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Using trace to scale the properties of composite materials

 The traditional use of composites for laminates and components is based on unidirectional tape stacking.Generating an allowable design has become a huge undertaking; several knockdown factors such as barely visible impact damage [BVID],moisture absorption and delamination are also involved. In spite of all these negative aspects,composites have begun to be widely used[more than 50% of Boeing 787 and Airbus 350 structures]due to notable design and manufacturing improvements in recent years. The introduction of bi-angle non-crimp fabric composites,pioneered by Stephen W.Tsai [Standford University] and Michel Cognet [Chomarat], may represent a break-through, and a radical change in the way composite structures can be designed and manufactured.Different case studies are carried out with the aim of showing how scaling can help simplify and enhance the way composite structures can be designed and how C-Ply NCF can replace existing composite structures.

 Material selection is a crucial element in the design of composite structures. Different parameters have to be taken into account, such as stiffness, strength,property stability under varying operating conditions,weight,costs,and availability.In terms of stiffness, there are significant differences between the modules(E11,E22,G12);in addition,the stiffness of a given ply or laminate is strongly dependent on the axis orientation. In order to achieve a faster and finer comparison between different types of composite materials, it could be useful to have one or more scalars that can identify trace of the stiffness and failure criteria in strain space. For stiffness, there is a scalar,directly related with Mohr’s circles,which remains constant regardless of the fiber orientation-the trace-for which the theoretical framework is provided..

 Seven different composite materials were considered in order to compare different materials;the traces were normalized taking the maximum.

 As explained,scaling is not possible for E-glass/epoxy plies since the normalized curves do not match the ones taken as reference.The same invariance noticed in the case of a single ply can be shown for the in-plane trace and flexural trace.

 Analytical and experimental results for the structural efficiency of aerospace structures under compression and shear loads have demonstrated the mass saving potential of advanced composite panels to meet buckling requirements.Several analytical works are available on buckling of composite panels under combined loads. In most cases, the experimental results relate to uniaxial compression or shear only;very few papers report results where a combination of the two loads was applied.In real conditions,however,biaxial compression and shear load may be applied simultaneously to a panel. Theoretical analysis can predict the buckling load when combined loads are applied.

 

 

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