• 한국전기전자재료학회논문지
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• 제32권6호
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• pp.444-447
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• 2019

It was proven that the light outputs of blue GaN-based light-emitting diodes (LEDs) was seriously influenced by the application of external stress. We have simulated the wave function overlap of an electron and hole, which are significantly reduced by the development of stress. Consequently, its internal quantum efficiency decreased from 67.0% to 37.5%. To experimentally investigate the effect of stress, we designed and prepared a special zig system. By applying external tensile stress to compensate for the compressive stress innately developed in Blue LEDs, it was found that the optical output was greatly enhanced from 83.1 mcd to 117.2 mcd at a current of 100 mA, an increase of approximately 41%. In contrast, when the compressive stress is developed more by external compressive stress, we observed that the light output power was reduced from 89.0 mcd to 80.7 mcd, a decrease of approximately 9.3%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.256-261
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• 2007

The purpose of this study is to investigate the effect of shot peening on the fatigue strength and fatigue life of two kinds of aluminum alloys. The fatigue strength behavior of aluminum alloys were estimated by the stress ratio and shot velocities. The fatigue life and strength increased with increasing the test shot velocity. However, at the shot velocity range between 50m/s and 70m/s, the compressive residual stress phenomena were observed in test conditions of different shot velocity. The optimal shot velocity is acquired by considering the peak values of the compressive residual stress, dislocations, brittle striation, slip, and fisheye on the fracture surface of test specimen. It was observed from the SEM observation on the deformed specimen that the brittle striation, fisheye were showed in the intergranular fracture structure boundaries at the this velocities. Therefore, fatigue strength and fatigue life would be considered that shot velocity has close relationship with the compressive residual stress.

• 한국안전학회지
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• 제21권4호
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• pp.1-6
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• 2006

The lightness of components that was required in automobile and machinery industry requires high strength of components. In particular, manufacturing process and new materials development for solving the fatigue facture problem attendant upon high strength of suspension of automobile are actively advanced. In this paper, the effect of compressive residual stress of spring steel(JISG SUP-9)by shot-peening on fatigue crack growth characteristics in high temperature($100^{\circ}C,\;150^{\circ}C,\;180^{\circ}C$)was investigated with considering fracture mechanics. So, we can obtaint the followings. (1) Compressive residual stress is decreased with increasing the test temperature. (2) The effect of compressive residual stress on fatigue crack growth behavior in high temperature is increased below ${\Delta}K=17{\sim}19MPa{\sqrt{m}}$. (3) It was investigated by SEM that the constraint of compress residual stress for plastic zone of fatigue crack tip was decreased in high temperature as compared with room temperature.

• 한국안전학회지
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• 제19권4호
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• pp.8-13
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• 2004

The purpose of this paper is to investigate the welding residual stress distribution according to the constraint or non-constraint welding condition with titanium commonly using power station, aircraft, and ship. The measuring method of the residual stress was applied stress release rating method with strain gages and a potable strain meter. The x direction residual stress generally showed the tensile residual stress in case of res03int welding. On the other hand, the x direction residual stress under non-restraint welding were changed tensile stress into compressive stress on 15mm away from welding bead center. Also, the y direction residual stress generally showed the tensile residual stress in case of non-restraint welding and the y direction residual stress under restraint welding were changed tensile stress into compressive stress about 60mm away from welding bead center.

• Advances in concrete construction
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• 제9권3호
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• pp.249-256
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• 2020

This paper aims at investigating the effect of crumb rubber size and content on compressive behaviors of concrete under axial compression. Concrete specimens are designed and produced by replacing natural aggregate with crumb rubber content of 0%, 5%, 10%, 15% and three different sized crumb rubbers (No. 20, No. 40, No. 80 crumb rubber). And the failure mode, compressive strength, elastic modulus, stress-strain curves, peak strain and ultimate strain are experimentally studied. Based on the test results, formulas have been presented to determine the compressive strength, elastic modulus, the relationship between prism compressive strength and cube compressive strength, stress-strain curves and peak strain of crumb rubber concrete (CRC). It is found that the proposed formulas agree well with the test result on the whole, which may be used to practical applications.

• 대한기계학회논문집
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• 제18권4호
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• pp.958-966
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• 1994

The postbuckling compressive strengths of $[0/90/\pm\theta]_s$ composite laminated cylindrical panels with various fiber angles and width-to-length ratios are characterized by the nonlinear finite element method. For the iteration and load-increment along the postbuckling equilibrium path a modified arc-length method in which the effect of failure can be considered is introduced. In the progressive failure analysis the maximum stress criterion and complete unloading model are used. Present finite element results show good agreement with experiments for $[0_3/90]_s$ cylindrical panel and $[0/\pm45/90/]_s$ plate. The postbuckling compressive strength of $[0/90/\pm\theta]_s$ composite laminated cylindrical panel is independent of the initial buckling stress but high in the panel with large value of the bending stiffness in axial direction. In the several cylindrical panels, it is observed that the prebuckling compressive failures occur and result into the collapse before the buckling.

