• Journal of Korean Society of Steel Construction
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• v.14 no.5 s.60
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• pp.613-625
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• 2002

This paper aimed to investigate the damage process of steel parts experiencing failure under strong repeated loading. Likewise, a damage index using various factors related to the damage was proposed. An analysis method for evaluating the damage state was also developed. The damage assessment method focused on the local strain history at the cross-section of the heaviest concentration of deformation. Cantilever-type steel parts were analyzed under uniaxial load combined with a constant axial load, considering horizontal displacement history, Loading patterns and steel types were considered as the main parameters in analyzing the models. The effects of the parameters on the failure modes, deformation capacity, and damage process as seen from the analysis results were also discussed. Each failure process was compared as steel types. In addition, the failure of steel parts under strong repeated loading was determined according to loading. Results revealed that the state of the failure is closely related to the local plastic strain.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.155-159
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• 2000

Microstructural processes during high cycle fatigue are investigated according to plastic-strain hardening, crack formation, crack propagation and fracture. It is shown that the fatigue test resembles the uniaxial tensile test. The logarithm of the number of cycles to failure is proportional to the elongation in the tensile test. Under high cycle fatigue test, the strain is normally elastic. If the strain is absolutly elastic, fatigue could not result. But this is over simplication. Nearly all metals undergo a minor amount of plastic strain even at low stress. Damage accumulation leadling to crack formation can continue in the persistent slip bands at very low average plastic strain amplitude. In the ten­s sile test the overall specimen follows the failure procedure whilst in the high cycle fatigue test the local persistent slip band follows the failure procedure. However accumulations of strain per unit volume in the deforming region before failure in both cases are equal locally.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.72-78
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• 2007

A diesel particulate filter causes progressive increase in back pressure of an exhaust system due to the loading of soot particles. To maintain the pressure drop caused by DPF under proper level, a regeneration process is mandatory when excessive loading of soot is detected in the filter. It is a major reason why the relation between the amount of soot and the pressure drop in a DPF becomes crucial. On the other hand, pressure drop varies with not only the soot loading but also conditions of exhaust gas such as mass flow rate. Therefore, the relation among them becomes complicated. Furthermore, the characteristics of heat transfer in a DPF is another crucial parameter in order for the filter to avoid thermal crack during regeneration period. This study presents characteristics of pressure drop under various conditions of soot loading and mass flow rate in catalyzed diesel particulate filter. This study also shows characteristics of heat transfer in DPF when high temperature gas flows into the filter. Experiments reveal that the soot loading and mass flow rate affect characteristics pressure drop independently. Experiments also indicate that the amount of coating material has little influence on pressure drop with changes in soot loading and mass flow rate. However, increased catalyst coating may lead to the improved heat transfer which is efficiency to reduce thermal stress of the filter.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.1-9
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• 2008

Fiber Reinforced Polymer (FRP) composites are used extensively in aerospace, marine, automotive, infrastructure, chemical processing and sporting good applications. A concern with using FRP composites in some engineering structures is their high flammability and poor fire resistance In this research, material properties of FRP composites at increasingly high temperatures was measured and verified. The obtained mechanical properties of FRP composites were performed according to ASTM D3039/D3039M and tested to a wide range of heat conditions with temperatures from Room-temp. to 300 for times up to 30 min. It is found that the mechanical properties of FRP composites dropped with increasing heat or temperature. The reduction to the properties was due mainly to thermal degradation and combustion of the polymer matrix.

• Journal of the Korean Society of Safety
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• v.21 no.1 s.73
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• pp.92-95
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• 2006

