AN INVESTIGATION OF NECKING INSTABILITY IN FIBER-REINFORCED POLYPROPYLENE

Thermoplastic composite materials hold considerable promise for increa sed use in low cost high volume applications because of the potential for processing by solid phase forming. Unfortunately, because of the w ide variety of such materials, inherent variability in properties, and complex temperature and strain rate dependence, large strain behavior of these materials has not been well characterized Of particular impo rtance is failure during processing due to localized necking instabili ty and it is this phenomenon that is the primary focus of this study. Large strain behavior under uniaxial tension is characterized over a r ange of temperatures and strain rates, and a simple linear viscoelasti c model is Pt to the observed data, The strain rare and temperature de pendence is then used to predict limiting tensile strains based on Mar ciniak imperfection theory. Excellent correlation was obtained between theory and experiment and the results are summarized in maps of formi ng limit as a function of temperature and strain rate, These results s uggest that excellent solid phase formability may be obtained for the materials tested under properly chosen conditions.