• Journal of the Korea Concrete Institute
• /
• v.24 no.6
• /
• pp.695-703
• /
• 2012

Recently, major infrastructure such as bridges, tunnels, PCCVs (Prestressed Concrete Containment Vessel), and gas tanks are Prestressed Concrete (PSC) structure types, which improve their safety by using confining effect from prestressing. Generally, concrete is known to be an outstanding fire resistant construction material. Because of this reason, researches related to extreme fire loaded PSC member behaviors are not often conducted even though PSC behavior under extreme fire loading is significantly different than that of ordinary reinforced concrete (RC) behavior. Therefore, in this study, RABT fire loading tests were performed on bi-directionally prestressed concrete panels with $1000{\times}1400{\times}300mm$ dimensions. The prestressed specimens were applied with 430 kN prestressing (PS) force using unbonded PS thread bars. Also, residual strength structural tests of fire tested PSC and ordinary RC structures were performed for comparison. The study results showed that PSC behavior under fire loading is significantly different than that of RC behavior.

• Journal of the Society of Disaster Information
• /
• v.11 no.4
• /
• pp.520-526
• /
• 2015

Reinforcing bar splices are inevitable in reinforced concrete structure. In these days, there are three main types of splices used in reinforced concrete construction site - lapped splice, mechanical splice and welded splice. Low cost, practicality in construction site, less time consuming and high performance make gas pressure welding become a favorable splice method. However, reinforcing bar splice experiences thermal loading history during the welding procedure. This may lead to the presence of residual stress in the vicinity of the splice which affects the fatigue life of the reinforcing bar. Therefore, residual stress analysis and tensile test of the gas pressure welded splice are carried out in order to verify the load bearing capacity of the gas pressure welded splice. The reinforcing bar used in this work is SD400, which is manufactured in accordance with KS D 3504. The results show that the residual stresses in welded splice is relatively small, thus not affecting the performance of the reinforcing bar. Moreover, the strength of the gas pressure welded splice is high enough for the development of yielding in the bar. As such, the reinforcing bar with gas pressure welded splice has enough capacity to behave as continuous bar.

• Journal of Korean Society of Steel Construction
• /
• v.24 no.4
• /
• pp.479-490
• /
• 2012

Flexural tests on full-scale H-shaped beams, built up from high-strength steels (HSB800 and HSA800) with a nominal tensile strength of 800 MPa, was carried out to study the effect of flange slenderness of high-strength steel on flexural strength and rotation capacity. The primary objective was to investigate the appropriateness of extrapolating current stability criteria (originally developed for ordinary steel) to high-strength steel. The performance of high-strength steel specimens was very satisfactory from the strength, but not from the rotation capacity, perspective. The inferior rotation capacity of high-strength steel beams was shown to be directly attributable to the absence of a distinct yield plateau and the high yield ratio of the material. Residual stress measurements reconfirmed that the magnitude of the residual stress is almost independent of the yield stress of the base metal.

• Journal of Korean Society of Steel Construction
• /
• v.27 no.4
• /
• pp.377-386
• /
• 2015

In this study, inelastic buckling strength of HSA800 steel columns were tested to investigate the applicability of current column curve (KBC2009, 2010 AISC-LRFD) to HSA800 steel. Key test variables included width-thickness ratio, plate-edge restraints, and column slenderness ratio. Specimens made of ordinary steel (SM490) were also tested for comparison purposes. All the concentrically loaded HSA800 specimens exhibited sufficient buckling strength compared to the current column curve, but some of SM490 specimens showed understrength. This difference can be explained by the lower residual stress present in HSA800 specimens.

• Journal of the Korean Vacuum Society
• /
• v.6 no.2
• /
• pp.151-158
• /
• 1997

Nitrogen incorporated diamond-like carbon films were deposited by r.f. glow discharge of mixtures of benzene and ammonia gases. Mechanical properties, composition and atomic bond structure were investigated when the fraction of ammonia increases from 0 to 0.79 and the negative self bias voltage of cathode from 100 to 900 V. Both the residual compressive stress and the hardness decrease from 1.7 to 1.0 GPa and from 2750Kgf/$\textrm{mm}^2$ to 1700Kgf/$\textrm{mm}^2$, respectively. In addition to hydrogen, triply bonded nitrogens also play a role of teminal sites of the three dimensional atomic bond network. By considering the hydrogen concentration and the nitrogen bond characteristics, it can be shown that the mechanical properties of the films are determined by the content of three dimensional inter-links of $sp^2$ clusters. Although the mechanical properties are affected by the nitrogen addition, its depedence on the negative bias voltage is qualitatively identical to that of pure diamond-like carbon films.

