Departamento de Mecánica de Medios Continuos y Teoría de Estructuras
http://hdl.handle.net/10016/7174
2020-10-26T19:35:05ZDynamic shear instabilities in metallic sheets subjected to shear-compression loading
http://hdl.handle.net/10016/31302
Dynamic shear instabilities in metallic sheets subjected to shear-compression loading
Rodríguez-Martínez, José A.; Vaz-Romero, Álvaro; N Souglo, Komi Espoir; Vadillo, Guadalupe
This paper presents an investigation on the formation of adiabatic shear bands in metallic sheets subjected to dynamic shear-compression loading under plane-stress conditions. For that purpose, we have developed a theoretical model based on perturbation analysis, and have performed finite element calculations. The material behavior has been modeled with von Mises plasticity, and the evolution of the yield stress has been considered dependent on plastic strain, plastic strain rate, and temperature. The theoretical model extends the linear stability analysis for simple-shear formulated by Molinari (1997) to shear-compression loading. The numerical simulations have been performed in ABAQUS/Explicit (2016) using a unit-cell model based on the work of Rodríguez-Martínez et al. (2015) in which the shear band formation is favored introducing geometric and material imperfections. Moreover, we have developed a calibration procedure for the stability analysis that enables to make qualitative and quantitative comparisons with the finite element calculations. Both stability analysis predictions and finite element results display the same overall trends, and show that any small negative triaxiality has a profound stabilizing effect on the material behavior delaying, or even preventing, the formation of a shear band. This key outcome has been substantiated for a wide range of strain rates and for materials with different strain hardening coefficients, strain rate sensitivities, and thermal softening behaviors.
2020-11-01T00:00:00ZModeling dynamic spherical cavity expansion in elasto-viscoplastic media
http://hdl.handle.net/10016/30755
Modeling dynamic spherical cavity expansion in elasto-viscoplastic media
Santos, T. dos; Brezolin, A.; Rossi, R.; Rodríguez-Martínez, José A.
In this paper, we extend the dynamic spherical cavity expansion model for rate-independent materials developed by Durban and Masri (Int J Solids Struct 41(20):5697-5716, 2004), Masri and Durban (J Appl Mech 72(6):887-898, 2005), and Cohen et al. (J Appl Mech 77(4):041009, 2010) to viscoplastic media. For that purpose, we describe the material behavior with an isotropic Perzyna-type overstress formulation (Perzyna in Q Appl Math 20:321&#-332, 1963; Adv Appl Mech 9:243-377, 1966) in which the material rate dependence is controlled by the viscosity parameter η. The theoretical predictions of the cavity expansion model, which assumes that the cavity expands at constant velocity, are compared with finite element simulations performed in ABAQUS/Explicit (Abaqus Explicit v6.13 User's Manual, ABAQUS Inc., Richmond). The agreement between theory and numerical simulations is excellent for the whole range of cavitation velocities investigated, and for different values of the parameter η. We show that, as opposed to the steady-state self-similar solutions obtained for rate-independent materials (Durban and Masri 2004; Masri and Durban 2005; Cohen et al. 2010), the material viscosity leads to time-dependent cavitation fields and stress relaxation as the cavity enlarges. In addition, we also show that the material viscosity facilitates to model the shock waves that emerge at the highest cavitation velocities investigated, controlling the amplitude and the width of the shock front.
2020-06-01T00:00:00ZRecovering added mass in nanoresonator sensors from finite axial eigenfrequency data
http://hdl.handle.net/10016/30487
Recovering added mass in nanoresonator sensors from finite axial eigenfrequency data
Dilena, M.; Fedele dell'Oste, M.; Fernández-Sáez, José; Morassi, Antonino; Zaera Polo, Ramón Eulalio
In this paper we present a method for solving a finite inverse eigenvalue problem arising in the determination of added distributed mass in nanoresonator sensors by measurements of the first N natural frequencies of the free axial vibration under clamped end conditions. The method is based on an iterative procedure that produces an approximation of the unknown mass density as a generalized Fourier partial sum of order N, whose coefficients are calculated from the first N eigenvalues. To avoid trivial non-uniqueness due to the symmetry of the initial configuration of the nanorod, it is assumed that the mass variation has support contained in half of the axis interval. Moreover, the mass variation is supposed to be small with respect to the total mass of the initial nanorod. An extended series of numerical examples shows that the method is efficient and gives excellent results in case of continuous mass variations. The determination of discontinuous coefficients exhibits no negligible oscillations near the discontinuity points, and requires more spectral data to obtain good reconstruction. A proof of local convergence of the iteration algorithm is provided for a family of finite dimensional mass coefficients. Surprisingly enough, in spite of its local character, the identification method performs well even for not necessarily small mass changes. To the authors' knowledge, this is the first quantitative study on the identification of distributed mass attached on nanostructures modelled within generalized continuum mechanics theories by using finite eigenvalue data.
2019-05-13T00:00:00ZHigh impact velocity on multi-layered composite of polyether ether ketone and aluminium
http://hdl.handle.net/10016/30473
High impact velocity on multi-layered composite of polyether ether ketone and aluminium
García González, Daniel; Rodríguez Millán, Marcos; Vaz-Romero, Álvaro; Arias Hernández, Ángel
Hybrid structures composed of multi-layer sheets of polymers and metals offer a great potential for impact protection systems in automotive and aeronautics industries. This work presents an experimental and numerical investigation on the perforation behaviour of layered polymer/metal composites. Penetration tests have been conducted on sandwich panels of aluminium 2024-T3 skins and polyether-ether-ketone (PEEK) cores, using spherical projectiles. The perforation experiment covered impact velocities in the range 250-500m/s. The initial and residual velocities of the projectile were measured, and the ballistic limit velocity was obtained. The impact mechanical behaviour of PEEK core is compared with Ti6Al4V titanium core, for the same areal density of protection. It has been shown high perforation efficiency of PEEK polymer and a promised application for aeronautical protections. A numerical modelling is presented and validated with experimental data.
2015-10-13T00:00:00Z