13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- the crack faces was made and a new method was proposed. This paper discusses, Mode II fatigue crack growth experiments that were conducted using the proposed method, along with the obtained results. 2. Experimental procedures 2.1. Mechanical model Figure 1(a) shows the mechanical model of the Mode II fatigue crack growth experiment that was proposed by Murakami et al. [3]. In this paper, this model is referred to as the “former mechanical model.” Load P was applied to the upper cantilever. By inserting a ceramic cylinder in the slit, load P was assumed to be divided into two equal halves and applied to both cantilevers. In a real machine, a Mode II crack propagates under the condition of compressive stress. Therefore compressive load S was applied using the pre-tightening force of bolts. Mode II fatigue crack growth experiments were performed by applying the former mechanical model. However, because of the plastic deformation of the specimen where the ceramic cylinder made contact with it, load P could not be divided as expected. In fact, dents were found on the specimen where the ceramic cylinder inserted into the slit made contact, and a considerable reduction in the slit width was observed during the fatigue experiment. This reduction in the slit width was thought to be caused by a gap formed as a result of plastic deformation when the load was applied and, as a result, the load applied to the lower cantilever was thought to be considerably reduced. In order to equally divide the load P between the cantilevers, a new mechanical model has been proposed [7, 8]. Figure 1(b) shows this new mechanical model, which was based on the experimental setup shown in Fig. 1(c). The new model was discussed with springs and rigid blocks in the previous study [7, 8]. This discussion showed that if the pre-tightening force S was larger than P/2, then the load was divided into two equal halves and applied to the two cantilevers, and the width of the slit did not change during the experiment even if a cylinder was not in place. In addition to the compressive load S by the pre-tightening force of the bolts, compressive load Q was applied on the fatigue crack face in order to avoid crack branching in Mode I during the fatigue crack propagation. 2.2. Material The experiments were carried out using commercial grade Japanese Industrial Standards (JIS) SS400 steel (400 MPa minimum tensile strength) which is rolled steel designed for general structures. Table 1 presents its chemical composition. (a) (b) (c) Figure 1. Mechanical models for Mode II experimental method: (a) former mechanical model [3], (b) new mechanical model [7, 8], and (c) new experimental setup
RkJQdWJsaXNoZXIy MjM0NDE=