Tensile fabric structures by gdf57j

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									New membrane finite element formulation                  Stochastic analysis
Membrane elements                                        We are developing a probabilistic approach to
currently used by all                                    replace the current permissible stress design with
major consultants                                        very high factors of safety (between 4 and 6).
for fabric structures                                    Implementation of reliability based analysis will
design have severe
limitations (i.e.
                                                         bring the design of tensile fabric structures in
                                                         line with other, better understood, construction            Tensile fabric
assumption of small
strain) that reduce
                                                         materials.                                                  structures:
the accuracy of the
analysis. Recent research at Newcastle University
has developed a curved, large strain six noded
triangular element. This provides accurate, rapid                                                                    new developments
analysis of membrane structures.                                                                                     in analysis, design
New materials                                                                                                        and materials
• Surface coatings – self cleaning
  photocatalyst (titanium dioxide),
  superhydrophobic (lotus effect),
• Translucent insulated fabrics
  (nanogel by Birdair),
                                                         Simulated installation
• Embedded electronics
  (monitoring, security, display,                        The fabrication and construction method affects the
                                       Lotus leaf (iTV   state of stress in the finished structure. This work
  communications, photovoltaics) Denkendorf)
• Flexible, highly translucent fabrics                   will, for the first time, enable these locked-in stresses
  (Gore Tenara with 20% or 40%                           to be included in the analysis. This will give more
  light transmission)                                    accurate prediction of maximum stress levels, and
• Eco-fabrics (Kenaf) and eco-                           provide a method of assessing proposed fabrication
  composites (e.g. hemp fibres)                          and installation procedures.
• Incorporation of phase                                 Applications
  change materials for building
                                                         This research is currently being
  temperature regulation               Gore Tenara
                                                         diversified to include the testing,
                                                         design and analysis of composite
                                                         materials for the aerospace,
                                                         automative and marine industries,
                                                         including analysis of functionally
                                                         graded materials.                     Image from
                                                         Other applications include design     Heriot-Watt
                                                         of biomedical textiles and biological University
                                                         substrates.


                                                         Professor Peter Gosling
                                                         p.d.gosling@ncl.ac.uk, 0191 222 6422
                                                         Dr Ben Bridgens
                                                         ben.bridgens@ncl.ac.uk, 0191 222 6409
Aims and objectives                                     Material testing                                             Predictive models
The aim of this work is to radically                    Biaxial                                                      A predictive model has been developed to determine
improve the tools and knowledge                                                                                      the biaxial stress-strain response of flexible woven
                                                        An innovative biaxial test rig has
available for the design of                                                                                          fabrics & composites, without the need for biaxial
                                                        been developed using a ‘floating
lightweight tensile structures.                                                                                      testing. All model parameters are determined from
                                                        frame’ which self-aligns with
This will reduce uncertainty in the                                                                                  standard tests: yarn and coating tensile moduli are
                                                        fabric warp and fill directions (not     Biaxial test rig
design process and enable rapid,                                                                                     inferred from uniaxial strip tests, weave geometry is
                                                        necessarily orthogonal). Biaxial
efficient utilisation of new materials.                                                                              measured from digital photographs of the material
                                                        strain is measured using laser
Fabric structures are increasingly                                                                                   cross-section. Detailed material testing enables
                                                        extensometers. The cruciform
relevant as they fit with current                                                                                    meaningful comparison to be made between the
                                                        test piece has been analysed and
and future trends of minimising                                                                                      model output and actual fabric response. The model
                                                        designed to ensure that strain
use of materials, low embodied                                                                                       is truly predictive: parameters are not optimised to
                                                        measurements are taken in an area
energy, natural ventilation, flexible                                                                                fit the model output to a particular data-set.
                                                        of fabric subjected to uniform,
& adaptable structures & striking                                                                Shear accessory     The model provides a more
                                                        known stresses.
architectural forms.                                                                                                 accurate representation
                                                        Shear                                                        of fabric behaviour than
                                                        A novel shear accessory has been developed for the           current industry best
Research outcomes                                       biaxial test rig. This enables biaxial conditioning of       practice (i.e. use of elastic
                                                        the fabric, with subsequent shear deformation at             constants based on biaxial
Combine advances in material                                                                                                                       Fabric cross sections
                                                        any specified biaxial load state. This will provide a        test data), but without
testing, modelling and analysis to
                                                        step-change in the understanding of ‘shear lock-up’          the need for specialist
enable structural engineers and
                                                        (i.e. the feasible level of shear strain before wrinkling    testing, equipment or
architects to push the boundaries of
                                                        occurs), vital for determining the fabric forms that         software. The model is
what is achievable with lightweight
                                                        can be achieved with a given type of fabric.                 currently being extended
fabric structures,
                                                        Test protocols                                               to include shear response,
• Less reliance on experience and                                                                                    again using purpose built,
  rules of thumb will enable full                       There are no British or European standards for
                                                        biaxial and shear testing of architectural fabrics. A        innovative test equipment
  utilisation of new materials without the usual slow                                                                and test protocols. The
  learning curve                                        new biaxial test protocol has been developed based
                                                        on extensive testing, industry best practice, and            model has been developed
• New materials will make fabrics more widely                                                                        for architectural fabrics,
                                                        tailored for the intended data end use. Application
  applicable                                                                                                         but is equally applicable to
                                                        of prestress followed by mechanical conditioning
• Environmental benefits - lightweight, low             provides repeatable stress-strain data suitable for          other woven composites
  embodied energy, new insulated fabrics will form                                                                   and could be applied          Constitutive model of fabric
                                                        medium to long term structural design. The test                                            unit cell
  an integral part of the building envelop, use for     protocol efficiently populates the space of feasible         to problems of feasible
  ‘semi-conditioned’ spaces, shading etc.               stress states; it is not limited to a few specified stress   drape during lay-up. A
• Increased reliability & robustness of fabric          ratios. It is proposed that strain-strain-stress data        key application is for
  structure design                                      is combined with residual strain data to provide             reverse engineering
                                                        an accurate model of the non-linear behaviour of             of woven composites:
• Application to a wide range of composite materials                                                                 appropriate fibre/yarn
                                                        architectural fabrics, without any limiting plane-
Research supported by:                                                                                               and matrix properties
                                                        stress assumptions.
                                                                                                                     and weave geometry can
                                    Buro Happold        Variability                                                  be calculated to provide
                                                        Extensive testing (initially uniaxial) to determine          a material with optimal
                                                        variability of fabric material properties for different      properties for a given        Comparison of model and test

           www.ceg.ncl.ac.uk                            materials and manufacturers.                                 application.                  data

								
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