Staff

Abstract:
In this paper, the influences of build orientation and post-fabrication processes, including stress-relief, machining, and shot-peening, on the fatigue behavior of stainless steel (SS) 316L manufactured using selective laser melting (SLM) are studied. It was found that horizontally-built (XY) and machined (M) test pieces, which had not been previously studied in the literature, in both stress-relieved (SR) or non-stress-relieved (NSR) conditions show superior fatigue behavior compared to vertically-built (ZX) and conventionally-manufactured SS 316L. The XY, M, and SR (XY-M-SR) test pieces displayed fatigue behavior similar to the XY-M-NSR test pieces, implying that SR does not have a considerable effect on the fatigue behavior of XY and M test pieces. ZX-M-SR test pieces, due to their considerably lower ductility, exhibited significantly larger scatter and a lower fatigue strength compared to ZX-M-NSR samples. Shot-peening (SP) displayed a positive effect on improving the fatigue behavior of the ZX-NSR test pieces due to a compressive stress of 58 MPa induced on the surface of the test pieces. Fractography of the tensile and fatigue test pieces revealed a deeper understanding of the relationships between the process parameters, microstructure, and mechanical properties for SS 316L produced by laser systems. For example, fish-eye fracture pattern or spherical stair features were not previously observed or explained for cyclically-loaded SLM-printed parts in the literature. This study provides comprehensive insight into the anisotropy of the static and fatigue properties of SLM-printed parts, as well as the pre- and post-fabrication parameters that can be employed to improve the fatigue behavior of steel alloys manufactured using laser systems.

Keywords:
selective laser melting, stainless steel 316L, fatigue, defect, fracture

Keywords:
kompozyty, żywice termoplastyczne, badania zmęczeniowe, udarność

Abstract:
Modern automobile and airplane structures made of sheet metals or composites require usage of thinner and stronger materials. On the other hand, manufacturers are trying to reduce production costs by shortening the fabrication processes and by application of computed simulation for forming operation. Therefore, it is necessary to better understand and more accurately investigate deformation behaviour of sheet alloys. Testing of flat specimens under compression and cyclic tension-compression within large deformation procures a lot of problems. One of them is the buckling phenomenon. A new version of the device mounted in a standard testing machine was developed and geometry of the specimen for validation of the device was proposed. Specimens of DP690 steel with nominal thickness equal to 1.6 mm were investigated at ambient temperature. Tension-compression cyclic tests within a strain range ± 0.04 were executed starting in tension direction. It is shown that the results are repeatable.

Keywords:
Buckling, cyclic loading, fixture, thin sheets

Keywords:
cyclic loading, damage evolution, laminate composites

Abstract:
Optimization of sheet metal forming processes requires a very good knowledge of material forming ability. During the forming of industrial parts, very complex strain paths are usually observed and can affect the formability of the sheet. Therefore, it is necessary to better understand and more accurately investigate deformation behaviour of sheet alloys. It should be noted that material testing of flat specimens under compression within a large deformation range procures many difficulties, and the buckling phenomenon seems to be the most im-portant. This paper shows the results of tension-compression tests carried out on specimens made of ultralight magnesium alloys AZ31B with nominal thickness equal to 1 mm using the anti-buckling fixture to avoid buckling problem.

Keywords:
Bauschinger effect, cyclic loading, buckling, fixture, thin sheet