| 1. |
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| 2. |
- Håkanson, J. M., et al.
(författare)
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Liquid permeability of an anisotropic fiber web
- 2005
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Ingår i: Textile research journal. - : SAGE Publications. - 0040-5175 .- 1746-7748. ; 75:4, s. 304-311
-
Tidskriftsartikel (refereegranskat)abstract
- The Darcian permeability of a dense network of fibers with general orientation is examined experimentally and analytically. The permeability of a carded PA6 fiber web is measured in the three principal directions using a saturated parallel flow technique. A model is introduced that generalizes existing theories for unidirectional fiber arrays to fiber networks of general orientation distribution. The average drag on a given fiber is assumed to be independent of the overall fiber orientation distribution. A second-order orientation tensor describes the orientation dependence. Our generalization applied to the models of Gebart predicts reasonably well the in-plane permeability, but overestimates the out-of-plane permeability by a factor of four.
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| 3. |
- Håkansson, Johan, 1974, et al.
(författare)
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Permeability of felts
- 2000
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Ingår i: Proc. Nordic Meeting on Materials and Mechanics, Aalborg 2000.
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Konferensbidrag (refereegranskat)
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| 4. |
- Håkansson, Johan, 1974, et al.
(författare)
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Permeability of felts: Modelling
- 2000
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Ingår i: Annual Meeting of the AIChE Los Angeles, CA, November 12-17, 2000.
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Konferensbidrag (refereegranskat)
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| 5. |
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| 6. |
- Lundström, Staffan, et al.
(författare)
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Measurement of the permeability tensor of compressed fibre beds
- 2002
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Ingår i: Transport in Porous Media. - 0169-3913 .- 1573-1634. ; 47:3, s. 363-380
-
Tidskriftsartikel (refereegranskat)abstract
- A new method to measure the permeability tensor of highly compressed fibre beds is developed. The method is based on saturated parallel flow and is evaluated through experiments with various textile materials: press fabrics used in papermaking and fibre reinforcements designed for composites. Since the materials are in the form of sheets, two measuring cells are used, one for the principal in-plane permeabilities and the other for the out-of-plane permeability. A unique feature is that the edge and the bulk flow are measured separately, so that any influence from enhanced or suppressed edge flow may be eliminated. The technique is evaluated with good results in terms of scatter in the measured permeability and the influence of test geometry, pressure, and liquid properties.
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| 7. |
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| 8. |
- Lundström, Staffan, et al.
(författare)
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Modelling of residual stresses and warpage in sandwich injection moulding
- 2003
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Ingår i: International polymer processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 18:1, s. 95-106
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Tidskriftsartikel (refereegranskat)abstract
- Sandwich injection moulding offers the possibility of combining materials with different properties and, for instance, hide a recycled constituent within a virgin ditto. This attractive potential puts great demands on the manufacturing and therefore also on the process modelling. In particular the effect on the final stress state and the deformation of the part due to the heterogeneity of the material must be clarified. This topic is addressed in this study. To start with it is confirmed that expressions for the temperature field can be much simplified without major loss of accuracy in the solution. This enables us to take an analytical approach to the modelling and the resulting equations can be solved on a spread-sheet or with a simple code. It is also shown that the derived models compare well to experiments made with a two-layered structure, indicating that the models presented can be used to estimate changes of processing conditions or material properties for sandwich structures.
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| 9. |
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| 10. |
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| 11. |
- Al-Zubaidy, M. N., et al.
(författare)
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Properties of orthotropic glass-polypropylene composites manufactured by weaving of prepreg tapes and other routes
- 2000
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Ingår i: Plastics, Rubber and Composites Processing and Applications. - : Informa UK Limited. - 0959-8111. ; 29:10, s. 520-526
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports a study of the melt impregnation and weaving of glass-polypropylene prepreg tapes into sheet for use as a precursor for pressed thermoplastic composite products and a comparison of the properties attainable with those achievable by other comparable routes. Melt impregnation has been used successfully to manufacture well impregnated tapes, with and without internal coupling agent. It appears that weaving could be an economically viable process for converting unidirectional tape into a conformable, press formable prepreg. The properties of glass-polypropylene laminates manufactured by pressing the tape woven product were compared with those of other glass-polypropylene composites, including crossply laminate made from Plytron and samples prepared by film stacking. Quasi-static mechanical properties were found to be comparable with those of Plytron and superior to those of the other materials. In the coupled samples, coupling was somewhat less effective than in Plytron. The impact behaviour of the pressed, tape woven products was impressive and superior to any of the other materials tested. © 2000 IoM Communications Ltd.
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| 12. |
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| 13. |
- Alfthan, Johan, 1974-
(författare)
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Micro-mechanically based modeling of mechano-sorptive creep in paper
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The creep of paper is accelerated by moisture content changes. This acceleration is known as mechano-sorptive creep, which is also found in wood and some other materials. Mechano-sorptive creep has been known for several decades but it is still not well understood, and there is no generally accepted model explaining the effect. In this thesis, it is assumed that mechano-sorptive creep is the result of transient redistributions of stresses during moisture content changes in combination with non-linear creep behaviour of the material. The stress redistributions are caused by the anisotropic hygroexpansion of the fibres, which will give a mismatch of hygroexpansive strains at the bonds and hence large stresses each time the moisture content changes. This redistribution will lead to an uneven stress state. If the creep of the material depends non-linearly on stresses this will give an increase in creep rate where the stresses are high, that is larger than the decrease of creep rate where stresses are low, so in average there will be an increase in creep rate. The stress distribution evens out as the stresses relax during creep, and the moisture content has to change again to create a new uneven stress state and maintain the accelerated creep. Two different network models based on this mechanism are developed in this thesis. Numerical simulations show that the models produce results similar to the mechano-sorptive creep found in paper. In the first model it is assumed that creep takes place in the fibre-fibre interfaces at the bonds, in the second the creep of the fibres themselves is accelerated. The second model is further developed. Experiments verify model predictions of the dependence of the amplitude of moisture changes. The second model shows a linear relationship between mechanical load and deformation, although creep of the fibres depends non-linearly on stresses. This linear behaviour is also found in applications. Further analysis shows that the mechanical load can be treated as a small perturbation of the internal stress state caused by moisture content changes. This can be used to develop a linearized model, from which a continuum model can be derived. This leads to a reduction of the necessary number of variables, and a significant increase in speed of calculations. Hence, this linearized continuum model can be used as a constitutive law of paper in problems with complicated geometries, for example a corrugated board box in varying humidity.
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| 14. |
- Alkhagen, M., et al.
(författare)
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A triaxial rheometer for soft compressible solids
- 2002
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Ingår i: Journal of Rheology. - : Society of Rheology. - 0148-6055 .- 1520-8516. ; 46:1, s. 31-47
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Tidskriftsartikel (refereegranskat)abstract
- The compression and the shear of soft compressible solids were studied using the triaxial rheometer. The sample was fixed between two parallel plates and the deformation was controlled by an x, y, z displacement on one plate while the stress was measured on the other. The triaxial stress transducer eliminates the edge effects by only measuring the stress on an interior region of the plate. The edge effects and the associated measurement errors were analyzed by the simple isotropic elastic theory and were compared to the measurements done on the chloroprene rubber foam.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Alkhagen, Mårten, 1971, et al.
(författare)
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Mechanics of textile solids
- 2000
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Ingår i: The Nordic Textile Journal. ; :1, s. 51-57
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 19. |
- Alkhagen, M., et al.
