环氧树脂在不同环境温度下的循环变形实验研究
EXPERIMENTAL STUDY ON CYCLIC DEFORMATION OF EPOXY RESIN UNDER DIFFERENT AMBIENT TEMPERATURES
-
摘要: 循环力载荷是环氧树脂和环氧树脂基复合材料构件常见的载荷形式, 同时构件服役时环境温度通常有较大变化. 为了保证结构的服役安全, 有必要对环氧树脂在不同温度下的循环变形特性进行研究. 本研究在−20 °C、25 °C、55 °C和85 °C四个环境温度下对环氧树脂进行了一系列单轴应变控制循环实验和应力控制循环实验, 研究了不同环境温度下环氧树脂的循环软/硬化、平均应力松弛以及棘轮行为特性, 探究了环境温度对环氧树脂循环变形行为的影响. 结果表明: 环氧树脂在对称应变控制循环变形过程中表现出循环稳定的特性, 在单轴非对称应变控制循环变形过程中出现应力松弛现象, 且温度越高应力松弛现象越明显. 环氧树脂在单轴非对称应力控制循环变形过程中表现出明显的棘轮行为, 环氧树脂的棘轮变形由可回复的粘弹性变形和不可回复的粘塑性变形组成. 降低环境温度会对材料的棘轮行为有抑制作用, 升高环境温度则会明显促进材料棘轮变形的发展. 高应力水平也会诱发更多棘轮变形. 环氧树脂的棘轮行为具有明显的时间依赖特性和率效应, 棘轮应变在较慢的加载速率和有峰值应力保持的情况下演化地更快, 且随着环境温度的升高, 加载速率和峰值保持时间对环氧树脂棘轮变形的影响愈加显著.Abstract: Epoxy resin and epoxy-based composite components are frequently subjected to cyclic loading during service. Meanwhile, the ambient temperature usually varies greatly. To ensure the service safety of the structures, it is necessary to investigate the cyclic deformation characteristics of epoxy resin under different temperatures. In this work, a series experiments under uniaxial strain-controlled and stress- controlled cyclic loading were performed on epoxy resin at four temperatures: −20 °C, 25 °C, 55 °C and 85 °C. The characteristic of cyclic softening/hardening, mean stress relaxation and ratchetting were studied under different temperatures, and the influence of temperature on the cyclic deformation behavior of epoxy resin was explored. It was shown that the epoxy resin exhibited cyclic stability during the symmetric strain-controlled cyclic loading, while mean stress relaxation occurred and became more obvious at higher temperatures during the uniaxial asymmetric strain-controlled cyclic loading. Epoxy resin exhibited distinct ratchetting behavior during uniaxial asymmetric stress-controlled cyclic loading. The ratchetting strain consistd of recoverable viscoelastic strain and irrecoverable viscoplastic strain. The ratchetting behavior was suppressed at lower temperatures, while the accumulation of ratchetting strain markedly promoted at higher temperatures. High stress levels also induce more ratchetting deformation. The ratchetting behavior of epoxy resin showed obvious time-dependence and rate-dependence. Ratchetting strain developed more quickly under slower loading rates and with peak holding. As the ambient temperature rised, the loading rate and peak holding time had a more significant impact on the ratchetting of the epoxy resin.
下载: