Rate dependent finite deformation stress-strain behavior of an ethylene methacrylic acid copolymer and an ethylene methacrylic acid butyl acrylate copolymer
Rate dependent finite deformation stress-strain behavior of an ethylene methacrylic acid copolymer and an ethylene methacrylic acid butyl acrylate copolymer
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DOI：
10.1016/j.polymer.2008.10.049
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发表时间：
2009-01-02
期刊：
影响因子：
4.6
通讯作者：
Boyce, M. C.
中科院分区：
文献类型：
--
作者：
Deschanel, S.;Greviskes, B. P.;Boyce, M. C.
评价和比较了乙烯-甲基丙烯酸共聚物和乙烯-甲基丙烯酸丁酯共聚物在近8个数量级的应变率(从10(-4)到近10(4)/S)下的大应变变形行为，并用动态力学分析量化了转变区域。这些共聚物的应力-应变行为表现出相对僵硬的初始行为，然后翻转到更柔顺的响应。低应变模数、滚动应力和大变形应力-应变行为强烈依赖于应变率。当人在应变速率范围内移动时，材料的玻璃化转变接近室温测试条件，导致应力-应变行为的速率敏感性的性质发生了实质性的变化。将EMAA与相应的EMAABA三元共聚物及其钠中和聚合物(EMAABA(Na))的力学行为进行了对比。EMAA的室温应力-应变行为的速率敏感性的本质是从低速率下接近皮革状态的玻璃化端行为转变为高速率下的近玻璃状态。EMAABA中丙烯酸丁酯的含量降低了玻璃化转变温度，并导致了室温下更顺应的力学行为(降低了初始刚性、降低了滚动应力、降低了滚动后应力水平)。EMAABA行为从最低速率下的橡胶行为转变为最高速率下的皮革行为。钠中和后，由于离子聚集体的存在，整体硬度和流动应力水平可能会提高：与EMAABA相比，EMAABA(Na)的玻璃化转变被加宽，给出了随应变速率增加而过渡到皮革区域的速率相关的室温行为。分别考虑晶区和非晶区不同变形阻力的本构模型能够反映本文所研究的EMAA共聚物的变形行为随速率的变化。晶区提供了在速率和温度的宽窗口中流动的阻力，而非晶区提供了随着应变速率的增加而增加的阻力，并且材料有效地通过玻璃化转变区域转变，从而提供了改变速率敏感性的机制。(C)2008爱思唯尔有限公司。保留所有权利。
The large strain deformation behaviors of an ethylene methacrylic acid (EMAA) copolymer and an ethylene methacrylic acid butyl acrylate (EMAABA) copolymer are evaluated and compared in compression over nearly eight orders of magnitude in strain rate, from 10(-4) to almost 10(4)/s. Transition regimes are quantified using dynamic mechanical analysis. The stress-strain behavior of these copolymers exhibits a relatively stiff initial behavior followed by a rollover to a more compliant response. The low strain modulus, the rollover stress and the large deformation stress-strain behavior are strongly dependent on strain rate. The proximity of the material glass transition to the room temperature test conditions results in a substantial change in the nature of the rate sensitivity of the stress-strain behavior as one moves over the range of strain rates. The mechanical behavior of the EMAA is contrasted to that of a corresponding EMAABA terpolymer and to its sodium-neutralized counterpart (EMAABA(Na)). The nature of the rate sensitivity of the room temperature stress-strain behavior of EMAA transitions from a behavior near the glassy end of the leathery regime at low rates to a near glassy behavior at high rates. The butyl acrylate content in the EMAABA lowers the glass transition temperature and leads to a more compliant mechanical behavior (reduced initial stiffness, reduced rollover stress, reduced post-rollover stress level) at room temperature. The EMAABA behavior transitions from a rubbery-like behavior at the lowest rates to a leathery-like behavior at the highest rates. Upon sodium neutralization, the overall stiffness and flow stress levels are enhanced likely due to the presence of the ionic aggregates: the glass transition of EMAABA(Na) is broadened in comparison to the EMAABA, giving a rate dependent room temperature behavior that transitions through the leathery regime with increasing strain rate. A constitutive model that separately accounts for the distinct deformation resistances of the crystalline domains and the amorphous domains is able to capture the changes in rate dependent deformation behavior of the EMAA copolymers studied herein. The crystalline domains provide resistance to flow across a wide window in rate and temperature whereas the amorphous domains provide increasing resistance as the strain rate is increased and the material effectively transitions through the glass transition regime, providing a mechanism for changing rate sensitivity. (C) 2008 Elsevier Ltd. All rights reserved.