Calibration and prediction assessment of different ductile damage models on Ti6Al4V and 17-4PH additive manufactured alloys

Nowadays, metal additive manufacturing is becoming always more popular, being able to deliver complex shaped high quality products. Though many studies have been conducted on the high cycle fatigue behavior of these materials, yet ductile failure has still not been completely investigated, to identify the failure limits under static complex stress states. In the present study, the calibration of three ductile damage models on two popular additive manufactured alloys was carried out. The selected alloys were Ti6Al4V, processed via Electron Beam Melting, and 17-4PH fabricated with Selective Laser Melting technology; both broadly used in actual industrial applications. For each material a set of samples, was fabricated to perform a thorough static mechanical characterization, involving tensile tests on round smooth bars, notched bars, tests under plane strain conditions and torsion tests. The stress state in the critical points was retrieved relying on FEM simulations, and the data collected via the hybrid experimental-numerical procedure subsequently used to tune the damage models. Specifically, the selected models are the Rice and Tracey, the Modified Mohr-Coulomb by Wierzbicki and the one proposed by Coppola and Cortese. While the former does not take into account the effect of Lode parameter, the latter two consider its influence on fracture onset. A minimization algorithm was used for their calibration, and different optimization strategies were adopted to check the robustness of identified parameters. The resulting strains to fracture as a function of damage parameters were plotted for each formulation. The failure prediction accuracy of all models was assessed and compared to the others

Shape Deviation Analysis on Sheet-Metal Parts through Reverse Engineering Techniques

Generally speaking, shape measurement by digital image processing has a large field of applications in engineering research and industrial practice: it allows to verify manufacturing tolerances, acquiring geometry for reproducing dies or monitoring cinematic problems. In body-in-white manufacturing it may help in assessing final shape of stamped parts both during die set-up and production. In fact, it allows to check the occurrence of geometrical defects, such as spring-back deviation or small waviness buckling, which can cause problems during assembling or unpleasant aesthetic effects. Choosing the most appropriate analysis method and defining the comparison procedure among different acquisitions of the same part are the two most critical problems that have been faced in the present paper. First of all, the measurement device should fulfil several requirements regarding shape complexity, surface reflectance and environmental conditions (such as lighting and vibrations). A second issue concerns with the output data manipulation; in this specific application measuring the absolute shape does not represent the final goal to achieve, but the goal is to evaluate how the acquired data fit a target shape. The adopted approach is based on the so-called phase shift method. In the proposed set-up, it requires a fixed CCD camera and a LCD projector. A PC generates and projects a set of fringe patterns and also processes the pictures grabbed through the camera. The output consists of clouds of about 105 points. Through a reverse engineering procedure a surface reconstruction of part shape can be done in a CAD environment and this allows to extend the analysis of variations to the whole geometry of the sheet-metal components with an accuracy of about +/–0.1 mm

Welding strength of dissimilar laser-welded NiTi and NiTiCu shape memory wires

NiTi shape memory alloys are widely used in various medical and aerospace products because of their outstanding preparties, namely superelasticity and shape memory effect. Joining of dissimilar NiTi shape memory wires can be applied in the design of smart components made up of different functionalities or properties. However, preserving the shape memory effect of the welded regions is really challenging due to the influence of laser heat on the microstructure and consequently activation temperature of the welded samples. This paper investigates the mechanical properties of the welded NiTi to NiTiCu wires using tensile test and microhardness analysis. In fact, the experimental results allow to identify the optimum operational parameters for joining of dissimilar NiTi shape memory wires. © 2019 Society of Manufacturing Engineers (SME