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The effect of double quenching on the behaviour of fatigue crack propagation in structural steel
correlation was found between crack growth and relatively high AE activity in this region. Active cracks deeper than 0.3-0.6 mm were detected, although the size of the AE indication was not proportional to the cracking activity and zoning calibration studies had to be taken into account. No significant cracks were missed. 11 refs.
Acoustic emission m o n i t o r i n g o f • fatigue mack in 50D steel In a sea w a t e r environment, Buttle, D. J. and Scruby, C. B. NDT Int. Apr. 1989 22, (2), 81-96 Four specimens of 4360-50D steel plates were fatigued under a range of simulated marine environments and loads. AE events were detected using four broadband point-contact transducers end location in 3D (< 1 mm accuracy) relative to the crock front. This information was used together with the load st which each emission occurred to distinguish between "primary' and 'secondary' source events. Little or no emission was observed from a dry fatigue crack, indicating that ductile crack growth by mode I loading in 50D steel plate is relatively quiet. In the presence of see water, however, secondary emissions were observed at discrete points behind the crack tip where subsequent chemical analysis indicated a high concentration of calcium carbonate deposit. A third, cathodicelly protected, specimen gave much more AE, consistent with an increase in calcium carbonate between the crack faces. The emissions occurred at loads between zero and maximum tension. The characteristics of the AlE signals did not change on reducing the maximum load, confirming that crack advance was not responsible. Crack face debonding, arising from fracture of calcareous deposits present, is believed to be the source of AE. A fourth specimen, also cethodicelly protected, was fatigued entirely in tension and gave less AE, consistent with much weaker crack face bonding. Measurements of the compressional wave arrival strengths at each probe were compared with calculated radiation patterns for different types of AE source. The experimental radiation patterns were always consistent with a double monopole combined with a micrncreck source in varying proportions. Under these testing conditions, secondary events associated with corrosion product fracture dominated the emission. Whilst little or no primary emission was detected during fatigue crack growth in parent plate, this may not be the case in welds, regions of low toughness or where the stress fields are more complex. 23 refs.
Electro-impulco de-icing research (fatigue end electromagnetic interforonse tests). (Final report). Zumwalt, G. W., Friedberg, R. A. and
Schwartz, J. A. Wichita State University, Report No. AD-A209 330/O/XAB Mar. 1989, 63 pp Electro-impulse de-icing (EIDI) has been recently developed and tested with very encouraging results. Questions remain, however, regarding the fatigue life and electromagnetic compatibility of the system. Fatigue tests were conducted on two production AI wing leading edges and one composite material leading edge. These were done at realistic temperatures and impulse energies for an estimated aircraft lifetime of ice protection. Coil mounting brackets were the main casualties. Wing components did not fail. Teats were also conducted for metal and composite wings of electromagnetic radiation of EIDI over a wide frequency range. The AI wing was found to be an excellent shield. All wires external to the AI wing were shown to require careful shielding. The composite wing required all wiring and the metal doublers to be shielded and grounded.
Investigations of cracks in Auckland Harbour Bridge. Spinks, A. CSNDTJ. 21-23 M a r c h - A p r i l . 1989 10, (2), 18 The New Zealand Ministry of Works and Development's Central Laboratories have been carrying out ultrasonic testing on Auckland Harbour Bridge, after the discovery of fatigue cracks in the deck stiffeners of the extension cerriegewsys in August 1985. The deck plates of the box girder sections forming the extensmn cerriagewsys are stiffened by a number of troughs formed from 6 mm steel plate running longitudinally. The troughs are joined at each box girder join by means of an overlapped section of trough, fillet welded at the edges; and a number of fillet welds have cracked as a result of flexing of the deck plates by traffic. Ultrasonic examination has revealed that many more fillet welds contain cracks below the surface, which have been shown to be due to fatigue, and a programme of replacement of the welds is under way. Central Laboratories staff are following the welders with 100% ultrasonic testing of the trough joints to ensure that no cracks remain. The equipment being used is a portable ultrasonic G-scan system, developed a number of years ago by Central Laboratories, and recently improved to produce detailed images of defects in steel 6 mm thick.
