Patrice Longère

Clément Ader Institute, Toulouse, France · ISAE-SUPAERO, DMSM

A series of high-strain rate tests has been carried out involving high-speed, kinematic and thermal metrology. The concomitant measurement of strain, stress and self-heating allowed the estimation of the inelastic heat fraction and further increase in inelastic stored energy. A thermo-viscoplastic constitutive model has then been developed within t...

The present study aims at studying the influence of some parameters on the numerical results obtained from the simulation of the high-speed machining process using a commercial finite element computation code, namely Abaqus-Exp. Starting from models available by default in the computation code, comparisons are made between full and weak thermo-mech...

The implementation of glass in various industries may cause some problems due to its brittleness characteristic. Its usage in the transportation sector has led to death and serious injuries to drivers and passengers in vehicles. It shows that the manufacturing process of the materials used requires an improvement in terms of brittleness to provide...

The objective of the present work is to propose an engineering-oriented numerical methodology capable of reproducing crack initiation and arrest in semi-brittle structures under high loading rate. With this aim in view, the SPH-based method implemented in LS-DYNA is employed to reproduce the three-dimensional crack initiation, propagation and arres...

The use of shock resistant RT-PMMA in engineering structures potentially subject to accidental overloading requires an evaluation of its crack arrest capability under impact loading. Based on experimental results obtained from a series of Kalthoff and Winkler (KW)-type impact tests, the present study aims at numerically reproducing the conditions f...

An extensive experimental campaign was run to investigate the influence of the loading direction, stress state (triaxiality ratio ranging from-0.5 to 1), and strain rate (from 10-3 to 1.5x10 3 s-1) on the ductile fracture of Ti-6Al-4V titanium alloy. Microscopic and macroscopic observations provided some insight into the shear-driven or micro-voidi...

The present work pertains to the numerical prediction of the current residual strength of large metallic engineering structures when submitted to accidental overloads. In this context, is developed a unified 3D numerical methodology reproducing the successive stages of the progressive failure of structures made of ductile metals, viz. (i) more or l...

A new experimental set-up mounted at the muzzle of a singlestage gas gun has been designed in order to study the fragmentation of metallic rings under dynamic radial expansion. This concept takes advantage of the quasi-incompressibility of HDPE whose radial flow under plate impact-like loading is used to apply a pressure boundary condition at the r...

The complexity of ballistic protections increases with their efficiency. On this basis, an exclusively empirical approach is not adapted to optimise complex protection systems and the resort to numerical simulations is preferred if not mandatory. The present study proposes a methodology aiming at optimising complex multi-layer ballistic armours bas...

The present work aims to investigate experimentally the crack arrest capability and dynamic fracture mechanisms under impact loading of three commercial, rubber-toughened (RT) PMMA grades differing by their rubber nano-particle concentration and resulting Charpy impact toughness. For that purpose, Kalthoff and Winkler (KW)-like impact tests were pe...

Aircraft engine fan blades are notably designed to withstand impact loading involving large deformation, high strain rate, non-proportional loading paths and self-heating. Due to their high strength-to-weight ratio and good toughness, Ti–6Al–4V titanium alloys are promising candidates for the blades leading edge. An extensive experimental campaign...

The main issue of the extended finite element method (XFEM) is the numerical integration of the system of equilibrium equations. Indeed, in order to have a correct displacement jump vector, the integration needs to be achieved on both sides of the discontinuity and thus requires the existence of integration points on both sides of the discontinuity...

The phenomenon of void coalescence induced strain localization plays an important role in the ductile failure process as the intermediate stage between diffuse damage and crack formation. The aim of the present work is double: (i) giving a framework for numerically treating the failure of ductile structures in the context of the X-FEM and (ii) asse...

Adiabatic shear bands (ASBs) are intense shear localisation zones resulting from thermomechanical instability in dynamically loaded, high strength structural materials. In the wake of the ASB, Micro-voids (MVs) have been observed which coalesce and ultimately rupture the material. ASBs thus favour premature MV induced damage and further material fa...

