously showed the suppression to be graded with the frequency of arm cycling but not largely influenced by changes in peripheral input associated with crank length. Here, we more explicitly explored the contribution of afferent feedback related to arm movement on the soleus H-reflex suppression. We explored the influence of load and rate of muscle stretch by manipulating crank-load and arm-muscle vibration during arm cycling. Furthermore, internally driven ("Active") and externally driven ("Passive") arm cycling was compared. Soleus H-reflexes were evoked with tibial nerve stimulation during stationary control and rhythmic arm-cycling conditions, including: 1) six different loads; 2) with and without vibration to arm muscles; and 3) Active and Passive conditions. No significant differences were seen in the level of suppression between the different crank loads or between conditions with and without arm-muscle vibration. Furthermore, in contrast to the clear effect seen during active cycling, passive arm cycling did not significantly suppress the soleus H-reflex amplitude. Current results, in conjunction with previous findings, suggest that the afferent feedback examined in these studies is not the primary source responsible for soleus H-reflex suppression. Instead, it appears that central motor commands (supraspinal or spinal in origin) associated with frequency of arm cycling are relatively more dominant sources.

Automatic load sharing in inverter modules

NASA Technical Reports Server (NTRS)

Nagano, S.

1979-01-01

Active feedback loads transistor equally with little power loss. Circuit is suitable for balancing modular inverters in spacecraft, computer power supplies, solar-electric power generators, and electric vehicles. Current-balancing circuit senses differences between collector current for power transistor and average value of load currents for all power transistors. Principle is effective not only in fixed duty-cycle inverters but also in converters operating at variable duty cycles.

Optimization of drug loading to improve physical stability of paclitaxel-loaded long-circulating liposomes.

PubMed

Kannan, Vinayagam; Balabathula, Pavan; Divi, Murali K; Thoma, Laura A; Wood, George C

2015-01-01

The effect of formulation and process parameters on drug loading and physical stability of paclitaxel-loaded long-circulating liposomes was evaluated. The liposomes were prepared by hydration-extrusion method. The formulation parameters such as total lipid content, cholesterol content, saturated-unsaturated lipid ratio, drug-lipid ratio and process parameters such as extrusion pressure and number of extrusion cycles were studied and their impact on drug loading and physical stability was evaluated. A proportionate increase in drug loading was observed with increase in the total phospholipid content. Cholesterol content and saturated lipid content in the bilayer showed a negative influence on drug loading. The short-term stability evaluation of liposomes prepared with different drug-lipid ratios demonstrated that 1:60 as the optimum drug-lipid ratio to achieve a loading of 1-1.3 mg/mL without the risk of physical instability. The vesicle size decreased with an increase in the extrusion pressure and number of extrusion cycles, but no significant trends were observed for drug loading with changes in process pressure or number of cycles. The optimization of formulation and process parameters led to a physically stable formulation of paclitaxel-loaded long-circulating liposomes that maintain size, charge and integrity during storage.

Static and cyclic loading of fiber-reinforced dental resin.

PubMed

Drummond, James L; Bapna, Mahendra S

2003-05-01

The aim of this study was to evaluate the flexure strength of unidirectional fiber-reinforced resins under static and cyclic loading with and without thermal cycling. The fiber-reinforced resin materials chosen for this project were commercially available endodontic posts and commercially procured bar samples. For all materials, controls for flexure strength were tested in air and in water using three-point loading. Specimens were thermal cycled between 7 and 63 degrees C for 6000 cycles. A staircase approach was used to determine the flexure fatigue limit and scanning microscopy was used to examine the microstructure. The carbon/graphite fiber-reinforced resin posts and the glass FiberKor posts were significantly stronger than the ceramic (zirconia) and the other glass-reinforced resin materials. Thermal cycling caused a significant lowering (11-24%) of the flexure strength for each resin based post system. The ceramic post system decreased only by 2%. Further, for standard size glass fiber-reinforced resin bars, no significant differences between testing in air and water was observed, but a significant difference between static and cyclic loading was noted. The decreases in the strength property due to thermal cycling and the cyclic loading of these materials indicates that their utilization in the oral environment enhances their degradation, and potentially shortens their clinical life.

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.

Distributed photovoltaic architecture powering a DC bus: Impact of duty cycle and load variations on the efficiency of the generator

NASA Astrophysics Data System (ADS)

Allouache, Hadj; Zegaoui, Abdallah; Boutoubat, Mohamed; Bokhtache, Aicha Aissa; Kessaissia, Fatma Zohra; Charles, Jean-Pierre; Aillerie, Michel

2018-05-01

This paper focuses on a photovoltaic generator feeding a load via a boost converter in a distributed PV architecture. The principal target is the evaluation of the efficiency of a distributed photovoltaic architecture powering a direct current (DC) PV bus. This task is achieved by outlining an original way for tracking the Maximum Power Point (MPP) taking into account load variations and duty cycle on the electrical quantities of the boost converter and on the PV generator output apparent impedance. Thereafter, in a given sized PV system, we analyze the influence of the load variations on the behavior of the boost converter and we deduce the limits imposed by the load on the DC PV bus. The simultaneous influences of 1- the variation of the duty cycle of the boost converter and 2- the load power on the parameters of the various components of the photovoltaic chain and on the boost performances are clearly presented as deduced by simulation.

Biomechanical behaviour of a jawbone loaded with a prosthetic system supported by monophasic and biphasic implants.

PubMed

Inchingolo, F; Paracchini, L; DE Angelis, F; Cielo, A; Orefici, A; Spitaleri, D; Santacroce, L; Gheno, E; Palermo, A

2016-01-01

Modern implantology is based on the use of endosseous dental implants and on the study of osseointegration processes. The loss of marginal bone around a dental implant can be caused by many factors; the proper distribution of the masticatory loads is important and is closely dependent on the quality and quantity of bone tissue surrounding the implant. In fact, bone has the ability to adapt its microstructure, through processes of resorption and neoformation of new bone matrix, as a result of the mechanical stimuli that are generated during the chewing cycles. The purpose of this article is to redefine in a modern key and in light of current industrial and engineering technology, clinical and biomechanical concepts that characterize the monophasic implants, in order to assess proper use by evaluating the biomechanical differences with the biphasic implants.

AGC-4 Experiment Irradiation Monitoring Data Qualification Interim Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hull, Laurence Charles

2016-08-01

The Graphite Technology Development Program is running a series of six experiments to quantify the effects of irradiation on nuclear grade graphite. The fourth experiment, Advanced Graphite Creep 4 (AGC 4), began with Advanced Test Reactor (ATR) cycle 157D on May 30, 2015, and has been irradiated for two cycles. The capsule was removed from the reactor after ATR cycle 158A, which ended on January 2, 2016, due to interference with another experiment. Irradiation will resume when the interfering experiment is removed from the reactor. This report documents qualification of AGC 4 experiment irradiation monitoring data for use by themore » Advanced Reactor Technologies (ART) Technology Development Office (TDO) Program for research and development activities required to design and license the first HTR nuclear plant. Qualified data meet the requirements for use as described in the experiment planning and quality assurance documents. Failed data do not meet the requirements and provide no useable information. Trend data may not meet all requirements, but still provide some useable information. Use of Trend data requires assessment of how any deficiencies affect a particular use of the data. All thermocouples (TCs) have functioned throughout the AGC-4 experiment. All temperature data are Qualified for use by the ART TDO Program. Argon, helium, and total gas flow data were within expected ranges and are Qualified for use by the ART TDO Program. Discharge gas line moisture values were consistently low during cycle 157D. At the start of cycle 158A, gas moisture briefly spiked to over 600 ppmv and then declined throughout the cycle. Moisture values are within the measurement range of the instrument and are Qualified for use by the ART TDO Program. Graphite creep specimens were subjected to one of three loads, 393, 491, or 589 lbf. For a brief period during cycle 157D between 12:19 on June 2, 2015 and 08:23 on June 11, 2015 the load cells were wired incorrectly resulting in missing stack load data. Missing stack loads were estimated from measured ram pressures using regression equations developed from the existing data from cycle 157D. Estimated stack loads during this period are considered to be an accurate representation of actual load applied to the stacks. These loads deviate slightly from the planned loads. This deviation does not prevent the data from being Qualified for use, but must be taken into account when analyzing the effect of load on creep. Stack displacement increased consistently throughout the first two cycles with total displacement ranging from 0.4 to 0.8 in. During ATR outages, a set of pneumatic rams raised the stacks of graphite creep specimens to ensure the specimens were not stuck within the test train. This stack raising was performed twice. All stacks were raised successfully each time. The load and displacement data are Qualified for use by the ART TDO Program.« less

AC loss, interstrand resistance and mechanical properties of prototype EU DEMO TF conductors up to 30 000 load cycles

NASA Astrophysics Data System (ADS)

Yagotintsev, K.; Nijhuis, A.

2018-07-01

Two prototype Nb3Sn cable-in-conduit conductors conductors were designed and manufactured for the toroidal field (TF) magnet system of the envisaged European DEMO fusion reactor. The AC loss, contact resistance and mechanical properties of two sample conductors were tested in the Twente Cryogenic Cable Press under cyclic load up to 30 000 cycles. Though both conductors were designed to operate at 82 kA in a background magnetic field of 13.6 T, they reflect different approaches with respect to the magnet winding pack assembly. The first approach is based on react and wind technology while the second is the more common wind and react technology. Each conductor was tested first for AC loss in virgin condition without handling. The impact of Lorentz load during magnet operation was simulated using the cable press. In the press each conductor specimen was subjected to transverse cyclic load up to 30 000 cycles in liquid helium bath at 4.2 K. Here a summary of results for AC loss, contact resistance, conductor deformation, mechanical heat production and conductor stiffness evolution during cycling of the load is presented. Both conductors showed similar mechanical behaviour but quite different AC loss. In comparison with previously tested ITER TF conductors, both DEMO TF conductors possess very low contact resistance resulting in high coupling loss. At the same time, load cycling has limited impact on properties of DEMO TF conductors in comparison with ITER TF conductors.

Building America Case Study: Advanced Boiler Load Monitoring Controllers, Chicago, Illinois (Fact Sheet)

DOE Office of Scientific and Technical Information (OSTI.GOV)

PARR

Beyond these initial system efficiency upgrades are an emerging class of Advanced Load Monitoring (ALM) aftermarket controllers that dynamically respond to the boiler load, with claims of 10% to 30% of fuel savings over a heating season. For hydronic boilers specifically, these devices perform load monitoring, with continuous measurement of supply and in some cases return water temperatures. Energy savings from these ALM controllers are derived from dynamic management of the boiler differential, where a microprocessor with memory of past boiler cycles prevents the boiler from firing for a period of time, to limit cycling losses and inefficient operation duringmore » perceived low load conditions. These differ from OTR controllers, which vary boiler setpoint temperatures with ambient conditions while maintaining a fixed differential. PARR installed and monitored the performance of one type of ALM controller, the M2G from Greffen Systems, at multifamily sites in the city of Chicago and its suburb Cary, IL, both with existing OTR control. Results show that energy savings depend on the degree to which boilers are over-sized for their load, represented by cycling rates. Also savings vary over the heating season with cycling rates, with greater savings observed in shoulder months. Over the monitoring period, over-sized boilers at one site showed reductions in cycling and energy consumption in line with prior laboratory studies, while less over-sized boilers at another site showed muted savings.« less

The effect of an overload on the rate of fatigue crack propagation under plane stress conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bao, H.; McEvily, A.J.

1995-07-01

It has been shown that the retardation in the rate of fatigue crack growth following an overload is largely the result of surface-related, plane-stress deformation. In the present article, in order to isolate the plane-stress behavior, the effect of an overload on the subsequent rate of fatigue crack growth of 0.3-mm-thick specimens of 9Cr-1Mo steel has been investigated and compared to results obtained using 6.35-mm-thick specimens. It was found that for the 0.3-mm thickness, as with thicker specimens, two opening load levels were associated with the overload process. The upper opening load is associated with plane-stress deformation in the overloadmore » plastic zone, and this opening process is more clearly observed with thin as compared to thicker specimens. Based upon the determined level of the upper opening load, a semiempirical analysis is developed for calculating the number of delay cycles due to an overload as a function of thickness.« less

Long Life Nickel Electrodes for a Nickel-hydrogen Cell: Cycle Life Tests

NASA Technical Reports Server (NTRS)

Lim, H. S.; Verzwyvelt, S. A.

1984-01-01

In order to develop a long life nickel electrode for a Ni/H2 cell, cycle life tests of nickel electrodes were carried out in Hi/H2 boiler plate cells. A 19 test cell matrix was made of various nickel electrode designs including three levels each of plaque mechanical strength, median pore size of the plaque, and active material loading. Test cells were cycled to the end of their life (0.5v) in a 45-minute low earth orbit cycle regime at 80% depth-of-discharge. The results show that the active material loading level affects the cycle life the most with the optimum loading at 1.6 g/cc void. Mechanical strength did not affect the cycle life noticeably in the bend strength range of 400 to 700 psi. The best plaque type appears to be one which is made of INCO nickel powder type 287 and has a median pore size of 13 micron.

Viscoplastic analysis of an experimental cylindrical thrust chamber liner

NASA Technical Reports Server (NTRS)

Arya, Vinod K.; Arnold, Steven M.

1991-01-01

A viscoplastic stress-strain analysis of an experimental cylindrical thrust chamber is presented. A viscoelastic constitutive model incorporating a single internal state variable that represents kinematic hardening was employed to investigate whether such a viscoplastic model could predict the experimentally observed behavior of the thrust chamber. Two types of loading cycles were considered: a short cycle of 3.5 sec. duration that corresponded to the experiments, and an extended loading cycle of 485.1 sec. duration that is typical of the Space Shuttle Main Engine (SSME) operating cycle. The analysis qualitatively replicated the deformation behavior of the component as observed in experiments designed to simulate SSME operating conditions. The analysis also showed that the mode and location in the component may depend on the loading cycle. The results indicate that using viscoplastic models for structural analysis can lead to a more realistic life assessment of thrust chambers.

Effects of Simulated Functional Loading Conditions on Dentin, Composite, and Laminate Structures

PubMed Central

Walker, Mary P.; Teitelbaum, Heather K.; Eick, J. David; Williams, Karen B.

2008-01-01

Use of composite restorations continues to increase, tempered by more potential problems when placed in posterior dentition. Thus, it is essential to understand how these materials function under stress-bearing clinical conditions. Since mastication is difficult to replicate in the laboratory, cyclic loading is frequently used within in vitro evaluations but often employs traditional fatigue testing, which typically does not simulate occlusal loading because higher stresses and loading frequencies are used, so failure mechanisms may be different. The present investigation utilized relevant parameters (specimen size; loading frequency) to assess the effects of cyclic loading on flexural mechanical properties and fracture morphology of (coronal) dentin, composite, and dentin-adhesive-composite “laminate” structures. Incremental monitoring of flexural modulus on individual beams over 60,000 loading cycles revealed a gradual increase across materials; post-hoc comparisons indicated statistical significance only for 1 versus 60k cycles. Paired specimens were tested (one exposed to 60k loading cycles, one to static loading only), and comparisons of flexural modulus and strength showed statistically significantly higher values for cyclically-loaded specimens across materials, with no observable differences in fracture morphology. Localized reorganization of dentin collagen and polymer chains could have increased flexural modulus and strength during cyclic loading, which may have implications toward the life and failure mechanisms of clinical restorations and underlying tooth structure. PMID:18823019

SLS Intertank Test Article, ITA, is attached to crosshead of loa

NASA Image and Video Library

2018-04-04

SLS Intertank Test Article, ITA, is attached to crosshead of load test Annex, Bldg. 4619, and removed from bed of KMAG transporter. Rob Ziegler, (L), and Roger Myrick (R), of Aerie Aerospace attach load lines to Aft Load Ring of Intertank Test Article.

Effects of varying material properties on the load deformation characteristics of heel cushions.

PubMed

Sun, Pi-Chang; Wei, Hung-Wen; Chen, Chien-Hua; Wu, Chun-Hao; Kao, Hung-Chan; Cheng, Cheng-Kung

2008-07-01

Various insole materials were used in attenuation of heel-strike impact. This study presented a compression test to investigate the deformation characteristics of common heel cushions. There were two materials (thermoplastic elastomer "TPE" and silicone) with three hardness and six thickness being analyzed. They underwent consecutive loading-unloading cycles with a load control mode. The displacement of material thickness was recorded during cyclic compression being applied and released from 0 to 1050 N. The energy input, return and dissipation were evaluated based on the load deformation curves when new and after repeated compression. The TPE recovered more deformed energy and thickness than the silicone after the first loading cycle. The silicone would preserve more strain energy with increasing its hardness for the elastic recovery in the unloading process. The deformed energy was decreased as the original thickness did not completely recover under cyclic tests. The reduction in hysteresis area was gradually converged within 20 cycles. The silicone attenuated more impact energy in the initial cycles, but its energy dissipation was reduced after repeated loading. To increase hardness or thickness should be considered to improve resilience or accommodate persistent compression without flattening. The careful selection of cushion materials is imperative to meet individual functional demands.

Exploring the Behaviour of Emerging Contaminants in the Water Cycle using the Capabilities of High Resolution Mass Spectrometry.

PubMed

Hollender, Juliane; Bourgin, Marc; Fenner, Kathrin B; Longrée, Philipp; Mcardell, Christa S; Moschet, Christoph; Ruff, Matthias; Schymanski, Emma L; Singer, Heinz P

2014-11-01

To characterize a broad range of organic contaminants and their transformation products (TPs) as well as their loads, input pathways and fate in the water cycle, the Department of Environmental Chemistry (Uchem) at Eawag applies and develops high-performance liquid chromatography (LC) methods combined with high-resolution tandem mass spectrometry (HRMS/MS). In this article, the background and state-of-the-art of LC-HRMS/MS for detection of i) known targets, ii) suspected compounds like TPs, and iii) unknown emerging compounds are introduced briefly. Examples for each approach are taken from recent research projects conducted within the department. These include the detection of trace organic contaminants and their TPs in wastewater, pesticides and their TPs in surface water, identification of new TPs in laboratory degradation studies and ozonation experiments and finally the screening for unknown compounds in the catchment of the river Rhine.

Maximising performance in triathlon: applied physiological and nutritional aspects of elite and non-elite competitions.

PubMed

Bentley, David J; Cox, Gregory R; Green, Daniel; Laursen, Paul B

2008-07-01

Triathlon is a sport consisting of sequential swimming, cycling and running. The main diversity within the sport of triathlon resides in the varying event distances, which creates specific technical, physiological and nutritional considerations for athlete and practitioner alike. The purpose of this article is to review physiological as well as nutritional aspects of triathlon and to make recommendations on ways to enhance performance. Aside from progressive conditioning and training, areas that have shown potential to improve triathlon performance include drafting when possible during both the swim and cycle phase, wearing a wetsuit, and selecting a lower cadence (60-80 rpm) in the final stages of the cycle phase. Adoption of a more even racing pace during cycling may optimise cycling performance and induce a "metabolic reserve" necessary for elevated running performance in longer distance triathlon events. In contrast, drafting in swimming and cycling may result a better tactical approach to increase overall performance in elite Olympic distance triathlons. Daily energy intake should be modified to reflect daily training demands to assist triathletes in achieving body weight and body composition targets. Carbohydrate loading strategies and within exercise carbohydrate intake should reflect the specific requirements of the triathlon event contested. Development of an individualised fluid plan based on previous fluid balance observations may assist to avoid both dehydration and hyponatremia during prolonged triathlon racing.

Cyclic load testing of biodegradable suture anchors containing 2 high-strength sutures.

PubMed

Barber, F Alan; Coons, David A; Ruiz-Suarez, Michell

2007-04-01

The purpose of this study was to test 4 different biodegradable suture anchors threaded with 2 high-strength sutures under cyclic loading conditions in humeral cadaveric specimens divided into 2 different age groups. Thirty-two paired human cadaveric humeri were stripped of all soft tissue. Two groups were studied: group 1, in which the mean age was 54 years, and group 2, in which the mean age was 70 years. We placed 1 suture anchor at 3 humeral sites per bone (anterior, middle, and posterior greater tuberosity). We tested 24 specimens using each of 4 anchors: TwinFix AB (Smith & Nephew Endoscopy, Andover, MA), BioZip (Stryker Endoscopy, San Jose, CA), Bio-Corkscrew FT (Arthrex, Naples, FL), and SpiraLok (DePuy Mitek, Raynham, MA). The anchor's sutures were grasped with an Instron clamp (Instron, Canton, MA), preloaded, and cycled from 10 to 60 N 500 times, followed by destructive testing. The mean displacement at 500 cycles, yield loads, failure modes, and ultimate loads were recorded. Most cyclic motion occurred during the first 100 cycles. More motion occurred in older bones than in younger bones (P < .05). The mean yield loads were greater for the young group for the SpiraLok anchors than for Bio-Corkscrew FT anchors in the young and old groups (P < .001), TwinFix anchors in the old group (P < .05), and BioZip anchors in the old group (P < .05). The ultimate failure loads for SpiraLok anchors in the young group were greater than for Bio-Corkscrew FT anchors in the young and old groups and BioZip anchors in the old group (P < .05). In group 1 TwinFix AB (P = .01) and BioZip (P = .02) ultimate loads were statistically greater than that for Bio-Corkscrew FT. The TwinFix AB failed by anchor pullout. The Bio-Corkscrew FT failed by eyelet pullout. The BioZip and SpiraLok pulled out in older bone and experienced eyelet breakage in younger bone. None of the 4 anchors reached 5 mm of displacement even after 500 loading cycles. Most of the displacement occurred in the first 100 cycles. Of all anchors tested, the Bio-Corkscrew FT recorded the lowest displacement after 500 cycles (P < .05). The SpiraLok had the highest ultimate load of all anchors tested (P < .01). Rotator cuff anchors perform differently in younger humeral bone than in older humeral bone. Most displacement with cyclic loading occurring between the anchor and bone takes place in the first 100 cycles. Anchors in older bones can be expected to fail at lower loads.

Effect of Repeated Screw Joint Closing and Opening Cycles and Cyclic Loading on Abutment Screw Removal Torque and Screw Thread Morphology: Scanning Electron Microscopy Evaluation.

PubMed

Arshad, Mahnaz; Mahgoli, Hosseinali; Payaminia, Leila

To evaluate the effect of repeated screw joint closing and opening cycles and cyclic loading on abutment screw removal torque and screw thread morphology using scanning electron microscopy (SEM). Three groups (n = 10 in each group) of implant-abutment-abutment screw assemblies were created. There were also 10 extra abutment screws as new screws in group 3. The abutment screws were tightened to 12 Ncm with an electronic torque meter; then they were removed and removal torque values were recorded. This sequence was repeated 5 times for group 1 and 15 times for groups 2 and 3. The same screws in groups 1 and 2 and the new screws in group 3 were then tightened to 12 Ncm; this was also followed by screw tightening to 30 Ncm and retightening to 30 Ncm 15 minutes later. Removal torque measurements were performed after screws were subjected to cyclic loading (0.5 × 10⁶ cycles; 1 Hz; 75 N). Moreover, the surface topography of one screw from each group before and after cyclic loading was evaluated with SEM and compared with an unused screw. All groups exhibited reduced removal torque values in comparison to insertion torque in each cycle. However, there was a steady trend of torque loss in each group. A comparison of the last cycle of the groups before loading showed significantly greater torque loss value in the 15th cycle of groups 2 and 3 compared with the fifth cycle of group 1 (P < .05). Nonetheless, torque loss values after loading were not shown to be significantly different from each other. Using a new screw could not significantly increase the value of removal torque. It was concluded that restricting the amount of screw tightening is more important than replacing the screw with a new one when an abutment is definitively placed.

Biomechanical comparison of suture anchor versus margin convergence plus suture anchor for rotator cuff repair.

PubMed

Chen, Shi-yi; Malcarney, Hilary L; Murrell, George A C

2009-02-01

To evaluate results of margin convergence versus suture anchors in rotator cuff repair, and to determine which method is mechanically superior. Eighteen kangaroo shoulders were randomly divided into three groups (n = 6). A full thickness tendon defect 1.0 cm × 1.5 cm in size was created in the supraspinatus tendon at humeral insertion, simulating a massive rotator cuff tear. Three different techniques were employed for rotator cuff repair: (i) Mitek GII suture anchor alone (Group 1); (ii) margin convergence alone (Group 2); and (iii) margin convergence plus Mitek GII suture anchor (Group 3). Combined loads were applied to each specimen. After completion of cyclic loading, the construct was loaded to failure. ANOVA and LSD (Least Significant Difference) multiple comparisons of the means were applied to results. Cyclic load testing showed progressive gap formation in each repaired specimen with increasing cycles. Group 1 reached 50% failure at an average of 34 cycles, Group 2 at 75 cycles and Group 3 at 73 cycles. There were significant difference between Groups 1 and 2, and Groups 1 and 3 (P ≤ 0.001). After 100 loading cycles, the average gap size was 6.8 mm, 6.1 mm and 4.7 mm in Groups 1, 2 and 3, respectively. There was a significant difference between Groups 1 and 3 (P ≤ 0.015). All specimens eventually reached failure. Rotator cuff repairs with margin convergence +/- suture anchor were far stronger than suture anchor alone, both in gap formation and ultimate failure load. However, progressive gap formation with cyclic loading seems inevitable after cuff repair, which may facilitate clinical understanding of the phenomena of re-tear or residual defect. © 2009 Tianjin Hospital and Blackwell Publishing Asia Pty Ltd.

Life cycle, cost, and loading characteristics of AASHO designed rigid and flexible pavements in Louisiana : final report.

DOT National Transportation Integrated Search

1989-02-01

This report represents a study undertaken to determine the life cycle, load characteristics, and associated costs of a representative sample of the oldest rigid and flexible pavements designed in Louisiana (1963-1967) using the AASHO Guide for Design...

Field Test of Boiler Primary Loop Temperature Controller

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glanville, P.; Rowley, P.; Schroeder, D.

Beyond these initial system efficiency upgrades are an emerging class of Advanced Load Monitoring (ALM) aftermarket controllers that dynamically respond to the boiler load, with claims of 10% to 30% of fuel savings over a heating season. For hydronic boilers specifically, these devices perform load monitoring, with continuous measurement of supply and in some cases return water temperatures. Energy savings from these ALM controllers are derived from dynamic management of the boiler differential, where a microprocessor with memory of past boiler cycles prevents the boiler from firing for a period of time, to limit cycling losses and inefficient operation duringmore » perceived low load conditions. These differ from OTR controllers, which vary boiler setpoint temperatures with ambient conditions while maintaining a fixed differential. PARR installed and monitored the performance of one type of ALM controller, the M2G from Greffen Systems, at multifamily sites in the city of Chicago and its suburb Cary, IL, both with existing OTR control. Results show that energy savings depend on the degree to which boilers are over-sized for their load, represented by cycling rates. Also savings vary over the heating season with cycling rates, with greater savings observed in shoulder months. Over the monitoring period, over-sized boilers at one site showed reductions in cycling and energy consumption in line with prior laboratory studies, while less over-sized boilers at another site showed muted savings.« less

A proposed procedure for expressing the behavior of a full engine cycle by identifying its critical load timings

NASA Astrophysics Data System (ADS)

Marius Andrei, Mihalache; Gheorghe, Nagit; Gavril, Musca; Vasile, Merticaru, Jr.; Marius Ionut, Ripanu

2016-11-01

In the present study the authors propose a new algorithm for identifying the right loads that act upon a functional connecting rod during a full engine cycle. The loads are then divided into three categories depending on the results they produce, as static, semi-dynamic and dynamic ones Because an engine cycle extends up to 720°, the authors aim to identify a method of substitution of values that produce the same effect as a previous value of a considered angle did. In other words, the proposed method aims to pin point the critical values that produce an effect different as the one seen before during a full engine cycle. Only those values will then be considered as valid loads that act upon the connecting rod inside FEA analyses. This technique has been applied to each of the three categories mentioned above and did produced different critical values for each one of them. The whole study relies on a theoretical mechanical project which was developed in order to identify the right values that correspond to each degree of the entire engine cycle of a Daewoo Tico automobile.

Effect of Cyclic Loading on Micromotion at the Implant-Abutment Interface.

PubMed

Karl, Matthias; Taylor, Thomas D

2016-01-01

Cyclic loading may cause settling of abutments mounted on dental implants, potentially affecting screw joint stability and implant-abutment micromotion. It was the goal of this in vitro study to compare micromotion of implant-abutment assemblies before and after masticatory simulation. Six groups of abutments (n = 5) for a specific tissue-level implant system with an internal octagon were subject to micromotion measurements. The implant-abutment assemblies were loaded in a universal testing machine, and an apparatus and extensometers were used to record displacement. This was done twice, in the condition in which they were received from the abutment manufacturer and after simulated loading (100,000 cycles; 100 N). Statistical analysis was based on analysis of variance, two-sample t tests (Welch tests), and Pearson product moment correlation (α = .05). The mean values for micromotion ranged from 33.15 to 63.41 μm and from 30.03 to 42.40 μm before and after load cycling. The general trend toward reduced micromotion following load cycling was statistically significant only for CAD/CAM zirconia abutments (P = .036) and for one type of clone abutment (P = .012), with no significant correlation between values measured before and after cyclic loading (Pearson product moment correlation; P = .104). While significant differences in micromotion were found prior to load cycling, no significant difference among any of the abutment types tested could be observed afterward (P > .05 in all cases). A quantifiable settling effect at the implant-abutment interface seems to result from cyclic loading, leading to a decrease in micromotion. This effect seems to be more pronounced in low-quality abutments. For the implant system tested in this study, retightening of abutment screws is recommended after an initial period of clinical use.

Pedicle screw anchorage of carbon fiber-reinforced PEEK screws under cyclic loading.

PubMed

Lindtner, Richard A; Schmid, Rene; Nydegger, Thomas; Konschake, Marko; Schmoelz, Werner

2018-03-01

Pedicle screw loosening is a common and significant complication after posterior spinal instrumentation, particularly in osteoporosis. Radiolucent carbon fiber-reinforced polyetheretherketone (CF/PEEK) pedicle screws have been developed recently to overcome drawbacks of conventional metallic screws, such as metal-induced imaging artifacts and interference with postoperative radiotherapy. Beyond radiolucency, CF/PEEK may also be advantageous over standard titanium in terms of pedicle screw loosening due to its unique material properties. However, screw anchorage and loosening of CF/PEEK pedicle screws have not been evaluated yet. The aim of this biomechanical study therefore was to evaluate whether the use of this alternative nonmetallic pedicle screw material affects screw loosening. The hypotheses tested were that (1) nonmetallic CF/PEEK pedicle screws resist an equal or higher number of load cycles until loosening than standard titanium screws and that (2) PMMA cement augmentation further increases the number of load cycles until loosening of CF/PEEK screws. In the first part of the study, left and right pedicles of ten cadaveric lumbar vertebrae (BMD 70.8 mg/cm 3  ± 14.5) were randomly instrumented with either CF/PEEK or standard titanium pedicle screws. In the second part, left and right pedicles of ten vertebrae (BMD 56.3 mg/cm 3  ± 15.8) were randomly instrumented with either PMMA-augmented or nonaugmented CF/PEEK pedicle screws. Each pedicle screw was subjected to cyclic cranio-caudal loading (initial load ranging from - 50 N to + 50 N) with stepwise increasing compressive loads (5 N every 100 cycles) until loosening or a maximum of 10,000 cycles. Angular screw motion ("screw toggling") within the vertebra was measured with a 3D motion analysis system every 100 cycles and by stress fluoroscopy every 500 cycles. The nonmetallic CF/PEEK pedicle screws resisted a similar number of load cycles until loosening as the contralateral standard titanium screws (3701 ± 1228 vs. 3751 ± 1614 load cycles, p = 0.89). PMMA cement augmentation of CF/PEEK pedicle screws furthermore significantly increased the mean number of load cycles until loosening by 1.63-fold (5100 ± 1933 in augmented vs. 3130 ± 2132 in nonaugmented CF/PEEK screws, p = 0.015). In addition, angular screw motion assessed by stress fluoroscopy was significantly smaller in augmented than in nonaugmented CF/PEEK screws before as well as after failure. Using nonmetallic CF/PEEK instead of standard titanium as pedicle screw material did not affect screw loosening in the chosen test setup, whereas cement augmentation enhanced screw anchorage of CF/PEEK screws. While comparable to titanium screws in terms of screw loosening, radiolucent CF/PEEK pedicle screws offer the significant advantage of not interfering with postoperative imaging and radiotherapy. These slides can be retrieved under Electronic Supplementary Material.

The sheltered genetic load linked to the s locus in plants: new insights from theoretical and empirical approaches in sporophytic self-incompatibility.

PubMed

Llaurens, Violaine; Gonthier, Lucy; Billiard, Sylvain

2009-11-01

Inbreeding depression and mating systems evolution are closely linked, because the purging of deleterious mutations and the fitness of individuals may depend on outcrossing vs. selfing rates. Further, the accumulation of deleterious mutations may vary among genomic regions, especially for genes closely linked to loci under balancing selection. Sporophytic self-incompatibility (SSI) is a common genetic mechanism in angiosperm that enables hermaphrodite plants to avoid selfing and promote outcrossing. The SSI phenotype is determined by the S locus and may depend on dominance relationships among alleles. Since most individuals are heterozygous at the S locus and recombination is suppressed in the S-locus region, it has been suggested that deleterious mutations could accumulate at genes linked to the S locus, generating a "sheltered load." In this article, we first theoretically investigate the conditions generating sheltered load in SSI. We show that deleterious mutations can accumulate in linkage with specific S alleles, and particularly if those S alleles are dominant. Second, we looked for the presence of sheltered load in Arabidopsis halleri using CO(2) gas treatment to overcome self-incompatibility. By examining the segregation of S alleles and measuring the relative fitness of progeny, we found significant sheltered load associated with the most dominant S allele (S15) of three S alleles tested. This sheltered load seems to be expressed at several stages of the life cycle and to have a larger effect than genomic inbreeding depression.

Load and Pi control flux through the branched kinetic cycle of myosin V.

PubMed

Kad, Neil M; Trybus, Kathleen M; Warshaw, David M

2008-06-20

Myosin V is a processive actin-based motor protein that takes multiple 36-nm steps to deliver intracellular cargo to its destination. In the laser trap, applied load slows myosin V heavy meromyosin stepping and increases the probability of backsteps. In the presence of 40 mm phosphate (P(i)), both forward and backward steps become less load-dependent. From these data, we infer that P(i) release commits myosin V to undergo a highly load-dependent transition from a state in which ADP is bound to both heads and its lead head trapped in a pre-powerstroke conformation. Increasing the residence time in this state by applying load increases the probability of backstepping or detachment. The kinetics of detachment indicate that myosin V can detach from actin at two distinct points in the cycle, one of which is turned off by the presence of P(i). We propose a branched kinetic model to explain these data. Our model includes P(i) release prior to the most load-dependent step in the cycle, implying that P(i) release and load both act as checkpoints that control the flux through two parallel pathways.

Behavior of a quasi-isotropic ply metal matrix composite under thermo-mechanical and isothermal fatigue loading. Master's thesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hart, K.A.

1992-12-01

This study investigated the behavior of the SCS6/Ti-15-3 metal matrix composite with a quasi-isotropic layup when tested under static and fatigue conditions. Specimens were subjected to in-phase and out-of-phase thermo-mechanical and isothermal fatigue loading. In-phase and isothermal loading produced a fiber dominated failure while the out-of-phase loading produced a matrix dominated failure. Also, fiber domination in all three profiles was present at higher maximum applied loads and al three profiles demonstrated matrix domination at lower maximum applied loads. Thus, failure is both profile dependent and load equipment. Additional analyses, using laminated plate theory, Halpin-Tsai equations, METCAN, and the Linear Lifemore » Fraction Model (LLFM), showed: the as-received specimens contained plies where a portion of the fibers are debonded from the matrix; during fatigue cycling, the 90 deg. plies and a percentage of the 45 deg. plies failed immediately with greater damage becoming evident with additional cycles; and, the LLFM suggests that there may be a non-linear combination of fiber and matrix domination for in-phase and isothermal cycling.« less

Effect of stress ratio on the fatigue behaviour of glass/epoxy composite

NASA Astrophysics Data System (ADS)

Syayuthi, A. R. A.; Majid, M. S. Abdul; Ridzuan, M. J. M.; Basaruddin, K. S.; Peng, T. L.

2017-10-01

The effect of stress ratio on the fatigue behaviour of the GFRE composite has been investigated. The glass fibre reinforced epoxy (GFRE) composite plates were fabricated using vacuum infusion method. Static tensile was performed in accordance with the ASTM D5766 standard, and the cyclic test was conducted according to ASTM D3479 with three different stress ratio, R = 0, 0.5, -1. Static tensile tests were carried out to determine the ultimate strength of this composite. Subsequently, fatigue tests loads ranging from 30% to 90% of the ultimate load were applied to each specimen. The S-N curve of different stress ratio loading of fibreglass/epoxy composites was then established. The results show that the number of cycles to failure increases as the loading is decreased. The specimens for fatigue tests loads 30% at R = 0 and -1 recorded the highest number of cycles at 2 million cycles. The results obtained from this test indicated a significant life reduction for R = -1 compared with the tension-tension loading, with the life reduction for R = -1 being greatest. The fatigue behaviour of the GFRE composite materials is not only influenced by the percentage of fatigue tests load but with different of stress ratio.

Buckling Test Results from the 8-Foot-Diameter Orthogrid-Stiffened Cylinder Test Article TA01. [Test Dates: 19-21 November 2008

NASA Technical Reports Server (NTRS)

Hilburger, Mark W.; Waters, W. Allen, Jr.; Haynie, Waddy T.

2015-01-01

Results from the testing of cylinder test article SBKF-P2-CYLTA01 (referred to herein as TA01) are presented. The testing was conducted at the Marshall Space Flight Center (MSFC), November 19?21, 2008, in support of the Shell Buckling Knockdown Factor (SBKF) Project.i The test was used to verify the performance of a newly constructed buckling test facility at MSFC and to verify the test article design and analysis approach used by the SBKF project researchers. TA01 is an 8-foot-diameter (96-inches), 78.0-inch long, aluminum-lithium (Al-Li), orthogrid-stiffened cylindrical shell similar to those used in current state-of-the-art launch vehicle structures and was designed to exhibit global buckling when subjected to compression loads. Five different load sequences were applied to TA01 during testing and included four sub-critical load sequences, i.e., loading conditions that did not cause buckling or material failure, and one final load sequence to buckling and collapse. The sub-critical load sequences consisted of either uniform axial compression loading or combined axial compression and bending and the final load sequence subjected TA01 to uniform axial compression. Traditional displacement transducers and strain gages were used to monitor the test article response at nearly 300 locations and an advanced digital image correlation system was used to obtain low-speed and high-speed full-field displacement measurements of the outer surface of the test article. Overall, the test facility and test article performed as designed. In particular, the test facility successfully applied all desired load combinations to the test article and was able to test safely into the postbuckling range of loading, and the test article failed by global buckling. In addition, the test results correlated well with initial pretest predictions.

Norton-Thevenin Receptance Coupling (NTRC) as a Payload Design Tool

NASA Technical Reports Server (NTRS)

Gordon, Scott; Kaufman, Dan; Majed, Arya

2017-01-01

The NASA Engineering and Safety Center (NESC) is funding a study to develop an alternate method for performing coupled loads analysis called Norton-Thevenin Receptance Coupling (NTRC). NTRC combines Receptance Coupling (RC), a frequency-domain synthesis method and Norton-Thevenin (NT) theory, an impedance based approach for simulating the interaction between dynamic systems. The goal of developing the NTRC method is to provide a tool that payload developers can use to reduce the conservatism in defining preliminary design loads, assess the impact of design changes between formal load cycles, and to perform trade studies for design optimization with a minimum amount of data required from the launch vehicle (LV) provider. NTRC also has the ability to perform parametric loads analysis where many different design configurations can be evaluated. This will result in cost and schedule benefits to the payload developer that are currently not possible under the standard coupled loads analysis (CLA) flow where typically only 2-3 official load cycles are performed by the LV provider over the life of a payload program. NTRC is not envisioned as a replacement for the official load cycles performed by the LV provider but rather as a means to address the types of design issues faced by the payload developer before and between official load cycles.The presentation provides an overview of the NTRC methodology and discusses how NTRC can be used to replicate the results from a standard LV CLA. The presentation covers the benchmarking that has been performed as part of the NESC study to demonstrate the accuracy of the technique for both frequency and time domain dynamic analyses. Future plans for benchmarking the NTRC approach against CLA results for NASAs Space Launch System (SLS) and commercial launch vehicles are discussed and the role that NTRC is envisioned to play in the payload development cycle.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Renlund, Anita Mariana; Tappan, Alexander Smith; Miller, Jill C.

The HMX {beta}-{delta} solid-solid phase transition, which occurs as HMX is heated near 170 C, is linked to increased reactivity and sensitivity to initiation. Thermally damaged energetic materials (EMs) containing HMX therefore may present a safety concern. Information about the phase transition is vital to predictive safety models for HMX and HMX-containing EMs. We report work on monitoring the phase transition with real-time Raman spectroscopy aimed towards obtaining a better understanding of physical properties of HMX through the phase transition. HMX samples were confined in a cell of minimal free volume in a displacement-controlled or load-controlled arrangement. The cell wasmore » heated and then cooled at controlled rates while real-time Raman spectroscopic measurements were performed. Raman spectroscopy provides a clear distinction between the phases of HMX because the vibrational transitions of the molecule change with conformational changes associated with the phase transition. Temperature of phase transition versus load data are presented for both the heating and cooling cycles in the load-controlled apparatus, and general trends are discussed. A weak dependence of the temperature of phase transition on load was discovered during the heating cycle, with higher loads causing the phase transition to occur at a higher temperature. This was especially true in the temperature of completion of phase transition data as opposed to the temperature of onset of phase transition data. A stronger dependence on load was observed in the cooling cycle, with higher loads causing the reverse phase transitions to occur at a higher cooling temperature. Also, higher loads tended to cause the phase transition to occur over a longer period of time in the heating cycle and over a shorter period of time in the cooling cycle. All three of the pure HMX phases ({alpha}, {beta} and {delta}) were detected on cooling of the heated samples, either in pure form or as a mixture.« less

Breast Cyst Aspiration

MedlinePlus

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Coupling Mars' Dust and Water Cycles: Effects on Dust Lifting Vigor, Spatial Extent and Seasonality

NASA Technical Reports Server (NTRS)

Kahre, M. A.; Hollingsworth, J. L.; Haberle, R. M.; Montmessin, F.

2012-01-01

The dust cycle is an important component of Mars' current climate system. Airborne dust affects the radiative balance of the atmosphere, thus greatly influencing the thermal and dynamical state of the atmosphere. Dust raising events on Mars occur at spatial scales ranging from meters to planet-wide. Although the occurrence and season of large regional and global dust storms are highly variable from one year to the next, there are many features of the dust cycle that occur year after year. Generally, a low-level dust haze is maintained during northern spring and summer, while elevated levels of atmospheric dust occur during northern autumn and winter. During years without global-scale dust storms, two peaks in total dust loading were observed by MGS/TES: one peak occurred before northern winter solstice at Ls 200-240, and one peak occurred after northern winter solstice at L(sub s) 305-340. These maxima in dust loading are thought to be associated with transient eddy activity in the northern hemisphere, which has been observed to maximize pre- and post-solstice. Interactive dust cycle studies with Mars General Circulation Models (MGCMs) have included the lifting, transport, and sedimentation of radiatively active dust. Although the predicted global dust loadings from these simulations capture some aspects of the observed dust cycle, there are marked differences between the simulated and observed dust cycles. Most notably, the maximum dust loading is robustly predicted by models to occur near northern winter solstice and is due to dust lifting associated with down slope flows on the flanks of the Hellas basin. Thus far, models have had difficulty simulating the observed pre- and post- solstice peaks in dust loading. Interactive dust cycle studies typically have not included the formation of water ice clouds or their radiative effects. Water ice clouds can influence the dust cycle by scavenging dust from atmosphere and by interacting with solar and infrared radiation, thereby modifying the thermal structure of the atmosphere and its circulation. Results presented in other papers at this workshop show that including the radiative effects of water ice clouds greatly influence the water cycle and the vigor of weather systems in both the northern and southern hemispheres. Our goal is to investigate the effects of fully coupling the dust and water cycles on the dust cycle. We show that including water ice clouds and their radiative effects greatly affect the magnitude, spatial extent and seasonality of dust lifting and the season of maximum atmospheric dust loading.

Biomechanical comparison of blade plate and intramedullary nail fixation for tibiocalcaneal arthrodesis.

PubMed

Lee, Arthur T; Sundberg, Eric B; Lindsey, Derek P; Harris, Alex H S; Chou, Loretta B

2010-02-01

Tibiocalcaneal arthrodesis is an uncommon salvage procedure used for complex problems of the ankle and hindfoot. A biomechanical evaluation of the fixation constructs of this procedure has not been studied previously. The purpose of this study was to compare intramedullary nail to blade plate fixation in a deformity model in fatigue endurance testing and load to failure. Nine matched pairs of fresh frozen cadaveric legs underwent talectomy followed by fixation with a blade plate and 6.5-mm fully threaded cancellous screw or an ankle arthrodesis intramedullary nail. The specimens were loaded to 270 N at a rate of 3 Hz for a total of 250,000 cycles, followed by loading to failure. Intramedullary nail fixation demonstrated greater mean stiffness throughout the fatigue endurance testing, from cycles 10 through 250,000 (blade plate versus intramedullary nail; cycle 10, 93 +/- 34 N/mm versus 117 +/- 40 N/mm (t = 2.33, p = 0.04); cycle 100, 89 +/- 34 N/mm versus 118 +/- 42 N/mm (t = 3.16, p = 0.01); cycle 1000, 86 +/- 32 N/mm versus 120 +/- 45 N/mm (t = 3.52, p = 0.01); cycle 10,000, 83 +/- 36 N/mm versus 128 +/- 50 N/mm (t = 3.80, p = 0.01); cycle 100,000, 82 +/- 34 N/mm versus 126 +/- 52 N/mm (t = 3.70, p = 0.01); cycle 250,000, 80 +/- 31 N/mm versus 125 +/- 49 N/mm (t = 4.2, p = 0.003). There was no statistically significant difference between the intramedullary nail and blade plate fixation in cycle one or in load to failure; cycle 10, blade plate 70 +/- 38 N/mm and intramedullary nail 67 +/- 20 N/mm (t = 0.60, p = 0.56); load to failure, blade plate 808 +/- 193 N, IMN 1074 +/- 290 N) (p = 0.15). Intramedullary nail fixation was biomechanically superior to blade plate and screw fixation in a tibiocalcaneal arthrodesis construct. The ankle arthrodesis intramedullary nail provides greater stiffness for fixation in tibiocalcaneal arthrodesis, which may improve healing.

Static, Dynamic, and Fatigue Analysis of the Mechanical System of Ultrasonic Scanner for Inservice Inspection of Research Reactors

NASA Astrophysics Data System (ADS)

Awwaluddin, Muhammad; Kristedjo, K.; Handono, Khairul; Ahmad, H.

2018-02-01

This analysis is conducted to determine the effects of static and dynamic loads of the structure of mechanical system of Ultrasonic Scanner i.e., arm, column, and connection systems for inservice inspection of research reactors. The analysis is performed using the finite element method with 520 N static load. The correction factor of dynamic loads used is the Gerber mean stress correction (stress life). The results of the analysis show that the value of maximum equivalent von Mises stress is 1.3698E8 Pa for static loading and value of the maximum equivalent alternating stress is 1.4758E7 Pa for dynamic loading. These values are below the upper limit allowed according to ASTM A240 standards i.e. 2.05E8 Pa. The result analysis of fatigue life cycle are at least 1E6 cycle, so it can be concluded that the structure is in the high life cycle category.

Effect of thermal cycling on flexural properties of carbon-graphite fiber-reinforced polymers.

PubMed

Segerström, Susanna; Ruyter, I Eystein

2009-07-01

To determine flexural strength and modulus after water storage and thermal cycling of carbon-graphite fiber-reinforced (CGFR) polymers based on poly(methyl methacrylate) and a copolymer matrix, and to examine adhesion between fiber and matrix by scanning electron microscopy (SEM). Solvent cleaned carbon-graphite (CG) braided tubes of fibers were treated with a sizing resin. The resin mixture of the matrix was reinforced with 24, 36, 47 and 58wt% (20, 29, 38 and 47vol.%) CG-fibers. After heat polymerization the specimens were kept for 90 days in water and thereafter hydrothermally cycled (12,000 cycles, 5/55 degrees C). Mechanical properties were evaluated by three-point bend testing. After thermal cycling, the adhesion between fibers and matrix was evaluated by SEM. Hydrothermal cycling did not decrease flexural strength of the CGFR polymers with 24 and 36wt% fiber loadings; flexural strength values after thermocycling were 244.8 (+/-32.33)MPa for 24wt% and 441.3 (+/-68.96)MPa for 36wt%. Flexural strength values after thermal cycling were not further increased after increasing the fiber load to 47 (459.2 (+/-45.32)MPa) and 58wt% (310.4 (+/-52.79)MPa). SEM revealed good adhesion between fibers and matrix for all fiber loadings examined. The combination of the fiber treatment and resin matrix described resulted in good adhesion between CG-fibers and matrix. The flexural values for fiber loadings up to 36wt% appear promising for prosthodontic applications such as implant-retained prostheses.

Joint and Soft Tissue Injections

MedlinePlus

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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 cycles, 38% in the SC group, 19% in the DNS group, and 43% in the DC group. The difference between the DC group and the DNS group yielded significance (P = 0.04). For vertebrae not surpassing 1000 cycles, the number of cycles at implant displacement greater than 2 mm in the SC group was 648.7 ± 280.2 cycles, in the DNS group was 478.8 ± 219.0 cycles, and in the DC group was 699.5 ± 150.6 cycles. Differences between the SC group and the DNS group were significant (P = 0.008) as between the DC group and the DNS group (P = 0.0009). Load to failure in the SC group was 444.3 ± 302 N, in the DNS group was 527.7 ± 273 N, and in the DC group was 664.4 ± 371.5 N. The DC group outperformed the other constructs. The difference between the SC group and the DNS group failed significance (P = 0.25), whereas there was a significant difference between the SC group and the DC group (P = 0.003). The DC group showed a strong trend toward increased load to failure compared with the DNS group but without significance (P = 0.067). Surpassing 1000 cycles had a significant impact on the maximum load to failure in the SC group (P = 0.0001) and in the DNS group (P = 0.01) but not in the DC group (P = 0.2), which had the highest number of vertebrae surpassing 1000 cycles. Constrained dual-screw fixation characteristics in modern AISF implants can improve resistance to cyclic loading and pullout forces. DC constructs bear the potential to reduce the mechanical shortcomings of AISF.

A Combined High and Low Cycle Fatigue Model for Life Prediction of Turbine Blades

PubMed Central

Yue, Peng; Yu, Zheng-Yong; Wang, Qingyuan

2017-01-01

Combined high and low cycle fatigue (CCF) generally induces the failure of aircraft gas turbine attachments. Based on the aero-engine load spectrum, accurate assessment of fatigue damage due to the interaction of high cycle fatigue (HCF) resulting from high frequency vibrations and low cycle fatigue (LCF) from ground-air-ground engine cycles is of critical importance for ensuring structural integrity of engine components, like turbine blades. In this paper, the influence of combined damage accumulation on the expected CCF life are investigated for turbine blades. The CCF behavior of a turbine blade is usually studied by testing with four load-controlled parameters, including high cycle stress amplitude and frequency, and low cycle stress amplitude and frequency. According to this, a new damage accumulation model is proposed based on Miner’s rule to consider the coupled damage due to HCF-LCF interaction by introducing the four load parameters. Five experimental datasets of turbine blade alloys and turbine blades were introduced for model validation and comparison between the proposed Miner, Manson-Halford, and Trufyakov-Kovalchuk models. Results show that the proposed model provides more accurate predictions than others with lower mean and standard deviation values of model prediction errors. PMID:28773064

A Combined High and Low Cycle Fatigue Model for Life Prediction of Turbine Blades.

PubMed

Zhu, Shun-Peng; Yue, Peng; Yu, Zheng-Yong; Wang, Qingyuan

2017-06-26

Combined high and low cycle fatigue (CCF) generally induces the failure of aircraft gas turbine attachments. Based on the aero-engine load spectrum, accurate assessment of fatigue damage due to the interaction of high cycle fatigue (HCF) resulting from high frequency vibrations and low cycle fatigue (LCF) from ground-air-ground engine cycles is of critical importance for ensuring structural integrity of engine components, like turbine blades. In this paper, the influence of combined damage accumulation on the expected CCF life are investigated for turbine blades. The CCF behavior of a turbine blade is usually studied by testing with four load-controlled parameters, including high cycle stress amplitude and frequency, and low cycle stress amplitude and frequency. According to this, a new damage accumulation model is proposed based on Miner's rule to consider the coupled damage due to HCF-LCF interaction by introducing the four load parameters. Five experimental datasets of turbine blade alloys and turbine blades were introduced for model validation and comparison between the proposed Miner, Manson-Halford, and Trufyakov-Kovalchuk models. Results show that the proposed model provides more accurate predictions than others with lower mean and standard deviation values of model prediction errors.

A proposal for unification of fatigue crack growth law

NASA Astrophysics Data System (ADS)

Kobelev, V.

2017-05-01

In the present paper, the new fractional-differential dependences of cycles to failure for a given initial crack length upon the stress amplitude in the linear fracture approach are proposed. The anticipated unified propagation function describes the infinitesimal crack length growths per increasing number of load cycles, supposing that the load ratio remains constant over the load history. Two unification fractional-differential functions with different number of fitting parameters are proposed. An alternative, threshold formulations for the fractional-differential propagation functions are suggested. The mean stress dependence is the immediate consequence from the considered laws. The corresponding formulas for crack length over the number of cycles are derived in closed form.

Carbon-Carbon Recuperators in Closed-Brayton-Cycle Space Power Systems

NASA Technical Reports Server (NTRS)

Barrett, Michael J.; Johnson, Paul K.

2006-01-01

The use of carbon-carbon (C-C) recuperators in closed-Brayton-cycle space power conversion systems was assessed. Recuperator performance was forecast based on notional thermodynamic cycle state values for planetary missions. Resulting thermal performance, mass and volume for plate-fin C-C recuperators were estimated and quantitatively compared with values for conventional offset-strip-fin metallic designs. Mass savings of 40-55% were projected for C-C recuperators with effectiveness greater than 0.9 and thermal loads from 25-1400 kWt. The smaller thermal loads corresponded with lower mass savings; however, at least 50% savings were forecast for all loads above 300 kWt. System-related material challenges and compatibility issues were also discussed.

Performance comparison of single-stage mixed-refrigerant Joule-Thomson cycle and reverse Brayton cycle for cooling 80 to 120 K temperature-distributed heat loads

NASA Astrophysics Data System (ADS)

Wang, H. C.; Chen, G. F.; Gong, M. Q.; Li, X.

2017-12-01

Thermodynamic performance comparison of single-stage mixed-refrigerant Joule-Thomson cycle (MJTR) and pure refrigerant reverse Brayton cycle (RBC) for cooling 80 to 120 K temperature-distributed heat loads was conducted in this paper. Nitrogen under various liquefaction pressures was employed as the heat load. The research was conducted under nonideal conditions by exergy analysis methods. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distribution in each process of refrigeration cycle was also investigated. The exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC in 90 to 120 K temperature zone, but still inferior to RBC at 80 K. The performance degradation of MJTR was caused by two main reasons: The high fraction of neon resulted in large entropy generation and exergy loss in throttling process. Larger duty and WLMTD lead to larger exergy losses in recuperator.

Compilation of load spectrum of loader drive axle

NASA Astrophysics Data System (ADS)

Wei, Yongxiang; Zhu, Haoyue; Tang, Heng; Yuan, Qunwei

2018-03-01

In order to study the preparation method of gear fatigue load spectrum for loaders, the load signal of four typical working conditions of loader is collected. The signal that reflects the law of load change is obtained by preprocessing the original signal. The torque of the drive axle is calculated by using the rain flow counting method. According to the operating time ratio of each working condition, the two dimensional load spectrum based on the real working conditions of the drive axle of loader is established by the cycle extrapolation and synthesis method. The two-dimensional load spectrum is converted into one-dimensional load spectrum by means of the mean of torque equal damage method. Torque amplification includes the maximum load torque of the main reduction gear. Based on the theory of equal damage, the accelerated cycles are calculated. In this way, the load spectrum of the loading condition of the drive axle is prepared to reflect loading condition of the loader. The load spectrum can provide reference for fatigue life test and life prediction of loader drive axle.

Loading direction regulates the affinity of ADP for kinesin.

PubMed

Uemura, Sotaro; Ishiwata, Shin'ichi

2003-04-01

Kinesin is an ATP-driven molecular motor that moves processively along a microtubule. Processivity has been explained as a mechanism that involves alternating single- and double-headed binding of kinesin to microtubules coupled to the ATPase cycle of the motor. The internal load imposed between the two bound heads has been proposed to be a key factor regulating the ATPase cycle in each head. Here we show that external load imposed along the direction of motility on a single kinesin molecule enhances the binding affinity of ADP for kinesin, whereas an external load imposed against the direction of motility decreases it. This coupling between loading direction and enzymatic activity is in accord with the idea that the internal load plays a key role in the unidirectional and cooperative movement of processive motors.

Energy Approach-Based Simulation of Structural Materials High-Cycle Fatigue

NASA Astrophysics Data System (ADS)

Balayev, A. F.; Korolev, A. V.; Kochetkov, A. V.; Sklyarova, A. I.; Zakharov, O. V.

2016-02-01

The paper describes the mechanism of micro-cracks development in solid structural materials based on the theory of brittle fracture. A probability function of material cracks energy distribution is obtained using a probabilistic approach. The paper states energy conditions for cracks growth at material high-cycle loading. A formula allowing to calculate the amount of energy absorbed during the cracks growth is given. The paper proposes a high- cycle fatigue evaluation criterion allowing to determine the maximum permissible number of solid body loading cycles, at which micro-cracks start growing rapidly up to destruction.

Acoustic-emissive memory effect in coal samples under triaxial axial-symmetric compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shkuratnik, V.L.; Filimonov, Y.L.; Kuchurin, S.V.

2006-05-15

The experimental data are presented for production and manifestation of the Kaiser effect in coal samples subjected to triaxial loading by the Karman scheme in the first cycle and to various loading modes in the second cycle. The Kaiser effect is identified with the help of a deformation memory effect.

Analytical and experimental investigation of aircraft metal structures reinforced with filamentary composites. Phase 2: Structural fatigue, thermal cycling, creep, and residual strength

NASA Technical Reports Server (NTRS)

Blichfeldt, B.; Mccarty, J. E.