• 한국진공학회지
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• 제13권4호
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• pp.157-163
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• 2004

라디오파 플라즈마 화학증착법 (radio frequency plasma assisted chemical vapor deposition: r.f.-PACVD) 법으로 증착된 다이아몬드성 카본 (Diamond-like Carbon : DLC) 필름에서 나타나는 습도에 따른 압축 잔류 응력의 변화 거동을 체계적으로 조사하였다. 합성에 사용된 탄화수소 가스의 종류와 -100V에서 -800V 범위의 기판 바이어스 전압의 조절을 통해 폴리머성 필름에서 흑연성 필름까지 광범위한 구조의 DLC 필름을 합성하였다. 상대습도가 10％-90％ 범위에서 변화하는 분위기 챔버 내에서 박막의 잔류응력의 변화를 실시간으로 측정하였다 박막의 경도와 잔류응력이 최고 값을 가지는 합성조건에서 얻어진 치밀한 DLC박막에서는 습도에 따른 잔류응력의 변화가 관찰되지 않았다. 그러나, 폴리머상이나 흑연상의 박막에서는 두 경우 모두 습도가 높아짐에 따라 압축 잔류응력이 증가함을 관찰할 수 있었으며, 습도의 변화에 대해 잔류응력이 즉각적으로 변화하였다. 한편, 동일한 습도에서 압축 잔류응력의 증가량은 필름의 두께에 반비례하는 것이 관찰되었다. 이 결과는 물분자가 필름의 구조내로 침투하면서 생기는 변화가 아니라, 박막의 표면에서 일어나는 물분자와의 반응에 의해 필름의 잔류응력이 변할 수 있음을 의미한다.

• 대한치과교정학회지
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• 제28권3호
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• pp.391-398
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• 1998

본 연구는 유한요소법을 사용하여 상악견치에 intrusion arch wire를 강제로 engage시켰을 때 상악 견치와 치근막에서 발생되는 압축력과 인장력의 분포의 양을 알아보고 어느 부분에 집중되는가를 분석하였다. 또한 각 부분에서의 압축력과 인장력의 비율을 비교하기 위해서 시행하여 다음과 같은 결과를 얻었다. 1. 상악 견치의 FA point와 백악법랑경계부분에서는 압축력과 인장력의 비율이 거의 비슷하게 나타났다. 2. 치근첨 부분에서는 압축력이 인장력의 거의 4배정도 크게 나타났다. Intrusion force적용시 치근흡수 정도가 치근첨에서 발생되는 것을 정량화시켜서 보여준 결과이다. 3. 백악법랑경계부분은 즉 FA point를 제외하고는 압축력과 인장력이 가장 큰 값을 보이고 있다. 즉 치아에 교정력이 직접 적용된 부분을 제외하고는 치아와 치주인대가 처음 접촉되는 백악법랑경계부에서 응력이 집중되는 것을 유추할 수 있다.

• 한국구조물진단유지관리공학회 논문집
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• 제16권4호
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• pp.9-17
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• 2012

선행연구에서는 강도이론을 바탕으로 영향인자들을 반영한 해석단면에 대해 허용압축응력($Kf_{ci}$)을 해석하였고, 해석결과를 바탕으로 허용압축응력산정식을 제안하였다. 이전 연구에 대한 일련의 연구로서, 본 연구에서는 서로 다른 편심비(e/h)를 갖는 프리텐션 보 부재에 대한 프리스트레스 도입 실험을 수행하였다. 실험결과를 토대로 제안식을 검증한 결과 낮은 e/h를 갖는 프리텐션 부재의 경우, ACI318-08 및 EC2-02의 설계기준이 $Kf_{ci}$를 비안전측으로 결정하고 있음을 확인하였다. 또한 높은 e/h를 갖는 프리텐션 부재의 경우 현행의 설계기준은 $Kf_{ci}$를 과도하게 안전측으로 제안하고 있다. 이에 비해 제안식은 e/h에 따른 $Kf_{ci}$를 합리적으로 평가하는 것으로 나타났다.

• 한국해양공학회지
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• 제16권5호
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• pp.73-79
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• 2002

In this paper, the effect of the compressive residual stresses was obtained at the test conditions of the higher temperature than the ambient temperature. The examination was performed with the CT specimen result of the material(JISG SUP9) which is being commonly used for the marine engine parts and the ocean structures. As a result, the test conditions at the higher temperature were acquired considering the peak values of the compressive residual stresses of the specimens and the effect on the fatigue crack propagation speed da／dN in stage II and the threshold stress intensity factor range Δth in stage I. Also the material constant C and the fatigue crack propagation index m in the formula of Paris Law da／dN＝C (ΔK)$^{m}$ were suggested to estimate the dependence on the test temperature.