• Composites Research
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• v.18 no.1
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• pp.45-54
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• 2005

The delamination in the filament-wound composite flywheel rotor often lowers the performance of the flywheel energy storage system. A conventional ring type hub usually causes tensile stresses on the inner surface of the composite rotor, resulting in lowering the maximum rotational speed of the rotor. In this work, the stress and strain distributions within a hybrid composite rotor were derived from the two-dimensional governing equation with the specified boundary conditions, and an optimum pressure at the inner surface of the rotor was proposed to minimize the strength ratio and maximize the storage energy. A split type hub was introduced to apply the calculated optimum pressure at the inner surface, and a spin test was performed up to 40,000 rpm to demonstrate the performance of the split type hub with radial and circumferential strains measured using a wireless telemetry system. From the analysis and the test, it was found that the split type hub successfully generates a compressive pressure on the inner surface of the rotor, which can enhance the performance of the composite rotor by lowering the strength ratio within the rotor.

• Korean Journal of Materials Research
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• v.33 no.5
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• pp.205-213
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• 2023

This paper reports the results of an experimental examination using X-rays to test annealing materials for lapped bearing steel (STB2), to confirm the validity of the weighted averaging analysis method. The distribution behavior for the α_𝜓-sin²𝜓 diagram and the presence or absence of differences in the peak method, half-value breadth method, and centroid method were investigated. When lapping the annealed bearing steel (STB2) material, a residual stress state with a non-directional steep gradient appeared in the surface layer, and it was found that the weighted averaging analysis method was effective. If there is a steep stress gradient, the sin²𝜓 diagram is curved and the diffraction intensity distribution curve becomes asymmetric, resulting in a difference between the peak method, half-value breadth method, and centroid method. This phenomenon was evident when the stress gradient was more than 2~3 kg/mm²/㎛. In this case, if the position of the diffraction line is determined using the centroid method and the weighted averaging analysis method is applied, the stress value on the surface and the stress gradient under the surface can be obtained more accurately. When the stress gradient becomes a problem, since the curvature of the sin²𝜓 diagram appears clearly in the region of sin²𝜓 > 0.5, it is necessary to increase the inclination angle 𝜓 as much as possible. In the case of a lapping layer, a more accurate value can be obtained by considering 𝜎₃ in the weighted averaging analysis method. In an isotropic biaxial residual stress state, the presence or absence of 𝜎₃ can be determined as the presence or absence of strain for sin²𝜓≈0.4.

• Journal of Ocean Engineering and Technology
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• v.29 no.1
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• pp.34-44
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• 2015

A hydraulic tensile test machine (HSTM) is one of the devices used to obtain the flow stress of a material during high-speed elongation. This paper first describes some features of a newly built HSTM. The improvement histories of the upper and lower jigs, which are the most vital parts of the HSTM, are also presented. We have frequently witnessed test failures with 1st generation jigs and specimens due to slip between the jig and specimen. 2nd generation jigs provide more stable test results, but the use of a longer upper jig induces excessive vibration and consequently makes it difficult to attach an environment chamber. 3rd generation jigs have some advances in terms of the symmetric fastening between the upper jig and specimen, as well as an exemption from direct contact between the lower jig and specimen. The performance of an environment chamber is verified by high and low temperature tests. A high-speed displacement measurement system is introduced based on a high-speed camera and motion-tracking software with aid of a surface grid device for the specimen.

• Composites Research
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• v.28 no.1
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• pp.6-14
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• 2015

Polymerization shrinkage stress analysis of dimethacrylate-based composite (Clearfil AP-X, Kuraray) and silorane-based composite (Filtek P90, 3M ESPE) used for dental composite restorations was performed using strain-gage measurement and FEM analysis. A theoretical equation based on Young's modulus and polymerization shrinkage of the composite resin was proposed to predict the polymerization shrinkage stress. Experimental results showed that the maximum shrinkage stress of Clearfil AP-X was about 2.8 times higher than Filtek P90. FEM analysis agreed with such experimental stress behaviours and showed that the maximum Von-Mises stress appeared near the margin of the filled resin adhered with PMMA ring. The stress concentration at the interface on the specimen surface was higher than that in the interior. The maximum error of shrinkage stress by the theoretical equation was reasonable within 5% in comparison to FEM results under plane stress.

