Abstract
When using a classical SHPB (split Hopkinson pressure bar) set-up, the useful measuring time is limited by the length of the bars, so that the maximum strain which can be measured in material testing applications is also limited. In this paper, a new method with no time limits is presented for measuring the force and displacement at any station on a bar from strain or velocity measurements performed at various places on the bar. The method takes the wave dispersion into account, as must inevitably be done when making long time measurements. It can be applied to one-dimensional and single-mode waves of all kinds propagating through a medium (flexural waves in beams, acoustic waves in wave guides, etc.). With bars of usual sizes, the measuring time can be up to 50 times longer than the time available with classical methods. An analysis of the sensitivity of the results to the accuracy of the experimental data and to the quality of the wave propagation modelling was also carried out. Experimental results are given which show the efficiency of the method.
Highlights
The SHPB has become a standard experimental technique for performing tests under dynamic loading conditions
To improve the accuracy of the basic force and displacement measurements, wave dispersion e ects in elastic bars have been studied (Davies, 1948; Yew and Chen, 1978; Follansbee and Franz, 1983; Gorham, 1983), and interactive simulation methods have been proposed to obtain an exact wave shift (Zhao and Gary, 1996)
Other aspects involving the analysis of the specimen response, such as three-dimensional e ects (Davies and Hunter, 1963; Klepaczko, 1969; Dharan and Hauser, 1970; Bertholf and Karnes, 1975; Malinowski and Klepaczko, 1986) and transient e ects (Lindholm, 1964; Conn, 1965; Bell, 1996; Jahsman, 1971) have been studied in recent decades
Summary
The SHPB (split Hopkinson pressure bar) has become a standard experimental technique for performing tests under dynamic loading conditions. Lundberg and Henchoz (1977) have proposed a simple explicit formula (based on a one-dimensional wave propagation assumption) separating the two elementary waves to measure the particle velocity, and using the signals recorded at two di erent cross-sections in a bar This method has been applied (Lundberg and Blanc, 1988) in a study on the viscoelastic properties of materials and (Lundberg et al, 1990) to the prediction of the wave propagation in a bar with a non-uniform impedance (due to a temperature gradient, for instance) and has been used successfully in high temperature SHPB testing (Bacon et al, 1991, 1994; Bacon and Brun 2000; Lataillade et al, 1994). A general n-strain gauge formula is proposed to stabilise the e ects of the noise
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