Fatigue growth of surface flaws in finite plates
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"The most commonly observed structural defect is the surface crack. The primary difficulty in analyzing the growth of surface cracks is the stress intensity factor which varies from point to point along the crack due to crack front curvature and the complex local geometry. The study of surface cracks started in 1950, where Green and Sneddon [1] characterized the distribution of stress in the neighborhood of a flat elliptical crack in an elastic solid. The first surface crack experiments to be reported were conducted independently at the Naval Research Laboratory [2], and at Douglas Aircraft Company [3] in 1960. In 1962 a technique for making shallow cracks in sheet metals was performed by Yen and Pendleberry [4]. The analysis of surface crack data according to fracture mechanics principles was made possible by Irwin [5] in the same year. Paris and Sih [6] in 1964, attempted to improve the applicability of Irwin's estimate of the stress intensity factor for plates of finite thickness by means of analogies to existing two dimensional solutions. Randall [7] in 1966 studied the effect of crack size and shape on apparent plane strain fracture toughness values. He also used crack opening displacement measurements as qualitative indicators of crack tip deformation phenomena. F. W. Smith [8] in this year investigated the problem of a semicircular surface crack by the finite difference numerical method. Ayres [9] applied a finite difference elastoplastic solution to one semi-elliptical surface crack geometry in 1968. Hall [10] in 1970 compared apparent fracture toughness values from surface crack specimens, with those obtained from other specimen types. Miyamoto, Miyoshi, Levy and Marcal [11] presented a finite element analysis for specific geometries. Marrs and Smith [12] presented a method of determining stress intensity factors in epoxy models by three dimensional photoelasticity in 1971. Corn [13] studied cracking techniques for obtaining partial thickness cracks of pre-selected depths and shapes in the same year. In 1972 Cruse [14] analyzed a semi-circular surface crack using boundary integral equations. F. W. Smith [15] performed the elastic analysis of the part circular surface flaw problem by the alternating method. J. C. Newman [16] in 1973 derived an equation which related the linear elastic stress intensity factor, the applied stress, and two dimensional parameters; an empirical equation for the elastic magnification factors of the stress intensity factor for a surface crack in finite thickness plates was also developed. Buck, C. L. Ho and H. L. Marcus [17] described experimental results of crack propagation in part through crack specimens in which they found that changes in the loading spectrum causes time dependent relaxation and retardation effects which are not only reflected in the crack growth rate but also in the crack closure behavior. F. W. Smith and Sorensen [18] studied the mixed mode stress intensity factors for semi-elliptical surface cracks in 1974. At the end of 1975 Kobayashi, Polvanic, Emery and Love [19] studied surface flaws in plates under bending loads. Kathiresan [20] performed thesis research in the area of three dimensional linear elastic fracture mechanics analyses by a displacement hybrid finite element model in 1976. In the same year J. C. Newman [21] performed an analysis to predict failure of specimens with either surface cracks or corner cracks at holes. In 1977, Raju, and J. C. Newman [22] improved the stress intensity factor solution for semi-elliptical surface cracks in a finite thickness plate. They also developed a three dimensional finite element analysis of finite thickness fracture specimens. During 1979 [23] they continued to study the stress intensity factors for a wide range of semi-elliptical surface cracks in finite thickness plates. To verify the accuracy of the three dimensional finite element model employed, convergence was studied by varying the number of degrees of freedom. Stress intensity factors for shallow and deep semi-elliptical surface cracks in plates subject to tension loads were presented. They later developed an equation to express the stress intensity factors for surface cracks which was presented for finite thickness plates in tension and bending [24]. T. A. Cruse, A. E. Gemma, R. T. Lacroix and T. G. Meyer [25] presented in this year an overview of surface crack life prediction. R. M. Engle, Jr. [26] presented a survey of various analytical solutions currently used in part-through crack life prediction taking into account effects of flaw shapes. J. L. Rudd [27] presented predictions for surface flaw growth using compact tension specimen crack growth rate data. W. S. Johnson [28] developed a technique to predict constant amplitude crack growth of surface flaws. J. B. Chang [29] used a computer routine, EFFGRO, to calculate crack growth predictions of surface flaws. J. L. Rudd, T. M. Hsu and H. A. Wood [30], worked in the most common types of flaws in aircraft structure, taking into account residual stresses and initial flaw geometries. J. H. Underwood and J. F. Throop [31] presented a method for describing quantitatively the effect of residual stresses in cylinders with shallow flaws. Although much attention has been focused on this important problem, the recent results cited above indicate the need for further understanding of surface flaw behavior and improvement in predictive methodology. In Chapter 2 geometry, material properties, and stress field are taken into account to derive an equation which relates changes in crack depth, and crack length at the free surface. Surface crack growth behavior is studied in Chapter 3, where the particular geometry of growth is analyzed for shallow and deep cracks. The effect of material properties is also considered in this chapter. Material, test procedure, and data reduction techniques are described in Chapter 4. Chapter 5 presents the analyses of geometry configuration and life prediction and a comparison with the experimental results. Chapter 6 introduces an analysis of surface crack behavior under bending stresses."--Introduction.
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