• Journal of Welding and Joining
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• v.8 no.3
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• pp.31-38
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• 1990

The bonding mechanism and bond strength were investigated for the cold pressure welding of Al to Al, Cu to Cu and Al to Cu by upsetting. A phenomenon of bonding betweenthe metallic components has been observed by a scanning electron microscope and metallurgical microscope. A modified equation for bond strength with respect to the reduction of height shows reasonably a good agreement with the experimental data. When the values of the hardening factor and threshold deformation for the given materials could be determined, the theoretical bond strength can be calculated.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.653-658
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• 1997

Recently, carbon Fiber sheet (CFS) is frequently used for strengthening deteriorated concrete structures. To strengthening damaged structures, the property and characteristic of the bond between CFS and the concrete surface must be understood. The tensile test of single lap shear specimen was performed to study bond strength, bond stress distribution and stress transfer between CFS and concrete surface according to the bond length. Based on the test results, there were ultimate influence length (UIL) in which bond stress was distributed, and ultimate strain reduction ratio (USRR) by which strain was reduced linearly. Bond resisting force (BRF) was estimated by UIL and USRR, and which was compared with ultimate loads. According to the results of comparison, it was shown that ultimate bond strength could be estimated reasonablely by BRF.

• Structural Engineering and Mechanics
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• v.17 no.6
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• pp.863-878
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• 2004

Steel corrosion in reinforced concrete structures leads to concrete cover cracking, reduction of bond strength, and reduction of steel cross section. Among theses consequences mentioned, reduction of bond strength between reinforcement and concrete is of great importance to study the behaviour of RC members with corroded reinforcement. In this paper, firstly, an analytical model based on smeared cracking and average stress-strain relationship of concrete in tension is proposed to evaluate the maximum bursting pressure development in the cover concrete for noncorroded bar. Secondly, the internal pressure caused by the expansion of the corrosion products is evaluated by treating the cracked concrete as an orthotropic material. Finally, bond strength for corroded reinforcing bar is calculated and compared with test results.

• Steel and Composite Structures
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• v.10 no.4
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• pp.317-329
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• 2010

According to the results of 9 circular concrete filled steel tube (CFT) push-out tests, a new theoretical model for average bond stress versus free end slip curve is proposed. The relationship between verage bond stress and free end slip is obtained considering some varying influential parameters such as slenderness ratio and diameter-to-thickness ratio. Based on measured steel tube strain and relative slip at different longitudinal positions, the distribution of bond stress and relative slip along the length of steel tube is obtained. An equation for predicting the varying bond-slip relationship along longitudinal length and a position function reflecting the variation are proposed. The presented method can be used in the application of finite element method to analyze the behavior of CFT structures.

• Structural Engineering and Mechanics
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• v.72 no.4
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• pp.479-489
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• 2019

The corrosion of reinforcement leads to a gradual decay of structural strength and durability. Several models for crack occurrence prediction and crack width propagation are investigated in this paper. Analytical and experimental models were used to predict the bond strength in the period of corrosion propagation. The manner of flexural strength loss is calculated by application of these models for different scenarios. As a new approach, the variation of the concrete beam neutral axis height has been evaluated, which shows a reduction in the neutral axis height for the scenarios without loss of bond. Alternatively, an increase of the neutral axis height was observed for the scenarios including bond and concrete section loss. The statistical properties of the parameters influencing the strength have been deliberated associated with obtaining the time-dependent bending strength during corrosion propagation, using Monte Carlo (MC) random sampling method. Results showed that the ultimate strain in concrete decreases significantly as a consequence of the bond strength reduction during the corrosion process, when the section reaches to its final limit. Therefore, such sections are likely to show brittle behavior.

