• 한국세라믹학회지
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• 제28권10호
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• pp.810-818
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• 1991

Fracture responses of Al2O3 tubes were investigated for various loading paths under combined tension/torsion. The fracture criterion did not depend on loading paths. Fracture angles agreed well with the maximum tensile stress criterion. As the loading condition approaches a shear dominant state, the tensile principal stress at fracture increases compared to the uniaxial fracture strength. By using the Weibull modulus obtained from tension and torsion tests, the Weibull statistical fracture strengths were compared with experimental data. This comparison suggests that fracture may occur at the surface of the specimen when tensile stress is dominant, but within the volume of the specimen when shear stress is dominant. The Weibull fracture strength increased as the loading conition approached a shear dominant state, but underestimated compared to experimental data. Finally, a new fracture criterion was proposed by including the effect of compressive principal stress. The proposed criterion agreed well with experimental data of Al2O3 tubes not only at combined tension/torsion but also at balanced biaxial tension.

• 센서학회지
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• 제29권5호
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• pp.348-353
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• 2020

This paper presents an adaptive method to avoid obstacles in various environmental settings, using a two-dimensional (2D) LiDAR sensor for mobile robots. While the conventional reaction based smooth nearness diagram (SND) algorithms use a fixed safety distance criterion, the proposed algorithm autonomously changes the safety criterion considering the obstacle density around a robot. The fixed safety criterion for the whole SND obstacle avoidance process can induce inefficient motion controls in terms of the travel distance and action smoothness. We applied a multinomial logistic regression algorithm, softmax regression, to classify 2D LiDAR point clouds into seven obstacle structure classes. The trained model was used to recognize a current obstacle density situation using newly obtained 2D LiDAR data. Through the classification, the robot adaptively modifies the safety distance criterion according to the change in its environment. We experimentally verified that the motion controls generated by the proposed adaptive algorithm were smoother and more efficient compared to those of the conventional SND algorithms.

• 자원환경지질
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• 제33권2호
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• pp.117-128
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• 2000

Regional evaluations of slope stability by the failure criterion and by environmental geological factors were conducted. The failure criterion is the general conditions for plane failure which consider the geometrical conditions between geological discontinuities and topographical slope planes. The factor focused in this condiction is dip and dip direction. Geostatics, named semivariogram was used for establishing structural domains in slope stability evaluation by the failure criterion. The influential range was calculated to 6 km in the case of dip direction of dominant joint set and 7 km in the case of dip of the same dominant joint set. Then applying this failure criterion to the study area produced a slope stability map using the established domains and slopes generated by TIN module of ARC/INFO GIS. This study considered another regional slope stability analysis. 5 failure-driven factors 9the unstable slope map, geology, engineering soil, groundwater, and lineament density) were selected and used as data coverages for regional slope stability evaluation by geoenvironmental factors. These factors were weighted and overlayed in GIS. From the graph of cumulatave area (%) and instability index, finding critical points classified the instability indices. The most unstable slopes are located in the southern area of Mt. Eorae, Dabul-ri, and the eastern area of Junkok-ri in the first area is plane failure. Also, the expected orientations of failure are 59/338 and 86/090 (dip/dip direction).

• 감성과학
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• 제15권4호
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• pp.517-526
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• 2012

This study investigated the impact of individual differences in motivational reactivity on cognitive effort, memory strength (sensitivity) and decision making (criterion bias) in response to Internet ads with positive and negative content. Individual variation in trait motivational activation was measured using the Motivational Activation Measurement developed by A. Lang and her colleagues (A. Lang, Bradley, Sparks, & Lee, 2007). MAM indexes an individual's tendency to approach pleasant stimuli (ASA, Appetitive System Activation) and avoid unpleasant stimuli (DSA, Defensive System Activation). Results showed that individuals higher in ASA exert more cognitive effort during positive ads than individuals lower in ASA. Individuals higher in DSA exert more cognitive effort during negative ads compared to individuals lower in DSA. ASA did not predict recognition memory. However, individuals higher in DSA recognized ads better than those lower in DSA. The criterion bias data revealed participants higher in ASA had more conservative decision criterion, compared to participants lower in ASA. Individuals higher in DSA also showed more conservative decision criterion compared to individuals lower in DSA. The theoretical and practical implications are discussed.

• Geomechanics and Engineering
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• 제8권3호
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• pp.391-414
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• 2015

In this paper, stabilities of a plane slide rock slope under different hydraulic distributions were studied based on the nonlinear Barton-Bandis (B-B) failure criterion. The influence of various parameters on the stability of rock slopes was analyzed. Parametric analysis indicated that studying the factor of safety (FS) of planar slide rock slopes using the B-B failure criterion is both simple and effective and that the effects of the basic friction angle of the joint (${\varphi}_b$), the joint roughness coefficient (JRC), and the joint compressive strength (JCS) on the FS of a planar slide rock slope are significant. Qualitatively, the influence of the JCS on the FS of a slope is small, whereas the influences of the ${\varphi}_b$ and the JRC are significant. The FS of the rock slope decreases as the water in a tension crack becomes deeper. This trend is more significant when the flow outlet is blocked, a situation that is particularly prevalent in regions with permafrost or seasonal frozen soil. Finally, the work is extended to study the reliability of the slope against plane failure according to the uncertainty from physical and mechanics parameters.

