• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.232-240
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• 1984

The plane elastostatic boundary value problem with the sharp V-notched singularity is formulated by a contour integral method for determining numerically the stress intensity factors. The integral formula is based on Somigliana type of reciprocal work in terms of displacement and traction vectors on the plate boundary. The characteristic singular solutions can be identified on the basis of traction free boundary conditions of two radial notch edges. Two numerical example examples are treated in detail; a symmetric mode-I type of notched plate with various interior angles and a mixed mode type of cantilever subjected to end shear.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.2
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• pp.357-364
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• 1996

The purpose of this study was to asses the shear bond strengths of 3 types of light-curing Glass Ionomer cement to dental amalgam with or without an intermediary agent. 60 amalgam adherent specimens were prepared and aged in water at $37^{\circ}C$ for 3 days. Before bonding, the amalgam surfaces were finished flat on 600-grit silicon carbide paper. 30 specimens among 60 were used for bonding in this condition, and the other 30 were covered with a thin layer of light-curing intermediary agent. Shear bond strengths were measured with universal testing machine (Instron, Model 4301) and statistically processed by ANOVA and t-test. On completion of bond test, the fracture surfaces were examined under light microscope so that the mode of bond failure could be assessed The results were as follows : 1. Bond strength of Fuji II LC group showed the hightest value and was followed by Vitremer, Vitrebond groups (p<0.05). 2. The bond strengths achieved without an intermediary agent were higher than those obtained with intermediary agent (p<0.05). 3. For the specimens bonded with intermediary agent, bond failures occured mostly at the agent-amalgam interface. So, the use of intermediary bonding agent was thought not recommendable at glass ionomer-amalgam interface.

• Structural Engineering and Mechanics
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• v.74 no.6
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• pp.723-735
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• 2020

This study is reported the adhesion failure in adhesive bonded composite and specifically for the T-joint structure. Three-dimensional finite element analysis has been performed using a commercial tool and the necessary outcomes are obtained via an eight noded solid element (Solid 185-element) from the library of ANSYS. The structural analysis input has been incurred through ANSYS parametric design language (APDL) code. The normal and shear stress distributions along different layers of the joint structure have been evaluated as the final outcomes. Based on the stress distributions, failure location in the composite joint structure has been identified by using the Tsai-Wu stress failure criterion. It has been found that the failure index is maximum at the interface between flange and web part of the joint (top layer) which indicates the probable location of failure initiation. This kind of failures are considered as adhesion failure and the failure propagation is governed by strain energy release rate (SERR) of fracture mechanics. The different adhesion failure lengths are also considered at the failure location to calculate the SERR values i.e. mode I fracture (opening), mode II fracture (sliding) and mode III fracture (tearing) along the failure front. Also, virtual crack closure technique (VCCT) principle of fracture mechanics steps is used to calculate the above said SERRs. It is found that the mode I SERR is more dominating compared to other two modes of failure for the joint considered. Finally, the influences of various parametric (geometrical and material) effect on SERR of the joint structure are evaluated and discussed in details.

• Composites Research
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• v.29 no.2
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• pp.45-52
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• 2016

An understanding of the failure mechanisms of the adhesive layer is decisive in interpreting the performance of a particular adhesive joint because the delamination is one of the most common failure modes of the laminated composites such as the fiber metal laminates. The interface between different materials, which is the case between the metal and the composite layers in this study, can be loaded through a combination of fracture modes. All loads can be decomposed into peel stresses, perpendicular to the interface, and two in-plane shear stresses, leading to three basic fracture mode I, II and III. To determine the load causing the delamination growth, the energy release rate should be identified in corresponding criterion involving the critical energy release rate ($G_C$) of the material. The critical energy release rate based on these three modes will be $G_{IC}$, $G_{IIC}$ and $G_{IIIC}$. In this study, to evaluate the fracture behaviors in the fracture mode I and II of the adhesive layer in fiber metal laminates, the double cantilever beam and the end-notched flexure tests were performed using the reference adhesive joints. Furthermore, it is confirmed that the experimental results of the adhesive fracture toughness can be applied by the comparison with the finite element analysis using cohesive zone model.

• Journal of the korean academy of Pediatric Dentistry
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• v.46 no.2
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• pp.158-164
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• 2019

The purpose of this study was to compare the bond strength of resin-modified glass ionomer (RMGI) to dentin with saliva contamination at different stages and using different decontamination procedures. Extracted human permanent molars were embedded onto acrylic resin with the dentin surface exposed. Group I was a control group that was conditioned with polyacrylic acid (PAA). Groups II and III were contaminated with saliva before PAA conditioning and Groups IV, V, and VI were contaminated with saliva after PAA conditioning. After saliva contamination, Groups II and IV were dried, Groups III and V were rinsed and dried, and Group VI was additionally conditioned with PAA. After surface treatment, the dentin specimens were filled with RMGI. Group I showed significantly higher bond strength than the other groups. Group VI showed a significantly higher bond strength than the other saliva contaminated groups. However, there were no significant differences in the failure mode between the different groups. Saliva contamination impaired the bond strength of RMGI to dentin, regardless of when the saliva contamination occurred. Decontamination with washing and drying could not improve the shear bond strength of RMGIC. When saliva contamination occurred after PAA conditioning, additional PAA conditioning improved the shear bond strength.

