The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform

Wilson C Hayes - One of the best experts on this subject based on the ideXlab platform.

  • trabecular bone modulus and strength can depend on Specimen Geometry
    Journal of Biomechanics, 1993
    Co-Authors: Tony M Keaveny, Robert E Borchers, L J Gibson, Wilson C Hayes
    Abstract:

    We performed a series of uniaxial compression tests on wet bovine trabecular bone to compare both modulus and strength when measured using 2:1 aspect ratio (10 mm long, 5 mm diameter) cylinders (n = 30) and 5 mm cubes (n = 29). We also compared the correlation coefficients in the resulting modulus-density and strength-density regressions and the standard errors of the estimate. When comparing the mean values of modulus and strength for each group, the confounding variations in apparent density were accounted for with an analysis of covariance. The Fisher's Z transformation was used to compare the correlation coefficients statistically. Results from the analysis of covariance indicated that the modulus and strength of the cubes were higher by 36% (p < 0.01) and 18% (p < 0.05), respectively, with respect to the 2:1 cylinder values. The correlation coefficients in the modulus-density and strength-density regressions were not sensitive to the regression model (linear versus power law). However, correlation coefficients for both modulus-density and strength-density regressions were higher (p < 0.05) for the 2:1 cylinders (r = 0.90, modulus; r = 0.94, strength) than for the cubes (r = 0.57, modulus; r = 0.82, strength). In addition, the standard errors of the estimate in both modulus and strength were substantially lower for the 2:1 cylinders. These data indicate that both modulus and strength can depend on the Specimen Geometry when using conventional compression testing techniques. We conclude, therefore, that inter-study comparisons of modulus and strength may be invalid if these confounding effects of different Specimen geometries are not addressed. Our data also indicate that density can better explain the observed variance in modulus and strength when 2:1 cylinders are used as opposed to cubes. Using this phenomenon as a rationale for choosing a standard Specimen gometry, we recommend that the 2:1 cylinder be used as a standard Specimen in studies designed to determine the effects of various treatments on the uniaxial compressive modulus and strength of trabecular bone.

Richard Curtis - One of the best experts on this subject based on the ideXlab platform.

  • finite element simulations for investigating the effects of Specimen Geometry in superplastic tensile tests
    Journal of Materials Engineering and Performance, 2011
    Co-Authors: Mohammad A. Nazzal, Fadi Abufarha, Richard Curtis
    Abstract:

    Characterizing the behavior of superplastic materials is largely based on the uniaxial tensile test; yet the unique nature of these materials requires a particularly tailored testing methodology, different to that used with conventional materials. One of the crucial testing facets is the Specimen Geometry, which has a great impact on the outcome of a superplastic tensile test, as a result of the associated extreme conditions. And while researchers agree that it should take a notably different form than the typical dog-bone shape; there is no universal agreement on the Specimen’s particular size and dimensions, as evident by the disparities in test Specimens used in the various superplastic testing efforts found throughout the literature. In view of that, this article is dedicated to understanding the effects of Specimen Geometry on the superplastic behavior of the material during tensile testing. Deformation of the Ti6Al4V titanium alloy is FE simulated based on a multitude of Specimen geometries, covering a wide range of gauge length, gauge width, grip length, and grip width values. The study provides key insights on the influences of each geometrical parameter as well as their interactions, and provides recommendations on selecting the Specimen’s proportions for accurate and unified tensile testing of superplastic materials.

  • Optimum Specimen Geometry for Accurate Tensile Testing of Superplastic Metallic Materials
    Experimental Mechanics, 2010
    Co-Authors: Fadi Abu-farha, Mohammad A. Nazzal, Richard Curtis
    Abstract:

    The high temperatures and large strain limits associated with superplastic materials amplify the possibility of the tensile test outcomes being sensitive to the shape and size of the Specimen Geometry. In spite of that, the disparities in the Specimen geometries used throughout the numerous efforts on characterising this unique class of materials are rather astonishing. There is an urge to evaluate the dependency of a superplastic tensile test on Specimen Geometry, before a much-needed universally-adopted standard Specimen can be designed; which is the main objective of this comprehensive experimental investigation. More than 20 geometries, covering multiple variations in gauge length, gauge width, grip length and grip width values, are tested at identical conditions, and the corresponding material behaviour is compared in terms of deformation uniformity, material flow and the extracted stress/strain curves. The results reveal the influences of each geometrical parameter, as well as their combined effects, and guide the selection of an optimum Specimen Geometry for accurate and unified tensile testing of superplastic metallic materials.

