Security and defence of mobile systems under impact

The Group “Dynamics and Fracture of Structural Elements” offers its experience in Solid Mechanics analysis for the study of the impact protection of vehicles, aircrafts and persons. The Group activities have a strong research component, in which numerical simulation tools as well as sophisticated experimental techniques are employed. This technological offer could be of interest to automobile companies (impact and collision security), aeronautical companies (impact of external body on fuselage, attack, and fragments o ice) and defence companies (special armours for mobile systems and persons).Contrato Programa de Comercialización e Internacionalización. Sistema Regional de Investigación Científica e Innovación Tecnológica. (Comunidad de Madrid; Universidad Carlos III de Madrid

A new constitutive model for polymeric matrices: Application to biomedical materials

Semi crystalline polymeric composites are increasingly used as bearing material in the biomedical sector, mainly because of their specific mechanical properties and the new advances in 3D printing technologies that allows for customised devices. Among these applications, total or partial prostheses for surgical purposes must consider the influence of temperature and loading rate. This paper proposes a new constitutive model for semi-crystalline polymers, commonly used as matrix material in a wide variety of biomedical composites, that enables reliable predictions under a wide range of loading conditions. Most of the recent models present limitations to predict the non-linear behaviour of the polymer when it is exposed to large deformations at high strain rates. The proposed model takes into account characteristic behaviours of injected and 3D printed thermoplastic polymers such as material hardening due to strain rate sensitivity, thermal softening, thermal expansion and combines viscoelastic and viscoplastic responses. These viscous-behaviours are relevant for biomedical applications where temperature evolution is expected during the deformation process due to heat generation induced by inelastic dissipation, being essential the thermo-mechanical coupling consideration. The constitutive model is formulated for finite deformations within a thermodynamically consistent framework. Additionally, the model is implemented in a finite element code and its parameters are identified for two biomedical polymers: ultra-high-molecular-weight polyethylene (UHMWPE) and high density polyethylene (HDPE). Finally, the influence of viscous behaviours on dynamic deformation of semi-crystalline polymeric matrices is analysed

An experimental method of measuring the confined compression strength of high-performance concretes to analyse their ballistic behaviour

6 pages, 4 figures.-- Issue title: "EURODYMAT 2006 - 8th International Conference on Mehanical and Physical Behaviour of Materials under Dynamic Loading" (Dijon, France, Sep 11-15, 2006).The test known as "quasi-oedometric compression" consists of the compression of a cylindrical specimen confined in a thick vessel. In this work, an original methodology is proposed to deduce the radial stress and strain within the specimen using hoop strains measured on the external surface of the vessel, taking into account its elasto-plastic deformation. On one hand the spherical and deviatoric behaviours of two concretes are deduced. On the other hand, their ballistic behaviour is analysed using impact tests. These experiments are simulated numerically by the plasticity model of Krieg, Swenson and Taylor, and the features of the model are identified by the previous confined compression tests. The capacity of the model to describe the ballistic behaviour of such materials is shown in a comparison of the numerical simulations with the ballistic tests.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) for the financial support of this work and to the Délégation Générale pour I'Armement (DGA/France) for the mobility grant provided to P. Forquin.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) for the financial support of this work and to the Délégation Générale pour l’Armement (DGA/France) for the mobility grant provided to P. Forquin.Publicad

