About the effect of plastic dissipation in heat at the crack tip on the stress intensity factor under cyclic loading

Abstract

Because of the reverse cyclic plastic zone at the crack tip, there is plastic dissipation in heat at the cracktip under cyclic loading. That creates a heterogeneous temperature field around the crack tip. A thermomechanicalmodel is proposed in this paper for evaluating the consequence of this temperature field onthe Mode I stress intensity factor. Two cases are studied: (i) the theoretical problem of an infinite platewith a semi-infinite through crack under Mode I cyclic loading, and (ii) a finite specimen with a centralthrough crack. In the first case, the main hypothesis and results are presented from the literature but noheat loss is taken into account. In second case, heat loss by convection is taken into account with a finiteelement analysis, while an analytical solution exists in the literature for the first case. In both cases, it isassumed that the heat source is located in the reverse cyclic plastic zone. The heat source within thereverse cyclic plastic zone is quantified by experiments on a mild steel under R = 0.1. It is shown thatthe crack tip is under compression due to thermal stresses coming from the heterogeneous temperaturefield around the crack tip. The effect of this stress field on the stress intensity factor (its maximum, minimumand its range) is calculated. This paper shows that experiments have to be carried out to determinethe heat source within the reverse cyclic plastic zone. This is the key parameter to quantify the effect ofdissipation at the crack tip on the stress intensity factor.