• Composites Research
• /
• v.33 no.1
• /
• pp.30-37
• /
• 2020

Stress distributions dependent on fiber arrangements are studied using the two-dimensional representative volume element (RVE) model for uni-directionally continuous fiber-reinforced composites subjected to transverse tensile loading. It is easily expected that the stresses around the fibers are concentrated mainly due to the stiffness mismatch between the fiber and matrix materials. In this presentation, it is shown that the stresses are not always increased although the distance between two fibers is shortened. The 2D RVE models, originally having a regular hexagonal fiber array, is utilized to study the effect of the fiber locations on the stress distributions. As the central fiber is relocated, the stress distributions around the fiber are obtained through finite element analysis. It is found that the stresses around the fiber are strongly dependent on the fiber distance as well as the angle between the loading direction and the line connecting two fibers.

• Restorative Dentistry and Endodontics
• /
• v.33 no.1
• /
• pp.28-38
• /
• 2008

This study was to investigate the influence of composite resins with different elastic modulus, cavity modification and occlusal loading condition on the stress distribution of restored notch-shaped noncarious cervical lesion using 3-dimensional (3D) finite element (FE) analysis. The extracted maxillary second premolar was scanned serially with Micro-CT. The 3D images were processed by 3D-DOCTOR. ANSYS was used to mesh and analyze 3D FE model. A notch-shaped cavity and a modified cavity with a rounded apex were modeled. Unmodified and modified cavities were filled with hybrid or flowable resin. After restoration, a static load of 500N was applied in a point-load condition at buccal cusp and palatal cusp. The stress data were analyzed using analysis of principal stress. The results were as follows: 1. In the unrestored cavity, the stresses were highly concentrated at mesial CEJ and lesion apex and the peak stress was observed at the mesial point angle under both loading conditions. 2. After restoration of the cavity, stresses were significantly reduced at the lesion apex, however cervical cavosurface margin, stresses were more increased than before restoration under both loading conditions. 3. When restoring the notch-shaped lesion, material with high elastic modulus worked well at the lesion apex and material with low elastic modulus worked well at the cervical cavosurface margin. 4. Cavity modification the rounding apex did not reduce compressive stress, but tensile stress was reduced.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.66 no.1
• /
• pp.35-41
• /
• 2024

측면구속은 지오그리드에서 골재 입자의 상호결합과 관련된 주요 보강 메커니즘으로 알려져 있다. 본 연구에서는 실내실험을 통해 얻은 지오그리드-골재 상호결합에 의한 국부적 강성증가에 대한 결과를 토대로, 지오그리드로 보강된 기층을 포함한 포장구조체의 탄성 반응 특성을 파악하고자 하였다. 기존의 실험적 연구에서는 지오그리드 배치된 시편 중간 높이로부터 거리가 멀어질수록 전단파 측정에서 추정된 전단탄성계수가 감소한다는 것을 보여주었다. 또한, 삼각형 지오그리드 근처의 강성 증가가 사각형 지오그리드 근처보다 크게 나타났다. 이러한 전단탄성계수 주상도를 기반으로, 수치해석적 연구에서는 기층의 4 개 하부층에 대한 탄성계수 값을 다르게 할당되었다. 층상 탄성해석 프로그램을 사용한 수치해석적 연구는 아스팔트층 하단에서 두 지오그리드 보강 포장시나리오의 수평방향 인장 응력과 변형이 미보강된 시나리오에 비해 감소했음을 보여주었다. 기층 중간깊이에서는 지오그리드 보강 포장시나리오의 압축응력이 미보강된 시나리오에 비해 보다 크게 나타났으며, 지오그리드 보강구간의 인장변형은 미보강된 구간보다 작게 나타났다. 삼각형 및 사각형 지오그리드의 사용은 기층 중간깊이에서 미보강된 시나리오에 비해 수직압축응력을 증가시키고 수직압축변형을 감소시켰다. 노상 상단에서는 지오그리드 보강 포장 구간의 수직 응력과 변형이 미보강된 구간보다 작았는데, 이는 노상의 침하 가능성이 낮다는 것을 보여주었다. 따라서, 지오그리드와 골재 간 미세역학적 상호결합을 기반으로 한 거시적 모델링 방법은 지오그리드로 보강된 아스팔트포장시스템의 역학적 분석에 효과적으로 사용될 수 있을 것으로 기대된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.7
• /
• pp.612-617
• /
• 2011

