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2/2/2015 | 1 MINUTE READ

Tsai book expands on invariant-based method for material characterization

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Dr. Stephen Tsai and José Daniel Diniz Melo are publishing "Composite Materials Design and Testing - Unlocking mystery with invarients," to help composites fabricators reduce material certification time.

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In the July 2014 issue of CW’s High-Performance Composites magazine, Dr. Stephen Tsai, professor research emeritus in the Department of Aeronautics & Astronautics at Stanford University, suggested an invariant-based method for accelerating aerospace certification testing. He identified trace (the sum of three components of stiffness, plus that of shear) as the one and only property of composites that can make composites easier to understand, and design and testing of composites simple and straightforward.

Now, Tsai and José Daniel Diniz Melo, a consulting professor at Stanford, have expanded on this topic in their upcoming book, “Composite Materials Design and Testing - Unlocking mystery with invariants.” In the book, they further explain that for all carbon/epoxy composites in use today, the stiffness of all laminates is simply a fixed fraction of trace. For example, they say, longitudinal stiffness is 88% trace, and stiffness of [π/4] is 34% of trace — all within an error of 1.5% or less. So, according to Tsai, if one measures the value of trace for each material, they can predict the stiffness of all laminates.

Among Tsai and Melo’s recommendations are homogenization through use of thin plies, continuous as opposed to discrete ply angles, a ranking procedure to reach optimal profile and ply drop, bi-angle instead of unitape building blocks, tapered edges to reduce scrap and edge delamination, and others. Such strategies, they say, may make composites more competitive, and make simultaneous weight and cost savings possible.

Chapter titles from the book include: Stress-Strain Relations, Ply Stiffness, In-Plane Stiffness, Flexural Stiffness of Symmetric Laminates, Stiffness of General Laminates, Micromechanics, Failure Criteria, Strength of Laminates, The Invariant-Based Approach to Stiffness, The Invariant-Based Approach to Strength, New Opportunities in Design and Testing and Mechanical Testing of Composites.

“Composite Materials Design and Testing - Unlocking mystery with invariants" is $110 is can be purchased at stanford.edu/group/composites. It will also be available for purchase at the JEC Europe trade show, March 10-12, Paris, France.

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