铝合金焊接接头疲劳评定的应力平均法

FATIGUE ASSESSMENT OF ALUMINIUM WELDED JOINTS BY THE STRESS AVERAGING APPROACH

应力平均法(thestress averaging approach,简称SAA)是局部应力方法之一,文中采用此方法对3A21铝合金焊接接头进行疲劳评定,用有限元计算局部应力值,建立试验结果和评定结果的S—N曲线,并分析接头形式、焊趾半径对疲劳强度的影响。结果表明,SAA法评定的结果是偏于安全的,但Neuber建议把焊趾处视为尖锐缺口(即令ρ=0,ρ=0.15mm),在工程上有一定的适用性,在理论上并不完全正确。这样在焊趾处将产生较大的应力集中,由此得到的局部应力值远远大于实际值。接头形式对采用名义应力幅值Δσ表示的疲劳强度有较大影响;焊趾是决定焊态接头疲劳性能的关键部位,应力集中区的最大应力存在于焊趾部位。

The stress averaging approsch （SAA） is one of the local stress approaches. Fatigue behavior of 3A21 aluminium alloy welded joints is assessed by the approach, It calculates the local stress by the finite element and establishes S-N curve of test results as well as S-N curve assessed by SAA. In addition, the influence on fatigue life such as joint geometry, weld toe radium is discussed. It shows that the result assessed by SAA is conservative. According to Neuber＇s propos＇al, the weld toe was regarded as a sharp notch, namely, ρ = 0 mm and ρ^＊ = 0.15 mm. Although this way has certain applicability in engineering, it is not absolutely accurate in theory. With the way, bigger stress will be concentrated in a weld toe, thus the local stress by calculation is by far bigger than actual one. Fatigue life based on nominal stress range △σ is affected by different joint geometries. The weld toe is important to fatigue properties of welding joints and it also leads to the biggest stress among stress concentration zone.