• Structural Engineering and Mechanics
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• v.68 no.4
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• pp.409-421
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• 2018

In the present paper, functionally graded (FG) materials are presented to investigate the bending analysis of simply supported plates. It is assumed that the material properties of the plate vary through their length according to the power-law form. The displacement field of the present model is selected based on quasi-3D hyperbolic shear deformation theory. By splitting the deflection into bending, shear and stretching parts, the number of unknowns and equations of motion of the present formulation is reduced and hence makes them simple to use. Governing equations are derived from the principle of virtual displacements. Numerical results for deflections and stresses of powerly graded plates under simply supported boundary conditions are presented. The accuracy of the present formulation is demonstrated by comparing the computed results with those available in the literature. As conclusion, this theory is as accurate as other shear deformation theories and so it becomes more attractive due to smaller number of unknowns. Some numerical results are provided to examine the effects of the material gradation, shear deformation on the static behavior of FG plates with variation of material stiffness through their length.

• Steel and Composite Structures
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• v.43 no.6
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• pp.821-837
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• 2022

This research is devoted to study the effects of humidity and temperature on the bending behavior of functionally graded (FG) ceramic-metal porous plates resting on Pasternak elastic foundation using a quasi-3D hyperbolic shear deformation theory developed recently. The present plate theory with only four unknowns, takes into account both transverse shear and normal deformations and satisfies the zero traction boundary conditions on the surfaces of the functionally graded plate without using shear correction factors. Material properties of porous FG plate are defined by rule of the mixture with an additional term of porosity in the through-thickness direction. The governing differential equations are obtained using the "principle of virtual work". Analytically, the Navier method is used to solve the equations that govern a simply supported FG porous plate. The obtained results are checked by comparing the results determined for the perfect and imperfect FG plates with those available in the scientific literature. Effects due to material index, porosity factors, moisture and thermal loads, foundation rigidities, geometric ratios on the FG porous plate are all examined. Finally, this research will help us to design advanced functionally graded materials to ensure better durability and efficiency for hygro-thermal environments.

• Steel and Composite Structures
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• v.44 no.4
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• pp.503-517
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• 2022

This paper presents the mechanical buckling of bi-directional functionally graded sandwich beams (BFGSW) with various boundary conditions employing a quasi-3D beam theory, including an integral term in the displacement field, which reduces the number of unknowns and governing equations. The beams are composed of three layers. The core is made from two constituents and varies across the thickness; however, the covering layers of the beams are made of bidirectional functionally graded material (BFGSW) and vary smoothly along the beam length and thickness directions. The power gradation model is considered to estimate the variation of material properties. The used formulation reflects the transverse shear effect and uses only three variables without including the correction factor used in the first shear deformation theory (FSDT) proposed by Timoshenko. The principle of virtual forces is used to obtain stability equations. Moreover, the impacts of the control of the power-law index, layer thickness ratio, length-to-depth ratio, and boundary conditions on buckling response are demonstrated. Our contribution in the present work is applying an analytical solution to investigate the stability behavior of bidirectional FG sandwich beams under various boundary conditions.

• Structural Engineering and Mechanics
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• v.85 no.3
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• pp.289-304
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• 2023

The main objective of this paper is to study the effect of porosity on the buckling behavior of thick functionally graded sandwich plate resting on various boundary conditions under different in-plane loads. The formulation is made for a newly developed sandwich plate using a functional gradient material based on a modified power law function of symmetric and asymmetric configuration. Four different porosity distribution are considered and varied in accordance with material propriety variation in the thickness direction of the face sheets of sandwich plate, metal foam also is considered in this study on the second model of sandwich which containing metal foam core and FGM face sheets. New quasi-3D high shear deformation theory is used here for this investigate; the present kinematic model introduces only six variables with stretching effect by adopting a new indeterminate integral variable in the displacement field. The stability equations are obtained by Hamilton's principle then solved by generalized solution. The effect of Pasternak and Winkler elastic foundations also including here. the present model validated with those found in the open literature, then the impact of different parameters: porosities index, foam cells distribution, boundary conditions, elastic foundation, power law index, ratio aspect, side-to-thickness ratio and different in-plane axial loads on the variation of the buckling behavior are demonstrated.

• Steel and Composite Structures
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• v.46 no.1
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• pp.1-13
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• 2023

Elastic bending of imperfect functionally graded sandwich plates (FGSPs) laying on the Winkler-Pasternak foundation and subjected to sinusoidal loads is analyzed. The analyses have been established using the quasi-3D sinusoidal shear deformation model. In this theory, the number of unknowns is condensed to only five unknowns using integral-undefined terms without requiring any correction shear factor. Moreover, the current constituent material properties of the middle layer is considered homogeneous and isotropic. But those of the top and bottom face sheets of the graded porous sandwich plate (FGSP) are supposed to vary regularly and continuously in the direction of thickness according to the trigonometric volume fraction's model. The corresponding equilibrium equations of FGSPs with simply supported edges are derived via the static version of the Hamilton's principle. The differential equations of the system are resolved via Navier's method for various schemes of FGSPs. The current study examine the impact of the material index, porosity, side-to-thickness ratio, aspect ratio, and the Winkler-Pasternak foundation on the displacements, axial and shear stresses of the sandwich structure.

• The Korean Journal of Emergency Medical Services
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• v.13 no.2
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• pp.87-98
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• 2009

Purpose : This study set out to compare the educational effects of a video self-instruction program for child CPR education on childcare teachers by applying the 2006 KACPR Guideline. By adopting the nonequivalent control group posttest quasi-experimental design, the study examined the educational effects on a group that did not receive instructions from the instructor, another group that received his instructions, and the other group that received an extra three-minute practice training session in addition to instructions. Methods : Data were gathered from August 6 to 18, 2008. As for research tools, the Knowledge Instrument of CPR by Connolly (2006) was used along with the National Practice Test Protocol for C1ass 1 Emergency Medical Technicians (2007) and Common Protocol for CPR (2006) to examine the performance of child CPR. By shooting the guide screen of $Resusci^{(R)}$ Junior CPR Manikin of Leardal with a video camera and using the Skill Guide Checklist of the Common Protocol for CPR (2006), the subjects' technical accuracy of chi1d CPR was evaluated. There were three subject groups: 29 childcare teachers randomly assigned to received the video self-instruction program training for chi1d CPR and no instructions from the instructor made up the control group; 22 childcare teachers randomly assigned to received the program training and instructions from the instructor made up experiment group I; 23 childcare teachers randomly assigned to received an extra three-minute practice training session in addition to the program training and the instructions made up experiment group II. The gathered data were analyzed with SPSS/PC+ (Version 14.0) in frequency, percentage, $X^2$-test, ANOVA, Scheffe test. Results : 1) There were no statistically significant differences (F=1.030, p=.362) among the groups in terms of knowledge scores after the child CPR education. 2) There were statistically significant differences (F=13.625, p=.000) among the groups in terms of performance abilities after the child CPR education. 3) There were no statistically significant differences (F=1.610, p=.207) among the groups in terms of technical accuracy of mouth-to-mouth resuscitation after the child CPR education 4) There were no statistically significant differences (F=1.484, p=.234) among the groups in terms of technical accuracy of chest compression after the child CPR education. Conclusion : The results indicate that childcare teachers can improve their performance abilities in child CPR when the instructors are active with their instructions and extra practice hours are secured through a VSI program. It's also needed to provide education with increasing concentration ratio about the items of lower knowledge points in order to help the teachers learn the accurate theory of child CPR. And there should be VSI programs of diverse conditions to increase the effects of child CPR training among childcare teachers.