Browsing by Author "Rocha, R.J.B."
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- Advanced numerical methods for the strength prediction of hybrid adhesively bonded T-peel jointsPublication . Faria, R.V.F.; Campilho, R.D.S.G.; Gonçalves, P.J.A.; Rocha, R.J.B.The market requirements impose searching for new joining solutions, which must be simple and effective. Adhesive joints are currently used, for example in the automotive and aeronautical industries, since welding is not possible in many cases and because drilling the base materials is not required. To analyse adhesive joints, the Finite Element Method (FEM) is increasingly used. The Extended Finite Element Method (XFEM) is able to predict crack growth and joint strength in adhesive structures. However, there are still not many case studies about its suitability. On the other hand, hybrid joints, which combine spot-welding with adhesive bonding, are being increasingly used in different industries. This study has the purpose of validating the XFEM to predict the performance of T-peel hybrid joints between DIN C45E steel adherends under tensile loads. A comparison is made with spot-welded and adhesive joints. Three adhesives are tested (Araldite® AV138, Araldite® 2015 and Sikaforce® 7752). Different damage initiation and growth criteria, and also damage law shapes, were evaluated for strength and dissipated energy predictions. The joints’ performance was found to highly vary between adhesives and bonding method, and the XFEM analysis is accurate for specific modelling conditions.
- Comparative evaluation of adhesively-bonded single-lap and stepped-lap jointsPublication . Silva, J.O.S.; Campilho, R.D.S.G.; Rocha, R.J.B.; Silva, F.J.G.Several adhesive joint configurations are available, namely butt joints, single-lap joints (SLJ), double-lap joints and scarf joints. Stepped-lap joints, which are not so studied, consist of a finite number of steps in the bonded area, possessing stress concentrations at all step edges instead of only at the bonded length edges. Stepped-lap joints increase the maximum load (Pm) over SLJ. The present study experimentally and numerically evaluates the static tensile strength of SLJ and stepped-lap joints bonded with the moderately ductile adhesive Araldite® 2015, considering varying values of overlap length (LO). A Finite Element Method (FEM) analysis was carried out to compare through-thickness normal (σy) and shear (τxy) stresses in the bondline between joint configurations. Additionally, a Cohesive Zone Modelling (CZM) analysis was considered to study the failure modes and to evaluate the CZM technique’s accuracy. Between SLJ and stepped-lap joints, the improved stress distributions of the stepped-lap joints resulted in higher joint performance, especially for higher LO. The CZM model revealed to be accurate in predicting Pm.
- Geometrical parameter study of adhesively-bonded T-joints by cohesive modelsPublication . Lopes, J.P.M.; Campilho, R.D.S.G.; Rocha, R.J.B.; Silva, Francisco J. G.A wide variety of adhesive joints architectures is available, offering several options to the designers, although the most common are single-lap joints (SLJ), double-lap joints, and scarf joints. Additional designs, less used and studied are the stepped-lap, T-joints and tubular joints. T-joints find application in different types of industry, such as aircraft to bond stiffeners to skin and in the cars between the B-pillar and the rocker. This work numerically evaluates the performance of the structural adhesive Araldite® 2015 in an aluminum T-joint, after validation with experimental results. A cohesive zone modelling (CZM) numerical study is carried out to capture the behavior of different T-joints geometrical configurations when subjected to peel loads. The work includes a parametric study, considering maximum load (Pm) and dissipated energy at failure (U) prediction, considering four geometrical parameters: flat adherend thickness (a), T-element thickness (t), overlap length (l) and T-element radius (r). A significant effect on Pm was found for the tested parameters, and the CZM method revealed to be a precious method for studying T joints with precision and accuracy.
- Mixed-mode evaluation of ductile adhesive joints by the single-leg bending testPublication . Ribeiro, J.P.S.M.B.; Campilho, Raul D. S. G.; Rocha, R.J.B.In the design of adhesive structures, it is extremely important to accurately predict their strength and fracture properties (critical strain energy release rate in tension, GIC, and shear, GIIC). In most cases, the loads occur in mixed-mode (tension plus shear). Thus, it is of great importance the perception of fracture in these conditions, namely of the strain energy release rates in tension, GI, and shear, GII, relative to different crack propagation criteria or fracture envelopes. This comparison allows to determine the most suitable energetic propagation criterion to be used in cohesive zone models (CZM). The main objective of this work is to verify, by CZM, which is the power law parameter (α) that best suits the energetic crack propagation criterion for CZM modelling, using single-lap joints (SLJ) and double-lap joints (DLJ) with aluminium adherends and bonded with a ductile adhesive. With this purpose, numerical simulations of the SLJ and DLJ are carried out, and the maximum load (Pm) is compared with experiments. For the tested materials and geometries, the energetic criterion resulting from the experimental work provided matching numerical results and, thus, the fracture envelope was validated.