Rian Seghir

Research Institute for Civil and Mechanical Engineering | GeM · Research Laboratory of Civil Engineering and Mechanics

Using the criterion that a crack will extend along the direction of maximum circumferential stress, this paper demonstrates the influence of the coupling between the crack-parallel T-stress and the tip speed on the directional (in)stability of dynamics cracks in brittle materials, i.e., branching, turning, and limiting velocities. The proposed (in)...

The alternate (stick-slip) cracking phenomenon in Poly(methyl methacrylate) (PMMA) was investigated using high-speed imaging and digital image correlation (DIC). PMMA is known to show a great variety of fracture behaviors by even small changes in loading conditions. With TDCB-shaped samples and under a range of constant extension rates, the phenome...

The alternate (stick-slip) cracking phenomenon in Poly(methyl methacrylate) (PMMA) was investigated using high-speed imaging and digital image correlation (DIC). PMMA is known to show a great variety of fracture behaviors by even small changes in loading conditions. With TDCB-shaped samples and under a range of constant extension rates, the phenome...

The present work proposes a metrological route for capturing spatially‐resolved ultra‐high‐speed kinematic full‐field data from high strain‐rate experiments and multi‐sensor camera technology. This paper focuses, from an application point of view, on highly resolved rotating mirror cameras, such as the Cordin‐580. This camera allows 78 frames of 8...

Brittle and ductile dynamic fracture in solids is a complex mechanical phenomenon which attracted much attention from both engineers and scientists due to its technological interests. Modeling cracks in dynamic cases based on a discontinuous description is difficult because it needs additional criteria for branching and widening. Due to the very sh...

This paper presents a versatile model-free approach for linking the damage in highly heterogeneous materials at multiple scales. The proposed scheme evolves from phase-field modelling at the microscopic scale to simulate brittle failure, towards the estimation of the effective elastic, toughness and strength properties of the material at the mesosc...

p>In many instances in life, materials are subject to deformation at high rates, for example: impact, crash, metal forming or pulsed welding. In this context, the transient and inhomogeneous nature of such loading as well as the strong multi-physic couplings induced by quasi-adiabatic conditions make: the experimental capture of the mechanical resp...

Data-driven computations propose a completely new paradigm to the computational mechanics research community and to experimentalists. Classically, admissible material states can only be obtained experimentally for homogeneous stress/strain configurations or using a parametric optimization of material laws based on heterogeneous tests. Data-driven a...

In many instances in life, materials are subject to deformation at high rates, for example: impact, crash, metal forming or pulsed welding. In this context, the transient and inhomogeneous nature of such loading as well as the strong multi-physic couplings induced by quasi-adiabatic conditions make: the experimental capture of the mechanical respon...

This paper presents the application of the new Image-Based Inertial Impact (IBII) test methodology to study the high strain rate response of adhesives. It relies on an inertial impact (spalling-like) test configuration and the use of ultra-high speed imaging to record the deformation of the test specimen in the MHz range. The underlying novelty is...

p> This paper presents the application of the new Image-Based Inertial Impact (IBII) test methodology to study the high strain rate response of adhesives. It relies on an inertial impact (spalling-like) test configuration and the use of ultra-high speed imaging to record the deformation of the test specimen in the MHz range. The underlying novelty...

Bone cement is widely used for the fixation of orthopaedic implants. It is a multi-component material that consists of a PMMA base with a small proportion of (usually ceramic) radiopacifier to enable the cement to be observed by X-ray. Bone cement is formed through an exothermic reaction in which a powder of pre-polymerised beads of PMMA reacts wit...

An innovative identification strategy based on high power ultrasonic loading together with both infrared thermography and ultra-high speed imaging is presented in this article. It was shown to be able to characterize the visco-elastic behaviour of a polymer specimen (PMMA) from a single sample over a range of temperatures and strain-rates. The pape...

We present here an innovative identificatfion strategy, using high power ultrasonic loadings together with both InfraRed Thermography and Ultra-High-Speed Imaging, able to fully-characterize the viscoelastic behaviour of polymer materials from a single sample. The main originality lies in the fact that contrary to conventional DMT Analysis, no freq...

In order to perform experimental identification of high strain rate material models, engineers only have a very limited toolbox based on test procedures developed decades ago. The best example is the so-called Split Hopkinson Pressure Bar (SHPB) which has proved extremely useful but has important intrinsic limitations due to the stringent assumptio...

In order to satisfy the economic constraints together with environmental requirements, the automotive industry has been forced to adopt a strategy of down-sizing, which has led into process modification of some engine parts like cylinder heads. Nowadays, the Lost Foam Casting process (LFC) replaces the conventional Die Casting (DC) process due to c...

The aim of this work is to analyse the strain field heterogeneity in an aluminium alloy subjected to low-cycle fatigue at high temperature. In the cylinder heads produced by a lost-foam casting process, the microstructure of the studied alloy consists hard intermetallic phases and large gas and microshrinkage pores. In order to study the influence...

This paper focuses on the development of an appropriate Digital Image Correlation (DIC) methodology based on Image Registration and dedicated for characterizing the plastic deformation in single crystals. A pure nickel single crystal specimen is plastically deformed in tension and investigated by DIC technique. Based on the measured kinematic field...

