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Papers by Philip Harrison
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2011
ABSTRACT This article describes uniaxial compression tests on a melt-extruded closed-cell low-den... more ABSTRACT This article describes uniaxial compression tests on a melt-extruded closed-cell low-density polyethylene foam. The stress–strain response shows that the mechanical behaviour of the foam is predominantly transversely isotropic viscoelastic and compressible. Image analysis is used to estimate the Poisson’s ratio under large strains. When the deformation is less than 5%, the compression kinematics and mechanical response of the polymer foam can be well described by a linear compressible transversely isotropic elastic model. For large strain, a simple method is proposed to estimate the uniaxial compression response of the foam at any arbitrary orientation by manipulating experimental data obtained from compression tests in the principal and transverse directions (stress vs. strain and Poisson’s ratio) and a simple shear test. An isotropic compressible hyperfoam model is then used to implement this behaviour in a finite element code.
This paper describes a force-based beam-column element implemented using a hybrid force-based sol... more This paper describes a force-based beam-column element implemented using a hybrid force-based solution strategy. The element can accommodate elastic-plastic strain hardening material behaviour under various loadings including axial, torsion, bending and shear deformation, both in and out of the plane of the element. In order to overcome difficulties associated with conventional displacement-based and force-based methods a hybrid force based-method is proposed. This alternative approach is based on simultaneous use of the principles of minimum total potential energy and minimum complementary potential energy. Here the primary equation is the equilibrium equation rather than the compatibility equation (the latter takes precedence when following a displacement based solution strategy). The predictions of the element using this solution procedure are compared against predictions from Abaqus TM , showing excellent agreement.
ABSTRACT An investigation has been conducted to evaluate the performance of normalisation methods... more ABSTRACT An investigation has been conducted to evaluate the performance of normalisation methods for the uniaxial bias extension test. The predictions of two published theories for rate-independent behaviour are examined and a third heuristic method is proposed. Using hypothetical test data, the predictions of the two rate-independent theories are shown to be equivalent for specimen dimensions of high aspect ratio; in this case the predictions can be well-represented using the simple heuristic formula. The predictions diverge for specimens of low aspect ratio, when specimens are sheared to very high shear angles. In order to examine the significance of this divergence on real data, results from tests on several different engineering fabrics are normalised. Differences in the predictions of the normalisation methods are observed and the question of the significance of these differences is discussed. The paper also examines the applicability of rate-independent theory for normalising rate-dependent materials.
Mechanics of Materials, 2013
A numerical investigation has been conducted to determine the influence of Representative Volume ... more A numerical investigation has been conducted to determine the influence of Representative Volume Element (RVE) size and degree of irregularity of polymer foam microstructure on its compressive mechanical properties, including stiffness, plateau stress and onset strain of densification. Periodic two-dimensional RVEs have been generated using a Voronoibased numerical algorithm and compressed. Importantly, self-contact of the foam's internal microstructure has been incorporated through the use of shell elements, allowing simulation of the foam well into the densification stage of compression; strains of up to 80% are applied. Results suggest that the stiffness of the foam RVE is relatively insensitive to RVE size but tends to soften as the degree of irregularity increases. Both the shape of the plateau stress and the onset strain of densification are sensitive to both the RVE size and degree of irregularity. Increasing the RVE size and decreasing the degree of irregularity both tend to result in a decrease of the gradient of the plateau region, while increasing the RVE size and degree of irregularity both tend to decrease the onset strain of densification. Finally, a method of predicting the onset strain of densification to an accuracy of about 10%, while reducing the computational cost by two orders of magnitude is suggested.
Geological Society, London, Special Publications, 2003
Composites Part A: Applied Science and Manufacturing, 2012
ABSTRACT A theoretical background is proposed for the normalisation of biaxial bias extension res... more ABSTRACT A theoretical background is proposed for the normalisation of biaxial bias extension results for rate-independent fabrics, whose shear compliance depends on both the shear angle and the fibre tension within the fabric. The theory is used to predict the form of biaxial bias extension results from known shear force–shear angle–fibre tension behaviours. Hypothetical data sets are used to perform a parametric study of the likely influence of the nature of the shear–tension coupling on the form of the biaxial bias extension test results. The theory is then used in implementing an iterative numerical code designed to retrieve the underlying material response from biaxial bias extension test results and examples predictions are given. A discussion of the information required in order to perform the normalisation, and the methods by which this information can be obtained, is presented. Finally, assumptions behind the theory are outlined and critically assessed.
ABSTRACT Structural woven composites made with high strength fibres are now widely used in automo... more ABSTRACT Structural woven composites made with high strength fibres are now widely used in automotive and aeronautic engineering due to their high strength/weight ratio as compared with metals. During the forming process, though the extension of the woven composite fabrics is usually small, the shear deformation (i.e., the angle change between weft and warp yarns) can be significant. Because of the anisotropy and the finite relative rotation between weft and warp yarns, it is usually difficult to model the macroscopic behaviour of the woven composites and several phenomenological non-
Advances in Materials Science and Engineering, 2013
Over the past few decades, outstanding progress in the science and technology of composite materi... more Over the past few decades, outstanding progress in the science and technology of composite materials has been made. Their unique characteristics make composites desirable for engineering applications across a wide variety of industrial sectors. New manufacturing methods are driving down costs, and emerging fields such as nanocomposites, green composites, 2D/3D textile composites, and multifunctional composites have been the focus of a great deal of exciting and innovative research activity. This special issue contains a snapshot of research, typical of this activity, and includes fifteen papers on topics such as structural and damage analysis, process modeling, fundamental mechanisms at the nano-and microscales in both nano-and biocomposites, and nondestructive test methods for advanced carbon composites.
