Search

This paper studies the influence of diverse friction models on the numerical analysis of an industrial skew rolling mill using FORGE®. The originality of the present contribution is the analysis of the effect of the friction model on important parameters, namely, consumed power, plastic deformation and surface temperature. The aim is to evaluate which of these friction models is appropriate for simulating these industrial processes. The high values of temperature, pressure and sliding velocity at the contacts make the assessment of the friction model incidence on the deformation and temperature evolution fundamental, given its importance on the thermomechanical processing of materials. As a conclusion, IFUM is not valid because of its sliding velocity approach. On the other hand, Neumaier presents the highest deviations in terms of experimental power. It is concluded that Tresca is valid for this sort of processes and Norton model gives the most accurate results for friction power, related to the high sliding conditions at the contact. [ABSTRACT FROM AUTHOR]

Shape-memory polymers (SMPs) represent a class of smart materials able to store a temporary shape and to recover the original shape upon an external stimulus, such as temperature. The present paper proposes a three-dimensional finite-strain phenomenological model for thermo-responsive SMPs, which distinguishes between two material phases presenting different properties and is based on a rule of mixtures. The proposed model is motivated by the earlier work of Reese et al. (2010) and it considers several significant material features that had not been addressed in previous phenomenological approaches. Specifically, the model reproduces both heating-stretching-cooling and cold drawing shape-fixing procedures and it takes into account the non-ideal behavior of realistic SMPs (i.e. imperfect shape-fixing and incomplete shape-recovery). Several numerical tests are reported to assess model performances, from simple uniaxial and biaxial tests to complex simulations of biomedical devices. Comparisons with experimental data taken from the literature are also provided to validate the model. The proposed improvements increase the model applicability over a wide range of polymer types and operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: Bone modeling and remodeling have been extensively studied in many fields of research. The process of adaptive bone remodeling can be described mathematically and simulated in a computer model, integrated with the finite element method (FEM). The FEM can determine the long-term behavior of bone and the impact on bone biomechanics produced by prosthetic models. As whole bone remodeling simulations are time consuming, the aim of this paper is to combine FE analyses with numerical extrapolation techniques to accelerate bone remodeling simulations. Two vector extrapolation methods, reduce ranked extrapolation (RRE) and minimal polynomial extrapolation (MPE), are used to reduce the simulation time. These extrapolation techniques are illustrated by numerical examples of 2D and 3D models based on a strain-adaptive bone remodeling theory. [Copyright &y& Elsevier]

Abstract: In this paper we present thermo-plasticity model for dealing with localized failure with softening, which is capable of accounting for mechanical loading and heat transfer simultaneously. The main point concerns the localized failure of the structure which results with heterogeneity of stress and strain field for temperature dependent properties. We discuss how to employ structured mesh for such case, and construct the appropriate enhancements of the displacement and temperature fields by using the finite element method with embedded discontinuities (ED-FEM). For clarity, we first consider 1D case, and provide several illustrative numerical simulations. We then provide the corresponding generalization of the proposed model to 2D case and its numerical implementation based upon structured ED-FEM mesh. [Copyright &y& Elsevier]

Abstract: In this paper, the ductile fracture of Al-alloy 5052 is studied by experiments and simulations using a modified Rousselier model. Although tension failure has been successfully predicted by the classical Rousselier model, its predictive capability on shear failure was seldom discussed. A modified Rousselier model was proposed by incorporating the recent extended damage evolution model by Nahshon and Hutchinson. The modified Rousselier model can capture both tension and shear failure. A stress integration algorithm based on the general backward-Euler return algorithm for this constitutive model was developed and implemented into finite element model by the user defined material subroutine VUMAT in the ABAQUS/Explicit. The tensile tests of smooth round bar and notched round bars with different sizes were carried out to investigate the mechanical behavior of Al-alloy 5052. Consequently, the material parameters of the classical Rousselier model were identified by an inverse method using these experimental data. A shear test was also performed to calibrate the new shear damage coefficient in the modified Rousselier model. For the shear test, the simulations show that although shear failure can be predicted by the Rousselier model, the ductility was over-estimated. However, the modified Rousselier model can give more accurate results. The simulations on uniaxial tension of the round bars also confirm that the modified Rousselier model can well predict the cup-cone fracture mode. The results indicate that the Lode parameter in the new damage evolution model is important to capture the cup-cone fracture mode transition. [Copyright &y& Elsevier]

