ABSTRACT There are a substantial amount of constitutive models that have been developed to captur... more ABSTRACT There are a substantial amount of constitutive models that have been developed to capture the finite deformation behavior of polymers for forming simulations. Most of these models have been used to capture the behavior in uniaxial and simultaneous biaxial modes of deformation. However, very few have attempted to model the sequential biaxial deformation behavior which is more appropriate for the stretch blow moulding process. The aim of this work is to develop a model for PET to successfully capture the sequential stress-strain behavior as a function of temperature and strain rate, thus making it suitable for use in simulations of stretch blow moulding. Biaxial test data has been generated at temperatures and strain rates appropriate for stretch blow moulding and a model developed by Buckley et al. has been implemented within the commercial finite element package Abaqus/Explicit. In parallel, an efficient automatic curve fitting procedure has been developed to enable the material parameters to be easily found from biaxial test data. The results show that the Buckley model can predict the stress response of equibiaxial deformation well, but cannot predict the sequential biaxial deformation.
ABSTRACT In this work the affects of laser characteristics on surface morphology, microstructure,... more ABSTRACT In this work the affects of laser characteristics on surface morphology, microstructure, microhardness and wear rates of high velocity oxygen fuel (HVOF) WC‐CoCr coatings were investigated. Continuous and pulsed laser treatments were applied on the HVOF coatings using a CO2 laser of 10.6 μm wavelength. Continuous laser treatment significantly improved homogeneity of the coatings. Pulsed laser treatment produced significantly higher discontinuities compared to continuous mode. Microhardness increased by 45% for continuous mode laser modified WC‐CoCr coatings. However, wear resistance deteriorated, with a notable 40% increase in wear rate. The variations in coating properties were attributed to the re‐melting and rapid quenching of the CoCr bonding matrix allowing for WC redistribution.
14th International Conference on Material Forming Esaform, 2011 Proceedings, 2011
Many fcc and bcc metals subjected to non-monotonic loading are known to exhibit different kinds o... more Many fcc and bcc metals subjected to non-monotonic loading are known to exhibit different kinds of anisotropic hardening. This is due to evolution of (and interaction in) the dislocation microstructure depending on loading type. One purpose of the current work is the investigation of such evolution and interaction in single crystals as well as its effect on their hardening behavior.
14th International Conference on Material Forming Esaform, 2011 Proceedings, 2011
In this paper, the material flow around the pin during friction stir welding (FSW) is simulated u... more In this paper, the material flow around the pin during friction stir welding (FSW) is simulated using a 2D plane strain model. A pin rotates without translation in a disc with elasto-viscoplastic material properties and the outer boundary of the disc is clamped. Two numerical methods are used to solve this problem and an analytical solution is derived. The analytical model is complementary to validate the two numerical methods, i.e. the arbitrary Lagrangian-Eulerian (ALE) method and the adaptive smoothed finite elements method (ASFEM).
14th International Conference on Material Forming Esaform, 2011 Proceedings, 2011
ABSTRACT Accumulative roll bonding (ARB) has been considered as one of the promising techniques f... more ABSTRACT Accumulative roll bonding (ARB) has been considered as one of the promising techniques for fabrication of ultra-fine grained (UFG) metallic materials. The ARB process consists of several cycles of cutting, stacking, and rolling of metal sheets, so very high strains can be induced in the material resulting in significant grain refinement and in the formation of UFG microstructures. The ARB technique has been applied to a wide range of metallic materials such as Al and Al alloys, Mg, Fe and steels, Zr, Cu, as well as composite materials. UFG metallic materials processed via ARB show increased strength. Despite a significant body of experimental research into the deformation behaviour of the ARB-processed materials, the fundamentals of their plastic deformation are not fully understood yet. This work focuses on the effect of grain refinement via ARB-processing on the mechanical behavior and on the strain-rate sensitivity of commercially pure Zr (99.8% purity). The mechanical properties of the as-received coarse-grained (CG) and UFG (as-ARB processed) samples were studied at room temperature at two different strain rates. Mechanical strain rate jump tests were performed during tensile deformation to estimate the instantaneous strain-rate sensitivity. The evolution of surface relief during plastic deformation of pure Zr in both CG and UFG conditions was studied. The features of plastic deformation of pure Zr in both CG and UFG conditions are discussed.
