Mode I Crack Propagation Experimental Analysis of Adhesive Bonded Joints Comprising Glass Fibre Composite Material under Impact and Constant Amplitude Fatigue Loading

The T-90 Calima is a low-wing monoplane aircraft. Its structure is mainly composed of different components of composite materials, which are mainly bonded by using adhesive joints of different thicknesses. The T-90 Calima is a trainer aircraft; thus, adverse operating conditions such as hard landings, which cause impact loads, may affect the structural integrity of aircrafts. As a result, in this study, the mode I crack propagation rate of a typical adhesive joint of the aircraft is estimated under impact and constant amplitude fatigue loading. To this end, effects of adhesive thickness on the mechanical performance of the joint under quasistatic loading conditions, impact and constant amplitude fatigue in double cantilever beam (DCB) specimens are experimentally investigated. Cyclic impact is induced using a drop-weight impact testing machine to obtain the crack propagation rate (da/dN) as a function of the maximum strain energy release rate (GImax) diagram; likewise, this diagram is also obtained under constant amplitude fatigue, and both diagrams are compared to determine the effect of each type of loading on the structural integrity of the joint. Results reveal that the crack propagation rate under impact fatigue is three orders of magnitude greater than that under constant amplitude fatigue.

A mode I crack with multiple islands of ideal contact between the crack faces: An asymptotic model

The problem of a mode I crack having multiple contacts between the crack faces is considered. In the case of small contact islands of arbitrary shapes, which are arbitrarily located inside the crack, the first-order asymptotic model for the crack opening displacement is constructed using the method of matched asymptotic expansions. The case of a penny-shaped crack has been studied in detail. A scaling hypothesis for the compliance reduction factor is formulated.

Molecular dynamics study on atomic elastic stiffness at mode I crack along bi-metal interface

Propagation of mode I crack along bi-metal (001) interfaces of Fe/W, Fe/Ni, Fe/Co and Ti/Mg is simulated by molecular dynamics and discussed with the eigenvalue/vector of the atomic elastic stiffness, B i j a = Δ σ i a / Δ ε j , and surface energy. The crack does not propagate at the interface but in the adjacent phase of smaller surface energy, except in Fe/Ni. The 1st eigenvalue η a (1) , or the solution of B i j a Δ ε j = η a Δ ε i of each atom, clarifies the difference of ‘soft/hard’ of both phases at the onset of crack propagation. In the case of Fe/Ni, the η a (1) of Ni atoms remarkably decreases in the Fe/Ni bi-metal structure, even though Ni has higher η a (1) than Fe at no-load perfect lattices. Thus the rupture occurs in the Ni side even though the Ni has slightly higher (001) surface energy than Fe. Deformation modes at the crack propagation are also visualized by the eigenvector of η a (1) < 0 unstable atoms. This article is part of the theme issue ‘Fracture dynamics of solid materials: from particles to the globe’.