Analysis of the mechanical characteristics of aluminum-lithium 2195 weldments
Abstract
Aluminum-lithium 2195 plate is a new generation of structural material used in space shuttle fuel tank. These aluminum-lithium plates are joined together by using Variable Polarity Plasma Arc (VPPA) welding process. Because of the low ductility of welds, the mechanical property of this structural material is limited, since the welding zone is the weakest area in the structure. The mechanical properties and microstructure of welds are influenced by many factors such as welding process parameters, filler material, welding geometry, and so on. By using experimental method this paper studied the deformation characteristics of the VPPA welds joined by 0.25 inch thick 2195 Al-Li alloy plates using 4043 Al-Si filler material. It describes the effect of weld defects such as porosity and micro-crack on the crack initiation and the fracture mode of the welds. It describes the flow strength and ductility of each zone in the weld. This study investigated the local strain distributions on the crown side and the root side of the welds. This study also investigated the effect of temperature, different solution treatment on the tensile properties of the welds. The aim of this study is also to better understand the effect of weld geometry on the failure mechanism of the welds and their mechanical properties. All examinations were performed on tensile specimens of the welds. The standard tensile tests were utilized to investigate the mechanical properties of the welds in different conditions. In order to investigate the mechanism of fracture and the effect of weld defects, some welds were tested after removal of fusion zone reinforcement. The fractographic examinations revealed that the fracture of aluminum-lithium alloy 2195 VPPA weld tensile specimen originates at the root corner then path to the crown corner in the same side of the fusion zone. However, the weld specimens without fusion zone reinforcement have crack initiation in the middle of the fusion zone. The failure is related to the instances of interdendritic ruptures and accompanying intergranular microcracks in the fusion zone. An elastic-plastic finite element model of 2195 VPPA weld was developed, which can treat the contributions of weld geometry, strength of fusion zone, strength of heat-affected zone, and the ductility of weld, and serve as an analytical tool for improving of weld performance. The calculations of the stress-strain curve from the model are compared to the results of tensile tests. The finite element models reproduce the main features of the deformation behavior of the welds and the strain distributions in the crown side and the root side of the welds. The finite element analysis indicates that the stress concentration occurs at the root corner of the weld, however, without fusion reinforcement the stress concentration is located in the middle of the fusion zone. These are in good agreement with the experimental results. The finite element analysis provides insights into the contributions of weld geometry and material properties of the three regions to the overall strength of the welds.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1999
- Bibcode:
- 1999PhDT.......138D