Fracture accuracy on cortical bone structure under bending load using different numerical methods

doi:10.12307/2024.035

Abstract

Abstract: BACKGROUND: Current fracture simulation for cortical bone structure is mainly based on three numerical methods: the element instantaneous failure, continuum damage mechanics, and extended finite element methods. Although many studies focus on cortical bone fracture simulation, few have compared the differences in prediction accuracy using the three numerical methods.
OBJECTIVE: To probe the accuracy and applicability of the three numerical methods in simulating cortical bone fracture under bending load.
METHODS: The rat femur samples were primarily used to perform the three-point bending experiment. The rat femoral finite element models were established based on the micro-CT images of the femur samples and the three numerical methods were used to conduct the fracture simulations under three-point bending loads. The predicted fracture loads and fracture patterns were compared with the experimental data to determine the accuracy of various numerical methods in simulating cortical bone fracture.
RESULTS AND CONCLUSION: (1) The discernible differences in the failure processes could be observed in the same finite element model under the three numerical simulations due to different element failure strategies. (2) The simulation results showed that the fracture simulation using the continuum damage mechanics method was in better agreement with the experimental results. (3) The numerical method that was suitable for simulating cortical bone fracture under bending load could be determined by comparing it with experimental results. The variations in the fracture parameters were observed, and the reason for the differences in the predicted results using different numerical methods was also discussed, which aided in determining the range of applicability of structural fracture simulation for each numerical method and then improving the simulation accuracy.

Key words: cortical bone, fracture simulation, element instantaneous failure, continuum damage mechanics, extended finite element

CLC Number:

Fan Ruoxun, Liu Jie, Jia Zhengbin. Fracture accuracy on cortical bone structure under bending load using different numerical methods[J]. Chinese Journal of Tissue Engineering Research, 2024, 28(12): 1895-1900.

Figures/Tables 2

通过对比断裂参数可以看出，EIF断裂模拟下，股骨有限元模型发生完全断裂时刻最早，但由于在弹性阶段表观刚度未见下降，其预测所得断裂载荷仍高于CDM仿真所得数值，而且该方法模拟下的断裂时间也明显早于实验结果，但断裂载荷与实验结果差异不大。XFEM模拟得到的断裂时间与实验较为吻合，但断裂载荷却明显大于实验结果。CDM仿真预测结果无论断裂时刻还是断裂载荷均与实验结果一致性更好。图4展示了应用3种不同数值方法模拟下的断裂模式对比以及与实验断裂模式的对比。图4A显示了应用EIF模拟所得断裂模式，其主裂纹出现在股骨中部上方区域，并从上方开始随弯曲增加逐渐向下方扩展，直至贯穿皮质骨外径导致表观断裂发生。应用XFEM与CDM模拟所预测断裂模式较为相似，与应用EIF模拟所得断裂模式存在一定差异。图4B，C显示主裂纹均出现在股骨中部下方区域，并且随弯曲增加，裂纹从下至上逐渐扩展，直至贯穿皮质骨外径，导致结构发生表观断裂，该断裂模式与图4D所示的实验断裂模式较为相似。应用XFEM与CDM模拟所得断裂模式的不同之处则在于损伤单元数量差异。应用CDM进行模拟，只要达到损伤条件，单元便会发生损伤，因此从图4B中可以看到在约束与加载区域，均出现一定数量的绿色损伤单元，而应用XFEM模拟，由于整个股骨有限元模型均设置为富集区域，根据XFEM仿真特点，损伤单元只出现在最先满足损伤条件的区域，因此从图4C中可以看到只有极少数损伤单元最初出现在上方刚性圆柱附近，但由于这些损伤单元无法达到失效条件，因此在股骨中部下方区域又重新出现损伤单元，并且随着载荷增加，正是这些损伤单元逐渐演化为失效单元，最终导致结构发生表观断裂。"

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