An experimental study was carried out for the Elbrodur-NIB(copper alloy) at room temperature under stress-controlled uniaxial fatigue loading with and without mean stress. As a result, the effects of stress amplitude, mean stress and stress rate on ratcheting behavior were investigated. The ratcheting strain increased with increasing stress amplitude for a given mean stress, and with mean stress for a given stress amplitude. But, the ratcheting strain decreased as the stress rate increased. The three mean stress models were investigated and the mean stress models of Smith-Watson-Topper and Walker yielded good correlation of fatigue lives in the life range of $10^2-10^5$cycles.

• Journal of the Korean Geotechnical Society
• /
• v.17 no.4
• /
• pp.87-91
• /
• 2001

얕은 기초의 침하는 기초에 가해지는 상재 하중의 지반에 전달될 때 분포되는 응력의 특성과 크기에 관련되어 일어난다. 일반적으로 지반의 보강재로 사용되는 지오그리드로 두께가 작은 토체를 보강하면 지중에 전달되는 응력을 재분포시켜 감소시킨다. 이 논문에서는 현장시험을 통하여 여러 층의 지오그리드로 토체를 보강시 토체 상부에 가해지는 원형 등분포 하중하에서 토체의 응력 분포를 측정하였다. 인천국제 공항 건설 현장의 준설 매립 구간에서 행하여진 이 시험을 통하여, 지오그리드로 보강된 토체의 하중 분포는 기초에 가해지는 하중 강도와, 보강재 포설층수, 토체의 두께의 함수로 나타낼 수 있다.

• International Journal of Highway Engineering
• /
• v.8 no.3 s.29
• /
• pp.143-153
• /
• 2006

The differences in the stress distribution and the critical stresses in concrete pavement systems were analyzed when the dual-wheel single-, tandem-, and tridem-axle loads were applied at the interior and the edge of the pavement. The effects of the concrete elastic modulus, slab thickness, foundation stiffness, and tire contact pressure were investigated. The stresses under the interior loads were calculated using the transformed field domain analysis and stresses under the edge loads were obtained using the finite element method. The critical stresses under the interior and the edge loads were compared with respect to various parameters and the equations to predict the ratio between the stresses under the edge and the interior loads were developed and verified. From this study, it was found that the trends of the changes in the critical concrete stresses under the interior and the edge loads were very similar and the critical stress locations under those loads were identical. The critical stress ratio, which was obtained by dividing the critical stress under the edge loads into that under the interior loads, decreased with increasing the number of axles. That ratio became larger as the concrete elastic modulus increased, the slab thickness increased, the foundation stiffness decreased, and the tire contact pressure increased.

• Journal of Forest and Environmental Science
• /
• v.14 no.1
• /
• pp.89-100
• /
• 1998

The study was carried to investigate the change of internal stress and physical properties of paper by the mutiplying of paper structuring that is an useful means to maximize the performance and use of the fiber raw material. The effects of recycled fiber on the physical properties of multiplied paper also were studied. The beating increased the internal stress of single layered paper, while filler loading decreased the internal stress. Multiplying the structure of paper decreased the internal stress and the most of physical properties except for tear index. It was found that the properties of paper could be changed by the pulp type, beating and the combination of raw materials. The introduction of filler in the middle and/or outer layer could improved the internal stress, tensile index, tear index and burst index. The addition of recycled fiber increased the opacity and stiffness of paper in both single layered and multiplied paper. Multiplying the structure of paper improved the air permeability and stiffness, while decreased burst index.