(författare)
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Micromechanics of a compressed fiber mass
- 2007
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 74:4, s. 723-731
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Tidskriftsartikel (refereegranskat)abstract
- A theory is presented for the rate modeling of flexible granular solids based on affine average motion of interparticle contacts. We allow contacts to form and break continually but assume the existence of a finite friction coefficient rendering contacts force free as they form or break. The resulting constitutive equations are of the hypoelastic type. A specific model for the deformation of a fiber mass is then developed. The model improves on previous theories for fiber masses in at least two respects: First, it is more general in that it is not restricted to uniaxial compression, although it is restricted to predominantly compressive deformations histories, due to neglect of frictional dissipation. Second, by allowing torsion as well as bending of fibers, this theory covers a larger deformation range. Compression experiments are performed on carded slivers of PA6 fibers under various conditions. The measured response is found to be in close agreement with that predicted by the model.
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| 20. |
- Alkhagen, M., et al.
(författare)
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The effect of fiber diameter distribution on the elasticity of a fiber mass
- 2009
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 76:4
-
Tidskriftsartikel (refereegranskat)abstract
- A random mass of loose fibers interacting by fiber-fiber contact is considered. As proposed in a previous paper, the elastic response is modeled based on the statistical mechanics of bending and torsion of fiber segments between fiber-fiber contact points. Presently we show how the statistical approach can be used to account for a distribution of fiber diameters rather than just a single diameter. The resulting expression has the same form and the same set of parameters as its single-diameter counterpart, except for two dimensionless reduction factors, which depend on the fiber diameter distribution only and reduce to unity for monodisperse fibers. Uniaxial compressibility experiments are performed on several materials with different bimodal fiber diameter distributions and are compared to model predictions. Even though no additional parameters were introduced to model the effect of mixed fiber diameters, the behavior is accurately predicted. Notably, the effect of the nonuniform fiber diameter is strong: A mixture of two fiber diameters differing by a factor of 2 can reduce the response by an order of magnitude, compared to the case of uniform diameter.
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| 21. |
- Allaoui, Aissa, et al.
(författare)
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On the compressive response of carbon nanotube tangles
- 2009
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Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 373:35, s. 3169-3173
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear bulk compressibility of entangled multiwalled carbon nanotubes is studied. The analogy with textile fibre assemblies is explored by means of the well established van Wyk model. In view of the small diameter of the nanotubes. the possible effect of adhesive van der Waals interactions at tube-tube contacts is analysed. It is found, however, that the contribution of adhesive contacts to the bulk stress should be negligible. Compression experiments are performed on multi-walled carbon nanotubes and show that van Wyk's model is able to describe the response, although the values of the dimensionless parameter k of van Wyk's model were lower than expected. There is indeed no indication that van der Waals interactions play any significant role.
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| 22. |
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| 23. |
- Carlsson, Allan, 1979-
(författare)
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Orientation of fibres in suspensions flowing over a solid surface
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The orientation of fibres suspended in a viscous fluid, flowing over a solid surface, has been studied experimentally. A shear layer was generated, by letting the suspension flow down an inclined plate. Far upstream from the measuring section the suspension was accelerated to obtain an initial orientation of the fibres aligned with the flow direction. A CCD-camera was used to visualise the fibres. The velocity profile of the fibres coincided with the theoretical expression for fully developed flow of Newtonian liquid down an inclined wall. The orientation of the fibres was analysed in planes parallel to the solid surface. At distances from the wall larger than one fibre length the fibres performed a tumbling motion in the flow-gradient plane in what appeared to be Jeffery-like orbits. Closer to the wall a difference was found between fibres of aspect ratio rp = 10 and 40. The longer fibres of rp = 40 kept their orientation, aligned with the flow, also in the near wall region. For the shorter fibres the orientation shifted gradually, to orientations closer to the vorticity axis, when the distance from the wall was decreased. In the very proximity to the wall the fibres were aligned with the vorticity, perpendicular to the direction of the flow. Another distinction, most likely related to the fibre orientation, was seen in the wall normal concentration profile. Due to sedimentation effects fibres accumulated in the near wall region. For fibres of rp = 10 a peak in concentration was found at the wall, while for r=40 the maximum concentration was found approximately half a fibre length from the wall. It is previously known that a fibre can interact with the wall in what is referred to as a "pole vaulting" motion away from the wall. It is suggested, as a likely explanation to the location of the maximum concentration, that fibres of rp = 40 perform this motion, while fibres of rp=10 do not. In another experiment the surface of the wall was modified with ridges. For fibres of rp = 10 there were no longer any fibres oriented perpendicular to the flow direction in the near wall region. The main application in mind throughout this work is papermaking. The study is considered to be of fundamental character and is not applicable in a direct sense. The difference between the flow situation in the experiments and the paper machine is discussed further.
