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EFFECTS OF STATIC LOAD ON FATIGUE STRENGTH

静载荷对疲劳强度的影响

基本信息

批准号：
06651084
负责人：
TOMITA Yasumitsu
金额：
$ 1.28万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

Boxing fillet weldments, which exist many parts of ship structure initially have residual stress approximately equal to yield stress of material around weld toe. Fatigue strength of the weldments has been evaluated by using experimental results of small as-welded specimens with initial residual stress. However, ship structural members undergo static loading, usually a tank test and ballast loading (ballasting) before going into service. This static pre-loading is expected to shake-down the initial residual stress.Both the initial welding residual stress distribution on as-welded boxing fillet weldments and the shake-down residual stress distribution on statically pre-loaded weldments were examined by using FEM analysis and actual measurement. Load-controlled axial fatigue tests were performed on these weldments to examine the influence of the shake-down residual stress on fatigue strength.The main points are as follows :1) When static tension load of 50% to 80% of yield stress is loaded onto a weldment, the initial welding residual stress of boxing fillet weldment reduces to almost zero, or compressive stress condition. This has been confirmed by FEM analysis and actual measurement.2) The fatigue strength of boxing fillet weldment with shake-down residual stresses increases. This becomes more dramatic in the longer life range.3) We propose S-N diagrams of boxing fillet weldments with shake-down residual stresses. Diagrams should be applied to fatigue strength evaluation of weldments in ship structure.

船舶结构中存在大量的箱体角焊缝，其初始残余应力近似等于焊趾周围材料的屈服应力。利用具有初始残余应力的小焊接试样的试验结果，对焊接件的疲劳强度进行了评定。然而，在投入使用之前，船舶结构构件要经受静载荷，通常是舱舱试验和压载（压载）。这种静态预加载有望消除初始残余应力。采用有限元分析和实测相结合的方法，研究了焊接状态下箱体角焊焊缝的初始残余应力分布和静预加载焊缝的振动残余应力分布。对这些焊接件进行了载荷控制轴向疲劳试验，考察了振动残余应力对疲劳强度的影响。主要观点如下：1)在焊件上施加屈服应力50% ~ 80%的静拉载荷时，箱体角焊件的初始焊接残余应力几乎为零，即压应力状态。通过有限元分析和实测证实了这一点。2)残余应力存在时，箱体角焊件的疲劳强度增大。在较长的寿命范围内，这一点变得更加明显。3)提出了含安定残余应力的装箱角焊缝的S-N图。船舶结构中焊接件的疲劳强度评定应采用结构图。