Staff

Abstract:
Stainless steel 316L tubes and bars were additively manufactured (AM) by using the Laser Powder Bed Fusion Melting (LPBF-M) method in three orientations. As-built specimens were then machined and the initial yield surface was determined for three printing orientations based on the yield stress definition for 0.005 % plastic offset strain. The as-received, wrought material was additionally tested using the same tension–compression-torsion conditions to compare the mechanical behaviour of AM and wrought SS316L. The sizes of yield surfaces elaborated for LPBF-M specimens increased along the tensile and compressive directions and shrunk when torsion was applied, as compared to the as-received specimen.

Keywords:
Stainless steel ,Yield surface ,Additive manufacturing

Abstract:
Uniaxial testing methods to characterize materials provide only limited data that is insufficient to fully understand all aspects of their behaviour, such as initial texture or anisotropy. Therefore, this research aims to conduct complex stress loading experiments to understand the physical mechanism accountable for plastic deformation caused by monotonic tension and tension assisted by proportional cyclic torsion in the CP-Ti (Commercially Pure Titanium). The yield surface approach was applied to assess the variation of mechanical properties in the as-received and predeformed material. It was found, that such monotonic tension associated with cyclic torsion caused a significant decrease of the tensile stress. The initial yield surface obtained for the asreceived material exhibits anisotropic behaviour, whereas, the sizes of subsequent yield surface reflecting pre-deformation were reduced in all directions with exception of the tension direction.

Keywords:
yield surface,pre-deformation,plastic anisotropy,cycle loading,tubular specimen

Abstract:
Al-Cr alloys are usually used in home appliances, automotive, marine and aerospace applications as these possess superior properties like high strength-to-weight ratio, good corrosion resistance and workability. In Al-Cr alloys, chromium has severely limited strengthening effects due to its relatively low solid solubility in the aluminium matrix. The high content of chromium in Al matrix leads to the discontinuous precipitation with coarse Al7Cr intermetallic phase. In this study, powder metallurgy (P/M) technique followed by microwave assisted sintering was adopted for the synthesis of Al-xCr (x = 0, 2.5 and 5 wt%) alloys to enhance the solid solubility of Cr. Specimens were sintered at 560 ºC for one hour and cooled inside the microwave atmosphere. Sintered specimens were hot extruded and characterized in terms of the mechanical properties. Mechanical characterization showed that the addition of Cr as alloying element leads to an increase in microhardness, 0.2% tensile yield strength (TYS) and ultimate tensile strength (UTS) of the Al-alloy. However, the ductility of the Al-alloys was significantly decreased by the incorporation of Cr particulates in the aluminium matrix.

Keywords:
Al-Cr system, powder metallurgy technique, hybrid microwave sintering, mechanical properties

Abstract:
The Laser Powder Bed Fusion Melting (LPBF-M) method was used to additively manufacture stainless steel 316L tubes in three different orientations. The yield surface approach was implemented to assess the variation of mechanical properties within the as-built specimens. Yield surfaces were determined for each build orientation based on the definition of yield stress for 0.005% plastic offset strain. The initial yield surfaces obtained for the as-built material exhibit anisotropic behaviour, possibly resulting from the preferred grain orientation developed during LPBF-M processing.

Abstract:
Investigating of the material properties and physical mechanisms responsible for plastic deformation caused by complex loading is crucial for bimetallic structures. These materials are a type of functionally graded multi-material structures designed to combine diverse material properties within the same framework while optimizing manufacturing costs. In the present work, the initial yield surface and its subsequent evolution were determined for a Ti-Cu bimetal based on the definition of yield stress for 0.01% plastic offset strain. The subsequent yield surfaces were determined after introducing monotonic axial tension and axial tension-cyclic torsion pre-deformation up to 1% permanent axial strain. It was found, that the determined initial yield surface was close to the Huber-Mises locus. Furthermore, subsequent yield surfaces were determined to assess a hardening/softening effect in the loading direction applied. Interestingly, only the monotonic tension caused a significant enhancement of the tensile yield strength as the monotonic tension associated with cyclic torsion caused its reduction. On the other hand, the sizes of subsequent yield surfaces reflecting pre-deformation were reduced in the axial compression direction.

Keywords:
yield surface, pre-deformation, plastic anisotropy, cycle loading

Keywords:
medical fixation devices, orthopedicimplants, SEM, fracture analysis, titanium alloy, stainless steel