Session: 01-01-01: General Topics of Aerospace Structures

Paper Number: 137209

137209 - Novel Approach for Simplifying Carbon/epoxy Composites Design Based on Invariants and Non-Conventional Laminates 

Carbon/epoxy composite laminate design usually relies on a large set of parameters, which are defined as properties of the material. Also, traditional aerospace industry designs are based on Quad laminates (0°, 90°, ±45° oriented plies) with additional rules (symmetry, balance, 10% minimum of each angle, etc.) that greatly restrict the potential of the material. Using the ply as the building block, designers need to know four independent elastic constants (E_x , E_y , G_xy , and ν_xy) plus a set of five or more strength allowables, depending on the failure criterion to be chosen. In the case of the more traditional failure criteria, five strength allowables are required (X, X’, Y, Y’ and S). A novel approach is then proposed, based on only three parameters to define all those properties: one for the elastic constants and two for the failure criterion. The elastic constants can be derived based on the invariant master ply theory and the Tsai’s modulus using just the Young’s modulus in the fiber direction (E_x). This single parameter is sufficient to define the Tsai’s modulus (trace of the ply stiffness matrix) which is invariant and thus considered a material property itself. Together with the master ply stiffness matrix derived for the carbon/epoxy class of composite materials, the particular stiffness matrix can be obtained for any material of this class. This concept can be extended from the case of plane stress ply, to plane strain thick ply and fully 3D bulk orthotropic material. Failure analysis is performed using either two (X and X' or their corresponding strains) or, more conservatively, one parameter based on whichever is smaller. Moreover, the introduction of non-conventional layups, specifically the Double-Double (DD) concept to replace the traditional Quad laminates, adds to the simplification of the design and manufacturing process. DD laminates are defined by a simple building-block of four-angle plies [±F/±Y] continuously stacked. Symmetry and balancing are achieved by the repetition of this building-block, due to homogenization of the laminate. Furthermore, ply-drops are greatly simplified and optimization can be easily achieved due to DD continuous domain (angle), instead of the discrete domain for the Quads. The theoretical foundation of this novel approach is briefly presented together with case studies intended to illustrate its simplicity and potential.

Presenting Author: Carlos Cimini UFMG - Federal University of Minas Gerais

Presenting Author Biography: Experienced aeronautical engineer, professor and researcher, with focus on structures and composites. Graduated in 1984 as mechanical engineer specialized in aerospace structures at the Federal University of Minas Gerais (UFMG), Brazil. Worked as aircraft structures analyst engineer at EMBRAER (Brazilian Aircraft Manufacturer). Joined UFMG faculty of the Department of Mechanical Engineering as a lecturer in 1989, finishing the Master's program in Structural Engineering in 1992 at this University, under the supervision of Prof. Estevam Barbosa de Las Casas and Dr. Edgardo Omar Taroco Aliano (LNCC). Concluded the Ph.D. program in 1997 at the Department of Aeronautics and Astronautics of Stanford University, under the supervision of Prof. Stephen W. Tsai. During his Ph.D. program, worked in the Advanced Ducted Propulsor program at Pratt & Whitney in the summer of 1995. Returned to Stanford Aero & Astro Department as visiting scholar from 2007 to 2009. Held the position of Associate Professor at the UFMG and was member of its Center for Aeronautical Studies (CEA) for 20 years. After a brief period as CEO of the consulting company Aero & Astro, returned to the academia as a Professor at the Department of Mechanical Design at UNICAMP (State University of Campinas). Returned to UFMG holding a full professor position (Professor Titular) at the Department of Structural Engineering two years later. After a one-year term as visiting scholar in the Department of Aeronautical and Vehicle Engineering at the Royal Institute of Technology (KTH) in Stockholm (Sweden), was back to the full professor position at UFMG. Recently, transferred back to the Department of Mechanical Engineering to support the Aerospace Engineering course. Develops research mainly on composites failure and life prediction, structural health monitoring, stress analysis, fatigue and fracture. Work as part of Prof. Steve Tsai's global group on the research topic of using of invariants and non-conventional laminates (Double-Double) for more efficient design and manufacturing of composite laminates.