Ductile fracture of tubular specimens under non-proportional loading condition

Ductile fracture under proportional and non-proportional multiaxial loading

The characterization of ductile damage evolution, and its description, have been the object of extensive research in the continuum damage mechanic field. Many different models have been developed since the pioneering works carried out a few decades ago. In detail, the stress triaxiality and the Lode angle parameters have been identified as the two main variables that affect the material ductility. The literature offers a great number of investigations under monotonic loading conditions, however, a proper characterization of the damage evolution under cyclic loading or non-proportional loading is still missing. In this paper, an unconventional coupled elastoplastic and damage constitutive model with a Mohr-Coulomb failure criterion is presented. The novelty of this study is represented by the modification of the ductile damage law in order to consider the damage evolution under non-proportional loading conditions. Therefore, the idea is to investigate the structural response of a steel bridge column subjected to a cyclic non-proportional loading, showing how, a different approach in the description of the ductile damage evolution, is necessary for a realistic description of the pier behavior.

Fatigue behaviors and life evaluation of AISI304 stainless steel under non-proportional multiaxial random loading

A novel model for prediction of burst capacity of corroded pipelines subjected to combined loads of bending moment and axial compression

A series of strain-controlled multiaxial low cycle fatigue (LCF) tests under proportional and non-proportional loading conditions have been conducted on notched specimens. Cylindrical bars of Al 6061 aluminum alloy and AISI 316L stainless steel with four values of stress concentration factors referred to the net section Kt,n were employed. The experimental results evidenced a reduction of fatigue life due to non-proportional loading. Furthermore, the crack initiation site has been detected to be moved from the notch tip in the case of steel for high values of notch radius under non-proportional loading. Stress concentration factor evaluated in the elastic field Kt,n has been included in the Itoh-Sakane parameter to evaluate the fatigue life, returning a general underestimation of fatigue life especially for high values of Kt,n. Material notch sensitivity and crack initiation position have been taken into account to further modify the model, improving the original results and showing a better assessment.

In this paper, the loading path effect on the elastic-plastic crack-front stress field in a thin plate is investigated. There different loading sequences include one proportional loading and two non-proportional loading paths are applied to the 3-D modified boundary layer (MBL) model under small-scale yielding conditions. For the same external displacement field applied at the outer boundary of the 3-D MBL model, the mode I K field and T-stress field combined as the different loading path is applied to investigate the influence of the nonproportional loading. The results show that for either the compressive or tensional T-stress, the loading path which applied K field followed by T field generates the lower crack-tip constraint. There is only slightly difference between the proportional loading path and the T-stress field following by K field loading path. The results show that it is very important to include the load sequence effects in fracture analysis when dealing with nonproportional loading conditions.

A new ductile fracture model for structural metals considering effects of stress state, strain hardening and micro-void shape

Strain gradient crystal plasticity model based on generalized non-quadratic defect energy and uncoupled dissipation

Study on fracture behaviour of pipeline girth welds based on curved wide plate specimens: Experimental and numerical analysis

Modeling the effects of helium-vacancy clusters on the stress-strain response of a grain boundary in iron by a mechanistic finite element approach informed by molecular dynamics data

Finite element analysis has been used extensively in the study of biomechanical modeling of the breast. However, issues regarding the complexity of material models and the influences of geometric boundary conditions on the accuracy of a breast Finite Element (FE) model are still under debate. This work demonstrates the importance of material modeling in FE models of the breast. A simple hemispherical geometry is used to model the shape of a human breast. Different material models are being investigated to accurately model changes in terms of displacement, stress, and reaction forces distribution. The results obtained using nonlinear material models are compared with those obtained employing their linear approximation. Results have shown that differences, in terms of displacement, ranging between 20% and more than 80%, may occur and that large differences are present in terms of maximum principal stresses when the displacement is correctly approximated. This study clearly shows that, in a FE model, simulating large deformations material modeling strongly influences the accuracy of the solution.

A nonlinear model for ductile damage accumulation under multiaxial non-proportional loading conditions

Evaluation of crack tip stress and strain fields under nonproportional loading in a viscoelastic material

<div class="htmlview paragraph">Detailed finite element modeling of the human body offers a potential major enhancement to the prediction of injury risk during vehicle impacts. Currently, vehicle crash safety countermeasure development is based on a combination of testing with established anthropomorphic test devices (i.e., ATD or dummy) and a mixture of multi-body (dummy) and finite element (vehicle) modeling. If a relatively simple finite element model can be developed to capture additional information beyond the capabilities of the multi-body systems, it would allow improved countermeasure development through more detailed prediction of performance.</div> <div class="htmlview paragraph">A simpler finite element model of human bones could be developed if it were shown that less complex finite element material modeling provides sufficient prediction of long bone macro-level strength. This study investigates the importance of including material anisotropy in the finite element model of a human femur. Four composite femur models were developed: linear orthotropic, linear transversely isotropic, linear isotropic, and non-linear isotropic. Each model was used to simulate anterior-posterior (AP) bending and external-internal rotation. Comparison of the results with physical tests indicates that the global elastic force-deflection response of the whole femur in AP bending is sufficiently described by isotropic material models of the two constituent tissues. The more complex (more detailed anisotropic) material models do not enhance the results of this simulation. However, the global response of the femur in external-internal rotation does indicate that increased material model complexity (or higher degree of detail in material anisotropy) can provide improved prediction capability.</div>

Numerical analysis of aluminium alloy gusset joints subjected to bending moment and axial force