A m e t h o d to obtain ideal fatigue crack propagation f o r steels. Masuda,
H. and Matsuoka, S. ASTM J. Test. Eval. Nov. 1989 17, (6), 394-400 To predicte fatigue crack growth rates under variable loading conditions, a new fatigue test method was developed. Fatigue crack propagation properties were studied for HTB0,SMSOBand SUS304 steels. Test resu Rsshowed that the acceleration of the crack propagation rate occurred at low AK regions when the intermittent compressive overload was applied. The maximum acceleration of crack propagation was dependent on both the frequency and amplitude of the overload. When the compressive overload is frequently applied, the crack propagation rate becomes proportional to the second power of ZLK.These accelerations of the crack propagation rate under compressive overloading conditions were discussed with respect to the deformation mode at the crack tip. 3 refs.
Int J Fatigue May 1990
An encapsulation technique f o r conducting medmnicol p r ~ tests o f metallic specimens in • controlled e n v i r o n m e n t w i t h o u t • retort.
Kschinka, B. A., Marriott, D. L., Stubbins, J. F. and Vaesos, N. ASTM J. Test. Eval. Nov. 1989 17, (6), 368-372 A novel technique to encapsulate metallic mechanical properties test specimens (eg 2.25Cr-lMo) in a controlled atmosphere has been developed that eliminates the need for cumbersome retort systems. The procedure consists of brazing stainless steel flexible bellows tubing on e test specimen in such a manner that the tubing acts as a miniature retort around the gauge section of the specimen. While convenient, this method demands a special correlation relating strain in the gauge section to displacement between the specimen shoulders to conduct displacementcontrolled fatigue tests. Results of such tests using vacuum encapsulated specimens was generally excellent and agreed reasonably well with data from related studies, supporting the validity of both the encapsulation technique and the subsequent correlation. 2 refs.
Thermal treatment T h • effect of d o u b l • quenching on the behaviour of fatigue crack propagation in structural cteoI.Sha, G., Meng, Q. and Fang, X. Heat Treat. Met. (China) June 1989 (6), 3 - 1 0 (in Chinese) The effect of double quenching (1200~C Q/650°C T.860°C Q.) on the microstructure and behaviour of fatigue crack propagation of 40Cr steel is investigated. Experimental results show that double quenching decreases austenita grain size, and increases the amount of lath martenslte and residual austenite film between martensite laths. After 200 or 400°C tempering, fatigue fracture of 40Cr steel is s mixture of intergranualr and tranegrenulsr. The effect of double quenching on the fracture mechanism at the earlier of crack propagation is not observed. Graphs, photomicrographs. 6 refs. M e t h o d s of heat t r e a t m e n t f o r 3Cr2WBV h o t - w o r k i n g die steel t o improve the dla lif•. Meng, X. M. Heat Treat. Met. (China) 1989 (5), 39-43 (in Chinese) Various heat treatment processes applied to the hot-working die steal, 3Cr2WBV, providing marked improvement of the service life of dies are outlined. The optimal technological parameters of each process and the sample applications are briefly discussed. It is shown that good results have been obtained by using these methods in practical production in saving energy and operation time, enhanced strength and impact toughness, good heat resistance, wear resistance, suitable structure, and the avoidance of cracks. 27 refs. Influence of l o w temperature tempering on the structure and p r o p e r t y of • carbonitrided layer in 20CrMnTi steel. Chang, T. y., Song, W., Me,
M. y., Yao, Y. k. andXing, D. z. Heat Treat. Met. (China) 1989 (5), 35-39 (in Chinese) The influence of low temperature tempering on the structure property and grinding crack tendency of a carbonltrided layer in 20CrMnTi steel is presented. The experimental results show that, along with an increase in tempering temperature, the amount of retained austenite in the cerbonitrided layer decreases, the tensile strength increases and the impact toughness decreases. When the cerbonitrided layer is tempered at 240°C, the contact fatigue strength will reach maximum, and when it is tempered at 260°(: the grinding crack tendency will fall to a minimum. The suitable tempering temperature should be in the range of 240-280°C. Graphs. 8 refs. Improving the impact fatigue resistance of WMAoSCr4V2 (M2) high
speed steel. Liu, F. and Chen, Z.-I. Heat Treat. Met. (China) 1989 (4), 20-25 (in Chinese) The infuence of the heat treating process on the impact fatigue behaviour of W6Mo5Cr4V2 (M2) steel was investigated. The results show that the impact fatigue life was decreased linearly with the auatenitizing temperature from 1170-1230°C, especially under the lower level of impact energy. The impact life of this steel reaches maximum after quenching at 1210°C and tempering at 500--560°C. Thus the suitable heat treatment of the steel with optimum impact fatigue resistance is suggested. Graphs, photomicrographs. 12 refs. Effect o f simultaneous B ÷ and N~- implantation on microh•rdness, f a t i g u • lif•, and microstructure in F e - 1 3 C r - 1 5 N l base alloys. Lee, E. H.
and Mansur, L. K.
