A Viscoelastic Constitutive Model for the Creep Response of Polyurethane Rubber (Progress Report to the NSWC, Carderock for the Period September, 1996 to December, 1997) Vincent Rouiller Gregory B. McKenna U.S. DEPARTMENT OF COMMERCE Technology Administration Polymers Division National Institute of Standards and Technology Gaithersburg, MD 20899-0001 QC 100 . U56 NO. 61 77 1998 NIST