The investigation on the yielding at crack tips, its implication on fracture, size effect and its relation to the Griffith criterion of fracture and to the failure of pressure cylinders, and finally the correlation of fracture of plates with that of cylinders are presented herein.
By means of the formula derived for the yielding zones at crack ends, it is shown that for failure besides the fulfilment of the Griffith condition, the yielding zones should attain critical dimensions and that in cylinders of all material and in fiat plates of high strength material the width of the fielding zone is the same for a given size over a wide range of stresses.
The size effect for plates of high strength material is expressed by a formula relating the Griffith stress to the applied stress, critical crack length and the width of specimen: but in the case of more ductile material different formula is derived on the basis that in different sizes of plates the yielding zones have the same width for crack lengths proportional to the width of specimens. The size effect obtained for cylinders not only yields the solution for failure mechanism of cylinders but furnishes the means of obtaining the rate of strain energy release when the formula is applied to test results.
Finally a correlation between the fracture of fiat plates and that of pressure cylinders on the basis of strain energy release is established. By means of this correlation and with the formula for failure of cylinders the computing of failing stresses for cylinders of different radii is made possible.
The test data used to substantiate theory consists of four materials. They are two aluminum alloys, stainless steel and a titanium alloy. The width of flat plate specimens in tests is in the range from 2.25 in. to 30 in. and the radii of cylinders are from 3.6 in. to 15 in. * Some results of this paper were originally presented under the title "Fundamentals of Fracture in Metallic Sheets" at the Fifth U. S. National Congress of Applied Mechanics, held in Minneapolis, Minnesota, 1966. ** Editorial Note: Through an administrative oversight, this paper, originally accepted for publication two years ago, inadvertently never reached publication. The paper is now published with apologies to the author.