Coupled elastoplasticity and viscoplasticity under thermomechanical loading

Abstract

A B S T R A C T This paper is a contribution to material behaviour modelling. Total strain is decomposed into elastoplastic and viscoplastic strains. Both parts are analysed separately and put together by the principle of superposition. The spring-slider model controlled by either stress or strain enables elastoplasticity modelling under constant or variable temperature with the Prandtl operators. Viscoplasticity is taken into account, if temperature exceeds creep temperature, by adding a nonlinear damper to existing spring-slider models, otherwise just elastoplasticity is considered. The material parameters result from isothermal strain-controlled low cycle fatigue (LCF) tests. Hysteresis loops are assumed to be stabilized. The high speed of computation that is characteristic of Masing and memory rules is retained. Solving of differential equations is not required. The model developed so far is uniaxial, but a multiaxial extension is possible. N O M E N C L A T U R EYoung's modulus i = data point index j = the play operator index k = temperature index, elastic limit K = temperature dependent material parameter K = cyclic hardening coefficient N = temperature dependent material parameter n = cyclic hardening exponent n q = index of the top fictive yield strain n r = index of the top yield stress n T = index of the top temperature nε = index of the top strain rate n σ = index of the top stress q j = fictive yield strain r j = yield stress t = time T = temperature T c = creep temperature α j = the Prandtl densityCorrespondence: M. Nagode.

Identification of material parameters from low cycle fatigue, thermomechanical fatigue and creep tests for damage prediction of thermomechanically loaded Ni-resist Type D-5S

“…It has been applied here to the Ni-resist Type D-5S but is discussed in detail elsewhere. 5 Elastoplastic and viscoplastic material parameters were extracted from both tests, with high and low strain rates. The second approach took into account LCF tests only at high strain rates (10 23 s 21 ) at several temperatures for the determination of elastoplastic material parameters ( Figure 6).…”

Damage Operator‐Based Lifetime Calculation Under Thermomechanical Fatigue and Creep for Application on Uginox F12T EN 1.4512 Exhaust Downpipes

“…To exclude the creep contribution from the fatigue damage, the strain‐life curves must be obtained at high strain rates [16]. Supposing that stable cyclic stress–strain curves for are available, elastoplastic strain ɛ ep ( t i ) can be modelled independently of viscoplastic strain ɛ vp ( t i ) [16].…”

“…Back stress σ α j ( t i ) follows the kinematic hardening rule for constant temperature. An additional multiplier is added for variable temperatures [16]. Pseudo‐elastic stress σ e ( t i ) can be obtained from the linear elastic FEA.…”

“…Next, the strain controlled non‐linear Maxwell model [16] (Figure 5) is used to convert the instantaneous strain ɛ ( t i ) = ɛ i ( t i ) into elastoplastic strain and true stress.…”

“…As stress remains constant between points 1 and 2 (Figure 6), the viscoplastic strain can be worked out first [16] as…”