A study of free surface effects on through cracks under impact loading

This paper deals with the implementation of a three-dimensional time-domain boundary integral formulation for a center-crack, finite solid under symme trically applied step loading. The BEM displacement time domain formulation s have, hitherto, been limited to analyzing two-dimensional crack problems, though hypersingular formulations have been used to analyze finite cracks in infinite domains. In this paper, variation of dynamic stress intensity f actor (DSIF) along the crack front for a stationary, through-thickness stra ight crack is studied for a finite solid under step loading. The state of s tress is evaluated at the crack vertex, where crack front meets the free su rface. The effect of free surface on DSIF is investigated. The effect of wa ves traveling in thickness direction is explained. It is possible to estima te accurately the critical intersection angle of the crack front with the f ree surface at which square-root singularity is restored at the crack verte x under step loading. A new partitioning scheme is proposed for spatial int egration of elastodynamic kernels. (C) 2001 Elsevier Science Ltd. All right s reserved.