Abstract: Existing models for the concrete confined show a great respect in terms of effectiveness of confinement. The concrete confinement which consists in preventing these strains can be carried out either by an external envelope, or by a weak spacing between the stirrups. All models consist of some modification factors multiplying the unconfined concrete properties; these modification factors depend on the strength ratio and the confinement level. The relation of the ultimate strength ‘and ultimate strain in many existing models is complexity by representing. Each author gauges his model according to the experimental data.
In this study, we present the results of a parametric analysis of some the most used models of confinement. The results show that the models of confinement have an important disparity between the values of the strength (fCC) and axial ultimate strain (εcc) of confined concrete.
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: 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: This paper considers damage development mechanisms in cross-ply laminates using an accurate numerical model. Under static three points bending, two modes of damage progression in cross-ply laminates are predominated: transverse cracking and delamination. However, this second mode of damage is not accounted in our numerical model. After a general review of experimental approaches of observed behavior of laminates, the focus is laid on predicting laminate behavior based on continuum damage mechanics. In this study, a continuum damage model based on ply failure criteria is presented, which is initially proposed by Ladevèze. To reveal the effect of different stacking sequence of the laminate; such as thickness and the interior or exterior disposition of the 0° and 90° oriented layers in the laminate, an equivalent damage accumulation which cover all ply failure mechanisms has been predicted. However, the solution algorithm using finite element analysis which implements progressive failure analysis is summarized. The results of the numerical computation have been justified by the previous published experimental observations of the authors.
Abstract: The main objective of this paper is to present a theoretical and numerical analysis of frictional contact problems for large deformation elasto-plastic based on the finite element method (FEM) and the mathematical programming. The study is done on an elasto-plastic material obeying to the von Mises criterion. The Coulomb’s friction contact is used to implement the frictional boundary conditions and is formulated by the bipotential concept leading us to minimize only one variational principle of minimum in displacement. In order to follow up the sequences of large deformations, we have used the sequential analysis procedure; it consists in the updating of material properties and geometrical configuration after each sequence.
Abstract: This paper deals with the advantages of the finite element modeling and design, especially, of delamination test coupons involved in fracture analysis of laminated composite plates. This is shown through two relevant aspects in delamination toughness measuring, say: data reduction and Iso-G delamination front design. Many experimental data reductions are based on beam theories and thus assumes straight delamination front during propagation, which is not true when investigating laminates with general anisotropy. Another aspect is also emphasized, and concern test procedure simplification to avoid displacement measurements. This is done through a direct energy release rate calculations via the crack closure integral method.
Abstract: This work deals with the Liquid Resin Infusion (LRI) process developed within the research program “FUSelage COMPosite” of DAHER SOCATA. This manufacturing process enables the realization of complex composite structures or fuselage elements in a single phase (mono-material), which considerably reduce connections and relative difficulties. The concern here is the investigation of non destructive testing (NDT) methods that can be applied to LRI-structures in order to define their capacities for defect detection, and especially their associated critical defect size. In aviation industry, the AITM standards require the ultrasonic testing as NDT for composite materials. Therefore the aim of this work is to characterize and compare three different and complementary ultrasonic techniques on composite specimens. Such analysis allows to define the NDT application field of each method in term of defect detection.
Abstract: Extreme working conditions affect material used as friction components in transportation field: they rapidly reach their limits and critical parts require to be regularly replaced. Alternative solutions withstanding higher operating conditions imply to find innovative materials. Stellite matrix composites including various solid lubricants, WS2 and h-BN, able to admitextreme conditions were developed using a Spark Plasma Sintering technique, which makes possible the formation of new microstructures out of reach by conventional means. Sliding tests were conducted using a pin-on-disc tribometer in air at 450°C, with a velocity of 0,25 m/s and various normal load ranged from 2.5 to 40 N. Influence of solid lubricant content and sensitivity to test parameters were studied in terms of friction and wear responses of the contacting materials. Friction properties are equivalent to Stellite ones and sometimes lesseffective. A reduction of wear is quantified for many composites, and the best behavior is observed for those that contain WS2. In agreement with the third body approach, interpretations are proposed to describe the interphase dynamics within the contact.
Abstract: This paper is devoted to procedures for the reliability-based optimization methods of engineering structures combining measurement and sensitivity technique, for the purpose of the better sensitivity in force-gradient detection. In the experiment part of this study, the mica muscovite cantilever beam clamped-free is used. The excitation of a cantilever beam with several small sheets of piezoelectric polymer adequately glued to it selects one high-frequency vibration mode of the cantilever. The proposed strategy is design into a framework that allows the solution of optimization problems involving a several number of design parameters that characterizes the systems, including dimensional tolerance, material properties, boundary conditions, loads, and model predictions, considered to be uncertainties or variables. The proposed methodology directly supports quality engineering aspects enabling to specify the manufacturing tolerances normally required to achieve desired product reliability. Within this context, the robust design obtained is optimal over the range of variable conditions because it considers uncertainties during the optimization process. The large number of exact evaluations of problem, combined with the typically high dimensions of FE models of industrial structures, makes reliability-based optimization procedures very costly, sometimes unfeasible. Those difficulties motivate the study reported in this paper, in which a strategy is proposed consisting in the use of reliability-based optimization strategy combined with measurement and sensitivity technique specially adapted to the structures of industrial interested.