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Sample records for mode ii fracture

  1. Combined mode I and mode II fracture of monolithic ceramics

    NASA Technical Reports Server (NTRS)

    Tikare, Veena; Choi, Sung R.

    1993-01-01

    The mode I, mode II, and combined mode I-mode II fracture behaviors of a coarse-grained silicon nitride, a fine-grained silicon nitride, and an alumina were investigated. These ceramics were fractured from two types of fracture initiating flaws: small surface flaws and large single edge precracks. The small surface flaws were introduced by Knoop indentation in flexural samples at various angles to the tensile stress direction and fractured in four-point bending. The samples with large precracks were fractured in the asymmetric four-point-bend geometry. The mixed-mode fracture toughness values obtained from the two flaw configurations were in good agreement with each other. All three ceramics displayed very similar mixed-mode fracture behavior, although their microstructures were not similar. Comparison of experimental data to mixed-mode fracture theories revealed that the minimum strain energy density theory best described the mixed-mode fracture behavior of all three ceramics.

  2. Fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, Dileep; Shetty, Dinesh K.

    1989-01-01

    The present investigation of the fracture of alumina and zirconia polycrystalline ceramic specimens of precracked-disk type, in diametral compression, evaluated fracture toughness in pure mode I, combined mode I/mode II, and pure mode II, depending on the alignment of the center crack relative to the loading diameter. The mixed-mode fracture-toughness envelope thus obtained exhibits significant deviation to higher fracture toughness in mode II, relative to the predictions of linear elastic fracture mechanics theory. Crack-surface resistance due to grain-interlocking and abrasion are identified as the primary sources of increased fracture resistance in mode II loading of the polycrystalline ceramics.

  3. Microstructural effects on fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, D.; Shetty, D. K.

    1988-01-01

    Fracture toughness of polycrystalline alumina and ceria partially-stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression. Stress states ranging from pure mode I, combined mode I and mode II, and pure mode II were obtained by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed-mode fracture toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda-lime glass and fracture surface observations showed that crack surface resistance arising from grain interlocking and abrasion was the main source of the increased fracture toughness in mode II loading of the polycrystalline ceramics. The normalized fracture toughness for pure mode II loading, (KII/KIc), increased with increasing grain size for the CeO2-TZP ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.

  4. Microstructural effects on fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, D.; Shetty, D. K.

    1988-01-01

    Fracture toughness of polycrystalline alumina and ceria partially-stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression. Stress states ranging from pure mode I, combined mode I and mode II, and pure mode II were obtained by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed-mode fracture toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda-lime glass and fracture surface observations showed that crack surface resistance arising from grain interlocking and abrasion was the main source of the increased fracture toughness in mode II loading of the polycrystalline ceramics. The normalized fracture toughness for pure mode II loading, (KII/KIc), increased with increasing grain size for the CeO2-TZP ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.

  5. Experimental investigations of the influence of material and thickness on fracture under pure mode II loading

    NASA Astrophysics Data System (ADS)

    Dong, H.

    2010-06-01

    Experimental investigation to the effects of thickness and material on mode II fracture were performed. Tension-shear specimens made of aluminium alloy LC4CS and 7050-T7452 with thicknesses of 2, 4, 8 and 14 mm were used. All crack tip appearances and fracture profiles of the specimens were observed. Mode II fracture toughness were calculated. It is shown that material and thickness play an important role in mode II fracture. The fracture of LC4CS appears shear fracture under all kinds of thicknesses, however the fracture of 7050-T7452 is tensile fracture when thickness is larger or equal to 8mm, and shear initiation along the original crack plane, then turnaround and tensile failure when thickness is smaller than 8mm. Mode II fracture toughness is independent of thickness.

  6. Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

    2003-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2- 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of K(sub I)/K(sub II) were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma-sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  7. Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

    2003-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2- 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of K(sub I)/K(sub II) were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma-sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  8. Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

    2003-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2 - 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of KI/KII were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma- sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  9. Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

    2003-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2 - 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of KI/KII were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma- sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  10. Mode II Interlaminar Fracture Toughness and Fatigue Characterization of a Graphite Epoxy Composite Material

    NASA Technical Reports Server (NTRS)

    O'Brien, T. Kevin; Johnston, William M.; Toland, Gregory J.

    2010-01-01

    Mode II interlaminar fracture toughness and delamination onset and growth characterization data were generated for IM7/8552 graphite epoxy composite materials from two suppliers for use in fracture mechanics analyses. Both the fracture toughness testing and the fatigue testing were conducted using the End-notched Flexure (ENF) test. The ENF test for mode II fracture toughness is currently under review by ASTM as a potential standard test method. This current draft ASTM protocol was used as a guide to conduct the tests on the IM7/8552 material. This report summarizes the test approach, methods, procedures and results of this characterization effort.

  11. Mode II interlaminar fracture toughness of carbon fabric composite laminates with carbon nanotube oriented by magnet

    NASA Astrophysics Data System (ADS)

    Xu, Xinguang; Zhou, Zhenggang

    2017-03-01

    Inspired by the residual iron nanoparticles wrapped in the CNTs tips, we developed a method to induce efficient orientation of multiwalled CNTs bundles by relatively low magnetic fields. Laminates were fabricated to investigate the effect of magnet oriented CNTs on GIIC properties. Microstructure anisotropy of nanotube bundles demonstrated the orientation of CNT bundles by magnet. Furthermore, the application of magnet increased mode II interlaminar fracture toughness by 29% compared to plain laminates.

  12. Ductile fracture in HY100 steel under mixed mode I/mode II loading

    SciTech Connect

    Bhattacharjee, D. . Dept. of Materials Science and Metallurgy); Knott, J.F. . School of Metallurgy and Materials)

    1994-05-01

    A number of criteria have been proposed which predict the direction of cracking under mixed Mode 1/Mode 2 loading. All have been evaluated for brittle materials, in which a crack subjected to tension and shear propagates normal to the maximum tensile stress (i.e. fracture is of the Mode 1 type). In a ductile material, however, a notch subjected to mixed Mode 1/Mode 2 loading may initiate a crack in the direction of maximum shear. This paper shows that the profile of the notch tip changes with increasing mixed mode load in such a way that one side of the tip blunts while the other sharpens. Various specimens, subjected to the same mixed mode ratio, were unloaded from different points on the load-displacement curves to study the change in notch-tip profile. Studies under the Scanning Electron Microscope (SEM) have shown that cracks initiate at the sharpened end, along a microscopic shear band. Using a dislocation pile-up model for decohesion of the carbide-matrix interface, a micromechanical model has been proposed for crack initiation in the shear band. It is shown that a theoretical prediction of the shear strain required for decohesion gives a result that is, of magnitude, similar to that of the shear strain at crack initiation measured in the experiments.

  13. A Mixed-Mode I/II Fracture Criterion and Its Application in Crack Growth Predictions

    NASA Technical Reports Server (NTRS)

    Sutton, Michael A.; Deng, Xiaomin; Ma, Fashang; Newman, James S., Jr.

    1999-01-01

    A crack tip opening displacement (CTOD)-based, mixed mode fracture criterion is developed for predicting the onset and direction of crack growth. The criterion postulates that crack growth occurs in either the Mode I or Mode II direction, depending on whether the maximum in either the opening or the shear component of CTOD, measured at a specified distance behind the crack tip, attains a critical value. For crack growth direction prediction, the proposed CTOD criterion is shown to be equivalent to seven commonly used crack growth criteria under linearly elastic and asymptotic conditions. Under elastic-plastic conditions the CTOD criterion's prediction of the dependence of the crack growth direction on the crack-up mode mixity is in excellent agreement with the Arcan test results. Furthermore, the CTOD criterion correctly predicts the existence of a crack growth transition from mode I to mode II as the mode mixity approaches the mode II loading condition. The proposed CTOD criterion has been implemented in finite element crack growth simulation codes Z1P2DL and FRANC2DL to predict the crack growth paths in (a) a modified Arcan test specimen and fixture made of AL 2024-T34 and (b) a double cantilever beam (DCB) specimen made of AL 7050. A series of crack growth simulations have been carried out for the crack growth tests in the Arcan and DCB specimens and the results further demonstrate the applicability of the mixed mode CTOD fracture criterion crack growth predictions and residual strength analyses for airframe materials.

  14. Mixed-mode I+II fracture characterization of human cortical bone using the Single Leg Bending test.

    PubMed

    Silva, F G A; de Moura, M F S F; Dourado, N; Xavier, J; Pereira, F A M; Morais, J J L; Dias, M I R

    2016-02-01

    Mixed-mode I+II fracture characterization of human cortical bone was analyzed in this work. A miniaturized version of the Single Leg Bending test (SLB) was used owing to its simplicity. A power law criterion was verified to accurately describe the material fracture envelop under mixed-mode I+II loading. The crack tip opening displacements measured by digital image correlation were used in a direct method to determine the cohesive law mimicking fracture behavior of cortical bone. Cohesive zone modeling was used for the sake of validation. Several fracture quantities were compared with the experimental results and the good agreement observed proves the appropriateness of the proposed procedure for fracture characterization of human bone under mixed-mode I+II loading.

  15. Effects of Temperature on Mode II Fracture Toughness of Multidirectional CFRP Laminates

    NASA Astrophysics Data System (ADS)

    Kim, Hyoung Soo; Wang, Wen Xue; Takao, Yoshihiro; Ben, Goichi

    End notched flexure (ENF) tests were performed to investigate the effects of temperature and fiber orientation on Mode II interlaminar fracture behavior, GIIC (GII at the crack initiation), of carbon fiber-reinforced epoxy composites, T800H/#3631. The values of GIIC for three kinds of laminates, [012//012], [22.5/-22.5/08/-22.5/22.5//-22.5/22.5/08/22.5/-22.5] and [45/-45/08/-45/45//-45/45/08/45/-45], with a pre-cracked interface, that is // in each laminate, were obtained at three temperatures, i.e. -100°C, 25°C and 150°C. It is shown that GIIC is obviously affected by the temperature and fiber orientation. The scanning electron microscope (SEM) observation was also carried out to investigate the fracture surface. SEM analysis suggested that the decreased Mode II interlaminar fracture toughness for all kinds of specimens at high temperature could be attributed to temperature-induced matrix property change or fiber-matrix interfacial weakening.

  16. A Mixed-Mode (I-II) Fracture Criterion for AS4/8552 Carbon/Epoxy Composite Laminate

    NASA Astrophysics Data System (ADS)

    Karnati, Sidharth Reddy

    A majority of aerospace structures are subjected to bending and stretching loads that introduce peel and shear stresses between the plies of a composite laminate. These two stress components cause a combination of mode I and II fracture modes in the matrix layer of the composite laminate. The most common failure mode in laminated composites is delamination that affects the structural integrity of composite structures. Damage tolerant designs of structures require two types of materials data: mixed-mode (I-II) delamination fracture toughness that predicts failure and delamination growth rate that predicts the life of the structural component. This research focuses determining mixed-mode (I-II) fracture toughness under a combination of mode I and mode II stress states and then a fracture criterion for AS4/8552 composite laminate, which is widely used in general aviation. The AS4/8552 prepreg was supplied by Hexcel Corporation and autoclave fabricated into a 20-ply unidirectional laminate with an artificial delamination by a Fluorinated Ethylene Propylene (FEP) film at the mid-plane. Standard split beam specimens were prepared and tested in double cantilever beam (DCB) and end notched flexure modes to determine mode I (GIC) and II (GIIC) fracture toughnesses, respectively. The DCB specimens were also tested in a modified mixed-mode bending apparatus at GIIm /GT ratios of 0.18, 0.37, 0.57 and 0.78, where GT is total and GIIm is the mode II component of energy release rates. The measured fracture toughness, GC, was found to follow the locus a power law equation. The equation was validated for the present and literature experimental data.

  17. Electron radiation effects on Mode II interlaminar fracture toughness of GFRP and CFRP composites

    SciTech Connect

    Takeda, N.; Tohdoh, M.; Takahashi, K.

    1989-01-01

    The degradation properties of epoxy-based fiber-reinforced-plastics (FRP) composites irradiated by high-energy electrons were studied using the Mode II interlaminar fracture toughness G/sub IIc/, measured by end-notched flexure tests. The radiation-induced degradation mechanisms were investigated through G/sub IIc/ and the scanning electron micrographs of fracture surfaces. For GFRP, the significant decrease in G/sub IIc/ was found. Debonding of glass fibers and epoxy matrix (or degradation of silane coupling agents) plays an important role in degradation in addition to resin degradation. Thus, the improvement of the radiation resistance of fiber-resin interfaces as well as matrix itself is of supreme importance in order to increase the radiation resistance of GFRP. For CFRP, on the other hand, no degradation in fiber-resin interfaces was found and the slight decrease in G/sub IIc/ seems to be due to the resin degradation. 18 references, 6 figures.

  18. Mode I, Mode II, and Mixed-Mode Fracture of Plasma-sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

    2003-01-01

    The mixed-mode fracture behavior of plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings was determined in air at 25 and 1316 C in asymmetric four-point flexure with single edge v-notched beam (SEVNB) test specimens. The mode I fracture toughness was found to be K(sub Ic) = 1.15 plus or minus 0.07 and 0.98 plus or minus 0.13 MPa the square root of m, respectively, at 25 and 1316 C. The respective mode II fracture toughness values were K(sub IIc) = 0.73 plus or minus 0.10 and 0.65 plus or minus 0.04 MPa the square root of m. Hence, there was an insignificant difference in either K(sub Ic or K(sub IIc) between 25 and 1316 C for the coating material, whereas there was a noticeable distinction between K(sub Ic) and K(sub IIc), resulting in K(sub IIc) per K(sub Ic) = 0.65 at both temperatures. The empirical mixed-mode fracture criterion best described the coatings' mixed-mode fracture behavior among the four mixed-mode fracture theories considered. The angle of crack propagation was in reasonable agreement with the minimum strain energy density criterion. The effect of the directionality of the coating material in on K(sub Ic) was observed to be insignificant, while its sintering effect at 1316 C on K(sub Ic) was significant.

  19. In-plane response and mode II fracture response of Z-pin woven laminates

    NASA Astrophysics Data System (ADS)

    Huang, Hseng-Ji

    Textile composites are proven to be an attractive choice over traditional pre-preg based composites because of reduced manufacturing costs and improved transverse mechanical properties. However, similar to traditional pre-preg composites, 2D laminates consisting of multiple layers of laminae still suffer from delamination under impact or transverse loads. Z-pin (carbon fiber of small diameter inserted in the thickness direction-z) composites are a means to provide higher through-thethickness stiffness and strength that 2D woven composites lack. In this thesis, The influences of Z-pin density and Z-pin diameter on the response of Z-pin under in-plane loads (compression) and transverse loads (mode II fracture) are examined. Both experiments and numerical simulations were performed to address the problems. Compression tests were conducted first and failure mechanism in each loading scenario was identified, through optical and mechanical measurements, during and after the tests. This was followed by the development of different numerical models of varying degree of sophistication, which include in-plane 2D models, (used to study fiber distortion and damage due to Z-pin insertion), multi-layer 2D models, (used to provide an inexpensive multi-layer model to study the effect of phase difference due to stacking consolidation), and multi-layer-multi-cell models (used to provide a full 3D multi-layer and multi-representative unit cell description). The second part of this thesis investigates the mode II fracture response under static and dynamic loading. Discrete Cohesive Zone Model (DCZM) was adopted to obtain the fracture toughness in conjunction with experimental data. In dynamic test, a crack advance gage (CAG) was designed to capture the exact time when the crack begins to propagate. By use of these CAGs, the corresponding crack propagation speed between different CAGs can be computed accordingly. These observations are supplemented through high speed optical images

  20. Fracture characterization of human cortical bone under mode II loading using the end-notched flexure test.

    PubMed

    Silva, F G A; de Moura, M F S F; Dourado, N; Xavier, J; Pereira, F A M; Morais, J J L; Dias, M I R; Lourenço, P J; Judas, F M

    2016-10-25

    Fracture characterization of human cortical bone under mode II loading was analyzed using a miniaturized version of the end-notched flexure test. A data reduction scheme based on crack equivalent concept was employed to overcome uncertainties on crack length monitoring during the test. The crack tip shear displacement was experimentally measured using digital image correlation technique to determine the cohesive law that mimics bone fracture behavior under mode II loading. The developed procedure was validated by finite element analysis using cohesive zone modeling considering a trapezoidal with bilinear softening relationship. Experimental load-displacement curves, resistance curves and crack tip shear displacement versus applied displacement were used to validate the numerical procedure. The excellent agreement observed between the numerical and experimental results reveals the appropriateness of the proposed test and procedure to characterize human cortical bone fracture under mode II loading. The proposed methodology can be viewed as a novel valuable tool to be used in parametric and methodical clinical studies regarding features (e.g., age, diseases, drugs) influencing bone shear fracture under mode II loading.

  1. Experiments on fracture toughness of thick-wall cylinder for modes I, II, III

    SciTech Connect

    Saegusa, T.; Urabe, N.; Ito, C.; Shirai, K.; Kosaki, A.

    1999-07-01

    There have been few data on fracture toughness for Mode 2 and 3 as compared with those for Mode 1. Experimental data on fracture toughness of plates made of ductile cast iron (ASTM A874-89) and forged steel (ASME SA350 LF5 C1.1) were obtained at a temperature range from 77K to 293K for Mode 1, 2 and 3. The results showed: J{sub IC} < J{sub IIC} < J{sub IIIC}, and K{sub IC} < K{sub IIC} K{sub IIIC}. Integrity of a thick-wall cylinder with artificial flaw was demonstrated against brittle fracture at 233K for Mode 1, 2 and 3, which is one of the design requirements of containers shipping radioactive materials.

  2. A revisit to high-rate mode-II fracture characterization of composites with Kolsky bar techniques.

    SciTech Connect

    Lu, Wei-Yang; Song, Bo; Jin, Huiqing

    2010-03-01

    Nowadays composite materials have been extensively utilized in many military and industrial applications. For example, the newest Boeing 787 uses 50% composite (mostly carbon fiber reinforced plastic) in production. However, the weak delamination strength of fiber reinforced composites, when subjected to external impact such as ballistic impact, has been always potential serious threats to the safety of passengers. Dynamic fracture toughness is a critical indicator of the performance from delamination in such impact events. Quasi-static experimental techniques for fracture toughness have been well developed. For example, end notched flexure (ENF) technique, which is illustrated in Fig. 1, has become a typical method to determined mode-II fracture toughness for composites under quasi-static loading conditions. However, dynamic fracture characterization of composites has been challenging. This has resulted in conflictive and confusing conclusions in regard to strain rate effects on fracture toughness of composites.

  3. Fracture Behavior Investigation of a Typical Sandstone Under Mixed-Mode I/II Loading Using the Notched Deep Beam Bending Method

    NASA Astrophysics Data System (ADS)

    Luo, Y.; Ren, L.; Xie, L. Z.; Ai, T.; He, B.

    2017-08-01

    The brittle fracture behavior of rocks under mixed-mode loading is important in rock engineering. First, a new configuration called the notched deep beam (NDB) specimen was introduced for the fracture testing of rock materials under mixed-mode I/II loading, and a series of finite element analyses were performed to calibrate the dimensionless fracture parameters (i.e., Y I, Y II and T^{*}). The results showed that an NDB specimen subjected to three-point bending is able to generate pure mode I loading, pure mode II loading, and any mixed-mode loading in between. Then, several NDB specimens made of sandstone were used to investigate the brittle fracture behavior of rock under mixed-mode I/II loading. The fracture surfaces were theoretically described using a statistical method, and the results indicated that all the fracture surfaces generated under different mixed-mode loading were statistically identical; to some extent, these results experimentally showed that only tensile fracture occurs under mixed-mode I/II loading. The obtained fracture strengths were then analyzed using several brittle fracture criteria. The empirical criterion, maximum energy release rate criterion, generalized maximum tangential stress (GMTS) criterion, and improved R-criterion accurately predicted the fracture strength envelope of the sandstone. Finally, based on the concepts of point stress and mean stress, the micro-crack zones (MCZs) under different mixed-mode loading were theoretically estimated based on the MTS and GMTS criteria. The critical radius of MCZ in the crack propagation direction was not a constant for all mixed-mode loading conditions regardless of whether the T-stress was considered. This result suggests that the size of the core region used to predict the crack initiation direction and fracture strength based on the GMTS criterion should be chosen more carefully.

  4. Mixed-mode fracture of ceramics

    SciTech Connect

    Petrovic, J.J.

    1985-01-01

    The mixed-mode fracture behavior of ceramic materials is of importance for monolithic ceramics in order to predict the onset of fracture under generalized loading conditions and for ceramic composites to describe crack deflection toughening mechanisms. Experimental data on surface flaw mixed-mode fracture in various ceramics indicate that the flaw-plane normal stress at fracture decreases with increasing in-flaw-plane shear stress, although present data exhibit a fairly wide range in details of this sigma - tau relationship. Fracture from large cracks suggests that Mode II has a greater effect on Mode I fracture than Mode III. A comparison of surface flaw and large crack mixed-mode I-II fracture responses indicated that surface flaw behavior is influenced by shear resistance effects.

  5. An analytical and experimental stress analysis of a practical mode II fracture-test specimen

    NASA Technical Reports Server (NTRS)

    Chisholm, D. B.; Jones, D. L.

    1975-01-01

    A boundary collocation method has been employed to determine the Mode II stress intensity factors for a pair of through-the-thickness edge cracks in a finite isotropic plate. An elastostatic analysis has been carried out in terms of the complete Williams stress function employing both even and odd components. The results of the numerical analysis were verified by a two-step procedure whereby the symmetric and antisymmetric portions of the solution were independently compared with existing solutions. The complete solution was verified by comparison with a photoelastic analysis. A compact shear specimen (CSS) of Hysol epoxy resin was loaded in a photoelastic experiment designed to study the isochromatic fringe patterns resulting from the Mode II crack tip stress distribution. The experiment verified that a pure Mode II stress distribution existed in the neighborhood of the crack tips and confirmed the accuracy of the boundary collocation solution for the Mode II stress intensity factors.

  6. An analytical and experimental stress analysis of a practical mode II fracture-test specimen

    NASA Technical Reports Server (NTRS)

    Chisholm, D. B.; Jones, D. L.

    1975-01-01

    A boundary collocation method has been employed to determine the Mode II stress intensity factors for a pair of through-the-thickness edge cracks in a finite isotropic plate. An elastostatic analysis has been carried out in terms of the complete Williams stress function employing both even and odd components. The results of the numerical analysis were verified by a two-step procedure whereby the symmetric and antisymmetric portions of the solution were independently compared with existing solutions. The complete solution was verified by comparison with a photoelastic analysis. A compact shear specimen (CSS) of Hysol epoxy resin was loaded in a photoelastic experiment designed to study the isochromatic fringe patterns resulting from the Mode II crack tip stress distribution. The experiment verified that a pure Mode II stress distribution existed in the neighborhood of the crack tips and confirmed the accuracy of the boundary collocation solution for the Mode II stress intensity factors.

  7. Fracture of a low-carbon steel under mode I, mode II, and mixed-mode loading conditions

    NASA Astrophysics Data System (ADS)

    Soldatenkov, A. P.; Botvina, L. R.; Tyutin, M. R.; Levin, V. P.; Zharkova, N. A.

    2013-10-01

    The effect of the shear component of static loading on the evolution of the plastic deformation zones and the mechanical and acoustic properties (acoustic emission parameters, ultrasonic wave velocity and attenuation coefficient) of a low-carbon grade 20 steel is studied. It is found that an increase in the shear loading component leads to a change in the shape of a plastic deformation zone, the appearance of an additional system of microcracks, an increase in the total fracture energy, a decrease in the slopes of the cumulative distributions of the acoustic signal amplitude and the microcrack length, and a significant increase in the ultrasound attenuation coefficient.

  8. Criterion for mixed mode fracture in composite bonded joints

    NASA Technical Reports Server (NTRS)

    Mall, S.; Kochhar, N. K.

    1986-01-01

    A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite-epoxy composite adherends bonded with a toughened epoxy adhesive. The mode I, mode II and mixed mode I-II fracture energies of the tested adhesives were found to be equal to each other. The criterion for mixed mode fracture in composite bonded joints was found.

  9. Interlaminar fracture reinforcement under mode-II loading: Post-cure through-thickness reinforcement of graphite epoxy, unidirectional laminates

    NASA Astrophysics Data System (ADS)

    Jacobson, Joel B.

    A novel through-thickness reinforcement method proposed by S. Kravchenko et al., has been static tested under mode II loading using end notched flexure (ENF), unidirectional laminate specimens to determine the impact on the apparent critical fracture toughness (GIIc) for the material tested. Both experimental and numerical methods have been employed in an attempt to characterize and model these effects. Testing and analysis were conducted on two different specimen thickness, 2.34 mm and 3.54 mm nominally. ASTM D7905/7905M -- 14 was followed during the experimental portion of the thick specimens. Multiple reinforcing configurations using the proposed technique were experimentally tested including single, double, and quadruple rows of orthogonal, pultruded carbon/epoxy pins located within the crack and ahead of the crack (pristine material) to determine the effect on the apparent critical fracture toughness for each configuration. Both pre-cracked and no pre-cracked specimens were evaluated. The results of this study indicate that specimens pinned in the crack experienced the highest supportable reaction force such that the crack was completely arrested and most of the specimens failed in flexure. Pre-cracked specimens that were pinned in the body exhibited stable crack growth as well as a shadowing phenomenon. Both pins and the crack surface topography due to this phenomenon are attributed to the increased apparent fracture toughness for these specimens. Similar outcomes were observed through numerical simulations for the models simulated in this study.

  10. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves.

    PubMed

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-06-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m(-2) VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%-73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates.

  11. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves

    PubMed Central

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-01-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m−2 VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%–73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates. PMID:27877680

  12. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves

    NASA Astrophysics Data System (ADS)

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-06-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m-2 VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%-73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates.

  13. On the localization of fracture in highly constrained polymeric layer subjected to mode II loading

    SciTech Connect

    Chiang, M.Y.M.; Chai, H.

    1996-12-31

    The tight spatial constraints imposed on the interlayer by the relatively rigid substrates in adhesive bonding may impede the natural development and growth of damage sources such as voids, kinks and microcracks. This may lead to extensive nonlinear deformations and intense strain localization prior to fracture in ductile or brittle adhesive systems. Moreover, the localized deformation in the bond may be highly triaxial regardless of the nature of the far-field loading. Fracture criteria based on conventional linear elastic fracture mechanics and small-scale yielding condition may not be applicable on large strain. Therefore, the purpose of the authors work is to focus on the local deformation at the crack tip in an effort to demonstrate a fracture criterion, which is independent of the specimen geometry, for the situation in large (or small) plastic deformation.

  14. Non-Linear Analysis of Mode II Fracture in the end Notched Flexure Beam

    NASA Astrophysics Data System (ADS)

    Rizov, V.

    2016-03-01

    Analysis is carried-out of fracture in the End Notched Flex- ure (ENF) beam configuration, taking into account the material nonlin- earity. For this purpose, the J-integral approach is applied. A non-linear model, based on the Classical beam theory is used. The mechanical be- haviour of the ENF configuration is described by the Ramberg-Osgood stress-strain curve. It is assumed that the material possesses the same properties in tension and compression. The influence is evaluated of the material constants in the Ramberg-Osgood stress-strain equation on the fracture behaviour. The effect of the crack length on the J-integral value is investigated, too. The analytical approach, developed in the present paper, is very useful for parametric analyses, since the simple formulae obtained capture the essentials of the non-linear fracture in the ENF con- figuration.

  15. Tests and Interpretation of Mixed Mode I and II Fully Plastic Fracture from Simulated Weld Defects.

    DTIC Science & Technology

    1986-07-31

    0.1). Tis means that with loi %-hardcning (t\\-nicallv highi strength) alloys, the surroiziding structure must be 3 tines stiffe’r :or fracture-stable...9 tauc / a dFxPfax.,)min t ’o a )/i) min (Eq. 7) Svm O.20050. 166 0.258 0.192 Asvm 0.072 .0 v. I 𔃿 0.18 0.215 0.181 Modified Tearing Modulus. T R E

  16. Criterion for mixed mode fracture in composite bonded joints

    NASA Technical Reports Server (NTRS)

    Mall, S.; Kochhar, N. K.

    1986-01-01

    A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite/epoxy (T300/5208) composite adherends bonded with a toughened epoxy (EC 3445) adhesive. The mode I, mode II and mixed-mode I-II fracture energies of the tested adhesive were found to be equal to each other. Furthermore, the criterion for mixed mode fracture in composite bonded joints was determined.

  17. Role of large-scale slip in mode II fracture of bimaterial interface produced by diffusion bonding

    NASA Astrophysics Data System (ADS)

    Fox, M. R.; Ghosh, A. K.

    2001-08-01

    Bimaterial interfaces present in diffusion-bonded (and in-situ) composites are often not flat interfaces. The unevenness of the interface can result not only from interface reaction products but also from long-range waviness associated with the surfaces of the component phases bonded together. Experimental studies aimed at determining interface mechanical properties generally ignore the departure in the local stress due to waviness and assume a theoretically flat interface. Furthermore, the commonly used testing methods involving superimposed tension often renders the interface so extremely brittle that if microplastic effects were present it becomes impossible to perceive them. This article examines the role of waviness of the interface and microplastic effects on crack initiation. To do this, a test was selected that provides significant stability against crack growth by superimposing compressive stresses. Mode II interface fracture was studied for NiAl/Mo model laminates using a recently developed asymmetrically loaded shear (ALS) interface shear test. The ALS test may be viewed as opposite of the laminate bend test. In the bend test, shear at the interface is created via tension on one surface of the bend, while in the ALS test, shear is created by compression on one side of the interface relative to the other. Normal to the interface, near the crack tip, an initially compressive state is replaced by slight tension due to Poisson’s expansion of the unbonded part of the compressed beam.

  18. 3-D Mixed Mode Delamination Fracture Criteria - An Experimentalist's Perspective

    NASA Technical Reports Server (NTRS)

    Reeder, James R.

    2006-01-01

    Many delamination failure criteria based on fracture toughness have been suggested over the past few decades, but most only covered the region containing mode I and mode II components of loading because that is where toughness data existed. With new analysis tools, more 3D analyses are being conducted that capture a mode III component of loading. This has increased the need for a fracture criterion that incorporates mode III loading. The introduction of a pure mode III fracture toughness test has also produced data on which to base a full 3D fracture criterion. In this paper, a new framework for visualizing 3D fracture criteria is introduced. The common 2D power law fracture criterion was evaluated to produce unexpected predictions with the introduction of mode III and did not perform well in the critical high mode I region. Another 2D criterion that has been shown to model a wide range of materials well was used as the basis for a new 3D criterion. The new criterion is based on assumptions that the relationship between mode I and mode III toughness is similar to the relation between mode I and mode II and that a linear interpolation can be used between mode II and mode III. Until mixed-mode data exists with a mode III component of loading, 3D fracture criteria cannot be properly evaluated, but these assumptions seem reasonable.

  19. A la Mode II.

    ERIC Educational Resources Information Center

    Stowe, Richard A.

    This paper describes two modes of educational decision-making: Mode I, in which the instructor makes such decisions as what to teach, to whom, when, in what order, at what pace, and at what complexity level; and Mode II, in which the learner makes the decisions. While Mode I comprises most of what is regarded as formal education, the learner in…

  20. Fracture - An Unforgiving Failure Mode

    NASA Technical Reports Server (NTRS)

    Goodin, James Ronald

    2006-01-01

    During the 2005 Conference for the Advancement for Space Safety, after a typical presentation of safety tools, a Russian in the audience simply asked, "How does that affect the hardware?" Having participated in several International System Safety Conferences, I recalled that most attention is dedicated to safety tools and little, if any, to hardware. The intent of this paper on the hazard of fracture and failure modes associated with fracture is my attempt to draw attention to the grass roots of system safety - improving hardware robustness and resilience.

  1. Fracture modes in notched angleplied composite laminates

    NASA Technical Reports Server (NTRS)

    Irvine, T. B.; Ginty, C. A.

    1984-01-01

    The Composite Durability Structural Analysis (CODSTRAN) computer code is used to determine composite fracture. Fracture modes in solid and notched, unidirectional and angleplied graphite/epoxy composites were determined by using CODSTRAN. Experimental verification included both nondestructive (ultrasonic C-Scanning) and destructive (scanning electron microscopy) techniques. The fracture modes were found to be a function of ply orientations and whether the composite is notched or unnotched. Delaminations caused by stress concentrations around notch tips were also determined. Results indicate that the composite mechanics, structural analysis, laminate analysis, and fracture criteria modules embedded in CODSTRAN are valid for determining composite fracture modes.

  2. Mode II fatigue crack propagation.

    NASA Technical Reports Server (NTRS)

    Roberts, R.; Kibler, J. J.

    1971-01-01

    Fatigue crack propagation rates were obtained for 2024-T3 bare aluminum plates subjected to in-plane, mode I, extensional loads and transverse, mode II, bending loads. These results were compared to the results of Iida and Kobayashi for in-plane mode I-mode II extensional loads. The engineering significance of mode I-mode II fatigue crack growth is considered in view of the present results. A fatigue crack growth equation for handling mode I-mode II fatigue crack growth rates from existing mode I data is also discussed.

  3. Growth Kinematics of Opening-Mode Fractures

    NASA Astrophysics Data System (ADS)

    Eichhubl, P.; Alzayer, Y.; Laubach, S.; Fall, A.

    2014-12-01

    Fracture aperture is a primary control on flow in fractured reservoirs of low matrix permeability including unconventional oil and gas reservoirs and most geothermal systems. Guided by principles of linear elastic fracture mechanics, fracture aperture is generally assumed to be a linear function of fracture length and elastic material properties. Natural opening-mode fractures with significant preserved aperture are observed in core and outcrop indicative of fracture opening strain accommodated by permanent solution-precipitation creep. Fracture opening may thus be decoupled from length growth if the material effectively weakens after initial elastic fracture growth by either non-elastic deformation processes or changes in elastic properties. To investigate the kinematics of fracture length and aperture growth, we reconstructed the opening history of three opening-mode fractures that are bridged by crack-seal quartz cement in Travis Peak Sandstone of the SFOT-1 well, East Texas. Similar crack-seal cement bridges had been interpreted to form by repeated incremental fracture opening and subsequent precipitation of quartz cement. We imaged crack-seal cement textures for bridges sampled at varying distance from the tips using scanning electron microscope cathodoluminescence, and determined the number and thickness of crack-seal cement increments as a function of position along the fracture length and height. Observed trends in increment number and thickness are consistent with an initial stage of fast fracture propagation relative to aperture growth, followed by a stage of slow propagation and pronounced aperture growth. Consistent with fluid inclusion observations indicative of fracture opening and propagation occurring over 30-40 m.y., we interpret the second phase of pronounced aperture growth to result from fracture opening strain accommodated by solution-precipitation creep and concurrent slow, possibly subcritical, fracture propagation. Similar deformation

  4. Mixed Mode Fracture of Plasma Sprayed Thermal Barrier Coatings: Effects of Anisotropy and Heterogeneity

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Choi, Sung R.; Ghosn, Louis L.

    2008-01-01

    The combined mode I-mode II fracture behavior of anisotropic ZrO2-8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of KI/KII were also determined. The mixed-mode fracture behavior of the microsplat coating material was modeled using Finite Element approach to account for anisotropy and micro cracked structures, and predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  5. The impact of hygrothermal preconditioning on mode II interlaminar fracture toughness in unidirectional carbon fiber reinforced epoxy composites: An experimental investigation

    NASA Astrophysics Data System (ADS)

    Hempowicz, Michael L.

    The correlation between the interlaminar Mode II fracture toughness (GIIC) of a carbon fiber reinforced epoxy and other material properties across different conditioning regimes was investigated. Specimens were preconditioned using select hygrothermal criteria to evaluate how changes in the material and mechanical properties in a carbon fiber/epoxy composite correlations with changes in GIIC for each regime. An increase in GIIC from baseline values was demonstrated across all conditions from end-notched flexure (ENF) testing. Dynamic mechanical analysis (DMA) and tensile tests had varying responses based on preconditioning environment. Since tensile and some DMA properties rely on fiber strength and show property loss with increased plasticization, fiber strength may not have a large impact on GIIC properties. Test data also implied that the GIIC increased when consolidation of the polymer chains occurred in the arid condition as well as when crosslink density increased in the moisture exposed conditions. From these results it is believed that the chemical and physical changes in matrix cohesion are more important to GIIC behavior prediction than fiber behavior.

  6. Mixed-Mode Fracture Behavior and Related Surface Topography Feature of a Typical Sandstone

    NASA Astrophysics Data System (ADS)

    Ren, L.; Xie, L. Z.; Xie, H. P.; Ai, T.; He, B.

    2016-08-01

    The geo-mechanical properties of reservoirs, especially the morphology of the rock surface and the fracture properties of rocks, are of great importance in the modeling and simulation of hydraulic processes. To better understand these fundamental issues, five groups of mixed-mode fracture tests were conducted on sandstone using edge-cracked semi-circular bend specimens. Accordingly, the fracture loads, growth paths and fracture surfaces for different initial mixities of the mixed-mode loadings from pure mode I to pure mode II were then determined. A surface topography measurement for each rough fracture surface was conducted using a laser profilometer, and the fractal properties of these surfaces were then investigated. The fracture path evolution mechanism was also investigated via optical microscopy. Moreover, the mixed-mode fracture strength envelope and the crack propagation trajectories of sandstone were theoretically modeled using three widely accepted fracture criteria (i.e., the MTS, MSED and MERR criterions). The published test results in Hasanpour and Choupani (World Acad Sci Eng Tech 41:764-769, 2008) for limestone were also theoretically investigated to further examine the effectiveness of the above fracture criteria. However, none of these criteria could accurately predict the fracture envelopes of both sandstone and limestone. To better estimate the fracture strength of mixed-mode fractures, an empirical maximum tensile stress (EMTS) criterion was proposed and found to achieve good agreement with the test results. Finally, a uniformly pressurized fracture model was simulated for low pressurization rates using this criterion.

  7. Mixed mode fracture of an HSLA-100 steel

    SciTech Connect

    Densley, J.M.; Hirth, J.P.

    1998-09-04

    Traditionally, mode I instability criteria have marked the conservative fracture toughness limit. However, some high-toughness, particle strengthened materials have been shown to have a lower resistance to the onset of stable crack growth under mixed-mode loading. By testing both standard compact tension specimens and modified mixed-mode compact tension specimens, the authors have determined the pure mode I plain strain fracture toughness and mixed-mode I/III fracture toughness for an HSLA 100 steel. Limited mixed-mode I/II tests of the type described by Kamat were also performed. The steel was provided by E. Czyryca of the Naval Research Laboratory and tested in the as received condition. Czyryca found {sigma}{sub ys} = 780 MPa, {sigma}{sub uts} = 800 MPa, and a two specimen average J{sub Ic} = 490 kJ/m{sup 2} for specimens tested in the T-L orientation. The steel was austenitized at 900 C for 40 minutes, water quenched then aged at 665 C for one hour than air cooled. The hardenability provided by manganese, molybdenum and nickel resulted in a mixed ferrite-bainite microstructure with fine carbonitride and copper precipitates. Such a microstructure gives high strength and toughness, improved weldability, lower DBTT as well as lower cost.

  8. Fracture of Sn-Ag-Cu Solder Joints on Cu Substrates. II: Fracture Mechanism Map

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Huang, Z.; Dutta, I.; Sidhu, R.; Renavikar, M.; Mahajan, R.

    2012-02-01

    A methodology to construct fracture mechanism maps for Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates has been developed. The map, which delineates the operative mechanisms of fracture along with corresponding joint fracture toughness values, is plotted in a space described by two microstructure-dependent parameters, with the abscissa describing the interfacial intermetallic compound (IMC) and the ordinate representing the strain-rate-dependent solder yield strength. The plot space encompasses the three major mechanisms by which joints fail, namely (i) cohesive fracture of solder, (ii) cleavage fracture of interfacial intermetallic compounds (IMC), and (iii) fracture of the solder-IMC interface. Line contours of constant fracture toughness values, as well as constant fraction of each of the above mechanisms, are indicated on the plots. The plots are generated by experimentally quantifying the dependence of the operative fracture mechanism(s) on the two microstructure-dependent parameters (IMC geometry and solder yield strength) as functions of strain rate, reflow parameters, and post-reflow aging. Separate maps are presented for nominally mode I and equi-mixed mode loading conditions (loading angle ϕ = 0° and 45°, respectively). The maps allow rapid assessment of the operative fracture mechanism(s) along with estimation of the expected joint fracture toughness value for a given loading condition (strain rate and loading angle) and joint microstructure without conducting actual tests, and may serve as a tool for both prediction and microstructure design.

  9. Subcritical crack growth in soda-lime glass in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, Dileep; Shetty, Dinesh K.

    1990-01-01

    Subcritical crack growth under mixed-mode loading was studied in soda-lime glass. Pure mode I, combined mode I and mode II, and pure mode II loadings were achieved in precracked disk specimens by loading in diametral compression at selected angles with respect to the symmetric radial crack. Crack growth was monitored by measuring the resistance changes in a microcircuit grid consisting of parallel, electrically conducting grid lines deposited on the surface of the disk specimens by photolithography. Subcritical crack growth rates in pure mode I, pure mode II, and combined mode I and mode II loading could be described by an exponential relationship between crack growth rate and an effective crack driving force derived from a mode I-mode II fracture toughness envelope. The effective crack driving force was based on an empirical representation of the noncoplanar strain energy release rate. Stress intensities for kinked cracks were assessed using the method of caustics and an initial decrease and a subsequent increase in the subcritical crack growth rates of kinked cracks were shown to correlate with the variations of the mode I and the mode II stress intensities.

  10. Subcritical crack growth in soda-lime glass in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, Dileep; Shetty, Dinesh K.

    1990-01-01

    Subcritical crack growth under mixed-mode loading was studied in soda-lime glass. Pure mode I, combined mode I and mode II, and pure mode II loadings were achieved in precracked disk specimens by loading in diametral compression at selected angles with respect to the symmetric radial crack. Crack growth was monitored by measuring the resistance changes in a microcircuit grid consisting of parallel, electrically conducting grid lines deposited on the surface of the disk specimens by photolithography. Subcritical crack growth rates in pure mode I, pure mode II, and combined mode I and mode II loading could be described by an exponential relationship between crack growth rate and an effective crack driving force derived from a mode I-mode II fracture toughness envelope. The effective crack driving force was based on an empirical representation of the noncoplanar strain energy release rate. Stress intensities for kinked cracks were assessed using the method of caustics and an initial decrease and a subsequent increase in the subcritical crack growth rates of kinked cracks were shown to correlate with the variations of the mode I and the mode II stress intensities.

  11. Experimental investigation of mode I fracture for brittle tube-shaped particles

    NASA Astrophysics Data System (ADS)

    Stasiak, Marta; Combe, Gaël; Desrues, Jacques; Richefeu, Vincent; Villard, Pascal; Armand, Gilles; Zghondi, Jad

    2017-06-01

    We focus herein on the mechanical behavior of highly crushable grains. The object of our interest, named shell, is a hollow cylinder grain with ring cross-section, made of baked clay. The objective is to model the fragmentation of such shells, by means of discrete element (DE) approach. To this end, fracture modes I (opening fracture) and II (in-plane shear fracture) have to be investigated experimentally. This paper is essentially dedicated to mode I fracture. Therefore, a campaign of Brazilian-like compression tests, that result in crack opening, has been performed. The distribution of the occurrence of tensile strength is shown to obey a Weibull distribution for the studied shells, and Weibull's modulus was quantified. Finally, an estimate of the numerical/physical parameters required in a DE model (local strength), is proposed on the basis of the energy required to fracture through a given surface in mode I or II.

  12. Comparison of Mode II and III Monotonic and Fatigue Delamination Onset Behavior for Carbon/Toughened Epoxy Composites

    NASA Technical Reports Server (NTRS)

    Li, Jian; OBrien, T. Kevin; Lee, Shaw Ming

    1997-01-01

    Monotonic and fatigue tests were performed to compare the Mode II and III interlaminar fracture toughness and fatigue delamination onset for Tenax-HTA/R6376 carbon/toughened epoxy composites. The Mode II interlaminar fracture toughness and fatigue delamination onset were characterized using the end-notched flexure (ENF) test while the Mode III interlaminar fracture toughness and fatigue delamination onset were characterized by using the edge crack torsion (ECT) test. Monotonic tests show that the Mode III fracture toughness is higher than the Mode II fracture toughness. Both Mode II and III cyclic loading greatly increases the tendency for a delamination to grow relative to a single monotonically increasing load. Under fatigue loading, the Mode III specimen also has a longer life than the Mode II specimen.

  13. Combined mode I-mode III fracture toughness of a particulate reinforced metal-matrix composite

    NASA Technical Reports Server (NTRS)

    Manoharan, M.; Lewandowski, J. J.

    1991-01-01

    The aim of this investigation was to determine the fracture behavior of a particulate reinfored aluminum alloy composite under combined mode I-mode III loading conditions. A modified three-point bend specimen was used to carry out these tests. It was found that the mode I loading condition was energetically most favorable. Addition of mode III components to the system seems to increase the amount of redundant work during fracture without affecting the critical fracture criterion.

  14. Combined mode I-mode III fracture toughness of a particulate reinforced metal-matrix composite

    NASA Technical Reports Server (NTRS)

    Manoharan, M.; Lewandowski, J. J.

    1991-01-01

    The aim of this investigation was to determine the fracture behavior of a particulate reinfored aluminum alloy composite under combined mode I-mode III loading conditions. A modified three-point bend specimen was used to carry out these tests. It was found that the mode I loading condition was energetically most favorable. Addition of mode III components to the system seems to increase the amount of redundant work during fracture without affecting the critical fracture criterion.

  15. Mixed-mode Mechanism of Hydraulic Fracture Segmentation

    NASA Astrophysics Data System (ADS)

    Hurt, R. S.; Germanovich, L.; Wu, R.

    2006-12-01

    Mixed-mode I+III loading is one of the primary causes of fracture front segmentation. Although such segmented fractures have been observed both in nature and laboratory, we are not aware of direct laboratory experiments on the mode III mechanism of segmentation of hydraulically induced fractures. In this work, we developed a laboratory technique and a theoretical model for studying not only the effect of mode III loading on the onset of hydraulic fracture segmentation, but also the effect of segmentation on the subsequent growth of hydraulic fractures. In quasi-brittle materials, even a small mode III component may cause fracture segmentation due to a tensile stress field induced near the fracture front [Rice, 1968]. Previously, this has been confirmed in experiments with non-hydraulic fractures [Knauss, 1970; Cooke and Pollard, 1996]. In one occasion, quasi-hydraulic fractures propagated in fast, uncontrollable manner [Sommer, 1969]. This is why, we focused on controlled hydraulic fractures with a rather small KIII/KI ratio (1-10 %). For mixed mode I+III experiments, we used transparent, cylindrical PMMA samples with circular internal fractures perpendicular to the sample axis. Fracture orientation was controlled by thermoelastic stresses induced in each sample by preheating it before creating a fracture. In order to apply mode III loading to the initial fracture, a constant torque was applied to the specimen while fluid was injected into the fracture at a constant rate to pressurize it and to induce mode I loading. The velocity of fracture propagation was constrained by controlling the rate of fluid injection. In spite of a small magnitude of the mode III component, we observed segmented fracture fronts in all tested samples. The segments had similar dimensions and shape elongated around the perimeter of the initial fracture. When the fractures were further pressurized by injecting additional fluid into the sample, second-order segments developed along the fronts

  16. The Influence of Temperature on Mode I Fracture Toughness and Fracture Characteristics of Sandstone

    NASA Astrophysics Data System (ADS)

    Feng, Gan; Kang, Yong; Meng, Tao; Hu, Yao-qing; Li, Xiao-hong

    2017-08-01

    This study investigated the influence of temperature on the mode I fracture toughness of sandstone using semicircular bend specimens. Fracture characteristics were studied using scanning electron microscopy and other means. The results showed that temperature influenced fracturing in three stages along a temperature gradient. In the low-temperature stage (20-100 °C), fracture toughness increases slowly, with a total increase of approximately 11%. At the medium-temperature stage (100-500 °C), fracture toughness decreases slowly, at a rate of approximately 18%. During the high-temperature stage (500-800 °C), fracture toughness was reduced by approximately 44%. The mode I fracture toughness has a clear temperature threshold (500-600 °C). Below this threshold, the fracture toughness decreases slowly. When the temperature threshold is reached, the fracture toughness decreases sharply. The sharp decrease is mainly caused by the creation of a fragmentation structure. The sandstone experiences more transgranular fracture mechanics in the low-temperature stage compared to the high-temperature stage. Above 100 °C, the mechanisms include transgranular fracturing, intergranular fracturing, thermal cracking, and mutual coupling fracturing. When the temperature exceeds 500 °C, several different fragmentation structures are seen. This research study provides significant data to evaluate fracture characteristics and rock safety and stability after heat treatment.

  17. Influence of the resin on interlaminar mixed-mode fracture

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Mangalgiri, P. D.

    1985-01-01

    Both literature review data and new data on toughness behavior of seven matrix and adhesive systems in four types of tests were studied in order to assess the influence of the resin on interlaminar fracture. Mixed mode (i.e., various combinations of opening mode 1, G sub 1, and shearing mode 2; G sub 2) fracture toughness data showed that the mixed mode relationship for failure appears to be linear in terms of G sub 1 and G sub 2. The study further indicates that fracture of brittle resins is controlled by the G sub 1 component, and that fracture of many tough resins is controlled by total strain-energy release rate, G sub T. Regarding the relation of polymer structure and the mixed mode fracture: high mode 1 toughness requires resin dilatation; dilatation is low in unmodified epoxies at room temperature/dry conditions; dilatation is higher in plasticized epoxies, heated epoxies, and in modified epoxies; modification improves mode 2 toughness only slightly compared with mode 1 improvements. Analytical aspects of the cracked lap shear test specimen were explored.

  18. Ceramic fracture mode-intergranular vs transgranular fracture

    SciTech Connect

    Rice, R.W.

    1996-12-31

    Available data on intergranular fracture (IGF) vs transgranular fracture (TGF) of ceramics is summarized and significantly extended. At 22 C, where there is most data, TGF is normally dominant. IGF generally increases with decreasing grain size (G, mainly at G {le} 1-10 {mu}m), increasing grain boundary phase content and the occurrence of (1) slow crack growth, (2) mist, hackle, and crack branching, and (3) (mainly finer, substantial, grain boundary) porosity, and possibly with increasing elastic anisotropy. Possible effects of grain orientation, stress rate and character, as well as microstructural stresses from thermal expansion anisotropy (TEA) are discussed. At higher temperatures, there is a general shift to more IGF, especially with more grain boundary impurities, finer G, and probably higher elastic anisotropy. This shift often starts with IGF only at the fracture origin, and may not commence until temperatures of the order of 1500 C or more in some materials. While IGF is often attributed to weaker grain boundaries (implying lower strengths), it is also often associated with fine grain size, and thus the highest strengths at lower temperatures. IGF vs TGF reflects not just grain boundary strength (as often emphasized), but a balance of this versus the fracture toughness for grain fracture (usually via cleavage, which may also entail the multiplicity of cleavage planes). Several factors may interact to shift differing balances in different materials, e.g. some increase in IGF at larger G in TiB{sub 2} with high TEA, but more IGF increase in Al{sub 2}O{sub 3}, at larger G with less TEA, and no IGF increase in BeO and all TGF in B{sub 4}C having similar TEA to Al{sub 2}O{sub 3}.

  19. An equivalent domain integral method for three-dimensional mixed-mode fracture problems

    NASA Technical Reports Server (NTRS)

    Shivakumar, K. N.; Raju, I. S.

    1991-01-01

    A general formulation of the equivalent domain integral (EDI) method for mixed mode fracture problems in cracked solids is presented. The method is discussed in the context of a 3-D finite element analysis. The J integral consists of two parts: the volume integral of the crack front potential over a torus enclosing the crack front and the crack surface integral due to the crack front potential plus the crack face loading. In mixed mode crack problems the total J integral is split into J sub I, J sub II, and J sub III representing the severity of the crack front in three modes of deformations. The direct and decomposition methods are used to separate the modes. These two methods were applied to several mixed mode fracture problems, were analyzed, and results were found to agree well with those available in the literature. The method lends itself to be used as a post-processing subroutine in a general purpose finite element program.

  20. An equivalent domain integral method for three-dimensional mixed-mode fracture problems

    NASA Technical Reports Server (NTRS)

    Shivakumar, K. N.; Raju, I. S.

    1992-01-01

    A general formulation of the equivalent domain integral (EDI) method for mixed mode fracture problems in cracked solids is presented. The method is discussed in the context of a 3-D finite element analysis. The J integral consists of two parts: the volume integral of the crack front potential over a torus enclosing the crack front and the crack surface integral due to the crack front potential plus the crack face loading. In mixed mode crack problems the total J integral is split into J sub I, J sub II, and J sub III representing the severity of the crack front in three modes of deformations. The direct and decomposition methods are used to separate the modes. These two methods were applied to several mixed mode fracture problems, were analyzed, and results were found to agree well with those available in the literature. The method lends itself to be used as a post-processing subroutine in a general purpose finite element program.

  1. An equivalent domain integral method for three-dimensional mixed-mode fracture problems

    NASA Technical Reports Server (NTRS)

    Shivakumar, K. N.; Raju, I. S.

    1992-01-01

    A general formulation of the equivalent domain integral (EDI) method for mixed mode fracture problems in cracked solids is presented. The method is discussed in the context of a 3-D finite element analysis. The J integral consists of two parts: the volume integral of the crack front potential over a torus enclosing the crack front and the crack surface integral due to the crack front potential plus the crack face loading. In mixed mode crack problems the total J integral is split into J sub I, J sub II, and J sub III representing the severity of the crack front in three modes of deformations. The direct and decomposition methods are used to separate the modes. These two methods were applied to several mixed mode fracture problems, were analyzed, and results were found to agree well with those available in the literature. The method lends itself to be used as a post-processing subroutine in a general purpose finite element program.

  2. The effect of mixed mode precracking on the mode 1 fracture toughness of composite laminates

    NASA Technical Reports Server (NTRS)

    Shankar, Prashanth; Bascom, Williard D.; Nairn, John A.

    1993-01-01

    We subjected double cantilever beam specimens from four different composite materials to mixed-mode precracking. Three different precracking mode 1 to mode 2 ratios were used--1 to 4, 1 to 1, and 4 to 1. Following precracking the specimens were tested for mode I fracture toughness. The mixed-mode precracking often influenced the mode 1 toughness and its influence persisted for as much as 60 mm of mode 1 crack growth. We tested composites with untoughened matrices, composites with rubber-toughened matrices, and composites with interlayer toughening. Depending on material type and precracking mode ratio, the precracking could cause either a significant increase or a significant decrease in the mode 1 fracture toughness.

  3. Fractographic study of epoxy fractured under mode I loading and mixed mode I/III loading

    SciTech Connect

    Ren, Fei; Wang, Jy-An John; Bertelsen, Williams D.

    2011-01-01

    Fiber reinforced polymeric composite materials are widely used in structural components such as wind turbine blades, which are typically subject to complicated loading conditions. Thus, material response under mixed mode loading is of great significance to the reliability of these structures. Epoxy is a thermosetting polymer that is currently used in manufacturing wind turbine blades. The fracture behavior of epoxy is relevant to the mechanical integrity of the wind turbine composite materials. In this study, a novel fracture testing methodology, the spiral notch torsion test (SNTT), was applied to study the fracture behavior of an epoxy material. SNTT samples were tested using either monotonic loading or cyclic loading, while both mode I and mixed mode I/III loading conditions were used. Fractographic examination indicated the epoxy samples included in this study were prone to mode I failure even when the samples were subject to mixed mode loading. Different fatigue precracks were observed on mode I and mixed mode samples, i.e. precracks appeared as a uniform band under mode I loading, and a semi-ellipse under mixed mode loading. Fracture toughness was also estimated using quantitative fractography.

  4. Dual mode fracture of composite laminates penetrated by spherical projectiles

    NASA Astrophysics Data System (ADS)

    Czarnecki, G. J.

    The basic for delamination initiation and propagation within an impacted laminate was studied, with an explanation provided for the fracture mode transformation along the projectile's path. Post-impact observations of graphite/epoxy (AS4/3501-6) laminates penetrated by steel spheres (0.5-inch diameter) reveal a fracture mode, similar to shear plugging adjacent to the impacted surface. This fracture mode is contrasted with that of delamination adjacent to the rear surface. The sudden transition from shear plugging to delamination is believed to occur when the projectile interacts with the returning impact-generated tensile wave. To demonstrate the transition, results are presented from ballistically impacted laminates containing a series of imbedded carbon stress and constantan strain gages. Results are based on impact velocities of 1300, 1850, and 2380 f/s. Transverse stress waves are shown capable of creating delamination until attenuated by a local zone of compressed material associated with the on-coming projectile. Based on experimental results, the location of the fracture mode transition plane is predicted both graphically and through a simple equation of motion.

  5. Monolithic zirconia dental crowns. Internal fit, margin quality, fracture mode and load at fracture.

    PubMed

    Schriwer, Christian; Skjold, Anneli; Gjerdet, Nils Roar; Øilo, Marit

    2017-09-01

    Dental all-ceramic restorations of zirconia, with and without an aesthetic veneering layer, have become a viable alternative to conventional metal-ceramic restorations. The aim of this study was to evaluate whether factors of the production methods or the material compositions affect load at fracture, fracture modes, internal fit or crown margins of monolithic zirconia crowns. Sixty crowns made from six different commercially available dental zirconias were produced to a model tooth with a shallow circumferential chamfer preparation. Internal fit was assessed by the replica method. The crown margin quality was assessed by light microscopy on an ordinal scale. The cemented crowns were loaded centrally in the occlusal fossa with a horizontal steel cylinder with a diameter of 13mm at 0.5mm/min until fracture. Fractographic analysis was performed on the fractured crowns. There were statistically significant differences among the groups regarding crown margins, internal fit and load at fracture (p<0.05, Kruskall Wallis). Fracture analyses revealed that all fractures started cervically and propagated to the occlusal surface similar to clinically observed fractures. There was statistically significant correlation between margin quality and load at fracture (Spearman's rank correlation, p<0,05). Production method and material composition of monolithic zirconia crowns affect internal fit, crown margin quality and the load at fracture. The hard-machined Y-TZP zirconia crowns had the best margin quality and the highest load at fracture. Reduction of margin flaws will improve fracture strength of monolithic zirconia crowns and thereby increase clinical success. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  6. Initiation and growth of mode II delamination in toughened composites

    NASA Astrophysics Data System (ADS)

    Russell, Alan J.

    The origins of nonlinearity in the mode-II delamination fracture of three organic-matrix carbon-fiber composite materials was investigated. This was accomplished by testing specimens with different types of starter cracks and by loading and unloading these specimens several times so that the change in nonlinearity as the delaminations grew could be measured. The load at which crack growth initiated was determined by acoustic emission. Slow crack growth as found to be the principal cause of nonlinearity in the materials tested. The crack velocity obeyed the same power law dependence on GII as is observed for slow crack growth in viscoelastic polymers. For the first loading from the end of the starter cracks, plastic deformation at the crack tip also contributed to the nonlinearity. Other sources of nonlinearity included an increasing fracture resistance in one of the materials as well as problems associated with producing a clean starter notch with a straight crack front.

  7. Dynamic deformation and fracture of single crystal silicon: Fracture modes, damage laws, and anisotropy

    SciTech Connect

    Huang, J. Y.; E, J. C.; Huang, J. W.; Sun, T.; Fezzaa, K.; Xu, S. L.; Luo, S. N.

    2016-05-25

    Impact fracture of single-crystal Si is critical to long-term reliability of electronic devices and solar cells for its wide use as components or substrates in semiconductor industry. Single-crystal Si is loaded along two different crystallographic directions with a split Hopkinson pressure bar integrated with an in situ x-ray imaging and diffraction system. Bulk stress histories are measured, simultaneously with x-ray phase contrast imaging (XPCI) and Laue diffraction. Damage evolution is quantified with grayscale maps from XPCI. Single-crystal Si exhibits pronounced anisotropy in fracture modes, and thus fracture strengths and damage evolution. For loading along [11¯ 0] and viewing along [001], (1¯1¯0)[11¯ 0] cleavage is activated and induces horizontal primary cracks followed by perpendicular wing cracks. However, for loading along [011¯] and viewing along [111], random nucleation and growth of shear and tensile-splitting crack networks lead to catastrophic failure of materials with no cleavage. The primary-wing crack mode leads to a lower characteristic fracture strength due to predamage, but a more concentrated strength distribution, i.e., a higher Weibull modulus, compared to the second loading case. Furthermore, the sequential primary cracking, wing cracking and wing-crack coalescence processes result in a gradual increase of damage with time, deviating from theoretical predictions. Particle size and aspect ratios of fragments are discussed with postmortem fragment analysis, which verifies fracture modes observed in XPCI.

  8. Dynamic deformation and fracture of single crystal silicon: Fracture modes, damage laws, and anisotropy

    DOE PAGES

    Huang, J. Y.; E, J. C.; Huang, J. W.; ...

    2016-05-25

    Impact fracture of single-crystal Si is critical to long-term reliability of electronic devices and solar cells for its wide use as components or substrates in semiconductor industry. Single-crystal Si is loaded along two different crystallographic directions with a split Hopkinson pressure bar integrated with an in situ x-ray imaging and diffraction system. Bulk stress histories are measured, simultaneously with x-ray phase contrast imaging (XPCI) and Laue diffraction. Damage evolution is quantified with grayscale maps from XPCI. Single-crystal Si exhibits pronounced anisotropy in fracture modes, and thus fracture strengths and damage evolution. For loading along [11¯ 0] and viewing along [001],more » (1¯1¯0)[11¯ 0] cleavage is activated and induces horizontal primary cracks followed by perpendicular wing cracks. However, for loading along [011¯] and viewing along [111], random nucleation and growth of shear and tensile-splitting crack networks lead to catastrophic failure of materials with no cleavage. The primary-wing crack mode leads to a lower characteristic fracture strength due to predamage, but a more concentrated strength distribution, i.e., a higher Weibull modulus, compared to the second loading case. Furthermore, the sequential primary cracking, wing cracking and wing-crack coalescence processes result in a gradual increase of damage with time, deviating from theoretical predictions. Particle size and aspect ratios of fragments are discussed with postmortem fragment analysis, which verifies fracture modes observed in XPCI.« less

  9. Dynamic deformation and fracture of single crystal silicon: Fracture modes, damage laws, and anisotropy

    SciTech Connect

    Huang, J. Y.; E, J. C.; Huang, J. W.; Sun, T.; Fezzaa, K.; Xu, S. L.; Luo, S. N.

    2016-05-25

    Impact fracture of single-crystal Si is critical to long-term reliability of electronic devices and solar cells for its wide use as components or substrates in semiconductor industry. Single-crystal Si is loaded along two different crystallographic directions with a split Hopkinson pressure bar integrated with an in situ x-ray imaging and diffraction system. Bulk stress histories are measured, simultaneously with x-ray phase contrast imaging (XPCI) and Laue diffraction. Damage evolution is quantified with grayscale maps from XPCI. Single-crystal Si exhibits pronounced anisotropy in fracture modes, and thus fracture strengths and damage evolution. For loading along [11¯ 0] and viewing along [001], (1¯1¯0)[11¯ 0] cleavage is activated and induces horizontal primary cracks followed by perpendicular wing cracks. However, for loading along [011¯] and viewing along [111], random nucleation and growth of shear and tensile-splitting crack networks lead to catastrophic failure of materials with no cleavage. The primary-wing crack mode leads to a lower characteristic fracture strength due to predamage, but a more concentrated strength distribution, i.e., a higher Weibull modulus, compared to the second loading case. Furthermore, the sequential primary cracking, wing cracking and wing-crack coalescence processes result in a gradual increase of damage with time, deviating from theoretical predictions. Particle size and aspect ratios of fragments are discussed with postmortem fragment analysis, which verifies fracture modes observed in XPCI.

  10. Modified Mode-I Cracked Sandwich Beam (CSB) Fracture Test

    NASA Technical Reports Server (NTRS)

    Smith, S. A.; Shivakumar, K. N.

    2001-01-01

    Five composite sandwich panels were fabricated using vacuum assisted resin transfer molding (VARTM). Four of these panels had E-glass/vinylester facesheets and one had carbon/epoxy facesheets. The sandwich panels had different density PVC foam cores. The four E-glass panels had core densities of 80, 100, 130, 200 kg/cu m. The sandwich with carbon/epoxy 3 facesheets had a core with density of 100 kg/cu m. Fracture tests were conducted using a modified Cracked Sandwich Beam (CSB) test configuration. Load displacement curves were obtained for loading and unloading of the specimens during crack growth. Various increments of crack growth were monitored. Critical Strain Energy Release Rates (SERR) were determined from the tests using the area method. The critical values of SERR can be considered the fracture toughness of the sandwich material. The fracture toughness ranged 367 J/sq m to 1350 J/sq m over the range of core densities. These results are compared to the Mode-I fracture toughness of the PVC foam core materials and values obtained for foam-cored sandwiches using the TSD specimen. Finite-element analyses (FEA) were performed for the test configuration and Strain Energy Release Rates were calculated using the Virtual Crack Closure Technique (VCCT). The SERR values determined from the FEA were scaled to the fracture loads, or critical loads, obtained from the modified CSB tests. These critical loads were in close agreement with the test values.

  11. Fracture-mode map of brittle coatings: Theoretical development and experimental verification

    NASA Astrophysics Data System (ADS)

    He, Chong; Xie, Zhaoqian; Guo, Zhenbin; Yao, Haimin

    2015-10-01

    Brittle coatings, upon sufficiently high indentation load, tend to fracture through either ring cracking or radial cracking. In this paper, we systematically study the factors determining the fracture modes of bilayer material under indentation. By analyzing the stress field developed in a coating/substrate bilayer under indentation in combination with the application of the maximum-tensile-stress fracture criterion, we show that the fracture mode of brittle coatings due to indentation is determined synergistically by two dimensionless parameters being functions of the mechanical properties of coating and substrate, coating thickness and indenter tip radius. Such dependence can be graphically depicted by a diagram called 'fracture-mode map', whereby the fracture modes can be directly predicated based on these two dimensionless parameters. Experimental verification of the fracture-mode map is carried out by examining the fracture modes of fused quartz/cement bilayer materials under indentation. The experimental observation exhibits good agreement with the prediction by the fracture-mode map. Our finding in this paper may not only shed light on the mechanics accounting for the fracture modes of brittle coatings in bilayer structures but also pave a new avenue to combating catastrophic damage through fracture mode control.

  12. Salter-Harris II forearm fracture reduction and fixation using a buttress plate.

    PubMed

    Barnes, Jonathan; Webb, Mark; v Fearon, Paul

    2014-01-31

    Distal radius fractures are common injuries in children. Those that affect the growth plate (physis) need to be managed carefully as inadequate management may lead to long-term deformity and a reduction in function. However, different management strategies all have drawbacks and controversy exists over how best to manage these cases. This is the case of a 13-year-old girl who presented with a Salter Harris II fracture, which was managed using a novel approach of utilising a T plate in a buttress mode to stabilise the fracture after anatomical reduction. This provided effective fracture fixation and should allow good bone healing without causing any iatrogenic growth plate damage and without fixing a plate across the physis, which may need removal in the future.

  13. Salter-Harris II forearm fracture reduction and fixation using a buttress plate

    PubMed Central

    Barnes, Jonathan; Webb, Mark; Fearon, Paul v

    2014-01-01

    Distal radius fractures are common injuries in children. Those that affect the growth plate (physis) need to be managed carefully as inadequate management may lead to long-term deformity and a reduction in function. However, different management strategies all have drawbacks and controversy exists over how best to manage these cases. This is the case of a 13-year-old girl who presented with a Salter Harris II fracture, which was managed using a novel approach of utilising a T plate in a buttress mode to stabilise the fracture after anatomical reduction. This provided effective fracture fixation and should allow good bone healing without causing any iatrogenic growth plate damage and without fixing a plate across the physis, which may need removal in the future. PMID:24488665

  14. Mode-II Crack Problem for a Long Rectangular Slab of Superconductor under an Electromagnetic Force

    NASA Astrophysics Data System (ADS)

    Gao, Zhi-Wen; Zhou, You-He

    2009-02-01

    We present a theoretical analysis to the fracture parameters of the large single domain YBCO superconductor with a tangential line crack under electromagnetic force. The mode-II fracture parameters are obtained due to coupled finite element and infinite element method, and the numerical results are conducted for two activation processes. For a zero-field cooling (ZFC) magnetization process, in the process of magnetic field descent, the larger the applied field is, the larger the stress intensity factors. In the case of field cooling (FC) magnetization process, the stress intensity factors have obvious differences between the two cases of bfc > 1 and bfc >= 1. Additionally, J-integral characteristic is obtained, and according to these results, the mode-II crack growth trend is predicted. These results are benefit for us to understand the fracture mechanism of superconductor both in theory and application.

  15. Influence of Mixed Mode I-Mode II Loading on Fatigue Delamination Growth Characteristics of a Graphite Epoxy Tape Laminate

    NASA Technical Reports Server (NTRS)

    Ratcliffe, James G.; Johnston, William M., Jr.