1972-01-01

Specimens representative of metal aircraft structural components reinforced with boron filamentary composites were manufactured and tested under cyclic loading, cyclic temperature, or continuously applied loading to evaluate some of the factors that affect structural integrity under cyclic conditions. Bonded, stepped joints were used throughout to provide composite-to-metal transition regions at load introduction points. Honeycomb panels with titanium or aluminum faces reinforced with unidirectional boron composite were fatigue tested at constant amplitude under completely reversed loading. Results indicated that the matrix material was the most fatigue-sensitive part of the design, with debonding initiating in the stepped joints. However, comparisons with equal weight all-metal specimens show a 10 to 50 times improved fatigue life. Fatigue crack propagation and residual strength were studied for several different stiffened panel concepts, and were found to vary considerably depending on the configuration. Composite-reinforced metal specimens were also subjected to creep and thermal cycling tests. Thermal cycling of stepped joint tensile specimens resulted in a ten percent decrease in residual strength after 4000 cycles.

Multiaxial Fatigue Damage Parameter and Life Prediction without Any Additional Material Constants

PubMed Central

Yu, Zheng-Yong; Liu, Qiang; Liu, Yunhan

2017-01-01

Based on the critical plane approach, a simple and efficient multiaxial fatigue damage parameter with no additional material constants is proposed for life prediction under uniaxial/multiaxial proportional and/or non-proportional loadings for titanium alloy TC4 and nickel-based superalloy GH4169. Moreover, two modified Ince-Glinka fatigue damage parameters are put forward and evaluated under different load paths. Results show that the generalized strain amplitude model provides less accurate life predictions in the high cycle life regime and is better for life prediction in the low cycle life regime; however, the generalized strain energy model is relatively better for high cycle life prediction and is conservative for low cycle life prediction under multiaxial loadings. In addition, the Fatemi–Socie model is introduced for model comparison and its additional material parameter k is found to not be a constant and its usage is discussed. Finally, model comparison and prediction error analysis are used to illustrate the superiority of the proposed damage parameter in multiaxial fatigue life prediction of the two aviation alloys under various loadings. PMID:28792487

Multiaxial Fatigue Damage Parameter and Life Prediction without Any Additional Material Constants.

PubMed

Yu, Zheng-Yong; Zhu, Shun-Peng; Liu, Qiang; Liu, Yunhan

2017-08-09

Based on the critical plane approach, a simple and efficient multiaxial fatigue damage parameter with no additional material constants is proposed for life prediction under uniaxial/multiaxial proportional and/or non-proportional loadings for titanium alloy TC4 and nickel-based superalloy GH4169. Moreover, two modified Ince-Glinka fatigue damage parameters are put forward and evaluated under different load paths. Results show that the generalized strain amplitude model provides less accurate life predictions in the high cycle life regime and is better for life prediction in the low cycle life regime; however, the generalized strain energy model is relatively better for high cycle life prediction and is conservative for low cycle life prediction under multiaxial loadings. In addition, the Fatemi-Socie model is introduced for model comparison and its additional material parameter k is found to not be a constant and its usage is discussed. Finally, model comparison and prediction error analysis are used to illustrate the superiority of the proposed damage parameter in multiaxial fatigue life prediction of the two aviation alloys under various loadings.

Load fatigue performance of four implant-abutment interface designs: effect of torque level and implant system.

PubMed

Quek, H C; Tan, Keson B; Nicholls, Jack I

2008-01-01

Biomechanical load-fatigue performance data on single-tooth implant systems with different implant-abutment interface designs is lacking in the literature. This study evaluated the load fatigue performance of 4 implant-abutment interface designs (Brånemark-CeraOne; 3i Osseotite-STA abutment; Replace Select-Easy abutment; and Lifecore Stage-1-COC abutment system). The number of load cycles to fatigue failure of 4 implant-abutment designs was tested with a custom rotational load fatigue machine. The effect of increasing and decreasing the tightening torque by 20% respectively on the load fatigue performance was also investigated. Three different tightening torque levels (recommended torque, -20% recommended torque, +20% recommended torque) were applied to the 4 implant systems. There were 12 test groups with 5 samples in each group. The rotational load fatigue machine subjected specimens to a sinusoidally applied 35 Ncm bending moment at a test frequency of 14 Hz. The number of cycles to failure was recorded. A cutoff of 5 x 10(6) cycles was applied as an upper limit. There were 2 implant failures and 1 abutment screw failure in the Brånemark group. Five abutment screw failures and 4 implant failures was recorded for the 3i system. The Replace Select system had 1 implant failure. Five cone screw failures were noted for the Lifecore system. Analysis of variance revealed no statistically significant difference in load cycles to failure for the 4 different implant-abutment systems torqued at recommended torque level. A statistically significant difference was found between the -20% torque group and the +20% torque group (P < .05) for the 3i system. Load fatigue performance and failure location is system specific and related to the design characteristics of the implant-abutment combination. It appeared that if the implant-abutment interface was maintained, load fatigue failure would occur at the weakest point of the implant. It is important to use the torque level recommended by the manufacturer.

Cognitive Load Theory: New Conceptualizations, Specifications, and Integrated Research Perspectives

ERIC Educational Resources Information Center

Paas, Fred; van Gog, Tamara; Sweller, John

2010-01-01

Over the last few years, cognitive load theory has progressed and advanced rapidly. The articles in this special issue, which document those advances, are based on contributions to the 3rd International Cognitive Load Theory Conference (2009), Heerlen, The Netherlands. The articles of this special issue on cognitive load theory discuss new…

Effects of Cyclic Loading on the Deformation and Elastic-Plastic Fracture Behavior of a Cast Stainless Steel

DTIC Science & Technology

1991-10-01

23 8. High Cycle Fatigue Crack Growth Data for Cast Stainless Steel Showing Comparison with Rolfe and Barsom Fit .......... 24 9. Cyclic Load...compared to the Rolfe /Barsom4 fatigue crack propagation equation for austenitic stainless steels in Fig. 8. ELASTIC-PLASTIC Cyclic J-testing was...place during both the compression and tensile loadings. The J-integral was calculated on each cycle using the Merkle -Corten 9 J equation as modified by

Loading Mode and Environment Effects on Surface Profile Characteristics of Martensite Plates in Cu-Based SMAs

NASA Astrophysics Data System (ADS)

Suru, Marius-Gabriel; Paraschiv, Adrian-Liviu; Lohan, Nicoleta Monica; Pricop, Bogdan; Ozkal, Burak; Bujoreanu, Leandru-Gheorghe

2014-07-01

The present work reports the influence of the loading mode provided during training under constant stress, in bending, applied to lamellar specimens of Cu-Zn-Al shape memory alloys (SMAs). During training, the specimens were bent by a load fastened at their free end, while being martensitic at room temperature and they lifted the load by one-way effect (1WE), during heating up to austenitic field. On cooling to martensite field, the lower concave surface of bent specimens was compressed, and during heating it was elongated, being subjected to a series of tension-compression cycles, during heating-cooling, respectively. Conversely, the upper convex surface of bent specimens was elongated during cooling and compressed during heating, being subjected to compression-tension cycles. Furthermore, 2WE-trained actuators were tested by means of a hydraulic installation where, this time heating-cooling cycles were performed in oil conditions. Considering that the lower concave surface of the specimens was kept in compressed state, while the upper convex surface was kept in elongated state, the study reveals the influence of the two loading modes and environments on the width of martensite plates of the specimens trained under various numbers of cycles. In this purpose, Cu-Zn-Al specimens, trained under 100-300-500 cycles, were prepared and analyzed by atomic force microscopy (AFM) as well as optical and scanning electron microscopy (OM and SEM, respectively). The analysis also included AFM micrographs corroborated with statistical evaluations in order to reveal the effects of loading mode (tension or compression) in different environmental conditions of the specimens, on the surface profile characteristics of martensite plates, revealed by electropolishing.

A PWM Buck Converter With Load-Adaptive Power Transistor Scaling Scheme Using Analog-Digital Hybrid Control for High Energy Efficiency in Implantable Biomedical Systems.

PubMed

Park, Sung-Yun; Cho, Jihyun; Lee, Kyuseok; Yoon, Euisik

2015-12-01

We report a pulse width modulation (PWM) buck converter that is able to achieve a power conversion efficiency (PCE) of > 80% in light loads 100 μA) for implantable biomedical systems. In order to achieve a high PCE for the given light loads, the buck converter adaptively reconfigures the size of power PMOS and NMOS transistors and their gate drivers in accordance with load currents, while operating at a fixed frequency of 1 MHz. The buck converter employs the analog-digital hybrid control scheme for coarse/fine adjustment of power transistors. The coarse digital control generates an approximate duty cycle necessary for driving a given load and selects an appropriate width of power transistors to minimize redundant power dissipation. The fine analog control provides the final tuning of the duty cycle to compensate for the error from the coarse digital control. The mode switching between the analog and digital controls is accomplished by a mode arbiter which estimates the average of duty cycles for the given load condition from limit cycle oscillations (LCO) induced by coarse adjustment. The fabricated buck converter achieved a peak efficiency of 86.3% at 1.4 mA and > 80% efficiency for a wide range of load conditions from 45 μA to 4.1 mA, while generating 1 V output from 2.5-3.3 V supply. The converter occupies 0.375 mm(2) in 0.18 μm CMOS processes and requires two external components: 1.2 μF capacitor and 6.8 μH inductor.

High heat flux properties of pure tungsten and plasma sprayed tungsten coatings

NASA Astrophysics Data System (ADS)

Liu, X.; Tamura, S.; Tokunaga, K.; Yoshida, N.; Noda, N.; Yang, L.; Xu, Z.

2004-08-01

High heat flux properties of pure tungsten and plasma sprayed tungsten coatings on carbon substrates have been studied by annealing and cyclic heat loading. The recrystallization temperature and an activation energy QR=126 kJ/mol for grain growth of tungsten coating by vacuum plasma spray (VPS) were estimated, and the microstructural changes of multi-layer tungsten and rhenium interface pre-deposited by physical vapor deposition (PVD) with anneal temperature were investigated. Cyclic load tests indicated that pure tungsten and VPS-tungsten coating could withstand 1000 cycles at 33-35 MW/m 2 heat flux and 3 s pulse duration, and inert gas plasma spray (IPS)-tungsten coating showed local cracks by 300 cycles but did not induce failure by further cycles. However, the failure of pure tungsten and VPS-tungsten coating by fatigue cracking was observed under higher heat load (55-60 MW/m 2) for 420 and 230 cycles, respectively.

Strength, Fatigue, and Fracture Toughness of Ti-6Al-4V Liner from a Composite Over-Wrapped Pressure Vessel

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.; Lerch, Brad; Thesken, John C.; Sutter, Jim; Russell, Richard

2008-01-01

It was demonstrated by way of experiment that Composite Over-wrapped Pressure Vessel (COPV) Ti-6Al-4V liner material can sustain the expected service loads and cycles. The experiments were performed as part of investigations on the residual life of COPV tanks being used in Space Shuttle Orbiters. Measured properties included tensile strength, compressive strength, reversed loading cycles to simulate liner proof strains, and cyclic fatigue loading to demonstrate the ability to sustain 1000 cycles after liner buckling. The liner material came from a salvaged 40 in. Columbia (orbiter 102) tank (SN029), and tensile strength measurements were made on both boss-transition (thick) and membrane regions (thin). The average measured yield strength was 131 ksi in the boss-transition and membrane regions, in good agreement with measurements made on 1970 s vintage forged plate stock. However, Young s modulus was 17.4+/-0.3 Msi, somewhat higher than typical handbook values (approx.16 Msi). The fracture toughness, as estimated from a failed fatigue specimen, was 74 ksi/sq in, in reasonable agreement with standardized measurements made on 1970 s vintage forged plate stock. Low cycle fatigue of a buckled test specimen implied that as-imprinted liners can sustain over 4000 load cycles.

Analysis of fatigue on surface course using dissipated energy approach

NASA Astrophysics Data System (ADS)

Michael; Setyawan, A.; Pramesti, F. P.

2018-03-01

As an important transportation infrastructure, pavement is subjected to repeated vehicle loads that may cause fatigue, which often leads to cracking. The point when this cracking initiates can be determined from the energy dissipated during the loading. This research investigates fatigue in Adi Soemarmo Airport mix-design using bitumen Pen 60/70 + EVA (Ethyl Vinyl Acetate) polymer. An Indirect Tensile Fatigue Test (ITFT) was conducted using stress-controlled loading mode to determine its fatigue life. The stress levels were 500, 600, and 700 kPa, while the loading frequency and the temperature were 10 Hz and 20°C, respectively. The test exhibits strain levels for each loading cycle, which were used to determine the dissipated energy (DE). The result indicates that the DE increases when the number of loading cycles increases, due to progress of the strain levels. The values of DE are 7122.8, 8614.3, and 2654.9 J/m3 for loading levels of 500, 600, and 700 kPa, respectively, whereas the failure points for stress levels of 500, 600, and 700 kPa are 8171, 5161, and 841 cycles, respectively. Thus, the longer the time until the pavement failure point is reached (fatigue life), the greater the amount of energy that is dissipated.

Study of the two-phase dummy load shut-down strategy for proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Zhang, Q.; Lin, R.; Cui, X.; Xia, S. X.; Yang, Z.; Chang, Y. T.

2017-02-01

This paper presents a new system strategy designed to alleviate the performance decay caused by start-up/shut-down (SU/SD) conditions in proton exchange membrane fuel cells (PEMFCs). The innovative method was tested using a two-phase dummy load composed of a linearly declined main load and a fixed small auxiliary load. The initial value of the main load must be controlled within a proper range, and a closed-ended air exhaust is necessary. According to the analysis of in-situ current density distribution during SD processes, the two-phase dummy load can continuously fit the process of oxygen reduction in the cathode, whereas the conventional dummy load leads to local air starvation. Polarization curves and cyclic voltammetry (CV) were employed to evaluate the performance decay during SU/SD repetition. After tests of 900 cycles, the highest voltage degradation rate of the PEMFC was 3.33 μV cycle-1 (800 mA cm-2), and the electrochemical surface area (ECSA) loss was 0.0046 m2 g-1 cycle-1 with the two-phase dummy load strategy. After comparing results with similar work on a single PEMFC, the authors confirmed the preeminent effectiveness of this strategy. This strategy will also improve fuel cell stack performance due to controllable SD duration and comparatively low performance decay rates.

Sensitivity analysis in a life cycle assessment of an aged red wine production from Catalonia, Spain.

PubMed

Meneses, M; Torres, C M; Castells, F

2016-08-15

Sustainability in agriculture and food processing is an issue with a clear growing interest; especially in products were consumers have particular awareness regarding its environmental profile. This is the case of wine industry depending on grape production, winemaking and bottling. Also viticulture and generally agricultural production is significantly affected by climate variations. The aim of this article is to determine the environmental load of an aged red wine from a winery in Catalonia, Spain, over its entire life cycle, including sensitivity analysis of the main parameters related to the cultivation, vinification and bottling. The life cycle assessment (LCA) methodology is used for the environmental analysis. In a first step, life cycle inventory (LCI) data were collected by questionnaires and interviews with the winemaker, all data are actual operating data and all the stages involved in the production have been taken into account (viticulture, vinification, bottling and the disposal subsystem). Data were then used to determine the environmental profile by a life cycle impact assessment using the ReCiPe method. Annual variability in environmental performance, stresses the importance of including timeline analysis in the wine sector. Because of that this study is accompanied with a sensitivity analysis carried out by a Monte Carlo simulation that takes into account the uncertainty and variability of the parameters used. In this manner, the results are presented with confidence intervals to provide a wider view of the environmental issues derived from the activities of the studied wine estate regardless of the eventualities of a specific harvesting year. Since the beverage packaging has an important influence in this case, a dataset for the production of green glass was adapted to reflect the actual recycling situation in Spain. Furthermore, a hypothetical variation of the glass-recycling rate in the glass production completes this article, as a key variable of sensitivity analysis, in order… in order to show the potential reduction of total greenhouse gas emissions. It was found that in almost all categories the production of the glass bottles has the highest environmental impact (10%-80% depending on the impact category) followed by the viticulture stage, i.e. the agricultural activities (17%-84% depending on the impact category). The vinification step, i.e. the winemaking itself, has an almost negligible effect on the overall load (1%-5%). The sensitivity analysis showed that the results do not differ by more than ±4% from the expected values except for the water depletion indicator. With the variation of the recycling rate, it could be shown that an increase in the rate from 60% to 85% allows for a reduction of 102gCO2eq. per bottle (-11.1%). The results show that glass production causes the highest environmental load. The key parameters that determine the impact are the recycling rate and the bottle weight. A glass container deposit legislation might be a promising way to enhance the glass recycling. Lightweight bottles and alternative packaging should also be considered. Copyright © 2016 Elsevier B.V. All rights reserved.

Carbon-Carbon Recuperators in Closed-Brayton-Cycle Space Power Systems

NASA Technical Reports Server (NTRS)

Barrett, Michael J.; Johnson, Paul K.; Naples, Andrew G.

2006-01-01

The feasibility of using carbon-carbon (C-C) recuperators in conceptual closed-Brayton-cycle space power conversion systems was assessed. Recuperator performance expectations were forecast based on notional thermodynamic cycle state values for potential planetary missions. Resulting thermal performance, mass and volume for plate-fin C-C recuperators were estimated and quantitatively compared with values for conventional offset-strip-fin metallic designs. Mass savings of 30 to 60 percent were projected for C-C recuperators with effectiveness greater than 0.9 and thermal loads from 25 to 1400 kWt. The smaller thermal loads corresponded with lower mass savings; however, 60 percent savings were forecast for all loads above 300 kWt. System-related material challenges and compatibility issues were also discussed.

Fracture morphologies of carbon-black-loaded SBR (styrene-butadiene rubber) subjected to low-cycle, high-stress fatigue. [Styrene-butadiene rubber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldberg, A.; Lesuer, D.R.; Patt, J.

Experimental results, together with an analytical model, related to the loss in tensile strength of styrene-butadiene rubber (SBR) loaded with carbon black (CB) that had been subjected to low-cycle, high-stress fatigue tests were presented in a prior paper. The drop in tensile strength relative to that of a virgin sample was considered to be a measure of damage induced during the fatigue test. The present paper is a continuation of this study dealing with the morphological interpretations of the fractured surfaces, whereby the cyclic-tearing behavior, resulting in the damage, is related to the test and material parameters. It was foundmore » that failure is almost always initiated in the bulk of a sample at a material flaw. The size and definition of a flaw increase with an increase in carbon-black loading. Initiation flaw sites are enveloped by fan-shaped or penny-shaped regions which develop during cycling. The size and morphology of a fatigue-tear region appears to be independent of the fatigue load or the extent of the damage (strength loss). By contrast, either an increase in cycling load or an increase in damage at constant load increases the definition of the fatigue-region morphology for all formulations of carbon-black. On the finest scale, the morphology can be described in terms of tearing of individual groups of rubber strands, collapsing to form a cell-like structure. 18 refs., 13 figs.« less

Smart sensing to drive real-time loads scheduling algorithm in a domotic architecture

NASA Astrophysics Data System (ADS)

Santamaria, Amilcare Francesco; Raimondo, Pierfrancesco; De Rango, Floriano; Vaccaro, Andrea

2014-05-01

Nowadays the focus on power consumption represent a very important factor regarding the reduction of power consumption with correlated costs and the environmental sustainability problems. Automatic control load based on power consumption and use cycle represents the optimal solution to costs restraint. The purpose of these systems is to modulate the power request of electricity avoiding an unorganized work of the loads, using intelligent techniques to manage them based on real time scheduling algorithms. The goal is to coordinate a set of electrical loads to optimize energy costs and consumptions based on the stipulated contract terms. The proposed algorithm use two new main notions: priority driven loads and smart scheduling loads. The priority driven loads can be turned off (stand by) according to a priority policy established by the user if the consumption exceed a defined threshold, on the contrary smart scheduling loads are scheduled in a particular way to don't stop their Life Cycle (LC) safeguarding the devices functions or allowing the user to freely use the devices without the risk of exceeding the power threshold. The algorithm, using these two kind of notions and taking into account user requirements, manages loads activation and deactivation allowing the completion their operation cycle without exceeding the consumption threshold in an off-peak time range according to the electricity fare. This kind of logic is inspired by industrial lean manufacturing which focus is to minimize any kind of power waste optimizing the available resources.

Apparatus and method for skin packaging articles

NASA Technical Reports Server (NTRS)

Madsen, B.; Pozsony, E. R.; Collin, E. E. (Inventor)

1973-01-01

A system for skin packaging articles including a loading zone for positioning articles to be packaged upon a substrate, a thermoplastic film heating and vacuum operated skin packaging zone for covering the articles with film laminated to the substrate and a slitting zone for separating and trimming the individual skin packaged articles. The articles are passed to the successive zones. The loading zone may be adapted for conveyorized instead of hand loading. In some cases, where only transverse cutting of the film web is necessary, it may be desirable to eliminate the slitting zone and remove the skin packaged article or articles directly from the packaging zone. A conveniently located operating panel contains controls for effecting automatic, semiautomatic or manual operation of the entire system of any portions in any manner desired.

Minor Actinides-Loaded FBR Core Concept Suitable for the Introductory Period in Japan

NASA Astrophysics Data System (ADS)

Fujimura, Koji; Sasahira, Akira; Yamashita, Junichi; Fukasawa, Tetsuo; Hoshino, Kuniyoshi

According to the Japan's Framework for Nuclear Energy Policy(1), a basic scenario for fast breeder reactors (FBRs) is that they will be introduced on a commercial basis starting around 2050 replacing light water reactors (LWRs). During the FBR introduction period, the Pu from LWR spent fuel is used for FBR startup. Howerver, the FBR core loaded with this Pu has a larger burnup reactivity due to its larger isotopic content of Pu-241 than a core loaded with Pu from an FBR multi-recycling core. The increased burnup reactivity may reduce the cycle length of an FBR. We investigated, an FBR transitional core concept to confront the issues of the FBR introductory period in Japan. Core specifications are based on the compact-type sodium-cooled mixed oxide (MOX)-fueled core designed from the Japanese FBR cycle feasibility studies, because lower Pu inventory should be better for the FBR introductory period in view of its flexibility for the required reprocessing amount of LWR spent fuel to start up FBRs. The reference specifications were selected as follows. Output of 1500MWe and average discharge fuel burnup of about 150GWd/t. Minor Actinides (MAs) recovered from LWR spent fuels which provide Pu to startup FBRs are loaded to the initial loading fuels and exchanged fuels during few cycles until equilibrium. We made the MA content of the initial loading fuel four kinds like 0%, 3%, 4%, 5%. The average of the initial loading fuel is assumed to be 3%, and that of the exchange fuel is set as 5%. This 5% maximum of the MA content is based on the irradiation results of the experimental fast reactor Joyo. We evaluated the core performances including burnup characteristics and the reactivity coefficient and confirmed that transitional core from initial loading until equilibrium cycle with loaded Pu from LWR spent fuel performs similary to an FBR multi-recycling core.

Novel evaporator architecture with entrance-length crossflow-paths for supercritical Organic Rankine Cycles

DOE PAGES

Sabau, Adrian S.; Nejad, Ali H.; Klett, James W.; ...

2017-11-26

Here in this article, a novel geometry is proposed for evaporators that are used in Supercritical Organic Rankine Cycles. The proposed geometry consists of successive plenums at several length-scale levels, creating a multi-scale heat exchanger (HX). The channels at the lowest length-scale levels were considered to have their length determined by the thermal entrance-length. Numerical simulations based on turbulent flow correlations for supercritical R134a and water were used to evaluate the performance of heat exchangers. Using the data on pumping power and area of heat exchange, the total present cost was evaluated using a cost model for shell-and-tube heat exchangers.more » With respect to the shell-and-tube baseline case, the cost per heat load and total costs of new HXs is lowered by approximately 20–26% and 15–30%, respectively. This reduction in present costs of the new HXs were found to be attributed to higher operational costs for the shell-and-tube HXs, as evidenced by the higher pumping power, as well their capital investment costs. The cost savings in the new HX designs compared to those of the shell-and-tube HXs, at similar heat load performance, indicate that the new HX architectures proposed in this paper are valid alternatives to traditional HX designs.« less

Axial and Torsional Load-Type Sequencing in Cumulative Fatigue: Low Amplitude Followed by High Amplitude Loading

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kalluri, Sreeramesh

2001-01-01

The experiments described herein were performed to determine whether damage imposed by axial loading interacts with damage imposed by torsional loading. This paper is a follow on to a study that investigated effects of load-type sequencing on the cumulative fatigue behavior of a cobalt base superalloy, Haynes 188 at 538 C Both the current and the previous study were used to test the applicability of cumulative fatigue damage models to conditions where damage is imposed by different loading modes. In the previous study, axial and torsional two load level cumulative fatigue experiments were conducted, in varied combinations, with the low-cycle fatigue (high amplitude loading) applied first. In present study, the high-cycle fatigue (low amplitude loading) is applied initially. As in the previous study, four sequences (axial/axial, torsion/torsion, axial/torsion, and torsion/axial) of two load level cumulative fatigue experiments were performed. The amount of fatigue damage contributed by each of the imposed loads was estimated by both the Palmgren-Miner linear damage rule (LDR) and the non-linear damage curve approach (DCA). Life predictions for the various cumulative loading combinations are compared with experimental results.

Stable isotope analyses on archived fish scales reveal the long-term effect of nitrogen loads on carbon cycling in rivers.

PubMed

Roussel, Jean-Marc; Perrier, Charles; Erkinaro, Jaakko; Niemelä, Eero; Cunjak, Richard A; Huteau, Dominique; Riera, Pascal

2014-02-01

Stable isotope analysis of organic matter in sediment records has long been used to track historical changes in productivity and carbon cycling in marine and lacustrine ecosystems. While flow dynamics preclude stratigraphic measurements of riverine sediments, such retrospective analysis is important for understanding biogeochemical cycling in running waters. Unique collections of riverine fish scales were used to analyse δ(15) N and δ(13) C variations in the food web of two European rivers that experience different degrees of anthropogenic pressure. Over the past four decades, dissolved inorganic N loading remained low and constant in the Teno River (70°N, Finland); in contrast, N loading increased fourfold in the Scorff River (47°N, France) over the same period. Archived scales of Atlantic salmon parr, a riverine life-stage that feeds on aquatic invertebrates, revealed high δ(15) N values in the Scorff River reflecting anthropogenic N inputs to that riverine environment. A strong correlation between dissolved inorganic N loads and δ(13) C values in fish scales was observed in the Scorff River, whereas no trend was found in the Teno River. This result suggests that anthropogenic N-nutrients enhanced atmospheric C uptake by primary producers and its transfer to fish. Our results illustrate for the first time that, as for lakes and marine ecosystems, historical changes in anthropogenic N loading can affect C cycling in riverine food webs, and confirm the long-term interactions between N and C biogeochemical cycles in running waters. © 2013 John Wiley & Sons Ltd.

Experimental Study of a Hot Structure for a Reentry Vehicle

NASA Technical Reports Server (NTRS)

Pride, Richard A.; Royster, Dick M.; Helms, Bobbie F.

1960-01-01

A large structural model of a reentry vehicle has been built incorporating design concepts applicable to a radiation-cooled vehicle. Thermal-stress alleviating features of the model are discussed. Environmental tests on the model include approximately 100 cycles of loading at room temperature and 33 cycles of combined loading and-heating up to temperatures of 1,6000 F. Measured temperatures are shown for typical parts of the model. Comparisons are made between experimental and calculated deflections and strains. The structure successfully survived the heating and loading environments.

Optimized Deposition Parameters & Coating Properties of Cobalt Phosphorus Alloy Electroplating for Technology Insertion Risk Reduction

DTIC Science & Technology

2010-10-01

of tensile yield strength (Fty) and the runout load (107 cycles), with no more than four points per load. Load and cycles to failure were used to...were coated with 0.002” nCo-P at Integran Technologies Inc. or 0.002” at FRC-SE. Testing was conducted using CS-17 wheels at FRC-SE. 3.2 RESULTS...Abrasive wear tests shall be conducted using the Taber wear test apparatus in accordance with ASTM D4060 using a CS-17 wheel . The wear rate of

A biomechanical comparison of tendon-bone interface motion and cyclic loading between single-row, triple-loaded cuff repairs and double-row, suture-tape cuff repairs using biocomposite anchors.

PubMed

Barber, F Alan; Drew, Otis R

2012-09-01

To compare tendon-bone interface motion and cyclic loading in a single-row, triple-loaded anchor repair with a suture-tape, rip-stop, double-row rotator cuff repair. Using 18 human shoulders from 9 matched cadaveric pairs, we created 2 groups of rotator cuff repairs. Group 1 was a double-row, rip-stop, suture-tape construct. Group 2 was a single-row, triple-loaded construct. Before mechanical testing, the supraspinatus footprint was measured with calipers. A superiorly positioned digital camera optically measured the tendon footprint motion during 60° of humeral internal and external rotation. Specimens were secured at a fixed angle not exceeding 45° in reference to the load. After preloading, each sample was cycled between 10 N and 100 N for 200 cycles at 1 Hz, followed by destructive testing at 33 mm/s. A digital camera with tracking software measured the repair displacement at 100 and 200 cycles. Ultimate load and failure mode for each sample were recorded. The exposed anterior footprint border (6.5% ± 6%) and posterior footprint border (0.9% ± 1.7%) in group 1 were statistically less than the exposed anterior footprint border (30.3% ± 17%) and posterior footprint border (29.8% ± 14%) in group 2 (P = .003 and P < .001, respectively). The maximal internal rotation and external rotation tendon footprint displacements in group 1 (1.6 mm and 1.4 mm, respectively) were less than those in group 2 (both 3.6 mm) (P = .007 and P = .004, respectively). Mean displacement after 100 cycles for group 1 and group 2 was 2.0 mm and 3.2 mm, respectively, and at 200 cycles, mean displacement was 2.5 mm and 4.2 mm, respectively (P = .02). The mean ultimate failure load in group 1 (586 N) was greater than that in group 2 (393 N) (P = .02). The suture-tendon interface was the site of most construct failures. The suture-tape, rip-stop, double-row rotator cuff repair had greater footprint coverage, less rotational footprint displacement, and a greater mean ultimate failure load than the triple-loaded, single-row repair on mechanical testing. No double-row or single-row constructs showed 5 mm of displacement after the first 100 cycles. The most common failure mode for both constructs was suture tearing through the tendon. Differences in cuff fixation influence rotational tendon movement and may influence postoperative healing. Stronger repair constructs still fail at the suture-tendon interface. Copyright © 2012 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Modification of Immobead 150 support for protein immobilization: effects on the properties of immobilized Aspergillus oryzae β-galactosidase.

PubMed

Gennari, Adriano; Herrmann Mobayed, Francielle; da Silva Rafael, Ruan; Rodrigues, Rafael C; Sperotto, Raul Antonio; Volpato, Giandra; Volken de Souza, Claucia Fernanda

2018-05-01

We studied the modification of Immobead 150 support by either introducing aldehyde groups using glutaraldehyde (Immobead-Glu) or carboxyl groups through acid solution (Immobead-Ac) for enzyme immobilization by covalent attachment or ion exchange, respectively. These two types of immobilization were compared with the use of epoxy groups that are now provided on a commercial support. We used Aspergillus oryzae β-galactosidase (Gal) as a model protein, immobilizing it on unmodified (epoxy groups, Immobead-Epx) and modified supports. Immobilization yield and efficiency were tested as a function of protein loading (10 to 500 mg.g -1 support). Gal was efficiently immobilized on the Immobeads with an immobilization efficiency higher than 75% for almost all supports and protein loads. Immobilization yields significantly decreased when protein loadings were higher than 100 mg.g -1 support. Gal immobilized on Immobead-Glu and Immobead-Ac retained approximately 60% of its initial activity after 90 days of storage at 4°C. The three immobilized Gal derivatives presented higher half-lifes than the soluble enzyme, where the half-lifes were twice higher than the free Gal at 73°C. All the preparations were moderately operationally stable when tested in lactose solution, whey permeate, cheese whey, and skim milk, and retained approximately 50% of their initial activity after 20 cycles of hydrolyzing lactose solution. The modification of the support with glutaraldehyde provided the most stable derivative during cycling in cheese whey hydrolysis. Our results suggest that the Immobead 150 is a promising support for Gal immobilization. This article is protected by copyright. All rights reserved. © 2018 American Institute of Chemical Engineers.

Fatigue Life of Bovine Meniscus under Longitudinal and Transverse Tensile Loading

PubMed Central

Creechley, Jaremy J.; Krentz, Madison E.; Lujan, Trevor J.

2017-01-01

The knee meniscus is composed of a fibrous matrix that is subjected to large and repeated loads. Consequently, the meniscus is frequently torn, and a potential mechanism for failure is fatigue. The objective of this study was to measure the fatigue life of bovine meniscus when applying cyclic tensile loads either longitudinal or transverse to the principal fiber direction. Fatigue experiments consisted of cyclic loads to 60, 70, 80 or 90% of the predicted ultimate tensile strength until failure occurred or 20,000 cycles was reached. The fatigue data in each group was fit with a Weibull distribution to generate plots of stress level vs. cycles to failure (S-N curve). Results showed that loading transverse to the principal fiber direction gave a two-fold increase in failure strain, a three-fold increase in creep, and a nearly four-fold increase in cycles to failure (not significant), compared to loading longitudinal to the principal fiber direction. The S-N curves had strong negative correlations between the stress level and the mean cycles to failure for both loading directions, where the slope of the transverse S-N curve was 11% less than the longitudinal S-N curve (longitudinal: S=108–5.9ln(N); transverse: S=112–5.2ln(N)). Collectively, these results suggest that the non-fibrillar matrix is more resistant to fatigue failure than the collagen fibers. Results from this study are relevant to understanding the etiology of atraumatic radial and horizontal meniscal tears, and can be utilized by research groups that are working to develop meniscus implants with fatigue properties that mimic healthy tissue. PMID:28088070

Extraction of human gait signatures: an inverse kinematic approach using Groebner basis theory applied to gait cycle analysis

NASA Astrophysics Data System (ADS)

Barki, Anum; Kendricks, Kimberly; Tuttle, Ronald F.; Bunker, David J.; Borel, Christoph C.

2013-05-01

This research highlights the results obtained from applying the method of inverse kinematics, using Groebner basis theory, to the human gait cycle to extract and identify lower extremity gait signatures. The increased threat from suicide bombers and the force protection issues of today have motivated a team at Air Force Institute of Technology (AFIT) to research pattern recognition in the human gait cycle. The purpose of this research is to identify gait signatures of human subjects and distinguish between subjects carrying a load to those subjects without a load. These signatures were investigated via a model of the lower extremities based on motion capture observations, in particular, foot placement and the joint angles for subjects affected by carrying extra load on the body. The human gait cycle was captured and analyzed using a developed toolkit consisting of an inverse kinematic motion model of the lower extremity and a graphical user interface. Hip, knee, and ankle angles were analyzed to identify gait angle variance and range of motion. Female subjects exhibited the most knee angle variance and produced a proportional correlation between knee flexion and load carriage.

A robust signal processing method for quantitative high-cycle fatigue crack monitoring using soft elastomeric capacitor sensors

NASA Astrophysics Data System (ADS)

Kong, Xiangxiong; Li, Jian; Collins, William; Bennett, Caroline; Laflamme, Simon; Jo, Hongki

2017-04-01

A large-area electronics (LAE) strain sensor, termed soft elastomeric capacitor (SEC), has shown great promise in fatigue crack monitoring. The SEC is able to monitor strain changes over a mesoscale structural surface and endure large deformations without being damaged under cracking. Previous tests verified that the SEC is able to detect, localize, and monitor fatigue crack activities under low-cycle fatigue loading. In this paper, to examine the SEC's capability of monitoring high-cycle fatigue cracks, a compact specimen is tested under cyclic tension, designed to ensure realistic crack opening sizes representative of those in real steel bridges. To overcome the difficulty of low signal amplitude and relatively high noise level under high-cycle fatigue loading, a robust signal processing method is proposed to convert the measured capacitance time history from the SEC sensor to power spectral densities (PSD) in the frequency domain, such that signal's peak-to-peak amplitude can be extracted at the dominant loading frequency. A crack damage indicator is proposed as the ratio between the square root of the amplitude of PSD and load range. Results show that the crack damage indicator offers consistent indication of crack growth.

The Circadian Clock Modulates Global Daily Cycles of mRNA Ribosome Loading[OPEN

PubMed Central

Missra, Anamika; Ernest, Ben; Jia, Qidong; Ke, Kenneth

2015-01-01

Circadian control of gene expression is well characterized at the transcriptional level, but little is known about diel or circadian control of translation. Genome-wide translation state profiling of mRNAs in Arabidopsis thaliana seedlings grown in long day was performed to estimate ribosome loading per mRNA. The experiments revealed extensive translational regulation of key biological processes. Notably, translation of mRNAs for ribosomal proteins and mitochondrial respiration peaked at night. Central clock mRNAs are among those subject to fluctuations in ribosome loading. There was no consistent phase relationship between peak translation states and peak transcript levels. The overlay of distinct transcriptional and translational cycles can be expected to alter the waveform of the protein synthesis rate. Plants that constitutively overexpress the clock gene CCA1 showed phase shifts in peak translation, with a 6-h delay from midnight to dawn or from noon to evening being particularly common. Moreover, cycles of ribosome loading that were detected under continuous light in the wild type collapsed in the CCA1 overexpressor. Finally, at the transcript level, the CCA1-ox strain adopted a global pattern of transcript abundance that was broadly correlated with the light-dark environment. Altogether, these data demonstrate that gene-specific diel cycles of ribosome loading are controlled in part by the circadian clock. PMID:26392078

Effect of augmentation techniques on the failure of pedicle screws under cranio-caudal cyclic loading.

PubMed

Bostelmann, Richard; Keiler, Alexander; Steiger, Hans Jakob; Scholz, Armin; Cornelius, Jan Frederick; Schmoelz, Werner

2017-01-01

Augmentation of pedicle screws is recommended in selected indications (for instance: osteoporosis). Generally, there are two techniques for pedicle screw augmentation: inserting the screw in the non cured cement and in situ-augmentation with cannulated fenestrated screws, which can be applied percutaneously. Most of the published studies used an axial pull out test for evaluation of the pedicle screw anchorage. However, the loading and the failure mode of pullout tests do not simulate the cranio-caudal in vivo loading and failure mechanism of pedicle screws. The purpose of the present study was to assess the fixation effects of different augmentation techniques (including percutaneous cement application) and to investigate pedicle screw loosening under physiological cyclic cranio-caudal loading. Each of the two test groups consisted of 15 vertebral bodies (L1-L5, three of each level per group). Mean age was 84.3 years (SD 7.8) for group 1 and 77.0 years (SD 7.00) for group 2. Mean bone mineral density was 53.3 mg/cm 3 (SD 14.1) for group 1 and 53.2 mg/cm 3 (SD 4.3) for group 2. 1.5 ml high viscosity PMMA bone cement was used for all augmentation techniques. For test group 1, pedicles on the right side of the vertebrae were instrumented with solid pedicle screws in standard fashion without augmentation and served as control group. Left pedicles were instrumented with cannulated screws (Viper cannulated, DePuy Spine) and augmented. For test group 2 pedicles on the left side of the vertebrae were instrumented with cannulated fenestrated screws and in situ augmented. On the right side solid pedicle screws were augmented with cement first technique. Each screw was subjected to a cranio-caudal cyclic load starting at 20-50 N with increasing upper load magnitude of 0.1 N per cycle (1 Hz) for a maximum of 5000 cycles or until total failure. Stress X-rays were taken after cyclic loading to evaluate screw loosening. Test group 1 showed a significant higher number of load cycles until failure for augmented screws compared to the control (4030 cycles, SD 827.8 vs. 1893.3 cycles, SD 1032.1; p < 0.001). Stress X-rays revealed significant less screw toggling for the augmented screws (5.2°, SD 5.4 vs. 16.1°, SD 5.9; p < 0.001). Test group 2 showed 3653.3 (SD 934) and 3723.3 (SD 560.6) load cycles until failure for in situ and cement first augmentation. Stress X-rays revealed a screw toggling of 5.1 (SD 1.9) and 6.6 (SD 4.6) degrees for in situ and cement first augmentation techniques (p > 0.05). Augmentation of pedicle screws in general significantly increased the number of load cycles and failure load comparing to the nonaugmented control group. For the augmentation technique (cement first, in situ augmented, percutaneously application) no effect could be exhibited on the failure of the pedicle screws. By the cranio-caudal cyclic loading failure of the pedicle screws occurred by screw cut through the superior endplate and the characteristic "windshield-wiper effect", typically observed in clinical practice, could be reproduced.

SLS Intertank Test Article, ITA, is attached to crosshead of loa

NASA Image and Video Library

2018-04-04

SLS Intertank Test Article, ITA, is attached to crosshead of load test Annex, Bldg. 4619, and removed from bed of KMAG transporter. Rob Ziegler, L, and Roger Myrick, R, of Aerie Aerospace attach load lines to Aft Load Ring of Intertank Test Articlle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stimpson, Shane G.

In this report, load-follow simulations using VERA-CS with one-way coupling to standalone BISON has been demonstrated including both a single rod with a full cycle of load-follow operations and a quarter-core model with a single month of load-follow.

The Effect of a Non-Gaussian Random Loading on High-Cycle Fatigue of a Thermally Post-Buckled Structure

NASA Technical Reports Server (NTRS)

Rizzi, Stephen A.; Behnke, marlana N.; Przekop, Adam

2010-01-01

High-cycle fatigue of an elastic-plastic beam structure under the combined action of thermal and high-intensity non-Gaussian acoustic loadings is considered. Such loadings can be highly damaging when snap-through motion occurs between thermally post-buckled equilibria. The simulated non-Gaussian loadings investigated have a range of skewness and kurtosis typical of turbulent boundary layer pressure fluctuations in the vicinity of forward facing steps. Further, the duration and steadiness of high excursion peaks is comparable to that found in such turbulent boundary layer data. Response and fatigue life estimates are found to be insensitive to the loading distribution, with the minor exception of cases involving plastic deformation. In contrast, the fatigue life estimate was found to be highly affected by a different type of non-Gaussian loading having bursts of high excursion peaks.

Optimal Design of a Resonance-Based Voltage Boosting Rectifier for Wireless Power Transmission.

PubMed

Lim, Jaemyung; Lee, Byunghun; Ghovanloo, Maysam

2018-02-01

This paper presents the design procedure for a new multi-cycle resonance-based voltage boosting rectifier (MCRR) capable of delivering a desired amount of power to the load (PDL) at a designated high voltage (HV) through a loosely-coupled inductive link. This is achieved by shorting the receiver (Rx) LC-tank for several cycles to harvest and accumulate the wireless energy in the RX inductor before boosting the voltage by breaking the loop and transferring the energy to the load in a quarter cycle. By optimizing the geometries of the transmitter (Tx) and Rx coils and the number of cycles, N , for energy harvesting, through an iterative design procedure, the MCRR can achieve the highest PDL under a given set of design constraints. Governing equations in the MCRR operation are derived to identify key specifications and the design guidelines. Using an exemplary set of specs, the optimized MCRR was able to generate 20.9 V DC across a 100 kΩ load from a 1.8 V p , 6.78 MHz sinusoid input in the ISM-band at a Tx/Rx coil separation of 1.3 cm, power transfer efficiency (PTE) of 2.2%, and N = 9 cycles. At the same coil distance and loading, coils optimized for a conventional half-wave rectifier (CHWR) were able to reach only 13.6 V DC from the same source.

Tendon fatigue in response to mechanical loading

PubMed Central

Andarawis-Puri, N.; Flatow, E. L.

2015-01-01

Tendinopathies are commonly attributable to accumulation of sub-rupture fatigue damage from repetitive use. Data is limited to late stage disease from patients undergoing surgery, motivating development of animal models, such as ones utilizing treadmill running or repetitive reaching, to investigate the progression of tendinopathies. We developed an in vivo model using the rat patellar tendon that allows control of the loading directly applied to the tendon. This manuscript discusses the response of tendons to fatigue loading and applications of our model. Briefly, the fatigue life of the tendon was used to define low, moderate and high levels of fatigue loading. Morphological assessment showed a progression from mild kinks to fiber disruption, for low to high level fatigue loading. Collagen expression, 1 and 3 days post loading, showed more modest changes for low and moderate than high level fatigue loading. Protein and mRNA expression of Ineterleukin-1β and MMP-13 were upregulated for moderate but not low level fatigue loading. Moderate level (7200 cycles) and 100 cycles of fatigue loading resulted in a catabolic and anabolic molecular profile respectively, at both 1 and 7 days post loading. Results suggest unique mechanisms for different levels of fatigue loading that are distinct from laceration. PMID:21625047

Cathode Loading Effect on Sulfur Utilization in Lithium–Sulfur Battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Ke; Liu, Helen; Gan, Hong

The Lithium-Sulfur (Li-S) battery is under intensive research in recent years due to its potential to provide higher energy density and lower cost than the current state-of-the-art lithium-ion battery technology. To meet cost target for transportation application, high sulfur loading up to 8 mAh cm -2 is predicted by modeling. In this work, we have investigated the sulfur loading effect on the galvanostatic charge/discharge cycling performance of Li-S cells with theoretical sulfur loading ranging from 0.5 mAh cm -2 to 7.5 mAh cm -2. We found that the low sulfur utilization of electrodes with sulfur loading of > 3.0 mAhmore » cm-2 is due to their inability to deliver capacities at the 2.1V voltage plateau, which corresponds to the conversion of soluble Li 2S 4 to insoluble Li 2S 2/Li 2S. This electrochemical conversion process recovers to deliver the expected sulfur utilization after several activation cycles for electrodes with sulfur loading up to 4.5 mAh cm -2. For electrodes with 7.0 mAh cm -2 loading, no sulfur utilization recovery was observed for 100 cycles. The root cause of this phenomenon is elucidated by SEM/EDS and EIS investigation. Carbon interlayer cell design and low rate discharge activation are demonstrated to be effective mitigation methods.« less

Cathode Loading Effect on Sulfur Utilization in Lithium–Sulfur Battery

DOE PAGES

Sun, Ke; Liu, Helen; Gan, Hong

2016-05-01

The Lithium-Sulfur (Li-S) battery is under intensive research in recent years due to its potential to provide higher energy density and lower cost than the current state-of-the-art lithium-ion battery technology. To meet cost target for transportation application, high sulfur loading up to 8 mAh cm -2 is predicted by modeling. In this work, we have investigated the sulfur loading effect on the galvanostatic charge/discharge cycling performance of Li-S cells with theoretical sulfur loading ranging from 0.5 mAh cm -2 to 7.5 mAh cm -2. We found that the low sulfur utilization of electrodes with sulfur loading of > 3.0 mAhmore » cm-2 is due to their inability to deliver capacities at the 2.1V voltage plateau, which corresponds to the conversion of soluble Li 2S 4 to insoluble Li 2S 2/Li 2S. This electrochemical conversion process recovers to deliver the expected sulfur utilization after several activation cycles for electrodes with sulfur loading up to 4.5 mAh cm -2. For electrodes with 7.0 mAh cm -2 loading, no sulfur utilization recovery was observed for 100 cycles. The root cause of this phenomenon is elucidated by SEM/EDS and EIS investigation. Carbon interlayer cell design and low rate discharge activation are demonstrated to be effective mitigation methods.« less

An approach to quantify sources, seasonal change, and biogeochemical processes affecting metal loading in streams: Facilitating decisions for remediation of mine drainage

USGS Publications Warehouse

Kimball, B.A.; Runkel, R.L.; Walton-Day, K.

2010-01-01

Historical mining has left complex problems in catchments throughout the world. Land managers are faced with making cost-effective plans to remediate mine influences. Remediation plans are facilitated by spatial mass-loading profiles that indicate the locations of metal mass-loading, seasonal changes, and the extent of biogeochemical processes. Field-scale experiments during both low- and high-flow conditions and time-series data over diel cycles illustrate how this can be accomplished. A low-flow experiment provided spatially detailed loading profiles to indicate where loading occurred. For example, SO42 - was principally derived from sources upstream from the study reach, but three principal locations also were important for SO42 - loading within the reach. During high-flow conditions, Lagrangian sampling provided data to interpret seasonal changes and indicated locations where snowmelt runoff flushed metals to the stream. Comparison of metal concentrations between the low- and high-flow experiments indicated substantial increases in metal loading at high flow, but little change in metal concentrations, showing that toxicity at the most downstream sampling site was not substantially greater during snowmelt runoff. During high-flow conditions, a detailed temporal sampling at fixed sites indicated that Zn concentration more than doubled during the diel cycle. Monitoring programs must account for diel variation to provide meaningful results. Mass-loading studies during different flow conditions and detailed time-series over diel cycles provide useful scientific support for stream management decisions.

Integral blow moulding for cycle time reduction of CFR-TP aluminium contour joint processing

NASA Astrophysics Data System (ADS)

Barfuss, Daniel; Würfel, Veit; Grützner, Raik; Gude, Maik; Müller, Roland

2018-05-01

Integral blow moulding (IBM) as a joining technology of carbon fibre reinforced thermoplastic (CFR-TP) hollow profiles with metallic load introduction elements enables significant cycle time reduction by shortening of the process chain. As the composite part is joined to the metallic part during its consolidation process subsequent joining steps are omitted. In combination with a multi-scale structured load introduction element its form closure function enables to pass very high loads and is capable to achieve high degrees of material utilization. This paper first shows the process set-up utilizing thermoplastic tape braided preforms and two-staged press and internal hydro formed load introduction elements. Second focuses on heating technologies and process optimization. Aiming at cycle time reduction convection and induction heating in regard to the resulting product quality is inspected by photo micrographs and computer tomographic scans. Concluding remarks give final recommendations for the process design in regard to the structural design.

Evaluation of Analysis Techniques for Fluted-Core Sandwich Cylinders

NASA Technical Reports Server (NTRS)

Lovejoy, Andrew E.; Schultz, Marc R.

2012-01-01

Buckling-critical launch-vehicle structures require structural concepts that have high bending stiffness and low mass. Fluted-core, also known as truss-core, sandwich construction is one such concept. In an effort to identify an analysis method appropriate for the preliminary design of fluted-core cylinders, the current paper presents and compares results from several analysis techniques applied to a specific composite fluted-core test article. The analysis techniques are evaluated in terms of their ease of use and for their appropriateness at certain stages throughout a design analysis cycle (DAC). Current analysis techniques that provide accurate determination of the global buckling load are not readily applicable early in the DAC, such as during preliminary design, because they are too costly to run. An analytical approach that neglects transverse-shear deformation is easily applied during preliminary design, but the lack of transverse-shear deformation results in global buckling load predictions that are significantly higher than those from more detailed analysis methods. The current state of the art is either too complex to be applied for preliminary design, or is incapable of the accuracy required to determine global buckling loads for fluted-core cylinders. Therefore, it is necessary to develop an analytical method for calculating global buckling loads of fluted-core cylinders that includes transverse-shear deformations, and that can be easily incorporated in preliminary design.

Mandibular corpus bone strains during mastication in goats (Capra hircus): a comparison of ingestive and rumination chewing.

PubMed

Williams, Susan H; Stover, Kristin K; Davis, Jillian S; Montuelle, Stephane J

2011-10-01

To compare the mechanical loading environment of the jaw in goats during ingestive and rumination chewing. Rosette strain gauges were attached to the external surface of the mandibular corpus in five goats to record bone strains during the mastication of hay and rumination. Strain magnitudes and maximum physiological strain rates during the mastication of hay are significantly higher than during rumination chewing on the working and balancing sides. Principal strain ratios and orientations are similar between the two chewing behaviours. Loading and chewing cycle duration are all longer during rumination chewing, whereas chew duty factor and variances in load and chewing cycle durations are higher during ingestive chewing. For most of the variables, differences in strain magnitudes or durations are similar at all three gauge sites, suggesting that rumination and ingestive chewing do not differentially influence bone at the three gauge sites. Despite lower strain magnitudes, the repetitive nature of rumination chewing makes it an important component of the mechanical loading environment of the selenodont artiodactyl jaw. However, similarities in principal strain orientations and ratios indicate that rumination chewing need not be considered as a unique loading behaviour influencing the biomechanics of the selenodont artiodactyl jaw. Differences in loading and chewing cycle durations during rumination and ingestion demonstrate flexibility in adult chewing frequencies. Finally, although the low within-sequence variability in chewing cycle durations supports the hypothesis that mammalian mastication is energetically efficient, chewing during rumination may not be more efficient than during ingestion. Copyright © 2011 Elsevier Ltd. All rights reserved.

Training Load and Fatigue Marker Associations with Injury and Illness: A Systematic Review of Longitudinal Studies.

PubMed

Jones, Christopher M; Griffiths, Peter C; Mellalieu, Stephen D

2017-05-01

Coaches, sport scientists, clinicians and medical personnel face a constant challenge to prescribe sufficient training load to produce training adaption while minimising fatigue, performance inhibition and risk of injury/illness. The aim of this review was to investigate the relationship between injury and illness and longitudinal training load and fatigue markers in sporting populations. Systematic searches of the Web of Science and PubMed online databases to August 2015 were conducted for articles reporting relationships between training load/fatigue measures and injury/illness in athlete populations. From the initial 5943 articles identified, 2863 duplicates were removed, followed by a further 2833 articles from title and abstract selection. Manual searching of the reference lists of the remaining 247 articles, together with use of the Google Scholar 'cited by' tool, yielded 205 extra articles deemed worthy of assessment. Sixty-eight studies were subsequently selected for inclusion in this study, of which 45 investigated injury only, 17 investigated illness only, and 6 investigated both injury and illness. This systematic review highlighted a number of key findings, including disparity within the literature regarding the use of various terminologies such as training load, fatigue, injury and illness. Athletes are at an increased risk of injury/illness at key stages in their training and competition, including periods of training load intensification and periods of accumulated training loads. Further investigation of individual athlete characteristics is required due to their impact on internal training load and, therefore, susceptibility to injury/illness.

Electric power generating plant having direct-coupled steam and compressed-air cycles

DOEpatents

Drost, M.K.

1981-01-07

An electric power generating plant is provided with a Compressed Air Energy Storage (CAES) system which is directly coupled to the steam cycle of the generating plant. The CAES system is charged by the steam boiler during off peak hours, and drives a separate generator during peak load hours. The steam boiler load is thereby levelized throughout an operating day.

Electric power generating plant having direct coupled steam and compressed air cycles

DOEpatents

Drost, Monte K.

1982-01-01

An electric power generating plant is provided with a Compressed Air Energy Storage (CAES) system which is directly coupled to the steam cycle of the generating plant. The CAES system is charged by the steam boiler during off peak hours, and drives a separate generator during peak load hours. The steam boiler load is thereby levelized throughout an operating day.

A Polysulfide-Infiltrated Carbon Cloth Cathode for High-Performance Flexible Lithium–Sulfur Batteries

PubMed Central

Song, Ji-Yoon; Lee, Hyeon-Haeng; Hong, Won Gi; Huh, Yun Suk; Lee, Yun Sung; Kim, Hae Jin; Jun, Young-Si

2018-01-01

For practical application of lithium–sulfur batteries (LSBs), it is crucial to develop sulfur cathodes with high areal capacity and cycle stability in a simple and inexpensive manner. In this study, a carbon cloth infiltrated with a sulfur-containing electrolyte solution (CC-S) was utilized as an additive-free, flexible, high-sulfur-loading cathode. A freestanding carbon cloth performed double duty as a current collector and a sulfur-supporting/trapping material. The active material in the form of Li2S6 dissolved in a 1 M LiTFSI-DOL/DME solution was simply infiltrated into the carbon cloth (CC) during cell fabrication, and its optimal loading amount was found to be in a range between 2 and 10 mg/cm2 via electrochemical characterization. It was found that the interwoven carbon microfibers retained structural integrity against volume expansion/contraction and that the embedded uniform micropores enabled a high loading and an efficient trapping of sulfur species during cycling. The LSB coin cell employing the CC-S electrode with an areal sulfur loading of 6 mg/cm2 exhibited a high areal capacity of 4.3 and 3.2 mAh/cm2 at C/10 for 145 cycles and C/3 for 200 cycles, respectively, with minor capacity loss (<0.03%/cycle). More importantly, such high performance could also be realized in flexible pouch cells with dimensions of 2 cm × 6 cm before and after 300 bending cycles. Simple and inexpensive preparation of sulfur cathodes using CC-S electrodes, therefore, has great potential for the manufacture of high-performance flexible LSBs. PMID:29414863

A Polysulfide-Infiltrated Carbon Cloth Cathode for High-Performance Flexible Lithium-Sulfur Batteries.

PubMed

Song, Ji-Yoon; Lee, Hyeon-Haeng; Hong, Won Gi; Huh, Yun Suk; Lee, Yun Sung; Kim, Hae Jin; Jun, Young-Si

2018-02-07

For practical application of lithium-sulfur batteries (LSBs), it is crucial to develop sulfur cathodes with high areal capacity and cycle stability in a simple and inexpensive manner. In this study, a carbon cloth infiltrated with a sulfur-containing electrolyte solution (CC-S) was utilized as an additive-free, flexible, high-sulfur-loading cathode. A freestanding carbon cloth performed double duty as a current collector and a sulfur-supporting/trapping material. The active material in the form of Li₂S₆ dissolved in a 1 M LiTFSI-DOL/DME solution was simply infiltrated into the carbon cloth (CC) during cell fabrication, and its optimal loading amount was found to be in a range between 2 and 10 mg/cm² via electrochemical characterization. It was found that the interwoven carbon microfibers retained structural integrity against volume expansion/contraction and that the embedded uniform micropores enabled a high loading and an efficient trapping of sulfur species during cycling. The LSB coin cell employing the CC-S electrode with an areal sulfur loading of 6 mg/cm² exhibited a high areal capacity of 4.3 and 3.2 mAh/cm² at C/10 for 145 cycles and C/3 for 200 cycles, respectively, with minor capacity loss (<0.03%/cycle). More importantly, such high performance could also be realized in flexible pouch cells with dimensions of 2 cm × 6 cm before and after 300 bending cycles. Simple and inexpensive preparation of sulfur cathodes using CC-S electrodes, therefore, has great potential for the manufacture of high-performance flexible LSBs.

Effect of load ratio on fatigue crack propagation behavior of solid-solution-strengthened Ni-based superalloys at elevated temperature

NASA Astrophysics Data System (ADS)

Ma, Longzhou; Roy, Shawoon K.

