Two-Intervals Hardening Function in a Phase-Field Damage Model for the Simulation of Aluminum Alloy Ductile Behavior

The aluminum alloys (AA) are among the most utilized materials in engineering structures, which induces the need for careful investigation, testing, and possibilities for accurate simulation of the structure’s response. AA 5083-H111 specimens were used to investigate the possibility of employing a Phase-Field Damage Model (PFDM) for the simulation of AA structures’ behavior. The specimens were mechanically tested by uniaxial tensile loading tests. Based on the obtained results, the PFDM was employed with a von Mises plasticity model, implemented in the Finite Element Method software. The plasticity model was extended by modification of the hardening function defined in two-intervals: a linear hardening and a Simo-type hardening. An excellent superposition of the simulation and experimental force-displacement response was recorded. These findings suggest that the AA structures’ response can be successfully simulated in the elastic-plastic domain, as well as its failure by damage being controlled.

Mathematical modeling of physically nonlinear 3D beams and plates made of multimodulus materials

In this work, mathematical models of physically nonlinear plates and beams made from multimodulus materials are constructed. Our considerations are based on the 3D deformation theory of plasticity, the von Mises plasticity criterion and the method of variable parameters of the theory of elasticity developed by Birger. The proposed theory and computational algorithm enable for solving problems of three types of boundary conditions, edge conditions and arbitrary lateral load distribution. The problem is solved by the finite element method (FEM), and its convergence and the reliability of the results are investigated. Based on numerical experiments, the influence of multimodulus characteristics of the material of the beam and the plate on their stress–strain states under the action of transverse loads is illustrated and discussed.

Numerical Simulations and Experimental Study on the Reeling Process of Submarine Pipeline by R-Lay Method

During the reeling process of the reel-lay method, the pipe will be subjected to combined loading of tension and bending. Excessive ovalization of the pipe will affect the structural performance and even lead to structural instability of the pipe. In this paper, a numerical simulation model of the pipe-reeling process is established by finite element tools. The Ramberg–Osgood material model is used to study the ovalization and bending moment of the pipe cross-section during the pipe-reeling process based on the Von Mises plasticity and nonlinear kinematic hardening rules. The results show that the ovalization and bending moment of the pipe section will change significantly during the pipe-reeling process. Subsequently, one set of 6-inch pipe-reeling experimental setups was designed to conduct a full-scale experiment. Compared with the experimental results, the feasibility of the finite element model is verified. Finally, the effects of diameter-to-thickness ratio, the material parameters of the pipe, and the pipe axial tension on the ovalization and bending moment changes are studied. Research shows that each parameter has a certain influence on the pipe of the reeling process, and the diameter-to-thickness ratio of the pipe has the most obvious effect. When the diameter-to-thickness ratio decreases, the bearing capacity for bending moments and the ability to resist ovalization of pipe are enhanced. At the same time, each parameter has a significant impact on the reeling process of the pipeline.

Correlation of Global Quantities at Material Characterization of Pressure-Sensitive Materials Using Sharp Indentation Testing

Correlation of sharp indentation problems is examined theoretically and numerically. The analysis focuses on elastic-plastic pressure-sensitive materials and especially the case when the local plastic zone is so large that elastic effects on the mean contact pressure will be small or negligible as is the case for engineering metals and alloys. The results from the theoretical analysis indicate that the effect from pressure-sensitivity and plastic strain-hardening are separable at correlation of hardness values. This is confirmed using finite element methods and closed-form formulas are presented representing a pressure-sensitive counterpart to the Tabor formula at von Mises plasticity. The situation for the relative contact area is more complicated as also discussed.

A Modified Phase-Field Damage Model for Metal Plasticity at Finite Strains: Numerical Development and Experimental Validation

Steel structures are designed to operate in an elastic domain, but sometimes plastic strains induce damage and fracture. Besides experimental investigation, a phase-field damage model (PFDM) emerged as a cutting-edge simulation technique for predicting damage evolution. In this paper, a von Mises metal plasticity model is modified and a coupling with PFDM is improved to simulate ductile behavior of metallic materials with or without constant stress plateau after yielding occurs. The proposed improvements are: (1) new coupling variable activated after the critical equivalent plastic strain is reached; (2) two-stage yield function consisting of perfect plasticity and extended Simo-type hardening functions. The uniaxial tension tests are conducted for verification purposes and identifying the material parameters. The staggered iterative scheme, multiplicative decomposition of the deformation gradient, and logarithmic natural strain measure are employed for the implementation into finite element method (FEM) software. The coupling is verified by the ‘one element’ example. The excellent qualitative and quantitative overlapping of the force-displacement response of experimental and simulation results is recorded. The practical significances of the proposed PFDM are a better insight into the simulation of damage evolution in steel structures, and an easy extension of existing the von Mises plasticity model coupled to damage phase-field.

Multiple necking patterns in elasto-plastic rings subjected to rapid radial expansion: The effect of random distributions of geometric imperfections

In this paper we have investigated, using finite element calculations performed in ABAQUS/Explicit [1], the effect of ab initio geometric imperfections in the development of multiple necking patterns in ductile rings subjected to dynamic expansion. Specifically, we have extended the work of Rodríguez-Martínez et al. [33], who studied the formation of necks in rings with sinusoidal spatial perturbations of predefined amplitude and constant wavelength, by considering specimens with random distributions of perturbations of varying amplitude and wavelength. The idea, which is based on the work of El Maï et al. [4], is to provide an idealized modeling of the surface defects and initial roughness of the rings and explore their effect on the collective behavior and spacing of the necks. The material behavior has been modeled with von Mises plasticity and constant yield stress, and the finite element simulations have been performed for expanding velocities ranging from 10 m/s to 1000 m/s, as in ref. [33]. For each speed, we have performed calculations varying the number of imperfections in the ring from 5 to 150. In order to obtain statistically significant results, for each number of imperfections, the computations have been run with five random distributions of imperfection wavelengths. For a small number of imperfections, the variability in the wavelengths distribution is large, which makes the imperfections play a major role in the necking pattern, largely controlling the spacing and growth rate of the necks. As the number of imperfections increases, the variability in the wavelengths distribution decreases, giving rise to an array of more regularly spaced necks which grow at more similar speed. A key outcome is to show that, for a large number of imperfections, the number of necks formed in the ring comes closer to the number of necks obtained in the absence of ab initio geometric imperfections.

A New Nodal-Integration-Based Finite Element Method for the Numerical Simulation of Welding Processes

This paper aims at introducing a new nodal-integration-based finite element method for the numerical calculation of residual stresses induced by welding processes. The main advantage of the proposed method is to be based on first-order tetrahedral meshes, thus greatly facilitating the meshing of complex geometries using currently available meshing tools. In addition, the formulation of the problem avoids any locking phenomena arising from the plastic incompressibility associated with von Mises plasticity and currently encountered with standard 4-node tetrahedral elements. The numerical results generated by the nodal approach are compared to those obtained with more classical simulations using finite elements based on mixed displacement–pressure formulations: 8-node Q1P0 hexahedra (linear displacement, constant pressure) and 4-node P1P1 tetrahedra (linear displacement, linear pressure). The comparisons evidence the efficiency of the nodal approach for the simulation of complex thermal–elastic–plastic problems.