The Experts below are selected from a list of 22896 Experts worldwide ranked by ideXlab platform
Jaydev P Desai - One of the best experts on this subject based on the ideXlab platform.
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constitutive modeling of liver tissue experiment and theory
Annals of Biomedical Engineering, 2010Co-Authors: Zhan Gao, Kevin Lister, Jaydev P DesaiAbstract:Realistic surgical simulation requires incorporation of the mechanical properties of soft tissue in mathematical models. In actual deformation of soft-tissue during surgical intervention, the tissue is subject to tension, compression, and Shear. Therefore, characterization and modeling of soft-tissue in all these three deformation modes are necessary. In this paper we applied two types of Pure Shear test, unconfined compression and uniaxial tension test to characterize porcine liver tissue. Digital image correlation technique was used to accurately measure the tissue deformation field. Due to gravity and its effect on the soft tissue, a maximum stretching band was observed from the relative strain field on sample undergoing tension and Pure Shear test. The zero strain state was identified according to the position of this maximum stretching band. Two new constitutive models based on combined exponential/logarithmic and Ogden strain energy were proposed. The models are capable to represent the observed non-linear stress–strain relation of liver tissue for full range of tension and compression and also the general response of Pure Shear.
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constitutive modeling of liver tissue experiment and theory
IEEE International Conference on Biomedical Robotics and Biomechatronics, 2008Co-Authors: Zhan Gao, Kevin Lister, Jaydev P DesaiAbstract:Mechanical models for soft organ tissues are necessary for a variety of medical applications, such as surgical planning, virtual reality surgery simulators, and for diagnostic purposes. An adequate quantitative description of the mechanical behavior of tissues requires adequate and accurate experimental data to be acquired and analyzed. We present results of three types of ex vivo tests on pig liver tissue, i.e. simple tension, unconfined compression and Pure Shear. A new constitutive model based on combined logarithmic and Ogden strain energy is proposed. The model accounts very well for observed non-linear stress-strain relations for full strain range of tension and compression and represents equally well the mechanical response of Pure Shear when strain is less than 35%.
Viggo Tvergaard - One of the best experts on this subject based on the ideXlab platform.
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study of localization in a void sheet under stress states near Pure Shear
ECF21, 2016Co-Authors: Viggo TvergaardAbstract:A recent study of a porous ductile material under Pure Shear has indicated that no failure is predicted, whereas a number of mirco-mechanical analyses for simple Shear have shown that a maximum Shear stress is reached and failure occurs. Both simple Shear and Pure Shear are characterized by zero stress triaxiality and in both types of stress states the analyses show that the voids collapse to micro-cracks. The possibility of failure in Pure Shear is further investigated here by studying the effect of an initial imperfection in the form of a row of circular cylindrical voids inclined to the principal tensile stress. A number of previous investigations have shown that such imperfections can lead to plastic flow localization in a Shear band and subsequently lead to void-sheet fracture inside the band. The present analyses confirm that the imperfection leads to localization failure, even at moderate or rather low stress triaxiality. But in Pure Shear with no stress triaxiality no failure is predicted. Initially the imperfection results in increasing Shearing along the row of voids, but this tendency towards increasing Shearing is interrupted if the voids collapse to micro-cracks. For the largest imperfection considered, i.e. a relatively large ratio of the void radius to void spacing, there is still a range of stress states in the vicinity of Pure Shear, where no localization is predicted, and for smaller imperfections this range is larger.
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study of localization in a void sheet under stress states near Pure Shear
International Journal of Solids and Structures, 2015Co-Authors: Viggo TvergaardAbstract:Abstract A recent study of a porous ductile material under Pure Shear has indicated that no failure is predicted, whereas a number of micro-mechanical analyses for simple Shear have shown that a maximum Shear stress is reached and failure occurs. Both simple Shear and Pure Shear are characterized by zero stress triaxiality and in both types of stress states the analyses show that the voids collapse to micro-cracks. The possibility of failure in Pure Shear is further investigated here by studying the effect of an initial imperfection in the form of a row of circular cylindrical voids inclined to the principal tensile stress. A number of previous investigations have shown that such imperfections can lead to plastic flow localization in a Shear band and subsequently lead to void-sheet fracture inside the band. The present analyses confirm that the imperfection results in localization failure, even at moderate or rather low stress triaxiality. But in Pure Shear, with zero stress triaxiality, no failure is predicted. Initially the imperfection results in increasing Shearing along the row of voids, but this tendency towards increasing Shearing is interrupted if the voids collapse to micro-cracks. For the largest imperfection considered, i.e. a relatively large ratio of the void radius to void spacing, there is still a range of stress states in the vicinity of Pure Shear, where no localization is predicted, and for smaller imperfections this range is larger.
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behaviour of porous ductile solids at low stress triaxiality in different modes of deformation
International Journal of Solids and Structures, 2015Co-Authors: Viggo TvergaardAbstract:Abstract The effect of low stress triaxiality on ductile failure is investigated for a material subject to Pure Shear or to stress states in the vicinity of Pure Shear. Many recent studies of ductile failure under low hydrostatic tension have focused on Shear with superposed tension, which can result in simple Shear or in stress states near that. A material with a periodic array of voids is subjected to tensile stresses in one direction and compressive stresses in the transverse direction. Numerical solutions for a plane strain unit cell model are obtained numerically. For stress states in the vicinity of Pure Shear it is found that the voids close up to micro-cracks, and these cracks remain closed during continued deformation, with large compressive stresses acting between crack surfaces. The same type of behaviour is found for different initial sizes of the voids and for cases where the two types of voids in the unit cell have very different initial size. The analyses do not indicate a final failure mode where the stress carrying capacity of the material drops off to zero. In previous analyses for stress states in the vicinity of simple Shear such final failure has been predicted, so it appears that the behaviour of a porous ductile material at low stress triaxiality depends a great deal on the mode of deformation.
