Cyclic tension and compression piezoresistivity of carbon nanotube/vinyl ester composites in the elastic and plastic regimes

The piezoresistive behavior of multi-walled carbon nanotube/vinyl ester composites tested under a low number of cycles and different levels of applied strain is investigated for specimens loaded in axial tension and compression. Since the vinyl ester thermosetting matrix is brittle in tension but ductile in compression, the piezoresistive behavior of the composite material is linear and reversible in tension for all levels of applied strain, but it is nonlinear and non-monotonic in compression. In compression, the reversibility of the electrical resistance upon unloading depends on the level of strain attained during loading, and the permanent changes of electrical resistance which occur after matrix yielding are correlated to matrix irreversible damage.