A three-dimensional finite element analysis is developed for the cold expansion process in two aluminum alloys, 2024-T351 and 7050-T7451. The entire cold working process including hole expansion, elastic recovery, and finish reaming is simulated. Both isotropic hardening and kinematic hardening models are considered in the numerical calculations. The results suggest that a three-dimensional nature exists in the residual stress fields surrounding the hole. There are significant differences in residual stresses at different sections through the thickness. However, residual stress at the surface is shown to remain the same for the different plastic hardening models after the hole has recovered and finish reaming has been performed. The reaming of the material around the hole has slight effect on the maximum value and distribution of residual stresses. A comparison has been drawn between the FEA of average through thickness strain and a previous experimental investigation of strain that utilized neutron diffraction and modified Sachs boring on a 7050 aluminum specimen containing a cold expanded hole. The different methods show very good agreement in the magnitude of strain as well as the general trend. The conclusions obtained here are beneficial to the understanding of the phenomenon of fatigue crack initiation and growth at the perimeter of cold worked holes.
A geometrically nonlinear finite-element analysis of cohesive failure in typical joints is presented. Cracked-lap-shear joints were chosen for analysis.Results obtained from linear and nonlinear analysis show that nonlinear effects, due to large rotations, significantly affect the calculated mode I, crack opening, and mode II, inplane shear, strain-energy-release rates.The ratio of the mode I to mode II strain-energy-release rates (_i/_ii) was found to be strongly affected by the adhesive modulus and the adherend thickness. #i/#ii ratios between 0.2 and 0.8 can be obtained by varying adherend thickness and using either a single or double cracked-lap-shear specimen configuration.Debond growth rate data, together with the analysis, indicate that mode I strainenergy-release rate governs debond growth.Results from the present analysis agree well with experimentally measured joint opening displacements.
A B S T R A C T This paper investigates the tensile and fatigue properties of a newly developed fibre metal laminate (FML) manufactured using the vacuum assisted resin transfer moulding (VARTM) method. This manufacturing method allows the glass fibre reinforced epoxy and 2024-T3 aluminium FML to be prepared at lower cost than conventionally manufactured FMLs. However, in order for the resin to infiltrate the FML, the metal sheets need to be perforated. These perforation holes act as crack initiators and reduce the FML's performance. Tension and fatigue test results of three different designs are reported and compared to mechanical property predictions. Additionally, single sheet Al alloy specimens were tested in order to analyse the influence of the drilling method.Keywords fatigue; fibre metal laminate (FML); hybrid composite; tensile behaviour; vacuum assisted resin transfer moulding (VARTM).
N O M E N C L A T U R E ARALL= aramid reinforced aluminium laminate CLT = classical lamination theory exp. = experiment E = Young's modulus/elastic modulus E Al = Young's modulus of the aluminium alloy E c = Young's modulus of the composite FML = fibre metal laminate GLARE = glass reinforced fibre metal laminate h = height R = stress ratio = min. stress/max. stress ROM = rule of mixtures VARTM = vacuum assisted resin transfer moulding α Al = thermal expansion coefficient of the aluminium alloy α C = thermal expansion coefficient of the composite ε = strain ε Al = strain of the aluminium alloy ε c = strain of the composite ε f = maximum strain/strain at failure ε total = overall specimen strain ν = Poisson's ratio σ = stress σ Al = stress in the aluminium alloy layer of the specimen
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