• The Journal of Korean Academy of Prosthodontics
• /
• v.31 no.4
• /
• pp.482-505
• /
• 1993

The purpose of this study was to evaluate the fracture characteristics and the effect of resin bonding of laminate porcelain. In order to characterize the indentation-induced crack, Young's moduli and characteristic indentation dimensions were measured. The fatigue life under three point flexure test was measured using the electro-dynamic type fatigue machine, and the crack propagation with thermocycling was investigated on the condition of 15 second dwell time each in $5^{\circ}C\;and\;55^{\circ}C$ bath. The Vickers indentation pattern and the fracture surface were examined by an optical microscope and a scanning electron microscope (SEM). The results obtained were summarized as follows ; 1. Young's moduli(E) of the laminate porcelain and the resin cement used in this experiment were $62.56{\pm}3.79GPa$ and $15.01{\pm}0.12GPa$, respectively. 2. The initial crack size of the laminate porcelain was $69.19{\pm}5.94{\mu}m$ when an indentation load of 9.8N was applied, and the fracture toughness was $1.065{\pm}0.156MPa\;m^{1/2}$. 3. The fatigue life of laminate porcelain showed the constant fracture range at the stress level 27.46-35.30MPa. 4. When a cyclic flexure load was applied, the fatigue life of resin-bonded laminate porcelain was more decreased than that of laminate porcelain. 5. When a thermocycling was conducted, the crack growth rate of resin-bonded laminate porcelain was more increased than that of laminate porcelain. 6. Fracture surface showed the radial crack, the lateral crack, and the macroscopic crack branching region beneath the plastic deformation region when an indentation load of 9.8N was applied.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.3 no.1 s.8
• /
• pp.133-140
• /
• 2003

The research was performed to evaluate the cracking resistance characteristics of cold-mixed reclaimed asphalt pavement (RAP) using indirect tensile strength test and fatigue tests. Indirect tensile tests were conducted to estimate the indirect tensile strength at variable temperatures($10^{\circ}C\;and\;20^{\circ}C$). Fatigue tests were also carried out using 500kgf, 400kgf, and 300kgf of dynamic loads, and the fatigue life (Nf) for each mixture was measured. Indirect tensile strength of cold-mixed reclaimed asphalt pavement was about 90% of conventional 13mm dense-graded asphalt mixture. Fatigue life of cold-mixed reclaimed asphalt mixture was 70%, 55%, 30% (for 500kgf, 400kgf, 300kgf of load level, respectively) of the conventional one.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.6 no.2
• /
• pp.85-91
• /
• 1986

Fatigue life is an important consideration for the design of offshore structures in deep sea and in hostile environments. In this paper, the effect of the bandwidth of random stresses on the fatigue life estimation of fixed offshore structures is investigated. The dynamic analysis is carried out in the frequency domain by using the equivalent linearization technique. Fatigue damages are calculated by two stress cycle counting methods; i.e., the narrow band method and the wide band method using rainflow counting technique. Example studies are carried out for two different structures. Numerical results indicate that the wide band approach, which is more complex but theoretically more appropriate pridicts smaller values of fatigue damages compared with those by the narrow band approach for all seastate conditions. Such trend becomes more apparent for the cases of severe seastates where the bandwidth of random stresses becomes large.

• Restorative Dentistry and Endodontics
• /
• v.42 no.3
• /
• pp.216-223
• /
• 2017

Objectives: The aim of this study was to compare the mechanical properties of various nickel-titanium (NiTi) files with similar tapers and cross-sectional areas depending on whether they were surface-treated. Materials and Methods: Three NiTi file systems with a similar convex triangular cross-section and the same ISO #25 tip size were selected for this study: G6 (G6), ProTaper Universal (PTU), and Dia-PT (DPT). To test torsional resistance, 5 mm of the straightened file's tip was fixed between polycarbonate blocks (n = 15/group) and continuous clockwise rotation until fracture was conducted using a customized device. To evaluate cyclic fatigue resistance, files were rotated in an artificial curved canal until fracture in a dynamic mode (n = 15/group). The torsional data were analyzed using 1-way analysis of variance and the Tukey post-hoc comparison test, while the cyclic fatigue data were analyzed using the Mann-Whitney U test at a significance level of 95%. Results: PTU showed significantly greater toughness, followed by DPT and G6 (p < 0.05). G6 showed the lowest resistance in ultimate torsional strength, while it showed a higher fracture angle than the other files (p < 0.05). In the cyclic fatigue test, DPT showed a significantly higher number of cycles to failure than PTU or G6 (p < 0.05). Conclusions: Within the limitations of this study, it can be concluded that the torsional resistance of NiTi files was affected by the cross-sectional area, while the cyclic fatigue resistance of NiTi files was influenced by the surface treatment.