ABSTRACT This article concerns the forming of a steel thin-wall short-tube by an innovative small... more ABSTRACT This article concerns the forming of a steel thin-wall short-tube by an innovative small surface contact deformation process. A Finite Element model was built to predict the forming of the workpiece. The model controls the complex kinematics of the process. The problems associated with contact control and computation time are also investigated. Compared with measurements taken by the industrial partner, the first results obtained are highly promising, with regard to predicting both the workpiece geometry and the forces acting on the tools.
This paper suggests a new method to take into account the kinematic hardening in constitutive beh... more This paper suggests a new method to take into account the kinematic hardening in constitutive behaviour of metallic face centred cubic single crystal. The keystone of this model is that kinematic effect arises from a description of the crystal dislocation microstructure based on a heterogeneous distribution of slip strength. In this paper, these concepts are applied to crystalline plasticity models.
ABSTRACT Nowadays, industrial and scientific communities are confronted with extremely complex me... more ABSTRACT Nowadays, industrial and scientific communities are confronted with extremely complex mechanical engineering problems. Therefore, to try to reduce this complexity and allow the simulation of different mechanical situations the investigation of the inverse engineering is increasing. Distinct inverse problems can be formulated, being one of the categories the initial geometry optimization, which is not extensively described in the literature. The aim of this kind of problems is to estimate the initial shape of a specimen or a blank in order to achieve the desired geometry after the forming process. In this work, the superplastic forming of a carter is described and studied. After the forming it is possible to verify that strain fields are not uniform in the whole carter surface, leading to a non-homogeneous thickness distribution in the final geometry. To avoid this problem, a non-uniform thickness of the initial undeformed blank can be found in order to obtain a regular final thickness of the sheet even with non-homogeneous strains. In this problem, the optimum final thickness was considered to be 4 mm in the whole carter. The carter surface is defined with a NURBS surface, where the coordinates of specific NURBS control net vertices are taken as the optimization variables. The presented optimization procedure was carried out from a combination of a FE program and an optimization code. The influence of the geometry definition in the mentioned problem is studied. Both the number and the location of the NURBS control net vertices influence the final optimized result and the optimization evolution in a critical way. Therefore, the geometry definition that leads to better results, considering computational cost and final result precision, is found and discussed in this work.
Recent work on incremental sheet forming processes has demonstrated that they induce non-planar s... more Recent work on incremental sheet forming processes has demonstrated that they induce non-planar stress states which give significantly increased forming limits. In previous work, we have extended the Marcinak-Kuczynski analysis for in-plane loading to include proportional loading with all six components of the stress tensor, and have represented the results as a generalised forming limit diagram. This paper proposes a first standardised test of forming limits under these conditions. A novel apparatus is constructed in which a sliding carriage can apply controllable compressive rolling, three-roll bending, or through thickness shearing to a sample undergoing uniaxial extension. Finite element analysis demonstrates the effect of this loading on deformation and details of equipment design are given. Initial trials are used to assess the repeatability of the tests and to confirm whether the strain states induced in the workpieces conform with finite element predictions. Tests to examine increases in formability under various loading conditions show greatly increased failure strains, but with some variability in results, and only partial agreement with analytical predictions.
To meet targeted 50% reductions in industrial CO2 emissions by 2050, demand for steel and alumini... more To meet targeted 50% reductions in industrial CO2 emissions by 2050, demand for steel and aluminium must be cut. Many steel and aluminium products include redundant material, and the manufacturing routes to produce them use more material than is necessary. Lightweight design and optimized manufacturing processes offer a means of demand reduction, whilst creating products to perform the same service as existing ones. This paper examines two strategies for demand reduction: lightweight product design; and minimizing yield losses through the product supply chain. Possible mass savings are estimated for specific case-studies on metal-intensive products, such as I-beams and food cans. These estimates are then extrapolated to other sectors to produce a global estimate for possible demand reductions. Results show that lightweight product design may offer potential mass savings of up to 30% for some products, whilst yield in the production of others could be improved by over 20%. If these two strategies could be combined for all products, global demand for steel and aluminium would be reduced by nearly 50%. The impact of demand reduction on CO2 emissions is presented, and barriers to the adoption of new, lightweight technologies are discussed.
