Linear Fracture Mechanics Methods Research Articles

Development of a Method for Determining the Residual Life of Structural Elements with Cracks Under the Action of Load and Corrosive Environment, as well as the Application of Corrosion Inhibitors to Enhance It

A developed method for determining the lifespan of structural elements with large-scale cracks of complex geometry under the influence of long-term static loads and corrosive environments. The method is based on an appropriate computational model, which relies on the first law of thermodynamics for the elementary act of local failure (crack propagation), some fundamental principles of physical chemistry, as well as the basic principles of fracture mechanics. The advantages of this method over existing ones are substantiated. The application of the method is demonstrated through examples involving the determination of the residual life of such structural elements as torsion and a pipe with small cracks made of 45KhN2MFA steel (tempered at 470 K and 725 K) under the influence of long-term static loading and distilled water. As the cracks are considered small, we have constructed a computational model in terms of deformation parameters, including a well-known counterpart in fracture mechanics, crack opening at the crack tip δt. At the same time, based on available experimental data from the literature, it is substantiated that the application of existing linear fracture mechanics methods in stress intensity factors KI for implementing the mentioned problems, the application of existing linear fracture mechanics methods is inappropriate. To determine the residual life of structural elements using this method, it is necessary to have kinetic diagrams in coordinates of the growth rate of small cracks and the crack opening at the crack tip, which means V ∼ δt. These diagrams are constructed here using the provided formulas for determining δt and diagrams are constructed here using the provided formulas and known experimental data for 45KhN2MFA steel under the influence of distilled water and static tension. Using the mentioned method, the residual lifespans of the torsion and the pipe were calculated under the influence of long-term static loading and distilled water. Additionally, the effectiveness of water solutions of well-known inorganic corrosion inhibitors on the residual lifespan of the mentioned structural elements was verified through calculations. It was found that the residual lifespan effectively characterizes the performance of corrosion inhibitors, which can be applied in engineering practice.

Modeling for manufacturability of the design of parts with concentrators by the method of photoelasticity

The article provides a methodology for the experimental determination of the concentration coefficients ασ and the gradients of the principal stresses. The effectiveness of the experimental method of photoelasticityis shown for studying the stress-strain state of parts of complex shape in the presence of stress concentrators, as well as for solving problems of brittle strength by methods of linear fracture mechanics.

Estimation of oil-and-gas reliability at longitudinal cracks

According to the theory of random numbers, a mathematical model for the probability of nonfailure of a diagnosed section of the oil-and-gas pipeline at longitudinal through cracks, when failure viscosity, working pressure, crack length, diameter, and wall thickness are normally distributed, is obtained by the methods of linear fracture mechanics. The residual lifetime of the oil-and-gas pipeline is predicted using the required nonfailure probability. The method implementation results in a reduction of emergency breakage of the pipelines of the north technical right-of-way.

Development of a numerical method for determination of stress intensity factor into the members with cracks

The linear fracture mechanics methods were applied for implementation a principle called safe damage. The problem of stress intensity coefficients determination was considered and a numerical method for their calculation was proposed. An application of the method for structure members with damages and cracks was shown. The analysis of stress-strain states for plates and strips with cracks were fulfilled. The values of stress intensity coefficients К1 for bodies in different configuration were determined based on solution of proper boundary problems and comparison obtained results with known solutions was carried out. Several options of points location at determination displacements fields on crack surface were analyzed.

CROSS-PLY BENDING EQUATION AND APPLICATION FOR COMPRESSED ROD WITH CRACK

The aim of this paper is the analysis of rod cross‐ply bending and stability of rod systems in the presence of cracks. The power concept (its theoretical base is Maxwell's theorem about the reciprocity of displacements) and linear fracture mechanics methods for research of mechanical properties of rod systems in the presence of cracks nave been used. The main equation of the rod cross‐ply bending and the common solution of this equation were obtained. The expression of the relationship between rod deflection and the disturbing cross‐force was obtained. Some transcendental equation allows defining the inferior boundary of critical force of rod with a crack.

