• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.361-370
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• 2017

Through the use of finite element analysis and acoustic emission techniques we have evaluated the interfacial failure of a carbon fiber reinforced polymer (CFRP) repair patch on a notched aluminum substrate. The repair of cracks is a very common and widely used practice in the aeronautics field to extend the life of cracked sheet metal panels. The process consists of adhesively bonding a patch that encompasses the notched site to provide additional strength, thereby increasing life and avoiding costly replacements. The mechanical strength of the bonded joint relies mainly on the bonding of the adhesive to the plate and patch stiffness. Stress concentrations at crack tips promote disbonding of the composite patch from the substrate, consequently reducing the bonded area, which makes this a critical aspect of repair effectiveness. In this paper we examine patch disbonding by calculating the influence of notch tip stress on disbond area and verify computational results with acoustic emission (AE) measurements obtained from specimens subjected to uniaxial tension. The FE results showed that disbonding first occurs between the patch and the substrate close to free edge of the patch followed by failure around the tip of the notch, both highest stress regions. Experimental results revealed that cement adhesion at the aluminum interface was the limiting factor in patch performance. The patch did not appear to strengthen the aluminum substrate when measured by stress-strain due to early stage disbonding. Analysis of the AE signals provided insight to the disbond locations and progression at the metal-adhesive interface. Crack growth from the notch in the aluminum was not observed until the stress reached a critical level, an instant before final fracture, which was unaffected by the patch due to early stage disbonding. The FE model was further utilized to study the effects of patch fiber orientation and increased adhesive strength. The model revealed that the effectiveness of patch repairs is strongly dependent upon the combined interactions of adhesive bond strength and fiber orientation.

• Composites Research
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• v.31 no.1
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• pp.1-7
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• 2018

In the case of a conventional composite patch repair using a heat blanket, the adhesive is pressurized using only a vacuum bag. In this study, however, a pressurization system has been developed to apply additional air pressure on the vacuum bag. In order to verify the performance of the developed system, the composite laminates were repaired with scarf patches and then tested under tensile load to be compared with the strength of the defect-free laminate. Tensile tests were also conducted on specimens with the same configuration but bonded in an autoclave. As a result of the test, the tensile strengths of the specimens repaired using the heat blanket with vacuum only without external pressure, the specimens repaired with additional pressure by the developed system, and the specimens repaired with the same external pressure in an autoclave, showed the strength recovery ratios of 74.9, 81.0, and 78.2%, respectively. The results of the tensile test after moisture saturation and the dried fatigue test also showed that the strength recovery ratios of the specimens repaired under the external pressure of 1 atm using the developed system are slightly higher than that of specimens bonded in autoclave.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.411-418
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• 2012

In this study, behavior of unpatched and patched cylindrical shells with through-wall cracks has been estimated using numerical experiments, and patching effect of them has been investigated according to various patching parameters. To show credibility of numerical models considered, two ways such as h- and p-methods have been adopted. Also, domain integral method and virtual crack extension method have been considered to calculate energy release rates based on linear elastic fracture mechanics. For examples, the unpatched cylindrical shells with circumferential cracks under remote tension have firstly been analyzed to show the validity of finite element modeling with h-method or p-method, and then the results have been compared with literature values published. Next, the sensitive analysis of patch repaired problems in terms of thickness of patch and adhesive, shear modulus of adhesive, composite material type of patch, crack length, etc. has been carried out.

• Journal of Chest Surgery
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• v.24 no.5
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• pp.445-450
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• 1991

Forty eight patients diagnosed as atrial septal defect, had been operated from April 1986 to December 1990 at the Department of Thoracic and Cardiovascular Surgery, Inha University Hospital, were analysed retrospectively. Of the 48 patients, 12 patients, were male and 36 patients were female, Their ranged from 8 months to 51 years old, and the mean was 18.0 years old. The proceeding two symptoms were exertional dyspnea and frequent upper respiratory infection. But 10 patients [20.8%] were asymptomatic. Electrocardiographic findings were regular sinus rhythm in 100.0%, RVH in 29.2%, incomplete RBBB in 27.1%, and first degree AV block in 2.1%. Hemodynamic studies were performed in 38 of 48 patients. Significant pulmonary hypertension[over 50mmHg in systolic pulmonary arterial pressure], which is the most serious risk factor, was developed in 4 patients[8.3%]. There was statistical significance between size of defect[cm2/BSA-M2] and systolic pulmonary arterial pressure[sPAP] retrospectively[p=0.036]. We could not find the correlationship between age and Qs % size. Anatomically, secundum type constituted 97.9%, in which 43 patients were PFO type[91.6%] and 3 patients were IVC type[6.3%]. 38 of 48 ASD patients were repaired with patch closure[72.9%] and remains were repaired with direct closure[27.1%]. The operative result was excellent except two cases of transient postoperative arrhythmia. There was no operative mortality.

