TOOLED THICK COMPOSITES by ARVEN H. SAUNDERS III ...

proportion of the applied pressure is applied to the fiber bed. As Vf approaches its maximum
value, all applied pressure is applied to the fiber bed, and the resin pressure can deteriorate.
Figure 3.4 presents the relationship between the effective stress ESS and Vf for a fiber bed of
AS4 fibers.
Fiber Bed Stress psi
250
200
150
100
50
0
Effective or Fiber Bed Stress
0.4 0.5 0.6 0.7 0.8
Fiber Volume Fraction
Figure 3.4. Effective or Fiber Bed Stress vs. Fiber Volume Fraction.
3.9 Hubert Fiber Bed Compaction Curve Experiments
The fiber bed compaction curve defines the relationship between the effective stress
and fiber bed deformation. Hubert (Hubert, 1996) conducted experiments that explored the
essence of laminate consolidation and demonstrated a method for determining the fiber bed
compaction curve. Special load apparatus and tooling were used to apply a clamping load to a
flat laminate while constraining its motion but allowing resin flow to exit from its sides. The
laminate was comprised of 16 plies of AS4/3501-6 (fiber/resin) and was compacted in a series
of constant displacement rate ramps followed by a displacement hold condition. For each
displacement step, a clamping pressure ramp was controlled to produce a uniform displacement
rate. As each displacement position was held, the required load necessary to maintain this
position was monitored and found to relax as the resin flowed out. When the required load
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