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Growth and coalescence of fatigue cracks at weld toes in steel
In addition, the influence of load ratios CR),the material strength. and grain size on fatigue threshold visa investigated. Compsct tension specimens with-trsnsverselongitudinal (TL) orientation in four different heat-treated conditions IHTCI and also without heat treatments were used. The heat treatment studies revealed a peak hardness after solution treatment st 1200 “C for 0.5 h, followed by sgeing st 600 “C for 434h. Among all the heat-treated conditions, the fatigue threshold was the highest and near-threshold crack growth rate the lowest in the peak hardened condition. Fatigue threshold values were observed to decrease with an increase in load ratio. while the increasing grain size resulted in a higher fatigue threshold. An earlier developed mathematical model wsa applicable to characterize the relationship between load ratio and fatigue threshold. A thin film of carbide precipitation was observed along the grain boundanl in the peak hardened condition. The carbide precipitation facilitated intergranular crack growth in the sample resulting in higher roughness-induced crack closure. The highest fatigue threshold in the peak aged condition is the result of this large roughness-induced crack closure process.
Fatigue liie evaluation under out-of-phase push- 1111and torsion. Ohkawa, b, Takahashi, H., Tomaru, T. and Misumi, &! J. Sot. Mater. Sci. Jpn 40 458 (Nov 1991) 1459-1465 (in Japanese) The stress-baaed evaluation of fatigue life under both in-phase and out-of-phase combined loading conditions is discussed. Load-controlled fatigue teaxa were performed on s low carbon steel leg CHlOA steel) under combined push-pull and completely reversed torsion in ths intermediate to high cycle regime. Phase differences between two loadings were 0, 45, and 90”. Experimental data showed that the increase of phase difference resulted in the increase of fatigue life under combined loadings. This may be explained by the decrease of plastic strain range due to material hardening in out-of-phase conditions. Gough’a ellipse quadrant wsa generalized to out-of-phase loadings by taking account of the phase differences. This criterion csn be easily applied but slightly overestimates the actual life. A modification of Lee’s criterion, which wsa also an extension of Gough’s equation. showed good agreement with the observed life. Furthermore, Brown-Miller’s theory expressed in terms of the shear and normal stresses on the maximum shear plane wsa applied to out-of-phase fatigue. As a result, the fatigue lives under push-pull, torsion and combined in- and out-of-phase loadings were well correlated by Brown-Miller’s criterion. Graphs. 23 refs.
A new approach to the prediction of fretting fati shift of contact edge. Nakamura, M., Hatton, T., .EEI~,e,PY,E%%F%! $ Sot. Mater. Sci. Jpn. 40 458 (Nov 1991) 1453-1458
(in Japanese)
In fretting fatigue, it has been known that the contact edge is shifted inward because of wear. The effect of the contact edge shift on crack propagation behsviour is considered to predict accurate fratting fatigue. The stress intensity factor & for fretting fatigue crack wsa calculated by using the S-N curves of fretting fatigue predicted by using the relationship between the calculated stress intsnaihl factor range (A&) and the crack proDagation rate (ds/dN) obtained from CT specimens. Fret&g fatigue tests were- p&f&med on Ni-Mo-V steel specimens I& Fe-0.24C2.76Ni-1.38Cr-0.34Mo-0.33Mn-0.11Vl. The S-N curves of exoerimentsl results were in good agreement with the anal&al results obtained by considering the contscl edge shift.
D~~tabase of non-metallic indusions end its applkation to the fatigue ktion method of high strength steels. Toriyama, T., -Pred Mura am,, Y. and Makino, T. J. Sot. Mater. Sci. Jpn 40 458 (Nov 1991) 1497-1503 (in Japanese) Non-metallic inclusions csuae relatively low fatigue strength for high-strength steels leg SUPS, SAE9254. S46C. SUJZ, SKH51. AMS5643, 17-4PH. 630 etc.) and also csuae s large scstter of fatigue strength. A method of inclusion w”nt on the basis of statistics of extreme is proposed to evaluate material quality. By combining the new inclusion counting method and fatigue strength prediction equation prop&ad bv Mursksmi et al. the lower bound of scatter band of fstiaue strength can be piediaed. The square root of the projection ares of inclusion r&t ares is-the crucial parameter both in inclusion counting end fatigue strength prediction. The database of cumulative frequency of the maximum inclusion size rwt ares mar of various commercial steels is presented. The scatter bends in rotating-bending fatigue strength of back up roll steel are estimated by the proposed method and are confirmed to be in good agreement with the experimental results. Graphs. 9 refa.
