High Rates and Impact Experiments
Experimental techniques for high-strain-rate measurements and for the study of impact-related problems are described. An approach to classifying these experimental techniques is presented, and the state-of-the-art is briefly described. An in-depth descrip
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High Rates an 33. High Rates and Impact Experiments
Kaliat T. Ramesh
From a mechanics viewpoint, the consequences of an impact are threefold. First, stress waves or shock waves are propagated inside the impacted bodies, and the propagation of these waves must be understood. Second, large inelastic deformations may be developed, typically at high rates of deformation. Third, the entire impacted structure may be excited by the impact, leading to structural dynamics and vibration problems, typically at long times. This chapter explicitly ignores the last of these consequences. Further, if the impact velocity is sufficiently small, all of the stress waves propagated inside the impacted bodies will be elastic. The measurement of elastic wave propagation is discussed in other chapters, notably those on ultrasonics and photoacoustic characterization. Thus, our focus is on the experimental techniques associated with the propagation of nonelastic waves, and with the measurement of high-strain-rate behavior. Our emphasis is therefore on the measurement of the phenomena that are
33.1 High Strain Rate Experiments ................ 33.1.1 Split-Hopkinson or Kolsky Bars ...... 33.1.2 Extensions and Modifications of Kolsky Bars .............................. 33.1.3 The Miniaturized Kolsky Bar........... 33.1.4 High Strain Rate Pressure-Shear Plate Impact ................................ 33.2 Wave Propagation Experiments ............. 33.2.1 Plate Impact Experiments.............. 33.3 Taylor Impact Experiments .................... 33.4 Dynamic Failure Experiments ................. 33.4.1 Void Growth and Spallation Experiments........... 33.4.2 Shear Band Experiments ............... 33.4.3 Expanding Ring Experiments ......... 33.4.4 Dynamic Fracture Experiments ....... 33.4.5 Charpy Impact Testing................... 33.5 Further Reading ................................... References ..................................................
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developed during the early times after a relatively high velocity impact. It is useful to develop a sense of the range of strain rates developed during typical impact problems (note that the strain rates developed as a result of an impact are always functions of time, and therefore we focus here on the peak strain rates developed). Thus during an asteroid impact on the Earth, the peak strain rates that are developed are likely to be of the order of 108 s−1 (this results from hypervelocity impact, i. e. impact velocities above 5 km/s). For impacts corresponding to typical velocities from defense-related terminal ballistics (≈ 1–2 km/s), the peak strain rates developed are of the order of 105 s−1 to 106 s−1 . All strain rates below the peak strain rate are likely to be developed during the event at sufficiently long times, and their significance to the problem must be determined on a case-by-case basis. In both the planetary impact and ballistic impact cases, for example, substantial parts of
Part D 33
Experimental techniques for high-s
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