The Experts below are selected from a list of 4173 Experts worldwide ranked by ideXlab platform
Kozaburo Hayashi - One of the best experts on this subject based on the ideXlab platform.
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theoretical study of the effects of vascular smooth muscle contraction on strain and stress distributions in arteries
Annals of Biomedical Engineering, 1999Co-Authors: Alexander Rachev, Kozaburo HayashiAbstract:To study the effects of smooth muscle contraction and relaxation on the strain and stress distribution in the vascular wall, a mathematical model was proposed. The artery was assumed to be a thick-walled orthotropic tube made of nonlinear, incompressible elastic material. ConsideRing that the contraction of smooth muscle generates an active circumferential stress in the wall, a numerical study was performed using data available in the literature. The results obtained showed that smooth muscle contraction affects the residual strains which exist in a Ring segment cut out from the artery and exposed to no external load. When the Ring Specimen is cut radially, it spRings open with an opening angle. The predicted monotonic increase of the opening angle with increasing muscular tone was in agreement with recent experimental results reported in the literature. It was shown that basal muscular tone, which exists under physiological conditions, reduces the strain gradient in the arterial wall and yields a near uniform stress distribution. DuRing temporary changes in blood pressure, the increase in muscular tone induced by elevated pressure tends to restore the distribution of circumferential strain in the arterial wall, and to maintain the flow-induced wall shear stress to normal level. © 1999 Biomedical EngineeRing Society.
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theoretical study of the effects of vascular smooth muscle contraction on strain and stress distributions in arteries
Annals of Biomedical Engineering, 1999Co-Authors: Alexander Rachev, Kozaburo HayashiAbstract:To study the effects of smooth muscle contraction and relaxation on the strain and stress distribution in the vascular wall, a mathematical model was proposed. The artery was assumed to be a thick-walled orthotropic tube made of nonlinear, incompressible elastic material. ConsideRing that the contraction of smooth muscle generates an active circumferential stress in the wall, a numerical study was performed using data available in the literature. The results obtained showed that smooth muscle contraction affects the residual strains which exist in a Ring segment cut out from the artery and exposed to no external load. When the Ring Specimen is cut radially, it spRings open with an opening angle. The predicted monotonic increase of the opening angle with increasing muscular tone was in agreement with recent experimental results reported in the literature. It was shown that basal muscular tone, which exists under physiological conditions, reduces the strain gradient in the arterial wall and yields a near uniform stress distribution. DuRing temporary changes in blood pressure, the increase in muscular tone induced by elevated pressure tends to restore the distribution of circumferential strain in the arterial wall, and to maintain the flow-induced wall shear stress to normal level. © 1999 Biomedical EngineeRing Society.
Jason Weiss - One of the best experts on this subject based on the ideXlab platform.
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Quantifying shrinkage cracking in fiber reinforced concrete using the Ring test
Materials and Structures, 2006Co-Authors: H. R. Shah, Jason WeissAbstract:Tensile stress can develop in concrete when rest raint prevents the concrete from shrinking freely in response to drying, chemical reaction, or temperature reduction. When these tensile stresses exceed the tensile strength of the concrete, visible cracking may be expected to occur. While several test methods have been developed to assess a material's potential for early-age shrinkage cracking, this paper describes the use of the ‘Ring-test’ for assessing the performance of a fiber reinforced concrete. An equation is presented that enables the residual stress that develops in the concrete Ring Specimen to be estimated. This expression is used to approximate the stress that is transferred across a crack. It is shown that for conventional fiber reinforced concrete (i.e., the mixtures described in this paper) the pre-peak mechanical properties (elastic modulus, splitting tensile strength and free shrinkage) are not influenced greatly by the addition of fibers. Rather, fibers appear to influence shrinkage-cracking behavior only after the crack begins to open. To better understand the role of fibers in mitigating early-age shrinkage cracking passive acoustic emission testing was used. Acoustic emission measurements indicate microcracking due to the heterogenous nature of the concrete and the presence of moisture gradients. The acoustic emission results highlight how a single crack begins to form into a visible crack. Finally, an approach is presented for estimating crack-width based on the strain data measured from the Ring test. The role of the Specimen geometry is discussed for compaRing the Ring test with field applications.