2013-04-01

The fatigue crack propagation (FCP) behavior of two solid-solution-strengthened Ni-based superalloys, INCONEL 617 and HAYNES 230, were studied simultaneously in laboratory air using a constant stress intensity factor (K)-controlled mode with different load ratios (R-ratio) at 700 °C. The FCP tests were performed in both cycle and time-dependent FCP domains to examine the effect of R-ratio on the FCP rate, da/dn. For cycle-dependent FCP test, a 1-s sinusoidal fatigue was applied for a compact tension (CT) specimen of INCONEL 617 and HAYNES 230 to measure their FCP rates. For time-dependent FCP test, a 3-s sinusoidal fatigue with a hold time of 300 s at maximum load was applied. Both cycle/time-dependent FCP behaviors were characterized and analyzed. The results showed that increasing R-ratio would introduce the fatigue incubation and decrease the FCP rates at cycle-dependent FCP tests. On the contrary, fatigue incubation was not observed at time-dependent FCP tests for both INCONEL 617 and HAYNES 230 at each tested R-ratio, suggesting that association of maximum load (Kmax) with crack tip open displacement (CTOD) and environmental factor governed the FCP process. Also, for time-dependent FCP, HAYNES 230 showed lower FCP rates than INCONEL 617 regardless of R-ratio. However, for cycle-dependent FCP, HAYNES 230 showed the lower FCP rates only at high R-ratios. Fracture surface of specimens were examined using SEM to investigate the cracking mechanism under cycle/time-dependent FCP condition with various R-ratios.

Influence of the loading frequency on the wear rate of a polyethylene-on-metal lumbar intervertebral disc replacement.

PubMed

Kettler, Annette; Bushelow, Michael; Wilke, Hans-Joachim

2012-06-01

Pre-clinical wear testing of intervertebral disc prostheses is commonly carried out according to ISO 18192-1. Ten million multiaxial loading cycles are applied at a frequency of 1 Hz. At this frequency, testing takes about 4 months. Testing at higher frequencies would therefore be desirable. ISO 18192-1 also offers testing at 2 Hz; however, it says the impact on the implant material behaviour as well as on the accuracy of the test machine shall be investigated by the user. Since such data are not available so far, the aim of this study was to carry out comparative wear tests at 1 and 2 Hz. Seven Prodisc-L lumbar disc prostheses were tested. After a pre-soak period, the implants were placed in specimen cups filled with calf serum, mounted to a Spine Wear Simulator and loaded according to ISO 18192-1. Testing was carried out at a temperature of 37 ± 2 °C. Four million loading cycles were applied at 1 Hz and eight million at 2 Hz in an alternating sequence. Each time after 12 days of testing the implants were removed to measure the weight and the height of the polyethylene cores. Then, the test serum was exchanged and the implants were remounted to the testing machine. The mean wear rate was 5.6 ± 2.3 mg per million cycles at 1 Hz and 7.7 ± 1.6 mg per million cycles at 2 Hz during the first six million loading cycles (p < 0.05) and 2.0 ± 0.6 and 4.1 ± 0.7 mg per million cycles during the second six million cycles (p < 0.05). Similarly, the mean heightloss was also smaller at 1 Hz than at 2 Hz (p < 0.05) with -0.02 ± 0.02 mm versus -0.04 ± 0.02 mm per million cycles during the first half of testing and -0.01 ± 0.01 versus -0.02 ± 0.01 mm per million cycles during the second half. The accuracy of the test machine was within the limits described by ISO 18192-1 at both frequencies. The results showed that the wear rate was higher at the beginning than at the end of testing. Also, the results indicated that testing at 2 Hz increases the wear rate compared with 1 Hz in case of a polyethylene-on-metal implant design. In the absence of retrieval studies it is difficult to decide which rate results in a more physiological wear pattern. However, a loading frequency of 1 Hz is probably closer to physiology than 2 Hz since the loading amplitudes prescribed by ISO 18192-1 are high. They rather represent movements like tying shoes or standing up from a chair than walking or sitting. The authors therefore suggest testing at 1 Hz.

Torque loss of different abutment sizes before and after cyclic loading.

PubMed

Moris, Izabela Cristina; Faria, Adriana Cláudia; Ribeiro, Ricardo Faria; Rodrigues, Renata Cristina

2015-01-01

The aim of this study was to compare 3.8- and 4.8-mm abutments submitted to simulations of masticatory cycles to examine whether abutment diameter and cemented vs screw-retained crowns affect torque loss of the abutments and crowns. Forty implant/abutment sets were divided into the following groups (n = 10 in each group): (1) G4.8S included 4.8-mm abutment with screw-retained crown; (2) G4.8C included 4.8-mm abutment with cemented crown; (3) G3.8S included 3.8-mm abutment with screw-retained crown; and (4) G3.8C included 3.8-mm abutment with cemented crown. All abutments were tightened with torque values of 20 Ncm, and 10 Ncm for screw-retained crowns. Torque loss was measured before and after cycling loading (300,000 cycles). Torque loss of screw-retained crowns significantly increased after cycling in abutments of groups G3.8S (P ≤ .05) and G4.8S (P = .001). No difference was noted between the abutments before cycling (P = .735), but G3.8S abutments presented greater torque loss than the other groups after cycling (P = .008). Significant differences were noted in the abutment torque loss before and after cycling loading only for the G3.8C group (P ≤ .05). The abutment diameter affects torque loss of screw-retained crowns and leads to failure during the test; mechanical cycling increases torque loss of abutment screw and screw-retained crowns.

Simulating Mars' Dust Cycle with a Mars General Circulation Model: Effects of Water Ice Cloud Formation on Dust Lifting Strength and Seasonality

NASA Technical Reports Server (NTRS)

Kahre, Melinda A.; Haberle, Robert; Hollingsworth, Jeffery L.

2012-01-01

The dust cycle is critically important for the current climate of Mars. The radiative effects of dust impact the thermal and dynamical state of the atmosphere [1,2,3]. Although dust is present in the Martian atmosphere throughout the year, the level of dustiness varies with season. The atmosphere is generally the dustiest during northern fall and winter and the least dusty during northern spring and summer [4]. Dust particles are lifted into the atmosphere by dust storms that range in size from meters to thousands of kilometers across [5]. Regional storm activity is enhanced before northern winter solstice (Ls200 degrees - 240 degrees), and after northern solstice (Ls305 degrees - 340 degrees ), which produces elevated atmospheric dust loadings during these periods [5,6,7]. These pre- and post- solstice increases in dust loading are thought to be associated with transient eddy activity in the northern hemisphere with cross-equatorial transport of dust leading to enhanced dust lifting in the southern hemisphere [6]. Interactive dust cycle studies with Mars General Circulation Models (MGCMs) have included the lifting, transport, and sedimentation of radiatively active dust. Although the predicted global dust loadings from these simulations capture some aspects of the observed dust cycle, there are marked differences between the simulated and observed dust cycles [8,9,10]. Most notably, the maximum dust loading is robustly predicted by models to occur near northern winter solstice and is due to dust lifting associated with down slope flows on the flanks of the Hellas basin. Thus far, models have had difficulty simulating the observed pre- and post- solstice peaks in dust loading.

Effects of Food Texture on Three-Dimensional Loads on Implants During Mastication Based on In Vivo Measurements.

PubMed

Yoda, Nobuhiro; Ogawa, Toru; Gunji, Yoshinori; Vanegas, Juan R; Kawata, Tetsuo; Sasaki, Keiichi

2016-08-01

The mechanisms by which the loads exerted on implants that support prostheses are modulated during mastication remain unclear. The purpose of this study was to evaluate the effects of food texture on 3-dimensional loads measured at a single implant using a piezoelectric transducer. Two subjects participated in this study. The transducer and the experimental superstructure, which had been adjusted to the subject's occlusal scheme, were attached to the implant with a titanium screw. The foods tested were chewing gum and peanuts. The mean maximum load on the implant in each chewing cycle was significantly higher during peanut chewing than during gum chewing. The direction of maximum load was significantly more widely dispersed during peanut chewing than during gum chewing. The range of changes in load direction during the force-increasing phase of each chewing cycle was significantly wider during peanut chewing than during gum chewing. The load on the implant was affected by food texture in both subjects. This measurement method can be useful to investigate the mechanisms of load modulation on implants during mastication.

Conductive polymer sensor arrays for smart orthopaedic implants

NASA Astrophysics Data System (ADS)

Micolini, Carolina; Holness, F. B.; Johnson, James A.; Price, Aaron D.

2017-04-01

This study proposes and demonstrates the design, implementation, and characterization of a 3D-printed smartpolymer sensor array using conductive polyaniline (PANI) structures embedded in a polymeric substrate. The piezoresistive characteristics of PANI were studied to evaluate the efficacy of the manufacturing of an embedded pressure sensor. PANI's stability throughout loading and unloading cycles together with the response to incremental loading cycles was investigated. It is demonstrated that this specially developed multi-material additive manufacturing process for polyaniline is a good candidate for the manufacture of implant components with smart-polymer sensors embedded for the analysis of joint loads in orthopaedic implants.

Effect of residual stresses induced by prestressing on rolling element fatigue life

NASA Technical Reports Server (NTRS)

Parker, R. J.; Zaretsky, E. V.

1972-01-01

A mechanical prestress cycle suitable to induce compressive stress beneath the surface of the inner race of radially loaded 207-size bearings was determined. Compressive residual stress in excess 0.69 x 10 to the 9th power N/sq m (100,000 psi), as measured by X-ray diffraction, were induced at the depth of maximum shearing stress. The prestress cycle consisted of running the bearings for 25 hours at 2750 rpm at a radial load which produced a maximum Hertz stress of 3.3 x 10 to the 9th power N/sq m (480,000 psi) at the contact of the inner race and the heaviest loaded ball. Bearings subjected to this prestress cycle and subsequently fatigue tested gave a 10 percent fatigue life greater than twice that of a group of baseline bearings.

Field Test of Boiler Primary Loop Temperature Controller

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glanville, P.; Rowley, P.; Schroeder, D.

Beyond these initial system efficiency upgrades are an emerging class of Advanced Load Monitoring (ALM) aftermarket controllers that dynamically respond to the boiler load, with claims of 10% to 30% of fuel savings over a heating season. For hydronic boilers specifically, these devices perform load monitoring, with continuous measurement of supply and, in some cases, return water temperatures. Energy savings from these ALM controllers are derived from dynamic management of the boiler differential, where a microprocessor with memory of past boiler cycles prevents the boiler from firing for a period of time, to limit cycling losses and inefficient operation duringmore » perceived low load conditions. These differ from OTR controllers, which vary boiler setpoint temperatures with ambient conditions while maintaining a fixed differential.« less

Training and shape retention in conducting polymer artificial muscles

NASA Astrophysics Data System (ADS)

Tominaga, Kazuo; Hashimoto, Hikaru; Takashima, Wataru; Kaneto, Keiichi

2011-12-01

Electrochemomechanical deformation (ECMD) of the conducting polymer polyaniline film is studied to investigate the behaviour of actuation under tensile loads. The ECMD was induced by the strains due to the insertion of ionic species (cyclic strain) and a creep due to applied loads during the redox cycle. The cyclic strain was enhanced by the experience of high tensile loads, indicating a training effect. The training effect was explained by the enhanced electrochemical activity of the film. The creep was recovered by removal of the tensile load and several electrochemical cycles. This fact indicates that the creep results from the one-dimensional anisotropic deformation, and is retained (shape retention) by the ionic crosslink. The recovery of creep results from the elastic relaxation of the polymer conformation.

High discharge rate characteristics of nickel-cadmium batteries for pulse load filtering

NASA Technical Reports Server (NTRS)

Gearing, G. M.; Cimino, M. B.; Fritts, D. H.; Leonard, J. F.; Terzuoli, A. J., Jr.

1985-01-01

Several tests of specially fabricated nickel-cadmium batteries having circular disk type electrodes were considered. These batteries were evaluated as filter elements between a constant current power supply and a five hertz pulsed load demanding approximately twice the power supply current during the load on portion of the cycle. Short tests lasting 10,000 cycles were conducted at up to a 21 C rate and an equivalent energy density of over 40 Joules per pound. In addition, two batteries were subjected to 10 to the 7 charge/discharge cycles, one at a 6.5 C rate and the other at a 13 C rate. Assuming an electrode to battery weight ratio of 0.5, these tests represent an energy density of about 7 and 14 Joules per pound respectively. Energy density, efficiency, capacitance, average voltage, and available capacity were tracked during these tests. After 10 to the 7 cycles, capacity degradation was negligible for one battery and about 20% for the other. Cadmium electrode failure may be the factor limiting lifetime at extremely low depth of discharge cycling. The output was examined and a simple equivalent circuit was proposed.

Fatigue induced changes in conical implant-abutment connections.

PubMed

Blum, Kai; Wiest, Wolfram; Fella, Christian; Balles, Andreas; Dittmann, Jonas; Rack, Alexander; Maier, Dominik; Thomann, Ralf; Spies, Benedikt Christopher; Kohal, Ralf Joachim; Zabler, Simon; Nelson, Katja

2015-11-01

Based on the current lack of data and understanding of the wear behavior of dental two-piece implants, this study aims for evaluating the microgap formation and wear pattern of different implants in the course of cyclic loading. Several implant systems with different conical implant-abutment interfaces were purchased. The implants were first evaluated using synchrotron X-ray high-resolution radiography (SRX) and scanning electron microscopy (SEM). The implant-abutment assemblies were then subjected to cyclic loading at 98N and their microgap was evaluated after 100,000, 200,000 and 1 million cycles using SRX, synchrotron micro-tomography (μCT). Wear mechanisms of the implant-abutment connection (IAC) after 200,000 cycles and 1 million cycles were further characterized using SEM. All implants exhibit a microgap between the implant and abutment prior to loading. The gap size increased with cyclic loading with its changes being significantly higher within the first 200,000 cycles. Wear was seen in all implants regardless of their interface design. The wear pattern comprised adhesive wear and fretting. Wear behavior changed when a different mounting medium was used (brass vs. polymer). A micromotion of the abutment during cyclic loading can induce wear and wear particles in conical dental implant systems. This feature accompanied with the formation of a microgap at the IAC is highly relevant for the longevity of the implants. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

A comprehensive energy approach to predict fatigue life in CuAlBe shape memory alloy

NASA Astrophysics Data System (ADS)

Sameallah, S.; Legrand, V.; Saint-Sulpice, L.; Kadkhodaei, M.; Arbab Chirani, S.

2015-02-01

Stabilized dissipated energy is an effective parameter on the fatigue life of shape memory alloys (SMAs). In this study, a formula is proposed to directly evaluate the stabilized dissipated energy for different values of the maximum and minimum applied stresses, as well as the loading frequency, under cyclic tensile loadings. To this aim, a one-dimensional fully coupled thermomechanical constitutive model and a cycle-dependent phase diagram are employed to predict the uniaxial stress-strain response of an SMA in a specified cycle, including the stabilized one, with no need of obtaining the responses of the previous cycles. An enhanced phase diagram in which different slopes are defined for the start and finish of a backward transformation strip is also proposed to enable the capture of gradual transformations in a CuAlBe shape memory alloy. It is shown that the present approach is capable of reproducing the experimental responses of CuAlBe specimens under cyclic tensile loadings. An explicit formula is further presented to predict the fatigue life of CuAlBe as a function of the maximum and minimum applied stresses as well as the loading frequency. Fatigue tests are also carried out, and this formula is verified against the empirically predicted number of cycles for failure.

Isothermal Damage and Fatigue Behavior of SCS-6/Timetal 21S [0/90](Sub S) Composite at 650 Deg C

NASA Technical Reports Server (NTRS)

Castelli, Michael G.

1994-01-01

The isothermal fatigue damage and life behaviors of SCS-6/Timetal 21S (0/90)s were investigated at 650 C. Strain ratcheting and degradation of the composite's static elastic modulus were carefully monitored as functions of cycles to indicate damage progression. Extensive fractographic and metallographic analyses were conducted to determine damage/failure mechanisms. Resulting fatigue lives show considerable reductions in comparison to (0) reinforced titanium matrix composites subjected to comparable conditions. Notable stiffness degradations were found to occur after the first cycle of loading, even at relatively low maximum stress levels, where cyclic lives are greater than 25,000 cycles. This was attributed to the extremely weak fiber/matrix bond which fails under relatively low transverse loads. Stiffness degradations incurred on first cycle loadings and degradations thereafter were found to increase with increasing maximum stress. Environmental effects associated with oxidation of the (90) fiber interfaces clearly played a role in the damage mechanisms as fracture surfaces revealed environment assisted matrix cracking along the (90) fibers. Metallographic analysis indicated that all observable matrix fatigue cracks initiated at the (90) fiber/matrix interfaces. Global de-bonding in the loading direction was found along the (90) fibers. No surface initiated cracks were evident and minimal if any (0) fiber cracking was visible.

Understanding the meaning of lactate threshold in resistance exercises.

PubMed

Garnacho-Castaño, M V; Dominguez, R; Maté-Muñoz, J L

2015-05-01

This study compares acute cardiorespiratory, metabolic, mechanical and rating of perceived effort (RPE) responses to 2 different prolonged constant-load exercises, half-squat (HS) and cycle ergometry, performed at a workload corresponding to the lactate threshold (LT). A total of 18 healthy subjects completed 5 exercise tests separated by 48 h rest periods: an incremental cycle ergometer test, a constant-load cycle ergometer test at LT intensity, a one-repetition maximum (1RM) HS test, an incremental HS test and a constant-load HS test at LT intensity. In both constant-load tests, cardiorespiratory, metabolic and RPE data were recorded. Mechanical responses before and after each test were assessed in terms of jump height and mean power measured in a counter movement jump (CMJ) test. In both exercises, cardiorespiratory and metabolic responses stabilized, though cardiorespiratory responses were significantly greater for cycle ergometry (P<0.001), with the exception of respiratory exchange ratio (RER), which was higher for HS (P=0.028). Mechanical fatigue was observed in only HS (P<0.001). In conclusion, different exercise modalities induced different yet stable acute cardiorespiratory and metabolic responses. Although such responses were significantly reduced in HS, greater mechanical fatigue was produced, most likely because of the particular muscle actions involved in this form of exercise. © Georg Thieme Verlag KG Stuttgart · New York.

Nitrogen and Phosphorus Loads to Temperate Seepage Lakes Associated With Allochthonous Dissolved Organic Carbon Loads

Treesearch

J.R. Corman; B.L. Bertolet; N.J. Casson; S.D. Sebestyen; R.K. Kolka; E.H. Stanley

2018-01-01

Terrestrial loads of dissolved organic matter (DOM) have increased in recent years in many north temperate lakes. While much of the focus on the "browning" phenomena has been on its consequences for carbon cycling, much less is known about how it influences nutrient loading to lakes. We characterize potential loads of nitrogen and phosphorus to seepage lakes...

Water in a Changing World

EPA Pesticide Factsheets

The module provides a link to an article that is part of a series of articles in Issues in Ecology. This article discusses the global water cycle, human influence on the cycle and the need for change.

Fatigue resistance and crack propensity of large MOD composite resin restorations: direct versus CAD/CAM inlays.

PubMed

Batalha-Silva, Silvana; de Andrada, Mauro Amaral Caldeira; Maia, Hamilton Pires; Magne, Pascal

2013-03-01

To assess the influence of material/technique selection (direct vs. CAD/CAM inlays) for large MOD composite adhesive restorations and its effect on the crack propensity and in vitro accelerated fatigue resistance. A standardized MOD slot-type tooth preparation was applied to 32 extracted maxillary molars (5mm depth and 5mm bucco-palatal width) including immediately sealed dentin for the inlay group. Fifteen teeth were restored with direct composite resin restoration (Miris2) and 17 teeth received milled inlays using Paradigm MZ100 block in the CEREC machine. All inlays were adhesively luted with a light curing composite resin (Filtek Z100). Enamel shrinkage-induced cracks were tracked with photography and transillumination. Cyclic isometric chewing (5 Hz) was simulated, starting with a load of 200 N (5000 cycles), followed by stages of 400, 600, 800, 1000, 1200 and 1400 N at a maximum of 30,000 cycles each. Samples were loaded until fracture or to a maximum of 185,000 cycles. Teeth restored with the direct technique fractured at an average load of 1213 N and two of them withstood all loading cycles (survival=13%); with inlays, the survival rate was 100%. Most failures with Miris2 occurred above the CEJ and were re-restorable (67%), but generated more shrinkage-induced cracks (47% of the specimen vs. 7% for inlays). CAD/CAM MZ100 inlays increased the accelerated fatigue resistance and decreased the crack propensity of large MOD restorations when compared to direct restorations. While both restorative techniques yielded excellent fatigue results at physiological masticatory loads, CAD/CAM inlays seem more indicated for high-load patients. Copyright © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

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 rights reserved.

Cognitive Load Theory and the Role of Learner Experience: An Abbreviated Review for Educational Practitioners

ERIC Educational Resources Information Center

Artino, Anthony R., Jr.

2008-01-01

The purpose of this review is to provide educational practitioners with a brief overview of cognitive load theory (CLT) and its major implications for learning. To achieve this objective, the article includes a short description of human cognitive architecture as conceived by cognitive load theorists. Following this overview, the article provides…

Alterations in redox homeostasis in the elite endurance athlete.

PubMed

Lewis, Nathan A; Howatson, Glyn; Morton, Katie; Hill, Jessica; Pedlar, Charles R

2015-03-01

The production of reactive oxygen (ROS) and nitrogen species (RNS) is a fundamental feature of mammalian physiology, cellular respiration and cell signalling, and essential for muscle function and training adaptation. Aerobic and anaerobic exercise results in alterations in redox homeostasis (ARH) in untrained, trained and well trained athletes. Low to moderate doses of ROS and RNS play a role in muscle adaptation to endurance training, but an overwhelming increase in RNS and ROS may lead to increased cell apoptosis and immunosuppression, fatigued states and underperformance. The objectives of this systematic review are: (a) to test the hypotheses that ARH occur in elite endurance athletes; following an acute exercise bout, in an endurance race or competition; across a micro-, meso- or macro-training cycle; following a training taper; before, during and after altitude training; in females with amenorrhoea versus eumenorrhoea; and in non-functional over-reaching (NFOR) and overtraining states (OTS); (b) to report any relationship between ARH and training load and ARH and performance; and (c) to apply critical difference values for measures of oxidative stress/ARH to address whether there is any evidence of ARH being of physiological significance (not just statistical) and thus relevant to health and performance in the elite athlete. Electronic databases, Embase, MEDLINE, and SPORTDiscus were searched for relevant articles. Only studies that were observational articles of cross-sectional or longitudinal design, and included elite athletes competing at national or international level in endurance sports were included. Studies had to include biomarkers of ARH; oxidative damage, antioxidant enzymes, antioxidant capacity, and antioxidant vitamins and nutrients in urine, serum, plasma, whole blood, red blood cells (RBCs) and white blood cells (WBCs). A total of 3,057 articles were identified from the electronic searches. Twenty-eight articles met the inclusion criteria and were included in the review. ARH occurs in elite endurance athletes, after acute exercise, a competition or race, across training phases, and with natural or simulated altitude. A reduction in ARH occurs across the season in elite athletes, with marked variation around intensified training phases, between individuals, and the greatest disturbances (of physiological significance) occurring with live-high-train-low techniques, and in athletes competing. A relationship with ARH and performance and illness exists in elite athletes. There was considerable heterogeneity across the studies for the biomarkers and assays used; the sport; the blood sampling time points; and the phase in the annual training cycle and thus baseline athlete fitness. In addition, there was a consistent lack of reporting of the analytical variability of the assays used to assess ARH. The reported biochemical changes around ARH in elite athletes suggest that it may be of value to monitor biomarkers of ARH at rest, pre- and post-simulated performance tests, and before and after training micro- and meso-cycles, and altitude camps, to identify individual tolerance to training loads, potentially allowing the prevention of non-functionally over-reached states and optimisation of the individual training taper and training programme.

Shield evaluation and performance testing at the USMB`s Strategic Structures Testing Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barczak, T.M.; Gearhart, D.F.

1996-12-31

Historically, shield performance testing is conducted by the support manufacturers at European facilities. The U.S. Bureau of Mines (USBM) has conducted extensive research in shield Mechanics and is now opening its Strategic Structures Testing (SST) Laboratory to the mining industry for shield performance testing. The SST Laboratory provides unique shield testing capabilities using the Mine Roof Simulator (MRS) load frame. The MRS provides realistic and cost-effective shield evaluation by combining both vertical and horizontal loading into a single load cycle; whereas, several load cycles would be required to obtain this loading in a static frame. In addition to these advantages,more » the USBM acts as an independent research organization to provide an unbiased assessment of shield performance. This paper describes the USBM`s shield testing program that is designed specifically to simulate in-service mining conditions using the unique the capabilities of the SST Laboratory.« less

Improvement of fatigue resistance for multilayer lead zirconate titanate (PZT)-based ceramic actuators by external mechanical loads

NASA Astrophysics Data System (ADS)

Yang, Gang; Yue, Zhenxing; Ji, Ye; Chu, Xiangcheng; Li, Longtu

2008-12-01

The influence of external compressive loads, applied along a direction perpendicular to polarization, on fatigue behaviors of multilayer lead zirconate titanate (PZT)-based ceramic actuators was investigated. Under no external mechanical load, a normal fatigue behavior was observed, demonstrating that both switching polarization (Pswitching) and remnant polarization (Pr) progressively decreased with increasing switching cycles due to domain pinning by charge point defects. However, an anomalous enhancement in both switching and remnant polarizations was observed upon application of the external compressive loads. After 5×106 cycles of polarization switching, Pswitching and Pr increase by about 13% and 6% at 40 MPa, respectively, while Pswitching and Pr increase by about 11% and 21% at 60 MPa, respectively. The improvement of fatigue resistance can be attributed to non-180° domain switching and suppression of microcracking, triggered by external mechanical loads.

Recent advances in the modelling of crack growth under fatigue loading conditions

NASA Technical Reports Server (NTRS)

Dekoning, A. U.; Tenhoeve, H. J.; Henriksen, T. K.

1994-01-01

Fatigue crack growth associated with cyclic (secondary) plastic flow near a crack front is modelled using an incremental formulation. A new description of threshold behaviour under small load cycles is included. Quasi-static crack extension under high load excursions is described using an incremental formulation of the R-(crack growth resistance)- curve concept. The integration of the equations is discussed. For constant amplitude load cycles the results will be compared with existing crack growth laws. It will be shown that the model also properly describes interaction effects of fatigue crack growth and quasi-static crack extension. To evaluate the more general applicability the model is included in the NASGRO computer code for damage tolerance analysis. For this purpose the NASGRO program was provided with the CORPUS and the STRIP-YIELD models for computation of the crack opening load levels. The implementation is discussed and recent results of the verification are presented.

Analysis and Assessment of Environmental Load of Vending Machines by a LCA Method, and Eco-Improvement Effect

NASA Astrophysics Data System (ADS)

Kimura, Yukio; Sadamichi, Yucho; Maruyama, Naoki; Kato, Seizo

These days the environmental impact due to vending machines'(VM) diffusion has greatly been discussed. This paper describes the numerical evaluation of the environmental impact by using the LCA (Life Cycle Assessment) scheme and then proposes eco-improvements' strategy toward environmentally conscious products(ECP). A new objective and universal consolidated method for the LCA-evaluation, so-called LCA-NETS(Numerical Eco-load Standardization ) developed by the authors is applied to the present issue. As a result, the environmental loads at the 5years' operation and the material procurement stages are found to dominate others over the life cycle. Further eco-improvement is realized by following the order of the LCA-NETS magnitude; namely, energy saving, materials reducing, parts' re-using, and replacing with low environmental load material. Above all, parts' re-using is specially recommendable for significant reduction of the environmental loads toward ECP.

Microstructure Evolution and Protrusion of Electroplated Cu-Filled Through-Silicon Vias Subjected to Thermal Cyclic Loading

NASA Astrophysics Data System (ADS)

Chen, Si; An, Tong; Qin, Fei; Chen, Pei

2017-10-01

Through-silicon vias (TSVs) have become an important technology for three-dimensional integrated circuit (3D IC) packaging. Protrusion of electroplated Cu-filled vias is a critical reliability issue for TSV technology. In this work, thermal cycling tests were carried out to identify how the microstructure affects protrusion during thermal cycling. Cu protrusion occurs when the loading temperature is higher than 149°C. During the first five thermal cycles, the grain size of Cu plays a dominant role in the protrusion behavior. Larger Cu grain size before thermal cycling results in greater Cu protrusion. With increasing thermal cycle number, the effect of the Cu grain size reduces and the microstrain begins to dominate the Cu protrusion behavior. Higher magnitude of microstrain within Cu results in greater protrusion increment during subsequent thermal cycles. When the thermal cycle number reaches 25, the protrusion rate of Cu slows down due to strain hardening. After 30 thermal cycles, the Cu protrusion stabilizes within the range of 1.92 μm to 2.09 μm.

Eddy-current testing of fatigue degradation upon contact fatigue loading of gas powder laser clad NiCrBSi-Cr3C2 composite coating

NASA Astrophysics Data System (ADS)

Savrai, R. A.; Makarov, A. V.; Gorkunov, E. S.; Soboleva, N. N.; Kogan, L. Kh.; Malygina, I. Yu.; Osintseva, A. L.; Davydova, N. A.

2017-12-01

The possibilities of the eddy-current method for testing the fatigue degradation under contact loading of gas powder laser clad NiCrBSi-Cr3C2 composite coating with 15 wt.% of Cr3C2 additive have been investigated. It is shown that the eddy-current testing of the fatigue degradation under contact loading of the NiCrBSi-15%Cr3C2 composite coating can be performed at high excitation frequencies 72-120 kHz of the eddy-current transducer. At that, the dependences of the eddy-current instrument readings on the number of loading cycles have both downward and upward branches, with the boundary between the branches being 3×105 cycles in the given loading conditions. This is caused, on the one hand, by cracking, and, on the other hand, by cohesive spalling and compaction of the composite coating, which affect oppositely the material resistivity and, correspondingly, the eddy-current instrument readings. The downward branch can be used to monitor the processes of crack formation and growth, the upward branch - to monitor the degree of cohesive spalling, while taking into account in the testing methodology an ambiguous character of the dependences of the eddy-current instrument readings on the number of loading cycles.

Testing system for ferromagnetic shape memory microactuators.

PubMed

Ganor, Y; Shilo, D; Messier, J; Shield, T W; James, R D

2007-07-01

Ferromagnetic shape memory alloys are a class of smart materials that exhibit a unique combination of large strains and fast response when exposed to magnetic field. Accordingly, these materials have significant potential in motion generation applications such as microactuators and sensors. This article presents a novel experimental system that measures the dynamic magnetomechanical behavior of microscale ferromagnetic shape memory specimens. The system is comprised of an alternating magnetic field generator (AMFG) and a mechanical loading and sensing system. The AMFG generates a dynamic magnetic field that periodically alternates between two orthogonal directions to facilitate martensitic variant switching and to remotely achieve a full magnetic actuation cycle, without the need of mechanical resetting mechanisms. Moreover, the AMFG is designed to produce a magnetic field that inhibits 180 degrees magnetization domain switching, which causes energy loss without strain generation. The mechanical loading and sensing system maintains a constant mechanical load on the measured specimen by means of a cantilever beam, while the displacement is optically monitored with a resolution of approximately 0.1 microm. Preliminary measurements using Ni(2)MnGa single crystal specimens, with a cross section of 100x100 microm(2), verified their large actuation strains and established their potential to become a material of great importance in microactuation technology.

Effects of Knee Alignments and Toe Clip on Frontal Plane Knee Biomechanics in Cycling

PubMed Central

Shen, Guangping; Zhang, Songning; Bennett, Hunter J.; Martin, James C.; Crouter, Scott E.; Fitzhugh, Eugene C.

2018-01-01

Effects of knee alignment on the internal knee abduction moment (KAM) in walking have been widely studied. The KAM is closely associated with the development of medial knee osteoarthritis. Despite the importance of knee alignment, no studies have explored its effects on knee frontal plane biomechanics during stationary cycling. The purpose of this study was to examine the effects of knee alignment and use of a toe clip on the knee frontal plane biomechanics during stationary cycling. A total of 32 participants (11 varus, 11 neutral, and 10 valgus alignment) performed five trials in each of six cycling conditions: pedaling at 80 rpm and 0.5 kg (40 Watts), 1.0 kg (78 Watts), and 1.5 kg (117 Watts) with and without a toe clip. A motion analysis system and a customized instrumented pedal were used to collect 3D kinematic and kinetic data. A 3 × 2 × 3 (group × toe clip × workload) mixed design ANOVA was used for statistical analysis (p < 0.05). There were two different knee frontal plane loading patterns, internal abduction and adduction moment, which were affected by knee alignment type. The knee adduction angle was 12.2° greater in the varus group compared to the valgus group (p = 0.001), yet no difference was found for KAM among groups. Wearing a toe clip increased the knee adduction angle by 0.95º (p = 0.005). The findings of this study indicate that stationary cycling may be a safe exercise prescription for people with knee malalignments. In addition, using a toe clip may not have any negative effects on knee joints during stationary cycling. Key points Varus or valgus alignment did not cause increased frontal-plane knee joint loading, suggesting stationary cycling is a safe exercise. This study supports that using a toe clip did not lead to abnormal frontal-plane knee loading during stationary cycling. Two different knee frontal plane loading patterns, knee abduction and adduction moment, were observed during stationary cycling, which are likely affected by the type of knee alignment. PMID:29769833

Proper Generalized Decomposition (PGD) for the numerical simulation of polycrystalline aggregates under cyclic loading

NASA Astrophysics Data System (ADS)

Nasri, Mohamed Aziz; Robert, Camille; Ammar, Amine; El Arem, Saber; Morel, Franck

2018-02-01

The numerical modelling of the behaviour of materials at the microstructural scale has been greatly developed over the last two decades. Unfortunately, conventional resolution methods cannot simulate polycrystalline aggregates beyond tens of loading cycles, and they do not remain quantitative due to the plasticity behaviour. This work presents the development of a numerical solver for the resolution of the Finite Element modelling of polycrystalline aggregates subjected to cyclic mechanical loading. The method is based on two concepts. The first one consists in maintaining a constant stiffness matrix. The second uses a time/space model reduction method. In order to analyse the applicability and the performance of the use of a space-time separated representation, the simulations are carried out on a three-dimensional polycrystalline aggregate under cyclic loading. Different numbers of elements per grain and two time increments per cycle are investigated. The results show a significant CPU time saving while maintaining good precision. Moreover, increasing the number of elements and the number of time increments per cycle, the model reduction method is faster than the standard solver.

Evaluation of Thin Kevlar-Epoxy Fabric Panels Subjected to Shear Loading

NASA Technical Reports Server (NTRS)

Baker, Donald J.

1996-01-01

The results of an analytical and experimental investigation of 4-ply Kevlar-49-epoxy panels loaded by in-plane shear are presented. Approximately one-half of the panels are thin-core sandwich panels and the other panels are solid-laminate panels. Selected panels were impacted with an aluminum sphere at a velocity of either 150 or 220 ft/sec. The strength of panels impacted at 150 ft/sec was not reduced when compared to the strength of the undamaged panels, but the strength of panels impacted at 220 ft/sec was reduced by 27 to 40 percent. Results are presented for panels that were cyclically loaded from a load less than the buckling load to a load in the postbuckling load range. The thin-core sandwich panels had a lower fatigue life than the solid panels. The residual strength of the solid and sandwich panels cycled more than one million cycles exceeded the baseline undamaged panel strengths. The effect of hysteresis in the response of the sandwich panels is not significant. Results of a nonlinear finite element analysis conducted for each panel design are presented.

Thermal analysis of the intact mandibular premolar: a finite element analysis.

PubMed

Oskui, I Z; Ashtiani, M N; Hashemi, A; Jafarzadeh, H

2013-09-01

To obtain temperature distribution data through human teeth focusing on the pulp-dentine junction (PDJ). A three-dimensional tooth model was reconstructed using computer-aided design software from computed tomographic images. Subsequently, temperature distribution was numerically determined through the tooth for three different heat loads. Loading type I was equivalent to a 60° C mouth temperature for 1 s. Loading type II started with a 60° C mouth temperature, decreasing linearly to 37° C over 10 s. Loading type III repeated the pattern of type II in three consecutive cycles, with a 5 s resting time between cycles. The maximum temperatures of the pulp were 37.9° C, 39.0° C and 41.2° C for loading types I, II, and III, respectively. The largest temperature rise occurred with the cyclic loading, that is, type III. For the heat loads considered, the predicted peak temperatures at the PDJ were less than the reported temperature thresholds of irreversible pulpal damage. © 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd.

Assessment of Embedded Conjugated Polymer Sensor Arrays for Potential Load Transmission Measurement in Orthopaedic Implants

PubMed Central

Micolini, Carolina; Holness, Frederick Benjamin; Johnson, James A.

2017-01-01

Load transfer through orthopaedic joint implants is poorly understood. The longer-term outcomes of these implants are just starting to be studied, making it imperative to monitor contact loads across the entire joint implant interface to elucidate the force transmission and distribution mechanisms exhibited by these implants in service. This study proposes and demonstrates the design, implementation, and characterization of a 3D-printed smart polymer sensor array using conductive polyaniline (PANI) structures embedded within a polymeric parent phase. The piezoresistive characteristics of PANI were investigated to characterize the sensing behaviour inherent to these embedded pressure sensor arrays, including the experimental determination of the stable response of PANI to continuous loading, stability throughout the course of loading and unloading cycles, and finally sensor repeatability and linearity in response to incremental loading cycles. This specially developed multi-material additive manufacturing process for PANI is shown be an attractive approach for the fabrication of implant components having embedded smart-polymer sensors, which could ultimately be employed for the measurement and analysis of joint loads in orthopaedic implants for in vitro testing. PMID:29186079

Optimum selection of an implantable secondary battery for an artificial heart by examination of the cycle life test.

PubMed

Okamoto, Eiji; Watanabe, Kazuya; Hashiba, Kunihiro; Inoue, Taku; Iwazawa, Eichi; Momoi, Masato; Hashimoto, Takuya; Mitamura, Yoshinori

2002-01-01

An implantable secondary battery is one of the key components in a total artificial heart system. Because a 2 year cycle life is required, the cycle life of the secondary battery as well as its charge and discharge properties are important parameters for selection of an appropriate battery. We carried out cycle life tests on four kinds of rechargeable batteries (a Ni-MH secondary battery, a Ni-Cd secondary battery, a Li-ion battery with a graphite anode, and a Li-ion battery with a nongraphitizable carbon electrode) to determine their suitability as implanted back-up batteries. Each of the batteries was charge/discharge cycled at 37 degrees C to 39 degrees C using a charge current of 1 C ampere, and they were each fully discharged under either pulsatile discharge loads, which mimicked pulsatile operation, or a nonpulsatile load equivalent to the average of the pulsatile loads. The two Li-ion batteries made by different manufacturers both met the minimum requirement of cycle life of more than 1,500 cycles, considering safety coefficient regardless of the discharge pattern. In addition, the temperature increase of these Li-ion batteries (3 degrees C) was lower than that of Ni-Cd and Ni-MH batteries (15-25 degrees C). Out of these four batteries, the two Li-ion batteries are the most suitable for use in a totally implantable artificial heart system.

Helicopter Fatigue. A Review of Current Requirements and Substantiation Procedures

DTIC Science & Technology

1979-01-01

which the applications differ between contractors based cn their individual experience. Load Application: The ideal method of measuring flight loads would... method is different for the parts mainly dimensioned by high cycle fatigue (rotors and gearboxes) and for those subjected to low cycle fatigue (e.g...into damage per hour. Z.. A 58 2.3. Calculation of the service life Two methods are available, both with advantages and drawbacks. They only differ by

Cognitive Load Theory: How Many Types of Load Does It Really Need?

ERIC Educational Resources Information Center

Kalyuga, Slava

2011-01-01

Cognitive load theory has been traditionally described as involving three separate and additive types of load. Germane load is considered as a learning-relevant load complementing extraneous and intrinsic load. This article argues that, in its traditional treatment, germane load is essentially indistinguishable from intrinsic load, and therefore…

Fatigue-environment interactions in a SiC/Ti-15-3 composite

NASA Technical Reports Server (NTRS)

Gayda, J.; Gabb, T. P.; Lerch, B. A.

1993-01-01

Load-controlled isothermal and nonisothermal fatigue lives of a (0-deg)s SiC/Ti-15-3 were evaluated at temperatures between 150 and 550 C and a target strain range of about 0.45 percent. In nonisothermal fatigue tests, load was first cycled at minimum temperature and then temperature was cycled at zero load. For fatigue tests with peak temperatures at or above 300 C, fatigue life was dramatically reduced compared to that at 150 C. The shortest life was produced by the nonisothermal test with the greatest temperature range (Delta T = 400 C) and highest peak temperature (T(max) = 550 C). Vacuum testing showed that much of the life reduction under isothermal and nonisothermal conditions was related to environmental effects, although the nature of the fatigue-environment interaction was decidedly different for the isothermal and nonisothermal test cycles which were studied.

Industrial research for transmutation scenarios

NASA Astrophysics Data System (ADS)

Camarcat, Noel; Garzenne, Claude; Le Mer, Joël; Leroyer, Hadrien; Desroches, Estelle; Delbecq, Jean-Michel

2011-04-01

This article presents the results of research scenarios for americium transmutation in a 22nd century French nuclear fleet, using sodium fast breeder reactors. We benchmark the americium transmutation benefits and drawbacks with a reference case consisting of a hypothetical 60 GWe fleet of pure plutonium breeders. The fluxes in the various parts of the cycle (reactors, fabrication plants, reprocessing plants and underground disposals) are calculated using EDF's suite of codes, comparable in capabilities to those of other research facilities. We study underground thermal heat load reduction due to americium partitioning and repository area minimization. We endeavor to estimate the increased technical complexity of surface facilities to handle the americium fluxes in special fuel fabrication plants, americium fast burners, special reprocessing shops, handling equipments and transport casks between those facilities.

Cold-tip off-state conduction loss of miniature Stirling cycle cryocoolers

NASA Technical Reports Server (NTRS)

Kotsubo, V.; Johnson, D. L.; Ross, R. G., Jr.

1991-01-01

For redundant miniature Stirling-cycle cryocoolers in space applications, the off-state heat conduction down the coldfinger of one cooler is a parasitic heat load on the other coolers. At JPL, a heat flow transducer specifically designed to measure this load has been developed, and measurements have been performed on the coldfinger of a British Aerospace 80 K Stirling cooler with the tip temperature ranging between 40 and 170 K. Measurements have also been made using a transient warmup technique, where the warmup rates of the coldtip under various applied heat loads are used to determine the static conduction load. There is a difference between the results of these two methods, and these differences are discussed with regard to the applicability of the transient warmup method to a nonoperating coldfinger.

Seasonal water storage, stress modulation, and California seismicity.

PubMed

Johnson, Christopher W; Fu, Yuning; Bürgmann, Roland

2017-06-16

Establishing what controls the timing of earthquakes is fundamental to understanding the nature of the earthquake cycle and critical to determining time-dependent earthquake hazard. Seasonal loading provides a natural laboratory to explore the crustal response to a quantifiable transient force. In California, water storage deforms the crust as snow and water accumulates during the wet winter months. We used 9 years of global positioning system (GPS) vertical deformation time series to constrain models of monthly hydrospheric loading and the resulting stress changes on fault planes of small earthquakes. The seasonal loading analysis reveals earthquakes occurring more frequently during stress conditions that favor earthquake rupture. We infer that California seismicity rates are modestly modulated by natural hydrological loading cycles. Copyright © 2017, American Association for the Advancement of Science.

Wave Fluid Film Bearing Tests for an Aviation Gearbox

NASA Technical Reports Server (NTRS)

Dimofte, Florin; Proctor, Margaret P.; Fleming, David P.; Keith, Theo G., Jr.

2000-01-01

An oil-lubricated wave journal-thrust bearing assembly was successfully tested at conditions found in general aviation engine gearboxes. The bearing performed well at both steady state conditions and in start-stop tests. It ran stably under all loading conditions, including zero load, at all speeds up to 16 000 rpm. The bearing carried 25 percent more load than required for the gearbox application, supporting 8900 N (94 bars average pressure), and showed very good thermal stability. 450 start-stop cycles were also performed, including 350 cycles without oil supply during starting and stopping. Test results and numerical predictions were in good agreement.

Theoretical modeling of the vapor cavitation in dynamically loaded journal bearings

NASA Technical Reports Server (NTRS)

Brewe, D. E.

1985-01-01

A theoretical investigation is made of the evolution of a vapor-bubble for a submerged journal bearing under dynamically loaded conditions using the Elrod algorithm. This method conserves mass throughout the computational domain. A comparison study is performed to determine some of the consequences of applying a nonconservative theory (pseudo-Gumbel BC) to a dynamic problem. A complete dynamic cycle of a journal whirling in a circular path is chosen for the basis of comparison. Significant differences are observed in the load components near the end of the cycle. Further, good agreement with experiment is found for stationary and nonstationary cavitation.

Long-life Li/polysulphide batteries with high sulphur loading enabled by lightweight three-dimensional nitrogen/sulphur-codoped graphene sponge

PubMed Central

Zhou, Guangmin; Paek, Eunsu; Hwang, Gyeong S.; Manthiram, Arumugam

2015-01-01

Lithium–sulphur batteries with a high theoretical energy density are regarded as promising energy storage devices for electric vehicles and large-scale electricity storage. However, the low active material utilization, low sulphur loading and poor cycling stability restrict their practical applications. Herein, we present an effective strategy to obtain Li/polysulphide batteries with high-energy density and long-cyclic life using three-dimensional nitrogen/sulphur codoped graphene sponge electrodes. The nitrogen/sulphur codoped graphene sponge electrode provides enough space for a high sulphur loading, facilitates fast charge transfer and better immobilization of polysulphide ions. The hetero-doped nitrogen/sulphur sites are demonstrated to show strong binding energy and be capable of anchoring polysulphides based on first-principles calculations. As a result, a high specific capacity of 1,200 mAh g−1 at 0.2C rate, a high-rate capacity of 430 mAh g−1 at 2C rate and excellent cycling stability for 500 cycles with ∼0.078% capacity decay per cycle are achieved. PMID:26182892

Biodegradation of organics in landfill leachate by immobilized white rot fungi, Trametes versicolor BCC 8725.

PubMed

Saetang, Jenjira; Babel, Sandhya

2012-12-01

Immobilized Trametes versicolor BCC 8725 was evaluated for the biodegradation of the organic components of four different types of landfill leachate collected at different time periods and locations from the Nonthaburi landfill site of Thailand in batch treatment. The effects of carbon source, ammonia and organic loading on colour, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) removal, and the reuse of immobilized fungi were investigated. It was found that fungi can remove 78% of colour, reduce BOD by 68% and reduce COD by 57% in leachate within 15 days at optimum conditions. Organic loading and ammonia were the factors that affected the biodegradation. When immobilized T versicolor on polyurethane foam (PUF) was subjected to repeated use for treatment over the course of three cycles, the decolourization efficiency of the first and the second cycle was very similar, whereas the third cycle was about 20% lower than the first cycle under similar conditions. The obtained removal of colour, BOD and COD indicates the effectiveness of fungi for leachate treatment with high organic loading and varied leachate characteristics.

An English Vocabulary Learning System Based on Fuzzy Theory and Memory Cycle

NASA Astrophysics Data System (ADS)

Wang, Tzone I.; Chiu, Ti Kai; Huang, Liang Jun; Fu, Ru Xuan; Hsieh, Tung-Cheng

This paper proposes an English Vocabulary Learning System based on the Fuzzy Theory and the Memory Cycle Theory to help a learner to memorize vocabularies easily. By using fuzzy inferences and personal memory cycles, it is possible to find an article that best suits a learner. After reading an article, a quiz is provided for the learner to improve his/her memory of the vocabulary in the article. Early researches use just explicit response (ex. quiz exam) to update memory cycles of newly learned vocabulary; apart from that approach, this paper proposes a methodology that also modify implicitly the memory cycles of learned word. By intensive reading of articles recommended by our approach, a learner learns new words quickly and reviews learned words implicitly as well, and by which the vocabulary ability of the learner improves efficiently.

Feasibility and operating costs of an air cycle for CCHP in a fast food restaurant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perez-Blanco, Horacio; Vineyard, Edward

This work considers the possibilities of an air-based Brayton cycle to provide the power, heating and cooling needs of fast-food restaurants. A model of the cycle based on conventional turbomachinery loss coefficients is formulated. The heating, cooling and power capabilities of the cycle are extracted from simulation results. Power and thermal loads for restaurants in Knoxville, TN and in International Falls, MN, are considered. It is found that the cycle can meet the loads by setting speed and mass flow-rate apportionment between the power and cooling functional sections. The associated energy costs appear elevated when compared to the cost ofmore » operating individual components or a more conventional, absorption-based CHP system. Lastly, a first-order estimate of capital investments is provided. Suggestions for future work whereby the operational costs could be reduced are given in the conclusions.« less

Advanced technology cogeneration system conceptual design study: Closed cycle gas turbines

NASA Technical Reports Server (NTRS)

Mock, E. A. T.; Daudet, H. C.

1983-01-01

The results of a three task study performed for the Department of Energy under the direction of the NASA Lewis Research Center are documented. The thermal and electrical energy requirements of three specific industrial plants were surveyed and cost records for the energies consumed were compiled. Preliminary coal fired atmospheric fluidized bed heated closed cycle gas turbine and steam turbine cogeneration system designs were developed for each industrial plant. Preliminary cost and return-on-equity values were calculated and the results compared. The best of the three sites was selected for more detailed design and evaluation of both closed cycle gas turbine and steam turbine cogeneration systems during Task II. Task III involved characterizing the industrial sector electrical and thermal loads for the 48 contiguous states, applying a family of closed cycle gas turbine and steam turbine cogeneration systems to these loads, and conducting a market penetration analysis of the closed cycle gas turbine cogeneration system.

Feasibility and operating costs of an air cycle for CCHP in a fast food restaurant

DOE PAGES

Perez-Blanco, Horacio; Vineyard, Edward

2016-05-06

This work considers the possibilities of an air-based Brayton cycle to provide the power, heating and cooling needs of fast-food restaurants. A model of the cycle based on conventional turbomachinery loss coefficients is formulated. The heating, cooling and power capabilities of the cycle are extracted from simulation results. Power and thermal loads for restaurants in Knoxville, TN and in International Falls, MN, are considered. It is found that the cycle can meet the loads by setting speed and mass flow-rate apportionment between the power and cooling functional sections. The associated energy costs appear elevated when compared to the cost ofmore » operating individual components or a more conventional, absorption-based CHP system. Lastly, a first-order estimate of capital investments is provided. Suggestions for future work whereby the operational costs could be reduced are given in the conclusions.« less

Fatigue behavior of a cross-ply ceramic matrix composite subjected to tension-tension cycling with hold time. Master`s thesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grant, S.A.

This study was carried out to investigate the elevated temperature behavior of the SiC-MAS5 cross- ply (O/9O)4S ceramic matrix composite manufactured by Corning Inc. to fatigue with loading waveforms that combine the characteristics of stress rupture and high cycle fatigue. The test results were compiled in the form of S-N (cycles to failure), S-T (exposure time versus cycles to failure), S-S (energy exposure versus cycles to failure), normalized modulus degradation, strain progression, and hysteresis loop progression. From the mechanical behavior demonstrated by these curves, relationships between the effect of the environment and loading waveform were developed. In addition, a post-mortemmore » SEM analysis of the fracture surface was conducted and the results compared to the mechanical behavior.« less

10 CFR Appendix C to Subpart B of... - Uniform Test Method for Measuring the Energy Consumption of Dishwashers

Code of Federal Regulations, 2014 CFR

2014-01-01

... Preconditioning cycle means any cycle that includes a fill, circulation, and drain to ensure that the water lines... truncated normal cycle without a test load if the dishwasher does not heat water in the normal cycle. 2.6.2... water temperatures encountered in the test cycle. 3.4 Water pressure gauge. The water pressure gauge...

Moderate temperature control technology for a lunar base

NASA Technical Reports Server (NTRS)

Swanson, Theodore D.; Sridhar, K. R.; Gottmann, Matthias

1993-01-01

A parametric analysis is performed to compare different heat pump based thermal control systems for a Lunar Base. Rankine cycle and absorption cycle heat pumps are compared and optimized for a 100 kW cooling load. Variables include the use or lack of an interface heat exchanger, and different operating fluids. Optimization of system mass to radiator rejection temperature is performed. The results indicate a relatively small sensitivity of Rankine cycle system mass to these variables, with optimized system masses of about 6000 kg for the 100 kW thermal load. It is quantitaively demonstrated that absorption based systems are not mass competitive with Rankine systems.

Start-stop testing of two self-acting air-lubricated spiral groove thrust bearing coatings

NASA Technical Reports Server (NTRS)

Dunfee, J. D.; Shapiro, W.

1974-01-01

Start-stop tests were conducted on air-lubricated spiral-groove thrust bearings. Application of a matrix-bonded molybdenum disulfide (MoS2) coating over a porous chrome oxide coating resulted in significantly lower friction, compared to bearings coated with chrome oxide only. The MoS2 coated bearing sustained 15,000 start-stop cycles at a maximum of 3600 rpm. Each cycle was 15 seconds on, 30 seconds off. The chrome oxide coated bearing failed by local welding after 2030 cycles. Both types of coatings exhibited early failures under higher thrust loads when operating films were insufficient to sustain the load without overheating.

Structural dynamics payload loads estimates

NASA Technical Reports Server (NTRS)

Engels, R. C.

1982-01-01

Methods for the prediction of loads on large space structures are discussed. Existing approaches to the problem of loads calculation are surveyed. A full scale version of an alternate numerical integration technique to solve the response part of a load cycle is presented, and a set of short cut versions of the algorithm developed. The implementation of these techniques using the software package developed is discussed.

Free-Standing Porous Carbon Nanofiber/Carbon Nanotube Film as Sulfur Immobilizer with High Areal Capacity for Lithium-Sulfur Battery.

PubMed

Zhang, Ye-Zheng; Zhang, Ze; Liu, Sheng; Li, Guo-Ran; Gao, Xue-Ping

2018-03-14

Low sulfur utilization and poor cycle life of the sulfur cathode with high sulfur loadings remain a great challenge for lithium-sulfur (Li-S) battery. Herein, the free-standing carbon film consisting of porous carbon nanofibers (PCNFs) and carbon nanotubes (CNTs) is successfully fabricated by the electrospinning technology. The PCNF/CNT film with three-dimensional and interconnected structure is promising for the uniformity of the high-loading sulfur, good penetration of the electrolyte, and reliable accommodation of volumetric expansion of the sulfur cathode. In addition, the abundant N/O-doped elements in PCNF/CNT film are helpful to chemically trap soluble polysulfides in the charge-discharge processes. Consequently, the obtained monolayer S/PCNF/CNT film as the cathode shows high specific capacity, excellent cycle stability, and rate stability with the sulfur loading of 3.9 mg cm -2 . Moreover, the high areal capacity of 13.5 mA h cm -2 is obtained for the cathode by stacking three S/PCNF/CNT layers with the high sulfur loading of 12 mg cm -2 . The stacking-layered cathode with high sulfur loading provides excellent cycle stability, which is beneficial to fabricate high-energy-density Li-S battery in future.

Identification of critical equipment and determination of operational limits in helium refrigerators under pulsed heat load

NASA Astrophysics Data System (ADS)

Dutta, Rohan; Ghosh, Parthasarathi; Chowdhury, Kanchan

2014-01-01

Large-scale helium refrigerators are subjected to pulsed heat load from tokamaks. As these plants are designed for constant heat loads, operation under such varying load may lead to instability in plants thereby tripping the operation of different equipment. To understand the behavior of the plant subjected to pulsed heat load, an existing plant of 120 W at 4.2 K and another large-scale plant of 18 kW at 4.2 K have been analyzed using a commercial process simulator Aspen Hysys®. A similar heat load characteristic has been applied in both quasi steady state and dynamic analysis to determine critical stages and equipment of these plants from operational point of view. It has been found that the coldest part of both the cycles consisting JT-stage and its preceding reverse Brayton stage are the most affected stages of the cycles. Further analysis of the above stages and constituting equipment revealed limits of operation with respect to variation of return stream flow rate resulted from such heat load variations. The observations on the outcome of the analysis can be used for devising techniques for steady operation of the plants subjected to pulsed heat load.

The Relationship Between Training Load and Injury in Athletes: A Systematic Review.

PubMed

Eckard, Timothy G; Padua, Darin A; Hearn, Darren W; Pexa, Brett S; Frank, Barnett S

2018-06-26

The relationship between training load and musculoskeletal injury is a rapidly advancing area of research in need of an updated systematic review. This systematic review examined the evidence for the relationship between training load and musculoskeletal injury risk in athlete, military, and first responder (i.e. law enforcement, firefighting, rescue service) populations. The CINAHL, EMBASE, MEDLINE, SportDISCUS, and SCOPUS databases were searched using a comprehensive strategy. Studies published prior to July 2017 were included if they prospectively examined the relationship between training load and injury risk. Study quality was assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS) and Oxford Centre for Evidence-Based Medicine levels of evidence. A narrative synthesis of findings was conducted. A total of 2047 articles were examined for potential inclusion. Forty-six met the inclusion criteria and 11 known to the authors but not found in the search were added, for a total of 57 articles. Overall, 47 studies had at least partially statistically significant results, demonstrating a relationship between training load and injury risk. Included articles were rated as poor (n = 15), fair (n = 6), and good (n = 36) based on NOS score. Articles assessed as 'good' were considered level 2b evidence on the Oxford Centre for Evidence-Based Medicine Model, and articles assessed as 'fair' or 'poor' were considered level 4 evidence. Our results demonstrate that the existence of a relationship between training load and injury continues to be well supported in the literature and is strongest for subjective internal training load. The directionality of this relationship appears to depend on the type and timeframe of load measured.

Microstructure: Property correlation. [multiaxial fatigue damage evolution in waspaloy

NASA Technical Reports Server (NTRS)

Jayaraman, N.

1990-01-01

Strain controlled torsional and biaxial (tension-torsion) low cycle fatigue behavior of Waspaloy was studied at room temperature as a function of heat treatment. Biaxial tests were conducted under proportional (when the axial and torsional strain cycles are in-phase) and non-proportional (when the axial and torsional strain cycles are 90 deg out-of-phase) cyclic conditions. The deformation behavior under these different cyclic conditions were evaluated by slip trace analysis. For this, a Schmidt-type factor was defined for multiaxial loading conditions and it was shown that when the slip deformation is predominant, non-proportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under non-proportional cyclic conditions, deformation was through multiple slip as opposed single slip for other loading conditions, which gave rise to increased hardening. The total life for a given test condition was found to be independent of heat treatment. This was interpreted as being due to the differences in the cycles to initiation and propagation of cracks.

Seasonal water storage, stress modulation and California seismicity

NASA Astrophysics Data System (ADS)

Johnson, C. W.; Burgmann, R.; Fu, Y.

