• Steel and Composite Structures
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• v.26 no.2
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• pp.151-161
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• 2018

The application of carbon fiber reinforced polymer (CFRP) composites for rehabilitation of steel structures has become vital in recent years. This paper presents an experimental program and a finite element (FE) modelling approach to study the effectiveness of CFRP patch for repair of notch damaged circular hollow sectional (CHS) steel beams. The proposed modeling approach is unique because it takes into account the orthotropic behavior and stacking sequence of composite materials. Parametric study was conducted to investigate the effect of initial damage (i.e., notch depth) on flexural performance of the notched beams and effectiveness of the repair system using the validated FE models. Results demonstrated the ability of CFRP patch to repair notched CHS steel beams, restoring them to their original flexural stiffness and strength. The effect of composite patch repair technique on post-elastic stiffness was more pronounced compared to the elastic stiffness. Composite patch repair becomes more effective when the level of initial damage of beam increases.

• Journal of the Korean Institute of Gas
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• v.20 no.5
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• pp.96-103
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• 2016

Proper repair methods of damaged city gas pipeline is important factor to safely transmit gas and to reduce economical loss caused by failure of gas pipelines. Repair methods such as surfacing, type-A and type-B welding and composite sleeve method have been used to repair damaged city gas pipelines. In this paper, among repair methods, composite sleeve repair methods were conducted since they are rather simple processes and their repair quality is not sensitive to workers' ability compared with other repair methods. We discussed composite repair processes especially using carbon fiber prepregs and the experimental results.

• Composites Research
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• v.37 no.2
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• pp.76-85
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• 2024

In this paper, a composite maintenance robot using carbon fiber spray method was developed that automatically sprays mixture was created for repair to damaged areas to repair them. To develop a robot, a repair process was developed in which a mixture of milled carbon fiber, epoxy resin, and hardener is sprayed and consolidated on the damaged area. To automate the repair process, an EOAT based on a collaborative robot was developed that can automatically suction and spray the mixture onto the damaged area. To evaluate the repair performance of the robot, 0° and 90° unidirectional specimens were manufactured and tested in accordance with ASTM D3039. Tests were performed on undamaged specimen, damaged specimen, and repaired specimen by a robot after damaged. As a result of the specimen test, the tensile strength of the 0° and 90° specimens was recovered by 10% and 90% after repair. Based on the test results, the repair performance of the developed composite maintenance robot was verified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.48-55
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• 2002

An Internet-based software called the Repair Advisory Service (RAS) was developed to assist aircraft composite repair. The RAS takes advantage of the web user interface and provides estimation of the failure loads of repaired composite laminates and Structural Repair Manual (SRM) with search capability. In this paper, a failure model of lap repair is discussed as an example of the modules in the RAS. The model takes into account anisotropy of each ply in the laminate and in the repair ply, and non-elastic behavior of the interlayer between the laminate and the repair patch. Failure loads calculated by the model were compared with test data, and a good agreement was found between the results of the model and the test.

• Composites Research
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• v.23 no.5
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• pp.15-21
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• 2010

In this study, repair and maintenance schemes of the damaged composite structure was investigated, and a repair process of the carbon/epoxy laminate composite structure was investigated numerically and experimentally. The composite laminates were damaged by drop weight type impact test machine. The damaged composite structure was repaired using external patch repair method after removing damaged area. The compressive strength test and analysis results after repairing the impact damaged specimens were compared with the compressive strength test and analysis results of undamaged specimens and impact damaged specimens. Finally, the strength recovery capability by repairing were investigated.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.33-37
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• 2002

Recently, composites have been widely applied in the sporting goods, automobile, aerospace industry. As the use of advanced composites increase, specific techniques have been developed to repair damaged composite structures. In order to repair the damaged part, it is required that the material in the damaged area be removed first by utilizing the proper method, and prepreg be laid up in the area and cured under vacuum using the vacuum bagging materials. In curing process, either in an oven or autoclave is to be delamination can be occurred in the sound areas during and/or after the exposure to the elevated curing temperature in case that the repair process is repeated. Therefore, this study was conducted to evaluate the degree of degradation of properties of the cured parts and how it affects to the delamination phenomenon between laminated skin and honeycomb core.

