Stress concentration

About: Stress concentration is a research topic. Over the lifetime, 23250 publications have been published within this topic receiving 422911 citations.

A fatigue crack closure mechanism in titanium

Abstract: — Fatigue crack closure in commercial titanium has been investigated by examining the crack profile using a two-stage replica technique and by monitoring the crack raouth opening displacement. The replicas show that when closure occurs the crack does not close back from the crack tip but at discrete contact points along the crack faces. The observed closure mechanism is therefore quite different from the generally accepted model. Assuming that the contact points wedge the crack open, the stress intensity at the minimum load is greater than expected and the range of the stress intensity is effectively reduced. Also, it was found that the crack growth rates measured in the range 0·05 ≦R≦ 0·7 showed a singular dependence on the parameter Δθ which for SEN specimens approximates to the change in angle subtended by the crack faces. It is therefore suggested that there is a direct link between Δθ and the effective stress intensity amplitude.

Validation of the K and J Parameters in a Compact Tension Specimen Containing Intergranular and Straight Crack Paths

Abstract: Methods have been examined to evaluate the fracture mechanics parameters J and K in finite element (FE) analyses on a compact tension, C(T), geometry using a mesh appropriate for the evaluation of both intergranular and transgranular microstructural damage processes. Realistic grain and grain boundary microstructures were modelled using ABAQUS. Both straight and deviating crack profiles were considered, representing transgranular and intergranular crack growth processes, respectively. Elastic and elastic-plastic finite element analyses were performed on a C(T) specimen model with a standard straight and deviating crack profile to derive and compare the stress intensity factor, K, and J parameter values under plane stress and plane strain conditions. Considerations as to the validity of the J domain integral calculations that ABAQUS computes are discussed. It has been found that the values of K and J obtained from FE simulations are consistent with theoretical solutions and the stress distribution ahead of the crack tip is very close to that of expected from analytical studies for the case of a straight fronted transgranular crack. Reasonable values of K and J parameters could also be achieved from the FE contour integral values of a deviating crack when the contours selected were adequately far from the crack tip. However, significant differences were found between the analytical and FE contour integral values of a deviating crack when the crack growth direction was considered to continue at the angle defined by its grain boundary. The values of J obtained by from the load line displacement measurements were uninfluenced by the crack profile and in good agreement with other analytical solutions.© 2010 ASME

The biomechanics of torsional fractures. The stress concentration effect of a drill hole.

Abstract: To determine the effect of a drill hole on the strength of long bones and on the fracture resulting from rapidly applied torsional loads, paired canine femora were tested, and the following results were obtained: 1. The presence of a 2.8-millimeter or a 3.6-millimeter drill hole in the femoral mid-shaft significantly weakens the bone as measured by a mean reduction in energy-absorbing capacity of 55.2 per cent. 2. The drill hole produces a significant increase in local stresses as demonstrated by a calculated stress concentration factor of 1.6. 3. Changes in the ratio of drill hole area to bone area from .12 to .28 are not accompanied by significant changes in the bone strength or in the stress concentration factor. 4. The resulting spiral fractures occur along planes of maximum tensile stress, and the drill hole does not alter their orientation. 5. In drilled specimens the fracture is localized to the region of the drill hole and is less comminuted.