    2014-01-01

    Mixed mode I-mode II interlaminar tests were conducted on IM7/8552 tape laminates using the mixed-mode bending test. Three mixed mode ratios, G(sub II)/G(sub T) = 0.2, 0.5, and 0.8, were considered. Tests were performed at all three mixed-mode ratios under quasi-static and cyclic loading conditions, where the former static tests were used to determine initial loading levels for the latter fatigue tests. Fatigue tests at each mixed-mode ratio were performed at four loading levels, Gmax, equal to 0.5G(sub c), 0.4G(sub c), 0.3G(sub c), and 0.2G(sub c), where G(sub c) is the interlaminar fracture toughness of the corresponding mixed-mode ratio at which a test was performed. All fatigue tests were performed using constant-amplitude load control and delamination growth was automatically documented using compliance solutions obtained from the corresponding quasi-static tests. Static fracture toughness data yielded a mixed-mode delamination criterion that exhibited monotonic increase in Gc with mixed-mode ratio, G(sub II)/G(sub T). Fatigue delamination onset parameters varied monotonically with G(sub II)/G(sub T), which was expected based on the fracture toughness data. Analysis of non-normalized data yielded a monotonic change in Paris law exponent with mode ratio. This was not the case when normalized data were analyzed. Fatigue data normalized by the static R-curve were most affected in specimens tested at G(sub II)/G(sub T)=0.2 (this process has little influence on the other data). In this case, the normalized data yielded a higher delamination growth rate compared to the raw data for a given loading level. Overall, fiber bridging appeared to be the dominant mechanism, affecting delamination growth rates in specimens tested at different load levels and differing mixed-mode ratios.

  16. The significance of crack-resistance curves to the mixed-mode fracture toughness of human cortical bone

    PubMed Central

    Zimmermann, Elizabeth A.; Launey, Maximilien E.; Ritchie, Robert O.

    2011-01-01

    The majority of fracture mechanics studies on the toughness of bone have been performed under tensile loading. However, it has recently been shown that the toughness of human cortical bone in the transverse (breaking) orientation is actually much lower in shear (mode II) than in tension (mode I); a fact that is physiologically relevant as in vivo bone is invariably loaded multiaxially. Since bone is a material that derives its fracture resistance primarily during crack growth through extrinsic toughening mechanisms, such as crack deflection and bridging, evaluation of its toughness is best achieved through measurements of the crack-resistance or R-curve, which describes the fracture toughness as a function of crack extension. Accordingly, in this study, we attempt to measure for the first time the R-curve fracture toughness of human cortical bone under physiologically relevant mixed-mode loading conditions. We show that the resulting mixed-mode (mode I + II) toughness depends strongly on the crack trajectory and is the result of the competition between the paths of maximum mechanical driving force and “weakest” microstructural resistance. PMID:20409579

  17. The significance of crack-resistance curves to the mixed-mode fracture toughness of human cortical bone

    SciTech Connect

    Zimmermann, Elizabeth A.; Launey, Maximilien E.; Ritchie, Robert O.

    2010-03-25

    The majority of fracture mechanics studies on the toughness of bone have been performed under tensile loading. However, it has recently been shown that the toughness of human cortical bone in the transverse (breaking) orientation is actually much lower in shear (mode II) than in tension (mode I); a fact that is physiologically relevant as in vivo bone is invariably loaded multiaxially. Since bone is a material that derives its fracture resistance primarily during crack growth through extrinsic toughening mechanisms, such as crack deflection and bridging, evaluation of its toughness is best achieved through measurements of the crack-resistance or R-curve, which describes the fracture toughness as a function of crack extension. Accordingly, in this study, we attempt to measure for the first time the R-curve fracture toughness of human cortical bone under physiologically relevant mixed-mode loading conditions. We show that the resulting mixed-mode (mode I + II) toughness depends strongly on the crack trajectory and is the result of the competition between the paths of maximum mechanical driving force and 'weakest' microstructural resistance.

  18. The significance of crack-resistance curves to the mixed-mode fracture toughness of human cortical bone.

    PubMed

    Zimmermann, Elizabeth A; Launey, Maximilien E; Ritchie, Robert O

    2010-07-01

    The majority of fracture mechanics studies on the toughness of bone have been performed under tensile loading. However, it has recently been shown that the toughness of human cortical bone in the transverse (breaking) orientation is actually much lower in shear (mode II) than in tension (mode I); a fact that is physiologically relevant as in vivo bone is invariably loaded multiaxially. Since bone is a material that derives its fracture resistance primarily during crack growth through extrinsic toughening mechanisms, such as crack deflection and bridging, evaluation of its toughness is best achieved through measurements of the crack-resistance or R-curve, which describes the fracture toughness as a function of crack extension. Accordingly, in this study, we attempt to measure for the first time the R-curve fracture toughness of human cortical bone under physiologically relevant mixed-mode loading conditions. We show that the resulting mixed-mode (mode I+II) toughness depends strongly on the crack trajectory and is the result of the competition between the paths of maximum mechanical driving force and "weakest" microstructural resistance.

  19. Numerical Study on Mixed-mode Fracture in Reinforced Concrete

    SciTech Connect

    Yu, Rena C.; Saucedo, Luis; Ruiz, Gonzalo

    2010-05-21

    The object of this work is to model the propagation of fracture in mixed-mode in lightly reinforced concrete beams. When a notched beam does not have enough shear reinforcement, fracture can initiate and propagate unstably and lead to failure through diagonal tension. In order to study this phenomenon numerically, a model capable of dealing with both static and dynamic crack propagation as well as the natural transition of those two regimes is necessary. We adopt a cohesive model for concrete fracture and an interface model for the deterioration between concrete and steel re-bar, both combined with an insertion algorithm. The static process is solved by dynamic relaxation (DR) method together with a modified technique to enhance convergence rate. The same DR method is used to detect a dynamic process and switch to a dynamic calculation. The numerically obtained load-displacement curves, load-CMOD curves and crack patterns fit reasonably well with their experimental counterparts, having in mind that we fed the calculations only with parameters measured experimentally.

  20. Mixed mode stress field effect in adhesive fracture

    NASA Technical Reports Server (NTRS)

    Anderson, G. P.; Devries, K. L.; Williams, M. L.

    1974-01-01

    Numerical or analytical analyses were performed on seven different test specimens including blister test, 90-degree peel test, torsion test, and various cone tests. These specimens are in general subjected to complex stress fields having various amounts of Mode I, Mode II, and Mode III loads. The specimens were then constructed using polymethyl methacrylate for the adherends and a transparent polyurethane elastomer (Solithane 113) for the adhesive. This combination permitted direct observation of the bondline as load was applied. Although initial debonds as well as bond end termination singularities were present in all specimens, in some cases the debond did not initiate at the singularity points as would normally have been expected. An explanation for this behavior is presented, as well as a comparison of loading mode effect on those specimens for which the debond did propagate from a bond terminus singular point.

  1. Mixed mode stress field effect in adhesive fracture

    NASA Technical Reports Server (NTRS)

    Anderson, G. P.; Devries, K. L.; Williams, M. L.

    1974-01-01

    Numerical or analytical analyses were performed on seven different test specimens including blister test, 90-degree peel test, torsion test, and various cone tests. These specimens are in general subjected to complex stress fields having various amounts of Mode I, Mode II, and Mode III loads. The specimens were then constructed using polymethyl methacrylate for the adherends and a transparent polyurethane elastomer (Solithane 113) for the adhesive. This combination permitted direct observation of the bondline as load was applied. Although initial debonds as well as bond end termination singularities were present in all specimens, in some cases the debond did not initiate at the singularity points as would normally have been expected. An explanation for this behavior is presented, as well as a comparison of loading mode effect on those specimens for which the debond did propagate from a bond terminus singular point.

  2. Fracture toughness in Mode I (GIC) for ductile adhesives

    NASA Astrophysics Data System (ADS)

    Gálvez, P.; Carbas, RJC; Campilho, RDSG; Abenojar, J.; Martínez, MA; Silva LFM, da

    2017-05-01

    Works carried out in this publication belong to a project that seeks the replacement of welded joints by adhesive joints at stress concentration nodes in bus structures. Fracture toughness in Mode I (GIC) has been measured for two different ductile adhesives, SikaTack Drive and SikaForce 7720. SikaTack Drive is a single-component polyurethane adhesive with high viscoelasticity (more than 100%), whose main use is the car-glass joining and SikaForce 7720 is double-component structural polyurethane adhesive. Experimental works have been carried out from the test called Double Cantilever Beam (DCB), using two steel beams as adherents and an adhesive thickness according to the problem posed in the Project, of 2 and 3 mm for SikaForce 7720 and SikaTack Drive, respectively. Three different methods have been used for measuring the fracture toughness in mode I (GIC) from the values obtained in the experimental DCB procedure for each adhesive: Corrected Beam Theory (CBT), Compliance Calibration Method (CCM) and Compliance Based Beam Method (CBBM). Four DCB specimens have been tested for each adhesive. Dispersion of each GIC calculation method for each adhesive has been studied. Likewise variations between the three different methods have been also studied for each adhesive.

  3. Composite interlaminar fracture toughness: Three-dimensional finite element modeling for mixed mode 1, 2 and 3 fracture

    NASA Technical Reports Server (NTRS)

    Murthy, P. L. N.; Chamis, C. C.

    1986-01-01

    A computational method/procedure is described which can be used to simulate individual and mixed mode interlaminar fracture progression in fiber composite laminates. Different combinations of Modes 1, 2, and 3 fracture are simulated by varying the crack location through the specimen thickness and by selecting appropriate unsymmetric laminate configurations. The contribution of each fracture mode to strain energy release rate is determined by the local crack closure methods while the mixed mode is determined by global variables. The strain energy release rates are plotted versus extending crack length, where slow crack growth, stable crack growth, and rapid crack growth regions are easily identified. Graphical results are presented to illustrate the effectiveness and versatility of the computational simulation for: (1) evaluating mixed-mode interlaminar fracture, (2) for identifying respective dominant parameters, and (3) for selecting possible simple test methods.

  4. Influence of restorative technique on the biomechanical behavior of endodontically treated maxillary premolars. Part I: fracture resistance and fracture mode.

    PubMed

    Soares, Paulo Vinicius; Santos-Filho, Paulo Cesar Freitas; Martins, Luis Roberto Marcondes; Soares, Carlos Jose

    2008-01-01

    Unresolved controversy exists concerning the preferred cavity design and restorative technique used to restore endodontically treated maxillary premolars to improve their resistance to fracture under occlusal load. The purpose of this study was to evaluate the fracture resistance, stress distribution, and cusp deformation of endodontically treated human maxillary premolars restored with different materials. The study is divided into 2 parts. In Part I, fracture resistance and fracture mode were determined. Seventy noncarious human maxillary premolars were selected and divided into 7 groups (n=10). The control group, ST, consisted of sound unprepared teeth. Teeth in the other 6 groups were endodontically treated and each received 1 of 2 cavity preparation designs: MODd, direct mesio-occlusal-distal preparation; MODi, indirect mesio-occlusal-distal preparation. Teeth were restored with 4 types of material: AM, MODd restored with amalgam; CR, MODd restored with composite resin; LPR, MODi restored with laboratory-processed composite resin; and LGC, MODi restored with leucite-reinforced glass ceramic. The fracture resistance (N) was assessed under compressive load in a universal testing machine. The data were analyzed by 1-way ANOVA and the Tukey HSD test (alpha =.05). Fracture modes were recorded based on the degree of tooth structure involvement and restoration damage. Statistical analysis showed that the ST group presented the highest fracture resistance values. The restored groups showed significantly higher fracture resistance values compared to the nonrestored groups. The groups restored with adhesive techniques (LPR, CR, and LGC) presented significantly higher fracture resistance values than the group restored with the nonadhesive technique (AM) (P<.001). The catastrophic fractures were prevalent in MODd, MODi, AM, and LPR groups, and less severe fractures were found in ST and LGC groups. For the CR group, there was no prevalent fracture mode. Teeth with the

  5. Mixed mode fracture characterization of hydroxylapatite-titanium alloy interface.

    PubMed

    Mann, K A; Edidin, A A; Kinoshita, R K; Manley, M T

    1994-01-01

    Cantilever beam and four-point bend specimen geometries were used to experimentally determine the critical energy release rates for a plasma sprayed hydroxylapatite-titanium alloy (HA-Ti alloy) interface. A locus of energy release rates as a function of crack tip phase angle was determined where a 0 degree phase angle represented tensile opening (mode I) loading and a 90 degree phase angle represented in-plane shear (mode II) loading. Energy release rates were found to increase substantially with an increase in phase angle. An energy release rate of 0.108 N/mm was determined for a phase angle of 0 degrees (mode I). Energy release rates of 0.221, 0.686, and 1.212 N/mm were determined for phase angles of 66 degrees, 69 degrees, and 72 degrees, respectively. The experimental data was matched to a phenomenological model for which crack propagation depended on mode I loading alone indicating that crack propagation at the Ha-Ti alloy interface is dominated by the mode I loading component. Therefore, regions of HA coated implants that experience compressive or shear loading across the HA-Ti alloy interface may be much less likely to debond than regions that experience tensile loading.

  6. Derivation of Path Independent Coupled Mix Mode Cohesive Laws from Fracture Resistance Curves

    NASA Astrophysics Data System (ADS)

    Goutianos, Stergios

    2017-08-01

    A generalised approach is presented to derive coupled mixed mode cohesive laws described with physical parameters such as peak traction, critical opening, fracture energy and cohesive shape. The approach is based on deriving mix mode fracture resistance curves from an effective mix mode cohesive law at different mode mixities. From the fracture resistance curves, the normal and shear stresses of the cohesive laws can be obtained by differentiation. Since, the mixed mode cohesive laws are obtained from a fracture resistance curve (potential function), path independence is automatically satisfied. The effective mix mode cohesive law can have different shape and cohesive law parameters at different mode mixities so that the approach can be applied to various material failure models.

  7. Effect of van der Waals interaction on the mode I fracture characteristics of graphene sheet

    NASA Astrophysics Data System (ADS)

    Parashar, Avinash; Mertiny, Pierre

    2013-11-01

    In this paper a study has been performed to investigate the effect of van der Waals interaction forces on the mode I (opening mode) fracture characteristics of a graphene sheet. Finite element based atomistic approach was employed to perform the investigation, where graphene structure was assumed to behave like a space frame structure. Few graphene sheets were modeled in finite element environment with different set of interlayer spacing. Modified virtual crack closure technique (VCCT) was employed to estimate the strain energy release rate (SERR) under mode I of fracture criteria. Significant effect of van der Waals forces was observed on the mode I fracture characteristics of graphene.

  8. Patient-reported outcome following nonsurgical management of type II odontoid process fractures in adults

    PubMed Central

    Fam, Maged D; Zeineddine, Hussein A; Nassir, Rafiq Muhammed; Bhatt, Pragnesh; Kamel, Mahmoud H

    2017-01-01

    Background: Transverse (type II) odontoid process fracture is among the most commonly encountered cervical spine fractures. Nonsurgical management through external immobilization is occasionally preferred to surgical management but is criticized for its higher rates of failure and lower patient satisfaction. Our aim is to analyze patient-reported outcomes in patients who underwent nonsurgical treatment for type II odontoid fractures. Methods: We identified patients >18-year-old who underwent external immobilization as a treatment for isolated type II odontoid fracture between 2007 and 2012. We collected demographic parameters, clinical presentation, mode of injury, imaging studies and modality and duration of treatment (soft collar, halo-vest, or both). Patients were contacted by telephone to participate in a 15-min survey addressing their recovery including their subjective rate of return to preinjury level of functioning. Results: Fifteen patients met the inclusion/exclusion criteria and participated in our survey. Patients were followed up for an average of 19 months after injury. Overall mean age was 61 years. Injury followed a mechanical fall or a road traffic accident in 11 and 4 cases, respectively. External immobilization was achieved by halo vest only in nine patients, soft collar only in two patients (13%), and through a sequential combination in the remaining 4 (27%). This was deployed for a mean of 7.8 months. Radiological studies at the last follow-up showed bony healing (27%), fibrous nonunion (60%), and persistent instability (13%). Patients reported gradual recovery of function throughout the 1st year after injury with levels above 70% of preinjury functioning achieved by 13% of patients at 6 months, 33% at 9 months, and 47% at 12 months. Overall satisfaction with nonsurgical management was 68%. Conclusion: In selected patients with type II odontoid fractures, external immobilization represents a good option with acceptable course of recovery. PMID

  9. 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

  10. Rock Fracture Toughness Study Under Mixed Mode I/III Loading

    NASA Astrophysics Data System (ADS)

    Aliha, M. R. M.; Bahmani, A.

    2017-07-01

    Fracture growth in underground rock structures occurs under complex stress states, which typically include the in- and out-of-plane sliding deformation of jointed rock masses before catastrophic failure. However, the lack of a comprehensive theoretical and experimental fracture toughness study for rocks under contributions of out-of plane deformations (i.e. mode III) is one of the shortcomings of this field. Therefore, in this research the mixed mode I/III fracture toughness of a typical rock material is investigated experimentally by means of a novel cracked disc specimen subjected to bend loading. It was shown that the specimen can provide full combinations of modes I and III and consequently a complete set of mixed mode I/III fracture toughness data were determined for the tested marble rock. By moving from pure mode I towards pure mode III, fracture load was increased; however, the corresponding fracture toughness value became smaller. The obtained experimental fracture toughness results were finally predicted using theoretical and empirical fracture models.

  11. Cell wall swelling, fracture mode, and the mechanical properties of cherry fruit skins are closely related.

    PubMed

    Brüggenwirth, Martin; Knoche, Moritz

    2017-04-01

    Cell wall swelling, fracture mode (along the middle lamellae vs. across cell walls), stiffness, and pressure at fracture of the sweet cherry fruit skin are closely related. Skin cracking is a common phenomenon in many crops bearing fleshy fruit. The objectives were to investigate relationships between the mode of fracture, the extent of cell wall swelling, and the mechanical properties of the fruit skin using sweet cherry (Prunus avium) as a model. Cracking was induced by incubating whole fruit in deionised water or by fracturing exocarp segments (ESs) in biaxial tensile tests. The fracture mode of epidermal cells was investigated by light microscopy. In biaxial tensile tests, the anticlinal cell walls of the ES fractured predominantly across the cell walls (rather than along) and showed no cell wall swelling. In contrast, fruit incubated in water fractured predominantly along the anticlinal epidermal cell walls and the cell walls were swollen. Swelling of cell walls also occurred when ESs were incubated in malic acid, in hypertonic solutions of sucrose, or in water. Compared to the untreated controls, these treatments resulted in more frequent fractures along the cell walls, lower pressures at fracture (p fracture), and lower moduli of elasticity (E, i.e., less stiff). Conversely, compared to the untreated controls, incubating the ES in CaCl2 and in high concentrations of ethanol resulted in thinner cell walls, in less frequent fractures along the cell walls, higher E and p fracture. Our study demonstrates that fracture mode, stiffness, and pressure at fracture are closely related to cell wall swelling. A number of other factors, including cultivar, ripening stage, turgor, CaCl2, and malic acid, exert their effects only indirectly, i.e., by affecting cell wall swelling.

  12. Identification of modes of fracture in a 2618-T6 aluminum alloy using stereophotogrammetry

    SciTech Connect

    Salas Zamarripa, A.; Mata, M.P. Guerrero; Morales, M. Castillo; Beber-Solano, T.P.

    2011-12-15

    The identification and the development of a quantification technique of the modes of fracture in fatigue fracture surfaces of a 2618-T6 aluminum alloy were developed during this research. Fatigue tests at room and high temperature (230 Degree-Sign C) were carried out to be able to compare the microscopic fractographic features developed by this material under these testing conditions. The overall observations by scanning electron microscopy (SEM) of the fracture surfaces showed a mixture of transgranular and ductile intergranular fracture. The ductile intergranular fracture contribution appears to be more significant at room temperature than at 230 Degree-Sign C. A quantitative methodology was developed to identify and to measure the contribution of these microscopic fractographic features. The technique consisted of a combination of stereophotogrammetry and image analysis. Stereo-pairs were randomly taken along the crack paths and were then analyzed using the profile module of MeX software. The analysis involved the 3-D surface reconstruction, the trace of primary profile lines in both vertical and horizontal directions within the stereo-pair area, the measurements of the contribution of the modes of fracture in each profile, and finally, the calculation of the average contribution in each stereo-pair. The technique results confirmed a higher contribution of ductile intergranular fracture at room temperature than at 230 Degree-Sign C. Moreover, there was no indication of a direct relationship between this contribution and the strain amplitudes range applied during the fatigue testing. - Highlights: Black-Right-Pointing-Pointer Stereophotogrammetry and image analysis as a measuring tool of modes of fracture in fatigue fracture surfaces. Black-Right-Pointing-Pointer A mixture of ductile intergranular and transgranular fracture was identified at room temperature and 230 Degree-Sign C testing. Black-Right-Pointing-Pointer Development of a quantitative methodology to

  13. Experimental and Numerical Investigation of Mixed-Mode Interlaminar Fracture of Carbon-Polyester Laminated Woven Composite by Using Arcan Set-up

    NASA Astrophysics Data System (ADS)

    Heydari, Mohammad Hossein; Choupani, Naghdali; Shameli, Moharram

    2011-12-01

    Composite materials are widely used in marine, aerospace and automobile industries. These materials are often subjected to defects and damages from both in-service and manufacturing process. Delamination is the most important of these defects. This paper reports investigation of mixed-mode fracture toughness in carbon-polyester composite by using numerical and experimental methods. All tests were performed by Arcan set-up. By changing the loading angle, α, from 0° to 90° at 15° intervals, mode-I, mixed-mode and mode-II fracture data were obtained. Correction factors for various conditions were obtained by using ABAQUS software. Effects of the crack length and the loading angle on fracture were also studied. The interaction j-integral method was used to separate the mixed-mode stress intensity factors at the crack tip under different loading conditions. As the result, it can be seen that the shearing mode interlaminar fracture toughness is larger than the opening mode interlaminar fracture toughness. This means that interlaminar cracked specimen is tougher in shear loading condition and weaker in tensile loading condition.

  14. Initiation and propagation of mixed mode fractures in granite and sandstone

    NASA Astrophysics Data System (ADS)

    Rück, Marc; Rahner, Roman; Sone, Hiroki; Dresen, Georg

    2017-10-01

    We investigate mixed mode fracture initiation and propagation in experimentally deformed granite and sandstone. We performed a series of asymmetric loading tests to induce fractures in cylindrical specimens at confining pressures up to 20 MPa. Loading was controlled using acoustic emission (AE) feedback control, which allows studying quasi-static fracture propagation for several hours. Location of acoustic emissions reveals distinct differences in spatial-temporal fracture evolution between granite and sandstone samples. Before reaching peak stress in experiments performed on granite, axial fractures initiate first at the edge of the indenter and then propagate through the entire sample. Secondary inclined fractures develop during softening of the sample. In sandstone, inclined shear fractures nucleate at peak stress and propagate through the specimen. AE source type analysis shows complex fracturing in both materials with pore collapse contributing significantly to fracture growth in sandstone samples. We compare the experimental results with numerical models to analyze stress distribution and energy release rate per unit crack surface area in the samples at different stages during fracture growth. We thereby show that for both rock types the energy release rate increases approximately linearly during fracture propagation. The study illuminates how different material properties modify fracture initiation direction under similar loading conditions.

  15. Failure Mode of the Water-filled Fractures under Hydraulic Pressure in Karst Tunnels

    NASA Astrophysics Data System (ADS)

    Dong, Xin; Lu, Hao; Huang, Houxu; Hao, Yiqing; Xia, Yuanpu

    2017-06-01

    Water-filled fractures continue to grow after the excavation of karst tunnels, and the hydraulic pressure in these fractures changes along with such growth. This paper simplifies the fractures in the surrounding rock as flat ellipses and then identifies the critical hydraulic pressure values required for the occurrence of tensile-shear and compression-shear failures in water-filled fractures in the case of plane stress. The occurrence of tensile-shear fracture requires a larger critical hydraulic pressure than compression-shear failure in the same fracture. This paper examines the effects of fracture strike and lateral pressure coefficient on critical hydraulic pressure, and identifies compression-shear failure as the main failure mode of water-filled fractures. This paper also analyses the hydraulic pressure distribution in fractures with different extensions, and reveals that hydraulic pressure decreases along with the continuous growth of fractures and cannot completely fill a newly formed fracture with water. Fracture growth may be interrupted under the effect of hydraulic tensile shear.

  16. Hinged external fixation for Regan-Morrey type I and II fractures and fracture-dislocations.

    PubMed

    Castelli, Alberto; D'amico, Salvatore; Combi, Alberto; Benazzo, Francesco

    2016-06-01

    Elbow fracture-dislocation is always demanding to manage due to the considerable soft-tissue swelling or damage involved, which can make an early open approach and ligamentous reconstruction impossible. The purpose of this study was to evaluate the role of elbow hinged external fixation (HEF) as a definitive treatment in patients with elbow dislocations associated with Regan-Morrey (R-M) type I and II coronoid fractures and soft-tissue damage. We treated 11 patients between 2010 and 2012 with HEF. Instability tests and standard X-ray examinations were performed before surgery and 1-3 to 3-6 months after surgery, respectively. All patients underwent a preoperative CT scan. Outcomes were assessed with a functional assessment scale (Mayo Elbow Performance Score, MEPS) that included 4 parameters: pain, ROM, stability, and function. The results were good or excellent in all 11 patients, and no patient complained of residual instability. Radiographic examination showed bone metaplasia involving the anterior and medial sides of the joint in 5 patients. HEF presented several advantages: it improves elbow stability and it avoids long and demanding surgery in particular in cases with large soft tissue damage. We therefore consider elbow HEF to be a viable option for treating R-M type I and II fracture-dislocations.

  17. Opening-mode fracture in siliceous mudstone at high homologous temperature—effect of surface forces

    NASA Astrophysics Data System (ADS)

    Eichhubl, Peter; Aydin, Atilla; Lore, Jason

    In analogy to high-temperature sintering of ceramics and metal powder compacts, the formation of opening-mode fractures in siliceous mudstone during natural in-situ combustion of hydrocarbons is attributed to contractile surface forces between mineral grains and an interstitial melt phase. A comparison between bulk density increase during sintering and created fracture space indicates that fracturing resulted from contraction of the rock matrix due to porosity reduction, grain-scale mass transfer, and high-temperature mineral formation. It is suggested that contractile surface forces between mineral grains and between mineral grains and pore fluid contribute to subcritical fracture formation under a wide range of subsurface conditions.

  18. Esthetic and biologic mode of reattaching incisor fracture fragment utilizing glass fiber post

    PubMed Central

    Manju, M.; Shanthraj, Srinivas L.; Savitha, K. C.; Sethi, Ntasha

    2015-01-01

    Trauma to the anterior teeth affects the esthetic and psychological well-being of the patient. Advancement in the adhesive dentistry has facilitated the restoration of the coronal tooth fractures by minimally invasive procedures when the original tooth fragment is available. Reattachment of fractured fragment offers immediate treatment with improved preponderant aesthetics and restoration of function. Here, we describe a case of complicated fracture of the maxillary left immature permanent central incisor, which was treated endodontically followed by esthetic reattachment of the fractured fragment using the glass fiber post. Functional demands and esthetic considerations of the patient were fully met with this biologic mode of fragment reattachment. PMID:26283849

  19. Slow crack growth in glass in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Shetty, D. K.; Rosenfield, A. R.

    1991-01-01

    Slow crack growth in soda-lime glass under combined mode I and mode II loading was investigated in precracked disk specimens in which pure mode I, pure mode II, and various combinations of mode I and mode II were achieved by loading in diametral compression at selected angles with respect to symmetric radial cracks. It is shown that slow crack growth under these conditions can be described by a simple exponential relationship with elastic strain energy release rate as the effective crack-driving force parameter. It is possible to interpret this equation in terms of theoretical models that treat subcritical crack growth as a thermally activated bond-rupture process with an activation energy dependent on the environment, and the elastic energy release rate as the crack-driving force parameter.

  20. Slow crack growth in glass in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Shetty, D. K.; Rosenfield, A. R.

    1991-01-01

    Slow crack growth in soda-lime glass under combined mode I and mode II loading was investigated in precracked disk specimens in which pure mode I, pure mode II, and various combinations of mode I and mode II were achieved by loading in diametral compression at selected angles with respect to symmetric radial cracks. It is shown that slow crack growth under these conditions can be described by a simple exponential relationship with elastic strain energy release rate as the effective crack-driving force parameter. It is possible to interpret this equation in terms of theoretical models that treat subcritical crack growth as a thermally activated bond-rupture process with an activation energy dependent on the environment, and the elastic energy release rate as the crack-driving force parameter.

  1. Standard solar model. II - g-modes

    NASA Technical Reports Server (NTRS)

    Guenther, D. B.; Demarque, P.; Pinsonneault, M. H.; Kim, Y.-C.

    1992-01-01

    The paper presents the g-mode oscillation for a set of modern solar models. Each solar model is based on a single modification or improvement to the physics of a reference solar model. Improvements were made to the nuclear reaction rates, the equation of state, the opacities, and the treatment of the atmosphere. The error in the predicted g-mode periods associated with the uncertainties in the model physics is predicted and the specific sensitivities of the g-mode periods and their period spacings to the different model structures are described. In addition, these models are compared to a sample of published observations. A remarkably good agreement is found between the 'best' solar model and the observations of Hill and Gu (1990).

  2. Experimental study on mixed mode fracture in unidirectional fiber reinforced composites

    NASA Astrophysics Data System (ADS)

    Gong, Kezhuang; Li, Zheng; Fu, Bin

    2008-11-01

    Fiber reinforced composites are applied broadly in aeronautic and astronautic fields as a structural material. But the investigation in dynamic fracture behavior of fiber reinforced composite stands in the breach for scientists due to a large number of aircraft disasters. In this paper, the mixed mode fracture problems in fiber reinforced composites under impact are studied. First, based on the theory of the reflective dynamic caustic method for mixed mode fracture, corresponding experiments are carried out to study the dynamic fracture behaviors of unidirectional fiber reinforced composites under two kinds load conditions. By recording and analyzing the shadow spot patterns during the crack propagation process carefully, the dynamic fracture toughness and crack growth velocity of fiber reinforced composites are obtained. Via the observation of the crack growth routes and fracture sections, we further reveal the fracture mechanism of unidirectional fiber reinforced composites. It concludes that opening mode still is the easier fracture type for the pre-crack initiation in fiber reinforced composites, while the interface between fibers and matrix becomes the fatal vulnerability during the crack propagation.

  3. A unified potential-based cohesive model of mixed-mode fracture

    NASA Astrophysics Data System (ADS)

    Park, Kyoungsoo; Paulino, Glaucio H.; Roesler, Jeffery R.

    2009-06-01

    A generalized potential-based constitutive model for mixed-mode cohesive fracture is presented in conjunction with physical parameters such as fracture energy, cohesive strength and shape of cohesive interactions. It characterizes different fracture energies in each fracture mode, and can be applied to various material failure behavior (e.g. quasi-brittle). The unified potential leads to both intrinsic (with initial slope indicators to control elastic behavior) and extrinsic cohesive zone models. Path dependence of work-of-separation is investigated with respect to proportional and non-proportional paths—this investigation demonstrates consistency of the cohesive constitutive model. The potential-based model is verified by simulating a mixed-mode bending test. The actual potential is named PPR (Park-Paulino-Roesler), after the first initials of the authors' last names.

  4. Fracture toughness of the F-82H steel-effect of loading modes, hydrogen, and temperature

    NASA Astrophysics Data System (ADS)

    Li, H.-X.; Jones, R. H.; Hirth, J. P.; Gelles, D. S.

    1996-10-01

    The effects of loading mode, hydrogen, and temperature on fracture toughness and tearing modulus were examined for a ferritic/martensitic steel (F-82H). The introduction of a shear load component, mode III, significantly decreased the initiation and propagation resistance of cracks compared to the opening load, mode I, behavior. Mode I crack initiation and propagation exhibited the highest resistance. A minimum resistance occurred when the mode I and mode III loads were nearly equal. The presence of 4 wppm hydrogen decreased the cracking resistance compared to behavior without H regardless of the loading mode. The minimum mixed-mode fracture toughness with the presence of hydrogen was about 30% of the hydrogen-free mode I fracture toughness. The mixed-mode toughness exhibited a lesser sensitivity to temperature than the mode I toughness. The JIC value was 284 kJ/m 2 at room temperature, but only 60 kJ/m 2 at -55°C and 30 kJ/m 2 at -90°C. The ductile to brittle transition temperature (DBTT) was apparently higher than -55°C.

  5. Simplified data reduction methods for the ECT test for mode 3 interlaminar fracture toughness

    NASA Technical Reports Server (NTRS)

    Li, Jian; Obrien, T. Kevin

    1995-01-01

    Simplified expressions for the parameter controlling the load point compliance and strain energy release rate were obtained for the Edge Crack Torsion (ECT) specimen for mode 3 interlaminar fracture toughness. Data reduction methods for mode 3 toughness based on the present analysis are proposed. The effect of the transverse shear modulus, G(sub 23), on mode 3 interlaminar fracture toughness characterization was evaluated. Parameters influenced by the transverse shear modulus were identified. Analytical results indicate that a higher value of G(sub 23) results in a low load point compliance and lower mode 3 toughness estimation. The effect of G(sub 23) on the mode 3 toughness using the ECT specimen is negligible when an appropriate initial delamination length is chosen. A conservative estimation of mode 3 toughness can be obtained by assuming G(sub 23) = G(sub 12) for any initial delamination length.

  6. Vibrational modes of hydraulic fractures: Inference of fracture geometry from resonant frequencies and attenuation

    NASA Astrophysics Data System (ADS)

    Lipovsky, Bradley P.; Dunham, Eric M.

    2015-02-01

    Oscillatory seismic signals arising from resonant vibrations of hydraulic fractures are observed in many geologic systems, including volcanoes, glaciers and ice sheets, and hydrocarbon and geothermal reservoirs. To better quantify the physical dimensions of fluid-filled cracks and properties of the fluids within them, we study wave motion along a thin hydraulic fracture waveguide. We present a linearized analysis, valid at wavelengths greater than the fracture aperture, that accounts for quasi-static elastic deformation of the fracture walls, as well as fluid viscosity, inertia, and compressibility. In the long-wavelength limit, anomalously dispersed guided waves known as crack or Krauklis waves propagate with restoring force from fracture wall elasticity. At shorter wavelengths, the waves become sound waves within the fluid channel. Wave attenuation in our model is due to fluid viscosity, rather than seismic radiation from crack tips or fracture wall roughness. We characterize viscous damping at both low frequencies, where the flow is always fully developed, and at high frequencies, where the flow has a nearly constant velocity profile away from viscous boundary layers near the fracture walls. Most observable seismic signals from resonating fractures likely arise in the boundary layer crack wave limit, where fluid-solid coupling is pronounced and attenuation is minimal. We present a method to estimate the aperture and length of a resonating hydraulic fracture using both the seismically observed quality factor and characteristic frequency. Finally, we develop scaling relations between seismic moment and characteristic frequency that might be useful when interpreting the statistics of hydraulic fracture events.

  7. Mode I Fracture Toughness of Rock - Intrinsic Property or Pressure-Dependent?

    NASA Astrophysics Data System (ADS)

    Stoeckhert, F.; Brenne, S.; Molenda, M.; Alber, M.

    2016-12-01

    The mode I fracture toughness of rock is usually regarded as an intrinsic material parameter independent of pressure. However, most fracture toughness laboratory tests are conducted only at ambient pressure. To investigate fracture toughness of rock under elevated pressures, sleeve fracturing laboratory experiments were conducted with various rock types and a new numerical method was developed for the evaluation of these experiments. The sleeve fracturing experiments involve rock cores with central axial boreholes that are placed in a Hoek triaxial pressure cell to apply an isostatic confining pressure. A polymere tube is pressurized inside these hollow rock cylinders until they fail by tensile fracturing. Numerical simulations incorporating fracture mechanical models are used to obtain a relation between tensile fracture propagation and injection pressure. These simulations indicate that the magnitude of the injection pressure at specimen failure is only depending on the fracture toughness of the tested material, the specimen dimensions and the magnitude of external loading. The latter two are known parameters in the experiments. Thus, the fracture toughness can be calculated from the injection pressure recorded at specimen breakdown. All specimens had a borehole diameter to outer diameter ratio of about 1:10 with outer diameters of 40 and 62 mm. The length of the specimens was about two times the diameter. Maximum external loading was 7.5 MPa corresponding to maximum injection pressures at specimen breakdown of about 100 MPa. The sample set tested in this work includes Permian and Carboniferous sandstones, Jurassic limestones, Triassic marble, Permian volcanic rocks and Devonian slate from Central Europe. The fracture toughness values determined from the sleeve fracturing experiments without confinement using the new numerical method were found to be in good agreement with those from Chevron bend testing according to the ISRM suggested methods. At elevated

  8. Rogue Mode Shileding in NSLS-II Multipole Vacuum Chambers

    SciTech Connect

    Ferreira, M.; Blednykh, A.; Bacha, B.; Borrelli, A.; Hseuh, H.-C.; Kosciuk, B.; Krinsky, S.; Singh, O.; Vetter, K.

    2011-03-28

    Modes with transverse electric field (TE-modes) in the NSLS-II multipole vacuum chamber can be generated at frequencies above 450MHz due to its geometric dimensions. Since the NSLS-II BPM system monitors signals within 10 MHz band at RF frequency of 500 MHz, frequencies of higher-order modes (HOM) can be generated within the transmission band of the band pass filter. In order to avoid systematic errors in the NSLS-II BPM system, we introduced frequency shift of HOMs by using RF metal shielding located in the antechamber slot. We demonstrated numerical modeling and experimental studies of the spurious TE modes in the NSLS-II vacuum chambers with antechamber slot. Calculated frequencies of TE-modes in considered chambers with and without RF shielding were verified experimentally. Flexible BeCu RF shielding inside each chamber at proper location shifts frequencies of H{sub 10p}-modes above {approx}900MHz, except chambers S6 odd and even. These chambers need special attention because of synchrotron radiation from downstream magnets. S6 odd multipole vacuum chamber needs to be measured and the RF shielding length has to be optimized. RF shielding looks adequate for baseline design. Fifty percent of open space provides adequate pumping speed.

  9. Anomalous transport in disordered fracture networks: Spatial Markov model for dispersion with variable injection modes

    NASA Astrophysics Data System (ADS)

    Kang, Peter K.; Dentz, Marco; Le Borgne, Tanguy; Lee, Seunghak; Juanes, Ruben

    2017-08-01

    We investigate tracer transport on random discrete fracture networks that are characterized by the statistics of the fracture geometry and hydraulic conductivity. While it is well known that tracer transport through fractured media can be anomalous and particle injection modes can have major impact on dispersion, the incorporation of injection modes into effective transport modeling has remained an open issue. The fundamental reason behind this challenge is that-even if the Eulerian fluid velocity is steady-the Lagrangian velocity distribution experienced by tracer particles evolves with time from its initial distribution, which is dictated by the injection mode, to a stationary velocity distribution. We quantify this evolution by a Markov model for particle velocities that are equidistantly sampled along trajectories. This stochastic approach allows for the systematic incorporation of the initial velocity distribution and quantifies the interplay between velocity distribution and spatial and temporal correlation. The proposed spatial Markov model is characterized by the initial velocity distribution, which is determined by the particle injection mode, the stationary Lagrangian velocity distribution, which is derived from the Eulerian velocity distribution, and the spatial velocity correlation length, which is related to the characteristic fracture length. This effective model leads to a time-domain random walk for the evolution of particle positions and velocities, whose joint distribution follows a Boltzmann equation. Finally, we demonstrate that the proposed model can successfully predict anomalous transport through discrete fracture networks with different levels of heterogeneity and arbitrary tracer injection modes.

  10. Alternate Operating Modes For NDCX-II

    NASA Astrophysics Data System (ADS)

    Sharp, W. M.; Friedman, A.; Grote, D. P.; Cohen, R. H.; Lund, S. M.; Vay, J.-L.; Waldron, W. L.

    2012-10-01

    NDCX-II is a newly completed accelerator facility at LBNL, built to study ion-heated warm dense matter and aspects of ion-driven targets for inertial-fusion energy. The baseline design calls for using twelve induction cells to accelerate 40 nC of Li+ ions to 1.2 MeV. During commissioning, though, we plan to extend the source lifetime by extracting less total charge. For operational flexibility, the option of using a helium plasma source is also being investigated. Over time, we expect that NDCX-II will be upgraded to substantially higher energies, necessitating the use of heavier ions to keep a suitable deposition range in targets. Each of these options requires development of an alternate acceleration schedule and the associated transverse focusing. The schedules here are first worked out with a fast-running 1-D particle-in-cell code ASP, then 2-D and 3-D Warp simulations are used to verify the 1-D results and to design transverse focusing.

  11. Characterization of the Edge Crack Torsion (ECT) Test for Mode III Fracture Toughness Measurement of Laminated Composites

    NASA Technical Reports Server (NTRS)

    Ratcliffe, James G.

    2004-01-01

    The edge crack torsion (ECT) test is designed to initiate mode III delamination growth in composite laminates. The test has undergone several design changes during its development. The objective of this paper was to determine the suitability of the current ECT test design a mode III fracture test. To this end, ECT tests were conducted on specimens manufactured from IM7/8552 and S2/8552 tape laminates. Three-dimensional finite element analyses were performed. The analysis results were used to calculate the distribution of mode I, mode II, and mode III strain energy release rate along the delamination front. The results indicated that mode IIIdominated delamination growth would be initiated from the specimen center. However, in specimens of both material types, the measured values of GIIIc exhibited significant dependence on delamination length. Load-displacement response of the specimens exhibited significant deviation from linearity before specimen failure. X-radiographs of a sample of specimens revealed that damage was initiated in the specimens prior to failure. Further inspection of the failure surfaces is required to identify the damage and determine that mode III delamination is initiated in the specimens.

  12. Effect of initial delamination on Mode 1 and Mode 2 interlaminar fracture toughness and fatigue fracture threshold

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen Bostaph; Martin, Roderick H.

    1991-01-01

    Static and fatigue double-cantilever beam (DCB) and end-notch flexure (ENF) tests were conducted to determine the effect of the simulated initial delamination in interlaminar fracture toughness, G(sub c), and fatigue fracture threshold, G(sub th). Unidirectional, 24-ply specimens of S2/SP250 glass/epoxy were tested using Kapton inserts of four different thickness - 13, 25, 75, and 130 microns, at the midplane at one end, or with tension or shear precracks, to simulate an initial delamination. To determine G(sub c), the fatigue fracture threshold below which no delamination growth would occur in less than 1 x 10(exp 6) cycles, fatigue tests were conducted by cyclically loading specimens until delamination growth was detected. Consistent values of model 1 fracture toughness, G(sub Ic), were measured from DCB specimens with inserts of thickness 75 microns or thinner, or with shear precracks. The fatigue DCB tests gave similar values of G(sub Ith) for the 13, 25, and 75 microns specimens. Results for the shear precracked specimens were significantly lower that for specimens without precracks. Results for both the static and fatigue ENF tests showed that measured G(IIc) and G(IIth) values decreased with decreasing insert thickness, so that no limiting thickness could be determined. Results for specimens with inserts of 75 microns or thicker were significantly higher than the results for precracked specimens or specimens with 13 or 25 microns inserts.

  13. Fixation of unstable type II clavicle fractures with distal clavicle plate and suture button.

    PubMed

    Johnston, Peter S; Sears, Benjamin W; Lazarus, Mark R; Frieman, Barbara G

    2014-11-01

    This article reports on a technique to treat unstable type II distal clavicle fractures using fracture-specific plates and coracoclavicular augmentation with a suture button. Six patients with clinically unstable type II distal clavicle fractures underwent treatment using the above technique. All fractures demonstrated radiographic union at 9.6 (8.4-11.6) weeks with a mean follow-up of 15.6 (12.4-22.3) months. American Shoulder and Elbow Surgeons, Penn Shoulder Score, and Single Assessment Numeric Evaluation scores were 97.97 (98.33-100), 96.4 (91-99), and 95 (90-100), respectively. One patient required implant removal. Fracture-specific plating with suture-button augmentation for type II distal clavicle fractures provides reliable rates of union without absolute requirement for implant removal.

  14. Non-universal aperture-length scaling of opening mode fractures

    NASA Astrophysics Data System (ADS)

    Mayrhofer, Franziska; Schöpfer, Martin P. J.; Grasemann, Bernhard

    2014-05-01

    Opening-mode fractures, such as joints, veins and dykes, typically exhibit a power-law aperture-length scaling with a power-law exponent of about 0.5. The fracture aperture is hence proportional to the square root of fracture length, a relation which is in fact predicted by linear elastic fracture mechanics (LEFM) for an isolated Mode I fracture subjected to remote tension. The existence of such a 'universal scaling law' is however a highly debated topic. High quality outcrop data illustrate that fracture aperture-length scaling may be 'non-universal' and indicate that below a certain length-scale scaling is super-linear (power-law exponent > 1). We use a numerical model comprised of a square lattice of breakable elastic beams to investigate the aperture-length scaling that emerges in thin plates subjected to remote tension. Strength heterogeneity is introduced in the regular lattice by randomly assigning beam strengths from a Weibull probability distribution. The model fracture system evolution is characterised by two stages which are separated by the strain at which peak-stress occurs. During the pre-peak stress stage fracture aperture-length scaling is universal with a power-law exponent of about 0.5 as expected from LEFM. Shortly after the material has attained its maximum load bearing capacity, aperture-length scaling becomes non-universal, so that the average aperture-length relation plotted on a log-log graph exhibits a distinct kink. Fractures with a length less than this critical length scale exhibit super-linear aperture-length scaling, whereas fractures with a greater length exhibit sub-linear scaling. The models illustrate that the emergence of non-universal aperture-length scaling is a result of fracture clustering, which occurs after peak-stress in the form of a localised fracture zone. Given that fracture clustering is a common phenomenon in natural fracture systems, we argue that a universal scaling law may be the exception rather than the rule.

  15. Mode I and Mode III fractures in intermediate zone of full-thickness porcine temporomandibular joint discs.

    PubMed

    Beatty, Mark W; Hohl, Rebecca H; Nickel, Jeffrey C; Iwasaki, Laura R; Pidaparti, Ramana M

    2008-05-01

    The aim of this study was to assess the critical energy required to induce flaw propagation in the temporomandibular joint (TMJ) disc when tensile and shear stresses were applied. J-integrals were measured for Mode I and III fractures because excessive tensile and shear stresses promote disc failure. Single edge notch (Mode I) and trouser tear (Mode III) specimens were constructed with flaws oriented parallel to the predominant anteroposteriorly oriented collagen fibers of the TMJ disc. Disks with and without an impulsive pre-load of 3 N s were studied to compare impact-damaged and healthy tissues. Results demonstrated that impulsive loading stiffened the tissues and significantly increased the Mode I fracture energy (J (IC)) but not Mode III (J (IIIC)) (p < or = 0.05). J (IC) and J (IIIC) values were similar for undamaged tissues, but J (IC) values were 2.3 times higher for impulsively loaded tissues (p < or = 0.05). This suggests that when flaws are introduced through impact, the TMJ disc responds by requiring more energy for tensile flaw extension. This research is a first step towards characterizing the mechanical microenvironment that initiates joint disease. This characterization is essential for successful integration of engineered replacement tissues for damaged TMJs.

  16. Fracture mode control: a bio-inspired strategy to combat catastrophic damage

    PubMed Central

    Yao, Haimin; Xie, Zhaoqian; He, Chong; Dao, Ming

    2015-01-01

    The excellent mechanical properties of natural biomaterials have attracted intense attention from researchers with focus on the strengthening and toughening mechanisms. Nevertheless, no material is unconquerable under sufficiently high load. If fracture is unavoidable, constraining the damage scope turns to be a practical way to preserve the integrity of the whole structure. Recent studies on biomaterials have revealed that many structural biomaterials tend to be fractured, under sufficiently high indentation load, through ring cracking which is more localized and hence less destructive compared to the radial one. Inspired by this observation, here we explore the factors affecting the fracture mode of structural biomaterials idealized as laminated materials. Our results suggest that fracture mode of laminated materials depends on the coating/substrate modulus mismatch and the indenter size. A map of fracture mode is developed, showing a critical modulus mismatch (CMM), below which ring cracking dominates irrespective of the indenter size. Many structural biomaterials in nature are found to have modulus mismatch close to the CMM. Our results not only shed light on the mechanics of inclination to ring cracking exhibited by structural biomaterials but are of great value to the design of laminated structures with better persistence of structural integrity. PMID:25619564

  17. FEMORAL NECK FRACTURES GARDEN I AND II: EVALUATION OF THE DEVIATION IN LATERAL VIEW.

    PubMed

    Leonhardt, Natália Zalc; Melo, Lucas da Ponte; Nordon, David Gonçalves; Silva, Fernando Brandão de Andrade E; Kojima, Kodi Edson; Silva, Jorge Santos

    2017-01-01

    To evaluate the rate of deviation in the lateral radiographic incidence in patients with femoral neck fracture classified as non-diverted in the anteroposterior view (Garden I and II). Nineteen selected patients with femoral neck fractures classified as Garden I and II were retrospectively evaluated, estimating the degree of deviation in the lateral view. Fifteen cases (79%) presented deviations in lateral view, with a mean of 18.6 degrees (±15.5). Most fractures of the femoral neck classified as Garden I and II present some degree of posterior deviation in the X-ray lateral view. Level of Evidence III, Retrospective Comparative Study.

  18. Influence of surface finishing on fracture load and failure mode of glass ceramic crowns.

    PubMed

    Mores, Rafael Tagliari; Borba, Márcia; Corazza, Pedro Henrique; Della Bona, Álvaro; Benetti, Paula

    2017-03-23

    Ceramic restorations often require adjustments using diamond rotary instruments, which damage the glazed surface. The effect of these adjustments on the fracture behavior of these restorations is unclear. The purpose of this in vitro study was to evaluate the influence of induced surface defects on the fracture load and mode of failure of lithium disilicate-based (LDS) glass ceramic restorations. Premolar crowns were obtained from LDS computer-aided design and computer-aided manufacturing blocks (n=60) and glazed. The crowns were bonded to dentin analog dies and divided into 5 groups (n=12), as follows: glaze; abrasion (diamond rotary instrument 2135); abrasion and reglaze; abrasion and polishing (diamond rotary instrument 2135F, 2135 FF, and polishing devices); and polishing. The topography of the crowns was examined by scanning electron microscopy, and roughness was measured. A compressive load (0.5 mm/min) was applied by a piston to the center of the lingual cusp until fracture. The fracture load was recorded and data were statistically analyzed by ANOVA and the Tukey HSD test (α=.05). Fractured crowns were examined to determine the fracture origin. Polishing and/or reglazing resulted in lower roughness than for the abraded group (P<.05), which did not affect the fracture loads (P=.696). Catastrophic fracture with origin at the intaglio surface was the mode of failure for all the crowns. The experiment design successfully submitted the crowns to a clinical stress state, resulting in a clinically relevant failure. Reglazing or polishing were effective in reducing surface defects. Surface treatments had no effect on the immediate catastrophic failure of LDS crowns. Copyright © 2017 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  19. Prediction of fracture risk. II: Other risk factors.

    PubMed

    Ross, P D

    1996-12-01

    Many osteoporotic fractures are probably preventable-by definition, prevention requires identification of those at risk prior to fracture. There is a continuum in fracture risk and a very wide range in risk among individuals. Bone density, previous fractures, and the frequency and types of falls are important risk factors for fractures. There are also many other risk factors for bone loss, falls, and fractures. People with multiple risk factors are at greater risk than those with either a single risk factor or none. Identification of risk factors can help when planning interventions. For example, dietary deficiencies are amenable to dietary modification or supplementation; however, the effects of many risk factors have not been quantified separately, making it difficult to determine the importance. In addition, it is not possible to accurately predict current bone density and fracture risk from risk factors for bone loss; bone density should always be measured directly.

  20. Thermoelastic stress analysis techniques for mixed mode fracture and stochastic fatigue of composite materials

    NASA Astrophysics Data System (ADS)

    Wei, Bo-Siou

    This study develops new quantitative thermoelastic stress analysis (TSA) techniques for fracture and fatigue damage analysis of composite materials. The first part deals with the thermo-mechanical derivation of two quantitative TSA techniques applied to orthotropic composites with and without a transversely-isotropic surface coating layer. The new TSA test procedures are derived in order to relate the thermal infrared (IR) images with the sum of in-plane strains multiplied by two newly defined material constants that can be experimentally pre-calibrated. Experiments are performed to verify the TSA methods with finite element (FE) numerical results along with available anisotropic elasticity solution. The second part of this study applies the quantitative TSA techniques together with the Lekhnitskii's general anisotropic elasticity solution to calculate mixed-mode stress intensity factors (SIFs) in cracked composite materials. The cracked composite coupons are subjected to off-axis loadings with respect to four different material angles in order to generate mixed-mode SIFs. A least-squares method is used to correlate the sum of in-plane strains from the elasticity solution with the measured TSA test results. The mode-I and mode-II SIFs are determined from eccentrically loaded single-edge-notch tension (ESE(T)) composite specimens. The FE models and virtual crack closure technique (VCCT) are utilized for comparisons. In the third part, a new stochastic model is proposed to generate S-N curves accounting for the variability of the fatigue process. This cumulative damage Markov chain model (MCM) requires a limited number of fatigue tests for calibrating the probability transition matrix (PTM) in the Markov chain model and mean fatigue cycles to failure from experiments. In order to construct the MCM stochastic S-N curve, an iterative procedure is required to predict the mean cycles to failure. Fatigue tests are conducted in this study to demonstrate the MCM method

  1. Characterization of the Edge Crack Torsion (ECT) Test for Mode III Fracture Toughness Measurement of Laminated Composites

    NASA Technical Reports Server (NTRS)

    Ratcliffe, James G.

    2004-01-01

    The edge crack torsion (ECT) test is designed to initiate mode III delamination growth in composite laminates. An ECT specimen is a rectangular laminate, containing an edge delamination at the laminate mid-plane. Torsion load is applied to the specimens, resulting in relative transverse shear sliding of the delaminated faces. The test data reduction schemes are intended to yield initiation values of critical mode III strain energy release rate, G(sub IIIc), that are constant with delamination length. The test has undergone several design changes during its development. The objective of this paper was to determine the suitability of the current ECT test design as a mode III fracture test. To this end, ECT tests were conducted on specimens manufactured from IM7/8552 and specimens made from S2/8552 tape laminates. Several specimens, each with different delamination lengths are tested. Detailed, three-dimensional finite element analyses of the specimens were performed. The analysis results were used to calculate the distribution of mode I, mode II, and mode III strain energy release rate along the delamination front. The results indicated that mode III-dominated delamination growth would be initiated from the specimen center. However, in specimens of both material types, the measured values of G(sub IIIc) exhibited significant dependence on delamination length. Furthermore, there was a large amount of scatter in the data. Load-displacement response of the specimens exhibited significant deviation from linearity before specimen failure. X-radiographs of a sample of specimens revealed that damage was initiated in the specimens prior to failure. Further inspection of the failure surfaces is required to identify the damage and determine that mode III delamination is initiated in the specimens.

  2. Matrix resin effects in composite delamination - Mode I fracture aspects

    NASA Technical Reports Server (NTRS)

    Hunston, Donald L.; Moulton, Richard J.; Johnston, Norman J.; Bascom, Willard D.

    1987-01-01

    A number of thermoset, toughened thermoset, and thermoplastic resin matrix systems were characterized for Mode I critical strain energy release rates, and their composites were tested for interlaminar critical strain energy release rates using the double cantilever beam method. A clear correlation is found between the two sets of data. With brittle resins, the interlaminar critical strain energy release rates are somewhat larger than the neat resin values due to a full transfer of the neat resin toughness to the composite and toughening mechanisms associated with crack growth. With tougher matrices, the higher critical strain energy release rates are only partially transferred to the composites, presumably because the fibers restrict the crack-tip deformation zones.

  3. NSLS-II BPM System Protection from Rogue Mode Coupling

    SciTech Connect

    Blednykh, A.; Bach, B.; Borrelli, A.; Ferreira, M.; Hseuh, H.-C.; Hetzel, C.; Kosciuk, B.; Krinsky, S.; Singh, O.; Vetter, K.

    2011-03-28

    Rogue mode RF shielding has been successfully designed and implemented into the production multipole vacuum chambers. In order to avoid systematic errors in the NSLS-II BPM system we introduced frequency shift of HOM's by using RF metal shielding located in the antechamber slot of each multipole vacuum chamber. To satisfy the pumping requirement the face of the shielding has been perforated with roughly 50 percent transparency. It stays clear of synchrotron radiation in each chamber.

  4. Fracture mechanics analyses of ceramic/veneer interface under mixed-mode loading.

    PubMed

    Wang, Gaoqi; Zhang, Song; Bian, Cuirong; Kong, Hui

    2014-11-01

    Few studies have focused on the interface fracture performance of zirconia/veneer bilayered structure, which plays an important role in dental all-ceramic restorations. The purpose of this study was to evaluate the fracture mechanics performance of zirconia/veneer interface in a wide range of mode-mixities (at phase angles ranging from 0° to 90°), and to examine the effect of mechanical properties of the materials and the interface on the fracture initiation and crack path of an interfacial crack. A modified sandwich test configuration with an oblique interfacial crack was proposed and calibrated to choose the appropriate geometry dimensions by means of finite element analysis. The specimens with different interface inclination angles were tested to failure under three-point bending configuration. Interface fracture parameters were obtained with finite element analyses. Based on the interfacial fracture mechanics, three fracture criteria for crack kinking were used to predict crack initiation and propagation. In addition, the effects of residual stresses due to coefficient of thermal expansion mismatch between zirconia and veneer on the crack behavior were evaluated. The crack initiation and propagation were well predicted by the three fracture criteria. For specimens at phase angle of 0, the cracks propagated in the interface; whereas for all the other specimens the cracks kinked into the veneer. Compressive residual stresses in the veneer can improve the toughness of the interface structure. The results suggest that, in zirconia/veneer bilayered structure the veneer is weaker than the interface, which can be used to explain the clinical phenomenon that veneer chipping rate is larger than interface delamination rate. Consequently, a veneer material with larger fracture toughness is needed to decrease the failure rate of all-ceramic restorations. And the coefficient of thermal expansion mismatch of the substrates can be larger to produce larger compressive

  5. Mode of action of lipid II-targeting lantibiotics.

    PubMed

    Bauer, R; Dicks, L M T

    2005-05-25

    The antimicrobial action of bacteriocins from Gram-positive bacteria is based on interaction with the cytoplasmic membrane of sensitive bacteria. Models based on studies with artificial membrane systems propose that nisin forms wedge-like poration complexes in the membrane by electrostatic interaction between the positively charged C terminus of the peptide and anionic membrane phospholipids. Nisin can also permeabilise membranes via a targeted mechanism by using lipid II, the bactoprenol-bound precursor of the bacterial cell wall, as a docking molecule. Another consequence of binding with lipid II is the inhibition of peptidoglycan biosynthesis. Mersacidine and actagardine also form a complex with lipid II, but binding only blocks the incorporation of lipid II into peptidoglycan, resulting in slow cell lysis rather than pore formation. Both peptides share a conserved sequence motif with plantaricin C and pediocin PD-1, which is most probably involved in the binding of these bacteriocins to lipid II. Although pediocin PD-1 and plantaricin C may inhibit peptidoglycan biosynthesis, pore formation is rather due to electrostatic interaction between the positively charged unbridged N-terminus and anionic phospholipids in the cytoplasmic membrane of sensitive cells. In the light of increased antibiotic resistance, this review focuses on the mode of action of lantibiotics that involve lipid II, possible candidates for the development of new-generation novel antibiotic drugs.

  6. Extensive Type II Muscle Fiber Atrophy in Elderly Female Hip Fracture Patients.

    PubMed

    Kramer, Irene Fleur; Snijders, Tim; Smeets, Joey S J; Leenders, Marika; van Kranenburg, Janneau; den Hoed, Marcel; Verdijk, Lex B; Poeze, Martijn; van Loon, Luc J C

    2017-10-01

    Sarcopenia, or the loss of muscle mass and strength, is known to increase the risk for falls and (hip) fractures in older people. The objective of this study was to assess the skeletal muscle fiber characteristics in elderly female hip fracture patients. Percutaneous needle biopsies were collected from the vastus lateralis muscle in 15 healthy young women (20 ± 0.4 years), 15 healthy elderly women (79 ± 1.7 years), and 15 elderly women with a fall-related hip fracture (82 ± 1.5 years). Immunohistochemical analyses were performed to assess Type I and Type II muscle fiber size, and myonuclear and satellite cell content. Type II muscle fiber size was significantly different between all groups (p < .05), with smaller Type II muscle fibers in the hip fracture patients (2,609 ± 185 µm2) compared with healthy elderly group (3,723 ± 322 µm2) and the largest Type II muscle fibers in the healthy young group (4,755 ± 335 µm2). Furthermore, Type I muscle fiber size was significantly lower in the hip fracture patients (4,684 ± 211 µm2) compared with the healthy elderly group (5,842 ± 316 µm2, p = .02). The number of myonuclei per Type II muscle fiber was significantly lower in the healthy elderly and hip fracture group compared with the healthy young group (p = .011 and p = .002, respectively). Muscle fiber satellite cell content did not differ between groups. Elderly female hip fracture patients show extensive Type II muscle fiber atrophy when compared with healthy young or age-matched healthy elderly controls. Type II muscle fiber atrophy is an important hallmark of sarcopenia and may predispose to falls and (hip) fractures in the older population.

  7. Management of Type II Odontoid Fracture for Osteoporotic Bone Structure: Preliminary Report.

    PubMed

    Cosar, Murat; Ozer, A Fahir; Alkan, Bahadır; Guven, Mustafa; Akman, Tarık; Aras, Adem Bozkurt; Ceylan, Davut; Tokmak, Mehmet

    2015-01-01

    Anterior transodontoid screw fixation technique is generally chosen for the management of type II odontoid fractures. The nonunion of type II odontoid fractures is still a major problem especially in elderly and osteoporotic patients. Eleven osteoporotic type II odontoid fracured patients were presented in this article. We have divided 11 patients in two groups as classical and Ozer's technique. We have also compared (radiologically and clinically) the classical anterior transodontoid screw fixation (group II: 6 cases) and Ozer's transodontoid screw fixation technique (group I: 5 cases) retrospectively. There was no difference regaring the clinical features of the groups. However, the radiological results showed 100% fusion for Ozer's screw fixation technique and 83% fusion for the classical screw fixation technique. In conclusion, we suggest that Ozer's technique may help to increase the fusion capacity for osteoporotic type II odontoid fractures.

  8. On the mode I fracture analysis of cracked Brazilian disc using a digital image correlation method

    NASA Astrophysics Data System (ADS)

    Abshirini, Mohammad; Soltani, Nasser; Marashizadeh, Parisa

    2016-03-01

    Mode I of fracture of centrally cracked Brazilian disc was investigated experimentally using a digital image correlation (DIC) method. Experiments were performed on PMMA polymers subjected to diametric-compression load. The displacement fields were determined by a correlation between the reference and the deformed images captured before and during loading. The stress intensity factors were calculated by displacement fields using William's equation and the least square algorithm. The parameters involved in the accuracy of SIF calculation such as number of terms in William's equation and the region of analysis around the crack were discussed. The DIC results were compared with the numerical results available in literature and a very good agreement between them was observed. By extending the tests up to the critical state, mode I fracture toughness was determined by analyzing the image of specimen captured at the moment before fracture. The results showed that the digital image correlation was a reliable technique for the calculation of the fracture toughness of brittle materials.

  9. Evaluation of the Edge Crack Torsion (ECT) Test for Mode 3 Interlaminar Fracture Toughness of Laminated Composites

    NASA Technical Reports Server (NTRS)

    Li, Jian; Lee, Edward W.; OBrien, T. Kevin; Lee, Shaw Ming

    1996-01-01

    An analytical and experimental investigation was carried out on G40-800/R6376 graphite epoxy laminates to evaluate the Edge Crack Torsion (ECT) test as a candidate for a standard Mode 3 interlaminar fracture toughness test for laminated composites. The ECT test consists of a (90/(+/- 45)(sub 3)/(+/- 45)(sub 3)/90))(sub s) laminate with a delamination introduced by a non-adhesive film at the mid-plane along one edge and loaded in a special fixture to create torsion along the length of the laminate. Dye penetrate enhanced X-radiograph of failed specimens revealed that the delamination initiated at the middle of the specimen length and propagated in a self similar manner along the laminate mid-plane. A three-dimensional finite element analysis was performed that indicated that a pure Mode 3 delamination exists at the middle of specimen length away from both ends. At the ends near the loading point a small Mode 2 component exists. However, the magnitude of this Mode 2 strain energy release rate at the loading point is small compared to the magnitude of Mode 3 component in the mid-section of the specimen. Hence, the ECT test yielded the desired Mode 3 delamination. The Mode 3 fracture toughness was obtained from a compliance calibration method and was in good agreement with the finite element results. Mode 2 End-Notched Flexure (ENF) tests and Mode 1 Double Cantilever Beam (DCB) tests were also performed for the same composite material. The Mode 1 fracture toughness was much smaller than both the Mode 2 and Mode 3 fracture toughness. The Mode 2 fracture toughness was found to be 75% of the Mode 3 fracture toughness.

  10. A Practical Test Method for Mode I Fracture Toughness of Adhesive Joints with Dissimilar Substrates

    SciTech Connect

    Boeman, R.G.; Erdman, D.L.; Klett, L.B.; Lomax, R.D.

    1999-09-27

    A practical test method for determining the mode I fracture toughness of adhesive joints with dissimilar substrates will be discussed. The test method is based on the familiar Double Cantilever Beam (DCB) specimen geometry, but overcomes limitations in existing techniques that preclude their use when testing joints with dissimilar substrates. The test method is applicable to adhesive joints where the two bonded substrates have different flexural rigidities due to geometric and/or material considerations. Two specific features discussed are the use of backing beams to prevent substrate damage and a compliance matching scheme to achieve symmetric loading conditions. The procedure is demonstrated on a modified DCB specimen comprised of SRIM composite and thin-section, e-coat steel substrates bonded with an epoxy adhesive. Results indicate that the test method provides a practical means of characterizing the mode I fracture toughness of joints with dissimilar substrates.

  11. The size effect of crystalline inclusions on the fracture modes in glass-ceramic materials.

    PubMed

    Charitidis, C A; Karakasidis, T E; Kavouras, P; Karakostas, Th

    2007-07-04

    The main parameters influencing the mechanical performance of glass-ceramic materials are the shape and mean size of the ceramic phase, i.e. the crystalline inclusions. The aim of the present work is twofold: first, to study the effect of the above parameters on the modes of fracture in two kinds of glass-ceramic materials by the use of the static microindentation technique; second, to interpret the experimental results by the application of a simple physical model. It was found that reduction in the size of granularly shaped crystallite inclusions or reduction of the width of needle-like crystalline inclusions results in an increase of the extent of crack propagation, while the fracture mode shifts from intergranular to transgranular. These observations were successfully interpreted in terms of energetic arguments related to the size of the crystalline inclusions with respect to the width of a disordered zone acting as an interface between them and the amorphous matrix.

  12. A Salter Harris type II fracture of the distal ulna in a fourteen month female neutered Great Dane.

    PubMed

    Langley-Hobbs, S J

    2005-01-01

    A displaced Salter Harris type II fracture of the distal ulna and a minimally displaced Salter Harris type II fracture of the distal radius were diagnosed in a fourteen month female neutered Great Dane dog. Fracture reduction was challenging but treatment was successful. Aetiology of the unusual fracture is discussed. Long bone physes may close later in giant breeds, early neutering can cause a further delay.

  13. Improvement of Mode I Interlaminar Fracture Toughness of Stitched Glass/Epoxy Composites

    NASA Astrophysics Data System (ADS)

    Göktaş, D.; Kennon, W. R.; Potluri, P.

    2016-11-01

    This study examines the improvement of Interlaminar Fracture Toughness (IFT) of multilayered 3D glass/epoxy textile composites when through thickness reinforcement is introduced. Three stitching techniques have been examined: Modified Lockstitch (ISO-301), Single-yarn Orthogonal-stitch (ISO-205) and Double-yarn Orthogonal-stitch (ISO-205). It was found that the use of class ISO-205 manual-type stitched reinforcement significantly enhanced the Mode I-IFT, GIC measured using a Double Cantilever Beam technique. Furthermore, in every case, the use of class ISO-205 stitching and high stitch densities offer a significant improvement of 74.5 % on Mode I-IFT against interlaminar delamination.

  14. Improvement of Mode I Interlaminar Fracture Toughness of Stitched Glass/Epoxy Composites

    NASA Astrophysics Data System (ADS)

    Göktaş, D.; Kennon, W. R.; Potluri, P.

    2017-04-01

    This study examines the improvement of Interlaminar Fracture Toughness (IFT) of multilayered 3D glass/epoxy textile composites when through thickness reinforcement is introduced. Three stitching techniques have been examined: Modified Lockstitch (ISO-301), Single-yarn Orthogonal-stitch (ISO-205) and Double-yarn Orthogonal-stitch (ISO-205). It was found that the use of class ISO-205 manual-type stitched reinforcement significantly enhanced the Mode I-IFT, GIC measured using a Double Cantilever Beam technique. Furthermore, in every case, the use of class ISO-205 stitching and high stitch densities offer a significant improvement of 74.5 % on Mode I-IFT against interlaminar delamination.

  15. Opening-mode fracture patterns and their shearing: an assessment of the state of knowledge and prediction capability

    NASA Astrophysics Data System (ADS)

    Aydin, A.