This paper presents the experimental investigation of the crack arrest capability under impact loading of two types of aluminum alloys that are mainly used in the field of aeronautics, viz. AA2024 and AA7175. Using gas launcher, impact tests were carried out on the edge of double notched plates made of the aluminum alloys. A range of impact speeds...

This chapter reviews adiabatic shear banding (ASB)‐oriented modeling approaches available in the literature that provide a better understanding of ASB and its consequences in structural metals and alloys. ASB is a mechanism of plastic flow localization known to be triggered by a thermo‐mechanical instability in the context of dynamic plasticity. Th...

The aim of the present work is to present two operational numerical methods allowing for integrating rate constitutive equations accounting for large strains and rotations. Both methods can be applied in the development of home-made computation codes or/and in the development of user material subroutines in commercial computation codes.

The present work aims at numerically predicting the current residual strength of large engineering structures made of ductile metals against accidental failure. With this aim in view, the challenge consists in reproducing within a unified finite element-based methodology the successive steps of micro-voiding-induced damage, strain localization and...

In the context of the design of aeronautical structures regarding accidental events, we are here investigating and comparing the shear failure of two aluminum alloys, namely AA2024 and AA7175, under high strain rate loading. With this aim in view, two experiments were carried out: (i) high strain rate shear compression of hat shaped structures, and...

We are here interested in the crack arrest capability under impact loading of metals and polymers used as structural and/or protection materials in aerospace engineering. Kalthoff and Winkler-type impact tests are carried out to that purpose on high strength AA7175 aluminum alloy and shock resistant polymethyl methacrylate (PMMA). Impact tests are...

Adiabatic shear bands are known to cause premature structural failure in high strength metals and alloys. The observation of adiabatic shear bands inside partially fractured specimens evidences the presence of micro-voids as the precursor of the ultimate failure. An enriched model containing the effects of adiabatic shear banding and micro-voiding...

High strength, lightweight materials, including notably titanium and aluminium alloys are widely used in aircraft and other structures. When subjected to high strain rate loading involving quasi adiabatic conditions, these materials may be subjected to a thermomechanical instability resulting in a dynamic localization in the form of narrow adiabati...

Adiabatic shear banding (ASB) is a dynamic localization phenomenon resulting from thermomechanical instability under high strain rate and low stress triaxiality loading conditions. High strength, steels and lightweight alloys of titanium and aluminum are highly susceptible to this phenomenon which leads to premature material failure. At an advanced...

The objective of the present work is to compare two different models aiming at numerically reproducing Adiabatic Shear Banding (ASB) assisted failure. ASB is herein considered as a deterioration mechanism whose consequences in the material are described via an internal damage variable. The first model called the (1-D) type model is engineering orie...

This work aims at evaluating the respective and combined roles of thermal softening and dynamic recrystallization (DRX) in adiabatic shear banding (ASB) initiation. A unified approach able to describe the whole process of deformation including the stage of ASB in the large scale postulate framework is presented. A physics-motivated model for strain...

Dans les matériaux ductiles, la rupture résulte d'un processus de dégradation en 3 étapes : endommagement diffus, localisation de l'endommagement dans une bande, et fissuration. Le travail présenté vise à reproduire dans une approche unifiée ces étapes dans le cadre de la méthode des éléments finis étendus (X-FEM). La phase intermédiaire de localis...

Adiabatic shear banding (ASB) is a precursor of failure of high strength metals and alloys when submitted to impact and other high strain rate loading. As a mechanism of plastic flow localization triggered by a thermo-mechanical instability in the context of dynamic plasticity, ASB causes a discontinuity of the strain/strain rate field. In the pres...

The present work aims at the numerical treatment of the crack propagation in engineering materials whose failure results from void initiation, growth and coalescence. With this aim in view, the objective is to describe the intermediate stage between more or less diffuse damage and the initiation of a macroscopic crack. This transient stage of damag...

