第八章 疲劳裂纹扩展2

1 第八章第八章第八章第八章第八章第八章第八章第八章 疲劳裂纹扩展疲劳裂纹扩展疲劳裂纹扩展疲劳裂纹扩展疲劳裂纹扩展疲劳裂纹扩展疲劳裂纹扩展疲劳裂纹扩展 8.1 8.1 8.1 8.1 8.1 8.1 8.1 8.1 疲劳裂纹扩展速率疲劳裂纹扩展速率疲劳裂纹扩展速率疲劳裂纹扩展速率疲劳裂纹扩展速率疲劳裂纹扩展速率疲劳裂纹扩展速率疲劳裂纹扩展速率 8.2 8.2 8.2 8.2 8.2 8.2 8.2 8.2 疲劳裂纹扩展寿命预测疲劳裂纹扩展寿命预测疲劳裂纹扩展寿命预测疲劳裂纹扩展寿命预测疲劳裂纹扩展寿命预测疲劳裂纹扩展寿命预测疲劳裂纹扩展寿命预测疲劳裂纹扩展寿命预测 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.3 影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 疲劳裂纹扩展速率试验疲劳裂纹扩展速率试验疲劳裂纹扩展速率试验疲劳裂纹扩展速率试验疲劳裂纹扩展速率试验疲劳裂纹扩展速率试验疲劳裂纹扩展速率试验疲劳裂纹扩展速率试验 返回主目录返回主目录 2 前节回顾前节回顾前节回顾前节回顾前节回顾前节回顾前节回顾前节回顾:::::::: The plot of log dThe plot of log dThe plot of log dThe plot of log dThe plot of log dThe plot of log dThe plot of log dThe plot of log daaaaaaaa/dN versus log /dN versus log /dN versus log /dN versus log /dN versus log /dN versus log /dN versus log /dN versus log ∆∆∆∆∆∆∆∆K is a sigmoidal (SK is a sigmoidal (SK is a sigmoidal (SK is a sigmoidal (SK is a sigmoidal (SK is a sigmoidal (SK is a sigmoidal (SK is a sigmoidal (S形形)))))))) curve. curve. curve. curve. curve. curve. curve. curve. This curve may be divided intoThis curve may be divided intoThis curve may be divided intoThis curve may be divided intoThis curve may be divided intoThis curve may be divided intoThis curve may be divided intoThis curve may be divided into three regions. three regions. three regions. three regions. three regions. three regions. three regions. three regions. At low stress intensities, cracking At low stress intensities, cracking At low stress intensities, cracking At low stress intensities, cracking At low stress intensities, cracking At low stress intensities, cracking At low stress intensities, cracking At low stress intensities, cracking behavior is associated with threshold effects. behavior is associated with threshold effects. behavior is associated with threshold effects. behavior is associated with threshold effects. behavior is associated with threshold effects. behavior is associated with threshold effects. behavior is associated with threshold effects. behavior is associated with threshold effects. In the mid-region, the curve is essentially linear. In the mid-region, the curve is essentially linear. In the mid-region, the curve is essentially linear. In the mid-region, the curve is essentially linear. In the mid-region, the curve is essentially linear. In the mid-region, the curve is essentially linear. In the mid-region, the curve is essentially linear. In the mid-region, the curve is essentially linear. Finally, at high Finally, at high Finally, at high Finally, at high Finally, at high Finally, at high Finally, at high Finally, at high ∆∆∆∆∆∆∆∆K values, crack growth rates are K values, crack growth rates are K values, crack growth rates are K values, crack growth rates are K values, crack growth rates are K values, crack growth rates are K values, crack growth rates are K values, crack