Damage mechanics-based failure model for sheet metals under large plastic deformation

This research aims to characterize the plastic behavior and ductile failure process of sheet metals commonly used in automotive and industrial applications. Emphasis is placed on the observed hardening behavior of the material at large plastic strain. This requires correction for triaxial stress condition and the damage-based prediction of ductile fracture of the material using Rice-Tracey void-growth model. These essential requirements are quantified and examined in the research for accurate simulation of sheet metal deformation and fracture. For this purpose, low carbon steel (LCS) and dual phase steel (DP600) sheets with a thickness of 2 mm were tension tested using various smooth and notched specimen geometries. The notched geometry introduces a different degree of the stress triaxiality to be quantified with respect to fracture of the specimen. The relationship between local ductility reduction and stress triaxiality is established using hybrid experimental-computational method employing tension test data and finite element (FE) simulations of the test. This relationship represents the damage initiation criterion for Rice-Tracey model. Stress triaxiality values in the range of 0.4 to 0.74 are found to be a strong function of the steel hardening characteristic. In addition, localized failure (necking) in low carbon steel is more pronounced compare to that of the high strength dual phase steel where only diffused necking is observed. The predictive capability of the Rice-Tracey damage model is demonstrated through simulation of the failure process of a spot welded lap joint under shear loading. Complementary test of identical spot welded joint specimen provided data for validation of the FE model. In the large strain region of the uniaxial stress-strain curve, the effect of local stress triaxiality on the fracture strain is eliminated through a novel large strain shear compression test procedure of the sheet metal. A shear compression jig assembly with a machined slot inclined at 35˚ to the transverse plane of the assembly is designed and fabricated. The design fulfills the requirement to establish a uniform distribution of plastic strain throughout the gage section of the Shear Compression Metal Sheet (SCMS) specimen. The global load and displacement data pairs are recorded throughout the test. FE simulation of the test set-up is performed to establish the corresponding internal states of stresses and strains in the gage section of the test specimen. This hybrid experimental-computational procedure, then establishes the true stress-plastic strain curve of the material directly from measured load-displacement readings of the test assembly. A plastic strain level of 49.2 % has successfully been established for 0.0627C steel sheet. The procedure has been validated for metallic materials with relative plastic modulus, Ep/E in the range of 5x10-4< Ep/E < 0.01. In addition, it is able to establish non-linear characteristic hardening of the material through piecewise linear consideration of the measured global load-displacement curve

Ionic Surface Dielectric Properties Distribution on Reservoir Sandstone

The petrophysical and dielectric properties for both carbonate and saturated sandstone with monovalent and divalent electrolyte they are accurately modeling of anisotropic dielectric properties has been the major research area in oil and gas industries for effective sweep efficiency. The reservoir petrophysical properties consist of cation and anion exchange capacity on a specific area and the sandstone porosity. The transportation of the ions is a charge carrier that mediates conduction in the pore fluids under the electrical double layers that exist between the minerals and the pore fluids interface. The dielectric anisotropic and the frequency-dependent behavior of reservoir sandstone with the minerals will be fully elucidated, it was revealed from the result obtained the effect of the anisotropic dielectric properties on the reservoir sandstone based on the influx of NaCl electrolyte modify the wettability of rock formation from oil-wet to water-wet at 9000 and 11000 ppm concentration with the aids of the electromagnetic field. The resistivity index of the reservoir sandstone reduces with the increase of electrolyte to the system

COST EVALUATION OF PROPOSED DECOMMISSIONING PLAN OF CANDU REACTOR

Nuclear decommissioning is the final technical and administrative process in the life cycle of nuclear power operation. Experience over the last decade has demonstrated that in general, the process of decommissioning and its cost evaluation has reached industrial maturity, although specific techniques continue to evolve. Owners and licensees of nuclear power plants are generally responsible for developing cost estimates of decommissioning, and a good understanding of these costs is fundamental for the development of estimates based on realistic decommissioning plans. The use of these techniques in the cost evaluation of the decommissioning of nuclear facilities continues to increase this experience. This research has been carried out keeping in mind to evaluate an economical and feasible cost for the proposed decommissioning plan of CANDU (Canada Deuterium Uranium) reactor. Work is done in the major areas of cost estimations for DECON (immediate dismantling), SAFESTOR (deferred dismantling) and ENTOMB (on site end-state). These alternatives were analysed and SAFSTOR method was recommended for 40+ years old, Canadian designed, first generation CANDU reactor decommissioning. This paper provides a cost estimation for a decommissioning as recommended in the analysis performed. A cost of 200 Million $ is evaluated for SAFSTOR decommissioning alternative of proposed CANDU reactor

Mathematical models for temperature distribution in oil wells

The oil temperature at the surface of the oil well is low compared to the oil temperature at the reservoir. The drop of temperature is due to heat transfer to the tubing wall. The temperature distribution of the oil from the reservoir to the surface and surrounding layers is studied in this paper. Two mathematical models for production and shut-in cases are developed to study the parameters affecting the temperature profile in oil wells. The natural flow of oil wells in Alwahat area located 70 Kilometres south of Marada area east of Libya in the Zaggut field called (6Q1-59) is taken as a study case. In production case, different mass flow rates in winter and summer seasons are studied. The temperature profile in the horizontal direction is estimated at different depths. In shut-in case, steady-state energy balance equation is solved using finite difference method, the results are compared with the actual date taken from the Waha company reports