Abstract: The helical-wedge rolling (HWR) process is a new metal forming technique for producing spherical parts of various dimensions. In this paper, the overall details of the HWR process are described and the important process parameters that control the HWR process are systematically discussed. A new experimental method, developed under laboratory conditions, showed that the HWR process can produce spherical steel parts (balls) with high manufacturing quality. Numerical simulations of the HWR process were carried out using a commercially available FEM software (Simufact) to show the stress, strain, and temperature distributions in the rolled balls. In addition, the variation of forces and rolling moments during the process are analyzed. Based on the experimental and numerical investigations, the HWR technique has been found to be a viable process for enhancing the quality and productivity of formed spherical products. [Copyright &y& Elsevier]

Abstract: The construction of tunnels in soft ground causes short and long term ground deformations resulting from the disturbance of the virgin stress state of the soil and the changing pore water conditions. In particular in urban tunneling, in each stage of the construction process, interactions between the construction process, the soil and existing building infrastructure need to be evaluated to limit the risk of damage on existing buildings and to decide on appropriate mitigation measures. Besides conventional tunneling, mechanized tunneling is a well established and flexible technology in particular in urban areas, which allows for tunnel advances in a wide range of soils and difficult conditions. The paper presents a finite element model for the simulation of interactions between mechanized tunnel construction, the surrounding soil and existing buildings resting on pile foundations in the framework of a process-oriented simulation model for mechanized tunneling. The performance of the model is demonstrated by means of selected prototype analyses. As a consequence of the high computational demand connected with this type of spatio-temporal simulations, problem specific parallelization techniques are investigated to increase the numerical efficiency of the numerical analyses. [Copyright &y& Elsevier]

Abstract: In this paper we revisit a strain-adaptive bone remodelling problem, assuming that the rate of the apparent density at a particular location is described as a local objective function and depending on a particular stimulus at that location. Normally, continuum mathematical descriptions of adaptive bone remodelling can lead to discontinuous solutions on the global apparent density distribution. To improve this numerical solution, in this work, as the main novelty, we include the diffusion of the bone remodelling into the model. The variational problem is written as a coupled system of a nonlinear variational equation for the displacement field and a parabolic elliptic variational inequality for the apparent density. An existence and uniqueness result is stated. Then, a fully discrete problem is introduced by using the finite element method to approximate the spatial variable and an Euler scheme to discretize the time derivatives. A priori error estimates are proved from which, under adequate additional regularity conditions, the linear convergence of the algorithm is deduced. Finally, some numerical simulations are presented to demonstrate the accuracy of the approximation and the behaviour of the solution. [Copyright &y& Elsevier]

This paper deals with the influence of interference fit coupling on the fatigue strength of holed plates. The effect was investigated both experimentally and numerically. Axial fatigue tests have been carried out on holed specimens made of high performance steel (1075MPa of Ultimate strength and 990MPa of Yield strength) with or without a pin, made of the same material, press fitted into their central hole. Three different conditions have been investigated: free hole specimens, specimens with 0.6% of nominal specific interference and specimens with 2% of nominal specific interference. The experimental stress-life (S--N) curves pointed out an increased fatigue life of the interference fit specimens compared with the free hole ones. The numerical investigation was performed in order to analyse the stress fields by applying an elastic plastic 2D simulation with a commercial Finite Element software. The stress history and distribution along the contact interference of the fitted samples indicates a significant reduction of the local stress range due to the externally applied loading (remote stress) since a residual and compressive stress field is generated by the pin insertion. [ABSTRACT FROM AUTHOR]

Abstract: During installation of a displacement pile, the soil around the pile is heavily distorted. The resulting changes in soil density and stress state around the pile determine the ultimate pile capacity. In most finite element models, the installation phase is not explicitly modelled. In this paper the full installation phase is modelled in two different ways, in a numerical code capable of large deformations. In the first approach the pile is fixed and the soil flows around the pile. This modelling approach requires somewhat unrealistic boundary conditions and requires that the results for the pile installation are for a non-stationary phase of the calculation, whereas formally only the values at the stationary full penetration phase are reliable. A second modelling approach has been introduced to overcome these limitations. In the new approach the initial conditions are set as a stress level, increasing linearly with depth, resulting from a gravity loading stage, and a stepwise penetration of the pile into the soil is prescribed. This approach updates the geometry of the problem domain and keeps updating the convective terms in a fixed mesh. Results are compared with experimental results from centrifuge tests. Although both models show the development of large effective vertical stress below the pile base and porosity change near the pile shaft, also differences with the experimental results are found. Especially the stiffness response during pile installation is difficult to model correctly. [Copyright &y& Elsevier]

