Numerical and experimental studies on the use of a Split Hopkinson Pressure Bar for high strain rate tension testing
The Split Hopkinson Pressure Bar (SHPB) technique is widely used to dynamically characterize metals and is increasingly being used to characterize non-metallic materials such as fiber reinforced polymeric composite materials. However, the tensile version of the SHPB apparatus requires specimen gripping devices and/or complex loading mechanisms that distort and attenuate the loading pulse. Strain estimations in the test specimen based on the one-dimensional wave propagation theory are found to differ from direct measurements of the same. The discrepancy between the measured and estimated strains along with a general lack of guidance for tensile load generation limit the broader application of the testing technique. The current investigation addresses tensile load generation in a tensile SHPB apparatus, establishes a reliable loading methodology, develops a correction methodology for one dimensional theory strain estimation, and identifies the factors that contribute to wave modulation. A correction methodology for one-dimensional wave propagation analysis is presented to address the discrepancy between strains estimated by one dimensional wave propagation theory and strains measured directly over the test specimen. A method for correcting the strains in the frequency domains using Fourier analysis is presented. The correction methodology is applied to virtual strain measurements from simulations to establish its applicability to experimental results. Subsequently, the methodology is validated with experimental data from carbon fabric laminated composite specimens.
Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering