• Restorative Dentistry and Endodontics
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• 제42권4호
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• pp.282-289
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• 2017

Objectives: It was aimed to compare the cyclic fatigue resistances of ProGlider (PG), One G (OG), and HyFlex EDM (HEDM) nickel titanium glide path files in single- and double-curved artificial canals. Materials and Methods: 40 PG (16/0.02), 40 OG (14/0.03), and 40 HEDM (10/0.05) single-file glide path files were used in the present study. Sixty files were subjected to cyclic fatigue test by using double-curved canals and 60 files by using single-curved canal (n = 20). The number of cycles to fracture (NCF) was calculated and the length of the fractured fragment (FL) was determined by a digital micro-caliper. Twelve pieces of fractured files were examined with scanning electron microscope to determine fracture types of the files (n = 2). The NCF and the FL data were analyzed using one-way analysis of variance and post hoc Tukey test using SPSS 21 software (p < 0.05). Results: In all of the groups, NCF values were significantly lower in double-curved canals when compared to single-curved canals (p < 0.05). For both of single- and double-curved canals, NCF values of HEDM group in apical and coronal curvatures were found to be significantly higher than NCF values of PG and OG groups (p < 0.05). In both of single- and double-curved canals, NCF value of PG group was found significantly higher than OG group (p < 0.05). Conclusions: Within the limitations of this study, HEDM glide path files were found to have the highest cyclic fatigue resistance in both of single- and double-curved canals.

• 대한기계학회논문집
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• 제11권2호
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• pp.191-197
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• 1987

본 논문에서는 이상과 같이 그 중요성이 인정되는 작은 표면피로균열의 성장 특성을 조사하기 위하여 연강과 중탄소강에 두 종류의 작은 표면결함을 가공한 네가지 종류의 시험편을 제작하고, 응력비 R=-1인 소야식 회전굽힘 피로시험을 통하여 작은 표면결함이 피로강도에 미치는 영향과 그 성장특성을 조사한 후 응력확대계수 K를 사 용하는 방법과 반복전스트레인 확대계수범위 .DELTA. $K_{\epsilon}$t/를 비교 검토하여 그 유효성 을 조사하고 이를 파괴역학적 측면에서 고찰하였다.다.

• Restorative Dentistry and Endodontics
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• 제42권3호
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• pp.224-231
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• 2017

Objectives: To determine the actual revolutions per minute (rpm) values and compare the cyclic fatigue life of Reciproc (RPC, VDW GmbH), WaveOne (WO, Dentsply Maillefer), and TF Adaptive (TFA, Axis/SybronEndo) nickel-titanium (NiTi) file systems using high-speed camera. Materials and Methods: Twenty RPC R25 (25/0.08), 20 WO Primary (25/0.08), and 20 TFA ML 1 (25/0.08) files were employed in the present study. The cyclic fatigue tests were performed using a dynamic cyclic fatigue testing device, which has an artificial stainless steel canal with a $60^{\circ}$ angle of curvature and a 5-mm radius of curvature. The files were divided into 3 groups (group 1, RPC R25 [RPC]; group 2, WO Primary [WO]; group 3, TF Adaptive ML 1 [TFA]). All the instruments were rotated until fracture during the cyclic fatigue test and slow-motion videos were captured using high-speed camera. The number of cycles to failure (NCF) was calculated. The data were analyzed statistically using one-way analysis of variance (ANOVA, p < 0.05). Results: The slow-motion videos were indicated that rpm values of the RPC, WO, and TFA groups were 180, 210, and 425, respectively. RPC ($3,464.45{\pm}487.58$) and WO ($3,257.63{\pm}556.39$) groups had significantly longer cyclic fatigue life compared with TFA ($1,634.46{\pm}300.03$) group (p < 0.05). There was no significant difference in the mean length of the fractured fragments. Conclusions: Within the limitation of the present study, RPC and WO NiTi files showed significantly longer cyclic fatigue life than TFA NiTi file.

• Restorative Dentistry and Endodontics
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• 제31권2호
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• pp.96-102
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• 2006

본 연구는 현재 시판중인 $Profile^{(R)},\;ProTaper^{(R)},\;K3^{(R)},\;Hero\;642^{(R)},\;Hero\;Shaper^{(R)}$를 단면을 비교하고 이들 5가지 NiTi 파일과 사용방법에 따른 피로 파절 소요 시간을 비교하고자 시행되었다. 각 NiTi전동파일의 치근단 1/3을 temporary resin에 매몰시키고 다이아몬드 표면처리된 버로 잘라내어, 초음파를 이용하여 세척 후, 주사전자현미경으로 단면을 관찰하였다. 주기적인 피로 실험을 수행하기 위해, 회전속도, pecking 거리를 자동적으로 조절할 수 있는 장치를 제작하고 파일을 만곡된 상태를 재현하기 위하여 15도 경사진 금속 토막에 위치시키고 분당 300회전의 속도로 회전시켜 파일이 파절될 때까지의 시간을 측정하였다. 사용방법에 따른 실험군은 동적군과 정적군으로 나누고 pecking 거리는 3 mm, 6 mm로 하였다. 실험결과 동적군 보다는 정적군의 피로파절 소요시간이 통계학적으로 유의차 있게 짧았으며 3 mm, 6 mm의 pecking distance에 따른 영향은 나타나지 않았다. 결론적으로 NiTi전동파일은 pecking motion으로 사용하는 것이 피로파절을 줄이는데 도움이 될 것으로 사료된다.

