Dynamic stress intensity factors for arresting cracks in DCB specimens

Abstract

The crack arrest experiments were performed in wedge-loaded DCB specimens (321x127x10 mm) made from an epoxy resin (Araldit B). Notches with different root radii were used to achieve different initial crack velocities. Dynamic stress intensity factors for propagating and subsequently arresting cracks were determined using the shadow spot method of Manogg [3] in combination with a Cranz~Schardin high speed camera; the static stress intensity factors for the corresponding crack lengths were obtained using the conventional stress intensity factor formulae from deflection measurements at the loading point. Experimental results for cracks, initiated at different values of the stress intensity factor at initiation (KI_) and thus propagating at different initial crack velocities, are summarized indFig, i. Fig. la shows values of the dynamic stress intensity factor KIyn (experimental points in the upper part of the diagram) as a function of crack length a compared with the corresponding static stress intensity factor K~ tat curve. The measured velocities are given in the lower par t of the diagram additionally. The same results as in Fig. la, but plotted in a different form, are shown in Fig. lb. Simplified curves have been drawn through the measured data points. The very early phase,of crack propagation (dashed lines), being of less importance in this context, has not been investigated. The following characteristics of the crack arrest process can be drawn from Figs. la and Ib: i. At the beginning of the crack propagation phase the dynamic stress intensity factor K~ yn is smaller than the corresponding static value K~ tat. At the end of the crack propagation phase the dynamic stress intensity factor K~yn is larger than the corresponding static value K~ tat. Only after arrest does the dynamic stress inten