    2012-12-01

    Two common opening-mode fracture patterns include those comprising one set (Figure 1a) and two orthogonal sets (Figure 1b). It is also possible to have three mutually orthogonal opening-mode fractures, but this situation is rare. The prediction of the orientation and dimensional attributes of these simple systems requires a basic knowledge of the medium in which they occur (lithology, bedding, shape and distribution of initial flaws, elastic modulus, subcritical index and other environmental conditions) and the driving stresses or strains responsible for their formation. The issues related to fracture patterns become more complex when initial patterns of predominantly opening-mode fractures were later subjected to shearing. Shearing of a single set of opening-mode fractures (Figure 1c) produces splay fractures whose orientations and lengths show a significant variation. Given the attributes of the initial set and the orientation and relative magnitudes of the new stress components responsible for the shearing, and the mechanical behavoir of the fractures, it is possible to constrain the splay geometry. It turns out that the natural progression of the system is such that the new splays are sheared in a sequential manner to form remarkably consistent fracture domain patterns, which may be called "apparent conjugate." Well-documented case studies, some of which will be used in this presentation as templates, indicate that these fracture domain patterns can be visualized, but mapping their variation (local orientation and geometry of the individual components) is not a trivial task and may require knowledge both of some of the parameters referred to above and of the stress distribution about larger regional structures such as folds and faults. The shearing of orthogonal arrays of opening-mode fractures produces splay fractures diagonal to both orthogonal sets (Figure 1d). New through-going shear fractures, again in apparent conjugate patterns, utilize both members of

  16. Mode and mechanism of fatigue fracture of a pearlitic steel in hydrogen

    NASA Technical Reports Server (NTRS)

    Lo, S. H.; Johnson, H. H.

    1986-01-01

    It is presently suggested that there are two mechanisms that cause fatigue crack initiation in a specimen subjected to a hydrogen environment: either a critical concentration of hydrogen is attained within the specimen, causing Mode I crack initiation, or the presence of some hydrogen (below critical concentration) promotes the early onset of plastic instability at the sites of maximum strain. It is further suggested that in the static loading condition, a high hydrogen concentration may be attained by way of mechanical factors, causing Mode I crack initiation. While cyclic fatigue specimens exhibited Mode II crack initiation in air, only Mode I crack initiation emerged in a hydrogen environment.

  17. Dependence of mode I and mixed mode I/III fracture toughness on temperature for a ferritic/martensitic stainless steel

    SciTech Connect

    Li, H.; Jones, R.H.; Gelles, D.S.

    1995-04-01

    The objective is to investigate the dependence of mode I and mixed mode I/III fracture toughness on temperature in the range of {minus}95{degrees}C to 25{degrees}C for a low activation ferritic/martensitic stainless steel (F82-H). Mode I and mixed Mode I/III fracture toughnesses were investigated in the range of {minus}95 to 25{degree}C for a F82-H steel heat-treated in the following way; 1000{degree}C/20 h/air-cooled (AC), 1100{degree}C/7 min/AC, and 700{degree}C/2 h/AC. The results indicate that crack tip plasticity was increased by mixed mode loading, and suggest that at low temperature, mode I fracture toughness is the critical design parameter, but at temperatures above room temperature, expecially concerning fatigure and creep-fatigue crack growth rate, a mixed mode loading may be more harmful than a mode I loading for this steel because a mixed mode loading results in lower fracture toughness and higher crack tip plasticity (or dislocation activity).

  18. Analysis of the Numerical and Geometrical Parameters Influencing the Simulation of Mode I and Mode II Delamination Growth in Unidirectional and Textile Composites

    NASA Astrophysics Data System (ADS)

    Jacques, S.; De Baere, I.; Van Paepegem, W.

    2015-12-01

    The reliability of composite structures depends, among other damage mechanisms, on their ability to withstand delaminations. In order to have a better understanding of the cohesive zone method technique for delamination simulations, a complete analysis of the multiple parameters influencing the results is necessary. In this paper the work is concentrated on the cohesive zone method using cohesive elements. First a summary of the theory of the cohesive zone method is given. A numerical investigation on the multiple parameters influencing the numerical simulation of the mode I and mode II delamination tests has been performed. The parameters such as the stabilization method, the output frequency, the friction and the computational efficiency have been taken into account. The results will be compared to an analytical solution obtained by linear elastic fracture mechanics. Additionally the numerical simulation results will be compared to the experimental results of a glass-fibre reinforced composite material for the mode I Double Cantilever Beam (DCB) and to a carbon fibre 5-harness satin weave reinforced polyphenylene sulphide composite for the mode I DCB and mode II End Notched Flexure (ENF).

  19. Mixed-mode I/III fracture toughness of a ferritic/martensitic stainless steel

    SciTech Connect

    Li, Huaxin; Jones, R.H.; Gelles, D.S.; Hirth, J.P.

    1993-10-01

    The critical J-integrals of mode I (J{sub IC}), mixed-mode I/III (J{sub MC}), and mode III (J{sub IIIC}) were examined for a ferritic stainless steel (F-82H) at ambient temperature. A determination of J{sub MC} was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 55 degrees from the load line. Results showed that J{sub MC} and tearing modulus (T{sub M}) values varied with the crack angles and were lower than their mode I and mode III counterparts. Both the minimum J{sub MC} and T{sub M} values occurred at a crack angle between 40 and 50 degrees, where the load ratio of {sigma}{sub i}/{sigma}{sub iii} was 1.2 to 0.84. The J{sub min} was 240 Kj/M{sup 2}, and ratios of J{sub IC}/J{sub min} and J{sub IIIC}/J{sub min} were 2.1 and 1.9, respectively. The morphology of fracture surfaces was consistent with the change of J{sub MC} and T{sub M} values. While the upper shelf-fracture toughness of F-82H depends on loading mode, the J{sub min} remains very high. Other important considerations include the effect of mixed-mode loading on the DBT temperature, and effects of hydrogen and irradiation on J{sub min}.

  20. Physeal fractures, part II: fate of interposed periosteum in a physeal fracture.

    PubMed

    Gruber, Helen E; Phieffer, Laura S; Wattenbarger, J Michael

    2002-01-01

    This study describes the histologic features of periosteum interposed into a physeal fracture of the rat proximal tibia. Periosteum was introduced into a physeal fracture in two groups of animals: those with an intact physis after fracture, and those with the medial half of the physis surgically ablated. Specimens of the proximal tibia underwent histologic analysis at 2, 4, 6, 10, and 21 days after fracture to determine the histologic features of interposed periosteum in a physeal fracture. In animals with an intact physis, interposed periosteum underwent one of two fates: it was degraded by giant cells in the fracture plane, which allowed cellular infiltration, or if the periosteum was closely surrounded by physeal cartilage, the physis grew around it and appeared to force it toward the metaphysis. In animals whose physis received surgical ablation, physeal bar formation was always present, with poor organization of the remaining lateral growth plate. Histologic evidence from this study also underscores the fact that physeal bar formation occurs from the migration of osteoblasts and osteoclasts along vertical septa.

  1. Kohn-Sham density functional theory prediction of fracture in silicon carbide under mixed mode loading

    NASA Astrophysics Data System (ADS)

    Leung, K. W. K.; Pan, Z. L.; Warner, D. H.

    2016-03-01

    The utility of silicon carbide (SiC) for high temperature structural application has been limited by its brittleness. To improve its ductility, it is paramount to develop a sound understanding of the mechanisms controlling crack propagation. In this manuscript, we present direct ab initio predictions of fracture in SiC under pure mode I and mixed mode loading, utilizing a Kohn-Sham Density Functional Theory (KSDFT) framework. Our results show that in both loading cases, cleavage occurs at a stress intensity factor (SIF) only slightly higher than the Griffith toughness, focusing on a (1 1 1) [1 \\bar{1} 0] crack in the 3C-SiC crystal structure. This lattice trapping effect is shown to decrease with mode mixity, due to the formation of a temporary surface bond that forms during decohesion under shear. Comparing the critical mode I SIF to the value obtained in experiments suggests that some plasticity may occur near a crack tip in SiC even at low temperatures. Ultimately, these findings provide a solid foundation upon which to study the influence of impurities on brittleness, and upon which to develop empirical potentials capable of realistically simulating fracture in SiC.

  2. Compartment syndrome with an isolated Salter Harris II fracture of the distal tibia.

    PubMed

    Cox, George; Thambapillay, Siva; Templeton, Peter A

    2008-02-01

    A 14-year-old boy sustained a Salter Harris II fracture to his right distal tibia after a fall from his skateboard. He rapidly went on to develop the signs and symptoms of compartment syndrome, and he underwent emergency fasciotomy. This resulted in relief of his symptoms. After this procedure, his fracture was fixed with a single anteroposterior screw. He made a full and uncomplicated recovery, with no clinical or radiological evidence of epiphyseal growth arrest.

  3. Teriparatide anabolic therapy as potential treatment of type II dens non-union fractures

    PubMed Central

    Pola, Enrico; Pambianco, Virginia; Colangelo, Debora; Formica, Virginia M; Autore, Giovanni; Nasto, Luigi A

    2017-01-01

    Odontoid fractures account for 5% to 15% of all cervical spine injuries and 1% to 2% of all spine fractures. Type II fractures are the most common fracture pattern in elderly patients. Treatment (rigid and non-rigid immobilization, anterior screw fixation of the odontoid and posterior C1-C2 fusion) remains controversial and represents a unique challenge for the treating surgeon. The aims of treatment in the elderly is to quickly restore pre-injury function while decreasing morbidity and mortality associated with inactivity, immobilization with rigid collar and prolonged hospitalization. Conservative treatment of type II odontoid fractures is associated with relatively high rates of non-union and in a few cases delayed instability. Options for treatment of symptomatic non-unions include surgical fixation or prolonged rigid immobilization. In this report we present the case of a 73-year-old woman with post-traumatic odontoid non-union successfully treated with Teriparatide systemic anabolic therapy. Complete fusion and resolution of the symptoms was achieved 12 wk after the onset of the treatment. Several animal and clinical studies have confirmed the potential role of Teriparatide in enhancing fracture healing. Our case suggests that Teriparatide may have a role in improving fusion rates of C2 fractures in elderly patients. PMID:28144584

  4. Distal humeral Salter Harris (Type II) fracture repair by an ulnar osteotomy approach in a horse.

    PubMed

    Ahern, Benjamin J; Richardson, Dean W

    2010-08-01

    To report repair of a comminuted distal humeral type II Salter-Harris fracture using an ulnar osteotomy approach and locking compression plates (LCP). Case report. A 3-month-old Standardbred filly with a type II Salter-Harris fracture of the distal humerus. Radiographic and computed tomography examinations were performed to assist surgical planning. The distal humeral fracture was approached by an ulnar osteotomy and repaired using a 7-hole broad LCP and screws inserted in lag fashion. The osteotomy was subsequently repaired using a 7-hole narrow LCP. The distal humeral fracture was successfully approached and stabilized by an ulnar osteotomy approach. At 6-month follow-up, the filly was ambulating comfortably with a normal cosmetic appearance. An ulnar osteotomy approach was readily performed and allowed for repair of a type II Salter-Harris fracture of the distal humerus. The equine distal humerus can be accessed readily using an ulnar osteotomy approach. LCPs allow for repair of complicated fractures that have previously been associated with a grave prognosis.

  5. A tension-mode fracture model for bolted joints in laminated composites

    SciTech Connect

    Schulz, K.C.; Packman, P.F.; Eisenmann, J.R.

    1995-06-01

    A failure prediction model for bolted joints in generally orthotropic laminated composite plates that fail in the tension mode under bearing loading conditions has been developed. The plate is analyzed as a bulk orthotropic plate whose material properties are determined through the application of classical lamination theory to facilitate practical application of the model. Ply-by-ply laminated analysis is not required. Fracture mechanics concepts are applied to a pseudo-flaw which is related to the physical cracking of the laminate at the joint. The maximum circumferential stress concept is extended to orthotropic materials where both the fracture toughness and stress intensity vary with orientation. Excellent correlation between experimental tests conducted on single-bolt joints for two laminate layups and analytical prediction was found.

  6. Factors influencing the Mode I interlaminar fracture toughness of a rubber toughened thermoplastic matrix composite

    NASA Technical Reports Server (NTRS)

    Parker, D. S.; Yee, A. F.

    1989-01-01

    The use of a rubber modified thermoplastic resin has been investigated as a method to improve the Mode I interlaminar fracture toughness of a unidirectional continuous carbon fiber composite. Test results show that the improvement in the fracture toughness is less than expected due to rubber particle agglomeration, solvent and molding induced crystallization of the matrix and poor fiber/matrix adhesion. The plastic zone in composites utilizing tough matrices can extend well beyond a single interfibrillar spacing. However, the development of the plastic zone is limited due to the failure of the fiber/matrix interface. In order to fully evaluate the potential of tough composites using toughened matrices, any improvement made in the matrix toughness must be coupled with improvements in the fiber/matrix adhesion.

  7. Fracture modes under uniaxial compression in hydroxyapatite scaffolds fabricated by robocasting.

    PubMed

    Miranda, Pedro; Pajares, Antonia; Saiz, Eduardo; Tomsia, Antoni P; Guiberteau, Fernando

    2007-12-01

    The fracture modes of hydroxyapatite (HA) scaffolds fabricated by direct-write assembly (robocasting) are analyzed in this work. Concentrated HA inks with suitable viscoelastic properties were developed to enable the fabrication of prototype structures consisting of a 3-D square mesh of interpenetrating rods. The fracture behavior of these model scaffolds under compressive stresses is determined from in situ uniaxial tests performed in two different directions: perpendicular to the rods and along one of the rod directions. The results are analyzed in terms of the stress field calculated by finite element modeling (FEM). This analysis provides valuable insight into the mechanical behavior of scaffolds for bone tissue engineering applications fabricated by robocasting. Copyright 2007 Wiley Periodicals, Inc.

  8. Self-Replicating Cracks: A Collaborative Fracture Mode in Thin Films

    NASA Astrophysics Data System (ADS)

    Marthelot, Joël; Roman, Benoît; Bico, José; Teisseire, Jérémie; Dalmas, Davy; Melo, Francisco

    2014-08-01

    Straight cracks are observed in thin coatings under residual tensile stress, resulting into the classical network pattern observed in china crockery, old paintings, or dry mud. Here, we present a novel fracture mechanism where delamination and propagation occur simultaneously, leading to the spontaneous self-replication of an initial template. Surprisingly, this mechanism is active below the standard critical tensile load for channel cracks and selects a robust interaction length scale on the order of 30 times the film thickness. Depending on triggering mechanisms, crescent alleys, spirals, or long bands are generated over a wide range of experimental parameters. We describe with a simple physical model, the selection of the fracture path and provide a configuration diagram displaying the different failure modes.

  9. Propagating mode-I fracture in amorphous materials using the continuous random network model

    NASA Astrophysics Data System (ADS)

    Heizler, Shay I.; Kessler, David A.; Levine, Herbert

    2011-08-01

    We study propagating mode-I fracture in two-dimensional amorphous materials using atomistic simulations. We use the continuous random network model of an amorphous material, creating samples using a two-dimensional analog of the Wooten-Winer-Weaire Monte Carlo algorithm. For modeling fracture, molecular-dynamics simulations were run on the resulting samples. The results of our simulations reproduce the main experimental features. In addition to achieving a steady-state crack under a constant driving displacement (which has not yet been achieved by other atomistic models for amorphous materials), the runs show microbranching, which increases with driving, transitioning to macrobranching for the largest drivings. In addition to the qualitative visual similarity of the simulated cracks to experiment, the simulation also succeeds in reproducing qualitatively the experimentally observed oscillations of the crack velocity.

  10. Results of ASTM round robin testing for mode 1 interlaminar fracture toughness of composite materials

    NASA Technical Reports Server (NTRS)

    Obrien, T. Kevin; Martin, Roderick H.

    1992-01-01

    The results are summarized of several interlaboratory 'round robin' test programs for measuring the mode 1 interlaminar fracture toughness of advanced fiber reinforced composite materials. Double Cantilever Beam (DCB) tests were conducted by participants in ASTM committee D30 on High Modulus Fibers and their Composites and by representatives of the European Group on Fracture (EGF) and the Japanese Industrial Standards Group (JIS). DCB tests were performed on three AS4 carbon fiber reinforced composite materials: AS4/3501-6 with a brittle epoxy matrix; AS4/BP907 with a tough epoxy matrix; and AS4/PEEK with a tough thermoplastic matrix. Difficulties encountered in manufacturing panels, as well as conducting the tests are discussed. Critical issues that developed during the course of the testing are highlighted. Results of the round robin testing used to determine the precision of the ASTM DCB test standard are summarized.

  11. Imaging appearance of entrapped periosteum within a distal femoral Salter-Harris II fracture.

    PubMed

    Chen, Johnathan; Abel, Mark F; Fox, Michael G

    2015-10-01

    Salter Harris II fractures of the distal femur are associated with a high incidence of complications, especially premature physeal closure. Many risk factors for this high rate of premature physeal closure have been proposed. More recently, entrapment of periosteum within the physis has been suggested as an additional predisposing factor for premature physeal closure. The radiographic diagnosis of entrapped soft tissues, including periosteum, can be suggested in the setting of a Salter-Harris II fracture when the fracture does not reduce and physeal widening >3 mm remains. We report a patient who sustained a distal femoral Salter-Harris II fracture following a valgus injury. The patient had persistent distal medial physeal widening >5 mm following attempted reduction. A subsequent MRI revealed a torn periosteum entrapped within the distal femoral physis. Following removal of the periosteum, the patient developed a leg length discrepancy which required physiodesis of the contralateral distal femur. We present this case to raise awareness of the importance of having a high index of suspicion of periosteal entrapment in the setting of Salter-Harris II fractures since most consider entrapped periosteum an indication for surgery.

  12. [Surgical treatment for Mayo II B comminuted fracture of the olecranon].

    PubMed

    Wang, Min; Ping, Li-yuan; Wang, Wei; Yang, Bao-gen

    2016-02-01

    To study clinical effects of surgery for the treatment of Mayo II B comminuted fracture in ulna olecranon. From May 2008 to March 2015, a total of 37 patients with Mayo II B comminuted fracture in ulua olecranon were treated, including 20 males and 17 females, ranging in age from 40 to 65 years old ,with an average of 53 years old. All the patients were treated with open reduction and internal fixation within 4 to 7 days after injuries. All the patients had pain and functional disorder uf elbow joint. The X-ray and CT examination showed ulna olecranon comminuted fracture of Mayo II B. Postoperative complications were observed ,and Broberg-Morrey criteria was used tu evaluate therapeutic effects. All the patients were followed up ,and the duraiton ranged from 9 to 30 months ,with a mean of 15 months. Two patients had surface infection around incision ,and were healed by changing dressings. No other complications occurred such as needle slipping to stimulate skin ,screw loosening and wire broken. One patient had slight uneveness of joint surface without obvious functional disorder. According to Broberg-Morrey elbow fracture curative effect criteria, 11 paients got an excellent result, 24 good and 2 fair,and the total score was 87.0 ± 7.3. For the Mayo II B comminuted fracture in ulna olecranon, preoperative preparation, intraoperative restoring of the articular surface smooth and reasonable internal fixation, and postoperative rehabilitation actively, can obtain satisfactory clinical effects.

  13. Operative treatment of type II supracondylar humerus fractures: does time to surgery affect complications?

    PubMed

    Larson, A Noelle; Garg, Sumeet; Weller, Amanda; Fletcher, Nicholas D; Schiller, Jonathan R; Kwon, Michael; Browne, Richard; Copley, Lawson A; Ho, Christine A

    2014-06-01

    Because of the changing referral patterns, operative pediatric supracondylar humerus fractures are increasingly being treated at tertiary referral centers. To expedite patient flow, type II fractures are sometimes pinned in a delayed manner. We sought to determine if delay in surgical treatment of modified Gartland type II supracondylar humerus fractures would affect the rate of complications following closed reduction and percutaneous pinning. We performed a retrospective review of a consecutive series of 399 modified Gartland type II supracondylar fractures treated operatively at a tertiary referral center over 4 years. Mean patient age in the type II group was 5 years (range, 1 to 15 y). A total of 48% were pinned within 24 hours, 52% pinned >24 hours after the injury. No difference was in detected in rates of major complications between the early and delayed treatment group. Four percent of patients sustained a complication (16 patients). There were no compartment syndromes, vascular injuries, or permanent nerve injuries. Complications included nerve injury (3), physical therapy referral for stiffness (3), pin site infection (2 treated with oral antibiotics, 4 treated with debridement), refracture (2), and loss of fixation or broken hardware (2). Of the 3 patients who sustained nerve injuries, all underwent surgery within 24 hours of injury. One patient developed an ulnar motor and sensory nerve palsy after fixation with crossed K-wires. This resolved by 7 weeks postoperatively. Two patients presented with an anterior interosseous nerve palsy-1 resolved 1 week after surgery, the other by 8 weeks postoperatively. Delay in surgery did not result in an increased rate of major complications following closed reduction and percutaneous pinning of type II supracondylar humerus fractures in children. Further prospective work is necessary to determine if there are subtle treatment benefits from emergent treatment of type II supracondylar humerus fractures. Level III

  14. Uncommon Variant of Type II Monteggia Fracture with Concomitant Distal Humeral Fracture

    PubMed Central

    Matta, Jihad F.; El Rassi, George S.; Abd El Nour, Hicham G.; El Asmar, Rachel

    2015-01-01

    Monteggia fracture-dislocation, a common injury sustained by pediatric population, is a rare entity in adults. It was first observed by Giovanni Battista Monteggia and later classified by Bado into 4 groups. The term “Monteggia equivalent or variant” was introduced to describe certain injuries with similar radiographic pattern and biomechanism of injury. Since then various types and their variants have been described in the literature. We present a complex fracture pattern in a 55-year-old male not previously described in the literature along with its treatment modality and favorable outcome. PMID:26550509

  15. Fracture Resistance and Mode of Failure of Ceramic versus Titanium Implant Abutments and Single Implant-Supported Restorations.

    PubMed

    Sghaireen, Mohd G

    2015-06-01

    The material of choice for implant-supported restorations is affected by esthetic requirements and type of abutment. This study compares the fracture resistance of different types of implant abutments and implant-supported restorations and their mode of failure. Forty-five Oraltronics Pitt-Easy implants (Oraltronics Dental Implant Technology GmbH, Bremen, Germany) (4 mm diameter, 10 mm length) were embedded in clear autopolymerizing acrylic resin. The implants were randomly divided into three groups, A, B and C, of 15 implants each. In group A, titanium abutments and metal-ceramic crowns were used. In group B, zirconia ceramic abutments and In-Ceram Alumina crowns were used. In group C, zirconia ceramic abutments and IPS Empress Esthetic crowns were used. Specimens were tested to failure by applying load at 130° from horizontal plane using an Instron Universal Testing Machine. Subsequently, the mode of failure of each specimen was identified. Fracture resistance was significantly different between groups (p < .05). The highest fracture loads were associated with metal-ceramic crowns supported by titanium abutments (p = .000). IPS Empress crowns supported by zirconia abutments had the lowest fracture loads (p = .000). Fracture modes of metal-ceramic crowns supported by titanium abutments included screw fracture and screw bending. Fracture of both crown and abutment was the dominant mode of failure of In-Ceram/IPS Empress crowns supported by zirconia abutments. Metal-ceramic crowns supported by titanium abutments were more resistant to fracture than In-Ceram crowns supported by zirconia abutments, which in turn were more resistant to fracture than IPS Empress crowns supported by zirconia abutments. In addition, failure modes of restorations supported by zirconia abutments were more catastrophic than those for restorations supported by titanium abutments. © 2013 Wiley Periodicals, Inc.

  16. Conventional and microfilled composite resins. Part II. Chip fractures.

    PubMed

    Lambrechts, P; Ameye, C; Vanherle, G

    1982-11-01

    Dentists are accustomed to advantages and disadvantages in the materials at their disposal. This article was concerned with one disadvantage of microfilled composite resins, namely, chip fractures. Probably due to their higher coefficient of thermal expansion, higher water sorption, higher polymerization shrinkage, and lower tensile strengths, cohesive as well as adhesive chip fractures occur three to four times more often with microfilled composite resins than with conventional composite resins. Microfilled composite resins are indicated for esthetic purposes. They are contraindicated for Class IV and stress-bearing restorations. They are indicated for limited use in Class I restorations where esthetics is of primary importance. The technique of use must include acid-etching and intermediate bonding. The microfilled composite resins enjoy a smooth finish and high luster. This offers advantages in areas where smoothness is paramount. They may replace conventional composite resins for resurfacing existing restorations and veneering stained or mottled anterior teeth. They are indicated for treatment of cervical erosion.

  17. Fracture resistance of premolars with bonded class II amalgams.

    PubMed

    Dias de Souza, Grace Mendonça; Pereira, Gisele Damiana Silveira; Dias, Carlos Tadeu Santos; Paulillo, Luis Alexandre Maffei Sartini

    2002-01-01

    This study evaluated the fracture resistance of maxillary premolars with MOD cavity preparation and simulated periodontal ligament. The teeth were restored with silver amalgam (G1), Scotchbond Multi-Purpose Plus and silver amalgam (G2) and Panavia F and silver amalgam (G3). After restorations were made, the specimens were stored at 37 degrees C for 24 hours at 100% humidity and submitted to the compression test in the Universal Testing Machine (Instron). The statistical analysis of the results (ANOVA and Tukey Test) revealed that the fracture resistance of group 2 (G2=105.720 kgF) was superior to those of groups 1 (G1=72.433 kgF) and 3 (G3=80.505 kgF) that did not differ between them.

  18. Subcritical crack growth under mode I, II, and III loading for Coconino sandstone

    NASA Astrophysics Data System (ADS)

    Ko, Tae Young

    of 34 to 38 and the parameter A has the range of 1.02x10-2 to 6.52x10-2 m/s. The effect of confining stress, specimen size, and water saturation on subcritical crack growth under mode II loading has also been investigated. Finally strength parameters for Coconino sandstone were determined experimentally, including tensile strength, uniaxial compressive strength, cohesion, internal friction angle, in-plane/our-of-plane shear strength and the fracture toughness under mode I, II, and III loading.

  19. Mixed-mode fracture in unidirectional graphite epoxy composite laminates with central notch

    NASA Technical Reports Server (NTRS)

    Binienda, Wieslaw K.; Reddy, E. S.

    1992-01-01

    Mixed-mode matrix fracture in central notched off-axis unidirectional composite laminates was investigated. A limited number of unidirectional tensile type specimens with a central, horizontal, notch were tested. Crack initiation and propagation were examined under various local stress fields that were controlled by fiber orientations. The tested specimens were simulated using a two dimensional finite element method with constant strain loading. The strain energy release rates along the crack were evaluated via crack closure technique. The variation of critical strain energy rates with off-axis angle was studied. The results from single (one-sided) and double (two-sided) crack simulations were presented and compared.

  20. A model for predicting crack growth rate for mixed mode fracture under biaxial loads

    NASA Astrophysics Data System (ADS)

    Shliannikov, V. N.; Braude, N. Z.

    1992-09-01

    A model for predicting the crack growth rate of an initially angled crack under biaxial loads of arbitrary direction is suggested. The model is based on a combination of both the Manson-Coffin equation for low cycle fatigue and the Paris equation for fatigue crack propagation. The model takes into consideration the change in material plastic properties in the region around the crack tip due to the stress state, together with the initial orientation of the crack and also its trajectory of growth. Predictions of crack growth rate for any mixed mode fracture is based on the results of uniaxial tension experiments.

  1. CSNI Project for Fracture Analyses of Large-Scale International Reference Experiments (FALSIRE II)

    SciTech Connect

    Bass, B.R.; Pugh, C.E.; Keeney, J.; Schulz, H.; Sievers, J.

    1996-11-01

    A summary of Phase II of the Project for FALSIRE is presented. FALSIRE was created by the Fracture Assessment Group (FAG) of the OECD/NEA`s Committee on the Safety of Nuclear Installations (CNSI) Principal Working Group No. 3. FALSIRE I in 1988 assessed fracture methods through interpretive analyses of 6 large-scale fracture experiments in reactor pressure vessel (RPV) steels under pressurized- thermal-shock (PTS) loading. In FALSIRE II, experiments examined cleavage fracture in RPV steels for a wide range of materials, crack geometries, and constraint and loading conditions. The cracks were relatively shallow, in the transition temperature region. Included were cracks showing either unstable extension or two stages of extensions under transient thermal and mechanical loads. Crack initiation was also investigated in connection with clad surfaces and with biaxial load. Within FALSIRE II, comparative assessments were performed for 7 reference fracture experiments based on 45 analyses received from 22 organizations representing 12 countries. Temperature distributions in thermal shock loaded samples were approximated with high accuracy and small scatter bands. Structural response was predicted reasonably well; discrepancies could usually be traced to the assumed material models and approximated material properties. Almost all participants elected to use the finite element method.

  2. Mode I Fracture Toughness Prediction for Multiwalled-Carbon-Nanotube Reinforced Ceramics

    SciTech Connect

    Nguyen, Ba Nghiep; Henager, Charles H.

    2015-08-27

    This article develops a multiscale model to predict fracture toughness of multiwalled-carbon-nanotube (MWCNT) reinforced ceramics. The model bridges different scales from the scale of a MWCNT to that of a composite domain containing a macroscopic crack. From the nano, micro to meso scales, Eshelby-Mori-Tanaka models combined with a continuum damage mechanics approach are explored to predict the elastic damage behavior of the composite as a function of MWCNT volume fraction. MWCNTs are assumed to be randomly dispersed in a ceramic matrix subject to cracking under loading. A damage variable is used to describe matrix cracking that causes reduction of the elastic modulus of the matrix. This damage model is introduced in a modified boundary layer modeling approach to capture damage initiation and development at a tip of a pre-existing crack. Damage and fracture are captured only in a process window containing the crack tip under plane strain Mode I loading. The model is validated against the published experimental fracture toughness data for a MWCNT 3 mol% yttria stabilized zirconia composite system. In addition, crack resistance curves as a function of MWCNT content are predicted and fitted by a power law as observed in the experiments on zirconia.

  3. Characterization of Mode I Fracture and Morphological Properties of PLLA Blends with Addition of Lysine Triisocyanate

    NASA Astrophysics Data System (ADS)

    Vannaladsaysy, Vilay; Todo, Mitsugu

    Poly(L-lactic acid) (PLLA) was toughened by blending with three different ductile biopolymers such as poly (ε-caprolactone) (PCL), poly(butylene succinate-co-e-caprolactone) (PBSC), poly (butylene succinate-co-L-lactate) (PBSL). The blend ratio was fixed to 50:50. Lysine triisocyanate (LTI) was added to the blends as a compatibilizer. Characterizations such as Fourier transform infra-red (FT-IR) spectroscopy, field-emission electron microscope (FE-SEM), and mode I fracture test were used to characterize the effectiveness of LTI on the mechanical and morphological properties of various PLLA blends. It was found that PLLA/PCL blend shows the highest toughness energy among the binary blends. On the other hand, addition of LTI in PLLA/PBSC blend exhibits the best toughness property. Based on the FE-SEM observation, fractured surfaces of PLLA blends with LTI indicate ductile fracture with dense elongated fibrils. The largest damage zone is generated in the vicinity of crack-trip, suggesting that high energy dissipation occurred in the crack-trip region. FT-IR analysis also suggested that the NCO groups of LTI were acted as a compatibilizer, as the results of interaction between the two phases of the polymer blends.

  4. Non-union (type II) odontoid fracture: A case report of a motor vehicle accident

    PubMed Central

    Kitchen, RG

    1986-01-01

    A case report is presented of a young man injured in a motor vehicle accident who subsequently suffered neck and shoulder pain with no radiation. The pain, aggravated by motion and relieved by neck massage, had persisted for five months. Investigation by plain film radiographs, prior to treatment suggested an odontoid fracture. Tomographic radiographs revealed a type II non-union odontoid fracture. Spinal manipulation was contraindicated and this patient went on to surgical stabilization. A type II odontoid fracture non-union should be ruled out in any patient presenting with a history of a motor vehicle accident with head trauma, before manipulation is considered. ImagesFigure 2aFigure 2bFigure 2cFigure 3aFigure 3bFigure 3cFigure 4aFigure 4bFigure 5aFigure 5b

  5. Heading the ball: a case of a Le Fort II fracture in a football match.

    PubMed

    Akoglu, Ebru; Onur, Ozge; Denizbasi, Arzu; Kosargelir, Mehmet; Akoglu, Haldun; Ibrahim, Abdullah

    2011-03-15

    Facial injuries can impair a patient's ability to eat, speak and interact with others. Severe injuries occur as a result of interpersonal or domestic violence, or in motor vehicle collisions, including those involving motorcycles and all-terrain vehicles. The authors present a case of LeFort II fracture caused by a collision of opponents while heading the ball in a football match.

  6. Influence of preparation design and ceramic thicknesses on fracture resistance and failure modes of premolar partial coverage restorations.

    PubMed

    Guess, Petra C; Schultheis, Stefan; Wolkewitz, Martin; Zhang, Yu; Strub, Joerg R

    2013-10-01

    Preparation designs and ceramic thicknesses are key factors for the long-term success of minimally invasive premolar partial coverage restorations. However, only limited information is presently available on this topic. The purpose of this in vitro study was to evaluate the fracture resistance and failure modes of ceramic premolar partial coverage restorations with different preparation designs and ceramic thicknesses. Caries-free human premolars (n=144) were divided into 9 groups. Palatal onlay preparation comprised reduction of the palatal cusp by 2 mm (Palatal Onlay Standard), 1 mm (Palatal-Onlay-Thin), or 0.5 mm (Palatal Onlay Ultrathin). Complete-coverage onlay preparation additionally included the buccal cusp (Occlusal Onlay Standard; Occlusal Onlay Thin; Occlusal Onlay Ultrathin). Labial surface preparations with chamfer reductions of 0.8 mm (Complete-Veneer-Standard), 0.6 mm (Complete-Veneer-Thin), and 0.4 mm (Complete Veneer Ultrathin) were implemented for complete veneer restorations. Restorations were fabricated from a pressable lithium disilicate ceramic (IPS-e.max-Press) and cemented adhesively (Syntac-Classic/Variolink-II). All specimens were subjected to cyclic mechanical loading (F=49 N, 1.2 million cycles) and simultaneous thermocycling (5°C to 55°C) in a mouth-motion simulator. After fatigue, restorations were exposed to single-load-to-failure. Two-way ANOVA was used to identify statistical differences. Pair-wise differences were calculated and P-values were adjusted by the Tukey-Kramer method (α=.05). All specimens survived fatigue. Mean (SD) load to failure values (N) were as follows: 837 (320/Palatal-Onlay-Standard), 1055 (369/Palatal-Onlay-Thin), 1192 (342/Palatal-Onlay-Ultrathin), 963 (405/Occlusal-Onlay-Standard), 1108 (340/Occlusal-Onlay-Thin), 997 (331/Occlusal-Onlay-Ultrathin), 1361 (333/Complete-Veneer-Standard), 1087 (251/Complete-Veneer-Thin), 883 (311/Complete-Veneer-Ultrathin). Palatal-onlay restorations revealed a significantly

  7. Influence of preparation design and ceramic thicknesses on fracture resistance and failure modes of premolar partial coverage restorations

    PubMed Central

    Guess, Petra C.; Schultheis, Stefan; Wolkewitz, Martin; Zhang; Strub, Joerg R.

    2015-01-01

    Statement of problem Preparation designs and ceramic thicknesses are key factors for the long-term success of minimally invasive premolar partial coverage restorations. However, only limited information is presently available on this topic. Purpose The aim of this in vitro study was to evaluate the fracture resistance and failure modes of ceramic premolar partial coverage restorations with different preparation designs and ceramic thicknesses. Material and methods Caries-free human premolars (n= 144) were divided into 9 groups. Palatal onlay preparation comprised reduction of the palatal cusp by 2 mm (Palatal-Onlay-Standard), 1 mm (Palatal-Onlay-Thin), or 0.5 mm (Palatal-Onlay-Ultra-Thin). Complete-coverage onlay preparation additionally included the buccal cusp (Occlusal-Onlay-Standard; Occlusal-Onlay-Thin; Occlusal-Onlay-Ultra-Thin). Labial surface preparations with chamfer reductions of 0.8 mm (Complete-Veneer-Standard), 0.6 mm (Complete-Veneer-Thin) and 0.4 mm (Complete-Veneer-Ultra-Thin) were implemented for complete veneer restorations. Restorations were fabricated from a pressable lithium-disilicate ceramic (IPS-e.max-Press) and cemented adhesively (Syntac-Classic/Variolink-II). All specimens were subjected to cyclic mechanical loading (F= 49 N, 1.2 million cycles) and simultaneous thermocycling (5°C to 55°C) in a mouth-motion simulator. After fatigue, restorations were exposed to single-load-to-failure. Two-way ANOVA was used to identify statistical differences. Pair-wise differences were calculated and P-values were adjusted by the Tukey–Kramer method (α= .05). Results All specimens survived fatigue. Mean (SD) load to failure values (N) were as follows: 837 (320/Palatal-Onlay-Standard), 1055 (369/Palatal-Onlay-Thin), 1192 (342/Palatal-Onlay-Ultra-Thin), 963 (405/Occlusal-Onlay-Standard), 1108 (340/Occlusal-Onlay-Thin), 997 (331/Occlusal-Onlay-Ultra-Thin), 1361 (333/Complete-Veneer-Standard), 1087 (251/Complete-Veneer-Thin), 883 (311/Complete

  8. Outcomes of Nonoperative Treatment of Salter-Harris II Distal Radius Fractures: A Systematic Review.

    PubMed

    Larsen, Meredith C; Bohm, Kyle C; Rizkala, Amir R; Ward, Christina M

    2016-03-01

    Despite the frequent occurrence of these injuries, we know little about the natural history of Salter-Harris II (SH II) distal radius fractures. We conducted a systematic review of studies examining the radiographic and clinical outcomes of nonoperatively managed SH II distal radius fractures. Systematic searches of the MEDLINE and Cochrane computerized literature databases and manual searches of bibliographies were performed. We reviewed both descriptive and quantitative data. Seven studies including 434 SH II fractures were reviewed. Two studies reported clinical outcomes based on patient age, but neither study described a statistical correlation between patient age and outcome. Two studies discussed the effect of age on radiographic outcome and reported higher rates of anatomic remodeling in children 10 years or younger. Two studies with long-term (average follow-up greater than 8 years) clinical results reported complication rates of 5%. Long-term follow-up of radiographic outcomes appeared in 4 studies with variable results. Five studies reported the frequency of premature physeal arrest after SH II fractures, with results ranging from 0% to 4.3%. Based on this review, no recommendations can be made as to what defines an acceptable reduction or which fractures would benefit from surgical intervention. Angular deformity seems to correct to an acceptable alignment in patients less than 10 years of age, but these younger patients seem to be at higher risk for symptomatic shortening if a growth arrest occurs. Redisplacement after reduction is fairly common, and other more severe complications such as pain, loss of motion, and nerve injury can occur.

  9. Outcomes of Nonoperative Treatment of Salter-Harris II Distal Radius Fractures

    PubMed Central

    Larsen, Meredith C.; Bohm, Kyle C.; Rizkala, Amir R.; Ward, Christina M.

    2016-01-01

    Background: Despite the frequent occurrence of these injuries, we know little about the natural history of Salter-Harris II (SH II) distal radius fractures. We conducted a systematic review of studies examining the radiographic and clinical outcomes of nonoperatively managed SH II distal radius fractures. Methods: Systematic searches of the MEDLINE and Cochrane computerized literature databases and manual searches of bibliographies were performed. We reviewed both descriptive and quantitative data. Results: Seven studies including 434 SH II fractures were reviewed. Two studies reported clinical outcomes based on patient age, but neither study described a statistical correlation between patient age and outcome. Two studies discussed the effect of age on radiographic outcome and reported higher rates of anatomic remodeling in children 10 years or younger. Two studies with long-term (average follow-up greater than 8 years) clinical results reported complication rates of 5%. Long-term follow-up of radiographic outcomes appeared in 4 studies with variable results. Five studies reported the frequency of premature physeal arrest after SH II fractures, with results ranging from 0% to 4.3%. Conclusions: Based on this review, no recommendations can be made as to what defines an acceptable reduction or which fractures would benefit from surgical intervention. Angular deformity seems to correct to an acceptable alignment in patients less than 10 years of age, but these younger patients seem to be at higher risk for symptomatic shortening if a growth arrest occurs. Redisplacement after reduction is fairly common, and other more severe complications such as pain, loss of motion, and nerve injury can occur. PMID:27418886

  10. Effects of pulp capping materials on fracture resistance of Class II composite restorations

    PubMed Central

    Kucukyilmaz, Ebru; Yasa, Bilal; Akcay, Merve; Savas, Selcuk; Kavrik, Fevzi

    2015-01-01

    Objective: The aim of this study was to investigate the effect of cavity design and the type of pulp capping materials on the fracture resistance of Class II composite restorations. Materials and Methods: Sixty freshly extracted, sound molar teeth were selected for the study. A dovetail cavity on the mesio-occlusal and a slot cavity on disto-occlusal surfaces of each tooth were prepared, and the teeth were divided 4 groups which one of them as a control group. The pulp capping materials (TheraCal LC, Calcimol LC, Dycal) applied on pulpo-axial wall of each cavity, and the restoration was completed with composite resin. The teeth were subjected to a compressive load in a universal mechanical testing machine. The surfaces of the tooth and restoration were examined under a stereomicroscope. The data were analyzed using factorial analysis of variance and Tukey's test. Results: For pulp capping materials, the highest fracture load (931.15 ± 203.81 N) and the lowest fracture load (832.28 ± 245.75 N) were calculated for Control and Dycal group, respectively. However, there were no statistically significant differences among all groups (P > 0.05). The fracture load of the dovetail groups was significantly higher than those of the slot cavity groups (P < 0.05). Conclusion: Dovetail cavity design shows better fracture resistance in Class II composite restorations, independent of used or not used pulp capping materials. PMID:26038653

  11. Effects of pulp capping materials on fracture resistance of Class II composite restorations.

    PubMed

    Kucukyilmaz, Ebru; Yasa, Bilal; Akcay, Merve; Savas, Selcuk; Kavrik, Fevzi

    2015-01-01

    The aim of this study was to investigate the effect of cavity design and the type of pulp capping materials on the fracture resistance of Class II composite restorations. Sixty freshly extracted, sound molar teeth were selected for the study. A dovetail cavity on the mesio-occlusal and a slot cavity on disto-occlusal surfaces of each tooth were prepared, and the teeth were divided 4 groups which one of them as a control group. The pulp capping materials (TheraCal LC, Calcimol LC, Dycal) applied on pulpo-axial wall of each cavity, and the restoration was completed with composite resin. The teeth were subjected to a compressive load in a universal mechanical testing machine. The surfaces of the tooth and restoration were examined under a stereomicroscope. The data were analyzed using factorial analysis of variance and Tukey's test. For pulp capping materials, the highest fracture load (931.15 ± 203.81 N) and the lowest fracture load (832.28 ± 245.75 N) were calculated for Control and Dycal group, respectively. However, there were no statistically significant differences among all groups (P > 0.05). The fracture load of the dovetail groups was significantly higher than those of the slot cavity groups (P < 0.05). Dovetail cavity design shows better fracture resistance in Class II composite restorations, independent of used or not used pulp capping materials.

  12. Fracture resistance and failure mode of posterior fixed dental prostheses fabricated with two zirconia CAD/CAM systems

    PubMed Central

    López-Suárez, Carlos; Gonzalo, Esther; Peláez, Jesús; Rodríguez, Verónica

    2015-01-01

    Background In recent years there has been an improvement of zirconia ceramic materials to replace posterior missing teeth. To date little in vitro studies has been carried out on the fracture resistance of zirconia veneered posterior fixed dental prostheses. This study investigated the fracture resistance and the failure mode of 3-unit zirconia-based posterior fixed dental prostheses fabricated with two CAD/CAM systems. Material and Methods Twenty posterior fixed dental prostheses were studied. Samples were randomly divided into two groups (n=10 each) according to the zirconia ceramic analyzed: Lava and Procera. Specimens were loaded until fracture under static load. Data were analyzed using Wilcoxon´s rank sum test and Wilcoxon´s signed-rank test (P<0.05). Results Partial fracture of the veneering porcelain occurred in 100% of the samples. Within each group, significant differences were shown between the veneering and the framework fracture resistance (P=0.002). The failure occurred in the connector cervical area in 80% of the cases. Conclusions All fracture load values of the zirconia frameworks could be considered clinically acceptable. The connector area is the weak point of the restorations. Key words:Fixed dental prostheses, zirconium-dioxide, zirconia, fracture resistance, failure mode. PMID:26155341

  13. Are C2 pars-pedicle screws alone for type II Hangman's fracture overrated?

    PubMed

    Salunke, Pravin; Sahoo, Sushanta K; Krishnan, Prasad; Chaterjee, Debarshi; Sodhi, Harsimrat Bir Singh

    2016-02-01

    The recent trend for treatment of certain cases of type II Hangman's fracture has been towards motion preserving surgery. This is claimed to be achieved with placement of pedicle screws across the fracture fragments. However, the long term outcome in clinical scenario is not yet clear, neither are the factors determining suitability of such a technique. We have retrospectively analyzed the results of 11 patients of type II Hangman's fracture, according to the extent of translation. Nine patients underwent stabilization of fracture with C2 pedicle screws and 2 were managed with halo immobilization. The conservative management failed in one and this patient underwent internal fixation using pars-pedicle screw as well. The long term clinical and radiological (CT and dynamic X-rays) outcome was analyzed. All patients including the one with halo immobilization, showed solid fusion across the fracture fragments. With the exception of one patient none had any clinical symptoms. This lone patient complained of restricted neck movements. Three different types of radiological results were observed. Two patients with translation >8mm showed C2-3 body fusion. Three of 6 patients with minimal translational (3-4mm) showed facet fusion. Three patients with moderate translational dislocation (4.5-5.5mm) showed persisting C2-3 angular instability. The C2 pedicle screw is a good technique for osteosynthesis. However, the claimed long term advantage of motion segment preservation with this technique remains doubtful. It may be suitable for those fractures with minimal translation (<4mm), where the superiority of surgery, itself, over external immobilization is questionable. C2-3 fusion is preferable for those fractures with translation >4mm as these are unstable and C2 pedicle screws alone are likely to have less desirable results. Copyright © 2015 Elsevier B.V. All rights reserved.

  14. Modification of fracture surfaces by dissolution. Part II

    SciTech Connect

    Johnson, B.

    1983-01-01

    This study focuses upon how and to what extent dissolution related fluid/rock interactions modify the morphology and roughness of surfaces on Sioux Quartzite. Dissolution experiments consisted of reacting small discs of Sioux Quartzite in sealed gold capsules containing either distilled water or 0.05 N to 4.0 N aqueous solutions of Na/sub 2/CO/sub 3/. Samples were reacted at 200/sup 0/C and 20 to 30 MPa fluid pressures for 2 to 5 days. Two markedly different starting surface textures were used: polished, optically flat surfaces and tensile fracture surfaces. An exploratory experiment also was performed to assess the occurrence of a pressure solution phenomenon on a polished quartzite surface at contact regions of indenting quartz sand grains. Scanning electron microscopy studies indicate progressive increases in the amount of dissolution produced significant changes of surface roughness for both initial surface textures. Surface roughness increased measurably, with the initially polished surfaces exhibiting the more dramatic changes. The pressure solution experiments did not produce definite results, but several surface features are suggestive of dissolution enhancement at load carrying contacts. 9 refs., 10 figs.

  15. Effect of thickness and loading mode on the fracture properties of V-4Cr-4Ti at room temperature

    SciTech Connect

    Li, H.; Kurtz, R.J.; Jones, R.H.

    1998-03-01

    The effect of thickness on the room temperature (RT) mode I fracture behavior of V-4Cr-4Ti has been investigated. Mode i fracture properties were measured from J-integral tests of compact tension (CT) specimens ranging in thickness from 6.4 mm to 25.4 mm. All specimens were machined in the T-L orientation and vacuum annealed following final matching. Two heats of V-4Cr-4Ti were tested. Specimens 6.4 mm and 12.7 mm thick were taken from ANL Heat No. 832665. The 25.4 mm thick specimens were obtained from GA Heat No. 832864. J-R curves were generated by the single specimen unload-compliance test technique in accordance with ASTM E813. All tests were performed in laboratory air at 25 C. Fracture of V-4Cr-4Ti under mixed-mode loading conditions showed the same trend observed previously for V-5Cr-5Ti and for other tough materials. For materials which fail by microvoid coalescence, the addition of an out-of-plane shear loading component introduces incompatibility stresses at particle interfaces in the trajectory of the crack. These incompatibility stresses cause particle/matrix decohesion or particle fracture which leads to void formation that limits the mode i plastic flow field. The present results demonstrates that fracture of V-4Cr-4Ti is sensitive to the addition of shear loading components and that model fracture toughness tests may not give the most conservative measure of resistance to ductile fracture.

  16. The influence of microstructure and strength on the fracture mode and toughness of 7XXX series aluminum alloys

    NASA Astrophysics Data System (ADS)

    Ludtka, Gerard M.; Laughlin, David E.

    1982-03-01

    The effects of microstructure and strength on the fracture toughness of ultra high strength aluminum alloys have been investigated. For this study three ultra high purity compositions were chosen and fabricated into 1.60 mm (0.063 inches) sheet in a T6 temper providing a range of yield strengths from 496 MPa (72 ksi) to 614 MPa (89 ksi). These alloys differ only in the volume fraction of the fine matrix strengthening precipitates (G. P. ordered + η' ). Fracture toughness data were generated using Kahn-type tear tests, as well as R-curve and J c analyses performed on data from 102 mm wide center cracked tension panel tests. Consistent with previous studies, it has been demonstrated that the toughness decreases as the yield strength is increased by increasing the solute content. Concomitant with this decrease in toughness, a transition in fracture mode was observed from predominantly transgranular dimpled rupture to predominantly intergranular dimpled rupture. Both quantitative fractography and X-ray microanalysis clearly demonstrate that fracture initiation for the two fracture modes occurred by void formation at the Cr-dispersoids ( E-phase). In the case of intergranular fracture, void coalescence was facilitated by the grain boundary η precipitates. The difference in fracture toughness behavior of these alloys has been shown to be dependent on the coarseness of matrix slip and the strength differential between the matrix and precipitate free zone (σM-σPFZ). A new fracture mechanism has been proposed to explain the development of the large amounts of intergranular fracture observed in the low toughness alloys.

  17. Off-fault heterogeneities promote supershear transition of dynamic mode II cracks

    NASA Astrophysics Data System (ADS)

    Albertini, Gabriele; Kammer, David S.

    2017-08-01

    The transition from sub-Rayleigh to supershear propagation of mode II cracks is a fundamental problem of fracture mechanics. It has extensively been studied in homogeneous uniform setups. When the applied shear load exceeds a critical value, transition occurs through the Burridge-Andrews mechanism at a well-defined crack length. However, velocity structures in geophysical conditions can be complex and affect the transition. Damage induced by previous earthquakes causes low-velocity zones surrounding mature faults and inclusions with contrasting material properties can be present at seismogenic depth. We relax the assumption of homogeneous media and investigate dynamic shear fracture in heterogeneous media using two-dimensional finite element simulations and a linear slip-weakening law. We analyze the role of heterogeneities in the elastic media, while keeping the frictional interface properties uniform. We show that supershear transition is possible due to the sole presence of favorable off-fault heterogeneities. Subcritical shear loads, for which propagation would remain permanently sub-Rayleigh in an equivalent homogeneous setup, will transition to supershear as a result of reflected waves. P wave reflected as S waves, followed by further reflections, affect the amplitude of the shear stress peak in front of the propagating crack, leading to supershear transition. A wave reflection model allows to uniquely describe the effect of off-fault inclusions on the shear stress peak. A competing mechanism of modified released potential energy affects transition and becomes predominant with decreasing distance between fault and inclusions. For inclusions at far distances, the wave reflection is the predominant mechanism.

  18. Zonation of shale reservoir stimulation modes: a conceptual model based on hydraulic fracturing data from the Baltic Basin (Poland).

    NASA Astrophysics Data System (ADS)

    Jarosiński, Marek; Pachytel, Radomir

    2017-04-01

    Depending on the pressure distribution within Stimulated Reservoir Volume (SRV), a different modes of hydraulic fracturing or tectonic fracture reactivation are active. Hydraulic pressure-driven shortening or expansion of reservoir produces changes in stress field that results in decrease of differential stress either by increasing of horizontal stress minimum (Shmin) or/and by decreasing of horizontal stress maximum (SHmax). For further considerations we assume initial strike-slip stress regime which prevails in the Polish part of the Lower Paleozoic Baltic Basin (BB), as well as in majority of the USA shale basins. The data come from vertical and horizontal shale gas exploration wells drilled from one pad located in the middle of the BB. Structural survey of a long core interval combined with stress analysis based on microfrac tests and fracturing tests allow to reconstruct the initial structural and geomechanical state of reservoir. Further geomechanical evolution of the SRV depends on the hydraulic pressure bubble growth, which is in general unknown. However, the state of pressure can be determined close to the injection borehole and in the front of the SRV migrating in time. In our case, we are able to distinguish four stimulation zones characterized by increasingly diverse stimulation modes and successively closer to the borehole injection zone: (1) shear on preexisting fractures generates microseismic events that produce open fractures propped by their natural asperities being impenetrable for proppant grains; (2) above + initial hydraulic opening of natural fractures that are preferentially oriented to the Shmin, which favors microseismic events triggered by secondary shear on bedding planes and produces open spaces supported by natural fracture asperities and fine-grained proppant; (3) above + failure of primary hydraulic fractures, which increases extensional component of the microseismic events and opens space for coarse-grained proppant; (4) above

  19. Evaluation of a fracture failure mode in the Space Shuttle hydrogen pressurization system flow control valves

    NASA Astrophysics Data System (ADS)

    Hauver, S. E.; Sueme, D. R.

    1992-07-01

    During acceptance testing of the Space Shuttle Endeavor hydrogen flow control valves, which are used in the Orbiter's fuel tank pressurization system, two of the valves experienced fracture of the poppet flange. The poppets are made of 440 C, a high strength, wear-resistant, low ductility, martensitic stainless steel. The investigation which was initiated to determine the cause of these failures is traced. All aspects of the poppet processing that may have introduced a defect were assessed. This included machining, heat treating, passivation, assembly, and test. In addition, several potential failure modes were investigated. The extensive investigation revealed no obvious cause of the failures, but did result in a recommendation for a different material application.

  20. Fracture toughness of the IEA heat of F82H ferritic/martensitic stainless steel as a function of loading mode

    SciTech Connect

    Li, Huaxin; Gelles, D.S.; Hirth, J.P.

    1997-04-01

    Mode I and mixed-mode I/III fracture toughness tests were performed for the IEA heat of the reduced activation ferritic/martensitic stainless steel F82H at ambient temperature in order to provide comparison with previous measurements on a small heat given a different heat treatment. The results showed that heat to heat variations and heat treatment had negligible consequences on Mode I fracture toughness, but behavior during mixed-mode testing showed unexpected instabilities.

  1. Nonsurgical treatment of Mason type II radial head fractures in athletes. A retrospective study.

    PubMed

    Guzzini, M; Vadalà, A; Agrò, A; Di Sanzo, V; Pironi, D; Redler, A; Serlorenzi, P; Proietti, L; Civitenga, C; Mazza, D; Lanzetti, R M; Ferretti, Andrea

    2017-01-01

    The best treatment for moderately displaced radial head fractures (Mason type II) still remains controversial. In cases of isolated fractures, there is no evidence that a fragment displacement of ≥ 2 mm gives poor results in conservatively treated fractures. We retrospectively reviewed 52 patients (31M, 21F) affected by an isolated Mason type II fracture, treated with a long arm cast for two weeks between 2008 and 2013. All patients had practiced sports before being injured. They were all either bicyclists, or baseball, boxers, basketball, rugby, tennis or football players. The mean follow-up was 36 months. Elbow and forearm range of motion were measured. The Mayo Elbow Performance Score, the Broberg and Morrey rating system and the Disabilities of the Arm, Shoulder and Hand Score (DASH score) were analyzed. Follow-up radiographs were examined for evidence of consolidation, late displacement, early arthritis and non-unions. Flexion was slightly impaired in the injured limb when compared to the uninjured limb (137°± 6° versus 139°±5°) as were extension (-3°±6° versus 1°±4°, p < 0.05), supination (86°±6° versus 88°±3°), pronation (87°±4° versus 88°±6°) and valgus deviation (10°±4° versus 8°±3°, p < 0.05). 40 patients had no elbow complaints; 9 patients experienced occasional pain, 2 a mild instability of the elbow, and 4 a mild loss of grip strength. The DASH score was excellent in 48 patients (92.31%). In only 6 cases (11.53%) degenerative changes were greater in formerly injured elbows than in uninjured elbows. All patients returned to their previous sports activities. Isolated Mason type II fractures can have a good or excellent mid-term functional outcome even when treated conservatively.

  2. Atlanto-axial dislocation complicating a type II odontoid fracture. Reduction and final fixation.

    PubMed

    Riouallon, G; Pascal-Moussellard, H

    2014-05-01

    A case of traumatic posterolateral C1-C2 dislocation associated with odontoid fracture is reported. This is a rare case of traumatic posterolateral C1-C2 dislocation associated with odontoid fracture. Its management is discussed. A traumatic dislocation of atlanto-axial joint associated with an odontoid fracture remains a rare injury. No case of posterior dislocation has been reported so far in the literature with this type of management. The case is of a 25 year-old-man with a primary atlanto-axial posterolateral dislocation associated with a type II displaced odontoid fracture without any neurological complication. The patient underwent gentle traction during 24 hours with a halo frame. An incomplete reduction was achieved. Two days later, a complete reduction was obtained thanks to a preoperative manual traction maintained by a Mayfield (R) modified skull clamp. Anterior C1-C2 fixation was performed according to Vaccaro's technique. The patient wore a cervical collar and underwent physiotherapy during three months. To our best knowledge, this case represents the first traumatic atlanto-axial dislocation associated with an odontoid fracture which was treated through retropaharyngeal approach. This had been rendered possible thanks to the final reduction maneuver in extension.

  3. Analysis of failure following anterior screw fixation of Type II odontoid fractures in geriatric patients.

    PubMed

    Osti, Michael; Philipp, Helmut; Meusburger, Berthold; Benedetto, Karl Peter

    2011-11-01

    Anterior screw fixation of Type II odontoid fractures has been recommended. Only few publications analyse the mechanism of failure in geriatric patients. We reviewed 18 male and 15 female patients aged 65 and above for parameters that influence the development of postoperative loss of correction, delayed union or non-union. Patients were stratified in two groups: 21 cases in Group A (union) and 12 patients in Group B (loss of correction, delayed union, non-union, revision surgery). Statistically significant correlation (p < 0.05) could be detected between failure to heal and: (1) degenerative changes in the atlanto-odontoid joint, (2) severity of osteoporosis in the odontoid process, (3) posterior oblique fracture type, (4) suboptimal fracture reduction, (5) suboptimal position of implant following demanding intraoperative conditions, (6) quality of fracture compression and (7) severity of fracture comminution. The overall morbidity and mortality rates were 29.0 and 8.6%, respectively. Our results indicate that these factors should be addressed regarding the selection of the operative treatment method in the geriatric patient.

  4. Non-smooth mode I fracture of fibre-reinforced composites: an experimental, numerical and analytical study.

    PubMed

    Davidson, Paul; Waas, Anthony M

    2012-04-28

    We present a novel approach to analyse the fracture of fibre-reinforced composites. Experimental results on mode I fracture of glass fibre and carbon fibre unidirectional laminates presented here and published by others in the open literature formed the basis for the analytical and numerical results presented. When details of the external loading rate are explicitly accounted for, a new picture of fracture emerges, which encompasses the possibility for non-smooth crack growth and the necessity to relax the use of a critical strain energy release rate as a criterion for crack advancement. Results predicted by adopting the analytical model presented here are seen to capture a wide variety of fracture responses that have been observed previously.

  5. Irreducible Salter Harris type II distal tibial physeal fracture secondary to interposition of the posterior tibial tendon: a case report.

    PubMed

    Soulier, Robert; Fallat, Lawrence

    2010-01-01

    Pediatric distal tibial fractures generally occur without significant long-term sequelae, and patients are commonly able to return to their preinjury activities after proper management. The literature reports excellent outcomes after anatomical reduction of distal tibial and ankle physeal fractures with closed or open treatment. Treatment options include simple immobilization of nondisplaced fractures, and closed or open reduction for restoration of anatomic alignment of displaced fractures. Soft tissue interposition within the fracture can threaten successful closed reduction, and may warrant open management if closed reduction fails to produce a satisfactory result. Despite the documented possibility of soft tissue interposition preventing closed reduction of pediatric ankle fractures, there is a paucity of literature reporting this complication. We report a unique case of an irreducible Salter-Harris type II distal tibial physeal fracture secondary to interposition of the posterior tibial tendon. Copyright 2010 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

  6. Simulations of flow mode distributions on rough fracture surfaces using a parallelized Smoothed Particle Hydrodynamics (SPH) model

    NASA Astrophysics Data System (ADS)

    Kordilla, J.; Shigorina, E.; Tartakovsky, A. M.; Pan, W.; Geyer, T.

    2015-12-01

    Under idealized conditions (smooth surfaces, linear relationship between Bond number and Capillary number of droplets) steady-state flow modes on fracture surfaces have been shown to develop from sliding droplets to rivulets and finally (wavy) film flow, depending on the specified flux. In a recent study we demonstrated the effect of surface roughness on droplet flow in unsaturated wide aperture fractures, however, its effect on other prevailing flow modes is still an open question. The objective of this work is to investigate the formation of complex flow modes on fracture surfaces employing an efficient three-dimensional parallelized SPH model. The model is able to simulate highly intermittent, gravity-driven free-surface flows under dynamic wetting conditions. The effect of surface tension is included via efficient pairwise interaction forces. We validate the model using various analytical and semi-analytical relationships for droplet and complex flow dynamics. To investigate the effect of surface roughness on flow dynamics we construct surfaces with a self-affine fractal geometry and roughness characterized by the Hurst exponent. We demonstrate the effect of surface roughness (on macroscopic scales this can be understood as a tortuosity) on the steady-state distribution of flow modes. Furthermore we show the influence of a wide range of natural wetting conditions (defined by static contact angles) on the final distribution of surface coverage, which is of high importance for matrix-fracture interaction processes.

  7. Analysis of Mode I and Mode II Crack Growth Arrest Mechanism with Z-Fibre Pins in Composite Laminated Joint

    NASA Astrophysics Data System (ADS)

    Jeevan Kumar, N.; Ramesh Babu, P.

    2017-08-01

    This paper presents the numerical study of the mode I and mode II interlaminar crack growth arrest in hybrid laminated curved composite stiffened joint with Z-fibre reinforcement. A FE model of hybrid laminated skin-stiffener joint reinforced with Z-pins is developed to investigate the effect of Z- fibre pins on mode I and mode II crack growth where the delamination is embedded inbetween the skin and stiffener interface. A finite element model was developed using S4R element of a 4-node doubly curved thick shell elements to model the composite laminates and non linear interface elements to simulate the reinforcements. The numerical analyses revealed that Z-fibre pinning were effective in suppressing the delamination growth when propagated due to applied loads. Therefore, the Z-fibre technique effectively improves the crack growth resistance and hence arrests or delays crack growth extension.

  8. A MODEL STUDY OF TRANSVERSE MODE COUPLING INSTABILITY AT NATIONAL SYNCHROTRON LIGHT SOURCE-II (NSLS-II).

    SciTech Connect

    BLEDNYKH, A.; WANG, J.M.

    2005-05-15

    The vertical impedances of the preliminary designs of National Synchrotron Light Source II (NSLS-II) Mini Gap Undulators (MGU) are calculated by means of GdfidL code. The Transverse Mode Coupling Instability (TMCI) thresholds corresponding to these impedances are estimated using an analytically solvable model.

  9. Salter-Harris I and II fractures of the distal tibia: does mechanism of injury relate to premature physeal closure?

    PubMed

    Rohmiller, Michael T; Gaynor, Tracey P; Pawelek, Jeff; Mubarak, Scott J

    2006-01-01

    The distal tibial physis is the second most commonly injured physis in long bones. Recent reports demonstrate a high rate of premature physeal closure (PPC) in Salter-Harris (SH) type I or II fractures of the distal tibia. At our institution, 137 distal tibial SH type I or II fractures were treated from 1994 to 2002. Reviews were performed on all patients and 91 fractures met inclusion criteria. Patients were categorized according to treatment. We report a PPC rate of 39.6% in SH type I or II fractures of the distal tibial physis. We found a difference in PPC based on injury mechanism. The rate of PPC in patients with a supination-external-rotation-type injury was 35%, whereas patients with pronation-abduction-type injuries developed PPC in 54% of cases. Type of treatment may prevent PPC in some fractures. The most important determinant of PPC is the fracture displacement following reduction. PPC is a common problem following SH type I or II fractures of the distal tibia. Operative treatment may decrease the frequency of PPC in some fractures. Regardless of treatment method, we recommend anatomic reduction to decrease the risk of PPC.

  10. A closed phalangeal neck fracture with 180-degree rotation of the phalangeal head and concurrent displaced Salter-Harris II fracture.

    PubMed

    Al-Qattan, Mohammad M

    2012-07-01

    Closed type III phalangeal neck fractures with 180-degree rotation is a rare iatrogenic injury that occurs following failed attempts at closed reduction. Prior to closed reduction, the phalangeal head is in 90-degree rotation. Longitudinal traction during closed reduction then converts the deformity into 180-degree rotation. We present the first documented noniatrogenic case of phalangeal neck fracture with 180-degree rotation that was also associated with a displaced Salter-Harris II fracture at the same joint. The blood supply of the phalangeal head in that scenario is discussed along with precautions that should be taken during open reduction and internal fixation to avoid avascular necrosis of the phalangeal head.

  11. Notch strengthening or weakening governed by transition of shear failure to normal mode fracture.

    PubMed

    Lei, Xianqi; Li, Congling; Shi, Xinghua; Xu, Xianghong; Wei, Yujie

    2015-05-29

    It is generally observed that the existence of geometrical discontinuity like notches in materials will lead to strength weakening, as a resultant of local stress concentration. By comparing the influence of notches to the strength of three typical materials, aluminum alloys with intermediate tensile ductility, metallic glasses with no tensile ductility, and brittle ceramics, we observed strengthening in aluminum alloys and metallic glasses: Tensile strength of the net section in circumferentially notched cylinders increases with the constraint quantified by the ratio of notch depth over notch root radius; in contrast, the ceramic exhibit notch weakening. The strengthening in the former two is due to resultant deformation transition: Shear failure occurs in intact samples while samples with deep notches break in normal mode fracture. No such deformation transition was observed in the ceramic, and stress concentration leads to its notch weakening. The experimental results are confirmed by theoretical analyses and numerical simulation. The results reported here suggest that the conventional criterion to use brittleness and/or ductility to differentiate notch strengthening or weakening is not physically sound. Notch strengthening or weakening relies on the existence of failure mode transition and materials exhibiting shear failure while subjected to tension will notch strengthen.

