Fatigue Performance of Piezoelectric Weigh-in-Motion Sensors

The results of the laboratory evaluation of the fatigue characteristics of the piezoelectric weigh-in-motion sensors of two manufacturers, Vibracoax (VC) and Measurements Specialties Incorporated (MSI), are presented. For each manufacturer, two sensor types were tested, one factory encapsulated and the other bare. The test was conducted in an accelerated fashion using a servo-hydraulic loading system, operated in a loadcontrolled fashion at a frequency of 4 Hz. Three loading conditions were tested: dry under a contact pressure of 860 kPa, wet under a contact pressure of 860 kPa, and dry under a contact pressure of 200 kPa. For each of these loading conditions, a concrete slab was built to allow simultaneous loading of sets of four sensors, one of each of the types evaluated. The results were plotted in the form of voltage output versus the number of load applications. Regression relationships were fitted to the data of maximum voltage versus the number of loading cycles. Under the dry conditions and at 860 kPa contact pressure, the MSI sensors exhibited a decrease in voltage output as the number of loading cycles increased, whereas the VC sensors exhibited an increase in voltage as the number of loading cycles increased. Under wet conditions, the bare sensors of both manufacturers exhibited considerably shorter lives (i.e., voltage output reduced to zero) than the encapsulated ones. No fatigue-related peak voltage changes were found for the sensors under the 200 kPa contact pressure and dry conditions.