Spallation in laser shock-loaded tin below and just above melting on release

Abstract

Spall damage in solid materials has been one of the most widely studied shock-induced phenomena for several decades, for both applied and basic scientific motivations. Comparatively, very little data can be found yet about spallation in liquid metals. In a recent paper, we have reported an exploratory investigation of liquid spall in tin samples melted upon laser shocks of very high intensities. Here, we present further experimental results obtained over a lower pressure range, where we focus on the transition from the ductile fracture behavior of solid tin to the cavitating spall expected above melting. This transition is clearly evidenced from both time-resolved free surface velocity measurements and post-test examination of the recovered targets. The drop in tensile strength associated with melting is evaluated from the velocity profiles. Detailed views of the fracture surfaces in the spall craters provide an insight into the cavitation process. Experimental data are compared to preliminary computations to determine the loading pressures and to assess the overall consistency of our interpretation of the results.

Experimental study of microjetting from triangular grooves in laser shock-loaded samples

“…This is consistent with the so-called "velocity pullback" associated with the material spall strength [10,15]. The drop of this shift in the high pressure shots on tin is consistent with the expected loss of tensile strength due to melting on release [14]. As reported in the literature and predicted by common theories, jet velocity increases with decreasing groove angle.…”

“…The short, 5 ns exposure time ensures minimum motion blur (~10 μm for a particle ejected at 2 km/s). The first two samples are tin, which is expected to partially melt upon release from shocked states above 20 GPa [13,14]. Thus, shock breakout and jetting probably occur in a mixed solid-liquid state in the second shot, while the first sample remains solid.…”

Spall fracture: methodological aspects, mechanisms and governing factors

“…There is also a temperature threshold related to melting of a solid body under tension. It has been found (Grady 1988;Kanel et al 1996b;Rességuier et al 2007) the spall strength of tin and lead gradually vanishes when the residual temperature after shock compression and release approaches the melting temperature. Figure 22 summarizes some results of measurements by Kanel et al (1996aKanel et al ( , 2001) and by Bogach et al (1998) of the spall strength for metals in the polycrystalline and monocrystalline states at temperatures up to the melting point.…”

Laser shock experiments to investigate and to model various aspects of the response of metals to shock loading

“…Upon reflection of a triangular compressive pulse (or "unsupported shock wave") from the free surface of a molten sample, cavitation is expected to occur under very low tension, very close to the free surface, and thus to lead to the ejection of a cloud of tiny droplets (referred to as "micro-spall") with a wide range of ejection velocities [10]. High pressure laser shocks have been applied onto tin samples to quantify the progressive loss of tensile strength associated with incipient melting on release [11], to investigate the debris ejection from relatively thick specimens after shock-induced melting [1,12], and to characterize more specifically the micro-spall ejected from thin foils [13]. In parallel, some theoretical issues have been addressed [14,15] and a well known, energy-based fragmentation model from the literature [16] has been adapted to the case of liquid metals then implemented in a hydrocode.…”