Stress-Intensity Factors for Three-Point Bend Specimens by Boundary Collocation
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
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A boundary value collocation procedure was applied to the Williams stress function to determine values of the stress intensity factor K for single edge in rectangular section specimens subjected to three point bending. The results are presented in terms of the dimensionless quantity Y2 K2B2W3M2 where B and W are the specimen thickness and depth and M is the bending moment at midspan. The values of Y2 as a function of relative crack depth aW for three-point bending are appreciably lower than the corresponding values for pure bending determined previously by the same method and decrease as the ratio of support span to specimen depth SW decreases. Plots of Y2 against aW are given for values of aW up to 0. 5 and SW equal to 4 and 8. The results were relatively insensitive to variations in the spread of the midspan load contact region, which was assumed to be related to the yield strength of the material. The results agreed fairly well with published results derived from experimental compliance measurements one set gave higher values of Y2 than the present method, and the other set gave lower values. The plane-strain fracture toughness measurement capacity of three-point bend specimens is somewhat lower than that of four- point bend specimens, but the difference is of negligible practical importance.