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Interfaces Interphases Mesomechanics

Interfaces Interphases Mesomechanics. John Summerscales. Outline of lecture. Interface/interphase Voids Meso-mechanics. Interface or Interphase. Interface: where fibre meets matrix as a sharp change between phases or a monomolecular layer of “sizing agent”

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Interfaces Interphases Mesomechanics

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  1. InterfacesInterphasesMesomechanics John Summerscales

  2. Outline of lecture Interface/interphase Voids Meso-mechanics

  3. 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 nanometer scale

  4. 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

  5. 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". 

  6. 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%.

  7. 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)

  8. 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

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