The work described here has been carried out to obtain a better understanding of the tooth rootudcracking failure mode of timing belts. Previous work has demonstrated the close dependence of this on theudtooth deflections of fully meshed teeth, generated by torque transmission, but has not considered theudadditional distortions generated in the partially meshed conditions at entry to and exit from a pulley groove.udApproximate compatibility and constitutive equations are combined with a rigorous consideration of toothudequilibrium in partial meshing to show how bending moments are generated at both exit from a drivenudpulley and entry to a driving pulley. Experimentally determined belt lives correlate very well with audcombined measure of fully meshed tooth strain and strain due to bending at entry or exit. The analysis alsoudshows that this strain measure reduces with increasing belt tooth stiffness, confirming the importance of audhigh tooth stiffness for a long belt life. Tooth force variations through the partial meshing cycle have alsoudbeen predicted and compared with measurements obtained from a special strain gauge instrumented pulley.udA greater pulley rotation than is predicted is required for a belt tooth to seat in a pulley groove. There isudroom for improvement in the modelling
展开▼
