压缩-剪切复合应力下PMMA材料的静态力学特性研究

通过压缩具有一定倾斜角(0°,10°,15°,20°和25°)试件和双剪切模型试件,实现了单轴压缩、压缩-剪切复合应力以及纯剪切三种应力状态,得到PMMA(聚甲基丙烯酸甲酯)在相应应力状态下的应力-应变曲线,同时对不同应力状态下试件的破坏模式进行了分析。结果表明:在不同受力环境中材料的强度和破坏的机理不同;同单轴压缩状态下相比,材料在压缩-剪切复合应力状态下屈服极限、强度极限以及破坏应变均不同程度的增大,呈现明显的"剪切增强"现象。单轴压缩与压缩-剪切应力状态下试件的破坏模式均为在试件短对角面上出现明显的剪切屈服带,由应力分析得出试件剪应力在短对角面上达到最大,引起在此平面上分子链间滑动从而产生应变软化形成剪切屈服带;双剪切试件的破坏模式为与剪切面呈45°的斜面。

Investigation on Static Mechanical Properties of PMMA Material Subjected to Compression-Shear Combined Stress

By using a universal material testing machine, through compressing specimens with beveled ends of different tilt angles (0°, 10°, 15°, 20°, and 25° respectively) and double shear model specimens, three stress states including uniaxial compression, combined compression-shear, and shear loading were achieved, quasi-static compression tests were conducted for PMMA polymer (polymethyl methacrylate) in order to obtain its stress-strain curves under corresponding stress states. While the failure modes of specimens under different stress states were analyzed. Experimental results show that the strength and the failure mechanism of material under different loading conditions are different. The yield stress, ultimate strength and failure strain of PMMA under combined shear-compression are larger than that under uniaxial compression at different levels and exhibit obvious shear strengthening. Both failure modes of PMMA under uniaxial compression and combined compression-shear exhibit shear yield zone occurred at short diagonal planes of specimens. It is found from stress analysis that the maximum shear stress appears at the short diagonal planes of specimens with tilt angle, which causing molecular chain sliding in this plane and forming shear yield zone due to strain softening. The failure mode of double shear specimens is the cross-sections in direction of 45 degree angle to shear plane.