• International Journal of Precision Engineering and Manufacturing
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• v.2 no.3
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• pp.5-10
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• 2001

Due to the development of high-strength fibers and adhesives, it is now possible to repair cracked metallic plates by bonding reinforced patches to the plate over the crack. In this study, pre-cracked aluminum 6061-T6 alloy plates repaired with bonded carbon/epoxy composite patch are applied to investigate the effect of various patch shapes on the tensile strength and the fatigue behavior of the structure. A non-patch-boned cased and 2 type-50$\times$50, 40$\times$20 mm-composite patch-bonded cases were tested to obtain fracture loads and fatigue crack growth rate. The results showed that the patch-bonded repair improves the static strength by 17% and the fatigue life by 200% compared to non-repaired case. It means that patch-boned repair is more effective in the fatigue life. It was also revealed that the patching method along crack growth direction is more efficient in cost and weight reduction. By observing the fractography, patch-bonded repair specimens demonstrated zigzag fracture patterns compared with the non-patched specimens, which shows a typical ductile fracture.

• The Journal of Advanced Prosthodontics
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• v.11 no.5
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• pp.297-304
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• 2019

PURPOSE. This in vitro study investigated the repair bond strength of the zirconia ceramic after different aging conditions. MATERIALS AND METHODS. In order to imitate the failure modes of veneered zirconia restorations, veneer ceramic, zirconia, and veneer ceramic-zirconia specimens were prepared and were divided into 4 subgroups as: control ($37^{\circ}C$ distilled water for 24 hours ) and 3000, 6000, 12000 thermal cycling groups (n=15). Then, specimens were bonded to composite resin using a porcelain repair kit according to the manufacturer recommendation. The repair bond strength (RBS) test was performed using a universal testing machine (0.5 mm/min). Failure types were analyzed under a stereomicroscope. Two-way ANOVA and Bonferroni test were used for statistical analysis. RESULTS. The RBS values of zirconia specimens were statistically significant and higher than veneer ceramic and veneer ceramic-zirconia specimens in control, 3000 and 6000 thermal cycling groups (P<.05). When 12000 thermal cycles were applied, the highest value was found in zirconia specimens but there was no statistically significant difference between veneer ceramic and veneer ceramic-zirconia specimens (P>.05). Veneer ceramic specimens exhibited cohesive failure types, zirconia specimens exhibited adhesive failure types, and veneer ceramic-zirconia specimens exhibited predominately mixed failure types. CONCLUSION. Thermal cycling can adversely affect RBS of composite resin binded to level of fractured zirconia ceramics.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.24-28
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• 2002

Composite reinforced fiber materials are used in lots of fields such as a part of aeronautic space, ship, machinery and so on because can make structure wished for necessary condition by control fiber direction and laminated sequence. As the use of advanced composites increase, specific techniques have been developed to repair changed composite structures. In order to repair the damaged part production high quality composite reinforced fiber are completed by control the surrounding temperature and press in autoclave. The quality is influenced heat exposure degree by chemical reaction for precessing. This study considerated influence limit of using by repair structure part and change of properties according to heat exposure degree for repairing.

• Structural Engineering and Mechanics
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• v.50 no.4
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• pp.525-539
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• 2014

Bonded composite-patch repair has been widely used to restore or extend the service life of damaged structures due to its effectiveness as a mechanical repair technique. In this paper using extended finite element method (XFEM), three-dimensional crack models are developed to examine the fracture behavior of centrally cracked aluminum plates repaired with single and double sided composite patches. Stress intensity factor (SIF) at the crack tip is used as the fracture criterion. In this regard, the effects of the crack lengths, patch materials, orientation of plies, adhesive and patch thickness are examined to estimate the SIF of the repaired plate and the repair performance. The obtained results show that composite patches have significant effect on reduction of the SIF at the crack tip. It is also proved that using double symmetric repair, in comparison to single one, reduces considerably SIF at the crack tip. Hence, the residual strength can be improved significantly as well as fatigue life of the structure. Investigation of ply orientation effects shows SIF increase as the ply orientation is changed from $0^{\circ}$ (perpendicular to the advancing crack) to $90^{\circ}$ (parallel to the crack line). However, the effectiveness of the ply orientation depends on the loading direction and the crack direction.