13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- 4.3. Effect of specimen geometry on fatigue crack growth Three different specimen geometries were used in the present study. All specimens were made of ED-Cu. The fatigue crack growth rate is shown in Fig. 6 (a). The relationship between stress intensity factor range calculated from FEM and experimental crack growth rate is fitted on one curve regardless of the geometries as shown in Fig. 6 (b). Figure 6. (a) Fatigue crack growth rate of ED-Cu specimens with three geometries. (b) Relationship between stress intensity factor range and fatigue crack growth rate of ED-Cu specimens with three geometries. 5. Discussion 5.1. Fatigue crack growth behavior Many studies about fatigue behavior in thin metal sheet have shown that fatigue life is associated with the grain structure and specimen thickness using smooth specimen [7-10]. In the present study, fatigue crack propagation experiments were performed with notched specimen under strain-controlled condition. The crack path of the specimen exhibited almost straight line as shown in Fig. 4 (a) and Fig. 5. (a). It allows us to measure the crack length in the sensor easily. Among them, the path observed from the deposition side in ED-Ni was relatively rough due to the development of columnar grains during electrodepositing process. The relationship between stress intensity factor range calculated from FEM and experimental crack growth rate is fitted to one equation regardless of strain amplitude, strain ratio and specimen geometry. Therefore, two specimens made of different materials are needed to apply the principle of smart stress-memory patch. The threshold value of stress intensity factor range was determined by Kohout equation, which is related to the minimum value of detectable stress amplitude. 5.2. Estimation of fatigue damage using two materials Based on fatigue testing results, a method to evaluate fatigue damage of structure using smart patch will be discussed. When the patch is attached to structure, the sensor is subjected to strain-controlled loading under the change in strain of the structure. A simple model for the attached sensor to structure is depicted in Fig. 7. It is assumed that the far-field stress in the plate is a uniaxial tension ( structure) in
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