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| 24. |
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| 25. |
- Connor, M., et al.
(författare)
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Model for the consolidation of aligned thermoplastic powder impregnated composites
- 1995
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Ingår i: Journal of Thermoplastic Composite Materials. - : SAGE Publications. - 0892-7057 .- 1530-7980. ; 8:2, s. 138-162
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the role of surface energy effects, externally applied pressure, resin flow and fiber bed elasticity on the consolidation of thermoplastic-matrix composites manufactured by the powder impregnation route. Surface energy effects in the spreading of polymer droplets on fiber surfaces are discussed; then a model for the consolidation process is developed, relating the variables mentioned above. Consolidation experiments on powder-impregnated composites of the FIT type (Fibres Impregnees de Thermoplastique) were carried out using a mold attached to a servo-hydraulic testing machine. The model accurately predicts variations in void content during consolidation of carbon fiber/PEEK (CF/PEEK) and carbon fiber/PEI (CF/PEI) laminates. It was found that, at the pressures needed to achieve rapid consolidation, surface energy has a negligible influence on impregnation rate, but its effects on the void topology can be considerable. It was also shown that, when laminates of low void content are required, a minimum pressure is needed to overcome the effect of fiber bed elasticity.
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| 26. |
- Connor, M., et al.
(författare)
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On surface energy effects in composite impregnation and consolidation
- 1995
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Ingår i: Composites Manufacturing. - 0956-7143. ; 6:3-4, s. 289-295
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Tidskriftsartikel (refereegranskat)abstract
- Macroscopic capillary pressure and microscopic interparticle forces due to surface tension are examined. A general equation for the capillary pressure during impregnation is derived and subsequently specialized to particular processes. For fibre composites, the capillary pressure can be of the order of ±104 Pa, the sign depending on the contact angle between solid and liquid. Next, the attractive and repulsive forces between particles connected by liquid droplets are analysed by two different model geometries. At contact angles between π/2 and π, an equilibrium particle separation distance is obtained in the absence of applied force. At lower contact angles, spontaneous impregnation can be achieved. The effect of capillary action on impregnation rate may be significant if applied pressures are small (e.g. filament winding) but negligible at applied pressures greater than ∌100 kPa (e.g. compression moulding). The topology and concentration of voids may, however, be greatly influenced by surface energies. © 1995.
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| 27. |
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| 28. |
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| 29. |
- Djalili-Moghaddam, M., et al.
(författare)
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A model for short-range interactions in fibre suspensions
- 2005
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257 .- 1873-2631. ; 132:1-3, s. 73-83
-
Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a model for short-range fibre-fibre interaction and combines it with the Shaqfeh-Fredrickson result for long-range hydrodynamic interactions. The short-range interactions are assumed to be localised, such that the interaction forces may be taken to act at points on the fibre axes. Only interactions of viscous Newtonian character are explored in this work; the approach, however, may be used to treat more general nonlinear interactions, such as non-Newtonian vicous forces or friction. To simulate the orientation evolution, a convective discretisation technique combined with a modification of the Folgar-Tucker rotary diffusion model is proposed. The rotational parallel-plate geometry is analysed, and transient as well as steady state responses are computed. Experiments are performed on suspensions of polyamide fibres in silicon oil, using a rotational parallel-plate rheometer. It is demonstrated that the effect of fibre volume fraction and aspect ratio are well captured by this theory. Normal force as well as torque is adequately predicted. Other effects, however, such as shear thinning and effect of absolute particle size, are not predicted by the linear theory.
