A New Model for Void Coalescence by Internal Necking

A micromechanical model for predicting the strain increment required to bring a damaged material element from the onset of void coalescence up to final fracture is developed based on simple kinematics arguments. This strain increment controls the unloading slope and the energy dissipated during the final step of material failure. Proper prediction of the final drop of the load carrying capacity is an important ingredient of any ductile fracture model, especially at high stress triaxiality. The model has been motivated and verified by comparison to a large set of finite element void cell calculations.

CORRODED GAS PIPELINE REMAINING LIFE UNDER VARIABLE OPERATING PRESSURE

Gas pipelines are subjected to mechanical and chemical stresses which lead to failures of various types such as corrosion, cracking, deformation and rupture. Corrosion damage to pipelines has become a growing concern in the gas industry. Corrosion defects in the form of pitting caused by the corrosion phenomenon cause high concentrations of stresses and plastic strains thus reducing the strength of the pipe by threatening its structural integrity. Indeed, the internal operating pressure is variable and can generate the phenomenon of fatigue, which is dangerous, given its insidious nature, causing damage to the corroded zone for stress levels well below the yield stress of the material. The standards used in the framework of the rehabilitation of corroded pipes allow the determination of their burst pressure but not their remaining life. To address this issue, we have developed a model based on damage mechanics to predict the remaining life of a pipe in the presence of an external corrosion defec

Behavior and damage of a pipe in the presence of a corrosion defect depth of 10% of its thickness and highlighting the weaknesses of the ASME / B31G method

The company DRC (pipe repair Department) located within the SONATRACH Company of oil and gas in Algeria, which is responsible for the repair of pipelines for the transport of gas or crude petroleum, will rehabilitate old pipes that have operated on-line for approximately 30 years or come from remaining projects. On the assumption that rehabilitating a pipeline means making it workable under the same conditions as a new structure and reducing the overall cost of the project. The abandonment of these tubes will have an important environmental and financial impact. The rehabilitation, which consists of recovering the maximum of tube, already used, therefore reduces the cost of the project. Inspection and evaluation of corrosion defects are carried out in accordance with ASME/31G method that is applied to low alloyed carbon steels with corrosion defects having soft profiles with low stress concentration. Our research will consist in developing a method using a behavior-damage coupling of the material to highlight the weaknesses of the ASME / B31G method and show for defects whose depth does not exceed 10%, these defects can survive hydrostatic testing but will develop during service when the pressure is variable

EFFECT OF NON-POLLUTING AND RENEWABLE LOAD ON DELAMINATION OF A COMPOSITE BIOMECHANICAL MATERIAL

The objective of this paper is to develop a delamination model that can predict delamination growth in a new woven composite for orthopedic use. This composite material is obtained from a laminated composite woven by incorporating a natural organic load (granulates of date cores) which becomes hybrid composite. The composite is made of an organic matrix containing methyl methacrylate, a woven reinforcement including a reinforcing glass fiber and a fabric perlon having an absorbing role. The walk cycle has been used to determine the operating conditions of tibiae prosthesis. Hence, the deflection tests were validated by orthopedist experts. Three end-notched flexure (3ENF) tests were carried out on the new woven composite to detect delamination phenomenon. The formulation is based on damage mechanics and uses only two constants for delamination damage. We assume that the interface has a bi-linear softening behaviour and regarded as being a whole of several interfacial bonds. The model has been implemented into the commercial (FE) code. Numerical simulations were carried out in end-notched flexure (3ENF) tests to detect initiation and growth of delamination in the new woven composite

Prediction of Cycle Life of Expansion Bellows for Fixed Tube sheet Heat Exchanger

Research on determining the lifetime of an expansion bellows designed to compensate the difference in expansion between the shell and the tubes in a fixed tube sheet heat exchanger has never ceased because of its Importance in a heat exchanger. The main function of the expansion bellows is to absorb the difference in expansion between the shell and the tube bundle while resisting the axial thermal deflection and the equivalent internal pressure on the shell side. TEMA-9 [1] edition attaches great importance to the finite element method in the case of an expansion bellows because of the disadvantages of the old design methods, which lead to overestimation and stress overload in the bellows. The objective of this work is to study the damage in the most stressed zone of the expansion bellows in order to construct a numerical simulation tool of the rupture to determine the lifetime that an expansion bellows can support during the operating conditions of a fixed tube heat exchanger. In a first step, the ANSYS FEM calculation code will allow the determination of the critical zone where the Von Mises is maximum and where potential cracks can develop. In a second step, a post-processor based on the concept of Continuum Damage Mechanics and using Newton's iterative method will be applied to this critical area for the determination of the bellows critical lifetime. The maximum lifetime will be the value of the number of cycles that corresponds to the critical value of the DC damage (crack initiation)