Examination of Validity for Viscoelastic Split Hopkinson Pressure Bar Method

Abstract

The examination of the accuracy for a split Hopkinson pressure bar method with viscoelastic input and output bars (viscoelastic SHPB method), which is one of the methods of evaluating the dynamic properties for viscoelstic materials, is executed. The key-point for accurately determining the dynamic properties of low impedance materials lies in how to measure the moderate size of reflected and transmitted waves. Moreover, the loading at both ends of the specimen should be equal each other in this method. Polymethyl methacrylate (PMMA) bars are used as the input and output bars. The viscoelastic properties of PMMA are approximated to a 3-element solid model in advance through preliminary wave propagation experiments. The same model is used as the mechanical properties of specimens, and the value of the instantaneous modulus is changed. The shape of waves at the boundary and the gage position of the input and output bars as well as the specimen are analyzed using the Elementary theory. The stress distribution in the specimen is also examined. It is found that the dynamic properties of viscoelastic materials can be evaluated with good precision by viscoelastic SHPB method when the ratio of the input / output bars and the specimen of mechanical impedance is about 10-20%. Then, the viscoelastic SHPB tests are actually performed. The complex compliance of the specimens which represent the characteristics of materials is obtained. The dynamic properties of the specimen satisfied the condition obtained by the previously mentioned analysis can be evaluated with high accuracy.