Robert E. Green

Asymmetric crystal topographic camera

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.

An experimental study of the double slip deformation hypothesis for face-centred cubic single crystals

Abstract Direct x-ray measurements during deformation are compared with single slip and double slip calculations for rotations beyond the symmetry line. Both a literature survey of 152 face-centred cubic tests since 1923 and the present studv of 16 aluminium tests reveal that the use of the automatic double slip calculation for resolved data is not a reliable procedure. No test since 1929, including the present series, for which rotations have been measured during deformation have turned at the symmetry line in the manner predicted for the double slip hypothesis.

A comparison of optically and piezoelectrically sensed acoustic emission signals

The usual sensor for acoustic emission is the piezoelectric transducer. Although this transducer is readily available, reasonably inexpensive, and very sensitive to ultrasonic transients, it has several serious drawbacks as a transducer: It distorts the signals being measured, it exhibits resonances, it has limited bandwidth, it responds differently to surface acoustic waves and bulk waves (because of its large sensitive area), and its calibration is a matter of considerable uncertainty. Essentially, it is a qualitative transducer. Furthermore, it cannot measure local effects within a millimeter of an emission source, where the mechanisms causing the ultrasonic transient are presumably most clearly distinguishable. Optical transducers, on the other hand, have the great advantage of providing accurate, quantitative, highly localized information; they do not disturb the waves being measured and are not limited by frequency response.

Narrow band laser-generated surface acoustic waves using a formed source in the ablative regime

A narrow band laser-generated acoustic signal was created using a 4-element lenticular array. This arrangement of the array produces an acoustical signal with frequency content that is compatible with the response of a noncontact and remote broadband receiver, such as a capacitive air-coupled transducer. To support the experimental observations, a simplified concept is presented to explain the effect of a line array source on the frequency content of a surface acoustic wave. The analytical model solution for the wave front shape is derived from the point load solution of Lambs problem that represents the displacement of a surface acoustic wave generated by an ablative line array. The distribution function, which was used for the model to represent the laser light energy, was tailored to depict the actual energy distribution that illuminates the lenticular array. Filtering functions are applied to the resultant surface displacement function to retain frequencies similar to those detected by the broadband 50 kHz-2.25 MHz receiver. The theoretical model showed good agreement with experimental results.

Image Intensifier System for Dynamic X‐Ray Diffraction Studies

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.

Light‐Wave/Elastic‐Wave Analogies in Crystals

General consideration is given to the analogies that exist between the propagation of light waves and the propagation of ultrasonic waves in anisotropic media. A historical survey is given of prior work in this area, followed by a comparison of present views of the analogies with those of other investigators. The inability to obtain a direct one‐to‐one analogy for all phenomena is discussed.

Governing Equations for the Shapes of Molten Zones

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.

Cure monitoring of carbon epoxy composites: an application of resonant ultrasound spectroscopy

A novel method is applied to the monitoring of the degree of cure of a unidirectional panel of AS4/3501-6 carbon epoxy composite during cure. The composite panel to be cured is vacuum bagged on a steel caul plate. The resonance spectrum of the steel caul plate is measured periodically as the temperature is raised to the cure temperature and during the subsequent cure and cool-down periods. Because the curing composite acts to change the boundary conditions, the resonance spectrum changes as the composite cures. The spectrum at each temperature is compared with that obtained from the caul plate alone at the same temperature. Differences in amplitude, frequency and damping are related to the degree of cure of the composite.

The Synchrotron Topography Project (STP) at the national Synchrotron light source

Abstract The collaborators have participated in the Synchrotron Topography Project (STP) which has designed and developed instrumentation for an X-ray topography station at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL). The two principle instruments constructed consist of a White Beam Camera (WBC) and (MCC) with high planar collimation and wide area image coverage. It is possible to perform in studies ina versatile environmental chamber equipped with a miniature mechanical testing stage for both the WBC and MCC systems. Real-time video imaging plus a rapid feed cassette holder for high resolution photographic plates is available for recording topographs. Provisions are made for other types of photon detection as welas spectroscopy. The facilities for the entire station have been designed for remote operation using a LSI-11/23 plus suitable interfacing. These instruments will be described briely and the current status of the program will be reviewed.

Multiparameter system for investigation of the effects of high‐power ultrasound on metals

A multiparameter system has been developed which, for the first time, permits simultaneous measurement of sufficient quantities to test all of the proposed mechanisms for the influence of high-power ultrasound on metal specimens. Results of measurements using this system give new insight into the mechanical and thermal processes involved. Data are presented which show typical results obtained during tensile elongation of polycrystalline and single-crystal aluminum specimens.