• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.74-81
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• 1996

The wave washer springs are widely used in non-return valves of fluid, especially in air check valves to confirm the rapid shut-off of valve propers. The stiffness of wave washer springs used in suction and exhaust valves of reciprocating air compressor play an important role on efficiency of the compressor. If the stiffness of the spring is too high, the pressure differences necessary to open the valves become high and the volumetric efficiency of cylinder decreasse. If the stiffness of the spring too low, the valve can not be closed rapidly and the inverse flow of air can take place. So, the optimum stiffness of valve spring is very important and it will be very helpful that the stiffness of wave washer springs to be used in suction and exhaust valves can be calculated in design stage of air compressor. In this paper the formula for calculating the spring constant of wave washer spring is introduced using bending and torsion theory of frames. The experiments are also carried out to measure the spring constants of several samples. It is proven that the calculated spring constants of wave washer springs are coincided well with measured values and that the formula presented in this paper for calculating the spring constants of wave washer spring is very useful for design of valves used in reciprocating air compressor.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.177-182
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• 2000

This paper predicted the equivalent stiffness of spatially reinforced composites (SRC) using the volume average of a fiber rod and matrix stiffness, and the strength of SRC using the stiffness reduction and the modified Tsai-Wu composite failure theory. Those equivalent engineering constants are used to analyze the mechanical behavior and the failure of SRC structures. Because the distribution of equivalent engineering constants is varying with the change in SRC shape, we made a program that predicts engineering constants of SRC. Both 3-D and 4-D SRC show the smallest tensile modulus and the largest shear modulus at the maximum rotated direction from each rod. Also the strength properties show the same tendency.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.467-473
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• 2017

This paper focuses on the investigation of three-dimensional (3D) warping effect on the stiffness constants of composite beams with closed section profiles. A finite element (FE) cross-sectional analysis is developed based on the Reissner's multifield variational principle. The 3D in-plane and out-of-plane warping displacements, and sectional stresses are approximated as linear functions of generalized sectional stress resultants at the global level and as FE shape functions at the local sectional level. The classical elastic couplings are taken into account which include transverse shear and Poisson deformation effects. A generalized Timoshenko level $6{\times}6$ stiffness matrix is computed for closed section composite beams with and without warping. The effect of neglecting the 3D warping on stiffness constants is shown to be significant indicating large errors as high as 93.3%.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.2
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• pp.153-158
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• 2016

The elastic material constants, stiffness constants ($c_{11}$, $c_{12}$, and $c_{44}$), are three unique coefficients that establish the relation between stress and strain. Accurate knowledge of mechanical properties and the stiffness coefficients for silicon is required for design of Micro-Electro-Mechanical Systems (MEMS) devices for proper modeling of stress and strain in electronic packaging. In this work, the stiffness coefficients for silicon as a function of temperature from $-150^{\circ}C$ to $+25^{\circ}C$ have been extracted by using the experimental measurements of Poisson's ratio (${\nu}$) of silicon in several directions.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.147-150
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• 2001

In the present work, a linear static analysis is presented for thin-walled prismatic box-beams made of generally anisotropic materials. A mixed beam theory has been used to model and carry out the analysis. Three different constitutive relations are assessed into the beam formulation. Simple layup cases having symmetric or anti-symmetric configuration have been chosen and tested to clearly show the effects of elastic couplings of the beam. Both 2D and 3D finite element structural analysis using the MSC/NASTRAN has been performed to validate the current analytical results. Results show that appropriate assumptions for the constitutive equations are important and prerequisite for the accurate prediction of beam stiffness constants and also for the beam behavior.

• Advances in aircraft and spacecraft science
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• v.2 no.3
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• pp.249-261
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• 2015

The mechanical characterization of composite materials is nowadays a major interest due to their increasing use in the aeronautic industry. The design of most of these materials is based on their stiffness, which is mainly obtained by means of tensile tests with strain gauge measurement. For thin laminated composites, this classical method requires adequate samples with specific orientation and does not provide all the independent elastic constants. Regarding ultrasonic characterization, especially immersion technique, only one specimen is needed and the entire determination of the stiffness tensor is possible. This paper presents a study of different methods to determine the mechanical properties of transversely isotropic carbon fibre composite materials (gauge and correlation strain measurement during tensile tests, ultrasonic immersion technique). Results are compared to ISO standards and manufacturer data to evaluate the accuracy of these techniques.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.57-60
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• 2002

The stiffness model has been proposed to predict elastic constants of twisted yarn composites. The model is based upon the unit cell structure, the coordinate transformation, and the volume averaging of compliance constants for constituent materials. For the correlation of analytic results with experiments, composite samples of various yarn twist angle were tested. The samples were fabricated by the RTM process using glass yarns and epoxy resin. The correlations of elastic constants showed relatively good agreements. The model provides the predictions of the three-dimensional engineering constants, which are valuable input data for the analytic characterization of textile composites made of twisted yarn.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.3
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• pp.77-85
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• 2020

In this study, we proposed a method to replace the solid finite element model of the boiler membrane wall for coal-fired power plants using an equivalent shell model. The application of a bending load to the membrane wall creates greater displacement at both ends of the central portion when compared with the middle when an isotropic elastic constant is used in the shell model. This is inconsistent with the results of the solid model where the central portion is uniformly deformed. Here, we presented a method to determine the orthotropic elastic constants of the shell model in terms of bending stiffness and vibration characteristics to solve this problem. Our analysis of the orthotropic shell model showed that the error ratio was 0.9% for the maximum displacement due to the bending load, 0.3% for the first natural frequency, and 2.5% for the second natural frequency when compared with the solid model. In conclusion, a complicated boiler membrane wall composed of a large number of pipes and fins can be replaced with a simple shell model that shows equivalent bending stiffness and vibration characteristics using our proposed method.

• Korean Journal of Materials Research
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• v.18 no.11
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• pp.592-596
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• 2008

Spring constants (displacement per unit applied load) of MEMS socket pins of given structures were computed by theoretical analysis and confirmed by the finite element method (FEM). In the theoretical analysis, the displacement of pins was calculated based on the 2-dimensional bending theory of the curved beam. For the 3-dimensional modeling, CATIA was used. After modeling, the raw data were transferred to ANSYS, which was employed in the 3-dimensional analysis for the calculation of the stress and strain and loaddisplacement The theoretical analysis and the FEM results were found to agree, with each showing the spring constants as 63.4 N/m within a reasonable load range. These results show that spring constants can be easily obtained through theoretical calculation without resorting to experiments and FEM analysis for simple and symmetric structures. For the some change of shape and structural stiffness, this theoretical analysis can be applied to MEMS socket pins.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1891-1897
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• 2006

In this study, a new model to predict the effective elastic constants of composites with spherical fillers is proposed. The original Eshelby model is extended to a finite filler volume fraction without using Mori-Tanaka's mean field approach. When single filler is embedded in the matrix, the effective elastic constants of the composite are computed. The composite is in turn considered as a new matrix, where new single filler is again embedded in the matrix. The predicted results by the present model with a series of embedding procedures are compared with those by Mori-Tanaka, self-consistent, and generalized self-consistent models. It is revealed through parametric studies such as stiffness ratio of the filler to the matrix and filler volume fraction that the present model gives more accurate predictions than Mori-Tanaka model without using the complicated numerical scheme used in self-consistent and generalized self-consistent models.