• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.219-220
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• 2017

Current domestic waterproofing market in Korea mainly uses single-ply waterproofing materials comprised of coatings or waterproof sheets and two or more-ply composite waterproofing methods. In order to evaluate these types of composite waterproofing systems, a new test equipment and method that incorporates various deterioration conditions (joint displacement, chemical exposure, water pressure etc) was developed. In a comparison testing, the results showed that flexible type materials have higher response performance towards joint displacement than the hardened material. Furthermore, the importance of securing the stability of the waterproofing method in the vulnerable over-lap joint areas of waterproofing sheets is emphasized.

• Journal of Welding and Joining
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• v.29 no.4
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• pp.54-60
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• 2011

Adhesive bonding is one of the most promising joining methods which may substitute for conventional metallurgical joining processes, such as welding, brazing and soldering. Curing behavior and mechanical properties of adhesive joint are largely dependent on the curing agent including hardener and catalyst. In this study, effects of curing system on the curing behavior and single-lap shear strength of epoxy adhesive joint are investigated. Dihydrazide, anhydride and dicyandiamide(DICY) were chosen as hardener and imidazole and triphenylphosphine(TPP) were chosen as catalyst. In curing behavior, TPP showed the delay of the curing rate for DICY and ADH at $160^{\circ}C$, compared to imidazole catalyst due to the high curing onset/peak temperature. DICY seemed to be most beneficial in the joint strength for both steel and Al adherends, although the type of adherends affected the shear strength of epoxy adhesive joint.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.7 s.262
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• pp.808-815
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• 2007

The optical performance of the mirror fur satellite camera is highly dependent on the adhesive properties between the mirror and its support. Therefore, in order to design a mirror with high optical performance, the mechanical properties of adhesives should be well defined. In this research, the mechanical properties of three kinds of space adhesives are studied. In case of the materials which show nearly incompressible behavior such as space adhesives, it is important to measure shear modulus which governs deviatoric stress components. Also the experiment should be performed in circumstances similar to real manufacturing process of mirror, because extra factors such as size effects, the adhesion effects of primer and reactions between adhesive and primer affect the properties of adhesive regions. In this research shear moduli of the adhesives are determined by using a single lap adhesively bonded joint. For the shear tests, several temperatures have been selected from $-20^{\circ}C$ to $55^{\circ}C$ which is operating temperature range of the adhesive. In the case of linear behavior materials, shear moduli are calculated through a linear curve fitting. Shear stress-strain relation is obtained by using an exponential curve fitting for material which shows non-linear behavior. The shear modulus of each adhesive is expressed as a function of temperature. Characteristics and adaptability of the adhesives are discussed regarding their temperature sensitivity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.2
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• pp.119-128
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• 2010

The hygrothermal effect on the strength of composite single-lap bonded joints were investigated. The specimens were manufactured in four different manufacturing methods and tested in three different environmental conditions. An interesting result is that the strengths of the joints in the elevated temperature and wet (ETW) conditions were found to be 11 ~ 23% higher than those in the room temperature and dry (RTD) environment. In contrast, the strengths of the joints in the cold temperature and dry (CTD) condition decrease by 8 ~ 21% compared to those in the RTD environment except for cobonded joint. The difference in the strength by testing environments is mainly attributed to the change of the material properties of adhesive by temperature and moisture.

• Composites Research
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• v.16 no.6
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• pp.16-22
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• 2003

This paper studied the AE(acoustic emission) characteristics of the laminated composite structures. The composite stiffened panels under the compressive loading emitted various AE signals when they buckled or changed the buckling modes. In addition, the failure initiated and propagation generated a lot of complex signals. From the continuous signal generation. we identified when the failures initiated and whether they propagated or not. The single lap joint of laminated plates under tensional load also generated AE signals when bonding region failed. The first failure occurrence and its propagation are monitored by generated AE signals. The characteristics of AE signals used in this analysis are cumulative hits, hit distribution, peak frequency of generated AE waveform and amplitude of signals. The analysis of AE signals shows that continuous increment of cumulative hits can be regarded as damage propagation and three dominant peak frequencies can correspond to typical failure modes in the laminated composites.