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quantifying the influence of Specimen geometry on the results of the restrained Ring test
Journal of Astm International, 2006Co-Authors: Jaeheum Moon, Bradley Justin Pease, Farshad Rajabipour, Jason WeissAbstract:Over the last decade, the restrained Ring test has trequently been used to assess the cracking susceptibility of a concrete mixture when it is restrained from shrinking treely. Despite the trequent use of the Ring test, limited analysis has been performed to understand how the Specimen geometry influences the results of the test. This paper discusses the influence of Specimen geometry on the results of the Ring test consideRing three conditions: (1) uniform shrinkage of the concrete Ring, (2) shrinkage caused by drying from the top and bottom surfaces of the concrete Ring, and (3) shrinkage caused by drying from the outer circumference of the concrete Ring. The role of moisture gradients, thickness of the concrete and the restraining (i.e., steel) Rings, and the stiffness of concrete are considered in a series of numerical simulations. Results from these simulations can enable better selection of test Specimen geometries and interpretation of the results from the Ring test. Analytical expressions are provided to use for determining the geometry of the Ring Specimen that better simulates specific field conditions while providing the most useful information from the test.
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estimating residual stress in the restrained Ring test under circumferential drying
Cement & Concrete Composites, 2006Co-Authors: Jaeheum Moon, Jason WeissAbstract:The restrained Ring test is becoming widely used as a standard test method to assess the potential for early-age cracking in concrete mixtures. Previous research focused on the development of analytical solutions for quantifying residual stress development in restrained Ring Specimens that either assumed that the Ring was thin (i.e., a thin wall approximation) or that the shrinkage was uniform along the radial direction for a thick-walled Ring. This paper presents an analytical solution to consider the influence of moisture gradients that occur when a thick-walled Ring Specimen dries from the outer circumference. Toward this end, the Ring that dries from the outer circumference is treated as the superposition of a stress field that is caused by external restraint and a stress field that arises due to differential shrinkage. An analytical expression is presented to estimate the stress components. To assess the suitability of the analytical solution, it was compared with results from a finite element analysis and a reasonably good agreement was observed.
Alexander Rachev - One of the best experts on this subject based on the ideXlab platform.
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theoretical study of the effects of vascular smooth muscle contraction on strain and stress distributions in arteries
Annals of Biomedical Engineering, 1999Co-Authors: Alexander Rachev, Kozaburo HayashiAbstract:To study the effects of smooth muscle contraction and relaxation on the strain and stress distribution in the vascular wall, a mathematical model was proposed. The artery was assumed to be a thick-walled orthotropic tube made of nonlinear, incompressible elastic material. ConsideRing that the contraction of smooth muscle generates an active circumferential stress in the wall, a numerical study was performed using data available in the literature. The results obtained showed that smooth muscle contraction affects the residual strains which exist in a Ring segment cut out from the artery and exposed to no external load. When the Ring Specimen is cut radially, it spRings open with an opening angle. The predicted monotonic increase of the opening angle with increasing muscular tone was in agreement with recent experimental results reported in the literature. It was shown that basal muscular tone, which exists under physiological conditions, reduces the strain gradient in the arterial wall and yields a near uniform stress distribution. DuRing temporary changes in blood pressure, the increase in muscular tone induced by elevated pressure tends to restore the distribution of circumferential strain in the arterial wall, and to maintain the flow-induced wall shear stress to normal level. © 1999 Biomedical EngineeRing Society.
