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

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.