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1

Study on constitutive behavior of Ti-45Nb alloy under transversal ultrasonic vibration-assisted compression

Wang Xingxing, Qi Zhenchao, Chen Wenliang

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

518--532

EN

Ultrasonic vibration technology has been widely applied in plastic forming processes due to its advantages of material properties improvement. In this study, a transverse ultrasonic vibration-assisted compression (TUVC) system with the range of vibration amplitude from 16 to 48 µm is developed to compress the difficult-to-deformation materials. The experiment found that the temperature of the compressed sample with the vibration amplitude of 38 µm arrived at 164 ℃, hence the current constitutive models are deficient for the description of TUVC deformation behavior with the large vibration amplitudes. The results show that the flow stress declines under the coupling action of volume effect and surface effect, especially the amplitude is larger than 38 µm. To accurately depict the constitutive behavior of titanium alloy under TUVC, a hybrid constitutive model considering the difference of softening mechanism was proposed based on crystal plasticity theory, and the predicted curves are in good agreement with experimental results. Finally, the microstructure further revealed the differences of softening mechanism in TUVC, and numerous secondary α phase was precipitated. Consequently, the studies provide an insight into the deformation mechanism of TUVC and promote the application of ultrasonic vibration-assisted forming for the difficult-to-deformation alloy.

2

Modeling of cyclic hardening of metals coupled with martensitic transformation

Mróz Z., Ziętek G.

Archives of Mechanics

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2007

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Vol. 59, nr 1

3-20

EN

The work presents an elasto-plastic material model with mixed hardening taking into account martensitic transformation. Modification of the kinematic hardening rule is proposed by relating back stress to the generalized thermodynarnic force by a nonlinear function dependent on the fraction of martensite. The martensitic evolution is expressed in terms of isotropic hardening parameter by introducing proper free energy related force. The proposed model has been applied to predict hysteretic response for cyclic tension and compression tests for austenitic steel.

3

Functional forms of hardening internal state variables in modeling elasto-plastic behavior

Dorgan R. J., Voyiadjis G. Z.

Archives of Mechanics

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2007

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Vol. 59, nr 1

35-58

EN

In this work use is made of functional forms of hardening state variables within a consistent thermodynamic formulation to model the elasto-plastic behavior of materials. The formulation is then numerically implemented using the developed plasticity model. In deriving the constitutive model, a local yield surface is used to determine the occurrence of plasticity. Isotropic hardening and kinematic hardening are incorporated as state variables to describe the change of the yield surface. The hardening conjugate forces (stress-like terms) are general nonlinear functions of their corresponding hardening state variables (strain-like terms) and can be defined basing on the desired material behavior. Various exponential and power law functional forms are studied in this formulation. The paper discusses the general concept of using such functional forms; however, it does not address the relevant appropriateness of certain forms to solve different problems. It is shown that, depending on the functions used, standard models known from the literature can be recovered. The use of this formulation in solving boundary value problems will be presented in future.