Dynamic stress intensity factor of the weak/micro-discontinuous interface crack of a FGM coating

Abstract

The concepts and classification are brought forth for the strong-discontinuous interface, the weak-discontinuous interface, the micro-discontinuous interface and the all-continuous interface. The mechanical model is established for the dynamic fracture problem of the weak-discontinuous interface between a FGM coating and a FGM substrate. The Cauchy singular integral equation for the crack is derived by integral transform, and the allocation method is used to get the numerical solution. Analysis of the numerical solution indicates that the weak discontinuity is an important factor affecting the SIFs of the interfacial crack. To reduce the weak discontinuity is beneficial to the decrease of the SIFs. Contrast between the solution of the weak-discontinuous interface and that of the micro-discontinuous one shows that the micro-discontinuity is a kind of connection relation of mechanical property better than the weak discontinuity for the coating-substrate structure. To make the interface be micro-discontinuous is helpful to enhance the capacity of the functionally gradient coating-substrate interface to resist dynamic fracture. The first rank micro-discontinuity is enough to reduce the SIFs notably, however, the higher-rank micro-discontinuous terms, which is equal to or higher than the second rank, have less effect on the SIFs. In addition, the thickness of the coating and the substrate and the applied peel stress are also important factors affecting the dynamic SIFs.

Fracture analysis of a weak-discontinuous interface in a symmetrical functionally gradient composite strip loaded by anti-plane impact

“…According to the new classification of functionally graded composite interfaces put forth by Li et al [17][18][19], the interface illustrated in Fig. 1 is weak-discontinuous.…”

“…Yong and Zhou [16] analyzed the model III fracture problem of a functionally graded coating-substrate system with an internal crack perpendicular to the interface, and presented the influences of the non-homogeneity constant, relative crack length and thickness ratio on the stress intensity factor. Recently, a new idea concerning FGMs interface has been brought forth by Li et al [17][18][19]. According to the discontinuity of material properties and their derivatives at interface, bi-material interfaces were classified into the following four categories: (1) the strong-discontinuous interface, (2) the weak discontinuous interface, (3) the micro-discontinuous interface, and (4) the all-continuous interface.…”

“…(2) that the material properties are continuous, but their derivatives are discontinuous at the interface, so the interface shown in Fig. 1 is weak discontinuous [17][18][19].…”

Dynamic stress intensity factor of a crack perpendicular to the weak-discontinuous interface in a nonhomogeneous coating–substrate structure

“…Huang et al [23][24][25] expressed the arbitrary variation of material properties by a series of continuous but piecewise-linear curves. The commonly used fracture analysis methods for FGMs include the half-analytical method based on integral transform [17,[26][27][28] and the pure numerical method based on finite element computation [29][30][31][32]. Most of the existing fracture analyses concerning FGM interfaces are focused on the FGM interlayer [15,21,22,25,33] and the interface between a FGM coating and a homogeneous substrate [17,19,23,24,[34][35][36][37].…”

“…Although there is a great deal of literature addressing fracture problems of FGMs, few have attempted to answer this significant question. Recently, the research team of this paper has brought forth a new viewpoint on bimaterial interfaces [27,28,32]. According to the discontinuity of material properties and their derivatives across interface, bimaterial interfaces were classified into four categories: (a) a strong-discontinuous interface, (b) the weak-discontinuous interface, (c) the micro-discontinuous interface, and (d) the all-continuous interface.…”