• Elastomers and Composites
• /
• v.39 no.2
• /
• pp.142-152
• /
• 2004

Tensile tests of two types of injection-molded polystyrene(PS) samples have been carried out over a wide range of temperature and strain rates in order to characterize their crazing behaviors. Mechanical properties were affected by the formation of crazes as well as test variables. Below the brittle-ductile transition temperature, the tensile stress and the ultimate elongation increased with the molecular weight, strain rate, and with decreasing temperature while the number and average length of crazes also increase. The crazing stress increased with molecular weight, strain rate, and with decreasing temperature. However, the dependence was small compared to the tensile stress. The gap between crazing stress and tensile stress which represents time fur craze formation and growth increased with molecular weight, strain rate, and with decreasing temperature. Crazing was activated near the ${\beta}$-relaxation temperature; crazing stress abruptly decreased at this temperature. During the tensile test, the craze density changed exponentially with the applied stress. At the initial stage, crazes formed slowly. Once a certain number of craze formed, however, the craze density increased rapidly. Craze nucleation and growth occur simultaneously.

• Korean Journal of Materials Research
• /
• v.9 no.11
• /
• pp.1069-1074
• /
• 1999

본 연구에서는 PbZr(sub)0.53Ti(sub)0.47O$_3$(PZT) 박막을 복수 도포함에 따른 박막내의 응력을 온도의 함수로 실시간(in situ) 측정하였으며, 응력발생의 원인에 박막의 건조, 열분해(pyrolysis), 치밀화 및 결정화 현상과 연관시켜 설명하였다. 도포직후 단층박막에 생성된 55MPa의 인장응력은 가열됨에 따라$ 300^{\circ}C$-$350^{\circ}C$에서 최대 145MPa로 증가하였으며, 박막내의 응력은 모든 온도구간에서 항상 인장응력을 나타내었더. 다층도포시 $650^{\circ}C$까지 열처리 주기를 완료한 층이 두꺼워질수록 새로 도포한 층의 영향은 점차 감소하였으며, 9층박막에 이르러서는 가열과 냉각에 따라 응력이 동일하게 변화하였다. 응력측정 결과 다층박막의 치밀화는 $350^{\circ}C$에서 시작되어 $520^{\circ}C$-$550^{\circ}C$ 부근에서 완료되는 것으로 나타났으며 치밀화가 시작하는 온도는 미세경도 측정결과와 일치하였다. $PbTiO_3$(PT)와 달리 PZT 다층박막은 Si 기판 위에서 perovskite로의 결정화가 일어나지 않았다.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.11b
• /
• pp.481-486
• /
• 1996

원자력 발전소의 증기 발생기 전열관으로 사용되는 합금 600MA는 미세 구조에 관계없이 가성 용액에서 입계 균열이 발생한다. 본 연구에서는 합금 600 2종과 합금 690 2종의 이음매없는 관 및 진공 용해한 합금 690M 2종의 MA 및 TT재에 대한 부식 조건의 변화에 응력 부식 균열 특성을 일정연신율법(CERT) 및 C-ring법으로 평가하였다. 가성 응력 부식 균열 저항성에 미치는 TT처리의 효과는 용액 조건에 관계없이 TT처리를 행하게 되면 응력 부식 균열에 대한 저항성이 증가하는 것으로 나타났으며, 분극 저항성과는 직접적인 관계가 나타나지 않고 다른 미세 조직 등에 의한 영향을 더 크게 받고 있는 것으로 판단된다. 가성 용액에서의 응력 부식 균열 저항성에 미치는 SO$_4$$^{=}$ 이온의 첨가 효과는 TT처리의 유무에 관계없이 응력 부식 균열 저항성을 크게 감소시키고 있다. 한편 합금 690의 가성 응력부식 균열 저항성에 미치는 Mo의 효과는 Mo이 첨가될수록 응력 부식 균열 저항성이 증가하는 것으로 나타났다.