Influence of fiber orientation on the high cycle tensile fatigue resistance of Ultra-High Performance Fiber Reinforced Cementitious Composites (UHPFRC)

This paper quantitatively studies the influence of fiber orientation on the high cycle tensile fatigue resistance of ultra-high performance fiber reinforced cementitious composites (UHPFRC) within and beyond elastic domain. Eight tensile fatigue tests and re-analysis of sixteen fatigue tests from a previous study are conducted, which have specimens statically preloaded to the strain from 0.19‰ to 0.5‰ and from 1.1‰ to 2‰, considered to be in the elastic and post-elastic domains in tension, respectively. For the eight fatigue tests, the local fiber orientation and dosage of each specimen are determined before testing using a magnetic probe. During testing, specimen behavior is characterized by displacement transducers, digital image correlation and acoustic emission. Based on the above, the fatigue endurance limit at 10 million cycles is determined to be about SUte,10%= 0.9 of the elastic limit tensile stress for UHPFRC within elastic domain. For UHPFRC preloaded beyond the elastic domain, the fatigue resistance decreases with increasing pre-applied strain and decreasing average fiber orientation (increasing average angle between fibers and principle tensile direction). With pre-applied strain from 1.1‰ to 2.0‰, the endurance limit may be taken as SUte,10%=0.60 to 0.65 for typical UHPFRC structures. Two original fatigue resistance models are proposed, which describe the relationship between average fiber orientation, number of cycles and maximum fatigue stress for UHPFRC within and beyond the elastic domain.