An Apparatus for Testing Static Fatigue at Sand Grain Contacts

Often referred to as aging, the time-dependent evolution of silica sand properties is particularly distinct after sand disturbance. A likely cause of this behavior is the process of time-delayed fracturing of microscopic features at grain surfaces in contact. This process is denoted as static fatigue or stress corrosion microcracking. An apparatus was constructed to test time-dependent behavior of contacts subjected to sustained loads. The device can measure displacements with a resolution of about 100 nm. The focus of the paper is on the device constructed and not on the process of static fatigue. The details of apparatus construction are presented in the paper, and challenges associated with measuring grain deflection owing to static fatigue at the contacts are discussed. The measurements are sensitive to changes in temperature and humidity and are affected by external vibration excitations. Example results are illustrated, the sources of possible measurement errors are debated, and the challenges of testing are discussed.