• Structural Engineering and Mechanics
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• 제65권6호
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• pp.699-706
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• 2018

In the present contribution, fracture resistance of U-notched GPPS members under mixed mode I/III loading conditions is assessed by using the Averaged Strain Energy Density (ASED) criterion. This criterion has been founded based on the ASED parameter averaged over a well-defined control volume embracing the notch edge. The validation of the theoretical criterion predictions is evaluated through comparing with the results of a series of mixed mode I/III fracture tests conducted on rectangular-shaped GPPS specimens weakened by a single edge U-notch. A recently developed apparatus for mixed mode I/III fracture experiments is employed for measuring the fracture loads of the specimens. The test samples are fabricated with different notch tip radii with the aim of evaluating the influence of this major feature of the U-notched components on the mixed mode I/III fracture behavior. It is shown that the onset of brittle fracture in U-notched GPPS specimens under various combinations of tension and out-of-plane shear can well be predicted by means of the ASED criterion.

• Structural Engineering and Mechanics
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• 제75권4호
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• pp.445-454
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• 2020

Structural damage identification (SDI) is a crucial step in structural health monitoring. However, some of the existing SDI methods cannot provide enough identification accuracy and efficiency in practice. A novel whale optimization algorithm (WOA) based method is proposed for SDI by weighting modal data and flexibility assurance criterion in this study. At first, the SDI problem is mathematically converted into a constrained optimization problem. Unlike traditional objective function defined using frequencies and mode shapes, a new objective function on the SDI problem is formulated by weighting both modal data and flexibility assurance criterion. Then, the WOA method, due to its good performance of fast convergence and global searching ability, is adopted to provide an accurate solution to the SDI problem, different predator mechanisms are formulated and their probability thresholds are selected. Finally, the performance of the proposed method is assessed by numerical simulations on a simply-supported beam and a 31-bar truss structures. For the given multiple structural damage conditions under environmental noises, the WOA-based SDI method can effectively locate structural damages and accurately estimate severities of damages. Compared with other optimization methods, such as particle swarm optimization and dragonfly algorithm, the proposed WOA-based method outperforms in accuracy and efficiency, which can provide a more effective and potential tool for the SDI problem.

• Wind and Structures
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• 제14권2호
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• pp.113-131
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• 2011

Excessive wind-induced motion in tall buildings can cause discomfort, affect health, and disrupt the daily activities of the occupants of a building. Dynamic vibration absorbers such as the tuned mass dampers (TMDs) can be used to reduce the wind-induced motion below a specified tolerable serviceability limit state (SLS) criterion. This study investigates whether the same probability of not exceeding specified wind-induced motion levels can be achieved by torsionally sensitive structures without/with linear/nonlinear TMDs subjected to partially correlated wind forces, if they are designed to just meet the same SLS criterion. For the analyses, different structures and the uncertainty in the response, wind load and perception of motion is considered. Numerical results indicate that for structures that are designed or retrofitted without or with optimum linear TMDs and satisfying the same SLS criterion, their probability of exceeding the considered criterion is very consistent, if the inherent correlation between the wind forces is considered in design. However, this consistency deteriorates if nonlinear TMDs are employed. Furthermore, if the correlation is ignored in the design, in many cases a slightly unconservative design, as compared to the designed by considering correlation, is achieved.

• 소성∙가공
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• 제14권7호
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• pp.601-606
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• 2005

A hole expansion process is an important process in producing a hub-hole in a wheel disc of a vehicle. In this process, the main parameter is the formability of a material that is expressed as the hole expansion ratio. In the process, a crack is occurred in the upper edge of a hole as the hole is expanded. Since prediction of the forming limit by hole expansion experiment needs tremendous time and effort, an appropriate fracture criterion has to be developed for finite element analysis to define forming limit of the material. In this paper, the hole expansion process of a hub-hole is studied by finite element analysis with ABAQUS/standard considering several ductile fracture criteria. The fracture mode and hole expansion ratio are compared with respect to the various fracture criteria. These criteria do not predict its fracture mode or hole expansion ratio adequately and show deviation from experimental results of hole expansion. A modified ductile fracture criterion is newly proposed to consider the deformation characteristics of a material accurately in a hole expansion process. A fracture propagation analysis at the hub-hole edge is also performed for high accuracy of prediction using the new fracture criterion proposed.

• 지구물리와물리탐사
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• 제2권2호
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• pp.112-121
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• 1999

This article reviews the development of geophysical inverse theory. In a series of articles published in 1967, 1968, and 1979, G. Backus and F. Gilbert a trade-off between model resolution and estimation errors in geophysical inverse problems, and gave a criterion to compromise the reciprocal relation. Although the criterion was not clear in the physical point of view, it had been extensively used in the interpretation of geophysical date in the 1970s. This was the starting point of the fruitful development of inverse theory in geophysics. A reasonable criterion to compromise the reciprocal relation was derived to solve linear problems by D. D. jackson in 1979, introducing the concept of a priori information about unknown model parameters. This Jackson's approach was extended to solve nonlinear problems on the basis o probabilistic approach to the inverse problems formulated by A. Tarantola and B. Vallete in 1982. At the end of 1980s ABIC (Akaike Bayesian Information Criterion) was introduced for selecting a more reasonable model in geophysics. Now the date inversion is regarded as the process of extracting new information from observed data, combining in with a priori information about model parameters, and constructing a more clear image of model.