The Experts below are selected from a list of 67599 Experts worldwide ranked by ideXlab platform
V. Fontanari - One of the best experts on this subject based on the ideXlab platform.
-
Evaluation of the stress–Strain Curve of metallic materials by spherical indentation
International Journal of Solids and Structures, 2006Co-Authors: M. Beghini, L. Bertini, V. FontanariAbstract:AbstractA method for deducing the stress–Strain uniaxial properties of metallic materials from instrumented spherical indentation is presented along with an experimental verification.An extensive finite element parametric analysis of the spherical indentation was performed in order to generate a database of load vs. depth of penetration Curves for classes of materials selected in order to represent the metals commonly employed in structural applications. The stress–Strain Curves of the materials were represented with three parameters: the Young modulus for the elastic regime, the stress of proportionality limit and the Strain-hardening coefficient for the elastic–plastic regime.The indentation Curves simulated by the finite element analyses were fitted in order to obtain a continuous function which can produce accurate load vs. depth Curves for any combination of the constitutive elastic–plastic parameters. On the basis of this continuous function, an optimization algorithm was then employed to deduce the material elastic–plastic parameters and the related stress–Strain Curve when the measured load vs. depth Curve is available by an instrumented spherical indentation test.The proposed method was verified by comparing the predicted stress–Strain Curves with those directly measured for several metallic alloys having different mechanical properties.This result confirms the possibility to deduce the complete stress–Strain Curve of a metal alloy with good accuracy by a properly conducted instrumented spherical indentation test and a suitable interpretation technique of the measured quantities
-
Evaluation of the stress-Strain Curve of metallic materials by spherical indentation
International Journal of Solids and Structures, 2005Co-Authors: M. Beghini, L. Bertini, V. FontanariAbstract:Abstract A method for deducing the stress–Strain uniaxial properties of metallic materials from instrumented spherical indentation is presented along with an experimental verification. An extensive finite element parametric analysis of the spherical indentation was performed in order to generate a database of load vs. depth of penetration Curves for classes of materials selected in order to represent the metals commonly employed in structural applications. The stress–Strain Curves of the materials were represented with three parameters: the Young modulus for the elastic regime, the stress of proportionality limit and the Strain-hardening coefficient for the elastic–plastic regime. The indentation Curves simulated by the finite element analyses were fitted in order to obtain a continuous function which can produce accurate load vs. depth Curves for any combination of the constitutive elastic–plastic parameters. On the basis of this continuous function, an optimization algorithm was then employed to deduce the material elastic–plastic parameters and the related stress–Strain Curve when the measured load vs. depth Curve is available by an instrumented spherical indentation test. The proposed method was verified by comparing the predicted stress–Strain Curves with those directly measured for several metallic alloys having different mechanical properties. This result confirms the possibility to deduce the complete stress–Strain Curve of a metal alloy with good accuracy by a properly conducted instrumented spherical indentation test and a suitable interpretation technique of the measured quantities.
Zhiliang Zhang - One of the best experts on this subject based on the ideXlab platform.
-
a method for determining material s equivalent stress Strain Curve with any axisymmetric notched tensile specimens without bridgman correction
International Journal of Mechanical Sciences, 2018Co-Authors: Shengwen Tu, Jianying He, Zhiliang ZhangAbstract:Abstract Large deformation analyses of problems such as plastic forming, ductile fracture with finite element method need a full range of material's equivalent stress-Strain Curve or flow stress-Strain Curve. The equivalent stress-Strain Curve determined from the smooth round bar specimen should be corrected after diffuse necking, since tri-axial stress state occurs in the neck. The well-known Bridgman correction method is a candidate, however, it is not accurate as the Strain increases. Furthermore, it is impossible to measure the equivalent stress-Strain Curve of each individual material zone in a weldment with cross weld tensile tests. To cope with these challenges, a correction function and an associated test procedure are proposed in this study. With the proposed procedure, the true stress-Strain Curve from any axisymmetric notched tensile specimen can be converted to the material's equivalent stress-Strain Curve accurately and no Bridgman correction is needed. The proposed procedure can be applied to both perfectly plastic and Strain hardening materials. The equivalent stress-Strain Curve of each individual material zone in a weldment can also be measured with the proposed procedure.
-
a special notched tensile specimen to determine the flow stress Strain Curve of hardening materials without applying the bridgman correction
Engineering Fracture Mechanics, 2017Co-Authors: Xiaobo Ren, Bard Nyhus, Odd M Akselsen, Zhiliang ZhangAbstract:Abstract Structural integrity assessment of weldments requires the input of flow stress-Strain Curve of each individual material zone. To cope with these challenges, a cylindrical cross weld tensile specimen with a notch located either in the weld metal, base metal or possibly heat affected zone has been previously developed by the authors to determine the true stress-Strain Curve for the material zone of interest. The disadvantage of this notched tensile testing method as well as the standard tensile testing method using a smooth specimen, is that the well-known Bridgman correction still has to be applied in order to obtain material’s equivalent or flow stress-Strain Curves. In this study, tensile specimens with various notch geometries have been scrutinized and a ‘magic’ specimen with a special notch geometry has been identified. By using this special notched tensile specimen, material’s flow stress-Strain Curve can be directly calculated from the recorded load versus diameter reduction Curve and no Bridgman correction is needed. The method is very accurate for power-law hardening materials and becomes less accurate for materials with significant Luders plateau in the initial yield region.