growth rates are extremely high and little fatigue life is involved.extremely high and little fatigue life is involved.extremely high and little fatigue life is involved.extremely high and little fatigue life is involved.extremely high and little fatigue life is involved.extremely high and little fatigue life is involved.extremely high and little fatigue life is involved.extremely high and little fatigue life is involved. lg dalg dalg dalg da////dNdNdNdN 1 2 31 2 31 2 31 2 3 10101010 -5 -6-5 -6-5 -6-5 -6 10101010 -9-9-9-9 lglglglg ( K)( K)( K)( K)∆∆∆∆ ~~~~ ccccKKKK=(1-=(1-=(1-=(1-R)R)R)R) ∆∆∆∆K=(1-R)KK=(1-R)KK=(1-R)KK=(1-R)Kmaxmaxmaxmax thththth∆∆∆∆ KKKK 3 Most of the current application of LEFM concepts Most of the current application of LEFM concepts Most of the current application of LEFM concepts Most of the current application of LEFM concepts Most of the current application of LEFM concepts Most of the current application of LEFM concepts Most of the current application of LEFM concepts Most of the current application of LEFM concepts to describe crack growth behavior are associated to describe crack growth behavior are associated to describe crack growth behavior are associated to describe crack growth behavior are associated to describe crack growth behavior are associated to describe crack growth behavior are associated to describe crack growth behavior are associated to describe crack growth behavior are associated with region 2. In this region the log da/dN versus with region 2. In this region the log da/dN versus with region 2. In this region the log da/dN versus with region 2. In this region the log da/dN versus with region 2. In this region the log da/dN versus with region 2. In this region the log da/dN versus with region 2. In this region the log da/dN versus with region 2. In this region the log da/dN versus log log log log log log log log ∆∆∆∆∆∆∆∆K curve is approximately linear and lies K curve is approximately linear and lies K curve is approximately linear and lies K curve is approximately linear and lies K curve is approximately linear and lies K curve is approximately linear and lies K curve is approximately linear and lies K curve is approximately linear and lies roughly between 10roughly between 10roughly between 10roughly between 10roughly between 10roughly between 10roughly between 10roughly between 10-7-7-7-7 and 10 and 10 and 10 and 10 and 10 and 10 and 10 and 10-4 -4 -4 -4 mm/cycle. Many mm/cycle. Many mm/cycle. Many mm/cycle. Many mm/cycle. Many mm/cycle. Many mm/cycle. Many mm/cycle. Many curve fits to this region have been suggested. The curve fits to this region have been suggested. The curve fits to this region have been suggested. The curve fits to this region have been suggested. The curve fits to this region have been suggested. The curve fits to this region have been suggested. The curve