• Computers and Concrete
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• v.31 no.3
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• pp.267-276
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• 2023

The main purpose of the current research is to develop an efficient two variables trigonometric shear deformation beam theory to investigate the buckling behavior of symmetric and non-symmetric functionally graded carbon nanotubes reinforced composite (FG-CNTRC) beam resting on an elastic foundation with various boundary conditions. The proposed theory obviates the use to shear correction factors as it satisfies the parabolic variation of through-thickness shear stress distribution. The composite beam is made of a polymeric matrix reinforced by aligned and distributed single-walled carbon nanotubes (SWCNTs) with different patterns of reinforcement. The material properties of the FG-CNTRC beam are estimated by using the rule of mixture. The governing equilibrium equations are solved by using new analytical solutions based on the Galerkin method. The robustness and accuracy of the proposed analytical model are demonstrated by comparing its results with those available by other researchers in the existing literature. Moreover, a comprehensive parametric study is presented and discussed in detail to show the effects of CNTs volume fraction, distribution patterns of CNTs, boundary conditions, length-to-thickness ratio, and spring constant factors on the buckling response of FG-CNTRC beam. Some new referential results are reported for the first time, which will serve as a benchmark for future research.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.4
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• pp.57-64
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• 2012

Ball shear test was performed by test variables such as loading speed and annealing time in order to investigate the effect of surface finishes on the bonding strength of Sn-1.2Ag-0.7Cu-0.4In Pb-free solder. The shear strength increased and the ductility decreased with increasing shear speed. With increasing shear speed, the electroless nickel immersion gold (ENIG) finish showed dominant brittle fracture mode, while organic solderability preservative (OSP) finish showed pad open fracture mode. The shear strength and toughness for both surface finishes decreased with increasing annealing time under the high-speed shear test of 500 mm/s. Typically, the thickness of intermetallic compound increased with increasing annealing time, which means that exposure of brittle fracture became much easier. With increasing annealing time, the both ENIG and OSP finishes exhibited the pad open fracture mode. Overall, ENIG finish showed higher shear strength rather than OSP finish due to its superior barrier stability.

• The Journal of Advanced Prosthodontics
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• v.1 no.3
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• pp.129-135
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• 2009

STATEMENT OF PROBLEM. Zirconia-based restorations have the common technical complication of delamination, or porcelain chipping, from the zirconia core. Thus the shear bond strength between the zirconia core and the veneering porcelain requires investigation in order to facilitate the material's clinical use. PURPOSE. The purpose of this study was to evaluate the bonding strength of the porcelain veneer to the zirconia core and to other various metal alloys (high noble metal alloy and base metal alloy). MATERIAL AND METHODS. 15 rectangular ($4\times4\times9mm$) specimens each of zirconia (Cercon), base metal alloy (Tillite), high noble metal alloy (Degudent H) were fabricated for the shear bond strength test. The veneering porcelain recommended by the manufacturer for each type of material was fired to the core in thickness of 3mm. After firing, the specimens were embedded in the PTFE mold, placed on a mounting jig, and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.5mm/min until fracture. The average shear strength (MPa) was analyzed with the oneway ANOVA and the Tukey's test ($\alpha$= .05). The fractured specimens were examined using SEM and EDX to determine the failure pattern. RESULTS. The mean shear strength ($\pm\;SD$) in MPa was 25.43 ($\pm\;3.12$) in the zirconia group, 35.87 ($\pm\;4.23$) in the base metal group, 38.00 ($\pm\;5.23$) in the high noble metal group. The ANOVA showed a significant difference among groups, and the Tukey' s test presented a significant difference between the zirconia group and the metal group. Microscopic examination showed that the failure primarily occurred near the interface with the residual veneering porcelain remaining on the core. CONCLUSION. There was a significant difference between the metal ceramic and zirconia ceramic group in shear bond strength. There was no significant difference between the base metal alloy and the high noble metal alloy.

