Cronin D S, Watson B, Khor F, Gierczycka D, Malcolm S
Department of MME, University of Waterloo, Waterloo, ON, Canada.
Honda Development and Manufacturing of America, Raymond, OH, United States.
Front Bioeng Biotechnol. 2022 Oct 17;10:1022506. doi: 10.3389/fbioe.2022.1022506. eCollection 2022.
A primary objective of finite element human body models (HBMs) is to predict response and injury risk in impact scenarios, including cortical bone fracture initiation, fracture pattern, and the potential to simulate post-fracture injury to underlying soft tissues. Current HBMs have been challenged to predict the onset of failure and bone fracture patterns owing to the use of simplified failure criteria. In the present study, a continuum damage mechanics (CDM) model, incorporating observed mechanical response (orthotropy, asymmetry, damage), was coupled to a novel phenomenological effective strain fracture criterion based on stress triaxiality and investigated to predict cortical bone response under different modes of loading. Three loading cases were assessed: a coupon level notched shear test, whole bone femur three-point bending, and whole bone femur axial torsion. The proposed material model and fracture criterion were able to predict both the fracture initiation and location, and the fracture pattern for whole bone and specimen level tests, within the variability of the reported experiments. There was a dependence of fracture threshold on finite element mesh size, where higher mesh density produced similar but more refined fracture patterns compared to coarser meshes. Importantly, the model was functional, accurate, and numerically stable even for relatively coarse mesh sizes used in contemporary HBMs. The proposed model and novel fracture criterion enable prediction of fracture initiation and resulting fracture pattern in cortical bone such that post-fracture response can be investigated in HBMs.
有限元人体模型(HBMs)的一个主要目标是预测冲击场景下的响应和损伤风险,包括皮质骨骨折的起始、骨折模式以及模拟骨折后对深层软组织损伤的可能性。由于使用了简化的失效准则,当前的HBMs在预测失效起始和骨折模式方面面临挑战。在本研究中,一个包含观察到的力学响应(正交各向异性、不对称性、损伤)的连续损伤力学(CDM)模型与基于应力三轴性的新型唯象有效应变断裂准则相结合,并进行研究以预测不同加载模式下皮质骨的响应。评估了三种加载情况:试样级缺口剪切试验、全股骨三点弯曲试验和全股骨轴向扭转试验。所提出的材料模型和断裂准则能够在已报道实验的变异性范围内预测全骨和试样级试验的骨折起始、位置以及骨折模式。骨折阈值依赖于有限元网格尺寸,与较粗的网格相比,更高的网格密度会产生相似但更精细的骨折模式。重要的是,即使对于当代HBMs中使用的相对较粗的网格尺寸,该模型也是功能完备、准确且数值稳定的。所提出的模型和新型断裂准则能够预测皮质骨中的骨折起始和由此产生的骨折模式,从而可以在HBMs中研究骨折后的响应。