• Journal of the Korean Society for Heat Treatment
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• v.31 no.2
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• pp.56-62
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• 2018

Many researchers have studied on the precipitation control after solution treatment to improve the damping capacity without decreasing the strength. However, studies on the damping capacity and microstructure changes after deformation in the solid solution strengthening alloys were inadequate, such as the Al-Zn series magnesium alloys. Therefore, in order to investigate the effect of annealing condition on microstructure change and damping a capacity of AZ61 magnesium alloy. In this study, it was confirmed that the microstructure changes affect the damping capacity and hardness when annealed AZ61 alloy. AZ61 magnesium alloy was rolled at $400^{\circ}C$ with rolling reduction of 30%. These specimens were annealed at $350^{\circ}C$ to $450^{\circ}C$ for 30-180 minutes. After annealing, microstructure was observed by using optical microscopy, and damping capacity was measured by using internal friction measurement machine. Hardness was measured by Vickers hardness tester under a condition of 0.3 N. In this study, static recrystallization was observed regardless of the annealing conditions. In addition, uniform equiaxed grain structure was developed by annealing treatment. Hardness is decreased with increasing grain size. This is associated with Hall-Petch equation and static recrystallization. In case of damping capacity, bigger grain size show the larger damping capacity.

• Steel and Composite Structures
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• v.51 no.6
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• pp.601-617
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• 2024

This work aims to explore the static behaviour of a tapered functionally graded porous plate (FGPP) with even and uneven porosity distributions resting on two parametric elastic foundations. The plate under investigation is subjected to bi-sinusoidal loading and the edges of the plate are exposed to different combinations of edge restrictions. In order to examin the static behaviour, bending factors (BF) related to bending and normal stresses have been evaluated using classical plate theory. To achieve this, the governing equations have been derived employing the energy concept. And to solve it, the Rayleigh-Ritz method with an algebraic function has been utilised; it is simple, precise, and computationally intensive. After convergence and validation analyses, new findings are made available. The BF of the plate have been exhaustively examined to explain the influence of aspect ratios, material property index, porosity factor, taper factor, and Winkler and Pasternak stiffness. It is observed that the BF of an elastically supported FGPP are influenced by the index of material propery and the aspect ratio. Findings also indicate that the impact of porosity is more when it is spread evenly, as opposed to when it is unevenly distributed. Further, the deformed plate's structure is significantly influenced by the different thickness variations. Examination of bending characteristics of FGPP having different new cases of thickness variations with different types of porosity distribution under fifteen different mixed edge constraints is the prime novality of this work. Results presented are reliable enough to be taken into account for future studies.

• IE interfaces
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• v.16 no.2
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• pp.222-228
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• 2003

Computer-dominated jobs and industrial automation have rapidly created work-related musculoskeletal disorders(WMSDs) and WMSDs are also founded in employees of other general industries. WMSDs has been growing problems for Korean industries with higher incidence rate every year. The objective of this paper is to analyze the effects of the neck muscle workload according to postures(joint angle) and load weights. Seven male students participated in this study. Neck workload was rated on each person using a Borg's CR-10 scale. ANOVA showed that the CR-10 ratings were statistically significant according to postures and load weights. To reduce the large number and severity of WMSDs, which employees have been experiencing, we need to redesign the job in workplace so that we can control hazards that are reasonably likely to be causing or contributing to the WMSDs. The results of this study can be used to establish the safety criteria of joint angle and weight of neck workload.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.541-550
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• 1997

Computational and experimental investigations on the three-dimensional flowfield through an automotive cooling fan are carried out in this work. Steady, incompressible, three-dimensional, turbulent flow through a rotating axial-flow fan is analyzed with Reynolds averaged Navier-Stokes equations and standard k-.epsilon. turbulence model. The governing equations are discretized with finite-volume approximations in non-orthogonal curvilinear coordinates. Computational static pressures on the casing wall agree well with the experimental data which are measured in this work. And, they are sensitive to the change of tip clearance. The flowfield is not significantly affected by the thickness of the blade. The k-.omega. model gives the static pressure rise on the casing wall which is similar to that with the k-.epsilon. model.

• Steel and Composite Structures
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• v.24 no.6
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• pp.659-670
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• 2017

In the present work, an analytical solution for the static analysis of laminated composites, functionally graded and sandwich singly and doubly curved panels on the rectangular plan-form, subjected to uniformly distributed transverse loading is presented. Mathematical formulation is based on the higher order shear deformation theory and principle of virtual work is applied to derive the equations of equilibrium subjected to small deformation. A solution methodology based on the fast converging finite double Chebyshev series is used to solve the linear partial differential equations along with the simply supported boundary condition. The effect of span to thickness ratio, radius of curvature to span ratio, stacking sequence, power index are investigated. The accuracy of the solution is checked by the convergence study of non-dimensional central deflection and moments. Present results are compared with those available in the literature.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.73-81
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• 2009

Casing leak tests using three kinds of static seals are performed by simulating test section for a 75 ton thrust class turbopump under ambient and cryogenic temperature environment. As results of application of Conical, PTFE, and C static seals to leak tests, even though they all work in normal temperature condition, only the PTFE and C static seals show good sealing performance in cryogenic condition. However, the Conical static seal fails because of the different thermal expansion rates due to the use of different materials in a LOX pump. It is found that unlike the PTFE and C static seals with sealing surfaces in axial direction, the sealing surface of the Conical static seal is in radial direction that may cause leak when the casings thermally shrink in radial direction. Especially, the C static seal reveals excellent sealing performance even for a used seal.

