Diego J. Celentano

Experimental and numerical analysis of the tensile test using sheet specimens

This paper presents an experimental and numerical study of the mechanical behaviour of SAE 1045 steel sheet specimens during the conventional tensile test. Due to the complex stress state that develops at the neck for high levels of axial deformation, an experimental-numerical methodology is proposed in order to derive the elastic and hardening parameters which characterize the material response. Such methodology is essentially an extension to sheet samples of the well established procedure used for cylindrical ones. The simulation of the deformation process during the whole test is performed with a finite element large strain elastoplasticity-based formulation. Finally, the experimental validation of the obtained numerical results allows to assess the performance of the proposed methodology for the 3D analysis of sheet specimens and, in addition, to discuss the range of applicability of plane stress conditions.

A moving Lagrangian interface technique for flow computations over fixed meshes

Abstract In this paper, an enhanced finite element formulation for unsteady incompressible flows with moving interfaces is presented. The weak form of the Navier–Stokes equations, written using a generalized streamline operator technique, is coupled with the movement of the interface between two immiscible fluids defined through an independent moving mesh. The position of the interface is updated using a Lagrangian formulation. In this framework, a global mass conservation corrector algorithm and an enhanced element integration technique are proposed to improve accuracy. The method is applied to a number of test problems with moving interfaces.

Mechanical behaviour and rupture of normal and pathological human ascending aortic wall

The mechanical properties of aortic wall, both healthy and pathological, are needed in order to develop and improve diagnostic and interventional criteria, and for the development of mechanical models to assess arterial integrity. This study focuses on the mechanical behaviour and rupture conditions of the human ascending aorta and its relationship with age and pathologies. Fresh ascending aortic specimens harvested from 23 healthy donors, 12 patients with bicuspid aortic valve (BAV) and 14 with aneurysm were tensile-tested in vitro under physiological conditions. Tensile strength, stretch at failure and elbow stress were measured. The obtained results showed that age causes a major reduction in the mechanical parameters of healthy ascending aortic tissue, and that no significant differences are found between the mechanical strength of aneurysmal or BAV aortic specimens and the corresponding age-matched control group. The physiological level of the stress in the circumferential direction was also computed to assess the physiological operation range of healthy and diseased ascending aortas. The mean physiological wall stress acting on pathologic aortas was found to be far from rupture, with factors of safety (defined as the ratio of tensile strength to the mean wall stress) larger than six. In contrast, the physiological operation of pathologic vessels lays in the stiff part of the response curve, losing part of its function of damping the pressure waves from the heart.

A large strain thermoviscoplastic formulation for the solidification of S.G. cast iron in a green sand mould

Abstract This paper presents a large strain thermoviscoplastic formulation for the analysis of the solidification process of spheroidal graphite (S.G.) cast iron in a green sand mould. This formulation includes two different non-associate constitutive models in order to describe the thermomechanical behaviour of each of such materials during the whole process. The performance of these models is evaluated in the analysis of a solidification test.

Mechanical characterisation of the human thoracic descending aorta: experiments and modelling

This work presents experiments and modelling aimed at characterising the passive mechanical behaviour of the human thoracic descending aorta. To this end, uniaxial tension and pressurisation tests on healthy samples corresponding to newborn, young and adult arteries are performed. Then, the tensile measurements are used to calibrate the material parameters of the Holzapfel constitutive model. This model is found to adequately adjust the material behaviour in a wide deformation range; in particular, it captures the progressive stiffness increase and the anisotropy due to the stretching of the collagen fibres. Finally, the assessment of these material parameters in the modelling of the pressurisation test is addressed. The implication of this study is the possibility to predict the mechanical response of the human thoracic descending aorta under generalised loading states like those that can occur in physiological conditions and/or in medical device applications.

Modeling fluid‐solid thermomechanical interactions in casting processes

An integrated formulation for the analysis of casting processes is presented in this work. This model involves the description of the evolution and the coupled interactions of the flow, thermal and mechanical fields occurring during the liquid‐solid transformation of the solidifying metal. The corresponding discretized formulation is solved in the context of a fixed‐mesh finite element method. Numerical results applying this methodology in two cylindrical casting specimens are first presented to assess the influence of different phenomena occurring during the process. Moreover, these simulations are compared with available experimental data.

A thermomechanical model with microstructure evolution for aluminium alloy casting processes

Abstract A thermomechanical-microstructural model for the analysis of aluminium alloy solidification processes is presented. This model is defined in a finite strain thermoplasticity framework considering microstructure-based liquid–solid phase-change effects for the solidifying alloy. Temperatures, displacements and microstructure results predicted by the model are validated with laboratory measurements of a gravity casting in a permanent composite mould.

A thermomechanical model for the analysis of light alloy solidification in a composite mould

A coupled thermomechanical model to simulate light alloy solidification problems in permanent composite moulds is presented. This model is based on a general isotropic thermoelasto-plasticity theory and considers the different thermomechanical behaviours of each component of the mould as well as those of the solidifying material during its evolution from liquid to solid. To this end, plastic evolution equations, a phase-change variable and a specific free energy function are proposed in order to derive temperature-dependent material constitutive laws. The corresponding finite element formulation and the staggered scheme used to solve the coupled nonlinear system of equations are also presented. Finally, the temperature and displacement predictions of the model are validated with laboratory measurements obtained during an experimental trial

Characterization of the mechanical behaviour of materials in the tensile test: Experiments and simulation

This paper presents an experimental analysis and a numerical simulation of the mechanical behaviour experienced during the tensile test by both cylindrical and strip specimens of different materials for which the classical so-called Bridgmans procedure aimed at predicting the stress distribution at the necking zone cannot be directly applied. A set of experiments has been carried out in order to derive the elastic and hardening parameters that characterize the material response. The simulation of the deformation process during the whole test is performed with a finite element large strain elastoplasticity-based formulation. Finally, the results obtained with the simulation are experimentally validated.

Computational simulation of microstructure evolution during solidification of ductile cast iron

Abstract This paper presents a thermomicrostructural model for the simulation of the solidification process of an eutectic ductile cast iron. The thermal balance is written at a macroscopic level and takes into account both the structural component being cast and its mould. Models of nucleation and growth represent the evolution of the microstructure, and the microsegregation of silicon is also considered. The resulting formulation is solved using a finite element discretisation of the macrodomain, in which the evolution of the microstructure is taken into account at the Gauss integration points. The numerical results are presented in terms of cooling curves and are compared with available experimental values. Furthermore, the sensitivity of the response with respect to changes in the cooling rate and nucleation parameters are investigated. The agreement between experimental and computational values is acceptable in both quantitative and qualitative aspects. Ways to improve the computational model are suggested.