• 한국항공운항학회지
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• 제20권1호
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• pp.103-111
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• 2012

This study reviews several fracture models for predicting the residual strength of notched composite laminates. Representative experimental results on the residual strength of composite laminates containing a notch subjected to static uniaxial tensile loading have been collected from open literature. And notched strength data for T300/5208 are analyzed. The various parameters associated with the fracture models have been determined for laminates. Notched strength data sets are compared with fracture models and the applicability of the different fracture models in predicting the notched strength of composite laminates is discussed. And static tests have been performed on 2.0mm depth notched specimen. And the test results are compared with analysis models.

• 대한기계학회논문집A
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• 제21권11호
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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.

• 항공우주기술
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• 제7권2호
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• pp.21-26
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• 2008

본 논문에서는 놋취가 있는 복합적층판의 강도를 예측하는 여러 가지 파손모델을 검토하였다. 놋취가 존재하는 복합적층판의 대표적인 정적 실험결과를 공개된 문헌을 통하여 수집하였다. T300/5208에 대한 강도데이타를 분석하였으며 파손모델에 관련된 여러 가지 매개변수를 결정하였다. 놋취 강도 데이터를 여러 가지 파손모델과 비교하였다.

• 대한기계학회논문집
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• 제16권7호
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• pp.1285-1293
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• 1992

본 연구에서는 glass/epoxy 직조된 복합재료에 있어서 원공 및 판폭의 크기가 노치강도에 미치는 영향을 명확히 하고, 또한 노치강도 및 파괴조건과 위에서 언급한 특성길이와의 관계를 검토하였다.

• Steel and Composite Structures
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• 제25권6호
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• pp.685-692
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• 2017

In this study, the effect of various adhesively bonded composite patches on mechanical properties of notched Al-Mg alloy plates was analyzed. For this purpose firstly, the un-notched and notched specimens were fabricated from 5086 Al-Mg alloys which have been used in armor-plated military vehicles. The surface notches as a flaw were machined with circular cutting tool to form notch aspect ratio a/c=0.15 and notch-to-thickness ratios a/t=0.5 in the radial direction on the test specimens. Then, various composite patches which reinforced by glass, carbon and Kevlar fibers were bonded adhesively at elliptically surface notches. Finally, experimental measurements conducted by applying tensile static loading. The experimental results showed that repairing with composite patches with order of carbon, glass and Kevlar fibers have remarkable effect on tensile strength of the notched plate. Also the finite element models were developed using Abaqus/Explicit code to predict the tensile strength and elongation of unrepaired notched specimen and specimen repaired by carbon fiber composite patch. The comparison between numerical and experimental results showed good agreement between them and proved the accuracy of numerical modeling.

• 한국세라믹학회지
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• 제35권8호
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• pp.850-856
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• 1998

The dynaamic fatigue behavior of alumina ceramics was observed at room temperature using four-point bending method. Dynamic fatigue fracture strength was observed as function of down speed and notch length. The crack growth exponent of the specimens was calculated from the fracture strength and lifetime in dynamic fatigue test. After loading the stresses in the range of 0% to 105% compared with the average in-ert strength the value of residual fracture strength was measured for unnotched and 0.5mm notched speci-mens at the 0.001 and 0.0005 mm/min down speed respectively. After the 95% stress of the average inert strength was applied repeatedly the value of rsidual fracture strength was measured for 0.5mm notched specimens at the 0.001 and 0.0005 mm/min down speed respectively. The material constant A was found to be almost the same and not to depend on the loading mode or the down speed for unnotched and notched specimen. The value of fracture strength with time calculated from the constants n and A was in good agreement with the measured value.

• 한국해양공학회지
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• 제13권2호통권32호
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• pp.41-50
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• 1999

As for the properties on both the aluminum and the CFRP which are used to make A17075/CFRP multi-layered hybrid composites, CRALL(carbon reinforced aluminum laminate). In the CRALL specimen for rule of mixture, we were analyzed notched strength by finite element method. The results obtained from FEM analysis are as follows; In the unnotch CRALL specimen, the stresses CFRP, epoxy, Al 7075 obtained by finite element method strength solution for A/C0001, when strain is 0.28%, are 1400MPa, 38MPa, 411MPa. respectively and for A/C9991, when strain 0.48%, are 392MPa, 26MPa and 321Mpa, respectively. the solpe of the stress-strain curve by FEM increases in keeping with the hole size and the yield strain decrease to 36% and 55% for A/C9993 and A/C9991 respectively.

