形状记忆合金智能混凝土电热驱动升温速率试验研究与分析

Research and analysis of electrothermally actuated heating rates of smart concrete beam embedded with Shape Memory Alloy

将形状记忆合金(Shape Memory Alloy,SMA)应用于混凝土结构中,利用SMA的形状记忆效应可以控制并恢复结构的变形,实现混凝土裂缝的主动修复。为提高SMA电热驱动升温速率,提出一种在SMA表面缠绕漆包线后再涂刷隔热胶的新型加热方法。通过SMA智能混凝土试件电热驱动试验和有限元瞬态热分析,研究分析升温速率、漆包线绝缘隔热方法以及温度场分布规律。试验结果表明,所提出的新型加热方法可以显著提高SMA升温效率,缩短加热激励时间;导热性能较差的隔热胶可以有效地减少传递给混凝土的热量,进而减轻温度变化对混凝土的不利影响,且隔热胶的隔热性能越好,混凝土温度变化程度越小;漆包线通电加热激励驱动SMA时,加热速率快,且漆包线通电电流强度远远小于SMA直接通电的电流强度;无黏结SMA混凝土试件梁内存在天然的空气隔热层,与有黏结SMA混凝土试件梁相比,采用相同的电热驱动方法和电流强度驱动SMA时,无黏结SMA混凝土试件梁的升温速率更快,且混凝土温度变化更小。有限元瞬态热分析结果表明,试件中混凝土各测点试验升温曲线与有限元计算升温曲线吻合较好,通电结束时,试件各测点的实测温度值与有限元计算温度值基本一致,最大相差2.5℃。研究成果可为SMA智能混凝土提供一种快速的电热驱动方法。

By applying Shape Memory Alloy(SMA)to concrete structures and utilizing the Shape Memory Effect(SME)of SMA to control and restore the deformation of the structure,active repair of concrete cracks can be achieved.To improve the electrothermally actuated heating rate of SMA,a novel heating method of wrapping enameled wires around the surface of SMA followed by the application of thermal insulation adhesive was proposed.Through electrothermal actuated tests of SMA smart concrete specimens and finite element(FE)transient thermal analysis,the heating rate,enameled wire insulation and thermal insulation method,and temperature field distribution were studied and analyzed.The test results show that the proposed novel heating method can significantly improve the SMA heating efficiency and shorten the heating excitation time.The insulation adhesive with poor thermal conductivity can effectively reduce the heat transferring to the concrete thereby reducing the adverse effects of temperature changes on concrete.The better the heat insulation performance of the insulation adhesive,the smaller the temperature variations of concrete.The heating rate is fast when the enameled wire is energized to drive the SMA,and the current intensity of the enameled wire energization is much less than that of the SMA direct energization.With the existence of a natural air insulation layer in the unbonded SMA concrete tested beam,the unbonded SMA concrete specimen has a quicker heating rate and less concrete temperature variation than the bonded SMA concrete specimen,when they were both driven by the same electrothermally actuated heating tests and current intensity.The results of the FE transient thermal analysis show that the test heating curve of the concrete at each measurement point in the specimen is in good agreement with the FE calculated heating curve.The measured temperature values of the specimen at each measurement point at the end of the energization are basically the same as the FE calculated temperature values,with a maximum difference of 2.5℃.The research results can provide a fast electrothermal driving method for SMA smart concrete.