Tensile Creep and Creep Rupture of Continuous Strand Mat Polypropylene Composites

ABSIXACT: This paper describes an experimental study on the tensile creep behavior of a random continuous fiber mat reinforced polypropylene composite, commercially known as Azdel. A special experimental setup was designed and used to conduct these creep tests at 75 and 100°C with stress levels ranging from 30 to 60 percent of the tensile strength of Azdel. The test duration was 3,000 hours or the time to creep rupture response, whichever occurred first. A straight line on a semi-log plot adequately described the rela-tionship between the imposed stress and the creep rupture response time for the range of stress levels studied. Moreover, the estimated secondary creep mte was inversely related to the observed creep rupture response time. INTRODUCI'ION ELEcriNG COMPOSITE MATERIALS for long term applications at elevated S temperatures requires knowledge of their creep behavior. In creep tests, a constant stress is applied on the specimen and the strain is measured as a function of time. The increase in strain with time is known as creep. Depending on the stress level and ambient temperature, the specimen can also fail, thereby termi-nating the creep test. This fidure phenomenon is known as creep rupture and oc-curs at stresses much lower than the static tensile strength of the material. Creep behavior of composite materials has been studied only to a limited ex-tent, mainly due to the fact that continuous fiber composites in thermosetting ma-trices do not exhibit large creep strains at their use temperature 111. However, creep deformation may be relatively large if the fiber orientation is random and/or the matrix is a thermoplastic resin. There are a few reported studies on the creep characteristics of random fiber sheet molding compound (SMC-R) com-posites [2-3]. In these studies, the matrix was a thermosetting resin, such a