Carbon fibers were employed to reinforce the modified epoxy resins by flexibilizer to enhance the overall. mech. properties, the tensile strength, modulus, impact strength, fracture toughness test at both 77 K and at room temperature were examined for carbon fiber reinforced composites. At last section finite element simulation by ANSYS-13 was analyzed for crack propagation anal. of unidirectional laminates used for exptl. by two methods-(a) Double cantilever beam (b) Single edge notch bending (J-Integral).