Recovery stress, bond resistance, and stiffness to slip of crimped SMA fibers with considering geometric variation

Bond resistance is critical for reinforcing fibers in cementitious materials. Recently, crimped shape memory alloy fibers (SMA) have been raised as candidates for providing abundant benefits such as improved strength, enhanced durability, and crack closing. This study aimed to examine the influence of wave-depth and wave-length of crimped SMA fibers on their bond behavior. The crimped fibers in this study were categorized in four groups based on the wave-length. Each group had four types of fibers that considered the ratio of wave-depth to wave-length (DLR). Thus, a total of sixteen types of fibers were prepared with variations in wave-length and wave-depth. The tensile test used bare crimped SMA fibers, while the pullout tests used half dog-bone specimens. After the tests, the finite element model was used to evaluate the interaction parameters that were difficult to measure in the experience test. The results showed that the fibers with the smallest wave-length showed the largest maximum bond resistance in the same dept-to-length ratio (DLR) group, and that values decreased with an increasing wave-length. In addition, the smallest wave-length fibers demonstrated the most effective stiffness. Furthermore, the finite element analysis discovered that the geometric friction coefficients of the crimped SMA fibers were affected significantly by the geometric variation. The longer wave-length fiber revealed the larger estimated frictional coefficient.