Key Engineering Materials Vol. 399

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: Ductile fracture process includes three stages: void nucleation, their growth and coalescence. The voids nucleate due to the fracture or separation of non-metallic inclusions and secondary-phase particles from the material matrix. Micromechanical models based on the Gurson plastic flow criterion are often used for analysis of ductile fracture. They consider the material as a porous medium in which the effect of voids on the stress-strain state and plastic flow cannot be neglected. Another important property of the Gurson criterion is that the hydrostatic stress component influences the plastic flow of the material.

Abstract: The purpose of this study was making evident the overload effect in a spectre with constant amplitude cycles. The crack growth simulation was made on cracked specimen and was studied for four loading cases. Fatigue crack growth rate was calculated applying NASGRO equation and the crack growth retardation analyzed.

Abstract: Fracture mechanics parameters can be applied for the analysis of failures of structures, and also for prevention of failures when defects in a structure are detected and defined. The approach is presented through stages: detection of defects, stress-strain analysis of loaded component, characterization of material properties required for structural integrity assessment and application of convenient procedure. In this way the decision about next use of defective component can be made (to continue the operation, increased care by inspection, exclusion the component from next service, with eventual repair, if possible). Special attention is paid to the most popular testing procedures for crack resistance parameters.

Abstract: The paper makes a review about the opportunity, forming conditions and obtaining methods of bulk amorphous alloys and their properties. There are also presented the experiments regarding the obtaining and characterization from mechanical and chemical point of view of some alloys from Fe70 (Cr5-x Nix)5 Ga4 P13 Si5 C3 ( x = 0,1,2,4) family, pointing out the negative effect of the nickel on their resistance characteristics.

Abstract: The article focuses on the technical measurements which could be applied to the fracture surfaces of the steel Charpy specimens in order to apply the Fractal Analysis. One could calculate the fractal dimension not directly for a fracture, but for a profile of the fracture. Most common methods for generation of fracture profile are cross-cut techniques and profile measurements techniques [1-2]. We apply three principal methods: Profilometer, Interferometer Light Microscope and the Vertical Section for a specimen made of XC65 after the Charpy test. We compare the advantages and the limits for each technique. We use the Box Counting algorithm applied in the Image J program for determining the fractal dimension of the fracture surface in all three experimental techniques. Then we could characterize the roughness of the fracture profile at different magnifying power by the estimated fractal dimension.

Abstract: The paper presents an application according the reliability and remining life assessment of the reactor (coxing box) from a petrochemical plant, after failure in welding joint of plated shell from W1.5423 (16Mo5) steel with 25 mm thickness, plated with W1.4002 stainless steel with 3 mm thickness. The reactor failure it has associated with initial flaws from welding process, which have accelerated remaining life exhaustion. The assessment made in two steps. It has used VII section of ASME code specifications and iRiS-Thermo expert system for preliminary remaining life assessment. Concomitantly, it was performed the experimental creep and thermal fatigue testing. The program results have defined creep and thermal fatigue exhaustion and its remaining life at common creep-fatigue action, in condition of safety exploitation. It was emphasized the possibility of use an extra 40,000 hours of rehabilitated reactor in the safety condition of normal parameters.

Abstract: A non-classical plate theory based on the direct approach is introduced and applied to plates composed of functionally graded materials (FGM). The governing two-dimensional equations are formulated for a deformable surface, the viscoelastic stiffness parameters are identified assuming linear-viscoelastic material behavior. In addition, the material properties are changing in the thickness direction. Solving some problems of the global structural analysis it can be shown that in some cases the results based on the presented theory significantly differ from the results based on the Kirchhofftype theory.