Measurement Of Grain Orientation Research Articles

Prediction of grain orientation in dissimilar metal weld using ultrasonic response of numerical simulation from deliberated scatterers

Ultrasonic nondestructive testing plays an important role in structural integrity monitoring of dissimilar metal weld (DMW) structures in pressure vessels and piping of nuclear power plants. Inspection of DMW components is too complicated due to its anisotropic behavior to ultrasonic beam propagation. Many researchers are working rigorously to model the grain orientation and ultrasonic beam skewing in DMW structures but still not completely resolved yet. This paper is intended to estimate the grain orientation with the help of numerical simulation for a given asymmetric DMW component with specified scatterers. The DMW is fabricated from austenite stainless steel and carbon steel base metals with austenite stainless steel filler metal using Gas Tungsten-Arc Welding. To study this research a finite element method (FEM) based numerical simulation has been used to exactly evaluate the grain structure. This model mainly depends on the elasticity matrix which is a function of the grain orientation and attenuation of ultrasonic energy of the weld. Iterative measurement of grain orientation using macrograph of the etched weldment with 5 × 5mm mesh size was carried out then the attenuated elasticity matrix was fed into the FEM COMSOL software model as input parameter. Result obtained from numerical simulation (time of flight and amplitude) are validated with the experimental result and good agreement (above 0.8 correlation coefficient) have been observed at higher iterations. This macro-graphic information based numerical model shows the potential to predict the grain orientation of DMW.

Twinning, grain orientation and texture variation of AZ31 Mg alloy during compression by EBSD tracing

In order to investigate the micro-mechanism of warm forming of Mg alloys, three specimens cut from a rolled AZ31 sheet were chosen to be compressed along the Rolling Direction (RD) at 100 °C, 170 °C and 230 °C, separately. During compression, an in situ measurement of grain orientation in the plane of RD × TD (Transverse Direction) was carried out with EBSD method. Experimental and analytical results show that temperature has remarkable impact on activation of twinning and variation of texture. As the temperature was raised from 100 °C to 230 °C, the number of grains with twins activated decreased substantially during deformation, and rolling texture varied from quick vanishing at 100 °C to always existing at 230 °C. Tracing for orientation of individual grains during deformation shows that there are obvious different orientation changes between grains with twins activated and those without twins activated. Twinning plays a significant effect on texture variation during compression. The extension twin variant really activated during deformation is the one with maximal Schmid factor.

Grain fabric of experimental gravity flow deposits

Grain fabric of deposits accumulated from a high-density surge-type gravity (turbidity) current in an experimental flume was measured. Vertical sequential change (0.2-mm interval) in imbrication shows that a bed can be divided into lower, middle, upper and uppermost parts. The lower part is characterized by both up-current and down-current imbrication with a wide range of angles. Dominant up-current imbrication and rare down-current imbrication characterize the middle part. The imbrication angle of this part tends to be smaller than in the lower part. The upper part is represented by intervals with up-current imbrication. Nearly flat imbrication is dominant in the uppermost intervals. Statistically significant preferred orientation was observed from the lower, middle and upper parts, and it deviates up to 13° in both clockwise and anticlockwise directions from the current direction. The lower and middle parts of the bed may correspond to the Bouma A-division judging from the wider range of imbrication angles and the presence of down-current imbrication which have been reported from natural turbidite beds. The upper part, which is characterized by up-current imbrication, is interpreted to be the Bouma B-division. The uppermost interval may coincide with the D-division. The episodically appearing down-current imbrication in the lower and middle parts can probably be attributed to oscillation of an interface between a denser basal layer and superjacent low-density layer of the turbidity current. Measurement of grain orientations in this and previous studies implies that at least 30° of deviation from the flow axis should be considered for paleoflow analyses based on grain fabrics.

Preferred Grain Orientation Relationships in Sintered Perovskite Ceramics

Sintered BaTiO3, SrTiO3, and Pb(ZrxTi1−x)O3 ceramics were examined using orientation imaging microscopy (OIMTM), which is a system for the automated measurement of grain orientations by evaluating electron backscatter diffraction patterns in scanning electron microscopy. As expected for sintered materials, none of the three materials exhibited a pronounced texture. However, analysis of the orientation relationships (ORs) between adjacent grains revealed a statistically significant preference of Σ= 3 ORs. Accordingly, the boundaries between grains with a Σ= 3 OR were particularly important for the macroscopic properties of the materials in question.

