Determination of Impact Stresses in an Automotive Chain Drive Component

A photoelastic stress analysis technique has been used to determine the contact stresses in an automotive chain drive tensioner. The tensioner in normal operation is subject to high magnitude, short duration impact stresses. These stresses are known to cause surface damage, wear, and surface pitting. In order to adequately design the drive system layout, a means for stress quantification is needed. A replica tensioner was made from epoxy resin and tested in a variety of configurations. A simple model has been created to relate the chain link load to the resulting tensioner sub-surface stress field. This model has been used to correlate the observed and predicted location of isochromatic fringes, and hence to evaluate the chain link load from the photoelastic fringe pattern. A series of static load tests were performed to calibrate the apparatus. The tensioner specimen was then assembled in a chain drive test facility. The apparatus was used to run a chain under realistic engine loading conditions. A high-speed digital camera was used to capture sequences of photoelastic images, which were then used to find the impact loading caused by individual links in the chain. Once the load was determined the contact model was used to determine the magnitude and location of the resultant peak stresses. Measured impact stresses were found to be several times higher than those which would have been calculated from a static analysis.