• Composites Research
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• v.16 no.3
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• pp.9-17
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• 2003

In order to simulate the crack connection between cords and the interply crack growth in the belt-layer of real tire, 2 ply rubber/cord laminate specimens with exposed edges were tested in 4~11mm displacement control. Measurement of the crack connection is evaluated when crack reaches the half of the length between 45$^{\circ}$ aligned cords, and the amount of the crack growth is measured by the steel probe method. 2 dimensional analytic modeling was performed to simulate the crack connection between cords at the exposed edges. Also, the theoretical life of the specimens was calculated from the crack connection life between cords(critical value) and from the critical value to the final failure by the use of Tearing energy(T); the strain energy release per unit area of one fracture surface of a crack. Then, theoretical life was compared with those of experiments. The life prediction up to the critical value has about 20% error compared to experimental life, and up to the final failure about 65% error. Therefore, total theoretical life has about 45% error compared to the experimental life, which is conceivable in the case of rubber.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.813-818
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• 1998

A simple method to measure the elastic modulus E and Poisson's ratio v of diamod-like carbon (DLC) films deposited on Si wafer was suggested. Using the anisotropic etching technique of Si we could make the edge of DLC overhang free from constraint of Si substrate. DLC film is chemically so inert that we could not on-serve any surface damage after the etching process. The edge of DLC overhang free from constraint of Si substrate exhibited periodic sinusoidal shape. By measuring the amplitude and the wavelength of the sinu-soidal edge we could determine the stain of the film required to adhere to the substrate. Since the residual stress of film can be determine independently by measurement of the curvature of film-substrate com-posite we could calculated the biaxial elastic modulus E/(1-v) using stress-strain relation of thin films. By comparing the biaxial elastic modulus with the plane-strain modulus E/(1-{{{{ { v}^{2 } }}) measured by nano-in-dentation we could further determine the elastic modulus and Poisson's ratio independently. This method was employed to measure the mechanical properties of DLC films deposited by {{{{ { {C }_{6 }H }_{6 } }} rf glow discharge. The was elastic modulus E increased from 94 to 169 GPa as the {{{{ { V}_{ b} / SQRT { P} }} increased from 127 to 221 V/{{{{ {mTorr }^{1/2 } }} Poisson's ratio was estimated to be abou 0.16∼0.22 in this {{{{ { V}_{ b} / SQRT { P} }} range. For the {{{{ { V}_{ b} / SQRT { P} }} less than 127V/{{{{ {mTorr }^{1/2 } }} where the plastic deformation can occur by the substrate etching process however the present method could not be applied.

• Coupled systems mechanics
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• v.4 no.4
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• pp.279-295
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• 2015

The article presents a theoretical-experimental approach developed for modeling the coefficient of sliding friction in the dynamic system tool-workpiece in slide diamond burnishing of low-alloy unhardened steels. The experimental setup, implemented on conventional lathe, includes a specially designed device, with a straight cantilever beam as body. The beam is simultaneously loaded by bending (from transverse slide friction force) and compression (from longitudinal burnishing force), which is a reason for geometrical nonlinearity. A method, based on the idea of separation of the variables (time and metric) before establishing the differential equation of motion, has been applied for dynamic modeling of the beam elastic curve. Between the longitudinal (burnishing force) and transverse (slide friction force) forces exists a correlation defined by Coulomb's law of sliding friction. On this basis, an analytical relationship between the beam deflection and the sought friction coefficient has been obtained. In order to measure the deflection of the beam, strain gauges connected in a "full bridge" type of circuit are used. A flexible adhesive is selected, which provides an opportunity for dynamic measurements through the constructed measuring system. The signal is proportional to the beam deflection and is fed to the analog input of USB DAQ board, from where the signal enters in a purposely created virtual instrument which is developed by means of Labview. The basic characteristic of the virtual instrument is the ability to record and visualize in a real time the measured deflection. The signal sampling frequency is chosen in accordance with Nyquist-Shannon sampling theorem. In order to obtain a regression model of the friction coefficient with the participation of the diamond burnishing process parameters, an experimental design with 55 experimental points is synthesized. A regression analysis and analysis of variance have been carried out. The influence of the factors on the friction coefficient is established using sections of the hyper-surface of the friction coefficient model with the hyper-planes.

