• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.25-33
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• 2020

To investigate the relationship between strain distribution and tensile properties of brittle material, five types of tensile coupon of carbon fiber reinforced polymer (CFRP) modified the tab portion in order to have a strain distribution including S0, SD1, SD2, SV1, SV2 were tested. The ultimate stress and strain of SD2 and SV2 which was intended to have larger strain distribution were smaller than those of SD1 and SV1, that was more clearly shown in the test results of the symmetric coupons (SV series) than the asymmetric coupons (SD series). In addition, the ultimate stress and strain of most coupons with strain distribution in this study were decreased when compared to the control group with uniform strain. These results were analyzed in various ways through 1) the average of the strain values directly measured by the strain gages, 2) the converted strain calculated by dividing the total deformation by the effective length, and 3) the ultimate effective strain derived from both the elastic modulus and the ultimate load. The values measured by strain gage indicates response of the local region precisely, but it does not represent the response from whole section. However, the converted strain and effective strain can supplement disadvantage of gage because they represent the average response of whole section. In particular, the effective strain can provide rupture strain conservatively, which can be utilized in practice, when the value obtained by strain gage was not effective due to gage damage or abnormal gage readings near ultimate load. This value provides a value that can be used even when partial rupture has occurred and is reasonably useful for specimens with strain distribution.

• Composites Research
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• v.31 no.6
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• pp.429-434
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• 2018

We investigate strain transmissions of a surface bonded distributed optical fiber sensor considering strain variation according to positions. We first derive a strain transmission ratio depending on a wavelength of a strain distribution of the host structure from an analysis model. The strain transmission ratio is compared with numerical results obtained from the finite element method using ABAQUS. We find that the analytical results agree well with the numerical results. The strain transmission ratio is a function of a wavelength, i.e. the strain transmission ratio decreases (increases) as the wavelength of the host strain decreases (increases). Therefore, if an arbitrary strain distribution containing various wavelengths is given to a host structure, a distorted strain distribution will be observed in the distributed optical fiber sensor compare to that of the host structure, because each wavelength shows different strain transmission ratio. The strain transmission ratio derived in this study will be useful for accurately identifying the host strain distribution based on the signal of a distributed optical fiber sensor.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.137-144
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• 2019

In coupon test of carbon fiber reinforced polymers (CFRP) as brittle materials, the converted strain derived from total deformation and effective length was introduced and its advantages were described. In general, measured value from strain gauge is used for determining the tensile properties of material, but it is not quite effective in CFRP because brittle material can not redistribute its stress and it only represents local behavior. For this reason, the converted strain response can be utilized effectively as a supplementary indicator, which evaluated the average value of tensile properties in brittle material and confirmed the strain measured by strain gauge. In addition, the converted strain clearly visualized 1) the effect of initial internal strain caused by fabrication errors and setup misalignment when applying gripping force and 2) post-response of partial rupture of CFRP caused by non-uniform strain distribution. non-uniform strain distribution.

• Journal of the Korean Geotechnical Society
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• v.27 no.5
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• pp.17-31
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• 2011

This paper presents the results of a numerical investigation on the behavior of earth retaining wall system with emphasis on the groundwater lowering. Using the 2D stress-pore pressure coupled analysis, the effects of ground excavation and groundwater interaction were examined using wall horizontal deformation, ground surface movement, plastic strain pattern, effective stress distribution and axial stress of strut. In addition, based on the results from a parametric study on a wide range of soil profile and initial ground water table level, the ranges of wall displacement and ground deformation were suggested quantitatively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1211-1219
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• 1995

An upper bound elemental technique (UBET) program has been developed to analyze forging load, die-cavity filling and effective strain distribution for flash and flashless forgings. The simulation for flash and flashless forgings are applied axisy mmetric and plane-strain closed-die forging with rib-web type cavity. Inverse triangular and inverse trapezoidal elements are used to analyze flashless forging. The analysis is described for merit of flashless precision forging. Experiments have been carried out with pure plasticine billets at room temperature. Theoretical predictions of the forging load and the flow pattern are in good agreement with experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.4
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• pp.427-436
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• 2014

