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Plate Warping when Unbalanced!? Not exactly...here's a Tip!

"There is a misconception that unbalanced laminates are not recommended because the laminates will warp when temperature and/or moisture content changes. Symmetric laminates, whether balance or not, will not warp, while unsymmetric laminates will. Material symmetry, such as orthotropy or anisotropy, has no effect on warpage."

Note: "Laminates have to be symmetric with reference to the mid-plane. The basis for this requirement is to prevent warping from cool-down after curing. [However], being symmetric is not required for laminates with many dispersed plies. The coupling matrix [B] in unsymmetric laminates diminishes when a laminate becomes homogenized...[it is recommended that the designer use a] repetition of sub-laminates to build thick laminates. When the repetition becomes large the effect of coupling matrix [B] approaches zero [reducing warpage]. Thus there is no longer need to keep laminates symmetric as long as they are homogenized. We call this continuous stacking, meaning continue stacking same sub-laminates until the desired thickness is reached. [Also], [t]here is no need to keep track [of] where the mid-plane is when laminates are homogenized." See figure below showing the homogenization effects on warpage as a function of repeated sub-laminates. 

Source: Stephen W. Tsai, Theory of  Composites Design, 2008.


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Wednesday, 17 July 2019
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