NADER HADDAR - Academia.edu (original) (raw)

Papers by NADER HADDAR

International Journal of Fatigue, 2009

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Journal of Thermoplastic Composite Materials, 2020

In this paper, an experimental study was conducted to characterize industrial PVC pipes and to in... more In this paper, an experimental study was conducted to characterize industrial PVC pipes and to investigate the effect of hydrothermal aging on their physico-chemical, thermal, and mechanical behavior. Three temperature (25°C, 60°C and 90°C) and full immersion in distilled water were retained as accelerated hydrothermal conditions. Kinetic of water absorption was examined and Fickian behavior was observed. The aging temperature was found to influence the water uptake behavior of PVC samples. Thermogravimetric analysis (TGA) has proved that the pipe material is not pure, while it consists of PVC reinforced with calcium carbonate (CaCO3). After exposure to accelerated aging, TGA and FTIR analysis exhibit preliminary signs of degradation of PVC samples under the retained conditions. Changes affecting the shape and the color of aged samples were examined. Mechanical properties have been characterized, after immersion of 30 days, with an improvement of strength and stiffness of the aged s...

Mechanics of Materials, 2018

NiTi SMA represents a popular group of metals with interesting properties like pseudoelasticity a... more NiTi SMA represents a popular group of metals with interesting properties like pseudoelasticity and a high energy dissipative capacity. Indeed, NiTi alloys, presents an interesting damping capacity due to solid-solid phase transformation. Such characteristics allow them to be used in many civil engineering fields mainly as actuators and damping devices. However, because of their complex behavior, the design process of these applications seems to be complicated and consequently, needs to build accuracy numerical models. One of these already existing models is the micromechanical Likhachev model. It seems to be very attractive thanks to its general formulation, numerical efficiency and model parameters relatively easy to determine. This paper concerns the numerical simulation of the pseudoelasticity behavior of NiTi wires dedicated to the application of damping devices, at different stress and strain rates. A thermomechanical coupling is introduced in the Likhachev formulation in order to simulate the thermomechanical behavior of NiTi under strain control. In this paper the model is adapted to a strain-controlled formulation, and 1D simulation is achieved using FORTRAN code. Parameters model are identified thanks to SiDoLo software and the corresponding results are presented and discussed. A good agreement with experimental data is found for the two formulations.

The International Journal of Advanced Manufacturing Technology, 2016

Friction conditions are very critical in metal forming because they can lead to important thinnin... more Friction conditions are very critical in metal forming because they can lead to important thinning in the final manufactured product. The value of the friction coefficient is then of particular importance for performing predictive finite element (FE) simulation of forming operations. Classically, numerical simulations are run with values of the friction coefficient found in technical database where the Coulomb’s coefficient has been evaluated with the pin-on-disk test. Moreover, the friction coefficient is often used as a set up parameter for running FE simulations. The pin-on-disk test is not automatically suitable for characterizing the friction coefficient in tube hydroforming. The “corner filling” test has been developed for tube hydroforming and several authors have developed analytical models for representing this test. Among them, the authors have chosen to exploit the Orban-Hu model. This model permits to build graphs. On those graphs, experimental data are overlaid in order to evaluate the friction coefficient. Thus, a friction coefficient (μ) of 0.4 has been found by the proposed method against the value of about 0.1 found in technical database. FE simulations with 3D shell and 3D solid models have been performed with the two values of the friction coefficients. The conclusion is that FE simulations with 3D shell model permit definitely better predictions for thickness evaluation. Moreover, running the simulations with μ = 0.4 leads to a more critical representation of the minimal thickness in the final component. Finally, an experimental method is proposed for the evaluation of the friction coefficient without advanced numerical methods.

