Fatigue Life Calculation of High-Strength Steel Perforated Plates
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摘要: 根据Q460D钢和Q690D钢开孔板的疲劳试验破坏模式,以椭球面断裂模型作为疲劳裂纹失稳扩展(断裂)判据,计算了疲劳裂纹失稳扩展面积、形成与稳定扩展面积和形成与稳定扩展长度。以椭球面断裂模型作为裂尖开裂判据,对内含椭圆柱体疲劳裂纹的Q460D钢和Q690D钢开孔板进行了疲劳裂纹扩展数值模拟。数值计算的疲劳裂纹扩展应力场显示,相对应力(σ1/fy、σ2/fy、σ3/fy)、应力三轴度σm/σseq和开裂指数Ic的峰值均位于疲劳裂纹裂尖,裂尖形成高度应力集中;疲劳裂纹失稳扩展面全截面塑性,平均Ic≈1.0,沿板宽方向的应力约束系数约为0.28,沿板厚方向几乎没有约束应力。根据Q460D钢和Q690D钢开孔板的试验疲劳寿命和数值计算的疲劳裂纹形成与稳定扩展长度,标定了统一计算疲劳裂纹形成与稳定扩展寿命的疲劳寿命计算模型参数。Q460D钢和Q690D钢开孔板的疲劳寿命评估结果表明,高强钢开孔板的疲劳寿命随钢材强度的提高而提高,不同强度等级的高强钢开孔板应采用不同的量化疲劳寿命计算模型。现行规范对不同强度等级的高强钢开孔板采用相同的允许应力幅进行疲劳寿命计算,与Q690D和Q460D高强钢开孔板的疲劳试验结果不符,计算误差为-76.2%~-14.3%。统一计算疲劳裂纹形成与稳定扩展寿命的疲劳寿命计算模型,对Q690D钢和Q460D钢开孔板疲劳寿命的计算误差为-61.8%~-0.01%,计算精度高于现行规范建议的允许应力幅疲劳寿命计算式。
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关键词:
- 高强钢 /
- 开孔板 /
- 疲劳寿命 /
- 疲劳裂纹 /
- 统一疲劳寿命计算模型
Abstract: According to the failure modes of perforated plates fabricated from Q460D steel and Q690D steel in the fatigue test, taking an ellipsoidal fracture model as the instability propagation (fracture) criterion of fatigue cracks, the instability propagation area, the area and the length of initiation and stable propagation of fatigue cracks were theoretically calculated. Taking the ellipsoidal fracture model as the cracking criterion of crack tips, the propagation of fatigue cracks in perforated plates fabricated from Q460D steel and Q690D steel with elliptical cylinder fatigue crack was numerically simulated. The numerical calculation of stress field of fatigue crack propagation showed that the peaks of the relative stresses (σ1/fy,σ2/fy,σ3/fy), stress triaxiality σm/σseq and cracking index Ic were located at the crack tips with high stress concentration. The unstable propagation area of fatigue cracks was fully plastic, and the average cracking index Ic≈1.0. The stress constraint coefficient along the width of the plate was about 0.28, and there was almost no constraint stress along the thickness of the plate. According to the experimental fatigue life of perforated plates fabricated from Q460D steel and Q690D steel,and the fatigue crack initiation and stable propagation length calculated numerically, the parameters of the fatigue life calculation model which uniformly calculated the fatigue crack initiation and stable propagation life were calibrated. The calculation results of the fatigue life of perforated plates fabricated from Q460D steel and Q690D steel showed that the fatigue life of the perforated plates increasesd with the increase of the strength of structural steel, and different quantitative fatigue life calculation models should be adopted for the perforated plates fabricated from high-strength steels with different strength grades. The fatigue life calculation formula with the same allowable stress amplitude recommended in China’s current code was adopted to calculate the fatigue life of the perforated plates fabricated from Q460D steel and Q690D steel. The calculation error of the fatigue life formula with allowable stress amplitudes recommended in China’s current codes was -76.2%--14.3%. The calculation error of the fatigue life calculation model which uniformly calculated the fatigue crack initiation and stable propagation life was -61.8%--0.01% and the calculation accuracy was higher than that of the fatigue life calculation formula with the same allowable stress amplitude recommended in China’s current codes. -
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