The adiabatic shear banding and its consequences are considered here as deterioration mechanisms incorporated in the dynamic plasticity modelling for high-strength metallic materials following earlier contributions of the present authors. A three-dimensional finite deformation model, starting from a specific scale postulate and devoted to cover a w...

This paper focuses on the resilience of titanium towards dynamic shocks such as military shocks. To extend even more the possibility of using Titanium in areas which must resist to military shock, a quality study of the behaviour of Titanium and its alloys with respect to dynamic stresses was required. The fracture behaviour of Titanium types was v...

The present work aims at the numerical simulation of the dynamic crack propagation in ductile materials which fail as a result of micro-void nucleation, growth and coalescence. The model is using a modified Gurson-Tvergaard-Needleman (GTN) material behavior accounting for combined effects of void growth induced damage, strain hardening, viscoplasti...

Impact tests on pre-notched plates are carried out to analyze qualitatively and quantitatively the crack development in high strength steel under high loading rate. Implementation of ultra-high speed camera (1M frame/s) allows on one hand observing the chronology of the failure mechanisms from adiabatic-shear-banding until full fracture. On the oth...

In the present work, the engineering, high strength ARMOX500T steel was submitted to a Kalthoff and Winkler type impact test in view of evaluating its crack arrest capability under dynamic loading. From an impact velocity of the order of 150 m/s, the crack propagation is seen to be preceded by adiabatic shear banding (ASB) leading to a premature pl...

http://cfrac2015.sciencesconf.org/55039

The present work aims at the numerical treatment of the crack propagation in engineering materials whose failure results from void initiation, growth and coalescence. With this aim in view, the objective is herein to describe the intermediate stage between more or less diffuse damage and the initiation of a macroscopic crack. This transient stage o...

The present work aims at studying numerically the influence of void concentration, number of voids and absence/presence of inclusion on void collapse/growth and coalescence in materials submitted to shear loading. Starting from the experimental observation that voiding mostly forms within bands of localised deformation in the form of void sheets, t...

Une méthode d’analyse numérique d’images est proposée permettant de suivre le déplacement de points localisés le long de lignes gravées sur une plaque. Cette technique permet d’une part d’identifier les champs cinématiques successifs conduisant à la ruine dynamique de la structure et d’autre part de quantifier les vitesses de propagation mises en j...

Experimental analysis of fracture mechanisms is a key point to understand and further reproduce physical phenomena involved in structural material failure. Actually, crack propagation under high loading rate is a strongly coupled thermo-mechanical problem involving large deformation, high strain rate and (quasi) adiabatic conditions. The work prese...

Ce travail a pour but de reproduire numériquement la propagation d'une fissure au sein d'un matériau dont la rupture résulte de l'amorçage, de la croissance et de la coalescence de cavités. Dans cette optique, une méthodologie est proposée combinant un modèle de type Gurson modifié, permettant de rendre compte de l'écrouissage et de l'endommagement...

The present work aims at reproducing numerically the crack propagation in engineering materials whose failure results from void initiation, growth and coalescence. With this aim in view, a methodology is proposed combining a modified Gurson based, finite strain, (ductile) damage-(visco)plasticity coupled constitutive model and the eXtended Finite E...

The present work is devoted to the numerical simulation of crack propagation in engineering materials whose failure results from void initiation, growth and coalescence. The behaviour of the plate material is described via a Gurson type model accounting for the combined effects of strain hardening, thermal softening, viscoplasticity and void growth...

Ductile fracture of metals by void nucleation, growth and coalescence under positive stress triaxiality is well admitted. This is not the case when metals are submitted to negative stress triaxiality. The present work aims at contributing to a better understanding of the competition between micro-mechanisms at the origin of failure of metals when s...

This paper deals with the numerical simulation of the dynamic failure of a ship structure steel plate under near-field air-blast loading. Various energetic levels of air-blast loading, involving variable explosive mass and charge-plate distance, were tested leading to the bulge of the loaded plate for the lowest energy level and to the failure of t...