The goal of this paper is to estimate proper hardfacing material and thickness of STD61 hot-working tool steel through three-dimensional heat transfer and thermal stress analyses. Stellite6, Stellite21 and 19-9DL superalloys are chosen as alternative hardfacing materials. The influence of hardfacing materials and thicknesses on temperature, thermal stress and thermal strain distributions of the hardfaced part are investigated using the results of the analyses. From the results of the investigation, it has been noted that a hardfacing material with a high conductivity and a thinner hardfaced layer are desired to create an effective hardfacing layer in terms of heat transfer characteristics. In addition, it has been revealed that the deviation of effective stress and principal strain in the vicinity of the joined region are minimized when the Stellite21 hardfaced layer with the thickness of 2 mm is created on the STD61. Based on the above results, a proper hardfacing material and thickness for STD61 tool steel have been estimated.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.979-984
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• 2008

This paper discusses how to use basic strut-and-tie models(STM) for practical application. Construction of STM starts with drawing of load paths with equilibrium conditions. Understanding of structural systems including form active systems, vector active systems, and section active systems help us select appropriate systems for possible STM. Simple circular fans can be employed for load paths from concentrated forces to distributed forces. Strength of struts depends on configuration of their nodal zones which meet tension ties and effective compressive strength. The effective compressive strength of struts are assumed to be mainly influenced by transverse strain.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.899-904
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• 2014

Thickness profiled blank is designed using optimization techniques for maximizing the bulged heights during the free bulging of Inconel 718. The thickness of the blank was described by the Bezier curve and the locations of the control points were used as the design variables for optimization. The maximization of the bulged heights within the limited strain range served as the objective function and constraints for optimization. The equivalent static loads method for non-linear static response structural optimization (ESLSO) was used and the result of the optimization revealed 22 increased bulged heights. A free bulging test using a blank with an optimized profile was conducted to verify the optimization process. The results were compared with those of numerical analysis in terms of bulged height and deformed shape.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.17-26
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• 2010

Pb-Sn solder is rapidly being replaced by lead-free solder for board-level interconnection in microelectronic package assemblies due to the environmental protection requirement. There is a general lack of mechanical reliability information available on the lead-free solder. In this study, thermo-mechanical behaviors of wire-bond plastic ball grid array (WB-PBGA) package assemblies are characterized by high-sensitivity moire interferometry. Experiments are conducted for two types of WB-PBGA packages that have Pb-Sn solder and lead-free solder as joint interconnections. Using real-time moire setup, fringe patterns are recorded and analyzed for several temperatures. Bending deformations of the assemblies and average strains of the solder balls are investigated and compared for the two type of WB-PBGA package assemblies. Results show that shear strain in #3 solder ball located near the chip shadow boundary is dominant for the failure of the package with Pb-Sn solder, while normal strain in #7 most outer solder ball is dominant for that with lead-free solder. It is also shown that the package with lead-free solder has much larger bending deformation and 10% larger maximum effective strain than the package with Pb-Sn solder at same temperature level.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.161-169
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• 2011

Two-way slabs reinforced with high-performance steels, which have several practical advantages of a reduction of congestion in heavily reinforced members, savings in the cost of labor and repair, the higher corrosion resistance, and a reduction of construction time, were constructed and tested. The influences of the flexural reinforcement ratio, concentrating the reinforcement in the immediate column region, and using steel fiber-reinforced concrete (SFRC) in the slab on the punching shear resistance and post-cracking stiffness were investigated, and compared with the punching shear test results of the slabs reinforced with conventional steels and GFRP bars. In addition, the strain distribution of flexural reinforcements and crack control were investigated, and the effective width calculating method for the average flexural reinforcement ratio was estimated. The use of high-performance steel reinforcement increased the punching shear strength of slabs, and decreased the amount of flexural reinforcements. The concentrating the top mat of flexural reinforcement increased the post-cracking stiffness, and showed better strain distribution and crack control. In addition, the use of SFRC showed beneficial effects on the punching shear strength and crack control. It was suggest that the effective width should be changed to larger than 2 times the slab thickness from the column faces.