• Journal of the Korean Society of Hazard Mitigation
• /
• v.11 no.2
• /
• pp.75-80
• /
• 2011

The main objective of this research is to develop fatigue prediction model for flexible pavements using energy ratio factor and phase angle. The two parameters are considered as fundamental properties of time and temperature dependent viscoelastic asphalt concrete materials. The energy ratio factor is defined as the ratio of the pseudo-total cumulative dissipated energy to the cumulative dissipated energy to failure during the test. The phase angle between the stress and strain ware signals stems from the intrinsic the dependent asphalt mixture behavior. The phase angle was computed and the relationship between the initial mixture stiffness and the initial phase angle is presented. As a result, fatigue prediction model for flexible pavements was proposed using intrinsic properties of viscoelastic asphalt concrete materials.

• Journal of the Korea Convergence Society
• /
• v.4 no.2
• /
• pp.21-27
• /
• 2013

Spot welding is automation of assembly process, without increasing the vehicle weight and economy, there is a fuel economy improvement of motor vehicles and to widely used in the automotive industry. But By irregular load from the road surface while at the vehicle is running, stress concentration occurs in the weld point, fatigue failure occurs frequently. Considering change of stiffness is the essential fatigue life of the evaluation spot weld. In this paper, by performing a linear static analysis was to understand the vulnerable part. Acquire to the fatigue properties of the spot weld, take the load history of the three levels in the time domain, was performed by setting as a condition of quasi-static fatigue analysis. and Fatigue life prediction method of the spot weld was by applying the method according to the fatigue damage accumulation and the conventional method was compared analyzed with the results shown.

• Smart Structures and Systems
• /
• v.14 no.3
• /
• pp.469-477
• /
• 2014

As a kind of intelligent materials, conductive asphalt concrete has a broad application prospect including melting ice and snow on the pavement, closing cracks in asphalt concrete, sensing pavement damage, and so on. Conductive pavement will be suffered from fatigue failure as conventional pavement in the process of service, and this fatigue damage of internal structure can be induced by electrical signal output. The characteristics of electrical signal variation of conductive asphalt concrete in the process of fatigue cracking were researched in this paper. The whole process was clearly divided into three stages according to resistance changes, and the development of fatigue damage wasn't obvious in stage I and stage II, while in stage III, the synchronicity between the resistance and damage began to appear. Thus, fatigue damage variable D and initial damage value $D_0$ represented by the functions of resistance were introduced in stage III. After calculating the initial damage value $D_0$ under different stress levels, it was concluded that the initial damage value $D_0$ had no noticeable change, just ranged between 0.24 and 0.25. This value represented a critical point which could be used to inform the repair time of early fatigue damage in the conductive asphalt pavement.

• Restorative Dentistry and Endodontics
• /
• v.42 no.3
• /
• pp.206-215
• /
• 2017

Objectives: To determine the combined effect of fatigue cyclic loading and thermocycling (CLTC) on the shear bond strength (SBS) of a resin cement to zirconia surfaces that were previously air-abraded with aluminum oxide ($Al_2O_3$) particles at different pressures. Materials and Methods: Seventy-two cuboid zirconia specimens were prepared and randomly assigned to 3 groups according to the air-abrasion pressures (1, 2, and 2.8 bar), and each group was further divided into 2 groups depending on aging parameters (n = 12). Panavia F 2.0 was placed on pre-conditioned zirconia surfaces, and SBS testing was performed either after 24 hours or 10,000 fatigue cycles (cyclic loading) and 5,000 thermocycles. Non-contact profilometry was used to measure surface roughness. Failure modes were evaluated under optical and scanning electron microscopy. The data were analyzed using 2-way analysis of variance and ${\chi}^2$ tests (${\alpha}=0.05$). Results: The 2.8 bar group showed significantly higher surface roughness compared to the 1 bar group (p < 0.05). The interaction between pressure and time/cycling was not significant on SBS, and pressure did not have a significant effect either. SBS was significantly higher (p = 0.006) for 24 hours storage compared to CLTC. The 2 bar-CLTC group presented significantly higher percentage of pre-test failure during fatigue compared to the other groups. Mixed-failure mode was more frequent than adhesive failure. Conclusions: CLTC significantly decreased the SBS values regardless of the air-abrasion pressure used.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.445-450
• /
• 2003

This study was performed 10 develop the accelerated life test method using Weibull-IPL(Inverse Power Law) model for mechanical components. Weibull-IPL model is concerned with determining the assurance life with confidence level and the accelerated life test time From the relation of weibull distribution factors and confidence limit, the testing times on the no number of failure acceptance criteria arc determined. The mechanical components generally represent wear and fatigue characteristics as a failure mode. IPL based on the cumulative damage theory is applied effectively the mechanical components to reduce the testing time and to achieve the accelerating test conditions. As the actual application example, accelerated life test method of agricultural tractor transmission was described. Life distribution of agricultural tractor transmission was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (MTBF) 3,000 hours and 90% confidence level for one test sample. According to IPL, because test time call be shorten in case increase test load test time could be reduced by 482 hours when we put the load 1.1 times of rated load than 0.73 times of rated load that is equivalent load calculated by load spectrum of the agricultural tractor. This time, acceleration coefficient was 11.7.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.27 no.5
• /
• pp.417-425
• /
• 2007

