×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Fatigue, yield & fracture criterion for fibre reinforced plastics in comparison to metal

Fatigue, yield & fracture criterion for fibre reinforced plastics in comparison to metal

Fatigue, yield & fracture criterion for fibre reinforced plastics in comparison to metal

(OP)
Hello All,

I would like to request from the interested folks, if anyone can suggest me fibre reinforced plastic CAE. I would like to know following;
-To predict fracture in Plastic, which theory we need to follow, max principal strain or max von Mises strain?
- Can we define a clear Yield strain (proof strain) for FRP? if it is, then what should be plastic strain?
- For fatigue, should we take linear stress or do a nonlinear analysis, may be at high operating temp E value may not be appropriate for the given load. Can we take stress criterion ( a factor of UTS) if we don't fatigue data? Which stress combination we need to take? Principal or von Mises?

Appreciate if I can get answers with theoritical backing. Thanks to everyone!

RE: Fatigue, yield & fracture criterion for fibre reinforced plastics in comparison to metal

What a great excuse to dust off my old Fracture Mechanics book ( By T.L. Anderson). While reading ch9 it states that "ASTM committee D20 has developed a standard method for K1c testing of plastics [10]." (pg 362) On the same pg there is a nice stress stain diagram that shows how yield strength is defined for plastics. As far as "predicting" cracks, I have been raised on the pedagogue of always assume the crack exist, the real question is at what stress does it go bang!

RE: Fatigue, yield & fracture criterion for fibre reinforced plastics in comparison to metal

Pure I reinforced plastics are very different from fiber reinforced plastics. And the latter highly depend on whether it is discontinuous or continuos fiber material.

For continuous fiber reinforced plastics, stress-strain is usually linear to failure, the is no "yield" and neither max prin or Von mises criteria are appropriate; need to use something like max stress or strain in the fiber directions (and ignore most of the failure criteria stuff in text books - it is wrong)

RE: Fatigue, yield & fracture criterion for fibre reinforced plastics in comparison to metal

(OP)
@SWComposites Thanx for your reply. What target should we use for glass filled plastics (Ex. PA6 GF30, PA66 GF30 etc)? whether it should be 0.2% strain or 20% of UTS or some other standard value. Thr is a great variation of mechanical properties with change in temperature(-40 to 140 deg C)so , it is getting very difficult to fix a standard target for every temperature range.

RE: Fatigue, yield & fracture criterion for fibre reinforced plastics in comparison to metal

Target?

RE: Fatigue, yield & fracture criterion for fibre reinforced plastics in comparison to metal

(OP)
I am talking about failure criterion. Like for steel we fix yield point as target or 0.2% Proof strain for ductile material.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources