• Design & Manufacturing
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• v.16 no.4
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• pp.46-51
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• 2022

The piercing process of creating holes in sheet metals for mechanical fastening generates high shear force. Real-time monitoring technology could predict tool damage and product defects due to this severe condition, but there are few applications for piercing high-strength aluminum. In this study, we analyzed the load signal to predict the punch's wear level during the process with a piezoelectric sensor installed piercing tool. Experiments were conducted on Al6061 T6 with a thickness of 3.0 mm using piercing punches whose edge angle was controlled by reflecting the wear level. The piercing load increases proportionally with the level of tool wear. For example, the maximum piercing load of the wear-shaped punch with the tip angle controlled at 6 degrees increased by 14% compared to the normal-shaped punch under the typical clearance of 6.7% of the aluminum piercing tool. In addition, the tool wear level increased compression during the down-stroke, which is caused by lateral force due to the decrease in the diameter of pierced holes. Our study showed the predictability of the wear level of punches through the recognition of changes in characteristic elements of the load signal during the piercing process.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.83-92
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• 1987

Fatigue fracture of reinforced concrete structures are characterized by considerably larger strains and microcracking as compared to fracture of R.C. structures under static loading. The strain of stirrup is increased suddenly by the occuring of inclined crack and the average strain ${\epsilon}_{\omega}$ of all stirrups in a structure at maximum load increase approximately in proportion to log N. The structures critical in longitudinal reinforcement seemed to have an endurance limit of 60~70 percent of static ultimate strengths for 1,000,000 cycles. In this test, the average fatigue strength at 1,000,000 cycles for all structures tested was approximately 65 percent of the static ultimate strength.

• Geomechanics and Engineering
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• v.12 no.3
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• pp.541-560
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• 2017

In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two non-coplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of $60^{\circ}$, before increasing to the maximum at the ligament angle of $120^{\circ}$, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when ${\alpha}$ < ${\beta}$, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using $PFC^{2D}$ were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.1
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• pp.13-22
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• 2015

In this study, a new RCSF (Reinforced Concrete Steel Frame) external connection method is proposed for seismic strengthening of medium-and low-rise reinforced concrete buildings. The RCSF method, proposed in this study, is capable of carrying out the seismic retrofitting construction while residents can live inside structures. The method is one of the strength design approach by retrofit which can easily increase the ultimate lateral load capacity of concrete buildings controlled by shear. The pseudo-dynamic test, designed using a existing school building in Korea, was carried out in order to verify the seismic strengthening effects of the proposed method in terms of the maximum load carrying capacity and ductility. Test results revealed that the proposed RCSF strengthening method installed in RC frame enhanced conspicuously the strength and displacement capacities, and the method can resist markedly under the large scaled earthquake intensity level.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.3
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• pp.155-161
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• 2009

An investigation of the deformation behavior of ${\gamma}'-Ni_3Al$ single crystals containing fine dispersion of disordered ${\gamma}$ particles was performed for several different crystal orientations. Deformation structures were observed by the weak-beam method of transmission electron microscopy (TEM). The critical resolved shear stress (CRSS) for (111) [$\bar{1}$01] slie. increases with increasing temperature in the temperature range where (111) slip operates. The CRSS for (111) [$\bar{1}$01] slip is dependent on crystal orientation in the corresponding temperature range. The temperature where the strenjlth reaches a maximum is dependent on crystal orientation; the higher the ratio of the Schmid factors of (010) [$\bar{1}$01] to that of (111) [$\bar{1}$01], the higher the peak temperature. The peak temperatures were increased by the precipitation of y particles for the samples of all orientations. Electron microscopy of deformation induced dislocation arrangements under peak temperature has revealed that most of dislocations are straight screw dislocations. The mobility of screw dislocations decreases with increasing temperature. Above the peak temperature, dislocations begin to cross slip from the (111) [$\bar{1}$01] slip system to the (010) [$\bar{1}$01] slip system, thus decreasing the strength.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.147-155
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• 2015

A new SRCF (Steel Reinforced Concrete Frame) external connection method for seismic strengthening of medium-and low-rise reinforced concrete buildings is reported in this paper. The SRCF method, proposed in this study, is capable of carrying out the seismic retrofitting construction while residents can live inside building. The method is one of the strength design approach by retrofit which can easily increase the ultimate lateral load capacity of concrete buildings controlled by shear. The pseudo-dynamic test, designed using a existing school building in Korea, was carried out in order to verify the seismic strengthening effects of the proposed method in terms of the maximum load carrying capacity and deformation. Test results revealed that the proposed SRCF strengthening method installed in RC frame enhanced conspicuously the strength and deformation capacities, and the method can resist markedly under the large scaled earthquake intensity level.

