Abstract
The Gleeble-1500D thermal simulation test machine was used to conduct the isothermal compression test on 21-4N at the strain rate () of 0.01–10 s−1, the deformation temperature (T) of 1273–1453 K and the maximum deformation is 0.916. The data of the stress-strain (σ-ε) were obtained. Based on the σ-ε data, the Johnson-Cook (J-C), modified J-C, Arrhenius and Back-Propagation Artificial Neural Network (BP-ANN) models were established. The accuracy of four models were verified, analyzed and compared. The results show that J-C model has a higher accuracy only under reference deformation conditions. When the deformation condition changes greatly, the accuracy of J-C model is significantly reduced. The coupling effect of T and of modified J-C model is considered, and the prediction accuracy is greatly improved The Arrhenius model introduces Zener-Hollomon (Z) to represent the coupling effect of T and , it has a fairly high prediction accuracy. And it can predict flow stress (σ) accurately at different conditions. The accuracy of BP-ANN model is the highest, but its learning rate is low, the learning and memory are unstable. It has no memory for the weights and thresholds of the completed training. So, there are certain limitations of it in use. Finally, a Finite Element Method (FEM) of the isothermal compression experiment for four models were established, and the distribution of the equivalent stress field, equivalent strain field and temperature field with the deformation degree of 60% were obtained.
Highlights
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Summary
In the 1980s, J-C model was proposed by Johnson and Cook to describe the σ-ε relationship of metals and alloys under high T, high ε. and large ε [46,47]. J-C model assumes materials stress conforms to yield criterion and isotropic strain hardening criterion, and its expression is shown as Equation (1):. In the equation: A—The yield stress, MPa; n—Strain hardening index; C—Strain rate sensitivity coefficient; ε. ∗—Dimensionless plastic strain rate; T*—Dimensionless temperature; m—Temperature sensitivity coefficient; ε. 0—Reference strain rate, s−1; Tr—Reference temperature, K; B—Strain hardening parameter, MPa; Tm—Melting temperature, K. From Equation (2), the J-C model contents three parts [48,49]: strain hardening effect part—(A + Bεn), strain rate enhancement effect ε. The Tr in this study was set as 1273 K, and the ε. Under this condition, the yield stress of 21-4N is 107 MPa (A = 107 MPa).
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