Using expired prepreg
Using expired prepreg
(OP)
Hello.
I'm wondering if anyone has experience with using expired prepreg (i.e. expired freezer-life and not out-life).
The material in question is an epoxy/glassfiber woven prepreg which will be used locally as a corrosion barrier on a larger epoxy/carbon fiber structure.
I'm thinking that we might get a lower Tg and degree of cure in the glassfiber plies but that might be acceptable since it's not providing any structural support. However what about possible moisture ingress etc.? Is there a risk that the expired prepreg might affect the carbon fiber prepreg in the product?
I should mention that we will be recertifying the prepreg before using it and the reason that we're considering using the expired material is the long delivery times of fresh material.
Any input on the matter is much appreciated.
I'm wondering if anyone has experience with using expired prepreg (i.e. expired freezer-life and not out-life).
The material in question is an epoxy/glassfiber woven prepreg which will be used locally as a corrosion barrier on a larger epoxy/carbon fiber structure.
I'm thinking that we might get a lower Tg and degree of cure in the glassfiber plies but that might be acceptable since it's not providing any structural support. However what about possible moisture ingress etc.? Is there a risk that the expired prepreg might affect the carbon fiber prepreg in the product?
I should mention that we will be recertifying the prepreg before using it and the reason that we're considering using the expired material is the long delivery times of fresh material.
Any input on the matter is much appreciated.





RE: Using expired prepreg
It must be realised that there are two separate but inter-related measures of material life; Shelf life in freezer, and bench life. It is unrealistic to expect that a material which has been in the freezer for 179 days can then be exposed for 30 days and still be considered "in life". Similarly, if the material has been out for the first 29 days since acceptance, it would be stupid to expect that you can put it back in the freezer and expect it to be useable after 150 days in the freezer.
We introduced a policy where the used bench life and the used freezer life are recorded, and then expressed as a fraction of the nominal bench and freezer life, and the if the total fraction exceeds 1.0 then the material must be requalified.
(Time on bench)/(bench life) + (Time in freezer/freezer life) must be less than 1.0.
Further, if the requalified material meets specs, then the life is extended by a full lifetime for both bench and freezer life for the second re-lifing. In the case of a third re-lifing, if the material meets qualification, then the permitted life is reduced to 50%. Once that life is exceeded, the material is scrapped even if it meets spec.
Regards
Blakmax
RE: Using expired prepreg