Neurotrauma and Repair Laboratory, Department of Biomedical Engineering, Columbia University, 351 Engineering Terrace, 1210 Amsterdam Avenue MC 8904, New York, NY, 10027, USA.
Biomech Model Mechanobiol. 2014 Jun;13(3):573-84. doi: 10.1007/s10237-013-0519-7. Epub 2013 Aug 9.
Indentation has several advantages as a loading mode for determining constitutive behavior of soft, biological tissues. However, indentation induces a complex, spatially heterogeneous deformation field that creates analytical challenges for the calculation of constitutive parameters. As a result, investigators commonly assume small indentation depths and large sample thicknesses to simplify analysis and then restrict indentation depth and sample geometry to satisfy these assumptions. These restrictions limit experimental resolution in some fields, such as brain biomechanics. However, recent experimental evidence suggests that conventionally applied limits are in fact excessively conservative. We conducted a parametric study of indentation loading with various indenter geometries, surface interface conditions, sample compressibility, sample geometry and indentation depth to quantitatively describe the deviation from previous treatments that results from violation of the assumptions of small indentation depth and large sample thickness. We found that the classical solution was surprisingly robust to violation of the assumption of small strain but highly sensitive to violation of the assumption of large sample thickness, particularly if the indenter was cylindrical. The ramifications of these findings for design of indentation experiments are discussed and correction factors are presented to allow future investigators to account for these effects without recreating our finite element models.
压痕作为一种用于确定软生物组织本构行为的加载方式具有多个优点。然而，压痕会引起复杂的、空间不均匀的变形场，这给本构参数计算带来了分析上的挑战。因此，研究人员通常假设小的压痕深度和大的样品厚度来简化分析，然后限制压痕深度和样品几何形状以满足这些假设。这些限制在某些领域（如脑生物力学）限制了实验的分辨率。然而，最近的实验证据表明，传统应用的限制实际上过于保守。我们对具有不同压头几何形状、表面界面条件、样品可压缩性、样品几何形状和压痕深度的压痕加载进行了参数研究，以定量描述违反小压痕深度和大样品厚度假设所导致的与先前处理的偏差。我们发现，经典解对小应变假设的违反具有惊人的鲁棒性，但对大样品厚度假设的违反非常敏感，尤其是当压头为圆柱形时。这些发现对压痕实验设计的影响进行了讨论，并提出了修正因子，以便未来的研究人员在不重新创建我们的有限元模型的情况下考虑这些影响。
