Edge Wedge Research Articles

Effect of specimen type and crack orientation on fracture toughness

The effect of specimen type on the room temperature plane strain fracture toughness of three aluminum alloys: 7079-T6,7075-T6, and 7001-T75, is presented. The difference in K IC as evaluated with center notch, single edge notch, slow bend, surface flaw and wedge opening loading specimens is discussed. The orientation of the crack plane and crack propagation direction with respect to the working direction, or grain orientation, of the alloys is considered. The possible influence of crack plane and propagation direction on the resulting plane strain fracture toughness value is discussed. The surface flaw specimens seem to yield the highest K IC value followed by slow bend, single edge notch and center notch specimens. The slow bend and surface flaw specimens were the most sensitive to material variability. Differences in orientation between crack propagation direction and material grain morphology are shown to effect K IC . For 7001-T75 and 7079-T6, the order of decreasing fracture resistance with respect to crack propagation direction is short transverse, short transverse and longitudinal. For 7075-T6, the order is long transverse, short transverse, and longitudinal.

A Simple Means of Measuring Vortex Strength, and the Performance of Triangular Ramp-Type Vortex Generators in a Uniform Velocity Field

The performance of triangular ramp vortex generators of a type used for boundary layer separation control, has been compared with that of equivalent wing or vane type of lifting generators, in a uniform velocity field, and was shown to be substantially inferior. Performance was established using a novel vortex strength measuring device of unusual simplicity, for which calibrations are given and applications are discussed.The usefulness of vortex generators in avoiding boundary layer separation due to an adverse pressure gradient has been established. Little, however, is known of the nature of vortex modified boundary layers. As part of an investigation into convective heat transfer through such layers it was desired to compare the circulation-drag performance of two representative generator configuration types, these being the popularly used stub wing or vane type, and the edge separation, plough or wedge type.