• Journal of the Korea Concrete Institute
• /
• v.22 no.6
• /
• pp.753-760
• /
• 2010

Ultra high performance concrete (UHPC), is characterized by its high compressive strength and advanced tensile behavior that is much superior to those of conventional concrete. In order to apply this new material in practice, the bond characteristics of UHPC were evaluated in this study. Pull-out tests between UHPC and deformed steel rebar were carried out according to the modified RILEM test method, and were verified by finite element analysis. From the test results showed that UHPC presents 5 to 10 times higher bond strength compared to normal strength concrete, this study suggested remarkably reduced development length and concrete cover comparing to existing specifications. The test results of 700 MPa high strength steel rebar demonstrated the applicability of high strength steel to UHPC. In addition, the transfer length measurements of seven-wire strand in UHPC specimens indicated that the transfer length limit set by the current design code is very conservative for UHPC.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.05a
• /
• pp.5-8
• /
• 2002

The use of the co-cured joining method for composite structures is attractive due to several benefits. However, since the design stress level in cyclic loads is often smaller than the joint strength obtained from the static tensile load test, it is important to establish proper fatigue design criteria. Although some researchers have reported on co-cured joints, there are only a few papers published on the fatigue characteristics of co-cured joints. In this paper, the effect of bond parameters on the fatigue characteristics of a steel-composite co-cured double lap joint under cyclic tensile loads was experimentally investigated. We considered the surface roughness of the steel adherend and the stacking sequence of the composite adherend as bond parameters. A fatigue failure mechanism of the co-cured double lap joint was explained systematically by investigating the surfaces of failed specimens.

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.33 no.1
• /
• pp.38-44
• /
• 2001

The effects of refining load on the paper properties were investigated. HwBKP, SwBKP and SwUKP were refined with PFI mill at the load of 3.33 N/mm and 6.00 N/mm. Higher Scott bond was obtained at the higher refining load for three pulp used in this study. However any changes in the light scattering coefficient with the change of refining load were not observed. Although the effect of refining load on the formation index for SwUKP was not observed, higher refining load gave the better formation for HwBKP and SwBKP. The fiber mass and fiber crowding factor were not affected by the refining load. Higher apparent density and tensile index were obtained with the higher refining load. However, the higher refining load did not improve the tensile index at the same apparent density. The tear index was decreased with the increase of refining load.

• Journal of Welding and Joining
• /
• v.8 no.4
• /
• pp.58-68
• /
• 1990

The formation of thermal stresses by plasma spraying is generally considered as adverse. Therefore, the knowledge of stress distribution in the deposited layer during and after plasma spraying will be of special interest. In this study finite difference heat transfer analysis and finite element stress analysis were carried out to predict the change of stress distribution in the plasma coated layer with the variations of preheat temperature, number of scan, particle size, and bond coat. The results of the numerical analysis were as follows: 1) Transient stresses developed in the coated layer were up to the level of yiedl strength at the temperature. 2) The tensile stresses were developed in the deposited layer and the surface of the substrate, but the compressive stresses were developed in the rest of the substrate. 3) Transient and residual stresses were significantly affected by the preheat temperature. 4) The variations of temperature of powder particle and number of torch scan changed tensile stress distribution, but made no difference on the magnitude of the stresses. 5) Bond coated layer reduced the stree level of deposited layer.

• Restorative Dentistry and Endodontics
• /
• v.24 no.1
• /
• pp.88-99
• /
• 1999

The purpose of this study was to investigate the physical properties of experimental composite resins made with the spherical and crushed fillers. The 14 experimental composite resins containing 0, 5, 10, 15, 20 and 25%(w/w) in spherical filler group and 0, 10, 20, 30, 40, 50, 60 and 70%(w/w) in crushed filler group, incorporated in a Bis-GMA matrix (Aldrich Co., USA), were made with 1% ${\gamma}$-methoxy silane treated fillers. The polymer matrix was made by dissolving 0.7%(w/w) of benzoyl peroxide(Janssen Chemical Co. Japan) in methacrylate monomer, whereupon 0.7%(v/v) N,N-dimethyl-p-toluidine(Tokyo Kasei Co. Japan) was added to the monomer. The weight percentage of each specific particle size distribution could be determined from a knowledge of the specific gravity, the weight(w/w), and corresponding volume %(v/v) of the filler sample in resin monomer. In crushed silica group and spherical silica group, the diametral tensile strengths and compressive strengths were measured with Instron Testing Machine(No.4467), and analyzed in 14 experimental composite resins made by filler fractions. The shear bond strength of 14 experimental composite resins to bovine enamel was measured with universal testing machine(Instron No.4467). The fracture surfaces were sputter-coated with a gold film and investigated by SEM. The results were as follows; 1. The diametral tensile strength was tendency to increase in crushed silica group, but not in spherical silica group. The highest diametral tensile strength was found in 20% filler fractions of two groups. 2. The compressive strength was higher in 15%(w/w) and 20%(w/w) in spherical silica group than in crushed silica group, but not in spherical silica group. 3. The significant correlation was noticed in increase in shear bond strength in crushed silica group, but not in spherical silica group. 4. The significantly highest shear bond strength was noticed in 50% filler concentration in crushed silica group, and in 15% filler concentration in spherical silica group, it was not significant in relation. 5. In crushed silica group, cut surface of resin matrix and the interface between resin and filler is obvious. In spherical silica group, fractures that occurred through the filler particles were round in shape.