Joris Degrieck - One of the best experts on this subject based on the ideXlab platform.

  • Experimental investigation of the influence of the Specimen Geometry on Hopkinson tensile test results
    2020
    Co-Authors: Patricia Verleysen, Joris Degrieck, J Van Slycken, Bruno De Cooman, Ludovic Samek
    Abstract:

    Split Hopkinson bar set-ups are considered to be valuable, if not indispensable, to study the strain rate dependent mechanical behaviour of materials. In recent years results of SHB experiments on a wide range of materials have been reported in literature. Given their importance for crash relevant applications, special attention has been paid to the tensile properties of steel sheets used in the automotive industry. For tensile experiments most often dogbone-shaped geometries are used, however with widely divergent dimensions. In this contribution results of an extensive experimental study on the influence of the Specimen Geometry are presented. Based on data found in literature, seven geometries are defined and subjected to strain rates ranging from 650/s to 1250/s. The material considered is a TRIP (TRansformation Induced Plasticity) steel sheet. An advanced measurement technique is used to monitor the true distribution of the deformation along the length of the Specimen. It is shown that the influence of the Specimen Geometry on the test results cannot be neglected, and that this can mainly be attributed to the fact that the true distribution of the deformation deviates from the assumed distribution.

  • Numerical study of the influence of the Specimen Geometry on split Hopkinson tensile test results
    WIT transactions on engineering sciences, 2020
    Co-Authors: Patricia Verleysen, Joris Degrieck, Benedict Verhegghe, Bruno De Cooman
    Abstract:

    In recent years numerous studies on the high strain rate tensile properties of sheet materials using Split Hopkinson Tensile Bar (SHTB) experiments have been reported in literature. For SHTB experiments no consensus exists on the Specimen Geometry to be used and its influence on the observed behaviour. However, previous studies have revealed that changes in the Specimen Geometry give rise to distinct differences in established mechanical behaviour. In this contribution results are presented of finite element simulations of SHTB experiments using different Specimen geometries. These simulations not only confirm previously obtained experimental results, but also give complimentary and detailed information on the true distribution of the stress and the strain in the Specimen, including the non-axial stresses. Attention is paid to the basic assumptions of Hopkinson experiments: the uniaxiality of the stress state and the homogeneity of the strain. It is shown that the validity of these assumption is highly Geometry dependent. The influence of the deviation from these assumptions on the material behaviour extracted from a Hopkinson experiment will be discussed.

  • Numerical study of the influence of the Specimen Geometry on split Hopkinson bar tensile test results
    2020
    Co-Authors: Patricia Verleysen, Joris Degrieck, Benedict Verhegghe, Bruno De Cooman
    Abstract:

    In recent years numerous studies on the high strain rate tensile properties of sheet materials using Split Hopkinson Tensile Bar (SHTB) experiments have been reported in literature. For SHTB experiments no consensus exists on the Specimen Geometry to be used and its influence on the observed behaviour. However, previous studies have revealed that changes in the Specimen Geometry give rise to distinct differences in established mechanical behaviour. In this contribution results are presented of finite element simulations of SHTB experiments using different Specimen geometries. These simulations not only confirm previously obtained experimental results, but also give complimentary and detailed information on the true distribution of the stress and the strain in the Specimen, including the non-axial stresses. Attention is paid to the basic assumptions of Hopkinson experiments: the uniaxiality of the stress state and the homogeneity of the strain. It is shown that the validity of these assumption is highly Geometry dependent. The influence of the deviation from these assumptions on the material behaviour extracted from a Hopkinson experiment will be discussed.

