• International Journal of Reliability and Applications
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• 제6권2호
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• pp.79-85
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• 2005

We show how comparative mean residual life functions (MRL) can be used to give unique insights into strengths of materials data. Recall that Weibull's original reliability function was developed studying and fitting strengths for various materials. This creative comparing of MRL functions approach can be used for regular life data or any time to response data. We apply graphical MRL's to real data from tests of tensile strength of high quality engineered wood.

• 한국세라믹학회지
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• 제33권2호
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• pp.127-134
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• 1996

The thermal residual stresses were estimated for brazed Si3N4/S.S.316 joints with Cu/Mo multi-interlayers using FEM, and their bending strengths at room temperature were measured for various interlayer configura-tions. The Cu, Mo multi-interlayer decreased the maximum residual stress in Si3N4 and caused the residual stress redistribution rsulting in the high residual stress at Mo interlayer. The stress distribution in the joints as well as the maximum residual stress in silicon nitride were found to be main factors for determining bending strengths and Weibull modulous of the joints. The bending strength of the brazed Si3N4/S.S.316 joints with specific Cu, Mo multi-interlayer system were found to be above 400 MPa.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권1호
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• pp.14-26
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• 2014

This paper provides the prediction of ultimate longitudinal strengths of the hull girders of a very large crude carrier considering probabilistic damage extent due to collision and grounding accidents based on IMO Guidelines (2003). The probabilistic density functions of damage extent are expressed as a function of non-dimensional damage variables. The accumulated probabilistic levels of 10%, 30%, 50%, and 70% are taken into account for the estimation of damage extent. The ultimate strengths have been calculated using the in-house software called Ultimate Moment Analysis of Damaged Ships which is based on the progressive collapse method, with a new convergence criterion of force vector equilibrium. Damage indices are provided for several probable heeling angles from $0^{\circ}$ (sagging) to $180^{\circ}$ (hogging) due to collision- and grounding-induced structural failures and consequent flooding of compartments. This paper proves from the residual strength analyses that the second moment of area of a damage section can be a reliable index for the estimation of the residual ultimate strength. A simple polynomial formula is also proposed based on minimum residual ultimate strengths.

• 대한기계학회논문집A
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• 제27권1호
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• pp.175-182
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• 2003

The fatigue life of welded joints is sensitive to welding residual stress and complexity of their geometric shapes. To predict the fatigue life more reasonably. the effects of welding residual stress and its relaxation on their fatigue strengths should be considered quantitatively, which are often regarded to be equivalent to the effects of mean stresses by external loads. The hot-spot stress concept should be also adopted which can reduce the dependence of fatigue strengths for various welding details. Considering the factors mentioned above, a fatigue life prediction model using the modified Goodman's diagram was proposed. In this model, an equivalent stress was introduced which is composed of the mean stress based on the hot-spot stress concept and the relaxed welding residual stress. From the verification of the proposed model to real welding details, it is proved that this model can be applied to predict reasonably their fatigue lives.

• Advances in concrete construction
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• 제10권3호
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• pp.247-256
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• 2020

In this paper the possibility of using different regression models to predict the mechanical properties of limestone concrete after exposure to high temperatures, based on the results of non-destructive techniques, that could be easily used in-situ, is discussed. Extensive experimental work was carried out on limestone concrete mixtures, that differed in the water to cement (w/c) ratio, the type of cement and the quantity of superplasticizer added. After standard curing, the specimens were exposed to various high temperature levels, i.e., 200℃, 400℃, 600℃ or 800℃. Before heating, the reference mechanical properties of the concrete were determined at ambient temperature. After the heating process, the specimens were cooled naturally to ambient temperature and tested using non-destructive techniques. Among the mechanical properties of the specimens after heating, known also as the residual mechanical properties, the residual modulus of elasticity, compressive and flexural strengths were determined. The results show that residual modulus of elasticity, compressive and flexural strengths can be reliably predicted using an artificial neural network approach based on ultrasonic pulse velocity, residual surface strength, some mixture parameters and maximal temperature reached in concrete during heating.

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.75-85
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• 2016

Fire ranks high among the potential risks faced by most buildings and structures. A full understanding of temperature effects on fiber reinforced concrete is still lacking. This investigation focuses on the study of the residual compressive strength, stress strain behavior and surface cracking of structural polypropylene fiber-reinforced concrete subjected to temperatures up to $300^{\circ}C$. A total of 48 cubes was cast with different fiber dosages and tested under compression after exposing to different temperatures. Concrete cubes with varying macro (structural) fiber dosages were exposed to different temperatures and tested to observe the stress-strain behavior. Digital image correlation, an advanced non-contacting method was used for measuring the strain. Trends in the relative residual strengths with respect to different fiber dosages indicate an improvement up to 15 % in the ultimate compressive strengths at all exposure temperatures. The stress-strain curves show an improvement in post peak behavior with increasing fiber dosage at all exposure temperatures considered in this study.

