Condition Assessment and Monitoring of Marine Ironware Based on Metal Magnetic Memory Technology:a Case Study on Iron Relics from Nanhai Ⅰ Shipwreck
To assess the preservation status of the iron relics from the Naihai Ⅰ shipwreck,metal magnetic memory technology was used to conduct a 4-channel dual-component line scan on iron bar samples made of wrought steel and a 4-channel single-component surface scan on the iron pot fragment samples made of hypereutectic white cast iron.The preservation status of iron bars placed in the atmospheric environment for 3 years with and without conservation was compared.Metal magnetic memory testing results are in good agreement with the X-ray imaging results.Metal magnetic memory indicates the location of cracks and corrosion development zones and effectively detects the stress concentration zones of the marine ironware.In risk areas,the basic characteristics of magnetic memory data are as follows:(1)the tangential component reaches the extreme value,and the direction of the normal component of the magnetic field intensity changes;(2)the gradient value of the magnetic field intensity is high and exceeds four times the average value of the detected section.The quantitative assessment parameters of the degree of risk areas are as follows:(1)magnetic memory signal characteristics,such as the average value,maximum value,peak-valley value of the magnetic field intensity,and magnetic field gradient(G);(2)stress concentration coefficient m=Gmax/Gave.The larger the quantitative assessment parameters,the higher the degree of risk.Magnetic memory technology offers an early warning for the occurrence and development of diseases of iron relics,providing a convenient and effective means for the assessment and monitoring of the preservation status of ironware out of water,and the safety monitoring and effectiveness assessment of the conservation and restoration process,which provides a powerful support for the conservation of iron cultural relics.
metal magnetic memoryiron cultural relicmarine ironwareNanhai Ⅰ shipwrecknon-destructive testingX-ray imaging
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