• Journal of the Korean Wood Science and Technology
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• v.25 no.1
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• pp.8-14
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• 1997

Stress wave velocity, wave impedance, and stress wave elasticity of small, clear bending specimens of five domestic softwoods (Pinus densiflora, Pinus koraiensis, Chamaecyparis obtusa, Cryptomeria japonica, and Larix leptolepis) and four tropical hardwoods(Kempas, Malas, Taun, and Terminalia) were correlated with static bending modulus of elasticity(MOE) and modulus of rupture(MOR). The degree of correlation between stress wave parameters and static bending properties was dependent on wood species tested. Stress wave elasticity and wave impedance were better predictors for static bending properties than stress wave velocity for each species individually and for softwood or hardwood species taken as a group, even though elasticity and impedance were nearly equally correlated with static bending properties apparently. Based upon the correlation coefficient between stress wave parameters and static properties, stress wave elasticity and wave impedance were found as stress wave parameters which can be used for the purpose of the reliable and successful prediction of bending properties. The degree of correlation between static MOE and MOR was also different according to wood species tested. Static MOE was nearly as well correlated with MOR as was stress wave elasticity. The results of this research are encouraging and can be considered as a basis for further work using full-size lumber. From the results of this study, it was concluded that stress wave measurements could provide useful predictions of static bending properties and was a feasible method for machine stress grading of domestic softwoods and tropical hardwoods tested in this study.

• Journal of the Korean Society of Safety
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• v.20 no.4 s.72
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• pp.148-153
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• 2005

Computer dominated jobs and industrial automation have rapidly created work-related musculoskeletal disorders(WMSDs) and WMSDS are expanding to employee of other general industry. Specific risk factors associated with WMSDs include repetitive motion, heavy lifting, forceful exertion, contact stress, vibration awkward posture and rapid hand and wrist movement. The purpose of this paper is to analyze the effects of the neck muscle workload according to posture(joint angle) and load weight. Seven male students participated in this study. To analyze neck muscle workload was studied on electromyographic(EMG) activity for sternocleidomastoid and trapezius, was subjectively rated using a Borg's CR-10 scale. ANOVA showed that the CR-10 ratings and most EMG root-mean-square (RMS) value were statistically significant improvement according to posture(joint angle) and load weight. The results of this study indicate the joint angle and weight of neck muscle workload to provide safe working conditions. To reduce the large number and severity of WMSDs employees have been experiencing, we need to redesign the job in workplace to identify and control hazards that are reasonably likely to be causing or contributing to the WMSDs.

• Ocean Systems Engineering
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• v.11 no.1
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• pp.59-81
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• 2021

The nonlinear formulation using the principle of virtual work-energy for free vibration of a large-sag extensible catenary riser in two dimensions is presented in this paper. A support at one end is hinged and the other is a free-sliding roller in the horizontal direction. The catenary riser has a large-sag configuration in the static equilibrium state and is assumed to displace with large amplitude to the motion state. The total virtual work of the catenary riser system involves the virtual strain energy due to bending, the virtual strain energy due to axial deformation, the virtual work done by the effective weight, and the inertia forces. The nonlinear equations of motion for two-dimensional free vibration in the Cartesian coordinate system is developed based on the difference between the Euler's equations in the static state and the displaced state. The linear and nonlinear stiffness matrices of the catenary riser are obtained and the eigenvalue problem is solved using the Galerkin finite element procedure. The natural frequencies and mode shapes are obtained. The results are validated with regard to the reference research addressing the accuracy and efficiency of the proposed nonlinear formulation. The numerical results for free vibration and the effect of the nonlinear behavior for catenary riser are presented.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.832-835
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• 2005

The objective of this research work is to investigate into static and dynamic characteristics of ISB panels with the expanded metal as an internally structured material. In order to investigate static and dynamic characteristics of ISB panels, several experiments, the tensile test, three-point bending test and impact test, are carried out. From the results of the experiments, the mechanical properties, bending stiffness and impact absorption energy of the ISB panel have been obtained. In addition, it has been shown that the static and dynamic characteristics of ISB panel are highly dependent on the crimping angle of the pyramidal structure for the expanded metal.