fits to this region have been suggested. The curve fits to this region have been suggested. The Paris equation, which was proposed in the early Paris equation, which was proposed in the early Paris equation, which was proposed in the early Paris equation, which was proposed in the early Paris equation, which was proposed in the early Paris equation, which was proposed in the early Paris equation, which was proposed in the early Paris equation, which was proposed in the early 19601960196019601960196019601960’’’’’’’’s, is the most widely accepted.s, is the most widely accepted.s, is the most widely accepted.s, is the most widely accepted.s, is the most widely accepted.s, is the most widely accepted.s, is the most widely accepted.s, is the most widely accepted. 大多数用线弹性断裂力学描述裂纹扩展的应用是与大多数用线弹性断裂力学描述裂纹扩展的应用是与 区域区域22222222相关的。在这一区域，相关的。在这一区域，logda/dN - log logda/dN - log logda/dN - log logda/dN - log logda/dN - log logda/dN - log logda/dN - log logda/dN - log ∆∆∆∆∆∆∆∆KKKKKKKK曲线曲线 近似线性且在近似线性且在1010101010101010-7-7-7-7-10-10-10-10-10-10-10-10-4 -4 -4 -4 mm/cmm/cmm/cmm/cmm/cmm/cmm/cmm/c间。间。已有许多拟合曲线已有许多拟合曲线 提出，提出，6060606060606060年代初的年代初的ParisParisParisParisParisParisParisParis公式是应用最广的。公式是应用最广的。 4 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.3 影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素影响疲劳裂纹扩展的若干因素 ∆∆∆∆∆∆∆∆KKKKKKKK是控制是控制ddddddddaaaaaaaa/dN/dN/dN/dN/dN/dN/dN/dN的最的最 主要因素。主要因素。 平均应力、加载频率、平均应力、加载频率、 环境等的影响较次要，但环境等的影响较次要，但 有时也不可忽略。有时也不可忽略。 同一材料同一材料, , , , , , , , 由不同形状、由不同形状、 尺寸的试件所得到的尺寸的试件所得到的 ddddddddaaaaaaaa/dN-/dN-/dN-/dN-/dN-/dN-/dN-/dN-∆∆∆∆∆∆∆∆KKKKKKKK曲线相同。曲线相同。 ddddaaaa/dN-/dN-/dN-/dN-∆∆∆∆KKKK曲线可以描述疲劳裂纹扩展性能。 ∆∆∆∆KKKK Mpa.m Mpa.m Mpa.m Mpa.m1/21/21/21/2 4 10 20 404 10 20 404 10 20 404 10 20 40 lgdlgdlgdlgdaaaa/dN/dN/dN/dN (m/c) (m/c) (m/c) (m/c) -9-9-9-9 -8-8-8-8 -7-7-7-7 -6-6-6-6 碳钢碳钢碳钢碳钢 R=0.05R=0.05R=0.05R=0.05 ∆∆∆∆K Mpa.mK Mpa.mK Mpa.mK Mpa.m1/21/21/21/2 5 1. 1. 1. 1. 1. 1. 1. 1. 平均应力或应力比的影响平均应力或应力比的影响平均应力或应力比的影响平均应力或应力比的影响平均应力或应力比的影响平均应力或应力比的影响平均应力或应力比的影响平均应力或应力比的影响 注意到注意到 σσσσσσσσ a a a a a a a a =(1-R)=(1-R)=(1-R)=(1-R)=(1-R)=(1-R)=(1-R)=(1-R)σσσσσσσσmaxmaxmaxmaxmaxmaxmaxmax/2/2/2/2/2/2/2/2，， σσσσσσσσmmmmmmmm=(1+R)=(1+R)=(1+R)=(1+R)=(1+R)=(1+R)=(1+R)=(1+R)σσσσσσσσmaxmaxmaxmaxmaxmaxmaxmax/2/2/2/2/2/2/2/2；； 有：有： 故故σσσσσσσσ a a a a a a a a 给定时，给定时， R R R R R R R R ，，σσσσσσσσm m m m m m m m 。。 讨论讨论应力比的影响，应力比的影响，应力比的影响，应力比的影响，应力比的影响，应力比的影响，应力比的影响，应力比的影响， 就是就是就是就是就是就是就是就是讨论讨论平均应力的影响。平均应力的影响。平均应力的影响。平均应力的影响。平均应力的影响。平均应力的影响。平均应力的影响。平均应力的影响。 a a a a a a a a m m m m m m m m R R R R R R R R R R R R R R R R σσσσσσσσσσσσσσσσ ))))))))11111111(((((((( ))))))))11111111(((((((( −−−−−−−− ++++++++ ======== R>0R>0R>0R>0R>0R>0R>0R>0、、R<0R<0R<0R<0R<0R<0R<0R<0影影 响趋势不同。响趋势不同。 