Tube cold drawing processes are used to reduce tube diameters and thickness, while pulling them t... more Tube cold drawing processes are used to reduce tube diameters and thickness, while pulling them through a conical converging die with or without inner plug. An accurate modelling of the material deformation and friction behaviour is required in order to well describe these processes. The study concerns a stainless steel platinum alloy. The material behaviour is characterised through tensile tests at strain rates as close as possible to the high strain rates reached during the drawing process. The results are fitted with an isotropic temperature-independent Johnson Cook constitutive equation. The modelling of floating plug drawing is performed on a ABAQUS/Explicit model. Friction coefficient is difficult to estimate with mechanical experimental tests, thus an inverse analysis is carried out to fit this parameter thanks to finite element simulation and experimental drawing tests. Drawing force measurements are recorded during the forming process. The Cockroft-Latham criterion is applied to understand the different process parameters influence on tube drawing and its accuracy for drawing process is evaluated.
TEM image analyses of PET nanocomposites were done to study the effect of equi-biaxial stretching... more TEM image analyses of PET nanocomposites were done to study the effect of equi-biaxial stretching and stretch ratio on the exfoliation and other tactoid properties. Though XRD spectra did not show any evidence of exfoliation, TEM image analysis revealed 10% exfoliation of clay platelets in the unstretched sheets. Stretching further improved the exfoliation as the concentration of thinner tactoids in
Proceedings of the 2012 UKACC International Conference on Control, CONTROL 2012, 2012
ABSTRACT The injection stretch-blow Moulding (ISBM) process is typically used to manufacture PET ... more ABSTRACT The injection stretch-blow Moulding (ISBM) process is typically used to manufacture PET containers for the beverage and consumer goods industry. The process is somehow complex and users often have to heavily rely on trial and error methods to setup and control it. In this paper, a novel identification method based on a radial basis function (RBF) network model and heuristic optimization methods, such as particle swarm optimization (PSO), deferential evolution (DE), and extreme learning machine (ELM) is proposed for the modelling and control of bottle section weights. The main advantage of the proposed method is that the non-linear parameters are optimized in a continuous space while the hidden nodes are selected one by one in a discrete space using a two-stage selection algorithm. The computational complexity is significantly reduced due to a recursive updating mechanism. Experimental results on simulation data from ABAQUS are presented to confirm the superiority of the proposed method.
ABSTRACT There are a substantial amount of constitutive models that have been developed to captur... more ABSTRACT There are a substantial amount of constitutive models that have been developed to capture the finite deformation behavior of polymers for forming simulations. Most of these models have been used to capture the behavior in uniaxial and simultaneous biaxial modes of deformation. However, very few have attempted to model the sequential biaxial deformation behavior which is more appropriate for the stretch blow moulding process. The aim of this work is to develop a model for PET to successfully capture the sequential stress-strain behavior as a function of temperature and strain rate, thus making it suitable for use in simulations of stretch blow moulding. Biaxial test data has been generated at temperatures and strain rates appropriate for stretch blow moulding and a model developed by Buckley et al. has been implemented within the commercial finite element package Abaqus/Explicit. In parallel, an efficient automatic curve fitting procedure has been developed to enable the material parameters to be easily found from biaxial test data. The results show that the Buckley model can predict the stress response of equibiaxial deformation well, but cannot predict the sequential biaxial deformation.
ABSTRACT In this work the affects of laser characteristics on surface morphology, microstructure,... more ABSTRACT In this work the affects of laser characteristics on surface morphology, microstructure, microhardness and wear rates of high velocity oxygen fuel (HVOF) WC‐CoCr coatings were investigated. Continuous and pulsed laser treatments were applied on the HVOF coatings using a CO2 laser of 10.6 μm wavelength. Continuous laser treatment significantly improved homogeneity of the coatings. Pulsed laser treatment produced significantly higher discontinuities compared to continuous mode. Microhardness increased by 45% for continuous mode laser modified WC‐CoCr coatings. However, wear resistance deteriorated, with a notable 40% increase in wear rate. The variations in coating properties were attributed to the re‐melting and rapid quenching of the CoCr bonding matrix allowing for WC redistribution.
14th International Conference on Material Forming Esaform, 2011 Proceedings, 2011
Many fcc and bcc metals subjected to non-monotonic loading are known to exhibit different kinds o... more Many fcc and bcc metals subjected to non-monotonic loading are known to exhibit different kinds of anisotropic hardening. This is due to evolution of (and interaction in) the dislocation microstructure depending on loading type. One purpose of the current work is the investigation of such evolution and interaction in single crystals as well as its effect on their hardening behavior.