2017-12-01

Establishing what controls the timing of earthquakes is fundamental to understanding the nature of the earthquake cycle and critical to determining time-dependent earthquake hazard. Seasonal loading provides a natural laboratory to explore the crustal response to a quantifiable transient force. In California, the accumulation of winter snowpack in the Sierra Nevada, surface water in lakes and reservoirs, and groundwater in sedimentary basins follow the annual cycle of wet winters and dry summers. The surface loads resulting from the seasonal changes in water storage produce elastic deformation of the Earth's crust. We used 9 years of global positioning system (GPS) vertical deformation time series to constrain models of monthly hydrospheric loading and the resulting stress changes on fault planes of small earthquakes. Previous studies posit that temperature, atmospheric pressure, or hydrologic changes may strain the lithosphere and promote additional earthquakes above background levels. Depending on fault geometry, the addition or removal of water increases the Coulomb failure stress. The largest stress amplitudes are occurring on dipping reverse faults in the Coast Ranges and along the eastern Sierra Nevada range front. We analyze 9 years of M≥2.0 earthquakes with known focal mechanisms in northern and central California to resolve fault-normal and fault-shear stresses for the focal geometry. Our results reveal 10% more earthquakes occurring during slip-encouraging fault-shear stress conditions and suggest that earthquake populations are modulated at periods of natural loading cycles, which promote failure by stress changes on the order of 1-5 kPa. We infer that California seismicity rates are modestly modulated by natural hydrological loading cycles.

40 CFR 86.108-00 - Dynamometer.

Code of Federal Regulations, 2010 CFR

2010-07-01

... load force and inertia specified for the vehicle being tested, and shall determine the distance... capable of dynamically controlling inertia load during the US06 test cycle as a function of a vehicle... equal to eight seconds, the test inertia load may be adjusted during any of five EPA specified...

40 CFR 86.108-00 - Dynamometer.

Code of Federal Regulations, 2011 CFR

2011-07-01

... load force and inertia specified for the vehicle being tested, and shall determine the distance... capable of dynamically controlling inertia load during the US06 test cycle as a function of a vehicle... equal to eight seconds, the test inertia load may be adjusted during any of five EPA specified...

40 CFR 86.108-00 - Dynamometer.

Code of Federal Regulations, 2013 CFR

2013-07-01

... load force and inertia specified for the vehicle being tested, and shall determine the distance... capable of dynamically controlling inertia load during the US06 test cycle as a function of a vehicle... equal to eight seconds, the test inertia load may be adjusted during any of five EPA specified...

40 CFR 86.108-00 - Dynamometer.

Code of Federal Regulations, 2014 CFR

2014-07-01

... load force and inertia specified for the vehicle being tested, and shall determine the distance... capable of dynamically controlling inertia load during the US06 test cycle as a function of a vehicle... equal to eight seconds, the test inertia load may be adjusted during any of five EPA specified...

40 CFR 86.108-00 - Dynamometer.

Code of Federal Regulations, 2012 CFR

2012-07-01

... load force and inertia specified for the vehicle being tested, and shall determine the distance... capable of dynamically controlling inertia load during the US06 test cycle as a function of a vehicle... equal to eight seconds, the test inertia load may be adjusted during any of five EPA specified...

The influence of loading frequency on the high-temperature fatigue behavior of a Nicalon-fabric-reinforced polymer-derived ceramic-matrix composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vanswijgenhoven, E.; Holmes, J.; Wevers, M.

Fiber-reinforced ceramic-matrix composites are under development for high-temperature structural applications. These applications involve fatigue loading under a wide range of frequencies. To date, high-temperature fatigue experiments have typically been performed at loading frequencies of 10 Hz or lower. At higher frequencies, a strong effect of loading frequency on fatigue life has been demonstrated for certain CMC`s tested at room temperature. The fatigue life of CMC`s with weak fiber-matrix interfaces typically decreases as the loading frequency increases. This decrease is attributed to frictional heating and frequency dependent interface and fiber damage. More recently, it has been shown that the room temperaturemore » fatigue life of a Nicalon-fabric-reinforced composite with a strong interface (SYLRAMIC{trademark}) appears to be independent of loading frequency. The high-temperature low-frequency fatigue behavior of the SYLRAMIC composite has also been investigated. For a fatigue peak stress {sigma}{sub peak} above a proportional limit stress of 70 MPa, the number of cycles to failure N{sub f} decreased with an increase in {sigma}{sub peak}. The material endured more than 10{sup 6} cycles for {sigma}{sub peak} below 70 MPa. In this paper, the influence of loading frequency on the high-temperature fatigue behavior of the SYLRAMIC composite is reported. It will be shown that the fatigue limit is unaffected by the loading frequency, that the number of fatigue cycles to failure N{sub f} increases with an increase in frequency, and that the time to failure t{sub f} decreases with an increase in frequency.« less

Fracture load of ceramic restorations after fatigue loading.

PubMed

Baladhandayutham, Balasudha; Lawson, Nathaniel C; Burgess, John O

2015-08-01

A clinician must decide what ceramic coping and veneer material to prescribe based on the amount of tooth reduction possible and the desired esthetic outcome of the restoration. The purpose of this in vitro study was to compare the fracture strength of monolithic and bilayered lithium disilicate (IPS e.max) and zirconia (LAVA) crowns at clinically relevant thicknesses after load cycling. Crowns (n=8) were fabricated from 6 groups: 1.2-mm monolithic lithium disilicate, 1.5-mm monolithic lithium disilicate, 1.5-mm bilayered lithium disilicate with hand-layered veneer, 0.6 mm monolithic zirconia, 1.2-mm bilayered zirconia with hand-layered veneer, and 1.2-mm bilayered zirconia with milled veneer (dimension represents thickness at the occlusal pit). Crowns were cemented to identical milled resin dies with resin-modified glass ionomer cement. Cemented crowns were stored at 37°C for 24 hours and load cycled for 200,000 cycles at 25 N at a rate of 40 cycles/minute. The ultimate fracture load for each specimen was measured in a universal testing machine. Data were analyzed with a 1-way ANOVA and Tukey honest significant difference post hoc analysis (α=.05). Mean ±SD fracture load values were 1465 ±330 N for monolithic lithium disilicate (1.2-mm thickness) and 2027 ±365 N (1.5-mm thickness) and 1732 ±315 N for bilayered hand-veneered lithium disilicate (1.5-mm thickness). Fracture loads were 1669 ±311 N for monolithic zirconia crowns (0.6mm thickness), 2625 ±300 N for zirconia milled-veneered (1.2-mm thickness), and 2655 ±590N for zirconia hand-veneered crowns (1.2mm thickness). One-way ANOVA showed a statistically significant difference among the groups (P<.01). Veneered zirconia crowns showed the highest fracture strength, 1.2-mm hand veneered zirconia was similar to that of 1.5-mm monolithic zirconia, and all other groups were not statistically different. Crowns of 1.2-mm bilayered zirconia had higher fracture loads than 0.6-mm zirconia or 1.2-mm lithium disilicate monolithic crowns. Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Fatigue life prediction of liquid rocket engine combustor with subscale test verification

NASA Astrophysics Data System (ADS)

Sung, In-Kyung

Reusable rocket systems such as the Space Shuttle introduced a new era in propulsion system design for economic feasibility. Practical reusable systems require an order of magnitude increase in life. To achieve this improved methods are needed to assess failure mechanisms and to predict life cycles of rocket combustor. A general goal of the research was to demonstrate the use of subscale rocket combustor prototype in a cost-effective test program. Life limiting factors and metal behaviors under repeated loads were surveyed and reviewed. The life prediction theories are presented, with an emphasis on studies that used subscale test hardware for model validation. From this review, low cycle fatigue (LCF) and creep-fatigue interaction (ratcheting) were identified as the main life limiting factors of the combustor. Several life prediction methods such as conventional and advanced viscoplastic models were used to predict life cycle due to low cycle thermal stress, transient effects, and creep rupture damage. Creep-fatigue interaction and cyclic hardening were also investigated. A prediction method based on 2D beam theory was modified using 3D plate deformation theory to provide an extended prediction method. For experimental validation two small scale annular plug nozzle thrusters were designed, built and tested. The test article was composed of a water-cooled liner, plug annular nozzle and 200 psia precombustor that used decomposed hydrogen peroxide as the oxidizer and JP-8 as the fuel. The first combustor was tested cyclically at the Advanced Propellants and Combustion Laboratory at Purdue University. Testing was stopped after 140 cycles due to an unpredicted failure mechanism due to an increasing hot spot in the location where failure was predicted. A second combustor was designed to avoid the previous failure, however, it was over pressurized and deformed beyond repair during cold-flow test. The test results are discussed and compared to the analytical and numerical predictions. A detailed comparison was not performed, however, due to the lack of test data resulting from a failure of the test article. Some theoretical and experimental aspects such as fin effect and round corner were found to reduce the discrepancy between prediction and test results.

Anaerobic cycling performance characteristics in prepubescent, adolescent and young adult females.

PubMed

Doré, E; Bedu, M; França, N M; Van Praagh, E

2001-05-01

The purpose of this study was to determine whether the relationships between short-term power and body dimensions in young females were similar whatever the age of the individuals. A cohort of 189 prepubescent (mean age 9.5 years), adolescent (mean age 14.4 years) and young adult (mean age 18.2 years) females performed three all-out sprints on a friction-loaded cycle ergometer against three braking forces corresponding to applied loads of 25, 50 and 75 g.kg-1 body mass (BM). For each sprint, peak power including flywheel inertia was calculated. Results showed that a braking load of 75 g.kg-1 BM was too high for prepubescent and adolescent girls. Therefore, when measuring short-term cycling performance in heterogeneous female populations, a braking load of 50 g.kg-1 BM (0.495 N.kg-1 BM) is recommended. During growth, cycling peak power (CPP; defined as the highest peak power obtained during the three sprints) increased, as did total BM, fat-free mass (FFM) and lean leg volume (LLV) (P < 0.001). Analysis of covariance revealed that the slopes of the linear relationships between CPP and biometric characteristics were similar in the three groups (P > 0.7 for the CPP/BM and CPP/FFM relationships, and P > 0.2 for the CPP/LLV relationship). However, the adjusted means were always significantly higher in young women (P < 0.001) compared with both of the other groups. Although differences in performance during anaerobic cycling in growing females are primarily dependent upon body dimensions, other as yet undetermined factors may be involved during late adolescence.

Ultrasonic Monitoring of Ply Crack and Delamination Formation in Composite Tube Under Torsion Load

NASA Technical Reports Server (NTRS)

Johnston, P. H.; Wright, C. W.; Zalameda, J. N.; Seebo, J. P.

2010-01-01

As a simple model of a rotor spar, a circular graphite-epoxy composite laminate cylinder was subjected to cyclic torsional load. The test section of the cylindrical specimen varied from four to six plies of plus or minus 45 degree fibers, due to intentional ply overlaps and gaps. A layer of 13-micrometer Teflon film was inserted between plies at three locations to serve as delamination initiators. A commercial X-Y scanner was mounted to the load frame to enable ultrasonic inspection without removing the specimen. A focused immersion probe was mounted in a captive water column with a rugged Nitrile membrane tip, which was coupled to the cylinder using a mist of soapy water. The transducer was aligned normal to the cylinder surface using the X-axis. Scanning was performed along the length of the specimen with the Y-axis and the specimen was incrementally rotated by the torsion head of the load frame. After 350k cycles of torsion, several linear 45 degree diagonal indications appeared as 5-40% attenuation of the back wall echo, with no apparent echoes from the interior of the composite, suggesting through-ply cracks in the innermost ply. Crack indications grew and new cracks appeared as torsion cycling continued. Internal reflections from delaminations associated with the growing ply cracks appeared after 500k cycles. Three areas of extensive multi-layer delaminations appeared after 1150k cycles. Failure of the specimen occurred at 1600k cycles. The observed progressive damage was not associated with the Teflon inclusions. Concurrent thermographic measurements provided lower resolution confirmation of the damage observed.

A biomechanical comparison of 2 techniques of footprint reconstruction for rotator cuff repair: the SwiveLock-FiberChain construct versus standard double-row repair.

PubMed

Burkhart, Stephen S; Adams, Christopher R; Burkhart, Sarah S; Schoolfield, John D

2009-03-01

The purpose of this study was to compare the biomechanical fixation parameters of a standard double-row rotator cuff repair with those of a knotless footprint reconstruction using the double-row SwiveLock-FiberChain technique (Arthrex, Naples, FL). Seven matched pairs of human cadaveric shoulders were used for testing (mean age, 48 +/- 10.3 years). A shoulder from each matched pair was randomly selected to receive a standard 4-anchor double-row repair of the supraspinatus tendon, and the contralateral shoulder received a 4-anchor double-row SwiveLock-FiberChain repair. The tendon was cycled from 10 N to 100 N at 1 Hz for 500 cycles, followed by a single-cycle pull to failure at 33 mm/s. Yield load, ultimate load, cyclic displacement, and mode of failure were recorded. Yield load and ultimate load were higher for the SwiveLock-FiberChain repair compared with the standard double-row repair for 6 of the 7 treatment pairs; however, 1 cadaver had a contrary outcome, so the overall mean differences in yield load and ultimate load were not significantly different from 0 by Student t test (P > .15). Furthermore, smaller differences between yield load and ultimate load for the SwiveLock-FiberChain repair in 5 of the 7 treatment pairs showed a self-reinforcing mechanism. Double-row footprint reconstruction with the knotless SwiveLock-FiberChain system in this study had yield loads, ultimate loads, and cyclic displacements that were statistically equivalent to those of standard double-row rotation cuff reconstructions. The SwiveLock-FiberChain system's combination of strength, self-reinforcement, and decreased operating time may offer advantages to the surgeon, particularly when dealing with older patients in whom poor tissue quality and total operative time are important considerations.

In vitro mechanical fatigue behavior of poly-ɛ-caprolactone macroporous scaffolds for cartilage tissue engineering: Influence of pore filling by a poly(vinyl alcohol) gel.

PubMed

Panadero, J A; Vikingsson, L; Gomez Ribelles, J L; Lanceros-Mendez, S; Sencadas, V

2015-07-01

Polymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and submitted to repeated loading cycles. In the case of articular cartilage engineering, an implanted scaffold is typically subjected to long-term dynamic compression. The evolution of the mechanical properties of the scaffold during bioresorption has been deeply studied in the past, but the possibility of failure due to mechanical fatigue has not been properly addressed. Nevertheless, the macroporous scaffold is susceptible to failure after repeated loading-unloading cycles. In this work fatigue studies of polycaprolactone scaffolds were carried by subjecting the scaffold to repeated compression cycles in conditions simulating the scaffold implanted in the articular cartilage. The behavior of the polycaprolactone sponge with the pores filled with a poly(vinyl alcohol) gel simulating the new formed tissue within the pores was compared with that of the material immersed in water. Results were analyzed with Morrow's criteria for failure and accurate fittings are obtained just up to 200 loading cycles. It is also shown that the presence of poly(vinyl alcohol) increases the elastic modulus of the scaffolds, the effect being more pronounced with increasing the number of freeze/thawing cycles. © 2014 Wiley Periodicals, Inc.

Crack Detection Using Combinations of Acoustic Emission and Guided Wave Signals from Bonded Piezoelectric Transducers

DTIC Science & Technology

2011-09-01

and bond integrity. Lastly, the PZT transducers are also utilized to track the lower frequency mechanical strains created during fatigue loading...face of the coupon and on either side of the gage section. Each coupon undergoes cyclic tensile loading to initiate and grow fatigue cracks. At...various intervals, the fatigue cycling is paused and the coupon is visually inspected for crack initiation and growth. While the cycling is paused

Primary and secondary use of electric mobility batteries from a life cycle perspective

NASA Astrophysics Data System (ADS)

Faria, Ricardo; Marques, Pedro; Garcia, Rita; Moura, Pedro; Freire, Fausto; Delgado, Joaquim; de Almeida, Aníbal T.

2014-09-01

With age and cycling, batteries used in Electric Vehicles (EVs) will reach a point in which they will no longer be suitable for electric mobility; however, they still can be used in stationary energy storage. This article aims at assessing the Life-Cycle (LC) environmental impacts associated with the use of a battery in an EV and secondly, at assessing the LC environmental impacts/benefits of using a battery, no longer suitable for electric mobility, for energy storage in a household. Three electricity mixes with different shares of renewable, nuclear and fossil energy sources are considered. For the primary battery use, three in-vehicle use scenarios are assessed, addressing three different driving profiles. For the secondary use, two scenarios of energy storage strategies are analyzed: peak shaving and load shifting. Results show that a light use of the battery in the EV has 42-50% less impacts per km than an intensive use. After its use in the vehicle, the battery life can be extended by 1.8-3.3 years; however, this is not always beneficial from an environmental point of view, since the impacts are strongly dependent on the electricity generation mix and on the additional efficiency losses in the battery.

Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns.

PubMed

Mitov, Gergo; Anastassova-Yoshida, Yana; Nothdurft, Frank Phillip; von See, Constantin; Pospiech, Peter

2016-02-01

The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method. An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃-55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture. The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly. The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns.

Effects of mechanical and thermal cycling on composite and hybrid laminates with residual stresses

NASA Technical Reports Server (NTRS)

Daniel, I. M.; Liber, T.

1977-01-01

The effects of tensile load cycling and thermal cycling on residual stiffness and strength properties of the following composite and hybrid angle-ply laminates were studied: boron/epoxy, boron/polyimide, graphite/low-modulus epoxy, graphite/high-modulus epoxy, graphite/polyimide, S-glass/epoxy, graphite/Kevlar 49/epoxy, and graphite/S-glass/epoxy. Specimens of the first six types were mechanically cycled up to 90% of static strength. Those that survived 10 million cycles were tested statically to failure, and no significant changes in residual strength and modulus were noted. Specimens of all types were subjected to thermal cycling between room temperature and 411 K for the epoxy-matrix composites and 533 K for the polyimide-matrix composites. The residual strength and stiffness remained largely unchanged, except for the graphite/low-modulus epoxy, which showed reductions in both of approximately 35%. When low-temperature thermal cycling under tensile load was applied, there was a noticeable reduction in modulus and strength in the graphite/low-modulus epoxy and some strength reduction in the S-glass/epoxy.

Simulating Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi

NASA Technical Reports Server (NTRS)

Manchiraju, Sivom; Gaydosh, Darrell J.; Noebe, Ronald D.; Anderson, Peter M.

2011-01-01

A microstructure-based FEM model that couples crystal plasticity, crystallographic descriptions of the B2-B19' martensitic phase transformation, and anisotropic elasticity is used to simulate thermal cycling and isothermal deformation in polycrystalline NiTi (49.9at% Ni). The model inputs include anisotropic elastic properties, polycrystalline texture, DSC data, and a subset of isothermal deformation and load-biased thermal cycling data. A key experimental trend is captured.namely, the transformation strain during thermal cycling is predicted to reach a peak with increasing bias stress, due to the onset of plasticity at larger bias stress. Plasticity induces internal stress that affects both thermal cycling and isothermal deformation responses. Affected thermal cycling features include hysteretic width, two-way shape memory effect, and evolution of texture with increasing bias stress. Affected isothermal deformation features include increased hardening during loading and retained martensite after unloading. These trends are not captured by microstructural models that lack plasticity, nor are they all captured in a robust manner by phenomenological approaches. Despite this advance in microstructural modeling, quantitative differences exist, such as underprediction of open loop strain during thermal cycling.

10 CFR Appendix C to Subpart B of... - Uniform Test Method for Measuring the Energy Consumption of Dishwashers

Code of Federal Regulations, 2013 CFR

2013-01-01

....8Preconditioning cycle means any cycle that includes a fill, circulation, and drain to ensure that the water lines... cycle without a test load if the dishwasher does not heat water in the normal cycle. 2.6.2Non-soil... cycle. 3.4Water pressure gauge. The water pressure gauge must have a resolution of one pound per square...

Modifying Operating Cycles to Increase Stability in a LITS

NASA Technical Reports Server (NTRS)

Burt, Eric; Tjoelker, Robert

2009-01-01

The short-term instability in the frequency of a linear-ion-trap frequency standard (LITS) can be reduced by modifying two cycles involved in its operation: (1) the bimodal (bright/dim) cycle of a plasma discharge lamp used for state preparation and detection and (2) a microwave-interrogation cycle. The purpose and effect of the modifications is to enable an increase in the microwave- interrogation cycle time, motivated by the general principle that the short-term uncertainty or instability decreases with increasing microwave-interrogation time. Stated from a slightly different perspective, the effect of modifications is to enable the averaged LITS readings to settle to their longterm stability over a shorter total observation time. The basic principles of a LITS were discussed in several NASA Tech Briefs articles. Here are recapitulated only those items of background information necessary to place the present modifications in context. A LITS includes a microwave local oscillator, the frequency of which is stabilized by comparison with the frequency of a ground-state hyperfine transition of Hg-199(+) ions. In a LITS of the type to which the modifications apply, the comparison involves a combination of optical and micro wave excitation and interrogation of the ions in two collinear ion traps: a quadrupole trap wherein the optical excitation used for state preparation and detection takes place, and a multipole (e.g., 12-pole) trap wherein the microwave interrogation of the clock transition takes place. The ions are initially loaded into the quadrupole trap and are thereafter shuttled between the two traps. This concludes the background information.

Verification of rain-flow reconstructions of a variable amplitude load history. M.S. Thesis, 1990 Final Report

NASA Technical Reports Server (NTRS)

Clothiaux, John D.; Dowling, Norman E.

1992-01-01

The suitability of using rain-flow reconstructions as an alternative to an original loading spectrum for component fatigue life testing is investigated. A modified helicopter maneuver history is used for the rain-flow cycle counting and history regenerations. Experimental testing on a notched test specimen over a wide range of loads produces similar lives for the original history and the reconstructions. The test lives also agree with a simplified local strain analysis performed on the specimen utilizing the rain-flow cycle count. The rain-flow reconstruction technique is shown to be a viable test spectrum alternative to storing the complete original load history, especially in saving computer storage space and processing time. A description of the regeneration method, the simplified life prediction analysis, and the experimental methods are included in the investigation.

Structures Division

NASA Technical Reports Server (NTRS)

1997-01-01

The NASA Lewis Research Center Structures Division is an international leader and pioneer in developing new structural analysis, life prediction, and failure analysis related to rotating machinery and more specifically to hot section components in air-breathing aircraft engines and spacecraft propulsion systems. The research consists of both deterministic and probabilistic methodology. Studies include, but are not limited to, high-cycle and low-cycle fatigue as well as material creep. Studies of structural failure are at both the micro- and macrolevels. Nondestructive evaluation methods related to structural reliability are developed, applied, and evaluated. Materials from which structural components are made, studied, and tested are monolithics and metal-matrix, polymer-matrix, and ceramic-matrix composites. Aeroelastic models are developed and used to determine the cyclic loading and life of fan and turbine blades. Life models are developed and tested for bearings, seals, and other mechanical components, such as magnetic suspensions. Results of these studies are published in NASA technical papers and reference publication as well as in technical society journal articles. The results of the work of the Structures Division and the bibliography of its publications for calendar year 1995 are presented.

Structures Division 1994 Annual Report

NASA Technical Reports Server (NTRS)

1996-01-01

The NASA Lewis Research Center Structures Division is an international leader and pioneer in developing new structural analysis, life prediction, and failure analysis related to rotating machinery and more specifically to hot section components in air-breathing aircraft engines and spacecraft propulsion systems. The research consists of both deterministic and probabilistic methodology. Studies include, but are not limited to, high-cycle and low-cycle fatigue as well as material creep. Studies of structural failure are at both the micro- and macrolevels. Nondestructive evaluation methods related to structural reliability are developed, applied, and evaluated. Materials from which structural components are made, studied, and tested are monolithics and metal-matrix, polymer-matrix, and ceramic-matrix composites. Aeroelastic models are developed and used to determine the cyclic loading and life of fan and turbine blades. Life models are developed and tested for bearings, seals, and other mechanical components, such as magnetic suspensions. Results of these studies are published in NASA technical papers and reference publication as well as in technical society journal articles. The results of the work of the Structures Division and the bibliography of its publications for calendar year 1994 are presented.

Effects of artificial aging conditions on yttria-stabilized zirconia implant abutments.

PubMed

Basílio, Mariana de Almeida; Cardoso, Kátia Vieira; Antonio, Selma Gutierrez; Rizkalla, Amin Sami; Santos Junior, Gildo Coelho; Arioli Filho, João Neudenir

2016-08-01

Most ceramic abutments are fabricated from yttria-stabilized tetragonal zirconia (Y-TZP). However, Y-TZP undergoes hydrothermal degradation, a process that is not well understood. The purpose of this in vitro study was to assess the effects of artificial aging conditions on the fracture load, phase stability, and surface microstructure of a Y-TZP abutment. Thirty-two prefabricated Y-TZP abutments were screwed and tightened down to external hexagon implants and divided into 4 groups (n = 8): C, control; MC, mechanical cycling (1×10(6) cycles; 10 Hz); AUT, autoclaving (134°C; 5 hours; 0.2 MPa); and TC, thermal cycling (10(4) cycles; 5°/55°C). A single-load-to-fracture test was performed at a crosshead speed of 0.5 mm/min to assess the assembly's resistance to fracture (ISO Norm 14801). X-ray diffraction (XRD) analysis was applied to observe and quantify the tetragonal-monoclinic (t-m) phase transformation. Representative abutments were examined with high-resolution scanning electron microscopy (SEM) to observe the surface characteristics of the abutments. Load-to-fracture test results (N) were compared by ANOVA and Tukey test (α=.05). XRD measurements revealed the monoclinic phase in some abutments after each aging condition. All the aging conditions reduced the fracture load significantly (P<.001). Mechanical cycling reduced the fracture load more than autoclaving (P=.034). No differences were found in the process of surface degradation among the groups; however, the SEM detected grinding-induced surface flaws and microcracks. The resistance to fracture and the phase stability of Y-TZP implant abutments were susceptible to hydrothermal and mechanical conditions. The surface microstructure of Y-TZP abutments did not change after aging conditions. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Influence of the height of the external hexagon and surface treatment on fatigue life of commercially pure titanium dental implants.

PubMed

Gil, Francisco Javier; Aparicio, Conrado; Manero, Jose M; Padros, Alejandro

2009-01-01

This study evaluated the effect of external hexagon height and commonly applied surface treatments on the fatigue life of titanium dental implants. Electropolished commercially pure titanium dental implants (seven implants per group) with three different external hexagon heights (0.6, 1.2, and 1.8 mm) and implants with the highest external hexagon height (1.8 mm) and different surface treatments (electropolishing, grit blasting with aluminium oxide, and acid etching with sulfuric acid) were tested to evaluate their mechanical fatigue life. To do so, 10-Hz triangular flexural load cycles were applied at 37 degrees C in artificial saliva, and the number of load cycles until implant fracture was determined. Tolerances of the hexagon/abutment fit and implant surface roughness were analyzed by scanning electron microscopy and light interferometry. Transmission electron microscopy and electron diffraction analyses of titanium hydrides were performed. First, the fatigue life of implants with the highest hexagon (8,683 +/- 978 load cycles) was more than double that of the implants with the shortest hexagons (3,654 +/- 789 load cycles) (P < .02). Second, the grit-blasted implants had the longest fatigue life of the tested materials (21,393 +/- 2,356 load cycles), which was significantly greater than that of the other surfaces (P < .001). The compressive surface residual stresses induced when blasting titanium are responsible for this superior mechanical response. Third, precipitation of titanium hydrides in grain boundaries of titanium caused by hydrogen adsorption from the acid solution deteriorates the fatigue life of acid-etched titanium dental implants. These implants had the shortest fatigue life (P < .05). The fatigue life of threaded root-form dental implants varies with the height of the external hexagon and/or the surface treatment of the implant. An external hexagon height of 1.8 mm and/or a blasting treatment appear to significantly increase fatigue life of dental implants.

Analysis of a Hybrid Wing Body Center Section Test Article

NASA Technical Reports Server (NTRS)

Wu, Hsi-Yung T.; Shaw, Peter; Przekop, Adam

2013-01-01

The hybrid wing body center section test article is an all-composite structure made of crown, floor, keel, bulkhead, and rib panels utilizing the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) design concept. The primary goal of this test article is to prove that PRSEUS components are capable of carrying combined loads that are representative of a hybrid wing body pressure cabin design regime. This paper summarizes the analytical approach, analysis results, and failure predictions of the test article. A global finite element model of composite panels, metallic fittings, mechanical fasteners, and the Combined Loads Test System (COLTS) test fixture was used to conduct linear structural strength and stability analyses to validate the specimen under the most critical combination of bending and pressure loading conditions found in the hybrid wing body pressure cabin. Local detail analyses were also performed at locations with high stress concentrations, at Tee-cap noodle interfaces with surrounding laminates, and at fastener locations with high bearing/bypass loads. Failure predictions for different composite and metallic failure modes were made, and nonlinear analyses were also performed to study the structural response of the test article under combined bending and pressure loading. This large-scale specimen test will be conducted at the COLTS facility at the NASA Langley Research Center.

Fatigue Failure in Extra-Articular Proximal Tibia Fractures: Locking Intramedullary Nail Versus Double Locking Plates-A Biomechanical Study.

PubMed

Kandemir, Utku; Herfat, Safa; Herzog, Mary; Viscogliosi, Paul; Pekmezci, Murat

2017-02-01

The goal of this study is to compare the fatigue strength of a locking intramedullary nail (LN) construct with a double locking plate (DLP) construct in comminuted proximal extra-articular tibia fractures. Eight pairs of fresh frozen cadaveric tibias with low bone mineral density [age: 80 ± 7 (SD) years, T-score: -2.3 ± 1.2] were used. One tibia from each pair was fixed with LN, whereas the contralateral side was fixed with DLP for complex extra-articular multifragmentary metaphyseal fractures (simulating OTA 41-A3.3). Specimens were cyclically loaded under compression simulating single-leg stance by staircase method out to 260,000 cycles. Every 2500 cycles, localized gap displacements were measured with a 3D motion tracking system, and x-ray images of the proximal tibia were acquired. To allow for mechanical settling, initial metrics were calculated at 2500 cycles. The 2 groups were compared regarding initial construct stiffness, initial medial and lateral gap displacements, stiffness at 30,000 cycles, medial and lateral gap displacements at 30,000 cycles, failure load, number of cycles to failure, and failure mode. Failure metrics were reported for initial and catastrophic failures. DLP constructs exhibited higher initial stiffness and stiffness at 30,000 cycles compared with LN constructs (P < 0.03). There were no significant differences between groups for loads at failure or cycles to failure. For the fixation of extra-articular proximal tibia fractures, a LN provides a similar fatigue performance to double locked plates. The locked nail could be safely used for fixation of proximal tibia fractures with the advantage of limited extramedullary soft tissue damage.

Reactivity-controlled compression ignition drive cycle emissions and fuel economy estimations using vehicle system simulations

DOE PAGES

Curran, Scott J.; Gao, Zhiming; Wagner, Robert M.

2014-12-22

In-cylinder blending of gasoline and diesel to achieve reactivity-controlled compression ignition has been shown to reduce NO X and soot emissions while maintaining or improving brake thermal efficiency as compared with conventional diesel combustion. The reactivity-controlled compression ignition concept has an advantage over many advanced combustion strategies in that the fuel reactivity can be tailored to the engine speed and load, allowing stable low-temperature combustion to be extended over more of the light-duty drive cycle load range. In this paper, a multi-mode reactivity-controlled compression ignition strategy is employed where the engine switches from reactivity-controlled compression ignition to conventional diesel combustionmore » when speed and load demand are outside of the experimentally determined reactivity-controlled compression ignition range. The potential for reactivity-controlled compression ignition to reduce drive cycle fuel economy and emissions is not clearly understood and is explored here by simulating the fuel economy and emissions for a multi-mode reactivity-controlled compression ignition–enabled vehicle operating over a variety of US drive cycles using experimental engine maps for multi-mode reactivity-controlled compression ignition, conventional diesel combustion, and a 2009 port-fuel injected gasoline engine. Drive cycle simulations are completed assuming a conventional mid-size passenger vehicle with an automatic transmission. Multi-mode reactivity-controlled compression ignition fuel economy simulation results are compared with the same vehicle powered by a representative 2009 port-fuel injected gasoline engine over multiple drive cycles. Finally, engine-out drive cycle emissions are compared with conventional diesel combustion, and observations regarding relative gasoline and diesel tank sizes needed for the various drive cycles are also summarized.« less

Present-day secular variations in the zonal harmonics of earth's geopotential

NASA Technical Reports Server (NTRS)

Mitrovica, J. X.; Peltier, W. R.

1993-01-01

The mathematical formulation required for predicting secular variation in the geopotential is developed for the case of a spherically symmetric, self-gravitating, viscoelastic earth model and an arbitrary surface load which can include a gravitational self-consistent ocean loading component. The theory is specifically applied to predict the present-day secular variation in the zonal harmonics of the geopotenial arising from the surface mass loading associated with the late Pleistocene glacial cycles. A procedure is outlined in which predictions of the present-day geopotential signal due to the late Pleistocene glacial cycles may be used to derive bounds on the net present-day mass flux from the Antarctic and Greenland ice sheets to the local oceans.

Aerospace Structures Design on Computers

DTIC Science & Technology

1989-03-01

loud or lter’itr- strm C M~eort load or mex~murn load AMeon strews o,. strvss (Q) hm’nur loS1 (b) me -im (a) Fluctuating tension load cycle; (b...constraint deletion techniques in the struc- tural applications of nonlinear programming algorithms. The way this concept is used in the optimality criteria

In vitro comparison of fracture load of implant-supported, zirconia-based, porcelain- and composite-layered restorations after artificial aging.

PubMed

Komine, Futoshi; Taguchi, Kohei; Fushiki, Ryosuke; Kamio, Shingo; Iwasaki, Taro; Matsumura, Hideo

2014-01-01

This study evaluated fracture load of single-tooth, implant-supported, zirconia-based, porcelain- and indirect composite-layered restorations after artificial aging. Forty-four zirconia-based molar restorations were fabricated on implant abutments and divided into four groups, namely, zirconia-based all-ceramic restorations (ZAC group) and three types of zirconia-based composite-layered restorations (ZIC-P, ZIC-E, and ZIC groups). Before layering an indirect composite material, the zirconia copings in the ZIC-P and ZIC-E groups were primed with Clearfil Photo Bond and Estenia Opaque Primer, respectively. All restorations were cemented on the abutments with glass-ionomer cement and then subjected to thermal cycling and cyclic loading. All specimens survived thermal cycling and cyclic loading. The fracture load of the ZIC-P group (2.72 kN) was not significantly different from that of the ZAC group (3.05 kN). The fracture load of the zirconia-based composite-layered restoration primed with Clearfil Photo Bond (ZIC-P) was comparable to that of the zirconia-based all-ceramic restoration (ZAC) after artificial aging.

Influence of multi-cycle loading on the structure and mechanics of marine mussel plaques.

PubMed

Wilhelm, Menaka H; Filippidi, Emmanouela; Waite, J Herbert; Valentine, Megan T

2017-10-18

The proteinaceous byssal plaque-thread structures created by marine mussels exhibit extraordinary load-bearing capability. Although the nanoscopic protein interactions that support interfacial adhesion are increasingly understood, major mechanistic questions about how mussel plaques maintain toughness on supramolecular scales remain unanswered. This study explores the mechanical properties of whole mussel plaques subjected to repetitive loading cycles, with varied recovery times. Mechanical measurements were complemented with scanning electron microscopy to investigate strain-induced structural changes after yield. Multicyclic loading of plaques decreases their low-strain stiffness and introduces irreversible, strain-dependent plastic damage within the plaque microstructure. However, strain history does not compromise critical strength or maximum extension compared with plaques monotonically loaded to failure. These results suggest that a multiplicity of force transfer mechanisms between the thread and plaque-substrate interface allow the plaque-thread structure to accommodate a wide range of extensions as it continues to bear load. This improved understanding of the mussel system at micron-to-millimeter lengthscales offers strategies for including similar fail-safe mechanisms in the design of soft, tough and resilient synthetic structures.

Assessment of the behavior of reinforced concrete beams retrofitted with pre-stressed CFPR subjected to cyclic loading

NASA Astrophysics Data System (ADS)

Hojatkashani, Ata; Zanjani, Sara

2018-03-01

Rehabilitation of weak and damaged structures has been considered widely during recent years. A relatively modern way of strengthening concrete components is to confine parts under tension and shear by means of carbon fiber reinforce polymer (CFRP). This way of strengthening due to the conditions of composite materials such as light weight, linear elastic behavior until failure point, high tensile strength, high elastic modulus, resistance against corrosion, and high fatigue resistance has become so common. During structural strengthening by means of not pre-stressed FRP materials, usually, it is not possible to benefit from the maximum capacity of FRP materials. In addition, sometimes, the expensive cost of such materials will not make a suitable balance between rates of strengthening and consuming spending. Thus, pre-stressing CFRP materials has an undeniable role in the effective use of materials. In the current research, general procedure of simulation using finite-element method (FEM) by means of the numerical package ABAQUS has been presented. In this article, 12 reinforced concrete (RC) models in two states (strengthened with simple and pre-stressed CFRP) under cycling loading have been considered. A parametric study has been carried out in this research on the effects of parameters such as CFRP surface area, percentage of tensile steel rebar and pre-stressing stress on ultimate load carrying capacity (ULCC), stiffness, and the ability of depreciation energy for the samples. In the current article also, for design parameters, percentages of tensile steel rebars, surface area of CFPR sheets, and the effective pre-stressing stress in RC beams retrofitted with pre-stressed CFPR sheets have investigated. In this paper, it was investigated that using different amount of parameters such as steel rebar percentage, CFRP surface area percentage, and CFRP pre-stressing, the resulted ULCC and energy depreciation of the specimens was observed to be increasing and decreasing. Results from examined specimens with optimum steel rebar percentage, CFRP surface area percentage, and CFRP pre-stressing which had the most enhancement on ULCC and energy depreciation are reported in the current article.

Further Testing of an Amine-based Pressure-Swing System for Carbon Dioxide and Humidity Control

NASA Technical Reports Server (NTRS)

Lin, Amy; Smith, Frederick; Sweterlitsch, Jeffrey; Nalette, Tim A.; Papale, William

2008-01-01

In a crewed spacecraft environment, atmospheric carbon dioxide (CO2) and moisture control are crucial. Hamilton Sundstrand has developed a stable and efficient amine-based CO2 and water vapor sorbent, SA9T, that is well suited for use in a spacecraft environment. The sorbent is efficiently packaged in pressure-swing regenerable beds that are thermally linked to improve removal efficiency and minimize vehicle thermal loads. Flows are all controlled with a single spool valve. This technology has been baselined for the new Orion spacecraft. However, more data was needed on the operational characteristics of the package in a simulated spacecraft environment. A unit was therefore tested with simulated metabolic loads in a closed chamber at Johnson Space Center during the last third of 2006. Those test results were reported in a 2007 ICES paper. A second test article was incorporated for a third phase of testing, and that test article was modified to allow pressurized gas purge regeneration on the launch pad in addition to the standard vacuum regeneration in space. Metabolic rates and chamber volumes were also adjusted to reflect current programmatic standards. The third phase of tests was performed during the spring and summer of 2007. Tests were run with a range of operating conditions, varying: cycle time, vacuum pressure (or purge gas flow rate), air flow rate, and crew activity levels. Results of this testing are presented and potential flight operational strategies discussed.

Mechanical Behavior of Advanced Materials for Aerospace Applications

NASA Technical Reports Server (NTRS)

Telesman, Ignancy (Technical Monitor); Kantzos, Peter; Shannon, Brian

2003-01-01

The purpose of this study was to determine whether High Cycle Fatigue (HCF) loading has any deleterious synergistic effect on life when combined with the typical Low Cycle Fatigue (LCF) loading present in engine disks. This interaction is particularly important in the rim region of blisk applications, where fatigue initiations from vibratory stresses (HCF) may be propagated to the disk by LCF. The primary effort in this study was focused on determining and documenting initiation sites and damage mechanisms. Under LCF loading conditions the failures were predominantly surface initiated, while HCF loading favored internal initiations. Deleterious HCF/LCF interactions would always result in a transition from internal to surface initiations. The results indicated that under the relative stress conditions evaluated there was no interaction between HCF and LCF. In FY99 this effort was extended to investigate several other loading conditions (R-ratio effects) as well as interactions between LCF and two-hour tensile dwells. The results will be published as a NASA Technical Memorandum.

Testing of a Miniature Loop Heat Pipe with Multiple Evaporators and Multiple Condensers for Space Applications

NASA Technical Reports Server (NTRS)

Nagano, Hosei; Ku, Jentung

2006-01-01

Thermal performance of a miniature loop heat pipe (MLHP) with two evaporators and two condensers is described. A comprehensive test program, including start-up, high power, low power, power cycle, and sink temperature cycle tests, has been executed at NASA Goddard Space Flight Center for potential space applications. Experimental data showed that the loop could start with heat loads as low as 2W. The loop operated stably with even and uneven evaporator heat loads, and even and uneven condenser sink temperatures. Heat load sharing between the two evaporators was also successfully demonstrated. The loop had a heat transport capability of l00W to 120W, and could recover from a dry-out by reducing the heat load to evaporators. Low power test results showed the loop could work stably for heat loads as low as 1 W to each evaporator. Excellent adaptability of the MLHP to rapid changes of evaporator power and sink temperature were also demonstrated.

Phase Transformation Evolution in NiTi Shape Memory Alloy under Cyclic Nanoindentation Loadings at Dissimilar Rates

PubMed Central

Amini, Abbas; Cheng, Chun; Kan, Qianhua; Naebe, Minoo; Song, Haisheng

2013-01-01

Hysteresis energy decreased significantly as nanocrystalline NiTi shape memory alloy was under triangular cyclic nanoindentation loadings at high rate. Jagged curves evidenced discrete stress relaxations. With a large recovery state of maximum deformation in each cycle, this behavior concluded in several nucleation sites of phase transformation in stressed bulk. Additionally, the higher initial propagation velocity of interface and thermal activation volume, and higher levels of phase transition stress in subsequent cycles explained the monotonic decreasing trend of dissipated energy. In contrast, the dissipated energy showed an opposite increasing trend during triangular cyclic loadings at a low rate and 60 sec holding time after each unloading stage. Due to the isothermal loading rate and the holding time, a major part of the released latent heat was transferred during the cyclic loading resulting in an unchanged phase transition stress. This fact with the reorientation phenomenon explained the monotonic increasing trend of hysteresis energy. PMID:24336228

Stand-alone flat-plate photovoltaic power systems: System sizing and life-cycle costing methodology for Federal agencies

NASA Technical Reports Server (NTRS)

Borden, C. S.; Volkmer, K.; Cochrane, E. H.; Lawson, A. C.

1984-01-01

A simple methodology to estimate photovoltaic system size and life-cycle costs in stand-alone applications is presented. It is designed to assist engineers at Government agencies in determining the feasibility of using small stand-alone photovoltaic systems to supply ac or dc power to the load. Photovoltaic system design considerations are presented as well as the equations for sizing the flat-plate array and the battery storage to meet the required load. Cost effectiveness of a candidate photovoltaic system is based on comparison with the life-cycle cost of alternative systems. Examples of alternative systems addressed are batteries, diesel generators, the utility grid, and other renewable energy systems.

High-Frequency ac Power-Distribution System

NASA Technical Reports Server (NTRS)

Hansen, Irving G.; Mildice, James

1987-01-01

Loads managed automatically under cycle-by-cycle control. 440-V rms, 20-kHz ac power system developed. System flexible, versatile, and "transparent" to user equipment, while maintaining high efficiency and low weight. Electrical source, from dc to 2,200-Hz ac converted to 440-V rms, 20-kHz, single-phase ac. Power distributed through low-inductance cables. Output power either dc or variable ac. Energy transferred per cycle reduced by factor of 50. Number of parts reduced by factor of about 5 and power loss reduced by two-thirds. Factors result in increased reliability and reduced costs. Used in any power-distribution system requiring high efficiency, high reliability, low weight, and flexibility to handle variety of sources and loads.

On rate-dependent polycrystal deformation: the temperature sensitivity of cold dwell fatigue

PubMed Central

Zhang, Zhen; Cuddihy, M. A.; Dunne, F. P. E.

2015-01-01

A temperature and rate-dependent crystal plasticity framework has been used to examine the temperature sensitivity of stress relaxation, creep and load shedding in model Ti-6Al polycrystal behaviour under dwell fatigue conditions. A temperature close to 120°C is found to lead to the strongest stress redistribution and load shedding, resulting from the coupling between crystallographic slip rate and slip system dislocation hardening. For temperatures in excess of about 230°C, grain-level load shedding from soft to hard grains diminishes because of the more rapid stress relaxation, leading ultimately to the diminution of the load shedding and hence, it is argued, the elimination of the dwell debit. Under conditions of cyclic stress dwell, at temperatures between 20°C and 230°C for which load shedding occurs, the rate-dependent accumulation of local slip by ratcheting is shown to lead to the progressive cycle-by-cycle redistribution of stress from soft to hard grains. This phenomenon is termed cyclic load shedding since it also depends on the material's creep response, but develops over and above the well-known dwell load shedding, thus providing an additional rationale for the incubation of facet nucleation. PMID:26528078

Markov model of fatigue of a composite material with the poisson process of defect initiation

NASA Astrophysics Data System (ADS)

Paramonov, Yu.; Chatys, R.; Andersons, J.; Kleinhofs, M.

2012-05-01

As a development of the model where only one weak microvolume (WMV) and only a pulsating cyclic loading are considered, in the current version of the model, we take into account the presence of several weak sites where fatigue damage can accumulate and a loading with an arbitrary (but positive) stress ratio. The Poisson process of initiation of WMVs is considered, whose rate depends on the size of a specimen. The cumulative distribution function (cdf) of the fatigue life of every individual WMV is calculated using the Markov model of fatigue. For the case where this function is approximated by a lognormal distribution, a formula for calculating the cdf of fatigue life of the specimen (modeled as a chain of WMVs) is obtained. Only a pulsating cyclic loading was considered in the previous version of the model. Now, using the modified energy method, a loading cycle with an arbitrary stress ratio is "transformed" into an equivalent cycle with some other stress ratio. In such a way, the entire probabilistic fatigue diagram for any stress ratio with a positive cycle stress can be obtained. Numerical examples are presented.

The Rehbinder effect in iron during giga-cycle fatigue loading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bannikov, M. V., E-mail: mbannikov@icmm.ru; Naimark, O. B.

The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. Themore » mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant.« less

The Rehbinder effect in iron during giga-cycle fatigue loading

NASA Astrophysics Data System (ADS)

Bannikov, M. V.; Naimark, O. B.

2015-10-01

The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. The mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant.

Temporal variations and scaling of streamflow and baseflow and their nitrate-nitrogen concentrations and loads

USGS Publications Warehouse

Zhang, Y.-K.; Schilling, K.

2005-01-01

The patterns of temporal variations of precipitation (P), streamflow (SF) and baseflow (BF) as well as their nitrate-nitrogen (nitrate) concentrations (C) and loads (L) from a long-term record (28 years) in the Raccoon River, Iowa, were analyzed using variogram and spectral analyses. The daily P is random but scaling may exist in the daily SF and BF with a possible break point in the scaling at about 18 days and 45 days, respectively. The nitrate concentrations and loads are shown to have a half-year cycle while daily P, SF, and BF have a one-year cycle. Furthermore, there may be a low-frequency cycle of 6-8 years in C. The power spectra of C and L in both SF and BF exhibit fractal 1/f scaling with two characteristic frequencies of half-year and one-year, and are fitted well with the spectrum of the gamma distribution. The nitrate input to SF and BF at the Raccoon watershed seems likely to be a white noise process superimposed on another process with a half-year and one-year cycle. ?? 2005 Elsevier Ltd. All rights reserved.

Rational Design of High-Loading Sulfur Cathodes with a Poached-Egg-Shaped Architecture for Long-Cycle Lithium–Sulfur Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Liu; Manthiram, Arumugam

A high-loading electrode is essential for establishing high-energy-density lithium-sulfur (Li-S) batteries, but it is confronted with critical challenges. Here in this paper, we present a freestanding poached-egg-shaped architecture through a facile template supported vacuum-filtration strategy and employ it as an efficient sulfur host for Li-S batteries. This unique architecture guarantees an effective encapsulation of the “sulfur yolk” inside the fully vacuum sealed framework, effectively limiting the active material loss and polysulfide diffusion. Also, the conductive and porous framework serves as an interlinked electron pathway and electrolyte channel, greatly facilitating fast electric/ionic transport along with active material reactivation and reutilization duringmore » cycling. A high peak discharge capacity (1200 mA h g -1), a low capacity-fade rate (0.09% cycle-1) for 500 cycles, and excellent rate capability (C/5-1C rates) are accomplished. Moreover, with such an advantageous architecture, the sulfur loading is successfully increased to 32 mg cm -2 to achieve an areal capacity of up to 16 mA h cm -2. This work provides guidelines for realizing optimized highloading Li-S batteries.« less

An optimal tuning strategy for tidal turbines

PubMed Central

2016-01-01

Tuning wind and tidal turbines is critical to maximizing their power output. Adopting a wind turbine tuning strategy of maximizing the output at any given time is shown to be an extremely poor strategy for large arrays of tidal turbines in channels. This ‘impatient-tuning strategy’ results in far lower power output, much higher structural loads and greater environmental impacts due to flow reduction than an existing ‘patient-tuning strategy’ which maximizes the power output averaged over the tidal cycle. This paper presents a ‘smart patient tuning strategy’, which can increase array output by up to 35% over the existing strategy. This smart strategy forgoes some power generation early in the half tidal cycle in order to allow stronger flows to develop later in the cycle. It extracts enough power from these stronger flows to produce more power from the cycle as a whole than the existing strategy. Surprisingly, the smart strategy can often extract more power without increasing maximum structural loads on the turbines, while also maintaining stronger flows along the channel. This paper also shows that, counterintuitively, for some tuning strategies imposing a cap on turbine power output to limit loads can increase a turbine’s average power output. PMID:27956870

High-performance flexible energy storage and harvesting system for wearable electronics

NASA Astrophysics Data System (ADS)

Ostfeld, Aminy E.; Gaikwad, Abhinav M.; Khan, Yasser; Arias, Ana C.

2016-05-01

This paper reports on the design and operation of a flexible power source integrating a lithium ion battery and amorphous silicon solar module, optimized to supply power to a wearable health monitoring device. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide, respectively, on thin flexible current collectors. It displays energy density of 6.98 mWh/cm2 and demonstrates capacity retention of 90% at 3C discharge rate and ~99% under 100 charge/discharge cycles and 600 cycles of mechanical flexing. A solar module with appropriate voltage and dimensions is used to charge the battery under both full sun and indoor illumination conditions, and the addition of the solar module is shown to extend the battery lifetime between charging cycles while powering a load. Furthermore, we show that by selecting the appropriate load duty cycle, the average load current can be matched to the solar module current and the battery can be maintained at a constant state of charge. Finally, the battery is used to power a pulse oximeter, demonstrating its effectiveness as a power source for wearable medical devices.

An optimal tuning strategy for tidal turbines

NASA Astrophysics Data System (ADS)

Vennell, Ross

2016-11-01

Tuning wind and tidal turbines is critical to maximizing their power output. Adopting a wind turbine tuning strategy of maximizing the output at any given time is shown to be an extremely poor strategy for large arrays of tidal turbines in channels. This `impatient-tuning strategy' results in far lower power output, much higher structural loads and greater environmental impacts due to flow reduction than an existing `patient-tuning strategy' which maximizes the power output averaged over the tidal cycle. This paper presents a `smart patient tuning strategy', which can increase array output by up to 35% over the existing strategy. This smart strategy forgoes some power generation early in the half tidal cycle in order to allow stronger flows to develop later in the cycle. It extracts enough power from these stronger flows to produce more power from the cycle as a whole than the existing strategy. Surprisingly, the smart strategy can often extract more power without increasing maximum structural loads on the turbines, while also maintaining stronger flows along the channel. This paper also shows that, counterintuitively, for some tuning strategies imposing a cap on turbine power output to limit loads can increase a turbine's average power output.

Rational Design of High-Loading Sulfur Cathodes with a Poached-Egg-Shaped Architecture for Long-Cycle Lithium–Sulfur Batteries

DOE PAGES

Luo, Liu; Manthiram, Arumugam

2017-08-31

A high-loading electrode is essential for establishing high-energy-density lithium-sulfur (Li-S) batteries, but it is confronted with critical challenges. Here in this paper, we present a freestanding poached-egg-shaped architecture through a facile template supported vacuum-filtration strategy and employ it as an efficient sulfur host for Li-S batteries. This unique architecture guarantees an effective encapsulation of the “sulfur yolk” inside the fully vacuum sealed framework, effectively limiting the active material loss and polysulfide diffusion. Also, the conductive and porous framework serves as an interlinked electron pathway and electrolyte channel, greatly facilitating fast electric/ionic transport along with active material reactivation and reutilization duringmore » cycling. A high peak discharge capacity (1200 mA h g -1), a low capacity-fade rate (0.09% cycle-1) for 500 cycles, and excellent rate capability (C/5-1C rates) are accomplished. Moreover, with such an advantageous architecture, the sulfur loading is successfully increased to 32 mg cm -2 to achieve an areal capacity of up to 16 mA h cm -2. This work provides guidelines for realizing optimized highloading Li-S batteries.« less

High-performance flexible energy storage and harvesting system for wearable electronics.

PubMed

Ostfeld, Aminy E; Gaikwad, Abhinav M; Khan, Yasser; Arias, Ana C

2016-05-17

This paper reports on the design and operation of a flexible power source integrating a lithium ion battery and amorphous silicon solar module, optimized to supply power to a wearable health monitoring device. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide, respectively, on thin flexible current collectors. It displays energy density of 6.98 mWh/cm(2) and demonstrates capacity retention of 90% at 3C discharge rate and ~99% under 100 charge/discharge cycles and 600 cycles of mechanical flexing. A solar module with appropriate voltage and dimensions is used to charge the battery under both full sun and indoor illumination conditions, and the addition of the solar module is shown to extend the battery lifetime between charging cycles while powering a load. Furthermore, we show that by selecting the appropriate load duty cycle, the average load current can be matched to the solar module current and the battery can be maintained at a constant state of charge. Finally, the battery is used to power a pulse oximeter, demonstrating its effectiveness as a power source for wearable medical devices.

An optimal tuning strategy for tidal turbines.

PubMed

Vennell, Ross

2016-11-01

Tuning wind and tidal turbines is critical to maximizing their power output. Adopting a wind turbine tuning strategy of maximizing the output at any given time is shown to be an extremely poor strategy for large arrays of tidal turbines in channels. This 'impatient-tuning strategy' results in far lower power output, much higher structural loads and greater environmental impacts due to flow reduction than an existing 'patient-tuning strategy' which maximizes the power output averaged over the tidal cycle. This paper presents a 'smart patient tuning strategy', which can increase array output by up to 35% over the existing strategy. This smart strategy forgoes some power generation early in the half tidal cycle in order to allow stronger flows to develop later in the cycle. It extracts enough power from these stronger flows to produce more power from the cycle as a whole than the existing strategy. Surprisingly, the smart strategy can often extract more power without increasing maximum structural loads on the turbines, while also maintaining stronger flows along the channel. This paper also shows that, counterintuitively, for some tuning strategies imposing a cap on turbine power output to limit loads can increase a turbine's average power output.

A comparison of lateral ankle ligament suture anchor strength.

PubMed

Barber, F Alan; Herbert, Morley A; Crates, John M

2013-06-01

Lateral ankle ligament repairs increasingly use suture anchors instead of bone tunnels. Our purpose was to compare the biomechanical properties of a knotted and knotless suture anchor appropriate for a lateral ankle ligament reconstruction. In porcine distal fibulae, 10 samples of 2 different PEEK anchors were inserted. The attached sutures were cyclically loaded between 10N and 60N for 200 cycles. A destructive pull was performed and failure loads, cyclic displacement, stiffness, and failure mode recorded. PushLock 2.5 anchors failed before 200 cycles. PushLock 100 cycle displacement was less than Morphix 2.5 displacement (p<0.001). Ultimate failure load for anchors completing 200 cycles was 86.5N (PushLock) and 252.1N (Morphix) (p<0.05). The failure mode was suture breaking for all PushLocks while the Morphix failed equally by anchor breaking and suture breakage. The knotted Morphix demonstrated more displacement and greater failure strength than the knotless PushLock. The PushLock failed consistently with suture breaking. The Morphix anchor failed both by anchor breaking and by suture breaking. Copyright © 2012 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.

High-performance flexible energy storage and harvesting system for wearable electronics

PubMed Central

Ostfeld, Aminy E.; Gaikwad, Abhinav M.; Khan, Yasser; Arias, Ana C.

2016-01-01

This paper reports on the design and operation of a flexible power source integrating a lithium ion battery and amorphous silicon solar module, optimized to supply power to a wearable health monitoring device. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide, respectively, on thin flexible current collectors. It displays energy density of 6.98 mWh/cm2 and demonstrates capacity retention of 90% at 3C discharge rate and ~99% under 100 charge/discharge cycles and 600 cycles of mechanical flexing. A solar module with appropriate voltage and dimensions is used to charge the battery under both full sun and indoor illumination conditions, and the addition of the solar module is shown to extend the battery lifetime between charging cycles while powering a load. Furthermore, we show that by selecting the appropriate load duty cycle, the average load current can be matched to the solar module current and the battery can be maintained at a constant state of charge. Finally, the battery is used to power a pulse oximeter, demonstrating its effectiveness as a power source for wearable medical devices. PMID:27184194

An investigation of strain cycling behavior of 7075-T6 aluminum under combined state of strain: The effects of out-of-phase, biaxial strain cycling on low cycle fatigue

NASA Technical Reports Server (NTRS)

Zamrik, S. Y.

1972-01-01

The effect of out-of-phase strain cycling on the low cycle fatigue of biaxially loaded specimens is discussed. A method to apply phase angles between two strains imposed in two different directions was developed. The data and the proposed theoretical analysis are part of a research program on biaxial strain cycling effect on fatigue life of structural materials.

Behavior of Lithium Metal Anodes under Various Capacity Utilization and High Current Density in Lithium Metal Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiao, Shuhong; Zheng, Jianming; Li, Qiuyan

Lithium (Li) metal batteries (LMBs) are regarded as the most promising power sources for electric vehicles. Besides the Li dendrite growth and low Li Coulombic efficiency, how to well match Li metal anode with a high loading (normally over 3.0 mAh cm-2) cathode is another key challenge to achieve the real high energy density battery. In this work, we systematically investigate the effects of the Li metal capacity usage in each cycle, manipulated by varying the cathode areal loading, on the stability of Li metal anode and the cycling performance of LMBs using the LiNi1/3Mn1/3Co1/3O2 (NMC) cathode and an additive-containingmore » dual-salt/carbonate-solvent electrolyte. It is demonstrated that the Li||NMC cells show decent long-term cycling performance even with NMC areal capacity loading up to ca. 4.0 mAh cm-2 and at a charge current density of 1.0 mA cm-2. The increase of the Li capacity usage in each cycle causes variation in the components of the solid electrolyte interphase (SEI) layer on Li metal anode and generates more ionic conductive species from this electrolyte. Further study reveals for the first time that the degradation of Li metal anode and the thickness of SEI layer on Li anode show linear relationship with the areal capacity of NMC cathode. Meanwhile, the expansion rate of consumed Li and the ratio of SEI thickness to NMC areal loading are kept almost the same value with increasing cathode loading, respectively. These fundamental findings provide new perspectives on the rational evaluation of Li metal anode stability for the development of rechargeable LMBs.« less

Axial displacement of external and internal implant-abutment connection evaluated by linear mixed model analysis.

