13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Figure 1. Specimen geometry of the micro cantilever based on single edge notch bending mimicking crack opening mode I. Figure 2. Three-dimensional finite element model of the micro cantilever showing the used mesh and the applied boundary conditions. The material parameters are fitted to experimental results of Argon and Maloof (1966) [14]. They investigated the mechanical behavior of single tungsten crystals via tensile tests at different orientations. The material parameters were fitted to the {112}-tensile orientation. Table 1 summarizes the found material parameters initial hardening modulus ℎ0, initial yield stress 0 and stage 1 stress for each slip system family. Table 1. Estimated material parameters of the two system families slip system {110}<111> {112}<111> ℎ0 [MPa] 3700 3800 0 [MPa] 140 145 [MPa] 385 400 3. Results and Discussion Elastic study of the bending of the micro cantilever In the fracture experiment an indenter moves with a speed of 20 nm per second in negative z-direction (see Fig. 2). Its reaction force (named RF3) is measured together with the prescribed displacement u in z-direction. As the crack opens during bending, the cantilever moves relative to the indenter and friction occurs resulting in a lateral force called RF1 and in a deviation from pure mode I. Its size and effect on the stress field around the crack tip are unknown and experimentally hardly accessible. To clarify the influence of the lateral forces, the purely elastic model presented in section 2 was applied to simulate displacement controlled bending of the micro cantilever. As the friction coefficients μ are not available, it was varied between 0 and 0.4. Additionally, different geometries of the indenter tip were applied in the FE simulations: 1. Indenter R2 (0.2 µm) 2. Indenter R10 (0.2 and 0.5 µm) 3. Wedge R10 (0.5 µm) 4. Concentrated Force 5. Pressure
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