Numerical/experimental investigation of bulge tests on a localized laser heat-treated magnesium alloy AZ31 sheet

Lightweight alloys can be considered among the most promising materials thanks to their capability to reduce the environmental impact, without affecting mechanical properties. In addition, when very complex shapes are required, a viable strategy could be represented by the adoption of non-conventional forming processes applied to tailored blanks that allow to obtain local variation of the material properties. In fact, referred to the Mg alloys, both grain size and temperature strongly influence the deformation behavior, as well as the mechanical properties. In this work, the effects of a selective Laser Heat Treatment (LHT) on a Mg AZ31B-H24 alloy sheet were investigated both numerically and experimentally. Experimental tests were performed, using a Diode laser source and keeping a square spot stationary in the center of the sample. The microstructure evolution was evaluated by means of light microscopy. Subsequently, the heat-treated samples were subjected to bulge tests under superplastic conditions (450°C) and using pressurized argon gas. The experimental microstructure distributions obtained were used for the numerical bulge tests analyses performed in the same conditions of the experimental trials. Experimental LHT results showed the capability to locally modify the microstructure when suitable temperatures and interaction times are selected. Regarding the bulge tests, the obtained results showed the possibility to effectively affect the thickness distribution of the final shapes.

Optical design of LED high mast lamp based on TIR freeform lens for annular lighting

The traditional square spot of street lamp is not suitable for the lighting requirements of the annular road lighting. In this paper, a lens design method for producing annular spot of high mast lamp is proposed. The method mainly contains three optical surfaces, in which the inner surface collimates the energy of the centre part of the light source, the total internal reflection surface collimates the light with large angle and low energy and the outer surface refracts all the collimated light to realise the annular illumination distribution on the target surface. In this design, we can change the diameter of the lighting spot through the variation of the inclination angle of the outer surface from 14° to 19° and the diameter of the spot changes from 10.2 m to 12.3 m at the distance of 30 m. The lighting requirements of high mast lighting are realised based on the TIR lens array, in which the average illuminance is more than 20 lx, the illuminance uniformity is more than 0.7 and the light optical utilisation factor is more than 90%.

Study on the Laser Shock Processing with Square Spot of Titanium Alloy Based on ABAQUS

Laser shock processing is a new kind of technology to improve the physical and mechanical properties of the metal surface. It uses the high-amplitude stress wave produced by the interaction of short-pulse laser and material, to make the material produce the compressive residual stress and refinement internal structure, and lead to the improved hardness and strength of material. In this paper, the simulation of laser shocking process with square spot of Titanium alloy plate was carried out through ABAQUS. The influences of the shock time, laser energy, plate thickness and spot size on the strengthening are investigated from the view of residual stress. The results show that: There are the compression residual stress in the workpiece surface after laser shcok processing, and its amplitude is about 300-400Mpa. With the increase of shock time, the surface residual stress increases, the area and depth of strengthening zone also increase. The strengthening area becomes a circular, while the distribution of residual stress becomes unhomogeneous. The surface residual stress increases as the laser energy increasing, but the amplitude is smaller. The plate thickness does not affect the amplitude of the surface residual stress. When the shock pressure is constant, surface residual stress does not change with the spot size. However, if the laser energy is constant, due to the shock pressure will decrease with the increase of spot size. Therefore, there should be an optimized spot size when the strengthening effectiveness and efficiency are both considered.

Characterization of TC17 Titanium Alloy Treated by Square-Spot Laser Shock Peening

Laser shock peening (LSP) is widely known as a cold-worked surface treatment, and this technology has been to greatly improve the fatigue life of many metallic components. Our works focused on laser shock peening with Nd: glass laser system (pulse duration 30ns) and square laser spot size of 4mm×4mm for TC17 titanium alloy. Surface morphology, residual stresses and fatigue performance had been studied for TC17 alloy specimens and blades processed by LSP treatment. The results show that plastic strains in shocked dents become more homogeneous than ones produced by original circle spot with gaussian energy distribution. Surface residual stresses which measured using x-ray diffraction method showed different characteristic as varying specimen thickness, and LSP with overlapping ratio of 8% provided uniform residual stresses on peened surface. Low fluence peening which was implemented at borderline of peened surface was effective to diminish the stress gradient. Compared with mechanical shot peening, LSP attained smoother surface, lower microhardness and better fatigue performance. In a word, Square-spot LSP is an excellent way to improve fatigue life of titanium blade.