QUALITATIVE ANALYSIS OF THE DYNAMIC CRACK INITIATION AND PROPAGATION

Résumé
Des résultats expérimentaux de fissuration rapide sont analysés à partire de l'équation de conservation de l'energie prenant en compte l'effet de microcavités générées au sommet de la fissure. Le rayon moyen des microcavités est supposé croître selon une loi de puissance [MATH] et le volume des microcavités est défini par r^D et leur densité de distribution par [MATH], les valeurs de [MATH] sont estimées en fonction de celles de [MATH]. La rugosité de surface peut être analysée qualitativement à partir de la détermination expérimentale des paramètres D et [MATH]. La condition postulée d'incitation de la fissure est étendue à la phase de propagation. Les résultats sont en accord qualitatif avec les expériences.

Abstract
Experimental results of the fast fracture of the crack is analyzed based on the extended energy balance equation in which the effect of micr ovoids generated at the tip of the crack is taken into account. We assume that the average radius r of microvoids grow in time as [MATH], i.e., microvoids grow in the self-similar manner, statistically. It's volume is defined as r^D and the density distribution function n(r) of the microvoids is assumed to be [MATH], where D and [MATH] are numbers. The surface roughness [MATH] defined as the average radius of microvoids is compared with the experiment. Thus we can estimate the numbers [MATH] and [MATH] as [MATH] and [MATH], respectively. We have shown that the surface roughness which is called as "mirror", "mist" and "hackle" can be qualitatively analyzed from the energy balance equation if the parameters D and [MATH] are measured experimentally. Fur ther more, we have postulated the initiation condition of the dynamically loaded crack and extended it to the propagation stage. This postulate and it' s extension show the qualitative agreement with the experimental observations.