Strain imaging of corroded steel fasteners using neutron transmission imaging

Abstract

Failures in bolted structural connections have caused in the past the collapse of various steel structures exposed to weather conditions, including wind turbine towers, oil and gas platforms, and bridges. Corrosion and the resulting loss of preloaded tension in the bolted connection were the root cause of such catastrophic failures in many cases. However, it is still not fully understood how strain is re-distributed in corroded bolted connections, nor how different factors influence the redistribution. Measuring non-destructively the strain inside the assembly has been the main obstacle. To this end, in this paper, we employed energy-resolved neutron transmission imaging and we present strain maps in corroded bolted connections for the first time. We examined and compared the strain distribution measurements in corroded and non-corroded assemblies for different bolt-tightening techniques. The specimens under investigation were artificially corroded without introducing any additional mechanical loads. The resulting strain maps illustrate how strain is re-distributed and provide insight into the influence of the bolt-tightening method.