Dynamic 3D effects of single fiber tensile break within unidirectional composites including resin plasticity, residual stress, interfacial debonding and sliding friction

To study the dynamics of a single fiber tensile break within an S-Glass/epoxy composite and the associated effects of stress wave propagation in the fibers, interface and matrix, a 3D micromechanical Finite Element (FE) model with a hexagonal packing of parallel fibers is developed. The effects of a dynamic fiber break on energy dissipation associated with resin plasticity and interface debonding using cohesive traction laws are included. The 3D FE model also incorporates process-induced residual stresses that induces radial compression at the fiber-matrix interface due the mismatch in CTE and Poisson’s ratios between the fiber and matrix. During dynamic fiber failure where interface debonding occurs, radial compressive residual stresses lead to additional frictional energy dissipation in the debond region of the interface. A map of the dynamic stress concentration factor (SCF) values on the surface (along the axial as well as circumferential directions) of the fibers which are neighboring the fiber break is generated. A stability criterion based on an energy balance between elastic strain energy released by the fiber and energy dissipation (resin plasticity, interphase debonding and frictional sliding) is established to predict maximum fiber strength that initiates unstable debonding of the interface characteristic of axial splitting of the unidirectional composite loaded in tension. The FE modeling results also indicate that the dynamic fiber break introduces strain rates on the order of 10 6 /s in the fiber and matrix, and up to 10 12 /s in the interphase.