Engineering Failure Analysis, 2016

Low cycle fatigue (LCF) tests were carried out on forged carbon steel (AISI 4130) used in V12 Die... more Low cycle fatigue (LCF) tests were carried out on forged carbon steel (AISI 4130) used in V12 Diesel engine crankshafts, at room temperature and 300°C, under total strain control. These tests were performed in order to study the cyclic mechanical behavior, lifetime and damage mechanisms of the material. Then, a Chaboche nonlinear isotropic-kinematic hardening model available in the commercial FE code Abaqus was identified and a 2D-FE evaluation of J-integral, chosen as a crack driven force, has been carried out to estimate the crankshaft life under cyclic bending loads when a macroscopic crack propagates. It has been found that i) material lifetime was not affected by temperature at the studied domain, ii) the fractured surfaces examined with SEM exhibit typical features of ductile fracture behavior, and iii) the number of cycles spent until the total crankshaft fracture is relatively short compared to its total fatigue life.

Materials Science and Engineering: A, 2016

Abstract This paper focused on the study of Low Cycle Fatigue of welded joints of superaustenitic... more Abstract This paper focused on the study of Low Cycle Fatigue of welded joints of superaustenitic (Alloy28) stainless steels. Chemical composition and microstructure investigation of Base Metal (BM) and Weld Metal (WM) were identified. The results showed that both of composition is fully austenitic with a dendritic microstructure in the WM. Low cycle fatigue tests at different strain levels were performed on Base Metal (BM) and Welded Joint (WJ) specimens with a strain ratio Re=−1. The results indicated that the fatigue life of welded joints is lower than the base metal. This is mainly due to the low ductility of the Welded Metal (WM) and the presence of welding defects. Simultaneously, Scanning Electron Microscope (SEM) observations of fractured specimens show that WJ have brittle behavior compared to BM with the presence of several welding defects especially in the crack initiation site. An estimation of the crack growth rate during LCF tests of BM and WJ was performed using distance between striations. The results showed that the crack initiation stage is shorter in the case of WJ compared to BM because of the presence of welding defects in WJ specimens.

Ce papier s’intéresse à la quantification de l’effet du vieillissement hygrothermique d’un compos... more Ce papier s’intéresse à la quantification de l’effet du vieillissement hygrothermique d’un composite à matrice de polyamide 6 renforcée par 50% en masse de fibre de verre courtes(PA6GF50). Soumis à un chargement monotone, le composite démontre une sensibilité accrue dans le milieu humide conduisant à la chute des propriétés mécaniques. Après vieillissement, quelque soit le milieu (eau distillée et eau saline), on constate une diminution considérable de la résistance à la traction et du module d’élasticité accompagné d’une augmentation de l’allongement à la rupture.

Résumé Le roulage est une opération de mise en forme qui consiste à obtenir une virole cylindriqu... more Résumé Le roulage est une opération de mise en forme qui consiste à obtenir une virole cylindrique à partir d'une tôle plate. matière première (coût important) en garantissant la réussite de l'opération de roulage. Mots clefs : roulage, modélisation numérique, méthode des éléments finis, comportement de l'acier, abaques. Abstract: This study was achieved in collaboration with SOCOMENIN industrial partner. The main objective summarize on the amelioration of the rolling machine performance. Rolling process is a shaping operation that consists in getting one cylindrical ferrule from a flat sheet metal. Computation of rolling process was performed using ABAQUS finite elements code. With changing of the distance between the two bottom rollers and the displacement of the top one, we obtained abacuses those given the needed machine parameters, to obtain ferrule with desired diameter. These abacuses make rolling process easier. Then allow a considerable gain of time and to avoid...

International Journal of Solids and Structures, 2005

Various components of nuclear reactors experience various thermo-mechanical loading. Thermal fati... more Various components of nuclear reactors experience various thermo-mechanical loading. Thermal fatigue cracking has been clearly detected in reactor heat removal system (RHRS) of Pressurized Water Reactors (PWRs). The study presented here is focused on the AISI 304L stainless steel used in PWRs. The thermal fatigue behavior of this steel has been investigated using a specific thermal fatigue facility called “SPLASH

This paper presents results of experimental investigations on creep, fatigue and creep-fatigue cr... more This paper presents results of experimental investigations on creep, fatigue and creep-fatigue crack growth behaviour of the 2650-T6 aluminium alloy in temperature, along with numerical simulation of stress distribution around the tip. The results will provide a preliminary database on the fatigue properties of the 2650 T6 alloy under loading representative of service conditions and predict the damage tolerance assessment of the future civil transport aircraft fuselage.