Ce travail est consacré à la simulation numérique de la propagation d’une fissure dans un matériau dont la rupture résulte de la création, la croissance et la coalescence de vides. Le comportement du matériau est décrit via un modèle de type Gurson prenant en compte les effets combinés de l’écrouissage, de l’adoucissement thermique, de la viscoplas...

Starting from experimental observations on hat shape samples of a Titanium alloy of Ti6Al4V family showing that the failure of ductile materials under low triaxiality may result (at least partially) from void growth, the present work develops an approach based on a damage related softening mechanism acting as a kinematic mean stress drop causing a...

This work aims at studying experimentally and reproducing numerically the failure mechanisms of a ship structure constitutive material when submitted to airblast loading. With this aim in view, a physically motivated approach has been developed and applied in order to describe the transition of behaviour between dense metal plasticity and micro-por...

The present work is devoted to the numerical simulation of crack propagation in engineering materials whose failure results from void initiation, growth and coalescence. The behavior of the plate material is described via a Gurson type model accounting for the combined effects of strain hardening, thermal softening, viscoplasticity and void growth...

This article presents a physically motivated approach, which has been developed in order to describe the transition of behavior between dense metal plasticity and microporous metal plasticity in the context of dynamic plasticity and adiabatic conditions. Considering that void germination requires a certain amount of plastic deformation, a ‘primary’...

This work aims at studying experimentally and reproducing numerically the failure mechanisms of a ship structure material when submitted to severe conditions of strain and strain rate. Laboratory tests and airblast experiments were accordingly carried out and a constitutive model has been built describing the salient effects of strain hardening, th...

This paper deals with the pressure dependence of plasticity in metallic glasses below glass transition. Recent results indicate that some metallic glasses have such a dependence and that it increases with temperature (Keryvin et al., Phil. Mag., 88, 1773, 2008). We investigate the possibility that such a situation could be a common feature for all...

Consistent constitutive modelling of material behaviour and further reliable numerical prediction of the response of structures under severe loading necessitate the knowledge of the microstructural mechanisms at the origin of failure.The present work deals notably with the identification of the microstructural damage mechanisms of a high purity (fe...

A phenomenological modelling approach has been developed, based on some salient physical effects regarding void growth vs. plastic straining, to describe the transition behaviour between dense metal plasticity and micro-porous metal plasticity. Considering that void germination requires a certain amount of plastic deformation, a 'primary' hole nucl...

The aim of the present numerical study was to predict the structural failure of airbag inflators undergoing destructive bust tests, while accounting for the thermomechanical history of the constitutive material. For this purpose, the material was previously characterized under tension, compression, torsion and shear loading conditions at various st...

The topic of the present work is mainly concerned with the numerical simulations of the response of a ship structure submitted to a far-field underwater explosion. The goal is to preserve sailing functions of the ship and the integrity of sensitive areas. We are in particular interested in the numerical response of ship hulls to the first, high ene...

The present contribution deals with the evaluation of the plastic work induced adiabatic heating during any dynamic loading path considering a wide class of constitutive models including physics based models and phenomenological ones. Various approaches are presented as well as their consequences in terms of adiabatic shear banding onset conditions...

This study aims at determining the shear behaviour of a tubular material. Simple shear tests are useful for this purpose, since they yield homogeneous strain fields up to 100% shear strain (γ=2ε=100%); whereas torsion tests yield heterogeneous strain fields at low strain (γ<50%) because of the instability of the structure resulting from the bucklin...

The evaluation of the temperature produced during adiabatic dissipative processes for a large class of engineering materials (metals and some polymers) remains a major subject of interest, notably in the fields of high-speed machining and impact dynamics. The hypothesis consisting in considering the proportion of plastic work dissipated as heat (qu...

This work brings forward a twofold contribution relevant to the adiabatic shear banding (ASB) process as a part of dynamic plasticity of high-strength metallic materials. The first contribution is a reassessment of a three-dimensional finite deformation model starting from a specific scale postulate and devoted to cover a wide range of dissipative...

