玻璃态高聚物PMMA的应变软化-强化效应

THE STRAIN SOFTENING AND HARDENING EFFECTS OF GLASSY POLYMER PMMA

讨论了玻璃态高聚物PMMA在单轴压缩下的受力变形行为。对加卸载循环的应力-应变曲线,建立了能作理论拟合计算的材料宏观本构理论模型和关系方程。拟合计算表明,理论和实测曲线吻合情况非常良好:相关系数>99.5％,最大应力偏差≯5MPa。着重讨论了屈服后的应变软化和强化效应。对于软化效应,提出了一种新的以粘弹变形的滞后松弛效应为内容的粘弹软化效应。对于强化效应,则讨论了取向强化和粘弹强化两种可能情况。在所研究的应变范围内,认为是粘弹软化和取向强化两种因素的抗衡,决定了屈服后应力-应变曲线的走向特性。

Discusses the deformation behaviour under loading of glassy polymer PMMA in this paper. Proposed a macroscopic constitutive model and relative equations which can be used to simulate theoretically measured stress-strain curves of loading -and unloading cycle. The results of simulating calculations show that the agreements of theoretical and measured curves are vary good with the corelation coefficients >99. 5% and the maximum stress departures>5MPa. Then discusses especially the strain softening and hardening effects post yield. Proposes a new theoretical explanation for the intrinic strain-softening effect of materials and can be named the viscoelastic softening effeet,the contents of which are mainly delayed relaxation effects of viscoelastic deformation. Discusses two possible processes for the strain hardening effect ,i. e. the viscoelastic hardening and orientation hardening ,and proposes that the trend characteristics of the stress-strain curves post yield are mainly determined by the competition of viscoelastic softenign and orientation hardening processes in the measured strain ranges.