• Advances in nano research
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• v.12 no.1
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• pp.73-79
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• 2022

Due to the extensive use of concrete structures in various applications, the improvement of their strength and quality has become of great importance. A new way of achieving this purpose is to add different types of nanoparticles to concrete admixtures. In this work, a mathematical model has been employed to analyze the vibration of concrete beams reinforced by graphene oxide (GO) nanoparticles. To verify the accuracy of the presented model, an experimental study has been conducted to compare the compressive strengths of these beams. Since GO nanoparticles are not readily dissolved in water, before producing the concrete samples, the GO nanoparticles are dispersed in the mixture by using a shaker, magnetic striker, ultrasonic devices, and finally, by means of a mechanical mixer. The sinusoidal shear deformation beam theory (SSDBT) is employed to model the concrete beams. The Mori-Tanaka model is used to determine the effective properties of the structure, including the agglomeration influences. The motion equations are calculated by applying the energy method and Hamilton's principle. The vibration frequencies of the concrete beam samples are obtained by an analytical method. Three samples containing 0.02% GO nanoparticles are made and their compressive strengths are measured and compared. There is a good agreement between our results and those of the mathematical model and other papers, with a maximum difference of 1.29% between them. The aim of this work is to investigate the effects of nanoparticle volume fraction and agglomeration and the influences of beam length and thickness on the vibration frequency of concrete structures. The results show that by adding the GO nanoparticles, the vibration frequency of the beams is increased.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.617-627
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• 2011

This paper presents the results of analytical simulation of shake-table responses of a 1:5 scale 10-story reinforcement concrete(RC) residential building model by using the PERFORM-3D program. The following conclusion are drawn based on the observation of correlation between experiment and analysis; (1) The analytical model simulated fairly well the global elastic behavior under the excitations representative of the earthquake with the return period of 50 years. Under the design earthquake(DE) and maximum considered earthquake(MCE), this model shows the nonlinear behavior, but does not properly simulate the maximum responses, and stiffness and strength degradation in experiment. The main reason is considered to be the assumption of elastic slab. (2) Although the analytical model in the elastic behavior closely simulated the global behavior, there were considerable differences in the distribution of resistance from the wall portions. (3) Under the MCE, the shear deformation of wall was relatively well simulated with the flexural deformation being overestimated by 10 times that of experiment. This overestimation is presumed to be partially due to the neglection of coupling beams in modeling.

• KIEAE Journal
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• v.15 no.1
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• pp.139-146
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• 2015

This is an experimental study on the engineering characteristics of perforated reinforced concrete beams with shells. In the material matter of this study, the water cement ratio put 60%, the ratio of substitution of oyster shells to fine aggregate 30%. And in the structural matter, the form of opening put circle and square, the size of opening as the radius and the length of it changed from one to three times of the beam depth with a change presence and absence of reinforced steel around opening. All thirteen reinforced concrete beam tests composed one standard beam and twelve six beams with the circle and square opening were tested in shear strength under two points loading and compared and analyzed the characteristics of test beams under the same conditions one another. The results of the study showed as followed. 1) The initial crack load value of the opening test beams is similar the standard beam but the maximum load value decreased with increase in proportion of the opening size, in the square opening than the circle opening and in the absence than the presence of reinforced steel. 2) As the difference between the circle opening and the square opening beams is represented 2.17~9.8% in the maximum load value and the load capacity of the square opening suddenly decrease than it of the circle opening, it is judged because of the shortage of concrete section, the concentration of the stress in the corner of the square opening and material influence of shell substitution. 3) The failure figure such as the pattern of the crack and so on is represented brittle failure as the opening size is the bigger and the ratio of substitution is higher because of the lack material properties.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.153-159
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• 2002

This paper is an experimental work of estimating friction angle of very coarse grained soil such as rubble mound by performing laboratory experiments. Two crushed rocks of rubble mound were used for tests. Triaxial compression tests with drained conditions were performed to measure friction angles of soils prepared by mixing the crushed soil having an identical coefficient of uniformity with different maximum grain size distribution. Centrifuge model experiments with those soils were also performed to measure angle of repose and to estimate friction angle of soil from measuring the slope of slip line in the active stress state. Model tests were carried out by changing the G-levels of 1G and 50G. From triaxial compression tests, the measured value of friction angle of soil is in the range of $41{\sim}57^{\circ}$. The measured value of repose angle is in the range of $32{\sim}35^{\circ}$. The values of friction angle are found not so sensitive to the maximum grain size of soil as long as the coefficient of uniformity is identical. Estimated value of friction angle from measuring the slope of slip line in the active stress state is in the range of $30{\sim}46^{\circ}$. Thus, the estimated angle of friction are found to be greater in the order of the measured angle of repose, the estimated value from the slope of active state, and triaxial compression test results. On the other hand, the measured values of friction angle from triaxial tests were compared with empirical equations, based on the relation between friction angle and void ratio. Equations proposed by Helenelund(l966) and Hansen(1967) found to be relatively reliable to estimate friction angles of soil.