Set‐up of a split hopkinson pressure bar. Calibration and wave dispersion correction
Tutor / director / evaluatorHughes, Kevin
Document typeMaster thesis (pre-Bologna period)
Rights accessRestricted access - author's decision
The mechanical properties of materials change depending upon the strain rate that they are subject to. Robust models that capture the materials response at different strain rates are important. High strain rates from 100s‐1 to 10000s‐1 are undergone in impact applications. The most widely used method to characterise materials at high strain rates is the Split Hopkinson Pressure Bar (SHPB). This project deals with the set‐up and calibration of a Split Hopkinson Pressure Bar for the dynamic testing of metallic materials at high strain rates. The features of the equipment needed are discussed, as well as the instrumentation and the connections between the different components. A calibration routine is also presented in this text. A finite element analysis of a SHPB calibration test has been performed with LS‐DYNA. The model consists of two bars put together and does not include a specimen. The time dependent strain and stress pulses obtained are very well correlated to the theory. The results from a calibration test in the laboratory at Cranfield University are also presented. It is observed that the level of accuracy of the finite element model is better than that of the experimental calibration test. A complete analysis of a SHPB with a metallic specimen is also performed with finite elements in LS‐DYNA. The results achieved are extremely close to those predicted by some hand calculations. The creation and application of a routine with Matlab that corrects the dispersion effect in the model is a key point to increase the accuracy of the results. The dispersion correction routine consists of a technique that enables to filter out the high frequency components of the sampled signal; therefore, part of the noise is removed. This is performed after the time domain data is converted into the frequency domain, after using the Fast Fourier Transform. This routine has also been applied to the experimental results obtained through the calibration test.
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