Seung Seok Lee

Measurement of grain moisture content using microwave attenuation at 10.5 GHz and moisture density

The dielectric properties of Korean short-grain rough rice, brown rice and barley with moisture content ranges of 11% to 27%, 11% to 18%, and 11 to 21%, wet basis, respectively, were characterized to develop a prototype grain moisture meter using microwave attenuation at 10.5 GHz and moisture density. A third-order polynomial regression model was proposed to describe the relationship between dielectric properties and moisture density. The prototype grain moisture meter consisted of a dielectric resonator type oscillator of 10.5 GHz, horn antenna, rectangular sample holder, load cell, temperature sensor, detector, and digital voltmeter. The calibration equation for measurement of grain moisture content was developed and estimated with Korean short-grain rough rice (12% to 26%). The coefficient of determination, standard error of prediction (SEP), and bias were 0.986, 0.52% moisture content and 0.07% moisture content, respectively.

Noncontact detection of ultrasonic waves using fiber optic Sagnac interferometer

This paper describes a fiber optic sensor suitable for noncontact detection of ultrasonic waves. This sensor is based on the fiber optic Sagnac interferometer, which has a path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. Ultrasonic oscillations produced by conventional ultrasonic piezoelectric transducers were successfully detected, and the performance of this interferometer was investigated by a power spectrum analysis of the output signal. Based on the validation of the fiber optic Sagnac interferometer, noncontact detection of laser-generated surface waves was performed. The configured Sagnac interferometer is very effective for the detection of small displacement with high frequency, such as ultrasonic waves used in conventional nondestructive testing (NDT).

ON-LINE MEASUREMENT OF GRAIN MOISTURE CONTENT USING RF IMPEDANCE

The dielectric properties of Korean short– and medium–grain rough rice, brown rice, barley, and wheat with moisture ranges of 11% to 27%, 11% to 18%, 11% to 21%, and 11% to 22%, wet basis, respectively, were characterized at 1 to 10 MHz for use in developing a prototype on–line moisture meter using RF impedance and moisture density (moisture content . bulk density). Moisture density was a materially significant parameter for moisture measurement. A linear regression model including oscillation frequency of the LC oscillator, moisture density, and grain temperature indicated coefficients of determination of 0.985 for rough rice, 0.934 for brown rice, 0.996 for barley, and 0.991 for wheat. The root mean square error of an on–line moisture meter was .0.40% moisture content, wet basis, compared with the oven method for moisture determination.

Elastic constants determination of thin cold-rolled stainless steels by dynamic elastic modulus measurements

Temperature dependence of elastic constants of thin cold-rolled stainless steel has been measured by using the acoustic resonance method. Identification of the vibration mode has been examined numerically and experimentally. The elastic constants at room temperature have also been measured by the pulse echo method. In addition, the texture effect on the elastic constants has been analysed by assuming the specimen has orthorhombic structure.

Non-contact detection of laser-generated surface acoustic waves using fiber optic Sagnac interferometer

A high powered Q-switched Nd:YAG laser was used to excite the surface waves, and an optical fiber sensor was used to detect the out-of-plane displacements due to the propagating waves. This sensor is based on the fiber optic Sagnac interferometer, which has the path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence in an optical path using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. The performance of the fiber optic Sagnac interferometer was investigated, and laser-generated surface wave signals were detected using this fiber optic sensor. The developed fiber optic sensor configured in this study is very simple and is effective for non-contact detection of ultrasonic waves.

Effect of microstructure of low carbon steels on ultrasonic attenuation

The ultrasonic attenuation in low carbon steel with 0.04 wt% C to 0.80 wt% C was measured over a frequency range of 5 to 15 MHz, and the effects of the carbon content and normalizing temperature were analyzed. In pure iron, the attenuation is determined from the average grain size, which increases as the normalizing temperature increases; there is a noticeable effect caused by a few large grains. In the case of the hypoeutectoid steels, the proeutectoid ferrite grain, the size of which depends on prior austenite grain size, acts as the main scatterer. The prior austenite grain size increases as the carbon content decreases and the normalizing temperature increases. The colony is responsible for scattering in the eutectoid steel; scattering by pearlite is greater than that by ferrite.

Microstructural Characterization of Creep Damaged 11Cr-3.5W-3Co Steel

The effects of the precipitate and martensite lath on the softening behavior have been investigated for 11Cr-3.5W-3Co steel during creep at 700. During creep, the precipitate on the PAG (prior austenite grain) boundaries and martensite lath boundaries coarsened. The recovery of dislocation density and an increase of martensite lath width took place. It is shown that the inverse of the size of the precipitates and the inverse of the square root of the martensite lath width have a linear relation with the Vickers hardness, which corresponds to the Hall-Petch relation and particle looping mechanism.

Characterization of delamination in titanium nitride coating on steel using acoustic microscopy

Wear resistance of Titanium Nitride (TiN) coating on steel is partly influenced by delamination located beneath the surface. Acoustic microscopy is particularly suited to analyze the subsurface defects. To examine the delamination defects introduced by sliding contacts in TiN coating on steel the Lamb wave velocities have been measured by V(z) curves and compared with the theoretically calculated velocities from dispersion curves.

Cure Monitoring and Stress-Strain Sensing of Single-Carbon Fiber Composites by the Measurement of Electrical Resistance

Cure monitoring and stress-strain sensing of single-carbon fiber composites were nondestructively evaluated by the measurement of electrical resistance. The difference of electrical resistance before and after curing increased highest when gauge length of the specimen was the smallest. As curing temperature increased, the electrical behavior of steel fiber was different from that of semi-conductive carbon and SiC fibers. Residual stress built in the fiber was the highest at the fiber axis direction. Whereas residual stress built in the matrix was relatively high at the fiber circumference and radius directions. Residual stress calculated from the experiment was consistent with the results from the finite element analysis (FEA). The strain at low curing temperature was larger than that of higher temperature until the load reached maximum value. The apparent modulus of the electrodeposited composites was higher than that of the untreated composites due to the improved interfacial shear strength (IFSS). The electrical resistance was responded quantitatively with stress-strain behavior during the test. Electrical resistance measurement can be feasible nondestructive techniques to evaluate cure monitoring and stress-strain sensing in the conductive fiber composites.

Simultaneous Detection of Size and Depth of Embedded Reinforcement in Concrete by Arraying Sensing Coils in a Probe

This study suggests an electromagnetic method for simultaneous detection of the size and depth of embedded reinforcement in concrete by using a developed probe with multiple sensing coils. The probe is made so that the sensing coils are located at the inside and the outside of an exciting coil. The signal characteristics of the sensing coils are investigated with the aid of an LCR meter. By using a commercial eddy current test system, with the developed probe, we simultaneously evaluated the size and cover depth of reinforcement. The voltage amplitudes of the sensing coils in contrast to the concrete cover depths show a unique value for each depth and size of reinforcement.