• The Journal of Korean Academy of Prosthodontics
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• v.31 no.2
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• pp.165-179
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• 1993

Dicor has not been prescribed routinely, in spite of many advantages, because of esthetic limitations by excessive translucency and external shading. In an attempt to solve these problems, the technique of veneering Dicor by aluminous poreclain has been used and recently Dicor Plus system was developed. The purpose of this study was to evaluate the compatibility between Dicor and several veneering porcelains by measuring the shear bond strength and observing the failure mode and interface appearance with SEM. Total 55 Dicor disks(10.0mm diam. X 3.0mm thickness) were fabricated by lost wax technique and divided into five groups of 11. Veneering porcelains such as Dicor Plus, Vitadur Alpha, Vitadur N, Vivodent, and Ceramco II were built up over the center of the treated Dicor surface using paper tube(5.0mm diam. X 4.0mm height) and fired according to the manufacturesr’instructions. A representative sample from each group was completely embedded in epoxy resin and crosssectioned, and remaining 50 samples were embedded in epoxy resin with the bonded area perpendicular to table base. The shear bond strengths were measured by applying the shear load parallel to Dicor surface close to the bonded area. Failure modes and interface appearances were observed using SEM at 15 and 1000 magnification respectively. The obtained results were as follows : 1. The mean shear bond strengths showed Dicor-Dicor Plus(10.53 MPa); Dicor-Vitadur Alpha(8.84 MPa); Dicor-Vitadur N(7.37 MPa); Dicor-Vivodent(4.28 MPa); Dicor-Ceramco II(0.89 MPa). 2. The shear bond strength of Dicor-CeramcoII was significantly decreased compared with Dicor-Dicor Plus(p<0.01), but had no significant difference compared with Dicor-Vivodent(p>0.01). 3. The shear bond strengths of Dicor-Vitadur Alpha and Dicor-Vitadur N were not significantly different compared with Dicor-Dicor Plus(p>0.01). 4. SEM examination of bond failure modes revealed that Dicor-Dicor plus, Dicor-Vitadur Alpha, Dicor-Vitadur N exhibited cohesive failure within Dicor and Dicor-Vivodent exhibited adhesive failure. And Dicor-Ceramco III exhibited adhesive failure and cohesive failure within CeramcoIII together. 5. SEM examination of interfaces revealed that Dicor-Dicor Plus exhibited the most tight contact and Dicor-Vitadur Alpha, Dicor-Vitadur N exhibited acceptible contacts. But Vivodent exhibited discontinuous gap and Ceramco II exhibited large continuous gap.

• Structural Engineering and Mechanics
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• v.47 no.4
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• pp.575-598
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• 2013

The study presents the results of an experimental program concerning the shear force transfer between reinforced concrete (RC) jackets and existing columns with damages. In order to investigate the effectiveness of the repair method applied and the contribution of each shear transfer mechanism of the interface. It includes 22 concrete columns (core) (of 24,37MPa concrete strength) with square section (150mm side, 500 mm height and scale 1:2). Ten columns had initial construction damages and twelve were subjected to initial axial load. Sixteen columns have full jacketing at all four faces with 80mm thickness (of 31,7MPa concrete strength) and contain longitudinal bars (of 500MPa nominal strength) and closed stirrups spaced at 25mm, 50mm or 100mm (of 220MPa nominal strength). Fourteen of them contain dowels at the interface between old and new concrete. All columns were subjected to repeated (pseudo-seismic) axial compression with increasing deformation cycles up to failure with or without jacketing. Two load patterns were selected to examine the difference of the behavior of columns. The effects of the initial damages, of the reinforcement of the interface (dowels) and of the confinement generated by the stirrups are investigated through axial- deformation (slip) diagrams and the energy absorbed diagrams. The results indicate that the initial damages affect the total behavior of the column and the capacity of the interface to shear mechanisms and to slip: a) the maximum bearing load of old column is decreased affecting at the same time the loading capacity of the jacketed element, b) suitable repair of initially damaged specimens increases the capacity of the jacketed column to transfer load through the interface.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.467-476
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• 2004

