An investigation on crack bridging in metal matrix composite using analytical and numerical approaches

Abstract

This paper is aimed to investigate the influence of fiber bridging on crack opening displacement (COD), stress intensity factor (SIF), and crack growth rate in unidirectional SCS-6/Ti–6Al–4V and/or SCS-6/Ti–6Al–7Nb matrix composites under cyclic loading. To model the closure pressure induced by fiber bridging, two modeling approaches were employed: the Shear lag (SL) model and the fiber pressure model (FPM). The finite element method and Bueckner weight function technique were utilized to compute the fracture mechanics parameters, viz. COD, SIF, and crack growth rate. Initially, the computed COD using the SL model near the crack tip of a partially bridged specimen made of SCS-6/Ti-15-3 matrix composite was validated with the reported experimental results. An effective frictional stress value for all subsequent analyses was obtained for the SCS-6/Ti–6Al–4V composite by comparing crack-opening displacement computed across various values of frictional shear stress using the SL model with that obtained using the FPM. Further, using both the FPM and SL model, the crack-driving force (ΔK) was calculated and used to predict fatigue crack growth rates through Paris’ law and the Hertzberg equation. For both composites, the quantitative estimates predict substantial reductions (for instance, for SCS-6/Ti–6Al–4V composite, the reduction is more than 70% at 198 MPa stress range) in crack-opening displacement, indicating a consistent suppression of local crack-tip deformation, and hence reveal a pronounced crack-shielding effect attributed to fiber bridging. While, the value of ΔK for crack of length 1.89 mm in SCS-6/Ti–6Al–7Nb composite is reduced from 29.78 MPa·m1/2 to 3.91 MPa·m1/2.