Papers by Author: Z. Azari

Abstract: There are a few years, it has become the use of artificial discs and effectively to compensate for damaged discs in humans due to the eccentric load applied on the spine. As we know very well that the success of a disc implantation depends strongly on the initial stability of the implant and the integration of the bone tissue of the vertebrae with these discs in the long term. Due to the optimal distribution of mechanical stresses in the surrounding bone. It is for this reason that the search for reasonable solutions to compensate the damaged disk and reduce the stresses in the cortical bone and spongy has become a very important research axis. Several alternatives have been studied, including implant design, prosthesis geometry, prosthetic components and biomaterials used. In this regard, we have proposed two new models for some innovative artificial disks by some of the biomechanics researchers and we have installed these discs between the two vertebrae L5 and S1 of the spine, to ensure spinal stability and avoid slipping, we installed a posterior attachment system (6 screws plus 2 rods) at the pedicular levels of the lumbar vertebra (S1-L5, L5-L4).It is for this technique that we have used finite elements in three dimensions and using the software ANSYS to know the extent of the realization of these discs under the influence of the load applied to them. The numerical results show that these disks played a very important role in the absorption of the stresses and to minimize, On the other hand, the lumbar inter-somatic cage (Model II) filled with cancellous bone is too great a role in reducing the stress compared to another synthetic (Model I) disc. In general, the new model of the inter-somatic cage filled with cancellous bone and reinforced by a posterior fixation system has given a lower level of stress in the cortical bone and the spongy bone of the lumbar vertebra (L5) compared to the healthy disk (D1).

Abstract: In industrial structures, the presence of cracks under critical loads leads to complete ruin. Fracture rupture mechanics allowed studying macroscopic defect harmfulness. This requires the knowledge of the stresses fields and the deformations near of the crack. Our work is an application of fracture mechanics into the domain of the pressurised structures with defects in the presence of the T-stress parameter. Design of this type of structures is subjected to standards, codes and regulations driven by the potential risk which they represent. The knowledge of the limit pressures in these structures allows appreciating the safety domain of. We present numerical solutions by the commercial code CASTEM2000 in three dimensional 3D and experimental results for the stress intensity factor SIF and the transverse stress noted T-stress, distribution at defect-tip in a Pipeline. The elastic structure modelling will be treated by the finites elements simulation. We study the influence of the geometrical parameters for surface notches and the measures of strains near defects in the studied model have been made by strain gauges. On the basis of the detailed 3D elastic FE analysis results, solutions presented are believed to be the most accurate, and thus provide valuable information for structural integrity assessment considering a notch-tip constraint. The experimental results validate allow numerical simulation. Keywords: Crack, Pressure, T-stress, Stress Intensity factor, Finite element simulation, Strain gauges,

Abstract: The objective of this study is examining the level of degradation caused by the welding process, the influence of defects by third parties and the speed of loading on the integrity of the pipeline. The use of Charpy instrumented pendulium coupled with the the volumetric method analysis allowed us to calculate the dynamic fracture toughness of the API 5L X52 pipeline steel in presence of a real defect characterized by its notch radius but also, to show the need for a second parameter to overcome the problem of fracture toughness transferability.

Abstract: The aim of this work is to study the effects of hydrogen absorption on mechanical properties of pipe API 5L X70 steel. This study is conducted in special soil solution NS4 with pH 6.7 It show that the tensile properties like yield stress, ultimate strength and elongation at failure reduced under hydrogen embrittlement. Several fatigue tests (three (03) points bending tests) on roman tile specimens with notch are performed. Fatigue initiation is detected by acoustic emission. A comparison between specimens electrolytically charged with hydrogen and specimens without hydrogen absorption is made and it has been noted that fatigue initiation time is reduced when hydrogen embrittlement occurs. The field of elastoplastic stresses near the notch is computed by the finite-element method with the Abaqus software package. Effective distance and stress are calculated with the volumetric approach and the Notch intensity Factor of the roman tile specimen is determined for each loading value used in our tests.

Abstract: Brittle materials in general and particularly glass are very sensitive to dynamic particles impacts of different nature. The ancient objects in glass (building, monuments) and some precious objects are subjected to atmospheric aggressions such as humidity, sand particles, hail,…etc.). Their surfaces are however, often exposed to severe climatic conditions in an environment where the sand wind is a daily phenomenon or beach wind. Many degradation processes due to erosion affect significantly surfaces of buildings that are part of the Cultural Heritage.

Abstract: The use of two parameters fracture mechanics criterion as a tool for structural design and analysis has increased significantly in recent years. First, we discuse the elastic solution for the stress distribution at crack tip for two dimensional geometries and particularly constraint as T-stress under various loading conditions. Secondly, using notch fracture mechanics and particularly the Volumetric Method approach, we study the stress distribution at the tip of a notch in pipes submitted to internal pressure. The Notch Stress Intensity Factor Kρ and the effective T-stress are combined into a two-parameter fracture criterion (KIρ-Tef). This approach is then used to quantify the constraint of notch-tip fields for various pipe geometry and loading conditions.

Abstract: Most of usual materials exhibit Poisson's ratio comprised between 0 and 0.5. But, for some kind of cellular materials, or for some stacking sequences of unidirectional plies, a composite material can exhibit negative or greater than 0.5 Poisson's ratios. In this paper, a study of different stacking sequences such as [±β/±θ]s plies made from highly anisotropic fibre pre-preg is presented. A special computer programme has been developed for this purpose. Eighteen stacking sequences, including the [±θ] ones, have been computed. The results show that at least one of Poisson's ratios varies between -0.8 to +0.4. Such kind of materials may find applications for particular cases, as their strength is significantly increased by this phenomenon.

Abstract: Problems for load carrying elements reside mainly in buckling, embrittlement and corrosion. These problems can be mainly solved by introduction of composite materials of a sandwich type. These materials ally lightness, rigidity and resistance to the corrosion. For the design of a large number of applications, static and cyclic properties are necessary. In this paper, first static and fatigue tests on four points bending of four types sandwich panels have been performed. Load/displacement and S-N fatigue curves are presented and analysed. Fatigue failure and damage modes are observed with an electronic microscope and are discussed. Numerical simulation applied to the static tests is compared to the experimental results. The second is to address such fatigue behaviour by using a damage model and check it by experimentation. This fatigue damage model is based on stiffness degradation, which is used as a damage indicator. Four non-linear cumulative damage models derived from the chosen stiffness degradation equation are examined with assumption of linear Miner’s damage summation. Predicted results are compared with available experimental data.