Experimental and numerical characterization of a mechanical expansion process for thin-walled tubes

Air heat exchangers are made with tubes joined to finned pack. The connection between tubes and fins can be obtained through a mechanical process where an ogive is pushed inside the tube with smaller internal diameter causing its expansion. Residual plastic deformation provides the assembly with the fins. Accurate connection over the whole contact area of the tubes and fins is essential for maximum heat exchange efficiency. The goal of this work is to study and develop a finite element model able to effectively simulate expansion forming, allowing process analysis and, eventually, process optimization. The paper is divided into a first experimental part, where the materials used for the heat exchangers are characterized, and a second numerical part where models have been developed on the basis of the experimental data. The developed models are used to identify the material properties with an inverse method, and then to study the technological process of tube expansion by using a simplified but sufficiently accurate description. The model has proved to be an effective design tool, as it can evaluate the influence of the main parameters on the process and so optimize production according to technological variations

Bonded structures improvement by the dual adhesive technique

1st Virtual European Conference on FractureA common technique to reduce stress gradients in adhesive joints is to use the dual adhesive technique, which has proven to reduce peak stresses in single-lap joints. However, other joint configurations could benefit from this technique. This work experimentally and numerically evaluates stepped-lap dual-adhesive joints (DAJ) between aluminum adherends, for various overlap lengths (LO), and carries out a detailed comparison with stepped-lap single-adhesive joints (SAJ) with the same individual adhesives (Araldite® AV138 and Araldite® 2015). The joint behavior was predicted by cohesive zone modelling (CZM) with a triangular law. The analysis of the results is presented in the form of failure modes, stress analysis, maximum load (Pm) and energy required to failure (U). It was concluded that, in general, CZM presented precise predictions and are a valuable tool for the design of both SAJ and DAJ. However, no significant increase in strength was achieved with DAJ, although using more ductile adhesive can promote better DAJ results.info:eu-repo/semantics/publishedVersio

Investigation of mechanical and fracture properties of wire and arc additively manufactured low carbon steel components

Wire and Arc Additive Manufacturing (WAAM) technology offers efficient fabrication of large scale products and is currently being implemented across various industries. In this study, an experimental investigation has been carried out to characterise the mechanical and fracture properties of WAAM components made of ER70S-6 and ER100S-1 metal wires. Microhardness, tensile and fracture toughness tests have been performed on the specimens extracted from the WAAM built walls which were fabricated using an oscillating pattern. The specimens were extracted from different locations, at the top and bottom of the WAAM walls, in two different orientations with respect to the deposition direction. The results show that the material hardness and yield strength of ER100S-1 built wall are higher than ER70S-6 by 62% and 42%, respectively. Moreover, in the walls made with both materials, the yield and ultimate tensile strength values were found to be slightly higher in specimens extracted in deposition (horizontal) direction when compared to specimens extracted in the built (vertical) direction. The average value of fracture toughness parameter for ER70S-6 has been found to be 88% higher than ER100S-1 material. Furthermore, the results show that the specimen extraction location in ER100S-1 wall significantly influences the fracture toughness values obtained from experiments. The results from this study have been compared with those available in the literature and discussed in terms of the mechanical and fracture properties effects on structural integrity assessment of WAAM components

Nanometre to Micrometre Length-scale Techniques for Characterising Environmentally-Assisted Cracking - An Appraisal

The appraisal is strongly focussed on challenges associated with the nuclear sector, however these are representative of what is generally encountered by a range of engineering applications. Ensuring structural integrity of key nuclear plant components is essential for both safe and economic operation. Structural integrity assessments require knowledge of the mechanical and physical properties of materials, together with an understanding of mechanisms that can limit the overall operating life. With improved mechanistic understanding comes the ability to develop predictive models of the service life of components. Such models often require parameters which can be provided only by characterisation of processes occurring in situ over a range of scales, with the sub-micrometre-scale being particularly important, but also challenging. This appraisal reviews the techniques currently available to characterise microstructural features at the nanometre to micrometre length-scale that can be used to elucidate mechanisms that lead to the early stages of environmentally-assisted crack formation and subsequent growth. Following an appraisal of the techniques and their application, there is a short discussion and consideration for future opportunities