In this work, the quasi-static and dynamic mechanical behavior of directional polymethylmethacrylate is investigated under conditions of uniaxial compression and tension. The main purpose of this investigation is to discuss the effect of strain rate and temperature on the deformation characteristics and failure of such material. Research was carried out with the use of an electric universal testing machine and split Hopkinson bars, which were equipped with high- and low-temperature control systems. The experimental methods for studying the tensile and compressive response of polymer materials under different testing conditions were validated by one-dimensional stress wave theory and digital-image correlation technique. The finite deformation stress–strain behaviors of the samples under different loading condition were obtained with a constant temperature ranging from 218 to 373 K. The experimental results showed that the uniaxial tensile and compressive behaviors of directional polymethylmethacrylate under finite deformation are strongly dependent on temperature, decreased tensile and compressive stress of the material under different strain levels, and increased temperature. Meanwhile, the dynamic tensile and compressive stresses of the material are much higher than the quasi-static stresses, showing the strain-rate strengthening effect. Moreover, the tensile and compressive mechanical behavior of directional polymethylmethacrylate has significant asymmetry. Finally, a visco-hyperelastic model is established to predict the rate-dependence mechanical behavior of directional polymethylmethacrylate at different temperatures.

Theoretical and experimental studies on the compressive mechanical behavior of 4-harness satin weave carbon/epoxy composite laminates under in-plane loading are conducted over the temperature range of 298–473 K and the strain rate range of 0.001–1700/s in this article. The stress–strain curves of 4-harness satin weave composites are obtained at different strain rates and temperatures, and key mechanical properties of the material are determined. The deformation mechanism and failure morphology of the samples are observed and analyzed by scanning electron microscope (SEM) micrographs. The results show that the uniaxial compressive mechanical properties of 4-harness satin weave composites are strongly dependent on the temperature but are weakly sensitive to strain rate. The peak stress and elastic modulus of the material have the trend of decrease with the increasing of temperature, and the decreasing trend can be expressed as the functional relationship of temperature shift factor. In addition, SEM observations show that the quasi-static failure mode of 4-harness satin weave composites is shear failure along the diagonal lines of the specimens, while the dynamic failure modes of the material are multiple delaminations and longitudinal splitting, and with the increasing of temperature, its longitudinal splitting is more serious, but the delamination is relatively reduced. A constitutive model with thermomechanical coupling effects is proposed based on the experimental results and the increment theory of elastic–plastic mechanics. The experimental verification and numerical analysis show that the model is shown to be able to predict the finite deformation behavior of 4-harness satin weave composites over a wide range of temperatures.

There are great challenges in studying the dynamic mechanical behavior of lightweight cellular materials by using the traditional split Hopkinson pressure bar (SHPB) system because of the unique microstructure of such materials. To overcome these challenges, we present in this article a new experimental framework for dynamic loading tests of low-strength cellular materials from the elastic stage to the densification stage. Nylon is utilized as the compression bar in the SHPB system, and its low elastic modulus can cause larger displacement during dynamic loading. Meanwhile, polymethyl methacrylate (PMMA) inserts are attached to the bar end to prevent plastic deformation in that part, and a data correction method is employed to reduce the error caused by inserts. For the problem of wave dispersion during propagation in nylon bars, we use the in situ test method for dispersion correction to obtain more accurate results. We test a closed-cell aluminum foam by this modified SHPB test method and get ideal results. The test results of the aluminum foam show that its mechanical behavior is insensitive to the strain rate at the elastic stage and plastic collapse stage but sensitive to the strain rate at the beginning of the densification stage.

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