Daniel F.O. Braga

Aluminium Friction-stir Weld-bonded Joints

A push towards more energy-efficient transport solutions has led to an increasing lightweight trend in structural design, requiring new materials, manufacturing, and assembly processes. The development of solid-state welding techniques, such as friction-stir welding (FSW), and the continuous improvement of adhesive technology, has created opportunities for new structural design concepts. Although FSW is capable of producing sound defect-free welds with high tensile strength efficiency in butt joint configuration, in the case of lap joints, the formation of a “hook”-like defect results in worse properties than base material. The combination of adhesive bonding (AB) with FSW aims to overcome this issue and create a hybrid joining technique. This work aims to develop a hybrid technique combining FSW and AB aggregating static strength testing and numerical modelling efforts. AB joints showed a 60% higher strength than FSW lap joints, but when combining FSW with adhesive, the hybrid joint managed to match the adhesive joints strength. Finite elements method (FEM) models developed for both AB and FSW lap joint showed some level of agreement, but when attempting to combine both models to discretize the hybrid joints the developed model failed to mimic the more complex failure mode.

SIF determination with digital image correlation

Purpose – Hybrid methods, wherefore numerical and experimental data are used to calculate a critical parameter, have been used for several years with great success in Experimental Mechanics and, in particular, in fracture mechanics. The purpose of this paper is to report on the comparison of the strain field from numerical modelling forecasts against the experimental data obtained with the digital image correlation method under Mode II loading in fatigue testing. The numerical dual boundary element method has been established in the past as a very reliable method near singular regions where stresses tend to grow abruptly. The results obtained from the strain data near the crack tip were used in Williams expansion and agree fairly well with both the numerical results and the analytical solution proposed for pure Mode II testing. Design/methodology/approach – The work presented in this note is experimental. The proposed methodology is of an hybrid experimental/numerical nature in that a numerical stress int...

4 – Mechanical properties

Friction stir welding (FSW) and friction stir processing (FSP) are two solid state processes that involve heating by friction and plastic deformation. As a result of these inputs, mechanical properties differ from those of base materials. For application of these techniques, it is necessary to know the hardness, static, fracture and fatigue properties associated with materials welded or treated. This chapter summarizes studies on each technique for several alloys. Process parameters have a high influence on mechanical properties achieved and residual stress and distortion are also of high importance. Due to their nature, residual stresses are unavoidable and play a fundamental role on properties such as fatigue behaviour. Residual stress and its associated distortion in FSW and FSP are discussed. These techniques are applicable to a high number of different alloys and applications of multi-material joining applications. Combined with the effect of process parameters, it is virtually impossible to study the mechanical properties for each case, therefore property prediction is highly important. A summary of studies regarding this issue is also presented.