Spall fracture: methodological aspects, mechanisms and governing factors

Abstract

The dynamic tensile strength of materials at load durations of a few microseconds or less is studied by analyzing the spall phenomena under shock pulse loading. The paper is devoted to discussing the methodology and capabilities of the technique to measure spall strength, its error sources, spall fracture of materials of different classes and the factors governing the high-rate fracture of metals and alloys under such conditions.

Spall strength of sapphire

“…In general, they are similar to the wave profiles observed in the spall fracture tests of ductile metals [6,8]. The short velocity spike observed on the shock wave front is due to the fact that the aluminum foil (used as the reflector) has lower dynamic impedance than that of sapphire and acquires a higher velocity after arrival of the shock wave.…”

“…The magnitude of tensile stress prior to the fracture (i.e., spall strength) was calculated using measured values of the velocity pullback ahead of the spall impulse [6,8]. The calculations employed the Hugoniot of elastic compression of sapphire expressed as U S = 11.19 + u p [9], where U S is the shock wave velocity and u p is the particle velocity.…”

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

“…Spall or dynamic fracture involves the generation of a plane of tensile damage within a dynamically loaded material; its effects can range from incipient spall where failure has just begun to break out to the creation of a detached spall plane. Measured spall strengths depend heavily upon loading conditions [18,19]. There are a number of techniques that can be used to monitor the evolution of spall inside materials.…”

“…These include approaches to monitor the free surface of loaded systems, visual interferometer system for any reflector (VISAR), heterodyne velocimetry as well as using embedded manganin gauges [20]. However, because such approaches monitor spall remote from the site of its evolution, the signal from the spall plane will inevitably evolve before detection, making interpretation of spall complex [18].…”

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

“…In this regard, the shock wave techniques present such advantages as extremely wide range of strain rates available for measurements, well controlled loading conditions, independence of testing apparatus, and possibility to get numerical data basing only on fundamental physical laws without additional assumptions and models. Strange as it may seen but, although main methods of studying elastic-plastic and strength properties of shocked solids are well developed [1][2][3][4][5][6][7], systematic data of such kind are very seldom. In this paper we present results of measurements of the precursor decay, rise time of plastic shock wave, and spall strength of Ma2-1 magnesium deformable alloy.…”