14th International Conference on Material Forming Esaform, 2011 Proceedings, 2011
In this paper, the material flow around the pin during friction stir welding (FSW) is simulated u... more In this paper, the material flow around the pin during friction stir welding (FSW) is simulated using a 2D plane strain model. A pin rotates without translation in a disc with elasto-viscoplastic material properties and the outer boundary of the disc is clamped. Two numerical methods are used to solve this problem and an analytical solution is derived. The analytical model is complementary to validate the two numerical methods, i.e. the arbitrary Lagrangian-Eulerian (ALE) method and the adaptive smoothed finite elements method (ASFEM).
14th International Conference on Material Forming Esaform, 2011 Proceedings, 2011
ABSTRACT Accumulative roll bonding (ARB) has been considered as one of the promising techniques f... more ABSTRACT Accumulative roll bonding (ARB) has been considered as one of the promising techniques for fabrication of ultra-fine grained (UFG) metallic materials. The ARB process consists of several cycles of cutting, stacking, and rolling of metal sheets, so very high strains can be induced in the material resulting in significant grain refinement and in the formation of UFG microstructures. The ARB technique has been applied to a wide range of metallic materials such as Al and Al alloys, Mg, Fe and steels, Zr, Cu, as well as composite materials. UFG metallic materials processed via ARB show increased strength. Despite a significant body of experimental research into the deformation behaviour of the ARB-processed materials, the fundamentals of their plastic deformation are not fully understood yet. This work focuses on the effect of grain refinement via ARB-processing on the mechanical behavior and on the strain-rate sensitivity of commercially pure Zr (99.8% purity). The mechanical properties of the as-received coarse-grained (CG) and UFG (as-ARB processed) samples were studied at room temperature at two different strain rates. Mechanical strain rate jump tests were performed during tensile deformation to estimate the instantaneous strain-rate sensitivity. The evolution of surface relief during plastic deformation of pure Zr in both CG and UFG conditions was studied. The features of plastic deformation of pure Zr in both CG and UFG conditions are discussed.
ABSTRACT This article concerns the forming of a steel thin-wall short-tube by an innovative small... more ABSTRACT This article concerns the forming of a steel thin-wall short-tube by an innovative small surface contact deformation process. A Finite Element model was built to predict the forming of the workpiece. The model controls the complex kinematics of the process. The problems associated with contact control and computation time are also investigated. Compared with measurements taken by the industrial partner, the first results obtained are highly promising, with regard to predicting both the workpiece geometry and the forces acting on the tools.
This paper suggests a new method to take into account the kinematic hardening in constitutive beh... more This paper suggests a new method to take into account the kinematic hardening in constitutive behaviour of metallic face centred cubic single crystal. The keystone of this model is that kinematic effect arises from a description of the crystal dislocation microstructure based on a heterogeneous distribution of slip strength. In this paper, these concepts are applied to crystalline plasticity models.
ABSTRACT Nowadays, industrial and scientific communities are confronted with extremely complex me... more ABSTRACT Nowadays, industrial and scientific communities are confronted with extremely complex mechanical engineering problems. Therefore, to try to reduce this complexity and allow the simulation of different mechanical situations the investigation of the inverse engineering is increasing. Distinct inverse problems can be formulated, being one of the categories the initial geometry optimization, which is not extensively described in the literature. The aim of this kind of problems is to estimate the initial shape of a specimen or a blank in order to achieve the desired geometry after the forming process. In this work, the superplastic forming of a carter is described and studied. After the forming it is possible to verify that strain fields are not uniform in the whole carter surface, leading to a non-homogeneous thickness distribution in the final geometry. To avoid this problem, a non-uniform thickness of the initial undeformed blank can be found in order to obtain a regular final thickness of the sheet even with non-homogeneous strains. In this problem, the optimum final thickness was considered to be 4 mm in the whole carter. The carter surface is defined with a NURBS surface, where the coordinates of specific NURBS control net vertices are taken as the optimization variables. The presented optimization procedure was carried out from a combination of a FE program and an optimization code. The influence of the geometry definition in the mentioned problem is studied. Both the number and the location of the NURBS control net vertices influence the final optimized result and the optimization evolution in a critical way. Therefore, the geometry definition that leads to better results, considering computational cost and final result precision, is found and discussed in this work.
