铁道建筑

铁路桥梁、雨棚等大跨度钢结构中，高强度螺栓连接是重要受力部位，其在低温环境下的强度变化和断裂行为对连接安全具有重要影响。为研究10.9级高强度螺栓在低温下的静态拉伸性能，本文以M16高强度螺栓加工圆棒拉伸试件，开展了20℃、0℃、-20℃和-40℃四种温度工况下的单轴拉伸试验，并分析了应力–应变关系、力学性能指标、静态韧性以及宏微观断口形貌。结果表明：随着温度降低，试件屈服强度和抗拉强度整体提高，-40℃时分别较20℃提高约5.76%和5.07%，表现出一定低温强化效应；弹性模量随温度变化较小，而断裂应变、断后伸长率和断面收缩率在低温下有所降低，说明试件断裂前塑性变形能力减弱。静态韧性分析表明，-40℃时试件静态韧性较常温下降约19.5%，低温削弱了材料断裂前的吸能能力。断口形貌分析显示，20℃和0℃下试件断口以纤维区、剪切唇和韧窝等延性断裂特征为主；当温度降至-20℃及以下时，放射状纹理、局部平坦区、微裂纹和准解理特征逐渐增多，断裂方式由延性断裂向韧脆混合断裂转变，-40℃时脆性断裂倾向显著增强。基于试验结果，建立了以20℃强度为基准的归一化线性温度修正公式，屈服强度和抗拉强度预测精度较高；结合Q690和Q960高强钢文献数据对比，表明该修正方法对高强钢低温强度变化趋势同样具有一定适用性，也证明了所提方法的合理性。研究结果可为铁路雨棚钢结构高强度螺栓连接在低温环境下的性能评估和强度指标修正提供参考。

In large-span steel structures such as railway bridges and station canopies， high-strength bolted connections are important load-bearing components， and the strength variation and fracture behavior of such connections at low temperatures directly affect structural safety. To investigate the static tensile properties of Grade 10.9 high-strength bolts at low temperatures， M16 bolts were machined into round bar specimens and tested at 20°C， 0°C， -20°C， and -40°C. The stress–strain curves， mechanical properties， static toughness， and macro- and microscopic fracture morphologies were analyzed. The results show that the yield strength and ultimate tensile strength increase with decreasing temperature. At -40°C， the yield strength and ultimate tensile strength increase by 5.76% and 5.07%， respectively， compared with those at 20°C， indicating a low-temperature strengthening effect. The elastic modulus changes slightly with temperature， while the fracture strain， elongation after fracture， and reduction of area decrease at low temperatures， indicating a reduction in plastic deformation capacity before fracture. The static toughness at -40°C decreases by about 19.5% compared with that at room temperature， showing that low temperature weakens the energy absorption capacity before fracture. Fracture morphology analysis shows that the fracture surfaces at 20°C and 0°C are mainly characterized by ductile features， including fibrous zones， shear lips， and dimples. When the temperature decreases to -20°C and below， radial patterns， local flat regions， microcracks， and quasi-cleavage features increase， and the fracture mode changes from ductile fracture to ductile–brittle mixed fracture. At -40°C， the brittle fracture tendency becomes more obvious. Based on the test results， a normalized linear temperature correction formula with the strength at 20°C as the reference value was established， and the predicted yield strength and ultimate tensile strength showed good accuracy. Comparison with Q690 and Q960 high-strength steel data from the literature indicates that the correction method is also applicable to the low-temperature strength variation trend of high-strength steels， demonstrating the rationality of the proposed method. The results can provide a reference for low-temperature performance evaluation and strength index correction of high-strength bolted connections in railway canopy steel structures.