The application of adhesively bonded joints in aerospace structural parts has increased significantly in recent years and the general advantages of their use are well-documented. One of the disadvantages of adhesive bonding is the relevant permanence, when compared to traditional mechanical fastening. End-of-life processes generally require the separation of the adherents for repair or recycling, and usually to achieve this, they combine large mechanical forces with a high temperature, thus damaging the adherents, while consuming large amounts of energy. In this work, a novel disassembly technique based on laser-induced shock waves is proposed for the disassembly of multi-material adhesively bonded structures. The laser shock technique can generate high tensile stresses that are able to break a joint, while being localized enough to avoid damaging the involved adherents. The process is applied to specimens made from a 3D-woven CFRP core bonded to a thin Ti layer, which is a common assembly used in state-of-the-art aircraft fan blades. The experimental process has been progressively developed. First, a single-sided shot is applied, while the particle velocity is measured at the back face of the material. This method proves ineffective for damage creation and led to a symmetric laser configuration, so that the tensile stress can be controlled and focused on the bond line. The symmetric approach is proved capable of generating a debonding between the Ti and the CFRP and propagating it by moving the laser spot. Qualitative assessment of the damage that is created during the symmetric experimental process indicates that the laser shock technique can be used as a material separation method.
In this work, a model for simulating the laser shock-based disassembly of composite components is developed using the LS-DYNA explicit code. The laser shock technique has been used in the past for the non-destructive testing of adhesive bonds, but with appropriate adjustments it is possible to create a localized tensile stress that is high enough for adhesive failure to occur, making it suitable for use in the disassembly of bonded parts. In this first attempt, we focus on the development of a multiple loading instances simulation process, aiming to completely debond two carbon fiber reinforced plastic (CFRP) plates. The process of laser shock for disassembly requires an increased number of loading instances in order to cover the full bonded area. That, in addition to the short time duration in which the phenomena are evolved, poses a serious challenge for the numerical simulations, and thus a reliable procedure must be defined in terms of functionality and computational cost. Indeed, an iterative method, where the deformed model is used as input in subsequent simulations is evaluated, optimized and compared with a more traditional single model simulation.
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