Fatigue Microdamage in Bovine Trabecular Bone

Microdamage, in the form of small cracks, may accumulate in trabecular bone loaded in fatigue. Specimens of bovine trabecular bone were loaded in compressive fatigue at one of four normalized stresses and loading was stopped after the specimens reached one of six maximum strains. Microdamage was identified using a fluorochrome staining technique, and microdamage parameters, including the number of damaged trabeculae and the damaged area fraction, were measured. No microdamage was observed during loading to strains below the yield strain; at higher strains, all microdamage parameters increased with increasing maximum compressive strain. Few significant differences were observed in the type or amount of microdamage accumulation between specimens loaded to the same maximum strain at different normalized stresses; however, more trabecular fractures were observed at high numbers of cycles, which corresponded to low normalized stresses.

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The Effect of Number of Cycles on Microdamage Accumulation in Bovine Trabecular Bone

10.1115/imece2001/bed-23026 ◽

2001 ◽

Author(s):

Tara L. Arthur Moore ◽

Lorna J. Gibson

Keyword(s):

Trabecular Bone ◽

Bone Remodeling ◽

Low Cycle Fatigue ◽

Cycle Fatigue ◽

Repetitive Motion ◽

Microdamage Accumulation ◽

Lower Load ◽

Small Cracks ◽

Number Of Cycles ◽

Fatigue Microdamage

Abstract Microdamage, in the form of small cracks, exists in healthy bone. Microdamage can be created by an overload or by repetitive motion (fatigue) during daily activities. Usually, microdamage is repaired during bone remodeling and a steady state is maintained. However, in cases of excessive microdamage creation or slowed bone remodeling, microdamage can coalesce to create a fracture. Our previous work [1,2] has investigated microdamage accumulation with increasing strain in bovine trabecular bone loaded in monotonic compression and compressive fatigue. Specimens fatigued at relatively high load levels fail after a few loading cycles, while specimens fatigued at lower load levels may undergo thousands of cycles before failure. During high cycle fatigue, microdamage may accumulate by the growth of pre-existing microcracks, as well as by the crack initiation seen in low cycle fatigue.

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Microdamage Accumulation in Bovine Trabecular Bone in Uniaxial Compression

Journal of Biomechanical Engineering ◽

10.1115/1.1428745 ◽

2001 ◽

Vol 124 (1) ◽

pp. 63-71 ◽

Cited By ~ 76

Author(s):

T. L. Arthur Moore ◽

L. J. Gibson

Keyword(s):

Trabecular Bone ◽

Compressive Strain ◽

Strain Curve ◽

Ultimate Strain ◽

Numerical Density ◽

Average Strain ◽

Stress Strain Curve ◽

Stress Strain ◽

Linear Elastic ◽

Microdamage Accumulation

In this study we investigated how microdamage accumulated with increasing compressive strain in bovine trabecular bone. We found that little damage is created in the linear elastic region, up to −0.4 percent strain. At an average strain of −0.76percent±0.25 percent, the stress-strain curve became nonlinear, and peaked at −1.91 percent±0.55 percent strain. Microdamage increases rapidly during the peak of the stress-strain curve, and a localized band of damage formed. At strains beyond the ultimate strain, the damaged band widened and the density of damage within the band increased. Microdamage occurred as groupings of cracks; the majority of damage occurred as regions of cross-hatching. All microdamage parameters increased with increasing maximum compressive strain. We also observed exponential relationships between crack numerical density and damage 1∘−∘Esec/E0 and between crack length density and damage.

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Modeling of Dynamic Fracture and Damage in Two-Dimensional Trabecular Bone Microstructures Using the Cohesive Finite Element Method

Journal of Biomechanical Engineering ◽

10.1115/1.2903434 ◽

2008 ◽

Vol 130 (2) ◽

Cited By ~ 24

Author(s):

Vikas Tomar

Keyword(s):