• 대한기계학회논문집
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• 제12권3호
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• pp.505-512
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• 1988

본 연구에서는 상술한 $\boxDr$한계정유길이$\boxUl$를 찾아내는 것을 주요수단으로 하여, 그 전파 하한계응력으로서의 피로한도와의 관계를 정량적으로 검토하고, 미소크랙전파 거동이 미시조직 또는 피로부하이력등에 민감함을 감안하여, 이들 인자가 미소크랙 전 파의 하한계조건에 미치는 영향에 관하여 검토하기로 하였다.

• Restorative Dentistry and Endodontics
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• 제48권1호
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• pp.4.1-4.10
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• 2023

Objectives: This study aimed to compare the torsional and cyclic fatigue resistance of ProGlider (PG), WaveOne Gold Glider (WGG), and TruNatomy Glider (TNG). Materials and Methods: A total of 15 instruments of each glide path system (n = 15) were used for each test. A custom-made device simulating an angle of 90° and a radius of 5 millimeters was used to assess cyclic fatigue resistance, with calculation of number of cycles to failure. Torsional fatigue resistance was assessed by maximum torque and angle of rotation. Fractured instruments were examined by scanning electron microscopy (SEM). Data were analyzed with Shapiro-Wilk and Kruskal-Wallis tests, and the significance level was set at 5%. Results: The WGG group showed greater cyclic fatigue resistance than the PG and TNG groups (p < 0.05). In the torsional fatigue test, the TNG group showed a higher angle of rotation, followed by the PG and WGG groups (p < 0.05). The TNG group was superior to the PG group in torsional resistance (p < 0.05). SEM analysis revealed ductile morphology, typical of the 2 fracture modes: cyclic fatigue and torsional fatigue. Conclusions: Reciprocating WGG instruments showed greater cyclic fatigue resistance, while TNG instruments were better in torsional fatigue resistance. The significance of these findings lies in the identification of the instruments' clinical applicability to guide the choice of the most appropriate instrument and enable the clinician to provide a more predictable glide path preparation.

• 한국정밀공학회지
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• 제19권2호
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• pp.65-71
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• 2002

Turbine blade is subject to cyclic bending force by steam pressure. Stress analysis by fractography is already established technology as means far seeking cause of fracture and has been widely employed. In the X-ray frctography, plastic deformation and residual stress near the fracture surface can be determined and information of internal structure of material can be obtained. Therefore, to find a fracture mechanism of torsion-mounted blade in nuclear power plant, based on the information from the fracture surface obtained by fatigue test, the correlation of X-ray parameter and fracture mechanics parameter was determined and then the stress intensity factor to actual broken turbine blade was predicted.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.778-783
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• 2001

Turbine blade is subject to cyclic bending force by steam pressure. Stress analysis by fractography is already established technology as means for seeking cause of fracture and has been widely employed. In the X-ray fractography, plastic deformation and residual stress near the fracture surface can by determined and information of internal structure of material can be obtained. Therefore, to find a fracture mechanism of torsion-mounted blade in nuclear power plant, based on the information from the fracture surface obtained by fatigue test, the correlation of X-ray parameter and fracture mechanics parameter was determined and then the load applied to actual broken turbine blade was predicted.

• 콘크리트학회논문집
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• 제22권2호
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• pp.263-271
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• 2010

이 연구는 국내에서 생산되고 있는 철근이 반복하중을 받는 경우의 파괴 특성에 대한 검증을 목적으로 한다. 이 논문은 철근콘크리트 하부구조(파일과 교각)에 배근된 축방향 철근에 대한 저주파 피로 거동을 다루었다. 전체 81개의 철근 실험체에 대하여 변형률 진폭에 따른 반복 축방향 변형률 제어 방식으로 저주파 피로 실험을 수행하였다. 실험 변수는 인장변형률과 압축변형률의 비율, 축방향 철근의 항복강도, 철근지름에 대한 철근길이의 비율, 철근의 크기와 변형률 진폭으로 선택하였다. 이 논문에서 실험 결과에 따른 저주파 피로 거동과 저주파 피로 수명을 분석하였다.

• Design & Manufacturing
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• 제14권1호
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• pp.49-55
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• 2020

In this study, the fatigue behavior and fatigue life characteristics of PA2200 specimens fabricated by SLS 3D printer were studied. Fatigue tests were performed according to the standard specification (ASTM E468) and fatigue life curves were obtained. In order to perform the fatigue test, mechanical properties were measured according to the test speed of the simple tensile test, and the self-heating temperature of the specimen according to the test speed was measured using an infrared temperature measuring camera in consideration of heat generation due to plastic deformation. There was no significant difference within the set test speed range and the average self-heating temperature was measured at 38.5 ℃. The mechanical strength at the measured temperature showed a relatively small difference from the mechanical strength at room temperature. Fatigue test conditions were established through the preceding experiments, and the loading conditions below the tensile strength at room temperature 23 ℃ were set as the cyclic load. The maximum number of replicates was less than 100,000 cycles, and the fracture behavior of the specimens with the repeated loads showed the characteristics of Racheting. It was confirmed that SLS 3D printing PA2200 material could be applied to the Basquin's S-N diagram for the fatigue life curve of metal materials. SEM images of the fracture surface was obtained to analyze the relationship between the characteristics of the fracture surface and the number of repetitions until failure. Brittle fracture, crazing fracture, grain melting, and porous fracture surface were observed. It was shown that the larger the area of crazing damage, the longer the number of repetitions until fracture.