PubMed

Seol, Hyon-Woo; Heo, Seong-Joo; Koak, Jai-Young; Kim, Seong-Kyun; Kim, Shin-Koo

2015-01-01

To analyze the axial displacement of external and internal implant-abutment connection after cyclic loading. Three groups of external abutments (Ext group), an internal tapered one-piece-type abutment (Int-1 group), and an internal tapered two-piece-type abutment (Int-2 group) were prepared. Cyclic loading was applied to implant-abutment assemblies at 150 N with a frequency of 3 Hz. The amount of axial displacement, the Periotest values (PTVs), and the removal torque values(RTVs) were measured. Both a repeated measures analysis of variance and pattern analysis based on the linear mixed model were used for statistical analysis. Scanning electron microscopy (SEM) was used to evaluate the surface of the implant-abutment connection. The mean axial displacements after 1,000,000 cycles were 0.6 μm in the Ext group, 3.7 μm in the Int-1 group, and 9.0 μm in the Int-2 group. Pattern analysis revealed a breakpoint at 171 cycles. The Ext group showed no declining pattern, and the Int-1 group showed no declining pattern after the breakpoint (171 cycles). However, the Int-2 group experienced continuous axial displacement. After cyclic loading, the PTV decreased in the Int-2 group, and the RTV decreased in all groups. SEM imaging revealed surface wear in all groups. Axial displacement and surface wear occurred in all groups. The PTVs remained stable, but the RTVs decreased after cyclic loading. Based on linear mixed model analysis, the Ext and Int-1 groups' axial displacements plateaued after little cyclic loading. The Int-2 group's rate of axial displacement slowed after 100,000 cycles.

Increasing the resource of high load compression springs

NASA Astrophysics Data System (ADS)

Zemlyanushnova, N. Y.; Zemlyanushnov, N. A.

2017-10-01

Valve springs of VAZ automobiles’ engines are manufactured by using a new method. The decrease of dispersion of operating load in experimental springs compared to serial ones has been proved. The springs have passed a stress cycling test. With the new method having been used, it has been proved that the resource of high load springs working at high loading speed with coils collision has increased up to 60%.

Muscle function during brief maximal exercise: accurate measurements on a friction-loaded cycle ergometer.

PubMed

Arsac, L M; Belli, A; Lacour, J R

1996-01-01

A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N.kg-1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137-180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17-214 rpm). Thus, the individual's muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (vopt) and individual maximal power output (Pmax) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since vopt has been demonstrated to be related to human fibre type composition both vopt, Pmax and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.

Fracture load of metal-ceramic, monolithic, and bi-layered zirconia-based posterior fixed dental prostheses after thermo-mechanical cycling.

PubMed

López-Suárez, Carlos; Castillo-Oyagüe, Raquel; Rodríguez-Alonso, Verónica; Lynch, Christopher D; Suárez-García, María-Jesús

2018-06-01

This study aims to evaluate the fracture load of differently fabricated 3-unit posterior fixed dental prostheses (FDPs) with an intermediate pontic. Fifty sets of two stainless-steel abutments were randomly assigned to five groups (n = 10 each) depending on the material and technique used for manufacturing the FDPs: (1) Metal-ceramic (MC, control); (2) Lava Zirconia (LZ, bi-layered); (3) Lava Plus (LM, monolithic); (4) VITA In-Ceram YZ (YZ, bi-layered); and (5) IPS e-max ZirCAD (ZZ, bi-layered). After being luted to the dies, all FDPs were submitted to thermo-mechanical cycling (120,000 masticatory cycles, 50 N; plus 774 thermal cycles of 5 °C/55 °C, dwell time: 30 s). Samples were then subjected to a three-point bending test until fracture in a universal testing machine (cross-head speed: 1 mm/min). Fracture load of the veneering ceramic (VF) and total fracture load (TF) were recorded. Microstructure and failure patterns were assessed. Data was analysed using one-way ANOVA and Tukey HSD post-hoc tests (α = 0.05). MC restorations recorded higher VF and TF values than did zirconia FDPs (p = 0.0001), which showed no between-group differences. Within the bi-layered groups, TF was significantly higher than VF. LM pieces registered lower average grain size than did LZ specimens (p = 0.001). Overall, the connector was the weakest part. All of the groups tested could withstand clinical chewing forces in terms of average fracture load. Zirconia-based samples performed similarly to each other, but showed lower mean fracture load values than did metal-ceramic ones. Monolithic zirconia may be recommendable for solving the chipping problem. Copyright © 2018 Elsevier Ltd. All rights reserved.

Investigation into the Cyclic Strength of the Bodies of Steam Shutoff Valves from 10Kh9MFB-Sh Steel

NASA Astrophysics Data System (ADS)

Skorobogatykh, V. N.; Kunavin, S. A.; Prudnikov, D. A.; Shchenkova, I. A.; Bazhenov, A. M.; Zadoinyi, V. A.; Starkovskii, G. L.

2018-02-01

Steam shutoff valves are operated under complex loading conditions at thermal and nuclear power stations. In addition to exposure to high temperature and stresses resulting in fatigue, these valves are subjected to cyclic loads in heating-up-cooling down, opening-closing, etc. cycles. The number of these cycles to be specified in designing the valves should not exceed the maximum allowable value. Hence, the problem of cyclic failure rate of steam shutoff valve bodies is critical. This paper continues the previous publications about properties of the construction material for steam shutoff valve bodies (grade 10Kh9MFB-Sh steel) produced by electroslag melting and gives the results of investigation into the cyclic strength of this material. Fatigue curves for the steal used for manufacturing steam shutoff valve bodies are presented. The experimental data are compared with the calculated fatigue curves plotted using the procedures outlined in PNAE G-002-986 and RD 10-249-98. It is confirmed that these procedures may be used in designing valve bodies from 10Kh9MFB-Sh steel. The effect of the cyclic damage after preliminary cyclic loading of the specimens according to the prescribed load conditions on the high-temperature strength of the steel is examined. The influence of cyclic failure rate on the long-term strength was investigated using cylindrical specimens with a smooth working section in the as-made conditions and after two regimes of preliminary cyclic loading (training) at a working temperature of 570°C and the number of load cycles exceeding the design value, which was 2 × 103 cycles. The experiments corroborated that the material (10Kh9MFB-Sh steel) of the body manufactured by the method of electroslag melting had high resistance to cyclic failure rate. No effect of cyclic damages in the metal of the investigated specimens on the high-temperature strength has been found.

Low load, high repetition resistance training program increases bone mineral density in untrained adults.

PubMed

Petersen, Bailey A; Hastings, Bryce; Gottschall, Jinger S

2017-01-01

High load, low repetition resistance training increases BMD in untrained adults; however, many older and untrained adults cannot maintain this type of strenuous program. Our goal was to evaluate whether a low load, high repetition resistance training program would increase BMD in untrained adults. Twenty sedentary, but otherwise healthy, adults (6 men and 14 women, age 28-63 yrs) completed a 27-week group exercise program. The participants were randomly assigned to one of two strength groups: one group completed full body, low load, high repetition weight training classes (S-WEIGHT), while the other group completed core focused fusion classes (S-CORE). Both groups also completed indoor cycling classes for cardiovascular conditioning. After a 3-week familiarization period, all participants completed a 12-week block of 5 fitness classes per week (3 cycling + 2 strength) and concluded with another 12-week block of 6 classes per week (3 cycling + 3 strength). We completed iDXA scans at baseline (week 3) and final (week 28). Compared to baseline, BMD significantly increased for S-WEIGHT in the arms (+4%, P<0.001), legs (+8%, P<0.01), pelvis (+6%, P<0.01) and lumbar spine (+4%, P<0.05), whereas BMD did not significantly change for S-CORE at any site. These results suggest that a low load, high repetition resistance training program may be an effective method to improve bone mass in adults.

Development of a biaxial compression device for biological samples: preliminary experimental results for a closed cell foam.

PubMed

Little, J P; Tevelen, G; Adam, C J; Evans, J H; Pearcy, M J

2009-07-01

Biological tissues are subjected to complex loading states in vivo and in order to define constitutive equations that effectively simulate their mechanical behaviour under these loads, it is necessary to obtain data on the tissue's response to multiaxial loading. Single axis and shear testing of biological tissues is often carried out, but biaxial testing is less common. We sought to design and commission a biaxial compression testing device, capable of obtaining repeatable data for biological samples. The apparatus comprised a sealed stainless steel pressure vessel specifically designed such that a state of hydrostatic compression could be created on the test specimen while simultaneously unloading the sample along one axis with an equilibrating tensile pressure. Thus a state of equibiaxial compression was created perpendicular to the long axis of a rectangular sample. For the purpose of calibration and commissioning of the vessel, rectangular samples of closed cell ethylene vinyl acetate (EVA) foam were tested. Each sample was subjected to repeated loading, and nine separate biaxial experiments were carried out to a maximum pressure of 204 kPa (30 psi), with a relaxation time of two hours between them. Calibration testing demonstrated the force applied to the samples had a maximum error of 0.026 N (0.423% of maximum applied force). Under repeated loading, the foam sample demonstrated lower stiffness during the first load cycle. Following this cycle, an increased stiffness, repeatable response was observed with successive loading. While the experimental protocol was developed for EVA foam, preliminary results on this material suggest that this device may be capable of providing test data for biological tissue samples. The load response of the foam was characteristic of closed cell foams, with consolidation during the early loading cycles, then a repeatable load-displacement response upon repeated loading. The repeatability of the test results demonstrated the ability of the test device to provide reproducible test data and the low experimental error in the force demonstrated the reliability of the test data.

Degradation of Li/S Battery Electrodes On 3D Current Collectors Studied Using X-ray Phase Contrast Tomography

PubMed Central

Zielke, L.; Barchasz, C.; Waluś, S.; Alloin, F.; Leprêtre, J.-C.; Spettl, A.; Schmidt, V.; Hilger, A.; Manke, I.; Banhart, J.; Zengerle, R.; Thiele, S.

2015-01-01

Lithium/sulphur batteries are promising candidates for future energy storage systems, mainly due to their high potential capacity. However low sulphur utilization and capacity fading hinder practical realizations. In order to improve understanding of the system, we investigate Li/S electrode morphology changes for different ageing steps, using X-ray phase contrast tomography. Thereby we find a strong decrease of sulphur loading after the first cycle, and a constant loading of about 15% of the initial loading afterwards. While cycling, the mean sulphur particle diameters decrease in a qualitatively similar fashion as the discharge capacity fades. The particles spread, migrate into the current collector and accumulate in the upper part again. Simultaneously sulphur particles lose contact area with the conducting network but regain it after ten cycles because their decreasing size results in higher surface areas. Since the capacity still decreases, this regain could be associated with effects such as surface area passivation and increasing charge transfer resistance. PMID:26043280

Life cycle contributions of copper from vessel painting and maintenance activities

PubMed Central

Earley, Patrick J.; Swope, Brandon L.; Barbeau, Katherine; Bundy, Randelle; McDonald, Janessa A.; Rivera-Duarte, Ignacio

2013-01-01

Copper-based epoxy and ablative antifouling painted panels were exposed in natural seawater to evaluate environmental loading parameters. In situ loading factors including initial exposure, passive leaching, and surface refreshment were measured utilizing two protocols developed by the US Navy: the dome method and the in-water hull cleaning sampling method. Cleaning techniques investigated included a soft-pile carpet and a medium duty 3M™ pad for fouling removal. Results show that the passive leach rates of copper peaked three days after both initial deployment and cleaning events (CEs), followed by a rapid decrease over about 15 days and a slow approach to asymptotic levels on approximately day 30. Additionally, copper was more bioavailable during a CE in comparison to the passive leaching that immediately followed. A paint life cycle model quantifying annual copper loading estimates for each paint and cleaning method based on a three-year cycle of painting, episodic cleaning, and passive leaching is presented. PMID:24199998

Degradation of Li/S Battery Electrodes On 3D Current Collectors Studied Using X-ray Phase Contrast Tomography

NASA Astrophysics Data System (ADS)

Zielke, L.; Barchasz, C.; Waluś, S.; Alloin, F.; Leprêtre, J.-C.; Spettl, A.; Schmidt, V.; Hilger, A.; Manke, I.; Banhart, J.; Zengerle, R.; Thiele, S.

2015-06-01

Lithium/sulphur batteries are promising candidates for future energy storage systems, mainly due to their high potential capacity. However low sulphur utilization and capacity fading hinder practical realizations. In order to improve understanding of the system, we investigate Li/S electrode morphology changes for different ageing steps, using X-ray phase contrast tomography. Thereby we find a strong decrease of sulphur loading after the first cycle, and a constant loading of about 15% of the initial loading afterwards. While cycling, the mean sulphur particle diameters decrease in a qualitatively similar fashion as the discharge capacity fades. The particles spread, migrate into the current collector and accumulate in the upper part again. Simultaneously sulphur particles lose contact area with the conducting network but regain it after ten cycles because their decreasing size results in higher surface areas. Since the capacity still decreases, this regain could be associated with effects such as surface area passivation and increasing charge transfer resistance.

Benchmark notch test for life prediction

NASA Technical Reports Server (NTRS)

Domas, P. A.; Sharpe, W. N.; Ward, M.; Yau, J. F.

1982-01-01

The laser Interferometric Strain Displacement Gage (ISDG) was used to measure local strains in notched Inconel 718 test bars subjected to six different load histories at 649 C (1200 F) and including effects of tensile and compressive hold periods. The measurements were compared to simplified Neuber notch analysis predictions of notch root stress and strain. The actual strains incurred at the root of a discontinuity in cyclically loaded test samples subjected to inelastic deformation at high temperature where creep deformations readily occur were determined. The steady state cyclic, stress-strain response at the root of the discontinuity was analyzed. Flat, double notched uniaxially loaded fatigue specimens manufactured from the nickel base, superalloy Inconel 718 were used. The ISDG was used to obtain cycle by cycle recordings of notch root strain during continuous and hold time cycling at 649 C. Comparisons to Neuber and finite element model analyses were made. The results obtained provide a benchmark data set in high technology design where notch fatigue life is the predominant component service life limitation.

Implementation of a gait cycle loading into healthy and meniscectomised knee joint models with fibril-reinforced articular cartilage.

PubMed

Mononen, Mika E; Jurvelin, Jukka S; Korhonen, Rami K

2015-01-01

Computational models can be used to evaluate the functional properties of knee joints and possible risk locations within joints. Current models with fibril-reinforced cartilage layers do not provide information about realistic human movement during walking. This study aimed to evaluate stresses and strains within a knee joint by implementing load data from a gait cycle in healthy and meniscectomised knee joint models with fibril-reinforced cartilages. A 3D finite element model of a knee joint with cartilages and menisci was created from magnetic resonance images. The gait cycle data from varying joint rotations, translations and axial forces were taken from experimental studies and implemented into the model. Cartilage layers were modelled as a fibril-reinforced poroviscoelastic material with the menisci considered as a transversely isotropic elastic material. In the normal knee joint model, relatively high maximum principal stresses were specifically predicted to occur in the medial condyle of the knee joint during the loading response. Bilateral meniscectomy increased stresses, strains and fluid pressures in cartilage on the lateral side, especially during the first 50% of the stance phase of the gait cycle. During the entire stance phase, the superficial collagen fibrils modulated stresses of cartilage, especially in the medial tibial cartilage. The present computational model with a gait cycle and fibril-reinforced biphasic cartilage revealed time- and location-dependent differences in stresses, strains and fluid pressures occurring in cartilage during walking. The lateral meniscus was observed to have a more significant role in distributing loads across the knee joint than the medial meniscus, suggesting that meniscectomy might initiate a post-traumatic process leading to osteoarthritis at the lateral compartment of the knee joint.

Comparison of Femoral Head Rotation and Varus Collapse Between a Single Lag Screw and Integrated Dual Screw Intertrochanteric Hip Fracture Fixation Device Using a Cadaveric Hemi-Pelvis Biomechanical Model.

PubMed

Santoni, Brandon G; Nayak, Aniruddh N; Cooper, Seth A; Smithson, Ian R; Cox, Jacob L; Marberry, Scott T; Sanders, Roy W

2016-04-01

This study compared the stabilizing effect of 2 intertrochanteric (IT) fracture fixation devices in a cadaveric hemi-pelvis biomechanical model. Eleven pairs of cadaveric osteopenic female hemi-pelves with intact hip joint and capsular ligaments were used. An unstable IT fracture (OTA 31-A2) was created in each specimen and stabilized with a single lag screw device (Gamma 3) or an integrated dual screw (IDS) device (InterTAN). The hemi-pelves were inverted, coupled to a biaxial apparatus and subjected to 13.5 k cycles of loading (3 months) using controlled, oscillating pelvic rotation (0-90 degrees) plus cyclic axial femoral loading at a 2:1 body weight (BW) ratio. Femoral head rotation and varus collapse were monitored optoelectonically. For specimens surviving 3 months of loading, additional loading was performed in 0.25 × BW/250 cycle increments to a maximum of 4 × BW or failure. Femoral head rotation with IDS fixation was significantly less than the single lag screw construct after 3 months of simulated loading (P = 0.016). Maximum femoral head rotation at the end of 4 × BW loading was 7× less for the IDS construct (P = 0.006). Varus collapse was significantly less with the IDS construct over the entire loading cycle (P = 0.021). In this worst-case model of an osteopenic, unstable, IT fracture, the IDS construct, likely owing to its larger surface area, noncylindrical profile, and fracture compression, provided significantly greater stability and resistance to femoral head rotation and varus collapse.

In vitro biomechanical comparison of equine proximal interphalangeal joint arthrodesis techniques: prototype equine spoon plate versus axially positioned dynamic compression plate and two abaxial transarticular cortical screws inserted in lag fashion.

PubMed

Sod, Gary A; Mitchell, Colin F; Hubert, Jeremy D; Martin, George S; Gill, Marjorie S

2007-12-01

To compare in vitro monotonic biomechanical properties of an equine spoon plate (ESP) with an axial 3-hole, 4.5 mm narrow dynamic compression plate (DCP) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws (DCP-TLS) inserted in lag fashion for equine proximal interphalangeal (PIP) joint arthrodesis. Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Cadaveric adult equine forelimbs (n=18 pairs). For each forelimb pair, 1 PIP joint was stabilized with an ESP (8 hole, 4.5 mm) and 1 with an axial 3-hole narrow DCP (4.5 mm) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion. Six matching pairs of constructs were tested in single cycle to failure under axial compression with load applied under displacement control at a constant rate of 5 cm/s. Six construct pairs were tested for cyclic fatigue under axial compression with cyclic load (0-7.5 kN) applied at 6 Hz; cycles to failure were recorded. Six construct pairs were tested in single cycle to failure under torsional loading applied at a constant displacement rate (0.17 radians/s) until rotation of 0.87 radians occurred. Mean values for each fixation method were compared using a paired t-test within each group with statistical significance set at P<.05. Mean yield load, yield stiffness, and failure load for ESP fixation were significantly greater (for axial compression and torsion) than for DCP-TLS fixation. Mean (+/- SD) values for the ESP and DCP-TLS fixation techniques, respectively, in single cycle to failure under axial compression were: yield load 123.9 +/- 8.96 and 28.5 +/- 3.32 kN; stiffness, 13.11 +/- 0.242 and 2.60 +/- 0.17 kN/cm; and failure load, 144.4 +/- 13.6 and 31.4 +/- 3.8 kN. In single cycle to failure under torsion, mean (+/- SD) values for ESP and DCP-TLS, respectively, were: stiffness 2,022 +/- 26.2 and 107.9 +/- 11.1 N m/rad; and failure load: 256.4 +/- 39.2 and 87.1 +/- 11.5 N m. Mean cycles to failure in axial compression of ESP fixation (622,529 +/- 65,468) was significantly greater than DCP-TLS (95,418 +/- 11,037). ESP was superior to an axial 3-hole narrow DCP with 2 abaxial transarticular screws inserted in lag fashion in resisting static overload forces and cyclic fatigue. In vitro results support further evaluation of ESP for PIP joint arthrodesis in horses. Its specific design may provide increased stability without need for external coaptation support.

Energy saving in ac generators

NASA Technical Reports Server (NTRS)

Nola, F. J.

1980-01-01

Circuit cuts no-load losses, without sacrificing full-load power. Phase-contro circuit includes gate-controlled semiconductor switch that cuts off applied voltage for most of ac cycle if generator idling. Switch "on" time increases when generator is in operation.

A discrete element model for damage and fracture of geomaterials under fatigue loading

NASA Astrophysics Data System (ADS)

Gao, Xiaofeng; Koval, Georg; Chazallon, Cyrille

2017-06-01

Failure processes in geomaterials (concrete, asphalt concrete, masonry, etc.) under fatigue loading (repeated moving loads, cycles of temperature, etc.) are responsible for most of the dysfunctions in pavements, brick structures, etc. In the beginning of the lifetime of a structure, the material presents only inner defects (micro cracks, voids, etc.). Due to the effect of the cyclic loading, these small defects tend to grow in size and quantity which damage the material, reducing its stiffness. With a relatively high number of cycles, these growing micro cracks become large cracks, which characterizes the fracture behavior. From a theoretical point of view, both mechanisms are treated differently. Fracture is usually described locally, with the propagation of cracks defined by the energy release rate at the crack tip; damage is usually associated to non-local approaches. In the present work, damage and fracture mechanics are combined in a local discrete element approach.

Aircraft stress sequence development: A complex engineering process made simple

NASA Technical Reports Server (NTRS)

Schrader, K. H.; Butts, D. G.; Sparks, W. A.

1994-01-01

Development of stress sequences for critical aircraft structure requires flight measured usage data, known aircraft loads, and established relationships between aircraft flight loads and structural stresses. Resulting cycle-by-cycle stress sequences can be directly usable for crack growth analysis and coupon spectra tests. Often, an expert in loads and spectra development manipulates the usage data into a typical sequence of representative flight conditions for which loads and stresses are calculated. For a fighter/trainer type aircraft, this effort is repeated many times for each of the fatigue critical locations (FCL) resulting in expenditure of numerous engineering hours. The Aircraft Stress Sequence Computer Program (ACSTRSEQ), developed by Southwest Research Institute under contract to San Antonio Air Logistics Center, presents a unique approach for making complex technical computations in a simple, easy to use method. The program is written in Microsoft Visual Basic for the Microsoft Windows environment.

Acute physical exercise affected processing efficiency in an auditory attention task more than processing effectiveness.

PubMed

Dutke, Stephan; Jaitner, Thomas; Berse, Timo; Barenberg, Jonathan

2014-02-01

Research on effects of acute physical exercise on performance in a concurrent cognitive task has generated equivocal evidence. Processing efficiency theory predicts that concurrent physical exercise can increase resource requirements for sustaining cognitive performance even when the level of performance is unaffected. This hypothesis was tested in a dual-task experiment. Sixty young adults worked on a primary auditory attention task and a secondary interval production task while cycling on a bicycle ergometer. Physical load (cycling) and cognitive load of the primary task were manipulated. Neither physical nor cognitive load affected primary task performance, but both factors interacted on secondary task performance. Sustaining primary task performance under increased physical and/or cognitive load increased resource consumption as indicated by decreased secondary task performance. Results demonstrated that physical exercise effects on cognition might be underestimated when only single task performance is the focus.

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.

Bithermal fatigue: A simplified alternative to thermomechanical fatigue

NASA Technical Reports Server (NTRS)

Verrilli, Michael J.

1988-01-01

A bithermal fatigue test technique was proposed as a simplified alternative to the thermomechanical fatigue test. Both the thermomechanical cycle and the bithermal technique can be used to study nonisothermal fatigue behavior. The difference between the two cycles is that in a conventional thermomechanical fatigue cycle the temperature is continuously varied concurrently with the applied mechanical strains, but in the bithermal fatigue cycle the specimen is held at zero load during the temperature excursions and all the loads are applied at the two extreme temperatures of the cycle. Experimentally, the bithermal fatigue test technique offers advantages such as ease in synchronizing the temperature and mechanical strain waveforms, in minimizing temperature gradients in the specimen gauge length, and in reducing and interpreting thermal fatigue such as the influence of alternate high and low temperatures on the cyclic stress-strain response characteristics, the effects of thermal state, and the possibility of introducing high- and low-temperature deformation mechanisms within the same cycle. The bithermal technique was used to study nonisothermal fatigue behavior of alloys such as single-crystal PWA 1480, single-crystal Rene N4, cast B1900+Hf, and wrought Haynes 188.

Comparison of microbiological loads and physicochemical properties of raw milk treated with single-/multiple-cycle high hydrostatic pressure and ultraviolet-C light

NASA Astrophysics Data System (ADS)

Hu, Guanglan; Zheng, Yuanrong; Wang, Danfeng; Zha, Baoping; Liu, Zhenmin; Deng, Yun

2015-07-01

The effects of ultraviolet-C radiation (UV-C, 11.8 W/m2), single-cycle and multiple-cycle high hydrostatic pressure (HHP at 200, 400 or 600 MPa) on microbial load and physicochemical quality of raw milk were evaluated. Reductions of aerobic plate count (APC) and coliform count (CC) by HHP were more than 99.9% and 98.7%, respectively. Inactivation efficiency of microorganisms increased with pressure level. At the same pressure level, two-cycle treatments caused lower APC, but did not show CC differences compared with single-cycle treatments. Reductions of APC and CC by UV-C were somewhere between 200 MPa and 400/600 MPa. Both HHP and UV-C significantly decreased lightness and increased pH, but did not change soluble solids content and thiobarbituric acid-reactive substances' values. Two 2.5 min cycles of HHP at 600 MPa caused minimum APC and CC, and maximum conductivity. Compared with HHP, UV-C markedly increased protein oxidation and reduced darkening.

Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns

PubMed Central

Anastassova-Yoshida, Yana; Nothdurft, Frank Phillip; von See, Constantin; Pospiech, Peter

2016-01-01

PURPOSE The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method. MATERIALS AND METHODS An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃–55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture. RESULTS The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly. CONCLUSION The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns. PMID:26949485

Changes in frontal plane dynamics and the loading response phase of the gait cycle are characteristic of severe knee osteoarthritis application of a multidimensional analysis technique.

PubMed

Astephen, J L; Deluzio, K J

2005-02-01

Osteoarthritis of the knee is related to many correlated mechanical factors that can be measured with gait analysis. Gait analysis results in large data sets. The analysis of these data is difficult due to the correlated, multidimensional nature of the measures. A multidimensional model that uses two multivariate statistical techniques, principal component analysis and discriminant analysis, was used to discriminate between the gait patterns of the normal subject group and the osteoarthritis subject group. Nine time varying gait measures and eight discrete measures were included in the analysis. All interrelationships between and within the measures were retained in the analysis. The multidimensional analysis technique successfully separated the gait patterns of normal and knee osteoarthritis subjects with a misclassification error rate of <6%. The most discriminatory feature described a static and dynamic alignment factor. The second most discriminatory feature described a gait pattern change during the loading response phase of the gait cycle. The interrelationships between gait measures and between the time instants of the gait cycle can provide insight into the mechanical mechanisms of pathologies such as knee osteoarthritis. These results suggest that changes in frontal plane loading and alignment and the loading response phase of the gait cycle are characteristic of severe knee osteoarthritis gait patterns. Subsequent investigations earlier in the disease process may suggest the importance of these factors to the progression of knee osteoarthritis.

Environmental Impact Assessment and End-of-Life Treatment Policy Analysis for Li-Ion Batteries and Ni-MH Batteries

PubMed Central

Yu, Yajuan; Chen, Bo; Huang, Kai; Wang, Xiang; Wang, Dong

2014-01-01

Based on Life Cycle Assessment (LCA) and Eco-indicator 99 method, a LCA model was applied to conduct environmental impact and end-of-life treatment policy analysis for secondary batteries. This model evaluated the cycle, recycle and waste treatment stages of secondary batteries. Nickel-Metal Hydride (Ni-MH) batteries and Lithium ion (Li-ion) batteries were chosen as the typical secondary batteries in this study. Through this research, the following results were found: (1) A basic number of cycles should be defined. A minimum cycle number of 200 would result in an obvious decline of environmental loads for both battery types. Batteries with high energy density and long life expectancy have small environmental loads. Products and technology that help increase energy density and life expectancy should be encouraged. (2) Secondary batteries should be sorted out from municipal garbage. Meanwhile, different types of discarded batteries should be treated separately under policies and regulations. (3) The incineration rate has obvious impact on the Eco-indicator points of Nickel-Metal Hydride (Ni-MH) batteries. The influence of recycle rate on Lithium ion (Li-ion) batteries is more obvious. These findings indicate that recycling is the most promising direction for reducing secondary batteries’ environmental loads. The model proposed here can be used to evaluate environmental loads of other secondary batteries and it can be useful for proposing policies and countermeasures to reduce the environmental impact of secondary batteries. PMID:24646862

Environmental impact assessment and end-of-life treatment policy analysis for Li-ion batteries and Ni-MH batteries.

PubMed

Yu, Yajuan; Chen, Bo; Huang, Kai; Wang, Xiang; Wang, Dong

2014-03-18

Based on Life Cycle Assessment (LCA) and Eco-indicator 99 method, a LCA model was applied to conduct environmental impact and end-of-life treatment policy analysis for secondary batteries. This model evaluated the cycle, recycle and waste treatment stages of secondary batteries. Nickel-Metal Hydride (Ni-MH) batteries and Lithium ion (Li-ion) batteries were chosen as the typical secondary batteries in this study. Through this research, the following results were found: (1) A basic number of cycles should be defined. A minimum cycle number of 200 would result in an obvious decline of environmental loads for both battery types. Batteries with high energy density and long life expectancy have small environmental loads. Products and technology that help increase energy density and life expectancy should be encouraged. (2) Secondary batteries should be sorted out from municipal garbage. Meanwhile, different types of discarded batteries should be treated separately under policies and regulations. (3) The incineration rate has obvious impact on the Eco-indicator points of Nickel-Metal Hydride (Ni-MH) batteries. The influence of recycle rate on Lithium ion (Li-ion) batteries is more obvious. These findings indicate that recycling is the most promising direction for reducing secondary batteries' environmental loads. The model proposed here can be used to evaluate environmental loads of other secondary batteries and it can be useful for proposing policies and countermeasures to reduce the environmental impact of secondary batteries.

Controllable embedding of sulfur in high surface area nitrogen doped three dimensional reduced graphene oxide by solution drop impregnation method for high performance lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Zegeye, Tilahun Awoke; Tsai, Meng-Che; Cheng, Ju-Hsiang; Lin, Ming-Hsien; Chen, Hung-Ming; Rick, John; Su, Wei-Nien; Kuo, Chung-Feng Jeffrey; Hwang, Bing-Joe

2017-06-01

High capacity lithium-sulfur batteries with stable cycle performance and sulfur loadings greater than 70 wt% are regarded as promising candidates for energy storage devices. However, it has been challenged to achieving practical application of sulfur cathode because of low loading of active sulfur and poor cycle performance. Herein, we design novel nanocomposite cathode materials consist of sulfur (80 wt%) embedded within nitrogen doped three-dimensional reduced graphene oxide (N-3D-rGO) by controllable sulfur-impregnation method. Nitrogen doping helps increase the surface area by ten times from pristine graphene, and pore volume by seven times. These structural features allow the cathode to hold more sulfur. It also adsorbs polysulfides and prevents their detachment from the host materials; thereby achieving stable cycle performance. The solution drop sulfur-impregnation method provides uniform distribution of nano-sulfur in controlled manner. The material delivers a high initial discharge capacity of 1042 mAhg-1 and 916 mAhg-1 with excellent capacity retention of 94.8% and 81.9% at 0.2 C and 0.5 C respectively after 100 cycles. Thus, the combination of solution drop and nitrogen doping opens a new chapter for resolving capacity fading as well as long cycling problems and creates a new strategy to increase sulfur loading in controlled mechanism.

Vaginal Pessary

MedlinePlus

... muscles can weaken over time or from certain events. Learn how to strengthen these muscles and regain…Plasma Viral Load TestingRead Article >>Procedures & DevicesPlasma Viral Load TestingA plasma viral load ...

Orion EM-1 Crew Module Structural Test Article loaded onto Guppy

NASA Image and Video Library

2017-04-25

The Orion Exploration Mission-1 (EM-1) structural test article, secured inside its transport container, is loaded into NASA's Super Guppy aircraft at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida. The test article will be transported to Lockheed Martin's Denver facility for testing. The Orion spacecraft will launch atop NASA’s Space Launch System rocket on EM-1, its first deep space mission.

SLS INTERTANK TEST ARTICLE IS ATTACHED TO CROSSHEAD OF LOAD TEST ANNEX, BLDG. 4619, AND REMOVED FROM BED OF KMAG TRANSPORTER

NASA Image and Video Library

2018-03-28

SLS INTERTANK TEST ARTICLE IS ATTACHED TO CROSSHEAD OF LOAD TEST ANNEX, BLDG. 4619, AND REMOVED FROM BED OF KMAG TRANSPORTER. Matt Cash conducts tag up meeting before lift of ITA from KMAG transporter

Green metacycles of attention: Reassessing the attention cycles of environmental news reporting 1961-2010.

PubMed

Djerf-Pierre, Monika

2013-05-01

This article examines the longitudinal development of environmental news reporting in Swedish television over an extended period of time, 1961-2010. It returns to Anthony Downs's (1972) seminal article on issue attention cycles when analyzing the cyclic nature of environmental news reporting and advances the issue attention cycle framework by introducing the concept of metacycles as it explores the trajectory of environmental news reporting. Metacycles refers to the major fluctuations in attention to the entire domain of environmental issues over time, while issue cycles refer to the oscillation in attention pertaining to single issues. The article analyzes the pattern of the metacycles, and investigates how cycles of attention to individual issues contribute to the shaping of the environmental metacycles in the news.

Molecular Mechanisms and Regulation of Urinary Acidification

PubMed Central

Kurtz, Ira

2015-01-01

The H+ concentration in human blood is kept within very narrow limits, ~ 40 nM, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: 1) reabsorb HCO3− that is filtered through the glomeruli to prevent its excretion in the urine; 2) generate a sufficient quantity of new HCO3− to compensate for the loss of HCO3− resulting from dietary metabolic H+ loads and loss of HCO3− in the urea cycle; and 3) excrete HCO3− (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~ 60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level. PMID:25428859

Residual thermal stress control in composite reinforced metal structures. [by mechanical loading of metal component prior to bonding

NASA Technical Reports Server (NTRS)

Kelly, J. B.; June, R. R.

1972-01-01

Advanced composite materials, composed of boron or graphite fibers and a supporting matrix, make significant structural efficiency improvements available to aircraft and aerospace designers. Residual stress induced during bonding of composite reinforcement to metal structural elements can be reduced or eliminated through suitable modification to the manufacturing processes. The most successful method employed during this program used a steel tool capable of mechanically loading the metal component in compression prior to the adhesive bonding cycle. Compression loading combined with heating to 350 F during the bond cycle can result in creep deformation in aluminum components. The magnitude of the deformation increases with increasing stress level during exposure to 350 F.

Element Interactivity and Intrinsic, Extraneous, and Germane Cognitive Load

ERIC Educational Resources Information Center

Sweller, John

2010-01-01

In cognitive load theory, element interactivity has been used as the basic, defining mechanism of intrinsic cognitive load for many years. In this article, it is suggested that element interactivity underlies extraneous cognitive load as well. By defining extraneous cognitive load in terms of element interactivity, a distinct relation between…

3 Steps to Great Coaching: A Simple but Powerful Instructional Coaching Cycle Nets Results

ERIC Educational Resources Information Center

Knight, Jim; Elford, Marti; Hock, Michael; Dunekack, Devona; Bradley, Barbara; Deshler, Donald D.; Knight, David

2015-01-01

In this article the authors describe a three-step instructional coaching cycle that can helps coaches become more effective. The article provides the steps and related components to: (1) Identify; (2) Learn; and (3) Improve. While the instructional coaching cycle is only one effective coaching program, coaches also need professional learning that…

Prediction of glycosaminoglycan synthesis in intervertebral disc under mechanical loading.

PubMed

Gao, Xin; Zhu, Qiaoqiao; Gu, Weiyong

2016-09-06

The loss of glycosaminoglycan (GAG) content is a major biochemical change during intervertebral disc (IVD) degeneration. Abnormal mechanical loading is one of the major factors causing disc degeneration. In this study, a multiscale mathematical model was developed to quantify the effect of mechanical loading on GAG synthesis. This model was based on a recently developed cell volume dependent GAG synthesis theory that predicts the variation of GAG synthesis rate of a cell under the influence of mechanical stimuli, and the biphasic theory that describes the deformation of IVD under mechanical loading. The GAG synthesis (at the cell level) was coupled with the mechanical loading (at the tissue level) via a cell-matrix unit approach which established a relationship between the variation of cell dilatation and the local tissue dilatation. This multiscale mathematical model was used to predict the effect of static load (creep load) on GAG synthesis in bovine tail discs. The predicted results are in the range of experimental results. This model was also used to investigate the effect of static (0.2MPa) and diurnal loads (0.1/0.3MPa and 0.15/0.25MPa in 12/12 hours shift with an average of 0.2MPa over a cycle) on GAG synthesis. It was found that static load and diurnal loads have different effects on GAG synthesis in a diurnal cycle, and the diurnal load effects depend on the amplitude of the load. The model is important to understand the effect of mechanical loading at the tissue level on GAG synthesis at the cellular level, as well as to optimize the mechanical loading in growing engineered tissue. Copyright © 2016 Elsevier Ltd. All rights reserved.

Impact of Intentional Overload on Joint Stability of Internal Implant-Abutment Connection System with Different Diameter.

PubMed

Lee, Ji-Hye; Lee, Won; Huh, Yoon-Hyuk; Park, Chan-Jin; Cho, Lee-Ra

2017-09-05

To evaluate the axial displacement of the implant-abutment assembly of different implant diameter after static and cyclic loading of overload condition. An internal conical connection system with three diameters (Ø 4.0, 4.5, and 5.0) applying identical abutment dimension and the same abutment screw was evaluated. Axial displacement of abutment and reverse torque loss of abutment screw were evaluated under static and cyclic loading conditions. Static loading test groups were subjected to vertical static loading of 250, 400, 500, 600, 700, and 800 N consecutively. Cyclic loading test groups were subjected to 500 N cyclic loading to evaluate the effect of excessive masticatory loading. After abutment screw tightening for 30 Ncm, axial displacement was measured upon 1, 3, 10, and 1,000,000 cyclic loadings of 500 N. Repeated-measure ANOVA and 2-way ANOVA were used for statistical analysis (α = 0.05). The increasing magnitude of vertical load and thinner wall thickness of implant increased axial displacement of abutment and reverse torque loss of abutment screw (p < 0.05). Implants in the Ø 5.0 diameter group demonstrated significantly low axial displacement, and reverse torque loss after static loading than Ø 4.0 and Ø 4.5 diameter groups (p < 0.05). In the cyclic loading test, all diameter groups of implant showed significant axial displacement after 1 cycle of loading of 500 N (p < 0.05). There was no significant axial displacement after 3, 10, or 1,000,000 cycles of loading (p = 0.603). Implants with Ø 5.0 diameter demonstrated significantly low axial displacement and reverse torque loss after the cyclic and static loading of overload condition. © 2017 by the American College of Prosthodontists.

Steam sterilisation's energy and water footprint.

PubMed

McGain, Forbes; Moore, Graham; Black, Jim

2017-03-01

Objective The aim of the present study was to quantify hospital steam steriliser resource consumption to provide baseline environmental data and identify possible efficiency gains. We sought to find the amount of steriliser electricity and water used for active cycles and for idling (standby), and the relationship between the electricity and water consumption and the mass and type of items sterilised. Methods We logged a hospital steam steriliser's electricity and water meters every 5min for up to 1 year. We obtained details of all active cycles (standard 134°C and accessory or 'test' cycles), recording item masses and types. Relationships were investigated for both the weight and type of items sterilised with electricity and water consumption. Results Over 304 days there were 2173 active cycles, including 1343 standard 134°C cycles that had an average load mass of 21.2kg, with 32% of cycles <15kg. Electricity used for active cycles was 32652kWh (60% of total), whereas the water used was 1243495L (79%). Standby used 21457kWh (40%) electricity and 329200L (21%) water. Total electricity and water consumption per mass sterilised was 1.9kWhkg -1 and 58Lkg -1 , respectively. The linear regression model predicting electricity use was: kWh=15.7+ 0.14×mass (in kg; R 2 =0.58, P<0.01). Models for water and item type were poor. Electricity and water use fell from 3kWhkg -1 and 200Lkg -1 , respectively, for 5-kg loads to 0.5kWhkg -1 and 20Lkg -1 , respectively, for 40-kg loads. Conclusions Considerable electricity and water use occurred during standby, load mass was only moderately predictive of electricity consumption and light loads were common yet inefficient. The findings of the present study are a baseline for steam sterilisation's environmental footprint and identify areas to improve efficiencies. What is known about the topic? There is increasing interest in the environmental effects of healthcare. Life cycle assessment ('cradle to grave') provides a scientific method of analysing environmental effects. Although data of the effects of steam sterilisation are integral to the life cycles of reusable items and procedures using such items, there are few data available. Further, there is scant information regarding the efficiency of the long-term in-hospital use of sterilisers. What does this paper add? We quantified, for the first time, long-term electricity and water use of a hospital steam steriliser. We provide useful input data for future life cycle assessments of all reusable, steam-sterilised equipment. Further, we identified opportunities for improved steriliser efficiencies, including rotating off idle sterilisers and reducing the number of light steriliser loads. Finally, others could use our methods to examine steam sterilisers and many other energy-intensive items of hospital equipment. What are the implications for practitioners? We provide useful input data for all researchers examining the environmental footprint of reusable hospital equipment and procedures using such equipment. As a result of the present study, staff in the hospital sterile supply department have reduced steam steriliser electricity and water use considerably without impeding sterilisation throughput (and reduced time inefficiencies). Many other hospitals could benefit from similar methods to improve steam steriliser and other hospital equipment efficiencies.

Benchmark cyclic plastic notch strain measurements

NASA Technical Reports Server (NTRS)

Sharpe, W. N., Jr.; Ward, M.

1983-01-01

Plastic strains at the roots of notched specimens of Inconel 718 subjected to tension-compression cycling at 650 C are reported. These strains were measured with a laser-based technique over a gage length of 0.1 mm and are intended to serve as 'benchmark' data for further development of experimental, analytical, and computational approaches. The specimens were 250 mm by 2.5 mm in the test section with double notches of 4.9 mm radius subjected to axial loading sufficient to cause yielding at the notch root on the tensile portion of the first cycle. The tests were run for 1000 cycles at 10 cpm or until cracks initiated at the notch root. The experimental techniques are described, and then representative data for the various load spectra are presented. All the data for each cycle of every test are available on floppy disks from NASA.

Clothes Dryer Automatic Termination Evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

TeGrotenhuis, Ward E.

Volume 2: Improved Sensor and Control Designs Many residential clothes dryers on the market today provide automatic cycles that are intended to stop when the clothes are dry, as determined by the final remaining moisture content (RMC). However, testing of automatic termination cycles has shown that many dryers are susceptible to over-drying of loads, leading to excess energy consumption. In particular, tests performed using the DOE Test Procedure in Appendix D2 of 10 CFR 430 subpart B have shown that as much as 62% of the energy used in a cycle may be from over-drying. Volume 1 of this reportmore » shows an average of 20% excess energy from over-drying when running automatic cycles with various load compositions and dryer settings. Consequently, improving automatic termination sensors and algorithms has the potential for substantial energy savings in the U.S.« less

Wheel load cycle tag for rail : final report.

DOT National Transportation Integrated Search

2015-12-01

The Federal Railroad Administration (FRA) has determined that there is a research need to collect and analyze statistical usage : data to help ascertain the cumulative load-induced fatigue on rail track segments. The estimation of rail segment burden...

Nitrogen balance for a plantation forest drainage canal on the North Carolina Coastal Plain

Treesearch

Timothy W. Appelboom; George M. Chescheir; R. Wayne Skaggs; J. Wendell Gilliam; Devendra M. Amatya

2009-01-01

Human alteration of the nitrogen cycle has led to increased riverine nitrogen loads, contributing to the eutrophication of lakes, streams, estuaries, and near-coastal oceans. These riverine nitrogen loads are usually less...

Comparison of the Mechanical Characteristics of a Universal Small Biplane Plating Technique Without Compression Screw and Single Anatomic Plate With Compression Screw.

PubMed

Dayton, Paul; Ferguson, Joe; Hatch, Daniel; Santrock, Robert; Scanlan, Sean; Smith, Bret

2016-01-01

To better understand the mechanical characteristics of biplane locked plating in small bone fixation, the present study compared the stability under cyclic cantilever loading of a 2-plate locked biplane (BPP) construct without interfragmentary compression with that of a single-plate locked construct with an additional interfragmentary screw (SPS) using surrogate bone models simulating Lapidus arthrodesis. In static ultimate plantar bending, the BPP construct failed at significantly greater load than did the SPS construct (556.2 ± 37.1 N versus 241.6 ± 6.3 N, p = .007). For cyclic failure testing in plantar bending at a 180-N starting load, the BPP construct failed at a significantly greater number of cycles (158,322 ± 50,609 versus 13,718 ± 10,471 cycles) and failure load (242.5 ± 25.0 N versus 180.0 ± 0.0 N) than the SPS construct (p = .002). For cyclic failure testing in plantar bending at a 120-N starting load, the results were not significantly different between the BPP and SPS constructs for the number of cycles (207,646 ± 45,253 versus 159,334 ± 69,430) or failure load (205.0 ± 22.4 N versus 185.0 ± 33.5 N; p = .300). For cyclic testing with 90° offset loading (i.e., medial to lateral bending) at a 120-N starting load, all 5 BPP constructs (tension side) and 2 of the 5 SPS constructs reached 250,000 cycles without failure. Overall, the present study found the BPP construct to have superior or equivalent stability in multiplanar orientations of force application in both static and fatigue testing. Thus, the concept of biplane locked plating, using 2 low profile plates and unicortical screw insertion, shows promise in small bone fixation, because it provides consistent stability in multiplanar orientations, making it universally adaptable to many clinical situations. Copyright © 2016 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

The ultimate state of polymeric materials and laminated and fibrous composites under asymmetric high-cycle loading

NASA Astrophysics Data System (ADS)

Golub, V. P.; Pogrebniak, A. D.; Kochetkova, E. S.

2008-01-01

The prediction of the high-cycle fatigue strength of polymeric and composite materials in asymmetric loading is considered. The problem is solved on the basis of a nonlinear model of ultimate state allowing us to describe all typical forms of the diagrams of ultimate stresses. The material constants of the model are determined from the results of fatigue tests in symmetric reversed cycling, in a single fatigue test with the minimum stress equal to zero, and in a short-term strength test. The fatigue strength characteristics of some polymers, glass-fiber laminates, glass-fiber-reinforced plastics, organic-fiber-reinforced plastics, and wood laminates in asymmetric tension-compression, bending, and torsion have been calculated and approved experimentally.

Cumulative fatigue damage behavior of MAR M-247

NASA Technical Reports Server (NTRS)

Mcgaw, Michael A.; Halford, Gary R.; Kalluri, Sreeramesh

1991-01-01

The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of tests were performed: one of the two baseline fatigue LCF (Low-Cycle Fatigue) life levels was used in the first loading block, and the HCF (High-Cycle Fatigue) baseline loading level was used in the second block in each series. For each series, duplicate tests were performed at each applied LCF life fraction.

The biomechanical strength of a hardware-free femoral press-fit method for ACL bone-tendon-bone graft fixation.

PubMed

Arnold, M P; Burger, L D; Wirz, D; Goepfert, B; Hirschmann, M T

2017-04-01

The purpose was to investigate graft slippage and ultimate load to failure of a femoral press-fit fixation technique for anterior cruciate ligament (ACL) reconstruction. Nine fresh-frozen knees were used. Standardized harvesting of the B-PT-B graft was performed. The femora were cemented into steel rods, and a tunnel was drilled outside-in into the native ACL footprint and expanded using a manual mill bit. The femoral bone block was fixed press-fit. To pull the free end of the graft, it was fixed to a mechanical testing machine using a deep-freezing technique. A motion capture system was used to assess three-dimensional micro-motion. After preconditioning of the graft, 1000 cycles of tensile loading were applied. Finally, an ultimate load to failure test was performed. Graft slippage in mm ultimate load to failure as well as type of failure was noted. In six of the nine measured specimens, a typical pattern of graft slippage was observed during cyclic loading. For technical reasons, the results of three knees had to be discarded. 78.6 % of total graft slippage occurred in the first 100 cycles. Once the block had settled, graft slippage converged to zero, highlighting the importance of initial preconditioning of the graft in the clinical setting. Graft slippage after 1000 cycles varied around 3.4 ± 3.2 mm (R = 1.3-9.8 mm) between the specimens. Ultimate loading (n = 9) revealed two characteristic patterns of failure. In four knees, the tendon ruptured, while in five knees the bone block was pulled out of the femoral tunnel. The median ultimate load to failure was 852 N (R = 448-1349 N). The implant-free femoral press-fit fixation provided adequate primary stability with ultimate load to failure pull forces at least equal to published results for interference screws; hence, its clinical application is shown to be safe.

Orion EM-1 Crew Module Structural Test Article loaded onto Guppy

NASA Image and Video Library

2017-04-25

On the tarmac at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida, the Orion Exploration Mission-1 (EM-1) structural test article, secured in its transport container, is loaded into the agency's Super Guppy aircraft. The test article will be transported to Lockheed Martin's Denver facility for testing. The Orion spacecraft will launch atop NASA’s Space Launch System rocket on EM-1, its first deep space mission.

Orion EM-1 Crew Module Structural Test Article loaded onto Guppy

NASA Image and Video Library

2017-04-25

The Orion Exploration Mission-1 (EM-1) structural test article, secured inside its transport container, arrives at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida. The test article will be loaded into NASA's Super Guppy aircraft, in view at left, and transported to Lockheed Martin's Denver facility for testing. The Orion spacecraft will launch atop NASA’s Space Launch System rocket on EM-1, its first deep space mission.

40 CFR 86.129-00 - Road load power, test weight, and inertia weight class determination.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 19 2013-07-01 2013-07-01 false Road load power, test weight, and... Light-Duty Trucks and New Otto-Cycle Complete Heavy-Duty Vehicles; Test Procedures § 86.129-00 Road load... running loss testing. Paragraphs (e) and (f) of this section are applicable to vehicles from engine...

40 CFR 86.129-00 - Road load power, test weight, and inertia weight class determination.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 19 2014-07-01 2014-07-01 false Road load power, test weight, and... Light-Duty Trucks and New Otto-Cycle Complete Heavy-Duty Vehicles; Test Procedures § 86.129-00 Road load... running loss testing. Paragraphs (e) and (f) of this section are applicable to vehicles from engine...

40 CFR 86.129-00 - Road load power, test weight, and inertia weight class determination.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 18 2011-07-01 2011-07-01 false Road load power, test weight, and... Light-Duty Trucks and New Otto-Cycle Complete Heavy-Duty Vehicles; Test Procedures § 86.129-00 Road load... running loss testing. Paragraphs (e) and (f) of this section are applicable to vehicles from engine...

40 CFR 86.129-00 - Road load power, test weight, and inertia weight class determination.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 18 2010-07-01 2010-07-01 false Road load power, test weight, and... Light-Duty Trucks and New Otto-Cycle Complete Heavy-Duty Vehicles; Test Procedures § 86.129-00 Road load... running loss testing. Paragraphs (e) and (f) of this section are applicable to vehicles from engine...

40 CFR 86.129-00 - Road load power, test weight, and inertia weight class determination.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 19 2012-07-01 2012-07-01 false Road load power, test weight, and... Light-Duty Trucks and New Otto-Cycle Complete Heavy-Duty Vehicles; Test Procedures § 86.129-00 Road load... running loss testing. Paragraphs (e) and (f) of this section are applicable to vehicles from engine...

FATIGUE OF DENTAL CERAMICS

PubMed Central

Zhang, Yu; Sailer, Irena; Lawn, Brian R

2013-01-01

Objectives Clinical data on survival rates reveal that all-ceramic dental prostheses are susceptible to fracture from repetitive occlusal loading. The objective of this review is to examine the underlying mechanisms of fatigue in current and future dental ceramics. Data/sources The nature of various fatigue modes is elucidated using fracture test data on ceramic layer specimens from the dental and biomechanics literature. Conclusions Failure modes can change over a lifetime, depending on restoration geometry, loading conditions and material properties. Modes that operate in single-cycle loading may be dominated by alternative modes in multi-cycle loading. While post-mortem examination of failed prostheses can determine the sources of certain fractures, the evolution of these fractures en route to failure remains poorly understood. Whereas it is commonly held that loss of load-bearing capacity of dental ceramics in repetitive loading is attributable to chemically-assisted 'slow crack growth' in the presence of water, we demonstrate the existence of more deleterious fatigue mechanisms, mechanical rather than chemical in nature. Neglecting to account for mechanical fatigue can lead to gross overestimates in predicted survival rates. Clinical significance Strategies for prolonging the clinical lifetimes of ceramic restorations are proposed based on a crack-containment philosophy. PMID:24135295

Fatigue of dental ceramics.

PubMed

Zhang, Yu; Sailer, Irena; Lawn, Brian R

2013-12-01

Clinical data on survival rates reveal that all-ceramic dental prostheses are susceptible to fracture from repetitive occlusal loading. The objective of this review is to examine the underlying mechanisms of fatigue in current and future dental ceramics. The nature of various fatigue modes is elucidated using fracture test data on ceramic layer specimens from the dental and biomechanics literature. Failure modes can change over a lifetime, depending on restoration geometry, loading conditions and material properties. Modes that operate in single-cycle loading may be dominated by alternative modes in multi-cycle loading. While post-mortem examination of failed prostheses can determine the sources of certain fractures, the evolution of these fractures en route to failure remains poorly understood. Whereas it is commonly held that loss of load-bearing capacity of dental ceramics in repetitive loading is attributable to chemically assisted 'slow crack growth' in the presence of water, we demonstrate the existence of more deleterious fatigue mechanisms, mechanical rather than chemical in nature. Neglecting to account for mechanical fatigue can lead to gross overestimates in predicted survival rates. Strategies for prolonging the clinical lifetimes of ceramic restorations are proposed based on a crack-containment philosophy. Copyright © 2013 Elsevier Ltd. All rights reserved.

Harmonic force spectroscopy reveals a force-velocity curve from a single human beta cardiac myosin motor

NASA Astrophysics Data System (ADS)

Sung, Jongmin; Nag, Suman; Vestergaard, Christian; Mortensen, Kim; Flyvbjerg, Henrik; Spudich, James

2014-03-01

A muscle contracts rapidly under low load, but slowly under high load. Its molecular mechanisms remain to be elucidated, however. During contraction, myosins in thick filaments interact with actin in thin filaments in the sarcomere, cycling between a strongly bound (force producing) state and a weakly bound (relaxed) state. Huxley et al. have previously proposed that the transition from the strong to the weak interaction can be modulated by a load. We use a new method we call ``harmonic force spectroscopy'' to extract a load-velocity curve from a single human beta cardiac myosin II motor. With a dual-beam optical trap, we hold an actin dumbbell over a myosin molecule anchored to the microscope stage that oscillates sinusoidally. Upon binding, the motor experiences an oscillatory load with a mean that is directed forward or backward, depending on binding location We find that the bound time at saturating [ATP] is exponentially correlated with the mean load, which is explained by Arrhenius transition theory. With a stroke size measurement, we obtained a load-velocity curve from a single myosin. We compare the curves for wild-type motors with mutants that cause hypertrophic cardiomyopathies, to understand the effects on the contractile cycle

Influence of load by high power on the optical coupler

NASA Astrophysics Data System (ADS)

Bednarek, Lukas; Poboril, Radek; Vanderka, Ales; Hajek, Lukas; Nedoma, Jan; Vasinek, Vladimir

2016-12-01

Nowadays, aging of the optical components is a very current topic. Therefore, some investigations are focused on this area, so that the aging of the optical components is accelerated by thermal, high power and gamma load. This paper deals by findings of the influence of the load by laser with high optical power on the transmission parameters of the optical coupler. The investigated coupler has one input and eight outputs (1x8). Load by laser with high optical power is realized using a fiber laser with a cascade configuration EDFA amplifiers. The output power of the amplifier is approximately 250 mW. Duration of the load is moving from 104 hours to 139 hours. After each load, input power and output powers of all branches are measured. Following parameters of the optical coupler are calculated using formulas: the insertion losses of the individual branches, split ratio, total losses, homogeneity of the losses and cross-talk between different branches. All measurements are performed at wavelengths 1310 nm and 1550 nm. Individual optical powers are measured 20 times, due to the exclusion of statistical error of the measurement. After measuring, the coupler is connected to the amplifier for next cycle of the load. The paper contains an evaluation of the results of the coupler before and after four cycles of the burden.

Land Use and Climate Variability Amplify Contaminant Pulses

EPA Science Inventory

Converting land to human-dominated uses has increased contaminant loads in streams and rivers and vastly transformed hydrological cycles (Vitousek et al. 1997). More recently, climate change has further altered hydrologic cycles and variability of precipitation (IPCC 2007). Toge...

Concurrent prediction of muscle and tibiofemoral contact forces during treadmill gait.

PubMed

Guess, Trent M; Stylianou, Antonis P; Kia, Mohammad

2014-02-01

Detailed knowledge of knee kinematics and dynamic loading is essential for improving the design and outcomes of surgical procedures, tissue engineering applications, prosthetics design, and rehabilitation. This study used publicly available data provided by the "Grand Challenge Competition to Predict in-vivo Knee Loads" for the 2013 American Society of Mechanical Engineers Summer Bioengineering Conference (Fregly et al., 2012, "Grand Challenge Competition to Predict in vivo Knee Loads," J. Orthop. Res., 30, pp. 503-513) to develop a full body, musculoskeletal model with subject specific right leg geometries that can concurrently predict muscle forces, ligament forces, and knee and ground contact forces. The model includes representation of foot/floor interactions and predicted tibiofemoral joint loads were compared to measured tibial loads for two different cycles of treadmill gait. The model used anthropometric data (height and weight) to scale the joint center locations and mass properties of a generic model and then used subject bone geometries to more accurately position the hip and ankle. The musculoskeletal model included 44 muscles on the right leg, and subject specific geometries were used to create a 12 degrees-of-freedom anatomical right knee that included both patellofemoral and tibiofemoral articulations. Tibiofemoral motion was constrained by deformable contacts defined between the tibial insert and femoral component geometries and by ligaments. Patellofemoral motion was constrained by contact between the patellar button and femoral component geometries and the patellar tendon. Shoe geometries were added to the feet, and shoe motion was constrained by contact between three shoe segments per foot and the treadmill surface. Six-axis springs constrained motion between the feet and shoe segments. Experimental motion capture data provided input to an inverse kinematics stage, and the final forward dynamics simulations tracked joint angle errors for the left leg and upper body and tracked muscle length errors for the right leg. The one cycle RMS errors between the predicted and measured tibia contact were 178 N and 168 N for the medial and lateral sides for the first gait cycle and 209 N and 228 N for the medial and lateral sides for the faster second gait cycle. One cycle RMS errors between predicted and measured ground reaction forces were 12 N, 13 N, and 65 N in the anterior-posterior, medial-lateral, and vertical directions for the first gait cycle and 43 N, 15 N, and 96 N in the anterior-posterior, medial-lateral, and vertical directions for the second gait cycle.