Quantitative evaluation of corrosion fetigue crack initiation process for high tensile strength steel. Konda, IV. and Toyama, K. J. Sot. Mater. Sci. Jpn 40 458 (Nov 1991) 1466-1471 (in Japanese) Materials for construction tend to be used in harsher environments nowadays. Much effort has been spent to understand the effect of environment on fatigue strength. Especially, the environmental effect on fatigue crack propagation behsviour has been clarified in many combinations of materials and environmental conditions. However, each atep if the corrosion fatigue process has not been evaluated in detail. Each period from initiation and growth of corrosion pita to initiation and propagation of corrosion fatigue cracks is estimated. Material used wsa s carbon steel HT60 of 630 MPe class tensile atrenath. A micro-drilled notch wsa introduced st the surface of teat specimen by mschi&tg. The notch of 60 pm diameter. which imitated corrosion pita, wsa expected to fill the role of concentrated streaa sites. Teat environments were 3.5 wt.% NsCl solution and 1.33 x lo-” Pa sir in s chamber of scanning electron microawpe (SEMI. Fatigue tests were conducted under s load ratio of 0.1 st s frequency of 1.5 Hz in NsCl solution and st 20 Hz in s vacuum. While under wntinu&a observation by SEM. s crack which reached 20-30 pm in length wsa defined as fatigue crack initiation. A regression equation, with an accuracy within a factor of 5. for fatigue crack initiation life wea derived for both environments. It becsme clear that the effect of Stress and notch shape on initiation life wea smaller in NsCl solution than that in s vecuum. In addition a relationship between atreaa solution and the initiation life of corrosion pita wea estimated to be quite shaft, and s ratio of fatigue crack initiation life to total failure life wss epprox 35% regardless of atreaa intensiN factors. Graphs, photomicrographs. 7 refs.
422
Effect of microstructure on fatigue propertks in low and ultra-low carbon steels. Yokomaku, T., Kinefuchi, M. and Minokata, Y. J. Sot. Mater. Sci. Jpn 40 (Nov 1991) 1415-1421 (in Japanese) Ultra-low carbon steel containing phosphorus and Cu (P-C& steel, eg Fe-O.OOJC1.26Mn-0.32Cu-0.26Si-O.O89P)has both a higher fatigue limit and better crsqk propagation resistance than conventional low C steels leg Fe-O.O9C-0.76Mn-O.OZSiO.OlZP) with the asme tensile strength. The mechanism for improving the fatigue properties of P-Cu steel is discussed on the basis of microscopic observations by electron microscope and measurements of crack closure behsviour for small and long fatigue cracks. The excellent fatigue limit and small-crack propagation resistance in P-Cu steel can be attributed to solution hardening csused.by P and precipitation hardening caused by r-Cu. On the other hand. the superior resistance to low-fstioue crack propagation was caused by grain coarsening which ocwra with red&n of C content, leading eventually to roughness-induced crack closure. Graphs, photomicrographs. 15 refs. Fracture mechanisms of fibre-reinforced titanium alloy matrix composites. IV. Low cycle fatigue. Jeng, S. M., Alassoeur, P., Yang, J.-M. and Aksoy, S. Mater. Ser. Eng. A. A148 1 (Nov 1991) 67-77 The low-cycle fatigue behsviour and mechanisms of fatigue damage initiation and propagation of several SCS-6 fibre-reinforced Ti alloy wmposities (Ti-6AI-4V. Ti15V-30-3A1-3Sn, Ti-25AI-lONb,-JV-1MoJ at room temperature were investigated. The fatigue damage diagram was constructed using the maximum stress in the fibre vs. fatigue life. Depending on the atreaa levels applied, the fatigue damage of the composites can be classified into three regions: (1 I fibra breakage dominated: 12) interfacial cracking, matrix cracking. and fibre breakage dominated (progressive); and (3) matrix cracking dominated. The microstrwtursl parameters which affect the low-cycle fatigue behsviour of these composites are also discussed. Graphs. photomicrogrsphs. 16 refs. Fatigue fractography 272
2E$Y-T
of patt.icukte-Sic-reinforced AZ,%
AI(A356)
cast alloy.