  12. Notch strengthening or weakening governed by transition of shear failure to normal mode fracture

    PubMed Central

    Lei, Xianqi; Li, Congling; Shi, Xinghua; Xu, Xianghong; Wei, Yujie

    2015-01-01

    It is generally observed that the existence of geometrical discontinuity like notches in materials will lead to strength weakening, as a resultant of local stress concentration. By comparing the influence of notches to the strength of three typical materials, aluminum alloys with intermediate tensile ductility, metallic glasses with no tensile ductility, and brittle ceramics, we observed strengthening in aluminum alloys and metallic glasses: Tensile strength of the net section in circumferentially notched cylinders increases with the constraint quantified by the ratio of notch depth over notch root radius; in contrast, the ceramic exhibit notch weakening. The strengthening in the former two is due to resultant deformation transition: Shear failure occurs in intact samples while samples with deep notches break in normal mode fracture. No such deformation transition was observed in the ceramic, and stress concentration leads to its notch weakening. The experimental results are confirmed by theoretical analyses and numerical simulation. The results reported here suggest that the conventional criterion to use brittleness and/or ductility to differentiate notch strengthening or weakening is not physically sound. Notch strengthening or weakening relies on the existence of failure mode transition and materials exhibiting shear failure while subjected to tension will notch strengthen. PMID:26022892

  13. Spacing and aperture of opening-mode fractures in layered materials

    NASA Astrophysics Data System (ADS)

    Bai, Taixu

    This dissertation investigates the mechanical control on spacing and aperture of equally-spaced fractures in layered materials using the Finite Element Method, based on the theories of elasticity and linear fracture mechanics. It also investigates the effects of fracture spacing and aperture on fluid flow through the equally-spaced fractures. The results show that under a remote extension in the direction perpendicular to the fractures the normal stress acting in this direction between adjacent fractures changes from tensile to compressive as the fracture spacing to layer thickness ratio changes from greater than to less than a critical value. This stress transition precludes further infilling of fractures unless they are driven by mechanisms other than an extension, or there are significant flaws between the fractures. Hence, it defines the condition of saturation for fractures formed under extension in flawless layered materials. When flaws are present, further infilling of fractures is possible depending upon the size and locations of the flaws. The aspect ratio of equally-spaced fractures is linearly related to the average strain, the overburden stress, and the internal fluid pressure. The aspect ratio increases nonlinearly with increasing fracture spacing to layer thickness ratio because of the mechanical interaction between adjacent fractures. The interaction becomes insignificant when the spacing to layer thickness ratio is greater than about 6.0. The aspect ratio also depends on the ratio of Young's modulus of the fractured layer to that of the neighboring layers. This dependence is significant when the fracture spacing to layer thickness ratio is less than 1.3, otherwise it is negligibe. The aspect ratio is insensitive to variations in Poisson's ratios. Fluid flow rate through equally-spaced fractures does not always increases with increasing fracture density, i.e., with decreasing spacing to layer thickness ratio. There is an optimum value for the ratio

  14. Delayed fixation of displaced type II and III pediatric femoral neck fractures

    PubMed Central

    Azam, Md Quamar; Iraqi, AA; Sherwani, MKA; Abbas, M; Alam, Afzal; Sabir, Amir Bin; Asif, Naiyer

    2009-01-01

    Background: Time from injury to fixation of femoral neck fractures has been postulated as a vital determinant for rate of complications; however, no prospective study is available in the English literature. Delay, unfortunately, is inevitable in developing countries. The aim of the present study is to retrospectively review the outcome after delayed fixation of displaced type II and III femoral neck fractures in children. Materials and Methods: Using a standard assessment chart, we retrospectively reviewed medical records of all pediatric patients having femoral neck fractures presenting to our institution from June 1999 to May 2006. Inclusion criteria were children between 5 and 15 years of age sustaining displaced Delbet type II and III femoral neck fractures having a complete follow-up of at least 2 years. Patients with known metabolic disease, poliomyelitis or cerebral palsy, were excluded from the study. After application of inclusion and exclusion criteria, 22 patients having 22 fractures (13 type II and 9 type III) were studied. Surgery could be performed after a mean delay of 11.22 days (ranging from 2 to 21 days). Closed reduction was achieved in 14 cases and 8 cases required open reduction through anterolateral approach. Result: Osteonecrosis was noted in eight patients (36.37%) who included two of nine patients (22.22%) operated in the first week, three of eight patients (37.51%) operated in the second week, and three of five patients (60%) operated in the third week of injury. Nonunion was seen in four (18.18%) cases, and two of them were associated with failure of implants. One was treated by valgus osteotomy and the other by Meyer's procedure. Fractures united in both children but the latter developed avascular necrosis. Functional results, as assessed using Ratliff's criteria, were good in 14 (63.63%), fair in 2 (9%), and poor in 6 (27.27%) patients. Conclusion: Delay in fixation, type of fracture, and ability to achieve and maintain reduction are

  15. The therapeutic attitude in distal radial Salter and Harris type I and II fractures in children.

    PubMed

    Bumei, Gheorghe; Gavriliu, Stefan; Georgescu, Ileana; Vlad, Costel; Draghici, Isabela; Hurmuz, Lucia; Dan, Daniela; Hodorogea, Dan

    2010-01-01

    Salter Harris Fractures type, especially type I and II are treated by orthopedic reduction in the emergency room or operating room, under general anesthesia, followed by plaster immobilization. Neglected or incorrectly treated fractures, leading to malunion and radiocarpal subluxations which require surgical procedure. This paper proposes to evaluate the correctly applied orthopedic treatment and the expose of an original surgical technique in case of neglected and incorrectly treated fractures, leading to mal-unions and impediments in the radiocarpal mobility and aesthetics. we studied a group of 238 children with Salter Harris fractures type I and II, treated in "M.S. Curie" Emergency Hospital for Children, Bucharest. Out of the studied group, 200 children were treated by orthopedic reduction and immobilization in a plaster device. Malunions present within 38 children due to neglected or mistreated fractures, underwent open reduction with internal osteosynthesis by a technique that avoids violating the growth cartilage. This technique involves making an internal fixation with the radial joint surface in a normal position. Children receiving proper orthopedic reduction and immobilization in plaster device, 200 patients, were cured after 30-45 days of immobilization, depending on age and joint mobility which were within normal range. The 38 children with malunions underwent surgery to rectify the position of the radial joint surface. Postoperative results were good, proper position of the radiocarpal joint were made during the surgical procedure. The intemal fixation is ensured by a transepiphyseal wire and after 30 days of immobilization in a plaster device the patients started the recovery treatment. Radiocarpal joint mobility returned to normal after a variable period of 3 to 6 months, depending on the patient's age. Salter Harris I and II fractures are absolute indication for orthopedic treatment, in a matter of emergency, preferably in the operating room under

  16. A discrete dislocation analysis of mixed mode fracture at bimaterial interfaces

    NASA Astrophysics Data System (ADS)

    O'Day, Michael; Curtin, William

    2004-03-01

    The influence of mode mixity on crack growth and failure at a metal/ceramic bimaterial interface is examined within the discrete dislocation (DD) plasticity framework. In this method, plasticity occurs via the motion of a large number of dislocations embedded in a linearly elastic medium. No plastic constitutive law is required, however a set of rules governing dislocation nucleation, motion and annihilation is necessary. The numerical procedure uses a superposition technique, developed specifically to allow the efficient solution of DD problems with elastic inhomogeneities. An interface crack exists in the unloaded configuration, and a mode independent cohesive zone law characterizes the interface ahead of the crack tip. The influence of mode mixity on crack growth resistance curve (R-curve) behavior is qualitatively similar to continuum plasticity calculations, where increasing mode mixity leads to increasing toughness. However, deviations can arise due to (i) statistical effects, and (ii) the discrete nature of plasticity. Crack blunting, dislocation patterning and the existence of preferential slip planes all emerge naturally from the boundary value problem solution and give insight into observed R-curve trends.

  17. Influence of preparation mode and depth on the fracture strength of zirconia ceramic abutments restored with lithium disilicate crowns.

    PubMed

    Koutayas, Spiridon-Oumvertos; Mitsias, Miltiadis; Wolfart, Stefan; Kern, Matthias

    2012-01-01

    Zirconia implant abutments offer enhanced esthetics and promote biologic sealing; however, the effect of laboratory or intraoral preparation on the mechanical stability of zirconia has not been investigated. The purpose of the study was to evaluate the influence of the preparation mode and depth on the fracture strength of zirconia abutments restored with lithium disilicate crowns. To replace a maxillary central incisor (11.0 mm in height and 8.0 mm in width), 35 lithium disilicate crowns were cemented onto zirconia abutments on 4.5- ° - 15-mm titanium implants. Lithium disilicate implant crowns were divided into five study groups (n = 7) according to the abutment preparation mode (milling by the manufacturer or milling by the Celay System [Mikrona] [P]) and preparation depth (0.5 mm [A], 0.7 mm [B], or 0.9 mm [C]). All groups were subjected to quasi-static loading (S) at 135 degrees to the implant axis in a universal testing machine. Mean fracture strengths were: group SA, 384 ± 84 N (control); group SB, 294 ± 95 N; group SPB, 332 ± 80 N; group SC, 332 ± 52; group SPC, 381 ± 101 N. All specimens presented a typical fracture mode within the implant/abutment internal connection. Multiple regression analysis revealed that preparation depth up to 0.7 mm statistically influenced the fracture strength (P = .034), whereas the preparation mode did not seem to play an important role (P = .175). Regardless of preparation mode, circumferential preparation of zirconia abutments might negatively affect the fracture strength of adhesively cemented single implant lithium disilicate crowns.

  18. Fractures

    MedlinePlus

    A fracture is a break, usually in a bone. If the broken bone punctures the skin, it is called an open ... falls, or sports injuries. Other causes are low bone density and osteoporosis, which cause weakening of the ...

  19. Comparison of fracture strength and failure mode of different ceramic implant abutments.

    PubMed

    Elsayed, Adham; Wille, Sebastian; Al-Akhali, Majed; Kern, Matthias

    2017-04-01

    The whitish color of zirconia (ZrO2) abutments offers favorable esthetics compared with the grayish color of titanium (Ti) abutments. Nonetheless, ZrO2 has greater opacity, making it difficult to achieve natural tooth color. Therefore, lithium disilicate (LaT) abutments have been suggested to replace metal abutments. The purpose of this in vitro study was to evaluate the fracture strength and failure mode of single-tooth implant restorations using ZrO2 and LaT abutments, and to compare them with titanium (Ti) abutments. Five different types of abutments, Ti; ZrO2 with no metal base; ZrO2 with a metal base (ZrT); LaT; and LaT combination abutment and crown (LcT) were assembled on 40 Ti implants and restored with LaT crowns. Specimens were subjected to quasistatic loading using a universal testing machine, until the implant-abutment connection failed. As bending of the metal would be considered a clinical failure, the values of force (N) at which the plastic deformation of the metal occurred were calculated, and the rate of deformation was analyzed. Statistical analysis was done using the Mann-Whitney U test (α=.05). Group ZrO2 revealed the lowest resistance to failure with a mean of 202 ±33 N. Groups ZrT, LaT, and LaC withstood higher forces without fracture or debonding of the ceramic suprastructure, and failure was due to deformation of metal bases, with no statistically significant differences between these groups regarding the bending behavior. Within the limitations of this in vitro study, it was concluded that LaT abutments have the potential to withstand the physiological occlusal forces that occur in the anterior region and that ZrO2 abutments combined with Ti inserts have much higher fracture strength than pure ZrO2 abutments. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  20. Clinical Features and Treatment Modes of Mandibular Fracture at the Department of Oral and Maxillofacial Surgery, Shimane University Hospital, Japan

    PubMed Central

    Nakatani, Eiji; Kagimura, Tatsuo; Sekine, Joji

    2015-01-01

    Background The number of elderly patients with maxillofacial trauma is rapidly increasing due to active lifestyles and longevity. Shimane prefecture has the fastest growing proportion of elderly individuals in Japan. The aim of this study was to reveal the distinctive features and treatment modes of mandibular fracture treatment mode in patients requiring hospitalization at the Department of Oral and Maxillofacial Surgery, Shimane University Hospital, Japan. Patients and Methods Patient age, sex, period between injury and first consultation, years since injury, cause of injury, fracture site, treatment, and duration of hospitalization were evaluated. Univariate Poisson regression, relative risk with 95% confidence interval based on the Wald test, Fisher’s exact test, and Kruskal-Wallis test were used to explore associations among clinical and demographic variables. Results In total, 305 patients were diagnosed with and hospitalized for mandibular fracture from 1980 to 2010. Younger age increased the risk for mandibular fracture. Incidence was higher in males than females, particularly in the young, but the male to female ratio decreased with age. The period until first hospital consultation decreased progressively over the study period. Fall was a much more frequent cause in patients aged ≥60 than in those aged <60 years. Mandibular fracture with condyle, symphysis, and angle involvement were most common and were associated with sex, age, and treatment mode. Length of hospitalization has decreased since 1980. Conclusion In our department, patients aged ≥60 years accounted for a greater proportion of mandibular fracture cases than in many previous studies, reflecting the greater proportion of elderly residents in Shimane prefecture. PMID:26334627

  1. Evaluation of cone-beam computed tomography in the diagnosis of vertical root fractures: the influence of imaging modes and root canal materials.

    PubMed

    Neves, Frederico Sampaio; Freitas, Deborah Queiroz; Campos, Paulo Sérgio Flores; Ekestubbe, Annika; Lofthag-Hansen, Sara

    2014-10-01

    The purpose of this study was to evaluate the influence of cone-beam computed tomography (CBCT) imaging modes in the diagnosis of vertical root fractures with different intracanal materials. The sample consisted of 30 single-rooted teeth divided into 3 groups (n = 10), control and complete and incomplete root fracture. In each tooth, different materials were used (gutta-percha, metal post, and fiber post) as well as no filling material. Each tooth/root was scanned in a 3D Accuitomo 170 CBCT device by using 4 different imaging modes (high-resolution, high-fidelity, high-speed, and standard). In addition, the dose-area product was calculated for each CBCT imaging mode. The images were randomly evaluated by 5 dentomaxillofacial radiologists. Complete root fractures were visualized more easily than incomplete fractures. The presence of metal post and gutta-percha negatively influenced the diagnosis of root fracture. Regarding the CBCT imaging modes, there was no influence for complete root fracture diagnosis. In cases of incomplete root fractures, high-fidelity, high-resolution, and standard had a higher diagnostic accuracy, especially in the fiber post and no filling groups. The CBCT imaging modes had little influence in the diagnosis of complete and incomplete root fractures, whereas the presence of intracanal material had greater impact on the diagnostic ability, demonstrating that CBCT is not beneficial for the diagnosis of root fractures when metal posts are present. Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  2. Comparison of Intralaminar and Interlaminar Mode-I Fracture Toughness of Unidirectional IM7/8552 Graphite/Epoxy Composite

    NASA Technical Reports Server (NTRS)

    Czabaj, Michael W.; Ratcliffe, James

    2012-01-01

    The intralaminar and interlaminar mode-I fracture-toughness of a unidirectional IM7/8552 graphite/epoxy composite were measured using compact tension (CT) and double cantilever beam (DCB) test specimens, respectively. Two starter crack geometries were considered for both the CT and DCB specimen configurations. In the first case, starter cracks were produced by 12.5 micron thick, Teflon film inserts. In the second case, considerably sharper starter cracks were produced by fatigue precracking. For each specimen configuration, use of the Teflon film starter cracks resulted in initially unstable crack growth and artificially high initiation fracture-toughness values. Conversely, specimens with fatigue precracks exhibited stable growth onset and lower initiation fracture toughness. For CT and DCB specimens with fatigue precracks, the intralaminar and interlaminar initiation fracture toughnesses were approximately equal. However, during propagation, the CT specimens exhibited more extensive fiber bridging, and rapidly increasing R-curve behavior as compared to the DCB specimens. Observations of initiation and propagation of intralaminar and interlaminar fracture, and the measurements of fracture toughness, were supported by fractographic analysis using scanning electron microscopy.

  3. Resistance to maxillary premolar fractures after restoration of class II preparations with resin composite or ceromer.

    PubMed

    de Freitas, Cláudia Regina Buainain; Miranda, Maria Isabel Serra; de Andrade, Marcelo Ferrarezi; Flores, Victor Humberto Orbegoso; Vaz, Luís Geraldo; Guimarães, Catanzaro

    2002-09-01

    The aim of this study was to evaluate the resistance to fracture of intact and restored human maxillary premolars. Thirty noncarious human maxillary premolars, divided into three groups of 10, were submitted to mechanical tests to evaluate their resistance to fracture. Group 1 consisted of intact teeth. Teeth in group 2 received mesio-occlusodistal cavity preparations and were restored with direct resin composite restorations. Teeth in group 3 received mesio-occlusodistal cavity preparations and were restored with ceromer inlays placed with the indirect technique. After restoration, teeth were stored at 37 degrees C for 24 hours and then thermocycled for 500 cycles at temperatures of 5 degrees C and 55 degrees C. Statistical analysis revealed that group 3 (178.765 kgf) had a significantly greater maximum rupture load than did group 1 (120.040 kgf). There was no statistically significant difference between groups 1 and 2 or between groups 2 and 3. Class II cavity preparations restored with indirect ceromer inlays offered greater resistance to fracture than did intact teeth. The fracture resistance of teeth restored with resin composite was not significantly different from that of either the ceromer or intact teeth.

  4. Fracture prediction for the proximal femur using finite element models: Part II--Nonlinear analysis.

    PubMed

    Lotz, J C; Cheal, E J; Hayes, W C

    1991-11-01

    In Part I we reported the results of linear finite element models of the proximal femur generated using geometric and constitutive data collected with quantitative computed tomography. These models demonstrated excellent agreement with in vitro studies when used to predict ultimate failure loads. In Part II, we report our extension of those finite element models to include nonlinear behavior of the trabecular and cortical bone. A highly nonlinear material law, originally designed for representing concrete, was used for trabecular bone, while a bilinear material law was used for cortical bone. We found excellent agreement between the model predictions and in vitro fracture data for both the onset of bone yielding and bone fracture. For bone yielding, the model predictions were within 2 percent for a load which simulated one-legged stance and 1 percent for a load which simulated a fall. For bone fracture, the model predictions were within 1 percent and 17 percent, respectively. The models also demonstrated different fracture mechanisms for the two different loading configurations. For one-legged stance, failure within the primary compressive trabeculae at the subcapital region occurred first, leading to load transfer and, ultimately, failure of the surrounding cortical shell. However, for a fall, failure of the cortical and trabecular bone occurred simultaneously within the intertrochanteric region. These results support our previous findings that the strength of the subcapital region is primarily due to trabecular bone whereas the strength of the intertrochanteric region is primarily due to cortical bone.

  5. Surgical treatment of intraarticular calcaneous fractures of sanders' types II and III. Systematic review

    PubMed Central

    Pelliccioni, Adriano Augusto Antoniazzi; Bittar, Cíntia Kelly; Zabeu, José Luis Amim

    2012-01-01

    Objective This paper aims to identify the most effective surgical technique for intraarticular calcaneal fractures of Sanders' types II and III. Methods Systematic review of comparative randomized clinical trials on surgical treatment of the intraarticular fractures of the calcaneus (Sanders types II and III) that used the questionnaire of the American Orthopaedic Foot and Ankle Society. The studies were identified and retrieved in the following databases - LILACS, MEDLINE/PubMed, Cochrane Library, SciELO, EMBASE, Science Direct, Scopus, Journals@Ovid, ISI Web of Knowledge, Evidence Based Medicine, besides consulting the references of studies accessed. The keywords used Boolean logic (AND and OR): "calcaneus fracture, calcaneous, calcaneal; surgical treatment, management; open reduction, minimally invasive, percutaneous reduction; internal fixation, external fixation. Results We identified only three randomized comparative trials. Each study compared a different technique (external fixation, percutaneous fixation with Kirchner wires and cannulated screws fixation) to the open reduction with internal fixation using plate and screws (considered the standard technique). Conclusion Comparing the series, percutaneous fixation using Kirschner wires presented the best results, however, evidence is insufficient to assert superiority of this treatment in comparison with other surgical techniques. PMID:24453579

  6. An Acoustic Plate Mode Sensor for Biowarfare Toxins, Phase II

    DTIC Science & Technology

    1997-10-01

    Biological agents -- such as bacteria , bacterial toxins and viruses -- must be detected rapidly to allow their neutralization or the quick treatment of...Mode Sensor for Biowarfare Toxins PRINCIPAL INVESTIGATOR: Douglas J. McAllister, Ph.D. CONTRACTING ORGANIZATION: Biode, Incorporated Bangor, Maine...OF PAGES Acoustic Plate Mode, Biowarfare Toxins 54 16. PRICE CODE 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION

  7. Biomechanical Assessment of Stabilization of Simulated Type II Odontoid Fracture with Case Study

    PubMed Central

    Daniel, Roy T.; Klocke, Noelle; Yandamuri, Soumya S.; Bobinski, Lukas; Duff, John M.; Bucklen, Brandon S.

    2017-01-01

    Study Design Researchers created a proper type II dens fracture (DF) and quantified a novel current posterior fixation technique with spacers at C1–C2. A clinical case study supplements this biomechanical analysis. Purpose Researchers explored their hypothesis that spacers combined with posterior instrumentation (PI) reduce range of motion significantly, possibly leading to better fusion outcomes. Overview of Literature Literature shows that the atlantoaxial joint is unique in allowing segmental rotary motion, enabling head turning. With no intervertebral discs at these joints, multiple ligaments bind the axis to the skull base and to the atlas; an intact odontoid (dens) enhances stability. The most common traumatic injury at these strong ligaments is a type II odontoid fracture. Methods Each of seven specimens (C0–C3) was tested on a custom-built six-degrees-of-freedom spine simulator with constructs of intact state, type II DF, C1–C2 PI, PI with joint capsulotomy (PIJC), PI with spacers (PIS) at C1–C2, and spacers alone (SA). A bending moment of 2.0 Nm (1.5°/sec) was applied in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). One-way analysis of variance with repeated measures was performed. Results DF increased motion to 320%, 429%, and 120% versus intact (FE, LB, and AR, respectively). PI significantly reduced motion to 41%, 21%, and 8%. PIJC showed negligible changes from PI. PIS reduced motion to 16%, 14%, and 3%. SA decreased motion to 64%, 24%, and 54%. Reduced motion facilitated solid fusion in an 89-year-old female patient within 1 year. Conclusions Type II odontoid fractures can lead to acute or chronic instability. Current fixation techniques use C1–C2 PI or an anterior dens screw. Addition of spacers alongside PI led to increased biomechanical rigidity over intact motion and may offer an alternative to established surgical fixation techniques. PMID:28243364

  8. Time-dependent, mixed-mode fracture of solid rocket motor bondline systems

    NASA Astrophysics Data System (ADS)

    Wu, Jenq-Dah

    1999-11-01

    This study deals with predicting the long-term durability of solid rocket motor bondline systems, with emphasis on the bond between the insulator and the case. The former is a filled rubber that is time-dependent and undergoes large deformations and rotations, particularly near the crack tip. The case material was steel, essentially rigid. The first phase of the study dealt with the development of a nonlinear, time-dependent constitutive model for the insulator. Several pseudo stress models and one pseudo strain model were considered. Measurements from and predictions of uniaxial and biaxial experiments were compared. In addition, the objectivity of the stress measures was considered. As a result, the transformed Cauchy stress and second Piola-Kirchhoff stresses were recommended as suitable pseudo stress models for the crack growth studies that followed. Interfacial fracture experiments were conducted over a range of mode-mixes and loading rates. They were modeled via finite element analyses that incorporated the nonlinear constitutive behavior above. The analysis also included a cohesive zone model that accounted for the breakdown of material near the crack tip, using a cohesive zone modeling approach. The cohesive zone was also rate-dependent. It captured the rate dependence of the highly strained material near the crack front. Reasonable agreement between experiments and models was obtained, making durability predictions possible.

  9. Magnetic antenna excitation of whistler modes. II. Antenna arrays

    NASA Astrophysics Data System (ADS)

    Stenzel, R. L.; Urrutia, J. M.

    2014-12-01

    The excitation of whistler modes from magnetic loop antennas has been investigated experimentally. The field topology of the excited wave driven by a single loop antenna has been measured for different loop orientations with respect to the uniform background field. The fields from two or more antennas at different locations are then created by superposition of the single-loop data. It is shown that an antenna array can produce nearly plane waves which cannot be achieved with single antennas. By applying a phase shift along the array, oblique wave propagation is obtained. This allows a meaningful comparison with plane wave theory. The Gendrin mode and oblique cyclotron resonance are demonstrated. Wave helicity and polarization in space and time are demonstrated and distinguished from the magnetic helicity of the wave field. The superposition of two oblique plane whistler modes produces in a "whistler waveguide" mode whose polarization and helicity properties are explained. The results show that single point measurements cannot properly establish the wave character of wave packets. The laboratory observations are relevant for excitation and detection of whistler modes in space plasmas.

  10. Magnetic antenna excitation of whistler modes. II. Antenna arrays

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2014-12-15

    The excitation of whistler modes from magnetic loop antennas has been investigated experimentally. The field topology of the excited wave driven by a single loop antenna has been measured for different loop orientations with respect to the uniform background field. The fields from two or more antennas at different locations are then created by superposition of the single-loop data. It is shown that an antenna array can produce nearly plane waves which cannot be achieved with single antennas. By applying a phase shift along the array, oblique wave propagation is obtained. This allows a meaningful comparison with plane wave theory. The Gendrin mode and oblique cyclotron resonance are demonstrated. Wave helicity and polarization in space and time are demonstrated and distinguished from the magnetic helicity of the wave field. The superposition of two oblique plane whistler modes produces in a “whistler waveguide” mode whose polarization and helicity properties are explained. The results show that single point measurements cannot properly establish the wave character of wave packets. The laboratory observations are relevant for excitation and detection of whistler modes in space plasmas.

  11. Effets de l'humidite sur la propagation du delaminage dans un composite carbone/epoxy sollicite en mode mixte I/II

    NASA Astrophysics Data System (ADS)

    LeBlanc, Luc R.

    In industries such as aerospace, motorsports, and even sporting equipment, composite materials are used more than ever, primarily due to their high stiffness and strength to weight ratios. Studies have shown that moisture exposure on carbon/epoxy composite materials can affect their delamination toughness, initiation and growth rate. Of these studies, only a few demonstrated the effects of moisture on delamination toughness and initiation with mixed mode I/II loadings, while none have investigated the effects of moisture exposure of composites on delamination growth rate with mixed mode I/II loadings. The first part of this thesis studies the effects of moisture exposure on delamination growth in a carbon/epoxy composite using mixed mode I/II loadings. Coupons were cut from plates of unidirectional carbon/epoxy (040-800/5276-1) and were submerged in a 70°C distilled water bath until they reached saturation. Quasi -static experimental tests were performed using a range of mode mixities (0%, 25%, 50%, 75% and 1 00%) on dry and conditioned coupons to determine the effects of humidity on delamination toughness. Fatigue tests with the same mode mixities were performed to determine the effects of moisture on delamination initiation and growth rate. Results from tests with quasi-static loadings demonstrated that delamination toughness decreased for all loading modes studied except for mode I after composites are exposed to moisture. When a conditioned composite is subject to mode I loadings, its delamination toughness increases compared to non-conditioned composites. Composites exposed to moisture showed accelerated delamination initiation and growth rates for all mixed mode I/II fatigue loadings. Experimental data was used to determine which fracture criterion and growth rate model for mixed mode I/II delamination better represented the studied composite. A regression curve and regression surface was used to fit the experimental data to the delamination fracture

  12. Interlaminar fracture toughness: Three-dimensional finite element modeling for end-notch and mixed-mode flexure

    NASA Technical Reports Server (NTRS)

    Murthy, P. L. N.; Chamis, C. C.

    1985-01-01

    A computational procedure is described for evaluating End-Notch-Flexure (ENF) and Mixed-Mode-Flexure (MMF) interlaminar fracture toughness in unidirectional fiber composites. The procedure consists of a three-dimensional finite element analysis in conjunction with the strain energy release rate concept and with composite micromechanics. The procedure is used to analyze select cases of ENF and MMF. The strain energy release rate predicted by this procedure is in good agreement with limited experimental data. The procedure is used to identify significant parameters associated with interlaminar fracture toughness. It is also used to determine the critical strain energy release rate and its attendant crack length in ENF and/or MMF. This computational procedure has considerable versatility/generality and provides extensive information about interlaminar fracture toughness in fiber composites.

  13. Resistive wall modes in the Reversatron II RFP

    SciTech Connect

    Barrick, G.; Greene, P.; Robertson, S.

    1990-01-01

    The Reversatron 2 RFP (R/a=50cm/8cm) has been operated with interchangeable shells to investigate resistive wall modes. Shell penetration times are 610, 100, and 4 {mu}sec (no shell). With the 610 {mu}sec shell, the plasma current is {le} 65 kA and the duration {le} 550 {mu}sec. With no shell, helium discharges are more resistive and hydrogen discharges cannot be sustained. An m=1, n=-6 mode resonant on axis grows to a relative amplitude of 20% during the setting-up phase. With the 100{mu}sec shell, deuterium discharges can be sustained but are degraded due to a broad spectrum of modes. The increased plasma resistance can be correlated with the flux intersecting the wall. 21 refs., 12 figs.

  14. Nonsurgical treatment of Mason type II radial head fractures in athletes. A retrospective study

    PubMed Central

    GUZZINI, M.; VADALÀ, A.; AGRÒ, A.; DI SANZO, V.; PIRONI, D.; REDLER, A.; SERLORENZI, P.; PROIETTI, L.; CIVITENGA, C.; MAZZA, D.; LANZETTI, R.M.; FERRETTI, A.

    2016-01-01

    Objective The best treatment for moderately displaced radial head fractures (Mason type II) still remains controversial. In cases of isolated fractures, there is no evidence that a fragment displacement of ≥ 2 mm gives poor results in conservatively treated fractures. Patients and methods We retrospectively reviewed 52 patients (31M, 21F) affected by an isolated Mason type II fracture, treated with a long arm cast for two weeks between 2008 and 2013. All patients had practiced sports before being injured. They were all either bicyclists, or baseball, boxers, basketball, rugby, tennis or football players. The mean follow-up was 36 months. Elbow and forearm range of motion were measured. The Mayo Elbow Performance Score, the Broberg and Morrey rating system and the Disabilities of the Arm, Shoulder and Hand Score (DASH score) were analyzed. Follow-up radiographs were examined for evidence of consolidation, late displacement, early arthritis and non-unions. Results Flexion was slightly impaired in the injured limb when compared to the uninjured limb (137°± 6° versus 139°±5°) as were extension (–3°±6° versus 1°±4°, p < 0.05), supination (86°±6° versus 88°±3°), pronation (87°±4° versus 88°±6°) and valgus deviation (10°±4° versus 8°±3°, p < 0.05). 40 patients had no elbow complaints; 9 patients experienced occasional pain, 2 a mild instability of the elbow, and 4 a mild loss of grip strength. The DASH score was excellent in 48 patients (92.31%). In only 6 cases (11.53%) degenerative changes were greater in formerly injured elbows than in uninjured elbows. All patients returned to their previous sports activities. Conclusions Isolated Mason type II fractures can have a good or excellent mid-term functional outcome even when treated conservatively. PMID:28098055

  15. RAB-plate versus sliding hip screw for unstable trochanteric hip fractures: stability of the fixation and modes of failure--radiographic analysis of 218 fractures.

    PubMed

    Buciuto, R; Hammer, R

    2001-03-01

    The sliding hip screw has gained considerable acceptance in the treatment of unstable trochanteric fractures. However, the new type of 120 degrees fixed angle blade-plate with a buttress rod (RAB-plate) showed encouraging clinical results. The purpose of this study was to assess stability of fixation and analyze modes of failure in unstable trochanteric hip fractures treated with these devices. A retrospective radiographic review of 218 unstable fractures was performed. Linear and angular displacements of the major fragments and implant migration into the femoral head during healing were assessed. Additionally, adequacy of the reduction and the location of the implant within the femoral head as predictors of fixation failure were evaluated. The postreduction neck-shaft angle was maintained in the majority of the fractures in both groups. However, there was a significantly higher incidence of varus angulation by 10 degrees or more by the completion of healing among fractures treated with the sliding hip screw (p = 0.04). There was no statistically significant difference in vertical migration of the device into the femoral head between the implants used (p = 0.3). There was a significant relationship between failure of the fixation and varus reduction (p = 0.04) as well as screw/neck angle deviation more than 20 degrees in the lateral projection (p = 0.005) or if the implant was in a superior or posterior position (p = 0.02). The RAB-plate provided a more stable fixation, especially with regard to maintained postoperative alignment. However, positive predictors for fixation failure were identical for both devices. Here, the screw/neck angle deviation has had the strongest significance for prediction of fixation failure.

  16. Influence of injection mode on transport properties in kilometer-scale three-dimensional discrete fracture networks

    SciTech Connect

    Hyman, Jeffrey De'Haven; Painter, S. L.; Viswanathan, H.; Makedonska, N.; Karra, S.

    2015-09-12

    We investigate how the choice of injection mode impacts transport properties in kilometer-scale three-dimensional discrete fracture networks (DFN). The choice of injection mode, resident and flux-weighted, is designed to mimic different physical phenomena. It has been hypothesized that solute plumes injected under resident conditions evolve to behave similarly to solutes injected under flux-weighted conditions. Previously, computational limitations have prohibited the large-scale simulations required to investigate this hypothesis. We investigate this hypothesis by using a high-performance DFN suite, dfnWorks, to simulate flow in kilometer-scale three-dimensional DFNs based on fractured granite at the Forsmark site in Sweden, and adopt a Lagrangian approach to simulate transport therein. Results show that after traveling through a pre-equilibrium region, both injection methods exhibit linear scaling of the first moment of travel time and power law scaling of the breakthrough curve with similar exponents, slightly larger than 2. Lastly, the physical mechanisms behind this evolution appear to be the combination of in-network channeling of mass into larger fractures, which offer reduced resistance to flow, and in-fracture channeling, which results from the topology of the DFN.

  17. Correlation of Fracture Mode Transition of Ceramic Particle with Critical Velocity for Successful Deposition in Vacuum Kinetic Spraying Process

    NASA Astrophysics Data System (ADS)

    Park, Hyungkwon; Kim, Jinyoung; Lee, Sung Bo; Lee, Changhee

    2017-02-01

    Vacuum kinetic spraying (VKS) is a promising room-temperature process to fabricate dense ceramic films. However, unfortunately, the deposition mechanism is still not clearly understood. In this respect, the critical conditions for successful deposition were investigated. Based on simulation and microstructural analysis, it was found that as the particle velocity increased, fracture mode transition from tensile fracture to shear fracture occurred and particle did not bounce off anymore above a certain velocity. Simultaneously, particle underwent shock-induced plasticity and dynamic fragmentation. The plasticity assisted to prevent the fragments from rebounding by spending the excessive kinetic energy and fragmentation is essential for fragment bonding and film growth considering that the deposition rate increased as the fraction of fragmentation increased. Accordingly, plasticity and fragmentation take a crucial role for particle deposition. In this respect, the velocity that fracture mode transition occurs is newly defined as critical velocity. Consequently, for successful deposition, the particle should at least exceed the critical velocity and thus it is very crucial for film fabrication in VKS process at room temperature.

  18. Correlation of Fracture Mode Transition of Ceramic Particle with Critical Velocity for Successful Deposition in Vacuum Kinetic Spraying Process

    NASA Astrophysics Data System (ADS)

    Park, Hyungkwon; Kim, Jinyoung; Lee, Sung Bo; Lee, Changhee

    2016-12-01

    Vacuum kinetic spraying (VKS) is a promising room-temperature process to fabricate dense ceramic films. However, unfortunately, the deposition mechanism is still not clearly understood. In this respect, the critical conditions for successful deposition were investigated. Based on simulation and microstructural analysis, it was found that as the particle velocity increased, fracture mode transition from tensile fracture to shear fracture occurred and particle did not bounce off anymore above a certain velocity. Simultaneously, particle underwent shock-induced plasticity and dynamic fragmentation. The plasticity assisted to prevent the fragments from rebounding by spending the excessive kinetic energy and fragmentation is essential for fragment bonding and film growth considering that the deposition rate increased as the fraction of fragmentation increased. Accordingly, plasticity and fragmentation take a crucial role for particle deposition. In this respect, the velocity that fracture mode transition occurs is newly defined as critical velocity. Consequently, for successful deposition, the particle should at least exceed the critical velocity and thus it is very crucial for film fabrication in VKS process at room temperature.

  19. Influence of injection mode on transport properties in kilometer-scale three-dimensional discrete fracture networks

    DOE PAGES

    Hyman, Jeffrey De'Haven; Painter, S. L.; Viswanathan, H.; ...

    2015-09-12

    We investigate how the choice of injection mode impacts transport properties in kilometer-scale three-dimensional discrete fracture networks (DFN). The choice of injection mode, resident and flux-weighted, is designed to mimic different physical phenomena. It has been hypothesized that solute plumes injected under resident conditions evolve to behave similarly to solutes injected under flux-weighted conditions. Previously, computational limitations have prohibited the large-scale simulations required to investigate this hypothesis. We investigate this hypothesis by using a high-performance DFN suite, dfnWorks, to simulate flow in kilometer-scale three-dimensional DFNs based on fractured granite at the Forsmark site in Sweden, and adopt a Lagrangian approachmore » to simulate transport therein. Results show that after traveling through a pre-equilibrium region, both injection methods exhibit linear scaling of the first moment of travel time and power law scaling of the breakthrough curve with similar exponents, slightly larger than 2. Lastly, the physical mechanisms behind this evolution appear to be the combination of in-network channeling of mass into larger fractures, which offer reduced resistance to flow, and in-fracture channeling, which results from the topology of the DFN.« less

  20. Shear Fracture of Dual Phase AHSS in the Process of Stamping: Macroscopic Failure Mode and Micro-level Metallographical Observation

    NASA Astrophysics Data System (ADS)

    Wang, Wurong; Wei, Xicheng; Yang, Jun; Shi, Gang

    2011-08-01

    Due to its excellent strength and formability combinations, dual phase (DP) steels offer the potential to improve the vehicle crashworthiness performance without increasing car body weight and have been increasingly used into new vehicles. However, a new type of crack mode termed as shear fracture is accompanied with the application of these high strength DP steel sheets. With the cup drawing experiment to identify the limit drawing ratio (LDR) of three DP AHSS with strength level from 600 MPa to 1000 MPa, the study compared and categorized the macroscopic failure mode of these three types of materials. The metallographical observation along the direction of crack was conducted for the DP steels to discover the micro-level propagation mechanism of the fracture.

  1. Do joints initiate as sharp mode I fractures or finite thickness dilatancy bands? Insights from laboratory experiments and field data

    NASA Astrophysics Data System (ADS)

    Petit, J.; Chemenda, A. I.; Jorand, C.

    2011-12-01

    Terminology on fracture and discontinuities in geological objects mainly relies on distinguishing between tabular and sharp forms of deformation localization/failure structures (Aydin et al, JSG 2006; Shultz and Fossen, AAPG, 2009). On this basis joints (considered as mode I fractures) and dilation bands (very rarely observed) are distinguished among extension discontinuities. The former propagate with the separation of the fracture walls due to strong stress concentration at the fracture tips. The plumose features or hackles typical of joints (these terms cover a wide variety of diverging fractographic features) are believed to result from the fracture front breakdown due to the loading mode change (the origin of this change remains unclear). This view is called into question by recent experimental results of extension tests conducted on a synthetic physical rock analogue (granular, frictional, cohesive and dilatant) material (GRAM1) and by field observations of embryonic (not yet open) joints in highly jointed dolomicrite Chemenda et al., JGR, 2011). The initial porosity and grain size of both materials are very different, but at SEM scale, both experimental and natural unopened discontinuities reveal a comparable dilatancy (dilation) band structure with a porosity increase over a width of several grains. This suggests that the distinction between tabular and sharp is a matter of observation scale. Both axisymetric and poly-axial extension tests show that dilatancy bands form at elevated mean stress and have plumose morphology. Mode I cracking occurs only at very low mean stres and the forming fractures do not bear plumose features. Thus the absence of plumose structures can be considered as the signature of mode I fracturing. Consequently, we propose that non- plumose bearing natural joints (provided their fractography is not eroded) could originate as mode I fractures and call them "mode I joints". We call the joints formed as closed dilatancy bands propagating

  2. Vibrational relaxation pathways of amide I and amide II modes in N-methylacetamide.

    PubMed

    Piatkowski, L; Bakker, H J

    2012-04-28

    We studied the vibrational energy relaxation mechanisms of the amide I and amide II modes of N-methylacetamide (NMA) monomers dissolved in bromoform using polarization-resolved femtosecond two-color vibrational spectroscopy. The results show that the excited amide I vibration transfers its excitation energy to the amide II vibration with a time constant of 8.3 ± 1 ps. In addition to this energy exchange process, we observe that the excited amide I and amide II vibrations both relax to a final thermal state. For the amide I mode this latter process dominates the vibrational relaxation of this mode. We find that the vibrational relaxation of the amide I mode depends on frequency which can be well explained from the presence of two subbands with different vibrational lifetimes (~1.1 ps on the low frequency side and ~2.7 ps on the high frequency side) in the amide I absorption spectrum.

  3. Development of fracture facets from a crack loaded in mode I+III: Solution and application of a model 2D problem

    NASA Astrophysics Data System (ADS)

    Leblond, Jean-Baptiste; Frelat, Joël

    2014-03-01

    It is experimentally well-known that a crack loaded in mode I+III propagates through formation of discrete fracture facets inclined at a certain tilt angle on the original crack plane, depending on the ratio of the mode III to mode I initial stress intensity factors. Pollard et al. (1982) have proposed to calculate this angle by considering the tractions on all possible future infinitesimal facets and assuming shear tractions to be zero on that which will actually develop. In this paper we consider the opposite case of well-developed facets; the stress field near the lateral fronts of such facets becomes independent of the initial crack and essentially 2D in a plane perpendicular to the main direction of crack propagation. To determine this stress field, we solve the model 2D problem of an infinite plate containing an infinite periodic array of cracks inclined at some angle on a straight line, and loaded through uniform stresses at infinity. This is done first analytically, for small values of this angle, by combining Muskhelishvili's (1953) formalism and a first-order perturbation procedure. The formulae found for the 2D stress intensity factors are then extended in an approximate way to larger angles by using another reference solution, and finally assessed through comparison with some finite element results. To finally illustrate the possible future application of these formulae to the prediction of the stationary tilt angle, we introduce the tentative assumption that the 2D mode II stress intensity factor is zero on the lateral fronts of the facets. An approximate formula providing the tilt angle as a function of the ratio of the mode III to mode I stress intensity factors of the initial crack is deduced from there. This formula, which slightly depends on the type of loading imposed, predicts somewhat smaller angles than that of Pollard et al. (1982).

  4. Tensile Fracture Modes in Fe-22Mn-0.6C and Fe-30Mn-3Si-3Al Twinning-Induced Plasticity (TWIP) Steels

    NASA Astrophysics Data System (ADS)

    Yang, H. K.; Tian, Y. Z.; Zhang, Z. J.; Yang, C. L.; Zhang, P.; Zhang, Z. F.

    2017-10-01

    Tensile tests were carried out to investigate the differences in fracture mechanisms between Fe -22Mn -0.6C and Fe -30Mn -3Si -3Al (wt pct) twinning-induced plasticity steels. Although both steels possess a strong twinning capability during tensile deformation, they display different tensile fracture modes of shear and necking. The Portevin -le Chatelier band is proposed as the key factor influencing the different fracture mechanisms.

  5. Posterior periosteal disruption in Salter-Harris Type II fractures of the distal femur: evidence for a hyperextension mechanism.

    PubMed

    Kritsaneepaiboon, Supika; Shah, Rajvee; Murray, Martha M; Kleinman, Paul K

    2009-12-01

    Patterns of periosteal disruption are important factors in assessing the mechanism of injury of radiologically evident Salter-Harris (SH) fractures. The purpose of this study is to assess the frequency of posterior periosteal disruption on MRI in radiographically occult or subtle SH type II fractures of the distal femur and to evaluate associated soft-tissue findings that support a hyperextension mechanism of injury. We found that all children in our experience with occult or subtle SH type II fractures of the distal femur have posterior periosteal disruption and other MRI findings to indicate a hyperextension mechanism of injury. Direct indicators of fracture may be inconspicuous, and the presence of posterior periosteal disruption is a clue that should prompt a search for other features of this serious pediatric injury, which may be followed by limb shortening or angular deformity.

  6. Mode I and Mode II Interlaminar Crack Growth Resistances of Ceramic Matrix Composites at Ambient Temperature

    DTIC Science & Technology

    2007-03-02

    Sci. Proc., 25[4] 71-78 (2004). 9. L. P. Zawada , “Longitudinal and Transthickness Tensile Behavior of Several Oxide/Oxide Composites,” Ceram. Eng...Unidirectional C-C Composite,” J. Nucl. Mater., 230 226-232 (1996). 11. S. Mall, R. P. Vozzola, and L. Zawada , “Characterization of Fracture in Fiber...Behavior of a Unidirectional C-C Composite,” J. Nucl. Mater., 230 226-232 (1996). 34. L. P. Zawada , “Longitudinal and Transthickness Tensile Behavior

  7. Operative Treatment of Fifth Metatarsal Jones Fractures (Zones II and III) in the NBA.

    PubMed

    O'Malley, Martin; DeSandis, Bridget; Allen, Answorth; Levitsky, Matthew; O'Malley, Quinn; Williams, Riley

    2016-05-01

    Proximal fractures of the fifth metatarsal (zone II and III) are common in the elite athlete and can be difficult to treat because of a tendency toward delayed union, nonunion, or refracture. The purpose of this case series was to report our experience in treating 10 NBA players, determine the healing rate, return to play, refracture rate, and role of foot type in these athletes. The records of 10 professional basketball players were retrospectively reviewed. Seven athletes underwent standard percutaneous internal fixation with bone marrow aspirate concentrate (BMAC) whereas the other 3 had open bone grafting primarily in addition to fixation and BMAC. Radiographic features evaluated included fourth-fifth intermetatarsal, fifth metatarsal lateral deviation, calcaneal pitch, and metatarsus adductus angles. Radiographic healing was observed at an overall average of 7.5 weeks and return to play was 9.8 weeks. Three athletes experienced refractures. There were no significant differences in clinical features or radiographic measurements except that the refracture group had the highest metatatarsus adductus angles. Most athletes were pes planus and 9 of 10 had a bony prominence under the fifth metatarsal styloid. This is the largest published series of operatively treated professional basketball players who exemplify a specific patient population at high risk for fifth metatarsal fracture. These players were large and possessed a unique foot type that seemed to be associated with increased risk of fifth metatarsal fracture and refracture. This foot type had forefoot metatarsus adductus and a fifth metatarsal that was curved with a prominent base. We continue to use standard internal fixation with bone marrow aspirate but advocate additional prophylactic open bone grafting in patients with high fourth-to-fifth intermetatarsal, fifth metatarsal lateral deviation, and metatarsus adductus angles as well as prominent fifth metatarsal styloids in order to improve fracture

  8. Fractionalization of optical beams: II. Elegant Laguerre Gaussian modes

    NASA Astrophysics Data System (ADS)

    Gutiérrez-Vega, Julio C.

    2007-05-01

    We apply the tools of fractional calculus to introduce new fractional-order solutions of the paraxial wave equation that smoothly connect the elegant Laguerre-Gaussian beams of integral-order. The solutions are characterized in general by two fractional indices and are obtained by fractionalizing the creation operators used to create elegant Laguerre-Gauss beams from the fundamental Gaussian beam. The physical and mathematical properties of the circular fractional beams are discussed in detail. The orbital angular momentum carried by the fractional beam is a continuous function of the angular mode index and it is not restricted to take only discrete values.

  9. Effect of loading mode on the fracture toughness of a reduced activation ferritic/martensitic stainless steel

    SciTech Connect

    Li, H.; Hirth, J.P.; Jones, R.H.; Gelles, D.S.

    1993-09-01

    The critical J integrals of mode I (J{sub IC}), mixed-mode I/III (J{sub MC}), and mode III (J{sub IIIC}) were examined for a ferritic stainless steel (F-82H) at ambient temperature. A determination of J{sub MC} was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 55 degrees from the load line. The results showed that J{sub MC}s and tearing moduli (T{sub M}) varied with the crack angles and were lower than their mode I and mode III counterparts. Both the minimum J{sub MC} and T{sub M} occurred at a crack angle between 40 and 50 degrees, where {sigma}{sub i}/{sigma}{sub iii} was 1.2 to 0.84. The J{sub min} was 240 kJ/m{sup 2}, and ratios of J{sub IC}/J{sub min} and J{sub IIIC}/J{sub min} were about 2.1 and 1.9, respectively. Morphology of fracture surfaces was consistent with the change of J{sub MC} and T{sub M} values. While the upper shelf-fracture toughness of F-82H depends on loading mode, the J{sub min} remains very high. Other important considerations include the effect of mixed-mode loading on the DBT temperature, and effects of hydrogen and irradiation on J{sub min}.

  10. Atomistic study on mixed-mode fracture mechanisms of ferrite iron interacting with coherent copper and nickel nanoclusters

    NASA Astrophysics Data System (ADS)

    Al-Motasem, Ahmed Tamer; Mai, Nghia Trong; Choi, Seung Tae; Posselt, Matthias

    2016-04-01

    The effect of copper and/or nickel nanoclusters, generally formed by neutron irradiation, on fracture mechanisms of ferrite iron was investigated by using molecular statics simulation. The equilibrium configuration of nanoclusters was obtained by using a combination of an on-lattice annealing based on Metropolis Monte Carlo method and an off-lattice relaxation by molecular dynamics simulation. Residual stress distributions near the nanoclusters were also calculated, since compressive or tensile residual stresses may retard or accelerate, respectively, the propagation of a crack running into a nanocluster. One of the nanoclusters was located in front of a straight crack in ferrite iron with a body-centered cubic crystal structure. Two crystallographic directions, of which the crack plane and crack front direction are (010)[001] and (111) [ 1 bar 10 ] , were considered, representing cleavage and non-cleavage orientations in ferrite iron, respectively. Displacements corresponding to pure opening-mode and mixed-mode loadings were imposed on the boundary region and the energy minimization was performed. It was observed that the fracture mechanisms of ferrite iron under the pure opening-mode loading are strongly influenced by the presence of nanoclusters, while under the mixed-mode loading the nanoclusters have no significant effect on the crack propagation behavior of ferrite iron.

  11. A new mixed-mode fracture criterion for large-scale lattice models

    NASA Astrophysics Data System (ADS)

    Sachau, T.; Koehn, D.

    2014-01-01

    Reasonable fracture criteria are crucial for the modeling of dynamic failure in computational lattice models. Successful criteria exist for experiments on the micro- and on the mesoscale, which are based on the stress that a bond experiences. In this paper, we test the applicability of these failure criteria to large-scale models, where gravity plays an important role in addition to the externally applied deformation. Brittle structures, resulting from these criteria, do not resemble the outcome predicted by fracture mechanics and by geological observations. For this reason we derive an elliptical fracture criterion, which is based on the strain energy stored in a bond. Simulations using the new criterion result in realistic structures. It is another great advantage of this fracture model that it can be combined with classic geological material parameters: the tensile strength σ0 and the shear cohesion τ0. The proposed fracture criterion is much more robust with regard to numerical strain increments than fracture criteria based on stress (e.g., Drucker-Prager). While we tested the fracture model only for large-scale structures, there is strong reason to believe that the model is equally applicable to lattice simulations on the micro- and on the mesoscale.

  12. Cooperative binding modes of Cu(II) in prion protein

    NASA Astrophysics Data System (ADS)

    Hodak, Miroslav; Chisnell, Robin; Lu, Wenchang; Bernholc, Jerry

    2007-03-01

    The misfolding of the prion protein, PrP, is responsible for a group of neurodegenerative diseases including mad cow disease and Creutzfeldt-Jakob disease. It is known that the PrP can efficiently bind copper ions; four high-affinity binding sites located in the octarepeat region of PrP are now well known. Recent experiments suggest that at low copper concentrations new binding modes, in which one copper ion is shared between two or more binding sites, are possible. Using our hybrid Thomas-Fermi/DFT computational scheme, which is well suited for simulations of biomolecules in solution, we investigate the geometries and energetics of two, three and four binding sites cooperatively binding one copper ion. These geometries are then used as inputs for classical molecular dynamics simulations. We find that copper binding affects the secondary structure of the PrP and that it stabilizes the unstructured (unfolded) part of the protein.

  13. The vibrational mode of the tibia and assessment of bone union in experimental fracture healing using the impulse response method.

    PubMed

    Nakatsuchi, Y; Tsuchikane, A; Nomura, A

    1996-10-01

    This study attempts to clarify the use of the impulse response method in the assessment of fracture healing. The vibrational mode as well as the effect of simulated callus consolidation on the vibrational parameters of excised human tibia were studied. Two separate vibrations were found, one vibrating strongly in the lateral direction and the other vibrating weakly in the antero-posterior direction. The ability to identify the primary vibrational mode in the lateral direction would make the impulse response method suitable for use in clinical practice. The callus consolidation process was simulated by the sequential consolidation of an adhesive material in an experimentally produced fracture gap. The change in hardness of the epoxy was found to correlate well with the change of resonant frequency of the bone. The resonant frequency demonstrated a steady increase during the initial phase of consolidation of the adhesive, up to about 40% of its final hardness. With the addition of various constructs for fracture fixation to the in vitro model such as a plate, Ender's pins, a Russell-Taylor intramedullary nail, or an Orthofix external fixator, the relationship between the consolidation of the 'callus' and the change in resonant frequency of the bone was not disturbed.

  14. Failure modes and fracture origins of porcelain veneers on bilayer dental crowns.

    PubMed

    Liu, Yihong; Liu, Guanghua; Wang, Yong; Shen, James Zhijian; Feng, Hailan

    2014-01-01

    The aims of this study were to determine the fracture origins and crack paths in the porcelain of clinically failed bilayer ceramic restorations and to reveal the correlation between the porcelain failures and material properties. Three clinically failed crowns of each material (bilayer zirconia crowns, galvano-ceramic crowns, and porcelain-fused-to-metal crowns) were collected and underwent failure analysis. The fractures found in porcelain veneers showed several characteristics including wear, Hertzian cone crack, chipping off, and delamination. The results indicated that the fracture origins and features of the porcelain in bilayer ceramic restorations might be affected by the rigidity of core materials and thickness of copings.

  15. Fracture mode, microstructure and temperature-dependent elastic moduli for thermoelectric composites of PbTe-PbS with SiC nanoparticle additions

    NASA Astrophysics Data System (ADS)

    Ni, Jennifer E.; Case, Eldon D.; Schmidt, Robert D.; Wu, Chun-I.; Hogan, Timothy P.; Trejo, Rosa M.; Lara-Curzio, Edgar; Kanatzidis, Mercouri G.

    2013-12-01

    Twenty-six (Pb0.95Sn0.05Te)0.92(PbS)0.08-0.055% PbI2-SiC nanoparticle (SiCnp) composite thermoelectric specimens were either hot pressed or pulsed electric current sintered (PECS). Bloating (a thermally induced increase in porosity, P, for as-densified specimens) was observed during annealing at temperatures >603 K for hot-pressed specimens and PECS-processed specimens from wet milled powders, but in contrast seven out of seven specimens densified by PECS from dry milled powders showed no observable bloating following annealing at temperatures up to 936 K. In this study, bloating in the specimens was accessed via thermal annealing induced changes in (i) porosity measured by scanning electron microscopy on fractured specimen surfaces, (ii) specimen volume and (iii) elastic moduli. The moduli were measured by resonant ultrasound spectroscopy. SiCnp additions (1-3.5 vol.%) changed the fracture mode from intergranular to transgranular, inhibited grain growth, and limited bloating in the wet milled PECS specimens. Inhibition of bloating likely occurs due to cleaning of contamination from powder particle surfaces via PECS processing which has been reported previously in the literature.

  16. Fracture mode, microstructure and temperature-dependent elastic moduli for thermoelectric composites of PbTe PbS with SiC nanoparticle additions

    SciTech Connect

    Ni, Jennifer E; Case, Eldon D; Hogan, Timophy P.; Trejo, Rosa M; Lara-Curzio, Edgar; Kanatzidis, Mercouri G.

    2013-01-01

    Twenty-six (Pb0.95Sn0.05Te)0.92(PbS)0.08 0.055% PbI2 SiC nanoparticle (SiCnp) composite thermoelectric specimens were either hot pressed or pulsed electric current sintered (PECS). Bloating (a thermally induced increase in porosity, P, for as-densified specimens) was observed during annealing at temperatures >603 K for hot-pressed specimens and PECS-processed specimens from wet milled powders, but in contrast seven out of seven specimens densified by PECS from dry milled powders showed no observable bloating following annealing at temperatures up to 936 K. In this study, bloating in the specimens was accessed via thermal annealing induced changes in (i) porosity measured by scanning electron microscopy on fractured specimen surfaces, (ii) specimen volume and (iii) elastic moduli. The moduli were measured by resonant ultrasound spectroscopy. SiCnp additions (1 3.5 vol.%) changed the fracture mode from intergranular to transgranular, inhibited grain growth, and limited bloating in the wet milled PECS specimens. Inhibition of bloating likely occurs due to cleaning of contamination from powder particle surfaces via PECS processing which has been reported previously in the literature.

  17. Pulsatile Support Mode of BJUT-II Ventricular Assist Device (VAD) has Better Hemodynamic Effects on the Aorta than Constant Speed Mode: A Primary Numerical Study

    PubMed Central

    Gu, Kaiyun; Gao, Bin; Chang, Yu; Zeng, Yi

    2016-01-01

    Background BJUT-II VAD is a novel left ventricular assist device (LVADs), directly implanted into the ascending aorta. The pulsatile support mode is proposed to achieve better unloading performance than constant speed mode. However, the hemodynamic effects of this support mode on the aorta are still unclear. The aim of this study was to clarify the hemodynamic effects BJUT-II VAD under pulsatile support mode on the aorta. Material/Methods Computational fluid dynamics (CFD) studies, based on a patient-specific aortic geometric model, were conducted. Wall shear stress (WSS), averaged WSS (avWSS), oscillatory shear index (OSI), and averaged helicity density (Ha) were calculated to compare the differences in hemodynamic effects between pulsatile support mode and constant speed mode. Results The results show that avWSS under pulsatile support mode is significantly higher than that under constant speed mode (0.955Pa vs. 0.675Pa). Similarly, the OSI value under pulsatile mode is higher than that under constant speed mode (0.104 vs. 0.057). In addition, Ha under pulsatile mode for all selected cross-sections is larger than that under constant mode. Conclusions BJUT-II VAD, under pulsatile control mode, may prevent atherosclerosis lesions and aortic remodeling. The precise effects of pulsatile support mode on atherosclerosis and aortic remodeling need to be further studied in animal experiments. PMID:27363758

  18. Pulsatile Support Mode of BJUT-II Ventricular Assist Device (VAD) has Better Hemodynamic Effects on the Aorta than Constant Speed Mode: A Primary Numerical Study.

    PubMed

    Gu, Kaiyun; Gao, Bin; Chang, Yu; Zeng, Yi

    2016-07-01

    BACKGROUND BJUT-II VAD is a novel left ventricular assist device (LVADs), directly implanted into the ascending aorta. The pulsatile support mode is proposed to achieve better unloading performance than constant speed mode. However, the hemodynamic effects of this support mode on the aorta are still unclear. The aim of this study was to clarify the hemodynamic effects BJUT-II VAD under pulsatile support mode on the aorta. MATERIAL AND METHODS Computational fluid dynamics (CFD) studies, based on a patient-specific aortic geometric model, were conducted. Wall shear stress (WSS), averaged WSS (avWSS), oscillatory shear index (OSI), and averaged helicity density (Ha) were calculated to compare the differences in hemodynamic effects between pulsatile support mode and constant speed mode. RESULTS The results show that avWSS under pulsatile support mode is significantly higher than that under constant speed mode (0.955Pa vs. 0.675Pa). Similarly, the OSI value under pulsatile mode is higher than that under constant speed mode (0.104 vs. 0.057). In addition, Ha under pulsatile mode for all selected cross-sections is larger than that under constant mode. CONCLUSIONS BJUT-II VAD, under pulsatile control mode, may prevent atherosclerosis lesions and aortic remodeling. The precise effects of pulsatile support mode on atherosclerosis and aortic remodeling need to be further studied in animal experiments.

  19. Characterization of Mode I and Mode II delamination growth and thresholds in AS4/PEEK composites

    NASA Technical Reports Server (NTRS)

    Martin, Roderick H.; Murri, Gretchen Bostaph

    1990-01-01

    Composite materials often fail by delamination. The onset and growth of delamination in AS4/PEEK, a tough thermoplastic matrix composite, was characterized for mode 1 and mode 2 loadings, using the Double Cantilever Beam (DCB) and the End Notched Flexure (ENF) test specimens. Delamination growth per fatigue cycle, da/dN, was related to strain energy release rate, G, by means of a power law. However, the exponents of these power laws were too large for them to be adequately used as a life prediction tool. A small error in the estimated applied loads could lead to large errors in the delamination growth rates. Hence strain energy release rate thresholds, G sub th, below which no delamination would occur were also measured. Mode 1 and 2 threshold G values for no delamination growth were found by monitoring the number of cycles to delamination onset in the DCB and ENF specimens. The maximum applied G for which no delamination growth had occurred until at least 1,000,000 cycles was considered the threshold strain energy release rate. Comments are given on how testing effects, facial interference or delamination front damage, may invalidate the experimental determination of the constants in the expression.

  20. Characterization of Mode I and Mode II delamination growth and thresholds in AS4/PEEK composites

    NASA Technical Reports Server (NTRS)

    Martin, Roderick H.; Murri, Gretchen Bostaph

    1990-01-01

    Composite materials often fail by delamination. The onset and growth of delamination in AS4/PEEK, a tough thermoplastic matrix composite, was characterized for mode 1 and mode 2 loadings, using the Double Cantilever Beam (DCB) and the End Notched Flexure (ENF) test specimens. Delamination growth per fatigue cycle, da/dN, was related to strain energy release rate, G, by means of a power law. However, the exponents of these power laws were too large for them to be adequately used as a life prediction tool. A small error in the estimated applied loads could lead to large errors in the delamination growth rates. Hence strain energy release rate thresholds, G sub th, below which no delamination would occur were also measured. Mode 1 and 2 threshold G values for no delamination growth were found by monitoring the number of cycles to delamination onset in the DCB and ENF specimens. The maximum applied G for which no delamination growth had occurred until at least 1,000,000 cycles was considered the threshold strain energy release rate. Comments are given on how testing effects, facial interference or delamination front damage, may invalidate the experimental determination of the constants in the expression.

  1. EFFECT OF RADIUS OF LOADING NOSE AND SUPPORTS IN SHORT BEAM TEST FIXTURE ON FRACTURE MODE AND INTERLAMINAR SHEAR STRENGTH OF GFRP AT 77 K

    SciTech Connect

    Nishimura, A.

    2008-03-03

    A short beam test is useful to evaluate interlaminar shear strength of glass fiber reinforced plastics, especially for material selection. However, effect of test fixture configuration on interlaminar shear strength has not been clarified. This paper describes dependence of fracture mode and interlaminar shear strength on the fixture radius using the same materials and procedure. In addition, global understanding of the role of the fixture is discussed. When small loading nose and supports are used for the tests, bending fracture or translaminar fracture happens and the interlaminar shear strength would become smaller. By adopting the large radius loading nose and supports (6 mm radius is recommended), it is newly recognized that some stress concentration is able to be reduced, and the interlaminar fracture tends to occur and the other fracture modes will be suppressed. The interlaminar shear strength of 2.5 mm thick GFRP plate of G-10CR is evaluated as 130-150 MPa at 77 K.

  2. Acoustic mode driven by fast electrons in TJ-II Electron Cyclotron Resonance plasmas

    NASA Astrophysics Data System (ADS)

    Sun, B. J.; Ochando, M. A.; López-Bruna, D.

    2016-08-01

    Intense harmonic oscillations in radiation signals (δ I/I∼ 5{%}) are commonly observed during Electron Cyclotron Resonance (ECR) heating in TJ-II stellarator plasmas at low line-averaged electron density, 0.15 < \\bar{n}e < 0.6 ×1019 \\text{m}-3 . The frequency agrees with acoustic modes. The poloidal modal structure is compatible with Geodesic Acoustic Modes (GAM) but an n \

  3. Physeal fractures of the distal tibia and fibula (Salter-Harris Type I, II, III, and IV fractures).

    PubMed

    Podeszwa, David A; Mubarak, Scott J

    2012-06-01

    Physeal fractures of the distal tibia and fibula are common and can be seen at any age, although most are seen in the adolescent. An understanding of the unique anatomy of the skeletally immature ankle in relation to the mechanism of injury will help one understand the injury patterns seen in this population. A thorough clinical exam is critical to the diagnosis and treatment of these injuries and the avoidance of potentially catastrophic complications. Nondisplaced physeal fractures of the distal tibia and fibula can be safely treated nonoperatively. Displaced fractures should undergo a gentle reduction with appropriate anesthesia while multiple reduction attempts should be avoided. Gapping of the physis >3 mm after reduction should raise the suspicion of entrapped periosteum that will increase the risk of premature physeal closure. Open reduction of displaced Salter-Harris type III and IV fractures is critical to maintain joint congruity and minimize the risk of physeal arrest.

  4. Mode-specific vibrational energy relaxation of amide I' and II' modes in N-methylacetamide/water clusters: intra- and intermolecular energy transfer mechanisms.

    PubMed

    Zhang, Yong; Fujisaki, Hiroshi; Straub, John E

    2009-04-02

    The mode-specific vibrational energy relaxation of the amide I' and amide II' modes in NMA-d(1)/(D(2)O)(n) (n = 0-3) clusters were studied using the time-dependent perturbation theory at the B3LYP/aug-cc-pvdz level. The amide modes were identified for each cluster based on the potential energy distribution of each mode. The vibrational population relaxation time constants were derived for the amide I' and II' modes. Results for the amide I' mode relaxation of NMA-d(1)/(D(2)O)(3) agree well with previous experimental results. The energy relaxation pathways were identified, and both intra- and intermolecular mechanisms were found to be important. The amide II' mode was identified in the energy transfer pathways from the excited amide I' mode of NMA-d(1)/(D(2)O)(n) (n = 1-3) clusters. The modes associated with methyl group deformation were found to play a role in the mechanism of energy transfer from both excited amide I' and II' modes. The kinetics of energy flow in the cluster were examined by solving a master equation describing the vibrational energy relaxation process from excited system mode as a multistep reaction with the third order Fermi resonance parameters as the reaction rate constants. The intramolecular energy transfer mechanism was found to dominate the short time energy flow dynamics, whereas the intermolecular mechanism was found to be dominant at longer times.

  5. Higher order mode damping studies on the PEP-II B-Factory RF cavity

    SciTech Connect

    Rimmer, R.; Goldberg, D.; Lambertson, G.; Voelker, F. ); Ko, K.; Kroll, N.; Pendleton, R.; Schwarz, H. ); Adams, F.; De Jong, M. )

    1992-03-01

    We describe studies of the higher-order-mode (HOM) properties of the prototype 476 MHz RF cavity for the proposed PEP-II B-Factory and a waveguide damping scheme to reduce possible HOM-driven coupled-bunch beam instability growth. Numerical studies include modelling of the HOM spectrum using MAFIA and ARGUS, and calculation of the loaded Q's of the damped modes using data from these codes and the Kroll-Yu method. We discuss briefly the experimental investigations of the modes, which will be made in a full-size low-power test cavity, using probes, wire excitation and bead perturbation methods.

  6. Higher order mode damping studies on the PEP-II B-Factory RF cavity

    SciTech Connect

    Rimmer, R.; Goldberg, D.; Lambertson, G.; Voelker, F.; Ko, K.; Kroll, N.; Pendleton, R.; Schwarz, H.; Adams, F.; De Jong, M.

    1992-03-01

    We describe studies of the higher-order-mode (HOM) properties of the prototype 476 MHz RF cavity for the proposed PEP-II B-Factory and a waveguide damping scheme to reduce possible HOM-driven coupled-bunch beam instability growth. Numerical studies include modelling of the HOM spectrum using MAFIA and ARGUS, and calculation of the loaded Q`s of the damped modes using data from these codes and the Kroll-Yu method. We discuss briefly the experimental investigations of the modes, which will be made in a full-size low-power test cavity, using probes, wire excitation and bead perturbation methods.

  7. Observations of a new SAGE II aerosol extinction mode following the eruption of Mt. Pinatubo

    NASA Technical Reports Server (NTRS)

    Thomason, Larry W.

    1992-01-01

    In the aftermath of the eruption of Mt. Pinatubo, multiwavelength stratospheric aerosol extinction measurements by the satellite-borne Stratospheric Aerosol and Gas Experiment (SAGE II) revealed the presence of a previously unobserved mode of aerosol that exhibited high extinction but a small inferred particle size. This mode may represent a transitional phase between the very small aerosol created by gas-to-particle conversion and a quasi-steady state, post-volcanic aerosol that exhibits both large extinction and large particle size. The presence of a transitional small aerosol mode may have a significant impact on chemical and radiative processes in the stratosphere.

  8. Salter-Harris type II fracture of the femoral bone in a 14-year-old boy - case report.

    PubMed

    Kuleta-Bosak, Elżbieta; Bożek, Paweł; Kluczewska, Ewa; Tomaszewski, Ryszard; Machnik-Broncel, Joanna

    2010-01-01

    Distal femoral physis fractures with displacement are rare injuries seen in adolescents related with high incidence of complication. They may lead to premature physeal closure consequently, to growth arrest and bone deformity. The case of a 14-year-old boy with Salter-Harris type II displaced fracture underwent surgery with open reduction has been described. CT examination with multiplanar reconstruction was used in pre-operative assessment of distal femur growth plate fracture. Knowledge of classification, prognosis and methods of treatment is necessary in accurate pre- and postoperative assessment of physial fractures in adolescents. CT and multiplanar reconstruction improve the understanding of patterns of injury, relative prevalence and accuracy of pre-operative planning.

  9. Salter-Harris type II fracture of the femoral bone in a 14-year-old boy – case report

    PubMed Central

    Kuleta-Bosak, Elżbieta; Bożek, Paweł; Kluczewska, Ewa; Tomaszewski, Ryszard; Machnik-Broncel, Joanna

    2010-01-01

    Summary Background: Distal femoral physis fractures with displacement are rare injuries seen in adolescents related with high incidence of complication. They may lead to premature physeal closure consequently, to growth arrest and bone deformity. Case Report: The case of a 14-year-old boy with Salter-Harris type II displaced fracture underwent surgery with open reduction has been described. CT examination with multiplanar reconstruction was used in pre-operative assessment of distal femur growth plate fracture. Conclusions: Knowledge of classification, prognosis and methods of treatment is necessary in accurate pre- and postoperative assessment of physial fractures in adolescents. CT and multiplanar reconstruction improve the understanding of patterns of injury, relative prevalence and accuracy of pre-operative planning. PMID:22802768

  10. Fracture modes in tubular LSFCO ceramic membranes under graded reducing conditions

    SciTech Connect

    Nagendra, N.; Biswas, S.; Nithyanantham, T.; Bandopadhyay, S.

    2013-06-01

    Highlights: ► Microstructural evolution in LSFCO membranes under graded environment is reported. ► The role of chemically induced stresses and oxygen deficiency is evaluated. ► The stress distribution is modeled by a point defect model. - Abstract: Chromium (III) oxide (Cr{sub 2}O{sub 3})-doped LaSrFeO{sub 3} perovskite, La{sub 0.2}Sr{sub 0.8}Fe{sub 0.8}Cr{sub 0.2}O{sub 3−δ} (LSFCO), is being considered as a potential material for applications in solid oxide fuel cells, gas separation membranes, and electrochemical reactors because of its high electro-catalytic activity. Similar to other perovskites, the performance and mechanical strength of LSFCO materials are significantly affected by environment and temperature. Here, we report a fracture gradient phenomenon in tubular C-ring-shaped LSFCO ceramic membranes under graded reducing conditions. The graded reducing condition was produced by flushing N{sub 2} on the outer side of the C-ring membranes at 1000 °C while keeping the inner side untreated. The rings were then diametrically compressed to fracture, and the resultant fracture morphology was analyzed with a scanning electron microscope (SEM). A fracture gradient with three distinct regions across the thickness of the membranes was identified on the split surfaces. In the outer region of the C-ring specimen exposed to N{sub 2}, a mixed inter/transgranular fracture with a predominant intergranular pattern was observed. In the middle section of the fracture surface, a characteristic transgranular fracture of the perovskite grains was found. At the inner region of the ring, a mixed inter/transgranular fracture with a predominant transgranular pattern occurred. The mechanism of gradient fractures was attributed both to chemically induced stresses caused by oxygen diffusion and to the formation of a separate phase of oxygen-deficient perovskite in the parent perovskite. The stresses generated were modeled by a point defect model. This work provides

  11. Unexpected Salter-Harris type II fracture of the proximal phalanx of the second toe: a chiropractic perspective.

    PubMed

    Murdock, Mark

    2015-12-01

    To discuss the diagnosis and management of a Salter-Harris type II fracture in a nine-year-old girl who was managed conservatively. A nine-year-old girl fell while playing in bare feet in the grass. She experienced pain when she walked or moved her toe. There was minor swelling and bruising. Plain film radiographs revealed a Salter-Harris type II fracture of the 2(nd) proximal phalanx. Her toe was stabilized and she was referred to an orthopedist. Orthopedic management involved a taping procedure. After three weeks, her fracture healed and she was pain free. Chiropractors may consider radiography of post-traumatic injury sites even with equivocal examination findings despite histories suggesting seemingly innocuous mechanisms of injury.

