Spall fracture properties of aluminum and magnesium at high temperatures

Abstract

Measurements of the dynamic tensile strength of aluminum and magnesium have been carried out by investigations of the spall phenomena over a wide range of temperatures, shock-wave intensities, and load durations. Free-surface velocity profiles were recorded with VISAR and used to provide the spall strength measurements. The initial temperature of samples was varied from room temperature to near the melting point. The peak compressive pressure in the shock waves was varied from 5 to 50 GPa for aluminum and from 2 to 10 GPa for magnesium. The load duration was varied by more than one order of magnitude. The free-surface velocity measurements showed a precipitous drop in the spall strength of preheated samples as temperatures approached the melting point. No significant influence of the peak pressure on the spall strength was observed. The strain-rate dependencies of the spall strength could be represented as power functions with a power index of 0.060 for aluminum and 0.072 for magnesium. Unexpectedly large amplitudes for the Hugoniot elastic limit of both aluminum and magnesium were observed at temperatures approaching the melting point.

The shock and spall response of three industrially important hexagonal close-packed metals: magnesium, titanium and zirconium

“…For instance, large values of the elastic precursor wave were observed at temperatures approaching the melting point. This was also seen in Al [48]. This was attributed to the Frenkel disorder [49], i.e.…”

“…Owing to its relatively low melting point (649 • C), a modest increase in testing temperature has also been shown to affect the shock response of Mg, primarily the elastic precursor [48]. For instance, large values of the elastic precursor wave were observed at temperatures approaching the melting point.…”

“…Examination of the spall behaviour of various magnesium alloys has been of interest to a number of researchers [52,53]-particularly at elevated temperatures [48,54,55]. Schmidt et al [56] measured the spall strength of AZ31B-H24 and reported a value of 1.5 GPa for the onset of incipient spall at room temperature.…”

“…Ordinarily, this might appear unsurprising. However, it is reported that when various metals have been shocked to a high stress, and where the temperature increase approaches melt for the material (owing to shock heating), the spall strength remains unaffected [48].…”

The resistance to deformation and facture of magnesium ma2-1 under shock-wave loading at 293 k and 823 k of the temperature

“…Figure 6 presents an example of the free surface velocity history measured at elevated temperature in comparison with the room temperature data at the same impact conditions. Unlike to aluminum [9][10][11] the alloy does not exhibit anomalous increase of the HEL with heating. Accounting for decreasing elastic moduli with growth of the temperature, it follows from presented data that the dynamic yield stress decreases with heating.…”