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| 30. |
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| 31. |
- Djalili-Moghaddam, M., et al.
(författare)
-
Fibre suspension rheology : Effect of concentration, aspect ratio and fibre size
- 2006
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 45:3, s. 315-320
-
Tidskriftsartikel (refereegranskat)abstract
- Viscosity data for fibre suspensions are produced using cone-and-plate geometry of enhanced dimensions for the reduced influence of fibre-wall interactions. Semi-concentrated suspensions of monodisperse polyamide fibres in silicone oil, with a variety of fibre concentrations (2, 5 and 8%), lengths and diameters, were studied. The suspension viscosity was measured in a range of shear stress in order to study the stress dependence. The study here focuses on the nature of the forces and interactions that contribute to the suspension viscosity. The results show that at sufficiently high stress levels, the suspension viscosity tends to reach a steady-state. At very low stress levels the suspension viscosity increases over time, most likely due to structures formed by adhesive forces. At higher concentrations, the viscosity depends on the absolute size of the fibres, again indicating the presence of non-hydrodynamic interactions.
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| 32. |
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| 33. |
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| 34. |
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| 35. |
- Djalili-Moghaddam, M., et al.
(författare)
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Study of geometry effects in torsional rheometry of fibre suspensionsIs The “Creative Class” Necessarily Urban?
- 2004
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 44:1, s. 29-37
-
Tidskriftsartikel (refereegranskat)abstract
- This work concerns the problem of measuring the viscosity of a suspension of fibres that are not short compared to the dimensions of the measurement device. We have examined various geometry effects in shear using parallel-plate and cone-and-plate configurations. Steady state viscosity, transient viscosity and first normal stress difference have been studied. Silicone oil with milled glass fibres at 8 vol.% was used as a model fibre suspension. The conventional parallel-plate geometry exhibits a significant gap dependence of the apparent viscous response. Too small gaps constrain the fibre rotations, thus lowering the initial stress peak and delaying the development of steady state. Too large gaps lead to a loss of liquid at the sample perimeter, which reduces the apparent steady state viscosity. The steady state response, however, seems to be correct for gaps in the range 1-2 mm when the maximum fibre length is 1.5 mm. The cone-and-plate geometry is less sensitive to large gaps. Too small a gap at the (truncated) cone apex leads to anomalous response due to bridging of the gap by fibres. The use of unusually large plates (100 mm diameter) and different cone angles and truncations was explored. It was shown that cone-and-plate configurations of large diameter and large truncation can effectively decrease the geometry disturbances both due to fibre bridging at the cone apex and loss of liquid at the edge.
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| 36. |
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| 37. |
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| 38. |
- Ericsson, K. A., et al.
(författare)
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Sliding plate rheometry of planar oriented concentrated fiber suspension
- 1997
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Ingår i: Rheologica Acta. - 0035-4511 .- 1435-1528. ; 36:4, s. 397-405
-
Tidskriftsartikel (refereegranskat)abstract
- The rheology of concentrated planar fiber suspensions is investigated. A new experimental technique for fiber suspensions based on a sliding plate rheometer incorporating a shear stress transducer is developed. It is shown that this instrument works well for the tested material systems. The Theological behavior in steady shear is subsequently investigated. The results can be largely explained by a combination of frictional and hydrodynamic interaction. Despite this evidence of friction no yield stress could be detected for the investigated shear rates. It was also found that the fiber aspect ratio did not influence the steady shear viscosity.
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| 39. |
- Ericsson, K. A., et al.