• Carbon letters
• /
• v.5 no.3
• /
• pp.108-112
• /
• 2004

Effect of silicon infiltration on the bend and tensile strength of 2D cross-ply carbon-carbon composites are studied. It is observed that bend strength higher than tensile strength in both types of composite is due to the different mode of fracture and loading direction. After silicon infiltrations bend and tensile strength suddenly decreases of carbon-carbon composites. This is due to the fact that, after silicon infiltration, silicon in the immediate vicinity of carbon forms the strong bond between carbon and silicon by formation silicon carbide and un-reacted silicon as free silicon. Therefore, these composites consist of three components carbon, silicon carbide and silicon. Due to mismatch between these three components secondary cracks developed and these cracks propagate from $90^{\circ}$ oriented plies to $0^{\circ}$ oriented plies by damaging the fibers (i.e., in-situ fiber damages). Hence, secondary cracks and in-situ fiber damages are responsible for degradation of mechanical properties of carbon-carbon composites after silicon infiltration which is revealed by microstructure investigation study by scanning electron microscope.

• Restorative Dentistry and Endodontics
• /
• v.32 no.1
• /
• pp.9-18
• /
• 2007

The purposes of this study were to examine the variability of adhesive thickness on the different site of the cavity wall when used total-etch system without filler and simplified self-etch system with filler and to evaluate the relationship between variable adhesive thickness and microtensile bond strength to the cavity wall. A class I cavity in six human molars was prepared to expose all dentinal walls. Three teeth were bonded with a filled adhesive, $Clearfil^{TM}$ SE bond ana the other three teeth were bonded with unfilled adhesives, $Scotchbond^{TM}$ Multi Purpose. Morphology and thickness of adhesive layer were examined using fluorescence microscope. Bonding agent thickness was measured at three points along the axial cavity wall edge of cavity margin (rim). halfway down each cavity wall (h1f), internal angle of the cavity (ang). After reproducing the adhesive thickness at rim, h1f and ang, micro-tensile bond strength were evaluated. For both bonding agents, adhesive thickness of ang was significantly thicker than that of rim and h1f (P <0.05). As reproduced the adhesive thickness, microtensile bond strength was increased as adhesive thickness was increased in two bonding agents. Adhesive thickness of internal angle of the cavity was significantly thicker than that of the cavity margin and the halfway cavity wall for both bonding agents. Microtensile bond strength of the thick adhesive layer at the internal angle of the cavity was higher than that of the thin adhesive layer at 1,he cavity margin and the halfway cavity in the two bonding systems.

• International Journal of Reliability and Applications
• /
• v.6 no.2
• /
• pp.79-85
• /
• 2005

We show how comparative mean residual life functions (MRL) can be used to give unique insights into strengths of materials data. Recall that Weibull's original reliability function was developed studying and fitting strengths for various materials. This creative comparing of MRL functions approach can be used for regular life data or any time to response data. We apply graphical MRL's to real data from tests of tensile strength of high quality engineered wood.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2018.05a
• /
• pp.335-336
• /
• 2018

This study discusses the development of asphalt based waterproofing sheet applied on the blind side of the concrete substrate. The inorganic coating membrane is applied on top of the waterproofing sheet surface for protection, and adhesive bond to the concrete substrate surface is secured via hydration reaction the cement. The study reveals the experimental results of the overlap section tensile strength to observe the effects of the adhesion strength of this material.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05a
• /
• pp.131-134
• /
• 2005

Until recently tensile stresses in concrete have not been considered, since it does not affect the ultimate strength of reinforced concrete flexural members significantly. However, to verify the load-deflection relationship, the effect of tensile stresses between reinforcing bars and concrete, so-called tension stiffening effect must be taken into account. Main parameters of the tension stiffening behavior are known as concrete strength, and bond between concrete and reinforcing bars. In this study a total of twenty specimen subject to bending was tested with different concrete strength, coverage, and de-bonding length of longitudinal bars. The effects of these parameters on the flexural rigidity, crack initiation and propagation were carefully checked and analyzed.