• Steel and Composite Structures
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• v.35 no.3
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• pp.439-447
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• 2020

This paper presents two sets of full three-dimensional thermoelastic finite element analyses of superimposed thermo-mechanically loaded Spar Wingskin Joints made with laminated Graphite Fiber Reinforced Plastic composites. The study emphasizes the influence of residual thermal stresses and material anisotropy on the inter-laminar delamination behavior of the joint structure. The delamination has been pre-embedded at the most likely location, i.e., in resin layer between the top and next ply of the fiber reinforced plastic laminated wingskin and near the spar overlap end. Multi-Point Constraint finite elements have been made use of at the vicinity of the delamination fronts. This helps in simulating the growth of the embedded delamination at both ends. The inter-laminar thermoelastic peel and shear stresses responsible for causing delamination damage due to a combined thermal and a static loading have been evaluated. Strain energy release rate components corresponding to the Mode I (opening), Mode II (sliding) and Mode III (tearing) of delamination are determined using the principle of Virtual Crack Closure Technique. These are seen to be different and non-self-similar at the two fronts of the embedded delamination. Residual stresses developed due to the thermoelastic anisotropy of the laminae are found to strongly influence the delamination onset and propagation characteristics, which have been reflected by the asymmetries in the nature of energy release rate plots and their significant variation along the delamination front.

• Restorative Dentistry and Endodontics
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• v.26 no.5
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• pp.409-417
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• 2001

The purpose of this study was to investigate the influence of light irradiation over self-priming adhesive on dentin bonding. After acid etching the exposed dentin, a self-priming adhesive (Prime&Bond$^{\circledR}$NT dental adhesive system Dentsply DeTrey, GmbH, Konstanz, Germany) was applied and light irradiation was done for 20 sec with regular intensity (600 mW/$\textrm{cm}^2$) in group I and for 3 sec with ultra-high intensity (1930 mW/$\textrm{cm}^2$) in group III. No light irradiation was done over self-priming adhesive in groups II and IV. Composite resin was added on the self-priming adhesive and irradiated for 40 sec with regular intensity (600 mW/$\textrm{cm}^2$) in groups I and II and for 3 sec with ultra-high intensity (1930 mW/$\textrm{cm}^2$) in groups III and IV. To see the effect of light curing time on dentin bonding, another 3 group specimens were prepared. Without light-irradiation over self-priming adhesive, added composite resin was irradiated for 3, 6, or 12 sec with ultra-high intensity light. After bonded specimens were stored in 37$^{\circ}C$ distilled water for 24 hours, shear bond strength were measured using a universal testing machine (4202, Instron, Instron Co., U.S.A.) and fractured surfaces were examined under a stereomicroscope (SZ-PT Olympus, Japan). Statistical analysis were done with one-way, two-way ANOVA and chi-square test. The results were as follows : 1. The shear bond strengths from the groups irradiated over self-priming adhesive were significantly higher than those from the groups without irradiation (p<0.05). 2. There was no significant shear bond strength difference between regular intensity light irradiation groups and ultra-high intensity ones (p>0.05). 3. There was no significant shear bond strength difference among various irradiation time groups with ultra-high intensity ones (p>0.05). 4. In stereomicroscopic examination of fractured surfaces, adhesive-cohesive mixed failure mode was mostly seen in all groups, and there was no significant difference in failure mode among groups (p>0.05).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.5542-5550
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• 2012

Third-order shear deformation theory is reformulated using the nonlocal elasticity of Eringen. The equation of equilibrium of the nonlocal elasticity are derived. This theory has ability to capture the both small scale effects and quadratic variation of shear strain through the plate thickness. Navier's method has been used to solve the governing equations for all edges simply supported boundary conditions. Analytical solutions of buckling of nano-scale plates are presented using this theory to illustrate the effect of nonlocal theory on buckling load of the nano-scale plates. The relations between nonlocal third-order and local theories are discussed by numerical results. Further, effects of (i) length (ii) nonlocal parameter, (iii) aspect ratio and (iv) mode number on nondimensional buckling load are studied. In order to validate the present solutions, the reference solutions are used and discussed. The present results of nano-scale plates using the nonlocal theory can provide a useful benchmark to check the accuracy of related numerical solutions.

• Composites Research
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• v.14 no.1
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• pp.8-14
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• 2001

A simplified method for determining the three mode(I, II, III) components of the strain energy release rate of free-edge delaminations in composite laminates is proposed. The interlaminar stresses are evaluated using the interface moment and the interface shear forces which are obtained from the equilibrium equations at the interface between the adjacent layers. Deformation of an edge-delaminated laminate is analysed by using a generalized quasi-three dimensional classical laminated plate theory. The analysis provides closed-form expression for the three components of the strain energy release rate. The analyses are performed for composite laminates subjected to uniaxial tension, with free-edge delaminations located symmetrically and asymmetrically with respect to the laminate midplane. The analysis results agreed with a finite element solution using the virtual crack closure technique.

• Steel and Composite Structures
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• v.23 no.3
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• pp.285-302
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• 2017

Buckling-restrained braced frames (BRBFs) are commonly used as the lateral force-resisting systems in building structures in the seismic regions. The nearly-symmetric hysteretic response and the delayed brace core fracture of buckling-restrained braces (BRBs) under the axial cyclic loading provide the adequate lateral force and deformation capacity to BRBFs under the earthquake excitation. However, the smaller axial stiffness of BRBs result in the undesirable higher residual drift response of BRBFs in the post-earthquake scenario. Two alternative approaches are investigated in this study to improve the elastic axial stiffness of BRBs, namely, (i) by shortening the yielding cores of BRBs; and (ii) by reducing the BRB assemblies and adding the elastic brace segments in series. In order to obtain the limiting yielding core lengths of BRBs, a modified approach based on Coffin-Manson relationship and the higher mode compression buckling criteria has been proposed in this study. Both non-linear static and dynamic analyses are carried out to analytically evaluate the seismic response of BRBFs fitted with short-core BRBs of two medium-rise building frames. Analysis results showed that the proposed brace systems are effective in reducing the inter-story and residual drift response of braced frames without any significant change in the story shear and the displacement ductility demands.