Finite Element Method ◽

Finite Element ◽

Trabecular Bone ◽

Bone Tissue ◽

Area Fraction ◽

Trabecular Architecture ◽

Two Dimensional ◽

Fracture Properties ◽

Microdamage Accumulation ◽

2D Space

Trabecular bone fracture is closely related to the trabecular architecture, microdamage accumulation, and bone tissue properties. Micro-finite-element models have been used to investigate the elastic and yield properties of trabecular bone but have only seen limited application in modeling the microstructure dependent fracture of trabecular bone. In this research, dynamic fracture in two-dimensional (2D) micrographs of ovine (sheep) trabecular bone is modeled using the cohesive finite element method. For this purpose, the bone tissue is modeled as an orthotropic material with the cohesive parameters calculated from the experimental fracture properties of the human cortical bone. Crack propagation analyses are carried out in two different 2D orthogonal sections cut from a three-dimensional 8mm diameter cylindrical trabecular bone sample. The two sections differ in microstructural features such as area fraction (ratio of the 2D space occupied by bone tissue to the total 2D space), mean trabecula thickness, and connectivity. Analyses focus on understanding the effect of the rate of loading as well as on how the rate variation interacts with the microstructural features to cause anisotropy in microdamage accumulation and in the fracture resistance. Results are analyzed in terms of the dependence of fracture energy dissipation on the microstructural features as well as in terms of the changes in damage and stresses associated with the bone architecture variation. Besides the obvious dependence of the fracture behavior on the rate of loading, it is found that the microstructure strongly influences the fracture properties. The orthogonal section with lesser area fraction, low connectivity, and higher mean trabecula thickness is more resistant to fracture than the section with high area fraction, high connectivity, and lower mean trabecula thickness. In addition, it is found that the trabecular architecture leads to inhomogeneous distribution of damage, irrespective of the symmetry in the applied loading with the fracture of the entire bone section rapidly progressing to bone fragmentation once the accumulated damage in any trabeculae reaches a critical limit.

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FINDING OF MICRODAMAGE MORPHOLOGY DIFFERENCES IN MOUSE FEMORAL BONES WITH DISTINCT MINERALIZATION LEVELS

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519410003757 ◽

2011 ◽

Vol 11 (02) ◽

pp. 423-432 ◽

Cited By ~ 4

Author(s):

X. NEIL DONG ◽

HUIJIE LENG ◽

QITAO RAN ◽

XIAODU WANG

Keyword(s):

Failure Analysis ◽

Numerical Study ◽

Staining Technique ◽

Pathological Changes ◽

Basic Fuchsin ◽

Four Point Bending ◽

Microdamage Accumulation ◽

Catastrophic Failures ◽

Bone Ultrastructure ◽

Probabilistic Failure Analysis

Microdamage progression in bone is dependent on the ultrastructure of the tissue. Thus, any pathological changes in bone ultrastructure may be reflected in the pattern and capacity of microdamage accumulation. A previous numerical study of microdamage progression in bone using a probabilistic failure analysis approach predicts that the microdamage morphology (either linear microcracks or diffuse damage) is very sensitive to the level of mineralization in bone, which is also implicated in some experimental observations. To examine the prediction, femurs from two strains of mice (C57BL/6J, N = 10 and C3H/HeJ, N = 11) that have distinct mineralization levels were fatigued under four-point bending to create damage in the bone tissues. After testing, the microdamage morphology of the bone samples was examined using bulk-staining technique with basic fuchsin. The results demonstrate that more linear microcracks are observed in femurs of C3H/HeJ (higher mineralization), whereas more diffuse-like damage is found in C57BL/6J femurs (less mineralized). Compared with linear microcracks, the formation of diffuse damage tends to dissipate more energy and help bone to avoid catastrophic failures. Therefore, results from this study may help explain why highly mineralized bone tends to be more brittle. Observations from this study are consistent with the numerical prediction from the previous study, suggesting that mineralization has a significant effect on the microdamage morphology of bone.

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Fracture Mechanics of Architecture Dependent Fracture in Trabecular Bone Using the Cohesive Finite Element Method

ASME 2007 Summer Bioengineering Conference ◽

10.1115/sbc2007-176072 ◽

2007 ◽

Author(s):

Vikas Tomar

Keyword(s):

Finite Element Method ◽

Finite Element ◽

Trabecular Bone ◽

Fracture Behavior ◽

Bone Microstructure ◽

Tissue Properties ◽

Rate Dependent ◽

Microdamage Accumulation ◽

Element Method ◽

Rate Of Loading

Trabecular bone fracture is closely related to the trabecular architecture and microdamage accumulation. Micro-finite element models have been used to investigate the elastic and yield properties of trabecular bone but have only seen limited application in modeling the microstructure dependent fracture of trabecular bone, [1, 2]. In the presented research a cohesive finite element method (CFEM) based approach that can be used to model microstructure and loading rate dependent fracture in trabecular bone is developed for the first time. The emphasis is on understanding the effect of the rate of loading and its correlation with the bone microstructure on the microdamage accumulation and fracture behavior in the trabecular bone. Analyses focus on understanding the effect of the rate of loading, change in bone tissue properties with aging, and their correlation with the bone microstructure on the microdamage accumulation and the fracture behavior in the trabecular bone.

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