The Propagation Threshold of a Through Crack in a Plate Under the Mixed Mode : (Plane Bending and Cyclic Torsion)

EVALUATION OF KII USING A COPPER FOIL WHEN ASSESSING FRICTIONAL FORCES ON CRACK SURFACES

“…8, where the solid line indicates the experimental values for the threshold stress for crack propagation at thicknesses of 2 and 4 mm reported in our previous papers [ 3,4].…”

“…7 and Table 3, the Ye, value for a crack which is subjected to cyclic torsion under the action of the frictional forces on the crack surface, is noticeably lower than the calculated value Y, [7]. Using the function YeX so obtained, and a function @ which is considered to be applicable to bending, the threshold stress zth for crack propagation of this cracked specimen under torsion or a combination of bending and torsion was determined on the basis of the S,, criterion using the same procedure as that used in previous papers [ 3,4] considering the threshold stress rth for crack propagation of the cracked specimen (A) due to bending. The value !…”

“…To determine a calibration curve for the grown copper foil strain gauge, a plate of JIS G3311 SK-5 was used. The same material was used in our previous papers [3,4] and will be used for cracked specimens for measuring K,. After machining both materials to the shape and dimensions shown in Figs 1 (a), (b) and (c), respectively, the surface was finished with emery paper of #600 grade.…”

“…This foil gauge was used to measure a correction factor Y of the mode I1 stress intensity factor K, thereby quantifying the action of the frictional force on the crack surfaces in a plate under torsion; see our previous papers [3,4]. The threshold stress for crack propagation under combined modes I and I1 was determined by using the S-criterion and the experimental Y values.…”

“…The grain size of a grown copper foil strain gauge [2] which is effective in measuring dynamic strains in a local area, was first adjusted to have a strain sensitivity suitable for measuring the K, value for a specimen. This foil gauge was used to measure a correction factor Y of the mode I1 stress intensity factor K, thereby quantifying the action of the frictional force on the crack surfaces in a plate under torsion; see our previous papers [3,4]. The threshold stress for crack propagation under combined modes I and I1 was determined by using the Scriterion and the experimental Y values.…”