SFX7%753-66
Fatigue frsctogrsphy of cast particulate-Sic-reinforced AI(A356) metal matrix composites wsa carried out. In the low-cycle regime, the features on the fracture surfaces, mainly distorted dimples and cracked and also debonded Sic particles, are similar to those found in unisxisl tension. However, in the high-cycle regime, extensive slip behsviour in the Al matrix end relative movement between the two sides of the fracture surface produced some special sppes~sncsa, large flat Al matrix sreaa with characteristic line patterns and step-like fracture surface regions. Mechanisms for the formation of the above phenomena sre Droposed. In psrticulsr. the constraint exerted by reinforcing psrticisa distributed &&I grain bbundsriea on the cyclic deformation and fatigue crack propagation in the corresponding Al grains sre discussed. In all samples studied, it is found that fatigue cracks were ~suslly initiated at processing defects, such as casting shrinkage and unwetted SIC particle clusters. Photomicrogrspha. 14 rafa. Improved methods for testing bond and intrinsic strength and feti ue of thermally sprayed metdlk and ceramic coatings. Schweitzer, I?.K., Ziehl, M.H. and Schwamin er, Ch. Surf Coat. Technol. 48 2 (itov 1991) 103-l 12 Conventional bond strength tests for thermally sprayed coatings represent only a rough mesna of obtaining overall strength vslues, with no differentiation between adhesion st the interface and intrinsic costing properties. To obtain information about the influence of substrate preparation on. the adhesion of e Tribsloy ‘I700 costing, tensile bond strength and modified crack-opening displacement (COD) specimens wsre tested by deliberate crack initiation st the interface. Crack initiation was achieved by weakening of the interface at the outer diameter in the case of bond strength specimens or at the notch mot in the teas of COD specimens. This made it possible to look at the influence of surface roughness end grit wnteminstion on the coating adhesion separately. Modified COD specimens with ths notch in the centre of the costing were used to determine crack-opening energies end critics1 stress intensity factors of atmospheric plasma-sprayed NiAl and low pressure plasma-sprayed CoNiCrAlY bond coatings, end s ZrOz 7Y203 thermal barrier costing ITBC). Additionally, bond strength specimens were stressed dynamically, and it could be demonstrated that Wohler (S-N) diagrams ten be established for s metallic NiAl bond costing and even for s ceramic i!rOz 7Y203 TBC. Coatings were sprayed on lnwnel 716. Graphs, photomicrographs. 10 refs. Improvement of mechankel propcnlier of type 403 steinless steel by puke-induction hardening. Albertin, L., Liaw, P.K., Burke, M.G. and Frohlich, R.L. Ser. Metal/. Mater. 25 11 (Nov 1991) 2449-2450 Pulse hardening is a high-power den&Y induction technique which heats s local surface ares of an Fe alloy by short, high-frequency induction phases. The effect of pulse-induction hardening on the met&lurgical, tensile. and fatigue properties of Tvpe 403 stainless steels can be summarized as follows: the Droceaa refined the g&n size, increased the local hardness, improved the notch tensile strength, introduced compressive residual stresses at the surface. and raised the notched fatigue strength. Photomicrogrsphs. graphs. 2 refs. Growth and coalescence of fati ue cricks at weld toes in steel. Otegui, J.L., Burns, D.J., Kerr, H. W. an d Mohaupt, U.H. Int. J. Pressure Vessels Piping 48 2 (Nov 1991) 129-165 The early fatigue growth of cracks starting from defects st the toe of good-quality manual and automatic steel (e.g. HSLA) T-plate welds was investigated. Evolution of aspect ratios and growth rates were monitored, and linear elastic fracture mechanics models of fatigue propagation were developed. It wsa found that smallcrack effects caused by crack closure, weld metal microstructure and notch plsaticitv, together with the uncertainty ssswiated with random initiation and eerly wslescen& of microcracks. made any deterministic linear elastic fracture mechanics modellina of cracks less than ai = 0.3 mm impossible. Fatigue cracks on automatic welds developed much smaller aspect ratios, and grew much faster. than cracks on manual welds. Models of the evolution of aspect ratios on both manual and automatic welds sre presented and discussed, and life predictions sre compared with experimental results. Graphs. 32 refs.
