1 / 12

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

waltonk
Download Presentation

Micromechanics Interfaces Interphases Mesomechanics Resin Rich Volumes Voids

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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)

More Related