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Prediction about short fatigue crack growth in compressive residual stress field
Prediction a b o u t short f a t i g u e crack g r o w t h in c o m p r e s s i v e residual stress field.
Hu, N. S., Wang, Q. Y., Lin, L. and Tao, Y. Xi'an Jiaotong Daxue Xuebao (J. Xi'an Jiaotong Univ.) (1992) 26 (3) 93-98, 126 (in Chinese) A model based on Newman's calculation is suggested. The central hole model is replaced by a single edge notch, end compressive residual stress is induced. The residual stress redistribution during crack growth is calculated with the finiteelement method. The short fatigue crack growth rate in this residual stress field is predicted. The experiment was carried out on a high-temperature-tempered mediumcarbon steel (eg 40Cr), of which the notched area was shot peened. Residual stress was measured with an X-ray diffractometer to detect its redistribution. The crack closure force end short crack length were monitored during fatigue. The experimental results show that the prediction curve agrees well with the tested data. The compressive residual stress increases the crack closure force and reduces the maximum stress intensity factor. The crack growth rate decreases with reduction of the effective stress intensity factor. Graphs, 7 ref.
The eppUcotion o f high s t r e n g t h steels f o r f a t i g u e loaded structures.
Sperle, J. O. and Nilsson, T. Proc. Conf. HSLA Steels: Processing, Properties and Applications, Beijing, China, 28 Oct.-2 Nov. 1990, pp 3 5 3 - 3 6 4
Fatigue is one of the main issues to be handled for the successful use of highstrength steels. Fatigue strength results from base metal and welded joints in hotend cold-roiled high-strength steels are presented. Low base metal fatigue strength values for QT-steels in comparison with strip steels initiated an investigation of the influence of microstructure and surface condition. The results show that the main reason for the difference in fatigue is probably a rougher surface rather than differences in residual stresses, decarburization or microstructure. Based on surface roughness measurements and fatigue results of base metal a relationship is presented between the surface factor Kr, the surface roughness Re, and the tensile strength. Fatigue results on welded joints show that improvements in fatigue strength of 55-75% are achieved by TIG-dreaaing the weld toes. Comparing tests results on welds in strip steels with literature data for thicker plates supports recent results suggesting that a thickness effect is present down to 5 mm thickness. Tests on spot-welded beams indicate that there is a positive influence of an increased base metal strength on the fatigue strength, not only for non-load-carrying but also for load-carrying beams.
Effects o f residual stresses o n high-cycle fatigue.
He, J.-W., Hu, N. S. and Zhang, D. Q. Xi'an Jiaotong Daxue Xuebao (J. Xi'an Jiaotong Univ.) (1992) 26 (3)
A brief i n t r o d u c t i o n t o fracture mechanics and t h e role o f NDT.
2 5 - 3 2 (in Chinese)
Pook, L. P. Br. J. Non-Destr. Test. (Dec. 1992) 34 (12) 5 9 5 - 6 0 0
The effect of residual stress on high-cycle fatigue for smooth specimens (eg medium-carbon steel, 20Cr, 40Cr. and GCr15 steels) is best evaluated by the Dang-Van diagram, for which s multiaxial stress state is emphasized, For the fatigue beheviour of e notched bar, the residual stress concentration and relaxation in the notched area are vital to the fatigue limit. The compressive residual stress in the cracked body acts as • closure force holding the crack from propagation. With the increase of compressive residual stress, a crack may decrease its growth rate and even stop cracking. Graphs, 16 ref.
During the past 30 years there have been very substantial advances in both fracture mechanics and NDT techniques. In particular, present-day fracture mechanics covers a vast body of knowledge. Some of its more important ideas are described, together with their interaction with come aspects of NDT. It is concluded that fracture mechanics and NDT are complementary disciplines that influence each other. Both are used in the measurement of material properties in the presence of a crack, and both are used in engineering assessments of components and structures in the presence of actual or postulated cracks or creck-like flaws. Graphs, 11 ref.
