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A method is developed for evaluating the displacement field around the tip of a crack in a plate under plane stress or strain conditions by executing a number of measurements in this area through the scanning electron microscope. Several spots were created around the crack tip by using the electron beam of the SEM, which were used as reference points. A theory was developed which yields the components of the in-plane displacements and their differences from the coordinates of the reference spots measured through SEM. The method presents the advantage that its results are independent of the exact position of the crack tip and therefore it is suitable for performing measurements very close to this tip. Experimental evidence with plexiglas plates showed the validity of the method for defining the displacement field as well as the values of crack opening displacements and the stress intensity factor.

An experimental technique based on the optical method of caustics for the solution of the two-dimensional problem of an arc-shaped crack lying along the interface of a circular inclusion embedded in a matrix and subjected to a uniaxial tension at infinity was developed. The study was directed towards the determination of the complex stress intensity factorK *characterizing the near to the crack tip stress field. A detailed analysis of the caustics obtained by illuminating the near to the crack tip region by a coherent light beam was undertaken and nomograms for the direct experimental determination ofK *in the Dundurs parallelogram, incorporating all the physically relevant material combinations of the two bodies, were given. Extensive experimental evidence for the new technique was given.

A study of ductile blunting edge cracks in tensile specimens was undertaken in this paper by detecting the forms of different stages of blunting of the cracks under conditions of mode-l deformation as the loading progressed. All three main types of blunting were detected, with identical specimens and cracks, that is, the rounded off, the multicornered and the pointed type, depending on the particular accidental instabilities appearing in the vicinity of the crack tip as the blunting process is progressing. It was shown that an intermediate type of blunting was detected on the surfaces of the specimens by the scanning electron microscope (SEM) and this was explained by the fact that at the surfaces of specimens possessing a significant thickness to width aspect ratio the state of stress at the surface is strongly influenced by the plane stress conditions prevailing at the lateral faces of the specimens.

The scanning electron microscope (SEM) is used for the study of slow crack propagation through a bimaterial interface. This work is concerned with the variation of crack velocity, the variation of crack tip opening angle (CTOA) and the stress intensity factor (K) at the crack tip, and the investigation of crack arrest phenomena at the bimaterial interface. It was observed that the crack accelerates to a maximum velocity as the crack tip approaches the interface and then decreases rapidly to a minimum value at the interface. The interface acts as a “decelerator” to crack propagation. The position and the value of the maximum velocity depends on the mechanical properties of two phases and specimen configuration. The crack propagates at a constant CTOA until it arrests at the interface. During the crack-arrest time the CTOA increases rapidly to a limiting value. Then the crack passes across the interface and propagates in the next phase with almost the same CTOA as the initial crack in phase I. The stress intensity factor,K, increases to a maximum value near the bimaterial interface.

An experimental technique based on the optical method of caustics for the solution of the two-dimensional problem of a narrow contact between two elastic disks was developed. In particular, an elliptical pressure distribution of the Hertz type was assumed, as well as a rectilinear contact form according to Muskhelishvili's solution. The method presents the advantage of yielding directly the contact length, from which the load applied on the disks can be readily evaluated.