ththththKKKK R=0.8R=0.8R=0.8R=0.8 0 0 0 0 -1-1-1-1 lgdlgdlgdlgdaaaa/dN/dN/dN/dN ∆∆∆∆ lg( K)lg( K)lg( K)lg( K)∆∆∆∆ 实验结果实验结果 6 ththththKKKK R=0.8R=0.8R=0.8R=0.8 0 0 0 0 -1-1-1-1 lgdlgdlgdlgdaaaa/dN/dN/dN/dN ∆∆∆∆ lg( K)lg( K)lg( K)lg( K)∆∆∆∆ RRRRRRRR＞＞＞＞＞＞＞＞00000000的情况的情况的情况的情况的情况的情况的情况的情况 RRRRRRRR>0>0>0>0>0>0>0>0时，时，σσσσσσσσminminminminminminminmin>0>0>0>0>0>0>0>0。。 σσσσσσσσ a a a a a a a a 给定，给定，R R R R R R R R ，， σσσσσσσσmin min min min min min min min ，， σσσσσσσσmax max max max max max max max 。。 三个速率区域内，三个速率区域内，da/dNda/dNda/dNda/dNda/dNda/dNda/dNda/dN均增大。均增大。 ddddddddaaaaaaaa/dN-/dN-/dN-/dN-/dN-/dN-/dN-/dN-∆∆∆∆∆∆∆∆K K K K K K K K 曲线整体向左移动。曲线整体向左移动。 FormanFormanFormanFormanFormanFormanFormanForman公式：公式： K K K K K K K K K K K K K K K K R R R R R R R R K K K K K K K K C C C C C C C C dN dN dN dN dN dN dN dN da da da da da da da da C C C C C C C C m m m m m m m m ∆∆∆∆∆∆∆∆---------------- ∆∆∆∆∆∆∆∆======== ))))))))11111111(((((((( ))))))))(((((((( ∆∆∆∆∆∆∆∆Κ=(1−Κ=(1−Κ=(1−Κ=(1−Κ=(1−Κ=(1−Κ=(1−Κ=(1−RRRRRRRR)Κ)Κ)Κ)Κ)Κ)Κ)Κ)Κmaxmaxmaxmaxmaxmaxmaxmax ΚΚΚΚΚΚΚΚmaxmaxmaxmaxmaxmaxmaxmax→→→→→→→→ΚΚΚΚΚΚΚΚcccccccc，， 分母分母→→→→→→→→00000000，， ddddddddaaaaaaaa/dN/dN/dN/dN/dN/dN/dN/dN→∞→∞→∞→∞→∞→∞→∞→∞。。 ∆∆∆∆∆∆∆∆KKKKKKKK→∆→∆→∆→∆→∆→∆→∆→∆KKKKKKKKthththththththth，， ddddddddaaaaaaaa/dN/dN/dN/dN/dN/dN/dN/dN→→→→→→→→00000000。。 若考虑若考虑∆∆∆∆∆∆∆∆KKKKKKKKthththththththth的影响，有：的影响，有： da da da da da da da da dN dN dN dN dN dN dN dN C C C C C C C C K K K K K K K K K K K K K K K K R R R R R R R R K K K K K K K K K K K K K K K K m m m m m m m m th th th th th th th th m m m m m m m m c c c c c c c c ======== −−−−−−−− −−−−−−−− −−−−−−−− [[[[[[[[(((((((( )))))))) (((((((( )))))))) ]]]]]]]] (((((((( )))))))) ∆∆∆∆∆∆∆∆ ∆∆∆∆∆∆∆∆ ∆∆∆∆∆∆∆∆11111111 7 ththththKKKK R=0.8R=0.8R=0.8R=0.8 0 0 0 0 -1-1-1-1 lgda/dNlgda/dNlgda/dNlgda/dN ∆∆∆∆ lg( K)lg( K)lg( K)lg( K)∆∆∆∆ 低速率区低速率区低速率区低速率区低速率区低速率区低速率区低速率区，，RRRRRRRR↑↑↑↑↑↑↑↑，，∆∆∆∆∆∆∆∆KKKKKKKKthththththththth↓↓↓↓↓↓↓↓。。 RRRRRRRR＜＜＜＜＜＜＜＜00000000的情况：的情况：的情况：的情况：的情况：的情况：的情况：的情况：负应力存在，负应力存在， 对对ddddddddaaaaaaaa/dN/dN/dN/dN/dN/dN/dN/dN三区域的影响不同。三区域的影响不同。 情况比情况比R>0R>0R>0R>0R>0R>0R>0R>0时复杂得多。时复杂得多。 0 .2 .4 .6 .8 1.00 .2 .4 .6 .8 1.00 .2 .4 .6 .8 1.00 .2 .4 .6 .8 1.0 8888 7777 6666 5555 4444 3333 2222 1111 低碳钢 低合金钢 不锈钢 A517-FA517-FA517-FA517-F 9301930193019301 A508CA508CA508CA508C A533BA533BA533BA533B ×××× 不同钢材的R-R-R-R-∆∆∆∆KKKKth th th th 关系 RRRR ∆∆∆∆KKKKth th th th Mpa.mMpa.mMpa.mMpa.m1/21/21/21/2 有经验关系为： ∆∆∆∆KKKKthththth= = = = ∆∆∆∆KKKK0000thththth(1-(1-(1-(1-ββββR)R)R)R)αααα ∆∆∆∆KKKKoooothththth是R=0R=0R=0R=0时的基本门槛 应力强度因子幅度。 参数αααα、ββββ由实验确定。 图中钢材的下限为： ∆∆∆∆KKKKthththth=7.03(1-0.85R)=7.03(1-0.85R)=7.03(1-0.85R)=7.03(1-0.85R) 8 FormanFormanFormanFormanFormanFormanFormanForman’’’’’’’’s equation is often used to predict stress s equation is often used to predict stress s equation is often used to predict stress s equation is often used to predict stress s equation is often used to predict stress s equation is often used to predict stress s equation is often used to predict stress s equation is often