Under dynamic adiabatic conditions, the plastic work is known to dissipate into heat and induce thermal softening. From both theoretical and numerical viewpoints, the proportion of effectively dissipated plastic work is commonly evaluated using the so-called Taylor–Quinney coefficient usually assumed to be a constant empirical value. On the other h...

In many engineering problems involving adiabatic (dynamic) conditions the temperature rise induced by plastic deformation is usually evaluated using the inelastic heat fraction. The latter is still frequently considered as a crudely determined constant value. On the other hand, experimental investigations have shown that the inelastic heat fraction...

Airbag inflator functioning is submitted to draconian safety rules for vehicle occupants. The bag inflation process is ensured by a pyrotechnic system which delivers combustion gases very quickly. This pyrotechnic device consisted of a thin tube closed at both extremities, crimped and perforated with exit ports for combustion gas release. Prior man...

Les sacs gonflables de sécurité passive (airbags) sont soumis à des règles draconiennes de sécurité vis-à-vis des occupants du véhicule. Avant sa mise sur le marché, le générateur de gaz constitué d'un tube à paroi mince fermé à ses deux extrémités par des sertis et percé d'orifices pour l'évacuation des gaz de combustion, doit subir des essais de...

RESUME: Dans ce travail, nous nous intéressons à la description du comportement d'un matériau métallique contenant des bandes de cisaillement adiabatique (BCA). Le cisaillement adiabatique par bande, assimilé dans le cadre de cette étude à un processus de dégradation anisotrope, est traité dans le contexte de la thermodynamique des processus irréve...

The present work deals with the three-dimensional modelling of the behaviour of structural metallic materials allowing for adiabatic shear banding (ASB) as a mode of dynamic failure precursor. The anisotropic deterioration induced in the material by the presence of the bands is described via the concept of a “super dislocation” (see [6-8]) in the c...

In the approach presented, adiabatic shear banding (ASB) is considered as a form of anisotropic deterioration. The anisotropic mechanical degradation induced in the structural material by the bands is dealt with by using a second-order tensor internal variable. The kinematical consequences of the presence of the bands are described by means of the...

In the present work, we are interested in the three-dimensional description of the behaviour of a high strength material susceptible to adiabatic shear banding. The high strain rate constitutive model, based on irreversible thermodynamics, bas been formulated in order to be applied in the context of high velocity impact and penetration mechanics, a...

DURING DYNAMIC LOADING PROCESSES, large plastic deformation associated with high strain rates leads, for a broad class of ductile metals, to degradation and failure by adiabatic shear banding. The paper presents an attempt to model some salient features of this process viewed as an anisotropic damage mechanism coupled with thermo-elastic/viscoplast...

L'objectif industriel du travail dans lequel s'inscrit ce papier est la simulation numérique de la réponse de structures à l'impact. Or, pour un grand nombre de matériaux métalliques à haute résistance soumis à des sollicitations à grande vitesse, le cisaillement adiabatique constitue un processus endommageant conduisant souvent à la ruine par macr...

Titanium alloys exhibit attractive ballistic performances due to their low density and their high mechanical properties. They are unfortunately very sensitive to adiabatic shear localization. This study aims to determine an empirical parameter which allows to characterise the sensitivity to the adiabatic shear banding of different grades of titaniu...

The split Hopkinson pressure bar device is used to study the dynamic response of pure cold-drawn end annealing irons to a sudden decrease of strain rate. Different strain rate history effects are pointed up for the both cold-drawn end annealing states. Applying different unloads to several dynamic microstructural states, allows to access the intern...

The aim of the present contribution is to embrace salient features of the adiabatic shear banding (ASB) within the framework of three-dimensional finite strain modelling regarding viscoplastic flow coupled with ASB-related microdamage process. The ASB damage-induced anisotropy is being accounted for. An application of the model is given for the hat...