Stress-Intensity Factors for Single-Edge-Notch Specimens in Bending or Combined Bending and Tension by Boundary Collocation of a Stress Function
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
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A boundary-value-collocation procedure was used in conjunction with the Williams stress function to determine values of the stress-intensity factor K for single edge cracks of various depths in specimens subjected to pure bending. The results are of use in connection with Ksub Ic fracture toughness tests, which utilize rectangular-section crack-notch beam specimens loaded in four-point bending, and are in good agreement with published results derived from experimental compliance measurements. The results are expressed in convenient, compact form in terms of the dimensionless quantity Yexp 2Kexp 2Bexp 2Wexp 3Mexp 2, which is a function of relative crack depth aW only, where B and W are the specimen width and thickness and M is the applied bending moment. On the assumption that the condition for a valid Ksub Ic test is that the maximum nominal stress at the crack tip should not exceed the yield strength of the material, the Ksub Ic measurement capacity of bend specimens was estimate as a function of aW. The measurement capacity is proportional to the yield strength and to the square root of the specimen depth, and it is greatest for aW in the range 0.2 to 0.3. Values of K for single-edge-notch specimens subjected to combined bending and tension were obtained by superposition of the present results and those of earlier work for specimens loaded in uniform tension. These values are of interest in connection with the use of single-edge-notch specimens that are off-center pin-loaded in tension. It is shown that the Ksub Ic measurement capacity of such specimens is not very sensitive to the eccentricity of loading.