Abstract
We present a new methodology for the identification of a zone cohesive model that describes material failure. The material under consideration fails by crazing. The study is conducted at the micron scale in order to capture and analyze the fracture mechanism. The crack tip displacement fields are measured optically by Digital Image Correlation. The local stress intensity factors (mode I and II) and the location of the equivalent elastic crack tip are calculated during the loading. The variation of the location of the equivalent crack tip is used to track the initiation and growth of the process zone, up to the onset of crack propagation. These experimental measurements are used to define the appropriate parameters in a cohesive zone model. The methodology addresses the onset of crazing, the traction–separation profile and the maximum opening corresponding to the local nucleation of a crack. The cohesive parameters that are derived from the experimental data are consistent with results available in the literature. In addition, the model enables the characterization of the normal and tangential mode of the cohesive model.
Highlights
The description of fracture mechanisms by cohesive zone models (Barenblatt, 1962) has been a subject of increased interest in the micromechanics community since the pioneering work of Needleman (1987) and Xu and Needleman (1994)
Such dimensions allow for an optical analysis of the crack tip displacement fields: by interferometry as reported by Doll, and by means of recently developed Digital Image Correlation (DIC) techniques
Unlike the derivations of cohesive zone models found in the literature (Abanto-Bueno and Lambros, 2005; Fedele et al, 2009), the formulation depicted in Fig. 7 is identified from the analysis of the displacement crack tip fields, as presented
Summary
The description of fracture mechanisms by cohesive zone models (Barenblatt, 1962) has been a subject of increased interest in the micromechanics community since the pioneering work of Needleman (1987) and Xu and Needleman (1994). The typical dimensions involved in crazing allow an analysis by optical interferometry and extensive work by Doll and coworkers (Doll, 1983; Doll and Konczol, 1990) have established that the critical opening is 2–10 mm, resulting in a length for the cohesive process zone of some tens of micrometers Such dimensions allow for an optical analysis of the crack tip displacement fields: by interferometry as reported by Doll, and by means of recently developed Digital Image Correlation (DIC) techniques. The extraction of cohesive zone model parameters requires (i) specific experiments to characterize craze initiation, (ii) numerous fracture tests at different loading rates for craze widening and related fibrillation, and (iii) optical interferometry of wedge cracks to measure the craze critical opening, cr d. The summation convention is not used for repeated Greek indices
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