• Structural Engineering and Mechanics
• /
• v.85 no.6
• /
• pp.755-764
• /
• 2023

The article examines the impact response of the sandwich beam furnished by a novel bilayer core as inspired by the woodpecker's head architecture under different repeatedly exerted low-velocity impact loadings by employing the finite element package, ABAQUS. The sandwich beam forms four essential parts comprising bottom and top carbon fiber reinforced polymer laminates encasing bilayer core made of laterally arched solid hot melt adhesive material and aluminum honeycomb. Impact loadings are implemented repeatedly with a steel hemisphere impactor for various impact energies, 7.28 J, 9.74 J, and 12.63 J. Essentially, the commonly concentrated stresses at the impact region are regulated away by the arched core in all considered cases thus reducing the threat of failure. The sandwich beam can resist up to 5 continual impacts at 7.28 J and 9.74 J but only up to 3 times repeated loads at 12.63 J before visible failure is noticed. In the examination of several key impact performance indicators under numerous loading cases, the proposed beam demonstrates favorably up to 1.3-11.2 higher impact resistance efficacies compared to existing designs, therefore displaying an improvement in repeated impact resistance of the new design.

• The Korean Journal of Applied Statistics
• /
• v.22 no.6
• /
• pp.1265-1275
• /
• 2009

In this paper, we investigated the composite covariance structure models for repeated measures data with multiple repeat factors. When the number of repeat factors is more than three, it is infeasible to fit the composite covariance models using the existing statistical packages. In order to fit the composite covariance structure models to real data, we proposed two approaches: the dimension reduction approach for repeat factors and the random effect model approximation approach. Our proposed approaches were illustrated by using the blood pressure data with three repeat factors obtained from 883 subjects.

• The Korean Journal of Applied Statistics
• /
• v.21 no.2
• /
• pp.291-299
• /
• 2008

This paper discusses model building for repeated binary response data with different time-dependent covariates each occasion. Since repeated measurements data are having correlated structure, weighed least squares(WLS) methodology is applied. Repeated measures designs are usually having different sizes of experimental units like split-plot designs. However repeated measures designs differ from split-plot designs in that the levels of one or more factors cannot be randomly assigned to one or more of the sizes of experimental units in the experiment. In this case, the levels of time cannot be assigned at random to the time intervals. Because of this nonrandom assignment, the errors corresponding to the respective experimental units may have a covariance matrix. So, the estimates of effects included in a suggested logit model are obtained by using covariance structures.

• The Journal of Advanced Prosthodontics
• /
• v.6 no.6
• /
• pp.427-433
• /
• 2014

PURPOSE. Surface color is one of the main criteria to obtain an ideal esthetic. Many factors such as the type of the material, surface specifications, number of firings, firing temperature and thickness of the porcelain are all important to provide an unchanged surface color in dental ceramics. The aim of this study was to evaluate the color changes in dental ceramics according to the material type and glazing methods, during the multiple firings. MATERIALS AND METHODS. Three different types of dental ceramics (IPS Classical metal ceramic, Empress Esthetic and Empress 2 ceramics) were used in the study. Porcelains were evaluated under five main groups according to glaze and natural glaze methods. Color changes (${\Delta}E$) and changes in color parameters (${\Delta}L$, ${\Delta}a$, ${\Delta}b$) were determined using colorimeter during the control, the first, third, fifth, and seventh firings. The statistical analysis of the results was performed using ANOVA and Tukey test. RESULTS. The color changes which occurred upon material-method-firing interaction were statistically significant (P<.05). ${\Delta}E$, ${\Delta}L$, ${\Delta}a$ and ${\Delta}b$ values also demonstrated a negative trend. The MC-G group was less affected in terms of color changes compared to other groups. In all-ceramic specimens, the surface color was significantly affected by multiple firings. CONCLUSION. Firing detrimentally affected the structure of the porcelain surface and hence caused fading of the color and prominence of yellow and red characters. Compressible all-ceramics were remarkably affected by repeated firings due to their crystalline structure.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.36 no.1
• /
• pp.19-26
• /
• 2023

