To estimate weld quality of the resistance spot-welding, the acoustic emission features are investigated from the total acoustic emission signal at the single-spot weld. Typically, the resistance spot welding process consists of several stages: set-down of the electrodes, squeeze, current flow, forging, hold time, and lift-off. Various types of acoustic emission response corresponding to each stage can be separately analyzed by using back-propagation neural network classifier and wavelet transform technique. The presented machine learning results provide a validation for using back-propagation neural network and wavelet transform technique as a valuable insights into the resistance spot-welding process. Especially, a wavelet transform technique is demonstrated and the plots are very powerful in the recognition of the acoustic emission features

The purpose of this study is to determine more variables in welding characteristics of ATOS(steel for automobile structure) 80 high tensile steel available in market, and in terms of welding using GMAW(gas metal arc welding), this study seeks to examine how welding characteristics of ATOS 80 may vary depending on protrusion length of wire electrode. The major characteristics of this study can be summed up as follows, this study analyzed welding characteristics of ATOS 80 by changing the protrusion length of wire electrode (10㎜, 15㎜ and 20㎜) in welding section, and also used visual inspection and radiograph test to examine observations of major defects on welding section.

The purpose of this study is to determine more variables in welding characteristics of ATOS(Steel for Automobile Structure) 80 high tensile steel available in market, and examine how welding characteristics of ATOS 80 vary depending on changes in improvement angle of welding sections. In regard to major characteristics of this study, it focused on analyzing welding characteristics of ATOS 80 by changing improvement angle of welding sections into 40°, 50° and 60° and by changing root gap into 2㎜ and 3㎜. And it also used radiograph test to examine observations of major defects on welding section.

In this study, carbon/epoxy composite DCB(double cantilever beam) specimens based on K-means clustering and wavelet transform analyses are presented. For the fracture Mode I, the fiber orientation θ = [0 ]24 and θ = [±45]12 both shown up stable crack growth in DCB testing. For the fiber orientation θ = [0 ]24 , the continuous type AE signal showed at central frequency 130～270kHz, which means that matrix micro cracking was occurred. The Burst type AE signal was occurred at central frequency 200～300kHz due to fiber bridging and fiber breaking. Other burst type AE signals were occurred at central frequency 130～180kHz with very high amplitude due to fiber bridging. For the fiber orientation θ = [±45]12 , the burst type signal showed at central frequency 220～300kHz, which means that fiber breaking was occurred. Mixed type of burst and continuous signals were captured at central frequency 250～480kHz due to fiber friction.

This study investigated tensile deformation of the stress aging heat-treated SM45C steel which are aging temperature at 250℃ and 300℃; aging time at 1 hour and, 3 hours; applied load at 300N and 400N by using an acoustic emission techniques (AEs). A signal processing technology is applied to evaluate an AE source characterization of different AE measurement systems DiSP & PCI-2. In this study, most suitable aging condition appeared at 250℃, 3 hours and 300N. But in cases of 250℃, 3 hours, 400N and 300℃, 3 hours, 400N conditions, yield load decreased compare to other conditions according to the over-aging phenomena. On the other hand, when arranged via AE amplitude results by K-means clustering pattern recognition of AE raw signals, tendency of signal strength appeared non-heat treatment condition, 'Class 1 < Class 2 < Class 3'; optimal condition, 'Class 3 < Class 2'; over-aging condition, 'Class 3 < Class 2 < Class 1'. This is judged by emitting a lot of AE energy when material causes plastic deformation because ductility increases on factor by over-aging phenomenon.

The amount of cargoes by cargo vessels has increased tremendously during the last decade due to the great growth of korea economy. But in spite of this trend, there is rarely the substantial analyzed on the operational status of coastal shipping. In this paper, the characteristics of seaborne cargo and traffic flow of coastal shipping surveyed in detail through the statistical and the origintain and destination (O.D) analysis. Also, the basic ship's tonnage of coastal shipping representing the minimum tonnage which is capable of carrying the given seaborne cargo is suggested through the computer simulation using the data of 1985 year. The results are as follows; 1) the about 80% of total coastal traffic volume is going in/out to the port of Incheon, Busan, Pohang, Samil, Bukpyung, Mukho, Samchuk, and Jeju. 2) The main cargo items such as oil, iron material, cement, anthracite grain, fertilizer, other ore are reached to the about 70% of total amount of coastal trade. 3) ship's tonnage going in/out to the port of Bukpyiung, Busan, Pohang is increasing linearly year by year, and the amount of oil, iron material, cement, anthracite, grain, fertilizer, other ore are also increasing in linear pattern. 4) As a result of simulation, the optimum (basic) ship's tonnage.