Recent work on incremental sheet forming processes has demonstrated that they induce non-planar s... more Recent work on incremental sheet forming processes has demonstrated that they induce non-planar stress states which give significantly increased forming limits. In previous work, we have extended the Marcinak-Kuczynski analysis for in-plane loading to include proportional loading with all six components of the stress tensor, and have represented the results as a generalised forming limit diagram. This paper proposes a first standardised test of forming limits under these conditions. A novel apparatus is constructed in which a sliding carriage can apply controllable compressive rolling, three-roll bending, or through thickness shearing to a sample undergoing uniaxial extension. Finite element analysis demonstrates the effect of this loading on deformation and details of equipment design are given. Initial trials are used to assess the repeatability of the tests and to confirm whether the strain states induced in the workpieces conform with finite element predictions. Tests to examine increases in formability under various loading conditions show greatly increased failure strains, but with some variability in results, and only partial agreement with analytical predictions.
To meet targeted 50% reductions in industrial CO2 emissions by 2050, demand for steel and alumini... more To meet targeted 50% reductions in industrial CO2 emissions by 2050, demand for steel and aluminium must be cut. Many steel and aluminium products include redundant material, and the manufacturing routes to produce them use more material than is necessary. Lightweight design and optimized manufacturing processes offer a means of demand reduction, whilst creating products to perform the same service as existing ones. This paper examines two strategies for demand reduction: lightweight product design; and minimizing yield losses through the product supply chain. Possible mass savings are estimated for specific case-studies on metal-intensive products, such as I-beams and food cans. These estimates are then extrapolated to other sectors to produce a global estimate for possible demand reductions. Results show that lightweight product design may offer potential mass savings of up to 30% for some products, whilst yield in the production of others could be improved by over 20%. If these two strategies could be combined for all products, global demand for steel and aluminium would be reduced by nearly 50%. The impact of demand reduction on CO2 emissions is presented, and barriers to the adoption of new, lightweight technologies are discussed.
Tube cold drawing processes are used to reduce tube diameters and thickness, while pulling them t... more Tube cold drawing processes are used to reduce tube diameters and thickness, while pulling them through a conical converging die with or without inner plug. An accurate modelling of the material deformation and friction behaviour is required in order to well describe these processes. The study concerns a stainless steel platinum alloy. The material behaviour is characterised through tensile tests at strain rates as close as possible to the high strain rates reached during the drawing process. The results are fitted with an isotropic temperature-independent Johnson Cook constitutive equation. The modelling of floating plug drawing is performed on a ABAQUS/Explicit model. Friction coefficient is difficult to estimate with mechanical experimental tests, thus an inverse analysis is carried out to fit this parameter thanks to finite element simulation and experimental drawing tests. Drawing force measurements are recorded during the forming process. The Cockroft-Latham criterion is applied to understand the different process parameters influence on tube drawing and its accuracy for drawing process is evaluated.
TEM image analyses of PET nanocomposites were done to study the effect of equi-biaxial stretching... more TEM image analyses of PET nanocomposites were done to study the effect of equi-biaxial stretching and stretch ratio on the exfoliation and other tactoid properties. Though XRD spectra did not show any evidence of exfoliation, TEM image analysis revealed 10% exfoliation of clay platelets in the unstretched sheets. Stretching further improved the exfoliation as the concentration of thinner tactoids in
Proceedings of the 2012 UKACC International Conference on Control, CONTROL 2012, 2012
ABSTRACT The injection stretch-blow Moulding (ISBM) process is typically used to manufacture PET ... more ABSTRACT The injection stretch-blow Moulding (ISBM) process is typically used to manufacture PET containers for the beverage and consumer goods industry. The process is somehow complex and users often have to heavily rely on trial and error methods to setup and control it. In this paper, a novel identification method based on a radial basis function (RBF) network model and heuristic optimization methods, such as particle swarm optimization (PSO), deferential evolution (DE), and extreme learning machine (ELM) is proposed for the modelling and control of bottle section weights. The main advantage of the proposed method is that the non-linear parameters are optimized in a continuous space while the hidden nodes are selected one by one in a discrete space using a two-stage selection algorithm. The computational complexity is significantly reduced due to a recursive updating mechanism. Experimental results on simulation data from ABAQUS are presented to confirm the superiority of the proposed method.
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Papers by G. Menary