3D Elastoplastic Model Research Articles

On the effect of microplasticity on crack initiation from subsurface defects in rolling contact fatigue

This work demonstrates numerically how microplasticity, i.e. the yielding behavior below the conventional 0.2% plastic strain threshold, can lead to initiation of cracks at subsurface defects, in rolling contact applications operating under realistic loads. A 3D elasto-plastic finite element model is employed to perform shakedown analysis of the bearing steel around a small spherical void with two different approximations of the steel constitutive behavior at the plastic micro-strain regime. When non-linear kinematic hardening is used to model a fast but smooth onset of plasticity, the fields of plastic strains and micro-residual stresses around the void evolve very distinctly to the case where a sharp transition is assumed. To further investigate the role of the tensile micro-residual stresses occurring in the former case on crack initiation, a planar circular crack is inserted at the equator of the void and an entire overrolling cycle is investigated by means of linear elastic fracture mechanics (LEFM). This analysis is repeated for different crack sizes and the respective stress intensity factors and their amplitudes, relevant for crack growth, are reported. The work also reports implementation details for the coupling of a 3D elasto-plastic model for shakedown analysis to a subsequent LEFM analysis model.

Tests and Numerical Study of Single-Lap Thermoplastic Composite Joints Bolted by Countersunk.

Tensile tests were carried out to investigate the effect of stacking sequences on the bearing strength of single-lap thermoplastic composite countersunk bolted joints. A 3D elastoplastic model was built based on a plastic theory for numerical analysis. The damage initiation was judged based on LaRC05 criteria, and the damage propagation was described by using a nonlinear, gradual unloading method based on crack band theory. The accuracy of the present model was validated by comparing the numerical results to those from the tests. The test results showed that the effects of stacking sequences on the ultimate bearing strength and the 2% offset bearing strength are limited. Moreover, the numerical results depicted that the ultimate bearing strength and the 2% offset bearing strength reduce when the bolt-tightening torque or the bolt–hole clearance is increased.

Experimental demonstration of the in-situ effect under transverse shear

Failure of composite laminates, in load cases where transverse shear prevail, involves shear cracks and delaminations, and yet it is unclear which damage mechanism triggers the other or how it depends on ply-thickness. Combining interrupted interlaminar shear strength tests with X-ray tomography inspections, we compared the damage sequence of [45°/0°/-45°/90°]ns short-beam specimens manufactured with standard- (n=2) or thin-ply (n=4) non-crimp fabrics (fibre areal weights of 134 and 67 gsm per ply). Failure manifested as a load drop in the force-displacement curve. In both materials, we associated the onset of instability to a shear crack tunnelling across the central 902° ply-cluster. The intersection of this crack with the ones developing in the adjacent layers induced a delamination which, in turn, activated the load drop. A 3D elasto-plastic model predicted that, for the same applied load, the ply-cluster of both laminates would display a similar maximum principal stress distribution. However, the thin-ply samples improved the interlaminar shear strength by 34%, evidencing the so called in-situ effect: the resistance to matrix cracking under transverse shear (τ23 in the local coordinates of the 90° plies) increases when ply-thickness is reduced.

3D Elastoplastic Model for Fine-Grained Gassy Soil Considering the Gas-Dependent Yield Surface Shape and Stress-Dilatancy

AbstractFine-grained sediments containing large discrete gas bubbles are widely distributed in the five continents throughout the world. The presence of gas bubbles could either degrade or enhance ...

A simple 3D elastoplastic constitutive model for soils based on the characteristic stress

This paper presents a direct method to establish a 3D elastoplastic constitutive model for soils based on the characteristic stress. In the established model, a new yield function is first formulated through an interpolation function in the characteristic stress space. A hardening parameter that suits for monotonic and cyclic loading conditions is established by introducing the concept of the subloading surface. Then, a 3D constitutive model for soils is established by combining the previously proposed plastic potential function. Only seven material parameters with clear physical meanings are included in the proposed 3D elastoplastic model. The deformation behaviours of soils under monotonic and cyclic loading conditions and the critical state properties under true triaxial stress conditions are analysed on the basis of the presented model. The capability of the model is verified by the comparisons between the model responses and the test results of soils under the 3D monotonic and cyclic loading conditions.

3D Elastoplastic Model for Crushable Soils with Explicit Formulation of Particle Crushing

AbstractAn extended version of the coupling breakage and friction dissipation (CBFD) model is developed based on the critical state concept for crushable soils. In the extended CBFD model, the sing...