Abstract The girth-weld joint of a pipeline can be divided into three parts: base metal, heat affected zone, and weld metal. This study investigates the local mechanical properties of X80 and Q235 girth-welded joints. Microscopic observations and micro-hardness measurements were carried out, and it was observed that the metallographic structure and hardness gradients of each region were evidently different. Tensile tests of the base metal and girth-welded joint were conducted using digital image correlation (DIC) technology, and the strain distributions on the specimens and local true stress-strain curves of different regions were obtained. A parameter calculation method for the Ramberg-Osgood model considering strain was proposed. Subsequently, model parameters and mismatch coefficients were obtained and analyzed, respectively. The yield strength and hardening property of welded joints can be determined using this method, which is of great significance in calculating the strength-matching relationship of girth-welded joints. Finite element analysis based on the Gurson-Tvergaard-Needleman model was used to study the strain field and local stress-strain curves of girth-welded joints. The results obtained by the finite element analysis were in line with the results obtained by the DIC method. This demonstrates the feasibility of the simulation method and that the proposed material model is reasonably accurate in predicting the stress-strain response.

中文翻译：

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基于数字图像相关和数值模拟的X80和Q235环焊接头局部真实应力应变响应确定

摘要 管道环焊缝可分为母材、热影响区和焊缝金属三部分。本研究调查了 X80 和 Q235 环焊接头的局部机械性能。进行了显微观察和显微硬度测量，观察到各区域的金相组织和硬度梯度存在明显差异。采用数字图像相关（DIC）技术对母材和环焊缝进行拉伸试验，得到试件的应变分布和不同区域的局部真实应力-应变曲线。提出了一种考虑应变的Ramberg-Osgood模型的参数计算方法。随后，分别获得并分析了模型参数和失配系数。利用该方法可以确定焊接接头的屈服强度和硬化性能，对计算环缝焊接接头的强度匹配关系具有重要意义。基于Gurson-Tvergaard-Needleman模型的有限元分析用于研究环焊缝的应变场和局部应力-应变曲线。有限元分析得到的结果与DIC方法得到的结果一致。这证明了模拟方法的可行性，并且所提出的材料模型在预测应力应变响应方面相当准确。基于Gurson-Tvergaard-Needleman模型的有限元分析用于研究环焊缝的应变场和局部应力-应变曲线。有限元分析得到的结果与DIC方法得到的结果一致。这证明了模拟方法的可行性，并且所提出的材料模型在预测应力应变响应方面相当准确。基于Gurson-Tvergaard-Needleman模型的有限元分析用于研究环焊缝的应变场和局部应力-应变曲线。有限元分析得到的结果与DIC方法得到的结果一致。这证明了模拟方法的可行性，并且所提出的材料模型在预测应力应变响应方面相当准确。