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.
Multiaxial stress rupture behaviour and stress-state sensitivity of creep damage distribution in Durehete 1055 and 2.25Cr1Mo steel
Abstract Creep rupture tests on uniaxial and double notched bar specimens have been performed at 550 °C to understand the multiaxial stress rupture behaviour in two different materials Durehete 1055 and 2.25Cr1Mo steel. The criterion for governing multiaxial rupture stress for the materials was established and compared from the relationship between the representative stress and the skeletal point stresses. Different multiaxial stress rupture criterion were produced. Semi-quantitative metallurgical evaluation of creep damage on the representative tested specimens has been carried out to investigate the stress-state sensitivity of creep damage distribution in two different materials. The steady state stress distribution from finite element solutions was correlated with the semi-quantitative damage map of the test specimens. The different governing multiaxial stress criterion between 2.25Cr1Mo steel and Durehete 1055 steel resulted in the significant difference in creep damage distribution across the notch throat of the materials.
Evaluation of Lapping Grains based on Shape Characteristics.
The shape and size of abrasive grains during lapping varies complicately and irregularly. In this study, the aspect ratio of grain size and the fractal dimension of the grain external form were used as shape characteristics of grain in order to evaluate grains with lapping time. The results obtained are summarized as follows : (1)The fractal dimension increases due to microscopic fracture and decreases due to macroscopic fracture or attritious wear. (2)The aspect ratio and the fractal dimension, which are grain shape characteristicsis of the macroscopic shape and the microscopic surface complication of grain respectively, can be used for evaluating grain shape variation during lapping.