Finite Element Modeling of Microcrack Growth in Cortical Bone

2011 ◽  
Vol 78 (4) ◽  
Author(s):  
Susan Mischinski ◽  
Ani Ural
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Elastic Modulus ◽  
Crack Growth ◽  
Line Strength ◽  
Crack Deflection ◽  
Cement Line ◽  
Fracture Properties ◽  
Cement Lines ◽  
Microcrack Growth

Bone is similar to fiber-reinforced composite materials made up of distinct phases such as osteons (fiber), interstitial bone (matrix), and cement lines (matrix-fiber interface). Microstructural features including osteons and cement lines are considered to play an important role in determining the crack growth behavior in cortical bone. The aim of this study is to elucidate possible mechanisms that affect crack penetration into osteons or deflection into cement lines using fracture mechanics-based finite element modeling. Cohesive finite element simulations were performed on two-dimensional models of a single osteon surrounded by a cement line interface and interstitial bone to determine whether the crack propagated into osteons or deflected into cement lines. The simulations investigated the effect of (i) crack orientation with respect to the loading, (ii) fracture toughness and strength of the cement line, (iii) crack length, and (iv) elastic modulus and fracture properties of the osteon with respect to the interstitial bone. The results of the finite element simulations showed that low cement line strength facilitated crack deflection irrespective of the fracture toughness of the cement line. However, low cement line fracture toughness did not guarantee crack deflection if the cement line had high strength. Long cracks required lower cement line strength and fracture toughness to be deflected into cement lines compared with short cracks. The orientation of the crack affected the crack growth trajectory. Changing the fracture properties of the osteon influenced the crack propagation path whereas varying the elastic modulus of the osteon had almost no effect on crack trajectory. The findings of this study present a computational mechanics approach for evaluating microscale fracture mechanisms in bone and provide additional insight into the role of bone microstructure in controlling the microcrack growth trajectory.

scholarly journals Effect of Crack Bridging on the Toughening of Ceramic/Graphene Composites

2018 ◽  
Vol 57 (1) ◽  
pp. 54-62 ◽  
Author(s):  
S.V. Bobylev ◽  
A.G. Sheinerman
Keyword(s):  
Experimental Data ◽  
Fracture Toughness ◽  
Crack Growth ◽  
Crack Deflection ◽  
Yttria Stabilized Zirconia ◽  
Stabilized Zirconia ◽  
Crack Bridging ◽  
The Matrix ◽  
Graphene Content ◽  
Graphene Platelets

Abstract A model is proposed describing the effect of crack bridging on the fracture toughness of ceramic/graphene composites. The dependences of the fracture toughness on the graphene content and the sizes of the graphene platelets are calculated in the exemplary case of yttria stabilized zirconia (YSZ)/graphene composites. The calculations predict that if crack bridging prevails over crack deflection during crack growth, the maximum toughening can be achieved in the case of long graphene platelets provided that the latter do not rupture and adhere well to the matrix. The model shows good correlation with the experimental data at low graphene concentrations.

Geometric Determinants to Cement Line Debonding and Osteonal Lamellae Failure in Osteon Pushout Tests

2004 ◽  
Vol 126 (3) ◽  
pp. 387-390 ◽  
Author(s):  
X. Neil Dong ◽  
X. Edward Guo
Keyword(s):  
Finite Element ◽  
Shear Failure ◽  
Bone Matrix ◽  
Element Model ◽  
Thin Specimen ◽  
Cement Line ◽  
Test Geometry ◽  
Dimensional Finite Element ◽  
Cement Lines ◽  
Secondary Osteons

Cement lines are the boundaries between secondary osteons and the surrounding interstitial bone matrix in cortical bone. The interfacial properties of cement lines have been determined by osteon pushout tests. However, distinctively different material properties were obtained when osteon pushout tests were performed under different test geometries. In the present study, an axisymmetric two-dimensional finite element model was used to simulate an osteon pushout test using the test geometry of actual experiments. The results indicated that shear failure within the osteonal lamellae would occur when the osteon pushout test was performed under the condition of a thick specimen and large supporting hole. On the other hand, cement line debonding occurred when the osteon pushout test was performed using a thin specimen and small supporting hole. The finite element results were consistent with previous experiments of osteon pushout tests under different test geometries. Furthermore, the finite-element results suggest that a smoothly curved punch would most likely cause debonding at the cement line instead of osteonal lamellae.

