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The internal microstructure of large melt‐grown paraffin (n‐eicosane, C20H42) single crystals was examined by the Lang x‐ray diffraction projection topographic technique. Crystal selection was facilitated by use of an electro‐optical system which permitted instantaneous display of Laue transmission x‐ray diffraction patterns on a television monitor. The crystals were oriented and topographic diffraction planes were selected by the use of a standard (001) stereographic projection plotted from computed angles between crystallographic planes. A second electro‐optical system which permitted direct viewing of the topographic images was use for rapid alignment of the Lang camera and ensured uniformly exposed topographs. X‐ray topographs were obtained from crystals in the as‐grown, plastically deformed, and γ‐irradiated states. The results indicate that both plastic deformation and γ irradiation caused marked changes in the microstructure of the crystals, and that x‐ray topography can be successfully exploited to determine such changes in hydrocarbon crystals.

With the increased use of acoustic emission as a nondestructive testing tool, it has become extremely important to document and to understand the emissions characteristic of various modes of deformation and fracture. In the present work, results are reported of acoustic emission measurements made during mechanical deformation of indium single crystals. Although the metal indium is of little structural importance, it develops well‐delineated twins with associated acoustic emissions, and therefore affords an excellent medium with which to develop techniques and to generate interpretations which can be applied to structurally important materials. By recording the acoustic emission signals on a video‐tape recorder it was possible to play them back as often as desired and to observe them in slow and stop motion. The experimental results show that a correspondence exists between the duration of the acoustic signal and the volume of twinned material as determined by cinematographic observation of the generation ...

Acoustic emission monitoring has become a well‐recognized technique for the nondestructive evaluation of materials and structures. The usual procedure is to count the number of acoustic emission bursts and record either the total count or the burst rate. A rough measure of the burst amplitude or of the burst duration is obtained by ringdown counting or by peak or threshold detection. In this paper we demonstrate that further information is obtainable from accurate waveform determinations, which can be obtained by our optical method. We find that there is good agreement between at least some natural acoustic emission waveforms and theoretical seismic pulse waveforms.

X‐ray transmission asymmetric crystal topography was used to investigate the changes in defect structure which occur during the solid‐state polymerization of macroscopic single crystals of a diacetylene. Comparison of x‐ray topographs made before and after gamma‐ray‐induced polymerization indicate that lattice strain increases during polymerization, but important defect structures present in monomer crystals are retained in the polymer crystals. A cross‐pattern defect structure along 〈201〉 crystallographic directions is typically observed in both monomer and polymer single crystals.

A flash x‐ray diffraction system has been constructed which permits x‐ray diffraction patterns to be recorded from shaped charge jets. The system was tested by recording an x‐ray diffraction pattern from an aluminum jet 80 μsec after charge detonation with a single pulse of 70 nsec duration. This result represents the first successful recording of an x‐ray diffraction pattern from a shaped charge jet and indicates that the system should be an important new device for determination of internal jet structure.

The practical aspects of asymmetric crystal topography are described. In this technique, asymmetric Bragg diffraction is utilized to obtain a monochromatic and well collimated x‐ray beam large enough to cover the entire area of sample crystals. Thus, the recording of diffracted beams from a sample crystal provides topographic images of the entire sample crystal. Advantages of this technique are simplicity (no scanning device), excellent sensitivity to crystal imperfections (strain fields), and versatility. Information is given on the general alignment of the camera, magnification of the x‐ray beam width, preparation of the first crystal, and divergence of the beam due to the first crystal. The practical aspects of this topographic system are demonstrated using thick Cu and Ni crystals of various degrees of perfection. An inexpensive image intensifier is also described, which is used routinely to aid in the alignment of sample crystals.

The orientation dependence of dislocation damping in the five hexagonal metals Mg, Cd, Be, Zn, and Ti has been predicted by calculation of the appropriate factors relating the stress field of the elastic waves to the slip systems in which the dislocations are moving. The four metals having basal slip systems have very similar qualitative behavior of the orientation factors. Titanium, with prismatic slip systems, has a quite different behavior and the orientation factors are smaller for all orientations than the values for the basal slip metals. For Zn, Cd, Mg, and Ti, the values of the orientation factors for standing waves (resonance technique) are larger than the corresponding values for the traveling waves (pulse‐echo technique). For Be, the orientation factors for both types of waves are nearly equal. Crystal orientations and wave types of particular interest for experimental study are delineated.

A cascaded image intensifier has been incorporated in a system which permits study of dynamic changes in x‐ray diffraction patterns. An RCA C70021A three stage, magnetically focused, image tube is coupled by a f/0.87 Super‐Farron lens to a 15.2 cm diam fluorescent screen to permit direct viewing of transmission x‐ray diffraction patterns. The image on the output phosphor is of sufficient intensity to be viewed directly, to be recorded cinematographically, or to be displayed by vidicon pick‐up on a television monitor.

Elastic wave velocities, particle displacement vectors, and directions of energy flux have been calculated and are given as a function of the polar angle θ in the five hexagonal metals Be, Cd, Mg, Ti, and Zn. Because of elastic transverse isotropy around the hexagonal axis, the wave characteristics are functions of the angle between the hexagonal axis and the direction of propagation in the crystal only. The results of these calculations are especially useful for experimental investigations utilizing the ultrasonic pulse‐echo technique.

Theoretical consideration is given to the equation governing the shapes of molten zones when they are not necessarily surfaces of revolution. This equation is seen to reduce to equations previously given for both vertical and horizontal molten zones when the shape is a surface of revolution. Solution of the equation governing the shape of the vertical molten zone when it is a surface of revolution gives corrected values for the maximum stable zone lengths for large rod radii. Detail consideration is given to the influence of a surface film on vertical zone stability.

A flash x‐ray diffraction system is described which weighs less than 27.2 kg and which permits Laue transmission x‐ray diffraction patterns to be obtained with exposure times as short as several microseconds using multiple pulses of 60 nsec duration each. The system consists of a pulsed x‐ray generator incorporating a tungsten target beryllium window x‐ray tube and a specially designed collimator. Diffraction photographs are presented which permit comparison of the pattern obtained with the portable flash x‐ray diffraction system with that obtained using a conventional x‐ray diffraction system incorporating a heated filament tube.

A simple technique to estimate the angular beam width of acoustic modes propagating along arbitrary directions in crystals is proposed. This technique is based on considerations of the relationship between the energy flux vectors and the geometry of the inverse speed surfaces of the acoustic modes. Experiments on sodium chloride and quartz single crystals and fused quartz, utilizing optical beam probing techniques, confirm the usefulness of the present method.