• Journal of the Korean Ceramic Society
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• v.34 no.8
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• pp.877-885
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• 1997

The dependence of strength, crack growth, fracture mode and degree of domain rearrangement of PZT ceramics on poling strength were studied. The PZT [(Pb0.94Sr0.06)(Zr0.46Ti0.54)O3+Nb(trace)] specimens were poled at 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 kv/mm, and the strength of the specimens was measured by 3 point flexure system. The bending strength of the specimen decreased in different modes according to the bending directions; xz, zx and yz plane direction with x axis of the poling direction in Cartesian coordinate system. The strength differences between the directions increased as the poling strength increased. The fracture mode transferred to intergranular fracture mode from transgranular one as the poling strength increased. The mechanical breakdown occurred when the poling strength higher than 3 kV/mm was applied to the specimen. It was observed that the crack length increased in the normal direction to the poling direction, however, decreased in the parallel direction to the poling direction when the poled PZT specimen was indented by the Vickers indenter. However, the crack produced by indentation continuously was continuously increased little by little after indentation on the specimen. The domain rearrangement occurred as the poling strength increased and the domains were rearranged more effectively when the electric field was continuously increased little by little.

• Journal of the Korean Society of Safety
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• v.38 no.3
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• pp.20-26
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• 2023

Fiber-reinforced composite materials with carbon, glass, and aramid fibers are widely applied to industrial field structures due to their excellent properties. However, carbon fibers are vulnerable to external impacts, whereas aramid fibers degrade when exposed to water. This study evaluated carbon/aramid fiber composites degraded and damaged by high-temperature saline environments using acoustic emission (AE). The test specimen was molded using an autoclave and immersed in seawater at 70 ℃ for 224 days. In order to imitate the damage, a 3-mm-diameter hole was drilled using a diamond drill. Additionally, the specimen with the perforation was repaired by patch attachment processing. Three-point bending was used to conduct the flexural experiment, and an AE sensor with a 150-kHz resonance frequency was attached to evaluate the damage and the effect of patch attachment. AE accumulative counts obtained at the maximum load were 69.2, 67.1, and 91.2 for a high-temperature seawater deteriorated condition, a hole specimen, and a repaired patch specimen, respectively. Furthermore, the maximum amplitude of AE was detected at low values of 28 dB, 31.3 dB, and 30.3 dB.

• Steel and Composite Structures
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• v.32 no.1
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• pp.79-90
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• 2019

This study introduces new connections that connect the beam to the column with slit dampers. Plastic deformations and damages concentrate on slit dampers. The slit dampers prevent plastic damages of column, beam, welds and panel zone and act as fuses. The slit dampers were prepared with IPE profiles that had some holes in the webs. In this paper, two experimental specimens were made. In first specimen (SDC1), just one slit damper connected the beam to the column and one IPE profile with no holes connected the bottom flange of the beam to the column. The second specimen (SDC2) had two similar dampers which connected the top and bottom flange of the beam to the column. Cyclic loading was applied on Specimens. The cyclic displacements conditions continued until 0.06 radian rotation of connection. The experimental observations showed that the bending moment of specimen SDC2 increased until 0.04 story drift. In specimen SDC1, the bending moment decreases after 0.03 story drift. Test results indicate the high performance of the proposed connection. Based on the results, the specimen with two slit damper (SDC2) has higher seismic performance and dissipates more energy in loading process than specimen SDC1. Theoretical formulas were extended for the proposed connections. Numerical studies have been done by ABAQUS software. The theoretical and numerical results had good agreements with the experimental data. Based on the experimental and numerical investigations, the high ductility of connection is obtained from plastic damages of slit dampers. The most flexural moment of specimen SDC1 occurred at 3% story drift and this value was 1.4 times the plastic moment of the beam section. This parameter for SDC2 was 1.73 times the plastic moment of the beam section and occurred at 4% story drift. The dissipated energy ratio of SDC2 to SDC1 is equal to 1.51.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.2
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• pp.164-171
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• 2005

This study aims to examine an effect of stacking sequence and curvature on the penetration characteristic of a composite laminated shell. For the purpose, we manufactured specimens with different stacking sequences and curvatures, and conducted a penetration test using an air-gun. To examine an influence according to stacking sequence, as flat plate and curvature specimen had more plies, their critical penetration energy was higher, Critical penetration energies of specimen A and C with less interfaces somewhat higher than those of B and D with more interfaces. The reason that with less interfaces, critical penetration energy was higher is pre-impact bending stiffness of composite laminated shell with less interfaces was lower than that of laminated shell with more interfaces, but bending stiffness after impact was higher. And it is because interface, the weakest part of the composite laminated shell, was influenced by transverse impact. As curvature increases, critical penetration energy increases linearly. It is because as curvature increases, resistance to in-plane deformation as well as bending deformation increases, which need higher critical penetration energy. Patterns of cracks caused by penetration of composite laminated shells include interlaminar crack, intralaminar crack, and laminar fracture. A 0$^{\circ}$ply laminar had a matrix crack, a 90$^{\circ}$ply laminar had intralaminar crack and laminar fracture, and interface between 0$^{\circ}$and 90$^{\circ}$laminar had a interlaminar crack. We examined crack length and delamination area through a penetration test. For the specimen A and C with 2 interface, the longest circumferential direction crack length and largest delamination area were observed on the first interface from the impact point. For the specimen B and D with 4 interface, the longest crack length and largest delamination area were observed on the third interface from the impact point.

