Lap shear fracture prediction of friction stir spot welds between AA6063-T6 and CRCA/IS-513 sheets

Abstract

Prediction of fracture of spot joints with complexities is of great concern during structural integrity testing of materials. In this context, the main aim of the work is to predict the fracture (peak load and fracture modes) of joints made by friction stir spot welding with a consumable sheet (FSSW-C) using the Freudenthal (Fr) model, Cockcroft–Latham (C&L) model, and normalized C&L (nC&L) model. Finite-element (FE) simulations of stirring and lap shearing are done sequentially. Such predictions will help design FSSW-C joints with complex morphologies, including several microstructural zones, interfaces, lap-butt configurations, and flash for a particular application. FSSW-C case studies are planned with AA6063-T6 and CRCA/IS-513 as base sheets at varying rotational speed (RS) and tool plunge depth (TPD). While predicting the fracture is the main aim, the relationship between FSSW-C parameters and fracture mode is also revealed. Among three RS and TPD, peak loads of 2.23 and 1.43 kN are reported for joints fabricated at 1.8 mm and 900 r/min. The nC&L model accurately predicted the peak load during lap shearing, showing a 2% to 8% difference from the experimental peak load. Therefore, it can be used with simple material properties of complex joints. The Fr model (5% to 20%) and the C&L model (6% to 18%) show significant differences. Moreover, the damage evolution reaches its critical level at peak load of lap shearing, validating the damage model. Another important outcome is that larger RS (900 and 1200 r/min) and TPD (1.8 and 2 mm) are characterized by partial plug failure and bond delamination fracture mode, which also exhibit a larger load-bearing ability suitable for FSSW-C of the sheets. Bond delamination is witnessed at lower levels of parameters (1.6 mm and 612 r/min). FE simulation prediction of lap shear fracture modes is accurate, supporting the modelling procedure with two boundary conditions.