Offset Cracks Research Articles

Threshold for Stress Corrosion Cracking Initiation of Alloy X750 under Long-Term Uniaxial Constant Load Test in High-Temperature Water

Abstract Uniaxial constant load (UCL) tests of the nickel-based alloy X750 (UNS N07550) were performed in high-temperature pure water (288°C, 8 ppm dissolved oxygen [DO]) to investigate stress corrosion cracking (SCC) fracture time and the crack initiation process. The SCC fracture was initiated at a stress level below the 0.2% offset yield stress and many small cracks were observed in the middle of the nonfractured test specimens. The distribution of the crack length for each observation time is shown by Weibull probability distributions. Crack initiation and propagation process had different behavior depending on the applied stress level and the stress intensity factor at the crack tip. SCC initiation at the minimum applied stress is discussed with respect to the grain size, which depended on the size of an initial crack.

A Finite Element Study on Constrained Deformation in an Intermetallic / Metallic Microlaminate Composite

AbstractThe mechanical properties of intermetallic / metallic microlaminates were studied by determining the fundamental composite properties that control the fracture behavior: namely, the stress-displacement functions of the metal layers. Finite element methods were used to model the stress-displacement function of a constrained metal layer and to examine the effect of constituentproperties, residual stress, offset cracks in adjacent intermetallic layers, and debonding inclusions in the metal layer. Finally, FEM models representative of four specific microlaminates weredeveloped and the results were compared to experimentally determined σ(u)'s for those composites. Determining these fundamental composite properties and showing how they control the mechanical behavior gives insight into the optimum design of this composite system.

Offset crack detection method for rail heads - uses scattered ultrsonic waves projected onto the underside faces and detects reflections: Matix Ind. European Patent No. 204,143 (10 Dec. 1986)

Offset crack detection method for rail heads - uses scattered ultrsonic waves projected onto the underside faces and detects reflections: Matix Ind. European Patent No. 204,143 (10 Dec. 1986)

THE PROPAGATION OF NON‐COPLANAR SEMI‐ELLIPTICAL FATIGUE CRACKS

Abstract— The results of fatigue tests on specimens containing parallel offset and parallel collinear configurations of multiple non‐coplanar cracks are presented. The fatigue growth of parallel collinear cracks is shown to be significantly affected by crack‐tip shielding and parallel offset cracks are shown to grow almost independently before their adjacent tips overlap. Subsequent growth in the region of overlap results in coalescence which begins when the deviating crack tips come into contact below the surfaces of the specimens. Simplified predictions of the propagation of offset non‐coplanar semi‐elliptical cracks are also presented and their implications for the prediction of fatigue lives in structures containing offset coplanar cracks are assessed.

Microstructural Aspects of the Fracture of Hardened Cement Paste

For microstructural studies, samples of hardened cement paste were fractured, impregnated with epoxy using a procedure that does not produce drying cracks, and examined using a scanning electron microscope. Cracks generally appear to pass around unhydrated cement grains and along calcium hydroxide cleavage planes. Cracks are often branched or forked at their tips, and a few microcracks are sometimes observed just ahead of the tips. Perhaps more importantly, the crack path is often offset, with the interjacent material between these offset crack segments forming a bridge across the crack. Even though the crack plane is most likely continuous in three dimensions, these bridging materials may provide local regions of ligamentary tractions across the crack, thereby providing a plausible explanation for the rising fracture resistance (R ‐curve behavior) of hardened cement paste.