HIGH STRAIN-RATE SHEAR RESPONSE OF POLYCARBONATE AND POLYMETHYL METHACRYLATE
HIGH STRAIN-RATE SHEAR RESPONSE OF POLYCARBONATE AND POLYMETHYL METHACRYLATE
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DOI：
10.1098/rspa.1990.0069
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发表时间：
1990-06-08
影响因子：
--
通讯作者：
LIU, JH
中科院分区：
文献类型：
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作者：
FLECK, NA;STRONGE, WJ;LIU, JH
采用分离式Hopkinson扭杆测量了聚碳酸酯（PC）和聚甲基丙烯酸甲酯（PMMA）在剪切应变率为500 s-1 ~ 2200 s-1、温度为-100 ° C ~ 200°C范围内的高应变率响应。的屈服和断裂行为进行了比较，与以前的数据和现有的理论为ε <1 s-1。我们发现，在β转变温度T β =-100 °C和玻璃化转变温度Tg = 147°C之间，PC的屈服符合粘流的Eyring理论。在较低的温度下，T<Tβ，主链运动变得冻结，剪切屈服应力大于Eyring预测。应变软化是PC在所有应变速率下屈服的基本特征。在T < 80°C的高应变速率试验中，聚甲基丙烯酸甲酯在屈服前断裂，该温度接近玻璃化转变温度Tg 120 °C。结果表明，两种材料的断裂应力均服从Eyring型热激活率理论。断裂被认为是成核控制的，并且是由于在断裂应力τf下银纹的引发和破裂。断裂表面的检查表明，失败是由成核和传播的倾斜模式I微裂纹连接形成一个阶梯状的断裂表面。这表明失效是由于拉伸开裂而不是由于材料的热不稳定性。剪切局部化的过程与钢和钛合金的剪切局部化过程有根本的不同。
The high strain rate response of polycarbonate (PC) and polymethyl methacrylate (PMMA) are measured using a split Hopkinson torsion bar for shear strain ratesẎfrom 500 s-1to 2200 s-1, and temperatures in the range —100°C to 200°C. The yield and fracture behaviours are compared with previous data and existing theories for Ẏ < I s-1. We find that PC yields in accordance with the Eyring theory of viscous flow, for temperatures between the beta transition temperatureTβ≈ — 100°C and the glass transition temperatureTg= 147°C. At lower temperatures,T<Tβ, backbone chain motion becomes frozen and the shear yield stress is greater than the Eyring prediction. Strain softening is an essential feature of yield of PC at all strain rates employed. Poly methyl methacrylate fractures before yield in the high strain rate tests forT< 80°C, which is close to the glass transition temperatureTg120°C. It is found that the fracture stress for both materials obeys a thermal activation rate theory of Eyring type. Fracture is thought to be nucleation controlled, and is due to the initiation and break down of a craze at the fracture stress τf. Examination of the fracture surfaces reveals that failure is by the nucleation and propagation of inclined mode I microcracks which link to form a stepped fracture surface. This reveals that failure is by tensile cracking and not by a thermal instability in the material. The process of shear localization is fundamentally different from that shown by steel and titanium alloys.