• Composites Research
• /
• v.27 no.3
• /
• pp.90-95
• /
• 2014

Cure shrinkage during cure process of polymer matrix composites develope residual stress that cause some structural deformation, such as spring-in, spring-out and warpage. The carbon/epoxy prepreg used in this study is Hexply M21EV/34%/UD268NFS/IMA-12K supplied by Hexcel corp. Cure shrinkage and degree of cure measured by TMA(thermomechanical analyzer) and DSC(differential scanning calorimetry). Cure shrinkages are measured by TMA within a temperature range of $140{\sim}240^{\circ}C$ in a nitrogen atmosphere, and degree of cure determined by the heat of reaction using dynamic and isothermal DSC runs in argon atmosphere. As a result, the cure shrinkage is increased dramatically in a degree of cure range between 27~80%. the higher the cure temperature, the lower the degree of cure occurring to begin cure shrinkage.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.11a
• /
• pp.439-442
• /
• 2009

In this study, the residual strength of CFRP filament winding pressure vessel after low velocity impact was evaluated quantitatively. After impact test, the pressure vessel was sectioned to produce 25 mm-wide ring specimen and the bursting pressure of this specimen was measured. A finite element model was also fabricated to investigate the deformation and stress distribution characteristics of the impacted CFRP vessel. The degradation of the residual strength along with the increase of impact energy was successfully measured and reviewed.

• Journal of Ocean Engineering and Technology
• /
• v.16 no.3
• /
• pp.54-58
• /
• 2002

This study investigates a relationship between fracture mechanics parameters (Stress Intensity Factor Range: ΔK, Maximum Stress Intensity Factor; Kmax) and X-ray parameters (residual stress:$\sigma$r half-value breadth: B) for SG365 steel at elevated temperature up to 30$0^{\circ}C$. The fatigue crack propagation test were carried out and X-ray diffraction technique according to the direction of crack length was applied to fatigue fractured surface. The residual stress on the fracture surface was found to increase at low ΔK region, to reach a maximum value at a certain value of Kmax or ΔK and then to decrease. Residual stress was independent of stress ratio by arrangement of ΔK and half value breadth were independent of the arrangement of Kmax. The equation of $\sigma$r-ΔK was established by the experimental data. therefore, fracture mechanics parameters could be estimated by the measurement of X-ray parameters.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2002.05a
• /
• pp.117-124
• /
• 2002

The lightness of components required in automobile and machinery industry is requiring high strength of components. In particular, manufacturing process and new materials development for solving the fatigue fracture problem attendant upon high strength of suspension of automobile are actively advanced. In this paper, the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in high temperatures($100^{\circ}C,\;150^{\circ}C,\;180^{\circ}C$) was investigated with considering fracture mechanics. So, we can obtain followings. (1) Compressive residual stress is decreased in high temperature, that is, with increasing temperature. (2) The effect of compressive residual stress on fatigue crack growth behavior in high temperature is increased below ${\Delta}K=17{\sim}19MPa\sqrt{m}$. The fatigue crack growth rate is increased with increasing temperature. The fatigue life is decreased with increasing temperature. (3) The dependence of temperature and compressive residual stress on the parameters C and m in Paris' law formed the formulas such as equations (3),(4),(5),(6),(7),(8),(9),(10). (4) It was investigated by SEM that the constraint of compress residual stress for plastic zone of fatigue crack tip was decreased in high temperature as compared with room temperature.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.1
• /
• pp.200-207
• /
• 2003

In this paper, the effect of the compressive residual stresses which were obtained under the various shot velocities of shot balls on the fatigue behaviors of a spring steel, were investigated. The examination of CT specimen test were executed with the materials(JISG SUP9) which are being commonly used for the springs of automotive vehicles. As a result, the optimal shot velocity of shot balls were acquired considering the peak values of the compressive residual stresses on the surface of specimen and effect on the speed of the fatigue crack propagation da/dN in stage II and the threshold stress intensity factor range Δ$K_{th}$ in stage I. Also the material constant C and the crack propagation index m in the formula of paris law da/dN= C $({\Delta}K^m)$ were suggested in this work to estimate the dependency on the shot velocity.