Laser-speckle is a random granular pattern appearing in the light scattered from a laser-illuminated diffuse surface or in its image. When the roughness structure is finer than the size of the incident spot or that of resolution of the imaging system, the size distribution of speckles is independent of the roughness and depends only on the optical system. The pattern exhibits displacement accompanied by decorrelation as a result of surface displacement or deformation. It can be thus used as a distinct marking for deformation measurement, whose size can be adjusted by optical systems to match the resolution of image detectors such as CCD. After the appearance and the minimum size of speckle are explained for various surface roughness and optical systems, speckle displacement and decorrelation due to surface deformation are discussed with physical backgrounds. Applications to measurement of surface deformation are then described. The first category is speckle interferometry that delivers contours of surface displacement by speckle multiplication. The second one consisting of speckle photography and speckle correlation detects speckle displacement by optical Fourrier transformation of specklegrams and correlation analysis of vidco signals. The speckle correlation methnod has been installed to encoders and strain gauges.
A novel inteferometric method named as ‘statistical interferometry’ is described. In the method, in contrast to the conventional deterministic interferometry, the complete randomness of the interfering two light fields, i. e., therandom interference of the fully developed speckle fields, plays an essential role and is used as a standard of phase in a statistical sense. Some experiments of in-plane strain of object were conducted to demonstrate the validity of the method. As an experimental result, the accuracy of the measurements of strain was estimated to 10-7 strain with the spatial resolution <100μm. The method has the advantages of simplicity of the optical system required and at the same time providing high accuracy.
We investigated a method to evaluate fatigue damage and estimate fatigue life using laser without contact. When a low carbon steel is loaded cyclically, slipbands appear on the specimen surface and slipband density increases and thus the specimen surface changes with progress of fatigue damage. The present method intends to detect the surface change caused by fatigue observing pattern change of diffused light when a laser illuminates the specimen surface. In this study, we observed change of surface and investigated correspondence with diffused light pattern during fatigue loading. We derived experimental equati ons expressing the relation between change of speckle pattern due to loading cycles, stress amplitude and fatigue life. We proposed a method to estimate fatigue life using these relationships.
The PIV method, which enables to measure instantaneous velocity distributions from visualized pictures of flow, was developed from the speckle method. The speckle method is not suitable to measure fluid motion. In order to generate clear speckle pattern, densely distributed micro-size irregularities are indispensable, whereas realizing such condition is difficult in fluid flow. PIV method was born by the idea of using actual particle image instead of speckle pattern. It enables us to measure fluid velocity distributions so efficiently than any other existing measuring method. And the measuring method has been achieving a great advancement in the last ten years. The advancement has been supported by the advancement of small computers, imaging instruments and lasers.
Constant strain rate tests are made on iron in a strain rate range from about 1×10-3 to 2×104/sec at temperatures of 293K, 208K and 79K. At high strain rates, decremental strain rate tests are also performed. In order to evaluate the strain rate dependency of the dynamic flow stress over the wide strain rate range, activation energy E (τ) for deformation of pure iron obtained by Aono et al. is used. The deformation mechanism is controlled mainly by a thermally activated process of a formation of kink pairs, however below the strain rate of about 1/sec at 293K, it seems to be controlled by the thermally activated process of interaction of moving dislocations with forest ones.
Impact tests were carried out with two different kinds of golf balls, a two piece ball and a wound ball. Dynamic contact time between the ball and target was experimentally determined by using FSR (Force Sensing Resister) sensor. To examine the applicability of FSR sensor to the impact measurement, the experimental results werecompared with those obtained from a load cell and high-speed pictures taken by a Cranz-Schardin type camera. The results showed that FSR sensor is applicable to the appropriate measurement of the dynamic contact time, especially at impact velocities lower than 25m/s.
This study deals with a simultaneous visualization technique and image analysis of particle/bubble behavior on its position of the center of gravity, shape, and attitude of movement, in addition to flow field around it. In the multiphase flow field, the interaction between a particle/bubble and surrounding fluid or two-way effect is very important to understand complex phenomena of dispersed flow. Therefore, simultaneous visualization of both particle/bubble motion and surrounding flow has been requested. In addition, determination of the positions of the center of gravity of the particle/bubble and the velocity field obtained has been required. In the study, such a visualization technique and image analysis of particle/bubble motion was developed to determine the positions of its center of gravity and the flow field obtained. Furthermore, image analysis for obtaining particle/bubble behavior on its shape and attitude was settled in order to obtain basic data for discussing the elemental interaction. The results of measurement made using both the developed visualization system and the image analysis method show that adequate data are obtainable for discussing the interaction or two-way effect based on the composite of two images of particle/bubble and flow field.
Shell and tube heat exchangers are among the most commonly used type of heat exchangers in the power generation, the chemical process, and the air conditioning industries. Shell-side cross-flow in tube bundles have received less attention due to the flow complexity and the measurement difficulty. In this study, the object was aimed to clarify the flow structure by obtaining detail velocity data in the whole flow area crossing the tube bundles with Particle Image Velocimetry (PIV). Experiments were conducted using two types of model of in-line and staggered tube bundle with pitch-to-diameter ratio is 1.50, containing 20 rows of five 15.0mm O.D. tubes in each row. The velocity data at the spacing between tubes was measured successfully by adjusting refraction index of the working fluid to the same one of tube material. The flow features were characterized in different tube bundle configurations. The results show that the flow is separated the vortex area at the back of tubes from main stream in the case of in-line array, while velocity distribution is more uniform by flow mixing in staggered array. And also three representative patterns of vortex were observed in in-line array but only one pattern of vortex was observed in staggered array.