(författare)
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The two-way interaction between anisotropic flow and fiber orientation in squeeze flow
- 1997
-
Ingår i: Journal of Rheology. - 0148-6055. ; 41:3, s. 491-511
-
Tidskriftsartikel (refereegranskat)abstract
- The rheology of a discontinuous fiber filled polypropylene in squeeze flow between parallel plates is studied. The material has an initial anisotropic fiber orientation distribution and therefore displays a strongly anisotropic in-plane flow behavior with predominant flow transverse to the axis of principal orientation. The kinematic field is computed using a linear, orthotropic constitutive model, where the fibers are assumed to move affinely with the surrounding fluid. The fiber orientation distribution is updated in each timestep thus coupling orientation and flow. Two different orientation descriptions are evaluated: orientation tensors with closure approximations, and a technique based on direct solution of the orientation of a set of test fibers. The two methods are first compared to exact solutions of the orientation distribution function in simple shear and pure extension; the direct solution is exact within numerical error, wheras the methods based on orientation tensors and quadratic and hybrid closure fail to correctly describe any transient fiber orientation evolution. Finally, the orientation representations are implemented in the kinematic model and compared to the experimental data; the direct solution method is found to give a very accurate prediction of the observed flow kinematics, whereas the other techniques result in substantial errors. © 1997 The Society of Rheology.
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| 40. |
- Gibson, A. G., et al.
(författare)
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Mechanics of the squeeze flow of planar fibre suspensions
- 1999
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - 0377-0257. ; 82:1, s. 1-24
-
Tidskriftsartikel (refereegranskat)abstract
- This paper discusses the axisymmetric squeeze flow of concentrated transversely isotropic fibre suspensions in a power-law matrix and relates to the processing of composite materials such as sheet moulding compounds (SMCs) and glass mat thermoplastics (GMTs). A solution to the squeeze flow problem for a transversely isotropic power-law fluid is presented first, followed by a more detailed micromechanical analysis. In the first part of the paper a variational approach is applied to the interpretation of squeeze flow behaviour. This gives a simple expression for the total pressure, which enables the contributions due to extension and shear to be separated. Applying the procedure to GMT data suggests that the dissipation is predominantly extensional, except at very low plate separations. In the second part, a non-local constitutive equation is derived based on a simple drag law for hydrodynamic interactions. This is then used to model the pressure distribution when the effective length of the fibres is comparable to or determined by the dimensions of the squeeze flow plates. The model is shown to describe the observed squeeze flow stresses in both long and short fibre systems and to relate behaviour to the underlying resin flow properties. © 1999 Elsevier Science B.V. All rights reserved.
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| 41. |
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| 42. |
- Gibson, Geffrey, et al.
(författare)
-
Squeeze flow
- 1998
-
Ingår i: Rheological Measurement, (2nd edition); Collyer, A.A. and D. W. Clegg, eds., Chapman & Hall. ; , s. 550-592
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 43. |
- Grauers, L., et al.
(författare)
-
Deformation processes in composites preforms
- 2012
-
Ingår i: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM. - 9788888785332
-
Konferensbidrag (refereegranskat)abstract
- The work concerns the inelastic response of composite preforms when subjected to large deformations. The Kawabata equipment has been used to measure the shear and bending properties of the textile reinforcements. In addition, the newly developed triaxial rheometer for out-of-plane shear and compression testing is presented and used. The triaxial rheometer is capable of simultaneous compression and two independent shear deformation modes, allowing for triaxial deformation states. Compared to previous techniques the main benefits are triaxiality, elimination of edge effects and suitability for anisotropic materials. Also, a constitutive theory for the modelling of a wide range of fibrous performs based on hypoplasticity is also presented. The experimental results indicates that even dry preforms behaves viscoelastoplastic as well as showing unsymmetrical behaviour in bending.
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| 44. |
- Håkansson, J., et al.
(författare)
-
Permability of felts
- 2000
-
Ingår i: Proceedings of the 3rd Nordic Meeting on Materials and Mechanics. - Aalborg : Inst of mechanical engineering, Aalborg university. - 8789206312 ; , s. 351-359
-
Konferensbidrag (refereegranskat)
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| 45. |
- Håkansson, J., et al.
(författare)
-
Permeability modelling of fibre networks
- 2002
-
Ingår i: Annual transactions of the Nordic Rheology Society. - : Nordic Rheology Society.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 46. |
- Hård af Segerstad, P., et al.