• Journal of the Korean Wood Science and Technology
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• 제27권3호
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• pp.51-62
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• 1999

본 연구는 자원환경적인 측면에서 산업폐기물이자 환경오염원인 제지 슬러지를 이용함에 있어 용융형 목질-플라스틱 복합재의 강화충전제로 적용하여 그 사용가능성을 알아보고 또한 복합재의 물성에 대한 기초적인 자료을 제시하는데 그 목적이 있다. 그 결과 제지 슬러지의 혼합비율이 증가할수록 복합재의 밀도는 증가하였으며 제지 슬러지의 입자 크기와 결합제 종류 및 함량은 복합재의 밀도에 크게 영향을 미치지 않았다. 제지 슐러지의 혼합비율이 증가할수록 복합재의 휨강도적 성질은 향상되었으며, 제지 슐러지의 입자 크기가 작을수룩 복합재의 휨강도는 증가하였으나 휨탄성계수는 증가하였다. 또한 복합재의 휨강도적 성질은 결합제의 종류에 관계없이 그 함량이 증가할수록 향상됨을 알 수 있었으며, 결합제의 분자량이 더 큰 Epolene G-3003의 경우 그 효과가 더 큼을 알 수 있었다. 대체로 제지 슬러지의 혼합비율이 증가할수록 복합재의 충격강도는 다소 감소하는 경향을 볼 수 있지만, 전체적으로 notched impact strength는 크게 감소하지는 않았다. unnotched impact strength의 경우 제지 슬러지의 혼합비율이 증가할수록 그 감소 폭이 컸다. 제지 슬러지의 입자크기가 복합재의 충격강도에 미치는 영향을 보면 notched impact strength의 경우 제지 슬러지의 입자 크기에 따라 충격강도에 미치는 영향은 거의 없었으며, unnotched impact strength의 경우 입자 크기가 가장 작은 100mesh 이하일 때 가장 우수하였고 그 다음으로 20~40mesh, 60~80mesh 순이었다. 복합재의 notched impact strength 는 결합제의 종류와 함량에 따라 미치는 영향은 거의 없음을 알 수 있었으나 unnotched impact strength는 Epolene E-43의 경우 첨가량이 증가할수록 충격강도가 감소하였고, Epolene G-3003의 경우는 첨가량이 증가할수록 충격강도가 감소하다가 다시 증가하는 경향을 보였다.

• 대한기계학회논문집A
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• 제24권4호
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• pp.1055-1064
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• 2000

First, various specimen geometries, namely, coupon type, waisted type and dog-bone type, were examined to determine appropriate fatigue specimen of thermoplastic composite material AS4/PEEK and the n, fatigue strength of smooth and notched specimens of AS4/PEEK [-45/0/+45/90]2s was investigated. Fatigue tests were performed under load controlled condition at a stress ratio of 0. 1 at a frequency of 5Hz. Stiffness degradation of specimens with fatigue cycling was monitored using an automated unloading compliance technique. The waisted type specimen is found appropriate for smooth fatigue specimen geometry of AS4/PEEK. As for the effect of stress concentration, it is found that fatigue strength is higher for a 2mm-diameter hole notched specimen than a 5mm-diameter one. Fatigue notch factor decreases with the increase of fatigue life. These results are far different from the trend of fatigue strength of metallic materials. The stiffness variation of smooth specimen was only 4% at maximum until final fracture. On the other hand, the stiffness of hole notched specimen was reduced by 45% at maximum. Notched fatigue strength was compared between thermoplastic composite AS4/PEEK and thermosetting composite Graphite/Epoxy. In long-life fatigue (>104), the AS4/PEEK composite shows superior fatigue strength, but in short-life fatigue, the fatigue strength of the Graphite/Epoxy composite is nearly equal or somewhat higher than that of the AS4/PEEK composite.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1818-1823
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• 2007

In this paper, notched bar tensile tests of Inconel 617 were performed at room ($20^{\circ}C$) and elevated ($800^{\circ}C$) temperature. Finite element analyses are also performed. It is found that, at the room temperature, smooth bar tensile test results could be used to simulate notched bar tensile tests. However, at the elevated temperature, notched bar tensile test results can not be simulated from smooth bar tensile test results. Metallurgical examination reveals that strength weakening results from many cavities over the specimens for smooth bar test at the elevated temperature. "True" tensile properties at the elevated temperature is found using FE simulations. It also suggests that cautious should be taken to determine tensile properties of Inconel 617 at elevated temperatures using smooth bar tests.