Mechanical Fatigue Simulation by Unconventional Plasticity Model

The subloading surface model was formulated in the Chaps. 6– 11 within the frameworks of the finite hypoelastic-based plasticity in detail and of the infinitesimal hyperelastic-based plasticity (Sect. 6.9) in brief. Finite deformation and rotation cannot be described in the exact sense by these formulations. The multiplicative elastoplastic constitutive equation will be formulated for the subloading surface model with the translation of the elastic-core, although the multiplicative constitutive equation for the initial subloading surface model, in which the elastic-core is fixed in the back stress point, was formulated in an immature form by Hashiguchi and Yamakawa (2012). One must formulate the constitutive equation possessing the generality and the universality to be inherited eternally, while any unconventional model, i.e. cyclic plasticity model other than the subloading surface model has not been extended to the multiplicative finite strain theory. The exact formulation of the multiplicative finite strain theory based on the extended subloading surface model has been attained by Hashiguchi (2016a, b, c, d), which will be explained in detail in this chapter.

A damage cyclic plasticity model for metal matrix composites

Cyclic mean stress relaxation behaviour of P91 steel: Experiments and constitutive modeling

Strain space based plasticity models have certain advantages in theoretical development and numerical implementation. Previous efforts have been made to formulate cyclic plasticity models in strain space using the idea of multiple-yield surface theory. Recently, however, Armstrong-Frederick type plasticity models have received increasingly more attention because of their enhanced performance in predicting ratchetting behavior. In this paper, the strain space formulation of the Armstrong-Frederick family of cyclic plasticity models is established, and several representative strain controlled loading paths are used to compare the results from the proposed formulation and previous experimental data. The excellent agreement suggests the proposed strain space formulation is very promising in strain controlled cyclic plasticity such as finite element analysis, strain gage rosette applications, and multiaxial notch analysis using pseudo-stress or pseudo-strain approaches.

Size effect on the cyclic deformation behavior of superalloy ultrathin sheet: Characterization and multiscale modelling

This paper deals with the development of a cyclic plasticity model suitable for predicting the strain range-dependent behavior of austenitic steels. The proposed cyclic plasticity model uses the virtual back-stress variable corresponding to a cyclically-stable material under strain control. This new internal variable is defined by means of a memory surface introduced in the stress space. The linear isotropic hardening rule is also superposed. First, the proposed model was validated on experimental data published for the SS304 material (Kang et al., Constitutive modeling of strain range dependent cyclic hardening. Int J Plast 19 (2003) 1801–1819). Subsequently, the proposed cyclic plasticity model was applied to our own experimental data from uniaxial tests realized on 08Ch18N10T at room temperature. The new cyclic plasticity model can be calibrated by the relatively simple fitting procedure that is described in the paper. A comparison between the results of a numerical simulation and the results of real experiments demonstrates the robustness of the proposed approach.

<p dir="ltr">Lightweighting is in the spotlight of innovations in the automotive industry owing to the demand of energy-efficient electric and hybrid vehicles. Lightweight aluminum (Al) alloys have been leading this global industrial trend as the primary materials for the structural components of vehicles. Due to the advancement in technologies, Al alloys can be fabricated via novel techniques that can improve certain traits like superior strength-ductility synergy in the same range as that of structural steels. As these industries grow, there is an impending need to tailor the alloy microstructures with a proper control of the process parameters like solidification thermodynamics and kinetics, along with the alloy chemistry. This dissertation begins with the primary goal to understand the deformation behavior of a newly-developed low-iron containing, vacuum-assisted high pressure die-cast aluminum-silicon alloy, commercially named Silafont®-36 alloy under static and cyclic loading conditions. Throughout the several investigations in this work, it was observed that the presence of a heterogeneous microstructure led to increased tensile and compressive strength, and elastic modulus than several other commercial Al-Si cast alloys. The cast alloy showed improved ductility owing to its uniquely modified eutectic structure. Load-bearing ability of the eutectic Si particles, dislocations generated due to thermal mismatch between Al matrix and Si particles, and Orowan looping were found to be the predominant strengthening mechanisms in the cast alloy. The alloy showed improved fatigue resistance and a strong cyclic hardening effect in the cast form. Upon solutionizing and overaging treatments of the cast alloy, changes in the microstructure significantly altered the static and cyclic deformation behavior. A novel method was proposed to evaluate the intrinsic fatigue toughness of the alloy in different conditions, which was established as a material constant. This further served as an important parameter to more accurately predict fatigue life of the alloy in cast and heat-treated conditions. In a nutshell, this work constituted an informative benchmark for unravelling the mysteries of the macro-, meso-, and micro-scale deformation behavior that led to improved mechanical performance of a lightweight automotive-grade Al-Si alloy.</p>

