• Journal of Power System Engineering
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• v.10 no.2
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• pp.117-123
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• 2006

Woven fabrics composites are used as primary structural components in many applications because of their superior properties that offer high specific strength and stiffness. However, the complexity of the fabric structure makes understanding of their failure behavior very difficult. Also, laminate woven fabrics CFRP have unique failure mechanisms such as fiber bridging, fiber/matrix crack and so on. In particular, the delamination phenomenon of the composite materials is one of the most frequent failure mechanisms. So, we estimated interlaminar fracture and damage in composites using as ENF specimen by a 3 point bending test. And AE characteristics were examined for crack propagation on plain woven CFRP. We obtained the following conclusions from the results of the evaluation of the 3 point bending fracture test and AE characteristic estimation. AE counts of maximum crack length were obtained as $85.97{\times}10^4\;and\;93{\times}10^3\;for\;a_0/L=0.3$ and 0.6, respectively. Also the maximum amplitudes were over 80dB at both $a_0/L=0.3\;and\;0.6$. $G_{IIc}$ at that's $a_0/L$ ratio were obtained with $1.07kJ/m^2\;and\;3.79kJ/m^2$.

• Korean Journal of Materials Research
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• v.3 no.2
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• pp.197-204
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• 1993

Abstract The effects of the hole size and the specimen width on the fracture behavior of several fabric composite plates are experimentally investigated in tension. Tests are performed on plain woven glass/ epoxy, plain woven carbon/epoxy and satin woven glass/polyester specimens with a circular hole. It is shown in this paper that the characteristic length according to the point stress criterion depends on the hole size and the specimen width. An excellent agreement is found between the experimental results and the analytical predictions of the modified failure criterion. The notched strength increase with an increase in the damage ratio, which is explained by a stress relaxation due to the formation of damage zone. When the unstable fracture occurred, the critical crack length equivalent for the damage zone is about twice the characteristic length. The critical energy release rate $G_c$ is independent of hole size for the same specimen width. The variation of $G_c$ according to the material system, fiber volume fraction and specimen width relates to the notch sensitivity factor. $G_c$ increases with a decrease in the notch sensitivity factor, which can be explained by a stress relaxation due to the increase of damage zone.

• Composites Research
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• v.20 no.3
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• pp.31-36
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• 2007

A quantitative prediction method for initial crack length in a carbon/epoxy (CF/EP) composite beam using active piezoelectric transducers was established in this study. Wavelet Transform (WT)-based signal processing and identification technique in time-frequency domain was developed to facilitate the determination of damage presence and severity. Dynamic response of a CF/EP composites beam containing a continuously expanding crack, coupled with a pair of active piezoelectric disks, was examined under a narrow band excitation, and then applied with the proposed signal processing technique.

• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.375-391
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• 2022

This paper discussed and analyzed the interfacial stress distribution characteristic of adjacent cracks in Carbon Fiber Reinforced Polymer (CFRP) plate strengthened concrete slabs. One un-strengthened concrete test beam and four CFRP plate-strengthened concrete test beams were designed to carry out four-point flexural tests. The test data shows that the interfacial shear stress between the interface of CFRP plate and concrete can effectively reduce the crack shrinkage of the tensile concrete and reduces the width of crack. The maximum main crack flexural height in pure bending section of the strengthened specimen is smaller than that of the un-strengthened specimen, the CFRP plate improves the rigidity of specimens without brittle failure. The average ultimate bearing capacity of the CFRP-strengthened specimens was increased by 64.3% compared to that without CFRP-strengthen. This indicites that CFRP enhancement measures can effectively improve the ultimate bearing capacity and delay the occurrence of debonding damage. Based on the derivation of mechanical analysis model, the calculation formula of interfacial shear stress between adjacent cracks is proposed. The distributions characteristics of interfacial shear stress between certain crack widths were given. In the intermediate cracking region of pure bending sections, the length of the interfacial softening near the mid-span cracking position gradually increases as the load increases. The CFRP-concrete interface debonding capacity with the larger adjacent crack spacing is lower than that with the smaller adjacent crack spacing. The theoretical calculation results of interfacial bonding shear stress between adjacent cracks have good agreement with the experimental results. The interfacial debonding failure between adjacent cracks in the intermediate cracking region was mainly caused by the root of the main crack. The larger the spacing between adjacent cracks exists, the easier the interfacial debonding failure occurs.

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.1932-1940
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• 2004

Although the previous researches evaluated the fatigue behavior of Al/GFRP laminates using the traditional fracture mechanism, their researches were not sufficient to do it : the damage zone of Al/GFRP laminates was occurred at the delamination zone instead of the crack-metallic damages. Thus, previous researches were not applicable to the fatigue behavior of Al/GFRP laminates. The major purpose of this study was to evaluate delamination behavior using the relationship between crack length (a) and delamination width (b) in Al/GFRP laminate. The details of investigation were as follows: 1) Relationship between the crack length (a) and the delamination width (b), 2) Relationship between the delamination aspect ratio (b/a) and the delamination area rate ((A$\_$D/)/subN// (A$\_$D/)$\_$All/), 3) The effect of delamination aspect ratio (b/a) on the delamination shape factor (f$\_$s/) and the delamination growth rate (dA$\_$D// da). As results, it was known that the delamination aspect ratio (b/a) was decreased and the delamination area rate ((A$\_$D/)$\_$N// (A$\_$D/)$\_$All/) was increased as the normalized crack size (a/W) was increased. And, the delamination shape factors (f$\_$s/) of the ellipse-II(f$\_$s3/) was greater than of the ellipse-I(f$\_$s2/) but that of the triangle (f$\_$s1/) was less than of the ellipse-I(f$\_$s2/).