This study is to find out how column with hole is behaved, compared to the normal one without hole. There might be existing buildings to make holes in the reinforced concrete column. Columns are made with commercially used compressive strength $240kg/cm^{2}$, air amount 5.0%, using re-bar of diameter D13 and D10 having yielding stress $4,000kg/cm^{2}$. The specimen were cured with temperature of $21{\pm}3^{\circ}C$. All specimens of five variables and all holes are geometrically considered and configurated. D3, D5 mean diameter 3cm and 5cm respectively. H1, H2 are the number of holes. Compressive pressure was forced in accordance with KS, following $0.6{\pm}0.4N/mm^{2}$ speed. Main re-bar's were strained with almost same shape through all the specimens. Hole diameter 5cm-having specimen showed cracking around hole. strains of back and front gauges of the specimen were showed similarly. Specimen having two holes in left and right from longitudinally axis resisted 7% less than the one having hole centrically from longitudinal axis. One hole having specimen with diameter 5cm resisted only 3% less than in case of 3cm diameter hole. Hole having in left and right from longitudinal axis will be less resistant than the case longitudinally arranged. Diameter 3cm hole showed less 10% capacity than normal one without hole. Capacity loss difference between diameter 3cm and 5cm showed almost none in case that they are arranged longitudinally.

• Journal of the Korean Society of Clothing and Textiles
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• v.26 no.11
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• pp.1672-1681
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• 2002

To evaluate the thermal environments and the workload of farmers in the rice field in summer, this study investigated rice farmers' physiological, psychological responses, work postures, work clothes, air temperature and air humidity during the spraying pesticide in the rice field. Five career farmers (3 males, 2 females) volunteered as the subjects. During the spraying pesticide in the rice field, physiological responses were monitored continuously. The results were as follows. l. Farmers wore only raincoats not pesticide-proof clothing. 2. The value of WBGT, rectal temperature($T_{re}$), mean skin temperature(${\={T}}_{sk}$) were $24.9∼28.9^{\circ}C,\;37.8({\pm}0.3)^{\circ}C\;and\;33.6({\pm}0.6)^{\circ}C$, respectively. Clothing microclimate temperature($T_{cl}$) on the chest and back were $32.5({\pm}2.6)^{\circ}C\;and\;33.6({\pm}2.6)^{\circ}C$, respectively(p<0.00l). Humidity inside of the clothing ($H_{cl}$) was over 80%RH and heart rate(HR) was 112(${\pm}27$)bpm. We evaluated that the spraying pesticide was 'heavy work' by the Tre and HR. To four subjective questionnaires, all farmers expressed 'hard, hot, humid and uncomfortable' without individual difference at the end of works. We suggested that 1) the spraying pesticide in the rice field was a heavy work, 2) because the workload of farmers in the raincoat/pesticide-proof clothing can't be evaluated by only WBGT, assessors should measure physiological, psychological responses as well as thermal environments, 3) to alleviate farmers' heat strain, clothing manufacturers must consider not only the improvement of textile materials and clothing weight but also the designing of personal cooling equipment.

• Journal of the Korean Society of Clothing and Textiles
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• v.28 no.5
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• pp.713-722
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• 2004

This study examined the effects of two kinds of functional sun hats through a head-manikin test and a climatic chamber trial for farm workers in summer. Experiment was composed of four conditions. The first condition was the condition without any hat (Control). The second was the condition with a sun hat on the market (Hat A). The third was the condition with a functional sun hat made of reflective fabric (Hat B). The last was the condition with a functional sun hat having a ventilating structure as well as reflective fabric (Hat C). For the subjects in the climatic chamber trials, 12 healthy males volunteered. Air temperature, relative humidity and globe temperature in the chamber was maintained at $33{\pm}0.5^{\circ}C,\;65{\pm}5%RH\;and\;39{\pm}1^{\circ}C\;(WBGT\;33^{\circ}C)$. Subjects did a simulated red pepper-work (50-min work and 10-min rest, twice repetition) for 120 min. As the result of head-manikin test, the surface temperature on middle of back-neck was the lowest in Hat B of four conditions and the surface temperature on top of head was the lowest in Hat C. As the result of climatic chamber trials, there were apparent differences between with (Hat A, Hat B, Hat C) and without a sun hat (Control). In rectal temperature ($T_{re}$), mean skin temperature ($\={T}_{sk}$), heart rate (HR), total sweat rate (TSR), The physiological heat strain was less in the condition with hats than in the condition without a sun hat. As the increasing rate in Tre, Hat B is the most effective hat for alleviation heat strain. As the subjective responses, Hat B was the most effective hat for thermal comfort even though the difference was not significant. Hat C was less effective than Hat B and the reason might be the increase of weight due to inserting the ventilating structure.