The Effects of Crack Growth History on Fracture Toughness

2019 ◽  
Author(s):  
M. A. Probert ◽  
H. E. Coules ◽  
C. E. Truman ◽  
M. Hofmann
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Crack Growth ◽  
Parametric Study ◽  
Finite Element Modelling ◽  
Crack Tip ◽  
High Yield ◽  
Element Modelling ◽  
History Effects ◽  
Apparent Fracture Toughness

Abstract The introduction of cracks into loaded versus unloaded components has a significant effect on the apparent fracture toughness within finite element modelling. The history effects of crack introduction can be beneficial to defect assessment procedures that do not consider prior plasticity specifically from crack introduction. It is assumed that as strain energy is released due to plastic deformation during crack formation a reduction in the energy available for crack propagation under fracture conditions is experienced. This can be characterized by the formation of a plastic wake behind the crack tip and leads to significant increases in load at critical J and other crack growth parameters for modelling situations. However experimental evidence validating this apparent fracture toughness increase are needed. A beneficial increase in apparent fracture toughness can prolong the life of components that might be taken out of service prematurely if history effects are not considered. This paper discusses a series of experimental and modelling approaches that have been taken to assess the magnitude of the benefit in increase of apparent fracture toughness by the manipulation of crack introduction history effects. An initial parametric study of material properties on the effect of introducing cracks into loaded and unloaded components indicates that most benefit be derived from high hardness, high yield materials such as Aluminum 7000 series alloys. Further work has been carried out with experimental C(T) specimens of Aluminum Alloy 7475 T7351. Cracks were introduced by fatigue into the samples. One set of specimens was fatigued with a low mean load and the other with a high mean load, this was achieved by keeping a consistent ΔKI between specimens and changing the load ratio one set of specimens. Fracture test results indicate that the influence of prior plasticity on fracture initiation is much subtler in experimental trials than in the finite element model. Crack growth resistance curves and neutron diffraction results measuring the residual stress created ahead of the crack tip by this method are be discussed and contrasted with the parametric study and finite element modelling of the two different crack introduction scenarios.

Crack Growth Behavior of Pipes Made From Polyvinyl Chloride Pipe Material1

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Tarek M. A. A. EL-Bagory ◽  
Maher Y. A. Younan
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Crack Growth ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Crosshead Speed ◽  
Strain Fracture ◽  
Mode Of Failure

The behavior of crack growth of polymeric materials is affected by several operating conditions such as crosshead speed, specimen thickness, load line, and specimen configurations, which reverse the behavior of crack from stable to unstable crack growth behavior. The main objective of the present paper is the determination of plane strain fracture toughness (KIC) for polyvinyl chloride (PVC) used in piping water transmission systems. The dimensions of the PVC pipe are outside diameter, Do = 315 mm, standard dimensions ratio, SDR = 13.23, ratio between outside to inside radii Ro/Ri = 1.179, and pipe thickness, t = 24 mm. Curved specimens are prepared from a pipe by cutting 12 mm thickness ring segments. The curved specimens are divided into two specimen configurations, namely, curved three-point bend (CTPB) and C-shaped tension (CST) specimens. All specimens are provided artificially with a precrack. CTPB specimen is further cut into five 72 deg sectors with each being centrally notched to a depth approximately a = 0.479 of the wall thickness. CST specimen configuration is characterized by the eccentricity X = 0, and 0.5 W, of the loading holes from the bore surface. The linear elastic fracture mechanics theory (LEFM) is used to predict the plane strain fracture. The tests are carried out at room temperature, Ta equal 20 °C, and different crosshead speeds of (10–500 mm/min). The numerical analysis carried out within the frame of the present work is done using the finite element program Cosmos 2.6. Finite element method (FEM) is used to compute the stress intensity factor KQ surrounding the crack tip. The computed stress intensity factor can then be compared with that obtained by theoretical equation. The experimental fracture test results reveal that the crosshead speed has been proven to affect the mode of failure and mode of fracture. At lower crosshead speeds, the mode of failure is ductile, while at higher crosshead speeds, it is brittle. The specimen configuration also affects the fracture toughness. CST specimens show higher fracture toughness in the case of pin loading location X = 0.5W than X = 0 by about (12%). The transitional crosshead speed is affected by specimen geometry. CST specimens (CST) at X = 0 and 0.5W have higher transitional crosshead speed compared with the CTPB specimen configuration.

