Papers by Keyword: Cyclic Plasticity

Abstract: In this work the durability assessment and the permanent deformation of a copper mold for continuous casting of steel have been investigated using mathematical models based on the Finite Element method. The cyclic plasticity behavior of the material is represented by a combined kinematic-isotropic model experimentally validated. Results from thermo-mechanical analysis are in good agreement with measurements. In particular, creep effects included into the model permit the evolution of bulging near the meniscus area to be correctly predicted. A life estimation is performed considering strain-life and stress-rupture time curves according to a cumulative damage law.

Abstract: Aseismic design of modern structures imposes a new requirement on structural engineers. Structural systems should withstand even very huge earthquakes. This goal cannot be achieved by standard design methods applying a linear elastic approach. An advanced aseismic design applies energy dissipating anti-seismic devices. During seismic event, these devices are exposed to a large plastic strain. The code EN 15129 is the standard on anti-seismic devices applicable in Europe. Mentioned standard defines a special material requirement imposed on devices working as energy absorbers. Material verification is possible only experimentally. In compliance with the instructions contained in the code EN15129, several cyclic tests of the materials S235 and DD11 have been used. Evaluation of the previous research and the current test results have proved that structural steel S235 is not applicable to the anti-seismic devices. As an alternative, steel DD11 has been suggested for this application. The test results have shown that the steel DD11 is applicable in specified range of target strain amplitudes.

Abstract: This paper proposes a cyclic plasticity model to describe the closure of a cyclic stress-strain hysteresis loop based on the Y-U model. In this model, the backstress moves in a cyclic memory surface following a newly proposed kinematic hardening law. For this model just the same Y-U parameters can be used, and no additional material parameters are needed. By using a supplementary rule, this model is also able to describe ratcheting.

Abstract: In this work our goal is to better understand the origin of the cyclic accumulation of the inelastic strain (often called ratcheting) observed in 304L SS subjected to uniaxial cyclic stress control at room temperature. Recent works performed in the frame of small strain assumption attribute this phenomenon essentially to creep [1]. However, outside this frame, it seems that creep is not the only contributor in this phenomenon [2]. New experiments are performed here in order to investigate the role played by creep, cyclic softening, fatigue damage and ratcheting in this observation.

Abstract: Thermo-mechanical cyclic experiments on 304 stainless steel were performed at several temperature ranges which had maximum temperatures ranging from 350°C to 1000°C and a minimum temperature of 150 °C. Related isothermal cyclic experiments were also performed. Temperature-history dependent cyclic hardening significantly occurred under thermo-mechanical cyclic loading with maximum temperatures around 600°C, whereas almost no cyclic hardening was observed when the maximum temperature was 1000°C. The observed thermo-mechanical cyclic plastic behavior in the saturated state of cyclic hardening was then simulated using a cyclic viscoplastic constitutive model, leading to the following findings. It was difficult to predict the saturated thermo-mechanical cyclic behavior using only the isothermal cyclic experimental data. The saturated thermo-mechanical cyclic behavior was simulated well by introducing a cyclic hardening parameter depending on the maximum temperature. This means that the cyclic hardening parameter should not change with temperature but depend on the maximum temperature in the saturated state of cyclic hardening under thermo-mechanical cyclic loading.

Abstract: Recently, Halt (Highly accelerated limit test) is widely employed for evaluation of reliability of electronic products. Halt condition is quite severe. The tested products are subjected to mechanical impacts, thermal shock, and vibration at same time. However, there has not been a reasonable and accurate evaluation method for Halt yet. To construct an accurate evaluation method of Halt, basic deformation mechanism of parts of the electronic products should be clarified from both experimental and theoretical points of view. In this paper, focusing on solder joints of circuit boards of electronic products, ratchetting deformation, especially, biaxial ratchetting deformation of solder joints is revealed from both experimentally and theoretically. The authors have already conducted biaxial ratchetting test combining axial and torsional cyclic loading using a tubular specimen of Type 304 stainless steel. However, as for solders, it is difficult to make tubular specimen. Since size of the solder joints is micron, a small size joint specimen of copper tube and solder is employed in this paper. First, to confirm the quality of the joint specimen such as boundary between copper and solder, both the tensile and cyclic loading tests are conducted at several temperatures using Sn-3Ag-0.5Cu. The basic characteristic of tensile and fatigue failure is obtained from these tests. After the confirmation of the accuracy of the joint specimen, biaxial ratchetting tests are conducted superposing the tensile load on cyclic torsion. The biaxial ratchetting tests are conducted using a biaxial loading testing machine developed for the joint specimens of solder and copper.

Abstract: The present paper proposed a cyclic plasticity model with a non-associativity parameter, i.e., the model includes non-associative flow rule and associative one. In the present model, the non-associative parameter controls the non-associativity. The model is derived based on the non-linear kinematical hardening rule with two hardening parameters for both the volumetric and deviatoric strains. From the simulation by the present model, we have found the strong non-associativity leads to the large decrease in the mean effective stress, i.e. almost zero mean effective stress during the cyclic deformations under undrained conditions while the model with associated flow rule is not.

Abstract: For the description of cracks in rolling/sliding contacts many overlapping interactions has to be regarded and most of them are non-linear phenomena. This paper emphasis the aspect of plasticity around cyclically loaded shear cracks which is omitted very often in the common literature. It is shown that this plasticity can be calculated and regarded in computed crack driving forces; however, the problem is not solved after doing this. It is a first estimate only to regard the crack driving force calculated in the finite elements surrounding the crack tip as a relevant measure.

Abstract: A plastic strain correction factor is used in a simplified elastic-plastic fatigue analysis of nuclear power plant components. Numerical investigation on the plastic strain correction factor is presented for the case of the primary and secondary stress range exceeding three times the design stress intensity value under thermal-mechanical loadings. The plastic strain correction factor was computed separately by following the RCC-M code and applying the elastic-plastic finite element analysis. The influence of loading ratio, loading controlled mode and ambient temperature on the plastic strain correction factor was discussed. It was shown that the plastic strain correction factor computed from the RCC-M code is not as conservative as that from the complete elastic-plastic finite element analysis when the primary plus secondary stress range is close to three times the design stress intensity value. However, it is too conservative when the primary plus secondary stress range is more than three times the design stress intensity value multiplying parameter m (use in RCC-M code). Additionally, a new formula of plastic strain correction factor was proposed to provide a complete envelope curve to the entire primary plus secondary stress range.

Abstract: The study presented in this paper uses a multi-mechanism model (MM) in order to simulate the cyclic behavior of an anisotropic aluminum alloy 2017A subjected to complex loading. Two sets of parameters were used. The first set is proposed in [1]; it is identified considering cyclic tests performed under strain control following proportional and non-proportional paths. The second set of parameters has been identified recently on a larger database [2]. In this work, we propose to evaluate the capability of the according to the set of parameters under consideration. Note that the identification process in both cases was performed using strain controlled experiments while the evaluation of the model uses stress controlled experiments.