This paper presents a combined experimental‐numerical technique for the calculation of the J‐integral as an area integral in cracked specimens. The proposed technique is based on full‐field measurement using digital image correlation (DIC) and the finite element method. The J‐integral is probably the most generalised and widely used parameter to quantify the fracture behaviour of both elastic and elastoplastic materials. The proposed technique has the advantage that it does not require crack length measurements nor is it limited to elastic fracture mechanics, provided that only small scale yielding is present. Evaluated are three test geometries; compact tension, three‐point bend and the double torsion beam. Possible errors and their magnitude and the limitations of the method are considered.

Current post-process heat treatments applied to selective laser melting produced Ti-6Al-4V do not achieve the same microstructure and therefore superior tensile behaviour of thermomechanical processed wrought Ti-6Al-4V. Due to the growing demand for selective laser melting produced parts in industry, research and development towards improved mechanical properties is ongoing. This study is aimed at developing post-process annealing strategies to improve tensile behaviour of selective laser melting produced Ti-6Al-4V parts. Optical and electron microscopy was used to study α grain morphology as a function of annealing temperature, hold time and cooling rate. Quasi-static uniaxial tensile tests were used to measure tensile behaviour of different annealed parts. It was found that elongated α’/α grains can be fragmented into equiaxial grains through applying a high temperature annealing strategy. It is shown that bi-modal microstructures achieve a superior tensile ductility to current heat treated selective laser melting produced Ti-6Al-4V samples.

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Purpose Selective laser melting (SLM) is a process that produces near net shape parts from metallic powders. A concern with SLM-produced metals is the achievable materials performance with respect to mechanical properties. Particularly, three important aspects strongly affect the mechanical properties of the material: internal stresses resulting from steep temperature gradients and high cooling rates, the resulting microstructure and the occurrence of pores and flaws. Design/methodology/approach This paper presents SLM-produced maraging steel 300 (18Ni-300), an iron-nickel steel alloy often used in applications where high fracture toughness and strength are required. The steel’s achievable tensile, crack growth and hardness properties and the manner in which these compare to the wrought counterpart are reported. In addition, this paper investigates the porosity distribution and achievable density, residual stress levels and post-processing procedures using heat-treatments. Findings It is found that tensile properties, hardness and microstructure compare well to its wrought counterpart. Fatigue growth rates are also comparable, though they are influenced by residual stresses and microstructure. Originality/value The investigation into the mechanical performance addresses two issues: the achievable mechanical properties and the understanding of the link between the manufacturing process and the achievable material performance.

Selective laser melting (SLM) of Ti-6Al-4V has significant potential in the aerospace and biotechnology industries. SLM employs a focused laser beam to melt successive layers of metallic powder into complex components. This process can result in the generation of high thermally-induced residual stresses. These residual stresses, together with micro-flaws/ pores from the inherent fabrication process, may lead to premature fatigue crack initiation and propagation at relatively low cyclic stresses. The hole-drilling strain gauge method was used to evaluate residual stresses within SLM Ti-6Al-4V specimens, with the intention of understanding the associated mechanisms for the successful application of SLM Ti-6Al-4V in industry. OPSOMMING'Selective laser melting' (SLM) van Ti-6Al-4V het aansienlike potentiaal in die lugvaart en biotegnologiese bedrywe. SLM maak gebruik van 'n gekonsentreerde laser straal om agtereenvolgende lae metaal poeier te smelt en sodoende intrieke metal komponente te vorm. Gedurende SLM kan hoë resterende spanning veroorsaak word as gevolg van hoë temperature. Hierdie spanning, asook mikrodefekte wat gedurende die vormingsproses ontstaan, mag lei tot voortydige materiaalverswakking deur spleet vorming en verspreiding gedurende betreklik lae sikliese spannings. Resterende spanning in Ti-6Al-4V eksemplare is bereken deur 'n boor-versonke rekstrokie metode om sodoende die meganismes verantwoordelik vir die suksessvolle toepassing van SLM in die Ti-6Al-4V bedryf te bepaal.