Impact experiments on low-temperature bumpers

This paper presents the results of hypervelocity impact experiments that were carried out at CISAS Impact Facility onto aluminum bumpers cooled down to −120°C with liquid nitrogen and to −60°C with solid carbon dioxide. The thickness of the targets was 0.8, 1, 2 and 3.17mm, the diameter of the spherical projectiles was 1.5, 1.9, 2.3 and 2.9 mm and the impact velocity did span between 4 and 5 km/s. To establish if any temperature dependence exists in the bumpers’ impact response, two different features were analyzed: the hole size and the bumper protection capabilities. The latter property, that is related to the bumper capacity of producing debris cloud composed of fragments as fine and slow as possible, was assessed through observation of the damage patterns on witness plates and through measurements of the debris cloud tip velocity. Moreover, qualitative analyses of high-speed shadowgraphs representing the debris cloud evolution were performed. On one hand, it was found that low temperature has only minor influence on the hole diameter. On the other hand, the examination of shadowgraphs showed that the debris cloud structure varies with bumper temperature, even though it was not proved that such differences correspond to significant dissimilarities between damage patterns recorded onto witness plates.