• Journal of the Korean Society for Precision Engineering
• /
• v.11 no.3
• /
• pp.105-121
• /
• 1994

In this paper, we proposed the two-parameter model for predicting the residual strength in CFRP laminated composites subjected to high velocity impact and developed and formulated it based upon Cparino's by using the ratio of impact and the normalized residual strength. Critical indentation was obtained by the statical indentation tests. Impact tests were carried out through air-gun type impact equipment with the velocities varied 30-100m/sec. Projectiles were steel balls with 5 and 7mm in diameter. Test material was carbon/epoxy. The specimens were composed of [ .+-. 45 .deg. /0 .deg. /90 .deg. ]$\_$2/ and [ .+-. 45 .deg. ]$\_$4/stacking sequences and had 0.75$\^$T/*0.26$\^$W/*100$\^$L/(mm) dimension. Results from the proposed model were in good agreement with the test data. And failure mechanism due to high velocity impact is given here to examine the initation and deveolpment of damage by fractography and ultrasonic image system. The effects of the 0 .deg. -direction ply position and the amount to damage area on the residual strength are considered here.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.43 no.12
• /
• pp.1116-1123
• /
• 2015

The lifetime of a geostationary satellite depends on the residual propellant amount and therefore the precise residual propellant gauging is very important for the mitigation of economic loss arised from premature removal of satellite from its orbit, satellites replacement planning, slot management and so on. In this paper, the thermal mass method and its uncertainty are described. The residual propellant analysis of a geostationary satellite is simulated based on the KOREASAT data and the uncertainty of thermal mass method is calculated by using the Monte Carlo method. The results of this study show the importance parameter of estimation residual propellant using the thermal mass method.

• Journal of Powder Materials
• /
• v.9 no.4
• /
• pp.235-244
• /
• 2002

The effects of residual impurities on solid state sintering of the powder injection molded (PIMed) W-15wt%Cu nanocomposite powder were investigated. The W-Cu nanocomposite powder was produced by the mech-ano-chemical process consisting of high energy ball-milling and hydrogen reduction of W blue powder-cuO mixture. Solid state sintering of the powder compacts was conducted at $1050^{\circ}C$ for 2~10 h in hydrogen atmosphere. The den-sification of PIM specimen was slightly larger than that of PM(conventional PM specimen), being due to fast coalescence of aggregate in the PIM. The only difference between PIM and PM specimens was the amount of residual impurities. The carbon as a strong reduction agent effectively reduced residual W oxide in the PIM specimen. The $H_2O$ formed by $H_2$ reduction of oxide disintegrated W-Cu aggregates during removal process, on the contrary to this, micropore volume rapidly decreased due to coalescence of the disintegrated W-Cu aggregates during evolution of CO.It can be concluded that the higher densification was due to the earlier occurred Cu phase spreading that was induced by effective removal of residual oxides by carbon.

• Journal of Ocean Engineering and Technology
• /
• v.10 no.2
• /
• pp.106-119
• /
• 1996

The ceramic has various high mechanical properties such as heat, abrasion, corrosion resistance and high temperature strength compared with metal. It also has low speciffic weight, low thermal expansibillity, low thermal conductivity. However, it could not be used as structural material since it is brittle and difficult for the machining. Therefore, there have been many researches to attempt to join ceramic with metal which is full of ductillity in order to compensate the weakness of ceramic.The problem is that residual stress develops around the joint area while the ceramic/metal joint material is cooled from high joining temperature to room temperature due to remarkable difference of thermal expansion coefficients between ceramic and metal. Especially, the residual stress at both edges of the specimen reduces the strngth of joint to a large amount by forming a singular stress field. In this study, two dimensional finite element method is attempted for the thermal elastic analysis. The joint residual stress of ceramic/metal developed in the cooling process is investigated and the change of joint residual stress resulted from the repetitive heat cycle is also examined. In addition, it is attempted to clarify the joint stress distribution of the case of tensile load and of the case of superposition of residual stress and actual loading stress.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.4
• /
• pp.677-682
• /
• 2002

Break-in is an intentional treatment to enhance the performance life of machinery parts and to maintain static friction behavior. Most studies on break-in have concerned only about surface conditions such as roughness or film formation. But the exact mechanism of break-in has not been found yet. Friction, scuffing behavior and wear of AISI 1045 were studied in relation to break-in and residual stress. The cylinder-on-disk type tribometer was used with the line-contact geometry. Scuffing tests were carried out using a constant load of 730N. In the break-in procedure the step load was applied from 100N to 200N. In this experiment, it was found that the break-in helps compressive residual stress to be formed well enough to enhance the scuffing life during the scuffing test. Specimens that had high compressive residual stress induced by shot-peening show better wear resistance than those were not shot-peened. Results of scuffing test, break-in procedure and wear amount in relation to residual stress have been discussed.