Wavelet-based AE characterization of composite materials

This paper addresses an application of recently developed wavelet-based signal processing technique on a composite fracture behavior study. Here, the wavelet methodology is introduced, and a complete procedure of wavelet-based acoustic emission (AE) analysis methods developed by the author are demonstrated. In this research, the AE signals from glass fiber reinforced (GFR) composites are collected during the standard quasi-static tensile testing and transformed by the Daubechies discrete wavelets using the programs developed by the author. Based on AE tests, the fracture behaviors are studied for the material. In the study of GFR composite fracture behavior, classical linear fracture mechanics method is used for comparison. The exponential constant m value used to determine the relationship between stress and stress intensity factor are compared relative to the classical fracture mechanics and the AE techniques. In order to demonstrate the advantage of the wavelet-based AE techniques, the conventional AE analysis is also provided side-by-side for comparison. The results verify that the wavelet-based method better approximates residual strength relative to the classical AE techniques. In this paper, the results of the wavelet-based AE analysis of glass fiber composites are presented. The results indicate that wavelets-based signal processing is an efficient tool in the analysis and the transformation of AE signals.

Evaluating the strength of composite plates with stress concentrators by the methods of linear fracture mechanics

Despite the extensive literature that has been devoted to analytical and experimental investigation of the fracture of plates made of laminated composite materials (LCM) with stress concentrators (SC: notches, through-cracklike defects), this problem demands further study, and no generally accepted approach to its solution has yet been found (see the surveys in [1-4], for example). In this article, we use singular integral equations (SIE) to solve two-dimensional problems of the theory of elasticity, and we employ the principles of linear fracture mechanics (LFM) to develop a general approach that makes it possible to estimate the stress-strain state and predict the strength of flat composite structural elements with notches and through cracks in a complex stress state. We will examine an elastic anisotropic plate of constant thickness h occupying a finite multiply-connected region D that is bounded by the contour L. The contour consists of closed curves LO, L1, . . . , L k (L 0 envelops all of the remaining contours) and curvilinear internal slits (cracks) Lk+ 1, Lk+ 2 . . . . . L n (Fig. 1). We will assume that the origin of the

Defects and strength levels for glass ceramics

1. Defects in glass ceramics of different systems have been studied by means of fluoroscopic flaw detection. It has been shown that according to the type of defects, glass ceramics may be divided into combined and homogeneous defect materials. An nlθ-criterion for glass ceramic defects has been developed. Linear fracture mechanics methods have been used to estimate strength levels for glass ceramics corresponding to grades of defects. 2. It has been shown that combined defect glass ceramics have three strength levels corresponding to processing and structural defects, and to interphase boundaries of the polycrystalline structure. A homogeneous defect glass ceramic has two strength levels governed by structural defects and by interphase boundaries. 3. The existence of calculated strength levels for glass ceramics has been demonstrated experimentally by determining strength, microstrength, and microbrittleness.

Fracture toughness of vitreous enamel coatings including reinforced coatings

1. It is possible to estimate the cohesive strength of vitreous enamel coatings from their fracture toughness G1C, determined in OHB-specimens with a glued layer by the applied linear fracture mechanics method. In particular, this method of estimation makes it possible to find the optimum firing schedule providing the maximum value of G1C for a given coating chemical composition. 2. Reinforcing vitreous enamel coatings with single-crystal ZrO2 filaments promotes an increase in their fracture toughness. 3. The relatively low crack propagation rate in the coating materials studied is apparently caused by their marked porosity.

Use of linear fracture mechanics methods for treatment of residual strength test results

Use of linear fracture mechanics methods for treatment of residual strength test results

Effect of the form and size of a fatigue crack on the fatigue fracture toughness of titanium alloy VT9

At present, one of the most important characteristics of the strength of metal products under fatigue loading, together with the endurance limit, is the fatigue fracture toughness. The introduction of the concept of fatigue fracture toughness [I] was associated with attempts to use the methods of linear fracture mechanics to analyze fatigue fracture. The use of numerical methods of fracture mechanics allowed the authors of [2] to account for the effect of the actual geometry and form of a macroscopic fatigue spot in the fracture of a cylindrical specimen in determining fracture toughness. Obviously, this data is important for engineering calculations and to qualitatively analyze the effect of fracture toughness on endurance if we consider that one of its important terms is the time of propagation Of a fatigue crack to critical size. The data is also important for analyzing the sensitivity of products to stress raisers.

Application of fracture mechanics methods in safety analysis of piping components in subcreep and creep behavior

Application of fracture mechanics methods in safety analysis of piping components in subcreep and creep behavior

Accuracy in determining the stress field at a crack tip by the linear fracture mechanics method

Accuracy in determining the stress field at a crack tip by the linear fracture mechanics method