Finite Element Analysis For Stress And Strain Field Of Titanium/Steel Composite Welded Jionts

Titanium/steel composite has replaced pure Ti alloy and became the chief structure material in titanium vessel production due to its low price, good corrosion resistance and the ability of withstanding higher pressure. However, it will bring several negative influences if the Ti alloy clad and the steel base are melted together during welding since titanium and steel are not metallurgical compatible at high temperature that normally accompanied with fusion-welding. Under this backgrand, transition weld joints are needed instead of direct ones. Thus the designation of suitable weld jiont types and the analysis for the stress/strain distribution of these jiont types are significant for the guarantee of pressure vessels'safety, while different loading conditions and possible welding flaws are taken into consideration.In this paper, finite element analysis models for 5 different kinds of transition weld joints are conducted, and stress distribution of these weld joints, when working under different loads, are calculated. During the process of calculation, impact from working temperature, inside pressure, welding residual stress and joint types are all taken into consideration. Then, failure loads of each weld joints are also brought out. Analysis of the calculated results reveals that different jiont types give birht to different welding residual stress distributions each of which have decreased the composite's loading capability. Moreover, among these five kinds of weld jionts, the first three would mitigate stress that induced by temperature but would also weaken loading capability of local area on the composite and are then suitable to be adopted when the working temperature is relatively high. On the contrast, the last two do not pose these effects and are suitable to be used when the working temperature is relatively low.As to cold crack problem, it adopts the J-integral criterion from fracture mechanics to research the safety of the weld joints with longitudinal surface crack. In this research, feasibility of conducting crack-body element models by using 1/4 node singular elements and accuracy of J-integral calculation on the platform of software MSC.Marc are certified at the foremost. And the effect of crack size on the value of J-integral is also studied. On the base of these previous works, it makes several suitable simplifications on the practical weld joints and computes the J-integral along the crack tip while working pressure, crack depth and welding residual stress are taken into account. The calculation results reveal that cracks with the depth less than 2.5mm do not tend to extend in depth direction when welding joints working under safe loads, which also means that the existance of crack of this kind would not impose great impact on the safety of those transition welded jionts.