Automated Measurement of Grain Orientations and On-Line Determination of Complete Deformation Systems with a TEM

An automated computer technique for the indexing of spot or transmission Kikuchi patterns from any crystal structure has been developed. The patterns are recorded from the fluorescence screen of a PHILIPS EM 430 TEM with an integrating, Peltier cooled CCD camera (PULNIX TM 86QN) through a window from outside by replacing the focusing binocular. The frame-grabber board PCLL2 (SPINDLER & HOYER) has a resolution of 8 bit which corresponds to 256 grey levels. To reduce the high range of image contrastj a circular continuous density filter is positioned directly in front of the camera lens.

The measurement of grain orientations in an extruded electrode graphite using image analysis

A new image analysis method is described for determining the orientation of needle coke grains relative to the extrusion direction of a thermic electrode graphite, by measuring the orientation of volumetric shrinkage cracks lying parallel to the long axis of grains. The method is used to determine the orientation of grains as a function of radial position in a graphite log. The orientation of grains in the log with respect to the extrusion direction is greatest at the edge and decreases progressively towards the centre. This variation in grain orientation is attributed to effects of velocity gradients during the extrusion stage of manufacture.

Method for silt and sand fabric analysis in deep-sea cores

A method is described for the palaeomagnetic orientation of soft sediment cores to geographical north and the measurement of grain orientation in thin silt laminae and sand layers using a Scanning Electron Microscope. Successful application of this method to cores from the deep water margin of Nova Scotia permits a distinction between coarse layers deposited by downslope currents and those reworked by alongslope currents.

Grain Orientation in Determination of Paleocurrents and Sandstone Trends

Measurement of grain orientation in relatively large samples by means of Shell's dielectric anisotropy device is both rapid and reliable. It corresponds quite accurately to other paleocurrent indicators, such as parting lineation, rib-and-furrow structures, sole marks, and cross-bedding. Because grains are imbricated upcurrent, current direction can be inferred accurately from analysis of grain orientation in the vertical plane paralleling the horizontal grain fabric. Dielectric anisotropy measurements of partly impregnated Cimarron River sand depict very well recent local current directions of the river. Grain orientation is normal to the sandstone trend of the lowermost unit of the Eagle Sandstone at Billings, Montana. Grain imbrication in that barrier-bar sandstone suggests that oncoming surf was the most important depositing current during local westward accretion. Grain orientation in three lenticular Permian sandstone bodies in Oklahoma parallels or subparallels the sandstone trends. Because the horizontal component of grain orientation in horizontally bedded or cross-bedded sands statistically corresponds to current trend, remote measurement of grain orientation in a borehole could make possible the determination of sandstone trend from a single well. As suggested by Rodriguez and Pirson, adaptation of the dipmeter log offers an available tool for such a technique.

AN OPTICAL METHOD OF MEASURING GRAIN ORIENTATION IN SEDIMENTS

SUMMARYA new method is presented for the measurement of grain orientation in clastic sediments.The method is based on the principle that when an inclined beam of light passes through an elliptical hole in a plate of a certain thickness, the amount of light passing through depends on the orientation of the long axis of the ellipse with respect to the direction of incidence of the light beam. If such a plate is rotated in its own plane, the amount of light passing through will fluctuate. Such fluctuations are larger the greater the eccentricity of the ellipse, the amount of light passed being maximal when the long axis coincides with the plane of incidence of the light.If the plate contains many holes, which need not be elliptical but for the ease of reasoning can be approximated by ellipses, their main orientation direction can be inferred from the maximum intensity of passed light.It is shown in the paper that results of a similar kind can be obtained by using a black and white picture of the grain packing in combination with a mirror. These pictures can be obtained either from thin‐sections or from printed replicas of etched polished sections of impregnated samples.The resulting data represent an integrated orientation pattern instead of a long‐axis distribution pattern as given by the grain‐by‐grain counting technique.The new method has been thoroughly checked against the visual counting method. Excellent agreement was observed.