536
Int J Fatigue November 1993
Hu, N. S., Wang, Q. Y., Lin, L. and Tao, Y. Xi'an Jiaotong Daxue Xuebao (J. Xi'an Jiaotong Univ.) (1992) 26 (3) 93-98, 126 (in Chinese) A model based on Newman's calculation is suggested. The central hole model is replaced by a single edge notch, end compressive residual stress is induced. The residual stress redistribution during crack growth is calculated with the finiteelement method. The short fatigue crack growth rate in this residual stress field is predicted. The experiment was carried out on a high-temperature-tempered mediumcarbon steel (eg 40Cr), of which the notched area was shot peened. Residual stress was measured with an X-ray diffractometer to detect its redistribution. The crack closure force end short crack length were monitored during fatigue. The experimental results show that the prediction curve agrees well with the tested data. The compressive residual stress increases the crack closure force and reduces the maximum stress intensity factor. The crack growth rate decreases with reduction of the effective stress intensity factor. Graphs, 7 ref.
The eppUcotion o f high s t r e n g t h steels f o r f a t i g u e loaded structures.
Sperle, J. O. and Nilsson, T. Proc. Conf. HSLA Steels: Processing, Properties and Applications, Beijing, China, 28 Oct.-2 Nov. 1990, pp 3 5 3 - 3 6 4
Fatigue is one of the main issues to be handled for the successful use of highstrength steels. Fatigue strength results from base metal and welded joints in hotend cold-roiled high-strength steels are presented. Low base metal fatigue strength values for QT-steels in comparison with strip steels initiated an investigation of the influence of microstructure and surface condition. The results show that the main reason for the difference in fatigue is probably a rougher surface rather than differences in residual stresses, decarburization or microstructure. Based on surface roughness measurements and fatigue results of base metal a relationship is presented between the surface factor Kr, the surface roughness Re, and the tensile strength. Fatigue results on welded joints show that improvements in fatigue strength of 55-75% are achieved by TIG-dreaaing the weld toes. Comparing tests results on welds in strip steels with literature data for thicker plates supports recent results suggesting that a thickness effect is present down to 5 mm thickness. Tests on spot-welded beams indicate that there is a positive influence of an increased base metal strength on the fatigue strength, not only for non-load-carrying but also for load-carrying beams.
Effects o f residual stresses o n high-cycle fatigue.
He, J.-W., Hu, N. S. and Zhang, D. Q. Xi'an Jiaotong Daxue Xuebao (J. Xi'an Jiaotong Univ.) (1992) 26 (3)
A brief i n t r o d u c t i o n t o fracture mechanics and t h e role o f NDT.
2 5 - 3 2 (in Chinese)
Pook, L. P. Br. J. Non-Destr. Test. (Dec. 1992) 34 (12) 5 9 5 - 6 0 0
The effect of residual stress on high-cycle fatigue for smooth specimens (eg medium-carbon steel, 20Cr, 40Cr. and GCr15 steels) is best evaluated by the Dang-Van diagram, for which s multiaxial stress state is emphasized, For the fatigue beheviour of e notched bar, the residual stress concentration and relaxation in the notched area are vital to the fatigue limit. The compressive residual stress in the cracked body acts as • closure force holding the crack from propagation. With the increase of compressive residual stress, a crack may decrease its growth rate and even stop cracking. Graphs, 16 ref.
During the past 30 years there have been very substantial advances in both fracture mechanics and NDT techniques. In particular, present-day fracture mechanics covers a vast body of knowledge. Some of its more important ideas are described, together with their interaction with come aspects of NDT. It is concluded that fracture mechanics and NDT are complementary disciplines that influence each other. Both are used in the measurement of material properties in the presence of a crack, and both are used in engineering assessments of components and structures in the presence of actual or postulated cracks or creck-like flaws. Graphs, 11 ref.
536
Int J Fatigue November 1993