Multi-impact mechanical behaviour of short fibre reinforced composites

High velocity transverse impact on reinforced composites is a matter of interest in the automotive, aeronautical and biomedical sectors. Most existing studies have addressed this problem by single isolated impacts; however, this work deals with the distinction between single, sequential and simultaneous impacts on composite structures. This paper proposes an experimental methodology to study the mechanical behaviour of materials under single and multi-impact loadings. The overall objective is to investigate the mechanical response of short carbon fibre reinforced PEEK when is subjected to single and multiple high velocity impacts. Experimental tests are conducted covering impact velocities from 90 m/s to 470 m/s. Energy absorption, damage extension and failure mechanisms are compared to assess additive and cumulative effects in high velocity impact scenarios. Experimental results show that the specific deformation and fracture mechanisms observed during multi-hitting events change with impact velocity. Compared to the behaviour of unreinforced thermoplastics, short fibre reinforced composites present significant limitations at velocities close to the ballistic limit, but multi-hit capability is observed at high impact velocity when the damage is mainly local. As key conclusion, the ballistic limit obtained in single impact test cannot be extrapolated to sequential and simultaneous tests. Multi-impact tests, especially close to the ballistic limit, are necessary to guarantee the structural integrity of composite structures in realistic impact scenarios.The researchers are indebted to Ministerio de Economía y Competitividad de España (Project DPI2014-57989-P) and Vicerrectorado de Política Científica UC3M (Project 2013-00219-002) for financial support

A continuum constitutive model for FDM 3D printed thermoplastics

Fused deposition modelling (FDM) is the most common additive manufacturing technology used for thermoplastic components. This layers-based manufacturing process results into direct links between printing parameters and the polymer mesostructure by means of porosity and structural anisotropy. These dependencies along with other features of thermoplastic polymers (i.e., nonlinearities, viscous and thermal responses) makes its constitutive modelling very challenging. This work distances from studies that model the 3D printing process. Instead, we aim at complementing such approaches with a continuum model to describe the macroscopic behaviour of FDM thermoplastics while preserving links with printing parameters. Prior to the modelling conceptualisation, experimental characterisation tests are conducted on ABS specimens to evaluate the influence of printing parameters on the macroscopic mechanical response. The physical fundamentals behind the deformation and failure mechanisms are identified and motivate the new constitutive model. This model is formulated for finite deformations within a thermodynamically consistent framework. The model accounts for: nonlinear response; anisotropic hyperelasticity related to a transversely isotropic distribution of porous; strain rate dependency; macroscopic stiffness dependent on 3D printing processing. Finally, the model is numerically implemented and calibrated for ABS with original experiments, demonstrating its suitability.The authors acknowledge support from Ministerio de Ciencia, Innovación y Universidades, Spain, Agencia Estatal de Investigación y Fondo Europeo de Desarrollo Regional, Spain, como entidades financiadoras (RTI2018-094318-B-I00). D.G.-G., S.G.-H. and A.A. acknowledge support from Programa de Apoyo a la Realización de Proyectos Interdisciplinares de I+D para Jóvenes Investigadores de la Universidad Carlos III de Madrid (BIOMASKIN-CM-UC3M). D.G.-G. acknowledges support from the Talent Attraction grant (CM 2018 - 2018-T2/IND- 9992) from the Comunidad de Madrid, Spain

An experimental method of measuring the confined compression strength of geomaterials

27 pages, 29 figures.Knowledge of the behaviour of geomaterials under confined compression is a pre-requisite for any analysis of their ballistic performance. This study proposes an experimental method of determining the spherical and deviatoric behaviour of these materials under high pressure. Known as the ‘quasi-oedometric compression test’ it consists of compressing a cylindrical specimen tightly enclosed in a thick confinement vessel. The principles of these quasi-oedometric tests are given first, and the steps taken for their execution, together with an examination of the steel used for the confinement vessel. An original way of analysing the data of the test is presented and validated by numerical simulations. These calculations provide valuable information about the influence of the interface product introduced between the vessel and the specimen, and that of friction. Tests are then presented with specimens of aluminium alloy to validate the experimental set-up and the method of analysis. In addition, quasi-oedometric compression tests of cement based material, with and without particles, illustrate the opportunities offered by this testing method, and show that its deviatoric strength and compaction law are significantly improved by ceramic granulates addition.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) for the financial support of this work and to the Délégation Générale pour l’Armement (DGA/France) for the mobility Grant provided to Dr. Forquin.Publicad