• Journal of Korean Society of Steel Construction
• /
• v.29 no.1
• /
• pp.49-60
• /
• 2017

As well as the strength check, fatigue life check is also mainly required for designing mooring lines of the floating structures. In general, forces which induce dynamic structural response significantly affect to fatigue design of the mooring lines. So, waves are mainly considered as the governing loading for fatigue design of the mooring lines. In this study, characteristics of the fatigue damage of the mooring lines for submerged floating tunnels (SFT) under irregular waves are investigated. For this study time domain hydrodynamic analysis is used to obtain motion of the tunnel and tension and stresses of the mooring lines under the specific environmental conditions. Also, the Rainflow-counting method, the Palmgren-Miner's rule, and S-N curves for floating offshore structures presented by DNV recommendation is applied to calculate the fatigue damage due to the fluctuating stresses. Referring to the design plactice of the tendon pipes for TLP (tension-leg platform), which is very similar structural system to SFT, it is assumed that a 100 year return period wave attacks the SFT systems during 48 hours and the fatigue damages due to the environmental loading are calculated. Following the analysis sequence, the effects of the tunnel draft, spacing and initial inclination angle of the mooring lines on the fatigue damage under the specific environmental loadings are investigated.

• Interaction and multiscale mechanics
• /
• v.5 no.3
• /
• pp.169-185
• /
• 2012

The concrete bridge is likely to produce fatigue cracks during long period of service due to the moving vehicular loads and the degeneration of materials. This paper deals with the time-frequency analysis of a coupled bridge-vehicle system. The bridge is modeled as an Euler beam with breathing cracks. The vehicle is represented by a two-axle vehicle model. The equation of motion of the coupled bridge-vehicle system is established using the finite element method, and the Newmark direct integration method is adopted to calculate the dynamic responses of the system. The effect of breathing cracks on the dynamic responses of the bridge is investigated. The time-frequency characteristics of the responses are analyzed using both the Hilbert-Huang transform and wavelet transform. The results of time-frequency analysis indicate that complicated non-linear and non-stationary features will appear due to the breathing effect of the cracks.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.875-879
• /
• 2007

The effects of the statistical properties of the Coulomb friction coefficients on the dynamic responses of a galloping quadruped robot are investigated in this paper. In general, the Coulomb friction coefficients are assumed to be deterministic for a controller design to achieve required motion characteristics. However, the friction coefficients between the ground and the robot legs are not constant in reality. Therefore, statistical characteristics of the friction coefficients need to be considered for a multi-body modeling of the robot galloping on the ground. The effects of the statistical properties on the dynamic responses of the quadruped robots are investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11a
• /
• pp.314.2-314
• /
• 2002

It is necessary first to understand dynamic characteristics of a bus full BIW assembly for fatigue endurance analysis. FE model has been used usually for analyzing the dynamic behavior of structures. A lot of experience and effort, however, is necessary to make a credible FE model. Experimental modal analysis of structures has been performed to verify the credibility of initial FE model and to update the model. (omitted)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.534-538
• /
• 2008

The vehicle system is exposed to random source in service. Therefore, it is important to consider dynamic effect of the system. But, fatigue analysis is traditionally performed by using time signal of loading. To obtain dynamic effect of resonance, we carried out resonance durability analysis with frequency response and the dynamic load on frequency domain. The study shows that the damage considering resonant frequency of fuel tank system can be effectively estimated.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.7 no.2
• /
• pp.69-73
• /
• 1998

With increased loads in steered wheels and wider section tires the effort required at the steering wheel makes the driver's job very tiring and difficult. Improvements such as an increase in the mechanical efficiency of the steering system or lower steering box ratios help the reduce driver fatigue. Now using of power steering is increasing. It needs to be considering parts size of steering system as using power steering. This paper presents adjust part size of steering system form estimating reliability according to reducing torque under the dynamic load, In this paper, the spider of universial joint is selected to prove relation between steering and power steering reliability.