13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Behavior of interface crack in layered structure under actions of both stress wave and residual stress ChenWu Wu1, 2*, XinXin Cheng1,3, YuChen Yuan1,3 1 Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China 2 Department of Engineering Technology and Industrial Distribution, Texas A&M University, College Station, Texas 77843, USA 3 School of Physics, University of Chinese Academy of Sciences, Beijing 100049, China * Corresponding author: chenwuwu@imech.ac.cn & cwwu@tamu.edu Abstract The propagation characteristic of stress wave impinging at the interface between initially stressed film and substrate is analyzed to reveal the effect of residual stress on the fracture behavior of such layered structure. In particular, the response of the layered structure to both stress wave and residual stress is investigated based on an axis-symmetric model including a centric coin-shape interface crack. The dispersion of the stress wave and the dynamic stress concentration around the interface crack tip are discussed with the crack surface contacting behavior being involved in the model. It is revealed that the strain energy release rate at the crack tip would be dependent on the interface crack length. The results also indicate that the residual stress would influence greatly the in-plane stress of the film and therefore determine the fracture pattern of the film. Keywords Layered structure, Residual stress, Stress wave, Interface crack 1. Introduction The impact method with coated bullet was developed by Wu et al [1] to evaluate the interface adhesion of film to substrate. In such measurement, an initial compressive stress pulse is produced by impacting the substrate of the specimen under test with the coated front end, of which the reflection would induce tensile stress around the tested interface. Theoretically, the initial compressive pulse can be calculated as 0 0 1 2 1 2 ()()/(()()) p v c c c c ρ ρ ρ ρ =− + . (1) Where 0v is the relative impinging velocity of the bullet to the specimen, 1 ( ) rc represents the acoustic impedance of the bullet coat and 2 ( ) rc the acoustic impedance of the specimen substrate [2]. The experimental results have revealed that the reflection of the input compressive pulse could separate the film off the substrate clearly [2]. Moreover, it is also indicated that the initial stress state of the specimen may influence the fracture behavior of the film and the interface. Generally speaking, the initial stress, also known as residual stress, varies according to the material treatment processes. Actually, the previous research verified that the film stress and the interface stress around the impact region edge will be greatly changed by the initial stress state in the specimen subjected to coated bullet impact [3]. The fracture may arise first within the film or at the interface depending on the comparison of the stress level to the toughness of the film or the interface. Once the interface crack exists before the specimen is impacted, the interface crack may influence the propagation and evolution of the impinged stress pulse. Therefore, this present work focus on the behavior of the interface crack between the film and substrate under impact test. First, the axis-symmetry cracked model was set up to investigate the impact responses of the structure with treating the initial impact as an input compressive stress pulse as shown in Fig. 1. Then, the propagation and evolution of the stress pulse and thereafter the deformation, stress and strain energy of the specimen are calculated for the cases of different crack length. Finally, the influence of the residual stress on the impact response of the cracked specimen is investigated for the three cases of initially stress free, initially compressed and
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