-
a study on determining true stress Strain Curve for anisotropic materials with rectangular tensile bars
International Journal of Solids and Structures, 2001Co-Authors: Zhiliang Zhang, J Odegard, O P Sovik, Christian ThaulowAbstract:Abstract Recently, a method has been proposed for determining material true stress–Strain Curve with rectangular tensile bars up to localized necking. In the proposed method, material true stress–Strain Curve can be directly calculated from the load versus thickness reduction (at the minimum cross-section) Curve. The method was established based on the finite element (FE) analysis for isotropic materials. In this study, this method has been extended for materials with isotropic elastic properties but anisotropic plastic properties. Two cases, transverse anisotropy and planar anisotropy, have been considered. Hill’s anisotropic material model implemented in abaqus was applied for the study. More than 30 three-dimensional FE analyses of rectangular specimens with different anisotropy value, hardening exponent and cross-section aspect ratio have been carried out. It is shown that the relation between thickness reduction and total area reduction of a given cross-section is influenced by material plastic anisotropy. It is, however, found that the anisotropic effect on the thickness–area reduction relation can be normalized by the width to thickness Strain increment ratio r, and a modified thickness–area reduction relation is proposed and numerically and experimentally verified. One practical problem in tensile test is that it is difficult to predict the necking location. In this regard, a study on the sensitivity of initial notch geometry has been carried out. It is found that for a fixed initial notch radius, the percentage of error is approximately equal to the percentage of initial width reduction. The accuracy of using large initial width reduction can be improved by using large notch radius.
-
determining material true stress Strain Curve from tensile specimens with rectangular cross section
International Journal of Solids and Structures, 1999Co-Authors: Zhiliang Zhang, Mons Hauge, J Odegard, Christian ThaulowAbstract:Abstract The uniaxial true stress logarithmic Strain Curve for a thick section can be determined from the load–diameter reduction record of a round tensile specimen. The correction of the true stress for necking can be performed by using the well-known Bridgman equation. For thin sections, it is more practical to use specimens with rectangular cross-section. However, there is no established method to determine the complete true stress–logarithmic Strain relation from a rectangular specimen. In this paper, an extensive three-dimensional numerical study has been carried out on the diffuse necking behaviour of tensile specimens made of isotropic materials with rectangular cross-section, and an approximate relation is established between the area reduction of the minimum cross-section and the measured thickness reduction. It is found that the area reduction can be normalized by the uniaxial Strain at maximum load which represents the material hardening and also the section aspect ratio. Furthermore, for the same material, specimens with different aspect ratio give exactly the same true average stress–logarithmic Strain Curve. This finding implies that Bridgmans correction can still be used for necking correction of the true average stress obtained from rectangular specimens. Based on this finding, a method for determining the true stress–logarithmic Strain relation from the load–thickness reduction Curve of specimens with rectangular cross-section is proposed.
Christian Thaulow - One of the best experts on this subject based on the ideXlab platform.
-
a study on determining true stress Strain Curve for anisotropic materials with rectangular tensile bars
International Journal of Solids and Structures, 2001Co-Authors: Zhiliang Zhang, J Odegard, O P Sovik, Christian ThaulowAbstract:Abstract Recently, a method has been proposed for determining material true stress–Strain Curve with rectangular tensile bars up to localized necking. In the proposed method, material true stress–Strain Curve can be directly calculated from the load versus thickness reduction (at the minimum cross-section) Curve. The method was established based on the finite element (FE) analysis for isotropic materials. In this study, this method has been extended for materials with isotropic elastic properties but anisotropic plastic properties. Two cases, transverse anisotropy and planar anisotropy, have been considered. Hill’s anisotropic material model implemented in abaqus was applied for the study. More than 30 three-dimensional FE analyses of rectangular specimens with different anisotropy value, hardening exponent and cross-section aspect ratio have been carried out. It is shown that the relation between thickness reduction and total area reduction of a given cross-section is influenced by material plastic anisotropy. It is, however, found that the anisotropic effect on the thickness–area reduction relation can be normalized by the width to thickness Strain increment ratio r, and a modified thickness–area reduction relation is proposed and numerically and experimentally verified. One practical problem in tensile test is that it is difficult to predict the necking location. In this regard, a study on the sensitivity of initial notch geometry has been carried out. It is found that for a fixed initial notch radius, the percentage of error is approximately equal to the percentage of initial width reduction. The accuracy of using large initial width reduction can be improved by using large notch radius.
