摘要:
耐候钢在使用过程中,会受到温度、碰撞、荷载等各类作用的影响,致使其力学性能发生改变。已有研究表明,腐蚀对耐候钢的力学性能影响显著,不容忽视。为获得Q235NH腐蚀后的拉伸性能,在35 ℃下,采用中性盐雾试验(浓度为(50±5)g/L、pH值为6.5~7.2的盐溶液)对Q235NH试件进行加速腐蚀,加速腐蚀时间分别为6,24,48,72,96 h,并对腐蚀后的试件进行拉伸试验研究,探明了Q235NH试件腐蚀形貌、拉伸断口、应力-应变关系曲线、以及力学性能参数变化规律,并对力学性能参数变化规律进行了算式拟合、对应力-应变关系进行了本构模型建立、对折减系数退化规律进行了分析。试验结果表明:1)腐蚀初期,仅出现局部腐蚀,随着腐蚀时间增加,锈蚀愈加明显,并伴有锈层脱落现象;试件的应力-应变关系曲线有明显屈服平台,腐蚀后Q235NH的应力-应变曲线均低于未腐蚀状态,屈服段有缩短的现象;随着腐蚀时间的增加,试件强度表现为先降低、后升高、再降低的趋势;引起这些现象的原因是耐候钢腐蚀后,其表面会形成保护性锈层,对基底有保护作用,随着腐蚀时间的增加,锈层吸附力增加,减缓了试件力学性能的下降。2)随腐蚀时间的增加,屈服强度、抗拉强度、屈强比及其折减系数随腐蚀时间的增加呈现出线性退化趋势,建立了屈服强度、抗拉强度、屈强比及其折减系数随腐蚀时间变化的线性退化关系。3)对二次塑流本构模型的强化阶段进行了β参数修正,得到修正的二次塑流本构模型可以很好地模拟腐蚀前后Q235NH的应力-应变关系,同时,对影响Q235NH的应力-应变关系曲线的形状参数k1、k2、k3进行分析,提出了Q235NH形状控制参数k2、k3的建议值、并得到了形状控制参数k1随时间变化的线性退化规律。通过对常态下Q235NH进行拉伸试验,得出相关参数,结合强度等随腐蚀时间折减规律及修正的二次塑流本构模型,可以推算材料腐蚀后力学性能折减情况。
Abstract:
In the process of using, wearthing steel will be affected by temperature, collision, load and other effects, resulting in changes in its mechanical properties. It has been shown that corrosion has a significant effect on the mechanical properties of weathering steel, which can not be ignored. In order to obtain the tensile properties of corroded Q235NH, accelerated corrosion test was carried out on Q235NH specimen with neutral salt spray (salt solution with concentration of (50±5) g/L and pH value between 6.5 to 7.2) at 35 ℃,and the accelerated corrosion time was 6, 24, 48, 72, 96 h respectively. The tensile test was also carried out on the corroded Q235NH specimen. The corrosion surfaces, tensile fracture, stress-strain relationship curve and the change law of mechanical property parameters of Q235NH specimen were investigated. The change law of mechanical property parameters was fitted by formula, the constitutive model of stress-strain relationship was established and the degradation law of reduction coefficient was analyzed. The test results showed that: 1)at the initial stage of corrosion, there was only local corrosion. With the increase of corrosion time, the corrosion became more obvious, and the rust layer fell off. The stress-strain relationship curves of the specimen had an obvious yield plateau, and the stress-strain curve of Q235NH after corrosion was lower than that in the non corroded state, and the yield stage was shortened. With the increase of the corrosion time, the strength of the specimens decreased first, then increased, and then decreased. The reason for these phenomena was that after corrosion of weathering steel, a protective rust layer formed on its surface, which could protect the substrate. With the increase of corrosion time, the adsorption force of the rust layer increased, which slowed down the decline of the mechanical properties of the specimen. 2)The yield strength, tensile strength, yield-to-tensile strength ratio and its reduction factors showed a linear degradation trend with the increase of corrosion time, and then the linear regression relation was established. 3)The secondary plastic flow constitutive model was modified by the parameter of β on the strengthening stage. The modified quadratic plastic flow constitutive model could well simulate the stress-strain relationship of Q235NH before and after corrosion. At the same time, the shape parameters k1, k2 and k3 that affected the stress-strain relationship curve of Q235NH were analyzed, the recommended values of Q235NH shape control parameters k2 and k3 were proposed, and the linear degradation law of shape control parameter k1 with time was established. Through the tensile test of Q235NH under normal conditions, the reduction law of relevant parameters and bonding strength with corrosion time and the modified secondary plastic flow constitutive model could be obtained, and the reduction of mechanical properties of the material after corrosion could be calculated.
登录
注册
点击查看大图
下载:
