• Proceedings of the KSME Conference
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• 2001.06a
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• pp.945-950
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• 2001

Vacuum interrupters that is used in various switchgear components such as circuit breakers, distribution switches, contactors, etc. spreads the arc uniformly over the surface of the contacts. The electrode of vacuum interrupters is used sintered Cu-Cr material satisfied with good electrical and mechanical characteristics. Because the closing velocity is 1-3m/s, the deformation of the material of electrodes depends on the strain rate and the dynamic behavior of the sintered Cu-Cr material is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at the high strain-rate is obtained from the split Hopkinson pressure bar test using cylinder type specimens. Experimental results from both quasi-static and dynamic compressive tests with the split Hopkinson pressure bar apparatus are interpolated to construct the Johnson-Cook equation as the constitutive relation that should be applied to simulation of the dynamic behavior of electrodes. To evaluate impact characteristic of a vacuum interrupter, simulation is carried out with five parameters such as initial velocity, added mass of a movable electrode, wipe spring constant, initial offset of a wipe spring and virtual fixed spring constant.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.387-394
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• 2000

Theoretical and experimental study is conducted on the contact pressure distribution of a radial tire in motion under various camber angles. Tire construction is modelled by a spring bedded elastic ring, consisted of sidewall springs and a composite belt ring. The contact area is assumed to be a trapezoidal shape varying with camber angles and weighted load. The basic equation in a quasi-static form is derived for the deformation of a running belt with a constant velocity by the aid of Lagrange-Euler transformation. Galerkin's method and stepwise calculation are applied for solving the basic equation and the mechanical boundary condition along both sides of the contact belt part subjected to shearing forces transmitted from the sidewall spring. Experimental results on the contact pressure, measured by pressure sensors embedded in the surface of the drum tester, correspond well with the calculated ones for the test tire under various camber angles, running velocities and weighted loads. These results indicate that a buckling phenomenon of the contact belt in the widthwise direction occurs due to the effect of camber angle.

• Journal of Theoretical and Applied Mechanics
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• v.2 no.1
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• pp.31-50
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• 1996

In this paper, a finite element analysis based on the local approach concept to fracture in the continuum damage mechanics is performed to analyze ductile fracture in two dimensional quasi-static state. First an isotropic damage model based on the generalized concept of effective stress is proposed for structural materials in the context of large deformation. In this model, the stiffness degradation is taken as a measure of damage and so, the fracture phenomenon can be explained as the critical deterioration of stiffness at a material point. The modified Riks' continuation technique is used to solve incremental iterative equations. Crack propagation is achieved by removing critically damaged elements. The mesh size sensitivity analysis and the simulation of the well known shearing mode failure in plane strain state are carried out to verify the present formulation. As numerical examples, an edge cracked plate and the specimen with a circular hole under plane stress are taken. Load-displacement curves and successively fractured shapes are shown. From the results, it can be concluded that the proposed model based on the local approach concept in the continuum damage mechanics may be stated as a reasonable tool to explain ductile fracture initiation and crack propagation.

• Steel and Composite Structures
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• v.16 no.3
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• pp.253-267
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• 2014

Based on the test on a 1/2.5-scaled model of a two-bay and three-story inner frame composed of reinforced concrete beams and lattice steel reinforced concrete (SRC) irregular section columns under low cyclic reversed loading, the failure process and the features of the frame were observed. The subsequence of plastic hinges of the structure, the load-displacement hysteresis loops and the skeleton curve, load bearing capacity, inter-story drift ratio, ductility, energy dissipation and stiffness degradation were analyzed. The results show that the lattice SRC inner frame is a typical strong column-weak beam structure. The hysteresis loops are spindle-shaped, and the stiffness degradation is insignificant. The elastic-plastic inter-story deformation capacity is high. Compared with the reinforced concrete frame with irregular section columns, the ductility and energy dissipation of the structure are better. The conclusions can be referred to for seismic design of this new kind of structure.

• Transactions of Materials Processing
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• v.20 no.4
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• pp.309-315
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• 2011

The behavior of metallic materials at high strain rates shows different characteristics from those in quasi-static deformation. Therefore, the strain rate should be considered when simulating crash events. The objective of this paper is to evaluate the dynamic tensile characteristics of SPRC440 as a function of the volume fraction of phases. As-received SPRC440 is composed of ferrite and pearlite phases. However, ferrite and martensite phases were observed after heat treatment at $730^{\circ}C$ and $780^{\circ}C$ for 5 minutes, as expected by calculations based on the curves from dilatometry tests. High cross-head speed tensile tests were performed to acquire strain-stress curves at various strain rates ranging from 0.001 to $300\;s^{-1}$, which are typical in real vehicle crashes. It was observed that the flow stress increases with the strain rate and this trend was more pronounced in the as-received specimens consisting of ferrite and pearlite phases. It is speculated that the dislocation density in each phase has an influence on the strain rate sensitivity.

