Failure analysis and the effect of material properties on the screw pull-out behaviour of polymer composite sleeper materials

The low pull-out resistance and the limited understanding of how the sleeper materials affect the screw pull-out behaviour is one of the key reasons for the lack of confidence in the wide adoption of available composite railway sleepers. In this study, the pull-out strength and the failure analysis through hole microstructure of different sleeper technologies including timber, synthetic composite, recycled plastic and Particulate Filled Resin sleepers were investigated. Also, the effect of material properties on the screw pull-out strength and failure behaviour was determined. The results showed a statistically significant difference in pull-out strength among different sleeper technologies and the paired samples test revealed a high correlation between the pull-out strength and the shear strength of the materials. A simplified prediction model was developed to predict the pull-out resistance for railway sleepers based on shear strength of the composite sleepers. This proposed equation shows a better agreement with the experimental results than an existing theoretical equation regardless of different pull-out behaviour.