基于小冲杆试验的管道钢断后伸长率研究

STUDY ON PERCENTAGE ELONGATION AFTER FRACTURE OF PIPELINE STEEL BASED ON SMALL PUNCH TEST

断后伸长率是表征管材塑性的典型指标,管道局部如焊接接头处受尺寸限制无法开展单轴拉伸试验,需要借助微试样试验方法完成取样及测试。小冲杆试验作为一种微试样试验方法,能够用于获取多种力学性能参数。当前研究中,主要通过经验关联方法将载荷-位移曲线中最大位移、最大载荷对应位移及试样断后弧长等关键参量关联至材料断后伸长率。然而,上述方法对管道钢的适用性不明确,使其对管道钢材料无法直接应用。针对这一问题,首先讨论了上述基于不同特征参量的经验关联方法对管道钢的适用性,之后提供了一种断后弧长简化计算方法,并形成了适用于管道钢的基于断后弧长的经验关联公式。在此基础上,进行厚度效应修正,建立了基于小厚度试样确定管道钢材料断后伸长率的经验公式并进行可靠性验证。结果表明,基于断后弧长简化计算方法的经验关联公式确定的断后伸长率最大误差为5.08%,厚度效应修正公式对小厚度试样计算结果的最大误差为5.53%,证明建立的经验关联公式拟合效果良好且对管道钢具有良好的适用性,可为其他钢级管道局部区域断后伸长率的计算提供理论基础。

Percentage elongation after fracture is a typical index to characterize the plasticity of the pipe,and the partial size of the pipe such as the welded joint can not carry out a single⁃axis tensile test,and it is necessary to complete the sampling and testing with the help of micro⁃specimen test methods.As a micro⁃specimen test method,the small punch test can be used to obtain a variety of mechanical property parameters.In the current study,the key parameters such as the maximum displacement,the corresponding displacement of the maximum load and the arc length after fracture are correlated to the percentage elongation after fracture of the material mainly through the empirical correlation method.However,the applicability of the above method to pipeline steel is not clear,making it impossible to directly apply to pipeline steel materials.In view of this problem,firstly,the applicability of the above⁃mentioned empirical association method based on different characteristic parameters to pipeline steel was discussed,and then a simplified calculation method for arc length after fracture was provided,and an empirical association formula based on the arc length after fracture for the pipeline steel was formed.On this basis,the thickness effect correction was carried out,and the empirical formula for determining the percentage elongation of pipeline steel material after fracture was established based on small thickness specimens and the reliability was verified.The results show that the maximum error of the percentage elongation after fracture determined by the empirical association formula based on the simplified calculation method of arc length after fracture is 5.08%,and the maximum error of the thickness effect correction formula for the calculation result of small thickness specimen is 5.53%,which proves that the established empirical association formula has good fitting effect and good applicability to pipeline steel,which can provide a theoretical basis for the calculation of percentage elongation after fracture in the local area of other steel grade pipelines.