  12. Unexpected Salter-Harris type II fracture of the proximal phalanx of the second toe: a chiropractic perspective

    PubMed Central

    Murdock, Mark

    2015-01-01

    Objectives: To discuss the diagnosis and management of a Salter-Harris type II fracture in a nine-year-old girl who was managed conservatively. Clinical Features: A nine-year-old girl fell while playing in bare feet in the grass. She experienced pain when she walked or moved her toe. There was minor swelling and bruising. Intervention and Outcome: Plain film radiographs revealed a Salter-Harris type II fracture of the 2nd proximal phalanx. Her toe was stabilized and she was referred to an orthopedist. Orthopedic management involved a taping procedure. After three weeks, her fracture healed and she was pain free. Summary: Chiropractors may consider radiography of post-traumatic injury sites even with equivocal examination findings despite histories suggesting seemingly innocuous mechanisms of injury. PMID:26816417

  13. The effects of glass ionomer and flowable composite liners on the fracture resistance of open-sandwich class II restorations.

    PubMed

    Güray Efes, Begüm; Yaman, Batu Can; Gümüştaş, Burak; Tıryakı, Murat

    2013-01-01

    This in vitro study aimed to investigate the effects of glass-ionomer and flowable composite liners on the fracture resistance of Class II amalgam and composite restorations. Group 1 cavities were restored with amalgam and Group 4 cavities with nanofill composite after the application of a dentin-bonding agent. For the remaining groups, light-cured-glass-ionomer liner was used in a gingival floor proximal box (Groups 2, 5) or flowable composite was used as a liner (Groups 3, 6), the remainder of the cavity was restored with amalgam (Groups 2, 3) or composite (Groups 5, 6). The restorations were loaded in compression to failure. The data was analyzed using Tukey's multiple comparison test. The fracture resistance was significantly higher (p<0.05) in Group 3 than in all other groups, except Group 2 (p>0.05). Flowable composite, glass-ionomer liners increased the fracture resistance of open-sandwich Class II amalgam restorations.

  14. The Feasibility of Two Screws Anterior Fixation for Type II Odontoid Fracture Among Arabs.

    PubMed

    Marwan, Yousef; Kombar, Osama Rabie; Al-Saeed, Osama; Aleidan, Aljarrah; Samir, Ahmed; Esmaeel, Ali

    2016-06-01

    Retrospective, cross-sectional study. To evaluate the feasibility of two screws anterior fixation of the odontoid process among Arab adults. Anterior screw fixation is the treatment of choice for type II odontoid fractures. In order to perform the procedure safely, the diameter of the odontoid process should be wide enough to allow for the placement of one or two screws. A retrospective review of 156 computed tomography scans of the cervical spine was done. The included patients were Arabs, adults (at least 18 years old), and had no evidence of upper cervical spine trauma, deformity, infection, tumor, or surgery. The minimum external transverse diameter (METD), minimum internal transverse diameter (MITD), minimum external anteroposterior diameter (MEAD), and minimum internal anteroposterior diameter (MIAD) of the odontoid process were measured. A P value of ≤0.05 was considered as the cutoff level of statistical significance. Our study included 94 (60.3%) males and 62 (39.7%) females. The mean age of the subjects was 37.8 ± 16.9 years (range 18-85). The mean values of the METD, MITD, MEAD, and MIAD were 8.7 ± 1.0 mm, 6.0 ± 1.1 mm, 10.3 ± 1.0 mm, and 7.4 ± 1.1 mm, respectively. Men had larger diameters compared to women. This was statistically significant for METD (P = 0.035) and MEAD (P < 0.001). The METD was <9.0 mm in 95 (60.9%) subjects, while the MITD was <8.0 mm in 153 (98.1%) subjects. These findings were not significantly different between males and females. Two screws anterior fixation of type II odontoid fracture is not feasible among the majority of Arabs. 3.

  15. A pentanuclear lead(II) complex based on a strapped porphyrin with three different coordination modes.

    PubMed

    Le Gac, Stéphane; Furet, Eric; Roisnel, Thierry; Hijazi, Ismail; Halet, Jean-François; Boitrel, Bernard

    2014-10-06

    We have previously described Pb(II) and Bi(III) bimetallic complexes with overhanging carboxylic acid strapped porphyrins in which one metal ion is bound to the N-core ("out-of-plane", OOP), whereas the second one is bound to the strap ("hanging-atop", HAT). In such complexes, the hemidirected coordination sphere of a HAT Pb(II) cation provides sufficient space for an additional binding of a neutral ligand (e.g., DMSO). Interestingly, investigations of the HAT metal coordination mode in a single strap porphyrin show that a HAT Pb(II) can also interact via intermolecular coordination bonds, allowing the self-assembly of two bimetallic complexes. In the pentanuclear Pb(II) complex we are describing in this Article, three different coordination modes were found. The OOP Pb(II) remains inert toward the supramolecular assembling process, whereas the HAT Pb(II) cation, in addition to its intramolecular carboxylate and regular exogenous acetate groups, coordinates an additional exogenous acetate. These two acetates are shared with a third lead(II) cation featuring a holo-directed coordination sphere, from which a centro-symmetric complex is assembled. Density functional theory calculations show some electron-density pockets in the vicinity of the hemidirected HAT Pb(II) atoms, which are associated with the presence of a stereochemically active lone pair of electrons. On the basis of the comparison with other HAT Pb(II) and Bi(III) systems, the "volume" of this lone pair correlates well with the bond distance distributions and the number of the proximal oxygen atoms tethered to the post-transition metal cation. It thus follows the order 6-coordinate Bi(III) > 6-coordinate Pb(II) > 5-coordinate Pb(II).

  16. Selection of stirling engine parameter and modes of joint operation with the Topaz II

    SciTech Connect

    Kirillov, E.Y.; Ogloblin, B.G.; Shalaev, A.I.

    1996-03-01

    In addition to a high-temperature thermionic conversion cycle, application of a low-temperature machine cycle, such as the Stirling engine, is being considered. To select the optimum mode for joint operation of the Topaz II system and Stirling engine, output electric parameters are obtained as a function of thermal power released in the TFE fuel cores. The hydraulic diagram used for joint operation of the Topaz II and the Stirling engine is considered. Requirements to hydraulic characteristics of the Stirling engine heat exchanges are formulated. Scope of necessary modifications to mount the Stirling Engine on the Topaz II is estimated. {copyright} {ital 1996 American Institute of Physics.}

  17. Facial fractures.

    PubMed Central

    Carr, M. M.; Freiberg, A.; Martin, R. D.

    1994-01-01

    Emergency room physicians frequently see facial fractures that can have serious consequences for patients if mismanaged. This article reviews the signs, symptoms, imaging techniques, and general modes of treatment of common facial fractures. It focuses on fractures of the mandible, zygomaticomaxillary region, orbital floor, and nose. Images p520-a p522-a PMID:8199509

  18. Effect of Interface Control on Mode I Interlaminar Fracture Toughness of Woven C/C Composite Laminates

    NASA Astrophysics Data System (ADS)

    Hojo, Masaki; Yamao, Taketoshi; Tanaka, Mototsugu; Ochiai, Shojiro; Iwashita, Norio; Sawada, Yoshihiro

    Effects of fiber/matrix interface and matrix microstructure on the mode I interlaminar fracture toughness of C/C composite materials were investigated by coating bismaleimide-triazine co-polymer (BT-resin) on the surface of carbon fiber and changing the heat-treatment temperature (HTT). For the case of laminates with HTT of 1600°C (carbonized C/C composites), the initial fracture toughness, GIC, was insensitive to BT-resin coating. Moreover, the fracture toughness during crack propagation, GIR, increased by coating BT-resin. On the other hand, both GIC and GIR decreased with BT-resin coating for the laminates with HTT of 2500°C. While both GIC and GIR are insensitive to HTT for laminates without BT-resin coating, they both decreased by increasing HTT for laminates with BT-resin coating. The difference of the effects of interface control and HTT was discussed on the basis of microscopic mechanism consideration. Comparison between in-plane and interlaminar strength indicated the possibility to optimize the interface control.

  19. Fracture resistance and failure mode of endodontically treated teeth restored using ceramic onlays with or without fiber posts-an ex vivo study.

    PubMed

    Keçeci, Ayşe Diljin; Heidemann, Detlef; Kurnaz, Safa

    2016-08-01

    This study aimed to compare the fracture resistance and fracture modes of ceramic onlay restorations with or without fiber posts in endodontically treated premolars. Fifty extracted human premolars with similar anatomic features were used in this study. Four groups (n = 10) were treated endodontically. Onlay cavities extended to the buccal and palatal cusps and reached out the endodontic accesses were prepared. Ceramic onlay restorations with or without fiber posts were categorized as Group CO (ceramic onlays without posts), Group COQF (ceramic onlays and quartz fiber posts), and Group COGF (ceramic onlays and glass fiber posts). Positive control group was left as non-restored (Group NR). Ten intact teeth were stored as negative control group (Group IT). Fracture resistance was measured using a universal load-testing machine applying compressive load at a crosshead speed of 1 mm min(-1) until fracture. Fracture resistance and modes were evaluated statistically. Ceramic onlay restorations (Groups CO, COQF, COGF) increased the fracture resistance significantly, when compared with non-restored teeth (P < 0.05). However, no significant differences were found in the groups with fiber posts in terms of fracture resistance (P > 0.05). Negative control group (IT) had significantly higher fracture resistance than all others (P < 0.05). Fracture types had significant differences among the groups (P < 0.01). Within the limitations of this ex-vivo study, partial coverage with ceramic onlays resulted in a significant improvement of the fracture resistance of endodontically treated premolars. However, insertion of glass or quartz fibers did not increase the fracture resistance significantly. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  20. Extension type II pediatric supracondylar humerus fractures: a radiographic outcomes study of closed reduction and cast immobilization.

    PubMed

    Camus, Tristan; MacLellan, Brent; Cook, Peter Christopher; Leahey, John Lorne; Hyndman, John C; El-Hawary, Ron

    2011-06-01

    The treatment of Gartland type II pediatric supracondylar humerus fractures remains controversial. Some argue that closed reduction and cast immobilization is sufficient to treat these fractures, whereas others advocate closed reduction and percutaneous pinning. The purpose of this radiographic outcomes study was to determine whether closed reduction and cast immobilization could successfully obtain and maintain acceptable reduction of extension type II supracondylar humerus fractures. Prereduction, immediate postreduction, and final radiographs of 155 extension type II fractures that were treated nonoperatively were measured according to the parameters determined earlier to assess the position and alignment of the fracture fragments. These included the anterior humeral line, humerocapitellar angle, Baumann's angle, the Gordon index, and the Griffet index. The average age of the 155 patients at the time of injury was 5.3 years (range: 1 to 13 y). Analysis of the final radiographs, at the final follow-up of 5.3 months, showed that in 80% of patients, the anterior humeral line remained anterior to the mid-third segment of the capitellum (radiographic extension deformity), the mean humerocapitellar angle was 23.77 degrees (range: -11 to 50 degrees), the mean Baumann's angle was 79.40 degrees (range: 62 to 97 degrees), the mean Gordon index was 4.59%, and 44% of patients had a Griffet index between 1 and 3. From this radiographic review, it was observed that not all fractures treated with closed reduction and cast immobilization achieved anatomic position and alignment at final follow-up; however, the long-term clinical and radiographic significance of these findings remains unknown.

  1. MRI diagnosis of trapped periosteum following incomplete closed reduction of distal tibial Salter-Harris II fracture.

    PubMed

    Raman, Subha; Wallace, E Christine

    2011-12-01

    Irreducible fracture of the distal tibial physis due to interposed soft tissue including periosteum is well documented in the orthopedic literature but is uncommon. This condition has been associated with subsequent growth disturbance and requires open reduction. There are very few prior reports of MRI depiction of soft tissue interposition and none of periosteal interposition in the distal tibial physis. This is a relatively common location of physeal injury and related growth disturbance. We present a case of periosteum trapped in the distal tibial physis, diagnosed on MRI, in a Salter-Harris II fracture and its management implications.

  2. Strain Rate Dependency of Fracture Toughness, Energy Release Rate and Geomechanical Attributes of Select Indian Shales

    NASA Astrophysics Data System (ADS)

    Mahanta, B.; Vishal, V.; Singh, T. N.; Ranjith, P.

    2016-12-01

    In addition to modern improved technology, it requires detailed understanding of rock fractures for the purpose of enhanced energy extraction through hydraulic fracturing of gas shales and geothermal energy systems. The understanding of rock fracture behavior, patterns and properties such as fracture toughness; energy release rate; strength and deformation attributes during fracturing hold significance. Environmental factors like temperature, pressure, humidity, water vapor and experimental condition such as strain rate influence the estimation of these properties. In this study, the effects of strain rates on fracture toughness, energy release rate as well as geomechanical properties like uniaxial compressive strength, Young's modulus, failure strain, tensile strength, and brittleness index of gas shales were investigated. In addition to the rock-mechanical parameters, the fracture toughness and the energy release rates were measured for three different modes viz. mode I, mixed mode (I-II) and mode II. Petrographic and X-ray diffraction (XRD) analyses were performed to identify the mineral composition of the shale samples. Scanning electron microscope (SEM) analyses were conducted to have an insight about the strain rate effects on micro-structure of the rock. The results suggest that the fracture toughness; the energy release rate as well as other geomechanical properties are a function of strain rates. At high strain rates, the strength and stiffness of shale increases which in turn increases the fracture toughness and the energy release rate of shale that may be due to stress redistribution during grain fracturing. The fracture toughness and the strain energy release rates for all the modes (I/I-II/II) are comparable at lower strain rates, but they vary considerably at higher strain rates. In all the cases, mode I and mode II fracturing requires minimum and maximum applied energy, respectively. Mode I energy release rate is maximum, compared to the other modes.

  3. What is the best treatment for displaced Salter-Harris II physeal fractures of the distal tibia?

    PubMed

    Park, Hoon; Lee, Dong Hoon; Han, Seung Hwan; Kim, Sungmin; Eom, Nam Kyu; Kim, Hyun Woo

    2017-09-19

    Background and purpose - The optimal treatment of displaced Salter-Harris (SH) II fractures of the distal tibia is controversial. We compared the outcomes of operative and nonoperative treatment of SH II distal tibial fractures with residual gap of >3 mm. Factors that may be associated with the incidence of premature physeal closure (PPC) were analyzed. Patients and methods - We retrospectively reviewed 95 patients who were treated for SH II distal tibial fractures with residual gap of >3 mm after closed reduction. Patients were assigned to 1 of 2 groups: Group 1 included 25 patients with nonoperative treatment, irrespective of size of residual gap (patients treated primarily at other hospitals). Group 2 included 70 patients with operative treatment. All patients were followed for ≥ 12 months after surgery, with a mean follow-up time of 21 months. Logistic regression analyses were performed to identify risk factors for the occurrence of PPC. Results - The incidence of PPC in patients who received nonoperative treatment was 13/52, whereas PPC incidence in patients who received operative treatment was 24/70 (p = 0.1). Multivariable logistic regression analysis determined that significant risk factors for the occurrence of PPC were age at injury, and injury mechanism. The method of treatment, sex, presence of fibular fracture, residual displacement after closed reduction, and implant type were not predictive factors for the occurrence of PPC. Interpretation - Operative treatment for displaced SH II distal tibial fractures did not seem to reduce the incidence of PPC compared with nonoperative treatment. We cannot exclude that surgery may be of value in younger children with pronation-abduction or pronation-external rotation injuries.

  4. Current concepts in the treatment of Anderson Type II odontoid fractures in the elderly in Germany, Austria and Switzerland.

    PubMed

    Löhrer, L; Raschke, M J; Thiesen, D; Hartensuer, R; Surke, C; Ochman, S; Vordemvenne, T

    2012-04-01

    Although currently there are many different recommendations and strategies in the therapy of odontoid fractures in the elderly, there are still no generally accepted guidelines for a structured and standardised treatment. Moreover, the current opinion of spine surgeons regarding the optimal treatment of odontoid fractures Type II of the elderly is unknown. In order to have an objective insight into the diverging strategies for the management of Anderson Type II odontoid fractures and form a basis for future comparisons, this study investigated the current concepts and preferences of orthopaedic, neuro- and trauma surgeons. Spine surgeons from 34 medical schools and 8 hospitals in Germany, 4 university hospitals in Austria and 5 in Switzerland were invited to participate in an online survey using a 12-item 1-sided questionnaire. A total of 44 interviewees from 34 medical institutions participated in the survey, consisting of trauma (50%), orthopaedic (20.5%) and neurosurgeons (27.3%). Out of these, 70.5% treated 1-20 fractures per year; 63.6% favoured the anterior screw fixation as therapy for Type II odontoid fractures, the open posterior Magerl transarticular C1/C2 fusion, the posterior Harms C1/C2 fusion, and conservative immobilisation by cervical orthosis was preferred by 9.1% in each case. 59.1% preferred the anterior odontoid screw fixation as an appropriate treatment of Anderson Type II odontoid fractures in the elderly. 79.5% chose cervical orthosis for postsurgical treatment. Following operative treatment, nonunion rates were reported to be <10% and <20% by 40.9% and 70% of the surgeons, respectively. 56.8% reported changing from primary conservative to secondary operative treatment in <10% of cases. The most favoured technique in revision surgery of nonunions was the open posterior Magerl transarticular fusion technique, chosen by 38.6% of respondents. 18.2% preferred the posterior Harms C1/C2 fusion technique, 11.4% the percutaneous posterior Magerl

  5. Method for measuring the mode-I fracture toughness in lead zirconate titanate (PZT)

    NASA Astrophysics Data System (ADS)

    Karastamatis, Thomas; Lynch, Christopher S.

    2000-06-01

    Previous measurements of the fracture toughness of PZT have relied on Vicker's indentations, bend specimens, and compact tension specimens. Vicker's indentations are qualitative and are not suitable for toughness measurements. Recent work has clearly shown that non-linear material behavior induces a non-linear stress gradient through other specimen geometries that must be accounted for to accurately determine the fracture toughness. This work describes the development of a measurement technique for the R-curve behavior of unpoled ferroelastic ceramics using 4-point bend specimens with semi-elliptical surface cracks. The model material is a soft, transparent composition of 8/65/35 lead lanthanum zirconate titanate. The aspect ratio is measured during crack growth. The non-linear stress gradient through the cross section calculated from strain gage data. A parametric study based on the analysis of Newman and Raju is used to elucidate the restrictions on application of this technique.

  6. C2-fractures: part II. A morphometrical analysis of computerized atlantoaxial motion, anatomical alignment and related clinical outcomes.

    PubMed

    Koller, Heiko; Acosta, Frank; Forstner, Rosemarie; Zenner, Juliane; Resch, Herbert; Tauber, Mark; Lederer, Stefan; Auffarth, Alexander; Hitzl, Wolfgang

    2009-08-01

    Knowledge on the outcome of C2-fractures is founded on heterogenous samples with cross-sectional outcome assessment focusing on union rates, complications and technical concerns related to surgical treatment. Reproducible clinical and functional outcome assessments are scant. Validated generic and disease specific outcome measures were rarely applied. Therefore, the aim of the current study is to investigate the radiographic, functional and clinical outcome of a patient sample with C2-fractures. Out of a consecutive series of 121 patients with C2 fractures, 44 met strict inclusion criteria and 35 patients with C2-fractures treated either nonsurgically or surgically with motion-preserving techniques were surveyed. Outcome analysis included validated measures (SF-36, NPDI, CSOQ), and a functional CT-scanning protocol for the evaluation of C1-2 rotation and alignment. Mean follow-up was 64 months and mean age of patients was 52 years. Classification of C2-fractures at injury was performed using a detailed morphological description: 24 patients had odontoid fractures type II or III, 18 patients had fracture patterns involving the vertebral body and 11 included a dislocated or a burst lateral mass fracture. Thirty-one percent of patients were treated with a halo, 34% with a Philadelphia collar and 34% had anterior odontoid screw fixation. At follow-up mean atlantoaxial rotation in left and right head position was 20.2 degrees and 20.6 degrees, respectively. According to the classification system of posttreatment C2-alignment established by our group in part I of the C2-fracture study project, mean malunion score was 2.8 points. In 49% of patients the fractures healed in anatomical shape or with mild malalignment. In 51% fractures healed with moderate or severe malalignment. Self-rated outcome was excellent or good in 65% of patients and moderate or poor in 35%. The raw data of varying nuances allow for comparison in future benchmark studies and metaanalysis. Detailed

  7. Microscopic defect induced slow-mode degradation in II VI based blue green laser diodes

    NASA Astrophysics Data System (ADS)

    Adachi, Masahiro; Min Aung, Zaw; Minami, Kouichirou; Koizumi, Keiichi; Watanabe, Masashi; Kawamoto, Seiji; Yamaguchi, Tsutomu; Kasada, Hirofumi; Abe, Tomoki; Ando, Koshi; Nakano, Kazushi; Ishibashi, Akira; Itoh, Satoshi

    2000-06-01

    We have studied the microdefect induced degradation mode in long-lifetime blue-green laser diodes (LDs) and light emitting diodes (LEDs) based on II-VI wide bandgap semiconductors. Microscopic deep defect centers in the LDs and LEDs are detected using mainly DLTS technique, coupled with ICTS methods. It is evidenced that a slow-mode degradation, commonly observed in dislocation-free LD devices, is caused by the generation and enhancement of microscopic deep centers during the device aging process. One possible degradation mechanism with a "carrier removal effect" is presented.

  8. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part II. Fatigue crack growth rate

    NASA Astrophysics Data System (ADS)

    Margolin, B.; Minkin, A.; Smirnov, V.; Sorokin, A.; Shvetsova, V.; Potapova, V.

    2016-11-01

    The experimental data on the fatigue crack growth rate (FCGR) have been obtained for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various radiation swelling. The performed study of the fracture mechanisms for cracked specimens under cyclic loading has explained why radiation swelling affects weakly FCGR unlike its effect on fracture toughness. Mechanical modeling of fatigue crack growth has been carried out and the dependencies for prediction of FCGR in irradiated austenitic steel with and with no swelling are proposed and verified with the obtained experimental results. As input data for these dependencies, FCGR for unirradiated steel and the tensile mechanical properties for unirradiated and irradiated steels are used.

  9. [6-endo-trig mode cyclization to a hydrindanone using samarium (II) iodide].

    PubMed

    Sono, Masakazu

    2003-08-01

    Samarium (II) iodide has been employed to promote the vinylogous pinacol coupling reaction of aldehyde to alpha, beta-unsaturated ketones. The diastereoselectivity of 6-endo-trig mode products was changed by the addition of a proton source and/or HMPA and by the reaction temperature. The stereochemistry of the hydrindanone was controlled by the coordinated samarium species, resulting in the cis-orientation in respect of the hydroxyl group at C-4 and the juncture proton at C-3a under mild reaction conditions. Coronafacic acid has been synthesized from a hydrindanone prepared by the cyclization reaction of the enone-aldehyde with samarium (II) iodide.

  10. Far-field stress dependency of the failure mode of damage-zone fractures in fault zones: Results from laboratory tests and field observations of siliceous mudstone

    NASA Astrophysics Data System (ADS)

    Ishii, Eiichi

    2016-01-01

    The macroscopic failure mode (tensile/hybrid/shear) of damage-zone fractures in fault zones may influence the hydrogeological properties of the fault zone. Application of the Griffith-Coulomb failure criterion, combined with the simple assumption that failures are predominantly induced by an increase in differential stresses and/or a decrease in effective normal stresses resulting from stress concentrations generated at the asperities/tips of faults, suggests that (1) only tensile fractures propagate from faults when the effective mean stress is less than the rock tensile strength, (2) tensile/hybrid fractures form when the effective mean stress is less than twice the rock tensile strength, and (3) shear fractures can develop when the effective mean stress is more than twice the rock tensile strength, which suppresses the formation of tensile/hybrid fractures. In this study, thin slots were precut in siliceous mudstone samples and mechanical experiments were conducted under a range of effective confining pressures using core samples with and without precut slots. A comparison of fractures formed in the samples at different applied effective mean stresses gave results consistent with the proposed model. The correspondence of model predictions and results was also corroborated by observations of natural damage-zone fractures observed in the field, in boreholes penetrating the same siliceous mudstone as used in the experiments. The results indicate that fault zones containing numerous tensile/hybrid fractures are limited to domains that have experienced effective mean stresses of less than twice the rock tensile strength.

  11. Damping Higher Order Modes in the PEP-II B-Factory Vertex Bellows

    SciTech Connect

    Weathersby, S.; Langton, J.; Novokhatski, A.; Seeman, J.; /SLAC

    2005-06-30

    Higher stored currents and shorter bunch lengths are requirements for increasing luminosity in colliding storage rings. As a result, more HOM power is generated in the IP region. This HOM power propagates to sensitive components causing undesirable heating, thus becoming a limiting issue for the PEP-II B-factory. HOM field penetration through RF shielding fingers has been shown to cause heating in bellows structures. To overcome these limitations, a proposal to incorporate ceramic absorbers within the bellows cavity to damp these modes is presented. Results show that the majority of modes of interest are damped, the effectiveness depending on geometrical considerations. An optimal configuration is presented for the PEP-II B-factory IR bellows component utilizing commercial grade ceramics with consideration for heat transfer requirements.

  12. Sliding mode control of the space nuclear reactor system TOPAZ II

    SciTech Connect

    Shtessel, Y.B.; Wyant, F.J.

    1996-03-01

    The Automatic Control System (ACS) of the space nuclear reactor power system TOPAZ II that generates electricity from nuclear heat using in-core thermionic converters is considered. Sliding Mode Control Technique was applied to the reactor system controller design in order to provide the robust high accuracy following of a neutron (thermal) power reference profile in a start up regime and a payload electric power (current) reference profile following in an operation regime. Extensive simulations of the TOPAZ II reactor system with the designed sliding mode controllers showed improved accuracy and robustness of the reactor system performances in a start up regime and in an electric power supply regime as well. {copyright} {ital 1996 American Institute of Physics.}

  13. Salter-Harris type II metacarpal and metatarsal fracture in three foals. Treatment by minimally-invasive lag screw osteosynthesis combined with external coaptation.

    PubMed

    Klopfenstein Bregger, Micaël D; Fürst, Anton E; Kircher, Patrick R; Kluge, Katharina; Kummer, Martin

    2016-05-18

    To describe minimally-invasive lag screw osteosynthesis combined with external coaptation for the treatment of Salter-Harris type II third metacarpal and third metatarsal bone fractures. Three foals aged two weeks to four months with a Salter-Harris type II third metacarpal or third metatarsal fracture. Surgery was carried out under general anaesthesia in lateral recumbency. After fracture reduction, the metaphyseal fragment was stabilized with two cortical screws placed in lag fashion under fluoroscopic control. A cast was applied for at least two weeks. All foals had a good outcome with complete fracture healing and return to complete soundness without any angular limb deformity. All foals had moderate transient digital hyperextension after cast removal. Internal fixation of Salter-Harris type II third metacarpal or third metatarsal fractures with two cortical screws in lag fashion, combined with external coaptation provided good stabilization and preserved the longitudinal growth potential of the injured physis.

  14. Cyclic loading of endodontically treated teeth restored with glass fibre and titanium alloy posts: fracture resistance and failure modes.

    PubMed

    Abdul Salam, Saridatun Nur; Banerjee, Avijit; Mannocci, Francesco; Pilecki, Peter; Watson, Timothy F

    2006-09-01

    The aims of this in-vitro investigation were to compare the fracture resistance and the failure modes of endodontically treated teeth restored with glass fibre-reinforced posts with those of teeth restored with titanium-alloy posts. A total of 60 single-rooted human mandibular premolars were endodontically treated. The teeth were divided into two experimental and one control group. Post spaces 9mm long were prepared in the roots of the experimental groups in which glass fibre-reinforced posts (Group A) and titanium-alloy posts (Group B) were cemented. In the control group (Group C), no post was inserted. The specimens were stored in normal saline for a period of three weeks before being intermittently loaded at an angle of 30 degrees degrees to the long axis of the tooth at a frequency of two loads of 40N per second. Log-rank test used for the overall analysis revealed that there was no significant difference of fracture resistance between teeth restored with glass fibre-reinforced posts (Group A) and titanium-alloy posts (Group B). The survival of the control group was found to be significantly inferior to that of the experimental groups. There was no significant difference in the number of failures between the two experimental groups. There was significantly more core and post failure for the glass fibre-reinforced posts, root and core failure for the titanium-alloy posts and core failure for the control group. The results suggest that post failures are more frequent in teeth restored with quartz fibre posts and root fractures are more frequent in teeth restored with titanium posts.

  15. Measurements and Analysis of Longitudinal HOM Driven Coupled Bunch Modes in PEP-II Rings

    SciTech Connect

    Mastorides, T; Rivetta, C.; Fox, J.D.; Winkle, D.Van; /SLAC

    2008-07-07

    The growth rates of the longitudinal higher-order impedance-driven beam modes have greatly increased since the initial PEP-II design and commissioning. This increase is attributed to the addition of 6 1.2MW RF stations with 8 accelerating cavities in the HER and 2 1.2MW RF stations with 4 accelerating cavities in the LER, which allowed operations at twice the design current and almost four times the luminosity. As a result, the damping requirements for the longitudinal feedback have greatly increased since the design, and the feedback filters and control schemes have evolved during PEP-II operations. In this paper, growth and damping rate data for the higher-order mode (HOM) driven coupled-bunch modes are presented from various PEP-II runs and are compared with historical estimates during commissioning. The effect of noise in the feedback processing channel is also studied. Both the stability and performance limits of the system are analyzed.

  16. Compressive fracture morphology and mechanism of metallic glass

    NASA Astrophysics Data System (ADS)

    Qu, R. T.; Zhang, Z. F.

    2013-11-01

    We quantitatively investigated the fracture morphologies of Zr52.5Cu17.9Ni14.6Al10Ti5 and Pd78Cu6Si16 metallic glasses (MGs) under compression. The characteristic features of the compressive fracture morphology were captured, and the shear vein patterns were found to be not a one-to-one correspondence between two opposing fracture surfaces in an identical sample. This finding experimentally confirms that the compressive failure behaves in a fracture mode of pure shear (mode II). Quantitative measurements show that a ˜1 μm thickness layer with materials not only inside but also adjacent to the major shear band contributes to the formation of shear vein patterns. The critical shear strain to break a shear band was found to be more than 105% and higher in more ductile MGs under compression than tension. Estimation on the temperature rise at the fracture moment indicates that only ˜5% of the total elastic energy stored in the sample converts into the heat required for melting the layer to form the vein patterns. The mode II fracture toughness was also estimated based on the quantitative measurements of shear vein pattern and found larger than the mode I fracture toughness. Finally, the deformation and fracture mechanisms of MGs under tension and compression were compared and discussed. These results may improve the understanding on the fracture behaviors and mechanisms of MGs and may provide instructions on future design for ductile MGs with high resistance for fracture.

  17. Effective representation of amide III, II, I, and A modes on local vibrational modes: Analysis of ab initio quantum calculation results

    NASA Astrophysics Data System (ADS)

    Hahn, Seungsoo

    2016-10-01

    The Hamiltonian matrix for the first excited vibrational states of a protein can be effectively represented by local vibrational modes constituting amide III, II, I, and A modes to simulate various vibrational spectra. Methods for obtaining the Hamiltonian matrix from ab initio quantum calculation results are discussed, where the methods consist of three steps: selection of local vibrational mode coordinates, calculation of a reduced Hessian matrix, and extraction of the Hamiltonian matrix from the Hessian matrix. We introduce several methods for each step. The methods were assessed based on the density functional theory calculation results of 24 oligopeptides with four different peptide lengths and six different secondary structures. The completeness of a Hamiltonian matrix represented in the reduced local mode space is improved by adopting a specific atom group for each amide mode and reducing the effect of ignored local modes. The calculation results are also compared to previous models using C=O stretching vibration and transition dipole couplings. We found that local electric transition dipole moments of the amide modes are mainly bound on the local peptide planes. Their direction and magnitude are well conserved except amide A modes, which show large variation. Contrary to amide I modes, the vibrational coupling constants of amide III, II, and A modes obtained by analysis of a dipeptide are not transferable to oligopeptides with the same secondary conformation because coupling constants are affected by the surrounding atomic environment.

  18. Effective representation of amide III, II, I, and A modes on local vibrational modes: Analysis of ab initio quantum calculation results.

    PubMed

    Hahn, Seungsoo

    2016-10-28

    The Hamiltonian matrix for the first excited vibrational states of a protein can be effectively represented by local vibrational modes constituting amide III, II, I, and A modes to simulate various vibrational spectra. Methods for obtaining the Hamiltonian matrix from ab initio quantum calculation results are discussed, where the methods consist of three steps: selection of local vibrational mode coordinates, calculation of a reduced Hessian matrix, and extraction of the Hamiltonian matrix from the Hessian matrix. We introduce several methods for each step. The methods were assessed based on the density functional theory calculation results of 24 oligopeptides with four different peptide lengths and six different secondary structures. The completeness of a Hamiltonian matrix represented in the reduced local mode space is improved by adopting a specific atom group for each amide mode and reducing the effect of ignored local modes. The calculation results are also compared to previous models using C=O stretching vibration and transition dipole couplings. We found that local electric transition dipole moments of the amide modes are mainly bound on the local peptide planes. Their direction and magnitude are well conserved except amide A modes, which show large variation. Contrary to amide I modes, the vibrational coupling constants of amide III, II, and A modes obtained by analysis of a dipeptide are not transferable to oligopeptides with the same secondary conformation because coupling constants are affected by the surrounding atomic environment.

  19. Fracture Analysis of Competing Failure Modes of Aluminum-CFRP Joints Using Three-Layer Titanium Laminates as Transition

    NASA Astrophysics Data System (ADS)

    Woizeschke, P.; Vollertsen, F.

    2015-09-01

    The structural properties of lightweight constructions can be adapted to specific local requirements using multi-material designs. Aluminum alloys and carbon fiber-reinforced plastics (CFRP) are materials of great interest requiring suitable joining techniques in order to transfer the advantages of combining the materials to structural benefits. Thus, the research group "Schwarz-Silber" investigates novel concepts to enable frontal aluminum-CFRP joints using transition structures. In the foil concept titanium foils are used as transition elements. Specimens have been produced using three-layer titanium laminates. In tensile tests, three failure locations have been observed: (1) Al-Ti seam, (2) Ti-CFRP hybrid laminate, and (3) CFRP laminate. In this paper, the fracture mechanisms of these failure modes are investigated by analyzing metallographic micrographs and fracture surfaces as well as by correlating load-displacement curves to video imaging of tensile tests. The results show that the cracking of the CFRP layers can be traced back to an assembly error. The laminate character of the titanium part tends to reduce the Al-Ti seam strength. However, two sub-joint tests demonstrate that the Al-Ti seam can endure loads up to 9.5 kN. The ductile failure behavior of the Ti-CFRP hybrid laminates is caused by plastic deformations of the titanium laminate liners.

  20. Mode I fracture toughness behavior of hydro-thermally aged carbon fibre reinforced DGEBA-HHPA-PES systems

    NASA Astrophysics Data System (ADS)

    Alessi, Sabina; Pitarresi, Giuseppe; Spadaro, Giuseppe; Tumino, Davide

    2012-07-01

    In this work the Mode I fracture toughness behavior of unidirectional CFRP laminates is investigated by means of Double Cantilever Beam (DCB) tests. The composite samples were manufactured by thermal curing after impregnation of a Carbon fabric with a DGEBA epoxy and anhydride HHPA curing agent. One resin batch was also mixed with a PES thermoplastic monomer to enhance the matrix toughness. Two lots of samples, toughened and untoughened, were then left to soak in hot water to achieve various degrees of aging. The influence of matrix toughening and hydrothermal aging on the delamination behavior of the composite have then been assessed and correlated with characterization data from Dynamic Mechanical Thermal Analysis (DMTA) and Scanning Electron Microscopy (SEM).

  1. Determination of the Mode I Interlaminar Fracture Toughness by Using a Nonlinear Double-Cantilever Beam Specimen

    NASA Astrophysics Data System (ADS)

    Pavelko, V.; Lapsa, K.; Pavlovskis, P.

    2016-07-01

    The aim of this study is estimation of the effect of large deflections of a double-cantilever beam (DCB) on the accuracy of determination of the mode I interlaminar fracture toughness GIc of layered composites by using the nonlinear theory of bending of beams. The differential equation of the deflection curve of arm of the DCB specimen in the natural form was used to analyze the strain energy of the specimen and its strain energy release rate GI upon propagation of delamination under the action of cleavage forces at the ends of cantilevers. An algorithm for calculating the strain energy and its release rate in the DCB specimens is realized in the form of a MATLAB code. An experimental study was carried out on DCB specimens of a highly flexible carbon/epoxy laminate. The validity of the nonlinear model developed is demonstrated. The standard methods used to determine GIc are refined for the case of highly flexible specimens.

  2. Stress corrosion-controlled rates of mode I fracture propagation in calcareous bedrock

    NASA Astrophysics Data System (ADS)

    Voigtlaender, Anne; Leith, Kerry; Krautblatter, Michael

    2014-05-01

    Surface bedrock on natural rock slopes is subject to constant and cyclic environmental stresses (wind, water, wave, ice, seismic or gravitational). Studies indicate that these stresses range up to several hundred kPa, generally too low to cause macroscopic changes in intact rock, although clear evidence of fracture generation, crack propagation and weathering of bedrock illustrates the effect of environmental stresses at the Earth's surface. We suggest that material degradation and its extent, is likely to be controlled by the rate of stress corrosion cracking (SCC). Stress corrosion is a fluid-material reaction, where fluids preferentially react with strained atomic bonds at the tip of developing fractures. Stress corrosion in ferrous and siliceous materials is often accepted as the fracture propagation and degradation rate-controlling process where materials are subject to stresses and fluids. Although evidence for chemical weathering in propagating bedrock fractures is clear in natural environments, the physical system and quantification of stress corrosion in natural rocks is yet to be addressed. Here, we present preliminary data on the relationship between stresses at levels commonly present on natural rock slopes, and material damage resulting from stress corrosion under constant or cyclic tensile loading. We undertake single notch three-point bending tests (SNBT) on fresh calcareous bedrock specimens (1100x100x100mm) over a two-month period. Two beams containing an artificial notch are stressed to 75% of their ultimate strength, and a constant supply of weak acid is applied at the notch tip to enhance chemical reactions. A third, unloaded, beam is also exposed to weak acid in order to elucidate the contribution of stress corrosion cracking to the material degradation. Stresses at the tip of propagating cracks affect the kinetics of the chemical reaction in the specimen exposed to both loading and corrosion, leading to an increase in degradation, and greater

  3. Experimental and Numerical Study on the Cracked Chevron Notched Semi-Circular Bend Method for Characterizing the Mode I Fracture Toughness of Rocks

    NASA Astrophysics Data System (ADS)

    Wei, Ming-Dong; Dai, Feng; Xu, Nu-Wen; Liu, Jian-Feng; Xu, Yuan

    2016-05-01

    The cracked chevron notched semi-circular bending (CCNSCB) method for measuring the mode I fracture toughness of rocks combines the merits (e.g., avoidance of tedious pre-cracking of notch tips, ease of sample preparation and loading accommodation) of both methods suggested by the International Society for Rock Mechanics, which are the cracked chevron notched Brazilian disc (CCNBD) method and the notched semi-circular bend (NSCB) method. However, the limited availability of the critical dimensionless stress intensity factor (SIF) values severely hinders the widespread usage of the CCNSCB method. In this study, the critical SIFs are determined for a wide range of CCNSCB specimen geometries via three-dimensional finite element analysis. A relatively large support span in the three point bending configuration was considered because the fracture of the CCNSCB specimen in that situation is finely restricted in the notch ligament, which has been commonly assumed for mode I fracture toughness measurements using chevron notched rock specimens. Both CCNSCB and NSCB tests were conducted to measure the fracture toughness of two different rock types; for each rock type, the two methods produce similar toughness values. Given the reported experimental results, the CCNSCB method can be reliable for characterizing the mode I fracture toughness of rocks.

  4. Mixed Mode Stable Tearing of Thin Sheet Al 6061-T6 Specimens: Experimental Measurements and Finite Element Simulations using a Modified Mohr-Coulomb Fracture Criterion

    DTIC Science & Technology

    2010-11-01

    grounding. Oliver (1996a,b), Teng (2008) andXue (2007a) reported on successful application of contin- uum damage mechanics in simulating initiation and...the accumulated damage should reach the critical value and the load carrying capacity must vanish in the post-initiate range. It should be noted that...specimen using fracture coupled with damage plastic- ity approach. Different from Mode I, little thickness reduction is observed for Mode III loading, as

  5. A boundary element alternating method for two-dimensional mixed-mode fracture problems

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Krishnamurthy, T.

    1992-01-01

    A boundary element alternating method, denoted herein as BEAM, is presented for two dimensional fracture problems. This is an iterative method which alternates between two solutions. An analytical solution for arbitrary polynomial normal and tangential pressure distributions applied to the crack faces of an embedded crack in an infinite plate is used as the fundamental solution in the alternating method. A boundary element method for an uncracked finite plate is the second solution. For problems of edge cracks a technique of utilizing finite elements with BEAM is presented to overcome the inherent singularity in boundary element stress calculation near the boundaries. Several computational aspects that make the algorithm efficient are presented. Finally, the BEAM is applied to a variety of two dimensional crack problems with different configurations and loadings to assess the validity of the method. The method gives accurate stress intensity factors with minimal computing effort.

  6. Kinetics of fracture in Fe-3Si steel under mode I loading

    NASA Technical Reports Server (NTRS)

    Bessendorf, Michael H.

    1989-01-01

    This paper deals with experimental studies of fatigue crack propagation (FCP) in Fe-3Si steel. The FCP experiments were performed on single-edge crack specimens. Results show that an extensive damage zone consisting of slip bands surrounds and precedes the propagating crack. The system of the crack and the damage zone constitutes the crack layer (CL). The results demonstrate that fracture propagates by the translation, expansion, and distortion of the part of CL called the active zone. The contours of the damage distribution show that different loading stresses may cause significantly different shapes of damage. Application of the stability criteria is demonstrated. It was shown that the critical energy release rate depends on the history of loading.

  7. A kinetic model for type I and II IP3R accounting for mode changes.

    PubMed

    Siekmann, Ivo; Wagner, Larry E; Yule, David; Crampin, Edmund J; Sneyd, James

    2012-08-22

    Based upon an extensive single-channel data set, a Markov model for types I and II inositol trisphosphate receptors (IP(3)R) is developed. The model aims to represent accurately the kinetics of both receptor types of IP(3)R depending on the concentrations of inositol trisphosphate (IP(3)), adenosine trisphosphate (ATP), and intracellular calcium (Ca(2+)). In particular, the model takes into account that for some combinations of ligands the IP(3)R switches between extended periods of inactivity alternating with intervals of bursting activity (mode changes). In a first step, the inactive and active modes are modeled separately. It is found that, within modes, both receptor types are ligand-independent. In a second step, the submodels are connected by transition rates. Ligand-dependent regulation of the channel activity is achieved by modulating these transitions between active and inactive modes. As a result, a compact representation of the IP(3)R is obtained that accurately captures stochastic single-channel dynamics including mode changes in a model with six states and 10 rate constants, only two of which are ligand-dependent.

  8. A Modified Edge Crack Torsion Test for Measurement of Mode III Fracture Toughness of Laminated Tape Composites

    NASA Technical Reports Server (NTRS)

    Czabaj, Michael W.; Davidson, Barry D.; Ratcliffe, James G.

    2016-01-01

    Modifications to the edge crack torsion (ECT) test are studied to improve the reliability of this test for measuring the mode-III fracture toughness, G (sub IIIc), of laminated tape fiber-reinforced polymeric (FRP) composites. First, the data reduction methods currently used in the ECT test are evaluated and deficiencies in their accuracy are discussed. An alternative data reduction technique, which uses a polynomial form to represent ECT specimen compliance solution, is evaluated and compared to FEA (finite element analysis) results. Second, seven batches of ECT specimens are tested, each batch containing specimens with a preimplanted midplane edge delamination and midplane plies with orientations of plus theta divided by minus theta, with theta ranging from 0 degrees to 90 degrees in 15-degree increments. Tests on these specimens show that intralaminar cracking occurs in specimens from all batches except for which theta = 15 degrees and 30 degrees. Tests on specimens of these two batches are shown to result in mode-III delamination growth at the intended ply interface. The findings from this study are encouraging steps towards the use of the ECT test as a standardized method for measuring G (sub IIIc), although further modification to the data reduction method is required to make it suitable for use as part of a standardized test method.

  9. Effect of ferrule height and glass fibre post length on fracture resistance and failure mode of endodontically treated teeth.

    PubMed

    Abdulrazzak, Shurooq S; Sulaiman, Eshamsul; Atiya, Basim K; Jamaludin, Marhazlinda

    2014-08-01

    The purpose of this study was to evaluate the combined effect of ferrule height and post length on fracture resistance and failure mode of endodontically treated teeth restored with glass fibre posts, composite resin cores and crowns. Ninety human maxillary central incisors were endodontically treated and divided into three groups (n = 30) according to the ferrule heights: 4, 2 and 0 mm, respectively. Post spaces in each group were prepared at 2/3, 1/2 and 1/3 of the root length (n = 10). The specimens were received fibre posts, composite resin core build up and cast metal crowns. After thermocycling, compressive static load was applied at an angle of 135° to the crowns. Two-way analysis of variance showed significant differences in the failure load in the ferrule height groups, no significant differences in post length groups and no significant interaction between ferrule heights and post lengths. More restorable failure modes were observed. © 2013 Australian Society of Endodontology.

  10. Different modes of synergistic toxicities between metam/copper (II) and metam/zinc (II) in HepG2 cells: apoptosis vs. necrosis.

    PubMed

    Fan, Rui-Mei; Zhu, Ben-Zhan; Huang, Chin-Pao; Sheng, Zhi-Guo; Mao, Li; Li, Ming-Xin

    2016-12-01

    Both metam sodium and copper/zinc-containing compounds are widely used as fungicides. They therefore may co-occur in the biosphere. Despite certain studies of individual toxicity for either metam or copper (II)/zinc (II), their synergistic toxicity has not been examined. In this paper, a remarkable synergistic toxicity was observed in HepG2 cells when metam and copper (II)/zinc (II) at non-toxic and sub-toxic levels were combined. Unexpectedly, cell death modes between metam/copper (II) and metam/zinc (II) were different: For metam/copper (II), apoptosis was evident from morphological characteristics including cytoplasm-chromatin condensation, phosphatidylserine (PS) exposure, SubG0 /G1 DNA fragmentation, mitochondrial membrane potential decrease, pro/anti-apoptotic protein activation, and cytochrome c release; for metam/zinc (II), necrosis was evident from organelle swelling and uncontrolled collapse. To our knowledge, this work first not only demonstrates the synergistic toxicities of metam and both copper (II)/zinc (II), but also verifies the different modes of apoptosis/necrosis between metam/copper (II) and metam/zinc (II). © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1964-1973, 2016. © 2015 Wiley Periodicals, Inc.

  11. Predicting the occurrence of mixed mode failure associated with hydraulic fracturing, part 2 water saturated tests

    SciTech Connect

    Bauer, Stephen J.; Broome, Scott Thomas; Choens, Charles; Barrow, Perry Carl

    2015-09-14

    Seven water-saturated triaxial extension experiments were conducted on four sedimentary rocks. This experimental condition was hypothesized more representative of that existing for downhole hydrofracture and thus it may improve our understanding of the phenomena. In all tests the pore pressure was 10 MPa and confirming pressure was adjusted to achieve tensile and transitional failure mode conditions. Using previous work in this LDRD for comparison, the law of effective stress is demonstrated in extension using this sample geometry. In three of the four lithologies, no apparent chemo-mechanical effect of water is apparent, and in the fourth lithology test results indicate some chemo-mechanical effect of water.

  12. Trapped modes in the PEP-II B-Factory Interaction Region

    SciTech Connect

    Henestroza, E.; Heifets, S.; Zolotorev, M.

    1995-04-01

    The design of the PEP-II B-Factory Interaction Region is based primarily on beam-stay-clear requirements and on synchrotron radiation background considerations (masks are required to shield the detector beam pipe from all sources of synchrotron radiation). A complicated 3-dimensional structure results from these requirements. A high intensity beam traversing this structure will generate wake fields that lead to energy deposition on the beam pipe, as well as to decelerating and deflecting forces acting back on the beam. Computation of wake fields and impedances in frequency-domain and time-domain using 2-D and 3-D electromagnetic codes revealed the existence of trapped modes in the interaction region, which if not controlled could enhance the higher order model heating of the beam pipe. We will present the simulation results and the design strategy to avoid resonant conditions between these trapped modes and the bunch train frequency.

  13. Quantifying voids effecting delamination in carbon/epoxy composites: static and fatigue fracture behavior

    NASA Astrophysics Data System (ADS)

    Hakim, I.; May, D.; Abo Ras, M.; Meyendorf, N.; Donaldson, S.

    2016-04-01

    On the present work, samples of carbon fiber/epoxy composites with different void levels were fabricated using hand layup vacuum bagging process by varying the pressure. Thermal nondestructive methods: thermal conductivity measurement, pulse thermography, pulse phase thermography and lock-in-thermography, and mechanical testing: modes I and II interlaminar fracture toughness were conducted. Comparing the parameters resulted from the thermal nondestructive testing revealed that voids lead to reductions in thermal properties in all directions of composites. The results of mode I and mode II interlaminar fracture toughness showed that voids lead to reductions in interlaminar fracture toughness. The parameters resulted from thermal nondestructive testing were correlated to the results of mode I and mode II interlaminar fracture toughness and voids were quantified.

  14. Effect of Embedded Piezoelectric Sensors on Fracture Toughness and Fatigue Resistance of Composite Laminates Under Mode I Loading

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.

    2006-01-01

    Double-cantilevered beam (DCB) specimens of a glass/epoxy composite material with embedded piezoelectric sensors were tested both statically and under fatigue loading to determine the effect of the embedded material on the Mode I fracture toughness and fatigue resistance compared to baseline data without the embedded elements. A material known as LaRC-Macrofiber Composite (LaRC-MFC (TradeMark)), or MFC, was embedded at the midplane of the specimen during the layup. Specimens were manufactured with the embedded MFC material either at the loaded end of the specimen to simulate an initial delamination; or with the MFC material located at the delaminating interface, with a Teflon film at the loaded end to simulate an initial delamination. There were three types of specimens with the embedded material at the delaminating interface: co-cured with no added adhesive; cured with a paste adhesive applied to the embedded element; or cured with a film adhesive added to the embedded material. Tests were conducted with the sensors in both the passive and active states. Results were compared to baseline data for the same material without embedded elements. Interlaminar fracture toughness values (G(sub Ic)) for the passive condition showed little change when the MFC was at the insert end. Passive results varied when the MFC was at the delaminating interface. For the co-cured case and with the paste adhesive, G(sub Ic) decreased compared to the baseline toughness, whereas, for the film adhesive case, G(sub Ic) was significantly greater than the baseline toughness, but the failure was always catastrophic. When the MFC was in the active state, G(sub Ic) was generally lower compared to the passive results. Fatigue tests showed little effect of the embedded material whether it was active or passive compared to baseline values.

  15. Normal Modes for Dynamic Motions of a Topoisomerase II enzyme upon DNA-Binding and Bending

    NASA Astrophysics Data System (ADS)

    Mentes, Ahmet

    We have used Molecular Dynamics (MD) simulation methods and two analytical approaches (the Gaussian Network Model (GNM) and Anisotropic Network Model (ANM)) to investigate the internal dynamic motions of the S. cerevisiae Topoisomerase (TopoII) during the first step of its catalytic cycle. At the initial state of the first step of its catalytic cycle, the protein and a 34 bp straight-DNA structure have no interaction. At the final state of the cycle, we have the bended-DNA/TopoII complex where the protein binds to DNA and, at this stage, the protein binds and bends the DNA, just before the DNA cleavage by TopoII. Normal mode analysis is used to characterize the functional flexibility of the protein, especially the C-gate domain closing/opening during the DNA binding/bending process and before DNA cleavage. Because of its clinical importance, our study might be helpful to better understand the next steps of its catalytic cycle and may provide new insight into the dynamics and structure of other TopoII-DNA complexes.

  16. Mixed-mode fatigue fracture of adhesive joints in harsh environments and nonlinear viscoelastic modeling of the adhesive

    NASA Astrophysics Data System (ADS)

    Arzoumanidis, Alexis Gerasimos

    A four point bend, mixed-mode, reinforced, cracked lap shear specimen experimentally simulated adhesive joints between load bearing composite parts in automotive components. The experiments accounted for fatigue, solvent and temperature effects on a swirled glass fiber composite adherend/urethane adhesive system. Crack length measurements based on compliance facilitated determination of da/dN curves. A digital image processing technique was also utilized to monitor crack growth from in situ images of the side of the specimen. Linear elastic fracture mechanics and finite elements were used to determine energy release rate and mode-mix as a function of crack length for this specimen. Experiments were conducted in air and in a salt water bath at 10, 26 and 90°C. Joints tested in the solvent were fully saturated. In air, both increasing and decreasing temperature relative to 26°C accelerated crack growth rates. In salt water, crack growth rates increased with increasing temperature. Threshold energy release rate is shown to be the most appropriate design criteria for joints of this system. In addition, path of the crack is discussed and fracture surfaces are examined on three length scales. Three linear viscoelastic properties were measured for the neat urethane adhesive. Dynamic tensile compliance (D*) was found using a novel extensometer and results were considerably more accurate and precise than standard DMTA testing. Dynamic shear compliance (J*) was determined using an Arcan specimen. Dynamic Poisson's ratio (nu*) was extracted from strain gage data analyzed to include gage reinforcement. Experiments spanned three frequency decades and isothermal data was shifted by time-temperature superposition to create master curves spanning thirty decades. Master curves were fit to time domain Prony series. Shear compliance inferred from D* and nu* compared well with measured J*, forming a basis for finding the complete time dependent material property matrix for this

  17. [Soft tissue protective and minimally invasive osteosynthesis for metacarpal fractures II-V].

    PubMed

    Dumont, C; Burchhardt, H; Tezval, M

    2012-09-01

    Soft tissue protection, closed reduction or short open reconstruction of length, rotation and articulation of metacarpals. Aftercare: early active exercises protected by additive orthesis. Closed or grade 1 open fractures with significant dislocation, deviation of rotation or loss of length. Fractures of the metacarpal, metaphyseal and extensive oblique or spiral fractures. Intra-articular fractures of the distal metacarpal that can be reduced without a step in articular surface. Proximal partial articular fractures that can be reduced without a step in articular surface in the mini-open technique. Grade 2 and 3 open fractures, extensive bending fractures in the middle third and absence of the palmar bony restraint. Multifragmentary proximal and distal metaphyseal fractures that cannot be reduced by closed methods. Intra-articular fractures that cannot be reduced without a step in articular surface. Intramedullary antegrade or percutaneous K-wires or mini-open repair screw/K-wire osteosynthesis. Two or three finger forearm cast for about 3-4 days, subsequent metacarpal orthesis, an integrated hard cast Longuette (Combicast) SoftCast™ is preferred beginning with active and passive exercises of the fingers. In this retrospective study we analyzed metacarpal (MC) fractures that were treated with minimally invasive osteosynthesis during the period 2009-2010 and 65 patients (mean age 34.8 years, female/male 13/52) with 75 metacarpal fractures were enrolled. Fractures affected MC-2 (n=9), MC-3 (n=5), MC-4 (n=15) and MC-5 (n=46). Removal of implant was performed after 6-12 weeks in 44 patients. All fractures except one showed bony healing in x-ray. At 2-months follow-up 61 patients could be evaluated and at 27-months (15-37) follow-up 34 patients could be evaluated according to the DASH score. Median DASH score results were 16 points (SD 49, n = 61) after 2 months and median DASH score results were 5 points (SD 23, n = 34) after 27 months (15-37). Range of

  18. Application of the J integral to fracture under mixed-mode loading. [MMJINT; 4330V steel

    SciTech Connect

    Riddle, R.A.

    1981-06-01

    The calculation of the J integral proved to be a successful method for characterizing the stress and displacement fields around a crack tip under mixed mode loading. A computer program was written to determine the symmetric and antisymmetric J integral quantities. The stress intensity factors from these J integral calculations were in excellent agreement with other calculations. The compact shear specimen used contains three loading holes, the load applied at the center hole being the opposite direction to the load applied at the two outer holes. For 7075-T6 aluminum, K/sub IIc/ was 1.9 times larger than K/sub Ic/. In the brittle photoelastic material K/sub IIc/ was less than K/sub Ic/. Failure of the 4330V steel compact shear specimens came as a result of the average shear stress in the region ahead of the crack tip exceeding the material flow shear stress. The experimental results suggest that the angle of crack growth is best predicted by the maximum tangential stress theory.

  19. Linear growth rates of types I and II convective modes within the rotating-cone boundary layer

    NASA Astrophysics Data System (ADS)

    Garrett, S. J.

    2010-04-01

    Experimental observations have shown that the transition characteristics of the boundary-layer flow over rotating cones depends on the cone half-angle. In particular, pairs of counter-rotating Görtler-type vortices are observed over cones with slender half-angles and co-rotating vortices are observed over broad cones. Garrett et al (2009 J. Fluid Mech. 622 209-32) have hypothesized the existence of a centrifugal instability mode over slender cones that is more dangerous than the types I (crossflow) and II (streamline curvature) modes which dominate over rotating disks and broad cones. Work is currently underway to clarify this alternative mode; however, a clear understanding of the growth rates of types I and II modes is crucial to the ultimate understanding of how the dominant mode changes with half-angle. In this paper, we demonstrate that the maximum growth rate for types I and II modes decreases with reduced half-angle, which clears the way for the dominance of the alternative instability mode. Furthermore, it is suggested that vortices travelling at 75% of the cone surface speed will be selected over smooth, clean rotating cones with half-angle such that the type I mode is dominant. Interestingly, this vortex speed has been experimentally observed by Kobayashi and Arai within the rotating-sphere boundary layer.

  20. In vitro evaluation of fracture resistance and failure mode of internally restored endodontically treated maxillary incisors with differing heights of residual dentin.

    PubMed

    Varvara, Giuseppe; Perinetti, Giuseppe; Di Iorio, Donato; Murmura, Giovanna; Caputi, Sergio

    2007-11-01

    Some of the associated effects of different restorative systems placed in endodontically treated teeth with varying heights of residual dentin have yet to be examined in a comprehensive manner. There is a need for additional information regarding fracture resistance and mode of failure. The purpose of this in vitro study was to evaluate the effect of 3 different restorative techniques with varying amounts of remaining dentin heights on the fracture resistance and failure mode of endodontically treated teeth. Three groups of 40 human maxillary incisors were subdivided into 4 subgroups (n=10) with respect to the uniform height of the residual coronal dentin, defined as 0-, 2-, 4-, or 5-mm from the cemento-enamel junction, and then restored internally using a composite resin (Z100 MP) (control group), a cobalt-chromium ceramic alloy custom-made cast post and core (IPS d.SIGN 30; CCPC group), or a carbon fiber post system (Tech Xop 2000; CFP group). All specimens were then restored with nonprecious cast crowns. Static loading tests were performed on each specimen until failure (crack without a complete fracture). The data were analyzed with 2-way ANOVA and Bonferroni-corrected t test for independent samples (alpha=.05). Failure was classified as either favorable (allowing repair) or catastrophic (not allowing repair). The fracture resistance values (N) for the 0-, 2-, 4-, and 5-mm residual dentin heights were: 88, 143, 154, and 202 for the control group, 230, 264, 364, and 383 for the CCPC group, and 153, 235, 346, and 357 for the CFP group, respectively. Generally, all the differences tested were statistically significant. The failure mode was catastrophic for no control specimens, for 36 CCPC specimens, and for 4 CFP specimens. The highest and lowest fracture resistances were recorded for the CCPC and control groups, respectively, at each residual dentin height. An increased height of residual dentin generally provided greater fracture resistance. The fracture

  1. Restoration of non-carious cervical lesions Part II. Restorative material selection to minimise fracture.

    PubMed

    Ichim, I P; Schmidlin, P R; Li, Q; Kieser, J A; Swain, M V

    2007-12-01

    It is still largely unknown as to what material parameter requirements would be most suitable to minimise the fracture and maximising the retention rate of the restoration of cervical non-carious lesions (NCCL). The present paper, as a first of its kind, proposes a radical approach to address the problems of material improvement, namely: numerical-based, fracture and damage mechanics materials optimisation engineering. It investigates the influence of the elastic modulus (E) on the failure of cervical restorative materials and aims to identify an E value that will minimise mechanical failure under clinically realistic loading conditions. The present work relies on the principle that a more flexible restorative material would partially buffer the local stress concentration. We employ a "most favourable" parametric analysis of the restorative's elastic modulus using a fracture mechanics model embedded into finite element method. The advanced numerical modelling adopts a Rankine and rotating crack material fracture model coupled to a non-linear analysis in an explicit finite element framework. The present study shows that the restorative materials currently used in non-carious cervical lesions are largely unsuitable in terms of resistance to fracture of the restoration and we suggest that the elastic modulus of such a material should be in the range of 1GPa. We anticipate that the presented methodology would provide more informative guidelines for the development of dental restorative materials, which could be tailored to specific clinical applications cognisant of the underlying mechanical environment.

  2. Type II olecranon fractures in patients over 65. Tension band or pre-formed plate? Analysis and results.

    PubMed

    Liñán-Padilla, A; Cáceres-Sánchez, L

    The objective of this study was to compare the clinical outcomes of surgical treatment using tension band with needles and preformed plates in type ii olecranon fractures according to the Mayo classification in patients older than 65 years. A descriptive, retrospective study of 49 patients with a mean age of 75.1 years who underwent surgery olecranon fracture using 2 different fixing systems. The Mayo classification was used to define them, excluding type i and iii, and the VAS to assess postoperative pain. Patients were assessed functionally by the questionnaire Quick DASH. All measurement was performed with goniometer and joint balance serial radiographs at one month, 3, 6 and 12 months. Minimum follow-up was one year. In 26 patients the tension band was used and the preformed plates in 23. There were no statistically significant differences in functional outcomes, joint balance or postoperative VAS between the 2 groups. There were a greater proportion of patients who had to be operated because of problems related to osteosynthesis material in those in which preformed plates were used. Treatment of olecranon fractures with tension band with needles and cerclage remains the surgery of choice in patients older than 65 years. Copyright © 2017 SECOT. Publicado por Elsevier España, S.L.U. All rights reserved.

  3. Temporary space maintainers retained with composite resin. Part II: Fracture load in vitro.

    PubMed

    Grajower, R; Stern, N; Zamir, S T; Kohavi, D

    1981-01-01

    The average fracture load during occlusal loading of pontics which were bonded to natural abutment teeth in vitro was found to be 56.1, 57.5 and 74.2 kg for natural, acrylic resin, and Restodent pontics, respectively. Coating the roots of the abutment teeth with a thin layer of silicone rubber before embedding them in stone slightly reduced the strength of the fixed partial dentures. Thermocycling the specimens with coated roots caused a considerable decrease in strength to fracture loads of 33.0, 17.9, and 37.3 kg for natural, acrylic resin, and Restodent pontics, respectively. Fracture of the enamel of natural tooth pontics was observed in a few specimens. The superior strength of the fixed partial dentures with natural tooth and Restodent pontics would indicate that these pontics are superior for clinical trials rather than acrylic resin pontics.

  4. Study of Load Transfer and Fracture on Composite-to-Metal-Wire Joints

    DTIC Science & Technology

    2009-03-01

    6 C. CRACK GEOMETRY ....................................................................................7 D. VIRTUAL CRACK CLOSURE TECHNIQUE ( VCCT ...fracture toughness icG , where i is either mode I, mode II or m ed mode. The virtual crack closure technique ( VCCT ) is widely used for computing energy...a a Figure 4. Crack Geometry. 8 D. VIRTUAL CRACK CLOSURE TECHNIQUE ( VCCT ) An overview of the virtual crack closure technique ( VCCT ) and

  5. Effect of TE Mode Power on the PEP II LER BPM System

    SciTech Connect

    Ng, Cho-K

    2011-08-26

    The beam chamber of the PEP-II B-Factory Low Energy Ring (LER) arc sections is connected to an antechamber for the absorption of synchrotron radiation on discrete photon stops. The presence of the antechamber substantially reduces the cutoff frequency of the vacuum chamber and, in particular, allows the propagation of higher-order-mode (HOM) TE power generated by beamline components at the BPM signal processing frequency. Calculations of the transmission properties of the TE mode in different sections of the vacuum chamber show that the power is trapped between widely separated bellows in the arc sections. Because of the narrow signal bandwidth and weak coupling of the TE mode to the BPM buttons, the noise contributed by the HOM TE power will not produce a noticeable effect on the BPM position signal voltage. The LER arc vacuum chamber employs an antechamber with a discrete photon stop for absorption of synchrotron radiation and with pumps for maintaining pressure below 10 nTorr [1]. The horizontal dimensions of the antechambers at the pumping chamber section and the magnet chamber section are larger or comparable to that of the beam chamber. Because of the increase in the horizontal dimension, the cutoff frequency of the TE10-like mode (in rectangular coordinates) of the vacuum chamber is considerably reduced and, in particular, is less than the BPM signal processing frequency at 952 MHz. TE power propagating in the vacuum chamber will penetrate through the BPM buttons and will affect the pickup signal if its magnitude is not properly controlled. It is the purpose of this note to clarify various issues pertaining to this problem. TE power is generated when the beam passes a noncylindrically symmetric beamline component such as the RF cavity, the injection region, the IR crotch and the IP region. The beampipes connected to these components have TE cutoff frequencies greater than 952 MHz (for example, the TE cutoff frequency of the RF cavity beampipe is 1.8 GHz

  6. Macro- and Micro-Mechanics of Mixed-Mode Dynamic Fracture of Concrete. Part 1. Micro-Mechanic Analysis

    DTIC Science & Technology

    1993-02-14

    fracture energy density of concrete were discussed by Hillerborg and Mindess [55-57]. The total external energy needed to quasi-statically fracture a...Composites.: Strzin Rate Effects on Fracture, eds. S. Mindess and S.P Shah, Materials Research Society Symposia Proceeding Vol. 64, 1986 18 S. Mindess ...Nijhoff Publishers, 1985, pp. 617-636. I 1 9 A. Benton, S. Mindess , and N. Benthur, "The Behavior of Concrete Under Impact Loading: Experimental

  7. Fracture strength and elastic modulus as a function of porosity for hydroxyapatite and other brittle materials, Part II

    SciTech Connect

    Fan, Xiaofeng; Case, Eldon D; Ren, Fei; Shu, Yutian; Baumann, Melissa

    2012-01-01

    Part I of this paper discussed the Weibull modulus m, versus porosity P behavior of brittle materials, including HA. While the Weibull modulus m deals with the scatter in fracture strength data, this paper (Part II) focuses on two additional key mechanical properties of porous materials, namely the average fracture strength f , and Young s modulus E, for P in the interval from P zero to P PG (the porosity of the unfired compacts). The f versus P data for HA from this study and the literature data for alumina, yttria stabilized zirconia (YSZ) and silicon nitride are describedwell by functions of , where = 1 P/PG = the degree of densification. A similar function of applies to the E versus P behavior of HA from this study and data from the literature for alumina, titanium and YSZ. All of the data analyzed in this study (Part II) are based on partially and fully sintered powder compacts (excluding green powder compacts), thus the f / 0 versus and E /E0 versus relationships may apply only to such specimens.

  8. Characterization of debond growth mechanism in adhesively bonded composites under mode II static and fatigue loadings

    NASA Technical Reports Server (NTRS)

    Mall, S.; Kochhar, N. K.

    1988-01-01

    An experimental investigation of adhesively bonded composite joint was conducted to characterize the debond growth mechanism under mode II static and fatigue loadings. For this purpose, end-notched flexure specimens of graphite/epoxy (T300/5208) adherends bonded with EC 3445 adhesive were tested. In all specimen tested, the fatigue failure occurred in the form of cyclic debonding. The present study confirmed the result of previous studies that total strain-energy-release rate is the driving parameter for cyclic debonding. Further, the debond growth resistance under cyclic loading with full shear reversal (i.e., stress ratio, R = -1) is drastically reduced in comparison to the case when subjected to cyclic shear loading with no shear reversal (i.e., R = 0.1).

  9. Stimuli Responsive/Rheoreversible Hydraulic Fracturing Fluids for Enhanced Geothermal Energy Production (Part II)

    SciTech Connect

    Bonneville, Alain; Jung, Hun Bok; Shao, Hongbo; Kabilan, Senthil; Um, Wooyong; Carroll, Kenneth C.; Varga, Tamas; Suresh, Niraj; Stephens, Sean A.; Fernandez, Carlos A.