• Development and Reproduction
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• v.13 no.3
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• pp.199-205
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• 2009

HSP70 has widely been induced in in vivo hyperthermia conditions in various organisms to study gene regulation and recently neuroprotectve roles of the induced gene expression under varying conditions. We investigated different responses among various tissues in zebrafish under heat shock to evaluate whether spatial and temporal expression pattern of zebrafish (z) hsp70 in transcriptional and translational level under heat shock stress in different brain regions. Heat shock groups were given for 1 h at $37^{\circ}C$ after recovery by transferring the treated animals back to $28^{\circ}C$ for 1, 2 and 24 h for recovery, respectively. Control (CTRL) group was kept at $28^{\circ}C$. At the end of treatments, five animals were collected and used for isolation of total RNAs and peptides from the corresponding tissues. Expression of zhsp70 mRNA showed different patterns in recovery periods in the tissues including the brain, eye, intestines, muscles, heart and testis by RT-PCR. Unlike the RT-PCR analysis, Northern blot analysis demonstrated nearly 30-fold increase in zhsp70 at 1 h heat shock, suggesting that RT-PCR may not be appropriate in unmasking regulation of the time-dependent zhsp70 expression. In the experiment involving different brain regions, the cerebellum showed gradual activation at 1 h to R1h and decreases in R2h and R24h, while the medulla oblongata and optic tectum showed gradual increase at R1h and decrease at R24h, indicating that different brain tissues respond specifically to heat shock in inducing zhsp70 and recovering from the heat shock status. Western blot analysis also demonstrated that the intracellular levels of zHSP70 in three different brain regions including the cerebellum, medulla oblongata and optic tectum are differently induced and recovered to normal state. These results clearly demonstrate that different regions of the body and the brain tissues are responding differently to heat shock in the aspects of its level of expression and speed of recovery.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.4
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• pp.237-242
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• 1993

The fatigue behaviors of mechanically alloyed Al-4Mg alloys dispersed with either $Al_2O_3$ or $MgAl_2O_4$ oxide particles were investigated. This study maily concerned with the role of coherency of dispersed particles with the matrix on the fatigue behavior of the alloys. The $MgAl_2O_4$ which has a spinel structure with the lattice parameter of exactly the twice of Al showed the habit relation with the matrix. The mechanically alloyed Al-4Mg alloys showed stable stress responses with fatigue cycles from start to failure regadless of strain amplitudes and of existence of dispersoids. The Al-4Mg alloy dispersed with $MgAl_2O_4$ showed not only the better static mechanical properties but also the better low cycle fatigue resistance than that with $Al_2O_3$, i.e., much higher plastic strain energy dissipated to failure, at low strain amplitude. However, this alloy showed inferior fatigue resistance to that dispersed with $Al_2O_3$ or that without dispersion at high strain amplitude. These results imply that $MgAl_2O_4$ may promote lowering the stacking fault energy of the alloy inherited from the coherency with the matrix so that dislocations shuttle back and forth on the same slip plane without cross slipping to other planes during fatigue at low strain amplitude resulting in long fatigue life.

• Journal of the Korean Geosynthetics Society
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• v.2 no.2
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• pp.13-24
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• 2003

This paper presents the results of investigation on the effects of foundation stiffness and surface loading on the performance of soil-reinforced segmental retaining walls using the finite element method of analysis. A parametric study was performed by varying the foundation stiffness and the location of surface loading. The results of the analyses indicate that the wall deformation and reinforcement tensile load tend to increase with decreasing foundation stiffness with little variation in the horizontal and vertical stress distributions at the back and the base of the reinforced soil zone. Also revealed is that the increment of reinforcement tensile load due to the presence of surface load may be significantly over-estimated when using the conventional approach. Furthermore, the external stability should be carefully examined when a surface loading is present just behind the reinforced soil zone. The implications of the findings from this study to current design approaches are discussed in detail.