Zhan Gao - One of the best experts on this subject based on the ideXlab platform.
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constitutive modeling of liver tissue experiment and theory
Annals of Biomedical Engineering, 2010Co-Authors: Zhan Gao, Kevin Lister, Jaydev P DesaiAbstract:Realistic surgical simulation requires incorporation of the mechanical properties of soft tissue in mathematical models. In actual deformation of soft-tissue during surgical intervention, the tissue is subject to tension, compression, and Shear. Therefore, characterization and modeling of soft-tissue in all these three deformation modes are necessary. In this paper we applied two types of Pure Shear test, unconfined compression and uniaxial tension test to characterize porcine liver tissue. Digital image correlation technique was used to accurately measure the tissue deformation field. Due to gravity and its effect on the soft tissue, a maximum stretching band was observed from the relative strain field on sample undergoing tension and Pure Shear test. The zero strain state was identified according to the position of this maximum stretching band. Two new constitutive models based on combined exponential/logarithmic and Ogden strain energy were proposed. The models are capable to represent the observed non-linear stress–strain relation of liver tissue for full range of tension and compression and also the general response of Pure Shear.
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constitutive modeling of liver tissue experiment and theory
IEEE International Conference on Biomedical Robotics and Biomechatronics, 2008Co-Authors: Zhan Gao, Kevin Lister, Jaydev P DesaiAbstract:Mechanical models for soft organ tissues are necessary for a variety of medical applications, such as surgical planning, virtual reality surgery simulators, and for diagnostic purposes. An adequate quantitative description of the mechanical behavior of tissues requires adequate and accurate experimental data to be acquired and analyzed. We present results of three types of ex vivo tests on pig liver tissue, i.e. simple tension, unconfined compression and Pure Shear. A new constitutive model based on combined logarithmic and Ogden strain energy is proposed. The model accounts very well for observed non-linear stress-strain relations for full strain range of tension and compression and represents equally well the mechanical response of Pure Shear when strain is less than 35%.
Ud I Din - One of the best experts on this subject based on the ideXlab platform.
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design of a new arcan fixture for in plane Pure Shear and combined normal Shear stress characterization of fiber reinforced polymer composites
Experimental Techniques, 2020Co-Authors: Ud I Din, P Hao, Stephane Panier, Kamran A Khan, Muhammad Aamir, Gerald Franz, K AkhtarAbstract:Engineering elastic constants and strength parameters shall be known to the designer in order to predict the structural response of composite materials. These properties shall be determined in various directions as per the designated standards. Testing of composite materials under the combined effect of in-plane Shear and normal stress is of great importance. In this work, a new Arcan fixture has been designed, and then manufactured from aluminum alloy AA7075-T73. This test fixture can be used for uniaxial as well as biaxial testing of fiber reinforced polymers (FRPs) laminates in Pure Shear, and combined normal/Shear stress states. Nevertheless, the fixture can be used for other materials where combined in-plane testing is required including metals and polymers. The special butterfly shape Arcan specimen was optimized based on the parametric study in ABAQUS environment by a Python scripting. The objective of the parametric study was to get a uniform Shear stress field in the notch section of the specimen which is the cross-sectional area between the two opposite V-notch roots. The domain of the uniform Shear stress-strain distribution in the notch section must be greater enough than the size of the strain gauge rosettes where these can be effectively installed for strain acquisition. The experimental set-ups for the realization of Pure Shear stress, normal stress, and combined normal/Shear stress scenarios are schematically elaborated. The Pure Shear stress-strain response based on the Arcan test was compared with the tensile testing of ±450 symmetric laminate.
Haibin Song - One of the best experts on this subject based on the ideXlab platform.
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weak depth and along strike variations in stretching from a multi episodic finite stretching model evidence for uniform Pure Shear extension in the opening of the south china sea
Journal of Asian Earth Sciences, 2013Co-Authors: Lin Chen, Zhongjie Zhang, Haibin SongAbstract:The South China Sea is widely believed to have been opened by seafloor spreading during the Cenozoic. The details of its lithospheric extension are still being debated, and it is unknown whether Pure, simple, or conjunct Shears are responsible for the opening of the South China Sea. The depth-dependent and along-strike extension derived from the single-stage finite stretching model or instantaneous stretching model is inconsistent with the observation that the South China Sea proto-margins have experienced multi-episodic extension since the Late Cretaceous. Based on the multi-episodic finite stretching model, we present the amount of lithosphere stretching at the northern continental margin of the South China Sea for different depth scales (upper crust, whole crust and lithosphere) and along several transects. The stretching factors are estimated by integrating seven deep-penetration seismic profiles, the Moho distribution derived from gravity modeling, and the tectonic subsidence data for 41 wells. The results demonstrate that the amount of stretching increases rapidly from 1.1 at the continent shelf to over 3.5 at the lower slope, but the stretching factors at the crust and lithosphere scales are consistent within error (from the uncertainty in paleobathymetry and sea-level change). Furthermore, the along-strike variation in stretching factor is within the range of 1.11–1.9 in west–east direction, accompanied by significant west–east differences in the thickness of high-velocity layers (HVLs) within the lowermost crust. This weak along-strike variation of the stretching factor is most likely produced by the preexisting contrasts in the composition and thermal structure of the lithosphere. The above observations suggest that the continental extension in the opening of the South China Sea mainly takes the form of a uniform Pure Shear rather than depth-dependent stretching.
