Multiscale shear failure mechanisms within a prestrained composite

The elastic fiber prestressing (EFP) technique has been developed to balance the thermal residual stress generated during curing of a polymeric composite, where continuous fibers were prestretched under either constant stress or constant strain throughout the curing process. The tension was only removed after the resin was fully cured. It has been demonstrated that EFP is able to enhance the shear properties of the composite, while the underlying mechanics is still unknown. Here, we investigated the multiscale shear failure mechanisms induced by the EFP within a carbon composite. A bespoke biaxial fiber prestressing rig was developed to apply biaxial tension to a plain‐weave carbon prepreg, where the constant strain‐based EFP method was employed to produce prestrained composites with different prestrain levels. Effects of EFP on macro‐scale shear failure were subsequently characterized through mechanical tests and micro‐morphological analysis. Both the micro‐ and meso‐scale representative volume element (RVE) finite element models were established and experimentally verified. These were then employed to reveal the underlying stress evolution mechanics induced by EFP. It is found that EFP would improve the shear performance of a composite by enhancing the fiber/matrix interfacial bonding strength. This attributes to the elastic strain recoveries of the prestrained fibers locked within a polymeric composite, which generate compressive stresses to counterbalance the external loading. The multiscale shear failure mechanisms were then proposed. These findings are expected to facilitate structural design and application of the EFP for aerospace composites.Highlights Biaxial tension is applied to produce prestrained woven composite. Prestrain effects on microstructural stress evolution mechanics are revealed. Multiscale shear failure mechanisms are proposed for prestrained composites.