• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.75-78
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• 2002

A simplified methodology is presented to predict fatigue life and residual strength of composite structures. To avoid excessive amount of tests that are required for model characterization, strength degradation parameter is assumed as function of fatigue life. S-N curve is used to extract fatigue life that is required to characterize the stress levels comprising a randomly-ordered load spectrum. And different stress ratios are handled with Goodman correction approach(fatigue envelope). It is assumed that the residual strength is a function of the number of loading cycles and applied fatigue stress amplitude. And the residual strength distribution after an arbitrary load cycles is represented by two parameter Weibull functions.

• Journal of Korean Society of Steel Construction
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• v.15 no.6 s.67
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• pp.621-628
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• 2003

Stud shear connectors are the most commonly used shear connectors: up to 22mm studs are usually used in steel-concrete composite structures. To expand the current design codes for stud connectors, large studs with a diameter of more than 25mm should be investigated. Through push-out tests on large stud shear connectors that transcend the limitation of current design codes, fatigue behavior was investigated and comparisons with design equations performed. The shear stiffness of the connectors in elastic range was evaluated through shear tests on 25mm, 27mm, and 30mm studs and compared with those from static tests. The fatigue behavior of large studs was discussed in terms of residual slip and load-slip curves. The initiation of fatigue cracks in the welding part could be detected through the history of displacement range. Test results showed that the design fatigue endurance of S-N curves in current design codes could be applied to large stud shear connector.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.5
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• pp.1-10
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• 2007

A laboratory investigation is conducted to characterize and quantify fatigue lives of continuously reinforced concrete pavements (CRCP) with initial design parameters. Eight specimens scaled were made based on results of finite-element analyses and stress-strain curve comparisons. Static tests were firstly performed to obtain magnitudes of static failure loads and to predict crack patterns before fatigue tests. The fatigue lives measured in the study were compared based on each initial design parameter. The comparison indicates that the fatigue lives of CRCP specimens with initial cracks increases with increasing the initial crack spacing, and CRCP specimens with reinforcements at top of the concrete slab have more fatigue lives than those with reinforcements at midheight of the concrete slab. In addition, the fatigue lives were significantly affected by soil conditions under the CRCP specimens. The results obtained in the study can be used for maintenance and retrofit of the continuously reinforced concrete pavements.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.154-159
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• 2004

In this study, in order to perform more efficiently reliability design and integrity assessment of structural members, the relational database management program on the engineering plastics was constructed. This program contained 476 grades for 14 kinds of the engineering plastics and was developed using MS-access and MS-visualbasic. This program consists of 3 modules; search condition, probabilistic characteristics of material property, evaluation of P-S-N curve. We perform fatigue test for probabilistic durability analysis and this results input the database program to estimate P-S-N.

• Journal of Biosystems Engineering
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• v.36 no.3
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• pp.163-170
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• 2011

Analysis of load on major parts of the tractor power drive line is critical for efficient and optimum design of a tractor. The purpose of this study was to evaluate severeness of the tractor PTO driving axle during rotary tillage operation. First, S-N (stress vs. number of cycle) curve of a PTO driving gear was obtained through the fatigue life test using a PTO dynamometer. Second, PTO severeness was evaluated during rotary tillage operation. Torque measurement system was constructed with strain-gauge sensors to measure torque of a PTO axle, an I/O interface to acquire the sensor signals, and an embedded system to calculate severeness. The severeness of PTO was analyzed using measured torque data during rotary tillage. In the PTO gear life fatigue test, breakage time and bending stress of the gear were measured by tooth widths and torque change during the fatigue life test. The S-N curve showed a good linear relationship between bending stress and number of cycle (life) with a coefficient of determination of 0.97. For PTO severenss evaluation, rotary tillage operations were conducted at two PTO rotational speeds (level-1, level-2) under different paddy and upland field sites with different soil conditions. Results of averaged relative severeness for PTO level-1 and PTO level-2 were 1.96 and 3.34, respectively, at paddy field sites, and they were 1.36 and 2.51, respectively, at upland field sites. The results showed that the PTO driving axle experienced more severe load during rotary tillage at paddy fields than at upland sites, and relative severeness was greater at the higher PTO rotational speed under all of the soil conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1965-1971
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• 1997

