Tensile and fatigue fracture behavior and water-environment effects in a SiC-whisker/7075-aluminum composite

Fatigue crack test was performed using a grain-orientated 3% silicon iron under constant amplitude loading. Growth behaviour of the fatigue crack and slip deformation behaviour near the crack tip were observed in detail by using an atomic force microscope. In the lower K region, only one preferential slip system of this material operated and the fatigue crack grew along that slip plane. It was found that constraint of slip deformation due to cyclic strain hardening resulted in crack arrest and crack branching. The fatigue crack grew in a zigzag manner as a result of such successive crack branching and deflection. In the high K region, two preferential slip systems operated simultaneously to an almost identical extent and the fatigue crack grew in a direction perpendicular to the loading axis. The slipping distance in one loading cycle was measured quantitatively by using the image processing technique and the crack growth mechanism is discussed.

Atomic force microscopy and the mechanism of fatigue crack growth

Atomic force microscopy of fatigue crack growth behavior in the low K region

Fractal Characteristics of Scanning Tunneling Microscopic Images of Brittle Fracture Surfaces on Molybdenum

The software which enables us to classify six typically different fracture surface morphologies, such as striations, equiaxed dimples, elongated dimples, transgranular failures, intergranular failures, and cleavage failures, has been developed based upon computer image processing and pattern recognition. The texture analyses used here are the Fourier power spectrum, generalized co-occurrence matrices, the three dimensional fracture surface topographies

Recognition of different fracture surface morphologies using computer image processing technique

Computer image processing technology has been applied to fracture surface analysis, and the generalized software for 3-dimensional fractography image analysis has been developed. By this software, it became possible to obtain 3-dimensional fracture surface topography from a stereo-pair of SEM fractograph with a sufficient precision. The fatigue fracture surface roughness of a hightensile strenght steel HT 55 in air and in vacuum was calculated, and the root mean square roughness of fracture surface in vacuum was made clear to be greater than that in air at R=-1, compared with those at R=0.1 and 0.5. The wedge effect induced by corrosion products was also clearly demonstrated on a matching-pair of corrosion-fatigue fracture surface topography of HT 55.

3-dimensional image analysis of fatigue fracture surface.

Reconstruction Technique of Three-Dimensional Shape by SEM Image

Two-dimensional quantitative analysis of SEM (Scanning Electron Microscope) images of fracture and corrosion damaged surfaces was made by using the computer image processing and pattern recognition technique. This SEM image analysis was found to be successful with enough accuracy for automatic measurement of fatigue striation spacing, identification of corrosion pits and their statistical distribution, and classification of intergranular and transgranular cracking portions. The quantitative and statistical analysis of SEM images, which have required specialists's experience, a great deal of labor and much time, can be carried out now quickly and accurately by using a digital computer with fast-processing capability.

Application of two-dimensional computer image processing to damaged surface in an aggressive environment.

Fractographical observations of low alloy steels in high temperature water were carried out, and the responsible mechanisms for corrosion fatigue crack growth were discussed. The fracture surface of a low sulfur content steel was wholly occupied by transgranular ductile cracking characterized by striation patterns. In a medium sulfur content steel, on the other hand, quasi-cleavage cracking characterized by both striation and river patterns was observed. The crack growth in the medium sulfur content steel was abruptly accelerated at ΔK≅19MPa·m1/2. This acceleration was caused by hydrogen embrittlement associated with dissolution of MnS. Fourier power spectrum analysis was found to be a very powerful tool for the striation spacing measurement, especially when the striation patterns were made indistinct by derusting treatment. Based on the linear summation hypothesis with consideration for fracture area fractions, the quasi-cleavage crack growth rate in the medium sulfur content steel was derived.

https://www.jstage.jst.go.jp/article/jsms1963/34/385/34_385_1223/_pdf

Jun Kikuchi

Papers

3-dimensional image analysis of fatigue fracture surface.

Reconstruction Technique of Three-Dimensional Shape by SEM Image

Application of two-dimensional computer image processing to damaged surface in an aggressive environment.

Fractography and mechanism of corrosion fatigue crack growth of low-alloy steel in high-temperature water