Engineering Failure Analysis, 2014

Thermal cracks in die-casting are often caused by thermal fatigue loading, surface stresses, low ... more Thermal cracks in die-casting are often caused by thermal fatigue loading, surface stresses, low material strength and surface irregularities. During the process cycle, alternate heating and cooling leads to thermal fatigue. Mechanical and thermal stress fluctuations initiate fine cracks on the cavity surface that grow larger and ultimately lead to failure of the die. Hardness or surface heat treatment can extend the die life time. The aim of this work is to study the thermal fatigue damage of AISI H13 tool steels that underwent different heat treatments. The results prove that the thermal fatigue resistance is closely related to the initial hardness. In fact, thermal fatigue tests prove that increases in the hardness of the steel lead to decreases in the crack growth rate. However, it seems that the heat treatment does any not major effect on the crack initiation period of thermal fatigue cracks.

Revue de Métallurgie, 2004

ABSTRACT Tests were performed on austenitic stainless steels. In order to investigate thermal fat... more ABSTRACT Tests were performed on austenitic stainless steels. In order to investigate thermal fatigue resistance of quasi-structural specimens, test facilities enforcing temperature variations similar to those found under the operative conditions have been developed. Multiple cracking networks similar to those detected during in-service inspections have been reproduced. Experiments and simulations deal with crack initiation and crack growth. In case of multiple cracking simulation, a Skelton's modelling has been used (1). A shielding effect between cracks is evidenced. It leads to a dramatic reduction of crack growth rate. Such effect is also crucial for the crack network stability under additional loading.

Nuclear Engineering and Design, 2005

Various components of nuclear reactors are submitted to various thermo-mechanical loadings. Therm... more Various components of nuclear reactors are submitted to various thermo-mechanical loadings. Thermal fatigue cracking has been clearly detected in reactor heat removal system (RHRS) of pressurized water reactors (PWRs). The present study focuses on AISI 304 L stainless steel used in PWRs. The thermal fatigue behavior of this steel has been investigated using a specific thermal fatigue facility called "SPLASH". This test equipment allows the reproduction of multiple crack networks similar to those detected during component inspections. The present study deals with the modeling of crack networks initiation and propagation. It is structured in two parts: (i) experimental details and main characteristics of the cracks networks, and (ii) numerical simulation of multiple cracks initiation and growth problem, using an elastic-plastic thermal-mechanical computation and a generalized Paris' law. The model presented in this study gives predictions in a good agreement with observations, as far as the evolution of the mean and deepest cracks during cycling is concerned.

Engineering Fracture Mechanics, 2013

Comptes Rendus Mécanique, 2012

The present study investigates the crack initiation in a 304L stainless steel under thermal fatig... more The present study investigates the crack initiation in a 304L stainless steel under thermal fatigue using volume element tests designed to assess the endurance to engineering crack initiation in real structures under middle range temperature and fairly large number of cycles. The inelastic cyclic strain is significant in most testing conditions for this alloy, even for long tests. Regarding tests, thermal-mechanical fatigue life is compared with low cycle fatigue tests under isothermal conditions. Noteworthy, throughout the different studied ranges of applied temperature cyclic behavior of the alloy has shown an initial hardening followed by a cyclic softening. In addition, no clear effect in lifetime for the high strain range has been discovered. In fact, when exposed to various increasing temperature levels, the material endurance tends to decreases for low strain range (correspond to high number of cycle). A different behavior in cyclic hardening tests is identified between the In-Phase thermal-mechanical fatigue tests and the Out-of-Phase tests at temperature levels ranges between 90 and 165 • C. In-Phase thermal-mechanical test increases lifetime with respect to the Out-of-Phase test. The fracture surfaces for all tested conditions are characterized by a fatigue striation.

