Application of a Composite Model in the Analysis of Creep Deformation at Low and Intermediate Temperatures
The creep behaviors of TA2 and R60702 at low and intermediate temperature were presented and discussed in this paper. Experimental results indicated that an apparent threshold stress exhibited in the creep deformation of R60702. Meanwhile, the primary creep phase was found as the main pattern in the room temperature creep behavior of TA2. Compared with exponential law, the power law has been proved to be a proper constitutive model in the description of primary creep phase. It also showed that θ projection method had its significant advantage in the evaluation of accelerated creep stage. Thus, a composite model which combined power law with θ projection method was applied in the creep curves evaluation at low and intermediate temperature. Based on the multiaxial creep deformation results, the model was modified and discussed. A linear relationship existed between composite model parameters and applied load. Finally, the creep life could be accurately predicted and the composite model method is suitable for application in low and intermediate temperature creep life analysis.
Comparative Analysis of Creep Behavior Prediction of Heat Resistant Steel Based on Theta Projection and Composite Model
The difference of the creep curves of P92 steel was comparatively analyzed by theta projection method and composite model.The results show that both the creep-time curves of P92 steel with two methods have a higher accuracy.However,when describing the creep rate-time curves,the theta projection method exhibits big error,while,the composite model can show more accurate results;When extrapolating creep rate,the theta projection method has large deflection,while,the composite model can predict more near the actual trend.When extrapolating creep rupture life based on creep curves,the results show that the fracture strain between 5% and 50% has little effect on the life prediction.The values of endurance life extrapolated by the two models are approximately the same.
Low temperature creep of Ti-6 Al-4 V
Creep tests were conducted at 295 K on Ti-6 Al-4 V in the solution treated and aged (4 h at 815 K) condition, and in the as-welded condition. Some aged specimens were tested after pre-straining. Creep stresses ranged from 40 to 90 pct of the aged material yield strength. Results showed that creep was of the primary or transient kind in all cases, and was much greater in welded than in aged material. In general, pre-strains reduced creep, although a strain larger than 10-3 was needed to do this at the highest creep stress. Activation areas A* were between 10 and 20 b2, and thus were similar to tensile results on titanium and its alloys. The microstructural rationale applied to Ti-5 Al-2.5 Sn in earlier work, based on the character of dislocation sources, proved successful in understanding the effects of prestrain in this work.