Seguridad y defensa de sistemas móviles sometidos a cargas de impacto

El grupo "Dinámica y Fractura de Elementos Estructurales" ofrece su experiencia en el análisis de problemas de mecánica de sólidos para estudiar la protección frente impacto de vehículos, aeronaves y personas. Para ello dispone de herramientas de simulación y equipamiento experimental específico y sus actividades tienen una alta componente de investigación. Su oferta tecnológica resulta atractiva para empresas del sector automóvil (seguridad frente a impacto y choques), aeronáutico (impactos debidos a accidente, ataque, fragmentos o hielo) y defensa (blindajes especiales para vehículos y protección personal ligera)

Analytical modelling of metallic circular plates subjected to impulsive loads

14 pages, 15 figures.This paper presents an analytical approach to the dynamic response of metallic circular plates subjected to impulsive loads. It is based on the plate energy balance equation and assumes that the plate material behaves viscoplastically. The proposed method permits a consideration of the influence of the different terms of the kinetic energy and the plastic work of the plate. A yield criterion is proposed, which involves the coupled effect of the radial and circumferential internal force resultants. By applying the normality rule, the distribution of the bending moments and membrane forces inside the plate are computed. For model validation, its analytical predictions are compared with experimental results.The authors are indebted to the Comunidad Autónoma de Madrid for the financial support of this work (project 07N/0004/1998).Publicad

An engineering model on penetration of eroding rods into ceramic/polymer composite

6 pages, 3 figures.-- Issue title: "EURODYMAT 2003 - 7th International Conference on Mechanical and Physical Behaviour of Materials under Dynamic Loading" (Porto, Portugal, Sep 8-10, 2003).A new material composed of a polymer matrix loaded with ceramic partiales, at low cost and of higher ballistic efficiency than that of the metallic materials used for armouring applications, is proposed as an alternative to the ceramic tiles traditionally adopted for mixed panels. An engineering model was developed to simulate normal impacts of projectiles against this particulate composite backed by a metallic plate. The equation governing the erosion of projectile and ceramic is that proposed by Tate and Alekseevskii, modifie to consider a moving target. For the volume of particulate composite between the projectile and the metallic plate, an equation was derived to include a momentum balance. For the metallic plate, an energy balance equation was used. When the projectile has eliminated the ceramic/polymer composite and meets the plate, the model of Awerbuch & Bodner is adopted, again modifie to consider a moving target. ln this way, the impact process is described by a set of non-linear differential equations, to be integrated in time. The model was validated with experimental results and with full numerical simulations and showed agreement with both of them.The authors are indebted to the Comunidad Autónoma de Madrid (Project 07N/0004/1998) for the financial support of this work.Publicad

Temperature and strain rate dependences on hardening and softening behaviours in semi-crystalline polymers: Application to PEEK

Semi-crystalline polymers often present a complex non-linear behaviour that combines thermo-viscoelastic and thermo-viscoplastic contributions associated to different deformation mechanisms. During the initial deformation stages, the process is influenced by the rupture and reorientation of crystalline phases while, during the final deformation stages, the process is mainly governed by the mobility and orientation of the amorphous molecular chains. Moreover, the level of reorientation of crystalline and amorphous phases is strongly affected by variables such as temperature and strain rate. This work focusses on the role of such mechanisms in the mechanical behaviour of polyether-ether-ketone (PEEK) within its different thermal-behaviour regions: initial glassy region, glass transition and final rubbery region. To this end, samples of PEEK are subjected to large deformations under uniaxial tension at temperatures from 20 to 240 °C, and strain rates from 0.0001 to 0.1s^-1 (covering both isothermal and adiabatic conditions). In addition, a constitutive model is proposed to complementarily explain the experimental observations by means of entropic strain hardening due to reorientation of polymer chains influenced by thermo-viscoelastic effects, as well as thermo-viscoplastic behaviours defining the material yielding by means of crystallites deformation and breaking. These results provide new insights into the deformation mechanisms of semi-crystalline polymers below and above glass transition, which are significantly relevant for thermoforming processes of biomedical prosthesis