Effects of Intracortical Porosity on Fracture Toughness in Aging Human Bone: A μCT-Based Cohesive Finite Element Study

2007 ◽  
Vol 129 (5) ◽  
pp. 625-631 ◽  
Author(s):  
Ani Ural ◽  
Deepak Vashishth
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Cortical Bone ◽  
Microcomputed Tomography ◽  
Compact Tension ◽  
Osteoporotic Bone ◽  
Initiation Toughness ◽  
Fracture Properties ◽  
Age Related ◽  
Age Related Changes

The extent to which increased intracortical porosity affects the fracture properties of aging and osteoporotic bone is unknown. Here, we report the development and application of a microcomputed tomography based finite element approach that allows determining the effects of intracortical porosity on bone fracture by blocking all other age-related changes in bone. Previously tested compact tension specimens from human tibiae were scanned using microcomputed tomography and converted to finite element meshes containing three-dimensional cohesive finite elements in the direction of the crack growth. Simulations were run incorporating age-related increase in intracortical porosity but keeping cohesive parameters representing other age-related effects constant. Additional simulations were performed with reduced cohesive parameters. The results showed a 6% decrease in initiation toughness and a 62% decrease in propagation toughness with a 4% increase in porosity. The reduction in toughnesses became even more pronounced when other age-related effects in addition to porosity were introduced. The initiation and propagation toughness decreased by 51% and 83%, respectively, with the combined effect of 4% increase in porosity and decrease in the cohesive properties reflecting other age-related changes in bone. These results show that intracortical porosity is a significant contributor to the fracture toughness of the cortical bone and that the combination of computational modeling with advanced imaging improves the prediction of the fracture properties of the aged and the osteoporotic cortical bone.

Mechanical properties of ion-implanted amorphous silicon

2004 ◽  
Vol 19 (1) ◽  
pp. 338-346 ◽  
Author(s):  
D.M. Follstaedt ◽  
J.A. Knapp ◽  
S.M. Myers
Keyword(s):  
Mechanical Properties ◽  
Phase Transition ◽  
Fracture Toughness ◽  
Finite Element ◽  
Elastic Modulus ◽  
Amorphous Silicon ◽  
Microelectromechanical Systems ◽  
Amorphous Structure ◽  
Alternative Material ◽  
Amorphous Si

We used nanoindentation coupled with finite element modeling to determine the mechanical properties of amorphous Si layers formed by self-ion implantation of crystalline Si at approximately 100 K. When the effects of the harder substrate on the response of the layers to indentation were accounted for, the amorphous phase was found to have a Young’s modulus of 136 ± 9 GPa and a hardness of 10.9 ± 0.9 GPa, which were 19% and 10% lower than the corresponding values for crystalline Si. The hardness agrees well with the pressure known to induce a phase transition in amorphous Si to the denser β–Sn-type structure of Si. This transition controls the yielding of amorphous Si under compressive stress during indentation, just as it does in crystalline Si. After annealing 1 h at 500 °C to relax the amorphous structure, the corresponding values increase slightly to 146 ± 9 GPa and 11.6 ± 1.0 GPa. Because hardness and elastic modulus are only moderately reduced with respect to crystalline Si, amorphous Si may be a useful alternative material for components in Si-based microelectromechanical systems if other improved properties are needed, such as increased fracture toughness.

scholarly journals A comparative study of nano-fillers to improve toughness and modulus of polymer-derived ceramics

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mohammad Mirkhalaf ◽  
Hamidreza Yazdani Sarvestani ◽  
Qi Yang ◽  
Michael B. Jakubinek ◽  
Behnam Ashrafi
Keyword(s):  
Carbon Nanotubes ◽  
Fracture Toughness ◽  
Elastic Modulus ◽  
Thermal Protection ◽  
Crack Deflection ◽  
Protection Device ◽  
Polymer Derived Ceramics ◽  
Technical Ceramics ◽  
Different Shapes ◽  
Micro Indentation