    2014-12-14

    We have used an environmentally friendly and recyclable hydraulic fracturing fluid - diluted aqueous solutions of polyallylamine or PAA – for reservoir stimulation in Enhanced Geothermal System (EGS). This fluid undergoes a controlled and large volume expansion with a simultaneous increase in viscosity triggered by CO2 at EGS temperatures. We are presenting here the results of laboratory-scale hydraulic fracturing experiment using the fluid on small cylindrical rock cores (1.59 cm in diameter and 5.08 cm in length) from the Coso geothermal field in California. Rock samples consisted of Mesozoic diorite metamorphosed to greenschist facies. The experiments were conducted on 5 samples for realistic ranges of pressures (up to 275 bar) and temperatures (up to 210 °C) for both the rock samples and the injected fluid. After fracturing, cores were subjected to a CO2 leakage test, injection of KI solution, and X-ray microtomography (XMT) scanning to examine the formation and distribution of fractures. The design and conduct of these experiments will be presented and discussed in details. Based on the obtained XMT images, Computational Fluid Dynamics (CFD) simulations were then performed to visualize hydraulic fractures and compute the bulk permeability. OpenFOAM (OpenCFD Ltd., Reading, UK), was used to solve the steady state simulation. The flow predictions, based upon the laminar, 3-D, incompressible Navier-Stokes equations for fluid mass and momentum, show the remarkable stimulation of the permeability in the core samples and demonstrate the efficiency of such a CO2 triggered fluid in EGS.

  10. Reassessment of the Unique Mode of Binding between Angiotensin II Type 1 Receptor and Their Blockers

    PubMed Central

    Matsuo, Yoshino; Saku, Keijiro; Karnik, Sadashiva S.

    2013-01-01

    While the molecular structures of angiotensin II (Ang II) type 1 (AT1) receptor blockers (ARBs) are very similar, they are also slightly different. Although each ARB has been shown to exhibit a unique mode of binding to AT1 receptor, different positions of the AT1 receptor have been analyzed and computational modeling has been performed using different crystal structures for the receptor as a template and different kinds of software. Therefore, we systematically analyzed the critical positions of the AT1 receptor, Tyr113, Tyr184, Lys199, His256 and Gln257 using a mutagenesis study, and subsequently performed computational modeling of the binding of ARBs to AT1 receptor using CXCR4 receptor as a new template and a single version of software. The interactions between Tyr113 in the AT1 receptor and the hydroxyl group of olmesartan, between Lys199 and carboxyl or tetrazole groups, and between His256 or Gln257 and the tetrazole group were studied. The common structure, a tetrazole group, of most ARBs similarly bind to Lys199, His256 and Gln257 of AT1 receptor. Lys199 in the AT1 receptor binds to the carboxyl group of EXP3174, candesartan and azilsartan, whereas oxygen in the amidecarbonyl group of valsartan may bind to Lys199. The benzimidazole portion of telmisartan may bind to a lipophilic pocket that includes Tyr113. On the other hand, the n-butyl group of irbesartan may bind to Tyr113. In conclusion, we confirmed that the slightly different structures of ARBs may be critical for binding to AT1 receptor and for the formation of unique modes of binding. PMID:24260317

  11. Damping higher order modes in the PEP-II B-Factory storage ring collider

    NASA Astrophysics Data System (ADS)

    Weathersby, Stephen

    2007-05-01

    The PEP-II B-Factory storage ring collider at SLAC provides crucial experimental evidence for the physics of CP violation. To investigate rare B-meson decays requires high luminosity which comes mainly from increasing bunch currents and reducing bunch sizes. Electromagnetic effects of intense bunch fields in the form of wake fields couple into accelerator components, inducing Joule heating at levels detrimental to vacuum chamber components. Additionally, wake fields contribute to beam instability, decreasing luminosity. These effects are limiting B-factory performance. Computer simulations and experimental evidence indicate that beam collimators produce wake fields in the form of dipole and quadrupole waveguide modes which can propagate tens of meters from their source before depositing energy at remote locations. Simulations confirm that coupling through narrow slots into bellows cavities occurs for beam pipe modes. Two proposals are set forth to mitigate wake field effects. The first proposal is to reduce the quality factor of resonant structures with a water cooled dielectric lossy material. Electromagnetic energy coupling into resonant structures can be isolated and safely dissipated. Prototype devices have been built and have been shown to reduce resistive heating in large pumping chambers coupled to the beam chamber. Designs and simulations which incorporate such techiques into bellows devices are presented. The second proposal incorporates novel devices introduced in the accelerator vacuum chamber which selectively traps dipole and quadrupole propagating wake fields before they can couple into sensitive beam line components without introducing impedance to the beam. Scattering parameter analysis is used to tailor device response to specific modes. Dangerous modes are extracted from the beam chamber, trapped and dissipated in a water cooled lossy material. Modes which represent an impedance to the beam are not affected. After design optimization, production

  12. Some recent theoretical and experimental developments in fracture mechanics

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Eftis, J.; Hones, D. L.

    1978-01-01

    Recent theoretical and experimental developments in four distinct areas of fracture mechanics research are described. These are as follows: experimental comparisons of different nonlinear fracture toughness measures, including the nonlinear energy, R curve, COD and J integral methods; the singular elastic crack-tip stress and displacement equations and the validity of the proposition of their general adequacy as indicated, for example, by the biaxially loaded infinite sheet with a flat crack; the thermodynamic nature of surface energy induced by propagating cracks in relation to a general continuum thermodynamic description of brittle fracture; and analytical and experimental aspects of Mode II fracture, with experimental data for certain aluminum, steel and titanium alloys.

  13. Pseudo-type-II tuning behavior and mode identification in whispering gallery optical parametric oscillators.

    PubMed

    Meisenheimer, Sarah-Katharina; Fürst, Josef Urban; Schiller, Annelie; Holderied, Florian; Buse, Karsten; Breunig, Ingo

    2016-06-27

    Wavelength tuning of conventional mirror-based optical parametric oscillators (OPOs) exhibits parabolically-shaped tuning curves (type-0 and type-I phase matching) or tuning branches that cross each other with a finite slope (type-II phase matching). We predict and experimentally prove that whispering gallery OPOs based on type-0 phase matching show both tuning behaviors, depending on whether the mode numbers of the generated waves coincide or differ. We investigate the wavelength tuning of optical parametric oscillation in a millimeter-sized radially-poled lithium niobate disk pumped at 1 μm wavelength generating signal and idler waves between 1.7 and 2.6 μm wavelength. Our experimental findings excellently coincide with the theoretical predictions. The investigated whispering gallery optical parametric oscillator combines the employment of the highest nonlinear-optical coefficient of the material with a controlled type-II-like wavelength tuning and with the possibility of self-phase locking.

  14. Effects of fiber-glass-reinforced composite restorations on fracture resistance and failure mode of endodontically treated molars.

    PubMed

    Nicola, Scotti; Alberto, Forniglia; Riccardo, Michelotto Tempesta; Allegra, Comba; Massimo, Saratti Carlo; Damiano, Pasqualini; Mario, Alovisi; Elio, Berutti

    2016-10-01

    The study evaluated the fracture resistance and fracture patterns of endodontically treated mandibular first molars restored with glass-fiber-reinforced direct composite restorations. In total, 60 extracted intact first molars were treated endodontically; a mesio-occluso-distal (MOD) cavity was prepared and specimens were then divided into six groups: sound teeth (G1), no restoration (G2), direct composite restoration (G3), fiber-post-supported direct composite restoration (G4), direct composite reinforced with horizontal mesio-distal glass-fibers (G5), and buccal-palatal glass-fibers (G6). Specimens were subjected to 5000 thermocycles and 20,000 cycles of 45° oblique loading force at 1.3Hz and 50N; they were then loaded until fracture. The maximum fracture loads were recorded in Newtons (N) and data were analyzed with one-way ANOVA and post-hoc Tukey tests (p<0.05). Fractured specimens were analyzed with a scanning electron microscope (SEM). The mean static loads (in Newtons) were: G1, 831.83; G2, 282.86; G3, 364.18; G4, 502.93; G5, 499.26; and G6, 582.22. Fracture resistance did not differ among G4, G5, and G6, but was significantly higher than G3 (p=0.001). All specimens fractured in a catastrophic way. In G6, glass fibers inducted a partial deflection of the fracture, although they were not able to stop crack propagation. For the direct restoration of endodontically treated molars, reinforcement of composite resins with glass-fibers or fiber posts can enhance fracture resistance. The SEM analysis showed a low ability of horizontal glass-fibers to deviate the fracture, but this effect was not sufficient to lead to more favorable fracture patterns above the cement-enamel junction (CEJ). The fracture resistance of endodontically treated molars restored with direct composite restorations seems to be increased by reinforcement with fibers, even if it is insufficient to restore sound molar fracture resistance and cannot avoid vertical fractures. Copyright © 2016

  15. Salter-Harris II fractures of the distal tibia: does surgical management reduce the risk of premature physeal closure?

    PubMed

    Russo, Franco; Moor, Molly A; Mubarak, Scott J; Pennock, Andrew T

    2013-01-01

    Premature physeal closure (PPC) is a common complication resulting from the management of a displaced Salter-Harris II (SH II) fracture of the distal tibia. The purpose of this study was to evaluate our institution's treatment approach to assess PPC and complication rates of fractures treated both surgically and nonsurgically. We performed a retrospective review of all patients presenting with a displaced SH II fracture between 2004 and 2010. Initial treatment was closed reduction in the emergency department. Further treatment and subsequent categorization was based on amount of residual displacement. Patients with <2 mm of postreduction displacement were treated with a non-weight-bearing long-leg cast (LLC; group 1), patients with residual displacement between 2 and 4 mm were treated with one of 2 approaches based on surgeon preference: either LLC (group 2) or open reduction and internal fixation (ORIF) with removal of any interposed tissue (group 3). Patients with >4 mm of residual displacement were treated with ORIF (group 4). Follow-up radiographs were performed for a minimum of 6 months. If there was clinical concern about PPC, computed tomography imaging was performed to assess for a bony bar. In total, 96 patients with a mean age of 12.6 years at presentation were included in the study. Among the 14 patients with <2 mm of postreduction displacement, 29% had a PPC and 7% had to undergo a subsequent procedure (epiphsyiodesis, osteotomy, etc.). Of the 33 patients with 2 to 4 mm of displacement who were treated with a LLC, 33% had a PPC and 15% had to undergo a subsequent procedure. Of the 11 patients with 2 to 4 mm of displacement treated with ORIF 46% had a PPC and 18% had a second procedure. Finally, 38 patients with >4 mm of displacement treated with ORIF had a PPC rate of 55% and 23% had a subsequent procedure. No statistical differences in PPC (P=0.19) or subsequent surgeries (P=0.57) were observed between groups. Among those with 2 to 4 mm of

  16. [Case-control study on bone setting manipulation for the treatment of over degree II supination-eversion fractures of ankle joint].

    PubMed

    Qi, Yue-Feng; Chen, Fa-Lin; Bao, Shu-Ren; Li, Cheng-Huan; Zhao, Xing-Wei; Liu, Shi-Ming; Chen, Wen-Xue; Li, Ye; Wang, Peng

    2012-08-01

    To explore therapeutic effects of bone setting manipulation for the treatment of over degree II supination-eversion fractures of ankle,and analyze manipulative reduction mechanism. From 2005 to 2008, 95 patients with over degree II supination-eversion fractures of ankle were treated respectively by manipulation and operation. There were 43 cases [11 males and 32 females with an average age of (44.95 +/- 12.65) years] in manipulation group, and 2 cases were degree II, 11 cases were degree III, and 30 cases were degree IV. There were 52 cases [21 males and 31 females with an average age of (39.96 +/- 13.28) years] in operative group,and 6 cases were degree II, 18 cases were degree III, and 28 cases were degree IV. Bone setting manipulation and hard splint external fixation were applied to manipulative group. Operative reduction internal fixation was performed in operative group. X-ray was used to evaluate reduction of fracture before and after treatment, 2 months after treatment. Ankle joint function was evaluated according to Olerud-Molander scoring system after 6 months treatment. All patients were followed up with good reduction. Three cases occurred wound complication in operative group, but not in manipulative group. In manipulation group, 19 cases got excellent results, 20 cases good and 4 cases fair; while in operative group, 30 cases got excellent results, 20 cases good and 2 cases poor. There were no significant differences in fracture reduction and ankle joint function recovery between two groups (P > 0.05). Efficacy of operative treatment was better than that of manipulative treatment at degree IV fracture (P < 0.05). Bone setting manipulation is a good method for treating supination-eversion ankle joint fractures, which has advantages of simple and safe operation, reliable efficacy. For ankle join fracture at degree IV, manipulative reduction should be adopted earlier, and operative treatment also necessary

  17. The effect of incomplete crown ferrules on fracture resistance and failure modes of endodontically treated maxillary incisors restored with quartz fiber post, composite core, and crowns

    PubMed Central

    Muangamphan, Panorjit; Sattapan, Boonrat; Kukiattrakoon, Boonlert; Thammasitboon, Kewalin

    2015-01-01

    Aim: To investigate the fracture resistance of restored endodontically treated teeth (RETT) with fiber posts, cores, and crowns with limited ferrules. Materials and Methods: Sixty maxillary anterior teeth were endodontically treated and decoronated 2 mm above the cemento-enamel junction, and then divided into 6 groups of 10 teeth each; Group circumferential ferrule (2FR), Group ferrule in the labial, mesial, and palatal region (2FR-LaMPa), Group ferrule in the labial, and palatal region (2FR-LaPa), Group 2FR-Pa and 2FR-La respectively, and Group 0FR (no ferrule). All 60 prepared teeth were then restored with quartz fiber posts, resin composite cores, and metal crowns. The specimens were subjected to load until failure occurred. Data were analyzed using one-way analysis of variance and Tukey's tests (α = 0.05). The mode of failure was determined under a stereoscope. Results: A statistical significant difference was found among groups 2FR-LaMPa, 2FR-Pa, 2FR-LaPa, and 2FR from the group 2FR-La, and from the group 0FR (P < 0.01). The predominant mode of failure was an oblique palatal to labial root fracture for the groups with remaining ferrules. Conclusion: For RETT that have incomplete crown ferrules, the location of the ferrules may affect their fracture resistance. PMID:26069401

  18. Successful fusion of remote type II odontoid fracture using anterior screw fixation of the odontoid and rhBMP-2: report of two cases.

    PubMed

    Morgan, Jeremy P; Asfora, Wilson T

    2013-05-01

    Anterior screw fixation of the odontoid is contraindicated in remote type II fractures. The alternative surgical treatment consists of a posterior C1 to C2 or an occiput to C3 fusion, which is met with much resistance by patients as this option limits head motion, especially rotational movement. Furthermore, elderly patients may not be medically fit to undergo surgery of this magnitude. This report presents two remote type II odontoid fractures in elderly patients (67 and 73 years of age) who were successfully treated by means of anterior screw fixation of the odontoid along with an injection of recombinant human bone morphogenic protein (rhBMP-2) (Medtronic Inc.) into the fracture line with infiltration of the fibrous union tissue and adjacent anterior longitudinal ligament. To our knowledge, this is the first documented report of solid fusion of remote type II odontoid fracture treated with rhBMP-2 and anterior screw fixation. The authors believe that this technique may be a viable alternative for the treatment of failed odontoid fractures older than six months.

  19. A fatal iatrogenic right vertebral injury after transoral odontoidectomy and posterior cervical stabilization for a type II odontoid fracture.

    PubMed

    Scalici, Edoardo; Indorato, Francesca; Portelli, Francesca; Savì, Tommaso; Maresi, Emiliano; Busardò, Francesco P

    2014-02-01

    The authors present a singular case of an iatrogenic right vertebral artery injury, involving a 67 year-old man, who reported a type II odontoid fracture (Anderson and D'Alonzo Classification) and posterior atlantoaxial dislocation following a road traffic accident. A small injury involving the right vertebral artery occurred as a consequence of transoral odontoidectomy and posterior cervical stabilization. It was caused by bone spicules of spinal origin and their presence was confirmed by the histological section of the right vertebral artery at the level of C1-C2. The case confirms how iatrogenic vertebral artery injuries during cervical spine surgery may be potentially lethal, especially where complications arise some days after surgery.

  20. A compendium of sources of fracture toughness and fatigue crack growth data for metallic alloys. II

    NASA Technical Reports Server (NTRS)

    Hudson, C. M.; Seward, S. K.

    1982-01-01

    A compendium is presented of sources for metallic alloy fracture toughness and fatigue crack growth data, which concentrates on technical reports as the primary source of references and updates the previous Hudson and Seward (1978) compendium references on technical journals. Where available, the accession numbers which are used as code numbers for the ordering of the reports from their publishers are given. The sources of these reports include the AIAA Technical Information Service, the Defense Technical Information Center, the National Technical Information Service, and NASA.

  1. The High Risk of Infection With Delayed Treatment of Open Seymour Fractures: Salter-Harris I/II or Juxta-epiphyseal Fractures of the Distal Phalanx With Associated Nailbed Laceration.

    PubMed

    Reyes, Bryan A; Ho, Christine A

    2017-06-01

    To describe treatment methods and complication rates of all open Seymour fractures (Salter-Harris I/II or juxta-epiphyseal fractures of the distal phalanx of the hand with associated nailbed laceration) treated at or referred to a pediatric level 1 trauma center over a 10-year time period. We hypothesized that delayed treatment of Seymour fractures results in higher infectious complication rates. We identified all patients treated for open Seymour fractures at the orthopaedic hand clinic at our level 1 pediatric trauma center between August 2002 and December 2012. All charts were reviewed retrospectively. Patients were divided into groups based on timing and completeness of treatment. "Appropriate" treatment was defined as irrigation and debridement, fracture reduction, and antibiotic administration. "Partial" treatment was defined as any type of incomplete treatment; "Acute" treatment was defined as management within 24 hours of the injury; and "Delayed" as having received treatment after 24 hours from the time of injury. Statistical comparisons were performed using the Fisher exact test. A total of 34 patients treated for 35 Seymour fractures met the inclusion criteria. In total, 31% (11/35) received acute, appropriate treatment, 37% (13/35) received acute, partial treatment, and 31% (11/35) received delayed treatment. There were 7 infectious complications: 2 superficial and 5 osteomyelitis. No infections occurred in the acutely, appropriately treated group (infection rate 0%, 0/11), 2 occurred in the acutely, partially treated group (15%, 2/13), and 5 occurred in the delayed treatment group (45%, 5/11). The timing and quality of treatment of open Seymour fractures significantly influences infection rates. This study highlights the importance of timely and appropriate treatment of this seemingly innocuous fracture. Level III-retrospective study, therapeutic.

  2. On waves in gases. Part II: Interaction of sound with magnetic and internal modes

    NASA Astrophysics Data System (ADS)

    Campos, L. M. B. C.

    1987-04-01

    This work completes a two-part review on waves in gases, of which the first part

    [Rev. Mod. Phys. 58, 117 (1986)]
    dealt with the modern aspects of acoustics of jets, turbulence, and ducts; this second part extends the range of topics from sound to magnetic, internal, and (to a lesser extent) inertial waves, thus considering all four restoring forces (pressure, gravity, and Lorentz and Coriolis forces). The motivations for the study of these waves were outlined in the introduction to Part I. Part II reviews the coupling of acoustic, magnetic, and internal waves, in four stages: in Sec. I dispersion relations are used to study the propagation and radiation of magneto-acoustic-gravity-inertial waves in media for which the wave speeds and scattering scales are constant; in Sec. II the case of linear waves in stratified media, with nonuniform propagation velocity, is then discussed by means of special functions, appearing as exact solutions of second-order problems; in Sec. III the study of linear waves with variable propagation speeds is extended to certain classes of higher-order problems including a discussion of cutoff frequencies, critical levels, partition of energy, mode coupling and conversion, etc; in Sec. IV the preceding studies are extended to damped and nonlinear waves, to include dissipation with variable damping scales and large disturbances in media under nonuniform external forces, such as magnetic flux tubes. The conclusion (Sec. V) sums up both parts of the review, in the sense that it deals with all types of waves in fluids; it mentions a few currently controversial topics, points out some directions for future research, and indicates methods available to address these issues.

  3. Probabilistic Fracture Analysis of Functionally Graded Materials—Part II: Implementation and Numerical Examples

    NASA Astrophysics Data System (ADS)

    Nguyen, Tam H.; Song, Junho; Paulino, Glaucio H.

    2008-02-01

    Probabilistic fracture analyses are performed for investigating uncertain fracture response of Functionally Graded Material (FGM) structures. The First-Order-Reliability-Method (FORM) is implemented into an existing Finite Element code for FGM (FE-FGM), which was previously developed at the University of Illinois at Urbana-Champaign [2]. The computational simulation will be used in order to estimate the probability of crack initiation with uncertainties in the material properties only. The two-step probability analysis method proposed in the companion paper (Part I, [1]) is illustrated by a numerical example of a composite strip with an edge crack. First, the reliability index of a crack initiation event is estimated as we vary the mean and standard deviation of the slope and the location of the inflection point of the spatial profile of Young's modulus. Secondly, the reliability index is estimated as we vary the standard deviation and the correlation length of the random field that characterize the random spatial fluctuation of Young's modulus. Also investigated is the relative importance of the uncertainties in the toughness compared to those in Young's modulus.

  4. Particle simulation of radio frequency stabilization of the flute mode in a tandem mirror. II. Perpendicular antenna

    SciTech Connect

    Abe, H.; Kadoya, Y.

    1988-10-01

    A two-and-a-half-dimensional electromagnetic particle code PS2M (J. Phys. Soc. Jpn. 56, 3899 (1987)) is used to study how an electric field applied perpendicularly to the magnetic field affects the radio frequency stabilization of flute modes in a tandem mirror plasma. The electric field perpendicular to the magnetic field stabilizes or destabilizes the flute mode through the mechanism of the ponderomotive force acting on electrons and ions and through the mechanism of sideband coupling. In the simulations two typical examples have been shown: (i) when the sideband coupling effects (in which the electron terms are dominant) stabilize the flute modes and (ii) when the perpendicular ponderomotive force acting on the electrons destabilizes the flute modes.

  5. Geothermal fracture stimulation technology. Volume II. High-temperature proppant testing

    SciTech Connect

    Not Available

    1980-07-01

    Data were obtained from a newly built proppant tester, operated at actual geothermal temperatures. The short term test results show that most proppants are temperature sensitive, particularly at the higher closure stresses. Many materials have been tested using a standard short-term test, i.e., fracture-free sand, bauxite, and a resin-coated sand retained good permeability at the high fluid temperatures in brine over a range of closure stresses. The tests were designed to simulate normal closure stress ranges for geothermal wells which are estimated to be from 2000 to 6000 psi. Although the ultra high closure stresses in oil and gas wells need not be considered with present geothermal resources, there is a definite need for chemically inert proppants that will retain high permeability for long time periods in the high temperature formations.

  6. Spectral estimation of plasma fluctuations. II. Nonstationary analysis of edge localized mode spectra

    SciTech Connect

    Riedel, K.S.; Sidorenko, A. ); Bretz, N. ); Thomson, D.J. )

    1994-03-01

    Several analysis methods for nonstationary fluctuations are described and applied to the edge localized mode (ELM) instabilities of limiter H-mode plasmas. The microwave scattering diagnostic observes poloidal [ital k][sub [theta

  7. Functional outcome after Mason II-III radial head and neck fractures: study protocol for a systematic review in accordance with the PRISMA statement.

    PubMed

    Hagelberg, Mårten; Thune, Alexandra; Krupic, Ferid; Salomonsson, Björn; Sköldenberg, Olof

    2017-01-27

    Fractures of the radial head and neck are the most common fractures of the elbow, and account for approximately one-third of all elbow fractures. Depending on the fracture type the treatment is either conservative or surgical. There is no absolute consensus regarding optimal treatment for different fracture types. The aim of this protocol is to present the method that will be used to collect, describe and analyse the current evidence regarding the treatment of Mason II-III radial head and neck fractures. We will conduct a systematic review in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocol (PRISMA-P) guidelines statement. We will search a number of databases with a predefined search strategy to collect both randomised and non-randomised studies. The articles will be summarised with descriptive statistics. If applicable a meta-analysis will be conducted. Ethical approval is not required since this is a protocol for a systematic review and no primary data will be collected. The authors will publish findings from this review in a peer-reviewed scientific journal. CRD42016037627. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

  8. Topical report on subsurface fracture mapping from geothermal wellbores. Phase I. Pulsed radar techniques. Phase II. Conventional logging methods. Phase III. Magnetic borehole ranging

    SciTech Connect

    Hartenbaum, B.A.; Rawson, G.

    1980-09-01

    To advance the state-of-the-art in Hot Dry Rock technology, an evaluation is made of (i) the use of radar to map far-field fractures, (ii) the use of more than twenty different conventional well logging tools to map borehole-fracture intercepts, and (iii) the use of magnetic dipole ranging to determine the relative positions of the injection well and the production well within the fractured zone. It is found that according to calculations, VHF backscatter radar has the potential for mapping fractures within a distance of 50 +- 20 meters from the wellbore. A new technique for improving fracture identification is presented. Analyses of extant data indicate that when used synergistically the (1) caliper, (2) resistivity dipmeter, (3) televiewer, (4) television, (5) impression packer, and (6) acoustic transmission are useful for mapping borehole-fracture intercepts. Improvements in both data interpretation techniques and high temperature operation are required. The surveying of one borehole from another appears feasible at ranges of up to 200 to 500 meters by using a low frequency magnetic field generated by a moderately strong dipole source (a solenoid) located in one borehole, a sensitive B field detector that traverses part of the second borehole, narrow band filtering, and special data inversion techniques.

  9. Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II

    NASA Astrophysics Data System (ADS)

    Melnikov, A. V.; Ochando, M.; Ascasibar, E.; Castejon, F.; Cappa, A.; Eliseev, L. G.; Hidalgo, C.; Krupnik, L. I.; Lopez-Fraguas, A.; Liniers, M.; Lysenko, S. E.; de Pablos, J. L.; Perfilov, S. V.; Sharapov, S. E.; Spong, D. A.; Jimenez, J. A.; Ufimtsev, M. V.; Breizman, B. N.; HIBP Group; the TJ-II Team

    2014-12-01

    Excitation of modes in the Alfvénic frequency range, 30 kHz < fAE < 300 kHz, was observed in hydrogen plasma heated by hydrogen neutral beam injection (NBI) in the TJ-II heliac. Co-field and counter-field NBI were injected, and the components of the poloidal magnetic field were varied one by one and in combinations, in order to investigate the beam-driven modes over an extended range of the rotational transform values, 1.51<\\unicode{7548} (0)<1.67 . Taking advantage of the unique TJ-II capabilities, a dynamic magnetic configuration experiment with \\unicode{7548} (ρ , t) variation during discharges has shown strong effects on the mode frequency via both vacuum \\unicode{7548} changes and induced net plasma current. A drastic frequency increase from ˜50 to ˜250 kHz was observed for some modes when plasma current as low as ±2 kA was induced by small (10%) changes in the vertical field. A comprehensive set of diagnostics including a heavy ion beam probe, magnetic probes and a multi-chord bolometer made it possible to identify the spatial spread of the modes and deduce the internal amplitudes of their plasma density and magnetic field perturbations. A simple analytical model for fAE, based on the local Alfvén eigenmode (AE) dispersion relation, was proposed to characterize the observation. It was shown that all the observations, including vacuum iota and plasma current variations, may be fitted by the model, so the linear mode frequency dependence on \\unicode{7548} (plasma current) and one over square root density dependence present the major features of the NBI-induced AEs in TJ-II, and provide the framework for further experiment-to-theory comparison.

  10. Two-View Gravity Stress Imaging Protocol for Nondisplaced Type II Supination External Rotation Ankle Fractures: Introducing the Gravity Stress Cross-Table Lateral View.

    PubMed

    Boffeli, Troy J; Collier, Rachel C; Gervais, Samuel J

    Assessing ankle stability in nondisplaced Lauge-Hansen supination external rotation type II injuries requires stress imaging. Gravity stress mortise imaging is routinely used as an alternative to manual stress imaging to assess deltoid integrity with the goal of differentiating type II from type IV injuries in cases without a posterior or medial fracture. A type II injury with a nondisplaced fibula fracture is typically treated with cast immobilization, and a type IV injury is considered unstable and often requires operative repair. The present case series (two patients) highlights a standardized 2-view gravity stress imaging protocol and introduces the gravity stress cross-table lateral view. The gravity stress cross-table lateral view provides a more thorough evaluation of the posterior malleolus owing to the slight external rotation and posteriorly directed stress. External rotation also creates less bony overlap between the tibia and fibula, allowing for better visualization of the fibula fracture. Gravity stress imaging confirmed medial-sided injury in both cases, confirming the presence of supination external rotation type IV or bimalleolar equivalent fractures. Open reduction and internal fixation was performed, and both patients achieved radiographic union. No further treatment was required at 21 and 33 months postoperatively. Copyright © 2017 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

  11. Les fractures distales de la clavicule type II de Neer: plaque à crochet versus brochage transacromiale

    PubMed Central

    Mechchat, Atif; Elidrissi, Mohammed; Shimi, Mohammed; Elibrahimi, Abdelhalim; Elmrini, Abdelmajid

    2015-01-01

    Cette étude a été menée afin de faire une comparaison entre deux techniques chirurgicales différentes: la plaque à crochet et l'embrochage dans les fractures instables du quart externe de la clavicule. Nous avons mené une étude prospective entre 2009 et 2013, incluant deux groupes de patients: un premier groupe de 14 patients traités par plaque à crochet par voie d'abord antéro-inférieure, un second de 12 patients traités par brochage. Tous les patients ont été hospitalisés 24 h après la chirurgie et ont été suivi pendant 1 an. Nous avons comparé les résultats des deux techniques en étudiant: le temps opératoire, le saignement, délai de consolidation, la douleur et la fonction selon le score de constant. L'analyse statistique des résultats fonctionnels et radiologiques a montré la supériorité d'une technique par rapport à l'autre; ainsi l’âge moyen global était de 32,6 ans (+/- 13,7), le sex-ratio (H/F) était de 1. Le temps opératoire moyen est de 35 min pour la plaque à crochet contre 45 minutes pour le brochage, le délai moyen de consolidation était de 6,1 (+/-0,7) semaines dans le groupe traité par plaque vissée, et de 6 (+/-0,7) semaines dans le groupe traité par embrochage (p = 0,5), le score de Constant absolu moyen était respectivement de 86 (+/-10,4) et de 90,92 (+/-2,5) (p = 0,04). L'analyse uni variée a montré une association statistiquement significative entre les paramètres d’évaluation et les deux techniques chirurgicales étudiées. Par conséquent, l’étude a noté la supériorité de la plaque à crochet contre l'embroche dans les fractures instables du quart externe de la clavicule. PMID:26090053

  12. Twenty-one-year follow-up of supination-external rotation type II-IV (OTA type B) ankle fractures: a retrospective cohort study.

    PubMed

    Donken, Christian C M A; Verhofstad, Michael H J; Edwards, Michael J; van Laarhoven, Cees J H M

    2012-08-01

    To evaluate long-term results after protocoled treatment of supination-external rotation (SER) Type II-IV ankle injuries. Retrospective cohort study. Level I trauma center. Two hundred seventy-six adult patients with an SER Type II-IV ankle fracture between January 1, 1985, and January 1, 1990. All patients were approached to participate in this study. Fractures with tibiotalar congruity were treated nonoperative and unstable fractures with joint incongruity were treated operatively. MEAN OUTCOME MEASUREMENTS: 1) a functional outcome questionnaire (Olerud score); 2) range of motion; 3) functional impairment (American Medical Association guidelines); and 4) radiologic anatomic result (medial clear space widening; osteoarthritis; Cedell score). After a median of 21 years in 54% (n = 148) of patients, follow-up was achieved. Seventy-six patients (51%) had a SER Type II injury, four patients (3%) a SER Type III injury, and 68 (46%) had sustained a SER Type IV. Excellent or good results were found in 92% (Olerud score), 97% (loaded dorsal range of motion), 92% (medial clear space widening), 97% (osteoarthritis), and 76% (Cedell score) of patients. Functional impairment expressed as percentage of whole person impairment varied between 0% and 16%. The various fracture types performed statistically equal on all outcome parameters. There was no difference between operative and nonoperative treatment. There was no correlation between the Olerud score and other parameters. The very long-term overall results of the stratified surgical treatment of SER Type II-IV ankle fractures is 'excellent' or 'good' in the majority of patients and therefore seems justified. Although additional soft tissue damage is unavoidable in case of operative treatment, it does not negatively affect outcome in the long term. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

  13. Commentary on the management of type II odontoid process fractures in octogenarians: Article by Graffeo et al. and Editorial by Falavigna (J Neurosurgery Spine August 19, 2016)

    PubMed Central

    Epstein, Nancy E.

    2016-01-01

    Background: Establishing a clear treatment paradigm for octogenarians with type II odontoid fractures in hampered by a literature replete with level III articles. Methods: In the study by Graffeo et al., the authors evaluated 111 patients over the age of 79 (average age: 87) with type II odontoid fractures undergoing nonoperative (94 patients) vs. operative intervention (17 total; 15 posterior and 2 anterior). They studied multiple variables and utilized several scales [abbreviated injury scale (AIS), injury severity score (ISS), and the Glasgow coma scale (GCS)] to determine the outcomes of nonoperative vs. operative management. Results: Graffeo et al. concluded that there were no significant differences between nonoperative and operative management for type II odontoid fractures in octogenarians. They found similar frequencies of additional cervical fractures, mechanisms of injury, GCS of 8 or under, AIS/ISS scores, and disposition to “nonhome” facilities. Furthermore, both appeared to have increased mortality rates at 1-year post injury; 13% during hospitalization, 26% within the first post-injury month, and 41% at 1 year. Conclusions: In the editorial by Falavigna, his major criticism of Graffeo's article was the marked disparity in the number of patients in the operative (17 patients) vs. the nonoperative group (94 patients), making it difficult to accept any conclusions as “significant”. He further noted that few prior studies provided level I evidence, and that most, like this one, were level III analyses that did not “significantly” advance our knowledge as to whether to treat octogenarians with type II odontoid fractures operatively vs. nonoperatively. PMID:28028444

  14. A Protocol for Percutaneous Transarticular Fixation of Sanders Type II and III Calcaneal Fractures With or Without an Added Mini-Open Approach.

    PubMed

    Gamal, Osama; Shams, Ahmed; El-Sayed Semaya, Ahmad

    Intra-articular fracture of the calcaneus is one of the most displeasing fractures if not properly managed. Open reduction and internal fixation have been associated with a high incidence of postoperative soft tissue complications. Closed reduction and percutaneous fixation have resulted in a greater incidence of postoperative subtalar osteoarthritis with improper reduction of the articular surface. In the present study, a mini-open approach was used in cases of failure of articular surface restoration with closed reduction. A total of 64 feet in 57 consecutive patients with an intra-articular calcaneal fracture underwent the proposed minimally invasive surgical protocol. Of the 57 patients, 7 (12.3%) had bilateral fractures. According to Sanders classification, 33 (51.6%) fractures were type II and 31 (48.4%) were type III. Seven (12.3%) patients had wedge fractures of the dorsolumbar spine without neurologic manifestations. The postoperative evaluation included radiographs and completion of the Maryland Foot Score and visual analog scale for pain. The mean follow-up period was 16 (range 12 to 36) months. The mean operative time was 42 (range 35 to 60) minutes. The mean period until union of the fracture was 12 (range 10 to 16) weeks. The clinical results according to the Maryland Foot Score revealed 52 (81%) with satisfactory (27 excellent and 25 good) and 12 (19%) with unsatisfactory (10 fair and 2 poor) results. The mean visual analog scale score was 1.5 ± 0.3 when radiographic fracture healing was observed. Six patients (9.4%) developed superficial pin tract infections that responded to local care and parenteral antibiotic therapy and resolved completely after removal of the Kirschner wires. In conclusion, the presented surgical protocol combining closed reduction with or without an added mini-open approach and percutaneous fixation improves the functional outcome and minimizes the incidence of complications.

  15. Investigation of the mechanical properties and failure modes of hybrid natural fiber composites for potential bone fracture fixation plates.

    PubMed

    Manteghi, Saeed; Mahboob, Zia; Fawaz, Zouheir; Bougherara, Habiba

    2017-01-01

    The purpose of this study is to investigate the mechanical feasibility of a hybrid Glass/Flax/Epoxy composite material for bone fracture fixation such as fracture plates. These hybrid composite plates have a sandwich structure in which the outer layers are made of Glass/Epoxy and the core from Flax/Epoxy. This configuration resulted in a unique structure compared to prior composites proposed for similar clinical applications. In order to evaluate the mechanical properties of this hybrid composite, uniaxial tension, compression, three-point bending and Rockwell Hardness tests were conducted. In addition, water absorption tests were performed to investigate the rate of water absorption for the specimens. This study confirms that the proposed hybrid composite plates are significantly more flexible axially compared to conventional metallic plates. Furthermore, they have considerably higher ultimate strength in tension, compression and flexion. Such high strength will ensure good stability of bone-implant construct at the fracture site, immobilize adjacent bone fragments and carry clinical-type forces experienced during daily normal activities. Moreover, this sandwich structure with stronger and stiffer face sheets and more flexible core can result in a higher stiffness and strength in bending compared to tension and compression. These qualities make the proposed hybrid composite an ideal candidate for the design of an optimized fracture fixation system with much closer mechanical properties to human cortical bone.

  16. Comparative evaluation of tensile-bond strength, fracture mode and microleakage of fifth, and sixth generation adhesive systems in primary dentition.

    PubMed

    Stalin, A; Varma, Balagopal R

    2005-06-01

    Conservative procedures using dentin-bonding agents are one of the important aspects of pediatric dental practice. The objectives of this in vitro study was to comparatively evaluate the tensile-bond strength, fracture mode (under SEM) and microleakage of total etching single bottle system to self-etching adhesive system in primary dentition. The flat buccal/lingual surfaces of 20 teeth were divided into two groups and treated with Single Bond (Group 1) and Adper Prompt (Group 2) to develop a composite resin cone. Then tensile-bond strength was measured using Instron machine. Fracture mode was evaluated in three specimens from each group under SEM. Microleakage of Class V composite restorations (in 20 teeth) with the above-mentioned adhesives was assessed under stereomicroscope after Basic fuschin dye immersion. Results showed no statistically significant difference between two groups. It was concluded that concerning the single step application with similar efficacy, the self-etching adhesive is better for bonding in primary dentition.

  17. ELECTROMAGNETIC FIELD MEASUREMENT OF FUNDAMENTAL AND HIGHER-ORDER MODES FOR 7-CELL CAVITY OF PETRA-II

    SciTech Connect

    Kawashima, Y.; Blednykh, A.; Cupolo, J.; Davidsaver, M.; Holub, B.; Ma, H.; Oliva, J.; Rose, J.; Sikora, R.; Yeddulla, M.

    2011-03-28

    The booster synchrotron for NSLS-II will include a 7-cell PETRA cavity, which was manufactured for the PETRA-II project at DESY. The cavity fundamental frequency operates at 500 MHz. In order to verify the impedances of the fundamental and higher-order modes (HOM), which were calculated by computer code, we measured the magnitude of the electromagnetic field of the fundamental acceleration mode and HOM using the bead-pull method. To keep the cavity body temperature constant, we used a chiller system to supply cooling water at 20 degrees C. The bead-pull measurement was automated with a computer. We encountered some issues during the measurement process due to the difficulty in measuring the electromagnetic field magnitude in a multi-cell cavity. We describe the method and apparatus for the field measurement, and the obtained results.

  18. Effect of fast electrons on the stability of resistive interchange modes in the TJ-II stellarator

    NASA Astrophysics Data System (ADS)

    García, L.; Ochando, M. A.; Carreras, B. A.; Carralero, D.; Hidalgo, C.; van Milligen, B. Ph.

    2016-06-01

    In this paper, we report on electromagnetic phenomena in low-β plasmas at the TJ-II stellarator, controlled by external heating. To understand the observations qualitatively, we introduce a simple modification of the standard resistive MHD equations, to include the potential impact of fast electrons on instabilities. The dominant instabilities of the modeling regime are resistive interchange modes, and calculations are performed in a configuration with similar characteristics as the TJ-II stellarator. The main effect of the trapping of fast electrons by magnetic islands induced by MHD instabilities is to increase the magnetic component of the fluctuations, changing the character of the instability to tearing-like and modifying the frequency of the modes. These effects seem to be consistent with some of the experimental observations.

  19. Check of Main Fracture Characteristics of the Wenchuan 8.0Ms Earthquake with EFO Modes Recorded by Three Superconducting Gravimeters

    NASA Astrophysics Data System (ADS)

    Lei, Xiange; Sun, Heping; Xu, Houze; Shi, Yaolin

    2010-05-01

    There was a large earthquake 8.0 Ms suddenly happened in the Wenchuan area of the Sichuan Province in China on May 12, 2008, which was one of the largest nature hazards in China in recent thirty years and resulted in the death of about seventy thousands of people. The effective rescue work needed to know the real position of the heavy disaster areas. As the geological structure is very complex in the area of the earthquake faults and the effect of possible multi-resolution problem, it was difficult to quickly determine the main fracture zones of the large earthquake with the seismic data of high-frequency P and S waves. Considering that the earthquake sources excited the Earth's free oscillations (EFO), we attempted to investigated the main fracture characteristics of the Wenchuan earthquake with the EFO modes recorded by the GGP superconducting gravimeters(SG). There was a distance of about 1242 km between the start epicenter of Wenchuan earthquake (30.94°N, 103.47°E)and the Wuhan SG station, which did not arrive at the near-earthquake condition for the P and S wave observation but satisfied the condition for the check of EFO modes. After the correction of gravity tides and atmospheric pressure, we gained the EFO data coming from the Wuhan SG station. The spectral peaks of EFO modes were obtained by applying the FFT technique to the EFO data. The spectral signals were very strong for the mid-class normal modes from 0S20 to 0S30 and we accurately investigated the frequencies and qualities of the mid-class modes, which were basically according to the predictions provided by PREM model. The epicenter of Wenchuan earthquake was an exciting pole for the Earth's free oscillations. If a station was located in the wave ridge of an EFO mode namely the epicentral distance of N+1/4 or N+3/4 multiple of wave length , the EFO mode would have the higher peak than other modes nearby. It was noticed that both 0S22 and 0S28 modes had this kind of phenomena at Wuhan station

  20. Asteroseismology of the nearby SN II Progenitor Rigel. II. epsilon-mechanism Triggering Gravity-mode Pulsations?

    NASA Astrophysics Data System (ADS)

    Moravveji, Ehsan; Moya, Andres; Guinan, Edward F.

    2012-04-01

    The cores of luminous B- and A-type (BA) supergiant stars are the seeds of later core-collapse supernovae. Thus, constraining the near-core conditions in this class of stars can place tighter constraints on the size, mass, and chemical composition of supernova remnants. Asteroseismology of these massive stars is one possible approach into such investigations. Recently, Moravveji et al. in 2012 (hereafter Paper I) extracted 19 significant frequencies from a 6-year radial velocity monitoring of Rigel (β Ori, B8 Ia). The periods they determined broadly range from 1.22 to 74.74 days. Based on our differentially rotating stellar structure and evolution model, Rigel, at its current evolutionary state, is undergoing core He burning and shell H burning. Linear fully non-adiabatic non-radial stability analyses result in the excitation of a dense spectrum of non-radial gravity-dominated mixed modes. The fundamental radial mode (l = 0) and its overtones are all stable. When the hydrogen-burning shell is located even partially in the radiative zone, a favorable condition for destabilization of g-modes through the so-called epsilon-mechanism becomes viable. Only those g-modes that have high relative amplitudes in the hydrogen-burning (radiative) zone can survive the strong radiative damping. From the entire observed range of variability periods of Rigel (found in Paper I), and based on our model, only those modes with periods ranging between 21 and 127 days can be theoretically explained by the epsilon-mechanism. The origin of the short-period variations (found in Paper I) still remains unexplained. Because Rigel is similar to other massive BA supergiants, we believe that the epsilon-mechanism may be able to explain the long-period variations in α Cygni class of pulsating stars.

  1. Solar seismology. II - The stochastic excitation of the solar p-modes by turbulent convection

    NASA Technical Reports Server (NTRS)

    Goldreich, P.; Keeley, D. A.

    1977-01-01

    We test the hypothesis that the solar p-modes are stabilized by damping due to turbulent viscosity in the convective zone. Starting from the assumption that the modes are stable, we calculate expectation values for the modal energies. We find that the interaction between a p-mode and the turbulent convection is such that the modal energy tends toward equipartition with the kinetic energy of turbulent eddies whose lifetimes are comparable to the modal period. From the calculated values of the modal energies, we compute rms surface velocity amplitudes. Our predicted rms surface velocities range from 0.01 cm/sec for the fundamental radial mode to 0.6 cm/sec for the radial mode whose period is approximately 5 minutes. The predicted surface velocities for the low order p-modes are much smaller than the velocities inferred from recent observations.

  2. Solar seismology. II - The stochastic excitation of the solar p-modes by turbulent convection

    NASA Technical Reports Server (NTRS)

    Goldreich, P.; Keeley, D. A.

    1977-01-01

    We test the hypothesis that the solar p-modes are stabilized by damping due to turbulent viscosity in the convective zone. Starting from the assumption that the modes are stable, we calculate expectation values for the modal energies. We find that the interaction between a p-mode and the turbulent convection is such that the modal energy tends toward equipartition with the kinetic energy of turbulent eddies whose lifetimes are comparable to the modal period. From the calculated values of the modal energies, we compute rms surface velocity amplitudes. Our predicted rms surface velocities range from 0.01 cm/sec for the fundamental radial mode to 0.6 cm/sec for the radial mode whose period is approximately 5 minutes. The predicted surface velocities for the low order p-modes are much smaller than the velocities inferred from recent observations.

  3. Oscillations of a vertically stratified dissipative atmosphere. II. Low frequency trapped modes

    NASA Astrophysics Data System (ADS)

    Rudenko, G. V.; Dmitrienko, I. S.

    2016-05-01

    Trapped atmosphere waves, such as IGW waveguide modes and Lamb modes, are described using dissipative solution above source (DSAS) (Dmitrienko and Rudenko, 2016). According to this description, the modes are disturbances penetrating without limit in the upper atmosphere and dissipating their energy throughout the atmosphere; leakage from a trapping region to the upper atmosphere is taken into consideration. The DSAS results are compared to those based on both accurate and WKB approximated dissipationless equations. It is shown that the spatial and frequency characteristics of modes in the upper atmosphere calculated by any of the methods are close to each other and are in good agreement with the observed characteristics of traveling ionospheric disturbances.

  4. VCD Robustness of the Amide-I and Amide-II Vibrational Modes of Small Peptide Models.

    PubMed

    Góbi, Sándor; Magyarfalvi, Gábor; Tarczay, György

    2015-09-01

    The rotational strengths and the robustness values of amide-I and amide-II vibrational modes of For(AA)n NHMe (where AA is Val, Asn, Asp, or Cys, n = 1-5 for Val and Asn; n = 1 for Asp and Cys) model peptides with α-helix and β-sheet backbone conformations were computed by density functional methods. The robustness results verify empirical rules drawn from experiments and from computed rotational strengths linking amide-I and amide-II patterns in the vibrational circular dichroism (VCD) spectra of peptides with their backbone structures. For peptides with at least three residues (n ≥ 3) these characteristic patterns from coupled amide vibrational modes have robust signatures. For shorter peptide models many vibrational modes are nonrobust, and the robust modes can be dependent on the residues or on their side chain conformations in addition to backbone conformations. These robust VCD bands, however, provide information for the detailed structural analysis of these smaller systems.

  5. Fracture channel waves

    NASA Astrophysics Data System (ADS)

    Nihei, Kurt T.; Yi, Weidong; Myer, Larry R.; Cook, Neville G. W.; Schoenberg, Michael

    1999-03-01

    The properties of guided waves which propagate between two parallel fractures are examined. Plane wave analysis is used to obtain a dispersion equation for the velocities of fracture channel waves. Analysis of this equation demonstrates that parallel fractures form an elastic waveguide that supports two symmetric and two antisymmetric dispersive Rayleigh channel waves, each with particle motions and velocities that are sensitive to the normal and tangential stiffnesses of the fractures. These fracture channel waves degenerate to shear waves when the fracture stiffnesses are large, to Rayleigh waves and Rayleigh-Lamb plate waves when the fracture stiffnesses are low, and to fracture interface waves when the fractures are either very closely spaced or widely separated. For intermediate fracture stiffnesses typical of fractured rock masses, fracture channel waves are dispersive and exhibit moderate to strong localization of guided wave energy between the fractures. The existence of these waves is examined using laboratory acoustic measurements on a fractured marble plate. This experiment confirms the distinct particle motion of the fundamental antisymmetric fracture channel wave (A0 mode) and demonstrates the ease with which a fracture channel wave can be generated and detected.

  6. Flow visualization of flow into 8 point-source fractures II: The effect of fracture non-uniformity and fluid crosslinking

    SciTech Connect

    Clark, P.E.; Zhu, Q.

    1994-12-31

    Recently, the flow of fluids into a fracture from a point source has been the subject of several different papers. Cleary and Fonseca first suggested that convective transport should play a major role in the placement of proppant when the flow into a fracture was from a point source. Clark and Courington presented data showing that for non-viscosified fluids convection was the dominant mechanism of transport. However, they showed, that for uniform fractures, viscosifying the fluid made a large difference in the transport mechanism. In a later paper, Clark and Zhu presented data for nonuniform fractures and viscosified fluids weighted with either salt or silica flour that showed that the presence of minor non-uniformities serve to negate the effect of convection even more than viscosifying the fluids. In this work, the authors have extended the work presented in the previous two papers to high viscosity Newtonian fluids and crosslinked fluids. The experiments have all been done with various concentrations of silica flour to simulate added proppant. Both changing the nature of the non-uniformities and crosslinking the polymer solution have a profound affect on the flow into the fracture and the convective process.

  7. Effects of proof loads and combined mode loadings on fracture and flaw growth characteristics of aerospace alloys

    NASA Technical Reports Server (NTRS)

    Shah, R. C.

    1974-01-01

    This experimental program was undertaken to determine the effects of (1) combined tensile and bending loadings, (2) combined tensile and shear loadings, and (3) proof overloads on fracture and flaw growth characteristics of aerospace alloys. Tests were performed on four alloys: 2219-T87 aluminum, 5Al-2.5Sn (ELl) titanium, 6Al-4V beta STA titanium and high strength 4340 steel. Tests were conducted in room air, gaseous nitrogen at -200F (144K), liquid nitrogen and liquid hydrogen. Flat center cracked and surface flawed specimens, cracked tube specimens, circumferentially notched round bar and surface flawed cylindrical specimens were tested. The three-dimensional photoelastic technique of stress freezing and slicing was used to determine stress intensity factors for surface flawed cylindrical specimens subjected to tension or torsion. Results showed that proof load/temperature histories used in the tests have a small beneficial effect or no effect on subsequent fracture strength and flaw growth rates.

  8. Marginal adaptation, fracture load and macroscopic failure mode of adhesively luted PMMA-based CAD/CAM inlays.

    PubMed

    Ender, Andreas; Bienz, Stefan; Mörmann, Werner; Mehl, Albert; Attin, Thomas; Stawarczyk, Bogna

    2016-02-01

    To evaluate marginal adaptation, fracture load and failure types of CAD/CAM polymeric inlays. Standardized prepared human molars (48) were divided into four groups (n=12): (A) PCG (positive control group); adhesively luted glass-ceramic inlays, (B) TRX; CAD/CAM polymeric inlays luted using a self-adhesive resin cement, (C) TAC; CAD/CAM polymeric inlays luted using a conventional resin cement, and (D) NCG (negative control group); direct-filled resin-based composite restorations. All specimens were subjected to a chewing simulator. Before and after chewing fatigue, marginal adaptation was assessed at two interfaces: (1) between dental hard tissues and luting cement and (2) between luting cement and restoration. Thereafter, the specimens were loaded and the fracture loads, as well as the failure types, were determined. The data were analysed using three- and one-way ANOVA with post hoc Scheffé test, two sample Student's t-test (p<0.05). Before and after chewing fatigue, marginal adaptation for interface 1 showed significantly better results for TRX and PCG than for TAC (p=0.001-0.02) and NCG (p=0.001-0.047). For interface 2, marginal adaptation for TAC was significantly inferior to TRX (p<0.001) and PCG (p<0.001). Chewing fatigue had a negative impact on the marginal adaptation of TAC and NCG. No significant differences in fracture load were found between all tested groups. Self-adhesive luted polymeric CAD/CAM inlays showed similar marginal adaptation and fracture load values compared to adhesively luted glass-ceramic inlays. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  9. [Emergency closed reduction and percutaneous Kirschner wire fixation for treatment of Gartland type II-III supracondylar fractures of the humerus in children].

    PubMed

    Fan, Jiang-rong; Xu, Yi-wen; Zheng, Yong; You, Jing-yang

    2015-05-01

    To analyze the clinical effect and related risk factors of Gartland type II-III supracondylar fractures of humerus in children in the emergency closed reduction and percutaneous Kirschner wire fixation. From January 2008 to June 2013,112 children of Gartland type II to III supracondylar humeral fractures were treated in children in emergency closed reduction and percutaneous K-wire fixation, including 72 males and 40 females with an average age of 6.2 years old ranging from 2 to 11 years old. Among them,74 cases were in Gartland type II fractures,38 cases were in type III; The duration from injury to surgery time was 2.5 to 8 hours (averaged 4.6 hours). Elbow cast was applied after operation with the elbow extended of 100 degrees for 4 to 6 weeks, then the gypsum and Kirschner wires were removed. All patients were follow-up from 6 to 60 months (averaged 12 months). All fractures reached clinical healing. The final follow-up was assessed by Flynn criteria, the result was excellent in 86 cases, good in 23 cases, general in 3 cases, excellent and good rate was 97.3%. Three patients had mild cubitus varus deformity without orthopedic treatment. No pin tract infections, iatrogenic ulnar nerve injury, compartment syndrome, and complications such as Volkmann ischemic contracture occurred. Closed reduction and percutaneous Kirschner wire fixation had advantages of exact reduction, firm fixation, fewer complications ,less pain in children undergoing emergency surgery, and.high success rate, so it is a safe and efficient treatment for humeral supracondylar fracture in children.

  10. Cryomacroscopy of vitrification, Part II: Experimental observations and analysis of fracture formation in vitrified VS55 and DP6

    PubMed Central

    Steif, Paul S.; Palastro, Matthew; Wan, Chen-rei; Baicu, Simona; Taylor, Michael J.; Rabin, Yoed

    2006-01-01

    A new imaging device, termed a “cryomacroscope”, was used to observe macrofractures in the cryoprotectant cocktails DP6 and VS55. Details of the design and construction of the cryomacroscope were presented in Part I of this report, which focused on describing the apparatus and observations of crystallization. Part I and the current paper (Part II) describe events that occur as 1 mℓ of cryoprotectant contained in a glass vial is cooled from room temperature down to cryogenic temperatures (∼ −135°C). The presence of cracking, as well as patterns in their position and orientation, are found to be dependent on the cooling rate and on the specific cryoprotectant cocktail. Cracks, if present, disappear upon rewarming, although they appear to be sites for later preferential crystallization. Computations which predict temperatures and mechanical stresses are used to explain observations of cracking. In conjunction with these reports, additional photos of cryomacroscopy of vitrification, crystallization, and fracture formation are available at http://www.me.cmu.edu/faculty1/rabin/CryomacroscopyImages01.htm. PMID:16900261

  11. An engineering treatise on the CARE II dual mode and coverage models

    NASA Technical Reports Server (NTRS)

    1976-01-01

    A mathematical model used to calculate the reliability of any dual-mode, spare-switching computer system was described, and some illustrative examples were presented. The possibility of extending the resultant computer program further was also examined, enabling it, in particular, to accommodate computer configurations involving more than two modes of operation.

  12. Deformation and damage mechanisms of zinc coatings on hot-dip galvanized steel sheets: Part II. Damage modes

    NASA Astrophysics Data System (ADS)

    Parisot, Rodolphe; Forest, Samuel; Pineau, André; Grillon, François; Demonet, Xavier; Mataigne, Jean-Michel

    2004-03-01

    Zinc-based coatings are widely used for protection against corrosion of steel-sheet products in the automotive industry. The objective of the present article is to investigate the damage modes at work in three different microstructures of a zinc coating on an interstitial-free steel substrate under tension, planestrain tension, and expansion loading. Plastic-deformation mechanisms are addressed in the companion article. Two main fracture mechanisms, namely, intergranular cracking and transgranular cleavage fracture, were identified in an untempered cold-rolled coating, a tempered cold-rolled coating, and a recrystallized coating. No fracture at the interface between the steel and zinc coating was observed that could lead to spalling, in the studied zinc alloy. A complex network of cleavage cracks and their interaction with deformation twinning is shown to develop in the material. An extensive quantitative analysis based on systematic image analysis provides the number and cumulative length of cleavage cracks at different strain levels for the three investigated microstructures and three loading conditions. Grain refinement by recrystallization is shown to lead to an improved cracking resistance of the coating. A model for crystallographic cleavage combining the stress component normal to the basal plane and the amount of plastic slip on the basal slip systems is proposed and identified from equibiaxial tension tests and electron backscattered diffraction (EBSD) analysis of the cracked grains. This analysis requires the computation of the nonlinear stress-strain response of each grain using a crystal-plasticity constitutive model. The model is then applied successfully to other loading conditions and is shown to account for the preferred orientations of damaged grains observed in the case of plane-strain tension.

  13. Rossby normal modes in nonuniform background configurations. I Simple fields. II - Equinox and solstice conditions

    NASA Technical Reports Server (NTRS)

    Salby, M. L.

    1981-01-01

    An investigation is conducted regarding the influence of mean field variations on the realization of planetary normal modes, taking into account the mode response and structure in the presence of simple background nonuniformities. It is found that mean field variations have the combined effect of depressing, shifting, and broadening the characteristic response of Rossby normal modes. While nonuniformities in both the mean wind and temperature fields contribute to the reduction in peak response, the former are primarily responsible for translation and spectral broadening. An investigation is conducted to determine which modes may be realized in actual atmospheric configurations and which may be identified. For both the equinox and solstice configurations, response peaks corresponding to all of the first four modes of wavenumbers 1, 2, and 3 are readily visible above the noise.

  14. A Numerical Study of Factors Affecting Fracture-Fluid Cleanup and Produced Gas/Water in Marcellus Shale: Part II

    DOE PAGES

    Seales, Maxian B.; Dilmore, Robert; Ertekin, Turgay; ...

    2017-04-01

    Horizontal wells combined with successful multistage-hydraulic-fracture treatments are currently the most-established method for effectively stimulating and enabling economic development of gas-bearing organic-rich shale formations. Fracture cleanup in the stimulated reservoir volume (SRV) is critical to stimulation effectiveness and long-term well performance. But, fluid cleanup is often hampered by formation damage, and post-fracture well performance frequently falls to less than expectations. A systematic study of the factors that hinder fracture-fluid cleanup in shale formations can help optimize fracture treatments and better quantify long-term volumes of produced water and gas. Fracture-fluid cleanup is a complex process influenced by mutliphase flow through porousmore » media (relative permeability hysteresis, capillary pressure), reservoir-rock and -fluid properties, fracture-fluid properties, proppant placement, fracture-treatment parameters, and subsequent flowback and field operations. Changing SRV and fracture conductivity as production progresses further adds to the complexity of this problem. Numerical simulation is the best and most-practical approach to investigate such a complicated blend of mechanisms, parameters, their interactions, and subsequent effect on fracture-fluid cleanup and well deliverability. Here, a 3D, two-phase, dual-porosity model was used to investigate the effect of mutliphase flow, proppant crushing, proppant diagenesis, shut-in time, reservoir-rock compaction, gas slippage, and gas desorption on fracture-fluid cleanup and well performance in Marcellus Shale. Our findings have shed light on the factors that substantially constrain efficient fracture-fluid cleanup in gas shales, and we have provided guidelines for improved fracture-treatment designs and water management.« less

  15. Composite materials: Fatigue and fracture. Vol. 3

    NASA Technical Reports Server (NTRS)

    O'Brien, T. K. (Editor)

    1991-01-01

    The present volume discusses topics in the fields of matrix cracking and delamination, interlaminar fracture toughness, delamination analysis, strength and impact characteristics, and fatigue and fracture behavior. Attention is given to cooling rate effects in carbon-reinforced PEEK, the effect of porosity on flange-web corner strength, mode II delamination in toughened composites, the combined effect of matrix cracking and free edge delamination, and a 3D stress analysis of plain weave composites. Also discussed are the compression behavior of composites, damage-based notched-strength modeling, fatigue failure processes in aligned carbon-epoxy laminates, and the thermomechanical fatigue of a quasi-isotropic metal-matrix composite.

  16. Composite materials: Fatigue and fracture. Vol. 3

    NASA Technical Reports Server (NTRS)

    O'Brien, T. K. (Editor)

    1991-01-01

    The present volume discusses topics in the fields of matrix cracking and delamination, interlaminar fracture toughness, delamination analysis, strength and impact characteristics, and fatigue and fracture behavior. Attention is given to cooling rate effects in carbon-reinforced PEEK, the effect of porosity on flange-web corner strength, mode II delamination in toughened composites, the combined effect of matrix cracking and free edge delamination, and a 3D stress analysis of plain weave composites. Also discussed are the compression behavior of composites, damage-based notched-strength modeling, fatigue failure processes in aligned carbon-epoxy laminates, and the thermomechanical fatigue of a quasi-isotropic metal-matrix composite.

  17. Physiological state, growth mode, and oxidative stress play a role in Cd(II)-mediated inhibition of Nitrosomonas europaea 19718.

    PubMed

    Chandran, Kartik; Love, Nancy G

    2008-04-01

    The goal of this study was to determine the impact of physiological growth states (batch exponential and batch stationary growth) and growth modes (substrate-limited chemostat, substrate-sufficient exponential batch, and substrate-depleted stationary batch growth) on several measures of growth and responses to Cd(II)-mediated inhibition of Nitrosomonas europaea strain 19718. The specific oxygen uptake rate (sOUR) was the most sensitive indicator of inhibition among the different responses analyzed, including total cell abundance, membrane integrity, intracellular 16S rRNA/DNA ratio, and amoA expression. This observation remained true irrespective of the physiological state, the growth mode, or the mode of Cd(II) exposure. Based on the sOUR, a strong time-dependent exacerbation of inhibition (in terms of an inhibition coefficient [K(i)]) in exponential batch cultures was observed. Long-term inhibition levels (based on K(i) estimates) in metabolically active chemostat and exponential batch cultures were also especially severe and comparable. In contrast, the inhibition level in stationary-phase cultures was 10-fold lower and invariable with exposure time. Different strategies for surviving substrate limitation (a 10-fold increase in amoA expression) and starvation (the retention of 16S rRNA levels) in N. europaea cultures were observed. amoA expression was most negatively impacted by Cd(II) exposure in the chemostat cultures, was less impacted in exponential batch cultures, and was least impacted in stationary batch cultures. Although the amoA response was consistent with that of the sOUR, the amoA response was not as strong. The intracellular 16S rRNA/DNA ratio, as determined by fluorescence in situ hybridization, also did not uniformly correlate with the sOUR under conditions of inhibition or no inhibition. Finally, Cd(II)-mediated inhibition of N. europaea was attributed partially to oxidative stress.

  18. Two-mode squeezed light source for quantum illumination and quantum imaging II

    NASA Astrophysics Data System (ADS)

    Masada, Genta

    2016-09-01

    Two-mode squeezed light is a macroscopic quantum entangled state of electro-magnetic fields and shows non-classical correlation between quadrature phase amplitudes in each optical mode. In this work the author is developing a high-quality two-mode squeezed light source for exploring the possibility of a quantum radar system based on a quantum illumination method and also expecting to apply it to quantum imaging. Two-mode squeezed light can be generated by combining two independent single-mode squeezed light beams using a beam splitter with a relative optical phase of 90 degrees between them. In current experimental progress the author developed two sub-threshold optical parametric oscillators to generate single-mode squeezed light beams. In the actual quantum radar or quantum imaging system, a turbulent atmosphere degrades quantum entanglement of a light source and affects performance of target detection. An optical loss is one of the simplest and most probable examples of environmental factors. In this work an evaluation method for quantum entanglement of two-mode squeezed light source is developed with consideration for the optical loss based on Duan's inseparability criteria.

  19. Tidal interactions of a Maclaurin spheroid - II. Resonant excitation of modes by a close, misaligned orbit

    NASA Astrophysics Data System (ADS)

    Braviner, Harry J.; Ogilvie, Gordon I.

    2015-02-01

    We model a tidally forced star or giant planet as a Maclaurin spheroid, decomposing the motion into the normal modes found by Bryan. We first describe the general prescription for this decomposition and the computation of the tidal power. Although this formalism is very general, forcing due to a companion on a misaligned, circular orbit is used to illustrate the theory. The tidal power is plotted for a variety of orbital radii, misalignment angles, and spheroid rotation rates. Our calculations are carried out including all modes of degree l ≤ 4, and the same degree of gravitational forcing. Remarkably, we find that for close orbits (a/R* ≈ 3) and rotational deformations that are typical of giant planets (e ≈ 0.4) the l = 4 component of the gravitational potential may significantly enhance the dissipation through resonance with surface gravity modes. There are also a large number of resonances with inertial modes, with the tidal power being locally enhanced by up to three orders of magnitude. For very close orbits (a/R* ≈ 3), the contribution to the power from the l = 4 modes is roughly the same magnitude as that due to the l = 3 modes.

  20. Three-dimensional to two-dimensional transition in mode-I fracture microbranching in a perturbed hexagonal close-packed lattice

    NASA Astrophysics Data System (ADS)

    Heizler, Shay I.; Kessler, David A.

    2017-06-01

    Mode-I fracture exhibits microbranching in the high velocity regime where the simple straight crack is unstable. For velocities below the instability, classic modeling using linear elasticity is valid. However, showing the existence of the instability and calculating the dynamics postinstability within the linear elastic framework is difficult and controversial. The experimental results give several indications that the microbranching phenomenon is basically a three-dimensional (3D) phenomenon. Nevertheless, the theoretical effort has been focused mostly on two-dimensional (2D) modeling. In this paper we study the microbranching instability using three-dimensional atomistic simulations, exploring the difference between the 2D and the 3D models. We find that the basic 3D fracture pattern shares similar behavior with the 2D case. Nevertheless, we exhibit a clear 3D-2D transition as the crack velocity increases, whereas as long as the microbranches are sufficiently small, the behavior is pure 3D behavior, whereas at large driving, as the size of the microbranches increases, more 2D-like behavior is exhibited. In addition, in 3D simulations, the quantitative features of the microbranches, separating the regimes of steady-state cracks (mirror) and postinstability (mist-hackle) are reproduced clearly, consistent with the experimental findings.

  1. Posterior Fixation with C1 Lateral Mass Screws and C2 Pars Screws for Type II Odontoid Fracture in the Elderly: Long-Term Follow-Up.

    PubMed

    Dobran, Mauro; Nasi, Davide; Esposito, Domenico Paolo; Iacoangeli, Maurizio

    2016-12-01

    We sought to evaluate the long-term C1-C2 fusion rates, fracture healing, and functional outcomes in geriatric patients with type II odontoid fracture treated with posterior fixation with polyaxial C1 lateral mass screws and C2 pars screws. Twenty-one consecutive patients between 2005 and 2011 with Anderson and D'Alonzo type II odontoid fracture underwent a posterior atlantoaxial fixation with polyaxial C1 lateral mass screws and C2 pars screws. A long-term clinical and radiologic follow-up was achieved in all patients with a mean follow-up period of 53.28 ± 15.41 months (range 38-91 months). All 21 patients had bilateral C1 lateral mass screws and bilateral C2 pars screws. Correct positioning of the C1 lateral mass screws and C2 pars screws was observed in all 42 placements by postoperative computed tomography scans. No vascular or neurologic complication was noted. At the last follow-up, 20 patients (95.24%) had a solid fusion (defined as Lenke fusion grade A or B) while 1 patient (4.76%) had a partial fusion (Lenke fusion grade C). Overall, no hardware failures occurred in any patient. Odontoid fracture healing was achieved in 18 patients out of 21 (85.71%). The mean postoperative Neck Disability Index score was 12.73%, and neck motion was within normal physiologic limits at 12 months. This study adds to the evidence that posterior atlantoaxial fixation with polyaxial C1 lateral mass screws and C2 pars screws is a safe and effective surgical option in the treatment of odontoid fractures including long-term stability. Copyright © 2016 Elsevier Inc. All rights reserved.

  2. Fracture mechanics; Proceedings of the Seventeenth National Symposium, Albany, NY, August 7-9, 1984

    NASA Technical Reports Server (NTRS)

    Underwood, J. M. (Editor); Chait, R. (Editor); Smith, C. W. (Editor); Wilhem, D. P. (Editor); Andrews, W. A. (Editor); Newman, J. C. (Editor)

    1986-01-01

    The present conference gives attention to topics in the application of fracture mechanics, subcritical crack growth phenomena, fracture testing methods, ductile fracture behavior, and fracture mechanisms and their analysis. Specific papers treat the resistance curve approach to composite materials characterization, fracture toughness in ductile iron and cast steel, hold-time effects in elevated temperature fatigue crack propagation, creep crack growth under nonsteady conditions, viscoplastic fatigue in a superalloy at elevated temperatures, fracture testing with arc bend specimens, one-point bend impact test application, and a compact mode II fracture specimen. Also discussed are the computation of stable crack growth using the J-integral, the use of plastic energy dissipation to characterize crack growth, the extension of surface cracks under cyclic loading, the minimum time criterion for crack instability in structural materials, dynamic crack propagation and branching under biaxial loading, and boundary layer effects in cracked bodies.