The ferritic 9Cr-1Mo-V-Nb heat-resisting steel was experimentally studied in order to characterize its microstructural evolution during creep-fatigue by coercivity measurement. The creep-fatigue test was conducted at $550\;^{\circ}C$ with the tensile holding time of 60s and 600s, respectively. The coercivity decreased until the failure and the hardness monotonously decreased for the whole fatigue life. As the life fraction of creep-fatigue increased, the $M_{23}C_6$ carbide coarsened following the Ostwald ripening mechanism. However, the MX carbonitrides did not grow during creep-fatigue due to so stable at $550\;^{\circ}C$. The width of martensite lath increased because of the dislocation recovery at the lath boundaries. The magnetic coercivity has an influence on the microstructural properties such as dislocation, precipitates and martensite lath boundaries, which interpreted in relation to microstructural changes. Consequently, this study proposes a magnetic coercivity to quantify the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-1Mo-V-Nb steel.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.962-965
• /
• 2002

Full scale durability test in the laboratory is an essential of any fatigue life evaluation of components or structures of the automotive vehicle. Component testing is particularly important in today's highly competitive industries where the design to reduce weight and production costs must be balanced with the necessity to avoid expensive service failure. Generally, Hydraulic road simulator is used to carry out the fatigue test and the vibration test. In this paper, the algorithm and software to realize the real road profile are developed. The operation software for simultaneously controlled multi-axial simulator is developed and the input and output data are displayed window based PC controller in real time. The software to generate the real road profile are developed. This paper developed a road profile reappearance software and simultaneously apply 3-axial actuator to white noise, so we verified the propriety of reappearance software through accomplishes an real test.

• Steel and Composite Structures
• /
• v.20 no.4
• /
• pp.913-930
• /
• 2016

It is common practice to use Reduced Web Beam Sections (RWBS) in steel moment resisting frames. Perforation of beam web in these members may cause stress and strain concentration around the opening area and facilitate ductile fracture under cyclic loading. This paper presents a numerical study on the cyclic fracture of these structural components. The considered connections are configured as T-shaped assemblies with beams of elongated circular perforations. The failure of specimens under Ultra Low Cycle Fatigue (ULCF) condition is simulated using Cyclic Void Growth Model (CVGM) which is a micromechanics based fracture model. In each model, CVGM fracture index is calculated based on the stress and strain time histories and then models with different opening configurations are compared based on the calculated fracture index. In addition to the global models, sub-models with refined mesh are used to evaluate fracture index around the beam to column weldment. Modeling techniques are validated using data from previous experiments. Results show that as the perforation size increases, opening corners experience greater fracture index. This is while as the opening size increases the maximum observed fracture index at the connection welds decreases. However, the initiation of fracture at connection welds occurs at lower drift angles compared to opening corners. Finally, a probabilistic framework is applied to CVGM in order to account for the uncertainties existing in the prediction of ductile fracture and results are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.5 s.248
• /
• pp.520-527
• /
• 2006

The design of major industrial facilities for the prevention of fatigue failure is customarily done by defining a set of transients and performing a calculation of cumulative usage factor. However, sometimes, the inherent conservatism or lack of details as well as unanticipated transients in old plant may cause maintenance problems. Even though several famous on-line monitoring and diagnosis systems have been developed world-widely, in this paper, a new system fur fatigue monitoring and life evaluation of crane is proposed to reduce customizing effort and purchasing cost. With regard to the system, at first, comprehensive operating transient data has been acquired at critical locations of crane. The real-time data were classified, by using adaptive resonance theory that is one of typical artificial neural network, into representative stress groups. Then the each classified stress pattern was mapped to calculated cumulative usage factor in accordance with ASME procedure. Thereby, promising results were obtained fur the crane and it is believed that the developed system can be applicable to other major facilities extensively.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.1320-1325
• /
• 2008

In the manufacture of automobile suspension modules at a company as parts supplier, the design process includes the detail design and the design modification via structural and fatigue durability analyses considering PoF(physics of failure) of their weldments that are repeated more than four times sequentially. The approval of the design and the release of final drawings follows. For the suspension modules, e.g. control arms and cross member, the man-hours per worker required in the process outlined above can reach as high as 1,414hours. Application of the developed integrated design system can reduce the man-hours of 1,004. In comparison with the conventional design process, this integrated design system reduces the required time by about 40%. If expense is taken into account, a savings of approximately $192,000 is estimated, assuming the design process accounts for 1.5% of total sales for the parts supplier