Chen J, Browne M, Taylor M, Gregson P J
Ably Shelters Ltd., Waterlooville, Portsmouth PO7 7UG, UK.
Comput Methods Programs Biomed. 2004 Mar;73(3):249-56. doi: 10.1016/S0169-2607(03)00042-7.
A novel computational modelling technique has been developed for the prediction of crack growth in load bearing orthopaedic alloys subjected to fatigue loading. Elastic-plastic fracture mechanics has been used to define a three-dimensional fracture model, which explicitly models the opening, sliding and tearing process. This model consists of 3D nonlinear spring elements implemented in conjunction with a brittle material failure function, which is defined by the fracture energy for each nonlinear spring element. Thus, the fracture energy criterion is implicit in the brittle material failure function to search for crack initiation and crack development automatically. A degradation function is employed to reduce interfacial fracture properties corresponding to the number of cycles; thus fatigue lifetime can be predicted. Unlike other failure modelling methods, this model predicts the failure load, crack path and residual stiffness directly without assuming any pre-flaw condition. As an example, fatigue of a cobalt based alloy (CoCrMo) femoral stem is simulated. Experimental fatigue data was obtained from four point bending tests. The finite element model simulated a fully embedded implant with a constant point load. Comparison between the model and mechanical test results showed good agreement in fatigue crack growth rate.
已开发出一种新型计算建模技术，用于预测承受疲劳载荷的承重骨科合金中的裂纹扩展。弹塑性断裂力学已被用于定义一个三维断裂模型，该模型明确模拟了张开、滑动和撕裂过程。该模型由与脆性材料失效函数结合实施的三维非线性弹簧单元组成，脆性材料失效函数由每个非线性弹簧单元的断裂能定义。因此，断裂能准则隐含在脆性材料失效函数中，以自动搜索裂纹萌生和裂纹扩展。采用退化函数来降低与循环次数相对应的界面断裂性能；从而可以预测疲劳寿命。与其他失效建模方法不同，该模型无需假设任何预缺陷条件即可直接预测失效载荷、裂纹路径和残余刚度。例如，模拟了钴基合金（CoCrMo）股骨柄的疲劳。实验疲劳数据来自四点弯曲试验。有限元模型模拟了一个带有恒定点载荷的完全植入式植入物。模型与力学试验结果之间的比较表明，在疲劳裂纹扩展速率方面具有良好的一致性。