• Composites Research
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• v.16 no.5
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• pp.45-53
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• 2003

The experimental and numerical investigations on the failure characteristics of the secondary bonded composite single-lap joints were performed. The initiations and growths of cracks were observed using CCD camera and acoustic emission sensor during the tension tests of the joint specimens. The structural behaviors of the specimens were predicted by the geometric nonlinear two-dimensional finite element analysis. The three types of observed initial cracks were included in each finite element models and the strain energy release rates of each specimen models were calculated by VCCT(Virtual Crack Closure Technique) technique. The tension tests showed that the initial cracks occurred in the 60∼90% of final failure loads and the major failure modes of the specimens were adhesive failure and the delamination between the 1st and 2nd ply of laminate. The specimens with the thicker bondline had earlier crack initiation loads but higher crack propagation resistance and eventually better loading capability. The delaminations were mostly observed in the thicker bondline specimens. The mode I values of calculated strain energy release rates were higher than the mode II values in the all specimen models considering the three types of initial cracks. The mode I and total strain energy release rates were calculated as higher values in the order of initial crack in the edge interface, comer interface and delamination between the plies of laminate.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.3
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• pp.157-164
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• 2003

The pulse-echo method is one of the most widely used ultrasonic techniques for application of nondestructive evaluation. Particularly, quantitative nondestructive evaluation of defects has been considered more important to assure the reliability and the safety of structure. Frequency energy in adhesive joints is based on the ultrasonic wave analysis. The attenuation coefficient upon wave amplitude and the frequency energy that is expressed in the term of wave pressure amplitude were utilized for the primary wave experiment. By means of a control experiment, it was confirmed that the variation of the frequency energy in adhesive joints depends on transition by stress variation. In this paper, the ultrasonic characteristics were measured for single lap joint and Double Cantilever Beam specimen with different fracture modes that was subjected to stress. Consequently, the data that was obtained from the adhesive specimen was analytically compared to the fracture mechanics parameter

• Progress in Superconductivity and Cryogenics
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• v.12 no.2
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• pp.5-8
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• 2010

In this study, the effect of bending strain on the transport property and critical current of lap and butt-jointed (non-laminated) BSCCO tapes has been investigated. The samples were joined using a mechanically controlled jointing procedure. To achieve a uniform thickness at the joint a single point loading contact has been devised. GFRP mandrels with different bending radii which support the sample during bending have been used. $I_c$ have been measured at 77 K and self field. In the case of easy bending test for jointed BSCCO tapes, sudden degradation of $I_c$ is caused by the local strain concentration due to non uniform deformation at the edge parts of the joint. In the case of hard bending test of jointed BSCCO tapes transverse macroscopic crack at specific subsection caused a large $I_c$ degradation. The transport property of jointed BSCCO tapes in each bending mode was discussed with the damage morphology occurred.

• Journal of Welding and Joining
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• v.23 no.6
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• pp.67-71
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• 2005

This paper is concerned with a study on fracture strength of composites in an adhesive single lap joint. The tests were carried out on joint specimens made with hybrid stacked composites consisting of the polyester and bamboo natural fiber layer. The main objective of this work was to evaluate the fracture properties adjacent to adhesive bonded joint of natural fiber reinforced composite specimens. From the results, natural fiber reinforced composites have lower tensile strength than the original polyester. But tensile-shear strength of natural fiber reinforced composites with bamboo layer far from adhesive bond is as high as that of the original polyester adhesive bonded joints. Spew filet at the end of the overlap reduced the stress concentration at the bonded area. Spew fillet and position of bamboo natural fiber layer have a peat effect on the tensile-shear strength of natural fiber reinforced composites including adhesive bonded joints.

• Journal of the Korean Wood Science and Technology
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• v.39 no.1
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• pp.53-59
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• 2011

A connection was made between a single stretcher and 2 headers with 2 threaded nails (Type-A), and another one between 2 stretchers and 2 headers with 4 threaded nails (Type-B) to use as specimens. Type-C was the stretchers that are connected with 2 threaded nails by half lap joint at end-distance 5D to reinforce Type-B, Type-C1 the stretchers that are connected by half lap joint at end-distance 10D, and Type-C2 with 3 threaded nails at end-distance 10D. Compressive shear strength of Type-C, the supplementation of Type-B, was decreased by 30%, compared with that of Type-B. Those of Type-B and Type-C1 that used longer end-distance than Type-C were about the same, and that of Type-C2 connected with 3 threaded nails was 1.28-times stronger than that of Type-C1. Connection of the retaining wall using existing square timber has a problem between long and short stretchers and 2 headers. So it was investigated in the experiment to replace it. Therefore, if Type-B is replaced with Type-C2 in constructing the retaining wall, the crack and the rupture of timber caused by threaded nail as well as construction period can be reduced, and also it can be expected to increase their own strength.