Deciphering tensile fatigue behavior of UHPFRC using magnetoscopy, DIC and acoustic emission

To explore the governing mechanism underlying the tensile fatigue behavior of Ultra-high Performance Fiber Reinforced Cementitious Composites (UHPFRC), this study tested eight specimens using four advanced non-destructive measurement techniques. First, magnetoscopy is conducted on each specimen to determine the local fiber orientation and volume. Afterward, seven specimens are statically preloaded to the tensile strain of 1.5 ‰, identified as the typical maximum strain of UHPFRC in structural applications; while one specimen to the strain of 0.19 ‰, within the tensile elastic domain. During testing, the specimen response is monitored using digital image correlation and acoustic emission, in addition to displacement transducers. All specimens show similar evolution of fatigue deformation, characterized by three development stages. It is found that the local fiber orientation governs the fatigue deformation behavior. Fatigue deformation concentrates in low fiber orientation zones and fatigue fracture always occurs at the zone with lowest fiber orientation coefficients. The acoustic emission measurement, represented by cumulative energy curve and Ib-values, can appropriately characterize specimen damage degree and distinguish cracking patterns.