US Army Research Laboratory, Aberdeen Proving Ground, MD 21005, USA.
J Biomech. 2012 Feb 2;45(3):434-9. doi: 10.1016/j.jbiomech.2011.12.017. Epub 2012 Jan 4.
Modeling and simulation of traumatic brain injury (TBI) resulted from collision or blast loading requires characterization of mechanical response over a wide range of loading rates under valid testing conditions. In this study, mechanical response of fresh bovine brain tissue was studied using the two modified Kolsky bar techniques. Radial deformation behavior of annular specimens, which are typically used to characterize the dynamic uniaxial compressive response of biological tissues, was examined using a modified Kolsky bar and a high speed camera to collect images while the specimen deforms at an axial strain rate of 2000s(-1). The high-speed images revealed inhomogeneous specimen deformation possibly brought about by radial inertia and causing a multi-axial stress state. To acquire valid stress-strain results that can be used to produce constitutive behavior of the soft materials, a novel torsion technique was developed to obtain pure shear response at dynamic loading rates. Experimental results show clear differences in the material response using the two methods. These results indicate that the previously demonstrated annular specimen geometry aimed at reducing inertia induced stress components for high rate soft materials uniaxial-compressive testing may still possess a significant component of radial inertia induced radial stress which consequently caused the observed inhomogeneous deformation in brain tissue test samples.
碰撞或爆炸加载导致的创伤性脑损伤 (TBI) 的建模和模拟需要在有效测试条件下，在较宽的加载速率范围内对力学响应进行特征描述。在这项研究中，使用两种改进的 Kolsky 杆技术研究了新鲜牛脑组织的力学响应。使用改进的 Kolsky 杆和高速摄像机检查了环形试样的径向变形行为，该环形试样通常用于表征生物组织的动态单轴压缩响应，同时在轴向应变速率为 2000s(-1) 的情况下收集试样变形时的图像。高速图像显示，由于径向惯性可能导致试样变形不均匀，从而产生多轴应力状态。为了获得可用于产生软材料本构行为的有效应力-应变结果，开发了一种新的扭转技术，以在动态加载速率下获得纯剪切响应。实验结果表明，这两种方法的材料响应有明显差异。这些结果表明，先前证明的旨在减少高应变率软材料单轴压缩试验中惯性引起的应力分量的环形试样几何形状，可能仍然具有显著的径向惯性引起的径向应力分量，从而导致脑组织试样观察到的不均匀变形。