Exploiting pattern formation-such as that observed in nature-in the context of micro/nanotechnology could have great benefits if coupled with the traditional top-down lithographic approach. Here, we demonstrate an original and simple method to produce unique, localized and controllable self-organised patterns on elastomeric films. A thin, brittle s...

Photo-hardenable and patternable PDMS/SU-8 hybrid functional material: A smart substrate for flexible systems

Certain applications of evolving flexible technologies demand that conducting metal features remain both mechanically robust (free of strain) and electrically stable (zero system piezoresistance) for large macroscopic mechanical deformation. Examples of this are flexible RF transmission line technologies and soft metamaterials where electromagnetic...

The crack initiation phenomenon in a metallic material under cyclic loadings is due to the localization of the deformation in some grains at the microstructure scale which induces damage. However, the engineering way to design structures conduct to establish macroscopic fatigue criteria which finally consider mean value of the mechanical fields, at...

Investigation of thermomechanical couplings in metallic polycrystals. • Research work on the understanding, the analysis and the numerical modelling of thermomechanical couplings at the mesoscopic level in metallic polycrystals. • Implementation of a new method for calibration and treatment of experimental thermal and kinematic measurements on hete...

The use of polymers in the context of flexible systems such as flexible sensors leads to an incompatibility issue: on the one hand, the flexibility of the polymer must not be to the detriment of the fabrication process, e.g. excessive thermal expansion leading to process failure and on the other hand, certain applications will require high flexibil...

Certain applications of evolving flexible technologies demand that metallic features remain both mechanically robust (crack-free) and electrically stable for large macroscopic mechanical deformation. Examples of this are flexible radio frequency transmission line technologies and soft metamaterials where electromagnetic properties (e.g., functional...

The fabrication of flexible electronics and systems, using rigid and brittle materials directly produced on stretchable substrate, leads to some issues and incompatibilities. These include rigidity for processing and modular flexibility for applications, macroscopic flexibility, and local rigidity to shield components from strain, compatibility wit...

Aluminum alloy automotive parts produced by the Lost Foam Casting (LFC) process have coarser microstructure and porosity defects than parts produced with conventional casting processes at faster cooling rates. This coarse microstructure has a major influence on the fatigue properties and crack initiation. In order to study its influence upon the me...

In cast aluminum alloys used in the automotive industry the microstructure inherited from the foundry process has a strong influence upon the fatigue behavior. In the cylinder heads produced by the Lost Foam Casting process, the microstructure consists of hard intermetallic phases and large gas and microshrinkage pores. In order to study the influe...

In this paper, thermomechanical couplings at the grain scale in metallic polycrystals are studied during the deformation process through an original experimental setup and improved calibration tools and full-field treatments. In order to perform intragranular thermomechanical analysis in a metallic polycrystal at the grain scale, a crystallography-...

In cast aluminum alloys used in the automotive industry the microstructure inherited from the foundry process has a strong influence upon the fatigue behavior. In the cylinder heads produced by the Lost Foam Casting process, the microstructure consists of hard intermetallic phases and large gas and microshrinkage pores. In order to study the influe...

Aluminum alloy automotive parts produced by the Lost Foam Casting (LFC) process have coarser microstructure and porosity defects than parts produced with conventional casting processes at faster cooling rates. This coarse microstructure has a major influence on the fatigue properties and crack initiation. In order to study its influence upon the me...

Polycrystalline metallic materials are made of an aggregate of grains more or less well oriented with respect to the loading axis. During mechanical loading, the diversity of grain orientations leads to a heterogeneous deformation at the local scale. It is well known that most of the plastic work generated during the deformation process reappears i...

This paper is based on additional treatments of the experimental results obtained by L. Bodelot, L. Sabatier, E. Charkaluk, P. Dufrenoy [Experimental setup for fully coupled kinematic and thermal measurements at the microstructure scale of an AISI 316] steel, Mater. Sci. Eng. A 501 (2009) 52-60]. In order to perform inter- and intragranular thermom...

Strain localization and damage criteria of materials and structures are commonly based on a dissipative framework and this work investigates the thermomechanical couplings accompanying the deformation micromechanisms. It is partly based on experimental data obtained previously in the laboratory by Bodelot for a A316L austenitic stainless steel poly...

Polycrystalline metallic materials are made of an aggregate of grains more or less well oriented with respect to the loading axis. During mechanical loading, the diversity of grain orientations leads to heterogeneous deformation and it is well known that most of the plastic work generated during the deformation process reappears in the form of heat...

Polycrystalline metallic materials are made of an aggregate of grains more or less well-oriented, with respect to the loading axis, for plastic gliding. Under mechanical loading, this leads to a heterogeneous deformation at the micro structure scale. This local plasticity triggers a heterogeneous thermal dissipation caused by mechanical irreversibi...

L'endommagement par fatigue des métaux débute à l'échelle des grains. Nous accédons, grâce à un dispositif unique, à une mesure couplée des champs thermique et cinématique d'une même zone à une échelle micrométrique. Ces champs sont confrontés ici à des simulations numériques réalisées dans Abaqus et basées sur un couplage thermoplastique implanté...

Polycrystalline metallic materials are made of an aggregate of grains more or less well-oriented, with respect to the loading axis, for plastic gliding. Under mechanical loading, this leads to a heterogeneous deformation at the microstructure scale. This local plasticity, linked to fatigue damage, triggers a heterogeneous thermal dissipation linked...