• Structural Engineering and Mechanics
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• v.64 no.3
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• pp.323-328
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• 2017

This paper presents a three-dimensional finite element method analysis of repairing plate with bonded composite patch subjected to tensile load. The effect of the corrosion on the damage of the adhesive (FM73) in the length of two horizontal cracks on the both sides is presented. The obtained results show that the crack on the left side creates a very extensive area of the damaged zone and gives values of the stress intensity factor (SIF) higher than that on the right side. We can conclude that the left crack is more harmful (dangerous) than that on the right side.

• Journal of Korean Society of Steel Construction
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• v.11 no.1 s.38
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• pp.33-42
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• 1999

In the present study, crack initiation criteria, static failure and tensile mode fatigue behavior for a rail steel are evaluated to assure the railway vehicle's safety. The transverse fissure, which is the most critical damage in the rail, is initiated by the maximum shear stress and its location is subsurface. In addition, the possibility of transition from the shear mode to the mixed mode increases with increasing the length of subsurface crack. Because of the brittleness by the welding, the fracture toughness of the welded part is lower than of the base metal. For low ${\Delta}K$, the stage II fatigue crack growth rates of the welded part is slower than of the base metal but, for high ${\Delta}K$, this different behavior for fatigue crack growth rate is nearly diminished. These trends are more remarkable for low stress ratio, R=0.1. It is believed that this behavior is caused by the change of the microstructure which that of the welded part is coarser than of base metal.

• Smart Structures and Systems
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• v.18 no.3
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• pp.569-584
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• 2016

This paper presents a method for stochastic modelling of fatigue crack growth and optimising inspection and maintenance strategy for the structural members of steel bridges. The fatigue crack evolution is considered as a stochastic process with uncertainties, and the Gamma process is adopted to simulate the propagation of fatigue crack in steel bridge members. From the stochastic modelling for fatigue crack growth, the probability of failure caused by fatigue is predicted over the service life of steel bridge members. The remaining fatigue life of steel bridge members is determined by comparing the fatigue crack length with its predetermined threshold. Furthermore, the probability of detection is adopted to consider the uncertainties in detecting fatigue crack by using existing damage detection techniques. A multi-objective optimisation problem is proposed and solved by a genetic algorithm to determine the optimised inspection and maintenance strategy for the fatigue affected steel bridge members. The optimised strategy is achieved by minimizing the life-cycle cost, including the inspection, maintenance and failure costs, and maximizing the service life after necessary intervention. The number of intervention during the service life is also taken into account to investigate the relationship between the service life and the cost for maintenance. The results from numerical examples show that the proposed method can provide a useful approach for cost-effective inspection and maintenance strategy for fatigue affected steel bridges.

• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.145-154
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• 2018

The damage investigation and inspection methods performed in concrete facilities such as bridges, tunnels, retaining walls and so on, are usually visually examined by the inspector using the surveying tool in the field. These methods highly depend on the subjectivity of the inspector, which may reduce the objectivity and reliability of the record. Therefore, the new image processing techniques are necessary in order to automatically detect the cracks and objectively analyze the characteristics of cracks. In this study, deep learning and image processing technique were developed to detect cracks and analyze characteristics in images for concrete facilities. Two-stage image processing pipeline was proposed to obtain crack segmentation and its characteristics. The performance of the method was tested using various crack images with a label and the results showed over 90% of accuracy on crack classification and segmentation. Finally, the crack characteristics (length and thickness) of the crack image pictured from the field were analyzed, and the performance of the developed technique was verified by comparing the actual measured values and errors.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.5
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• pp.74-81
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• 2019

This study reports the CW $CO_2$ laser scribing of soda lime glass. In this study, scribing experiments are carried out at different laser powers, scan speeds, and focal positions to investigate the effect of the process parameters on the interaction characteristics between a laser beam and glass. In particular, the interaction characteristics are analyzed and described with the input laser energy per unit length. According to the experimental results, the damage threshold for the glass surface was found to exist between 0.072 and 0.08 J/mm. The input laser energy in this region induced partial melting of the surface and grain-shaped cracks. These cracks tended to increase as the input laser energy increased. At the laser input energy larger than 1 J/mm, a huge crack propagating along the scan direction was produced, and the volume below the scribed area was fully melted. The growth of this crack finally resulted in the complete cutting of the glass at the input laser energy above 8 J/mm. It was found that both the width and depth of the scribed line increased with increasing input laser energy. For the beam focusing at the rear surface, the width of the scribed line varied irregularly. This could be ascribed to the increased asymmetry of the beam intensity distribution when the laser beam was focused at the rear surface. Under this condition, a large burr was only produced on one side of the scribed line.