Life Prediction, Durability, and Damage Tolerance of High Temperature Polymer Composite Structures

1
Life Prediction, Durability, and Damage Tolerance
of High Temperature Polymer Composite Structures

• S.R. Patel, S.W. Case and K.L. Reifsnider
• Materials Response Group
• Virginia Tech
• sponsored by Pratt and Whitney

2
Objectives

• To investigate the durability, under service
  conditions, of a graphite reinforced polymer
  being considered for use by Pratt and Whitney in
  an aircraft engine
• To develop a life-prediction method based on
  remaining strength that may be applied to the
  specified material system
• To validate the method by comparing with
  experimental evidence

3
Experimental Testing

• Advanced subsonic aircraft engine service
  conditions
• Ambient 72F - benchmark
• Elevated Temperature 250F
• Moisture 85 RH and 85F
• Hygrothermal cycling between elevated temperature
  and moisture conditions

90 min
250F,dry
85F, 85 RH
24 hours
Time
4
Experimental Testing

• Specimens
• 8 long by 1 wide coupons
• unaged
• aged hygrothermally for 6000 hours and 12000
  hours
• Quasi-Static Testing
• Apply load monotonically until the specimen fails
• Fatigue Testing
• Cycle load on specimen between predetermined
  loads
• Max Load 10Min Load
• Frequency 10 Hz

5
Initial Tensile Properties
Xt 104 8 ksi E 9.2 0.7 msi ef 1.1 0.1

6
S-N Curves
7
Residual Properties
8
Conclusions

• Strength and life of material minimally,if at
  all, affected by elevated temperature or moisture
• Though aged specimens show signs of damage due to
  aging alone and increased levels of damage due to
  fatigue, the initial and residual strengths
  remain relatively unchanged or minimally changed
  from that of unaged material
• In all cases, very little degradation of residual
  properties indicates that fatigue failure is a
  sudden death event. This behavior will limit
  the usefulness of the intended residual strength
  based approach to life predicition.