A carbon/epoxy single fiber test specimen is subjected to a uniaxial tensile stress that is increased until the fiber breaks up into pieces having a length of \(0.625 \mathrm{~mm}\). If the fiber has a diameter of \(0.01 \mathrm{~mm}\), a longitudinal modulus of \(240 \mathrm{GPa}\), and an ultimate tensile strength of \(2.5 \mathrm{GPa}\), what is the interfacial shear strength of the specimen? If the composite longitudinal modulus is \(80 \mathrm{GPa}\), what applied composite stress is required to produce the condition above?