• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.9
• /
• pp.707-712
• /
• 2008

The fatigue characteristics of a material or a structure are generally derived from fatigue tests of standard specimens. However, test results of standard specimens are different from those of real structures or components. Therefore, to calculate more accurate fatigue life, the geometrical effect and surface condition must be considered by comparing test results of standard specimens with those of real structures or components. Thus the object of this paper is to evaluate the fatigue characteristics of a real waterwork pipe. Also, to evaluate fatigue characteristic based on life distribution, the statistical fatigue characteristics were analyzed by the normal distribution and related data of P-S-N curve.

• Journal of the Korean Society for Precision Engineering
• /
• v.31 no.6
• /
• pp.551-557
• /
• 2014

Ideally, it is preferable to obtain the fracture characteristics of a piping from the fracture toughness of real pipes. However, a fracture toughness test on real pipes not only incurs much expense, but is very difficult to perform. Therefore fracture toughness tests have been carried out with standard specimens instead of real pipes. But, the estimates of fracture toughness obtained from standard specimens are more conservative than those of real pipes owing to the difference in the constraint effect between real pipes and standard specimens. Therefore, we have been studied with equivalent stress gradient specimen (ESG) which is designed to behave equally compared to real pipe about stress gradient on crack tip. In this study, we will evaluate fracture characteristics of equivalent stress gradient specimen by using analytical methods and compare with those of real pipe. And finally investigate suitability of equivalent stress gradient specimen.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.29 no.3
• /
• pp.219-223
• /
• 2009

This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.

• Journal of Industrial Technology
• /
• v.23 no.A
• /
• pp.149-156
• /
• 2003

The development and maintenance of a sound bond are essential requirements of concrete repair and replacement. The bond property of a overlay to its substrate concrete during the lifetime is one of the most important performance requirements which should be quantified. A standard or a verified bond strength measurement method is required at field for screening, selecting materials and quality control for overlay or repair materials, but no test method has been adopted as a standard. In this study, a concrete pull off bond strength measurement method for field application is proposed and evaluated. This study compares the splitting tensile test, slant shear test, nipple pipe direct tensile test, flexural adhesion test, briquette tensile test, jumbo nail pull-out test and core pull-off test with their test procedures. From these comparison and investigation, core pull-off test is selected as a main topic of this study because of it's suitability for in situ testing, simplicities in field application and clearness at interface boundary condition. Thus, the proposed core pull off test is evaluated to be the most appropriate method for field application in a simple manner. The fracture surface and fracture mode could be easily determined by visual observation of failure surface of the field specimen. The core pull off test was found to be sensitive to surface condition and latex contents at latex modified concrete.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.389-396
• /
• 2003

This paper presents experimental validation of the enhanced reference stress based J estimates for circumferential through-wall cracked pipes, recently proposed by authors. Using the pipe test data for circumferential through-wall cracked pipes, the predicted fracture initiation and maximum moments according to the proposed enhanced reference stress method are compared with experimental ones as well as predictions from the R6 method. The results show that both the R6 method and the proposed method give conservative estimates of initiation and maximum moments for circumferential through-wall cracked pipes, compared to experimental data. For longer cracks, the proposed method reduces conservatism embedded in estimated J according to the R6 method, and the resulting predictions are less conservative, compared to those from the R6 method. For shorter cracks, on the other hand, the proposed method reduces possible non-conservatism embedded in estimated J according to the R6 method, and the resulting predictions are slightly more conservative.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.4
• /
• pp.638-646
• /
• 2003

This paper presents experimental validation of the enhanced reference stress based J estimates for circumferential through-wall cracked pipes. recently proposed by authors. Using the pipe test data for circumferential through-wall cracked pipes, the predicted fracture initiation and maximum moments according to the proposed enhanced reference stress method are compared with experimental ones as well as predictions from the R6 method. The results show that both the R6 method and the proposed method give conservative estimates of initiation and maximum moments for circumferential through-wall cracked pipes, compared to experimental data. For longer cracks, the proposed method reduces conservatism embedded in estimated J according to the R6 method, and the resulting predictions are less conservative, compared to those from the R6 method. For shorter cracks, on the other hand, the proposed method reduces possible non-conservatism embedded in estimated J according to the R6 method, and the resulting predictions are slightly more conservative.

• Journal of the Korean Society of Safety
• /
• v.9 no.1
• /
• pp.121-126
• /
• 1994

In this thesis, a series of loading tests are conducted in order to investigate the fracture safety as structural materials of GFRP(Glass Fiber Reinforced Plastics) which we wifely used in the developed countries becauses of their natural of anticorrosion and lightweight etc.. In the fracture test, the mid-span displacement, the strain and the yield load of the GFRP pipes are measured for different number of laminates, and fracture energy is estimated. From this study, it is known that GFRP pipe could be used as structural materials in underground buried pipes if their ductility and strength are increased by controlling number of laminates. Furthermore, because of their merit of lightweight, they can contribute greatly to reduction of construe-tlon cost when they are employed.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.1
• /
• pp.113-118
• /
• 2010

A straight pipe is used after complicated bending work in a mechanical system. In this work process, the plastic deformation of the pipe produces residual stress in the pipe. This residual stress significantly affects the behavior of pipe fracture. For this reason, residual stress must be evaluated. Measuring the residual stress of a U-shaped pipe is difficult with existing destructive and nondestructive measurement methods. In this paper, the residual stress of a U-shaped aluminum pipe (99.7% pure aluminum) was evaluated from the Raman shift by Raman spectroscopy and FEM(Finite Element Method, FEM) analysis. The results of the stiffness test by FEM analysis are compared with those by experiments. The analyzed results of the Raman spectra showed a similar tendency with the results of the FEM analysis with respect to the residual stress distributions in U-shaped pipes. Also, the results of the bending tests showed resemblance to each other.

• Journal of Power System Engineering
• /
• v.7 no.1
• /
• pp.82-85
• /
• 2003

This study is to look at the effect for deformation of Polyethylene, on the wave forms produced by tensile test. Signals collected were then classified visually into three types according to their shapes in the time and frequency domain. Each type should contain signals which could be correlated to a certain micro failure mechanism that occurs during the tensile process. The result showed that the acoustic emission method could be effectively used for analysis of fracture mechanism in Polyethylene structures.

• Journal of Ocean Engineering and Technology
• /
• v.21 no.1 s.74
• /
• pp.51-58
• /
• 2007

This study on the effects of local wall-thinned location on the fracture behavior of pipes was carried out, and the results were compared with the analytical results. Local wall-thinning for the bending test was machined with various sizes on the outside of pipes, in order to simulate the metal loss, due to erosion/corrosion. In addition, we had carried out FE analysis for the pipes with local wall thinning on the inside, and its results were comparatively studied with that of the outside. Three-dimensional elasto-plastic analyses were able to accurately simulate fracture behaviors of inner or outer wall thinning. Fracture types, obtained from the experiments and analyses, could be classified into ovalization, local buckling and crack initiation, depending on the thinned length and thinned ratio. Based on the results, the fracture behaviors of pipes with the outer wall thinning can be applied to estimate the fracture behaviors of pipes with the inner wall thinning.