  • INFLUENCE OF Specimen Geometry ON THE FATIGUE BEHAVIOR OF A CARBON FABRIC REINFORCED PPS
    2020
    Co-Authors: Ives De Baere, Wim Van Paepegem, Joris Degrieck
    Abstract:

    This manuscript studies the tension-tension fatigue behavior of a carbon fabric reinforced PPS and the influence of the Specimen Geometry on the obtained results. First, the fatigue experiments are preformed according to the ASTM D3479/D3479M standard using the rectangular shaped Specimen, but virtually all Specimens fail in the tabbed section. This, however, means that fatigue lifetime may be underestimated. Therefore, a new dumbbell-like shape was assessed. Based on the occurring stress concentrations in the tabbed section, the dog bone-like shape was first optimised numerically using FEM, and then, the optimised Specimen was tested in tension-tension fatigue. It can be concluded that this dumbbell shape yields better results in terms of acceptable failure and that the used shape has a significant influence on the fatigue lifetime.

  • novel pure shear sheet Specimen Geometry for dynamic material characterisation
    DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2009
    Co-Authors: Jan Peirs, Patricia Verleysen, W Van Paepegem, Joris Degrieck
    Abstract:

    A novel sheet Specimen Geometry for dynamic pure-shear experiments is proposed. Finite element simulations in ABAQUS/Explicit are used to optimize the Specimen Geometry. Main objective is to obtain a homogeneous stress state with a low stress tridxiality in the Specimen zone subjected to shear. The proposed Geometry is used to characterize the dynamic shear behaviour of a Ti-6Al-4V alloy. High speed photography and digital image correlation are used to study the local behaviour of the Specimen. The experiments are compared with the simulations. It is found that the maximal strain reached is higher than in tensile tests of this material. The shear experiments thus provide valuable information for material modelling.

Frank Madsen - One of the best experts on this subject based on the ideXlab platform.

Tony M Keaveny - One of the best experts on this subject based on the ideXlab platform.

  • trabecular bone modulus and strength can depend on Specimen Geometry
    Journal of Biomechanics, 1993
    Co-Authors: Tony M Keaveny, Robert E Borchers, L J Gibson, Wilson C Hayes
    Abstract:

    We performed a series of uniaxial compression tests on wet bovine trabecular bone to compare both modulus and strength when measured using 2:1 aspect ratio (10 mm long, 5 mm diameter) cylinders (n = 30) and 5 mm cubes (n = 29). We also compared the correlation coefficients in the resulting modulus-density and strength-density regressions and the standard errors of the estimate. When comparing the mean values of modulus and strength for each group, the confounding variations in apparent density were accounted for with an analysis of covariance. The Fisher's Z transformation was used to compare the correlation coefficients statistically. Results from the analysis of covariance indicated that the modulus and strength of the cubes were higher by 36% (p < 0.01) and 18% (p < 0.05), respectively, with respect to the 2:1 cylinder values. The correlation coefficients in the modulus-density and strength-density regressions were not sensitive to the regression model (linear versus power law). However, correlation coefficients for both modulus-density and strength-density regressions were higher (p < 0.05) for the 2:1 cylinders (r = 0.90, modulus; r = 0.94, strength) than for the cubes (r = 0.57, modulus; r = 0.82, strength). In addition, the standard errors of the estimate in both modulus and strength were substantially lower for the 2:1 cylinders. These data indicate that both modulus and strength can depend on the Specimen Geometry when using conventional compression testing techniques. We conclude, therefore, that inter-study comparisons of modulus and strength may be invalid if these confounding effects of different Specimen geometries are not addressed. Our data also indicate that density can better explain the observed variance in modulus and strength when 2:1 cylinders are used as opposed to cubes. Using this phenomenon as a rationale for choosing a standard Specimen gometry, we recommend that the 2:1 cylinder be used as a standard Specimen in studies designed to determine the effects of various treatments on the uniaxial compressive modulus and strength of trabecular bone.