Abstract
In a strain controlled low cycle fatigue test it is customary to use a contacting extensometer. However the extensometer can cause premature fracture at the contact points by inducing localized plastic deformation, particularly in a soft metal such as a lead-tin solder. In order to avoid this problem, a non-contacting, digital-image measurement system has been developed to measure the displacement of the specimen gage length during a cyclic loading. The capability of this system for strain-controlled fatigue testing was studied in preliminary experiments, and the effect of variables in the digital image measurement system on the accuracy and the reliability were established. Low cycle fatigue tests on three solder materials at 20℃ were then carried out using this system. The solders were: Ag-Sn eutectic solder (3.5Ag/96.5Sn), Sn-Pb eutectic solder (63Sn/37Pb) and Sn-Pb solid solution solder (5Sn/956Pb). The results confirmed that this system was capable of measuring the displacements in strain-controlled fatigue tests.
