Time dependence of the mechanical properties of an immiscible polymer blend

Lifetime of a 35/65 PS/HDPE immiscible polymer blend, IMPB, railroad crosstie was investigated. Predictive techniques were developed to predict creep and stress relaxation behavior from short-term compressive stress-strain experiments, and predicted values were compared with experimental results. The weathering effect on the IMPB mechanical properties and the environmental benefits of replacing chemically treated wood crossties with IMPB crossties were investigated.; Creep and stress relaxation experiments were performed under conditions simulating the maximum lateral load acting on a crosstie on a Class 1 railroad, and spike pull out experiments were performed using cut spikes.; Cyclic uniaxial compressive creep experiments left nearly no residual strain remaining in the IMPB samples. Experimental results suggest the track gage will not widen more than 1/8 of an inch when IMPB crossties are utilized. Thus, creep and track gage widening do not limit the lifetime of IMPB crossties in track.; Uniaxial compressive stress relaxation experiments and spike pull out experiments conducted at various time intervals from the day of installation were performed to illustrate the similarity of a spike pull out force versus time from the day of installation curve and a stress relaxation curve. The force decreases exponentially with time, in both cases. Research determined that spike killing due to biological attack is irrelevant, and there is no evidence of spike killing on any IMPB crossties currently in track.; Predicted creep strain and stress relaxation were in good agreement with experimental data. A correlation is drawn between predicted long-term creep behavior for the IMPB and experimental creep behavior of polyethylene over 25 years. Theories developed for this work were determined reasonable and provide an alternative to performing long-term experiments.; Natural and accelerated weathering experiments indicated no degradation in IMPB mechanical properties. Accelerated weathering experiments indicated an increase in IMPB mechanical properties while those of creosote treated oak crossties decreased. The environmental study revealed a reduction in greenhouse gases emitted into the atmosphere by this material substitution.; Research suggests the current 50-year guarantee for this 35/65 PS/HDPE IMPB crosstie is conceivable and credible, and the possibility exists for IMPB crossties to last indefinitely in certain locations.