This paper presents the determination of virtual micro-forming limit diagrams from two types of numerical simulations based on the finite element method: one with modelling of the full tool for micro-deep drawing and a thin blank with geometric imperfections, based on a defined roughness; and a second called "reduced simulation" where different deformation paths were simulated with appropriate boundary conditions by introducing the same type of geometric imperfections on aluminium 1050A (99.5%). A new test for detecting the onset of necking, called the "change of slope" criterion has been defined. Several methods based on histograms to represent the distributions of major and minor strains, have been used to determine the strain at the onset of necking. The numerical micro-forming limit diagrams (MFLD) were then compared to one obtained experimentally. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents experimental and numerical results of dynamic cyclic tests carried out on two full-scale specimens of welded beam-to-column connections. In order to simulate the nonlinear dynamic behaviour of tested specimens, a fibre-based finite element beam is used to model beam and column members and a nonlinear rotational spring is also used to model welded connections. The effect of strain rate on beam and column behaviour is taken into account for each constitutive fibre using the Perzyna law. The effect of strain rate on welded connection is taken into account by extending the static Richard model to simulate its dynamic behaviour. The Krawinkler–Zoheri model, expressed as a function of normalized cumulative plastic strain, is introduced to quantify damage and degrading behaviour in terms of the strain-rate effect. The finite element Drain-2dx software is first upgraded for this purpose to carry out numerical investigations. The analytical results obtained from the numerical simulation, taking the strain rate effect and damage accumulation into account, predict well the structural dynamic behaviour up to failure of welded connections when compared with available experimental data. [Copyright &y& Elsevier]

The paper presents a computational and experimental investigation of integrated high-performance joints (IHPJs). The first type of the joints is presented by composite lugs and multiloop joints. Experimental and numerical stress analyses were carried out for single-loop specimens with different materials and geometrical parameters. Static and fatigue tension tests of IHPJs were also performed. The finite-element method and analytical methods were in good agreement in calculating the maximum tangential stress in the loop. Static failure criteria are proposed for the engineering design procedure. [ABSTRACT FROM AUTHOR]

Abstract: Resistance upset welding (UW) is a widely used process for joining metal parts. In this process current, time and upsetting force are three parameters that affect the quality of welded products. This paper considers numerical simulation and experimental investigation of UW process parameters. The investigated parameters include heating and post-weld heating current and their corresponding duration as well as interference of the part features that form the joint. In this study, evaluation of tensile strength of the welded joint with variation of the process parameters is also reported. For numerical analysis, a two-dimensional axisymmetric model using a coupled electro-thermal finite element method is developed to study the thermal behavior of the welded joints. The results of this numerical simulation are used to determine the status of the weldment and therefore evaluate the quality of the weld at the joint. Both numerical and experimental results suggest an optimum set of welding parameters, i.e. time and electrical current that yields a maximum value for the tensile strength of the joint. Also the effects of post-weld heating time and current on the tensile strength are evaluated and show that these parameters have a remarkable effect on improving tensile strength of the weldment. [Copyright &y& Elsevier]

In this paper, the influences of low heat transfer condition at the outer walls on the microcombustor are investigated due to the fact that a sufficiently small heat transfer coefficient at the outer wall incurs the upstream burning in the recirculation jacket, results in the high wall temperature, and hence possibly damages the microcombustor. Numerical simulation approaches focused on the microcombustor with the flame burning in the recirculation jacket. Combustion characteristics of the combustor were first analyzed based on 2D computational fluid dynamics (CFD), and then the most dangerous locations on the combustor were predicted by means of the 3D finite element analysis method. The study demonstrates the effectiveness of CFD and stress modeling for the design and improvement of the microcombustors. [ABSTRACT FROM AUTHOR]