  3. Mixed-Mode Fracture and Fatigue Analysis of Cracked 3D Complex Structures using a 3D SGBEM-FEM Alternating Method

    NASA Astrophysics Data System (ADS)

    Bhavanam, Sharada

    The aim of this thesis is to numerically evaluate the mixed-mode Stress Intensity Factors (SIFs) of complex 3D structural geometries with arbitrary 3D cracks using the Symmetric Galerkin Boundary Element Method-Finite Element Method (SGBEM-FEM) Alternating Method. Various structural geometries with different loading scenarios and crack configurations were examined in this thesis to understand the behavior and trends of the mixed-mode SIFs as well as the fatigue life for these complex structural geometries. Although some 3D structures have empirical and numerical solutions that are readily available in the open literature, some do not; therefore this thesis presents the results of fracture and fatigue analyses of these 3D complex structures using the SGBEM-FEM Alternating Method to serve as reference for future studies. Furthermore, there are advantages of using the SGBEM-FEM Alternating Method compared to traditional FEM methods. For example, the fatigue-crack-growth and fatigue life can be better estimated for a structure because different fatigue models (i.e. Walker, Paris, and NASGRO) can be used within the same framework of the SGBEM-FEM Alternating Method. The FEM (un-cracked structure)/BEM(crack model) meshes are modeled independently, which speeds up the computation process and reduces the cost of human labor. A simple coarse mesh can be used for all fracture and fatigue analyses of complex structures. In this thesis, simple coarse meshes were used for 3D complex structures, which were below 5000 elements as compared to traditional FEM, which require meshes where the elements range on the order of ˜250,000 to ˜106 and sometimes even more than that.

  4. Fractures in anisotropic media

    NASA Astrophysics Data System (ADS)

    Shao, Siyi

    Rocks may be composed of layers and contain fracture sets that cause the hydraulic, mechanical and seismic properties of a rock to be anisotropic. Coexisting fractures and layers in rock give rise to competing mechanisms of anisotropy. For example: (1) at low fracture stiffness, apparent shear-wave anisotropy induced by matrix layering can be masked or enhanced by the presence of a fracture, depending on the fracture orientation with respect to layering, and (2) compressional-wave guided modes generated by parallel fractures can also mask the presence of matrix layerings for particular fracture orientations and fracture specific stiffness. This report focuses on two anisotropic sources that are widely encountered in rock engineering: fractures (mechanical discontinuity) and matrix layering (impedance discontinuity), by investigating: (1) matrix property characterization, i.e., to determine elastic constants in anisotropic solids, (2) interface wave behavior in single-fractured anisotropic media, (3) compressional wave guided modes in parallel-fractured anisotropic media (single fracture orientation) and (4) the elastic response of orthogonal fracture networks. Elastic constants of a medium are required to understand and quantify wave propagation in anisotropic media but are affected by fractures and matrix properties. Experimental observations and analytical analysis demonstrate that behaviors of both fracture interface waves and compressional-wave guided modes for fractures in anisotropic media, are affected by fracture specific stiffness (controlled by external stresses), signal frequency and relative orientation between layerings in the matrix and fractures. A fractured layered medium exhibits: (1) fracture-dominated anisotropy when the fractures are weakly coupled; (2) isotropic behavior when fractures delay waves that are usually fast in a layered medium; and (3) matrix-dominated anisotropy when the fractures are closed and no longer delay the signal. The

  5. Investigations of the Binding of [Pt2(DTBPA)Cl2](II) and [Pt2(TPXA)Cl2](II) to DNA via Various Cross-Linking Modes

    PubMed Central

    Yue, Hongwei; Yang, Bo; Wang, Yan; Chen, Guangju

    2013-01-01

    We have constructed models for a series of platinum-DNA adducts that represent the binding of two agents, [Pt2(DTBPA)Cl2](II) and [Pt2(TPXA)Cl2](II), to DNA via inter- and intra-strand cross-linking, and carried out molecular dynamics simulations and DNA conformational dynamics calculations. The effects of trans- and cis-configurations of the centers of these di-nuclear platinum agents, and of different bridging linkers, have been investigated on the conformational distortions of platinum-DNA adducts formed via inter- and intra-strand cross-links. The results demonstrate that the DNA conformational distortions for the various platinum-DNA adducts with differing cross-linking modes are greatly influenced by the difference between the platinum-platinum distance for the platinum agent and the platinum-bound N7–N7 distance for the DNA molecule, and by the flexibility of the bridging linkers in the platinum agent. However, the effects of trans/cis-configurations of the platinum-centers on the DNA conformational distortions in the platinum-DNA adducts depend on the inter- and intra-strand cross-linking modes. In addition, we discuss the relevance of DNA base motions, including opening, shift and roll, to the changes in the parameters of the DNA major and minor grooves caused by binding of the platinum agent. PMID:24077126

  6. Structure and mode of action of cyclic lipopeptide pseudofactin II with divalent metal ions.

    PubMed

    Janek, Tomasz; Rodrigues, Lígia R; Gudiña, Eduardo J; Czyżnikowska, Żaneta

    2016-10-01

    The interaction of natural lipopeptide pseudofactin II with a series of doubly charged metal cations was examined by matrix-assisted laser-desorption ionization-time of flight (MALDI-TOF) mass spectrometry and molecular modelling. The molecular modelling for metal-pseudofactin II provides information on the metal-peptide binding sites. Overall, Mg(2+), Ca(2+) and Zn(2+) favor the association with oxygen atoms spanning the peptide backbone, whereas Cu(2+) is coordinated by three nitrogens. Circular dichroism (CD) results confirmed that Zn(2+) and Cu(2+) can disrupt the secondary structure of pseudofactin II at high concentrations, while Ca(2+) and Mg(2+) did not essentially affect the structure of the lipopeptide. Interestingly, our results showed that the addition of Zn(2+) and Cu(2+) helped smaller micelles to form larger micellar aggregates. Since pseudofactin II binds metals, we tested whether this phenomena was somehow related to its antimicrobial activity against Staphylococcus epidermidis and Proteus mirabilis. We found that the antimicrobial effect of pseudofactin II was increased by supplementation of culture media with all tested divalent metal ions. Finally, by using Gram-positive and Gram-negative bacteria we showed that the higher antimicrobial activity of metal complexes of pseudofactin II is attributed to the disruption of the cytoplasmic membrane. Copyright © 2016 Elsevier B.V. All rights reserved.

  7. Seismic transmission operator reciprocity - II: impedance-operator symmetry via elastic lateral modes

    NASA Astrophysics Data System (ADS)

    Thomson, C. J.

    2015-08-01

    The properties of the overburden transmission response are of particular interest for the analysis of reflectivity illumination or blurring in seismic depth imaging. The first step to showing a transmission-operator reciprocity property is to identify the symmetry of the so-called displacement-to-traction operators. The latter are analogous to Dirichlet-to-Neumann operators and they may also be called impedance operators. Their symmetry is deduced here after development of a formal spectral or modal theory of lateral wavefunctions in a laterally heterogeneous generally anisotropic elastic medium. The elastic lateral modes are displacement-traction 6-vectors and they are built from two auxiliary 3-vector lateral-mode bases. These auxiliary modes arise from Hermitian and anti-Hermitian operators, so they have familiar properties such as orthogonality. There is no assumption of down/up symmetry of the elasticity tensor, but basic assumptions are made about the existence and completeness of the elastic modes. A point-symmetry property appears and plays a central role. The 6-vector elastic modes have a symplectic orthogonality property, which facilitates the development of modal expansions for 6-vector functions of the lateral coordinates when completeness is assumed. While the elastic modal theory is consistent with the laterally homogeneous case, numerical work would provide confidence that it is correct in general. An appendix contains an introductory overview of acoustic lateral modes that were studied by other authors, given from the perspective of this new work. A distinction is drawn between unit normalization of scalar auxiliary modes and a separate energy-flux normalization of 2-vector acoustic modes. Neither is crucial to the form of acoustic pressure-to-velocity or impedance operators. This statement carries over to the elastic case for the 3-vector auxiliary- and 6-vector elastic-mode normalizations. The modal theory is used to construct the kernel of the

  8. Development and Application of Benchmark Examples for Mixed-Mode I/II Quasi-Static Delamination Propagation Predictions

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald

    2012-01-01

    The development of benchmark examples for quasi-static delamination propagation prediction is presented and demonstrated for a commercial code. The examples are based on finite element models of the Mixed-Mode Bending (MMB) specimen. The examples are independent of the analysis software used and allow the assessment of the automated delamination propagation prediction capability in commercial finite element codes based on the virtual crack closure technique (VCCT). First, quasi-static benchmark examples were created for the specimen. Second, starting from an initially straight front, the delamination was allowed to propagate under quasi-static loading. Third, the load-displacement relationship from a propagation analysis and the benchmark results were compared, and good agreement could be achieved by selecting the appropriate input parameters. Good agreement between the results obtained from the automated propagation analysis and the benchmark results could be achieved by selecting input parameters that had previously been determined during analyses of mode I Double Cantilever Beam and mode II End Notched Flexure specimens. The benchmarking procedure proved valuable by highlighting the issues associated with choosing the input parameters of the particular implementation. Overall the results are encouraging, but further assessment for mixed-mode delamination fatigue onset and growth is required.

  9. Structure of the Human Angiotensin II Type 1 (AT1) Receptor Bound to Angiotensin II from Multiple Chemoselective Photoprobe Contacts Reveals a Unique Peptide Binding Mode*

    PubMed Central

    Fillion, Dany; Cabana, Jérôme; Guillemette, Gaétan; Leduc, Richard; Lavigne, Pierre; Escher, Emanuel

    2013-01-01

    Breakthroughs in G protein-coupled receptor structure determination based on crystallography have been mainly obtained from receptors occupied in their transmembrane domain core by low molecular weight ligands, and we have only recently begun to elucidate how the extracellular surface of G protein-coupled receptors (GPCRs) allows for the binding of larger peptide molecules. In the present study, we used a unique chemoselective photoaffinity labeling strategy, the methionine proximity assay, to directly identify at physiological conditions a total of 38 discrete ligand/receptor contact residues that form the extracellular peptide-binding site of an activated GPCR, the angiotensin II type 1 receptor. This experimental data set was used in homology modeling to guide the positioning of the angiotensin II (AngII) peptide within several GPCR crystal structure templates. We found that the CXC chemokine receptor type 4 accommodated the results better than the other templates evaluated; ligand/receptor contact residues were spatially grouped into defined interaction clusters with AngII. In the resulting receptor structure, a β-hairpin fold in extracellular loop 2 in conjunction with two extracellular disulfide bridges appeared to open and shape the entrance of the ligand-binding site. The bound AngII adopted a somewhat vertical binding mode, allowing concomitant contacts across the extracellular surface and deep within the transmembrane domain core of the receptor. We propose that such a dualistic nature of GPCR interaction could be well suited for diffusible linear peptide ligands and a common feature of other peptidergic class A GPCRs. PMID:23386604

  10. Structure of the human angiotensin II type 1 (AT1) receptor bound to angiotensin II from multiple chemoselective photoprobe contacts reveals a unique peptide binding mode.

    PubMed

    Fillion, Dany; Cabana, Jérôme; Guillemette, Gaétan; Leduc, Richard; Lavigne, Pierre; Escher, Emanuel

    2013-03-22

    Breakthroughs in G protein-coupled receptor structure determination based on crystallography have been mainly obtained from receptors occupied in their transmembrane domain core by low molecular weight ligands, and we have only recently begun to elucidate how the extracellular surface of G protein-coupled receptors (GPCRs) allows for the binding of larger peptide molecules. In the present study, we used a unique chemoselective photoaffinity labeling strategy, the methionine proximity assay, to directly identify at physiological conditions a total of 38 discrete ligand/receptor contact residues that form the extracellular peptide-binding site of an activated GPCR, the angiotensin II type 1 receptor. This experimental data set was used in homology modeling to guide the positioning of the angiotensin II (AngII) peptide within several GPCR crystal structure templates. We found that the CXC chemokine receptor type 4 accommodated the results better than the other templates evaluated; ligand/receptor contact residues were spatially grouped into defined interaction clusters with AngII. In the resulting receptor structure, a β-hairpin fold in extracellular loop 2 in conjunction with two extracellular disulfide bridges appeared to open and shape the entrance of the ligand-binding site. The bound AngII adopted a somewhat vertical binding mode, allowing concomitant contacts across the extracellular surface and deep within the transmembrane domain core of the receptor. We propose that such a dualistic nature of GPCR interaction could be well suited for diffusible linear peptide ligands and a common feature of other peptidergic class A GPCRs.

  11. [Salter and Harris type-II distal femoral physeal fracture-separations at adolescent age: a new therapeutic approach (preliminary study)].

    PubMed

    Edgard-Rosa, G; Launay, F; Glard, Y; Guillaume, J-M; Jouve, J-L; Bollini, G

    2008-10-01

    The prognosis of distal femoral physeal fracture-separation is poor in children. In adolescents, more than half of the cases are classified as Salter and Harris type-II. The gold-standard treatment for a displaced fracture combines anatomic reduction with internal fixation with a pin or screw, preserving the growth cartilage. Despite this treatment, the rate of mid- and long-term complications has been high in the literature, most problems being related to leg length discrepancy and misalignments (genu valgum and genu varum). In order to avoid these problems, for adolescents, we propose and osteosynthesis system which bridges the entire growth cartilage with a blade-plate. Depending on the bone age, puberty and thus potential for further growth, we combine this osteosynthesis with a contralateral distal femoral epiphysiodesis to prevent invalidating leg length discrepancy. We reviewed retrospectively the cases of 21 patients aged 11 to 15 years treated between 1990 and 2005 for Salter and Harris type-II distal femoral physeal fracture- separation. Clinical and radiographic outcome was compared between the 16 patients treated with the classical internal fixation system or cast immobilization and the five patients treated with a blade-plate. A complete physical examination was available for the follow-up in all cases. A full stance view was used for the radiographic analysis. The mean follow-up was 6.7 years (range 2-17), minimal two years. In patients treated with the classical fixation system or a plaster cast, four of 16 (25 %) developed frontal misalignment of more than 5 degrees and five of 16 (32 %) leg length discrepancy of more than 2cm. No misalignment or leg length discrepancy (>2cm) was observed among the five patients treated with a blade-plate. The results observed in our patients treated with the classical fixation systems are comparable with those reported by others. Our patients treated with the blade-plate system constitute the only series with no

  12. Single-screw Fixation of Adolescent Salter-II Proximal Humeral Fractures: Biomechanical Analysis of the "One Pass Door Lock" Technique.

    PubMed

    Miller, Mark Carl; Redman, Christopher N; Mistovich, R Justin; Muriuki, Muturi; Sangimino, Mark J

    2017-09-01

    Pin fixation of Salter-II proximal humeral fractures in adolescents approaching skeletal maturity has potential complications that can be avoided with single-screw fixation. However, the strength of screw fixation relative to parallel and diverging pin fixation is unknown. To compare the biomechanical fixation strength between these fixation modalities, we used synthetic composite humeri, and then compared these results in composite bone with cadaveric humeri specimens. Parallel pinning, divergent pinning, and single-screw fixation repairs were performed on synthetic composite humeri with simulated fractures. Six specimens of each type were tested in axial loading and other 6 were tested in torsion. Five pair of cadaveric humeri were tested with diverging pins and single screws for comparison. Single-screw fixation was statistically stronger than pin fixation in axial and torsional loading in both composite and actual bone. There was no statistical difference between composite and cadaveric bone specimens. Single-screw fixation can offer greater stability to adolescent Salter-II fractures than traditional pinning. Single-screw fixation should be considered as a viable alternative to percutaneous pin fixation in transitional patients with little expected remaining growth.

  13. Pediatric Phalanx Fractures.

    PubMed

    Abzug, Joshua M; Dua, Karan; Bauer, Andrea Sesko; Cornwall, Roger; Wyrick, Theresa O

    2016-11-01

    Phalangeal fractures are the most common type of hand fracture that occurs in the pediatric population and account for the second highest number of emergency department visits for fractures in the United States. The incidence of phalangeal fractures is the highest in children aged 10 to 14 years, which coincides with the time that most children begin playing contact sports. Younger children are more likely to sustain a phalangeal fracture in the home setting as a result of crush and laceration injuries. Salter-Harris type II fractures of the proximal phalanx are the most common type of finger fracture. An unmineralized physis is biomechanically weaker compared with the surrounding ligamentous structures and mature bone, which makes fractures about the physis likely. A thorough physical examination is necessary to assess the digital cascade for signs of rotational deformity and/or coronal malalignment. Plain radiographs of the hand and digits are sufficient to confirm a diagnosis of a phalangeal fracture. The management of phalangeal fractures is based on the initial severity of the injury and depends on the success of closed reduction techniques. Nondisplaced phalanx fractures are managed with splint immobilization. Stable, reduced phalanx fractures are immobilized but require close monitoring to ensure maintenance of fracture reduction. Unstable, displaced phalanx fractures require surgical management, preferably via closed reduction and percutaneous pinning.

  14. Pediatric Phalanx Fractures.

    PubMed

    Abzug, Joshua M; Dua, Karan; Sesko Bauer, Andrea; Cornwall, Roger; Wyrick, Theresa O

    2017-02-15

    Phalangeal fractures are the most common type of hand fracture that occurs in the pediatric population and account for the second highest number of emergency department visits in the United States for fractures. The incidence of phalangeal fractures is the highest in children aged 10 to 14 years, which coincides with the time that most children begin playing contact sports. Younger children are more likely to sustain a phalangeal fracture in the home setting as a result of crush and laceration injuries. Salter-Harris type II fractures of the proximal phalanx are the most common type of finger fracture. An unmineralized physis is biomechanically weaker compared with the surrounding ligamentous structures and mature bone, which make fractures about the physis likely. A thorough physical examination is necessary to assess the digital cascade for signs of rotational deformity and/or coronal malalignment. Plain radiographs of the hand and digits are sufficient to confirm a diagnosis of a phalangeal fracture. The management of phalangeal fractures is based on the initial severity of the injury and depends on the success of closed reduction techniques. Nondisplaced phalanx fractures are managed with splint immobilization. Stable, reduced phalanx fractures are immobilized but require close monitoring to ensure maintenance of fracture reduction. Unstable, displaced phalanx fractures require surgical management, preferably via closed reduction and percutaneous pinning.

  15. Fracture toughness of silicon

    NASA Technical Reports Server (NTRS)

    Chen, C. P.; Leipold, M. H.

    1980-01-01

    The paper presents a study to determine the fracture toughness and to characterize fracture modes of silicon as a function of the orientation of single-crystal and polycrystalline material. It is shown that bar specimens cracked by Knoop microhardness indentation and tested to fracture under four-point bending at room temperature were used to determine the fracture toughness values. It is found that the lowest fracture toughness value of single crystal silicon was 0.82 MN/m to the 3/2 in the 111 plane type orientation, although the difference in values in the 111, 110, and 100 planes was small.

  16. Geomechanical Parameters in Fracturing Process of Layered Rocks

    NASA Astrophysics Data System (ADS)

    Mighani, S.; Sondergeld, C. H.; Rai, C. S.

    2013-12-01

    Hydraulic fracturing is crucial to geothermal and hydrocarbon recovery. Predicting performance based on rock characteristics (micro and macro) is essential to effective stimulation. We studied two extreme rock types: 1) Lyons sandstone, a brittle, low porosity, low permeability, weakly anisotropic material and 2) pyrophyllite, a strongly anisotropic metamorphic rock similar chemically and mechanically to shale, having extremely low porosity and permeability. Mineralogy, porosity, permeability, mercury capillary pressure, grain size, μ-CT imaging and elastic anisotropy analysis describe these rocks. Brazilian disk tests were carried to observe the fracture initiation and propagation under tension. Fracture propagation velocity is measured using a high speed digital camera. Strain gauges and acoustic emission (AE) sensors recorded deformation leading to and during failure. SEM imaging and surface profilometry were used to study the post-failure fracture systems and failed surface topology. The fracture process zone (FPZ) is mapped and evaluated using a mosaic of stitched SEM images. The fracture permeability was measured as a function of effective stress and compared to fracture permeability models. The effect of anisotropy on fracturing (Mode I and Mode II fractures) was also investigated rotating the fabric direction of the tested disks relative to the loading axis through increments of 15 degrees. Results indicate differences in fracturing process of these two rock types. Pyrophyllite displays a localized ductile behavior in the process zone resulting in a narrower fracture with a higher propagation velocity and far less AE activity. Pyrophyllite shows 70 % higher tensile strength compared to Lyons sandstone even though it becomes ductile at much lower pressures. The sandstone shows a wide brittle fracture with larger FPZ and better permeability at elevated effective pressures. The greater number of AE activity associated with higher energy events confirms the

  17. Fracture toughness of materials

    SciTech Connect

    Burns, S.J.

    1988-01-01

    Crack tip dislocation emission in bulk specimens have been measured in single crystal specimens and the measurements are well below the accepted theoretical values for dislocation emission. The image forces on a dislocation due to the presence of a semi-infinite crack are used to calculate the potential energy of the dislocation around the crack. Expressions for the radial and tangential forces and for slip and climb forces have been found. Crack tip deformation in Mode I and Mode II fractures on both {l brace}100{r brace} and {l brace}110{r brace} planes have been observed in crystals of LiF. The deformation is shown to nearly completely shield {l brace}110{r brace} plane cracks and prevent their propagation while deformation is less effective in shielding {l brace}100{r brace} plane cracks. The fracture toughness of MgO-partially-stabilized ZrO{sub 2} exhibiting transformation toughening been measured. The equations of linear elastic fracture mechanics have been self-consistantly formulated to include the residual displacement from the transformation wake. MgO single crystals were fatigued in plastic strain control at elevated temperatures. At high temperatures, dense bundles of dislocations were observed in transmission electron microscopy aligned perpendicular to the Burgers' vector directions. The thermodynamics of a superconducting second order phase transformation has been related to jumps in physical properties. A simple energy balance, without assuming an equation of state, is used to relate the rate of change of state variables to measurable physical properties. There are no preconceived assumptions about the superconducting mechanism.

  18. Single-mode tapered optical fiber loop immunosensor II: assay of anti-cholera toxin immunoglobulins

    NASA Astrophysics Data System (ADS)

    Marks, Robert S.; Hale, Zoe M.; Levine, Myron M.; Lowe, C. R.; Payne, Frank P.

    1994-07-01

    An evanescent wave immunoassay for cholera antitoxin immunoglobulins was performed using a single mode tapered optical fiber loop sensor. The transducer was silanized with 3- glycidoxypropyltrimethoxysilane and chemically modified to link covalently either cholera toxin B subunit or a synthetic peptide derived from it, CTP3. The sensor was exposed to seral fluids, obtained from human volunteers having been exposed to live virulent Vibrio cholerae 01 and shown to produce rice-water stools. Other toxins of interest, such as Clostridium botulinum toxin A, have been tested on similar systems. The bound unlabelled immunoglobulins were then exposed to a mixture of FITC-anti-IgG and TRITC-anti-IgA, without requirement for a separation step. The emanating fluorescent emissions of fluorescein and rhodamine, excited by the input laser light, were coupled back into the guided mode of the tapered fiber, and used to determine the concentrations of the complementary antigens.

  19. [Fracture toughness of cortical bone in tension, shear, and tear--a comparison of longitudinal and transverse fracture].

    PubMed

    Feng, Z

    1997-09-01

    The fracture toughness at crack initiation was determined for bovine cortical bone under tension (mode I), shear (mode II), and tear (mode III). A total of 130 compact tension specimens, compact shear specimens and triple pantleg specimens were used for the measurement of fracture toughness under tension, shear, and tear, respectively. Multiple-sample compliance method was utilized to measure the critical strain energy release rate (Gc) at the a/W = 0.55 (crack length, a, to specimen width, W, ratio). The critical stress intensity factor (Kc) was also calculated from the critical loading (PQ) of the specimens at the a/W = 0.55. The effect of the anisotropy of bone on its resistance to crack initiation under shear and tear loading was investigated as well. The fracture toughness of bone with precrack orientations parallel(designed as longitudinal fracture) to and that with precrack orientations normal (designed as transverse fracture) to the longitudinal axis of bone were compared. In longitudinal fracture, the critical strain energy release rates(Gc) of cortical bone under tension, shear, and tear were 644 +/- 102, 2430 +/- 836, and 1723 +/- 486 N/m, respectively. In transverse fracture, the critical strain energy release rates(Gc) of cortical bone under tesion, shear, and tear were 1374 +/- 183, 4710 +/- 1284, and 4016 +/- 948 N/m, respectively. An analysis of variance demonstrated that the crack initiation fracture toughness of bone under shear and tear loading is significantly greater than that under tensile loading in both longitudinal and transverse fracture. Our results also suggest that cortical bone has been "designed" to prevent crack initiation in transverse fracture under tension, shear, and tesar.

  20. Effects of core-to-dentin thickness ratio on the biaxial flexural strength, reliability, and fracture mode of bilayered materials of zirconia core (Y-TZP) and veneer indirect composite resins.

    PubMed

    Su, Naichuan; Liao, Yunmao; Zhang, Hai; Yue, Li; Lu, Xiaowen; Shen, Jiefei; Wang, Hang

    2017-01-01

    Indirect composite resins (ICR) are promising alternatives as veneering materials for zirconia frameworks. The effects of core-to-dentin thickness ratio (C/Dtr) on the mechanical property of bilayered veneer ICR/yttria-tetragonal zirconia polycrystalline (Y-TZP) core disks have not been previously studied. The purpose of this in vitro study was to assess the effects of C/Dtr on the biaxial flexural strength, reliability, and fracture mode of bilayered veneer ICR/ Y-TZP core disks. A total of 180 bilayered 0.6-mm-thick composite resin disks in core material and C/Dtr of 2:1, 1:1, and 1:2 were tested with either core material placed up or placed down for piston-on-3-ball biaxial flexural strength. The mean biaxial flexural strength, Weibull modulus, and fracture mode were measured to evaluate the variation trend of the biaxial flexural strength, reliability, and fracture mode of the bilayered disks with various C/Dtr. One-way analysis of variance (ANOVA) and chi-square tests were used to evaluate the variation tendency of fracture mode with the C/Dtr or material placed down during testing (α=.05). Light microscopy was used to identify the fracture mode. The mean biaxial flexural strength and reliability improved with the increase in C/Dtr when specimens were tested with the core material either up and down, and depended on the materials that were placed down during testing. The rates of delamination, Hertzian cone cracks, subcritical radial cracks, and number of fracture fragments partially depended on the C/Dtr and the materials that were placed down during testing. The biaxial flexural strength, reliability, and fracture mode in bilayered structures of Y-TZP core and veneer ICR depend on both the C/Dtr and the material that was placed down during testing. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  1. An animal model for open femur fracture and osteomyelitis--Part II: Immunomodulation with systemic IL-12.

    PubMed

    Lindsey, Brock A; Clovis, Nina B; Smith, E Suzanne; Salihu, Sydha; Hubbard, David F

    2010-01-01

    Infection resulting from open fracture is a common problem in orthopedics. The purpose of this project was to study the effect of Interleukin-12 (IL-12) systemic therapy on a previously established open fracture model. One hundred seven male Sprague-Dawley rats were assigned to five groups: (1) normal (baseline), (2) control (controlled for anesthesia), (3) fracture, (4) staph, and (5) staph and IL-12 (SIL). Each group was divided into four time periods: 6, 10, 14, and 21 days after injury and fixation. The operative groups had a standardized femur fracture and fixation using a Kirschner wire as an intramedullary device. The two infection groups (staph and SIL) were inoculated with Staphylococcus aureus following fracture and fixed with an identical technique. The SIL group was treated with systemic IL-12 for a total of 10 doses over 10 days. Significantly decreased serum IL-12 levels were noted at day 10 in the operative groups compared to the normal and control groups. The SIL group showed significantly higher macrophage activation levels and total platelet counts at day 21 compared to all the other groups. The overall infection rate was not changed by IL-12 supplementation; however, bacterial qualitative growth scores were significantly lower in the SIL group at day 10, which corresponded to the lowest level of systemic IL-12 in the fracture group.

  2. Novel fracture technology proves marginal Viking prospect economic, part II: Well clean-up, flowback and testing

    SciTech Connect

    Haidar, S.; Rylance, M.; Tybero, G.

    1996-12-31

    Having completed both fracture treatments as discussed in a companion paper, this paper continues on to describe the post fracture shut-in, clean-up and well testing operations that took place on the Viking Wx exploration well 49/17-12. These operations involved the removal of Resin Coated Proppant (RCP) from the wellbore, via Coiled Tubing (CT), through the use of a specially designed jetting nozzle. The RCP pack stability at a concentration of 3.0 lb/ft{sup 2} (as per planned design) had already been tested in a flowback cell. The use of a Surface Read-Out (SRO) gauge, combined with gas, water and proppant flow rates as well as the viscosity of fracturing fluids returns, enabled real time calculation of the drag forces, on the proppant pack, during clean-up. The flow rate, in the field, was controlled such that the calculated drag forces remained below those observed in the laboratory. Following the clean-up a flow and build-up test was conducted, to evaluate the fracture half length and fracture conductivity, from which a Pseudo-radial skin was calculated. The Non-Darcy effects in the fracture were also evaluated, and finally the short term and long term well deliverabilities were assessed.

  3. Development and Application of Benchmark Examples for Mixed-Mode I/II Quasi-Static Delamination Propagation Predictions

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald

    2012-01-01

    The development of benchmark examples for quasi-static delamination propagation prediction is presented. The example is based on a finite element model of the Mixed-Mode Bending (MMB) specimen for 50% mode II. The benchmarking is demonstrated for Abaqus/Standard, however, the example is independent of the analysis software used and allows the assessment of the automated delamination propagation prediction capability in commercial finite element codes based on the virtual crack closure technique (VCCT). First, a quasi-static benchmark example was created for the specimen. Second, starting from an initially straight front, the delamination was allowed to propagate under quasi-static loading. Third, the load-displacement as well as delamination length versus applied load/displacement relationships from a propagation analysis and the benchmark results were compared, and good agreement could be achieved by selecting the appropriate input parameters. The benchmarking procedure proved valuable by highlighting the issues associated with choosing the input parameters of the particular implementation. Overall, the results are encouraging, but further assessment for mixed-mode delamination fatigue onset and growth is required.

  4. Measurements of higher-order mode damping in the PEP-II low-power test cavity

    SciTech Connect

    Rimmer, R.A.; Goldberg, D.A.

    1993-05-01

    The paper describes the results of measurements of the Higher-Order Mode (HOM) spectrum of the low-power test model of the PEP-II RF cavity and the reduction in the Q`s of the modes achieved by the addition of dedicated damping waveguides. All the longitudinal (monopole) and deflecting (dipole) modes below the beam pipe cut-off are identified by comparing their measured frequencies and field distributions with calculations using the URMEL code. Field configurations were determined using a perturbation method with an automated bead positioning system. The loaded Q`s agree well with the calculated values reported previously, and the strongest HOMs are damped by more than three orders of magnitude. This is sufficient to reduce the coupled-bunch growth rates to within the capability of a reasonable feedback system. A high power test cavity will now be built to validate the thermal design at the 150 kW nominal operating level, as described elsewhere at this conference.

  5. Skull fracture

    MedlinePlus

    ... may have been drinking alcohol or is otherwise impaired. Alternative Names Basilar skull fracture; Depressed skull fracture; Linear skull fracture Images Skull of an adult Skull fracture Skull fracture ...

  6. An In Vitro Comparison of Fracture Load of Zirconia Custom Abutments with Internal Connection and Different Angulations and Thicknesses: Part II.

    PubMed

    Zandparsa, Roya; Albosefi, Abdalah

    2016-02-01

    The purpose of part II of this in vitro study was to compare the fracture load of two-piece zirconia custom abutments with different thicknesses and angulations. Forty zirconia custom abutments were divided into four groups as follows: group A1: 0.7 mm thickness and 0° angulations; group A2: 0.7 mm thickness and 15° angulations; group B1: 1 mm thickness and 0° angulations; group B2: 1 mm thickness and 15° angulations. As in part I, in all groups, implant replicas were mounted in self-cure acrylic jigs to support the abutments. The zirconia custom abutments were engaged in the implant replicas using a manual torque wrench. All jigs were secured and mounted in a metallic vice and subjected to shear stress till failure using a universal testing machine with a 0.5 mm/min crosshead speed with the force transferred to the lingual surface of the zirconia custom abutments 2 mm below the incisal edge. The test specimens used in this study did not include a crown. The universal testing machine was controlled via a computer software system, which also completed the stress-strain diagram and recorded the breaking fracture load. The fracture loads were recorded for comparison among the groups and subjected to statistical analysis (two-way ANOVA and Kolmogorov-Smirnov). The mean fracture load of zirconia custom abutments across the groups (A1 to B2) ranged from 432 ± 97 N to 746 ± 275 N. The angulated zirconia custom abutment exhibited the highest fracture load, which was statistically significant (p = 0.045). The thickness of the zirconia custom abutment also had a positive influence on the strength of the specimens (p = 0.005). In this study, the 15° angulated zirconia custom abutments showed the highest fracture load of those investigated. The 1 mm thick zirconia custom abutments also exhibited significantly higher fracture load compared to 0.7 mm abutments. The results of this in vitro study will help dental practitioners with their decision-making process in

  7. Nucleosynthesis Modes in the High-Entropy-Wind Scenario of Type II Supernovae

    SciTech Connect

    Farouqi, K.; Kratz, K.-L.; Cowan, J. J.; Mashonkina, L. I.; Pfeiffer, B.; Sneden, C.; Thielemann, F.-K.; Truran, J. W.

    2008-03-11

    In an attempt to constrain the astrophysical conditions for the nucleosynthesis of the classical r-process elements beyond Fe, we have performed large-scale dynamical network calculations within the model of an adiabatically expanding high- entropy wind (HEW) of type II supernovae (SN II). A superposition of several entropy-components (S) with model-inherent weightings results in an excellent reproduction of the overall Solar System (SS) isotopic r-process residuals (N{sub r,{center_dot}}), as well as the more recent observations of elemental abundances of metal-poor, r-process rich halo stars in the early Galaxy. For the heavy r-process elements beyond Sn, our HEW model predicts a robust abundance pattern up to the Th, U r-chronometer region. For the lighter neutron-capture region, an S-dependent superposition of (i) a normal {alpha}-component directly producing stable nuclei, including s-only isotopes, and (ii) a component from a neutron-rich {alpha}-freezeout followed by the rapid recapture of {beta}-delayed neutrons ({beta}dnrpar; emitted from the far-unstable seed nuclei is indicated. In agreement with several recent halo-star observations in the 60

  8. Fracture in the Elderly Multidisciplinary Rehabilitation (FEMuR): a phase II randomised feasibility study of a multidisciplinary rehabilitation package following hip fracture

    PubMed Central

    Williams, Nefyn H; Roberts, Jessica L; Din, Nafees Ud; Totton, Nicola; Charles, Joanna M; Hawkes, Claire A; Morrison, Val; Hoare, Zoe; Williams, Michelle; Pritchard, Aaron W; Alexander, Swapna; Lemmey, Andrew; Woods, Robert T; Sackley, Catherine; Logan, Pip; Edwards, Rhiannon T; Wilkinson, Clare

    2016-01-01

    Objective To conduct a rigorous feasibility study for a future definitive parallel-group randomised controlled trial (RCT) and economic evaluation of an enhanced rehabilitation package for hip fracture. Setting Recruitment from 3 acute hospitals in North Wales. Intervention delivery in the community. Participants Older adults (aged ≥65) who received surgical treatment for hip fracture, lived independently prior to fracture, had mental capacity (assessed by clinical team) and received rehabilitation in the North Wales area. Intervention Remote randomisation to usual care (control) or usual care+enhanced rehabilitation package (intervention), including six additional home-based physiotherapy sessions delivered by a physiotherapist or technical instructor, novel information workbook and goal-setting diary. Primary and secondary outcome measures Primary: Barthel Activities of Daily Living (BADL). Secondary measures included Nottingham Extended Activities of Daily Living scale (NEADL), EQ-5D, ICECAP capability, a suite of self-efficacy, psychosocial and service-use measures and costs. Outcome measures were assessed at baseline and 3-month follow-up by blinded researchers. Results 62 participants were recruited, 61 randomised (control 32; intervention 29) and 49 (79%) completed 3-month follow-up. Minimal differences occurred between the 2 groups for most outcomes, including BADL (adjusted mean difference 0.5). The intervention group showed a medium-sized improvement in the NEADL relative to the control group, with an adjusted mean difference between groups of 3.0 (Cohen's d 0.63), and a trend for greater improvement in self-efficacy and mental health, but with small effect sizes. The mean cost of delivering the intervention was £231 per patient. There was a small relative improvement in quality-adjusted life year in the intervention group. No serious adverse events relating to the intervention were reported. Conclusions The trial methods were feasible in terms of

  9. Characterization and modelling of naturally fractured granites in the Redang Island, Terengganu, Malaysia

    NASA Astrophysics Data System (ADS)

    Abd Kadir, Askury; Rahman, Mohd Razlan Abdul; Chee Meng, Choong; Jamaludin, Fathiyah; Talib, Jasmi Ab

    2015-04-01

    The Redang Island is situated in the east coast of Peninsular Malaysia, in the state of Terengganu. Geologically, it is mainly composed of medium- to coarse-grained biotite-hornblend granite and overlain by sedimentary and metamorphic rocks. The close-spaced fractured pattern gave an indicator for the active tectonic, which create a fractured basement in Anding Utara that situated 200km SE of the study area. The main primary objective is to characterize the fracture orientation, fracture density as well as to create the static DFN model based on the surface outcrops. A systematic and accurate data collection is crucial for a proper statistical analysis of fracture parameters for fracture modeling. A total of five scan-lines at different length was captured to represent the area. The mode I (extension) and mode II (sheared) fractures are identified during the data aquisition. Hence, the maximum stresses (α1) were interpreted from rose diagram and stereoplots, which are trending towards NE-SW and ENE-WSW. The regional stresses obtained is almost identical to FMI data from the Malay Basin (Anding). Hence, this study suggests that the fracture networking are genetically correlated between fractured basement in the Malay Basin and the Redang Island. Therefore, it can become a good analogue for in-depth studies for better understanding of fracture reservoir.

  10. Methane clathrate hydrate infrared spectrum. II. Near-infrared overtones, combination modes and cages assignments

    NASA Astrophysics Data System (ADS)

    Dartois, E.; Deboffle, D.; Bouzit, M.

    2010-05-01

    Context. Recently, we recorded the infrared spectrum of the methane clathrate hydrate stretching mode at low temperature, a caged compound of possible interest for solar system studies as well as interstellar ice mantles. Aims: We provide a practical infrared spectroscopic identification for methane clathrate hydrate to examine its astrophysical presence or absence. We investigate the crystal field induced shifts, and assign the different transitions to the different encaged molecules environments in this clathrate hydrate. Methods: A methane clathrate crystal is produced in an infrared transmitting moderate-pressure closed cell. Using Fourier transform infrared (FTIR) spectroscopy, the overtones (3ν4, 2ν3) and combination modes (ν2+2ν4, ν1+ν4, ν3+ν4, ν2+ν3, ν3+2ν4, 2ν2+2ν4, ν2+ν3+ν4) falling in the 6000-3000 cm-1 (~1.65-3.4 μm) and their temperature behaviour are investigated. In addition, non-astrophysical CH4/CF4 gas mixtures are used to build clathrates with different methane large and small cage occupancies to help in assignments. Results: Combination modes show the two distinct cages and the quasi-free rotor low temperature ro-vibrational structure expected for methane clathrate hydrates. A comparison with the pure phase I is performed. Implications for methane clathrate hydrate detection are clearly identified. Conclusions: Solid methane actual remote observations of solar system objects surfaces do not display the clathrate hydrates' specific shift and occupancy signatures. Observationnally, a search for their infrared spectroscopic specific signatures should be performed, focusing on thermodynamically favourable objects like trans- neptunian objects (TNOs) or recently exposed (e.g. fresh impact) planet (or their satellites) surfaces. On the modeling side, efforts must be undertaken to progressively implement clathrate formation kinetics.

  11. Collisional damping of the geodesic acoustic mode with toroidal rotation. II. Gyrokinetic formulation

    SciTech Connect

    Xie, Baoyi; Yu, Jun; Chen, You; Gong, Xueyu; Guo, Wenfeng

    2016-03-15

    The collisional damping of the geodesic acoustic mode (GAM) is analytically investigated in toroidally rotating tokamaks by using the gyrokinetic equation. It is found that the toroidal rotation could decrease the collisional damping of the GAM in the small safety factor region and increase the collisional damping of the GAM in the large safety factor region at low ion collision rate; while at high ion collision rate, the toroidal rotation will increase the collisional damping of the GAM with arbitrary safety factor. Furthermore, the change quantity of collisional damping rate of the GAM due to the toroidal rotation at high collision rate is larger than that at low collision rate.

  12. Phase effects in guided mode resonances II: measuring the angular phase of a surface plasmon polariton

    NASA Astrophysics Data System (ADS)

    Theisen, M. J.; Brown, T. G.

    2015-02-01

    We show how the phase of a resonant interaction between a focused beam and a guided mode can be directly observed in a pupil imaging experiment, in which the irradiance leaving the pupil of a standard microscope is relayed to an image sensor through a combination Wollaston prism, calcite beam splitter and polarizer. We apply the method to the observation of a surface plasmon polariton resonance excited in a corrugated silver film fabricated using electron beam lithography. We discuss how this particular imaging configuration could be adapted for applications in plasmonic optical sensing.

  13. Interlaminar Fracture Toughness of CF/PEI and GF/PEI Composites at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Kim, Ki-Young; Ye, Lin; Phoa, Kim-Meng

    2004-05-01

    An experimental study has been conducted to assess temperature effects on mode-I and mode-II interlaminar fracture toughness of carbon fibre/polyetherimide (CF/PEI) and glass fibre/polyetherimide (GF/PEI) thermoplastic composites. Mode-I double cantilever beam (DCB) and mode-II end notched flexure (ENF) tests were carried out in a temperature range from 25 to 130°C. For both composite systems, the initiation toughness, G IC, ini and G IIC, ini, of mode-I and mode-II interlaminar fracture decreased with an increase in temperature, while the propagation toughness, G IC, prop and G IIC, prop, displayed a reverse trend. Three main mechanisms were identified to contribute to the interlaminar fracture toughness, namely matrix deformation, fibre/matrix interfacial failure and fibre bridging during the delamination process. At delamination initiation, the weakened fibre/matrix interface at elevated temperatures plays an overriding role with the delamination growth initiating at the fibre/matrix interface, rather than from a blunt crack tip introduced by the insert film, leading to low values of G IC, ini and G IIC, ini. On the other hand, during delamination propagation, enhanced matrix deformation at elevated temperatures and fibre bridging promoted by weakened fibre/matrix interface result in greater G IC, prop values. Meanwhile enhanced matrix toughness and ductility at elevated temperatures also increase the stability of mode-II crack growth.

  14. SIF-based fracture criterion for interface cracks

    NASA Astrophysics Data System (ADS)

    Ji, Xing

    2016-06-01

    The complex stress intensity factor K governing the stress field of an interface crack tip may be split into two parts, i.e., hat{K} and s^{-iɛ}, so that K=hat{K}s^{-iɛ}, s is a characteristic length and ɛ is the oscillatory index. hat{K} has the same dimension as the classical stress intensity factor and characterizes the interface crack tip field. That means a criterion for interface cracks may be formulated directly with hat{K}, as Irwin (ASME J. Appl. Mech. 24:361-364, 1957) did in 1957 for the classical fracture mechanics. Then, for an interface crack, it is demonstrated that the quasi Mode I and Mode II tip fields can be defined and distinguished from the coupled mode tip fields. Built upon SIF-based fracture criteria for quasi Mode I and Mode II, the stress intensity factor (SIF)-based fracture criterion for mixed mode interface cracks is proposed and validated against existing experimental results.

  15. Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-standing Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

    2003-01-01

    Strength, fracture toughness and fatigue behavior of free-standing thick thermal barrier coatings of plasma-sprayed ZrO2-8wt % Y2O3 were determined at ambient and elevated temperatures in an attempt to establish a database for design. Strength, in conjunction with deformation (stress-strain behavior), was evaluated in tension (uniaxial and trans-thickness), compression, and uniaxial and biaxial flexure; fracture toughness was determined in various load conditions including mode I, mode II, and mixed modes I and II; fatigue or slow crack growth behavior was estimated in cyclic tension and dynamic flexure loading. Effect of sintering was quantified through approaches using strength, fracture toughness, and modulus (constitutive relations) measurements. Standardization issues on test methodology also was presented with a special regard to material's unique constitutive relations.

  16. Experimental investigation of CNT effect on curved beam strength and interlaminar fracture toughness of CFRP laminates

    NASA Astrophysics Data System (ADS)

    Arca, M. A.; Coker, D.

    2014-06-01

    High mechanical properties and light weight structures of composite materials and advances in manufacturing processes have increased the use of composite materials in the aerospace and wind energy industries as a primary load carrying structures in complex shapes. However, use of composite materials in complex geometries such as L-shaped laminates creates weakness at the radius which causes delamination. Carbon nanotubes (CNTs) is preferred as a toughening materials in composite matrices due to their high mechanical properties and aspect ratios. However, effect of CNTs on curved beam strength (CBS) is not investigated in literature comprehensively. The objective of this study is to investigate the effect of CNT on Mode I and Mode II fracture toughness and CBS. L-shaped beams are fabric carbon/epoxy composite laminates manufactured by hand layup technique. Curved beam composite laminates were subjected to four point bending loading according to ASTM D6415/D6415M-06a. Double cantilever beam (DCB) tests and end notch flexure (ENF) tests were conducted to determine mode-I and mode-II fracture toughness, respectively. Preliminary results show that 3% CNT addition to the resin increased the mode-I fracture toughness by %25 and mode-II fracture toughness by %10 compared to base laminates. In contrast, no effect on curved beam strength was found.

  17. Majorana modes in InSb nanowires (II): resolving the topological phase diagram

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Gül, Önder; de Moor, Michiel; de Vries, Fokko; van Veen, Jasper; van Woerkom, David; Zuo, Kun; Mourik, Vincent; Cassidy, Maja; Geresdi, Attila; Car, Diana; Bakkers, Erik; Goswami, Srijit; Watanabe, Kenji; Taniguchi, Takashi; Kouwenhoven, Leo

    Majorana modes in hybrid superconductor-semiconductor nanowire devices can be probed via tunnelling spectroscopy which shows a zero bias peak (ZBP) in differential conductance (1). Majoranas are formed when the Zeeman energy EZ and the chemical potential μ satisfy the condition EZ >√{Δ2 +μ2 } , with Δ the superconducting gap. This Majorana condition outlines the topologically non-trivial phase and predicts a particular dependence of ZBPs on the gate voltage and the external magnetic field. In this talk we show that the magnetic field range of ZBPs can be tuned by gate voltage and vice versa, consistent with these Majorana predictions. Supported by measurements in different external magnetic field orientations, these observations pave the way for exploring the topological phase diagram of spin-orbit coupled semiconductor nanowires with induced superconductivity.

  18. Biomechanical Comparison of Two Kinds of Internal Fixation in a Type C Zone II Pelvic Fracture Model

    PubMed Central

    Wu, Tao; Chen, Wei; Zhang, Qi; Zheng, Zhan-Le; Lyu, Hong-Zhi; Cui, Yun-Wei; Cheng, Xiao-Dong; Zhang, Ying-Ze; Yang, Yan-Jiang

    2015-01-01

    Background: Unstable pelvic fractures are complex and serious injuries. Selection of a fixation method for these fractures remains a challenging problem for orthopedic surgeons. This study aimed to compare the stability of Tile C pelvic fractures fixed with two iliosacral (IS) screws and minimally invasive adjustable plate (MIAP) combined with one IS screw. Methods: This study was a biomechanical experiment. Six embalmed specimens of the adult pelvis were used. The soft tissue was removed from the specimens, and the spines from the fourth lumbar vertebra to the proximal one-third of both femurs were retained. The pubic symphysis, bilateral sacroiliac joints and ligaments, bilateral hip joints, bilateral sacrotuberous ligaments, and bilateral sacrospinous ligaments were intact. Tile C pelvic fractures were made on the specimens. The symphysis pubis was fixed with a plate, and the fracture on the posterior pelvic ring was fixed with two kinds of internal fixation in turn. The specimens were placed in a biomechanical machine at a standing neutral posture. A cyclic vertical load of up to 500 N was applied, and displacement was recorded. Shifts in the fracture gap were measured by a grating displacement sensor. Statistical analysis used: Paired-samples t-test. Results: Under the vertical load of 100, 200, 300, 400, and 500 N, the average displacement of the specimens fixed with MIAP combined with one IS screw was 0.46, 0.735, 1.377, 1.823, and 2.215 mm, respectively, which was significantly lower than that of specimens fixed with two IS screws under corresponding load (P < 0.05). Under the vertical load of 500 N, the shift in the fracture gap of specimens fixed with MIAP combined with one IS screw was 0.261 ± 0.095 mm, and that of specimens fixed with two IS screws was 0.809 ± 0.170 mm. The difference was significant (P < 0.05). Conclusion: The stability of Tile C pelvic fractures fixed with MIAP combined with one IS screw was better than that fixed with two IS screws

  19. Effect of argon purity on mechanical properties, microstructure and fracture mode of commercially pure (cp) Ti and Ti-6Al-4V alloys for ceramometal dental prostheses.

    PubMed

    Bauer, José; Cella, Suelen; Pinto, Marcelo M; Filho, Leonardo E Rodrigues; Reis, Alessandra; Loguercio, Alessandro D

    2009-12-01

    Provision of an inert gas atmosphere with high-purity argon gas is recommended for preventing titanium castings from contamination although the effects of the level of argon purity on the mechanical properties and the clinical performance of Ti castings have not yet been investigated. The purpose of this study was to evaluate the effect of argon purity on the mechanical properties and microstructure of commercially pure (cp) Ti and Ti-6Al-4V alloys. The castings were made using either high-purity and/or industrial argon gas. The ultimate tensile strength (UTS), proportional limit (PL), elongation (EL) and microhardness (VHN) at different depths were evaluated. The microstructure of the alloys was also revealed and the fracture mode was analyzed by scanning electron microscopy. The data from the mechanical tests and hardness were subjected to a two-and three-way ANOVA and Tukey's test (alpha = 0.05). The mean values of mechanical properties were not affected by the argon gas purity. Higher UTS, PL and VHN, and lower EL were observed for Ti-6Al-4V. The microhardness was not influenced by the argon gas purity. The industrial argon gas can be used to cast cp Ti and Ti-6Al-4V.

  20. Strain energy release rates of composite interlaminar end-notch and mixed-mode fracture: A sublaminate/ply level analysis and a computer code

    NASA Technical Reports Server (NTRS)

    Valisetty, R. R.; Chamis, C. C.

    1987-01-01

    A computer code is presented for the sublaminate/ply level analysis of composite structures. This code is useful for obtaining stresses in regions affected by delaminations, transverse cracks, and discontinuities related to inherent fabrication anomalies, geometric configurations, and loading conditions. Particular attention is focussed on those layers or groups of layers (sublaminates) which are immediately affected by the inherent flaws. These layers are analyzed as homogeneous bodies in equilibrium and in isolation from the rest of the laminate. The theoretical model used to analyze the individual layers allows the relevant stresses and displacements near discontinuities to be represented in the form of pure exponential-decay-type functions which are selected to eliminate the exponential-precision-related difficulties in sublaminate/ply level analysis. Thus, sublaminate analysis can be conducted without any restriction on the maximum number of layers, delaminations, transverse cracks, or other types of discontinuities. In conjunction with the strain energy release rate (SERR) concept and composite micromechanics, this computational procedure is used to model select cases of end-notch and mixed-mode fracture specimens. The computed stresses are in good agreement with those from a three-dimensional finite element analysis. Also, SERRs compare well with limited available experimental data.

  1. Natural history of unreduced Gartland type-II supracondylar fractures of the humerus in children: a two to thirteen-year follow-up study.

    PubMed

    Moraleda, Luis; Valencia, María; Barco, Raúl; González-Moran, Gaspar

    2013-01-02

    The preferred treatment of type-II supracondylar humeral fractures remains controversial. The purpose of this study was to evaluate the long-term clinical and radiographic outcome of type-II supracondylar humeral fractures in children treated with immobilization in a splint without reduction. The medical records of forty-six consecutive patients who sustained a supracondylar Gartland type-II fracture of the humerus treated with immobilization in a splint were reviewed. Age at the time of fracture, sex, side involved, dominant extremity, duration of immobilization, and complications were recorded. Radiographic assessment included the Baumann angle, carrying angle, and lateral humerocapitellar angle. Patients returned for clinical evaluation, and the Mayo Elbow Performance Score and the criteria of Flynn et al. were recorded. Patients completed the QuickDASH, an abbreviated form of the Disabilities of the Arm, Shoulder and Hand questionnaire, to measure disability. The average age (and standard deviation) at the time of fracture was 5.5 ± 2.6 years. The average duration of follow-up was 6.6 ± 2.8 years. The initial lateral humerocapitellar angle was a mean of 12.8° ± 9.8°, the mean Baumann angle was 12° ± 5.7°, and the mean radiographic carrying angle was 9° ± 11.3°. There were significant differences between injured and uninjured elbows at the time of follow-up with regard to flexion (mean, 137.9° ± 9.1° for injured and 144.8° ± 7.1° for uninjured elbows; p < 0.001), extension (mean, 13.2° ± 5.9° for injured and 7.4° ± 5.1° for uninjured elbows; p < 0.001), clinical carrying angle (mean, 9° ± 8.1° for injured and 12.1° ± 4.9° for uninjured elbows; p = 0.003), radiographic carrying angle (mean, 8.9° ± 8.1° for injured and 14.2° ± 5.5° for uninjured elbows; p < 0.001), and lateral humerocapitellar angle (mean, 30.5° ± 11° for injured and 41.9° ± 9.9° for uninjured elbows; p < 0.001). The mean score was 10 ± 15.3 points for the

  2. Measurement of higher-order mode losses in SPEAR II by shift in synchrotron phase and increase in net cavity power

    SciTech Connect

    Not Available

    1988-01-01

    It has been estimated that the loss to higher-order cavity modes in SPEAR II will be 135 keV per cavity at 100 mA for a 10-cm bunch (sigma/sub z/ = 5 cm). This corresponds to a loss of 10 MeV for a 50-m PEP structure. The power lost to higher modes in each SPEAR II cavity at 100 mA would be 13.5 kW. A loss of this order can be measured by calorimetry. This loss is also large enough to cause a significant increase in the net rf power input into the cavities over the power input with no higher-mode excitation. In addition, the higher-mode loss can also produce a measurable shift in the synchronous phase angle. Numbers for these effects are computed in this paper.

  3. Comparison of fracture resistance and failure pattern of endodontically treated premolars with different esthetic onlay systems: An in vitro study

    PubMed Central

    Mynampati, Praffulla; Babu, Mandava Ramesh; Saraswathi, Devabhaktuni Disha; Kumar, Janga Ravi; Gudugunta, Leneena; Gaddam, Divya

    2015-01-01

    Aim: To compare the fracture resistance and modes of failures of three different aesthetic MOD onlays on endodontically treated premolars. Materials and Methods: Forty sound maxillary premolars were selected of which 10 untreated teeth were taken as control (Group I). The other thirty premolars were subjected to standardized MOD onlay preparations and root canal treatments and divided into 3 equal groups. Onlays were prepared in Group II- Indirect composite, Group III- Lithium Disilicate ceramic and Group IV- Full Zirconia. All onlays were cemented using Multilink Automix. All the 40 samples were subjected to fracture resistance testing on Universal testing machine. Also fractured specimens were observed under stereo-microscope for modes of failure. Results: Group IV presented the highest fracture resistance. Groups II and III presented no significant difference in fracture resistance from each other (P > 0.05). Group II and Group III showed significantly lower fracture resistance values than Group I. Coming to modes of failure, only Group IV had showed no cracks in any of the restorations. Conclusion: Full Zirconia MOD onlays increased the fracture resistance of endodontically treated premolars to a significantly higher level than the sound teeth. PMID:25829694

  4. Comparison of fracture resistance and failure pattern of endodontically treated premolars with different esthetic onlay systems: An in vitro study.

    PubMed

    Mynampati, Praffulla; Babu, Mandava Ramesh; Saraswathi, Devabhaktuni Disha; Kumar, Janga Ravi; Gudugunta, Leneena; Gaddam, Divya

    2015-01-01

    To compare the fracture resistance and modes of failures of three different aesthetic MOD onlays on endodontically treated premolars. Forty sound maxillary premolars were selected of which 10 untreated teeth were taken as control (Group I). The other thirty premolars were subjected to standardized MOD onlay preparations and root canal treatments and divided into 3 equal groups. Onlays were prepared in Group II- Indirect composite, Group III- Lithium Disilicate ceramic and Group IV- Full Zirconia. All onlays were cemented using Multilink Automix. All the 40 samples were subjected to fracture resistance testing on Universal testing machine. Also fractured specimens were observed under stereo-microscope for modes of failure. Group IV presented the highest fracture resistance. Groups II and III presented no significant difference in fracture resistance from each other (P > 0.05). Group II and Group III showed significantly lower fracture resistance values than Group I. Coming to modes of failure, only Group IV had showed no cracks in any of the restorations. Full Zirconia MOD onlays increased the fracture resistance of endodontically treated premolars to a significantly higher level than the sound teeth.

  5. Development and Application of Benchmark Examples for Mode II Static Delamination Propagation and Fatigue Growth Predictions

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald

    2011-01-01

    The development of benchmark examples for static delamination propagation and cyclic delamination onset and growth prediction is presented and demonstrated for a commercial code. The example is based on a finite element model of an End-Notched Flexure (ENF) specimen. The example is independent of the analysis software used and allows the assessment of the automated delamination propagation, onset and growth prediction capabilities in commercial finite element codes based on the virtual crack closure technique (VCCT). First, static benchmark examples were created for the specimen. Second, based on the static results, benchmark examples for cyclic delamination growth were created. Third, the load-displacement relationship from a propagation analysis and the benchmark results were compared, and good agreement could be achieved by selecting the appropriate input parameters. Fourth, starting from an initially straight front, the delamination was allowed to grow under cyclic loading. The number of cycles to delamination onset and the number of cycles during delamination growth for each growth increment were obtained from the automated analysis and compared to the benchmark examples. Again, good agreement between the results obtained from the growth analysis and the benchmark results could be achieved by selecting the appropriate input parameters. The benchmarking procedure proved valuable by highlighting the issues associated with choosing the input parameters of the particular implementation. Selecting the appropriate input parameters, however, was not straightforward and often required an iterative procedure. Overall the results are encouraging, but further assessment for mixed-mode delamination is required.

  6. Effects of ammonium sulfate aerosols on vegetation—II. Mode of entry and responses of vegetation

    NASA Astrophysics Data System (ADS)

    Gmur, Nicholas F.; Evans, Lance S.; Cunningham, Elizabeth A.

    These experiments were designed to provide information on the rates of aerosol deposition, mode of entry, and effects of deposition of submicrometer ammonium sulfate aerosols on foliage of Phaseolus vulgaris L. A deposition velocity of 3.2 × 10 3cms-1 was constant during 3-week exposures of plants to aerosol concentrations of 26mg m -3 (i.e. about two orders of magnitude above ambient episode concentrations). Mean deposition rate on foliage was 4.1 × 10 -11 μg cm -2s -1. Visible injury symptoms included leaf chlorosis, necrosis and loss of turgor. Chlorosis was most frequent near leaf margins causing epinasty and near major veins. Internal injury occurred initially in spongy mesophyll cells. Eventually abaxial epidermal and palisade parenchyma cells were injured. These results suggest that submicrometer aerosols enter abaxial stomata and affect more internal cells before affecting leaf surface cells. Exposure to aerosols decreased both abaxial and adaxial leaf resistances markedly. Although visible injury to foliage occurred, no changes in dry mass of roots and shoots or leaf area occurred. These results suggest that for the plant developmental stage studied, while leaf resistances decreased and cellular injury occurred in foliage, these factors were not significantly related to plant growth and development.

  7. Transit time instabilities in an inverted fireball. II. Mode jumping and nonlinearities

    SciTech Connect

    Stenzel, R. L.; Gruenwald, J.; Fonda, B.; Ionita, C.; Schrittwieser, R.

    2011-01-15

    A fireball is formed inside a highly transparent spherical grid immersed in a dc discharge plasma. The ambient plasma acts as a cathode and the positively biased grid as an anode. A strong nearly current-free double layer separates the two plasmas. Electrons are accelerated into the fireball, ionize, and establish a discharge plasma with plasma potential near the grid potential. Ions are ejected from the fireball. Since electrons are lost at the same rate as ions, most electrons accelerated into the fireball just pass through it. Thus, the electron distribution contains radially counterstreaming electrons. High-frequency oscillations are excited with rf period given by the electron transit time through the fireball. Since the frequency is well below the electron plasma frequency, no eigenmodes other than a beam space-charge wave exists. The instability is an inertial transit-time instability similar to the sheath-plasma instability or the reflex vircator instability. In contrast to vircators, there is no electron reflection from a space-charge layer but counterstreaming arises from spherical convergence and divergence of electrons. While the basic instability properties have been presented in a companion paper [R. L. Stenzel et al., Phys. Plasmas 18, 012104 (2011)], the present paper focuses on observed mode jumping and nonlinear effects. The former produce frequency jumps and different potential profiles, the latter produce harmonics associated with electron bunching at large amplitudes. In situ probe measurements are presented and interpreted.

  8. The ice nucleating ability of pollen:. Part II. Laboratory studies in immersion and contact freezing modes

    NASA Astrophysics Data System (ADS)

    Diehl, K.; Matthias-Maser, S.; Jaenicke, R.; Mitra, S. K.

    Laboratory tests were conducted of the ice nucleating ability of four kinds of pollen in the immersion and the contact freezing modes. The diameters of the selected pollen were between 25 and 70 μm. The experiments were carried out at the Mainz vertical wind tunnel with freely suspended supercooled droplets at temperatures down to -28 °C. The immersion freezing experiments were conducted with drops of radii between 250 and 375 μm formed from distilled water with a defined amount of pollen added. The drops were freely floated in the wind tunnel while being supercooled. For the contact freezing experiments, a short burst of pollen was allowed to collide with freely suspended, supercooled pure water drops of 360-μm radius. The results showed that particle-free water drops in particle-free air in the wind tunnel did not freeze at temperatures above -28 °C while water drops containing pollen froze at temperatures as high as -9 °C, and water drops colliding with pollen froze at temperatures -5 °C and lower. Combined with earlier results about the ice nucleating ability of some bacteria, marine plankton, and leaf litters, the present results confirm the importance of biological aerosol particles as potential ice nuclei at relatively warm temperatures.

  9. FORWARD MODELING OF STANDING KINK MODES IN CORONAL LOOPS. II. APPLICATIONS

    SciTech Connect

    Yuan, Ding; Doorsselaere, Tom Van

    2016-04-15

    Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modeling) of the observables into the thermal and magnetic structures of the plasma. However, due to the limited availability of observables, this is an ill-posed issue. Forward modeling is designed to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses, and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We demonstrate that forward models could be effectively used to identify the oscillation overtone and polarization, to reproduce the general profile of oscillation amplitude and phase, and to predict multiple harmonic periodicities in the associated emission intensity and loop width variation.

  10. An assessment of BWR (boiling water reactor) Mark-II containment challenges, failure modes, and potential improvements in performance

    SciTech Connect

    Kelly, D.L.; Jones, K.R.; Dallman, R.J. ); Wagner, K.C. )

    1990-07-01

    This report assesses challenges to BWR Mark II containment integrity that could potentially arise from severe accidents. Also assessed are some potential improvements that could prevent core damage or containment failure, or could mitigate the consequences of such failure by reducing the release of fission products to the environment. These challenges and improvements are analyzed via a limited quantitative risk/benefit analysis of a generic BWR/4 reactor with Mark II containment. Point estimate frequencies of the dominant core damage sequences are obtained and simple containment event trees are constructed to evaluate the response of the containment to these severe accident sequences. The resulting containment release modes are then binned into source term release categories, which provide inputs to the consequence analysis. The output of the consequences analysis is used to construct an overall base case risk profile. Potential improvements and sensitivities are evaluated by modifying the event tree spilt fractions, thus generating a revised risk profile. Several important sensitivity cases are examined to evaluate the impact of phenomenological uncertainties on the final results. 75 refs., 25 figs., 65 tabs.

  11. Concentration-dependent mode of interaction of angiotensin II receptor blockers with uric acid transporter.

    PubMed

    Iwanaga, Takashi; Sato, Masanobu; Maeda, Tomoji; Ogihara, Toshio; Tamai, Ikumi

    2007-01-01

    Serum uric acid (SUA) is currently recognized as a risk factor for cardiovascular disease. It has been reported that an angiotensin II receptor blocker (ARB), losartan, decreases SUA level, whereas other ARBs, such as candesartan, have no lowering effect. Because the renal uric acid transporter (URAT1) is an important factor controlling the SUA level, we examined the involvement of URAT1 in those differential effects of various ARBs on SUA level at clinically relevant concentrations. This study was done by using URAT1-expressing Xenopus oocytes. Losartan, pratosartan, and telmisartan exhibited cis-inhibitory effects on the uptake of uric acid by URAT1, whereas at higher concentrations, only telmisartan did, and these ARBs reduced the uptake in competitive inhibition kinetics. On the other hand, candesartan, EXP3174 [2-n-butyl-4-chloro-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yI)methyl]imidazole-5-carboxylic acid] (a major metabolite of losartan), olmesartan, and valsartan were not inhibitory. Preloading of those ARBs in the oocytes enhanced the URAT1-mediated uric acid uptake, showing a trans-stimulatory effect. The present study is a first demonstration of the differential effects of ARBs on URAT1 that some ARBs are both cis-inhibitory and trans-stimulatory, depending on concentration, whereas others exhibit either a trans-stimulatory or cis-inhibitory effect alone, which could explain the clinically observed differential effects of ARBs on SUA level. Furthermore, it was found that such differential effects of ARBs on URAT1 could be predicted from the partial chemical structures of ARBs, which will be useful information for the appropriate use and development of ARBs without an increase of SUA.

  12. Multiple Modes of Calcium-Induced Calcium Release in Sympathetic Neurons II

    PubMed Central

    Hongpaisan, Jarin; Pivovarova, Natalia B.; Colegrove, Stephen L.; Leapman, Richard D.; Friel, David D.; Andrews, S. Brian

    2001-01-01

    CICR from an intracellular store, here directly characterized as the ER, usually refers to net Ca2+ release that amplifies evoked elevations in cytosolic free calcium ([Ca2+]i). However, the companion paper (Albrecht, M.A., S.L. Colegrove, J. Hongpaisan, N.B. Pivovarova, S.B. Andrews, and D.D. Friel. 2001. J. Gen. Physiol. 118:83–100) shows that in sympathetic neurons, small [Ca2+]i elevations evoked by weak depolarization stimulate ER Ca accumulation, but at a rate attenuated by activation of a ryanodine-sensitive CICR pathway. Here, we have measured depolarization-evoked changes in total ER Ca concentration ([Ca]ER) as a function of [Ca2+]i, and found that progressively larger [Ca2+]i elevations cause a graded transition from ER Ca accumulation to net release, consistent with the expression of multiple modes of CICR. [Ca]ER is relatively high at rest (12.8 ± 0.9 mmol/kg dry weight, mean ± SEM) and is reduced by thapsigargin or ryanodine (5.5 ± 0.7 and 4.7 ± 1.1 mmol/kg, respectively). [Ca]ER rises during weak depolarization (to 17.0 ± 1.6 mmol/kg over 120s, [Ca2+]i less than ∼350 nM), changes little in response to stronger depolarization (12.1 ± 1.1 mmol/kg, [Ca2+]i ∼700 nM), and declines (to 6.5 ± 1.0 mmol/kg) with larger [Ca2+]i elevations (>1 μM) evoked by the same depolarization when mitochondrial Ca2+ uptake is inhibited (FCCP). Thus, net ER Ca2+ transport exhibits a biphasic dependence on [Ca2+]i. With mitochondrial Ca2+ uptake enabled, [Ca]ER rises after repolarization (to 16.6 ± 1.8 mmol/kg at 15 min) as [Ca2+]i falls within the permissive range for ER Ca accumulation over a period lengthened by mitochondrial Ca2+ release. Finally, although spatially averaged [Ca]ER is unchanged during strong depolarization, net ER Ca2+ release still occurs, but only in the outermost ∼5-μm cytoplasmic shell where [Ca2+]i should reach its highest levels. Since mitochondrial Ca accumulation occurs preferentially in peripheral cytoplasm, as demonstrated

  13. Effect of fracture surface roughness on shear crack growth

    SciTech Connect

    Gross, T.S.; Watt, D.W. . Dept. of Mechanical Engineering); Mendelsohn, D.A. . Dept. of Engineering Mechanics)

    1992-12-01

    A model of fracture surface interference for Mode I fatigue crack profiles was developed and evaluated. Force required to open the crack faces is estimated from point contact expressions for Mode I stress intensity factor. Force transfer across contacting asperities is estimated and used to calculate Mode II resistance stress intensity factor (applied factor is sum of effective and resistance factors). Electro-optic holographic interferometry was used to measure 3-D displacement field around a Mode I fatigue pre-crack in Al loaded in Mode II shear. Induced Mode I crack face displacements were greater than Mode II displacements. Plane stress shear lip caused displacement normal to surface as the crack faces are displaced. Algorithms are being developed to track the displacements associated with the original coordinate system in the camera. A 2-D boundary element method code for mixed mode I and II loading of a rough crack (sawtooth asperity model) has been completed. Addition of small-scale crack tip yielding and a wear model are completed and underway, respectively.

  14. Fractional Diffusion Analysis of the Electromagnetic Field In Fractured Media Part II: 2.5-D Approach

    NASA Astrophysics Data System (ADS)

    Ge, J.; Everett, M. E.; Weiss, C. J.