The relaxation of stress concentration in notched members can be very significant in the improvement of notched strength and fatigue life. This paper investigated the relationship of stress concentration factor, and notched strength and fatigue life. The stress concentration factors were analyzed by FEM. Uniaxial tensile and fatigue tests were carried on plain woven composite specimens which have a main hole and two defence holes. From experimental results, the notched strength and the fatigue limit increased up to about 50% and 30% respectively due to the reduction in stress concentration. The fatigue lives predicted by Juvinall's approach were underestimated than test results and this trends were remarkable as nothed strength increased. This is because of the underestimation of a coefficient. A in S-N curve (.sigma.$_{ar}$ =A $N_{f}$ $^{B}$). Therefore, considering notched strength the coefficient A was modified. The fatigue lives by this process were agreed well with the experimental results.sults.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.10
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• pp.77-83
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• 2008

In terms of saving costs, energy and materials, the weight of cars has been gradually reduced by optimizing design of structure, which also gives us good performance. In compliance with this, it should satisfy the lifetime of cars for 25 years under the operation. The purpose of this study is to evaluate the strength of fatigue using date from strain gauges attached carbody and bogie frame. This dynamic stress can be evaluated using S-N curve based on stress amplitude. Modified S-N curve by CORTON-DOLAN is used for more conservative and substantial evaluation. In addition, !he loadings itself of carbody and bogie frame are considered by calculating the rate of the differences which are occurred between empty car and fuiiy occupied car with passengers. Rainflow cycle counting method is applied to arrange the stress data for the modified S-N curve to predict lifetime of the materials. Conclusively the cumulative damages are not only calculated by Miner's Rule, but the safety factors are also determined by Goodman diagram.

• Proceedings of the KIPE Conference
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• 2002.11a
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• pp.205-208
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• 2002

Thermal design is required with considering thermal stability to verify the reliability of electric power device with using IGBT. Numerical analysis is performed to analyzed the change in thermal resistance with respect to the various thermal density of heating element. Correlations between thermal resistance and heat generation density are established. With using these correlations, performance curve is composed with respect to the change in thermal resistance of cooling conditions for natural convection and forced convection. Thermal fatigue is occurred at the Inside and outside of IGBT by repeated heat load. The crack is occurred between base plate and ceramic substrate for the inside. When the crack length is 4mm, the failure is occurred. Therefore, Thermal design method considering thermal density, thermal fatigue resistance is presented on this study and it is expected to thermal design with considering life prediction.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.28-33
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• 2014

Recently, the actuator worked by the driving recovery-force of the thermo elastic martensitic transformation of shape memory alloys(SMA) has been studied. This paper presents a study on the fatigue life of shape memory alloy (SMA) actuators undergoing thermally induced martensitic phase transformation under various stress levels. shape memory recoverable stress and strain of Ti-44.5at.%Ni-8at.%Cu alloys were by means of constant temperature tensile tests. Differential scanning calorimetry (DSC) was employed in order to investigate the transformation characteristics of the alloy before the tests. the results were summarized as follows. The martensite inducing stress incerased with the increasing of the Cu-contents. The fatigue life decreased with the increasing of the test load and the Cu-content. The data acquired will be very useful during the design process of an SMA NiTiCu element as a functional part of an actuator.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.93-101
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• 2018

FDM is one of the popular 3D printing technologies because of an inexpensive extrusion machine and multi-material printing. FDM can use thermoplastics such as ABS and PLA. The 3D-printed ABS parts fabricated by FDM are attractive in the automotive industry because of their weight. A 10% reduction in weight can increase the fuel economy by approximately 7%. To use 3D-printed ABS parts as automotive parts, we should evaluate the 3D-printed parts in terms of automotive reliability. In this study, 3D-printed ABS samples were evaluated using Ono's rotary bending fatigue test. We obtained an S-N curve for the 3D-printed ABS specimen from the finite-element analysis. The S-N curve can be useful in early-stage design decisions for 3D-printed ABS parts.