As a typical welding structure, the girth weld of high-grade pipelines has obvious heterogeneity. Therefore, the axial mechanical properties of girth weld materials cannot be accurately tested, and the safety evaluation of the girth weld of the pipeline is seriously affected. Based on MATLAB-PYTHON-ABAQUS co-simulation, an optimization inversion method of the material stress-strain constitutive relationship in the weld zone of the high-grade pipeline is proposed in this paper. Four groups of uniaxial tensile tests with different notch sizes are carried out, and the load-displacement curves of each specimen are obtained. The true stress-strain constitutive relationship of the weld zone material is obtained by the Bayesian regularization back propagation (BRBP) neural network and the Grey wolf optimizer (GWO). The accuracy of the constitutive relationship is fully verified by the test data, and the relative error is less than 1%. In addition, taking the weld material of the oil and gas pipeline as an example, this paper proposes a universal design method of specimen size with a notch. The proposed method is convenient for researchers in different fields to measure the stress-strain constitutive relationship of different materials. It is worth mentioning that the inversion method proposed in this paper is also applicable to the measurement of the stress-strain constitutive relationship of homogeneous metallic materials in a large strain range. The proposed inversion method can provide an accurate stress-strain constitutive relationship for the safety evaluation of girth welds of high-grade pipelines.

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