• Earthquakes and Structures
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• v.7 no.5
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• pp.797-815
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• 2014

This research aimed to investigate retrofitting methods for damaged RC columns with SRF (Super Reinforced with Flexibility) and aramid composites and their impacts on the seismic responses. In the first stage, two original (undamaged) column specimens, designed to have a flexural- or shear-controlled failure mechanism, were tested under quasi-static lateral cyclic and constant axial loads to failure. Afterwards, the damaged column specimens were retrofitted, utilizing SRF composites and aramid rods for the flexural-controlled specimen and only SRF composites for the shear-controlled specimen. In the second stage, the retrofitted column specimens were tested again under the same conditions as the first stage. The hysteretic responses such as strength, ductility and energy dissipation were discussed and compared to clarify the specific effects of each retrofitting material on the seismic performances. Generally, SRF composites contributed greatly to the ductility of the specimens, especially for the shear-controlled specimen before retrofitting, in which twice the deformation capacity was obtained in the retrofitted specimen. The shear-controlled specimen also experienced a flexural failure mechanism after retrofitting. In addition, aramid rods moderately fortified the specimen in terms of the maximum shear strength. The maximum strength of the aramid-retrofitted specimen was 12% higher than the specimen without aramid rods. In addition, an analytical modeling of the undamaged specimens was conducted using Response-2000 and Zeus Nonlinear in order to further validate the experimental results.

• Interaction and multiscale mechanics
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• v.6 no.2
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• pp.173-195
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• 2013

Meshfree methods are known to have the capability to overcome the strict regularization requirements and numerical instabilities that encumber the finite element method (FEM) in large deformation problems. They are also more naturally suited for problems involving material perforation and fragmentation. To take advantage of the high efficiency of FEM and high accuracy of meshfree methods, a coupled finite element (FE) and reproducing kernel (RK, one of the meshfree approximations) formulation is described in this paper. The coupling of FE and RK approximation is implemented in an evolutionary fashion, where the extent and location of the evolution is dependent on a triggering criteria provided by the material constitutive laws. To enhance computational efficiency, Gauss quadrature is applied to integrate both FE and RK domains so that no state variable transfer is required when mesh conversion is performed. To control the hourglassing that might occur with 1-point integrated hexahedral grids, viscous type hourglass control is implemented. Meanwhile, the FEM version of the K&C concrete (KCC) model was modified to make it applicable in both FE and RK formulations. Results using this code and the KCC model are shown for the modeling of concrete responses under quasi-static, blast and impact loadings. These analyses demonstrate that fragmentation phenomena of the sort commonly observed under blast and impact loadings of concrete structures was able to be realistically captured by the coupled formulation.

• Smart Structures and Systems
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• v.24 no.6
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• pp.783-791
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• 2019

Prefabricated reinforced-concrete shear walls are used extensively in building structures because they are convenient to construct and environmentally sustainable. To make large walls easier to transport, they are divided into smaller segments and then assembled at the construction site using a variety of connection methods. The present paper proposes a precast shear wall assembled using steel shear keys, wherein the shear keys are fixed on the embedded steel plates of adjacent wall segments by combined plug and fillet welding. The anchoring strength of shear keys is known to affect the mechanical properties of the wall segments. Loading tests were therefore performed to observe the behavior of precast shear wall specimens with different anchoring components for shear keys. The specimen with insufficient strength of anchoring components was found to have reduced stiffness and lateral resistance. Conversely, an extremely high anchoring strength led to a short-column effect at the base of the wall segments and low deformation ability. Finally, for practical engineering purposes, a design approach involving the safety coefficient of anchoring components for steel shear keys is suggested.

• Steel and Composite Structures
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• v.11 no.3
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• pp.251-271
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• 2011

To make direct comparisons regarding the cyclic behavior of thin steel plate shear walls (TSPSWs) with different infill-to-boundary frame connections, two TSPSWs were tested under quasi-static conditions, one having the infill plate attached to the boundary frame members on all edges and the other having the infill plate connected only to the beams. Also, the bare frame that was used in the TSPSW specimens was tested to provide data for the calibration of numerical models. The connection of infill plates to surrounding frames was achieved through the use of self-drilling screws to fish plates that were welded to the frame members. The behavior of TSPSW specimens are compared and discussed with emphasis on the characteristics important in seismic response, including the initial stiffness, ultimate strength and deformation modes observed during the tests. It is shown that TSPSW specimens achieve significant ductility and energy dissipation while the ultimate failure mode resulted from infill plate fracture at the net section of the infill plate-to-boundary frame connection after substantial infill plate yielding. Experimental results are compared to monotonic pushover predictions from computer analysis using strip models and the models are found to be capable of approximating the monotonic behavior of the TSPSW specimens.

• Transactions of Materials Processing
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• v.27 no.6
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• pp.331-338
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• 2018

Electrohydraulic forming (EHF) process is a high speed forming process that utilizes the electric energy discharge in fluid-filled chamber to deform a sheet material. This process is completed in a very short time of less than 1ms. Therefore, finite element analysis is essential to observe the deformation mechanism of the material in detail. In addition, to perform the numerical simulation of EHF, the material properties obtained from the high-speed status, not quasi static conditions, should be applied. In this study, to obtain the parameters in the constitutive equation of Al 6061-T6 at high strain rate condition, a surrogate model using an artificial neural network (ANN) technique was employed. Using the results of the numerical simulation with free-bulging die in LS-DYNA, the surrogate model was constructed by ANN technique. By comparing the z-displacement with respect to the x-axis position in the experiment with the z-displacement in the ANN model, the parameters for the smallest error are obtained. Finally, the acquired parameters were validated by comparing the results of the finite element analysis, the ANN model and the experiment.