Numerical modelling of through-thickness reinforced structural joints

摘要

The main objective of this research study was to develop numerical modelsto analyse the mechanical and fracture properties of through-thickness reinforced(TTR) structural joints. The development of numerical tools was mainlybased on the finite element (FE) method. A multi-scale approach was used:the bridging characteristics of a single reinforcement was studied at micromechanicallevel by simulating the single-pin response loaded either in mode-Ior in mode-II. The force-displacement curve (bridging law) of the pin was usedto define the constitutive law of cohesive elements to be used in a FE analysisof the global structure.This thesis is divided into three main parts: (I) Background, context andmethodology, (II) Development for composite joints, and (III) Developmentfor hybrid metal-composite joints. In the first part the objectives of the thesisare identified and a comprehensive literature review of state-of-art throughthicknessreinforcement methods and relative modelling techniques has beenundertaken to provide a solid background to the reader.The second part of the thesis deals with TTR composite/composite joints. Themulti-scale modelling technique was firstly applied to predict delamination behaviourof mode-I and in mode-II test coupons. The bridging mechanismsof reinforcements and the way these increase the delamination resistance ofbonded interfaces was deeply analysed, showing how the bridging characteristicsof the reinforcement features affected the delamination behaviour. Themodelling technique was then applied to a z-pin reinforced composite T-jointstructure. The joint presented a complicated failure mode which involved multiplecrack path and mixed-mode delamination, demonstrating the capabilityof the model of predicting delamination propagation under complex loadingstates.The third part of the thesis is focused on hybrid metal/composite joints. Mode-I and mode-II single-pin tests of metal pin reinforcements embedded into acarbon/epoxy laminate were simulated. The model was validated by comparingwith experimental tests. Then the effects of the pin geometry on thepin bridging characteristics were analysed. The model revealed that both inmode-I and mode-II small pins perform better than large pins and also thatthe pin shape plays an important role in the pin failure behaviour. The modellingtechnique was then applied to simulate a metal-composite double-lapjoint loaded in traction. The model showed that to obtain the best performanceof the joint an accurate selection of pin geometry, pin arrangement andthickness of the two adherends should be done.