ABSTRACT
A simple procedure for determining dynamic stress intensity Factor K as a function of crack velocity has been proposed. This method assumes that the dynamic stress intensity factor in a center-pin-loaded single-edge-notched (CPL-SEN) tensile specimen may be represented by (mathematical equation) (available in full paper)
where KQ is the initial stress intensity factor at the onset of rapid crack propagation, ao is the initial crack length, a is, the instantaneous crack length, G (å) is the crack velocity correction factor and (mathematical equation) (available in full paper)
INTRODUCTION
It has been recognized that the stress intensity factor (fracture toughness) for a running crack depends upon crack velocity and that analysis of dynamic fracture phenomena such as crack branching, crack propagation and arrest requires understanding of the relationship between the stress intensity factor (K) and crack valocity (å). In recent years extensive efforts have been made to develop analytical and experimental procedures to establish this å vs K relationship for various materials. Among them, dynamic photoelasticity coupled with high-speed photography has been particularly successful in generating the å vs K relationship for transparent birefringent brittle polymeric materials (2, 7, 9, 0, 1). In this method the instantaneous stress intensity factor K is determined from photographs of isochromatic fringe loops associated with a running crack. The method of K determination from the isochromatic fringe loop was first developed by Irwin (8) and recently improved by Etheridge (4). Series of high-speed photographs also provide information on, the crack position (crack length) as a function of time. Crack velocity information can be obtained as a slope of the curve of the crack position vs time. The K vs å relationship thus obtained (e.g., by Kobayashi and Dally for Homalite-100 as shown in Fig. l) clearly defines the values of the stress intensity factor associated with such phenomena as crack branching, crack arrest, and also crack propagation behavior in general. For nontransparent materials such as metals and rocks, however, simple analytical or experimental procedures to establish the å vs K relationship have not yet been developed. One of the reasons for this may be that, unlike transparent birefringent polymers, simple and adequate experimental means of characterizing the dynamic stress or strain fields in the vicinity of a running crack tip in nontransparent materials have not yet been developed. As a result, most of the work performed concentrates on characterization of crack velocities (1, 6, 4) The work described in this paper is an attempt to develop a simple experimental procedure to estimate the dynamic stress intensity factor based on apriori data such as the static preload, initial crack length, geometric dimensions of the specimen, and to establish the å vs K relationship which can be applicable to nontransparent materials.
PRINCIPLE
The procedure assumes that the stress intensity factor K associated with a running crack in a geometrically simple specimen such as a center-pin-loaded single-edge-notch (CPL-SEN) tension specimen may be represented by the following functional equation: (mathematical equation) (available in full paper)
