  Composites of direct-spun carbon nanotube (CNT) mats and epoxy are
manufactured and tested in order to determine their mechanical and electrical
properties. The mats are spun directly from a floating catalyst, chemical
vapour deposition reactor. The volume fraction of epoxy is varied widely by
suitable dilution of the epoxy resin with acetone. Subsequent evaporation of
the acetone, followed by a cure cycle, leads to composites of varying volume
fraction of CNT, epoxy and air. The modulus, strength, electrical conductivity
and piezoresistivity of the composites are measured. The CNT mats and their
composites exhibit an elastic-plastic stress-strain response under uniaxial
tensile loading, and the degree of anisotropy is assessed by testing specimens
in 0{\deg}, 45{\deg} and 90{\deg} directions with respect to the draw direction
of mat manufacture. The electrical conductivity scales linearly with CNT volume
fraction, irrespective of epoxy volume fraction. In contrast, the modulus and
strength depend upon both CNT and epoxy volume fractions in a non-linear
manner. The macroscopic moduli of the CNT mat-epoxy composites are far below
the Voigt bound based on the modulus of CNT walls and epoxy. A micromechanical
model is proposed to relate the macroscopic modulus and yield strength of a CNT
mat-epoxy composite to the microstructure.