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theoretical study of the effects of vascular smooth muscle contraction on strain and stress distributions in arteries
Annals of Biomedical Engineering, 1999Co-Authors: Alexander Rachev, Kozaburo HayashiAbstract:To study the effects of smooth muscle contraction and relaxation on the strain and stress distribution in the vascular wall, a mathematical model was proposed. The artery was assumed to be a thick-walled orthotropic tube made of nonlinear, incompressible elastic material. ConsideRing that the contraction of smooth muscle generates an active circumferential stress in the wall, a numerical study was performed using data available in the literature. The results obtained showed that smooth muscle contraction affects the residual strains which exist in a Ring segment cut out from the artery and exposed to no external load. When the Ring Specimen is cut radially, it spRings open with an opening angle. The predicted monotonic increase of the opening angle with increasing muscular tone was in agreement with recent experimental results reported in the literature. It was shown that basal muscular tone, which exists under physiological conditions, reduces the strain gradient in the arterial wall and yields a near uniform stress distribution. DuRing temporary changes in blood pressure, the increase in muscular tone induced by elevated pressure tends to restore the distribution of circumferential strain in the arterial wall, and to maintain the flow-induced wall shear stress to normal level. © 1999 Biomedical EngineeRing Society.
Noriaki Fukushima - One of the best experts on this subject based on the ideXlab platform.
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iron loss model for rotating machines using direct eddy current analysis in electrical steel sheets
IEEE Transactions on Energy Conversion, 2010Co-Authors: Katsumi Yamazaki, Noriaki FukushimaAbstract:In this paper, we propose and validate a method for the accurate estimation of iron loss in rotating machines. In this method, the eddy current loss in electrical steel sheets is directly calculated by nonlinear time-domain electromagnetic field analysis with a simple approximation of the excess loss. The hysteresis loss is also estimated by consideRing the flux distribution along the thickness of the steel sheet. The advantage of the method is that the high-frequency harmonic losses can be calculated accurately using only few material constants. The validity of this method is confirmed by experiments performed on a Ring Specimen and several types of motors. The experimental and calculated iron losses in each experiment are found to be in good agreement. It is clarified that the proposed method is useful for the accurate estimation of higher order harmonic losses, particularly, carrier losses caused by inverters.
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experimental validation of iron loss model for rotating machines based on direct eddy current analysis of electrical steel sheets
International Electric Machines and Drives Conference, 2009Co-Authors: Katsumi Yamazaki, Noriaki FukushimaAbstract:In this study, we propose and confirm an accurate estimation method of iron loss in rotating machines. In the method, the eddy-current loss in the electrical steel sheets is directly calculated by a nonlinear time-domain electromagnetic field analysis with a simple approximation of the excess loss. The hysteresis loss is also estimated with the consideration of flux distribution along the thickness of the steel sheet. The advantage of the method is the accuracy of the high-frequency harmonic losses using only several material constants. The validity of the method is confirmed by two experiments. The first experiment is carried out by a Ring Specimen of the electrical steel sheets. In this case, superimposed fundamental and harmonic fluxes are applied to the Specimen. The second experiment is carried out by an induction motor driven by an inverter as well as a sinusoidal power supply. The carrier harmonic loss by the inverter is separated for the purpose of confirming the accuracy of the calculated harmonic losses. The experimental and calculated iron losses in both experiments are found to be in good agreement.
M A G Calle - One of the best experts on this subject based on the ideXlab platform.
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limiting the influence of friction on the split hopkinson pressure bar tests by using a Ring Specimen
International Journal of Impact Engineering, 2012Co-Authors: Marcilio Alves, D Karagiozova, G B Micheli, M A G CalleAbstract:Abstract The deformation of a Ring under axial compression is analyzed in order to estimate a favorable Ring Specimen geometry capable of limiting the influence of friction on the stress–strain curve obtained from SHPB tests. The analysis shows that the use of a Ring Specimen with a large inner diameter and a small radial thickness offers some advantages compaRing with the traditional disk sample. In particular, it can improve the reliability of the test results for ductile materials in the presence of friction. Based on the deformation analysis of a ductile Ring under compression, a correction coefficient is proposed to relate the actual material stress–strain curve with the reading from the SHPB. It is shown using finite element simulation that the proposed correction can be used for a wide range of conventional ductile materials. Experimental results with steel alloys indicate that the correction procedure is an effective technique for an accurate measurement of the dynamic material strength response.
