Q345冷成型钢高温力学性能试验研究

冷成型钢高温材料特征指标是进行冷成型钢结构抗火设计及数值模拟的重要参数。现有的钢材高温材性数据大多基于稳态试验方法得到，而瞬态试验方法较前者更接近实际火灾情况。利用MTS810试验系统对1.5mm厚Q345冷成型钢进行了高温力学性能试验研究，将瞬态、稳态试验结果进行对比分析。试验结果表明： Q345冷成型钢瞬态试验抗拉强度折减系数在430～700 ℃时普遍高于稳态试验结果，二者相对误差27%～57%；超过100 ℃，Q345冷成型钢瞬态试验高温弹性模量明显低于稳态试验结果，相对误差17%～156%；450～550 ℃时，相同温度、应变水平下，Q345冷成型钢瞬态试验应力-应变曲线弹塑性阶段应力值明显高于稳态试验应力值，导致瞬态试验高温屈服强度高于稳态试验结果，相对误差28%～40%。通过数值拟合给出Q345冷成型钢高温材性折减系数及本构关系表达式，表达式与试验结果基本吻合。

Experimental investigation on mechanic behavior of Q345 cold-formed steel material at elevated temperatures

The mechanical properties index of cold-formed steel at elevated temperatures are the major parameters not only for the fire protection design,but also for numerical analysis of cold-formed steel structures.Previous research on the material behavior of steel at elevated temperatures mainly focused on the steady state test.However,the transient state test is more realistic in simulating the actual fire conditions than steady state test.This paper presents the details of an experimental study on Q345 cold-formed steel with a thickness of 1.5 mm at elevated temperatures.A careful comparison was carried out between the results by transient and steady state tests.It shows that reduction factors of ultimate strength of Q345 cold-formed steel by transient state test are higher than those by steady state test at temperatures between 430 ℃ and 700 ℃,the relative error ranges from 27% to 57%.Elastic modulus of Q345 cold-formed steel by transient state test are lower than those by steady state test beyond 100 ℃,the relative error is between 17% and 156%.At the elastic-plastic region of stress-strain curves and temperatures between 450 ℃ and 550 ℃,the stresses of Q345 steel by transient state test are much bigger than those by steady state test under the same conditions of temperatures and strains,resulting in a much higher yield strength with relative error between 28% and 40%.Then,the calculation expressions of both reduction factors of material behavior and stress-strain curves at elevated temperatures are developed by numerical fitting method.The proposed expressions are in good agreement with test results.