• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.1708-1711
• /
• 2007

This paper presents high cycle fatigue properties of an Al-3%Ti thin film, used in a RF (radio-frequency) MEMS switch for a mobile phone and also describes new test method for obtaining static and dynamic characteristics of thin film and reliability evaluation method on MEMS device with thin film developed by authors. Durability should be ensured for such devices under cycling load. Therefore, with the proposed specimen and test procedure, tensile and fatigue tests were performed to obtain mechanical and fatigue properties. The specimen was made with dimensions of $1000{\mu}m$ long, $1.0{\mu}m$ thickness, and 3 kinds of width, 50, 100 and $150{\mu}m$. High cycle fatigue tests for each width were also performed, from which the fatigue strength coefficient and the fatigue strength exponent were found to be 193MPa and .0.02319 for $50{\mu}m$, 181MPa and -0.02001 for $100{\mu}m$, and 164MPa and -0.01322 for $150{\mu}m$, respectively. We found that the narrower specimen is, the longer fatigue life of Al-3%Ti is and the wider specimen is, the more susceptible to stress level fatigue life of Al-3%Ti was.

• Nuclear Engineering and Technology
• /
• 제43권1호
• /
• pp.83-88
• /
• 2011

To define the effect of strain rate variation from 0.04% to 0.004%/s on environmental fatigue of CF8M cast stainless steel, which is used as a primary piping material in nuclear power plants, low-cycle fatigue tests were conducted at operating pressure and temperature condition of a pressurized water reactor, 15 MPa and $315^{\circ}C$, respectively. A high-pressure and high-temperature autoclave and cylindrical solid fatigue specimens were used for the strain-controlled low-cycle environmental fatigue tests. It was observed that the fatigue life of CF8M stainless steel is shortened as the strain rate decreases. Due to the effect of test temperature, the fatigue data of NUREG-6909 appears a slightly shorter than that obtained by KEPRI at the same stress amplitude of $1{\times}10^3$ MPa. The environmental fatigue correction factor $F_{en}$'s calculated with inputs of the test data increases with high strain amplitude, while the $F_{en}$'s of NUREG-6909 remain constant regardless of strain amplitude.

• 산업기술연구
• /
• 제23권A호
• /
• pp.139-147
• /
• 2003

The purpose of this study was to investigate and analyze the fatigue test data of pavement concrete. The static strength tests were carried out to check the compressive strength, flexural strength, and split tension strength at 56 days in order to minimize strength variation effect during test. The specimens were fabricated at twelves sections at a construction site of highway. The stress level and stress ratio of fatigue test were determined from static test results. The results are as follow: The flexural strength at 28 days mostly satisfied the criterion for design, but the compressive strength at 28 days were slightly below the criterion even though it satisfied at 56 days. The fatigue limit was 2 million cycles if the specimen was not failed to that cycles. The S-N curves were developed from the fatigue test results at each stress levels and each stress ratio. Then, the fatigue life of pavement concrete at a given stress level and fatigue strength of pavement concrete could be derived from these curves. Analysis using method No.2 was more acceptable because resulting of comparison and analysis using method No.2 was presented 2 sections were presented $R^2$ < 0.7, and other 2 sections were presented 0.7 < $R^2$ < 0.8, and the others 8 sections were $R^2{\geq}0.8$.

• 대한기계학회논문집A
• /
• 제31권6호
• /
• pp.701-709
• /
• 2007

To clarify the characteristics of surface damage due to fretting in press-fitted shaft, experimental methods were applied to small scale specimen with different bending load condition. Fatigue tests and interrupted fatigue tests of press-fitted specimen were carried out by rotate bending fatigue test. Macroscopic and microscopic characteristics were examined using scanning electron microscope (SEM), optical microscope or profilometer. It is found that small fatigue cracks are nucleated early in life regardless of bending stress, and thus the most portion of fatigue life on press fits can be considered to be crack propagation process. Most of surface cracks are initiated near the contact edge, and multiple cracks are nucleated and interconnected. Furthermore, the fretting wear rates at the contact edge are increased rapidly at the initial stage of total fatigue life. It is thus suggested that the fatigue crack nucleation and propagation process is strongly related to the evolution of surface profile by fretting wear in press fits.