J. Mater. Res. Nov.-Dec. 1989 4, (6), 1371-1378 M~crohardness and cantilever beam fatigue measurements were conducted on Fe-13Cr-15Ni base austenitic alloys that were implanted with boron and nitrogen ions either singly or simultaneously. The microstructure of the modified surface layer and dislocation slip modes after fatigue tests were investigated by optical and transmission electron microscopy. Both hardness and fatigue life were improved by ion implantation, but the greatest improvement was achieved when B and N were implanted simultaneously. The degree of fatigue life improvement also varied with minor changes in the base alloying compositions: N was detrimental or ineffective in the presence of Ti, and B was much more effective in the presence of Mo. Comparison of slip bend morphology between the compression and tension cycles indicated that implantation improved the reversibility of surface slip and delayed crack initiation. 20 refs.
231
Acoustic emission m o n i t o r i n g o f • fatigue mack in 50D steel In a sea w a t e r environment, Buttle, D. J. and Scruby, C. B. NDT Int. Apr. 1989 22, (2), 81-96 Four specimens of 4360-50D steel plates were fatigued under a range of simulated marine environments and loads. AE events were detected using four broadband point-contact transducers end location in 3D (< 1 mm accuracy) relative to the crock front. This information was used together with the load st which each emission occurred to distinguish between "primary' and 'secondary' source events. Little or no emission was observed from a dry fatigue crack, indicating that ductile crack growth by mode I loading in 50D steel plate is relatively quiet. In the presence of see water, however, secondary emissions were observed at discrete points behind the crack tip where subsequent chemical analysis indicated a high concentration of calcium carbonate deposit. A third, cathodicelly protected, specimen gave much more AE, consistent with an increase in calcium carbonate between the crack faces. The emissions occurred at loads between zero and maximum tension. The characteristics of the AlE signals did not change on reducing the maximum load, confirming that crack advance was not responsible. Crack face debonding, arising from fracture of calcareous deposits present, is believed to be the source of AE. A fourth specimen, also cethodicelly protected, was fatigued entirely in tension and gave less AE, consistent with much weaker crack face bonding. Measurements of the compressional wave arrival strengths at each probe were compared with calculated radiation patterns for different types of AE source. The experimental radiation patterns were always consistent with a double monopole combined with a micrncreck source in varying proportions. Under these testing conditions, secondary events associated with corrosion product fracture dominated the emission. Whilst little or no primary emission was detected during fatigue crack growth in parent plate, this may not be the case in welds, regions of low toughness or where the stress fields are more complex. 23 refs.
Electro-impulco de-icing research (fatigue end electromagnetic interforonse tests). (Final report). Zumwalt, G. W., Friedberg, R. A. and
Schwartz, J. A. Wichita State University, Report No. AD-A209 330/O/XAB Mar. 1989, 63 pp Electro-impulse de-icing (EIDI) has been recently developed and tested with very encouraging results. Questions remain, however, regarding the fatigue life and electromagnetic compatibility of the system. Fatigue tests were conducted on two production AI wing leading edges and one composite material leading edge. These were done at realistic temperatures and impulse energies for an estimated aircraft lifetime of ice protection. Coil mounting brackets were the main casualties. Wing components did not fail. Teats were also conducted for metal and composite wings of electromagnetic radiation of EIDI over a wide frequency range. The AI wing was found to be an excellent shield. All wires external to the AI wing were shown to require careful shielding. The composite wing required all wiring and the metal doublers to be shielded and grounded.
Investigations of cracks in Auckland Harbour Bridge. Spinks, A. CSNDTJ. 21-23 M a r c h - A p r i l . 1989 10, (2), 18 The New Zealand Ministry of Works and Development's Central Laboratories have been carrying out ultrasonic testing on Auckland Harbour Bridge, after the discovery of fatigue cracks in the deck stiffeners of the extension cerriegewsys in August 1985. The deck plates of the box girder sections forming the extensmn cerriagewsys are stiffened by a number of troughs formed from 6 mm steel plate running longitudinally. The troughs are joined at each box girder join by means of an overlapped section of trough, fillet welded at the edges; and a number of fillet welds have cracked as a result of flexing of the deck plates by traffic. Ultrasonic examination has revealed that many more fillet welds contain cracks below the surface, which have been shown to be due to fatigue, and a programme of replacement of the welds is under way. Central Laboratories staff are following the welders with 100% ultrasonic testing of the trough joints to ensure that no cracks remain. The equipment being used is a portable ultrasonic G-scan system, developed a number of years ago by Central Laboratories, and recently improved to produce detailed images of defects in steel 6 mm thick.
