Miller-Young Janice E, Duncan Neil A, Baroud Gamal
Human Performance Laboratory, University of Calgary, 2500 University Drive, NW, Alta, T2N 1N4, Calgary, Canada.
J Biomech. 2002 Dec;35(12):1523-31. doi: 10.1016/s0021-9290(02)00090-8.
The structural behaviour of the human heel pad has been studied extensively due to its ability to absorb shock, protect against excessive local stress, and reduce plantar pressures. However, the material properties of the tissue have not been adequately measured. These must be known in order to perform a finite element analysis of the effect of factors such as foot geometry and shoe/surface construction on heel pad function. Therefore, the purposes of this study were to (a). measure the viscoelastic behaviour of the fat pad in compression, and (b). to determine an appropriate constitutive equation to model the tissue. A series of unconfined compression tests were performed on 8mm diameter cylinders of fat pad tissue, consisting of quasi-static, 175, 350 mm/s and stress-relaxation tests to approximately 50% deformation. The tissue exhibited nonlinear, viscoelastic behaviour. No significant difference was found in the quasi-static behaviour between samples from different locations and orientations in the heel. The stress-relaxation tests were used to determine the time constant (tau(1)=0.5s), the 175 mm/s test to determine the relaxation coefficient (g(1)=28), and the 350 mm/s compression test to determine the material constants (C(100)=C(010)=0.01, C(200)=C(020)=0.1 Pa) of a single-phase, hyperelastic, linear viscoelastic strain energy function (r(2)=0.98).
由于人类足跟垫具有吸收冲击、防止局部应力过大以及降低足底压力的能力，其结构行为已得到广泛研究。然而，该组织的材料特性尚未得到充分测量。为了对足部几何形状和鞋/表面结构等因素对足跟垫功能的影响进行有限元分析，必须了解这些特性。因此，本研究的目的是：(a)测量脂肪垫在压缩时的粘弹性行为，以及(b)确定一个合适的本构方程来模拟该组织。对直径8mm的脂肪垫组织圆柱体进行了一系列无侧限压缩试验，包括准静态试验、175、350mm/s的试验以及应力松弛试验，变形量约为50%。该组织表现出非线性粘弹性行为。在足跟不同位置和方向的样本之间，准静态行为未发现显著差异。利用应力松弛试验确定时间常数（τ(1)=0.5s），175mm/s的试验确定松弛系数（g(1)=28），350mm/s的压缩试验确定单相、超弹性、线性粘弹性应变能函数的材料常数（C(100)=C(010)=0.01，C(200)=C(020)=0.1Pa）（相关系数r(2)=0.98）。