Int J Fatigue November
1992
Fatigue liie evaluation under out-of-phase push- 1111and torsion. Ohkawa, b, Takahashi, H., Tomaru, T. and Misumi, &! J. Sot. Mater. Sci. Jpn 40 458 (Nov 1991) 1459-1465 (in Japanese) The stress-baaed evaluation of fatigue life under both in-phase and out-of-phase combined loading conditions is discussed. Load-controlled fatigue teaxa were performed on s low carbon steel leg CHlOA steel) under combined push-pull and completely reversed torsion in ths intermediate to high cycle regime. Phase differences between two loadings were 0, 45, and 90”. Experimental data showed that the increase of phase difference resulted in the increase of fatigue life under combined loadings. This may be explained by the decrease of plastic strain range due to material hardening in out-of-phase conditions. Gough’a ellipse quadrant wsa generalized to out-of-phase loadings by taking account of the phase differences. This criterion csn be easily applied but slightly overestimates the actual life. A modification of Lee’s criterion, which wsa also an extension of Gough’s equation. showed good agreement with the observed life. Furthermore, Brown-Miller’s theory expressed in terms of the shear and normal stresses on the maximum shear plane wsa applied to out-of-phase fatigue. As a result, the fatigue lives under push-pull, torsion and combined in- and out-of-phase loadings were well correlated by Brown-Miller’s criterion. Graphs. 23 refs.
A new approach to the prediction of fretting fati shift of contact edge. Nakamura, M., Hatton, T., .EEI~,e,PY,E%%F%! $ Sot. Mater. Sci. Jpn. 40 458 (Nov 1991) 1453-1458
(in Japanese)
In fretting fatigue, it has been known that the contact edge is shifted inward because of wear. The effect of the contact edge shift on crack propagation behsviour is considered to predict accurate fratting fatigue. The stress intensity factor & for fretting fatigue crack wsa calculated by using the S-N curves of fretting fatigue predicted by using the relationship between the calculated stress intsnaihl factor range (A&) and the crack proDagation rate (ds/dN) obtained from CT specimens. Fret&g fatigue tests were- p&f&med on Ni-Mo-V steel specimens I& Fe-0.24C2.76Ni-1.38Cr-0.34Mo-0.33Mn-0.11Vl. The S-N curves of exoerimentsl results were in good agreement with the anal&al results obtained by considering the contscl edge shift.
D~~tabase of non-metallic indusions end its applkation to the fatigue ktion method of high strength steels. Toriyama, T., -Pred Mura am,, Y. and Makino, T. J. Sot. Mater. Sci. Jpn 40 458 (Nov 1991) 1497-1503 (in Japanese) Non-metallic inclusions csuae relatively low fatigue strength for high-strength steels leg SUPS, SAE9254. S46C. SUJZ, SKH51. AMS5643, 17-4PH. 630 etc.) and also csuae s large scstter of fatigue strength. A method of inclusion w”nt on the basis of statistics of extreme is proposed to evaluate material quality. By combining the new inclusion counting method and fatigue strength prediction equation prop&ad bv Mursksmi et al. the lower bound of scatter band of fstiaue strength can be piediaed. The square root of the projection ares of inclusion r&t ares is-the crucial parameter both in inclusion counting end fatigue strength prediction. The database of cumulative frequency of the maximum inclusion size rwt ares mar of various commercial steels is presented. The scatter bends in rotating-bending fatigue strength of back up roll steel are estimated by the proposed method and are confirmed to be in good agreement with the experimental results. Graphs. 9 refa.
