Stress equilibrium effects within Hopkinson bar specimens

Abstract

Resume Dans le split Hopkinson barre technique pour compression, un echantillon en forme de disque serre entre deux fastes barres d'acier est compresse par une impulsion compressive. Les proprietes de la contrainte et deformation de l'echantillon peut h r e derive par la quantite d'impulsion compressive, renvoye et transmit par l'echantillon, en supposant que l'equilibre contrainte existe tout le long de l'echantillon. Neanmoins pendant la periode initiale de compression, les multiples reflexions generes aux deux barre/echantiBon interfaces cree une distribution compressive non-uniforme, qui anive a une evaluation peut-&tre incorrecte des proprietes initials de contrainte/deformation. Cette publication decrit une analyse de microordinateur afin d'etudier plusiers parametres importants qui influencent l'accumulation de l'equilibre contrainte d'ClasticitC et predit les formes d'impulsion refletes et transmit pour des impulsions de compression differents. Abstract In the compression testing version of the split Hopkinson pressure bar technique a small disc-shaped specimen, sandwiched between two high-strength steel bars, is compressed by a stress pulse. The stress/strain properties of the specimen can be derived from the amount of the stress pulse reflected and transmitted by the specimen, assuming that stress equilibrium exists throughout the specimen. However, during the initial loading phase the multiple reflections generated at the two specimenbar interfaces cause a non-uniform stress distribution, leading to possibly inaccurate estimates of the initial stresslstrain properties. The paper describes a microcomputer analysis to study many of the important parameters affecting the build-up to elastic stress equilibrium and to predict the reflected and transmitted pulse shapes for different loading pulses.

Improved specimen recovery in tensile split Hopkinson bar

“…Based on the solutions (B 5) and (B 6), the axial force in the specimen during time step t = i is given by Similar to the method presented by Parry et al [8], equations (B 5)-(B 7) allow the evaluation of the force generated by an arbitrary-shaped incident pulse ε i (t). This feature can be used to evaluate the effects of individual residual stress waves, i.e.…”

“…The method is based on elastic wave calculations within the specimen and is similar to the techniques used by previous authors [8,9] for specimen stress equilibrium calculations. The details of the calculation procedure are given in appendix B.…”

High strain rate behavior of a SiC particulate reinforced Al2O3 ceramic matrix composite

“…It should be mentioned here that data from the SHPB in the initial several microseconds of the test can not be interpreted to show the correct material property response because of the absence of an equilibrium stress state in the sample. It has been shown previously that the stress in the sample closely approaches a uniform state after 4 or 5 wave reflections [5]. Hence, by multiplying by 5 the elastic wave transit time, which is specimen length divided by wave velocity, the lower (time) limit for stress equilibrium can be easily calculated for the composite.…”

Dynamic properties of metal matrix composites: a comparative study

“…More information on these assumptions and their effects on SHPB test results can be found elsewhere [10,11]. It must, however, be emphasized here that the initial region (4-6 ms) of the stress/strain curves corresponding to the elastic region cannot be accurately described by these equations because finite time is required in order to establish stress equilibrium in the specimen [12,13]. Two further techniques were applied during SHPB testing in this study.…”