The present study investigates the evolution of the residual stresses in TWIP steels induced by manufacturing chain for the production of automotive body-in-white. Two different manufacturing routes were considered. The first route encompassed a plastic deformation prior to the welding stage, whereas the second involved the spot welding followed by a baking treatment. A convergent approach was adopted to isolate the effects of the first and final manufacturing steps. The findings showed that the plastic deformation prior to the welding stage is not annihilated by the welding thermomechanical cycle. Abrupt hardness gradients along small material fractions are observed. The residual stresses state changes, although its profile is still defined by the welding stage. The post-weld bake treatment showed to promote slight residual stresses relaxation, but it is not effective in inducing the same post-weld residual stresses state for different RSW parameters set.

The development of biodegradable polymers has advanced in recent years, mainly due to the overwhelming need to reduce the impact of polymeric materials when improperly discarded in nature. However, there are major challenges to be surpassed, especially regarding characteristics such as mechanical strength and cost of such materials, when compared to commodity polymers widely used today. Motivated by this goal, this study focused on the development of a composite material consisting of a biodegradable polymer the poly(hydroxybutyrate-co-valerate) (PHBV) reinforced with cellulose fibers, which are cheap and abundant. Mechanical and thermal properties of the polymer reinforced with different fiber contents were analyzed and compared with the neat material. Also, a burial-soil test was carried out to evaluate the environmentally degradable characteristics of the compositions studied. Results showed that the incorporation of cellulose fibers into the biodegradable matrix can both optimize the mechanical properties in use, and accelerating the environmental degradation of the polymeric material after use, when properly disposed, showing that biodegradable composites are environmentally friendly.

This study discusses the microstructure, quasi-static mechanical strength and failure modes of TWIP steel weld spots. Weld spots were produced by varying the main resistance spot welding parameters: welding current, welding time and electrode compression force. All the samples showed a remarkable material hardness mismatch between the fusion zone, the heat affected zone and the base material, as evidenced by microindentation maps. Hardness at the fusion zone is lower than that of heat-affected zone and base metal, which facilitates interfacial failure mode during tensile-shear tests. However, high heat inputs promoted the failure mode changes to partial interfacial mode and then to pullout mode during tensile-shear tests as confirmed by Scanning Electron Micrographs. These changes in failure mode were accompanied by a notable increase in tensile-shear strength and energy absorption capability.

This study discusses the microstructure, quasi-static mechanical strength and failure modes of TWIP steel weld spots. Weld spots were produced by varying the main resistance spot welding parameters: welding current, welding time and electrode clamping force. All the samples showed a remarkable material hardness mismatch between the fusion zone, the heat affected zone and the base material. Hardness at the fusion zone is lower than that of heat affected zone and base metal, as evidenced by microindentation maps, which facilitates interfacial failure mode during tensile-shear tests. However, high heat inputs promoted the failure mode changes to partial interfacial mode and then to pullout mode during tensile-shear tests, which was confirmed by Scanning Electron Micrographs, accompanied by a notable increase in tensile-shear strength and energy absorption capability.