In this work, a modified cyclic plasticity model for FEM analysis of SA333 C–Mn steel has been developed. A memory stress based isotropic formulation is integrated into the modified Ohno-Wang model to revamp its nonmasing and hardening/softening characteristics. Accurate estimation of stress–strain hysteresis loops is a prerequisite for performing fatigue life analysis. The inbuilt classical cyclic plasticity model available in commercial FE software cannot precisely describe the material behavior. The proposed model has been implemented by using user-defined material (UMAT) subroutine with FORTRAN code on the ABAQUS platform. To evaluate the material constants for the proposed model, a set of experiments has been carried out under uniaxial loading condition. The same material constants are used for predicting simulation response for other loading conditions. To verify the proposed model, the simulation results are compared with experimental results which reveal good agreement under uniaxial loading condition

Evaluation of cyclic plasticity models in ratcheting simulation of straight pipes under cyclic bending and steady internal pressure

Based on the framework of critical state soil mechanics, a subloading surface plastic model for sand, being applicable to cyclic loading, was proposed. The model can be used to describe strain softening behaviour of sand under monotonic loading when the similarity-ratio equals to unity. The characteristics of the model are as follows: 1) A reverse bullet-shaped yield surface is adopted to ensure accurate prediction of the behavior of sand, instead of bullet-shaped or elliptical yield surface in Cam-Clay model. 2) No unique relationship between void ratio and the mean normal stress for sand prevents the direct coupling of yield surface size to void ratio, so incremental deviatoric strain hardening rule is used. 3) The model combines the concept of state-dependent dilatancy by incorporating state parameter in Rowe’s stress dilatancy equation, which accounts for the dependence of dilatancy on the stress state and the material internal state. A single set of model constants, which is calibrated, can simulate stress—strain response under different initial void ratios and different confine pressures. The model is validated true by comparing predicted results with experimental results under monotonic and cyclic loading conditions.

The ability of the constitutive model to simulate the ratcheting behavior of metastable austenitic stainless steel S30408 is significant to ensure the safety of the liquefied natural gas (LNG) semi-trailer tanks in the lightweight process of the inner containers. This is because the lightweight inner vessels often encounter cyclic stresses due to the road inertia loads together with high mean stresses due to internal pressures. In this study, we performed cryogenic uniaxial tension experiments and a series of ratcheting experiments to investigate the cyclic plasticity behavior of the metastable austenitic stainless steel S30408. Based on the Ohno-Wang II model, we proposed a new cyclic plasticity constitutive model with martensitic transformation, which relates the content of deformation-induced martensite with isotropic hardening and kinematic hardening. The ratcheting behaviors of S30408 were first simulated by the proposed model with the incremental loading method using MATLAB. The results showed that the model could reasonably predict the ratcheting behavior of S30408, and the evolution law of martensite content could well predict the content of deformation-induced martensite. Under the assumption of the von Mises yield criterion and normal plasticity flow rule, we developed a numerical algorithm of plastic strain with the proposed model to implement the finite element calculation of the model. Internal iteration in the numerical algorithm was implemented with the Euler backward method, which calculated the trial strain for each equilibrium iteration using the consistent tangent matrix. With a user subroutine, the proposed model was programmed into ANSYS for a user - executable version. By simulating the uniaxial ratcheting of a S30408 round bar, we found that the calculated results were in good agreement with the experimental results, which promises further applications in the design of structures, such as LNG semi-trailer tanks.

Multiaxial fatigue life assessment of sintered porous iron under proportional and non-proportional loadings

A cyclic small-strain plasticity model for wrought Mg alloys under multiaxial loading: Numerical implementation and validation

An elastoplastic model with combined isotropic–kinematic hardening to predict the cyclic behavior of stiff clays

Mechanistically informed data-driven modeling of cyclic plasticity via artificial neural networks