球形压头压入中摩擦对材料参数识别的影响

Effect of friction on identification of materials properties from spherical indentation

利用量纲分析原理和有限元方法,研究了球形压头压入中摩擦对于幂强化材料塑性材料参数识别的影响.通过定义一种基于能量的表征应变,根据识别的两个压入深度的表征应变和表征应力,得到材料的塑性特性;最后研究了摩擦对压入响应、表征应力及材料参数提取的影响.研究结果表明,摩擦对压入的影响与材料的应变硬化指数、弹性模量与屈服极限的比值及弹性功与总功的比值密切相关,弹性功与总功的比值越大,摩擦的影响越小;摩擦对材料参数提取的影响不可忽略,当摩擦系数未知时,对于压入过程中弹性功与总功的比值较大的材料,近似取摩擦系数为0.15,能得到较合理的材料参数识别的结果.

By using the dimensional analysis and finite element computations, the frictional effects on spherical indentation of strain hardening solids to exact the plastic properties of material are examined. By defining a representative strain dependent on the energy, based on the representative strains and representative stresses corresponding to two different indentation depth, the plastic properties of materials are uniquely determined. Then the frictional effects on the indentation response, representative stress and identification of the mechanical properties can be obtained. It is shown that the effect of friction on the indentation is closely related to the strain hardening exponent, the ratio of the elastic modulus to yield stress and the ratio of the reversible work to the total work done by the indenter. The bigger the ratio of the reversible work to the total work is, the smaller the effect of friction is. The effect of friction on extracting the mechanical properties cannot be ignored. While the friction coefficient is unknown, for the materials with the bigger ratio of the reversible work to the total work, the reasonable result can be obtained using the coefficient taken as 0.15 to extract mechanical properties.