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


Reverse Classical Laminate Theory

Reverse Classical Laminate Theory

Reverse Classical Laminate Theory

Hi, has anyone tried performing classical laminate theory in reverse, i.e. getting lamina stiffness and strength values from experimental laminate data? I have been attempting to do so but I can’t seem to get my formulation to work correctly. I’m 99% sure it is correct because I can go from Q Matrix ---> A Matrix, but not the reverse calculation.

Surprisingly there doesn’t appear to be any commercial software that calculates this, and I have only found two academic papers which mention the reverse process. I’ve attached a PDF showing my workings as that will be a lot clearer than writing it out here.

Thanks for any help

RE: Reverse Classical Laminate Theory

You are trying to solve for 4 unknowns. You will need data for at least 4 different laminates in order to back out the values. I don't have time to bother working thru all of the algebra, but it should be do able. But the values for E2, G12 and nu12 for many laminates only have a small effect on Ex so experimental error may be too large to accurately back those values out. Best to assume reasonable values for E2, G12, nu12 and back out E1 values (this assumes you are dealing with uni tape).

RE: Reverse Classical Laminate Theory

I am actually testing woven fabrics but I am trying to back out an equivalent unidirectional laminate so I can use the properties for FEA. In the end I managed to get my program to work but I had to make some tweaks to it after working out what was the problem. Basically for a balanced laminate the A11 and A22 equations are the same, e.g. for a 0/90/90/0 laminate:

A11 = [2*Q11 + 2*Q22] * t
A22 = [2*Q11 + 2*Q22] * t

(Note that Q11 and Q22 are of course reversed for 0 and 90 plies but as they are the same value the summation is still the same result)

This means that it is impossible to find a unique solution of Q11 and Q22. The only way you can do this is if you eliminate one of the unknowns and choose a value for it – so I got rid othe Q22 equation as I can calculate E2 from micromechanics. It’s quite annoying and feels wrong to have to use a theoretical calculation to derive experimental results. I am not a mathematician so I can’t explain why these equations won’t reverse to a unique solution.

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! Already a Member? Login


eBook - Rethink Your PLM
A lot has changed since the 90s. You don't surf the Web using dial-up anymore, so why are you still using a legacy PLM solution that's blocking your ability to innovate? To develop and launch products today, you need a flexible, cloud-based PLM, not a solution that's stuck in the past. Download Now
White Paper - Using Virtualization for IVI and AUTOSAR Consolidation on an ECU
Current approaches used to tackle the complexities of a vehicle’s electrical and electronics (E/E) architecture are both cost prohibitive and lacking in performance. Utilizing virtualization in automotive software architecture provides a better approach. This can be achieved by encapsulating different heterogeneous automotive platforms inside virtual machines running on the same hardware. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close