AbstractBrittleness is a major limitation of polymer-derived ceramics (PDCs). Different concentrations of three nanofillers (carbon nanotubes, Si3N4 and Al2O3 nanoparticles) were evaluated to improve both toughness and modulus of a commercial polysilazane (PSZ) PDC. The PSZs were thermally cross-linked and pyrolyzed under isostatic pressure in nitrogen. A combination of mechanical, chemical, density, and microscopy characterizations was used to determine the effects of these fillers. Si3N4 and Al2O3 nanoparticles (that were found to be active fillers) were more effective than nanotubes and improved the elastic modulus, hardness, and fracture toughness (JIC) of the PDC by ~ 1.5 ×, ~ 3 ×, and ~ 2.5 ×, respectively. Nanotubes were also effective in maintaining the integrity of the samples during pyrolysis. The modulus and hardness of PDCs correlated positively with their apparent density; this can provide a fast way to assess future PDCs. The improvement in fracture toughness was attributed to crack deflection and bridging observed in the micro-indentation cracks in the modified PDCs. The specific toughness of the modified PDCs was 4 × higher than that of high-purity alumina, and its specific modulus reached that of commercially available technical ceramics. These PDCs can also easily take different shapes and therefore are of interest in protective armor, propulsion, thermal protection, device packaging and biomaterial systems.

scholarly journals Thermo-mechanical characterization of shale using nanoindentation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yanbo Wang ◽  
Debora Lyn Porter ◽  
Steven E. Naleway ◽  
Pania Newell
Keyword(s):  
Fracture Toughness ◽  
Elastic Modulus ◽  
Elevated Temperature ◽  
Mechanical Response ◽  
Mechanical Performance ◽  
Substantial Impact ◽  
Fracture Properties ◽  
Nano Scale ◽  
Bedding Planes ◽  
Mechanical And Fracture Properties

AbstractShale can be a potential buffer for high-level radioactive nuclear wastes. To be an effective buffer while subject to waste heat, shale's mechanical response at elevated temperature must be known. Many researchers have experimentally characterized the mechanical behavior of various shales at different length scales in adiabatic conditions. However, its mechanical performance at elevated temperatures at the nano-scale remains unknown. To investigate the temperature dependency of nanomechanical properties of shale, we conducted both experimental and numerical studies. In this study, we measured mechanical and fracture properties of shale, such as hardness, elastic modulus, anisotropy, and fracture toughness from 25 °C up to 300 °C at different bedding planes. Statistical analysis of the results suggests that hardness and fracture toughness significantly increased at temperatures from 100 to 300 °C; while, temperature does not have a significant impact on elastic modulus. Data also shows that the bedding plane orientations have a substantial impact on both mechanical and fracture properties of shale at the nano-scale leading to distinct anisotropic behavior at elevated temperature below 100 °C. Additionally, we numerically investigated the mechanical performance of the shale samples at room temperature to gain an insight into its mechanical response through the thickness. Numerical results were validated against the experimental results, confirming the simulation can be used to predict shale deformation at the nano-scale or potentially be used in multi-scale simulations.

Fracture Properties of Ultra-High Strength Cement-Based Materials

2017 ◽  
Vol 726 ◽  
pp. 553-557
Author(s):  
Qing Bi ◽  
Wu Yao
Keyword(s):  
Fracture Toughness ◽  
Elastic Modulus ◽  
Bending Strength ◽  
Strain Energy Release ◽  
High Strength ◽  
Defect Size ◽  
Theoretical Derivation ◽  
Fracture Properties ◽  
Working Stress ◽  
Cement Based Materials

By combining the three-point bending beam test with theoretical derivation, the elastic modulus, fracture toughness, surface energy and the maximum defect size permissible under certain working stress of ultra-high strength cement-based materials were obtained. The fracture properties were studied with the water to binder ratios (W/B) from 0.18 to 0.14. Test results showed that the ultra-high strength cement-based materials are quasi-brittle and the net bending strength of specimen decreased substantially when there was a notch. The elastic modulus of ultra-high strength cement-based materials can be up to 74.0 GPa, obviously higher than that of ordinary cement-based materials, showing greater elastic deformation resistance. Moreover, with decrease of W/B ratio, the compressive strength, fracture toughness, critical strain energy release rate as well as the maximum defect size permissible under certain working stress of ultra-high strength cement-based materials increased significantly, indicating that the anti-cracking ability increased with the decrease of W/B ratio.

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