• Journal of Periodontal and Implant Science
• /
• v.31 no.1
• /
• pp.257-269
• /
• 2001

Removal of subgingival calculus is essential for the success in periodontal treatment. Subgingival instrumentation is used for the removal of all bacterial plaque and calculus. In this study, Gracey curet and Ultrasonic curet were used on single rooted teeth to conduct subgingval scaling and root planning. The remaining amount of calculus was evaluated according to type of instrument, depth of pocket, and tooth surface. 24 teeth were extracted from 14 patients being treated at department Periodontology Seoul Advantist dental hospital were used. Total 96 area(4 surface per teeth) were evaluated. 12 teeth treated with Gracey curet were used as the control group and the other 12 teeth treated with Ultrasonic curet were examined for experimental group. The 4 surface of the teeth(buccal, mesial, lingual or palatal, distal) were observed through the stereomicroscope and the images of the surface were captured and saved in CCD. The images were displayed on the monitor and the amount of calculus remained was evaluated by overlapping $10{\times}10$ grid pixel screen produced by Microsoft power point. The results evaluated were as follows 1. There was no statistically significant difference in residual calculus and tooth position following scaling and root planning of all group, but statistically significant correlation with residual calculus, probing depth, instruments and tooth surface. 2. There was statistically significant correlation between residual calculus and probing depth, but no statistically significant difference in residual calculus, tooth surface and tooth position on experimental(Ultrasonic curet) group. 3. There was no statistically significant difference in residual calculus according to the pre-treatment pocket depth and tooth position, but statistically significant correlation with tooth surface. The amount of residual calculus increase with mesial, distal, buccal and lingual(or palatal) surface on control(Gracey curet) group. 4. The Gracey showed better results than ultrasonic curet in mesial and distal surface, and there is significant difference. The results demonstrate that ultrasonic curet alone is inadequate for thorough subgingival debridement and suggest that Ultrasonic curet with Gracey curet should be more effective.

• Journal of the Korean Society for Environmental Technology
• /
• v.19 no.6
• /
• pp.536-542
• /
• 2018

A system combining an electrochemical method and an adsorption system using activated carbon was assessed to facilitate the reuse of cabbage-salting brine. IrOx/Ti insoluble catalyst electrodes were used in the experiment. The results were analyzed to identify any changes in the residual chlorine concentration according to variations in the current density at a salinity of 10 %, as well as the capacity of the activated carbon to adsorb the residual chlorine and organic matter. For current densities of $500A/m^2$ and $1,000A/m^2$, the residual chlorine concentration did not increase, instead stabilizing once the current reached 0.33 Ah/L. To assess the adsorption efficiency according to the residual chlorine concentration, the unit amount of the adsorption can be estimated from $Y=0.0066+2.087{\times}10^{-4}b$. For both residual chlorine generation using an electrochemical method and chlorine removal through activated-carbon adsorption, the unit amount of adsorption was 0.33 g/g. The maximum amount of $COD_{Cr}$ organic matter adsorbed by the activated carbon was 0.021 g/g, while for $COD_{Mn}$, the value was 0.004 g/g.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
• /
• v.2 no.1
• /
• pp.69-78
• /
• 1998

Contents of heavy metals (Cr, Cu, Zn, Cd, and Pb) in the sediments of Ulsan Bay were investigated by the sequential extraction methods that classifies heavy metals into five types of chemical forms: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual. The analytes were determined by using an ICP-MS. Total Cr concentrations in the sediments were in the range of 41.6-96.4, Cu 60.7-680, Zn 189-1954, Cd 33.1-83.4, and Pb 138-567 mg/kg. Results of sequential fractionation indicates that relatively high proportion $(\~44\%)$ of Cu is associated with organic matter A large proportion of Pb is associated with three types of chemical forms: Fe-Mn oxides, organic matter, and residual. There were significant correlation in concentrations between the exchangeable components and total organic carbons. The heavy metals in the residual phase cannot be easily released to the environment since these are bound to the crystal lattice. But, reducible and organic Phases cfn a significant amount of most heavy metals. Therefore. there is potential danger of a substantial amount of metals becoming chemically mobile with environmental changes.

• The Korea Journal of Herbology
• /
• v.21 no.4
• /
• pp.37-41
• /
• 2006

Objectives : This study has been conducted to investigate the amount of residual pesticide in herbal medicine of Osterici Radix which are purchased on Kwangju(Hanyaksarang). Methods : In order to analyze many pesticides in Osterici Radix, simultaneous multi-residue analysis of pesticides by GC-ECD/NFD was used. Results : But the amount of residual pesticide in Osterici Radix, simultaneous multi-residue analysis of pesticides by GC-ECD/NFD was used. Conclusion : These results indicate that Osterici Radix in current has safety. In future, it is considered the results of this study will be furnished the basis to succeeding studies and it is needed to extensive comparative study for the same genus-degree of relatedness.

• Journal of Welding and Joining
• /
• v.3 no.2
• /
• pp.16-26
• /
• 1985

Post weld heat treatment(PWHT), at more than 600.deg. C, is essential to remove residual stress and hydrogen in weld HAZ and improve fatigue characteristics. However, residual stress during PWHT is responsible for PWHT embitterment and it promotes precipitation of impurities to grain boundary. In this paper, the effect of stress simulated residual stress on fatigue failure was evaluated by fatigue test, microhardness test and fractograph. The obtained results are summarized as follows; (1) The fatigue crack growth rate(da/dN) of parent and heat treated parent was affected by microstructure due to heat treatment and it depended on stress intensity factor (.DELTA.k). (2) The fatigue strength of weld HAZ was dependent on applied stress during PWHT and da/dN after PWHT was slower than as-weld. (3) Softening amount of weld HAZ was bigger than any other due to PWHT. Hardness value of weld HAZ was affected by heat treatment under the applied stress of 10 $kgf/mm^2$, but beyond 20 $kgf/mm^2$ it was increased by the applied stress rather than heat treatment. (4) Beyond the applied stress of 20 $kgf/mm^2$ during PWHT, intergranular fracture surface was observed and its amount was increased with applied stress during PWHT. (5) Effect of applied stress during PWHT on aspect of fracture surface was larger rather than that on fatigue crack growth behavior.