Non-Crimp Fabric Composites, 2011
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2011
ABSTRACT This article describes uniaxial compression tests on a melt-extruded closed-cell low-den... more ABSTRACT This article describes uniaxial compression tests on a melt-extruded closed-cell low-density polyethylene foam. The stress–strain response shows that the mechanical behaviour of the foam is predominantly transversely isotropic viscoelastic and compressible. Image analysis is used to estimate the Poisson’s ratio under large strains. When the deformation is less than 5%, the compression kinematics and mechanical response of the polymer foam can be well described by a linear compressible transversely isotropic elastic model. For large strain, a simple method is proposed to estimate the uniaxial compression response of the foam at any arbitrary orientation by manipulating experimental data obtained from compression tests in the principal and transverse directions (stress vs. strain and Poisson’s ratio) and a simple shear test. An isotropic compressible hyperfoam model is then used to implement this behaviour in a finite element code.
This paper describes a force-based beam-column element implemented using a hybrid force-based sol... more This paper describes a force-based beam-column element implemented using a hybrid force-based solution strategy. The element can accommodate elastic-plastic strain hardening material behaviour under various loadings including axial, torsion, bending and shear deformation, both in and out of the plane of the element. In order to overcome difficulties associated with conventional displacement-based and force-based methods a hybrid force based-method is proposed. This alternative approach is based on simultaneous use of the principles of minimum total potential energy and minimum complementary potential energy. Here the primary equation is the equilibrium equation rather than the compatibility equation (the latter takes precedence when following a displacement based solution strategy). The predictions of the element using this solution procedure are compared against predictions from Abaqus TM , showing excellent agreement.
ABSTRACT An investigation has been conducted to evaluate the performance of normalisation methods... more ABSTRACT An investigation has been conducted to evaluate the performance of normalisation methods for the uniaxial bias extension test. The predictions of two published theories for rate-independent behaviour are examined and a third heuristic method is proposed. Using hypothetical test data, the predictions of the two rate-independent theories are shown to be equivalent for specimen dimensions of high aspect ratio; in this case the predictions can be well-represented using the simple heuristic formula. The predictions diverge for specimens of low aspect ratio, when specimens are sheared to very high shear angles. In order to examine the significance of this divergence on real data, results from tests on several different engineering fabrics are normalised. Differences in the predictions of the normalisation methods are observed and the question of the significance of these differences is discussed. The paper also examines the applicability of rate-independent theory for normalising rate-dependent materials.
Mechanics of Materials, 2013
A numerical investigation has been conducted to determine the influence of Representative Volume ... more A numerical investigation has been conducted to determine the influence of Representative Volume Element (RVE) size and degree of irregularity of polymer foam microstructure on its compressive mechanical properties, including stiffness, plateau stress and onset strain of densification. Periodic two-dimensional RVEs have been generated using a Voronoibased numerical algorithm and compressed. Importantly, self-contact of the foam's internal microstructure has been incorporated through the use of shell elements, allowing simulation of the foam well into the densification stage of compression; strains of up to 80% are applied. Results suggest that the stiffness of the foam RVE is relatively insensitive to RVE size but tends to soften as the degree of irregularity increases. Both the shape of the plateau stress and the onset strain of densification are sensitive to both the RVE size and degree of irregularity. Increasing the RVE size and decreasing the degree of irregularity both tend to result in a decrease of the gradient of the plateau region, while increasing the RVE size and degree of irregularity both tend to decrease the onset strain of densification. Finally, a method of predicting the onset strain of densification to an accuracy of about 10%, while reducing the computational cost by two orders of magnitude is suggested.
Geological Society, London, Special Publications, 2003
Composites Part A: Applied Science and Manufacturing, 2012
ABSTRACT A theoretical background is proposed for the normalisation of biaxial bias extension res... more ABSTRACT A theoretical background is proposed for the normalisation of biaxial bias extension results for rate-independent fabrics, whose shear compliance depends on both the shear angle and the fibre tension within the fabric. The theory is used to predict the form of biaxial bias extension results from known shear force–shear angle–fibre tension behaviours. Hypothetical data sets are used to perform a parametric study of the likely influence of the nature of the shear–tension coupling on the form of the biaxial bias extension test results. The theory is then used in implementing an iterative numerical code designed to retrieve the underlying material response from biaxial bias extension test results and examples predictions are given. A discussion of the information required in order to perform the normalisation, and the methods by which this information can be obtained, is presented. Finally, assumptions behind the theory are outlined and critically assessed.
ABSTRACT Structural woven composites made with high strength fibres are now widely used in automo... more ABSTRACT Structural woven composites made with high strength fibres are now widely used in automotive and aeronautic engineering due to their high strength/weight ratio as compared with metals. During the forming process, though the extension of the woven composite fabrics is usually small, the shear deformation (i.e., the angle change between weft and warp yarns) can be significant. Because of the anisotropy and the finite relative rotation between weft and warp yarns, it is usually difficult to model the macroscopic behaviour of the woven composites and several phenomenological non-
Advances in Materials Science and Engineering, 2013
Over the past few decades, outstanding progress in the science and technology of composite materi... more Over the past few decades, outstanding progress in the science and technology of composite materials has been made. Their unique characteristics make composites desirable for engineering applications across a wide variety of industrial sectors. New manufacturing methods are driving down costs, and emerging fields such as nanocomposites, green composites, 2D/3D textile composites, and multifunctional composites have been the focus of a great deal of exciting and innovative research activity. This special issue contains a snapshot of research, typical of this activity, and includes fifteen papers on topics such as structural and damage analysis, process modeling, fundamental mechanisms at the nano-and microscales in both nano-and biocomposites, and nondestructive test methods for advanced carbon composites.
Non-Crimp Fabric Composites, 2011