III COMPORTEMENT EN FATIGUE DE L'ACIER INOXYDABLE AUSTENITIQUE 304L Ce chapitre traite le comport... more III COMPORTEMENT EN FATIGUE DE L'ACIER INOXYDABLE AUSTENITIQUE 304L Ce chapitre traite le comportement et l'endommagement de l'acier inoxydable austénitique 304L sous sollicitations de fatigue isotherme et mécano-thermique.

Fatigue & Fracture of Engineering Materials & Structures, 2014

The fatigue cracks growth rate of a forged HSLA steel (AISI 4130) was investigated using thin sin... more The fatigue cracks growth rate of a forged HSLA steel (AISI 4130) was investigated using thin single edge notch tensile specimen to simulate the crack development on a diesel train crankshafts. The effect of load ratio, R, was investigated at room temperature. Fatigue fracture surfaces were examined by scanning electron microscopy. An approach based on the crack tip opening displacement range (ΔCTOD) was proposed as fatigue crack propagation criterion. ΔCTOD measurements were carried out using 2D-digital image correlation techniques. J-integral values were estimated using ΔCTOD. Under test conditions investigated, it was found that the use of ΔCTOD as a fatigue crack growth driving force parameter is relevant and could describe the crack propagation behaviour, under different load ratio R.

Fusion Science and Technology

The joining of stainless clad steel plates (SCSPs) by welding processes is relatively difficult d... more The joining of stainless clad steel plates (SCSPs) by welding processes is relatively difficult due to differences in the chemical compositions and the physical and mechanical properties between both the carbon and the stainless steels comprising the clad material. These welded structures often suffer from several structural integrity problems such as bulging phenomena that can appear after bending tests, in the welded zone, due to the presence of a local hardening zone (LHZ). The main purpose of this paper is to investigate the origin of the LHZ typically produced in the welded joint of SCSPs after the bending operation. Optical micrographs revealed the presence of a typical pearlitic-ferritic structure in the welded zone filled with E7018 metal and a dendritic δ-ferrite structure solidified under a skeletal form in the welded zone filled with ER316L metal. The microstructure of the weld metal transition zone (WMTZ) filled with ER309L metal shows the presence of martensitic laths as well as cellular and columnar structures. In addition, the WMTZ revealed the presence of three types of grain boundaries, which are formed during the gas tungsten arc welding process: solidification sub-grain boundary, solidification grain boundary, and migrated grain boundary. Vickers microhardness measurements performed along the thickness of the welded joint showed that the highest microhardness value (406 HV) was observed at the WMTZ. The significant increase of the microhardness value in this transition zone was attributed to the presence of martensitic laths as well as cellular and columnar structures.

Journal of Natural Fibers, 2021

The International Journal of Advanced Manufacturing Technology, 2021

The stainless clad steel materials (particularly A283-Gr-C hot-rolled to austenitic stainless ste... more The stainless clad steel materials (particularly A283-Gr-C hot-rolled to austenitic stainless steel plate SA240 TP 316L) have become widely used in the fabrication of heat exchangers, pressure vessels, and other components owing to their very interesting properties and low production cost. These cladded materials are mostly joined using multi-pass welding techniques. The temperature distribution that supervenes during welding affects the microstructures and the mechanical properties and may generate residual stresses in the heat-affected zone of the welded plates. Since limited experimental data are available in the literature regarding the complex cases of multi-pass welding of cladded steel materials, a thorough experimental study was performed in order to evaluate the temperature distribution on the welded plates. In fact, eight K-type thermocouples were fixed at different distances from the weld centerline in order to record the temperature evolution along longitudinal, transversal, and thickness directions during the welding process. Due to the unavoidable effects of the generated heat fluxes that always follow the welding, several dimensional changes were occurred on the welded plates. In this study, the longitudinal shrinkage and the angular distortion generated during the welding process by the effect of the heat fluxes were investigated. Then, tensile and bending tests were performed in order to check the welded plate reliability. It was found that (i) the welded joint presents a higher mechanical tensile strength than the parent metal and (ii) no separations, fractures, or tearing appear on the weld joint surface after the bending test.