The time dependant, super-viscoelastic behavior of NiTi shape memory alloy fiber reinforced polymer matrix composites

The present work presents the development of a new quantitative model which predicts the time dependant mechanical behavior of viscid matrix composites reinforced by small volume fractions of continuous NiTi shape memory alloy fibers. The paper further compares example calculations and experimental measurements from a pseudo-elastic NiTi fiber reinforced viscoelastic polymer matrix composite subjected to an isothermal tensile cycle composed of a constant strain rate tensile loading followed by a constant stress rate tensile unloading. Upon loading, the composite exhibited a near linear tensile elongation until yielding was initiated by the NiTi reinforcement austenite to martensite transformation. The fiber transformation then continued while the matrix suffered viscoelastic yielding until the completion of loading. During unloading, the fiber exhibited a strong martensite to austenite shape recovery transformation while the matrix suffered an accelerated viscoelastic strain recovery. In summary, the NiTi fiber reinforced viscoelastic low density polyethylene matrix composite exhibits a form of large strain super-viscoelasticity characterized by large increases in strength, stiffness, and shape recovery energy relative to the homogeneous polymer matrix.