Talk about dynamic strength and damage evolution
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摘要: 材料强度在传统上常理解为材料在外载荷下抵抗流动/变形和破断的能力。由流变阶段到貌似突发的破断，其实源于一个隐含的应变率/时间相关的损伤演化过程。动态损伤演化研究的难点在于损伤与流变总是耦合在一起发展的。研究发现，热激活损伤演化模型可成功描述材料宏观损伤的动态演化。在此基础上，从实测的含损伤演化的表观应力应变曲线，可将两者解耦分开，并可确定各自相关的材料参数。这一思路可推广到中医脉诊的客观化研究，通过脉搏波信息定量反演脉搏波系统的正常及病态本构关系，可诊断生命体偏离正常状态的程度(病情)，这可视为一种广义的损伤演化和强度问题。上述思路还可推广到地震预报研究，即“对地球把脉”。与加卸载响应比理论相结合，通过相邻3处的地震波信息来反演地球相关板块含损伤演化的非线性载荷-响应曲线，再区分出损伤演化程度，将有利于改进地震预报，这可视为另一种广义的损伤演化和强度问题。Abstract: The strength of a material is traditionally understood as its ability to resist flow/deformation and breakage (brittle fracture or ductile rupture) under applied load. The breakage, though looking like an abrupt occurrence, actually results from a strain-rate/time dependent process of damage evolution. The difficulty in studying dynamic damage evolution lies in that the damage evolution and the flow/deformation process are coupled and influence each other. It was found that the dynamic evolution of macro-damage could be successfully described by the thermo-activated damage evolution model. Based on this model, the damage evolution and the flow/deformation can be decoupled from the experimentally measured apparent stress-strain curve with damage evolution, and the related material parameters can be determined. Such an approach is then generalized to the objective study of the TCM pulse. The normal and pathological constitutive relations of the pulse wave system can be inversely determined by pulse wave signals, and then the degree of deviation from the normal condition (illness state) of patients can be diagnosed, and their illness state can be regarded as a kind of generalized damage. The same approach is further generalized to the study of earthquake prediction through the 'pulse-taking for the earth'. Combined with the load-unload response ratio theory, by measuring the seismic wave signals on three adjacent positions, the nonlinear constitutive load-response curve with damage evolution can be inversely determined for the tectonic plates of the earth concerned, then the degree of the damage can be finally discriminated, which is the key information for an improved earthquake prediction.
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Key words:
- dynamic strength /
- damage evolution /
- dynamics of materials /
- pulse wave /
- earthquake prediction
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图 2 PMMA不同应变率下的理论曲线与实验数据的对比
Figure 2. Comparisons between the experimental data and theoretical predictions for PMMA
图 3 PP/PA共混高聚物BP神经网络预示曲线与实验曲线对比
Figure 3. Comparisons between the BP neural networks predictions and experimental data for PP/PA polymer blend
图 4 PP/PA共混高聚物由BP神经网络确定的D=(ε, ${\mathit{\dot \varepsilon }}$)
Figure 4. The D=(ε, ${\mathit{\dot \varepsilon }}$) determined by the BP neural networks for PP/PA polymer blend
图 5 计及损伤演化的材料率-温相关的动态力学行为的示意图
Figure 5. Rate-temperature dependent behavior of materialstaking account of damage evolution
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