-
determining material true stress Strain Curve from tensile specimens with rectangular cross section
International Journal of Solids and Structures, 1999Co-Authors: Zhiliang Zhang, Mons Hauge, J Odegard, Christian ThaulowAbstract:Abstract The uniaxial true stress logarithmic Strain Curve for a thick section can be determined from the load–diameter reduction record of a round tensile specimen. The correction of the true stress for necking can be performed by using the well-known Bridgman equation. For thin sections, it is more practical to use specimens with rectangular cross-section. However, there is no established method to determine the complete true stress–logarithmic Strain relation from a rectangular specimen. In this paper, an extensive three-dimensional numerical study has been carried out on the diffuse necking behaviour of tensile specimens made of isotropic materials with rectangular cross-section, and an approximate relation is established between the area reduction of the minimum cross-section and the measured thickness reduction. It is found that the area reduction can be normalized by the uniaxial Strain at maximum load which represents the material hardening and also the section aspect ratio. Furthermore, for the same material, specimens with different aspect ratio give exactly the same true average stress–logarithmic Strain Curve. This finding implies that Bridgmans correction can still be used for necking correction of the true average stress obtained from rectangular specimens. Based on this finding, a method for determining the true stress–logarithmic Strain relation from the load–thickness reduction Curve of specimens with rectangular cross-section is proposed.
M. Beghini - One of the best experts on this subject based on the ideXlab platform.
-
Evaluation of the stress–Strain Curve of metallic materials by spherical indentation
International Journal of Solids and Structures, 2006Co-Authors: M. Beghini, L. Bertini, V. FontanariAbstract:AbstractA method for deducing the stress–Strain uniaxial properties of metallic materials from instrumented spherical indentation is presented along with an experimental verification.An extensive finite element parametric analysis of the spherical indentation was performed in order to generate a database of load vs. depth of penetration Curves for classes of materials selected in order to represent the metals commonly employed in structural applications. The stress–Strain Curves of the materials were represented with three parameters: the Young modulus for the elastic regime, the stress of proportionality limit and the Strain-hardening coefficient for the elastic–plastic regime.The indentation Curves simulated by the finite element analyses were fitted in order to obtain a continuous function which can produce accurate load vs. depth Curves for any combination of the constitutive elastic–plastic parameters. On the basis of this continuous function, an optimization algorithm was then employed to deduce the material elastic–plastic parameters and the related stress–Strain Curve when the measured load vs. depth Curve is available by an instrumented spherical indentation test.The proposed method was verified by comparing the predicted stress–Strain Curves with those directly measured for several metallic alloys having different mechanical properties.This result confirms the possibility to deduce the complete stress–Strain Curve of a metal alloy with good accuracy by a properly conducted instrumented spherical indentation test and a suitable interpretation technique of the measured quantities
-
Evaluation of the stress-Strain Curve of metallic materials by spherical indentation
International Journal of Solids and Structures, 2005Co-Authors: M. Beghini, L. Bertini, V. FontanariAbstract:Abstract A method for deducing the stress–Strain uniaxial properties of metallic materials from instrumented spherical indentation is presented along with an experimental verification. An extensive finite element parametric analysis of the spherical indentation was performed in order to generate a database of load vs. depth of penetration Curves for classes of materials selected in order to represent the metals commonly employed in structural applications. The stress–Strain Curves of the materials were represented with three parameters: the Young modulus for the elastic regime, the stress of proportionality limit and the Strain-hardening coefficient for the elastic–plastic regime. The indentation Curves simulated by the finite element analyses were fitted in order to obtain a continuous function which can produce accurate load vs. depth Curves for any combination of the constitutive elastic–plastic parameters. On the basis of this continuous function, an optimization algorithm was then employed to deduce the material elastic–plastic parameters and the related stress–Strain Curve when the measured load vs. depth Curve is available by an instrumented spherical indentation test. The proposed method was verified by comparing the predicted stress–Strain Curves with those directly measured for several metallic alloys having different mechanical properties. This result confirms the possibility to deduce the complete stress–Strain Curve of a metal alloy with good accuracy by a properly conducted instrumented spherical indentation test and a suitable interpretation technique of the measured quantities.
Philippe Pilvin - One of the best experts on this subject based on the ideXlab platform.
-
Experimental evaluation of the stress-Strain Curve by continuous indentation using different indenter shapes
Materials Science and Engineering: A, 2009Co-Authors: Jean-marc Collin, Gérard Mauvoisin, Olivier Bartier, Rochdi El Abdi, Philippe PilvinAbstract:Experimental applications of the methodology developed for spherical indentation are proposed in this paper. Two quasi-spherical indenters with different shapes were used in order to evaluate the stress–Strain Curve of five steels. Although the shape of the indenter was not perfectly spherical, it was shown that models developed for spherical indentation can be used with an adequate correction. The results are in good agreement with those obtained by tensile tests. Moreover, the case of the austenitic alloy (AISI 316L) revealed the importance of sample preparation for the experimental results.
