【作者】 刘毅；

【导师】 杨飏；

【作者基本信息】 大连理工大学 ， 船舶与海洋工程（专业学位）， 2022， 硕士

【摘要】 海水腐蚀损伤以及焊接损伤都会对海工结构造成严重影响,不仅使钢材力学性能发生明显下降,使得结构承载力储备能力和变形储备能力发生退化。由于海水腐蚀的作用,受腐蚀区域会因力学性能的下降产生塑性变形而导致结构失效。由于腐蚀通常在焊缝附近热影响区处最为严重,因此受到外载荷情况下最容易发生失效。船舶与海洋工程构件中除了受到拉、压载荷,还会面临复杂的受力情况,因此焊缝方向与受力方向之间的夹角变得不可控。因此衡量焊接接头在不同焊缝方向与受力方向之间的夹角下的力学性能,给出损伤力学模型,对于实现船舶与海洋工程构件安全性十分重要。因此,本文以D36钢板作为研究对象,研究多角度焊接D36钢板接头在以海水为介质的电化学腐蚀作用下的损伤分布特点及其受拉和受压力学性能。借助电镜扫描实验,分析焊接及腐蚀损伤对钢材微观结构的影响。提出了不同焊缝角度情况下焊接接头的屈服强度计算公式以及带焊缝区域的弹性模量计算公式。研究了不同焊缝角度以及腐蚀程度对焊接接头损伤分布、结构承载能力和变形能力以及结构失效模式和失效位置的影响机理。研究发现腐蚀程度大小有影响试件受压情况下的失效模式的趋势,并且会影响试件的抵抗变形能力、承载力储备能力以及变形储备能力,但是并不会对试件的失效位置产生影响;焊缝方向与受力方向的夹角大小决定了试件的失效位置,会对试件的抵抗变形能力优良、承载力储备能力优良以及变形储备能力优良造成影响,但是对试件的失效模式影响较小。提出了不同MLR下,垂向焊缝和斜焊缝两种情况下焊接接头的静载强度计算公式,并根据试验得到的数据对公式进行验证,研究发现该公式在一定情况下可以很好地和试验数据吻合,可以用来预测实际工程构件中焊缝与母材强度相近情况下,不同焊缝角度以及不同MLR情况下焊接接头处的静载强度,从而进一步保证工程构件的安全性和可靠性。为了进一步研究焊接腐蚀试件的损伤机理,对具有不同焊缝角度和不同腐蚀损伤程度的试件进行了电镜扫描实验。将试件切成包含母材、热影响区以及焊缝三个区域的小块,对其三个区域进行高倍电镜扫描实验,对其微观结构进行分析研究。依据各种不同焊缝角度试件的实验曲线关系,通过回归分析建立以腐蚀质量损失率为变量的腐蚀损伤单角度焊接钢材广义本构模型。通过不同焊缝角度试件本构模型间的特征关系分析研究,对单变量焊接钢材广义本构模型进行二次回归分析,建立以腐蚀质量损失率和焊缝角度为双变量的焊接-腐蚀双重损伤钢材广义本构模型。更多还原

【Abstract】 The double effect of seawater corrosion and welding will cause serious damage to offshore structures,which not only reduces the mechanical properties of steel,but also adversely affects the bearing capacity and deformation capacity of structures.Due to the action of seawater corrosion,the corroded area will produce plastic deformation due to the decline of mechanical properties and lead to structural failure.Due to the most serious corrosion in the heat-affected zone near the weld,so the heat-affected zone is most likely to buckle under the action of external load.In addition to the tension and compression loads,ships and Marine engineering components also face complex stress conditions,so the included angle between the weld direction and the stress direction becomes uncontrollable.Therefore,it is very important to measure the mechanical properties of welded joints under the angle between different welding directions and stress directions,and to establish the damage mechanical model for the realization of the safety of ships and marine engineering components.Therefore,this paper takes D36 steel plate as the research object to study the damage distribution characteristics and tensile and compression mechanical properties of multi-angle welded D36 steel plate joint under the action of electrochemical corrosion with seawater as the medium.The effects of welding and corrosion damage on steel microstructure were studied by scanning electron microscope.The formulas for calculating the yield strength and elastic modulus of welded joints with different weld angles are presented.The influence mechanism of different weld angles and corrosion degree on the damage distribution of welded joints,bearing capacity and deformation capacity of structures,failure mode and failure location of structures was studied.It is found that the degree of corrosion has a tendency to change the failure mode,and also affects the deformation resistance,bearing capacity and deformation reserve capacity of specimens,but does not affect the failure position of specimens.The Angle between the weld direction and the force direction determines the failure position of the specimen,which affects the excellent deformation resistance,bearing capacity and deformation reserve capacity of the specimen,but it has little effect on the mode of destruction.The formulas for calculating the static load strength of welded joints in vertical and oblique welds under different MLR conditions were put forward,and the formulas were verified according to the experimental data.It was found that the curves obtained by the formulas fit well with the experimental curves,and could be used to predict the strength of welded joints in actual engineering components when the strength of welded joints was similar to that of base metal.The static load strength of welded joints under different weld angles and different MLR conditions can further ensure the safety and reliability of engineering components.In order to further analyze the welding corrosion specimens,scanning electron microscope(SEM)experiments were carried out on the specimens with different weld angles and different degrees of corrosion damage.The specimen was cut into three areas including base metal,heat affected zone and weld,and the microstructure of the three areas was analyzed by scanning electron microscopy with high power.According to the stress-strain relationship characteristics of each weld Angle specimen,the generalized constitutive model of corrosion-damaged single-angle welded steel was established by regression analysis with the rate of corrosion mass loss as the variable.According to the characteristic relationship between the steel specimens with different weld angles,the univariate stress-strain curve constitutive model was analyzed by quadratic regression,and the generalized constitutive model of welded and corroded steel specimens with double damage was established with the corrosion mass loss rate and weld Angle as two variables.更多还原