Mixed Mode Fatigue Crack Thresholds From Bending and Cyclic Torsion of a Plate

Abstract

The effects of plate thickness and crack shape on the threshold condition for crack propagation under cyclic bending or torsion, was studied using a through or a surface pre-crack in a carbon steel plate of various thicknesses. It was concluded that the magnitude of the frictional stress acting on the crack surface at the propagation threshold under cyclic torsion was significantly affected by the plate thickness. An estimation method for the threshold condition for crack propagation under mixed-mode loading for a particular plate thickness was proposed on the basis of the strain energy density criterion.

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 !…”

“…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.…”

A mixed mode crack growth model taking account of fracture surface contact and friction

“…There is increasing recognition of the importance of fracture surface roughness on crack propagation tendencies for cracks subjected to mixed mode I, II and/or III loading (Gross and Mendelsohn, 1989;Reardon and Quesnel, 1995;Egami and Kitaoka, 1996;Tanaka et al, 1996;Soh and Bian, 2001). Tong et al (1995a) developed a physical model to quantify the sliding mode crack closure (SMCC) experienced in cyclic mode II loading conditions.…”

Status Quo and Countermeasures of Windproof Capability of Crane Working Condition

“…For this, we must focus on strengthening the protection of large cranes. More specifically, this paper mainly evaluates and strengthens the windproof capacity of the crane [3], because if the windy wind causes the crane to roll over in the worst case, then this loss and some chain reactions are beyond our means. .…”