• 한국강구조학회 논문집
• /
• 제16권6호통권73호
• /
• pp.847-855
• /
• 2004

피로설계에 대한 기준, 시방서 또는 추천안 등은 일반적으로 두께 10~30mm의 강판으로 만든 실험체의 피로실험을 통해 얻은 피로강도곡선을 근거하고 있다. 그러나 강판의 두께가 증가함에 따라서 피로강도가 감소하게 될 가능성에 대해 관심을 갖게 되었고, 파괴역학적 방법에 의한 분석과 강재 용접에 따른 영향을 근거로 하여 강판의 두께에 따른 영향이 상당히 클 수도 있다고 지적되었다. 기존의 몇몇 피로실험 결과로부터 얻은 피로강도곡선으로부터 강판 두께에 대한 영향을 고려하여 피로강도를 수정하는 식이 제안되어왔다. 본 연구에서는, 두께 80mm까지의 국내생산 SM520C-TMC 강재에 대한 피로강도시험을 실시하고, 그 결과로부터 강재의 두께에 따른 영향을 평가하였다. 최종적으로, 강판 두께에 대한 영향을 고려하여 피로강도를 수정하는 제한적인 시편에 대한 수정식을 제공하고, 이를 기존의 연구결과와 비교 검토하였다. 결과로서, 두께에 따른 강도감소효과는 기존의 연구와 유사한 경향을 갖고 감소하나 그 정도는 적어지고 있는 결과를 얻을 수 있었다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.17-22
• /
• 2007

Low-cycle environmental fatigue tests of cast austenitic stainless steel CF8M at the condition of fatigue strain rate 0.04%/sec were conducted at the pressure and temperature, 15MPa, $315^{\circ}C$ of a operating pressurized water reactor. The used test rig was limited to install an extensometer at the gauge length of the cylindrical fatigue specimen inside the small autoclave. So the magnet type LVDT's were used to measure the fatigue displacement at the specimen shoulders inside the high temperature and high pressure water autoclave. However, the displacement and strain measured at the specimen shoulders is different from the one at the gauge length for the geometry and the cyclic strain hardening effect. FEM calculated the displacement and the strain of the gauge length from the data measured at the shoulders. Tensile test properties in elastic and plastic behavior of CF8M material were used in the FEM analysis. A series of low cycle fatigue tests simulating the cyclic strain hardening effect verified that the FEM calculation was well agreed with the simulated tests. The process and method developed in this study would be so useful to produce reliable environmental fatigue curves of CF8M stainless steel in pressurized water reactors.

• Journal of Mechanical Science and Technology
• /
• 제20권1호
• /
• pp.42-50
• /
• 2006

To evaluate the fatigue lifetime of structures, it is necessary to identify the values of parameters through tests. From the viewpoint of time and cost it is difficult for engineers to get the necessary data through tests. In this study, we surveyed literature and proposed a procedure to identify the fatigue parameters expressed with the Brinell hardness and elastic modulus. After obtaining stress concentration factors by finite element analysis, we calculated fatigue notch factors using Peterson's formula. Taking into account the welding residual stress, which was also obtained by finite element analysis, we evaluated the fatigue lifetime of four kinds of welded joints using the proposed approach. The estimated results are in a good agreement with the experimental results.

• Steel and Composite Structures
• /
• 제19권1호
• /
• pp.223-236
• /
• 2015

Despite the proliferation of the industrial application of steel tubes, the effect of collision on the surface of steel tubes subject to cyclic loading has largely remained untouched. This paper studies the fatigue behavior of steel tubes which are impacted by an external object. A dent imperfection caused by a collision was modeled and fatigue tests were conducted using a MTS machine. Fatigue life as well as the failure modes were thoroughly discussed in a way that the fatigue life of the dented tubes with similar geometrical specifications at full-scale can be generalized.

• 한국자동차공학회논문집
• /
• 제9권1호
• /
• pp.216-221
• /
• 2001

In this study, the effects of nitriding methods and times on the fatigue strength of SACM 645 steel were investigated. The rotary bending tests were carried out to obtain and compare the fatigue strengths of plasma ion nitrided specimens and gas nitride specimen. The 70 hr. gas nitrided specimen had the highest fatigue strength of 1.05$\times$$10^3$ MPa over the 40 hr., 70 hr. and 90 hr. plasma ion nitrided specimens, which had the fatigue strength of 3.48$\times$$10^2$, 4.57$\times$$10^2$ and 4.64$\times$$10^2$ respectively. Also, the microhardness tests were conducted to measure the effective case depths. The plasma ion nitrided specimens showed much higher surface hardness values than the gas nitrided specimen overall.

• 한국철도학회논문집
• /
• 제8권4호
• /
• pp.299-307
• /
• 2005

In general, structural integrity of rolling stock structures should last more than 25 years. During the lifetime corrosive degradation occurs. For structural design and diagnosis, quantitative relationship between corrosive degradation and variation of mechanical properties such as tensile strength and fatigue strength is needed. In this study, first of all we established the atmospheric corrosion test procedure. At regular intervals using specimens of SM490A and SS400 on the atmospheric corrosion test bed, we carried out tensile and fatigue tests. The fatigue strength decreases as the atmospheric corrosion period increases. In addition we studied the effect of post-weld heat treatment on the tensile and fatigue behaviour and performed electrochemical corrosion tests.