形状记忆聚氨酯粘弹性行为的纳米压痕实验及有限元模拟

Nano-indentation experiments and finite element simulations on viscoelastic behaviors of shape memory polyurethane

为了揭示形状记忆聚氨酯(SMPU)在微小尺度下的粘弹性力学行为,开展了不同加载速率和保载时间下的纳米压痕实验,获取了硬度和模量与加载速率和保载时间的关系,利用有限元软件ABAQUS建立了纳米压痕轴对称有限元模型,通过三单元粘弹性模型模拟了SMPU在纳米压痕下的力学响应。研究表明:SMPU表现出显著的粘弹性,压入的最大深度随着加载速率的增大而减小,随着保载时间的增大而增大,卸载段的“鼻子”现象随加载速率及保载时间的减小而逐渐显著。SMPU的弹性模量和硬度随加载速率的增加而增加,随保载时间的增加而减小;通过应变率灵敏度模型和无量纲时间灵敏度模型预测了SMPU的固有模量和硬度。通过有限元模拟结果与实验结果的对比,三单元粘弹性模型可以合理地模拟出不同加载速率和保载时间下的压痕实验。为获取微小尺度下SMPU粘弹性本构模型参数提供了一种有效方法。

In order to indicate the viscoelastic mechanical behaviors of shape memory polyurethane(SMPU)on a micro scale,this paper carries out nano-indentation experiments under different loading rates and holding times,and establishes the relations between both hardness and modulus and both the loading rate and the holding time.Furthermore,by using the finite element software ABAQUS,this paper establishes an axisymmetric nano-indentation finite element model to simulate the mechanical responses of SMPU under nano-indentation through a three-element viscoelastic model.The results show that the SMPU exhibits significant viscoelasticity,and the maximum indentation depth decreases with the increase of the loading rate,and increases with the increase of the holding time.At the same time,the‘nose’phenomenon in the unloading segment becomes significant with the decrease of the loading rate and the holding time.The elastic modulus and the hardness of SMPU increase with the increase of the loading rate and decrease with the increase of the holding time.The intrinsic modulus and the hardness of SMPU are predicted by a strain rate sensitivity model and a dimensionless time sensitivity model.Comparing the finite element simulation results with experimental results,the three-element viscoelastic model can reasonably simulate nano-indentation experiments under different loading rates and holding time,indicating that this study provides an effective method to obtain the parameters of SMPU viscoelastic constitutive model of on a micro scale.