• Structural Engineering and Mechanics
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• v.74 no.3
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• pp.313-323
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• 2020

Non-destructive tests are commonly used in construction industry to access the quality and strength of concrete. However, till date there is no non-destructive testing method that can be adopted to evaluate the bond condition of reinforced concrete beams. In this regard, the presented research work details the use of ultra-sonic pulse velocity test method to evaluate the bond condition of reinforced concrete beam. A detailed experimental research was conducted by testing four identical reinforced concrete beam samples. The samples were loaded in equal increments till failure and ultra-sonic pulse velocity readings were recorded along the length of the beam element. It was observed from experimentation that as the cracks developed in the sample, the ultra-sonic wave velocity reduced for the same path length. This reduction in wave velocity was used to identify the initiation, development and propagation of internal micro-cracks along the length of reinforcement. Using the developed experimental methodology, researchers were able to identify weak spots in bond along the length of the specimen. The proposed method can be adopted by engineers to access the quality of bond for steel reinforcement in beam members. This allows engineers to carryout localized repairs thereby resulting in reduction of time, cost and labor needed for strengthening. Furthermore, the methodology to apply the proposed technique in real-world along with various challenges associated with its application have also been highlighted.

• Computers and Concrete
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• v.6 no.3
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• pp.235-252
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• 2009

Due to the reduction of bond strength resulting from the high corrosion level of reinforcing bars, influence of this reduction on flexural capacity of reinforced concrete (RC) beam should be considered. An extreme case is considered, where bond strength is complete lost and/or the tensile steel are exposed due to heavy corrosion over a fraction of the beam length. A compatibility condition of deformations of the RC beam with partially unbonded length is proposed. Flexural capacity of this kind of RC beam is predicted by combining the proposed compatibility condition of deformations with equilibrium condition of forces. Comparison between the model's predictions with the experimental results published in the literature shows the practicability of the proposed model. Finally, influence of some parameters on the flexural capacity of RC beam with partially unbonded length is discussed. It is concluded that the flexural capacity of the beam may not be influenced by the completely loss of bond of the whole beam span as long as the tensile steel can yield; whether or not the reduction of the flexural capacity of the beam resulting from the loss of bond over certain length may occur depends on the detailed parameters of the given beam.

• Journal of the Korean Chemical Society
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• v.18 no.5
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• pp.341-353
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• 1974

The electrochemical reduction of triphenylphosphine penylimide in nonaqueous media has been examined by polarography, cyclic voltammetry, controlled-potential coulometry and electron spin resonance spectroscopy. The reduction of triphenylphosphine phenylimide proceeds by a one-electron transfer to form anion radical which undergoes both protonation and a second one-electron reduction followed by cleavage of the phosphorus-nitrogen double bond. Aniline is a major product. The cleavage of a phosphorus-phenyl bond was also observed after reduction of triphenylphosphine oxide which is one of the major products of the chemical reaction which follow the primary process.

• Journal of Welding and Joining
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• v.3 no.2
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• pp.27-34
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• 1985

The mechanical properties and bonding mechanism of aluminum, copper and mild steel have been determined in cold pressure welding. The brittle cover layer to be established by scratch-brushing plays an important role in bond strength and has an influence on the threshold of deformation. The cold pressure welding was achieved at 54% of height reduction in A1-A1, 75% in Cu-Cu, 56% in Al-Cu, and 74% in Cu-steel. The height reduction at which the bond strength of weld interface was the same as the tensile strength of base metal should be over 76% in Al-Al, 82% in Cu-Cu, and 78% in Al-Cu.

• Structural Engineering and Mechanics
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• v.72 no.3
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• pp.305-312
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• 2019

This paper investigates the effect of utilizing vacuum bagging process to enhance the bond behavior between fiber reinforced polymer (FRP) composites and concrete substrate. Sixty specimens were prepared and tested using double-shear bond test. The effect of various parameters such as vacuum, fiber type, and FRP sheet length and width on the bond strength were investigated. The experimental results revealed that utilizing vacuum leads to improve the bond behavior between FRP composites and concrete. Both the ultimate bond forces and the maximum displacements were enhanced when applying the vacuum which leads to reduction in the amount of FRP materials needed to achieve the required bond strength compared with the un-vacuumed specimens. The efficiency of the enhancement in bond behavior due to vacuum highly depends on the fiber type; using carbon fiber showed higher enhancement in the bond strength compared to the glass fiber when vacuum was applied. On the contrary, specimens with glass fiber showed higher enhancement in the maximum slippage compared to specimens with carbon fibers. Utilizing vacuum does not affect the debonding failure modes but lead to increase in the amount of attached concrete on the surface of the debonded FRP sheet.