    2012-12-01

    A 2.5D finite difference (FD) frequency-domain modeling algorithm based on the theory of fractional diffusion of electromagnetic (EM) fields generated by a loop source lying above a fractured geological medium is addressed in this paper. The presence of fractures in the subsurface, usually containing highly conductive pore fluids, gives rise to spatially hierarchical flow paths of induced EM eddy currents. The diffusion of EM eddy currents in such formations is anomalous, generalizing the classical Gaussian process described by the conventional Maxwell equations. Based on the continuous time random walk (CTRW) theory, the diffusion of EM eddy currents in a rough medium is governed by the fractional Maxwell equations. Here, we model the EM response of a 2D subsurface containing fractured zones, with a 3D loop source, which results the so-called 2.5D model geometry. The governing equation in the frequency domain is converted using Fourier transform into k domain along the strike direction (along which the model conductivity doesn't vary). The resulting equation system is solved by the multifrontal massively parallel solver (MUMPS). The data obtained is then converted back to spatial domain and the time domain. We find excellent agreement between the FD and analytic solutions for a rough halfspace model. Then FD solutions are calculated for a 2D fault zone model with variable conductivity and roughness. We compare the results with responses from several classical models and explore the relationship between the roughness and the spatial density of the fracture distribution.

  15. Crack Extension in Hydraulic Fracturing of Shale Cores Using Viscous Oil, Water, and Liquid Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Bennour, Ziad; Ishida, Tsuyoshi; Nagaya, Yuya; Chen, Youqing; Nara, Yoshitaka; Chen, Qu; Sekine, Kotaro; Nagano, Yu

    2015-07-01

    We performed hydraulic fracturing experiments on cylindrical cores of anisotropic shale obtained by drilling normal to the sedimentary plane. Experiments were conducted under ambient condition and uniaxial stresses, using three types of fracturing fluid: viscous oil, water, and liquid carbon dioxide (L-CO2). In the experiments using water and oil, cracks extended along the loading direction normal to the sedimentary plane under the uniaxial loading and extended along the sedimentary plane without loading. These results suggest that the direction of crack extension is strongly affected by in situ stress conditions. Fluorescent microscopy revealed that hydraulic fracturing with viscous oil produced linear cracks with few branches, whereas that with water produced cracks with many branches inclining from the loading axis. Statistical analysis of P wave polarity of acoustic emission waveforms showed that viscous oil tended to induce Mode I fracture, whereas both water and L-CO2 tended to induce Mode II fracture. Crack extension upon injection of L-CO2 was independent of loading condition unlike extension for the other two fluids. This result seemed attributable to the low viscosity of L-CO2 and was consistent with previous observations for granite specimens that low-viscosity fluids like CO2 tend to induce widely extending cracks with many branches, with Mode II fractures being dominant. These features are more advantageous for shale gas production than those induced by injection of conventional slick water.

  16. Analytic modeling of instabilities driven by higher-order modes in the HLS II RF system with a higher-harmonic cavity

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Ning; Li, Wei-Min; Wu, Cong-Feng; Wang, Lin

    2013-08-01

    The utility of a passive fourth-harmonic cavity plays a key role in suppressing longitudinal beam instabilities in the electron storage ring and lengthens the bunch by a factor of 2.6 for the phase II project of the Hefei Light Source (HLS II). Meanwhile, instabilities driven by higher-order modes (HOM) may limit the performance of the higher-harmonic cavity. In this paper, the parasitic coupled-bunch instability, which is driven by narrow band parasitic modes, and the microwave instability, which is driven by broadband HOM, are both modeled analytically. The analytic modeling results are in good agreement with those of our previous simulation study and indicate that the passive fourth-harmonic cavity suppresses parasitic coupled-bunch instabilities and microwave instability. The modeling suggests that a fourth-harmonic cavity may be successfully used at the HLS II.

  17. Insights into the binding mode of sulphamates and sulphamides to hCA II: crystallographic studies and binding free energy calculations.

    PubMed

    De Simone, Giuseppina; Langella, Emma; Esposito, Davide; Supuran, Claudiu T; Monti, Simona Maria; Winum, Jean-Yves; Alterio, Vincenzo

    2017-12-01

    Sulphamate and sulphamide derivatives have been largely investigated as carbonic anhydrase inhibitors (CAIs) by means of different experimental techniques. However, the structural determinants responsible for their different binding mode to the enzyme active site were not clearly defined so far. In this paper, we report the X-ray crystal structure of hCA II in complex with a sulphamate inhibitor incorporating a nitroimidazole moiety. The comparison with the structure of hCA II in complex with its sulphamide analogue revealed that the two inhibitors adopt a completely different binding mode within the hCA II active site. Starting from these results, we performed a theoretical study on sulphamate and sulphamide derivatives, demonstrating that electrostatic interactions with residues within the enzyme active site play a key role in determining their binding conformation. These findings open new perspectives in the design of effective CAIs using the sulphamate and sulphamide zinc binding groups as lead compounds.

  18. Viscoelastic-damage interface model formulation with friction to simulate the delamination growth in mode II shear

    NASA Astrophysics Data System (ADS)

    Goodarzi, Mohammad Saeed; Hosseini-Toudeshky, Hossein

    2017-02-01

    In this paper a formulation of a viscoelastic-damage interface model with friction in mode-II is presented. The cohesive constitutive law contains elastic and damage regimes. It has been assumed that the shear stress in the elastic regime follows the viscoelastic properties of the matrix material. The three element Voigt model has been used for the formulation of relaxation modulus of the material. Damage evolution proceeds according to the bilinear cohesive constitutive law combined with friction stress consideration. Combination of damage and friction is based on the presumption that the damaged area, related to an integration point, can be dismembered into the un-cracked area with the cohesive damage and cracked area with friction. Samples of a one element model have been presented to see the effect of parameters on the cohesive constitutive law. A comparison between the predicted results with available results of end-notched flexure specimens in the literature is also presented to verify the model. Transverse crack tension specimens are also simulated for different applied displacement velocities.

  19. Preoperative posterior tilt of at least 20° increased the risk of fixation failure in Garden-I and -II femoral neck fractures

    PubMed Central

    Dolatowski, Filip C; Adampour, Mina; Frihagen, Frede; Stavem, Knut; Erik Utvåg, Stein; Hoelsbrekken, Sigurd Erik

    2016-01-01

    Background and purpose It has been suggested that preoperative posterior tilt of the femoral head may increase the risk of fixation failure in Garden-I and -II femoral neck fractures. To investigate this association, we studied a cohort of 322 such patients. Patients and methods Patients treated with internal fixation between 2005 and 2012 were retrospectively identified using hospital records and the digital image bank. 2 raters measured the preoperative posterior tilt angle and categorized it into 3 groups: < 10°, 10–20°, and ≥ 20°. The inter-rater reliability (IRR) was determined. Patients were observed until September 2013 (with a minimum follow-up of 18 months) or until failure of fixation necessitating salvage arthroplasty. The risk of fixation failure was assessed using competing-risk regression analysis, adjusting for time to surgery. Results Patients with a posterior tilt of ≥ 20° had a higher risk of fixation failure: 19% (8/43) as compared to 11% (14/127) in the 10–20° category and 6% (9/152) in the < 10° category (p = 0.03). Posterior tilt of ≥ 20° increased the risk of fixation failure, with an adjusted hazard ratio of 3.4 (95% CI: 1.3–8.9; p = 0.01). The interclass correlation coefficient for angular measurements of posterior tilt was 0.90 (95% CI: 0.87–0.92), and the IRR for the categorization of posterior tilt into 3 groups was 0.76 (95% CI: 0.69–0.81). Interpretation Preoperative posterior tilt of ≥ 20° in Garden-I and -II femoral neck fractures increased the risk of fixation failure necessitating salvage arthroplasty. The reliability of the methods that we used to measure posterior tilt ranged from good to excellent. PMID:26937557

  20. Anterior single odontoid screw placement for type II odontoid fractures: our modified surgical technique and initial results in a cohort study of 15 patients

    PubMed Central

    Munakomi, Sunil; Tamrakar, Karuna; Chaudhary, Pramod Kumar; Bhattarai, Binod

    2016-01-01

    Objective: Anterior odontoid screw fixation for type II odontoid fracture is the ideal management option. However in the context of unavailability of an O-arm or neuro-navigation and poor images from the available C-arm may be an obstacle to ideal trajectory and placement of the odontoid screw. We herein detail  our surgical technique so as to ensure a correct trajectory and subsequent good fusion in Type II odontoid fractures. This may be advantageous  in clinical set ups lacking state of the art facilities.  Methods and Results: In this cohort study we included 15 consecutive patients who underwent anterior odontoid screw placement. We routinely dissect the longus colli to completely visualize the entire width of C3 body. We then perform a median C2-C3 disectomy followed by creating a gutter in the superior end of C3 body. We then guide the Kirchsner (K) wire purchasing adequate anterior cortex of C2. Rest of the procedure follows the similar steps as described for odontoid screw placement. We achieved 100% correct trajectory and screw placement in our study. There were no instances of screw break out, pull out or nonunion. There was one patient mortality following myocardial infarction in our study. Conclusion: Preoperative imaging details, proper patient positioning, meticulous dissection, thorough anatomical knowledge and few added surgical nuances are the cornerstones in ideal odontoid screw placement. This may be pivotal in managing  patients in developing nations having rudimentary neurosurgical set up. PMID:27990259

  1. 3D-RISM-MP2 Approach to Hydration Structure of Pt(II) and Pd(II) Complexes: Unusual H-Ahead Mode vs Usual O-Ahead One.

    PubMed

    Aono, Shinji; Mori, Toshifumi; Sakaki, Shigeyoshi

    2016-03-08

    Solvation of transition metal complexes with water has been one of the fundamental topics in physical and coordination chemistry. In particular, Pt(II) complexes have recently attracted considerable interest for their relation to anticancer activity in cisplatin and its analogues, yet the interaction of the water molecule and the metal center has been obscured. The challenge from a theoretical perspective remains that both the microscopic solvation effect and the dynamical electron correlation (DEC) effect have to be treated simultaneously in a reasonable manner. In this work we derive the analytical gradient for the three-dimensional reference interaction site model Møller-Plesset second order (3D-RISM-MP2) free energy. On the basis of the three-regions 3D-RISM self-consistent field (SCF) method recently proposed by us, we apply a new layer of the Z-vector method to the CP-RISM equation as well as point-charge approximation to the derivatives with respect to the density matrix elements in the RISM-CPHF equation to remarkably reduce the computational cost. This method is applied to study the interaction of H2O with the d(8) square planar transition metal complexes in aqueous solution, trans-[Pt(II)Cl2(NH3)(glycine)] (1a), [Pt(II)(NH3)4](2+) (1b), [Pt(II)(CN)4](2-) (1c), and their Pd(II) analogues 2a, 2b, and 2c, respectively, to elucidate whether the usual H2O interaction through O atom (O-ahead mode) or unusual one through H atom (H-ahead mode) is stable in these complexes. We find that the interaction energy of the coordinating water and the transition metal complex changes little when switching from gas to aqueous phase, but the solvation free energy differs remarkably between the two interaction modes, thereby affecting the relative stability of the H-ahead and O-ahead modes. Particularly, in contrast to the expectation that the O-ahead mode is preferred due to the presence of positive charges in 1b, the H-ahead mode is also found to be more stable. The O

  2. Size effect law and fracture mechanics of the triggering of dry snow slab avalanches

    NASA Astrophysics Data System (ADS)

    Bažant, ZdeněK. P.; Zi, Goangseup; McClung, David

    2003-02-01

    A size effect law for fracture triggering in dry snow slabs of high enough length-to-thickness ratio is formulated, based on simplified one-dimensional analysis by equivalent linear elastic fracture mechanics. Viscoelastic effects during fracture are neglected. The derived law, which is analogous to Bažant's energetic size effect law developed for concrete and later for sea ice, fiber composites, rocks, and ceramics, is shown to agree with two-dimensional finite element analysis of mode II cohesive crack model with a finite residual shear stress. Fitting the proposed size effect law to fracture data for various slab thicknesses permits identifying the material fracture parameters. The value of preexisting shear stress in a thin weak zone of finite length is shown to have significant effect. There exists a certain critical snow depth, depending on the preexisting stress value, below which the size effect disappears. Practical applications require considering that the material properties (particularly the mode II fracture toughness or fracture energy) at the snow slab base are not constant but depend strongly on the slab thickness. This means that one must distinguish the material size effect from the structural size effect, and the combined size effect law must be obtained by introducing into the structural size effect law dependence of its parameters on snow thickness. The thickness dependence of these parameters can be obtained by matching the combined law to avalanche observations. Matching Perla's field data on 116 avalanches suggests that the mode II fracture toughness is approximately proportional to 1.8 power of snow thickness.

  3. Influence of ceramic inlays and composite fillings on fracture resistance of premolars in vitro.

    PubMed

    Ragauska, Antra; Apse, Peteris; Kasjanovs, Vladimirs; Berzina-Cimdina, Liga

    2008-01-01

    The aim of this study was to assess the resistance of fracture of mesio-occlusal-distal (MOD) ceramic inlays and composite fillings in premolars and to compare fracture modes between the groups. Twenty seven extracted intact human premolars were selected and divided into three groups: I - intact teeth (control group), II - MOD cavities restored with indirect ceramic inlays (Finesse, Dentsply Ceramco, USA), III - MOD cavities restored with direct composite fillings (Filtek P60, 3M ESPE, USA). The fracture resistance (N) was assessed under axial compressive loading with a metal cylinder 3.2 mm in diameter at a cross-head speed of 0.5 mm/min in a universal testing machine. The data were analyzed with ANOVA and t-test (pd< or =0.05). Fracture modes were recorded based on the degree of tooth structure and restoration damage. The mean force applied to cause failure for group I was 1.218 kN +/-0.223, for group II - 1.407 kN +/-0.374 and for group III - 0.941 kN +/-0.258. T-test showed significant difference between groups I and III (p=0.027), and groups II and III (p=0.008). The fracture modes observed in all groups tended to involve restoration's and cusp's fracture. It was observed that ceramic inlays in premolars have higher load to fracture value than composite fillings and similar to intact teeth. Both restorations, ceramic and composite in the premolars, tended to fracture together with palatal cusp of tooth.

  4. Binding mode and thermodynamic studies on the interaction of the anticancer drug dacarbazine and dacarbazine-Cu(II) complex with single and double stranded DNA.

    PubMed

    Temerk, Yassien; Ibrahim, Hossieny

    2014-07-01

    The binding mode and thermodynamic characteristics of the anticancer drug dacarbazine (Dac) with double and single stranded DNA were investigated in the absence and presence of Cu(II) using cyclic voltammetry, square wave voltammetry and fluorescence spectroscopy. The interaction of Dac and Dac-Cu(II) complex with dsDNA indicated their intercalation into the base stacking domain of dsDNA double helix and the strength of interaction is independent on the ionic strength. The interaction of Dac with dsDNA in the presence of Cu(II) leads to a much stronger intercalation. The interaction mode of Dac molecules with ssDNA is electrostatic attraction via negative phosphate on the exterior of the ssDNA with Dac. The binding constants, stoichiometric coefficients and thermodynamic parameters of Dac and Dac-Cu(II) complex with dsDNA and ssDNA were evaluated. Comparison of the mode interaction of Dac with dsDNA and ssDNA was discussed. The decrease of peak current of Dac was proportional to DNA concentration, which was applied for determination of dsDNA and ssDNA concentration.

  5. Surface enhanced Raman scattering, natural bond orbitals and Mulliken atomic charge distribution in the normal modes of diethyldithiocarbamate cadmium (II) complex, [Cd(DDTC)₂].

    PubMed

    Soto, C A Téllez; Costa, A C; Versiane, O; Lemma, T; Machado, N C F; Mondragón, M A; Martin, A A

    2015-07-05

    Theoretical and experimental bands have been assigned to the Fourier Transform Infrared (FT-IR) and FT-Raman spectra of the bis(diethyldithiocarbamate)Cd(II) complex, abbreviated as ([Cd(DDTC)2]). The calculations and spectral interpretation have been based on the DFT/B3LYP method, infrared and Raman second derivative spectra, and band deconvolution analysis to assist in the assignment of observed fundamentals. This study validated the unusual pseudo tetrahedral molecular structure formed around the Cd(II) cation. Surface-enhanced Raman scattering (SERS) was used to determine the interactions of the normal-modes of the diethyldithiocarbamate cadmium (II) complex on nano-structured silver surfaces. Natural bond orbital (NBO) analysis was also carried out to study the Cd(II) hybridization causing the pseudo tetrahedral geometry of the framework of the [Cd(DDTC)2] complex, and to confirm the charge transfer mechanisms through second order perturbation theory analysis of the Fox Matrix. In order to find out the electronic dispersion of the Mulliken atomic charges (MAC) in the normal modes, we calculated the MAC for each normal mode and correlated these values with the SERS effect. Experimental UV-Vis spectra were obtained and charge transfer bands were assigned. Good agreement between the calculated and experimental values for the vibrational and UV-Vis spectra was obtained. Copyright © 2015 Elsevier B.V. All rights reserved.

  6. Surface enhanced Raman scattering, natural bond orbitals and Mulliken atomic charge distribution in the normal modes of diethyldithiocarbamate cadmium (II) complex, [Cd(DDTC)2

    NASA Astrophysics Data System (ADS)

    Téllez Soto, C. A.; Costa, A. C.; Versiane, O.; Lemma, T.; Machado, N. C. F.; Mondragón, M. A.; Martin, A. A.

    2015-07-01

    Theoretical and experimental bands have been assigned to the Fourier Transform Infrared (FT-IR) and FT-Raman spectra of the bis(diethyldithiocarbamate)Cd(II) complex, abbreviated as ([Cd(DDTC)2]). The calculations and spectral interpretation have been based on the DFT/B3LYP method, infrared and Raman second derivative spectra, and band deconvolution analysis to assist in the assignment of observed fundamentals. This study validated the unusual pseudo tetrahedral molecular structure formed around the Cd(II) cation. Surface-enhanced Raman scattering (SERS) was used to determine the interactions of the normal-modes of the diethyldithiocarbamate cadmium (II) complex on nano-structured silver surfaces. Natural bond orbital (NBO) analysis was also carried out to study the Cd(II) hybridization causing the pseudo tetrahedral geometry of the framework of the [Cd(DDTC)2] complex, and to confirm the charge transfer mechanisms through second order perturbation theory analysis of the Fox Matrix. In order to find out the electronic dispersion of the Mulliken atomic charges (MAC) in the normal modes, we calculated the MAC for each normal mode and correlated these values with the SERS effect. Experimental UV-Vis spectra were obtained and charge transfer bands were assigned. Good agreement between the calculated and experimental values for the vibrational and UV-Vis spectra was obtained.

  7. Investigation of Explosively Driven Fragmentation of Metals - Two Dimensional Fracture and Fragmentation of Metal Shells: Progress Report II

    SciTech Connect

    Grady, D

    2003-02-01

    High explosive enclosed by a metal case qualitatively describes an essential component of high energy systems of importance to the Department of Energy. Detonation of the high explosive causes intense transient pressure loading of the metal following arrival of normal or obliquely incident explosive detonation wave. Subsequent expansion and deformation of the metal case leads to eventual rupture and the opening of fractures and fissures. Details of the rupture process are critical to performance of the system. Consequently, it is essential that the material and kinematic issues governing the processes of dynamic loading and subsequent failure of an explosive-metal case component within a functioning system be adequately understood. Among the reasons are to quantify existing performance, characterize potential degradation of performance resulting from system aging, and optimizing or maintaining system performance through implementation of structural or material changes. The physical and engineering issues underlying this dynamic response and failure phenomena are not adequately understood. The purpose of the present program is to identify the key issues and develop theoretical, computational and experimental models needed to achieve a satisfactory theoretical and analysis framework for analysis of metal case failure in the explosive environment. Specific tasks within the present program include: (1) Models and theories currently being pursued based on physical principles of both the statistical fragmentation concepts of Mott and the energy-based concept of others show promise of providing the analytic and computational methodology capable of predicting explosion-induced fracture and fragmentation of metal components. Experimental studies initiated in the earlier effort offer promise to provide critical test data for validation. The present task shall involve the further refinement and development of the dynamic failure and fragmentation models and theories, and the

  8. Progressive Fracture of Composite Structures

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Minnetyan, Levon

    2008-01-01

    A new approach is described for evaluating fracture in composite structures. This approach is independent of classical fracture mechanics parameters like fracture toughness. It relies on computational simulation and is programmed in a stand-alone integrated computer code. It is multiscale, multifunctional because it includes composite mechanics for the composite behavior and finite element analysis for predicting the structural response. It contains seven modules; layered composite mechanics (micro, macro, laminate), finite element, updating scheme, local fracture, global fracture, stress based failure modes, and fracture progression. The computer code is called CODSTRAN (Composite Durability Structural ANalysis). It is used in the present paper to evaluate the global fracture of four composite shell problems and one composite built-up structure. Results show that the composite shells and the built-up composite structure global fracture are enhanced when internal pressure is combined with shear loads.

  9. Multiaxial loading fracture of A1/sub 2/O/sub 3/ tubes: II. Weibull theory and analysis

    SciTech Connect

    Petrovic, J.J.; Stout, M.G.

    1984-01-01

    The Weibull statistical fracture theory for multiaxial loading was developed for thick- and thin-walled tube geometries subjected to multiaxial loading in tension-internal pressure, compression-internal pressure, and pure torsion. As compared to uniaxial tension, lower strengths are predicted for tension-tension stress states and higher strengths for tension-compression stress states. Comparison to experimental results for A1/sub 2/O/sub 3/ tubes indicates a reasonable agreement with Weibull theory predictions for tension-internal pressure and compression-internal pressure conditions, but an underestimation of stress state effects in pure torsion. Results indicate a weakening effect of in-flaw-plane tensile stresses, with no observed influence of in-plane compressive stresses.

  10. Angular momentum redistribution by mixed modes in evolved low-mass stars. II. Spin-down of the core of red giants induced by mixed modes

    NASA Astrophysics Data System (ADS)

    Belkacem, K.; Marques, J. P.; Goupil, M. J.; Mosser, B.; Sonoi, T.; Ouazzani, R. M.; Dupret, M. A.; Mathis, S.; Grosjean, M.

    2015-07-01

    The detection of mixed modes in subgiants and red giants by the CoRoT and Kepler space-borne missions allows us to investigate the internal structure of evolved low-mass stars, from the end of the main sequence to the central helium-burning phase. In particular, the measurement of the mean core rotation rate as a function of the evolution places stringent constraints on the physical mechanisms responsible for the angular momentum redistribution in stars. It showed that the current stellar evolution codes including the modelling of rotation fail to reproduce the observations. An additional physical process that efficiently extracts angular momentum from the core is thus necessary. Our aim is to assess the ability of mixed modes to do this. To this end, we developed a formalism that provides a modelling of the wave fluxes in both the mean angular momentum and the mean energy equations in a companion paper. In this article, mode amplitudes are modelled based on recent asteroseismic observations, and a quantitative estimate of the angular momentum transfer is obtained. This is performed for a benchmark model of 1.3 M⊙ at three evolutionary stages, representative of the evolved pulsating stars observed by CoRoT and Kepler. We show that mixed modes extract angular momentum from the innermost regions of subgiants and red giants. However, this transport of angular momentum from the core is unlikely to counterbalance the effect of the core contraction in subgiants and early red giants. In contrast, for more evolved red giants, mixed modes are found efficient enough to balance and exceed the effect of the core contraction, in particular in the hydrogen-burning shell. Our results thus indicate that mixed modes are a promising candidate to explain the observed spin-down of the core of evolved red giants, but that an other mechanism is to be invoked for subgiants and early red giants.

  11. Mathematical and numerical analysis of non-planer static mode-II crack in a two-layered medium

    NASA Astrophysics Data System (ADS)

    Hirano, S.; Yamashita, T.

    2009-12-01

    A crack in an infinite homogeneous medium is widely assumed as a model for earthquake fault. It is, however, well known that the earth's crust is heterogeneous and its structure is approximated well by a layered medium. Hence, such structure should be taken into account to model earthquake fault reasonably. We mathematically analyze the behavior of a 2-D static mode-II non-planar crack in a two-layered elastic medium in order to understand the effect of layer boundary on earthquake faulting. Although Rani and Singh (1993) and Rivalta et al.(2002) studied similar problems, focuses of their studies were quite narrow probably because of inherent mathematical difficulty. Actually the former assumed a planar crack with uniform slip and the latter assumed a planar crack perpendicular to the layer boundary. While a serious difficulty of the analysis of mode-II crack lies in the derivation of stress distribution due to point source as a kernel function, we first overcome the difficulty by writing its expression in a sequence of complex functions in the real (not the Fourier) domain. A very important characteristic in the sequence is that it has recursive property, which makes possible to derive the kernel function explicitly and to integrate it by parts; the integration by parts is required before the boundary integral equation method (BIEM) is applied. Our kernel function is much easier to treat than the expression given by Rani and Singh (1993). This enables us to analyze arbitrarily oriented non-planar crack in a two-layered medium. Next, we calculate the spatial distribution of stress due to crack that does not intersect the layer boundary using the above derived kernel function. We find in the calculation that the existence of layer boundary amplifies or reduces the stress at the crack tip when the crack is located close to the boundary; the stress is amplified when the crack exists in the layer with lower rigidity. Our method of analysis can easily be applied to the

  12. Did King Philip II of Ancient Macedonia Suffer a Zygomatico-Orbital Fracture? A Maxillofacial Surgeon's Approach.

    PubMed

    Stathopoulos, Panagiotis

    2017-09-01

    Philip II, father of Alexander the Great, succeeded his brother, Perdiccas III, to the throne of Macedonia in 360 BC. He has been described by historians as a generous king and military genius who managed to achieve his ambitious plans by expanding the Macedonian city-state over the whole Greek territory and the greater part of the Balkan Peninsula. The aim of our study was to present the evidence with regard to the facial injury of King Philip II of Macedonia and discuss the treatment of the wound by his famous physician, Critobulos. We reviewed the literature for historical, archaeological, and paleopathological evidence of King Philip's facial injury. We include a modern reconstruction of Philip's face based on the evidence of his injury by a team of anatomists and archaeologists from the Universities of Bristol and Manchester. In the light of the archaeological findings by Professor Andronikos and the paleopathological evidence by Musgrave, it can be claimed with confidence that King Philip II suffered a significant injury of his zygomaticomaxillary complex and supraorbital rim caused by an arrow as can be confirmed in many historical sources. To the best of our knowledge, this is the first attempt to present the trauma of King Philip II from a maxillofacial surgeon's point of view.

  13. DAMPING THE HIGH ORDER MODES IN THE PUMPING CHAMBER OF THE PEP-II LOW ENERGY RING

    SciTech Connect

    Novokhatski, A

    2004-06-30

    The Low Energy Ring of the PEP-II B-factory operates with extremely high currents of short positron bunches. Any discontinuity in the vacuum chamber can excite a broad-band spectrum of high order modes (HOM). A temperature rise has been found in the vacuum chamber elements in one junction of straight and arc chambers. The power in the wake fields was high enough to char beyond use the feed-through for the titanium sublimation pump (TSP). This pumping section is 5.5 m long and consists of the beam chamber and an ante-chamber. Electromagnetic fields, excited in the beam chamber penetrate to the ante-chamber and then through the heater feed-through come out. To be sure that these electromagnetic fields are present a small ceramic tile with a high loss tangent was placed near the TSP feed-through outside of the pumping chamber. A thermocouple that was attached to this tile showed a strong temperature rise. A short wire antenna was also placed there. The antenna was connected directly to a spectrum analyzer. Measurements show a wide frequency HOM spectrum with a maximum in the 2-3 GHz region. Based on these measurements a special water cooled HOM absorber was designed and installed in the vacuum chamber. As a result, the HOM power in the section decreased and the temperature rise went down. The power loss in the absorber reaches 1200 W for a positron beam current of 2.4 A. The absorber helped to find the source of HOM. Steering the beam on the vertical collimators upstream of the absorber resulted in the significant HOM power change in the absorber.

  14. Stress Fractures

    MedlinePlus

    Stress fractures Overview By Mayo Clinic Staff Stress fractures are tiny cracks in a bone. They're caused by ... up and down or running long distances. Stress fractures can also arise from normal use of a ...

  15. Greenstick Fractures

    MedlinePlus

    Greenstick fractures Overview By Mayo Clinic Staff A greenstick fracture occurs when a bone bends and cracks, instead of breaking completely into separate pieces. The fracture looks similar to what happens when you try ...

  16. Near infra-red emission from a mer-Ru(II) complex: consequences of strong σ-donation from a neutral, flexible ligand with dual binding modes.

    PubMed

    Pal, Amlan K; Zaccheroni, Nelsi; Campagna, Sebastiano; Hanan, Garry S

    2014-07-04

    A rare example of dual coordination modes by a novel tridentate ligand gives rise to unique fac-and mer-Ru((II/III)) complexes. The mer-Ru(II)-complex displays the farthest red-shift of a triplet metal-to-ligand charge transfer ((3)MLCT) emission with a tridentate ligand for a mononuclear complex. This observation is a consequence of large bite angle and strong σ-donation by the ligand, the combined effect of which helps to separate the energy of the (3)MLCT and (3)MC states.

  17. Effets de l'humidite sur la propagation du delaminage dans un composite carbone/epoxy sollicite en mode mixte I/II

    NASA Astrophysics Data System (ADS)

    LeBlanc, Luc R.

    Les materiaux composites sont de plus en plus utilises dans des domaines tels que l'aerospatiale, les voitures a hautes performances et les equipements sportifs, pour en nommer quelques-uns. Des etudes ont demontre qu'une exposition a l'humidite nuit a la resistance des composites en favorisant l'initiation et la propagation du delaminage. De ces etudes, tres peu traitent de l'effet de l'humidite sur l'initiation du delaminage en mode mixte I/II et aucune ne traite des effets de l'humidite sur le taux de propagation du delaminage en mode mixte I/II dans un composite. La premiere partie de cette these consiste a determiner les effets de l'humidite sur la propagation du delaminage lors d'une sollicitation en mode mixte I/II. Des eprouvettes d'un composite unidirectionnel de carbone/epoxy (G40-800/5276-1) ont ete immergees dans un bain d'eau distillee a 70°C jusqu'a leur saturation. Des essais experimentaux quasi-statiques avec des chargements d'une gamme de mixites des modes I/II (0%, 25%, 50%, 75% et 100%) ont ete executes pour determiner les effets de l'humidite sur la resistance au delaminage du composite. Des essais de fatigue ont ete realises, avec la meme gamme de mixite des modes I/II, pour determiner 1'effet de 1'humidite sur l'initiation et sur le taux de propagation du delaminage. Les resultats des essais en chargement quasi-statique ont demontre que l'humidite reduit la resistance au delaminage d'un composite carbone/epoxy pour toute la gamme des mixites des modes I/II, sauf pour le mode I ou la resistance au delaminage augmente apres une exposition a l'humidite. Pour les chargements en fatigue, l'humidite a pour effet d'accelerer l'initiation du delaminage et d'augmenter le taux de propagation pour toutes les mixites des modes I/II. Les donnees experimentales recueillies ont ete utilisees pour determiner lesquels des criteres de delaminage en statique et des modeles de taux de propagation du delaminage en fatigue en mode mixte I/II proposes dans la

  18. Experimental and simulation predicted crack paths for al-2024-t351 under mixed-mode i/ii fatigue loading using an arcan fixture

    NASA Astrophysics Data System (ADS)

    Miller, Eileen

    Mixed mode I/II fatigue experiments and simulations are performed for an Arcan fixture and a 6.35mm thick Al-2024-T351 specimen. Experiments were performed for Arcan loading angles that gave rise to a range of Mode I/II crack tip conditions from 0 ¡U ¦¤KII/¦¤KI ¡U ¡TH. Measurements include the crack paths, loading cycles and maximum and minimum loads for each loading angle. Simulations were performed using three-dimensional finite element analysis (3D-FEA) with 10-noded tetrahedral elements via CRACK3D. While modeling the entire fixture-specimen geometry, a modified version of VCCT with automatic crack tip re-meshing and a maximum normal stress criterion were used to predict the direction of crack growth. Results indicate excellent agreement between experiments and simulations for the measured crack paths during the first several millimeters of crack extension.

  19. Molecular interactions of DNA-topoisomerase I and II inhibitor with DNA and topoisomerases and in ternary complexes: binding modes and biological effects for intoplicine derivatives.

    PubMed

    Nabiev, I; Chourpa, I; Riou, J F; Nguyen, C H; Lavelle, F; Manfait, M

    1994-08-02

    Molecular interactions of intoplicine, dual DNA-topoisomerases (Topo) I and II inhibitor, with topoisomerases, plasmid DNA, in ternary cleavable complexes with enzymes and plasmid DNA, and in the reversed cleavable complexes were examined by means of surface-enhanced Raman scattering (SERS) and CD spectroscopy and by biochemical techniques. Detailed spectral analysis of intoplicine derivatives allowed us to assign SERS vibrational modes of chromophores and to propose the models for these complexes. Intoplicine was found to be able to interact specifically with the Topo II alone, but with Topo I only when in the presence of DNA. It shows at least two modes of binding to the DNA: the first was found to be dominant for its derivative 1c (most potent Topo I inhibitor), and the second was dominant for derivative 2a (most potent Topo II inhibitor). The possibility of forming these two types of complexes simultaneously is suggested to be one of the main factors enabling the drug to be a dual Topo I and Topo II inhibitor. The "deep intercalation mode" of the drug from the DNA minor groove with the long axis of the chromophore oriented roughly parallel to the dyad axis has been suggested to be responsible for induction of distortions of the DNA structure by the intercalating drug. Being involved in the formation of Topo I-mediated cleavable ternary complex, the molecules participating in the deep intercalation mode within the DNA do not change their molecular interactions as compared with their complex with the DNA alone. The stabilization of the Topo I-mediated cleavable complex was shown to be followed by the local denaturation of DNA in the AT-rich regions of the helix. When the ternary cleavable complex was reversed, the drug was shown to be in the complex with the plasmid. The "outside binding mode" from the DNA major groove via the hydroxyl group of the A-ring of the chromophore has been suggested to be responsible for Topo II inhibition. These molecules did not

  20. Temporary fusionless posterior occipitocervical fixation for a proximal junctional type II odontoid fracture after previous C2-pelvis fusion: case report, description of a new surgical technique, and review of the literature.

    PubMed

    Theologis, Alexander A; Deviren, Vedat; Tay, Bobby

    2017-05-01

    Axial fractures in patients with a previous C2-pelvis posterior instrumented fusion are rare and may be challenging to manage. Motion preservation in the axial spine for these patients is important, as the C1-2 and Occipit-C1 joints are their only remaining mobile spinal segments. In this unique report, we present for the first time the use of a fusionless occipitocervical operation for the treatment of a type II odontoid fracture and unilateral C2 pars fracture adjacent to a previous C2-pelvis posterior instrumented fusion. Case report. Three years after proximal extension of a T3-pelvis posterior instrumented fusion to C2, the patient sustained a displaced odontoid fracture and unilateral C2 pars fracture after a mechanical fall. She underwent fracture stabilization with extension of instrumentation to the occiput. No attempt at fusion was performed. Post-operatively, she was distraught by severely limited neck range of motion, which was reflected in worsening of health-related quality of life (HRQoL) scores. The fracture healed uneventfully after which the instrumentation from the occiput and C1 were removed, which resulted in improvement of neck range of motion. Two years post-operatively, HRQoL scores showed minimal neck disability (NDI 12), no neck or arm pain (VAS 0), and outstanding general health (EQ-5D 85 out of 100, SF-36 PCS 35.3, SF-36 MCS 41.1). In this one patient, instrumentation without fusion allowed for successful and timely union of a displaced odontoid fracture in a patient with a previous C2-pelvis fusion. Axial range of motion was preserved after instrumentation removal.

  1. Crack path determination for non-proportional mixed-mode fatigue

    NASA Astrophysics Data System (ADS)

    Highsmith, Shelby, Jr.

    Turbine engine components such as fan and compressor blades experience complex combinations of steady and vibratory loads that lead to in-service cracking in directions that cannot be predicted by current fracture criteria. Accurate crack path predictions are required in order to characterize the risk and extent of damage resulting from liberation of a fractured ligament from rotating components. Under proportional in-phase mixed Mode I/Mode II loading conditions, crack growth direction has been observed in some materials to shift from tensile-dominated Mode I to shear-dominated Mode II or mixed-mode crack growth at higher proportions of initial Mode II loading, but non-proportional loads are not well-characterized. An extensive database of crack growth direction under non-proportional 2-D mixed-mode loading conditions is required to expand crack path prediction models, which are likely to vary between alloys. An approach based on linear elastic fracture mechanics (LEFM) is desired in order to implement the model in crack growth software such as the boundary element-based fracture analysis package FRANC3D. A novel specimen configuration has been designed and analyzed for generation of wide ranges of mixed-mode loading conditions in a single test. This specimen and a more conventional thin-walled tubular specimen have been used to test polycrystalline nickel-base superalloy Inconel 718 under proportional in-phase and 3 kinds of non-proportional fatigue loading. Stress intensity factors for the various configurations have been analyzed with FRANC3D. Modal transition from Mode I (tensile) to Mode II (shear) crack branching has been observed in several load cases. Qualitative microscopy of fracture surfaces was used to characterize the crack growth behavior. An LEFM approach based on an effective stress intensity factor range, which incorporates the maximum value and range of each appropriate stress intensity (Mode I or Mode II), has been used to successfully predict

  2. Improving the accuracy of derivation of the Williams’ series parameters under mixed (I+II) mode loading by compensation of measurement bias in the stress field components data

    NASA Astrophysics Data System (ADS)

    Lychak, Oleh V.; Holyns'kiy, Ivan S.

    2016-12-01

    A new method for compensation of bias in the stress field components measurement data used for Williams’ series parameters derivation was presented. Essential increase of accuracy of derivation of SIF-related leading terms in series under mixed (I+II) mode loading was demonstrated. It was shown that a relatively low value of bias in the stress field components data error could result in the essential deviation of the values of derived Williams’ coefficients and the crack tip coordinates.

  3. Fracture Mechanisms of Layer-By-Layer Polyurethane/Poly(Acrylic Acid) Nanocomposite

    NASA Astrophysics Data System (ADS)

    Kheng, Eugene R.

    A layer-by-layer(LBL) manufactured material is examined in detail in this thesis. Improvements are made to the method of its manufacture. Efforts are made to understand its fracture mechanisms and take advantage of these fracture mechanisms in the absorption of impact energy. A novel series of experiments has been performed on LBL manufactured thin films to demonstrate their unique fracture mechanisms. Polyurethane/Poly(Acrylic Acid) (PU/PAA) and PU/PAA/(PU/Clay)5 nanocomposite films readily undergo Interlaminar mode II fracture, because of the relatively weak elctrostatic bonds between monolayers. Tensile tests performed while under observation by a scanning electron microscope demonstrate the tendency of these nanocomposite films to undergo interlaminar mode II fracture even when loads are applied in the plane of nanocomposite film. It is concluded that these mechanisms of energy dissipation are responsible for the enhanced toughness of these films when used as layers between glass blocks in the prevention of impact damage to the glass. A novel automated manufacturing facility has been designed and built to deposit large sheets of Layer-by-Layer nanocomposite film. These large sheets are incorporated into a borosillicate glass composite in order to compare the ballistic characteristics of LBL PU based nanocomposite films to a single cast layer of polyurethane. It is demonstrated that shear fracture is the mode of failure in the blocks containing the nanocomposite film. The shear fracture surface in the nanocomposite after it has undergone a ballistic impact is characterized. Additional experiments are performed to characterize the interlaminar fracture stresses and toughnesses of the nanocomposite LBL layers, to assist in the implementation of a numerical crack band model that describes the nanocomposite film. The computational model predicts the failure of the ballistic nanocomposite samples, and the predicted V50 velocity is found to be in good agreement with

  4. A theoretical analysis of the coordination modes of CuII with penicillins: activation of the beta-lactam C-N bond.

    PubMed

    Campomanes, Pablo; Menéndez, M Isabel; López, Ramón; Sordo, Tomás L

    2005-02-01

    The interaction of CuII with 6-formylamino-3alpha-carboxypenam and 6-acetylamino-3alpha-carboxypenam was investigated by means of DFT calculations with the UB3LYP functional. Nine different modes of complexation between CuII and 6-formylamino-3alpha-carboxypenam were located. When two water molecules directly bonded to CuII are included in the calculations on 6-acetylamino-3alpha-carboxypenam as penicillin model, only six CuII(H2O)2-6-acetylamino-3alpha-carboxypenam complexes (1S-6S) are found. In solution the four most stable complexes obtained from our calculations, 6S, 1S, 2S, and 3S, exhibit CuII in square-planar coordination with at least one bond to the carboxylate group, in agreement with experimental evidence. Complexes 6S, 1S, and 3S were previously suggested by available experimental evidence. In three of the most stable complexes (6S, 2S, and 3S) the beta-lactam C-N bond is remarkably activated and displays C-N bond lengths similar to those found in some tetrahedral intermediates located for the hydrolysis of 2-azetidinones. This suggests that these kinds of complexes belong to the reaction coordinate for the degradation of beta-lactam antibiotics in the presence of CuII.

  5. The fracture behaviour of dental enamel.

    PubMed

    Bechtle, Sabine; Habelitz, Stefan; Klocke, Arndt; Fett, Theo; Schneider, Gerold A

    2010-01-01

    Enamel is the hardest tissue in the human body covering the crowns of teeth. Whereas the underlying dental material dentin is very well characterized in terms of mechanical and fracture properties, available data for enamel are quite limited and are apart from the most recent investigation mainly based on indentation studies. Within the current study, stable crack-growth experiments in bovine enamel have been performed, to measure fracture resistance curves for enamel. Single edge notched bending specimens (SENB) prepared out of bovine incisors were tested in 3-point bending and subsequently analysed using optical and environmental scanning electron microscopy. Cracks propagated primarily within the protein-rich rod sheaths and crack propagation occurred under an inclined angle to initial notch direction not only due to enamel rod and hydroxyapatite crystallite orientation but potentially also due to protein shearing. Determined mode I fracture resistance curves ranged from 0.8-1.5 MPa*m(1/2) at the beginning of crack propagation up to 4.4 MPa*m(1/2) at 500 microm crack extension; corresponding mode II values ranged from 0.3 to 1.5 MPa*m(1/2).

  6. A Dual-Signaling Ferrocene-Pyrene Dyad: Triple-Mode Recognition of the Cu(II) Ions in Aqueous Medium.

    PubMed

    Wani, Manzoor Ahmad; Pandey, Mrituanjay D; Pandey, Rampal; Maurya, Sandeep Kumar; Goswami, Debabrata

    2017-08-24

    We report a structure of ferrocene-pyrene conjugate (1) comprising electro and photo-active dual-signaling units. In particular, 1 upon interaction with Cu(II), displays selectively one-photon fluorescence quenching, but it shows two-photon absorption (TPA) cross-section 1230 GM (at 780 nm). Further, 1 displayed two irreversible oxidative waves at 0.39 V and 0.80 V (vs Ag/AgCl), in the electrochemical analysis which upon addition of Cu(2+), led to the negative potential shift in both the oxidative waves to appear at 0.25 V and 0.68 V. The triple mode changes in presence of Cu(II) suggesting the possible application of 1 for the detection of Cu(II) in aqueous media. Graphical Abstract.

  7. New insulinomimetic zinc(II) complexes of alpha-amino acids and their derivatives with Zn(N2O2) coordination mode.

    PubMed

    Yoshikawa, Y; Ueda, E; Suzuki, Y; Yanagihara, N; Sakurai, H; Kojima, Y

    2001-05-01

    Zinc(II) complexes of alpha-amino acids and their derivatives with a Zn(N2O2) coordination mode were found to have in vitro insulinomimetic activity as estimated with the inhibition of free fatty acid release in isolated rat adipocytes treated with epinephrine. It was revealed that the insulinomimetic activities of zinc(II) complexes with over-all stability constants (log beta) less than 10.5 are higher than those of ZnSO4 and VOSO4. The high blood glucose level of KK-Ay mice with type 2 diabetes mellitus was lowered by daily intraperitoneal injections of a zinc(II) complex, cis-[Zn(L-Thr)2(H2O)2], for 14 d. The improvement of diabetes mellitus was confirmed with the oral glucose tolerance test.

  8. Crustal magnetization and accretion at the Southwest Indian Ridge near the Atlantis II fracture zone, 0-25 Ma

    USGS Publications Warehouse

    Hosford, A.; Tivey, M.; Matsumoto, T.; Dick, H.; Schouten, Hans; Kinoshita, H.

    2003-01-01

    We analyze geophysical data that extend from 0 to 25-Myr-old seafloor on both flanks of the Southwest Indian Ridge (SWIR). Lineated marine magnetic anomalies are consistent and identifiable within the study area, even over seafloor lacking a basaltic upper crust. The full spreading rate of 14 km/Myr has remained nearly constant since at least 20 Ma, but crustal accretion has been highly asymmetric, with half rates of 8.5 and 5.5 km/Myr on the Antarctic and African flanks, respectively. This asymmetry may be unique to a ???400 km wide corridor between large-offset fracture zones of the SWIR. In contrast to the Mid-Atlantic Ridge, crustal magnetization amplitudes correlate directly with seafloor topography along the present-day rift valleys. This pattern appears to be primarily a function of along-axis variations in crustal thickness, rather than magnetic mineralogy. Off-axis, magnetization amplitudes at paleo-segment ends are more positive than at paleo-segment midpoints, suggesting the presence of an induced component of magnetization within the lower crust or serpentinized upper mantle. Alteration of the magnetic source layer at paleo-segment midpoints reduces magnetization amplitudes by 70-80% within 20 Myr of accretion. Magnetic and Ocean Drilling Program (ODP) Hole 735B data suggest that the lower crust cooled quickly enough to lock in a primary thermoremanent magnetization that is in phase with that of the overlying upper crust. Thus magnetic polarity boundaries within the intrusive lower crust may be steeper than envisioned in prior models of ocean crustal magnetization. As the crust ages, the lower crust becomes increasingly important in preserving marine magnetic stripes.

  9. Rock fracture processes in chemically reactive environments

    NASA Astrophysics Data System (ADS)

    Eichhubl, P.

    2015-12-01

    Rock fracture is traditionally viewed as a brittle process involving damage nucleation and growth in a zone ahead of a larger fracture, resulting in fracture propagation once a threshold loading stress is exceeded. It is now increasingly recognized that coupled chemical-mechanical processes influence fracture growth in wide range of subsurface conditions that include igneous, metamorphic, and geothermal systems, and diagenetically reactive sedimentary systems with possible applications to hydrocarbon extraction and CO2 sequestration. Fracture processes aided or driven by chemical change can affect the onset of fracture, fracture shape and branching characteristics, and fracture network geometry, thus influencing mechanical strength and flow properties of rock systems. We are investigating two fundamental modes of chemical-mechanical interactions associated with fracture growth: 1. Fracture propagation may be aided by chemical dissolution or hydration reactions at the fracture tip allowing fracture propagation under subcritical stress loading conditions. We are evaluating effects of environmental conditions on critical (fracture toughness KIc) and subcritical (subcritical index) fracture properties using double torsion fracture mechanics tests on shale and sandstone. Depending on rock composition, the presence of reactive aqueous fluids can increase or decrease KIc and/or subcritical index. 2. Fracture may be concurrent with distributed dissolution-precipitation reactions in the hostrock beyond the immediate vicinity of the fracture tip. Reconstructing the fracture opening history recorded in crack-seal fracture cement of deeply buried sandstone we find that fracture length growth and fracture opening can be decoupled, with a phase of initial length growth followed by a phase of dominant fracture opening. This suggests that mechanical crack-tip failure processes, possibly aided by chemical crack-tip weakening, and distributed

  10. In-Situ Study of the Tensile Deformation and Fracture Modes in Peak-Aged Cast Mg-11Y-5Gd-2Zn-0.5Zr (Weight Percent)

    NASA Astrophysics Data System (ADS)

    Yin, D. D.; Wang, Q. D.; Boehlert, C. J.; Chen, Z.; Li, H. M.; Mishra, R. K.; Chakkedath, A.

    2016-12-01

    Tensile deformation and fracture modes in peak-aged cast Mg-11Y-5Gd-2Zn-0.5Zr (wt pct) (WGZ1152) samples at temperatures between 298 K [25 °C, room temperature (RT)] and 623 K (350 °C) (0.33 to 0.69 T m) were studied in situ inside a scanning electron microscope (SEM) using electron backscatter diffraction (EBSD) and slip trace analysis. The ultimate tensile strength (UTS) (265 MPa) and yield strength (YS) (193 MPa) at 523 K (250 °C) were 91 and 80 pct of those at RT, respectively. The observed dominant slip mode transitioned from basal slip (100 pct) to basal slip (81 pct) combined with prismatic slip (12 pct) from RT to 473 K (200 °C). As the temperature increased to 623 K (350 °C), basal slip (67 pct) and pyramidal slip (25 pct) became the dominant slip modes. The estimated critical resolved shear stress (CRSS) ratio of pyramidal slip/basal slip (7.3) was lower than that of prismatic slip/basal slip (12.7) at temperatures above 573 K (300 °C). Prismatic slip and pyramidal slip were more active at higher strains for moderate temperatures [473 K to 523 K (200 °C to 250 °C)] and at high temperatures [573 K to 623 K (300 °C to 350 °C)], respectively. A transition in the dominant fracture mode occurred from transgranular cracking (40 pct) combined with intergranular cracking (60 pct) to intergranular cracking as temperatures increased from RT to 623 K (350 °C). The intergranular crack nucleation sites tended to be located at grain boundaries and the interface between the Mg matrix and the large intermetallic grain boundary X phase. Slip bands were associated with transgranular crack nucleation.

  11. Effect of fracture surface interference on shear crack growth

    SciTech Connect

    Gross, T.S.; Watt, D.W. . Dept. of Mechanical Engineerng); Mendelsohn, D.A. . Dept. of Engineering Mechanics)

    1992-02-01

    A joint analytical-experiment program to investigate the effect of fracture surface interference on shear modes of crack growth is progressing satisfactorily. A general two-dimensional, boundary element model has been formulated by the group at Ohio State University that is capable of calculating the effective Mode I and Mode II stress intensity factors for flat or curved cracks with small scale yielding. The model can calculate K{sub I} and K{sub II} for an arbitrary constitutive law for displacement of the crack faces. The constitutive law proposed in our earlier work is being used in the new boundary element model. The experimental portion of the effort at UNH was to use an as-yet undeveloped electro-optic holographic interferometry (EOH) system to measure the crack face displacement field while the crack is loaded in shear. The algorithms for obtaining the interferograms have been developed, the testing machine modifications necessary for interferometric measurements are complete, and interferograms of specimens under load have been obtained. Techniques for digitizing the fracture surface profile have been developed and preliminary numerical experiments have been conducted to determine the {Delta}K dependence of fracture asperity interference on an actual crack.

  12. Fracture strength of teeth restored with ceramic inlays and overlays.

    PubMed

    Morimoto, Susana; Vieira, Glauco Fioranelli; Agra, Carlos Martins; Sesma, Newton; Gil, Carlos

    2009-01-01

    This study evaluated the fracture strength of teeth restored with bonded ceramic inlays and overlays compared to sound teeth. Thirty sound human maxillary premolars were assigned to 3 groups: 1- sound/unprepared (control); 2- inlays and 3- overlays. The inlay cavity design was Class II MOD preparation with an occlusal width of 1/2 of the intercuspal distance. The overlay cavity design was similar to that of the inlay group, except for buccal and palatal cusp coverage The inlay and overlay groups were restored with feldspathic porcelain bonded with adhesive cement. The specimens were subjected to a compressive load until fracture. Data were analyzed statistically by the Kruskal-Wallis test at 5% significance level. The fracture strength means (KN) were: Sound/unprepared group = 1.17, Inlay group= 1.17, and Overlay group = 1.14. There were no statistically significant differences (p>0.05) among the groups. For inlays and overlays, the predominant fracture mode involved fragments of one cusp (70% of simple fractures). The fracture strength of teeth restored with inlay and overlay ceramics with cusp coverage was similar to that of intact teeth.

  13. Potential-based and non-potential-based cohesive zone formulations under mixed-mode separation and over-closure-Part II: Finite element applications

    NASA Astrophysics Data System (ADS)

    Máirtín, Éamonn Ó.; Parry, Guillaume; Beltz, Glenn E.; McGarry, J. Patrick

    2014-02-01

    This paper, the second of two parts, presents three novel finite element case studies to demonstrate the importance of normal-tangential coupling in cohesive zone models (CZMs) for the prediction of mixed-mode interface debonding. Specifically, four new CZMs proposed in Part I of this study are implemented, namely the potential-based MP model and the non-potential-based NP1, NP2 and SMC models. For comparison, simulations are also performed for the well established potential-based Xu-Needleman (XN) model and the non-potential-based model of van den Bosch, Schreurs and Geers (BSG model). Case study 1: Debonding and rebonding of a biological cell from a cyclically deforming silicone substrate is simulated when the mode II work of separation is higher than the mode I work of separation at the cell-substrate interface. An active formulation for the contractility and remodelling of the cell cytoskeleton is implemented. It is demonstrated that when the XN potential function is used at the cell-substrate interface repulsive normal tractions are computed, preventing rebonding of significant regions of the cell to the substrate. In contrast, the proposed MP potential function at the cell-substrate interface results in negligible repulsive normal tractions, allowing for the prediction of experimentally observed patterns of cell cytoskeletal remodelling. Case study 2: Buckling of a coating from the compressive surface of a stent is simulated. It is demonstrated that during expansion of the stent the coating is initially compressed into the stent surface, while simultaneously undergoing tangential (shear) tractions at the coating-stent interface. It is demonstrated that when either the proposed NP1 or NP2 model is implemented at the stent-coating interface mixed-mode over-closure is correctly penalised. Further expansion of the stent results in the prediction of significant buckling of the coating from the stent surface, as observed experimentally. In contrast, the BSG model

  14. The onset of mixed-mode intralaminar cracking in a cross-ply composite laminate

    NASA Astrophysics Data System (ADS)

    Andersons, J.; Spārniņš, E.; Joffe, R.

    2008-12-01

    The intralaminar fracture toughness of a unidirectionally reinforced glass/epoxy composite is determined experimentally at several mode I and mode II loading ratios. The crack propagation criterion, expressed as a quadratic form in terms of single-mode stress intensity factors (alternatively, linear in terms of energy release rates), approximates the test results reasonably well. The mixed-mode cracking criterion obtained is used to predict the intralaminar crack on set in a cross-ply glass/epoxy composite under off-axis tensile loading.

  15. Experimental study of stable imbibition displacements in a model open fracture. II. Scale-dependent avalanche dynamics.

    PubMed

    Clotet, Xavier; Santucci, Stéphane; Ortín, Jordi

    2016-01-01

    We report the results of an experimental investigation of the spatiotemporal dynamics of stable imbibition fronts in a disordered medium, in the regime of capillary disorder, for a wide range of experimental conditions. We have used silicone oils of various viscosities μ and nearly identical oil-air surface tension, and forced them to slowly invade a model open fracture at very different flow rates v. In this second part of the study we have carried out a scale-dependent statistical analysis of the front dynamics. We have specifically analyzed the influence of μ and v on the statistical properties of the velocity V_{ℓ}, the spatial average of the local front velocities over a window of lateral size ℓ. We have varied ℓ from the local scale defined by our spatial resolution up to the lateral system size L. Even though the imposed flow rate is constant, the signals V_{ℓ}(t) present very strong fluctuations which evolve systematically with the parameters μ, v, and ℓ. We have verified that the non-Gaussian fluctuations of the global velocity V_{ℓ}(t) are very well described by a generalized Gumbel statistics. The asymmetric shape and the exponential tail of those distributions are controlled by the number of effective degrees of freedom of the imbibition fronts, given by N_{eff}=ℓ/ℓ_{c} (the ratio of the lateral size of the measuring window ℓ to the correlation length ℓ_{c}∼1/sqrt[μv]). The large correlated excursions of V_{ℓ}(t) correspond to global avalanches, which reflect extra displacements of the imbibition fronts. We show that global avalanches are power-law distributed, both in sizes and durations, with robustly defined exponents-independent of μ, v, and ℓ. Nevertheless, the exponential upper cutoffs of the distributions evolve systematically with those parameters. We have found, moreover, that maximum sizes ξ_{S} and maximum durations ξ_{T} of global avalanches are not controlled by the same mechanism. While ξ_{S} are also

  16. Experimental study of stable imbibition displacements in a model open fracture. II. Scale-dependent avalanche dynamics

    NASA Astrophysics Data System (ADS)

    Clotet, Xavier; Santucci, Stéphane; Ortín, Jordi

    2016-01-01

    We report the results of an experimental investigation of the spatiotemporal dynamics of stable imbibition fronts in a disordered medium, in the regime of capillary disorder, for a wide range of experimental conditions. We have used silicone oils of various viscosities μ and nearly identical oil-air surface tension, and forced them to slowly invade a model open fracture at very different flow rates v . In this second part of the study we have carried out a scale-dependent statistical analysis of the front dynamics. We have specifically analyzed the influence of μ and v on the statistical properties of the velocity Vℓ, the spatial average of the local front velocities over a window of lateral size ℓ . We have varied ℓ from the local scale defined by our spatial resolution up to the lateral system size L . Even though the imposed flow rate is constant, the signals Vℓ(t ) present very strong fluctuations which evolve systematically with the parameters μ , v , and ℓ . We have verified that the non-Gaussian fluctuations of the global velocity Vℓ(t ) are very well described by a generalized Gumbel statistics. The asymmetric shape and the exponential tail of those distributions are controlled by the number of effective degrees of freedom of the imbibition fronts, given by Neff=ℓ /ℓc (the ratio of the lateral size of the measuring window ℓ to the correlation length ℓc˜1 /√{μ v } ). The large correlated excursions of Vℓ(t ) correspond to global avalanches, which reflect extra displacements of the imbibition fronts. We show that global avalanches are power-law distributed, both in sizes and durations, with robustly defined exponents—independent of μ , v , and ℓ . Nevertheless, the exponential upper cutoffs of the distributions evolve systematically with those parameters. We have found, moreover, that maximum sizes ξS and maximum durations ξT of global avalanches are not controlled by the same mechanism. While ξS are also determined by

  17. Application of the Pegasus II Pulsed-Power Facility to the Study of Inertial Instability and Fracture of Cylindrical Tubes of Solid Aluminum

    SciTech Connect

    Chandler, E.A.; Stokes, J.; Fulton, R.D.; Morgan, D.V.; Obst, A.W.; Oro, D.M.; Oona, H.; Anderson, W.E.

    1999-06-23

    Understanding the surface stability of metals undergoing dynamic fracture at shock breakout is important to several applications in metals processing. The advantages of using the Pegasus II facility to investigate the phenomena occurring at shock break out are described. As an example of the data collected, we concentrate on brief descriptions of two experiments that compared the tensile failure, i.e. ''spall'', patterns in the presence of sinusoidal perturbations seeded on the free inner surface of cylindrical samples of 3 types of Al. These samples were composed variously of soft Al 1100-O, structural grade Al 6061-T6, and ultra-pure 99.99% Al and were subjected to Taylor waves with shock pressures of 14 GPa. We show that the material behind the exiting surface undergoes a type of failure termed here ''microspall'', resulting in the production of a significant volume of low-density, probably granular, material. The failure mechanism, combined with the forces that cause inertial instability, leads to rapid pattern growth in the failed material and subsequent pattern growth on the surface. Pattern growth was studied as a function of perturbation wavelength and amplitude. The different Al samples vary by an order of magnitude in yield strength, and some increase in pattern instability was observed at lower yield strength. The ultra-pure Al has exceptionally large grain size, in the mm range. No appreciable variation of spall pattern was observed due to grain size.

  18. Different modes of anthracycline interaction with topoisomerase II. Separate structures critical for DNA-cleavage, and for overcoming topoisomerase II-related drug resistance.

    PubMed

    Jensen, P B; Sørensen, B S; Sehested, M; Demant, E J; Kjeldsen, E; Friche, E; Hansen, H H

    1993-05-25

    In contrast to the classic anthracyclines (doxorubicin and daunorubicin), aclarubicin (ACLA) does not stimulate topoisomerase II (topo II) mediated DNA-cleavage. This distinction may be important with respect to topo II-related drug resistance, and the aim of this study was to clarify drug-structures responsible for this difference. Various ACLA analogs were tested for: (a) interaction with purified topo II, (b) induction of DNA cleavage in cells, (c) cellular uptake and (d) cytotoxicity. A remarkable distinction was seen between analogs containing the chromophore aklavinone (AKV) (e.g. ACLA) which have a carboxymethyl group (COOCH3) at C-10 and drugs with a beta-rhodomycinone (RMN) chromophore with hydroxyl groups at C-10 and at C-11. Thus, RMN-containing analogs, including the aglycone RMN itself, effectively stimulated topo II-mediated DNA cleavage. In contrast, AKV-containing drugs inhibited DNA cleavage and antagonized cytotoxicity mediated by RMN-containing drugs. In OC-NYH/VM cells, exhibiting multidrug resistance due to an altered topo II phenotype (at-MDR), cross-resistance was only seen to the RMN-containing drugs whereas no cross-resistance was seen to the non-DNA cleaving AKV-containing compounds. Thus, our data show that one domain in the anthracycline is of particular importance for the interaction with topo II, namely the positions C-10 and C-11 in the chromophore, and further that at-MDR was circumvented by a COOCH3 substitution at position C-10. These findings may provide guidance for the synthesis and development of new analogs with activity in at-MDR cells.

  19. Numerical investigations with a hybrid isentropic-sigma model. I - Normal-mode characteristics. II - The inclusion of moist processes

    NASA Technical Reports Server (NTRS)

    Pierce, R. B.; Johnson, Donald R.; Reames, Fred M.; Zapotocny, Tom H.; Wolf, Bart J.

    1991-01-01

    The normal-mode characteristics of baroclinically amplifying disturbances were numerically investigated in a series of adiabatic simulations by a hybrid isentropic-sigma model, demonstrating the effect of coupling an isentropic-coordinate free atmospheric domain with a sigma-coordinate PBL on the normal-mode characteristics. Next, the normal-mode model was modified by including a transport equation for water vapor and adiabatic heating by condensation. Simulations with and without a hydrological component showed that the overall effect of latent heat release is to markedly enhance cyclogenesis and frontogenesis.

  20. Fracture resistance of endodontically treated maxillary premolars restored with CAD/CAM ceramic inlays.

    PubMed

    Hannig, Christian; Westphal, Christoph; Becker, Klaus; Attin, Thomas

    2005-10-01

    . Mean fracture load +/- SD was recorded as follows: 291.6 +/- 113.7 N for group END, 363.2 +/- 140.3 N for group CER, and 296.5 +/- 170.5 N for group CTR. Regarding fracture modes, significantly more teeth from group END exhibited fractures of type III and II compared with control specimens. Teeth restored with bonded CAD/CAM ceramic inlays (CEREC) fractured with a significantly higher number of severe fractures compared to the control group.

  1. Failure modes and materials design for biomechanical layer structures

    NASA Astrophysics Data System (ADS)

    Deng, Yan

    Ceramic materials are finding increasing usage in the area of biomechanical replacements---dental crowns, hip and bone implants, etc.---where strength, wear resistance, biocompatibility, chemical durability and even aesthetics are critical issues. Aesthetic ceramic crowns have been widely used in dentistry to replace damaged or missing teeth. However, the failure rates of ceramic crowns, especially all-ceramic crowns, can be 1%˜6% per year, which is not satisfactory to patients. The materials limitations and underlying fracture mechanisms of these prostheses are not well understood. In this thesis, fundamental fracture and damage mechanisms in model dental bilayer and trilayer structures are studied. Principle failure modes are identified from in situ experimentation and confirmed by fracture mechanics analysis. In bilayer structures of ceramic/polycarbonate (representative of ceramic crown/dentin structure), three major damage sources are identified: (i) top-surface cone cracks or (ii) quasiplasticity, dominating in thick ceramic bilayers; (iii) bottom-surface radial cracks, dominating in thin ceramic bilayers. Critical load P for each damage mode are measured in six dental ceramics: Y-TZP zirconia, glass-infiltrated zirconia and alumina (InCeram), glass-ceramic (Empress II), Porcelain (Mark II and Empress) bonded to polymer substrates, as a function of ceramic thickness d in the range of 100 mum to 10 mm. P is found independent of d for mode (i) and (ii), but has a d 2 relations for mode (iii)---bottom surface radial cracking. In trilayer structures of glass/core-ceramic/polycarbonate (representing veneer porcelain/core/dentin structures), three inner fracture origins are identified: radial cracks from the bottom surface in the (i) first and (ii) second layers; and (iii) quasiplasticity in core-ceramic layer. The role of relative veneer/core thickness, d1/d 2 and materials properties is investigated for three core materials with different modulus (114--270GPa

  2. Study of NBI-driven chirping mode properties and radial location by the heavy ion beam probe in the TJ-II stellarator

    NASA Astrophysics Data System (ADS)

    Melnikov, A. V.; Eliseev, L. G.; Castejón, F.; Hidalgo, C.; Khabanov, P. O.; Kozachek, A. S.; Krupnik, L. I.; Liniers, M.; Lysenko, S. E.; de Pablos, J. L.; Sharapov, S. E.; Ufimtsev, M. V.; Zenin, V. N.; HIBP Group; TJ-II Team

    2016-11-01

    Alfvén eigenmodes (AEs) were studied in low magnetic shear flexible heliac TJ-II (B 0  =  0.95 T, R 0  =  1.5 m, < a>   =  0.22 m) neutral beam injection (NBI) heated plasmas (P NBI  ⩽  1.1 MW, E NBI  =  32 keV) using the heavy ion beam probe (HIBP). L-mode hydrogen plasmas heated with co-, counter- and balanced-NBI and electron cyclotron resonance heating (ECRH) were investigated in various magnetic configurations with rotational transform ι(a)/2π  =  1/q ~ 1.5-1.6. The HIBP diagnostic is capable of simultaneously measuring the oscillations of the plasma electric potential, density and poloidal magnetic field. In earlier studies chirping modes have been observed with 250 kHz  <  f AE  <  380 kHz in combined ECR and NBI heated plasmas at low density {{\\bar{n}}\\text{e}}   =  (0.3-1.5)  ×  1019 m-3. In this paper we report the observation of chirping modes obtained with NBI only in plasmas with densities similar to those of earlier studies and obtained after lithium evaporation in the vacuum vessel. The absence of ECRH in the discharges studied here shows that ECRH is not a necessary ingredient to obtain chirping modes in TJ-II but rather a tool for obtaining low-density discharges. Using the HIBP we deduce that the location of the AE chirping mode is  -0.8  <  ρ  <  0.8. Chirping modes have a specific spatial structure: electric potential perturbations have a ballooning character, while the density and B pol perturbations are nearly symmetric for both ECRH  +  NBI and NBI-only plasmas. On TJ-II, the dominant effect on the nonlinear evolution of the AE from the chirping state to the steady-frequency state is the magnetic configuration, determined by the vacuum ι and plasma current I pl.

  3. Numerical Modeling of Fracture Propagation in Naturally Fractured Formations

    NASA Astrophysics Data System (ADS)

    Wang, W.; Prodanovic, M.; Olson, J. E.; Schultz, R.

    2015-12-01

    Hydraulic fracturing consists of injecting fluid at high pressure and high flowrate to the wellbore for the purpose of enhancing production by generating a complex fracture network. Both tensile failure and shear failure occur during the hydraulic fracturing treatment. The shear event can be caused by slip on existing weak planes such as faults or natural fractures. From core observation, partially cemented and fully cemented opening mode natural fractures, often with considerable thickness are widely present. Hydraulic fractures can propagate either within the natural fracture (tensile failure) or along the interface between the natural fracture and the rock matrix (tensile/shear failure), depending on the relative strength of cement and rock matrix materials, the bonding strength of interface, as well as the presence of any heterogeneities. In this study, we evaluate the fracture propagation both experimentally and numerically. We embed one or multiple inclusions of different mechanical properties within synthetic hydrostone samples in order to mimic cemented natural fractures and rock. A semi-circular bending test is performed for each set of properties. A finite element model built with ABAQUS is used to mimic the semi-circular bending test and study the fracture propagation path, as well as the matrix-inclusion bonding interface status. Mechanical properties required for the numerical model are measured experimentally. The results indicate that the match between experiment and modeling fracture path are extremely sensitive to the chosen interface (bonding) model and related parameters. The semi-circular bending test is dry and easily conducted, providing a good platform for validating numerical approaches. A validated numerical model will enable us to add pressurized fluid within the crack and simulate hydraulic fracture-natural fracture interaction in the reservoir conditions, ultimately providing insights into the extent of the fracture network.

  4. Physical Investigations of Small Particles: (I) Aerosol Particle Charging and Flux Enhancement and (II) Whispering Gallery Mode Sensing

    NASA Astrophysics Data System (ADS)

    Lopez-Yglesias, Xerxes

    of the molecule and the electromagnetic interaction between the molecule and particle, especially for the neutral particle case, are completely ignored, or, as is often the case for a permanent dipole vapor species, strongly underestimated. Comparing our model to these classical models we determine an "enhancement factor" to characterize how important the addition of these physical parameters and processes is to the understanding of particle nucleation and growth. Part II: Whispering gallery mode (WGM) optical biosensors are capable of extraordinarily sensitive specific and non-specific detection of species suspended in a gas or fluid. Recent experimental results suggest that these devices may attain single-molecule sensitivity to protein solutions in the form of stepwise shifts in their resonance wavelength, lambdaR, but present sensor models predict much smaller steps than were reported. This study examines the physical interaction between a WGM sensor and a molecule adsorbed to its surface, exploring assumptions made in previous efforts to model WGM sensor behavior, and describing computational schemes that model the experiments for which single protein sensitivity was reported. The resulting model is used to simulate sensor performance, within constraints imposed by the limited material property data. On this basis, we conclude that nonlinear optical effects would be needed to attain the reported sensitivity, and that, in the experiments for which extreme sensitivity was reported, a bound protein experiences optical energy fluxes too high for such effects to be ignored.