• Journal of Chest Surgery
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• v.28 no.9
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• pp.811-816
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• 1995

Repairs of atrial septal defect utilizing cardiopulmonary bypass were performed in 50 adults, ranging age from 16 to 53 years, since April 1986 up to October 1994. They occupied 38.8% of all adult congenital heart disease operated in the same period. Preoperatively, 16 patients were functional class II, 12 patients class III and 4 patients class IV[New York Heart Association Classification , respectively. Five patients combined with atrial fibrillation and the remainders revealed regular sinus rhythm. Cardiac catheterizations were performed in 43 out of 50 patients, and revealed a systolic pulmonary arterial pressure in excess of 51 mmHg in 4 patients but none had reversed shunt. 40 patients[80% were repaired with patch closure and remainings were repaired with direct closure. 49 patients were followed up for 2 months up to 102 months[average 55 months . A comparison of the preoperative and postoperative functional class demonstrated a mean decrease of one NYHA functional level[2.5$\pm$0.63 to 1.4$\pm$0.56 . There was no operative mortality. One patient died during the follow-up period and the death was unrelated to heart disease. Operative treatment is indicated for repair of atrial septal defect with left to right shunt in the adult patient and a considerable clinical improvement can be anticipitated with low mortality.

• 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.

• Journal of Chest Surgery
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• v.27 no.3
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• pp.202-208
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• 1994

We reviewed 30 patients with tetralogy of Fallot who had underwent transannular patch reconstruction of the right ventricular outflow tract from January 1990 to May 1993. The patients were divided into two groups according to the approaching pattern for the corrective surgery: 12 patients[aged 11 months to 4 years; mean age, 2.3 years] in transatrial group who were repaired by transatrial-transpulmonary approach; 18 patients[aged 13 months to 6 years; mean age, 3.2 years] in transventricular group who were repaired by transventricular approach. The incidence of postoperative right bundle branch block was not statistically different between two groups. With follow up from 3 months to 32 months after operation, none in transatrial group revealed a remnant RVOT stenosis over 50mmHg or tricuspid regurgitation more than grade II with 2D-echocardiography, but two cases[7.7%] in transventricular group revealed these complications. Early postoperative death was 4 cases[13.3%] which all belonged to transventricular group. In conclusion successful repair of tetralogy of Fallot can be accomplished in most patients by transatrial-transpulmonary approach and we can anticipate better results by this approach in terms of postoperative right ventricular function and arrhythmia than conventional transventricular approach.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.487-492
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• 2007

The enhancement of the service life of damaged or cracked structures is a major issue for researchers and engineers. The hierarchical void element with the integrals of Legend polynomials is used to characterize the fracture behavior of unpatched crack as well as repaired crack with bonded composite patches by computing the stress intensity factors and stress contours at the crack tip. The numerical approach is based on the v-version degenerate shell element including the theory of anisotropic laminated composites. Since the equivalent single layer approach is adopted in this study, the proposed element is necessary to represent a discontinuous crack part as a continuum body with zero stiffness of materials. Thus the aspect ratio of this element to represent the crack should be extremely slender. The sensitivity of numerical solution with respect to energy release rate, displacement and stress has been tested to show the robustness of hierarchical void element as the aspect ratio is increased up to 2000. The stiffness derivative method and displacement extrapolation method have been applied to calculate the stress intensity factors of Mode I problem.

• Composites Research
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• v.27 no.2
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• pp.77-81
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• 2014

In this study, it was performed damage assessment and repair of small scale aircraft adopted on composite. This aircraft adopted the sandwich structure to skin of wing. This study aims to investigate the residual strength of sandwich composites with nomex honeycomb core and carbon fiber face sheets after the open hole damage by the experimental investigation. The 4-point bending tests were used to find the bending strength, and the open hole was applied to introduce the simulated damage on the specimen. The bending strength test results after open hole were compared with the results of no damaged specimen test. In addition, The damaged composite structure was repaired using external patch repair method after removing damaged area. After that, this study presents comparison results of the experimental investigation between the damaged and the repaired specimen. It was found that the bending strength of repaired specimen was recovered up to 95% of undamaged specimen.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.5
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• pp.463-474
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• 2009

Double symmetric patch repair of existing structures always causes membrane action only, however, in many cases this technique is not practical. On the other hand, the bending stiffness of the patch and the skin increases as tensile loading is increased and affects the bending deformation significantly in the case of single-sided patch repair. In this study, the p-convergent full layerwise model has been proposed to determine the stress concentration factor in the vicinity of a circular hole as well as across the thickness of plates with single-sided patch repair. In assumed displacement field, the strain-displacement relations and 3-D constitutive equations of a layer are obtained by the combination of 2-D and 3-D hierarchical shape functions. The transfinite mapping technique has been used to represent a circular boundary and Gauss-Lobatto numerical integration is implemented in order to directly obtain stresses occurred at the nodal points of each layer without other extrapolation techniques. The accuracy and simplicity of the present model are verified with comparison of the previous results in literatures using experiment and conventional 3-D finite element. Also, the bending effect has been investigated with various patch types like square, circular and annular shape.