Simulation and evaluation of thermal fatigue cracking of hot work tool steels

My purpose here is to outline a method for calculating the fundamental behavior of speckle patterns in imaging systems. The theory of speckle displacement and decorrelation to include imaging at a general oblique angle is extended to more imaging systems, and explicit formulas are given for the image-point–object-point relationship that is important when defocused speckle is used. The intermediate results can be reused for optical systems other than those presented here. The image-speckle displacement analyzed in the three systems is expressed equivalently. The speckle decorrelation is in general larger in a single-lens system than in a two-lens system and can be minimized by proper design of the system.

Calculation of speckle displacement, decorrelation, and object-point location in imaging systems.

Holography, speckle, and computers

A laser range finder includes a laser and a photosensitive element. The laser projects a beam onto a target surface. A backscattered portion of the laser beam returns to the laser from the target surface and enters the laser emitting cavity. Variations in laser output power are detected by the photosensitive element, which provides a “beat” signal to a frequency detection circuit. The frequency detection circuit includes a difference frequency analog phase locked loop (DFAPLL) providing a purified form of the beat signal. The frequency of the purified beat signal is determined and used to calculate distance to the target surface.

Self-mixing laser range sensor

The paper describes the possibility of using the speckle pattern decorrelation for determination of small deformation tensor components of an elementary object surface area in an optical image field. The relationship between the small-deformation tensor and the speckle field displacement is analysed in detail. The studied problem is presented from the approximation viewpoint of both wave and geometrical optics.

Full theory of speckle displacement and decorrelation in the image field by wave and geometrical descriptions and its application in mechanics

We have improved the stability and temporal response of the laser speckle strain gauge that detects strain from speckle displacement caused by surface deformation. In the gauge, a narrow laser beam is incident on a diffuse surface, and speckle patterns appearing in the light scattered through the symmetrical angles are detected by a pair of linear image sensors. Speckle displacement is derived by a real-time correlator as the peak of the cross correlation between the current frame and a reference frame of the sensor driven at 1000 frames per second. The reference frame is fixed until the correlation peak becomes lower than a threshold. Using a pair of image sensors, followed by the correlators, and a laser of output power of a few tens of milliwatts, we could measure dynamic strain of polymer films at the frequency between a fraction of hertz and 100 Hz. The resolution of the gauge, which only depends on geometry of the optical system and the sensor pitch, is a few tens of microstrains. The upper limit of the measurement can be extended arbitrarily because small incremental strain is integrated.

Stabilized and accelerated speckle strain gauge

We have improved stability and temporal response of the laser speckle strain gauge. In the gauge a narrow laser beam is incident on a diffuse surface and speckle patterns appearing in the light scattered to certain directions are detected by linear image sensors. The correlator computes the correlation peak between the current frame and a reference one of the sensor which is driven at 1000 frames per second. The reference frame is fixed until the correlation peak becomes lower than a threshold. By employing a pair of the correlators and a laser of output power of a few tens of mW, we could measure dynamic strain of polymer films, between a fraction of Hertz and one hundred Hertz. The resolution of the gauge which only depends on geometry of the optical system and the sensor pitch, is a few tens of microstrains. The upper limit of the measurement can be extended arbitrarily much because small incremental strain is integrated.

Stabilized And Accelerated Speckle Strain Gauge

PURPOSE:To measure the Poisson's ratio of an object with a high accuracy by obtaining a difference between the correlated peak positions of the output of opposed image sensors and measuring strains in the x- and y- axis (two axes) directions of an object to be measured. CONSTITUTION:Laser light radiated from a semiconductor YLF laser 10 is led to the surface of a test piece 11. In a detector, one-dimensional image sensors 12, 12'; 13, 13' are arranged in positions theta=45 deg. and L=230mm as opposed to each other. Diffused reflected light generated from the test piece 11 is detected by the sensors 12, 12'; 13, 13' and video signals are outputted. Then, the outputs of the sensors are respectively led to correlation meters 14, 14'; 15, 15' and mutual correlation peaks with respect to a reference frame are calculated in real time. Then, differences between the correlation peak positions A of the outputs of opposed image sensors, namely, a difference between the outputs of the correlation meters 14 and 14' and a difference between the outputs of the correlation meters 15 and 15' multiplied by a constant are outputted to calculators 16 and 16', respectively, the values epsilonx and epsilony of strains in the x- and y-axis directions can be obtained.

Biaxial laser speckle strain gage

PROBLEM TO BE SOLVED: To provide a surface roughness measuring method by laser reflected light and its device capable of measuring surface roughness of a measuring object in a noncontact way without being influenced by the measuring surface such as the material or the shape of the measuring object, and measuring the surface roughness with a fixed accuracy regardless of experience of a measurer without damaging the surface of the measuring object. SOLUTION: A laser floodlight is tilted at a standard angle from the normal direction of the surface of the measuring object, and a laser beam is irradiated toward the surface of the measuring object. Then, the laser beam is irradiated, while the irradiation angle of the laser beam is changed from the standard angle by deflecting the laser floodlight in the tilted direction around the irradiation point to the measuring object of the laser beam, and simultaneously a granular spotted pattern which is reflected light of the laser beam is imaged by an imaging machine fixed in the direction opposite to the surface of the measuring object. The change of a changed granular spotted pattern which is a granular spotted pattern acquired when the irradiation angle of the laser beam is changed from the standard angle is measured based on a standard granular spotted pattern which is a granular spotted pattern acquired when the laser beam is irradiated from the standard angle. Hereby, the surface roughness of the measuring object is determined. COPYRIGHT: (C)2004,JPO

Koichi Kobayashi

Papers

Stabilized and accelerated speckle strain gauge

Stabilized And Accelerated Speckle Strain Gauge

Biaxial laser speckle strain gage

Surface roughness measuring method by laser reflected light and its device

Deformation measurement by electronic speckle correlation