Why Do Athletes Drink Sports Drinks? A Learning Cycle to Explore the Concept of Osmosis

ERIC Educational Resources Information Center

Carlsen, Brook; Marek, Edmund A.

2010-01-01

Why does an athlete reach for a sports drink after a tough game or practice? The learning cycle presented in this article helps students answer this question. Learning cycles (Marek 2009) are designed to guide students through direct experiences with a particular concept. In this article, students learn about "osmosis," or the moving of water into…

Influence of the implant abutment types and the dynamic loading on initial screw loosening

PubMed Central

Kim, Eun-Sook

2013-01-01

PURPOSE This study examined the effects of the abutment types and dynamic loading on the stability of implant prostheses with three types of implant abutments prepared using different fabrication methods by measuring removal torque both before and after dynamic loading. MATERIALS AND METHODS Three groups of abutments were produced using different types of fabrication methods; stock abutment, gold cast abutment, and CAD/CAM custom abutment. A customized jig was fabricated to apply the load at 30° to the long axis. The implant fixtures were fixed to the jig, and connected to the abutments with a 30 Ncm tightening torque. A sine curved dynamic load was applied for 105 cycles between 25 and 250 N at 14 Hz. Removal torque before loading and after loading were evaluated. The SPSS was used for statistical analysis of the results. A Kruskal-Wallis test was performed to compare screw loosening between the abutment systems. A Wilcoxon signed-rank test was performed to compare screw loosening between before and after loading in each group (α=0.05). RESULTS Removal torque value before loading and after loading was the highest in stock abutment, which was then followed by gold cast abutment and CAD/CAM custom abutment, but there were no significant differences. CONCLUSION The abutment types did not have a significant influence on short term screw loosening. On the other hand, after 105 cycles dynamic loading, CAD/CAM custom abutment affected the initial screw loosening, but stock abutment and gold cast abutment did not. PMID:23509006

The Role of Adaptation in Body Load-Regulating Mechanisms During Locomotion

NASA Technical Reports Server (NTRS)

Ruttley, Tara; Holt, Christopher; Mulavara, Ajitkumar; Bloomberg, Jacob

2010-01-01

Body loading is a fundamental parameter that modulates motor output during locomotion, and is especially important for controlling the generation of stepping patterns, dynamic balance, and termination of locomotion. Load receptors that regulate and control posture and stance in locomotion include the Golgi tendon organs and muscle spindles at the hip, knee, and ankle joints, and the Ruffini endings and the Pacinian corpuscles in the soles of the feet. Increased body weight support (BWS) during locomotion results in an immediate reorganization of locomotor control, such as a reduction in stance and double support duration and decreased hip, ankle, and knee angles during the gait cycle. Previous studies on the effect during exposure to increased BWS while walking showed a reduction in lower limb joint angles and gait cycle timing that represents a reorganization of locomotor control. Until now, no studies have investigated how locomotor control responds after a period of exposure to adaptive modification in the body load sensing system. The goal of this research was to determine the adaptive properties of body load-regulating mechanisms in locomotor control during locomotion. We hypothesized that body load-regulating mechanisms contribute to locomotor control, and adaptive changes in these load-regulating mechanisms require reorganization to maintain forward locomotion. Head-torso coordination, lower limb movement patterns, and gait cycle timing were evaluated before and after a 30-minute adaptation session during which subjects walked on a treadmill at 5.4 km/hr with 40% body weight support (BWS). Before and after the adaptation period, head-torso and lower limb 3D kinematic data were obtained while performing a goal directed task during locomotion with 0% BWS using a video-based motion analysis system, and gait cycle timing parameters were collected by foot switches positioned under the heel and toe of the subjects shoes. Subjects showed adaptive modification in the body load-regulating mechanisms that included increased head movement amplitude, increased knee and ankle flexion, and increased stance, stride, and double support time, with no change in the performance of the task with respect to that measured before exposure to BWS. These changes in locomotor control are opposite to that reported during 40% BWS exposure and indicative of an after-effect after removal of the adaptive stimulus. Therefore, it is evident that just 30 minutes of 40% BWS during locomotion was sufficient to induce adaptive modifications in the body load sensing systems that contribute to reorganization of sensory contributions to stable locomotor control.

Estimation of fatigue life using electromechanical impedance technique

NASA Astrophysics Data System (ADS)

Lim, Yee Yan; Soh, Chee Kiong

2010-04-01

Fatigue induced damage is often progressive and gradual in nature. Structures subjected to large number of fatigue load cycles will encounter the process of progressive crack initiation, propagation and finally fracture. Monitoring of structural health, especially for the critical components, is therefore essential for early detection of potential harmful crack. Recent advent of smart materials such as piezo-impedance transducer adopting the electromechanical impedance (EMI) technique and wave propagation technique are well proven to be effective in incipient damage detection and characterization. Exceptional advantages such as autonomous, real-time and online, remote monitoring may provide a cost-effective alternative to the conventional structural health monitoring (SHM) techniques. In this study, the main focus is to investigate the feasibility of characterizing a propagating fatigue crack in a structure using the EMI technique as well as estimating its remaining fatigue life using the linear elastic fracture mechanics (LEFM) approach. Uniaxial cyclic tensile load is applied on a lab-sized aluminum beam up to failure. Progressive shift in admittance signatures measured by the piezo-impedance transducer (PZT patch) corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression. With the use of LEFM, prediction of the remaining life of the structure at different cycles of loading is possible.

The study of fix composite panel and steel plates on testing stand

NASA Astrophysics Data System (ADS)

Wróbel, A.; Płaczek, M.; Wachna, M.

2016-08-01

In this paper the practical possibilities of strength verification analysis of composite materials used in the manufacture of selected components of railway wagons are presented. Real laboratory stand for measurements in a scale controlled by PLC controller were made. The study of different types of connections of composite materials with sheet metal is presented. In one of the chapter of this paper principles construction of testing stand with pneumatic cylinder were presented. Mainly checking of displacements and stresses generated on the sheet as a result of pneumatic actuators load for composite boards was carried out. The use of the controller with operating panel allows to easy programming testing cycle. The user can define the force generated by the actuator by change of air pressure in cylinder. Additionally the location of acting cylinders and their jump can be changed by operator. The examination of the volume displacements was done by displacement sensor, and the tensile strain gauge. All parameters are written in CatmanEasy - data acquisition software. This article presents the study of stresses and displacements in the composite plates joined with sheet metal, in summary of this article, the authors compare the obtained results with the computer simulation results in the article: "Simulation of stresses in an innovative combination of composite with sheet".

Determination of the critical plane and durability estimation for a multiaxial cyclic loading

NASA Astrophysics Data System (ADS)

Burago, N. G.; Nikitin, A. D.; Nikitin, I. S.; Yakushev, V. L.

2018-03-01

An analytical procedure is proposed to determine the critical plane orientation according to the Findley criterion for the multiaxial cyclic loading. The cases of in-phase and anti-phase cyclic loading are considered. Calculations of the stress state are carried out for the system of the gas turbine engine compressor disk and blades for flight loading cycles. The formulas obtained are used for estimations of the fatigue durability of this essential element of structure.

Effect of Loading Rate Upon Conventional Ceramic Microindentation Hardness

PubMed Central

Quinn, George D.; Patel, Parimal J.; Lloyd, Isabel

2002-01-01

The world standards for conventional ceramic hardness have varying requirements for control of loading rate during the indentation cycle. A literature review suggests that loading rate may affect measured hardness in some instances. In view of the uncertainty over this issue, new experiments over a range of indentation loading rates were performed on a steel, sintered silicon carbide, and an aluminum oxynitride. There was negligible effect upon Vickers hardness when loading rate was varied by almost four orders of magnitude from approximately 0.03 N/s to 10 N/s. PMID:27446732

All-Ceramic Single Crown Restauration of Zirconia Oral Implants and Its Influence on Fracture Resistance: An Investigation in the Artificial Mouth

PubMed Central

Kohal, Ralf-Joachim; Kilian, Jolanta Bernadette; Stampf, Susanne; Spies, Benedikt Christopher

2015-01-01

The aim of the current investigation was to evaluate the fracture resistance of one-piece zirconia oral implants with and without all-ceramic incisor crowns after long-term thermomechanical cycling. A total of 48 implants were evaluated. The groups with crowns (C, 24 samples) and without crowns (N, 24 samples) were subdivided according to the loading protocol, resulting in three groups of 8 samples each: Group “0” was not exposed to cyclic loading, whereas groups “5” and “10” were loaded with 5 and 10 million chewing cycles, respectively. This resulted in 6 different groups: C0/N0, C5/N5 and C10/N10. Subsequently, all 48 implants were statically loaded to fracture and bending moments were calculated. All implants survived the artificial aging. For the static loading the following average bending moments were calculated: C0: 326 Ncm; C5: 339 Ncm; C10: 369 Ncm; N0: 339 Ncm; N5: 398 Ncm and N10: 355 Ncm. To a certain extent, thermomechanical cycling resulted in an increase of fracture resistance which did not prove to be statistically significant. Regarding its fracture resistance, the evaluated ceramic implant system made of Y-TZP seems to be able to resist physiological chewing forces long-term. Restauration with all-ceramic single crowns showed no negative influence on fracture resistance. PMID:28788018

The deformation and acoustic emission of aluminum-magnesium alloy under non-isothermal thermo-mechanical loading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makarov, S. V.; Plotnikov, V. A., E-mail: plotnikov@phys.asu.ru; Lysikov, M. V.

2015-10-27

The following study investigates the deformation behavior and acoustic emission in aluminum-magnesium alloy under conditions of non-isothermal thermo-mechanical loading. The accumulation of deformation in the alloy, in conditions of change from room temperature to 500°C, occurs in two temperature intervals (I, II), characterized by different rates of deformation. The rate of deformation accumulation is correlated with acoustic emission. With load increasing in cycles from 40 to 200 MPa, the value of the boundary temperature (T{sub b}) between intervals I and II changes non-monotonically. In cycles with load up to 90 MPa, the T{sub b} value increases, while an increase up to 200 MPamore » makes T{sub b} shift toward lower temperatures. This suggests that the shift of boundaries in the region of low temperatures and the appearance of high-amplitude pulses of acoustic emission characterize the decrease of the magnitude of thermal fluctuations with increasing mechanical load, leading to the rupture of interatomic bonds in an elementary deformation act.« less

Non-linear programming in shakedown analysis with plasticity and friction

NASA Astrophysics Data System (ADS)

Spagnoli, A.; Terzano, M.; Barber, J. R.; Klarbring, A.

2017-07-01

Complete frictional contacts, when subjected to cyclic loading, may sometimes develop a favourable situation where slip ceases after a few cycles, an occurrence commonly known as frictional shakedown. Its resemblance to shakedown in plasticity has prompted scholars to apply direct methods, derived from the classical theorems of limit analysis, in order to assess a safe limit to the external loads applied on the system. In circumstances where zones of plastic deformation develop in the material (e.g., because of the large stress concentrations near the sharp edges of a complete contact), it is reasonable to expect an effect of mutual interaction of frictional slip and plastic strains on the load limit below which the global behaviour is non dissipative, i.e., both slip and plastic strains go to zero after some dissipative load cycles. In this paper, shakedown of general two-dimensional discrete systems, involving both friction and plasticity, is discussed and the shakedown limit load is calculated using a non-linear programming algorithm based on the static theorem of limit analysis. An illustrative example related to an elastic-plastic solid containing a frictional crack is provided.

Aortic root dynamics and surgery: from craft to science.

PubMed

Cheng, Allen; Dagum, Paul; Miller, D Craig

2007-08-29

Since the fifteenth century beginning with Leonardo da Vinci's studies, the precise structure and functional dynamics of the aortic root throughout the cardiac cycle continues to elude investigators. The last five decades of experimental work have contributed substantially to our current understanding of aortic root dynamics. In this article, we review and summarize the relevant structural analyses, using radiopaque markers and sonomicrometric crystals, concerning aortic root three-dimensional deformations and describe aortic root dynamics in detail throughout the cardiac cycle. We then compare data between different studies and discuss the mechanisms responsible for the modes of aortic root deformation, including the haemodynamics, anatomical and temporal determinants of those deformations. These modes of aortic root deformation are closely coupled to maximize ejection, optimize transvalvular ejection haemodynamics and-perhaps most importantly-reduce stress on the aortic valve cusps by optimal diastolic load sharing and minimizing transvalvular turbulence throughout the cardiac cycle. This more comprehensive understanding of aortic root mechanics and physiology will contribute to improved medical and surgical treatment methods, enhanced therapeutic decision making and better post-intervention care of patients. With a better understanding of aortic root physiology, future research on aortic valve repair and replacement should take into account the integrated structural and functional asymmetry of aortic root dynamics to minimize stress on the aortic cusps in order to prevent premature structural valve deterioration.

Hip contact forces in asymptomatic total hip replacement patients differ from normal healthy individuals: Implications for preclinical testing.

PubMed

Li, Junyan; Redmond, Anthony C; Jin, Zhongmin; Fisher, John; Stone, Martin H; Stewart, Todd D

2014-08-01

Preclinical durability testing of hip replacement implants is standardised by ISO-14242-1 (2002) which is based on historical inverse dynamics analysis using data obtained from a small sample of normal healthy individuals. It has not been established whether loading cycles derived from normal healthy individuals are representative of loading cycles occurring in patients following total hip replacement. Hip joint kinematics and hip contact forces derived from multibody modelling of forces during normal walking were obtained for 15 asymptomatic total hip replacement patients and compared to 38 normal healthy individuals and to the ISO standard for pre-clinical testing. Hip kinematics in the total hip replacement patients were comparable to the ISO data and the hip contact force in the normal healthy group was also comparable to the ISO cycles. Hip contact forces derived from the asymptomatic total hip replacement patients were comparable for the first part of the stance period but exhibited 30% lower peak loads at toe-off. Although the ISO standard provides a representative kinematic cycle, the findings call into question whether the hip joint contact forces in the ISO standard are representative of those occurring in the joint following total hip replacement. Copyright © 2014. Published by Elsevier Ltd.

Localized Versus Distributed Deformation as a Control on the Evolution of Permeability in Anhydrite Rocks

NASA Astrophysics Data System (ADS)

Collettini, C.; de Paola, N.; Faulkner, D.

2007-12-01

We have taken an experimental approach to understand and quantify the deformation processes and fluid flow within anhydrite-bearing fault damage zones during the seismic cycle. Triaxial loading tests have been performed on borehole samples of anhydrites at room temperature, 100 MPa confining pressure (Pc), and range of pore fluid pressures (Pf). Permeability and porosity development was continuously measured throughout the deformation experiments. The tests were conducted on samples with different grain sizes (10 microns to 1 mm) that were cored in different directions relative to the macroscopic foliation. Static permeability measurements have been carried out to determine the permeability anisotropy and sensitivity of the permeability on the effective pressure (Pc - Pf). Our results show that the brittle-ductile transition occurs for effective pressures (Pe) between 20 to 40 MPa and is almost independent of fabric orientation and grain size. Brittle failure is localized along discrete fractures and is always associated with a sudden stress drop. Conversely, ductile failure occurs by distributed deformation along cataclastic bands. In this case no stress drop is observed. Static permeability measurements show increasing values of permeability for decreasing values of Pe, (k = 10E-20 - 10E-22 m2). During single cycle loading tests, the evolution of the permeability is controlled by the failure mode: permeability begins to increase significantly at 40% and 80% of the max load for samples displaying brittle and ductile behaviour, respectively. The permeability values, immediately prior to failure, are about three orders of magnitude higher than the initial values. Multiple cycling tests, within the ductile field, show that permeability starts increasing at only 40% and 30% of the max load during the second and third loading cycle, respectively. Our results show that the history of deformation and the mode of deformation can control the evolution of the permeability, and that they are more significant than other factors such as fabric and grain size. In natural environments, fluid pressure fluctuations, such as might be experienced during the seismic cycle, can promote a switch from localized (brittle behaviour) to more distributed (ductile behaviour) deformation, leading to complex permeability patterns.

How oral environment simulation affects ceramic failure behavior.

PubMed

Lodi, Ediléia; Weber, Kátia R; Benetti, Paula; Corazza, Pedro H; Della Bona, Álvaro; Borba, Márcia

2018-05-01

Investigating the mechanical behavior of ceramics in a clinically simulated scenario contributes to the development of new and tougher materials, improving the clinical performance of restorations. The optimal in vitro environment for testing is unclear. The purpose of this in vitro study was to investigate the failure behavior of a leucite-reinforced glass-ceramic under compression loading and fatigue in different simulated oral environment conditions. Fifty-three plate-shaped ceramic specimens were produced from computer-aided design and computer-aided manufactured (CAD-CAM) blocks and adhesively cemented onto a dentin analog substrate. For the monotonic test (n=23), a gradual compressive load (0.5 mm/min) was applied to the center of the specimens, immersed in 37ºC water, using a universal testing machine. The initial crack was detected with an acoustic system. The fatigue test was performed in a mechanical cycling machine (37ºC water, 2 Hz) using the boundary technique (n=30). Two lifetimes were evaluated (1×10 6 and 2×10 6 cycles). Failure analysis was performed using transillumination. Weibull distribution was used to evaluate compressive load data. A cumulative damage model with an inverse power law (IPL) lifetime-stress relationship was used to fit the fatigue data. A characteristic failure load of 1615 N and a Weibull modulus of 5 were obtained with the monotonic test. The estimated probability of failure (P f ) for 1×10 6 cycles at 100 N was 31%, at 150 N it was 55%, and at 200 N it was 75%. For 2×10 6 cycles, the P f increased approximately 20% in comparison with the values predicted for 1×10 6 cycles, which was not significant. The most frequent failure mode was a radial crack from the intaglio surface. For fatigue, combined failure modes were also found (radial crack combined with cone crack or chipping). Fatigue affects the fracture load and failure mode of leucite-reinforced glass-ceramic. Copyright © 2017 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Mapping HIV community viral load: space, power and the government of bodies

PubMed Central

Gagnon, Marilou; Guta, Adrian

2012-01-01

HIV plasma viral load testing has become more than just a clinical tool to monitor treatment response at the individual level. Increasingly, individual HIV plasma viral load testing is being reported to public health agencies and is used to inform epidemiological surveillance and monitor the presence of the virus collectively using techniques to measure ‘community viral load’. This article seeks to formulate a critique and propose a novel way of theorizing community viral load. Based on the salient work of Michel Foucault, especially the governmentality literature, this article critically examines the use of community viral load as a new strategy of government. Drawing also on the work of Miller and Rose, this article explores the deployment of ‘community’ through the re-configuration of space, the problematization of viral concentrations in specific microlocales, and the government (in the Foucauldian sense) of specific bodies which are seen as ‘risky’, dangerous and therefore, in need of attention. It also examines community viral load as a necessary precondition — forming the ‘conditions of possibility’ — for the recent shift to high impact prevention tactics that are being scaled up across North America. PMID:23060688

Bond–Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading

PubMed Central

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-01-01

The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results. PMID:29495383

Bond-Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading.

PubMed

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-02-26

The objective of this paper was to explore the bond-slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond-slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond-slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond-slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond-slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond-slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

Load to failure of different zirconia implant abutments with titanium components.

PubMed

Mascarenhas, Faye; Yilmaz, Burak; McGlumphy, Edwin; Clelland, Nancy; Seidt, Jeremy

2017-06-01

Abutments with a zirconia superstructure and a titanium insert have recently become popular. Although they have been tested under static load, their performance under simulated mastication is not well known. The purpose of this in vitro study was to compare the cyclic load to failure of 3 types of zirconia abutments with different mechanisms of retention of the zirconia to the titanium interface. Fifteen implants (n=5 per system) and abutments (3 groups: 5 friction fit [Frft]; 5 bonded; and 5 titanium ring friction fit [Ringfrft]) were used. Abutments were thermocycled in water between 5°C and 55°C for 15000 cycles and then cyclically loaded for 20000 cycles or until failure at a frequency of 2 Hz by using a sequentially increased loading protocol up to a maximum of 720 N. The load to failure for each group was recorded, and 1-way analysis of variance was performed. The mean load-to-failure values for the Frft group was 526 N, for the Bond group 605 N, and for the Ringfrft group 288 N. A statistically significant difference was found among all abutments tested (P<.05). Abutments with the bonded connection showed the highest load-to-failure value, and the abutment with the titanium ring friction fit connection showed the lowest load-to-failure value. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Fatigue loading history reconstruction based on the rain-flow technique

NASA Technical Reports Server (NTRS)

Khosrovaneh, A. K.; Dowling, N. E.

1989-01-01

Methods are considered for reducing a non-random fatigue loading history to a concise description and then for reconstructing a time history similar to the original. In particular, three methods of reconstruction based on a rain-flow cycle counting matrix are presented. A rain-flow matrix consists of the numbers of cycles at various peak and valley combinations. Two methods are based on a two dimensional rain-flow matrix, and the third on a three dimensional rain-flow matrix. Histories reconstructed by any of these methods produce a rain-flow matrix identical to that of the original history, and as a result the resulting time history is expected to produce a fatigue life similar to that for the original. The procedures described allow lengthy loading histories to be stored in compact form.

Orion EM-1 Crew Module Structural Test Article loaded onto Guppy

NASA Image and Video Library

2017-04-25

A view from inside NASA's Super Guppy aircraft at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida, as the Orion Exploration Mission-1 (EM-1) structural test article, secured inside its transport container, is loaded into the aircraft. The test article will be transported to Lockheed Martin's Denver facility for testing. The Orion spacecraft will launch atop NASA’s Space Launch System rocket on EM-1, its first deep space mission.

Seasonal Water Storage, the Resulting Deformation and Stress, and Occurrence of Earthquakes in California

NASA Astrophysics Data System (ADS)

Johnson, C. W.; Burgmann, R.; Fu, Y.; Dutilleul, P.

2015-12-01

In California the accumulated winter snow pack in the Sierra Nevada, reservoirs and groundwater water storage in the Central Valley follow an annual periodic cycle and each contribute to the resulting surface deformation, which can be observed using GPS time series. The ongoing drought conditions in the western U.S. amplify the observed uplift signal as the Earth's crust responds to the mass changes associated with the water loss. The near surface hydrological mass loss can result in annual stress changes of ~1kPa at seismogenic depths. Similarly, small static stress perturbations have previously been associated with changes in earthquake activity. Periodicity analysis of earthquake catalog time series suggest that periods of 4-, 6-, 12-, and 14.24-months are statistically significant in regions of California, and provide documentation for the modulation of earthquake populations at periods of natural loading cycles. Knowledge of what governs the timing of earthquakes is essential to understanding the nature of the earthquake cycle. If small static stress changes influence the timing of earthquakes, then one could expect that events will occur more rapidly during periods of greater external load increases. To test this hypothesis we develop a loading model using GPS derived surface water storage for California and calculate the stress change at seismogenic depths for different faulting geometries. We then evaluate the degree of correlation between the stress models and the seismicity taking into consideration the variable amplitude of stress cycles, the orientation of transient load stress with respect to the background stress field, and the geometry of active faults revealed by focal mechanisms.

75 FR 81409 - Airworthiness Directives; The Boeing Company Model 737-200, -300, -400, and -500 Series Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-28

... cracking, caused by high flight cycle stresses from both pressurization and maneuver loads. We are issuing... sections, in addition to stub beam cracking, caused by high flight cycle stresses from both pressurization...

Analysis of a modular generator for high-voltage, high-frequency pulsed applications, using low voltage semiconductors (< 1 kV) and series connected step-up (1:10) transformers.

PubMed

Redondo, L M; Fernando Silva, J; Margato, E

2007-03-01

This article discusses the operation of a modular generator topology, which has been developed for high-frequency (kHz), high-voltage (kV) pulsed applications. The proposed generator uses individual modules, each one consisting of a pulse circuit based on a modified forward converter, which takes advantage of the required low duty cycle to operate with a low voltage clamp reset circuit for the step-up transformer. This reduces the maximum voltage on the semiconductor devices of both primary and secondary transformer sides. The secondary winding of each step-up transformer is series connected, delivering a fraction of the total voltage. Each individual pulsed module is supplied via an isolation transformer. The assembled modular laboratorial prototype, with three 5 kV modules, 800 V semiconductor switches, and 1:10 step-up transformers, has 80% efficiency, and is capable of delivering, into resistive loads, -15 kV1 A pulses with 5 micros width, 10 kHz repetition rate, with less than 1 micros pulse rise time. Experimental results for resistive loads are presented and discussed.

A MODELLING FRAMEWORK FOR MERCURY CYCLING IN LAKE MICHIGAN

EPA Science Inventory

A time-dependent mercury model was developed to describe mercury cycling in Lake Michigan. The model addresses dynamic relationships between net mercury loadings and the resulting concentrations of mercury species in the water and sediment. The simplified predictive modeling fram...

Fatigue study of a GRP pedestrian bridge : final report.

DOT National Transportation Integrated Search

1986-01-01

Static and cyclic load tests were conducted on a 16-ft long bridge constructed with fiberglass materials. Approximately 1.6 million cycles of loads were applied to the deck to study the fatigue characteristics of the bridge. The location and magnitud...

Bone healing response in cyclically loaded implants: Comparing zero, one, and two loading sessions per day.

PubMed

de Barros E Lima Bueno, Renan; Dias, Ana Paula; Ponce, Katia J; Wazen, Rima; Brunski, John B; Nanci, Antonio

2018-05-31

When bone implants are loaded, they are inevitably subjected to displacement relative to bone. Such micromotion generates stress/strain states at the interface that can cause beneficial or detrimental sequels. The objective of this study is to better understand the mechanobiology of bone healing at the tissue-implant interface during repeated loading. Machined screw shaped Ti implants were placed in rat tibiae in a hole slightly bigger than the implant diameter. Implants were held stable by a specially-designed bone plate that permits controlled loading. Three loading regimens were applied, (a) zero loading, (b) one daily loading session of 60 cycles with an axial force of 1.5 N/cycle for 7 days, and (c) two such daily sessions with the same axial force also for 7 days. Finite element analysis was used to characterize the mechanobiological conditions produced by the loading sessions. After 7 days, the implants with surrounding interfacial tissue were harvested and processed for histological, histomorphometric and DNA microarray analyses. Histomorphometric analyses revealed that the group subjected to repeated loading sessions exhibited a significant decrease in bone-implant contact and increase in bone-implant distance, as compared to unloaded implants and those subjected to only one loading session. Gene expression profiles differed during osseointegration between all groups mainly with respect to inflammatory and unidentified gene categories. The results indicate that increasing the daily cyclic loading of implants induces deleterious changes in the bone healing response, most likely due to the accumulation of tissue damage and associated inflammatory reaction at the bone-implant interface. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Neuquén Group (Upper Cretaceous): A case of underfilled-overfilled cycles in an Andean foreland basin, Neuquén basin, Argentina

NASA Astrophysics Data System (ADS)

Asurmendi, Estefanía; Sánchez, María Lidia; Fennell, Lucas

2017-12-01

The Nenquén Group was deposited during a period dominated by the Cretaceous Greenhouse and can be divided in three cycles correlated with large-scale changes in the evolution of the Andean foreland basin. The filling of the Neuquén Group is constituted by a complete cycle and two incomplete cycles of underfilled-overfilled, separated by first-order discontinuities assigned to the uplift of the Agrio fold-and-thrust belt during the Chasca/Catequil, Mid Ocean Ridge (CCMOR) collision, coinciding with first-order climatic changes within the Cretaceous greenhouse cycle. The Candeleros Formation in the base of this group was deposited in late underfilled conditions, showing prominent forebulge zones. It is demonstrated that during the Albian, with the cratonward migration of the uplifting forebulge zones, the axis of backbulge zones also migrated cratonwards and a wide uplifted forebulge zone was formed. On top, the Huincul Formation was deposited in an overfilled period without orogenic load, while the Cerro Lisandro Formation was deposited in early underfilled conditions with orogenic load. The Río Neuquén Subgroup started with a late underfilled period (Portezuelo Formation -second-order discontinuity), and after wards the Plottier Formation was deposited in an overfilled period without orogenic load. Finally, the Río Colorado Subgroup was deposited under late and early underfilled conditions (Bajo de la Carpa and Anacleto Formations respectively).

Voice amplification as a means of reducing vocal load for elementary music teachers.

PubMed

Morrow, Sharon L; Connor, Nadine P

2011-07-01

Music teachers are over four times more likely than classroom teachers to develop voice disorders and greater than eight times more likely to have voice-related problems than the general public. Research has shown that individual voice-use parameters of phonation time, fundamental frequency and vocal intensity, as well as vocal load as calculated by cycle dose and distance dose are significantly higher for music teachers than their classroom teacher counterparts. Finding effective and inexpensive prophylactic measures to decrease vocal load for music teachers is an important aspect for voice preservation for this group of professional voice users. The purpose of this study was to determine the effects of voice amplification on vocal intensity and vocal load in the workplace as measured using a KayPENTAX Ambulatory Phonation Monitor (APM) (KayPENTAX, Lincoln Park, NJ). Seven music teachers were monitored for 1 workweek using an APM to determine average vocal intensity (dB sound pressure level [SPL]) and vocal load as calculated by cycle dose and distance dose. Participants were monitored a second week while using a voice amplification unit (Asyst ChatterVox; Asyst Communications Company, Inc., Indian Creek, IL). Significant decreases in mean vocal intensity of 7.00-dB SPL (P<0.001) were found using amplification, along with significant decreases (P=0.001) in cycle dose and distance dose. In addition, mean phonation time was found to decrease using amplification (P=0.023). These data suggest that voice amplification may be an effective intervention to decrease the potentially damaging vocal loads experienced by elementary music teachers in the classroom. Copyright © 2011 The Voice Foundation. Published by Mosby, Inc. All rights reserved.

Acid loading test (pH)

MedlinePlus

... medlineplus.gov/ency/article/003615.htm Acid loading test (pH) To use the sharing features on this page, please enable JavaScript. The acid loading test (pH) measures the ability of the kidneys to send ...

T-Cap Pull-Off and Bending Behavior for Stitched Structure

NASA Technical Reports Server (NTRS)

Lovejoy, Andrew E.; Leone, Frank A., Jr.

2016-01-01

The Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) is a structural concept that was developed by The Boeing Company to address the complex structural design aspects associated with a pressurized hybrid wing body aircraft configuration. An important design feature required for assembly is the integrally stitched T-cap, which provides connectivity of the corner (orthogonal) joint between adjacent panels. A series of tests were conducted on T-cap test articles, with and without a rod stiffener penetrating the T-cap web, under tension (pull-off) and bending loads. Three designs were tested, including the baseline design used in largescale test articles. The baseline had only the manufacturing stitch row adjacent to the fillet at the base of the T-cap web. Two new designs added stitching rows to the T-cap web at either 0.5- or 1.0-inch spacing along the height of the web. Testing was conducted at NASA Langley Research Center to determine the behavior of the T-cap region resulting from the applied loading. Results show that stitching arrests the initial delamination failures so that the maximum strength capability exceeds the load at which the initial delaminations develop. However, it was seen that the added web stitching had very little effect on the initial delamination failure load, but actually decreased the initial delamination failure load for tension loading of test articles without a stiffener passing through the web. Additionally, the added web stitching only increased the maximum load capability by between 1% and 12.5%. The presence of the stiffener, however, did increase the initial and maximum loads for both tension and bending loading as compared to the stringerless baseline design. Based on the results of the few samples tested, the additional stitching in the T-cap web showed little advantage over the baseline design in terms of structural failure at the T-cap web/skin junction for the current test articles.

Tension and Bending Testing of an Integral T-Cap for Stitched Composite Airframe Joints

NASA Technical Reports Server (NTRS)

Lovejoy, Andrew E.; Leone, Frank A., Jr.

2016-01-01

The Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) is a structural concept that was developed by The Boeing Company to address the complex structural design aspects associated with a pressurized hybrid wing body aircraft configuration. An important design feature required for assembly is the integrally stitched T-cap, which provides connectivity of the corner (orthogonal) joint between adjacent panels. A series of tests were conducted on T-cap test articles, with and without a rod stiffener penetrating the T-cap web, under tension (pull-off) and bending loads. Three designs were tested, including the baseline design used in large-scale test articles. The baseline had only the manufacturing stitch row adjacent to the fillet at the base of the T-cap web. Two new designs added stitching rows to the T-cap web at either 0.5- or 1.0-inch spacing along the height of the web. Testing was conducted at NASA Langley Research Center to determine the behavior of the T-cap region resulting from the applied loading. Results show that stitching arrests the initial delamination failures so that the maximum strength capability exceeds the load at which the initial delaminations develop. However, it was seen that the added web stitching had very little effect on the initial delamination failure load, but actually decreased the initial delamination failure load for tension loading of test articles without a stiffener passing through the web. Additionally, the added web stitching only increased the maximum load capability by between 1% and 12.5%. The presence of the stiffener, however, did increase the initial and maximum loads for both tension and bending loading as compared to the stringerless baseline design. Based on the results of the few samples tested, the additional stitching in the T-cap web showed little advantage over the baseline design in terms of structural failure at the T-cap web/skin junction for the current test articles.

Transient Load Following and Control Analysis of Advanced S-CO2 Power Conversion with Dry Air Cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moisseytsev, Anton; Sienicki, James J.

2016-01-01

Supercritical carbon dioxide (S-CO2) Brayton cycles are under development as advanced energy converters for advanced nuclear reactors, especially the Sodium-Cooled Fast Reactor (SFR). The use of dry air cooling for direct heat rejection to the atmosphere ultimate heat sink is increasingly becoming a requirement in many regions due to restrictions on water use. The transient load following and control behavior of an SFR with an S-CO2 cycle power converter utilizing dry air cooling have been investigated. With extension and adjustment of the previously existing control strategy for direct water cooling, S-CO2 cycle power converters can also be used for loadmore » following operation in regions where dry air cooling is a requirement« less

Acoustic emission characteristics of copper alloys under low-cycle fatigue conditions

NASA Technical Reports Server (NTRS)

Krampfner, Y.; Kawamoto, A.; Ono, K.; Green, A.

1975-01-01

The acoustic emission (AE) characteristics of pure copper, zirconium-copper, and several copper alloys were determined to develop nondestructive evaluation schemes of thrust chambers through AE techniques. The AE counts rms voltages, frequency spectrum, and amplitude distribution analysis evaluated AE behavior under fatigue loading conditions. The results were interpreted with the evaluation of wave forms, crack propagation characteristics, as well as scanning electron fractographs of fatigue-tested samples. AE signals at the beginning of a fatigue test were produced by a sample of annealed alloys. A sample of zirconium-containing alloys annealed repeatedly after each fatigue loading cycle showed numerous surface cracks during the subsequent fatigue cycle, emitting strong-burst AE signals. Amplitude distribution analysis exhibits responses that are characteristic of certain types of AE signals.

Experience Gained from Construction of Low-Emission Combustion Chambers for On-Land Large-Capacity Gas-Turbine Units: GT24/26

NASA Astrophysics Data System (ADS)

Bulysova, L. A.; Vasil'ev, V. D.; Berne, A. L.; Gutnik, M. M.

2018-06-01

This article is the third in a planned series of articles devoted to the experience gained around the world in constructing low-emission combustion chambers for on-land large-capacity (above 250 MW) gas-turbine units (GTUs). The aim of this study is to generalize and analyze the ways in which different designers apply the fuel flow and combustion arrangement principles and the fuel feed control methods. The considered here GT24 and GT26 (GT24/26) gas-turbine units generating electric power at the 60 and 50 Hz frequencies, respectively, are fitted with burners of identical designs. Designed by ABB, these GTUs were previously manufactured by Alstom, and now they are produced by Ansaldo Energia. The efficiency of these GTUs reaches 41% at the 354 MW power output during operation in the simple cycle and 60.5% at the 505MW power output during operation in the combined cycle. Both GTUs comply with all requirements for harmful emissions. The compression ratio is equal to 35. In this article, a system is considered for two-stage fuel combustion in two sequentially arranged low-emission combustion chambers, one of which is placed upstream of the high-pressure turbine (CC1) and the other upstream of the low-pressure turbine (CC2). The article places the main focus on the CC2, which operates with a decreased content of oxygen in the oxidizer supplied to the burner inlets. The original designs of vortex generators and nozzles placed in the flow of hot combustion products going out from the high-pressure turbine are described in detail. The article also presents an original CC2 front plate cooling system, due to which a significantly smaller amount of air fed for cooling has been reached. The article also presents the pressure damping devices incorporated in the chamber, the use of which made it possible to obtain a significantly wider range of CC loads at which its low-emission operation is ensured. The fuel feed adjustment principles and the combustion control methods implemented in the low-emission combustion chambers of this GTU are of interest from the scientific and practical points of view.

The Effect of Fatigue Cracks on Fastener Flexibility, Load Distribution and Fatigue Crack Growth

DTIC Science & Technology

2012-05-01

fastener will transfer within a given fastener pattern. iv iv However, current methods do not account for the change in flexibility at a fastener...affects the growth of the crack. Thus, as the effect of the crack starts to impact the load transfer of the joint there is a need to account for...not account for spectrum loading but typically were cycled from 1g to limit or maximum flight load and then correlated to measured usage using

Characterization of Ternary NiTiPd High-Temperature Shape-Memory Alloys under Load-Biased Thermal Cycling

NASA Technical Reports Server (NTRS)

Bigelow, Glen S.; Padula, Santo A.; Noebe, Ronald D.; Garg, Anita; Gaydosh, Darrell

2010-01-01

While NiTiPd alloys have been extensively studied for proposed use in high-temperature shape-memory applications, little is known about the shape-memory response of these materials under stress. Consequently, the isobaric thermal cyclic responses of five (Ni,Pd)49.5Ti50.5 alloys with constant stoichiometry and Pd contents ranging from 15 to 46 at. pct were investigated. From these tests, transformation temperatures, transformation strain (which is proportional to work output), and unrecovered strain per cycle (a measure of dimensional instability) were determined as a function of stress for each alloy. It was found that increasing the Pd content over this range resulted in a linear increase in transformation temperature, as expected. At a given stress level, work output decreased while the amount of unrecovered strain produced during each load-biased thermal cycle increased with increasing Pd content, during the initial thermal cycles. However, continued thermal cycling at constant stress resulted in a saturation of the work output and nearly eliminated further unrecovered strain under certain conditions, resulting in stable behavior amenable to many actuator applications.

Apparatus and methods for supplying auxiliary steam in a combined cycle system

DOEpatents

Gorman, William G.; Carberg, William George; Jones, Charles Michael

2002-01-01

To provide auxiliary steam, a low pressure valve is opened in a combined cycle system to divert low pressure steam from the heat recovery steam generator to a header for supplying steam to a second combined cycle's steam turbine seals, sparging devices and cooling steam for the steam turbine if the steam turbine and gas turbine lie on a common shaft with the generator. Cooling steam is supplied the gas turbine in the combined cycle system from the high pressure steam turbine. Spent gas turbine cooling steam may augment the low pressure steam supplied to the header by opening a high pressure valve whereby high and low pressure steam flows are combined. An attemperator is used to reduce the temperature of the combined steam in response to auxiliary steam flows above a predetermined flow and a steam header temperature above a predetermined temperature. The auxiliary steam may be used to start additional combined cycle units or to provide a host unit with steam turbine cooling and sealing steam during full-speed no-load operation after a load rejection.

High-speed thermal cycling system and method of use

DOEpatents

Hansen, A.D.A.; Jaklevic, J.M.

1996-04-16

A thermal cycling system and method of use are described. The thermal cycling system is based on the circulation of temperature-controlled water directly to the underside of thin-walled polycarbonate plates. The water flow is selected from a manifold fed by pumps from heated reservoirs. The plate wells are loaded with typically 15-20 microliters of reagent mix for the PCR process. Heat transfer through the thin polycarbonate is sufficiently rapid that the contents reach thermal equilibrium with the water in less than 15 seconds. Complete PCR amplification runs of 40 three-step cycles have been performed in as little as 14.5 minutes, with the results showing substantially enhanced specificity compared to conventional technology requiring run times in excess of 100 minutes. The plate clamping station is designed to be amenable to robotic loading and unloading of the system. It includes a heated lid, thus eliminating the need for mineral oil overlay of the reactants. The present system includes three or more plate holder stations, fed from common reservoirs but operating with independent switching cycles. The system can be modularly expanded. 13 figs.

High-speed thermal cycling system and method of use

DOEpatents

Hansen, Anthony D. A.; Jaklevic, Joseph M.

1996-01-01

A thermal cycling system and method of use are described. The thermal cycling system is based on the-circulation of temperature-controlled water directly to the underside of thin-walled polycarbonate microtiter plates. The water flow is selected from a manifold fed by pumps from heated reservoirs. The plate wells are loaded with typically 15-20 .mu.l of reagent mix for the PCR process. Heat transfer through the thin polycarbonate is sufficiently rapid that the contents reach thermal equilibrium with the water in less than 15 seconds. Complete PCR amplification runs of 40 three-step cycles have been performed in as little as 14.5 minutes, with the results showing substantially enhanced specificity compared to conventional technology requiring run times in excess of 100 minutes. The plate clamping station is designed to be amenable to robotic loading and unloading of the system. It includes a heated lid, thus eliminating the need for mineral oil overlay of the reactants. The present system includes three or more plate holder stations, fed from common reservoirs but operating with independent switching cycles. The system can be modularly expanded.

Effects of High Mean Stress on High-cycle Fatigue Behavior of PWA 1480

NASA Technical Reports Server (NTRS)

Majumdar, S.; Antolovich, S. D.; Milligan, W. W.

1985-01-01

PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the space shuttle main engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. The present paper describes the results obtained in an ongoing program at the Argonne National Laboratory, sponsored by NASA Lewis, to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material. Straight-gauge high-cycle fatigue specimens, 0.2 inch in diameter and with the specimen axis in the 001 direction, were supplied by NASA Lewis. The nominal room temperature yield and ultimate strength of the material were 146 and 154 ksi, respectively. Each specimen was polished with 1-micron diamond paste prior to testing. However, the surface of each specimen contained many pores, some of which were as large as 50 micron. In the initial tests, specimens were subjected to axial-strain-controlled cycles. However, very little cyclic plasticity was observed.

Quantifying Solar Cell Cracks in Photovoltaic Modules by Electroluminescence Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spataru, Sergiu; Hacke, Peter; Sera, Dezso

2015-06-14

This article proposes a method for quantifying the percentage of partially and totally disconnected solar cell cracks by analyzing electroluminescence images of the photovoltaic module taken under high- and low-current forward bias. The method is based on the analysis of the module's electroluminescence intensity distribution, applied at module and cell level. These concepts are demonstrated on a crystalline silicon photovoltaic module that was subjected to several rounds of mechanical loading and humidity-freeze cycling, causing increasing levels of solar cell cracks. The proposed method can be used as a diagnostic tool to rate cell damage or quality of modules after transportation.more » Moreover, the method can be automated and used in quality control for module manufacturers, installers, or as a diagnostic tool by plant operators and diagnostic service providers.« less

Stress fractures of the foot and ankle.

PubMed

Welck, M J; Hayes, T; Pastides, P; Khan, W; Rudge, B

2017-08-01

Stress fractures occur as a result of microscopic injuries sustained when bone is subjected to repeated submaximal stresses. Overtime, with repeated cycles of loading, accumulation of such injuries can lead to macro-structural failure and frank fracture. There are numerous stress fractures about the foot and ankle of which a trauma and orthopaedic surgeon should be aware. These include: metatarsal, tibia, calcaneus, navicular, fibula, talus, medial malleolus, sesamoid, cuneiform and cuboid. Awareness of these fractures is important as the diagnosis is frequently missed and appropriate treatment delayed. Late identification can be associated with protracted pain and disability, and may predispose to non-union and therefore necessitate operative intervention. This article outlines the epidemiology and risk factors, aetiology, presentation and management of the range of stress fractures in the foot and ankle. Copyright © 2015 Elsevier Ltd. All rights reserved.

Source of electrical power for an electric vehicle and other purposes, and related methods

DOEpatents

LaFollette, Rodney M.

2000-05-16

Microthin sheet technology is disclosed by which superior batteries are constructed which, among other things, accommodate the requirements for high load rapid discharge and recharge, mandated by electric vehicle criteria. The microthin sheet technology has process and article overtones and can be used to form thin electrodes used in batteries of various kinds and types, such as spirally-wound batteries, bipolar batteries, lead acid batteries, silver/zinc batteries, and others. Superior high performance battery features include: (a) minimal ionic resistance; (b) minimal electronic resistance; (c) minimal polarization resistance to both charging and discharging; (d) improved current accessibility to active material of the electrodes; (e) a high surface area to volume ratio; (f) high electrode porosity (microporosity); (g) longer life cycle; (h) superior discharge/recharge characteristics; (j) higher capacities (A.multidot.hr); and k) high specific capacitance.

Source of electrical power for an electric vehicle and other purposes, and related methods

DOEpatents

LaFollette, Rodney M.

2002-11-12

Microthin sheet technology is disclosed by which superior batteries are constructed which, among other things, accommodate the requirements for high load rapid discharge and recharge, mandated by electric vehicle criteria. The microthin sheet technology has process and article overtones and can be used to form corrugated thin electrodes used in batteries of various kinds and types, such as spirally-wound batteries, bipolar batteries, lead acid batteries, silver/zinc batteries, and others. Superior high performance battery features include: (a) minimal ionic resistance; (b) minimal electronic resistance; (c) minimal polarization resistance to both charging and discharging; (d) improved current accessibility to active material of the electrodes; (e) a high surface area to volume ratio; (f) high electrode porosity (microporosity); (g) longer life cycle; (h) superior discharge/recharge characteristics; (i) higher capacities (A.multidot.hr); and (j) high specific capacitance.

Battery with a microcorrugated, microthin sheet of highly porous corroded metal

DOEpatents

LaFollette, Rodney M.

2005-09-27

Microthin sheet technology is disclosed by which superior batteries are constructed which, among other things, accommodate the requirements for high load rapid discharge and recharge, mandated by electric vehicle criteria. The microthin sheet technology has process and article overtones and can be used to form thin electrodes used in batteries of various kinds and types, such as spirally-wound batteries, bipolar batteries, lead acid batteries silver/zinc batteries, and others. Superior high performance battery features include: (a) minimal ionic resistance; (b) minimal electronic resistance; (c) minimal polarization resistance to both charging and discharging; (d) improved current accessibility to active material of the electrodes; (e) a high surface area to volume ratio; (f) high electrode porosity (microporosity); (g) longer life cycle; (h) superior discharge/recharge characteristics; (i) higher capacities (A.multidot.hr); and (j) high specific capacitance.

Toward a virtual platform for materials processing

NASA Astrophysics Data System (ADS)

Schmitz, G. J.; Prahl, U.

2009-05-01

Any production is based on materials eventually becoming components of a final product. Material properties being determined by the microstructure of the material thus are of utmost importance both for productivity and reliability of processing during production and for application and reliability of the product components. A sound prediction of materials properties therefore is highly important. Such a prediction requires tracking of microstructure and properties evolution along the entire component life cycle starting from a homogeneous, isotropic and stress-free melt and eventually ending in failure under operational load. This article will outline ongoing activities at the RWTH Aachen University aiming at establishing a virtual platform for materials processing comprising a virtual, integrative numerical description of processes and of the microstructure evolution along the entire production chain and even extending further toward microstructure and properties evolution under operational conditions.

Life Cycle Analysis of a SpaceCube Printed Circuit Board Assembly Using Physics of Failure Methodologies

NASA Technical Reports Server (NTRS)

Sood, Bhanu; Evans, John; Daniluk, Kelly; Sturgis, Jason; Davis, Milton; Petrick, David

2017-01-01

In this reliability life cycle evaluation of the SpaceCube 2.0 processor card, a partially populated version of the card is being evaluated to determine its durability with respect to typical GSFC mission loads.

Dry etch challenges for CD shrinkage in memory process

NASA Astrophysics Data System (ADS)

Matsushita, Takaya; Matsumoto, Takanori; Mukai, Hidefumi; Kyoh, Suigen; Hashimoto, Kohji

2015-03-01

Line pattern collapse attracts attention as a new problem of the L&S formation in sub-20nm H.P feature. Line pattern collapse that occurs in a slight non-uniformity of adjacent CD (Critical dimension) space using double patterning process has been studied with focus on micro-loading effect in Si etching. Bias RF pulsing plasma etching process using low duty cycle helped increase of selectivity Si to SiO2. In addition to the effect of Bias RF pulsing process, the thin mask obtained from improvement of selectivity has greatly suppressed micro-loading in Si etching. However it was found that micro-loading effect worsen again in sub-20nm space width. It has been confirmed that by using cycle etch process to remove deposition with CFx based etching micro-loading effect could be suppressed. Finally, Si etching process condition using combination of results above could provide finer line and space without "line pattern collapse" in sub-20nm.

An elastoplastic analysis of a uniaxially loaded sheet with an interference-fit bolt. [using the finite element method

NASA Technical Reports Server (NTRS)

Crews, J. H., Jr.

1974-01-01

The stresses and strains in a uniaxially loaded sheet with an unloaded interference-fit bolt were calculated by an elastoplastic finite-element analysis. The material properties represented a 7075-T6 aluminum alloy sheet and a steel bolt. The analysis considered the two ideal cases of no slip and no friction at the bolt-sheet interface for a single combination of bolt diameter, interference level, and cyclic loading. When the bolt was inserted, the sheet deformed plastically near the hole; the first tensile load cycle produced additional yielding, but subsequent cycles to the same level caused only elastic cyclic stresses. These stresses together with fatigue data for unnotched specimens were used to estimate crack initiation periods and initiation sites. The cases analyzed with interference-fit bolts were predicted to have crack initiation periods which were about 50 times that for a clearance-fit bolt. Crack initiation was predicted to occur on the transverse axis at a distance of about one radius from the hole.

Effect of Thermal Storage on the Performance of a Wood Pellet-fired Residential Boiler

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, Butcher

Interest in the direct use of biomass for thermal applications as a renewable technology is increasing as is also focus on air pollutant emissions from these sources and methods to minimize the impact. This work has focused on wood pellet-fired residential boilers, which are the cleanest fuel in this category. In the residential application the load varies strongly over the course of a year and a high fraction of the load is typically under 15% of the maximum boiler capacity. Thermal storage can be used even with boilers which have modulation capacity typically to 30% of the boiler maximum. Onemore » common pellet boiler was tested at full load and also at the minimum load used in the U.S. certification testing (15%). In these tests the load was steady over the test period. Testing was also done with an emulated load profile for a home in Albany, N.Y. on a typical January, March, and April day. In this case the load imposed on the boiler varied hourly under computer control, based on the modeled load for the example case used. The boiler used has a nominal output of 25 kW and a common mixed hardwood/softwood commercial pellet was used. Moisture content was 3.77%. A dilution tunnel approach was used for the measurement of particulate emissions, in accordance with U.S. certification testing requirements. The test results showed that the use of storage strongly reduces cycling rates under part load conditions. The transients which occur as these boilers cycle contribute to increased particulate emissions and reduced efficiency. The time period of a full cycle at a given load condition can be increased by increasing the storage tank volume and/or increasing the control differential range. It was shown that increasing the period strongly increased the measured efficiency and reduced the particulate emission (relative to the no storage case). The impact was most significant at the low load levels. Storage tank heat loss is shown to be a significant factor in thermal efficiency, particularly at low load. Different methods to measure this heat loss were explored. For one of the tanks evaluated the efficiency loss at the 15% load point was found to be as high as 7.9%. Where storage is used good insulation on the tank, insulation on the piping, and attention to fittings are recommended.« less

The influence of implant-abutment connection on the screw loosening and microleakage.

PubMed

Tsuruta, Katsuhiro; Ayukawa, Yasunori; Matsuzaki, Tatsuya; Kihara, Masafumi; Koyano, Kiyoshi

2018-04-09

There are some spaces between abutment and implant body which can be a reservoir of toxic substance, and they can penetrate into subgingival space from microgap at the implant-abutment interface. This penetration may cause periimplantitis which is known to be one of the most important factors associated with late failure. In the present study, three kinds of abutment connection system, external parallel connection (EP), internal parallel connection (IP), and internal conical connection (CC), were studied from the viewpoint of microleakage from the gap between the implant and the abutment and in connection with the loosening of abutment screw. We observed dye leakage from abutment screw hole to outside through microgap under the excessive compressive and tensile load and evaluated the anti-leakage characteristics of these connection systems. During the experiment, one abutment screw for EP and two screws for IP, out of seven samples in each group, were fractured. After the 2000 cycles of compressive tensile loadings, removal torque value (RTV) of abutment screw represented no statistical differences among three groups. Standard deviation was largest in the RTV of EP and smallest in that of CC. The results of microleakage of toluidine blue from implant-abutment connection indicated that microleakage generally increased as loading procedure progressed. The amount of microleakage was almost plateau at 2000 cycles in CC, but still increasing in other two groups. The value of microleakage greatly scattered in EP, but the deviation of that in CC is significantly smaller. At 500 cycles of loading, there were no significant differences in the amount of microleakage among the groups, but at 1000, 1500, and 2000 cycles of loading, the amount of microleakage in CC was significantly smaller than that in IP. Throughout the experiment, the amount of microleakage in EP was largest, but no statistical difference was indicated due to the high standard deviation. Within the limitation of the present study, CC was stable even after the loading in the RTV of abutment screw and it prevented microleakage from the microgap between the implant body and the abutment, among the three tested connections.

Orion EM-1 Crew Module Structural Test Article loaded onto Guppy

NASA Image and Video Library

2017-04-25

The Orion Exploration Mission-1 (EM-1) structural test article, secured inside its transport container, is lifted up by crane from its transport vehicle at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida. The test article will be loaded into NASA's Super Guppy aircraft, in view at left, and transported to Lockheed Martin's Denver facility for testing. The Orion spacecraft will launch atop NASA’s Space Launch System rocket on EM-1, its first deep space mission.

Orion EM-1 Crew Module Structural Test Article loaded onto Guppy

NASA Image and Video Library

2017-04-25

On the tarmac at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida, NASA and contractor workers review procedures before beginning loading of the Orion Exploration Mission-1 (EM-1) structural test article in its transport container into NASA's Super Guppy aircraft. The test article will be transported to Lockheed Martin's Denver facility for testing. The Orion spacecraft will launch atop NASA’s Space Launch System rocket on EM-1, its first deep space mission.

Solar-powered compression-enhanced ejector air conditioner

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sokolov, M.; Hershgal, D.

1993-09-01

This article is an extension of an earlier investigation into the possibility of adaptation of the ejector refrigeration cycle to solar air-conditioning. In a previous work the ejector cycle has been proven a viable option only for a limited number of cases. These include systems with combined (heating, cooling, and hot water supply) loads where means for obtaining low condensing temperature are available. The purpose of this work is to extend the applicability of such systems by enhancing their efficiency and thereby improving their economical attractiveness. This is done by introducing the compression enhanced ejector system in which mechanical (rathermore » than thermal) energy is used to boost the pressure of the secondary stream into the ejector, Such a boost improves the performance of the whole system. Similar to the conventional ejector, the compression-enhanced ejector system utilizes practically the same hardware for solar heating during the winter and for solar cooling during the summer. Thus, it is capable of providing a year-round space air-conditioning. Optimization of the best combination in which the solar and refrigeration systems combine through the vapor generator working temperature is also presented.« less

Model-based optimal design of active cool thermal energy storage for maximal life-cycle cost saving from demand management in commercial buildings

DOE PAGES

Cui, Borui; Gao, Dian-ce; Xiao, Fu; ...

2016-12-23

This article provides a method in comprehensive evaluation of cost-saving potential of active cool thermal energy storage (CTES) integrated with HVAC system for demand management in non-residential building. The active storage is beneficial by shifting peak demand for peak load management (PLM) as well as providing longer duration and larger capacity of demand response (DR). In this research, a model-based optimal design method using genetic algorithm is developed to optimize the capacity of active CTES aiming for maximizing the life-cycle cost saving concerning capital cost associated with storage capacity as well as incentives from both fast DR and PLM. Inmore » the method, the active CTES operates under a fast DR control strategy during DR events while under the storage-priority operation mode to shift peak demand during normal days. The optimal storage capacities, maximum annual net cost saving and corresponding power reduction set-points during DR event are obtained by using the proposed optimal design method. Lastly, this research provides guidance in comprehensive evaluation of cost-saving potential of CTES integrated with HVAC system for building demand management including both fast DR and PLM.« less

Model-based optimal design of active cool thermal energy storage for maximal life-cycle cost saving from demand management in commercial buildings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, Borui; Gao, Dian-ce; Xiao, Fu

This article provides a method in comprehensive evaluation of cost-saving potential of active cool thermal energy storage (CTES) integrated with HVAC system for demand management in non-residential building. The active storage is beneficial by shifting peak demand for peak load management (PLM) as well as providing longer duration and larger capacity of demand response (DR). In this research, a model-based optimal design method using genetic algorithm is developed to optimize the capacity of active CTES aiming for maximizing the life-cycle cost saving concerning capital cost associated with storage capacity as well as incentives from both fast DR and PLM. Inmore » the method, the active CTES operates under a fast DR control strategy during DR events while under the storage-priority operation mode to shift peak demand during normal days. The optimal storage capacities, maximum annual net cost saving and corresponding power reduction set-points during DR event are obtained by using the proposed optimal design method. Lastly, this research provides guidance in comprehensive evaluation of cost-saving potential of CTES integrated with HVAC system for building demand management including both fast DR and PLM.« less

Evaluation of a new methodology to simulate damage and wear of polyethylene hip replacements subjected to edge loading in hip simulator testing.

