Elastic-Plastic Mixed-Mode Fracture Criteria and Parameters

This book contains an elastic-plastic analysis of accumulate damage and fracture with practical applications to engineering materials and structure fatigue life estimations. Models as well as practical applications are presented which makes the book interesting for both practitioners and theoretical researchers. Particular emphasis is laid on new approaches to the mixed-mode problem in fatigue and fracture, and especially to the fracture damage zone (FDZ) approach. The results of the demonstrated experimental and theoretical researches leads to the presentation of different crack growth models, predicting the crack growth rate and fatigue life of an initially angled crack under biaxial loads of arbitrary direction. Special attention is paid to the practical applications of the suggested models.

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My wife Tatyana, daughter Mariya, son Alexandr It is well known that the mixed-mode conditions appear when the direction of the applied loading does not coincide with the orthogonal K,-Kn-Km space. In general, in the industrial practice the mixed-mode fracture and the mixed-mode crack growth are more likely to be considered the rule than the exception. Miller et al. considers that cracks can grow due to a mixture of processes (ductile and brittle), mechanisms (static, fatigue, creep) and loading modes (tension, torsion, biax­ ial/multiaxial). Additionally mixed-mode crack-extension can be affected by many other considerations such as artifact geometry (thin plates, thick shells, and the size, shape and orientation of the defect), environmental effects (temperature, gaseous and liquid surroundings), material state (crystallographic structure, heat treatment and route of manufacture) and stress conditions (out-of-phase and ran­ dom loading effects). The main feature of the mixed-mode fracture is that the crack growth would no longer take place in a self-similar manner and does not follow a universal trajec­ tory that is it will grow on a curvilinear path. There are various fracture criteria, which predict the behavior of cracks in brittle and ductile materials loaded in combined modes. Linear elastic fracture mechanics (LEFM) criteria predict basi­ cally the same direction for crack propagation. Cracks in brittle materials have been shown to propagate normal to the maximum tangential stress. In ductile ma­ terials yielding occurs at the crack tip and LEFM is no longer applicable.

Contenu

I. Mixed-mode crack behavior under plane stress and plane strain small scale yielding.- 1.1 Governing equations.- 1.1.1 Plane strain.- 1.1.2 Plane stress.- 1.1.3 Boundary conditions for different types of dominating fracture mechanism.- 1.2 Numerical iterative method for solving the nonlinear eigenvalue problems.- 1.3 Application of J-integral to plastic stress intensity factor determination.- 1.3.1 Plane strain.- 1.3.2 Plane stress.- 1.4 Family of crack-tip fields characterized by dominating fracture mechanism.- 1.4.1 Plane strain.- 1.4.2 Plane stress.- 1.5 Finite element analysis of stress distributions at the crack tip.- 1.6 Conditions of existence for mixed mode fracture.- II. Modeling of crack growth by fracture damage zone.- 2.1 A modified strain-energy density approach.- 2.1.1 Elastic strain energy density.- 2.1.2 Plastic strain energy density.- 2.2 Strain energy density distributions.- 2.3 Fracture damage zone.- 2.3.1 A brief review.- 2.3.2 Fracture damage zone size.- 2.4 Relation between cracks growth resistance and fracture process parameters in elastic-plastic solids.- 2.5 Elastic-plastic approach for modeling of fatigue crack behavior.- 2.6 Some aspects of the fatigue crack path prediction.- III. Experimental investigation of fatigue crack propagation.- 3.1 Specimens for study of fatigue and fracture processes and material properties.- 3.2 Method of interpretation for cyclic crack resistance characteristics.- 3.3 Effect of biaxial stress on fatigue crack growth in aluminum alloys.- 3.4 Influence of mixed mode loading on fatigue fracture of high strength steels.- 3.5 Fatigue crack growth trajectories for the aluminum alloys and steels.- IV. Models for predicting crack growth rate and fatigue life.- 4.1 Crack growth direction criterion.- 4.2 Criteria of equivalent plastic strain under a complex stress state.- 4.3 A model for predicting crack growth rate under biaxial loads.- 4.4 An analysis of crack growth under complex stress state with taking into account their orientation.- V. Practical applications.- 5.1 Fracture analysis of gas turbine engine disks and simulation modeling of operational conditions.- 5.1.1 Stress state analysis.- 5.1.2 Crack growth model.- 5.1.3 Full size disk experiments.- 5.2 Modeling fatigue crack behavior in a pressurized cylinder.- 5.2.1 Crack growth model.- 5.2.2 Results and discussion.- Reference.