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Micromechanics Interfaces Interphases Mesomechanics Resin Rich Volumes Voids

Micromechanics Interfaces Interphases Mesomechanics Resin Rich Volumes Voids. John Summerscales. Outline of lecture. Micromechanics Interface/interphase Voids Meso-mechanics Resin Rich Volumes (RRV) Voids. Micromechanics I. composite material modelled using rules-of-mixtures

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Micromechanics Interfaces Interphases Mesomechanics Resin Rich Volumes Voids

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  1. MicromechanicsInterfacesInterphasesMesomechanicsResin Rich VolumesVoids John Summerscales

  2. Outline of lecture Micromechanics Interface/interphase Voids Meso-mechanics Resin Rich Volumes (RRV) Voids

  3. Micromechanics I • composite material modelled usingrules-of-mixtures • composite structure may be laminatewith complex stacking sequence • [0/90]s four-ply laminate in-plane:Ex = (2E1+2E2)/4 Ey = (2E2+2E1)/4 • for out-of-plane (bending)need to calculate effect of layer/ply/lamina propertiesw.r.t. neutral axis

  4. Micromechanics II • assumptions in classical laminate analysis • data integrity • linear elasticity • perfect fibre/matrix & layer/layer bonding • continuous strain throughout • plane stress • small deflections (beam theory)

  5. Micromechanics III • FEA for orthotropic platesuses 2D shell elements withfour (4) elastic constants: E1, E2, G12, 12 • FEA for orthotropic solidsuses 3D brick elements withnine (9) elastic constants • sandwich panels/beamshave a specific option in Autodesk Helius

  6. Interface or Interphase • Interface: where fibre meets matrix as a sharp change between phasesor a monomolecular layer of “sizing agent” • Interphase: where fibre meets matrix with a graded transition between phases:usually metal- or ceramic-matrix composites at >10 nanometerscale

  7. Meso-mechanics • bridges the microstructure-property relationship of materials with non-continuum mechanics • uniform distribution of fibres gives • highest strengths • low in-plane permeability • hence fibre clustering is • bad for strength • good for processing by LCM processes

  8. Resin Rich Volumes (RRV) • … or … areas (RRA), regions (RRR) or zones (RRZ) • three-dimensional (3-D) features associated with • low fibre volume fraction • high areal weight fabrics • inhomogenous strain fields • … leading to early failure • permits larger voids

  9. Voids • Stone and Clarke (Non-Destructive Testing, 1975) suggested • at low void content (<1.5%), the voids tend to be spherical with diameter 5-20 μm • at higher void contents, the voids are cylindrical and the length can be an order of magnitude greater than the diameter • cylindrical voids are generally oriented parallel to the fibre

  10. Voids • Judd and Wright (SAMPE J, 1978)reviewed 47 papers and concluded: • considerable scatter in results • the interlaminar shear strength of composites decreases by about 7% for each 1% voids up to at least the 4% void content level, beyond which the rate of decrease diminishes. • other mechanical properties may be affected to a similar extent. • true for all composites regardless of the resin, fibre or fibre surface treatment used in their fabrication". 

  11. Voids • Ghiorse (SAMPE Q, 1993) found that: • in the range zero to 5%, each 1% increase in void content decreased the interlaminar shear strength of carbon fibre epoxy composites by 10% anddecreased the flexural modulus by 5%.

  12. Volume fractions • Vf + Vm + Vi +Vv = 1where Vx is the volume fraction of x and ... • x = f for fibre • x = m for matrix • x = i for interface (normally negligible) • x = v for voids (normally in the matrix)

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