• 비파괴검사학회지
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• 제28권2호
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• pp.125-130
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• 2008

레이저 용접부의 국소 잔류응력을 측정하기 위한 비파괴 기법으로 구형압입시험이 제안되었다. 용접상태 절단휠의 구형압입시험으로 얻어진 겉보기 항복강도와 절단횔 용접부에 대한 응력완화 열처리 이후 동등한 위치에서 구한 고유 항복강도를 정량적으로 비교하였다. 고유항복강도가 탄성한도 내의 잔류응력에 의해서 변화하지 않는다고 고려하면 용융선으로부터 거리에 따른 두 항복강도의 차이가 용접잔류응력의 분포로 나타난다. 레이저 용접된 다이아몬드 절단휠의 구형압입시험으로부터 약 10 mm 폭에 걸친 잔류응력의 분포를 확인하였으며, 잔류응력은 쌩크와 절단팁 내에서 각각 최대 압축 및 인장 잔류응력치를 나타내었다.

• 대한치과보철학회지
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• 제29권2호
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• pp.67-84
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• 1991

This study was carried out to investiagate the residual stress caused by the mismatch of thermal expansion and the bond failure resistance of alloy-porcelain specimens. The thermal expansions of alloys and porcelains were measured by using a straight push-rod dilatometer. Porcelain glass transition temperatures, thermal expansion coefficients, and thermal compatibility indices were derived from length-versus-temperature curves. Strain gauges were used to experimentally determine the Young's moduli of porcelains, the residual stresses of porcelain surface, and tensile bond strengths of the specimens of simulated porcelain metal crown. The obtained results were as follows: 1. The coefficients of thermal expansion for alloys were the minimum of $13.53\mu/^{\circ}C$ and the maximum of $20.11\mu/^{\circ}C$ in the range of $100\sim600^{\circ}C$ and those for porcelains were the minimum of $7.72\mu/^{\circ}C$ and the maximum of $31.24\mu/^{\circ}C$ in the range of $100\sim500^{\circ}C$. 2. The glass transition temperature of porcelains exhibited the same value without my relation to the healing rate, and the thermal disharmony of porcelain and alloy was more affected by porcelains than by the alloys. 3. The Young's moduli of body porcelains were larger than those of opaque porcelains(P<0.01) 4. It seemed that the residual stresses of porcelain surfaces in the porcelainalloy systems were more affected by porcelains than by alleys. 5. The bond strengths of the procelain-base metal alloy systems were larger than those of the porcelain-precious metal alloy systems. The fracture strengths of porcelain surfaces showed significant difference between porcelains (P<0.05).

• 한국산학기술학회논문지
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• 제14권12호
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• pp.6521-6526
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• 2013

판형보강재의 강성 및 세장비의 영향이 보강판시스템의 면내압축강도에 미치는 영향을 살펴보기 위해 탄성 및 비탄성 극한강도해석이 수행되었다. 탄성좌굴해석에서는 보강재의 국부좌굴현상이 고려될 수 없지만 보강재의 강성이 일정정도 확보되면 역대칭모드 좌굴형상이 발생되면서 보강판의 면내압축강도가 확보되는 것으로 파악되었다. 초기결함 및 잔류응력이 고려된 극한강도해석에서는 초기결함의 모드형상이 극한강도에 민감하게 영향을 미친다는 사실이 확인되었다. 도로교설계기준에서 제시하는 판형보강재의 세장비제한은 해석 결과와 비교하였을 때 보수적인 수치로 평가되었다.

• Computers and Concrete
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• 제21권6호
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• pp.681-695
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• 2018

This pioneer study investigates the size effect on the compressive and tensile strengths of fiber-reinforced self-compacting concrete (FR-SCC) with different specimens, before and after exposure to elevated temperatures. 432 self-compacting concrete (SCC) specimens with two concrete grades (50 and 80MPa) and three steel fiber ratios (0%, 0.5% and 1%) were prepared and tested. Moreover, based on the experimental results, new formulations were proposed to predict the residual strengths for different specimens. A parametric study was also carried out to investigate the accuracy of proposed formulations. Residual strength results showed that the cylinder specimen with dimensions of $100{\times}200mm$ was the most affected, while the cube with a size of 100 mm maintained a constant difference with the standard cylinder ($150{\times}300mm$). Temperature effect on the cube specimen (150 mm) was the least in comparison to other specimen sizes and types. In general, provision of steel fibers in SCC mixtures resulted in a reduction in temperature effect on the variance of a conversion factor. Parametric study results confirm that the proposed numerical models are safe to be used for all types of SCC specimens.