Cohesive Zone Modelling in Adhesively Bonded Joints

Abstract

Laminated composites is a material that is rapidly being adapted in the aircraft industry and new joining techniques are being researched for new structural designs. One such technique is adhesive bonding, which can result in decreased weight, fuel saving and improved strength of aircraft components. Robust strength and failure analysis methods are required to assess new designs beforehand. One of these methods is co-hesive zone modelling. Cohesive zone modelling is a technique based on cohesive forces and energy within a material or interface region which keeps material together. Damage can be tracked progressively along a region with cohesive elements and damage propagation can be monitored in a structure. This thesis work relies on cohesive zone modelling to monitor damage propagation of the bondline and in between plies of simple bonded joints, together with progressive failure criteria to assess any failure within the plies of a joint. A composite Cracked Lap Shear (CLS) specimen was tested with results of a possible crack jump from bondline to adherend. The objective of this thesis was to assess and recreate damage propagation and the possibility of a jumpof damage growth frombondline to adherend in theCLS specimen. Thiswas done by us-ing cohesive zone modelling and progressive failure criteriawith the finite element package MSC.Mentat and its solver MSC.Marc. A validation with another test report on mixed-mode bending and interlaminar failure was performed using a cohesive zone model with the settings MSC.Marc has to offer. This wielded accurate results in terms of loading and damage. With the aid of this validation, the options within the cohesive zone model which had the best results in the validation were used for simulations of the CLS specimen. Cohesive zone elements representing the bondline and the adhesive within the laminate adherends in the CLS model are used to assess cohesive and interlaminar failure, while progressive failure criteria are used to assess in-tralaminar failure. The results of the current simulation setupswere unsatisfying as the failure load and strain results had large errors. Further detailed analyses will be needed to recreate the multiple failure modes in the CLS specimen in MSC.Marc with acceptable results. On the other hand, the thesis has proven that MSC.Marc and its own cohesive zone model perform well enough for mixed-mode bending and interlaminar failure in simple geometries.