PubMed

Partridge, Susan; Tipper, Joanne L; Al-Hajjar, Mazen; Isaac, Graham H; Fisher, John; Williams, Sophie

2018-05-01

Wear and fatigue of polyethylene acetabular cups have been reported to play a role in the failure of total hip replacements. Hip simulator testing under a wide range of clinically relevant loading conditions is important. Edge loading of hip replacements can occur following impingement under extreme activities and can also occur during normal gait, where there is an offset deficiency and/or joint laxity. This study evaluated a hip simulator method that assessed wear and damage in polyethylene acetabular liners that were subjected to edge loading. The liners tested to evaluate the method were a currently manufactured crosslinked polyethylene acetabular liner and an aged conventional polyethylene acetabular liner. The acetabular liners were tested for 5 million standard walking cycles and following this 5 million walking cycles with edge loading. Edge loading conditions represented a separation of the centers of rotation of the femoral head and the acetabular liner during the swing phase, leading to loading of the liner rim on heel strike. Rim damage and cracking was observed in the aged conventional polyethylene liner. Steady-state wear rates assessed gravimetrically were lower under edge loading compared to standard loading. This study supports previous clinical findings that edge loading may cause rim cracking in liners, where component positioning is suboptimal or where material degradation is present. The simulation method developed has the potential to be used in the future to test the effect of aging and different levels of severity of edge loading on a range of cross-linked polyethylene materials. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1456-1462, 2018. © 2017 Wiley Periodicals, Inc.

Anterior cement augmentation of adjacent levels after vertebral body replacement leads to superior stability of the corpectomy cage under cyclic loading-a biomechanical investigation.

PubMed

Oberkircher, Ludwig; Krüger, Antonio; Hörth, Dominik; Hack, Juliana; Ruchholtz, Steffen; Fleege, Christoph; Rauschmann, Michael; Arabmotlagh, Mohammad

2018-03-01

In the operative treatment of osteoporotic vertebral body fractures, a dorsal stabilization in combination with a corpectomy of the fractured vertebral body might be necessary with respect to the fracture morphology, whereby the osteoporotic bone quality may possibly increase the risk of implant failure. To achieve better stability, it is recommended to use cement-augmented screws for dorsal instrumentation. Besides careful end plate preparation, cement augmentation of the adjacent end plates has also been reported to lead to less reduction loss. The aim of the study was to evaluate biomechanically under cyclic loading whether an additional cement augmentation of the adjacent end plates leads to improved stability of the inserted cage. Methodical cadaver study. Fourteen fresh frozen human thoracic spines with proven osteoporosis were used (T2-T7). After removal of the soft tissues, the spine was embedded in Technovit (Kulzer, Germany). Subsequently, a corpectomy of T5 was performed, leaving the dorsal ligamentary structures intact. After randomization with respect to bone quality, two groups were generated: Dorsal instrumentation (cemented pedicle screws, Medtronic, Minneapolis, MN, USA)+cage implantation (CAPRI Corpectomy Cage, K2M, Leesburg, VA, USA) without additional cementation of the adjacent endplates (Group A) and dorsal instrumentation+cage implantation with additional cement augmentation of the adjacent end plates (Group B). The subsequent axial and cyclic loading was performed at a frequency of 1 Hz, starting at 400 N and increasing the load within 200 N after every 500 cycles up to a maximum of 2,200 N. Load failure was determined when the cages sintered macroscopically into the end plates (implant failure) or when the maximum load was reached. One specimen in Group B could not be clamped appropriately into the test bench for axial loading because of a pronounced scoliotic misalignment and had to be excluded. The mean strength for implant failure was 1,000 N±258.2 N in Group A (no cement augmentation of the adjacent end plates, n=7); on average, 1,622.1±637.6 cycles were achieved. In Group B (cement augmentation of the adjacent end plates, n=6), the mean force at the end of loading was 1,766.7 N±320.4 N; an average of 3,572±920.6 cycles was achieved. Three specimens reached a load of 2,000 N. The differences between the two groups were significant (p=.006 and p=.0047) regarding load failure and number of cycles. Additional cement augmentation of the adjacent end plates during implantation of a vertebral body replacement in osteoporotic bone resulted in a significant increased stability of the cage in the axial cyclic loading test. Copyright © 2017 Elsevier Inc. All rights reserved.

A research on motion design for APP's loading pages based on time perception

NASA Astrophysics Data System (ADS)

Cao, Huai; Hu, Xiaoyun

2018-04-01

Due to restrictions caused by objective reasons like network bandwidth, hardware performance and etc., waiting is still an inevitable phenomenon that appears in our using mobile-terminal products. Relevant researches show that users' feelings in a waiting scenario can affect their evaluations on the whole product and services the product provides. With the development of user experience and inter-facial design subjects, the role of motion effect in the interface design has attracted more and more scholars' attention. In the current studies, the research theory of motion design in a waiting scenario is imperfect. This article will use the basic theory and experimental research methods of cognitive psychology to explore the motion design's impact on user's time perception when users are waiting for loading APP pages. Firstly, the article analyzes the factors that affect waiting experience of loading APP pages based on the theory of time perception, and then discusses motion design's impact on the level of time-perception when loading pages and its design strategy. Moreover, by the operation analysis of existing loading motion designs, the article classifies the existing loading motions and designs an experiment to verify the impact of different types of motions on the user's time perception. The result shows that the waiting time perception of mobile's terminals' APPs is related to the loading motion types, the combination type of loading motions can effectively shorten the waiting time perception as it scores a higher mean value in the length of time perception.

Ratcheting fatigue behaviour of Al-7075 T6 alloy: Influence of stress parameters

NASA Astrophysics Data System (ADS)

Amarnath, Lala; Bhattacharjee, Antara; Dutta, K.

2016-02-01

The use of aluminium and aluminium based alloys are increasing rapidly on account of its high formability, good thermal and electrical conductivity, high strength and lightness. Aluminium alloys are extensively used in aerospace, automobile, marine and space research industries and are also put into structural applications where chances of fatigue damage cannot be ruled out. In the current work, it is intended to study the ratcheting fatigue behavior of 7075-T6 aluminium alloy at room temperature. This Al alloy is potentially used in aviation, marine and automotive components as well as in bicycle parts, rock mounting equipment and parts of ammunition where there is every chance of failure of the parts due to deformation caused by ratcheting. Ratcheting is the process of accruement of plastic stain produced when a component is subjected to asymmetric cyclic loading under the influence of low cycle fatigue. To accomplish the requirements of the projected research, stress-controlled cyclic loading experiments were done using a ±250 kN servo-hydraulic universal testing machine (Instron: 8800R). The effect of stress parameters such as mean stress and stress amplitude were investigated on the ratcheting behavior of the selected aluminium alloy. It was observed that, ratcheting strain increased with increase in the value of stress amplitude at any constant mean stress while a saturation in strain accumulation attained in the investigated material after around 10-20 cycles, under all test conditions. The analyses of hysteresis loop generated during cyclic loading indicate that the material exhibits cyclic hardening in the initial fifty cycles which gets softened in further loading up to about 70-80 cycles and finally attains a steady state. The increase in the ratcheting strain value with stress parameters happens owing to increased deformation domain during cycling. The cyclic hardening accompanied by softening is correlated with characteristic precipitation features of the investigated Al 7075 alloy.

Fracture resistance of metal-free composite crowns-effects of fiber reinforcement, thermal cycling, and cementation technique.

PubMed

Lehmann, Franziska; Eickemeyer, Grit; Rammelsberg, Peter

2004-09-01

The improved mechanical properties of contemporary composites have resulted in their extensive use for the restoration of posterior teeth. However, the influence of fiber reinforcement, cementation technique, and physical stress on the fracture resistance of metal-free crowns is unknown. This in vitro study evaluated the effect of fiber reinforcement, physical stress, and cementation methods on the fracture resistance of posterior metal-free Sinfony crowns. Ninety-six extracted human third molars received a standardized tooth preparation: 0.5-mm chamfer preparation and occlusal reduction of 1.3 to 1.5 mm. Sinfony (nonreinforced crowns, n=48) and Sinfony-Vectris (reinforced crowns, n=48) crowns restoring original tooth contour were prepared. Twenty-four specimens of each crown type were cemented, using either glass ionomer cement (GIC) or resin cement. Thirty-two crowns (one third) were stored in humidity for 48 hours. Another third was exposed to 10,000 thermal cycles (TC) between 5 degrees C and 55 degrees C. The remaining third was treated with thermal cycling and mechanical loading (TCML), consisting of 1.2 million axial loads of 50 N. The artificial crowns were then vertically loaded with a steel sphere until failure occurred. Significant differences in fracture resistance (N) between experimental groups were assessed by nonparametric Mann-Whitney U-test (alpha=.05). Fifty percent of the Sinfony and Sinfony-Vectris crowns cemented with glass ionomer cement loosened after thermal cycling. Thermal cycling resulted in a significant reduction in the mean fracture resistance for Sinfony crowns cemented with GIC, from 2037 N to 1282 N (P=.004). Additional fatigue produced no further effects. Fiber reinforcement significantly increased fracture resistance, from 1555 N to 2326 N (P=.001). The minimal fracture resistance was above 600 N for all combinations of material, cement and loading. Fracture resistance of metal-free Sinfony crowns was significantly increased by fiber reinforcement. Adhesive cementation may be recommended to avoid cementation failure.

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.

Modeling of thermo-mechanical fatigue and damage in shape memory alloy axial actuators

NASA Astrophysics Data System (ADS)

Wheeler, Robert W.; Hartl, Darren J.; Chemisky, Yves; Lagoudas, Dimitris C.

2015-04-01

The aerospace, automotive, and energy industries have seen the potential benefits of using shape memory alloys (SMAs) as solid state actuators. Thus far, however, these actuators are generally limited to non-critical components or over-designed due to a lack of understanding regarding how SMAs undergo thermomechanical or actuation fatigue and the inability to accurately predict failure in an actuator during use. The purpose of this study was to characterize the actuation fatigue response of Nickel-Titanium-Hafnium (NiTiHf) axial actuators and, in turn, use this characterization to predict failure and monitor damage in dogbone actuators undergoing various thermomechanical loading paths. Calibration data was collected from constant load, full cycle tests ranging from 200-600MPa. Subsequently, actuator lifetimes were predicted for four additional loading paths. These loading paths consisted of linearly varying load with full transformation (300-500MPa) and step loads which transition from zero stress to 300-400MPa at various martensitic volume fractions. Thermal cycling was achieved via resistive heating and convective cooling and was controlled via a state machine developed in LabVIEW. A previously developed fatigue damage model, which is formulated such that the damage accumulation rate is general in terms of its dependence on current and local stress and actuation strain states, was utilized. This form allows the model to be utilized for specimens undergoing complex loading paths. Agreement between experiments and simulations is discussed.

Efficient load rating and quantification of life-cycle damage of Indiana bridges due to overweight loads.

DOT National Transportation Integrated Search

2016-02-01

In this study, a computational approach for conducting durability analysis of bridges using detailed finite element models is developed. The underlying approach adopted is based on the hypothesis that the two main factors affecting the life of a brid...

Characterization and development of truck load spectra and growth factors for current and future pavement design practices in Louisiana.

DOT National Transportation Integrated Search

2011-07-01

For pavement design practices, several factors must be considered to ensure good pavement performance over the anticipated life cycle. : Such factors include, but are not limited to, the type of paving materials, traffic loading characteristics, prev...

From Cycling Between Coupled Reactions to the Cross-Bridge Cycle: Mechanical Power Output as an Integral Part of Energy Metabolism

PubMed Central

Diederichs, Frank

2012-01-01

ATP delivery and its usage are achieved by cycling of respective intermediates through interconnected coupled reactions. At steady state, cycling between coupled reactions always occurs at zero resistance of the whole cycle without dissipation of free energy. The cross-bridge cycle can also be described by a system of coupled reactions: one energising reaction, which energises myosin heads by coupled ATP splitting, and one de-energising reaction, which transduces free energy from myosin heads to coupled actin movement. The whole cycle of myosin heads via cross-bridge formation and dissociation proceeds at zero resistance. Dissipation of free energy from coupled reactions occurs whenever the input potential overcomes the counteracting output potential. In addition, dissipation is produced by uncoupling. This is brought about by a load dependent shortening of the cross-bridge stroke to zero, which allows isometric force generation without mechanical power output. The occurrence of maximal efficiency is caused by uncoupling. Under coupled conditions, Hill’s equation (velocity as a function of load) is fulfilled. In addition, force and shortening velocity both depend on [Ca2+]. Muscular fatigue is triggered when ATP consumption overcomes ATP delivery. As a result, the substrate of the cycle, [MgATP2−], is reduced. This leads to a switch off of cycling and ATP consumption, so that a recovery of [ATP] is possible. In this way a potentially harmful, persistent low energy state of the cell can be avoided. PMID:24957757

Impacts of Wind and Solar on Fossil-Fueled Generators: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lew, D.; Brinkman, G.; Kumar, N.

2012-08-01

High penetrations of wind and solar power will impact the operations of the remaining generators on the power system. Regional integration studies have shown that wind and solar may cause fossil-fueled generators to cycle on and off and ramp down to part load more frequently and potentially more rapidly. Increased cycling, deeper load following, and rapid ramping may result in wear-and-tear impacts on fossil-fueled generators that lead to increased capital and maintenance costs, increased equivalent forced outage rates, and degraded performance over time. Heat rates and emissions from fossil-fueled generators may be higher during cycling and ramping than during steady-statemore » operation. Many wind and solar integration studies have not taken these increased cost and emissions impacts into account because data have not been available. This analysis considers the cost and emissions impacts of cycling and ramping of fossil-fueled generation to refine assessments of wind and solar impacts on the power system.« less

Analysis of suture anchor eyelet position on suture failure load.

PubMed

Aktay, Sevima A; Kowaleski, Michael P

2011-06-01

To compare mechanical performance of 2 orientations of the 5 mm Corkscrew® suture anchor with #5 Fiberwire® . In vitro biomechanical study. Suture anchor-suture constructs (n=40). Acute and cyclic tensile loads were applied to suture threaded through eyelets of 40 anchors perpendicular to the long axis of the anchor. Eyelets were positioned so that the suture pull was in line with (anchor rotation angle of 0° [ARA 0]) or 90° (ARA 90) to the eyelet plane. Load at failure, stiffness, and cycles to failure were determined. All constructs failed by suture breakage at the eyelet. Mean load at failure was significantly higher in the ARA 90 group (634 ± 93 N) compared with the ARA 0 group (495 ± 52 N; P=.0015). No significant difference was found between groups for mean number of cycles to failure (270 ± 177 versus 178 ± 109; P=.2166) and stiffness (50 ± 4 versus 48 ± 5 N/mm; P=.3141). The Corkscrew® 5 mm suture anchor with Fiberwire® suture fails via suture breakage at the eyelet under higher acute loads if the suture is loaded at an angle of 90° compared with 0° with respect to the plane of the eyelet. © Copyright 2011 by The American College of Veterinary Surgeons.

A simple method for assessment of muscle force, velocity, and power producing capacities from functional movement tasks.

PubMed

Zivkovic, Milena Z; Djuric, Sasa; Cuk, Ivan; Suzovic, Dejan; Jaric, Slobodan

2017-07-01

A range of force (F) and velocity (V) data obtained from functional movement tasks (e.g., running, jumping, throwing, lifting, cycling) performed under variety of external loads have typically revealed strong and approximately linear F-V relationships. The regression model parameters reveal the maximum F (F-intercept), V (V-intercept), and power (P) producing capacities of the tested muscles. The aim of the present study was to evaluate the level of agreement between the routinely used "multiple-load model" and a simple "two-load model" based on direct assessment of the F-V relationship from only 2 external loads applied. Twelve participants were tested on the maximum performance vertical jumps, cycling, bench press throws, and bench pull performed against a variety of different loads. All 4 tested tasks revealed both exceptionally strong relationships between the parameters of the 2 models (median R = 0.98) and a lack of meaningful differences between their magnitudes (fixed bias below 3.4%). Therefore, addition of another load to the standard tests of various functional tasks typically conducted under a single set of mechanical conditions could allow for the assessment of the muscle mechanical properties such as the muscle F, V, and P producing capacities.

Effect of fatigue loading on critical current in stainless steel-laminated DI-BSCCO superconducting composite tape

NASA Astrophysics Data System (ADS)

Hojo, M.; Osawa, K.; Adachi, T.; Inoue, Y.; Osamura, K.; Ochiai, S.; Ayai, N.; Hayashi, K.

2010-11-01

Tensile strain tolerance of the critical current in (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) composite superconductor is dramatically improved when the tape is laminated with stainless steel. For practical applications, it is important to understand whether this reinforcement by lamination is effective under fatigue loading. In the present study, we carried out fatigue tests in LN2 and measured the critical current at the specific fatigue cycles to clarify the strain tolerance of the critical current in stainless steel-laminated drastically innovative Bi2223 (DI-BSCCO®) tapes. The fatigue tests were carried out using a computer-controlled 10 kN servo-hydraulic fatigue testing machine with a load cell capacity of 2.5 kN. Tests under static loading showed that the irreversible stress at which the critical current is reduced by 1% from the original value (tensile stress at Ic/Ic0 = 0.99) was 315 MPa when measured at unloading state. The present fatigue tests results indicated that the critical current was maintained at over 98% of the original value at unloading state after stress cycles of 106 when the static irreversible stress was selected as the maximum stress under fatigue loading. Thus, laminated DI-BSCCO tapes showed excellent mechanical properties even under fatigue loading.

Fatigue Tests with Random Flight Simulation Loading

NASA Technical Reports Server (NTRS)

Schijve, J.

1972-01-01

Crack propagation was studied in a full-scale wing structure under different simulated flight conditions. Omission of low-amplitude gust cycles had a small effect on the crack rate. Truncation of the infrequently occurring high-amplitude gust cycles to a lower level had a noticeably accelerating effect on crack growth. The application of fail-safe load (100 percent limit load) effectively stopped subsequent crack growth under resumed flight-simulation loading. In another flight-simulation test series on sheet specimens, the variables studied are the design stress level and the cyclic frequency of the random gust loading. Inflight mean stresses vary from 5.5 to 10.0 kg/sq mm. The effect of the stress level is larger for the 2024 alloy than for the 7075 alloy. Three frequencies were employed: namely, 10 cps, 1 cps, and 0.1 cps. The frequency effect was small. The advantages and limitations of flight-simulation tests are compared with those of alternative test procedures such as constant-amplitude tests, program tests, and random-load tests. Various testing purposes are considered. The variables of flight-simulation tests are listed and their effects are discussed. A proposal is made for performing systematic flight-simulation tests in such a way that the compiled data may be used as a source of reference.

Biomechanical comparison of stability of tibiotalocalcaneal arthrodesis with two different intramedullary retrograde nails.

PubMed

Richter, Martinus; Evers, Julia; Waehnert, Dirk; Deorio, Jim K; Pinzur, Michael; Schulze, Martin; Zech, Stefan; Ochman, Sabine

2014-03-01

The aim of the study was to compare the initial construct stability of two retrograde intramedullary nail systems for tibiotalocalcaneal arthrodesis (TTCF) (A3, Small Bone Innovations; HAN, Synthes) in a biomechanical cadaver study. Nine pairs of human cadaver bones were instrumented with two different retrograde nail systems. One tibia from each pair was randomized to either rod. The bone mineral density was determined via tomography to ensure the characteristics in each pair of tibiae were similar. All tests were performed in load-control. Displacements and forces were acquired by the sensors of the machine at a rate of 64Hz. Specimens were tested in a stepwise progression starting with six times ±125N with a frequency of 1Hz for 250cycles each step was performed (1500cycles). The maximum load was then increased to ±250N for another 14 steps or until specimen failure occurred (up to 3500cycles). Average bone mineral density was 67.4mgHA/ccm and did not differ significantly between groups (t-test, p=.28). Under cyclic loading, the range of motion (dorsiflexion/plantarflexion) at 250N was significantly lower for the HAN-group with 7.2±2.3mm compared to the A3-group with 11.8±2.9mm (t-test, p<0.01). Failure was registered for the HAN after 4571±1134cycles and after 2344±1195cycles for the A3 (t-test, p=.031). Bone mineral density significantly correlated with the number of cycles to failure in both groups (Spearman-Rho, r>.69, p<0.01). The high specimen age and low bone density simulates an osteoporotic bone situation. The HAN with only lateral distal bend but two calcaneal locking screws showed higher stability (higher number of cycles to failure and lower motion such as dorsiflexion/plantarflexion during cyclic loading) than the A3 with additional distal dorsal bend but only one calcaneal locking screw. Both constructs showed sufficient stability compared with earlier data from a similar test model. The data suggest that both implants allow for sufficient primary stability for TTCF in osteoporotic and consequently also in non-osteoporotic bone. Not applicable, experimental basic science study. Copyright © 2013 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.

Dynamic assessment of reinforced concrete beams repaired with externally bonded FRP sheets

NASA Astrophysics Data System (ADS)

Bonfiglioli, B.; Pascale, G.

2006-01-01

This research deals with RC beams strengthened with FRP. An experimental research is presented which is aimed at evaluating the capability of an experimental modal analysis to assess the stiffness decrease due to damage, as well as the stiffness recovery due to strengthening. Ten beams were tested. All of them were subjected to loading cycles with increasing load levels in order to induce cracking of different severity in them. The beams were then retrofitted by externally bonded FRP sheets. Three types of composites were used. The number of layers was varied, too. Modal tests were carried out after each loading-unloading cycle. The modal frequencies and damping ratios were determined for the first four vibration modes. The results obtained indicate that an experimental modal analysis can give useful information on the severity of damage and the effectiveness of strengthening.

Fatigue behavior of a thermally-activated NiTiNb SMA-FRP patch

NASA Astrophysics Data System (ADS)

El-Tahan, M.; Dawood, M.

2016-01-01

This paper presents the details of an experimental study that was conducted to characterize the fatigue behavior of a thermally-activated shape memory alloy (SMA)/carbon fiber reinforced polymer (CFRP) patch that can be used to repair cracked steel members. A total of 14 thermally-activated patches were fabricated and tested to evaluate the stability of the prestress under fatigue loading. The parameters considered in this study are the prestress level in the nickel-titanium-niobium SMA wires and the applied force range. An empirical model to predict the degradation of the prestress is also presented. The results indicate that patches for which the maximum applied loads in a fatigue cycle did not cause debonding of the SMA wires from the CFRP sustained two million loading cycles with less than 20% degradation of the prestress.

Compositional Effects on Electromechanical Degradation of RAINBOW Actuators

NASA Technical Reports Server (NTRS)

Dausch, David E.; Wise, Stephanie A.

1998-01-01

The effect of ceramic composition on the electromechanical displacement degradation of RAINBOW (Reduced and Internally Biased Oxide Wafer) actuators was investigated. RAINBOWs were fabricated from commercially available PZT-5H and PZT-5A piezoelectric disks as well as from tape cast PLZT piezoelectric 7/65/35 and electrostrictive 9/65/35 compositions. Displacement properties were measured at low electric fields (10 to 13 kV/cm) under loads of 0 to 500 g, and displacement degradation as a function of time was observed over 107 cycles. The PZT-5A and PLZT 9/65/35 compositions exhibited minimal decrease in displacement when load was applied. Furthermore, these compositions retained approximately 65 percent of their initial displacement after 10(exp 7) cycles under a load of 300 g. PZT-5H and PLZT 7/65/35 degraded completely under these conditions.

Combined bending-torsion fatigue reliability of AISI 4340 steel shafting with K sub t = 2.34. [stress concentration factor

NASA Technical Reports Server (NTRS)

Kececioglu, D.; Chester, L. B.; Dodge, T. M.

1974-01-01

Results generated by three, unique fatigue reliability research machines which can apply reversed bending loads combined with steady torque are presented. Six-inch long, AISI 4340 steel, grooved specimens with a stress concentration factor of 2.34 and R sub C 35/40 hardness were subjected to various combinations of these loads and cycled to failure. The generated cycles-to-failure and stress-to-failure data are statistically analyzed to develop distributional S-N and Goodman diagrams. Various failure theories are investigated to determine which one represents the data best. The effect of the groove and of the various combined bending-torsion loads on the S-N and Goodman diagrams are determined. Three design applications are presented. The third one illustrates the weight savings that may be achieved by designing for reliability.

Knotless single-row rotator cuff repair: a comparative biomechanical study of 2 knotless suture anchors.

PubMed

Efird, Chad; Traub, Shaun; Baldini, Todd; Rioux-Forker, Dana; Spalazzi, Jeffrey P; Davisson, Twana; Hawkins, Monica; McCarty, Eric

2013-08-01

The purpose of this study was to compare the gap formation during cyclic loading, maximum repair strength, and failure mode of single-row full-thickness supraspinatus repairs performed using 2 knotless suture anchors with differing internal suture-retention mechanisms in a human cadaver model. Nine matched pairs of cadaver shoulders were used. Full-thickness tears were induced by detaching the supraspinatus tendon from the greater tuberosity. Single-row repairs were performed with either type I (Opus Magnum PI; ArthroCare, Austin, Texas) or type II (ReelX STT; Stryker, Mahwah, New Jersey) knotless suture anchors. The repaired tendon was cycled from 10 to 90 N for 500 cycles, followed by load to failure. Gap formation was measured at 5, 100, 200, 300, 400, and 500 cycles with a video digitizing system. Anchor type or location (anterior or posterior) had no effect on gap formation during cyclic loading regardless of position (anterior, P=.385; posterior, P=.389). Maximum load to failure was significantly greater (P=.018) for repairs performed with type II anchors (288±62 N) compared with type I anchors (179±39 N). Primary failure modes were anchor pullout and tendon tearing for type II anchors and suture slippage through the anchor for type I anchors. The internal ratcheting suture-retention mechanism of type II anchors may have helped this anchor outperform the suture-cinching mechanism of type I anchors by supporting significantly higher loads before failure and minimizing suture slippage, potentially leading to stronger repairs clinically. Copyright 2013, SLACK Incorporated.

Reliability and Creep/Fatigue Analysis of a CMC Component

NASA Technical Reports Server (NTRS)

Murthy, Pappu L. N.; Mital, Subodh K.; Gyekenyesi, John Z.; Gyekenyesi, John P.

2007-01-01

High temperature ceramic matrix composites (CMC) are being explored as viable candidate materials for hot section gas turbine components. These advanced composites can potentially lead to reduced weight and enable higher operating temperatures requiring less cooling; thus leading to increased engine efficiencies. There is a need for convenient design tools that can accommodate various loading conditions and material data with their associated uncertainties to estimate the minimum predicted life as well as the failure probabilities of a structural component. This paper presents a review of the life prediction and probabilistic analyses performed for a CMC turbine stator vane. A computer code, NASALife, is used to predict the life of a 2-D woven silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) turbine stator vane due to a mission cycle which induces low cycle fatigue and creep. The output from this program includes damage from creep loading, damage due to cyclic loading and the combined damage due to the given loading cycle. Results indicate that the trends predicted by NASALife are as expected for the loading conditions used for this study. In addition, a combination of woven composite micromechanics, finite element structural analysis and Fast Probability Integration (FPI) techniques has been used to evaluate the maximum stress and its probabilistic distribution in a CMC turbine stator vane. Input variables causing scatter are identified and ranked based upon their sensitivity magnitude. Results indicate that reducing the scatter in proportional limit strength of the vane material has the greatest effect in improving the overall reliability of the CMC vane.

Advanced zinc-doped adhesives for high performance at the resin-carious dentin interface.

PubMed

Toledano, Manuel; Osorio, Raquel; Osorio, Estrella; García-Godoy, Franklin; Toledano-Osorio, Manuel; Aguilera, Fátima S

2016-09-01

The purpose of this study was to evaluate the remineralization ability of an etch-and-rinse Zn-doped resin applied on caries-affected dentin (CAD). CAD surfaces were subjected to: (i) 37% phosphoric acid (PA) or (ii) 0.5M ethylenediaminetetraacetic acid (EDTA). 10wt% ZnO nanoparticles or 2wt% ZnCl2 were added into the adhesive Single Bond (SB), to create the following groups: PA+SB, PA+SB-ZnO, PA+SB-ZnCl2, EDTA+SB, EDTA+SB-ZnO, EDTA+SB-ZnCl2. Bonded interfaces were submitted to mechanical loading or stored during 24h. Remineralization of the bonded interfaces was studied by AFM nano-indentation (hardness and Young׳s modulus), Raman spectroscopy [mapping with principal component analysis (PCA), and hierarchical cluster analysis (HCA)] and Masson׳s trichrome staining technique. Dentin samples treated with PA+SB-ZnO attained the highest values of nano-mechanical properties. Load cycling increased both mineralization and crystallographic maturity at the interface; this effect was specially noticed when using ZnCl2-doped resin in EDTA-treated carious dentin. Crosslinking attained higher frequencies indicating better conformation and organization of collagen in specimens treated with PA+SB-ZnO, after load cycling. Trichrome staining technique depicted a deeper demineralized dentin fringe that became reduced after loading, and it was not observable in EDTA+SB groups. Multivariate analysis confirmed de homogenizing effect of load cycling in the percentage of variances, traces of centroids and distribution of clusters, especially in specimens treated with EDTA+SB-ZnCl2. Copyright © 2016 Elsevier Ltd. All rights reserved.

Three-dimensional deformation response of a NiTi shape memory helical-coil actuator during thermomechanical cycling: experimentally validated numerical model

NASA Astrophysics Data System (ADS)

Dhakal, B.; Nicholson, D. E.; Saleeb, A. F.; Padula, S. A., II; Vaidyanathan, R.

2016-09-01

Shape memory alloy (SMA) actuators often operate under a complex state of stress for an extended number of thermomechanical cycles in many aerospace and engineering applications. Hence, it becomes important to account for multi-axial stress states and deformation characteristics (which evolve with thermomechanical cycling) when calibrating any SMA model for implementation in large-scale simulation of actuators. To this end, the present work is focused on the experimental validation of an SMA model calibrated for the transient and cyclic evolutionary behavior of shape memory Ni49.9Ti50.1, for the actuation of axially loaded helical-coil springs. The approach requires both experimental and computational aspects to appropriately assess the thermomechanical response of these multi-dimensional structures. As such, an instrumented and controlled experimental setup was assembled to obtain temperature, torque, degree of twist and extension, while controlling end constraints during heating and cooling of an SMA spring under a constant externally applied axial load. The computational component assesses the capabilities of a general, multi-axial, SMA material-modeling framework, calibrated for Ni49.9Ti50.1 with regard to its usefulness in the simulation of SMA helical-coil spring actuators. Axial extension, being the primary response, was examined on an axially-loaded spring with multiple active coils. Two different conditions of end boundary constraint were investigated in both the numerical simulations as well as the validation experiments: Case (1) where the loading end is restrained against twist (and the resulting torque measured as the secondary response) and Case (2) where the loading end is free to twist (and the degree of twist measured as the secondary response). The present study focuses on the transient and evolutionary response associated with the initial isothermal loading and the subsequent thermal cycles under applied constant axial load. The experimental results for the helical-coil actuator under two different boundary conditions are found to be within error to their counterparts in the numerical simulations. The numerical simulation and the experimental validation demonstrate similar transient and evolutionary behavior in the deformation response under the complex, inhomogeneous, multi-axial stress-state and large deformations of the helical-coil actuator. This response, although substantially different in magnitude, exhibited similar evolutionary characteristics to the simple, uniaxial, homogeneous, stress-state of the isobaric tensile tests results used for the model calibration. There was no significant difference in the axial displacement (primary response) magnitudes observed between Cases (1) and (2) for the number of cycles investigated here. The simulated secondary responses of the two cases evolved in a similar manner when compared to the experimental validation of the respective cases.

[Sports participation after joint arthroplasty].

PubMed

Dauty, M; Letenneur, J

2007-12-01

To recommand sports activities after joint arthroplasty from the literature analysis, the French surgeon's opinion and wish patients. From the Medline data base interrogation according to keywords: Sports, Arthroplasty, Athletics, Physical training, two different readers, an orthopedic surgeon and a Physical Medicine and Rehabilitation physician selected articles in French or English language according to the level of proofs of the french classification of the Accreditation and Health Evaluation National Agency (Anaes). Professional practices were estimated by the interrogation of 30 orthopedic surgeons members of the french West Orthopaedics Society (SOO). The demand of sports practice was studied with patients recently operated for a primary total knee arthroplasty (TKA) after gonarthrosis. Twenty-two articles were selected from 305 articles obtained by the search according to keywords. Ten literature reviews are limited by the absence of prospective randomized study. A level II study and eleven level IV articles are reported. According to the subjective orthropedic surgeon's opinion, the objective results based on the joint load studied and the percentage of arthroplasty revision, sport is beneficial for the individual health but perhaps not for the arthroplasty survey. However, aerobic and leisure activities are recommended (walking, swimming, cycling) in agreement with the demand of the patients recently operated with a TKA. TKA differs from Total Hip Arthroplasty for jogging because of knee joint constraints during the knee flexion. A single study reports sports possibilities after shoulder arthroplasty and ankle arthroplasty and no study reports results after elbow arthroplasty.

The Reliability of Microalloyed Sn-Ag-Cu Solder Interconnections Under Cyclic Thermal and Mechanical Shock Loading

NASA Astrophysics Data System (ADS)

Mattila, Toni T.; Hokka, Jussi; Paulasto-Kröckel, Mervi

2014-11-01

In this study, the performance of three microalloyed Sn-Ag-Cu solder interconnection compositions (Sn-3.1Ag-0.52Cu, Sn-3.0Ag-0.52Cu-0.24Bi, and Sn-1.1Ag-0.52Cu-0.1Ni) was compared under mechanical shock loading (JESD22-B111 standard) and cyclic thermal loading (40 ± 125°C, 42 min cycle) conditions. In the drop tests, the component boards with the low-silver nickel-containing composition (Sn-Ag-Cu-Ni) showed the highest average number of drops-to-failure, while those with the bismuth-containing alloy (Sn-Ag-Cu-Bi) showed the lowest. Results of the thermal cycling tests showed that boards with Sn-Ag-Cu-Bi interconnections performed the best, while those with Sn-Ag-Cu-Ni performed the worst. Sn-Ag-Cu was placed in the middle in both tests. In this paper, we demonstrate that solder strength is an essential reliability factor and that higher strength can be beneficial for thermal cycling reliability but detrimental to drop reliability. We discuss these findings from the perspective of the microstructures and mechanical properties of the three solder interconnection compositions and, based on a comprehensive literature review, investigate how the differences in the solder compositions influence the mechanical properties of the interconnections and discuss how the differences are reflected in the failure mechanisms under both loading conditions.

Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Wei; An, Ke

The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

High cycle fatigue in the transmission electron microscope

DOE PAGES

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.; ...

2016-06-28

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 10 6 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10 –12 m·cycle –1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

High cycle fatigue in the transmission electron microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 10 6 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10 –12 m·cycle –1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

DOE PAGES

Wu, Wei; An, Ke

2015-10-03

The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

Effect of resin coating on adhesion and microleakage of computer-aided design/computer-aided manufacturing fabricated all-ceramic crowns after occlusal loading: a laboratory study.

PubMed

Kitayama, Shuzo; Pilecki, Peter; Nasser, Nasser A; Bravis, Theodora; Wilson, Ron F; Nikaido, Toru; Tagami, Junji; Watson, Timothy F; Foxton, Richard M

2009-08-01

This study investigated the effect of resin coating and occlusal loading on adhesion and microleakage of all-ceramic crowns. Molars were prepared for an all-ceramic crown and were divided into two groups: non-coated (control) and resin-coated with Clearfil Tri-S Bond. Crowns were fabricated using CEREC 3 and cemented using Clearfil Esthetic Cement. After 24 h of storage in water, the restored teeth in each group were divided into two subgroups: unloaded, or loaded while stored in water. Mechanical loading was achieved with an axial force of 80 N at 2.5 cycles s(-1) for 250,000 cycles. After immersion in Rhodamine B, the specimens were sectioned and processed for microleakage evaluation by confocal microscopy, which was followed by further sectioning for microtensile bond testing. Loading had no significant effect on microleakage in either the resin-coated or non-resin-coated groups. Resin coating did not reduce the microleakage at the dentine interface but increased the microleakage at the enamel interface. All the beams fractured during slicing when non-coated and loaded. The bond strengths of non-coated and unloaded, resin-coated and unloaded, and resin-coated and loaded groups were 15.82 +/- 4.22, 15.17 +/- 5.24, and 12.97 +/- 5.82 MPa, respectively. Resin coating with Clearfil Tri-S Bond improved the bonding of resin cement to dentine for loaded specimens. However, it was not effective in reducing the microleakage, regardless of whether it was loaded or unloaded.

In-pile testing of ITER first wall mock-ups at relevant thermal loading conditions

NASA Astrophysics Data System (ADS)

Litunovsky, N.; Gervash, A.; Lorenzetto, P.; Mazul, I.; Melder, R.

2009-04-01

The paper describes the experimental technique and preliminary results of thermal fatigue testing of ITER first wall (FW) water-cooled mock-ups inside the core of the RBT-6 experimental fission reactor (RIAR, Dimitrovgrad, Russia). This experiment has provided simultaneous effect of neutron fluence and thermal cycling damages on the mock-ups. A PC-controlled high-temperature graphite ohmic heater was applied to provide cyclic thermal load onto the mock-ups surface. This experiment lasted for 309 effective irradiation days with a final damage level (CuCrZr) of 1 dpa in the mock-ups. About 3700 thermal cycles with a heat flux of 0.4-0.5 MW/m 2 onto the mock-ups were realized before the heater fails. Then, irradiation was continued in a non-cycling mode.

Using Dynamic Simulation to Evaluate Attemperator Operation in a Natural Gas Combined Cycle With Duct Burners in the Heat Recovery Steam Generator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liese, Eric; Zitney, Stephen E.

A generic training simulator of a natural gas combined cycle was modified to match operations at a real plant. The objective was to use the simulator to analyze cycling operations of the plant. Initial operation of the simulator revealed the potential for saturation conditions in the final high pressure superheater as the attemperator tried to control temperature at the superheater outlet during gas turbine loading and unloading. Subsequent plant operational data confirmed simulation results. Multiple simulations were performed during loading and unloading of the gas turbine to determine operational strategies that prevented saturation and increased the approach to saturation temperature.more » The solutions included changes to the attemperator temperature control setpoints and strategic control of the steam turbine inlet pressure control valve.« less

Cycle life test of secondary spacecraft cells

NASA Technical Reports Server (NTRS)

Harkness, J. D.

1980-01-01

The results of the life cycling program on rechargeable calls are reported. Information on required data, the use of which the data will be put, application details, including orbital description, charge control methods, load rquirements, etc., are given. Cycle tests were performed on 660 sealed, nickel cadmium cells. The cells consisted of seven sample classifications ranging form 3.0 to 20 amp. hours. Nickel cadmium, silver cadmium, and silver zinc sealed cells, excluding synchronous orbit and accelerated test packs were added. The capacities of the nickel cadmium cells, the silver cadmium and the silver zinc cells differed in range of amp hrs. The cells were cylced under different load, charge control, and temperature conditions. All cell packs are recharged by use of a pack voltage limit. All charging is constant current until the voltage limit is reached.

Passive load follow analysis of the STAR-LM and STAR-H2 systems

NASA Astrophysics Data System (ADS)

Moisseytsev, Anton

A steady-state model for the calculation of temperature and pressure distributions, and heat and work balance for the STAR-LM and the STAR-H2 systems was developed. The STAR-LM system is designed for electricity production and consists of the lead cooled reactor on natural circulation and the supercritical carbon dioxide Brayton cycle. The STAR-H2 system uses the same reactor which is coupled to the hydrogen production plant, the Brayton cycle, and the water desalination plant. The Brayton cycle produces electricity for the on-site needs. Realistic modules for each system component were developed. The model also performs design calculations for the turbine and compressors for the CO2 Brayton cycle. The model was used to optimize the performance of the entire system as well as every system component. The size of each component was calculated. For the 400 MWt reactor power the STAR-LM produces 174.4 MWe (44% efficiency) and the STAR-H2 system produces 7450 kg H2/hr. The steady state model was used to conduct quasi-static passive load follow analysis. The control strategy was developed for each system; no control action on the reactor is required. As a main safety criterion, the peak cladding temperature is used. It was demonstrated that this temperature remains below the safety limit during both normal operation and load follow.

A Multi-Cycle Q-Modulation for Dynamic Optimization of Inductive Links.

PubMed

Lee, Byunghun; Yeon, Pyungwoo; Ghovanloo, Maysam

2016-08-01

This paper presents a new method, called multi-cycle Q-modulation, which can be used in wireless power transmission (WPT) to modulate the quality factor (Q) of the receiver (Rx) coil and dynamically optimize the load impedance to maximize the power transfer efficiency (PTE) in two-coil links. A key advantage of the proposed method is that it can be easily implemented using off-the-shelf components without requiring fast switching at or above the carrier frequency, which is more suitable for integrated circuit design. Moreover, the proposed technique does not need any sophisticated synchronization between the power carrier and Q-modulation switching pulses. The multi-cycle Q-modulation is analyzed theoretically by a lumped circuit model, and verified in simulation and measurement using an off-the-shelf prototype. Automatic resonance tuning (ART) in the Rx, combined with multi-cycle Q-modulation helped maximizing PTE of the inductive link dynamically in the presence of environmental and loading variations, which can otherwise significantly degrade the PTE in multi-coil settings. In the prototype conventional 2-coil link, the proposed method increased the power amplifier (PA) plus inductive link efficiency from 4.8% to 16.5% at ( R L = 1 kΩ, d 23 = 3 cm), and from 23% to 28.2% at ( R L = 100 Ω, d 23 = 3 cm) after 11% change in the resonance capacitance, while delivering 168.1 mW to the load (PDL).

Waste-to-energy: A review of life cycle assessment and its extension methods.

PubMed

Zhou, Zhaozhi; Tang, Yuanjun; Chi, Yong; Ni, Mingjiang; Buekens, Alfons

2018-01-01

This article proposes a comprehensive review of evaluation tools based on life cycle thinking, as applied to waste-to-energy. Habitually, life cycle assessment is adopted to assess environmental burdens associated with waste-to-energy initiatives. Based on this framework, several extension methods have been developed to focus on specific aspects: Exergetic life cycle assessment for reducing resource depletion, life cycle costing for evaluating its economic burden, and social life cycle assessment for recording its social impacts. Additionally, the environment-energy-economy model integrates both life cycle assessment and life cycle costing methods and judges simultaneously these three features for sustainable waste-to-energy conversion. Life cycle assessment is sufficiently developed on waste-to-energy with concrete data inventory and sensitivity analysis, although the data and model uncertainty are unavoidable. Compared with life cycle assessment, only a few evaluations are conducted to waste-to-energy techniques by using extension methods and its methodology and application need to be further developed. Finally, this article succinctly summarises some recommendations for further research.

Evaluating Aquatic Life Benefits of Reducing Nutrient Loading to Remediate Episodic and Diel Cycling Hypoxia in a Shallow Hypereutrophic Estuary

EPA Science Inventory

Theoretical linkages between excess nutrient loading, nutrient-enhanced community metabolism (i.e., production and respiration), and hypoxia in estuaries are well-understood. In seasonally-stratified estuaries and coastal systems (e.g., Chesapeake Bay, northern Gulf of Mexico), h...

Laboratory investigation of a novel method to accelerate healing in asphalt mixtures using thermal treatment.

DOT National Transportation Integrated Search

2009-08-01

Asphalt binders have an inherent ability to reverse damage in the form of micro-cracks that is caused : due to the repeated action of external loads. This reversal occurs during rest periods between load : cycles. The phenomenon of crack reversal is ...

Dynamic loads during failure risk assessment of bridge crane structures

NASA Astrophysics Data System (ADS)

Gorynin, A. D.; Antsev, V. Yu; Shaforost, A. N.

2018-03-01

The paper presents the method of failure risk assessment associated with a bridge crane metal structure at the design stage. It also justifies the necessity of taking into account dynamic loads with regard to the operational cycle of a bridge crane during failure risk assessment of its metal structure.

Investigation of Failed Components from a 7-in High Altitude Research Program (HARP) Cannon

DTIC Science & Technology

2011-11-01

figure 39. The crack directions were determined from the oblique lighting fractography . Although there were three primary origins, there is redundancy...photograph in the collage of figure 39). The fractography supports that this part failed under two loading cycles. An initial high load cracked it

Damage assessment, characterization, and modeling for enhanced design of concrete bridge decks in cold regions : [project brief].

DOT National Transportation Integrated Search

2015-07-01

Freeze-thaw and fatigue-type loading processes degrade concrete materials and reduce the load carrying capacity of concrete decks. Damage to concrete decks is caused by the formation of cracks and micro-cracks during fatigue and freeze-thaw cycles. T...

Nitrogen Bsalance for a Plantation Forest Drainage Canal on the North Carolina Coastal Plain

USDA-ARS?s Scientific Manuscript database

Human alteration of the nitrogen cycle has led to increased riverine nitrogen loads, contributing to the eutrophication of lakes, streams, estuaries, and near-coastal oceans. These riverine nitrogen loads are usually less than the total nitrogen inputs to the system, indicating nitrogen removal duri...

Biomechanical comparison of fixation methods in transverse patella fractures.

PubMed

Scilaris, T A; Grantham, J L; Prayson, M J; Marshall, M P; Hamilton, J J; Williams, J L

1998-01-01

To compare monofilament wire versus braided cable for stabilizing transverse patella fractures using the modified AO tension band technique. A randomized blocked (paired) study comparing two fixation methods. Statistical analysis was performed using a nested repeated measures analysis, followed by Bonferroni post hoc testing. Seven paired embalmed knees (mean age 71.8 years, SD 14.6 years) were dissected, and transverse fractures were simulated. The knees were reduced and randomly fixed by either two parallel 0.062-inch Kirschner wires with a 1.0-millimeter-diameter 316L stainless steel monofilament wire tension loop or two Kirschner wires with a 1.0-millimeter-diameter 316L stainless steel braided cable tension loop. Knees were tested by applying a cyclic load through the suprapatellar tendon between twenty and 300 newtons for thirty cycles. The maximum fracture displacement increased with each cycle of loading for both the braided cable and monofilament wire tension loop configurations (p = 0.0001). The average peak displacement at the thirtieth cycle was 2.25 millimeters for monofilament wire and 0.73 millimeters for the cable. When comparing both methods for all cycles, the braided cable allowed less fracture displacement than did the monofilament wire (p = 0.002), and the rate of increase per cycle of maximum fracture displacement was less for the cable than for the wire (p = 0.0001). In transverse, noncomminuted patella fractures, fixation with two Kirschner wires and a 1.0-millimeter braided cable tension loop was superior to the monofilament wire tension loop. Most importantly, the braided cable afforded more predictable results during cyclic loading.

A New Experimental Design for Bacterial Microleakage Investigation at the Implant-Abutment Interface: An In Vitro Study.

PubMed

Zipprich, Holger; Miatke, Sven; Hmaidouch, Rim; Lauer, Hans-Christoph

2016-01-01

This study aimed to test bacterial microleakage at the implant-abutment interface (IAI) before and after dynamic loading using a new chewing simulation. Fourteen implant systems (n = 5 samples of each) were divided into two groups: (1) systems with conical implant-abutment connections (IACs), and (2) systems with flat IACs. For collecting samples without abutment disconnection, channels (Ø = 0.3 mm) were drilled into implants perpendicularly to their axes, and stainless-steel cannulas were adhesively glued inside these channels to allow a sterilized rinsing solution to enter the implant interior and to exit with potential contaminants for testing. Implants were embedded in epoxy resin matrices, which were supported by titanium cylinders with lateral openings for inward and outward cannulas. Abutments were tightened and then provided with vertically adjustable, threaded titanium balls, which were cemented using composite cement. Specimens were immersed in a bacterial liquid and after a contact time of 15 minutes, the implant interior was rinsed prior to chewing simulation (0 N ≘ static seal testing). Specimens were exposed to a Frankfurt chewing simulator. Two hundred twenty force cycles per power level (110 in ± X-axis) were applied to simulate a daily masticatory load of 660 chewing cycles (equivalent to 1,200,000 cycles/5 years). The applied load was gradually increased from 0 N to a maximum load of 200 N in 25-N increments. The implant interior was rinsed to obtain samples before each new power level. All samples were tested using fluorescence microscopy; invading microorganisms could be counted and evaluated. No bacterial contamination was detected under static loading conditions in both groups. After loading, bacterial contamination was detected in one sample from one specimen in group 1 and in two samples from two specimens in group 2. Controlled dynamic loading applied in this study simulated a clinical situation and enabled time-dependent analysis regarding the bacterial seal of different implant systems. Conical IACs offer a better bacterial seal compared with flat IACs, which showed increased microleakage after dynamic loading. IAC design plays a crucial role in terms of bacterial colonization. Taking samples of the implant interior without abutment disconnection eliminates an error source.

Fatigue History and in-situ Loading Studies of the overload Effect Using High Resolution X-ray Strain Profiling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Croft,M.; Jisrawi, N.; Zhong, Z.

High-energy synchrotron X-ray diffraction experiments are used to perform local crack plane strain profiling of 4140 steel compact tension specimens fatigued at constant amplitude, subjected to a single overload cycle, then fatigued some more at constant amplitude. X-ray strain profiling results on a series of samples employing in-situ load cycling are correlated with the crack growth rate (da/dN) providing insight into the da/dN retardation known as the 'overload effect'. Immediately after the overload, the strain under maximum load is greatly reduced but the range of strain, between zero and maximum load, remains unchanged compared to the pre-overload values. At themore » point of maximum retardation, it is the strain range that is greatly reduced while the maximum-load strain has begun to recover to the pre-overload value. For a sample that has recovered to approximately half of the original da/dN value following the overload, the strain at maximum load is fully recovered while the strain range, though partially recovered, is still substantially reduced. The dominance of the strain range in the overload effect is clearly indicated. Subject to some assumptions, strong quantitative support for a crack growth rate driving force of the suggested form [(K{sub max}){sup -p}({Delta}K){sup p}]{sup {gamma}} is found. A dramatic nonlinear load dependence in the spatial distribution of the strain at maximum retardation is also demonstrated: at low load the response is dominantly at the overload position; whereas at high loads it is dominantly at the crack tip position. This transfer of load response away from the crack tip to the overload position appears fundamental to the overload effect for high R-ratio fatigue as studied here.« less

Satellite control of electric power distribution

NASA Technical Reports Server (NTRS)

Bergen, L.

1981-01-01

An L-band frequencies satellite link providing the medium for direct control of electrical loads at individual customer sites from remote central locations is described. All loads supplied under interruptible-service contracts are likely condidates for such control, and they can be cycled or switched off to reduce system loads. For every kW of load eliminated or deferred to off-peak hours, the power company reduces its need for additional generating capacity. In addition, the satellite could switch meter registers so that their readings automatically reflected the time of consumption. The system would perform load-shedding operations during emergencies, disconnecting large blocks of load according to predetermined priorities. Among the distribution operations conducted by the satellite in real time would be: load reconfiguration, voltage regulation, fault isolation, and capacitor and feeder load control.

Elevated temperature biaxial fatigue

NASA Technical Reports Server (NTRS)

Jordan, E. H.

1983-01-01

Biaxial fatigue is often encountered in the complex thermo-mechanical loadings present in gas turbine engines. Engine strain histories can involve non-constant temperature, mean stress, creep, environmental effects, both isotropic and anisotropic materials and non-proportional loading. Life prediction for the general case involving all the above factors is not a practicable research project. The current research program is limited to isothermal fatigue at room temperature and 1200 F of Hastalloy-X for both proportional and non-proportional loading. An improved method for predicting the fatigue life and deformation response under biaxial cycle loading is sought.

Single ball bearing lubricant and material evaluator

NASA Technical Reports Server (NTRS)

Hall, Philip B. (Inventor); Novak, Howard L. (Inventor)

2005-01-01

A test apparatus provides an applied load to a monoball through a trolley which moves along a loading axis. While applying the load to the monoball, the torque meter is in communication with the spherical monoball, and a load cell senses the application of applied force to the monoball. Meanwhile, a rotary actuary imports rotary oscillating motion to the monoball which is sensed by a position sensor and a torque meter. Accordingly, a processor can determine the coefficient of friction in substantially real time along with a cycles per second rate.

Single Ball Bearing Lubricant and Material Evaluator

NASA Technical Reports Server (NTRS)

Hall, Philip B. (Inventor); Novak, Howard L. (Inventor)

2005-01-01

A test apparatus provides an applied load to a monoball through a trolley which moves along a loading axis. While applying the load to the monoball, the torque meter is in communication with the spherical monoball, and a load cell senses the application of applied force to the monoball. Meanwhile, a rotary actuary imports rotary oscillating motion to the monoball which is sensed by a position sensor and a torque meter. Accordingly, a processor can determine the coefficient of friction in substantially real time along with a cycles per second rate.

Deformation Cycling of a Ti - Ni Alloy with Superelasticity Effect Applied in Cardiology

NASA Astrophysics Data System (ADS)

Kaputkin, D. E.; Morozova, T. V.

2014-07-01

The study concerns the effect of the conditions and of the force of loading experienced by an implanted device from a Ti - Ni alloy during its transfer to the working zone, for example, in endoscopic implantation into the coronary sinus of the greater vena cava of heart. It is shown that preliminary deformation cycling (10 - 15 cycles) stabilizes the set of mechanical properties of the alloy.

Cycle-to-cycle IMEP fluctuations in a stoichiometrically-fueled S. I. engine at low speed and load

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sztenderowicz, M.L.; Heywood, J.B.

1990-01-01

In a previous experimental investigation of the effects of residual gas nonuniformity on S.I. engine combustion variability, it was found that eliminating residual gas nonuniformity by skip firing has no detectable impact on the flame development process, but nonetheless caused IMEP fluctuations to drop by about half under very light load conditions. This paper reports that under further investigation, it has been determined that the observed IMEP fluctuations, particularly for optimally-phased cycles, are controlled by cyclic variations in the amount of fuel burning per cycle. Real-time sampling of the hydrocarbon concentration in the exhaust port has shown that the variationmore » in fuel burned per cycle is not primarily due to variations in combustion completeness, and must therefore be attributed to variations in the amount of fuel trapped within the cylinder prior to combustion. Several mechanisms for this variation were identified, all of which are plausible but none of which are likely to dominate: variations in fuel quantity left in the cylinder from the previous cycle; variations in the fluid dynamics of the intake process; fresh charge displacement due to variations in residual gas temperature; variations in leakage through valves; and fluctuations in crevice effects and blow-by.« less

Structural Testing of a 6m Hypersonic Inflatable Aerodynamic Decelerator System

NASA Technical Reports Server (NTRS)

Swanson, G. T.; Kazemba, C. D.; Johnson, R. K.; Hughes, S. J.; Calomino, A. M.

2015-01-01

NASA is developing low ballistic coefficient technologies to support the Nations long-term goal of landing humans on Mars. Current entry, decent, and landing technologies are not practical for this class of payloads due to geometric constraints dictated by current and future launch vehicle fairing limitations. Hypersonic Inflatable Aerodynamic Decelerators (HIADs) are being developed to circumvent this limitation and are now considered a leading technology to enable landing of heavy payloads on Mars. At the beginning of 2014, a 6m diameter HIAD inflatable structure with an integrated flexible thermal protection system (TPS) was subjected to a static load test series to verify its structural performance under flight-relevant loads. The inflatable structure was constructed into a 60 degree sphere-cone configuration using nine inflatable torus segments composed of fiber-reinforced thin films. The inflatable tori were joined together using adhesives and high-strength textile woven structural straps. These straps help distribute the load throughout the inflatable structure. The 6m flexible TPS was constructed using multiple layers of high performance materials that are designed to protect the inflatable structure from heat loads that would be seen in flight during atmospheric entry. A custom test fixture was constructed to perform the static load test series. The fixture consisted of a round structural tub with enough height and width to allow for displacement of the HIAD test article as loads were applied. The bottom of the tub rim had an airtight seal with the floor. The rigid centerbody of the HIAD was mounted to a pedestal in the center of the structural tub. Using an impermeable membrane draped over the HIAD test article, an airtight seal was created with the top rim of the static load tub. This seal allowed partial vacuum to be pulled beneath the HIAD resulting in a uniform static pressure load applied to the outer surface. Using this technique, the test article was subjected to loads of up to 50,000lbs. During the test series an extensive amount of instrumentation was used to provide a rich data set, including deflected shape, structural strap loads, torus cord loads, inflation pressures, and applied static load. In this paper the 2014 6m HIAD static load test series will be discussed in detail, including the design of the 6m HIAD test article, the test setup, and test execution. Analysis results will be described supporting the conclusions that were drawn from the test series..

UNIX helps integrate control packages for combined cycle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forbes, H.W.

1994-05-01

This article describes the use of integrated UNIX based control systems in a combined-cycle power plant. The topics of the article include equipment configuration, control domains and functions for the gas turbine, steam turbine, balance of plant, unit-coordination, and plant master control, device gateway functions, and data-acquisition environment.

Effects of the Physical Environment on Cognitive Load and Learning: Towards a New Model of Cognitive Load

ERIC Educational Resources Information Center

Choi, Hwan-Hee; van Merriënboer, Jeroen J. G.; Paas, Fred

2014-01-01

Although the theoretical framework of cognitive load theory has acknowledged a role for the learning environment, the specific characteristics of the physical learning environment that could affect cognitive load have never been considered, neither theoretically nor empirically. In this article, we argue that the physical learning environment, and…

Examining the existence of the underwriting cycle in managed care organizations.

PubMed

Brotman, B A

2000-01-01

This article examines the existence of the underwriting or profitability cycle in the health insurance industry. Researchers have reported that a six-year cycle exists for health care insurers. That is, three years of profits then are followed by three years of losses. This article suggests that insurers react more quickly to losses and adjust their cost structures almost immediately. Health insurers react to both expected changes and current increases in the payoff ratio.

Evaluation of Inelastic Constitutive Models for Nonlinear Structural Analysis

NASA Technical Reports Server (NTRS)

Kaufman, A.

1983-01-01

The influence of inelastic material models on computed stress-strain states, and therefore predicted lives, was studied for thermomechanically loaded structures. Nonlinear structural analyses were performed on a fatigue specimen which was subjected to thermal cycling in fluidized beds and on a mechanically load cycled benchmark notch specimen. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic-kinematic, combined plus transient creep) were exercised. Of the plasticity models, kinematic hardening gave results most consistent with experimental observations. Life predictions using the computed strain histories at the critical location with a Strainrange Partitioning approach considerably overpredicted the crack initiation life of the thermal fatigue specimen.

In-Plane Shear Testing of Medium and High Modulus Woven Graphite Fiber Reinforced/Polyimide Composites

NASA Technical Reports Server (NTRS)

Gentz, M.; Armentrout, D.; Rupnowski, P.; Kumosa, L.; Shin, E.; Sutter, J. K.; Kumosa, M.

2004-01-01

Iosipescu shear tests were performed at room temperature and at 316 C (600 F) o woven composites with either M40J or M60J graphite fibers and PMR-II-50 polyimide resin matrix. The composites were tested as supplied and after thermo-cycling, with the thermo-cycled composites being tested under dry and wet conditions. Acoustic emission (AE) was monitored during the room and high temperature Iosipescu experiments. The shear stresses at the maximum loads and the shear stresses at the significant onset of AE were determined for the composites as function of temperature and conditioning. The combined effects of thermo-cycling and moisture on the strength and stiffness properties of the composites were evaluated. It was determined that the room and high temperature shear stresses at the maximum loads were unaffected by conditioning. However, at room temperature the significant onset of AE was affected by conditioning; the thermal conditioned wet specimens showed the highest shear stress at the onset of AE followed by thermal-conditioned and then as received specimens. Also, at igh temperature the significant onset of AE occurred in some specimens after the maximum load due to the viscoelastoplastic nature of the matrix material.