(författare)
-
A constitutive equation for open-cell cellular solids, including viscoplasticity, damage and deformation induced anisotropy
- 2008
-
Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 24:5, s. 896-914
-
Tidskriftsartikel (refereegranskat)abstract
- A thermodynamically consistent approach is developed for modelling the response of an open-cell cellular solid at finite compressive strains. The cellular solid is considered as a network of struts, where each strut connects two vertex points. A hypothesis is proposed that the vertex points move affinely in the finite strain regime, where the struts buckle plastically. The strut deformation is assumed to be 1-dimensional and depend directly on the macroscopic deformation; thus the description of the strut response requires only a scalar valued response function. Owing to this simple ansatz it is possible to include multiple nonlinear mechanisms, such as hyperelasto-viscoplasticity and damage. The macrostress is obtained by averaging over a statistical ensemble of struts. The model has been implemented in the context of finite strains and damage coupled to viscoplastic Perzyna type behaviour. All model parameters may be determined by performing tests in simple compression. The model is well capable of reproducing data from compression experiments on various open-cell aluminium foams.
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| 47. |
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| 48. |
- Hård af Segerstad, Per, 1977, et al.
(författare)
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A micropolar theory for the finite elasticity of open-cell cellular solids
- 2009
-
Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 465:2103, s. 843-865
-
Tidskriftsartikel (refereegranskat)abstract
- A mechanistic model is presented for an open-cell cellular solid consisting of a threedimensional network of elastic struts. By considering the bending and torsion as well as stretching and buckling of the struts, we allow for length-scale effects in the macroscopic response. Constitutive equations are developed for the force and couple stress tensors, accounting for finite deformations and anisotropy. The consistent tangent stiffness operators are derived and the equations are fully implemented in a nonlinear twodimensional finite-element solution scheme for the coupled displacement/rotation problem. A boundary-value problem of a shear gap with prescribed boundary rotations is analysed, and the model is shown to predict the well-known gap size effect. The mechanistic model allows some detailed interpretation of the micropolar behaviour, such as the effects of strut slenderness, strut length and anisotropy.
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| 49. |
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| 50. |
- Hård af Segerstad, Per, 1977, et al.
(författare)
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Computational modelling of dissipative open-cell cellular solids at finite deformations
- 2009
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 25:5, s. 802-821
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Tidskriftsartikel (refereegranskat)abstract
- This study concerns the constitutive modelling of dissipative open-cell structural cellular solids under primarily finite compressive deformations and the corresponding non-linear finite element implementation. A thermodynamically consistent, mechanistic approach presented in Hard of Segerstad et al. [Hard of Segerstad, P., Larsson, R., Toll, S., 2008. A constitutive equation for open-cell cellular solids, including viscoplasticity, damage and deformation induced anisotropy. International Journal of Plasticity. 24, 896-914.] is adopted for modelling the initial linear-elastic response and the subsequent plateau behaviour. In these regions the cellular solid is considered as a network of struts, where each strut connects two vertex points. A hypothesis is proposed that the vertex points move affinely in the finite strain regime, where the struts buckle plastically. The strut deformation is further assumed to be one-dimensional and depend directly on the macroscopic deformation; thus the description of the strut response requires only a scalar valued response function. Owing to this simple ansatz, the introduction of multiple non-linear mechanisms, such as hyperelasto-viscoplasticity and damage becomes feasible for large scale computations. An additional hyperelastic volumetric response, activated near the point-of-compaction, is introduced for two reasons, (i) to capture the stiffness recovery at high compressive volumetric deformations, where the struts come into contact, and (ii) to prevent numerical instability. The model is implemented as a user defined constitutive driver in the implicit version of the finite element code ABAQUS and tested experimentally for an open-cell aluminium alloy foam (Duocel 6101-0,40 ppi). All material parameters are determined by a simple compression test, and subsequently used to simulate the indentation of a rigid sphere into a foam cylinder. The model accurately captures the experimental load-displacement relation and the deformed geometry. (C) 2008 Elsevier Ltd. All rights reserved.
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