• Journal of TMJ Balancing Medicine
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• v.12 no.1
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• pp.1-6
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• 2022

Objectives: For the deviation phenomenon occurring during the treatment process in temporo-mandibular balancing medicine (TBM), hypotheses were established regarding the cause and mechanism of formation from the perspective of neuro-science and material mechanics, and a verification method was proposed. Methods: The deviation phenomenon was theoretically analyzed based on the structure theories of material mechanics of the joint and the neurological pain mechanism. Results: Deviation occurs due to temporary yield by the accumulation of heterogeneous stress in the temporo-mandibular joint and the affected joint. Because the joint structures are corresponding with material mechanics showing compressive and tensile properties. The size of the deviation is expressed in terms of strain. The occlusal surface of the teeth is level with the axial joint. Since the magnitude of the deviation has a proportional relationship with the degree of abnormality of the temporo-mandibular joint, the magnitude of the deviation calculated by the balance measurement can be replaced by the strain. The major variables involved in the occurrence of deviations are the strength of joint structures and neurological conditions. Therefore plastic deformation and adaptation occur as a long-term depression of neural circuits is strengthened in different ways at different locations each time in various clinical situations. This is the reason why the sequence of the restoration process while correcting deviations is following reverse order of the accumulation in many layers in the muscular nervous system. Conclusions: From the above results, it can be inferred that the occurrence and correction of the deviations are corresponding with the plastic deformation and neuro-plasticity.

• Smart Structures and Systems
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• v.8 no.4
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• pp.385-398
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• 2011

This paper discusses the applicability of Acoustic Emission (AE) to assess the damage in reinforced concrete (RC) structures subjected to complex dynamic loadings such as those induced by earthquakes. The AE signals recorded during this type of event can be complicated due to the arbitrary and random nature of seismicity and the fact that the signals are highly contaminated by many spurious sources of noise. This paper demonstrates that by properly filtering the AE signals, a very good correlation can be found between AE and damage on the RC structure. The basic experimental data used for this research are the results of fourteen seismic simulations conducted with a shake table on an RC slab supported on four steel columns. The AE signals were recorded by several low-frequency piezoelectric sensors located on the bottom surface of the slab. The evolution of damage under increasing values of peak acceleration applied to the shake table was monitored in terms of AE and dissipated plastic strain energy. A strong correlation was found between the energy dissipated by the concrete through plastic deformations and the AE energy calculated after properly filtering the signals. For this reason, a procedure is proposed to analyze the AE measured in a RC structure during a seismic event so that it can be used for damage assessment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.170-175
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• 2005

The focus of this paper is to observe the aerodynamic and vibration characteristics of the NACA0012 blade(AR=16.6) fixed on the lower surface of the wind tunnel, by changing air speed and the blade's angle of attack. After fixing a slit-typed vortex generator on the front of the blade, it could be observed that the vibrational characteristics caused by interactions between vortex and blade through the 5-hole pilot tubes. And, also, two different blades in stiffness had been prepared for observing those characteristics above in this experiment. The results were compared with the given stiffness of blade, as well. According to the results, it is clear to recognize that the vibration spectrum increases while air speed and angle of attack increase, and, also, less stiffness means bigger vibration spectrum.