An easy-to-use calculating machine to simulate steady state and non-steady-state preparative separations by multiple dual mode counter-current chromatography with semi-continuous loading of feed mixtures.

PubMed

Kostanyan, Artak E; Shishilov, Oleg N

2018-06-01

Multiple dual mode counter-current chromatography (MDM CCC) separation processes with semi-continuous large sample loading consist of a succession of two counter-current steps: with "x" phase (first step) and "y" phase (second step) flow periods. A feed mixture dissolved in the "x" phase is continuously loaded into a CCC machine at the beginning of the first step of each cycle over a constant time with the volumetric rate equal to the flow rate of the pure "x" phase. An easy-to-use calculating machine is developed to simulate the chromatograms and the amounts of solutes eluted with the phases at each cycle for steady-state (the duration of the flow periods of the phases is kept constant for all the cycles) and non-steady-state (with variable duration of alternating phase elution steps) separations. Using the calculating machine, the separation of mixtures containing up to five components can be simulated and designed. Examples of the application of the calculating machine for the simulation of MDM CCC processes are discussed. Copyright © 2018 Elsevier B.V. All rights reserved.

Tribological measurements on a Charnley-type artificial hip joint

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.

1983-01-01

A total hip simulator was used to determine the friction and wear properties of Charnley-type (316L stainless steel balls and sterile ultrahigh molecular weight polyethylene cups) hip prostheses. Three different sets of specimens were tested to 395,000, 101,500 and 233,000 walking cycles, respectively. All tests were run unlubricated, at ambient conditions (22 to 26 C, 30 to 50 percent relative humidity), at 30 walking cycles per minute, under a dynamic load simulating walking. Polyethylene cup wear rates ranged from 1.4 to 39 ten billions cu m which corresponds to dimensional losses of 4.0 to 11 microns per year. Although these wear rates are lower than those obtained from other hip simulators and from in vivo X-ray measurements, they are comparable when taking run-in and plastic deformation into account. Maximum tangential friction forces ranged from 93 to 129 N under variable load (267 to 3090 N range) and from 93 to 143 N under a static load of 3090 N. A portion of one test 250,000 walking cycles) run under dry air ( 1 percent relative humidity) yielded a wear rate almost 6 times greater than that obtained under wet air ( 70 percent relative humidity) conditions.

Musculoskeletal multibody dynamics simulation of the contact mechanics and kinematics of a natural knee joint during a walking cycle.

PubMed

Hu, Jiayu; Chen, Zhenxian; Xin, Hua; Zhang, Qida; Jin, Zhongmin

2018-05-01

Detailed knowledge of the in vivo loading and kinematics in the knee joint is essential to understand its normal functions and the aetiology of osteoarthritis. Computer models provide a viable non-invasive solution for estimating joint loading and kinematics during different physiological activities. However, the joint loading and kinematics of the tibiofemoral and patellofemoral joints during a gait cycle were not typically investigated concurrently in previous computational simulations. In this study, a natural knee architecture was incorporated into a lower extremity musculoskeletal multibody dynamics model based on a force-dependent kinematics approach to investigate the contact mechanics and kinematics of a natural knee joint during a walking cycle. Specifically, the contact forces between the femoral/tibial articular cartilages and menisci and between the femoral and tibial/patellar articular cartilages were quantified. The contact forces and kinematics of the tibiofemoral and patellofemoral joints and the muscle activations and ligament forces were predicted simultaneously with a reasonable level of accuracy. The developed musculoskeletal multibody dynamics model with a natural knee architecture can serve as a potential platform for assisting clinical decision-making and postoperative rehabilitation planning.

Rotary Stirling-Cycle Engine And Generator

NASA Technical Reports Server (NTRS)

Chandler, Joseph A.

1990-01-01

Proposed electric-power generator comprises three motor generators coordinated by microprocessor and driven by rotary Stirling-cycle heat engine. Combination offers thermodynamic efficiency of Stirling cycle, relatively low vibration, and automatic adjustment of operating parameters to suit changing load on generator. Rotary Stirling cycle engine converts heat to power via compression and expansion of working gas between three pairs of rotary pistons on three concentric shafts in phased motion. Three motor/generators each connected to one of concentric shafts, can alternately move and be moved by pistons. Microprocessor coordinates their operation, including switching between motor and generator modes at appropriate times during each cycle.

A Characteristics-Based Approach to Radioactive Waste Classification in Advanced Nuclear Fuel Cycles

NASA Astrophysics Data System (ADS)

Djokic, Denia

The radioactive waste classification system currently used in the United States primarily relies on a source-based framework. This has lead to numerous issues, such as wastes that are not categorized by their intrinsic risk, or wastes that do not fall under a category within the framework and therefore are without a legal imperative for responsible management. Furthermore, in the possible case that advanced fuel cycles were to be deployed in the United States, the shortcomings of the source-based classification system would be exacerbated: advanced fuel cycles implement processes such as the separation of used nuclear fuel, which introduce new waste streams of varying characteristics. To be able to manage and dispose of these potential new wastes properly, development of a classification system that would assign appropriate level of management to each type of waste based on its physical properties is imperative. This dissertation explores how characteristics from wastes generated from potential future nuclear fuel cycles could be coupled with a characteristics-based classification framework. A static mass flow model developed under the Department of Energy's Fuel Cycle Research & Development program, called the Fuel-cycle Integration and Tradeoffs (FIT) model, was used to calculate the composition of waste streams resulting from different nuclear fuel cycle choices: two modified open fuel cycle cases (recycle in MOX reactor) and two different continuous-recycle fast reactor recycle cases (oxide and metal fuel fast reactors). This analysis focuses on the impact of waste heat load on waste classification practices, although future work could involve coupling waste heat load with metrics of radiotoxicity and longevity. The value of separation of heat-generating fission products and actinides in different fuel cycles and how it could inform long- and short-term disposal management is discussed. It is shown that the benefits of reducing the short-term fission-product heat load of waste destined for geologic disposal are neglected under the current source-based radioactive waste classification system, and that it is useful to classify waste streams based on how favorable the impact of interim storage is on increasing repository capacity. The need for a more diverse set of waste classes is discussed, and it is shown that the characteristics-based IAEA classification guidelines could accommodate wastes created from advanced fuel cycles more comprehensively than the U.S. classification framework.

Distinctive viscoelastic and viscoplastic nanomechanics of ionically cross-linked polyelectrolyte complexes under intermittent relaxation and creep

NASA Astrophysics Data System (ADS)

Han, Biao; Ma, Tianzhu; Lee, Daeyeon; Shenoy, Vivek; Han, Lin

This study aims to reveal unique nanoscale viscoelastic and viscoplastic properties of ionically linked polyelectrolyte networks. Layer-by-layer PAH/PAA complexes were tested by four continuous loading cycles in aqueous solutions. In each cycle, AFM-nanoindentation via a microspherical tip (R =5 μm) was applied up to 1 μN force, followed by a 30-60 sec hold at either a constant indentation depth to measure relaxation, or a constant force to measure creep. At a highly cross-linked, net neutral state (0.01M, pH 5.5), instantaneous modulus increased by 2.7-fold from first to last cycle, while the degree of relaxation (>95%) remain consistent. These results indicate repeated loading increases local cross-link density, while relaxation is consistently dominated by cross-link breaking and re-formation. In contrast, under creep, modulus increased by a similar 3.5-fold, and degree of creep is significantly attenuated from ~50% to 45% from first to last cycle. Results from creep suggest constant viscous flow of polymer chains in the absence of permanent anchorage. As a result, an irreversible deformation (~370nm) was observed after multiple creep cycles, suggesting the presence of viscoplasticity.

Hydrodynamic air lubricated compliant surface bearing for an automotive gas turbine engine. 2: Materials and coatings

NASA Technical Reports Server (NTRS)

Bhushan, B.; Ruscitto, D.; Gray, S.

1978-01-01

Material coatings for an air-lubricated, compliant journal bearing for an automotive gas turbine engine were exposed to service test temperatures of 540 C or 650 C for 300 hours, and to 10 temperature cycles from room temperatures to the service test temperatures. Selected coatings were then put on journal and partial-arc foils and tested in start-stop cycle tests at 14 kPa (2 psi) loading for 2000 cycles. Half of the test cycles were performed at a test chamber service temperature of 540 C (1000 F) or 650 C (1200 F); the other half were performed at room temperature. Based on test results, the following combinations and their service temperature limitations are recommended: HL-800 TM (CdO and graphite) on foil versus chrome carbide on journal up to 370 C (700 F); NASA PS 120 (Tribaloy 400, silver and CaF2 on journal versus uncoated foil up to 540 C (1000 F); and Kaman DES on journal and foil up to 640 C (1200 F). Kaman DES coating system was further tested successfully at 35 kPa (5 psi) loading for 2000 start-stop cycles.

Laminar flow control perforated wing panel development

NASA Technical Reports Server (NTRS)

Fischler, J. E.

1986-01-01

Many structural concepts for a wing leading edge laminar flow control hybrid panel were analytically investigated. After many small, medium, and large tests, the selected design was verified. New analytic methods were developed to combine porous titanium sheet bonded to a substructure of fiberglass and carbon/epoxy cloth. At -65 and +160 F test conditions, the critical bond of the porous titanium to the composite failed at lower than anticipated test loads. New cure cycles, design improvements, and test improvements significantly improved the strength and reduced the deflections from thermal and lateral loadings. The wave tolerance limits for turbulence were not exceeded. Consideration of the beam column midbay deflections from the combinations of the axial and lateral loadings and thermal bowing at -65 F, room temperature, and +160 F were included. Many lap shear tests were performed at several cure cycles. Results indicate that sufficient verification was obtained to fabricate a demonstration vehicle.

Thermal-mechanical fatigue test apparatus for metal matrix composites and joint attachments

NASA Technical Reports Server (NTRS)

Westfall, L. J.; Petrasek, D. W.

1985-01-01

Two thermal-mechanical fatigue (TMF) test facilities were designed and developed, one to test tungsten fiber reinforced metal matrix composite specimens at temperature up to 1430C (2600F) and another to test composite/metal attachment bond joints at temperatures up to 760C (1400 F). The TMF facility designed for testing tungsten fiber reinforced metal matrix composites permits test specimen temperature excursions from room temperature to 1430C (2600F) with controlled heating and loading rates. A strain-measuring device measures the strain in the test section of the specimen during each heating and cooling cycle with superimposed loads. Data is collected and recorded by a computer. The second facility is designed to test composite/metal attachment bond joints and to permit heating to a maximum temperature of 760C (1400F) within 10 min and cooling to 150C (300F) within 3 min. A computer controls specimen temperature and load cycling.

Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.; Ghosn, Louis J.; Kalluri, Sreeramesh

2004-01-01

The development of advanced high performance constant-volume-combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high cycle fatigue (HCF) testing of some laser pre-exposed specimens has also been conducted under a frequency of 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions.

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

NASA Astrophysics Data System (ADS)

Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Van Herpen, Alain; Zhang, Weihong

2016-03-01

This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

Thermal-mechanical fatigue test apparatus for metal matrix composites and joint attachments

NASA Technical Reports Server (NTRS)

Westfall, Leonard J.; Petrasek, Donald W.

1988-01-01

Two thermal-mechanical fatigue (TMF) test facilities were designed and developed, one to test tungsten fiber reinforced metal matrix composite specimens at temperature up to 1430C (2600F) and another to test composite/metal attachment bond joints at temperatures up to 760F (1400F). The TMF facility designed for testing tungsten fiber reinforced metal matrix composites permits test specimen temperature excursions from room temperature to 1430C (2600F) with controlled heating and loading rates. A strain-measuring device measures the strain in the test section of the specimen during each heating and cooling cycle with superimposed loads. Data is collected and recorded by a computer. The second facility is designed to test composite/metal attachment bond joints and to permit heating to a maximum temperature of 760C (1400F) within 10 min and cooling to 150C (300F) within 3 min. A computer controls specimen temperature and load cycling.

Selection criteria of the addendum modification coefficients of spur gear pairs with smaller number of pinion teeth

NASA Astrophysics Data System (ADS)

Atanasiu, V.; Oprişan, C.; Leohchi, D.

2016-08-01

A design procedure for the optimum distribution of the addendum modification coefficients of spur gear pairs with smaller number of pinion teeth is presented for the case of a fixed centred distance. The geometrical, kinematics and load capacity criteria are considered in the design analysis. The geometric and kinematics criteria are used to prevent the negative phenomena of the generating and engagement processes. The relation between the contact pressure of meshing teeth and specific sliding are analysed in relation with addendum modification coefficients. A dynamic model is developed to simulate the load sharing characteristics through a mesh cycle. The specific phenomenon of contact tooth pairs alternation during mesh cycle is integrated in this dynamic load modelling. A comparative study is included, which shows the effects of the distribution factor of the addendum modification coefficients on the contact surface characteristics of the gear pairs.

Reusable LH2 tank technology demonstration through ground test

NASA Technical Reports Server (NTRS)

Bianca, C.; Greenberg, H. S.; Johnson, S. E.

1995-01-01

The paper presents the project plan to demonstrate, by March 1997, the reusability of an integrated composite LH2 tank structure, cryogenic insulation, and thermal protection system (TPS). The plan includes establishment of design requirements and a comprehensive trade study to select the most suitable Reusable Hydrogen Composite Tank system (RHCTS) within the most suitable of 4 candidate structural configurations. The 4 vehicles are winged body with the capability to deliver 25,000 lbs of payload to a circular 220 nm, 51.6 degree inclined orbit (also 40,000 lbs to a 28.5 inclined 150 nm orbit). A prototype design of the selected RHCTS is established to identify the construction, fabrication, and stress simulation and test requirements necessary in an 8 foot diameter tank structure/insulation/TPS test article. A comprehensive development test program supports the 8 foot test article development and involves the composite tank itself, cryogenic insulation, and integrated tank/insulation/TPS designs. The 8 foot diameter tank will contain the integrated cryogenic insulation and TPS designs resulting from this development and that of the concurrent lightweight durable TPS program. Tank ground testing will include 330 cycles of LH2 filling, pressurization, body loading, depressurization, draining, and entry heating.

Reuse of bituminous pavements: A mini-review of research, regulations and modelling.

PubMed

Anthonissen, Joke; Van den Bergh, Wim; Braet, Johan

2017-04-01

Bituminous pavement can be recycled - even multiple times - by reusing it in new bituminous mixtures. If the mechanical properties of the binder get worse, this reclaimed asphalt is often used in the sub-structure of the road. Apparently, up till now, no end-of-life phase exists for the material. Actually, defining the end-of-life and the end-of-waste stage of a material is important for life cycle assessment modelling. Various standards and scientific studies on modelling life cycle assessment are known, but the crucial stages are not yet defined for reclaimed asphalt pavement. Unlike for iron, steel and aluminium scrap, at this moment, no legislative end-of-waste criteria for aggregates are formulated by the European Commission. More research is necessary in order to develop valuable end-of-life criteria for aggregates. This contribution is a mini-review article of the current regulations, standards and studies concerning end-of-life and end-of-waste of reclaimed asphalt pavement. The existing methodology in order to define end-of-waste criteria, a case study on aggregates and the argumentation used in finished legislative criteria are the basis to clarify some modelling issues for reclaimed asphalt material. Hence, this contribution elucidates the assignment of process environmental impacts to a life cycle stage as defined by EN15804, that is, end-of-life stage (C) and the supplementary information Module D with benefits and loads beyond the system boundary.

An in vitro biomechanical comparison of hydroxyapatite coated and uncoated ao cortical bone screws for a limited contact: dynamic compression plate fixation of osteotomized equine 3rd metacarpal bones.

PubMed

Durham, Myra E; Sod, Gary A; Riggs, Laura M; Mitchell, Colin F

2015-02-01

To compare the monotonic biomechanical properties of a broad 4.5 mm limited contact-dynamic compression plate (LC-DCP) fixation secured with hydroxyapatite (HA) coated cortical bone screws (HA-LC-DCP) versus uncoated cortical bone screws (AO-LC-DCP) to repair osteotomized equine 3rd metacarpal (MC3) bones. Experimental. Adult equine cadaveric MC3 bones (n = 12 pair). Twelve pairs of equine MC3 were divided into 3 test groups (4 pairs each) for: (1) 4 point bending single cycle to failure testing; (2) 4 point bending cyclic fatigue testing; and (3) torsional single cycle to failure testing. For the HA-LC-DCP-MC3 construct, an 8-hole broad LC-DCP (Synthes Ltd, Paoli, PA) was secured on the dorsal surface of each randomly selected MC3 bone with a combination of four 5.5 mm and four 4.5 mm HA-coated cortical screws. For the AO-LC-DCP-MC3 construct, an 8-hole 4.5 mm broad LC-DCP was secured on the dorsal surface of the contralateral MC3 bone with a combination of four 5.5 mm and four 4.5 mm uncoated cortical screws. All MC3 bones had mid-diaphyseal osteotomies. Mean test variable values for each method were compared using a paired t-test within each group. Significance was set at P < .05. Mean yield load, yield bending moment, composite rigidity, failure load, and failure bending moment, under 4 point bending, single cycle to failure, of the HA-LC-DCP fixation were significantly greater than those of the AO-LC-DCP fixation. Mean ± SD values for the HA-LC-DCP and the AO-LC-DCP fixation techniques, respectively, in single cycle to failure under 4 point bending were: yield load, 26.7 ± 2.15 and 16.3 ± 1.38 kN; yield bending moment, 527.4 ± 42.4 and 322.9 ± 27.2 N-m; composite rigidity, 5306 ± 399 and 3003 ± 300 N-m/rad; failure load, 40.6 ± 3.94 and 26.5 ± 2.52 kN; and failure bending moment, 801.9 ± 77.9 and 522.9 ± 52.2 N-m. Mean cycles to failure in 4 point bending of the HA-LC-DCP fixation (116,274 ± 13,211) was significantly greater than that of the AO-LC-DCP fixation 47,619 ± 6580. Mean yield load, mean composite rigidity, and mean failure load under torsional testing, single cycle to failure was significantly greater for the broad HA-LC-DCP fixation compared with the AO-LC-DCP fixation. In single cycle to failure under torsion, mean ± SD values for the HA-LC-DCP and the AO-LC-DCP fixation techniques, respectively, were: yield load, 101.3 ± 14.68 and 70.54 ± 10.20 N-m; composite rigidity, 437.9 ± 32.9 and 220.7 ± 17.6 N-m/rad; and failure load: 105.7 ± 15.5 and 75.28 ± 10.1 N-m. HA-LC-DCP was superior to AO-LC-DCP in resisting the static overload forces (palmarodorsal 4 point bending and torsional) and in resisting cyclic fatigue under palmarodorsal 4 point bending. © Copyright 2014 by The American College of Veterinary Surgeons.

Menstrual cycle perturbation by organohalogens and elements in the Cree of James Bay, Canada.

PubMed

Wainman, Bruce C; Kesner, James S; Martin, Ian D; Meadows, Juliana W; Krieg, Edward F; Nieboer, Evert; Tsuji, Leonard J

2016-04-01

Persistent organohalogens (POHs) and metals have been linked to alterations in menstrual cycle function and fertility in humans. The Cree First Nations people living near James Bay in Ontario and Quebec, Canada, have elevated levels of POHs, mercury and lead compared to other Canadians. The present study examines the interrelationships between selected POHs and elements on menstrual cycle function in these Cree women. Menstrual cycle characteristics were derived from structured daily diaries and endocrine measurements from daily urine samples collected during one cycle for 42 women age 19-42. We measured 31 POHs in blood plasma and 18 elements in whole blood, for 31 of the participants. POHs and elements detected in ≥ 70% of the participants were transformed by principal component (PC) analysis to reduce the contaminant exposure data to fewer, uncorrelated PCA variables. Multiple regression analysis revealed that, after adjusting for confounders, PC-3 values showed significant negative association with cycle length, after adjusting for confounders (p = 0.002). PC-3 accounted for 9.2% of the variance and shows positive loadings for cadmium, selenium, and PBDE congeners 47 and 153, and a negative loading for copper. Sensitivity analysis of the model to quantify likely effect sizes showed a range of menstrual cycle length from 25.3 to 28.3 days using the lower and upper 95% confidence limits of mean measured contaminant concentrations to predict cycle length. Our observations support the hypothesis that the menstrual cycle function of these women may be altered by exposure to POHs and elements from their environment. Copyright © 2015. Published by Elsevier Ltd.

Specific modes of vibratory technological machines: mathematical models, peculiarities of interaction of system elements

NASA Astrophysics Data System (ADS)

Eliseev, A. V.; Sitov, I. S.; Eliseev, S. V.

2018-03-01

The methodological basis of constructing mathematical models of vibratory technological machines is developed in the article. An approach is proposed that makes it possible to introduce a vibration table in a specific mode that provides conditions for the dynamic damping of oscillations for the zone of placement of a vibration exciter while providing specified vibration parameters in the working zone of the vibration table. The aim of the work is to develop methods of mathematical modeling, oriented to technological processes with long cycles. The technologies of structural mathematical modeling are used with structural schemes, transfer functions and amplitude-frequency characteristics. The concept of the work is to test the possibilities of combining the conditions for reducing loads with working components of a vibration exciter while simultaneously maintaining sufficiently wide limits in variating the parameters of the vibrational field.

Analysis of the type II robotic mixed-model assembly line balancing problem

NASA Astrophysics Data System (ADS)

Çil, Zeynel Abidin; Mete, Süleyman; Ağpak, Kürşad

2017-06-01

In recent years, there has been an increasing trend towards using robots in production systems. Robots are used in different areas such as packaging, transportation, loading/unloading and especially assembly lines. One important step in taking advantage of robots on the assembly line is considering them while balancing the line. On the other hand, market conditions have increased the importance of mixed-model assembly lines. Therefore, in this article, the robotic mixed-model assembly line balancing problem is studied. The aim of this study is to develop a new efficient heuristic algorithm based on beam search in order to minimize the sum of cycle times over all models. In addition, mathematical models of the problem are presented for comparison. The proposed heuristic is tested on benchmark problems and compared with the optimal solutions. The results show that the algorithm is very competitive and is a promising tool for further research.

Bone health in endurance athletes: runners, cyclists, and swimmers.

PubMed

Scofield, Kirk L; Hecht, Suzanne

2012-01-01

Weight-bearing exercise has been recognized widely to be beneficial for long-term bone health. However inherent differences in bone-loading characteristics and energy expenditure during participation in endurance sports place many endurance athletes at a relative disadvantage with regard to bone health compared with other athletes. Adolescents and adults who participate in endurance sports, such as running, and non-weight-bearing sports, such as biking and swimming, often have lower bone mineral density (BMD) than athletes participating in ball and power sports, and sometimes their BMD is lower than their inactive peers. Low BMD increases the risk of stress and fragility fractures, both while an athlete is actively competing and later in life. This article reviews the variable effects of distance running, cycling, swimming, and triathlons on bone health; the evaluation of stress and fragility fractures; and the diagnosis, management, and prevention of low BMD in endurance athletes.

Effect of in vitro chewing and bruxism events on remineralization, at the resin-dentin interface.

PubMed

Toledano, Manuel; Cabello, Inmaculada; Aguilera, Fátima S; Osorio, Estrella; Osorio, Raquel

2015-01-02

The purpose of this study was to evaluate if different in vitro functional and parafunctional habits promote mineralization at the resin-dentin interface after bonding with three different adhesive approaches. Dentin surfaces were subjected to distinct treatments: demineralization by (1) 37% phosphoric acid (PA) followed by application of an etch-and-rinse dentin adhesive, Single Bond (SB) (PA+SB); (2) 0.5 M ethylenediaminetetraacetic acid (EDTA) followed by SB (EDTA+SB); (3) application of a self-etch dentin adhesive, Clearfil SE Bond (SEB). Different loading waveforms were applied: No cycling (I), cycled in sine (II) or square (III) waves, sustained loading hold for 24 h (IV) or sustained loading hold for 72 h (V). Remineralization at the bonded interfaces was assessed by AFM imaging/nano-indentation, Raman spectroscopy and Masson's trichrome staining. In general, in vitro chewing and parafunctional habits, promoted an increase of nano-mechanical properties at the resin-dentin interface. Raman spectroscopy through cluster analysis demonstrated an augmentation of the mineral-matrix ratio in loaded specimens. Trichrome staining reflected a narrow demineralized dentin matrix after loading in all groups except in PA+SB and EDTA+SB samples after sustained loading hold for 72 h, which exhibited a strong degree of mineralization. In vitro mechanical loading, produced during chewing and bruxism (square or hold 24 and 72 h waveforms), induced remineralization at the resin-dentin bonded interface. Copyright © 2014 Elsevier Ltd. All rights reserved.

Characterizing the proton loading site in cytochrome c oxidase.

PubMed

Lu, Jianxun; Gunner, M R

2014-08-26

Cytochrome c oxidase (CcO) uses the energy released by reduction of O2 to H2O to drive eight charges from the high pH to low pH side of the membrane, increasing the electrochemical gradient. Four electrons and protons are used for chemistry, while four more protons are pumped. Proton pumping requires that residues on a pathway change proton affinity through the reaction cycle to load and then release protons. The protonation states of all residues in CcO are determined in MultiConformational Continuum Electrostatics simulations with the protonation and redox states of heme a, a3, Cu(B), Y288, and E286 used to define the catalytic cycle. One proton is found to be loaded and released from residues identified as the proton loading site (PLS) on the P-side of the protein in each of the four CcO redox states. Thus, the same proton pumping mechanism can be used each time CcO is reduced. Calculations with structures of Rhodobacter sphaeroides, Paracoccus denitrificans, and bovine CcO derived by crystallography and molecular dynamics show the PLS functions similarly in different CcO species. The PLS is a cluster rather than a single residue, as different structures show 1-4 residues load and release protons. However, the proton affinity of the heme a3 propionic acids primarily determines the number of protons loaded into the PLS; if their proton affinity is too low, less than one proton is loaded.

Characterizing the proton loading site in cytochrome c oxidase

PubMed Central

Lu, Jianxun; Gunner, M. R.

2014-01-01

Cytochrome c oxidase (CcO) uses the energy released by reduction of O2 to H2O to drive eight charges from the high pH to low pH side of the membrane, increasing the electrochemical gradient. Four electrons and protons are used for chemistry, while four more protons are pumped. Proton pumping requires that residues on a pathway change proton affinity through the reaction cycle to load and then release protons. The protonation states of all residues in CcO are determined in MultiConformational Continuum Electrostatics simulations with the protonation and redox states of heme a, a3, CuB, Y288, and E286 used to define the catalytic cycle. One proton is found to be loaded and released from residues identified as the proton loading site (PLS) on the P-side of the protein in each of the four CcO redox states. Thus, the same proton pumping mechanism can be used each time CcO is reduced. Calculations with structures of Rhodobacter sphaeroides, Paracoccus denitrificans, and bovine CcO derived by crystallography and molecular dynamics show the PLS functions similarly in different CcO species. The PLS is a cluster rather than a single residue, as different structures show 1–4 residues load and release protons. However, the proton affinity of the heme a3 propionic acids primarily determines the number of protons loaded into the PLS; if their proton affinity is too low, less than one proton is loaded. PMID:25114210

Adaptation to a cortex controlled robot attached at the pelvis and engaged during locomotion in rats

PubMed Central

Song, Weiguo; Giszter, Simon F.

2011-01-01

Brain Machine Interfaces (BMIs) should ideally show robust adaptation of the BMI across different tasks and daily activities. Most BMIs have used over-practiced tasks. Little is known about BMIs in dynamic environments. How are mechanically body-coupled BMIs integrated into ongoing rhythmic dynamics, e.g., in locomotion? To examine this we designed a novel BMI using neural discharge in the hindlimb/trunk motor cortex in rats during locomotion to control a robot attached at the pelvis. We tested neural adaptation when rats experienced (a) control locomotion, (b) ‘simple elastic load’ (a robot load on locomotion without any BMI neural control) and (c) ‘BMI with elastic load’ (in which the robot loaded locomotion and a BMI neural control could counter this load). Rats significantly offset applied loads with the BMI while preserving more normal pelvic height compared to load alone. Adaptation occurred over about 100–200 step cycles in a trial. Firing rates increased in both the loaded conditions compared to baseline. Mean phases of cells’ discharge in the step cycle shifted significantly between BMI and the simple load condition. Over time more BMI cells became positively correlated with the external force and modulated more deeply, and neurons’ network correlations on a 100ms timescale increased. Loading alone showed none of these effects. The BMI neural changes of rate and force correlations persisted or increased over repeated trials. Our results show that rats have the capacity to use motor adaptation and motor learning to fairly rapidly engage hindlimb/trunk coupled BMIs in their locomotion. PMID:21414932

Effect of hygroscopic treatments and load applications on engineering properties of flakeboards

Treesearch

M.C. Yeh; R.C. Tang; C.Y. Hse

1991-01-01

The study of mechanical properties of hardwood structural flakeboards (white oak, red oak, and sweetgum) as affected by hygroscopic treatments and load applications, individually or collectively, is reported. The shear moduli and moduli of elasticty determined by stress waves (Esw) are drastically reduced by cycle conditions of 65/95/65 percent...

Estimating Summer Nutrient Concentrations in Northeastern Lakes from SPARROW Load Predictions and Modeled Lake Depth and Volume

EPA Science Inventory

Global nutrient cycles have been altered by use of fossil fuels and fertilizers resulting in increases in nutrient loads to aquatic systems. In the United States, excess nutrients have been repeatedly reported as the primary cause of lake water quality impairments. Setting nutr...

The multiaxial fatigue response of cylindrical geometry under proportional loading subject to fluctuating tractions

NASA Astrophysics Data System (ADS)

Martinez, Rudy D.

A multiaxial fatigue model is proposed, as it would apply to cylindrical geometry in the form of industrial sized pressure vessels. The main focus of the multiaxial fatigue model will be based on using energy methods with the loading states confined to fluctuating tractions under proportional loading. The proposed fatigue model is an effort to support and enhance existing fatigue life predicting methods for pressure vessel design, beyond the ASME Boiler and Pressure Vessel codes, ASME Section VIII Division 2 and 3, which is currently used in industrial engineering practice for pressure vessel design. Both uniaxial and biaxial low alloy pearlittic-ferritic steel cylindrical cyclic test data are utilized to substantiate the proposed fatigue model. Approximate material hardening and softening aspects from applied load cycling states and the Bauschinger effect are accounted for by adjusting strain control generated hysteresis loops and the cyclic stress strain curve. The proposed fatigue energy model and the current ASME fatigue model are then compared with regards to the accuracy of predicting fatigue life cycle consistencies.

Finite element based contact analysis of radio frequency MEMs switch membrane surfaces

NASA Astrophysics Data System (ADS)

Liu, Jin-Ya; Chalivendra, Vijaya; Huang, Wenzhen

2017-10-01

Finite element simulations were performed to determine the contact behavior of radio frequency (RF) micro-electro-mechanical (MEM) switch contact surfaces under monotonic and cyclic loading conditions. Atomic force microscopy (AFM) was used to capture the topography of RF-MEM switch membranes and later they were analyzed for multi-scale regular as well as fractal structures. Frictionless, non-adhesive contact 3D finite element analysis was carried out at different length scales to investigate the contact behavior of the regular-fractal surface using an elasto-plastic material model. Dominant micro-scale regular patterns were found to significantly change the contact behavior. Contact areas mainly cluster around the regular pattern. The contribution from the fractal structure is not significant. Under cyclic loading conditions, plastic deformation in the 1st loading/unloading cycle smooth the surface. The subsequent repetitive loading/unloading cycles undergo elastic contact without changing the morphology of the contacting surfaces. The work is expected to shed light on the quality of the switch surface contact as well as the optimum design of RF MEM switch surfaces.

Tensile and fatigue behavior of polymer composites reinforced with superelastic SMA strands

NASA Astrophysics Data System (ADS)

Daghash, Sherif M.; Ozbulut, Osman E.

2018-06-01

This study explores the use of superelastic shape memory alloy (SMA) strands, which consist of seven individual small-diameter wires, in an epoxy matrix and characterizes the tensile and fatigue responses of the developed SMA/epoxy composites. Using a vacuum assisted hand lay-up technique, twelve SMA fiber reinforced polymer (FRP) specimens were fabricated. The developed SMA-FRP composites had a fiber volume ratio of 50%. Tensile response of SMA-FRP specimens were characterized under both monotonic loading and increasing amplitude loading and unloading cycles. The degradation in superelastic properties of the developed SMA-FRP composites during fatigue loading at different strain amplitudes was investigated. The effect of loading rate on the fatigue response of SMA-FRP composites was also explored. In addition, fractured specimens were examined using the scanning electron microscopy (SEM) technique to study the failure mechanisms of the tested specimens. A good interfacial bonding between the SMA strands and epoxy matrix was observed. The developed SMA-FRP composites exhibited good superelastic behavior at different strain amplitudes up to at least 800 cycle after which significant degradation occurred.

Reponse dynamique des structures sous charges de vent

NASA Astrophysics Data System (ADS)

Gani, Ferawati

The main purpose of this research is to assemble numerical tools that allows realistic dynamic study of structures under wind loading. The availability of such numerical tools is becoming more important for the industry, following previous experiences in structural damages after extreme wind events. The methodology of the present study involves two main steps: (i) preparing the wind loading according to its spatial and temporal correlations by using digitally generated wind or real measured wind; (ii) preparing the numerical model that captures the characteristics of the real structures and respects all the necessary numerical requirements to pursue transient dynamic analyses. The thesis is presented as an ensemble of four articles written for refereed journals and conferences that showcase the contributions of the present study to the advancement of transient dynamic study of structures under wind loading, on the wind model itself (the first article) and on the application of the wind study on complex structures (the next three articles). The articles presented are as follows: (a) the evaluation of three-dimensional correlations of wind, an important issue for more precise prediction of wind loading for flexible and line-like structures, the results presented in this first article helps design engineers to choose a more suitable models to define three-dimensional wind loading; (b) the refinement of design for solar photovoltaic concentrator-tracker structure developed for utility scale, this study addressed concerns related strict operational criteria and fatigue under wind load for a large parabolic truss structure; (c) the study of guyed towers for TLs, the applicability of the static-equivalent method from the current industry documents for the design of this type of flexible TL support was questioned, a simplified method to improve the wind design was proposed; (d) the fundamental issue of nonlinear behaviour under extreme wind loading for single-degree-of-freedom systems is evaluated here, the use of real measured hurricane and winter storm have highlighted the possible interest of taking into account the ductility in the extreme wind loading design. The present research project has shown the versatility of the use of the developed wind study methodology to solve concerns related to different type of complex structures. In addition, this study proposes simplified methods that are useful for practical engineers when there is the need to solve similar problems. Key words: nonlinear, dynamic, wind, guyed tower, parabolic structure, ductility.

Guatemala switch to crude saves over $1 million a month

DOE Office of Scientific and Technical Information (OSTI.GOV)

de Biasi, V.

1980-03-01

In a two-step program designed to reduce fuel costs and improve operating efficiency, Empresa Electrica de Guatemala has modified two General Electric PG 5341 gas turbines at Laguna to run on crude oil and installed heat recovery equipment for repowering two existing steam turbines. The gas turbines, nominally rated at around 19,000 kW for base load operation at 70/sup 0/F average ambient temperature and 4000 feet altitude, were installed in 1977-78 as a base load backup to hydro power during the dry season. Original plan was to put them into immediate service as simple cycle units and then convert tomore » combined cycle operation. Priorities were shifted to switch over from distillate to crude oil firing before going ahead with the combined cycle istallation. Their economic evaluation showed the initial investment would be paid off in a few months by the savings in fuel costs.« less

A hip joint simulator study using simplified loading and motion cycles generating physiological wear paths and rates.

PubMed

Barbour, P S; Stone, M H; Fisher, J

1999-01-01

In some designs of hip joint simulator the cost of building a highly complex machine has been offset with the requirement for a large number of test stations. The application of the wear results generated by these machines depends on their ability to reproduce physiological wear rates and processes. In this study a hip joint simulator has been shown to reproduce physiological wear using only one load vector and two degrees of motion with simplified input cycles. The actual path of points on the femoral head relative to the acetabular cup were calculated and compared for physiological and simplified input cycles. The in vitro wear rates were found to be highly dependent on the shape of these paths and similarities could be drawn between the shape of the physiological paths and the simplified elliptical paths.

Transparent and Self-Supporting Graphene Films with Wrinkled- Graphene-Wall-Assembled Opening Polyhedron Building Blocks for High Performance Flexible/Transparent Supercapacitors.

PubMed

Li, Na; Huang, Xuankai; Zhang, Haiyan; Li, Yunyong; Wang, Chengxin

2017-03-22

Improving mass loading while maintaining high transparency and large surface area in one self-supporting graphene film is still a challenge. Unfortunately, all of these factors are absolutely essential for enhancing the energy storage performance of transparent supercapacitors for practical applications. To solve the above bottleneck problem, we produce a novel self-supporting flexible and transparent graphene film (STF-GF) with wrinkled-wall-assembled opened-hollow polyhedron building units. Taking advantage of the microscopic morphology, the STF-GF exhibits improved mass loading with high transmittance (70.2% at 550 nm), a large surface area (1105.6 m 2 /g), and good electrochemical performance: high energy (552.3 μWh/cm 3 ), power densities (561.9 mW/cm 3 ), a superlong cycle life, and good cycling stability (the capacitance retention is ∼94.8% after 20,000 cycles).

Finite Element Modeling of Thermal Cycling Induced Microcracking in Carbon/Epoxy Triaxial Braided Composites

NASA Technical Reports Server (NTRS)

Zhang, Chao; Binienda, Wieslaw K.; Morscher, Gregory; Martin, Richard E.

2012-01-01

The microcrack distribution and mass change in PR520/T700s and 3502/T700s carbon/epoxy braided composites exposed to thermal cycling was evaluated experimentally. Acoustic emission was utilized to record the crack initiation and propagation under cyclic thermal loading between -55 C and 120 C. Transverse microcrack morphology was investigated using X-ray Computed Tomography. Different performance of two kinds of composites was discovered and analyzed. Based on the observations of microcrack formation, a meso-mechanical finite element model was developed to obtain the resultant mechanical properties. The simulation results exhibited a decrease in strength and stiffness with increasing crack density. Strength and stiffness reduction versus crack densities in different orientations were compared. The changes of global mechanical behavior in both axial and transverse loading conditions were studied. Keywords: Thermal cycles; Microcrack; Finite Element Model; Braided Composite

Modelling of optimal training load patterns during the 11 weeks preceding major competition in elite swimmers.

PubMed

Hellard, Philippe; Scordia, Charlotte; Avalos, Marta; Mujika, Inigo; Pyne, David B

2017-10-01

Periodization of swim training in the final training phases prior to competition and its effect on performance have been poorly described. We modeled the relationships between the final 11 weeks of training and competition performance in 138 elite sprint, middle-distance, and long-distance swimmers over 20 competitive seasons. Total training load (TTL), strength training (ST), and low- to medium-intensity and high-intensity training variables were monitored. Training loads were scaled as a percentage of the maximal volume measured at each intensity level. Four training periods (meso-cycles) were defined: the taper (weeks 1 to 2 before competition), short-term (weeks 3 to 5), medium-term (weeks 6 to 8), and long-term (weeks 9 to 11). Mixed-effects models were used to analyze the association between training loads in each training meso-cycle and end-of-season major competition performance. For sprinters, a 10% increase between ∼20% and 70% of the TTL in medium- and long-term meso-cycles was associated with 0.07 s and 0.20 s faster performance in the 50 m and 100 m events, respectively (p < 0.01). For middle-distance swimmers, a higher TTL in short-, medium-, and long-term training yielded faster competition performance (e.g., a 10% increase in TTL was associated with improvements of 0.1-1.0 s in 200 m events and 0.3-1.6 s in 400 m freestyle, p < 0.01). For sprinters, a 60%-70% maximal ST load 6-8 weeks before competition induced the largest positive effects on performance (p < 0.01). An increase in TTL during the medium- and long-term preparation (6-11 weeks to competition) was associated with improved performance. Periodization plans should be adapted to the specialty of swimmers.

Fatigue resistance and microleakage of CAD/CAM ceramic and composite molar crowns.

PubMed

Kassem, Amr S; Atta, Osama; El-Mowafy, Omar

2012-01-01

The aim of this study was to determine effect of compressive cyclic loading on fatigue resistance and microleakage of monolithic CAD/CAM molar ceramic and composite crowns. Thirty-two extracted molars were prepared to receive CEREC crowns according to manufacturer's guidelines using a special paralleling device (Parallel-A-Prep). Sixteen feldspathic ceramic crowns (VITABLOCS Mark II) (VMII) and 16 resin-composite crowns (Paradigm-MZ100 blocks) (PMZ) were milled using a CEREC-3D machine. Eight crowns of each group were cemented to their respective teeth using self-etching resin cement (Panavia-F-2.0) (PAN), and eight were cemented using self-adhesive resin cement (RelyX-Unicem-Clicker) (RXU). Following storage for 1 week in water, specimens were subjected to uniaxial compressive cyclic loading in an Instron testing machine at 12 Hz for 1,000,000 cycles. Load was applied at the central fossa, and the cycle range was 60-600 N. Specimens were then subjected to microleakage testing. Data were statistically analyzed using factorial ANOVA and Post Hoc (Tukey HSD) tests. All composite crowns survived compressive cyclic loading without fracture, while three ceramic crowns from the subgroup cemented with RXU developed surface cracks at the center of occlusal surfaces, extending laterally. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other three subgroups (p < 0.05). After 1,000,000 cycles of compressive cyclic loading, PMZ composite molar crowns were more fatigue-resistant than VMII ceramic crowns. Cement type had a significant effect on fatigue resistance of the ceramic crowns but not the composite ones. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other subgroups (p < 0.05). © 2011 by The American College of Prosthodontists.

Characteristics and thermal behavior analysis of lithium-ion batteries for application in hybrid locomotives

NASA Astrophysics Data System (ADS)

Chatterjee, Krishnashis

The locomotive industry accounts for 2.5 % of the total fuel consumption in the US. Thus the necessity for reducing fuel consumption and emissions led to the development of the concept of hybrid locomotive which is dual powered by the diesel engine and electric motors. But the energy dissipated in braking such a locomotive in a year is enough to power over 9100 average US households over the same period of time. Recovering this energy using regenerative braking system and storing it in a electric battery is of great interest among researchers for improving overall efficiency and reducing consumption of fuels. In the present study, LiFePO4 batteries, a type of the state-of-art lithium-ion batteries, have been tested under different environmental and load conditions. Environmental temperatures were varied to analyze their effects on the charging and discharging patterns of the battery by using the CADEX battery analyzer in order to find the temperature range for optimum battery performance. The fluctuations of temperature of the battery surface were monitored along the length of the tests, using Infra-Red imaging and thermocouple probes at different points on the battery surface. Both battery performance characteristics and the variation of the battery surface temperature were also recorded for different load cycles in order to get a comprehensive picture of the heat generation and its effect on the behavior of the battery under different load conditions. Lastly a practical Load Cycle analysis of the battery has been performed which gave a picture of the heat generated by the battery and also the performance characteristics as it is subjected to a practical Load Cycle.

Misfit and fracture load of implant-supported monolithic crowns in zirconia-reinforced lithium silicate.

PubMed

Gomes, Rafael Soares; Souza, Caroline Mathias Carvalho de; Bergamo, Edmara Tatiely Pedroso; Bordin, Dimorvan; Del Bel Cury, Altair Antoninha

2017-01-01

In this study, marginal and internal misfit and fracture load with and without thermal-mechanical aging (TMA) of monolithic ZLS and lithium disilicate (LDS) crowns were evaluated. Crowns were milled using a computer-aided design/computer-aided manufacturing system. Marginal gaps (MGs), absolute marginal discrepancy (AMD), axial gaps, and occlusal gaps were measured by X-ray microtomography (n=8). For fracture load testing, crowns were cemented in a universal abutment, and divided into four groups: ZLS without TMA, ZLS with TMA, LDS without TMA, and LDS with TMA (n=10). TMA groups were subjected to 10,000 thermal cycles (5-55°C) and 1,000,000 mechanical cycles (200 N, 3.8 Hz). All groups were subjected to compressive strength testing in a universal testing machine at a crosshead speed of 1 mm/min until failure. Student's t-test was used to examine misfit, two-way analysis of variance was used to analyze fracture load, and Pearson's correlation coefficients for misfit and fracture load were calculated (α=0.05). The materials were analyzed according to Weibull distribution, with 95% confidence intervals. Average MG (p<0.001) and AMD (p=0.003) values were greater in ZLS than in LDS crowns. TMA did not affect the fracture load of either material. However, fracture loads of ZLS crowns were lower than those of LDS crowns (p<0.001). Fracture load was moderately correlated with MG (r=-0.553) and AMD (r=-0.497). ZLS with TMA was least reliable, according to Weibull probability. Within the limitations of this study, ZLS crowns had lower fracture load values and greater marginal misfit than did LDS crowns, although these values were within acceptable limits.

Fatigue loading and R-curve behavior of a dental glass-ceramic with multiple flaw distributions.

PubMed

Joshi, Gaurav V; Duan, Yuanyuan; Della Bona, Alvaro; Hill, Thomas J; St John, Kenneth; Griggs, Jason A

2013-11-01

To determine the effects of surface finish and mechanical loading on the rising toughness curve (R-curve) behavior of a fluorapatite glass-ceramic (IPS e.max ZirPress) and to determine a statistical model for fitting fatigue lifetime data with multiple flaw distributions. Rectangular beam specimens were fabricated by pressing. Two groups of specimens (n=30) with polished (15 μm) or air abraded surface were tested under rapid monotonic loading in oil. Additional polished specimens were subjected to cyclic loading at 2 Hz (n=44) and 10 Hz (n=36). All fatigue tests were performed using a fully articulated four-point flexure fixture in 37°C water. Fractography was used to determine the critical flaw size and estimate fracture toughness. To prove the presence of R-curve behavior, non-linear regression was used. Forward stepwise regression was performed to determine the effects on fracture toughness of different variables, such as initial flaw type, critical flaw size, critical flaw eccentricity, cycling frequency, peak load, and number of cycles. Fatigue lifetime data were fit to an exclusive flaw model. There was an increase in fracture toughness values with increasing critical flaw size for both loading methods (rapid monotonic loading and fatigue). The values for the fracture toughness ranged from 0.75 to 1.1 MPam(1/2) reaching a plateau at different critical flaw sizes based on loading method. Cyclic loading had a significant effect on the R-curve behavior. The fatigue lifetime distribution was dependent on the flaw distribution, and it fit well to an exclusive flaw model. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Fatigue loading and R-curve behavior of a dental glass-ceramic with multiple flaw distributions

PubMed Central

Joshi, Gaurav V.; Duan, Yuanyuan; Bona, Alvaro Della; Hill, Thomas J.; John, Kenneth St.; Griggs, Jason A.

2013-01-01

Objectives To determine the effects of surface finish and mechanical loading on the rising toughness curve (R-curve) behavior of a fluorapatite glass-ceramic (IPS e.max ZirPress) and to determine a statistical model for fitting fatigue lifetime data with multiple flaw distributions. Materials and Methods Rectangular beam specimens were fabricated by pressing. Two groups of specimens (n=30) with polished (15 μm) or air abraded surface were tested under rapid monotonic loading in oil. Additional polished specimens were subjected to cyclic loading at 2 Hz (n=44) and 10 Hz (n=36). All fatigue tests were performed using a fully articulated four-point flexure fixture in 37°C water. Fractography was used to determine the critical flaw size and estimate fracture toughness. To prove the presence of R-curve behavior, non-linear regression was used. Forward stepwise regression was performed to determine the effects on fracture toughness of different variables, such as initial flaw type, critical flaw size, critical flaw eccentricity, cycling frequency, peak load, and number of cycles. Fatigue lifetime data were fit to an exclusive flaw model. Results There was an increase in fracture toughness values with increasing critical flaw size for both loading methods (rapid monotonic loading and fatigue). The values for the fracture toughness ranged from 0.75 to 1.1 MPa·m1/2 reaching a plateau at different critical flaw sizes based on loading method. Significance Cyclic loading had a significant effect on the R-curve behavior. The fatigue lifetime distribution was dependent on the flaw distribution, and it fit well to an exclusive flaw model. PMID:24034441

An in vitro biomechanical comparison of two fixation methods for transverse osteotomies of the medial proximal forelimb sesamoid bones in horses.

PubMed

Wilson, D A; Keegan, K G; Carson, W L

1999-01-01

This study compared the mechanical properties of the normal intact suspensory apparatus and two methods of fixation for repair of transverse, midbody fractures of the proximal sesamoid bones of adult horses: transfixation wiring (TW) and screws placed in lag fashion (LS). An in vitro, paired study using equine cadaver limbs mounted in a loading apparatus was used to test the mechanical properties of TW and LS. Seventeen paired (13 repaired, 4 normal) equine cadaver limbs consisting of the suspensory apparatus third metacarpal bone, and first and second phalanges. The two methods of repair and normal intact specimens were evaluated in single cycle-to-failure loading. Yield failure was defined to occur at the first notable discontinuity (>50 N) in the load-displacement curve, the first visible failure as evident on the videotape, or a change in the slope of the moment-fetlock angle curve. Ultimate failure was defined to occur at the highest load resisted by the specimen. Corresponding resultant force and force per kg of body weight on the suspensory apparatus, fetlock joint moment, and angle of fetlock dorsiflexion were calculated by use of specimen dimensions and applied load. These were compared along with specimen stiffness, and ram displacement. Load on the suspensory apparatus, load on the suspensory apparatus per kg of body weight, moment, applied load, and angle of fetlock dorsiflexion at yield failure were significantly greater for the TW-repaired than for the LS-repaired specimens. A 3 to 5 mm gap was observed before yield failure in most TW-repaired osteotomies. Transfixation wiring provided greater strength to yield failure than screws placed in lag fashion in single cycle load-to-failure mechanical testing of repaired transverse osteotomized specimens of the medial proximal forelimb sesamoid bone.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Garrett N.; Russell, Renee L.; Peterson, Reid A.

This report summarizes the work performed to evaluate multiple, cesium loading, and elution cycles for small columns containing SRF resin using a simple, high-level waste (HLW) simulant. Cesium ion exchange loading and elution curves were generated for a nominal 5 M Na, 2.4E-05 M Cs, 0.115 M Al loading solution traced with 134Cs followed by elution with variable HNO3 (0.02, 0.07, 0.15, 0.23, and 0.28 M) containing variable CsNO3 (5.0E-09, 5.0E-08, and 5.0E-07 M) and traced with 137Cs. The ion exchange system consisted of a pump, tubing, process solutions, and a single, small ({approx}15.7 mL) bed of SRF resin withmore » a water-jacketed column for temperature-control. The columns were loaded with approximately 250 bed volumes (BVs) of feed solution at 45 C and at 1.5 to 12 BV per hour (0.15 to 1.2 cm/min). The columns were then eluted with 29+ BVs of HNO3 processed at 25 C and at 1.4 BV/h. The two independent tracers allowed analysis of the on-column cesium interaction between the loading and elution solutions. The objective of these tests was to improve the correlation between the spent resin cesium content and cesium leached out of the resin in subsequent loading cycles (cesium leakage) to help establish acid strength and purity requirements.« less

Extended burnup core management for once-through uranium fuel cycles in LWRS. First annual report for the period 1 July 1979-30 June 1980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sesonske, A.

1980-08-01

Detailed core management arrangements are developed requiring four operating cycles for the transition from present three-batch loading to an extended burnup four-batch plan for Zion-1. The ARMP code EPRI-NODE-P was used for core modeling. Although this work is preliminary, uranium and economic savings during the transition cycles appear of the order of 6 percent.

Improving the Quality of Online Discussion: The Effects of Strategies Designed Based on Cognitive Load Theory Principles

ERIC Educational Resources Information Center

Darabi, Aubteen; Jin, Li

2013-01-01

This article focuses on heavy cognitive load as the reason for the lack of quality associated with conventional online discussion. Using the principles of cognitive load theory, four online discussion strategies were designed specifically aiming at reducing the discussants' cognitive load and thus enhancing the quality of their online discussion.…

Cycles of Discrimination: Older Women, Cumulative Disadvantages, and Retirement Consequences

ERIC Educational Resources Information Center

Davis, Nanette J.

2005-01-01

This article identifies typical life course situations that women experience, which contribute to a cycle of discrimination or a recurrence of disadvantages simply because of their sex, race, or age. Although men suffer social, health, psychological, and economic disadvantages as they age, this article focuses primarily on women as a more deprived…

Frequency effects on the stability of a journal bearing for periodic loading

NASA Technical Reports Server (NTRS)

Vijayaraghavan, D.; Brewe, D. E.

1992-01-01

The stability of a journal bearing is numerically predicted when an unidirectional periodic external load is applied. The analysis is performed using a cavitation algorithm, which mimics the JFO theory by accounting for the mass balance through the complete bearing. Hence, the history of the film is taken into consideration. The loading pattern is taken to be sinusoidal and the frequency of the load cycle is varied. The results are compared with the predictions using Reynolds boundary conditions for both film rupture and reformation. With such comparisons, the need for accurately predicting the cavitation regions for complex loading patterns is clearly demonstrated. For a particular frequency of loading, the effects of mass, amplitude of load vibration and frequency of journal speed are also investigated.

Maximum von Mises Stress in the Loading Environment of Mass Acceleration Curve

NASA Technical Reports Server (NTRS)

Glaser, Robert J.; Chen, Long Y.

2006-01-01

Method for calculating stress due to acceleration loading: 1) Part has been designed by FEA and hand calculation in one critical loading direction judged by the analyst; 2) Maximum stress can be due to loading in another direction; 3) Analysis procedure to be presented determines: a) The maximum Mises stress at any point; and b) The direction of maximum loading associated with the "stress". Concept of Mass Acceleration Curves (MAC): 1) Developed by JPL to perform preliminary structural sizing (i.e. Mariners, Voyager, Galileo, Pathfinder, MER,...MSL); 2) Acceleration of physical masses are bounded by a curve; 3) G-levels of vibro-acoustic and transient environments; 4) Convergent process before the couple loads cycle; and 5) Semi-empirical method to effectively bound the loads, not a simulation of the actual response.

Constant-torque thermal cycling and two-way shape memory effect in Ni50.3Ti29.7Hf20 torque tubes

NASA Astrophysics Data System (ADS)

Benafan, O.; Gaydosh, D. J.

2018-07-01

Ni-rich Ni50.3Ti29.7Hf20 (at%) high-temperature shape memory alloy tubes were thermomechanically cycled under constant torques. Four loading configurations were examined that consisted of a series of ascending stresses (low-to-high stress from 0 to 500 MPa outer fiber shear stress), a series of descending stresses (high-to-low stress from 500 to 0 MPa), and a series of thermal cycles at a constant stress of 500 MPa, all using an upper cycle temperature (UCT) of 300 °C. The last configuration consisted of another series of ascending stress levels using a lesser UCT of 250 °C. It was found that the descending series trial stabilized the material response in fewer cycles than the other loading paths. Similarly, cycling at a constant stress of 500 MPa for approximately 100 cycles reached near stabilization (<0.05% residual strain accumulation). Transformation shear strains were the highest and most stable when cycled from lower-to-higher stresses (ascending series), reaching 5.78% at 400 MPa. Cycling to lesser UCTs of 250 °C (versus 300 °C) resulted in the highest two-way shape memory effect (TWSME), measuring over 3.25%. This was attributed to the effect of retained martensite and any transformation dislocations that served to stabilize the TWSME at the lower UCT. Results of this study suggest that different training paths might be used, depending on actuator performance requirements, whether the principal need is to maximize transformation strain, maximize the two-way shear strain, or stabilize the response in fewer cycles.

Chopper-controlled discharge life cycling studies on lead-acid batteries

NASA Technical Reports Server (NTRS)

Kraml, J. J.; Ames, E. P.

1982-01-01

State-of-the-art 6 volt lead-acid golf car batteries were tested. A daily charge/discharge cycling to failure points under various chopper controlled pulsed dc and continuous current load conditions was undertaken. The cycle life and failure modes were investigated for depth of discharge, average current chopper frequency, and chopper duty cycle. It is shown that battery life is primarily and inversely related to depth of discharge and discharge current. Failure mode is characterized by a gradual capacity loss with consistent evidence of cell element aging.

The effect of plasma electrolytic oxidation on the mean stress sensitivity of the fatigue life of the 6082 aluminum alloy

NASA Astrophysics Data System (ADS)

Winter, L.; Morgenstern, R.; Hockauf, K.; Lampke, T.

2016-03-01

In this work the mean stress influence on the high cycle fatigue behavior of the plasma electrolytic oxidized (PEO) 6082 aluminum alloy (AlSi1MgMn) is investigated. The present study is focused on the fatigue life time and the susceptibility of fatigue-induced cracking of the oxide coating and their dependence on the applied mean stress. Systematic work is done comparing conditions with and without PEO treatment, which have been tested using three different load ratios. For the uncoated substrate the cycles to failure show a significant dependence on the mean stress, which is typical for aluminum alloys. With increased load ratio and therefore increased mean stress, the fatigue strength decreases. The investigation confirms the well-known effect of PEO treatment on the fatigue life: The fatigue strength is significantly reduced by the PEO process, compared to the uncoated substrate. However, also the mean stress sensitivity of the fatigue performance is reduced. The fatigue limit is not influenced by an increasing mean stress for the PEO treated conditions. This effect is firstly shown in these findings and no explanation for this effect can be found in literature. Supposedly the internal compressive stresses and the micro-cracks in the oxide film have a direct influence on the crack initiation and growth from the oxide film through the interface and in the substrate. Contrary to these findings, the susceptibility of fatigue-induced cracking of the oxide coating is influenced by the load ratio. At tension-tension loading a large number of cracks, which grow partially just in the aluminum substrate, are present. With decreasing load ratio to alternating tension-compression stresses, the crack number and length increases and shattering of the oxide film is more pronounced due to the additional effective compressive part of the load cycle.

Passive Orbital Disconnect Strut (PODS 3) structural test program

NASA Technical Reports Server (NTRS)

Parmley, R. T.

1985-01-01

A passive orbital disconnect strut (PODS-3) was analyzed structurally and thermally. Development tests on a graphite/epoxy orbit tube and S glass epoxy launch tube provided the needed data to finalize the design. A detailed assembly procedure was prepared. One strut was fabricated. Shorting loads in both the axial and lateral direction (vs. load angle and location) were measured. The strut was taken to design limit loads at both ambient and 78 K (cold end only). One million fatigue cycles were performed at predicted STS loads (half in tension, half in compression) with the cold end at 78 K. The fatigue test was repeated at design limit loads. Six struts were then fabricated and tested as a system. Axial loads, side loads, and simulated asymmetric loads due to temperature gradients around the vacuum shell were applied. Shorting loads were measured for all tests.