used to predict stress ratio effects. As R increases, the crack growth rate ratio effects. As R increases, the crack growth rate ratio effects. As R increases, the crack growth rate ratio effects. As R increases, the crack growth rate ratio effects. As R increases, the crack growth rate ratio effects. As R increases, the crack growth rate ratio effects. As R increases, the crack growth rate ratio effects. As R increases, the crack growth rate increases. This is consistent with test observations. increases. This is consistent with test observations. increases. This is consistent with test observations. increases. This is consistent with test observations. increases. This is consistent with test observations. increases. This is consistent with test observations. increases. This is consistent with test observations. increases. This is consistent with test observations. FormanFormanFormanFormanFormanFormanFormanForman’’’’’’’’s equation is valid only when R>0. s equation is valid only when R>0. s equation is valid only when R>0. s equation is valid only when R>0. s equation is valid only when R>0. s equation is valid only when R>0. s equation is valid only when R>0. s equation is valid only when R>0. Generally, it is believed that when R<0, no Generally, it is believed that when R<0, no Generally, it is believed that when R<0, no Generally, it is believed that when R<0, no Generally, it is believed that when R<0, no Generally, it is believed that when R<0, no Generally, it is believed that when R<0, no Generally, it is believed that when R<0, no significant change in growth rate occurs compared significant change in growth rate occurs compared significant change in growth rate occurs compared significant change in growth rate occurs compared significant change in growth rate occurs compared significant change in growth rate occurs compared significant change in growth rate occurs compared significant change in growth rate occurs compared with the R=0. Again this is material dependent, as with the R=0. Again this is material dependent, as with the R=0. Again this is material dependent, as with the R=0. Again this is material dependent, as with the R=0. Again this is material dependent, as with the R=0. Again this is material dependent, as with the R=0. Again this is material dependent, as with the R=0. Again this is material dependent, as some researchers have obtained data for certain some researchers have obtained data for certain some researchers have obtained data for certain some researchers have obtained data for certain some researchers have obtained data for certain some researchers have obtained data for certain some researchers have obtained data for certain some researchers have obtained data for certain materials which show higher growth rates for R<0 materials which show higher growth rates for R<0 materials which show higher growth rates for R<0 materials which show higher growth rates for R<0 materials which show higher growth rates for R<0 materials which show higher growth rates for R<0 materials which show higher growth rates for R<0 materials which show higher growth rates for R<0 loading. loading. loading. loading. loading. loading. loading. loading. FormanFormanFormanFormanFormanFormanFormanForman公式常用于预测应力比的影响。