• Journal of the Korea Concrete Institute
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• v.12 no.5
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• pp.121-130
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• 2000

Currently, in evaluating a flexural strength of a concrete member, the effect of specimen depth has not been systematically studied, even though its effect on ultimate strength of a section is very important. For all types of loading conditions, the trend is that the strength of a member tends to decrease when the member depth increases. In this study, the influence of specimen depth on flexural compressive strength of concrete member was examined experimentally. A series of C-shaped specimens subjected to axial compressive force and bending moment were tested using three geometrically similar specimens with different length-to depth ratios (h/c = 1, 2 and 4) which have compressive strength of 55 MPa. The results indicate that the flexural compressive strength decreased as the specimen depth increased. A model equation was derived based on regression analyses of the experimental data. Also, the results show that ultimate strain decreases as the specimen depth increases. Finally, a general model equation for the depth effect is proposed.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.76-79
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• 2005

Bending deformation and energy absorption characteristics of aluminum-composite hybrid tube beams have been analyzed for improvement in the bending performance of aluminum space frame by using experimental tests combined with theoretical and finite element analyses. Hybrid tube beams composed of glass fabric/epoxy layer wrapped around on aluminum tube were made in autoclave with the recommended curing cycle. Basic properties of aluminum material used for initial input data of the finite element simulation and theoretical analysis were obtained from the true stress-true strain curve of specimen which had bean extracted from the Al tube beam. A modified theoretical model was developed to predict the resistance to the collapse of hybrid tube beams subjected to a bending load. Theoretical moment-rotation angle curves of hybrid tube beams were in good agreement with experimental ones, which was comparable to the results obtained from finite element simulation. Hybrid tube beams strengthened by composite layer on the whole web and flange showed an excellent bending strength and energy absorption capability.

• Journal of the Korea Furniture Society
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• v.18 no.1
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• pp.20-30
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• 2007

This experiment was carried out to investigate the effects of number and location of finger joints on the bending strength of glue-laminated lumbers. Urea resin adhesives were used in this experiment and the resin content was 70% for cold pressing. The lamina were edge-jointed and end-jointed. The specimen were composed of one or three layers. The obtained results are summarized as follows; The effects of finger joints on the decrease of bending strength of glue laminated woods were different according to the number and location of finger joints. The decrease of MOR was highest on the middle position of laminated woods. The effects of several arrangements of finger joints on the bending strength of glue laminated woods showed on Figure 7 and 8. The variance of thickness-laminating on the bending strength of glue laminated woods were larger than those of width-laminating.

• Journal of the Korean Wood Science and Technology
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• v.46 no.1
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• pp.85-92
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• 2018

In order to use glued built up timber beam as a structural member for post and beam construction, it must be possible to manufacture long-span lumber. In this study, the researchers conducted a performance evaluation for longitudinal bonding of lumber (cross-section $89{\times}120mm$) made from larch. The specimens were prepared in six different forms using the longitudinal bonding method. The bonding strength of these specimens was tested through tensile strength tests and bending strength tests. The tensile strength test result of the longitudinally bonded parts was better than that of the double lap specimens. And, the tensile strength value of the scarf specimen was better than that of the hooked scarf specimen. The tensile strength of the GFRP (Glass Fiber Reinforced Plastic) rod insertion bonding specimen was 3.6 MPa, which was the highest. As for the bending strength test result of the longitudinally bonded part, the average MOR (modulus of rupture) of the specimen where a GFRP rod was inserted and bonded measured 29 MPa, while the specimens of other bonded parts showed a MOR no more than 11 MPa. Toughness destruction was observed in specimens where a GFRP rod was insertion-bonded. The rest of the specimens showed brittle destruction. The average MOR strength of the Rod + Lap specimen was 30.5 MPa, which was the highest among all longitudinally bonded specimens. The bending strength of the Rod + Lap specimens showed an effective strength that was 66% of that of the control group which were not longitudinally bonded.

• Journal of the Korean Wood Science and Technology
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• v.42 no.3
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• pp.258-265
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• 2014

By replacing the previous metal connector on the joints of timber structure, the GFRP reinforced laminated wooden pin was produced using a wooden material and Glass fiber reinforced plastic(GFRP) composite laminate. In addition, using the reinforced wooden pin, the tensile type shear strength test was conducted. Based on the result of the bending strength test of the reinforced laminated wooden pin according to the GFRP arrangement, a specimen(Type-A) with a single insertion of GFRP for each layer have shown the most favorable performance. Also, it was verified that densified specimen hot pressed for an hour at the temperature of $150^{\circ}C$ and with the oppression pressure $1.96N/mm^2$ have shown the improved performance of 1.57 times than the specimen without the densification. And in the bending strength test considering the load direction, edgewise have shown a higher performance of 3.51 times than the flatwise. A shear strength test was conducted using the Type-A reinforced laminated wooden pin which have shown a moderate performance on the test. Based on the test conducted by differentiating the type of the joint plate and the connector, compared to the specimen(Type-DS) applied with the drift pin and steel plate, the specimen( Type-WL) applied with the GFRP reinforced laminated wooden pin and GFRP reinforced wooden laminated plate have shown 1.12 times higher shear strength and also have shown an excellent toughness even after the maximum load.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.701-713
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• 2000

In this study, the 4-point bending test been performed in order to estimate effect of grinding on fatigue characteristics quantitatively for as-welded specimen, grinding specimen & TIG-dressing specimen for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strength at $2{\times}106$cycles of grinding specimen and TIG-dressing specimen has been increased compared with as-welded specimen and satisfied the grade of fatigue strength prescribed in specifications of domestics and AASHTO & JSSC. As a result of beachmark test, fatigue cracks on all specimens have occurred at several points where stress