Cyclic Plastic Response Research Articles

CYCLIC PLASTICITY MODELLING FOR ANDES THIN SHELL AND LINE-SPRING FINITE ELEMENTS

This paper presents a proposed methodology to account for cyclic plastic response of the thin shell ANDES and line-spring finite elements. A through thickness integration scheme is employed for the shell element and stress resultant plasticity is used for the line-spring element. A simplified contact formulation to account for crack closure in the line-spring element is also presented. Numerical comparisons between the proposed models and detailed 3D analyses (pipes) are carried out and presented herein. A comparison between the present implementation and large scale experiment of a surface cracked pipe subjected to large cyclic plastic strains is also presented. The purpose of the presented implementation is to account for cyclic loading in pipeline technology where significant amount of plasticity in the loading cycles occurs.

Discrete dislocation plasticity analysis of single crystalline thin beam under combined cyclic tension and bending

The cyclic plastic response of a single crystalline thin beam subject to combined cyclic tension and bending is analyzed using two-dimensional discrete dislocation plasticity. In this contribution, special attention is paid to the difference in the inherent mechanism of the size effect for different cyclic loads. Results show that the cyclic plastic response has a strong size effect for both cyclic pure tension–compression and pure bending. However, the inherent mechanisms are different. The dislocation starvation mechanism dominates the cyclic tension–compression while the geometrically necessary dislocation dominates the cyclic pure bending. When the combined cyclic tension and bending are applied to the thin beam, the cyclic moment–rotation response shows strong size effect while the stress–strain response shows weak or even no size effect. In addition, it is also found that the cyclic loading paths have considerable influences on the shape of the cyclic stress–strain loops.

Cyclic Plastic Response and Fatigue Life of Materials

Recently the decisive role of plastic strain amplitude for the initiation and the growth rate of short cracks has been demonstrated. The plastic strain amplitude can be related to the rate of short crack growth and also to the fatigue life. Since the cyclic stress-strain response of a material determines the plastic strain amplitude it influences basically its fatigue life. The experiments in stress and plastic strain controlled loading and short crack growth are presented and used to demonstrate the importance of the cyclic plastic response for the evaluation of the fatigue life.

Micromechanical modelling of cyclic plasticity incorporating damage

In this paper a numerical investigation on the possibility to simulate and predict cyclic plastic response incorporating damage has been performed. To this purpose, unit cell and continuum approaches based on porous metal plasticity and continuum damage mechanics (CDM) have been considered. In particular, the porous metal plasticity model of Leblond, Perrin and Devaux (LPD model) and the CDM model developed by Pirondi and Bonora were used. Finite element (FE) simulations were performed for each approach with different degrees of triaxiality and the results are analyzed and compared.

Analysis of low cycle fatigue in AlMgSi aluminium alloys

In this study low-cycle fatigue tests were performed in two AlMgSi aluminium alloys with different chemical composition, namely 6082-T6 and 6060-T6 alloys, using standard round specimens and tube specimens, respectively. The tests were undertaken in strain control with a strain ratio R ε =−1. The cyclic stress–strain curves were determined using one specimen for each imposed strain level. The low-cycle fatigue results are used for the characterisation of the cyclic plastic response and the fatigue live of the alloys. Moreover, the geometry of the hysteresis loops and the occurrence of Masing behaviour are also analysed. The observed behaviour is discussed in terms of the chemical composition of the alloys (Mg 2Si hardening particles and Mn dispersoid content) and fracture mechanisms. Alloy 6060-T6 exhibits nearly ideal Masing behaviour, while alloy 6082-T6 presents significant deviations from the Masing model. The type of cyclic deformation behaviour in AlMgSi alloys seems to be influenced by the dispersoid phase.

Fatigue softening of X10CrAl24 ferritic steel

Cyclic plastic response of X10CrAl24 ferritic stainless steel in a wide domain of plastic strain amplitude was measured. Cyclic hardening–softening curves show important cyclic softening during most of the fatigue life. Cyclic stress-strain curves have different slopes in the domain of low and high strain amplitudes. These two domains in cyclic stress–strain curve correspond to two types of internal structure as observed by transmission electron microscopy (TEM). The areas of condensed dislocation structure in the interior and the bands of extrusions and intrusions on the surface indicate the localization of cyclic strain. Fatigue softening was discussed in terms of properties of dislocations in b.c.c. structure and localization of the cyclic plastic strain.

Effects of cyclic plasticity on creep crack growth

This paper presents an analytical model for analysing the onset and the subsequent growth of cracks in solids subject to cyclic creep loading conditions. The model incorporates features such as: 1. (1) the constitutive relationship for creep deformation based on continuum damage mechanics theory; 2. (2) the multi-yield surfaces coupled with the Mroz's kinematic hardening rule for cyclic plastic response; 3. (3) the hybrid explicit-implicit integration scheme for the finite element analysis of creep stress; 4. (4) the modified breakable element algorithm coupled with the damage criterion for the proposed creep fracture analysis. This model has been shown to provide explicit and effective prediction of crack growth under cyclic creep loadings. Numerical study by the proposed model indicates that plastic strains play a significant role in cyclic creep fracture. In the creep dominated fracture unloading and reloading can interrupt the stress relaxation near the crack tip and cause a significant stress increase in the regions. Consequently, the creep damage accumulation along the crack extension line is accelerated by the load cycling. An earlier onset of crack growth with faster rate of propagation was thus observed.