Experimental study of hydrogen embrittlement properties in metallic materials using acoustic emission and digital image correlation
[Objective]The"Blue Book on Infrastructure Development of China's Hydrogen Energy Industry(2016)"highlights that a key mid-term goal(2020-2030)for the development of China's hydrogen energy industry is to demonstrate the application of hydrogen-doped natural gas pipeline transportation technology.This initiative will pave the way for the transition into a carbon-neutral"hydrogen energy era."At present,while China's natural gas pipeline transportation technology has matured,the issue of hydrogen embrittlement in metal materials,resulting from the addition of hydrogen for transportation,remains unresolved.Traditional methods for determining hydrogen embrittlement performance primarily rely on static measurement techniques,which lack a combination of static and dynamic measurement methods to assess hydrogen embrittlement performance from the perspective of its evolution process.[Methods]To address this gap,our experiment employs a simulation of the hydrogen environment encountered by pipeline steel during the hydrogen storage process in pipelines.This is achieved through mechanical axial tension,following the electrochemical hydrogenation of X80 pipeline steel.The testing is divided into two parts:hydrogen concentration testing and dynamic tensile testing of the hydrogen specimens.Digital image correlation(DIC)technology plays a crucial role in assessing the static parameters related to the hydrogen embrittlement performance of hydrogen-filled specimens.These parameters include the strain distribution,elongation,cross-sectional shrinkage,and hydrogen embrittlement sensitivity coefficient.The dynamic parameters of the material hydrogen embrittlement performance under different diffusion hydrogen concentrations can be derived by combining the peak time-domain distribution of the acoustic emission counting rate.Both acoustic emission and DIC technology can achieve full dynamic testing of the entire tensile damage evolution process during the experiment.[Results]The experimental results show the following:1)Analysis of hydrogen embrittlement performance measurement data reveals that the yield strength of samples undergoes significant changes with different hydrogen charging durations.Specifically,after 5 h of hydrogen charging treatment,the yield strength decreased by 27.4%.Furthermore,as the hydrogen charging time increases,the elongation and cross-sectional shrinkage of the sample continue to decrease,accompanied by a notable increase in the hydrogen embrittlement sensitivity coefficient.2)Dynamic DIC measurement results highlight that the maximum strain area of specimens subjected to 3-5 h of hydrogen charging significantly exceeds that of specimens either uncharged or charged for just 1 h.An increase in the maximum strain area indicates an increase in the material deformation area.3)Acoustic emission monitoring data on hydrogen embrittlement evolution reveal that the time-domain distribution of the peak acoustic emission counting rate reflects the degree of evolution of microcracks and dislocations within the material.As the hydrogen charging time is prolonged,the occurrence of peak impact counts tends to occur earlier.This indicates that a higher hydrogen concentration accelerates the development of internal dislocations,crack propagation,and other phenomena within the material.[Conclusions]This experiment has successfully established a dynamic parameter-testing platform for assessing the hydrogen embrittlement performance of metal materials after hydrogen charging by combining DIC and acoustic emission technologies.Using static parameters such as elongation and hydrogen embrittlement sensitivity coefficient,as well as dynamic parameters such as the peak time-domain distribution of acoustic emission ringing counts and equivalent strain cloud maps,allows for the delineation of the relationship between hydrogen embrittlement performance and hydrogen diffusion concentration in X80 steel.In the teaching process,the system setup,application of acoustic emission technology,and collection,analysis,and processing of experimental data elevate students'theoretical knowledge and enhance their practical skills.This hands-on approach effectively bridges theory with practice,fostering students'problem-solving capabilities.Moreover,it provides strong assistance to students interested in exploring hydrogen energy storage and transportation in the future.
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