Quantitative evaluation of corrosion fetigue crack initiation process for high tensile strength steel. Konda, IV. and Toyama, K. J. Sot. Mater. Sci. Jpn 40 458 (Nov 1991) 1466-1471 (in Japanese) Materials for construction tend to be used in harsher environments nowadays. Much effort has been spent to understand the effect of environment on fatigue strength. Especially, the environmental effect on fatigue crack propagation behsviour has been clarified in many combinations of materials and environmental conditions. However, each atep if the corrosion fatigue process has not been evaluated in detail. Each period from initiation and growth of corrosion pita to initiation and propagation of corrosion fatigue cracks is estimated. Material used wsa s carbon steel HT60 of 630 MPe class tensile atrenath. A micro-drilled notch wsa introduced st the surface of teat specimen by mschi&tg. The notch of 60 pm diameter. which imitated corrosion pita, wsa expected to fill the role of concentrated streaa sites. Teat environments were 3.5 wt.% NsCl solution and 1.33 x lo-” Pa sir in s chamber of scanning electron microawpe (SEMI. Fatigue tests were conducted under s load ratio of 0.1 st s frequency of 1.5 Hz in NsCl solution and st 20 Hz in s vacuum. While under wntinu&a observation by SEM. s crack which reached 20-30 pm in length wsa defined as fatigue crack initiation. A regression equation, with an accuracy within a factor of 5. for fatigue crack initiation life wea derived for both environments. It becsme clear that the effect of Stress and notch shape on initiation life wea smaller in NsCl solution than that in s vecuum. In addition a relationship between atreaa solution and the initiation life of corrosion pita wea estimated to be quite shaft, and s ratio of fatigue crack initiation life to total failure life wss epprox 35% regardless of atreaa intensiN factors. Graphs, photomicrographs. 7 refs.
422
Effect of microstructure on fatigue propertks in low and ultra-low carbon steels. Yokomaku, T., Kinefuchi, M. and Minokata, Y. J. Sot. Mater. Sci. Jpn 40 (Nov 1991) 1415-1421 (in Japanese) Ultra-low carbon steel containing phosphorus and Cu (P-C& steel, eg Fe-O.OOJC1.26Mn-0.32Cu-0.26Si-O.O89P)has both a higher fatigue limit and better crsqk propagation resistance than conventional low C steels leg Fe-O.O9C-0.76Mn-O.OZSiO.OlZP) with the asme tensile strength. The mechanism for improving the fatigue properties of P-Cu steel is discussed on the basis of microscopic observations by electron microscope and measurements of crack closure behsviour for small and long fatigue cracks. The excellent fatigue limit and small-crack propagation resistance in P-Cu steel can be attributed to solution hardening csused.by P and precipitation hardening caused by r-Cu. On the other hand. the superior resistance to low-fstioue crack propagation was caused by grain coarsening which ocwra with red&n of C content, leading eventually to roughness-induced crack closure. Graphs, photomicrographs. 15 refs. Fracture mechanisms of fibre-reinforced titanium alloy matrix composites. IV. Low cycle fatigue. Jeng, S. M., Alassoeur, P., Yang, J.-M. and Aksoy, S. Mater. Ser. Eng. A. A148 1 (Nov 1991) 67-77 The low-cycle fatigue behsviour and mechanisms of fatigue damage initiation and propagation of several SCS-6 fibre-reinforced Ti alloy wmposities (Ti-6AI-4V. Ti15V-30-3A1-3Sn, Ti-25AI-lONb,-JV-1MoJ at room temperature were investigated. The fatigue damage diagram was constructed using the maximum stress in the fibre vs. fatigue life. Depending on the atreaa levels applied, the fatigue damage of the composites can be classified into three regions: (1 I fibra breakage dominated: 12) interfacial cracking, matrix cracking. and fibre breakage dominated (progressive); and (3) matrix cracking dominated. The microstrwtursl parameters which affect the low-cycle fatigue behsviour of these composites are also discussed. Graphs. photomicrogrsphs. 16 refs. Fatigue fractography 272
2E$Y-T
of patt.icukte-Sic-reinforced AZ,%
AI(A356)
cast alloy.
