【作者】 陈熙；

【导师】 张永祥；

【作者基本信息】 重庆大学 ， 工程（航空工程）（专业学位）， 2021， 硕士

【摘要】 随着社会经济的快速发展,起重机作为一种大型起重设备,广泛应用于多个国民经济领域,确保起重机主梁结构长期安全使用是起重机疲劳研究领域的一个关键问题。由于主梁存在大量焊接结构,这导致起重机主梁结构的疲劳寿命预测愈加困难,目前常用的研究方法是按照单轴疲劳进行研究;面对着日益复杂的载荷环境,对于起重机尤其是起重机主梁焊接结构的安全性提出了更加严格的要求,结合实际载荷工况,开展多轴载荷状态下起重机主梁焊接结构的疲劳行为研究具有重大工程意义。本文基于起重机主梁焊接结构所处的实际工况,以起重机主梁常用材料Q345钢焊接结构为研究对象,开展了不同加载参量下的多轴疲劳高周疲劳试验,研究了不同应力幅比、相位差、拉伸平均应力和扭转平均应力对多轴疲劳失效行为的影响规律,对不同加载参量下的失效模式进行了分析。本文的主要工作及成果如下:1)研究了应力幅比、相位差及平均应力等加载参量对焊接试件多轴疲劳失效疲劳的影响规律。在恒定等效应力幅值下进行多轴疲劳试验,研究了比例加载下应力幅比对焊接试件多轴疲劳寿命的影响规律;研究了恒定应力幅比下、相位差对焊接试件多轴疲劳寿命的影响规律;研究了平均应力对焊接试件多轴疲劳寿命的影响规律。2)对不同加载参量下最大切应力幅值及平面方向、最大正应力及平面方向进行了理论分析。根据多轴疲劳公式进行了理论推导,得到了比例加载下不同应力幅比对最大切应力幅值和方向及最大正应力和方向的影响规律;得到了恒定应力幅比下不同相位差对最大切应力幅值和方向及最大正应力和方向的影响规律。3)对焊接试件的疲劳断口进行宏观及微观分析,研究了不同加载参量对焊接试件的失效模式的影响规律。对焊接试件断口进行了宏观分析,发现拉扭复合加载下焊接试件的失效模式为Ⅰ型和Ⅱ型的混合模式;随着加载参量的变化,其失效形式并不相同,总体上呈现规律性变化。通过扫描电镜对焊接断口疲劳源区、扩展区及瞬断区进行了微观分析,发现加载参量对断口微观特征有显著影响。更多还原

【Abstract】 With the rapid development of society and economy,cranes,as a large-scale lifting equipment,are widely used in many areas of the national economy.It is a key issue in the field of crane fatigue research to ensure the long-term safe use of crane main beam structures.Due to the large number of welded structures in the main girder,it is more difficult to predict the fatigue life of the crane main girder structure.Currently,the commonly used research method is to study according to uniaxial fatigue;in the face of increasingly complex load environments,the crane,especially the crane main girder The safety of the welded structure puts forward more stringent requirements.Combined with the actual load conditions,it is of great engineering significance to carry out the fatigue behavior research of the crane main girder welded structure under multi-axial loading.Based on the actual working conditions of the crane main girder welding structure,this paper takes the commonly used material of the crane main girder Q345 steel welding structure as the research object.The influence of phase difference,average tensile stress and average torsional stress on the failure behavior of multiaxial fatigue,and the failure modes under different loading parameters are analyzed.The main work and results of this paper are as follows:1)The effects of loading parameters such as stress-amplitude ratio,phase difference and average stress on the fatigue of multiaxial fatigue failure of welded specimens are studied.The multiaxial fatigue test was carried out under the constant equivalent stress amplitude,and the influence of the stress amplitude ratio on the multiaxial fatigue life of the welded specimen under proportional loading was studied.The influence of the phase difference on the multiaxial fatigue life of the welded specimen under the constant stress amplitude ratio was studied.The influence law of fatigue life;the influence law of average stress on the multi-axial fatigue life of welded specimens is studied.2)The maximum shear stress amplitude and plane direction,maximum normal stress and plane direction under different loading parameters are theoretically analyzed.According to the theory of multiaxial fatigue formula,the influence law of different stress amplitude ratio on the maximum shear stress amplitude and direction and the maximum normal stress and direction under proportional loading is obtained;The influence law of stress amplitude and direction and maximum normal stress and direction.3)The fatigue fracture of the welded specimen was analyzed macroscopically and microscopically,and the influence of different loading parameters on the failure mode of the welded specimen was studied.A macroscopic analysis of the fracture of the welded specimen was carried out,and it was found that the failure mode of the welded specimen under the combined tensile and torsion loading was a mixed mode of type I and type II;with the change of the loading parameters,the failure modes were not the same,and the overall pattern was regular.Sexual change.A microscopic analysis of the fatigue source area,expansion area and instantaneous failure area of the welding fracture was carried out by scanning electron microscope,and it was found that the loading parameters had a significant effect on the microscopic characteristics of the fracture.更多还原