Real-time monitoring of deformation of large structure parts is of great significance and the deformation of such structure parts is often accompanied with the change of curvature. The curvature can be obtained by measuring changes of strain, surface curve and modal displacement of the structure. However, many factors are faced with difficulty in measurement and low sensitivity at a small deformation level. In order to measure curvature in an effective way, a novel fibre Bragg grating (FBG) curvature sensor is proposed, which aims at removing the deficiencies of traditional methods in low precision and narrow adjusting. The sensor combines two FBGs with a specific structure of stainless steel elastomer. The elastomer can transfer the strain of the structure part to the FBG and then the FBG measures the strain to obtain the curvature. The performed simulation and experiment show that the sensor can effectively amplify the strain to the FBG through the unique structure of the elastomer, and the accuracy of the sensor used in the experiment is increased by 14% compared with that of the FBG used for direct measurement.
This paper presents results obtained from a laboratory investigation conducted on material from a pressure vessel after longterm operation in the oil refinery industry. The tested material contained structural defects which arose from improper heat treatment during steel plate manufacturing. Complex tensile tests with acoustic emission signal recording were conducted on both notched and unnotched specimens. The detailed analysis of different acoustic emission criteria allowed as to detect each stage of plastic deformation and microstructural damage processes after a long-term operation, and unused carbon steels during quasi-static axial tension testing. The acoustic emission activity, generated in the typical stages of material deformation, was correlated by microscopy observations during the tensile test. The results are to be used as the basis for new algorithms for the assessment of the structural condition of in-service pressure equipment.