SFX7%753-66
Fatigue frsctogrsphy of cast particulate-Sic-reinforced AI(A356) metal matrix composites wsa carried out. In the low-cycle regime, the features on the fracture surfaces, mainly distorted dimples and cracked and also debonded Sic particles, are similar to those found in unisxisl tension. However, in the high-cycle regime, extensive slip behsviour in the Al matrix end relative movement between the two sides of the fracture surface produced some special sppes~sncsa, large flat Al matrix sreaa with characteristic line patterns and step-like fracture surface regions. Mechanisms for the formation of the above phenomena sre Droposed. In psrticulsr. the constraint exerted by reinforcing psrticisa distributed &&I grain bbundsriea on the cyclic deformation and fatigue crack propagation in the corresponding Al grains sre discussed. In all samples studied, it is found that fatigue cracks were ~suslly initiated at processing defects, such as casting shrinkage and unwetted SIC particle clusters. Photomicrogrspha. 14 rafa. Improved methods for testing bond and intrinsic strength and feti ue of thermally sprayed metdlk and ceramic coatings. Schweitzer, I?.K., Ziehl, M.H. and Schwamin er, Ch. Surf Coat. Technol. 48 2 (itov 1991) 103-l 12 Conventional bond strength tests for thermally sprayed coatings represent only a rough mesna of obtaining overall strength vslues, with no differentiation between adhesion st the interface and intrinsic costing properties. To obtain information about the influence of substrate preparation on. the adhesion of e Tribsloy ‘I700 costing, tensile bond strength and modified crack-opening displacement (COD) specimens wsre tested by deliberate crack initiation st the interface. Crack initiation was achieved by weakening of the interface at the outer diameter in the case of bond strength specimens or at the notch mot in the teas of COD specimens. This made it possible to look at the influence of surface roughness end grit wnteminstion on the coating adhesion separately. Modified COD specimens with ths notch in the centre of the costing were used to determine crack-opening energies end critics1 stress intensity factors of atmospheric plasma-sprayed NiAl and low pressure plasma-sprayed CoNiCrAlY bond coatings, end s ZrOz 7Y203 thermal barrier costing ITBC). Additionally, bond strength specimens were stressed dynamically, and it could be demonstrated that Wohler (S-N) diagrams ten be established for s metallic NiAl bond costing and even for s ceramic i!rOz 7Y203 TBC. Coatings were sprayed on lnwnel 716. Graphs, photomicrographs. 10 refs. Improvement of mechankel propcnlier of type 403 steinless steel by puke-induction hardening. Albertin, L., Liaw, P.K., Burke, M.G. and Frohlich, R.L. Ser. Metal/. Mater. 25 11 (Nov 1991) 2449-2450 Pulse hardening is a high-power den&Y induction technique which heats s local surface ares of an Fe alloy by short, high-frequency induction phases. The effect of pulse-induction hardening on the met&lurgical, tensile. and fatigue properties of Tvpe 403 stainless steels can be summarized as follows: the Droceaa refined the g&n size, increased the local hardness, improved the notch tensile strength, introduced compressive residual stresses at the surface. and raised the notched fatigue strength. Photomicrogrsphs. graphs. 2 refs. Growth and coalescence of fati ue cricks at weld toes in steel. Otegui, J.L., Burns, D.J., Kerr, H. W. an d Mohaupt, U.H. Int. J. Pressure Vessels Piping 48 2 (Nov 1991) 129-165 The early fatigue growth of cracks starting from defects st the toe of good-quality manual and automatic steel (e.g. HSLA) T-plate welds was investigated. Evolution of aspect ratios and growth rates were monitored, and linear elastic fracture mechanics models of fatigue propagation were developed. It wsa found that smallcrack effects caused by crack closure, weld metal microstructure and notch plsaticitv, together with the uncertainty ssswiated with random initiation and eerly wslescen& of microcracks. made any deterministic linear elastic fracture mechanics modellina of cracks less than ai = 0.3 mm impossible. Fatigue cracks on automatic welds developed much smaller aspect ratios, and grew much faster. than cracks on manual welds. Models of the evolution of aspect ratios on both manual and automatic welds sre presented and discussed, and life predictions sre compared with experimental results. Graphs. 32 refs.
Int J Fatigue November
1992