NHIGInvestigating Failure Mechanisms in Historical and Modern Wrought Irons During Tensile Testing with Acoustic Emission Monitoring and Imaging
Kutsi Akcicek, Jiaxu Zuo, Heather Viles, and Sinan Acikgoz
Department of Engineering Science, University of Oxford, Oxford, UK; School of Geography and the Environment, University of Oxford, Oxford, UK
ABSTRACT
Wrought irons from the 14th (Salisbury Cathedral), 18th (Blenheim Palace), and 20th (Topp & Co., recently re-rolled) centuries are subjected to tensile testing. Failures are investigated using acoustic emission (AE) data, digital image correlation (DIC) strain measurements, post-mortem scanning electron microscopy (SEM), and micro-computed tomography (micro-CT). Analysis of the AE results using principal component analysis and DBSCAN clustering identified three major failure mechanisms, differentiated by the signal’s peak frequency. By analysing the datasets comparatively, three mechanisms are identified and attributed to specific frequency ranges: plastic deformation (35–87 kHz), debonding (125–156 kHz), and fracture (197–298 kHz). The modern specimens exhibited ductile failure, with post-yield behaviour characterised by plastic deformations. In contrast, the historical irons exhibited defect-driven failure, characterised by local strain concentrations dominated by debonding and fracture events. Visual inspections and micro-CT segmentation analyses demonstrated that the failure events were due to the presence of transverse slags, oxide products, and voids. The influence of these defects is systematically evaluated to provide new insight into how macro-mechanical properties are influenced by micro-mechanical failure mechanisms in three different wrought irons.
In-situ acoustic emission monitoring of accelerated corrosion of wrought irons
Kutsi Akcicek 1) , Sinan Acikgoz 1) and Heather Viles 2)
1) Department of Engineering Science, University of Oxford, Oxford, United Kingdom 2) School of Geography and the Environment, University of Oxford, Oxford, United Kingdom
ABSTRACT
Wrought iron bars, with attached waterproofed acoustic emission (AE) sensors, were subject to accelerated degradation in a corrosion chamber. During the transition from the wet to dry stages of the sample, a significant rise in AE hits was observed. Conversely, in fully dry or wet stages, fewer AE hits were detected. Based on the AE activity between transition stages, the results support existing theories of atmospheric corrosion of iron and the significance of wet to dry cycles in this process. Waterproofing of sensors for in-situ corrosion studies has also shown to be viable without causing damage to the sensor itself.
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