Because of the development of computational resources, an entire structure in which many components are combined can be analyzed. To do so, the calculation time and number of data points are increased. In many practical industry structures, there are many parts with repeated patterns. To analyze the repetitive structures effectively, a homogenization method is usually employed. In a homogenization module, including commercial programs, it is generally assumed that a unit cell is repeated in all directions. However, the practical industry structures usually have complicated, repeated patterns or structures. Complicated patterns are difficult to address using the conventional homogenization method. Therefore, in this study, a multilevel homogenization method was devised to consider complex regularities. The proposed homogenization method divides the structure into several areas and performs multiple homogenizations, resulting in a more accurate analysis than that provided by the previous method.

• Journal of Sensor Science and Technology
• /
• v.20 no.6
• /
• pp.393-399
• /
• 2011

In this paper, we designed and fabricated the novel air flow sensor using air drag force, which can be applied to the low air flow detection. To measure the low air flow, we should enlarge the air drag force and the output signal at the given air flow. The paddle structure is applied to the device, and the device is vertically located against the air flow to magnify the air drag force. We also adapt the corrugation structure to improve the output signals on the given air velocity. The device structure is made up of the silicon nitride layer and the output signal is measured with the piezoresistive layer. The output signals from the corrugated device show the better measurement sensitivity and the response time than that of flat one. The repeated measurement also shows the stabilized signals.

• Korean Journal of Child Studies
• /
• v.26 no.1
• /
• pp.15-29
• /
• 2005

This study investigated 2- and 3-year-olds' story comprehension by story structure, Sixty-eight children from day-care centers in Seoul and Kyunggi province were tested story comprehension about causal, noncausal, discontinuous story presented by pictures. Story comprehension included literal, inferential, & empathic comprehension, Data were analysed by ANOVA(repeated measure) and t-test. The result showed that 3-year-olds scored higher in literal and inferential comprehension than 2-year-olds. Children's story comprehension(literal, inferential, & empathic) scores were higher in causal structure than discontinuous and noncausal structure.

• Structural Engineering and Mechanics
• /
• v.45 no.2
• /
• pp.201-209
• /
• 2013

A new dynamic reliability analysis of structure under repeated random loads is proposed in this paper. The proposed method is developed based on the idea that the probability density of several times random loads can be derived from the probability density of single-time random load. The reliability prediction models of structure based on time responses under several times random loads with and without strength degradation are obtained by using the stress-strength interference theory and probability density evolution method. The resulting differential equations in the prediction models can be solved by using the forward finite difference method. Then, the probability density functions of strength redundancy of the structures can be obtained. Finally, the structural dynamic reliability can be calculated using integral method. The efficiency of the proposed method is demonstrated numerically through a speed reducer. The results have shown that the proposed method is practicable, feasible and gives reasonably accurate prediction.

• Journal of the Korea Concrete Institute
• /
• v.20 no.6
• /
• pp.705-712
• /
• 2008

This study carried out simulation for structural layout design for concrete structures by using the models of the ground structure method. The micro lattice truss is modeled as assemblage of a number of unit cells. The progress of analysis repeat to undergo finite element analysis to feed-back results of stress to the stiffness of each member. Through the repeated this analysis, truss model is represented to form the topological materials and the structural shape with the use of the local stress condition without mathematical optimum tools. It is successful to analyse the shape-layout problem as numerical samples on the lattice truss model.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.6 s.171
• /
• pp.175-182
• /
• 2005

Inner structured and bonded panel, or ISB Panel, as a kind of sandwich type panel, has metallic inner structures which have low relative density, because of their dimensional shape of metal between a pare of metal skin sheets or face sheets. In this work, ISB panels and inner structures formed as repeated pyramidal shapes are introduced. Pyramidal structures are formed easily with expanded metal sheet by the crimping process. Three kinds of pyramidal structures are made and used to fabricate test specimen. Through the multi-point electrical resistance welding, inner structures are bonded with skin sheet. 3-point bending tests are carried out to measure the bending stiffness of ISB panel and experimental results are discussed.