A Flash X-Ray Technique to Measure Strain Distribution at Interfaces Sliding at High Pressure and Velocity

Winter, R. E.; Taylor, Peter; Carley, D. J.; Barlow, Andrew; Pragnell, H.; Markland, L.

doi:10.1063/1.1483588

Cited by 2 publications

(1 citation statement)

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“…An important recent development which aims to understand the underlying physics, and thereby supports the development of friction modelling, is the exploration of experimental techniques for measuring the material flows near the interface between metal blocks moving relative to one another under the influence of a shock wave [2][3][4][5][6]. The initial focus of this work has been to measure the sub-surface flows and, by comparing the observed deformation with that computed using different friction treatments, to provide data for evaluation and optimization of computer models.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of shock-induced dynamic friction

Winter¹,

Ball²,

Keightley³

2006

J. Phys. D: Appl. Phys.

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The mechanism of shock-induced dynamic friction has been explored through an integrated programme of experiments and numerical simulations. A novel experimental technique has been developed for observing the sub-surface deformation in aluminium when sliding against a steel anvil at high velocity and pressure. The experimental observations suggest that slight differences in conditions at the interface between the metals affect frictional behaviour even at the very high-velocity, high-pressure regime studied here. However, a clear finding from the experimental work is the presence of two distinct modes of deformation termed deep and shallow. The deep deformation is observed in a region of the aluminium specimen where the interfacial velocity is relatively low and the shallow deformation is observed in a region where the interfacial velocity is higher. A 1D numerical treatment is presented which predicts the existence of two mechanisms for dynamic friction termed ‘asymptotic melting’ and ‘slide-then-lock’. In both modes there is a warm-up phase in which the interface temperature is increased by frictional heating. For high initial sliding velocity, this is followed by the onset of the asymptotic melting state, in which the temperature is almost constant and melting is approached asymptotically. This mechanism produces low late-time frictional stress and shallow deformation. For lower initial sliding velocity, the warm-up terminates in a violent work hardening event that locks the interface and launches a strong plastic shear wave into the weaker material. This slide-then-lock mechanism is characterized by sustained high frictional stress and deep plastic deformation. These predicted mechanisms offer a plausible and consistent explanation for the abrupt transitions in the depth of sub-surface deformation observed in the experiments. A key conclusion arising from the current work is that the frictional stress does not vary smoothly with pressure or sliding velocity. Instead the pressure and sliding velocity determine whether the impulse will be very high or very low. The next generation of friction models for hydrocodes will need to account for these factors.

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Section: Introductionmentioning

confidence: 99%