CCT CCT Curing Processes & Autoclave Operations 2 — Questions and Answers
Question 1: What is 'out-time' for prepreg composite materials?
- The cure dwell time inside the autoclave
- The total accumulated time a prepreg has been outside the freezer at room temperature (Correct answer)
- The time elapsed after demolding the cured part
- The shelf life remaining at frozen storage temperature
Correct answer: The total accumulated time a prepreg has been outside the freezer at room temperature
Out-time tracks cumulative room-temperature exposure of prepreg; exceeding the limit causes premature partial cure that degrades part quality and processability.
Question 2: What is the purpose of a bleeder layer in an autoclave vacuum bag layup?
- To provide additional structural reinforcement plies
- To absorb excess resin squeezed out from the laminate during cure (Correct answer)
- To apply a surface finish to the part
- To measure internal temperature during cure
Correct answer: To absorb excess resin squeezed out from the laminate during cure
The bleeder layer absorbs excess resin expressed from the laminate during cure, controlling fiber volume fraction and preventing resin-rich areas.
Question 3: What does a 'dwell' mean in the context of a composite cure cycle?
- A rapid temperature ramp-up segment
- A period of constant temperature held for a specified time (Correct answer)
- The final cooling rate at cycle end
- The pressure release step at the end of cure
Correct answer: A period of constant temperature held for a specified time
A dwell is a hold period at a specified temperature, providing adequate time for resin flow, volatile removal, or crosslinking reactions to complete.
Question 4: What is the gelation point in epoxy resin cure?
- The point when the resin is fully and completely cured
- The point where resin transitions from liquid to gel and loses the ability to flow (Correct answer)
- The temperature at which the resin first begins to melt
- The moment vacuum is first applied to the bag
Correct answer: The point where resin transitions from liquid to gel and loses the ability to flow
Gelation is the critical transition where epoxy resin changes from a flowable liquid to an elastic gel due to crosslink network formation, after which resin can no longer flow.
Question 5: What is post-cure in composite processing?
- Quality inspection performed after demolding
- A secondary heat treatment after initial cure to achieve full glass transition temperature and mechanical properties (Correct answer)
- The cooling phase at the end of the autoclave run
- Application of protective surface finish after demolding
Correct answer: A secondary heat treatment after initial cure to achieve full glass transition temperature and mechanical properties
Post-cure is a free-standing oven heat treatment after demolding that advances the degree of cure to achieve the material's design Tg and full mechanical properties.
Question 6: What is the significance of glass transition temperature (Tg) for a cured composite structure?
- It indicates the tensile strength of the reinforcing fibers
- It defines the maximum service temperature above which the matrix softens and structural properties degrade (Correct answer)
- It measures the electrical conductivity of the laminate
- It indicates the quality of fiber-to-matrix adhesion
Correct answer: It defines the maximum service temperature above which the matrix softens and structural properties degrade
Tg is the temperature at which the polymer matrix transitions from rigid to rubbery, setting the maximum service temperature for structural composite applications.
CCT CCT Curing Processes & Autoclave Operations 2
What is 'out-time' for prepreg composite materials?