Because of crack control by steel bars after cracking the material models for reinforced concrete(RC) differ from those for plain concrete(PL). The nonlinear behavior of columns subjected to lateral load was simulated with reasonable accuracy in 3D analysis by applying distinct material models for RC and PL zone subdivided properly on the section. The shear strain is confirmed to develope unstably with ununiform distribution in out-of-plane direction. And this tendency becomes stronger as the thickness of column member increases in out-of-plane direction. If this ununiformity in strain distribution is not taken into consideration the capacity and the deformability of columns in shear dominant failure are overestimated excessively in two dimensional analysis. By introducing equivalent softening model a behavior of columns can be predicted too in two dimensional analysis.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.667-675
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• 2004

This paper presents the failure mode and strengthening design of reinforced concrete slab strengthened with Carbon Fiber Reinforced Polymer(CFRP) grid. Parameters involved in this experimental study are FRP grid reinforcement quantity, repair mortar thickness, the presence of anchor, and strengthening in compression. In this study, there are different failure types with increasing the CFRP grid strengthening reinforcement. On the low strengthening level, CFRP grid in repair mortar cover ruptures. On the moderate strengthening level, there is a debonding shear failure in the interface of carbon FRP grid because of the excessive shear deformation. On the high strengthening level, diagonal shear failure occurs. With the increasing of FRP grid reinforcement, the strengthening effect increased, but the ductility decreased. By limiting the strengthening level, it can be achieved to prevent shear failure which result in sudden loss in the resisting load capacity. CFRP rupture failure is desirable, because CFRP ruptured concrete slab keeps the same load capacity and ductility haying before strengthening even after failure. Finally, design guideline and procedure are given for strengthening of concrete slab with CFRP grid.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.247-258
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• 2004

The composite shell element is developed for the solution of undamped forced vibration problem of composite curved panels. The finite element used in the current study is an 4-node enhanced assumed shell element with six degrees of freedom per node. The composite shell element is free of both shear and membrane locking phenomenon by using the enhanced assumed strain(EAS) method. A modification to the first-order shear deformation shell theory is proposed, which results in parabolic thorough-thickness distribution of the transverse shear strains and stresses. It eliminates the need for shear correction factors in the first order theory. Newmark's direct integration technique is used for carrying out the integration of the equation motion, to obtain the repones history. Parametric studies of curved composite panels are carried out for forced vibration analysis by geometrical shapes and by laminated composite; such as fiber orientation, stacking sequence.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.457-463
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• 2016

The newly developed super ductile duplex stainless steel (SDSS) has good strength and ductility, and it can be used to reduce weight and improve the fabrication efficiency of a carbody of a rolling stock. In this study, spot weldability tests were conducted to take advantage of SDDSS in a carbody for an intermodal tram. Specimens of various thickness (0.4 to 5.0 mm) were prepared to find the proper welding conditions, and tensile load tests were conducted to evaluate the tensile-shear strength of spot welded joints. Then, nugget diameters were measured to verify the quality. The tensile-shear strength was found to be proportional to the heat parameter. It was verified that the tensile-shear strengths and nugget sizes of the joints satisfy the standard requirements. The overall weldability tests confirmed that SDDSS can be used effectively for the carbody of an intermodal tram.

• Computers and Concrete
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• v.26 no.2
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• pp.185-201
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• 2020

This research is devoted to investigate the bending and free vibration behaviour of laminated composite/sandwich plates and shells, by applying an analytical model based on a generalized and simple refined higher-order shear deformation theory (RHSDT) with four independent unknown variables. The kinematics of the proposed theoretical model is defined by an undetermined integral component and uses the hyperbolic shape function to include the effects of the transverse shear stresses through the plate/shell thickness; hence a shear correction factor is not required. The governing differential equations and associated boundary conditions are derived by employing the principle of virtual work and solved via Navier-type analytical procedure. To verify the validity and applicability of the present refined theory, some numerical results related to displacements, stresses and fundamental frequencies of simply supported laminated composite/sandwich plates and shells are presented and compared with those obtained by other shear deformation models considered in this paper. From the analysis, it can be concluded that the kinematics based on the undetermined integral component is very efficient, and its use leads to reach higher accuracy than conventional models in the study of laminated plates and shells.