Composite Materials Design and Testing

Composite Materials Design and Testing

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In the beginning, there was carbon fiber with high stiffness and strength.  We were able to generate all the data and design to build B-787 and A-350.  What we do not know even today is the transverse and shear stiffness and strength of the fiber.  We have learned to live without them.  Authors Tsai and Melo discovered trace as the heart and soul of composites.  It is the one and only one property that is needed.  Just like carbon fiber they need to know only the longitudinal properties.  They can be obtained from [0] coupons.  Their tensile and compressive stiffness and strength are measured without need to know their transverse and shear properties.  The mystery of composites being complicated and difficult to understand can be unlocked by this straightforward path of design and testing.  By using trace and trace alone the authors can define the stiffness and strength of all laminates. 


Instead of hundreds of coupons as the building blocks of a strength pyramid, Tsai and Melo see one block that can support an inverted strength pyramid.  This block is the uniaxial tensile and compressive stiffness and strength of [0].  The data from this panel stand as the upper bound because there are no defects from lamination process, residual stress, and edge delamination.  The authors used “logic and ingenuity” to rate as-built laminates in their lamination efficiency in a master stress-strain template.   Templates are easy to build (in Excel) and to compare directly different laminates and different materials.  Improvements in materials and processes can be demonstrated by test data in minutes without extensive laminate data that can take days if not weeks.  If design allowable is demanded, many materials and processes never have a chance.  Trace-based technology makes design and testing of composites no different or difficult from those of metals.  One panel of [0] can map out instantly the upper bound stiffness and strength of all as-built laminates.  When actual data of as-built laminates become available they will reveal the quality of processing and effects of defects. 


Several critical steps in the evolvement of this trace-based theory include the small variation of lamination factors for the most popular CFRP laminates; omni strain envelopes covering all ply angles; matrix degradation factor that defines convergent strain anchors for LPF envelope for both interactive and non-interactive failure criteria; conservative omni envelopes for principal strains; the master stress-strain template that defined the upper bound values for failure strains; and other current practices in laminate design that have made composite materials more costly and less weight savings.  Such practices that were defined in the 1960’s, some 50 years ago, include discrete, fixed ply angles of [0], [±45] and [90] (instead of more flexible continuous ply of [0/±phi/±psi/90]); up to 10-ply thick sub-laminates (instead less than 4 with thick-thin ply combinations); heterogeneous patch-work stacking (instead of homogenized layup); 4-axis layup (instead of 1- or 2-axis); and use of [0] tape only for tape laying (instead of bi-angle tape like C-Ply).  In this book, other examples of strength-enhancing and cost-reducing opportunities can unlock the shackle by the half-a-century-old practice.   The authors wish to see many innovations that would make composite material a truly unmatched energy-savings and life-long-service system.


  • Stress-Srain 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