公式常用于预测应力比的影响。RRRRRRRR增大，增大， 裂纹扩展速率增大，与试验观察是一致的。裂纹扩展速率增大，与试验观察是一致的。 FormanFormanFormanFormanFormanFormanFormanForman公式只在公式只在R>0R>0R>0R>0R>0R>0R>0R>0时正确。一般认为与时正确。一般认为与R=0R=0R=0R=0R=0R=0R=0R=0相相 比，比，R<0R<0R<0R<0R<0R<0R<0R<0对对da/dNda/dNda/dNda/dNda/dNda/dNda/dNda/dN没有显著影响。这仍与材料有关，没有显著影响。这仍与材料有关， 对有些材料，也有研究者在对有些材料，也有研究者在R<0R<0R<0R<0R<0R<0R<0R<0时得到较高时得到较高da/dNda/dNda/dNda/dNda/dNda/dNda/dNda/dN。。 9 但是，在但是，在高温或腐蚀环境下高温或腐蚀环境下高温或腐蚀环境下高温或腐蚀环境下高温或腐蚀环境下高温或腐蚀环境下高温或腐蚀环境下高温或腐蚀环境下，频率及波形对，频率及波形对ddddddddaaaaaaaa/dN/dN/dN/dN/dN/dN/dN/dN 的影响显著增大，是不容忽视的。的影响显著增大，是不容忽视的。 2. 2. 2. 2. 2. 2. 2. 2. 加载频率的影响加载频率的影响加载频率的影响加载频率的影响加载频率的影响加载频率的影响加载频率的影响加载频率的影响 30Cr30Cr30Cr30Cr30Cr30Cr30Cr30Cr22222222WmoVWmoVWmoVWmoVWmoVWmoVWmoVWmoV钢钢(30(30(30(30(30(30(30(30万千瓦汽轮万千瓦汽轮 机高压转子钢机高压转子钢))))))))频率影响实验。频率影响实验。 低速区：加载频率对低速区：加载频率对ddddddddaaaaaaaa/dN/dN/dN/dN/dN/dN/dN/dN基基 本无影响。本无影响。 中速率区：中速率区：ffffffff↓↓↓↓↓↓↓↓，，ddddddddaaaaaaaa/dN/dN/dN/dN/dN/dN/dN/dN↑↑↑↑↑↑↑↑。。有：有： ddddddddaaaaaaaa/dN=C(f )(/dN=C(f )(/dN=C(f )(/dN=C(f )(/dN=C(f )(/dN=C(f )(/dN=C(f )(/dN=C(f )(∆∆∆∆∆∆∆∆K)K)K)K)K)K)K)K)mmmmmmmm=(A-Blgf)(=(A-Blgf)(=(A-Blgf)(=(A-Blgf)(=(A-Blgf)(=(A-Blgf)(=(A-Blgf)(=(A-Blgf)(∆∆∆∆∆∆∆∆K)K)K)K)K)K)K)K)mmmmmmmm lg (dlg (dlg (dlg (daaaa/dN)/dN)/dN)/dN) 0.70.70.70.7 11111111 104104104104 980980980980 10000100001000010000 30Cr WMoV30Cr WMoV30Cr WMoV30Cr WMoV lg ( K)lg ( K)lg ( K)lg ( K) 2222 ∆∆∆∆ f(f(f(f(次////分)))) 在室温、无腐蚀环境中，在室温、无腐蚀环境中，f=0.1f=0.1f=0.1f=0.1f=0.1f=0.1f=0.1f=0.1∼∼∼∼∼∼∼∼100Hz100Hz100Hz100Hz100Hz100Hz100Hz100Hz时时, , , , , , , , 对对da/dNda/dNda/dNda/dNda/dNda/dNda/dNda/dN 的影响可不考虑。循环波形影响是更次要的。的影响可不考虑。循环波形影响是更次要的。 10 腐蚀介质作用下，裂纹可在低于KKKK1C1C1C1C时发生扩展。 试件加载到KKKK1111，置于腐蚀介质中。记录裂纹开始扩 展的时间ttttffff。 腐蚀疲劳是腐蚀疲劳是介质引起的介质引起的介质引起的介质引起的介质引起的介质引起的介质引起的介质引起的腐蚀破坏腐蚀破坏腐蚀破坏腐蚀破坏腐蚀破坏腐蚀破坏腐蚀破坏腐蚀破坏过程过程过程过程过程过程过程过程 和和应力引起的应力引起的应力引起的应力引起的应力引起的应力引起的应力引起的应力引起的疲劳破坏疲劳破坏疲劳破坏疲劳破坏疲劳破坏疲劳破坏疲劳破坏疲劳破坏过程过程过程过程过程过程过程过程的共同作用。的共同作用。 这二者的共同作用，比任何一种单独作用更有害。这二者的共同作用，比任何一种单独作用更有害。 11）） 应力腐蚀开裂应力腐蚀开裂应力腐蚀开裂应力腐蚀开裂应力腐蚀开裂应力腐蚀开裂应力腐蚀开裂应力腐蚀开裂 (Stress corrosion cracking)(Stress corrosion cracking)(Stress corrosion cracking)(Stress corrosion cracking)(Stress corrosion cracking)(Stress corrosion cracking)(Stress corrosion cracking)(Stress corrosion cracking) 3. 3. 3. 3. 3. 3. 3. 3. 腐蚀环境对腐蚀环境对腐蚀环境对腐蚀环境对腐蚀环境对腐蚀环境对腐蚀环境对腐蚀环境对ddddddddaaaaaaaa/dN/dN/dN/dN/dN/dN/dN/dN的影响的影响的影响的影响的影响的影响的影响的影响 KKKK1111→→→→ K K K K1scc1scc1scc1scc，ttttffff→∞→∞→∞→∞，((((约1000100010001000小时))))。 KKKK1scc1scc1scc1scc是应力腐蚀开裂门槛值。 KKKK1111K>K>K>K1scc1sc