A m e t h o d to obtain ideal fatigue crack propagation f o r steels. Masuda,
H. and Matsuoka, S. ASTM J. Test. Eval. Nov. 1989 17, (6), 394-400 To predicte fatigue crack growth rates under variable loading conditions, a new fatigue test method was developed. Fatigue crack propagation properties were studied for HTB0,SMSOBand SUS304 steels. Test resu Rsshowed that the acceleration of the crack propagation rate occurred at low AK regions when the intermittent compressive overload was applied. The maximum acceleration of crack propagation was dependent on both the frequency and amplitude of the overload. When the compressive overload is frequently applied, the crack propagation rate becomes proportional to the second power of ZLK.These accelerations of the crack propagation rate under compressive overloading conditions were discussed with respect to the deformation mode at the crack tip. 3 refs.
Int J Fatigue May 1990
An encapsulation technique f o r conducting medmnicol p r ~ tests o f metallic specimens in • controlled e n v i r o n m e n t w i t h o u t • retort.
Kschinka, B. A., Marriott, D. L., Stubbins, J. F. and Vaesos, N. ASTM J. Test. Eval. Nov. 1989 17, (6), 368-372 A novel technique to encapsulate metallic mechanical properties test specimens (eg 2.25Cr-lMo) in a controlled atmosphere has been developed that eliminates the need for cumbersome retort systems. The procedure consists of brazing stainless steel flexible bellows tubing on e test specimen in such a manner that the tubing acts as a miniature retort around the gauge section of the specimen. While convenient, this method demands a special correlation relating strain in the gauge section to displacement between the specimen shoulders to conduct displacementcontrolled fatigue tests. Results of such tests using vacuum encapsulated specimens was generally excellent and agreed reasonably well with data from related studies, supporting the validity of both the encapsulation technique and the subsequent correlation. 2 refs.
Thermal treatment T h • effect of d o u b l • quenching on the behaviour of fatigue crack propagation in structural cteoI.Sha, G., Meng, Q. and Fang, X. Heat Treat. Met. (China) June 1989 (6), 3 - 1 0 (in Chinese) The effect of double quenching (1200~C Q/650°C T.860°C Q.) on the microstructure and behaviour of fatigue crack propagation of 40Cr steel is investigated. Experimental results show that double quenching decreases austenita grain size, and increases the amount of lath martenslte and residual austenite film between martensite laths. After 200 or 400°C tempering, fatigue fracture of 40Cr steel is s mixture of intergranualr and tranegrenulsr. The effect of double quenching on the fracture mechanism at the earlier of crack propagation is not observed. Graphs, photomicrographs. 6 refs. M e t h o d s of heat t r e a t m e n t f o r 3Cr2WBV h o t - w o r k i n g die steel t o improve the dla lif•. Meng, X. M. Heat Treat. Met. (China) 1989 (5), 39-43 (in Chinese) Various heat treatment processes applied to the hot-working die steal, 3Cr2WBV, providing marked improvement of the service life of dies are outlined. The optimal technological parameters of each process and the sample applications are briefly discussed. It is shown that good results have been obtained by using these methods in practical production in saving energy and operation time, enhanced strength and impact toughness, good heat resistance, wear resistance, suitable structure, and the avoidance of cracks. 27 refs. Influence of l o w temperature tempering on the structure and p r o p e r t y of • carbonitrided layer in 20CrMnTi steel. Chang, T. y., Song, W., Me,
M. y., Yao, Y. k. andXing, D. z. Heat Treat. Met. (China) 1989 (5), 35-39 (in Chinese) The influence of low temperature tempering on the structure property and grinding crack tendency of a carbonltrided layer in 20CrMnTi steel is presented. The experimental results show that, along with an increase in tempering temperature, the amount of retained austenite in the cerbonitrided layer decreases, the tensile strength increases and the impact toughness decreases. When the cerbonitrided layer is tempered at 240°C, the contact fatigue strength will reach maximum, and when it is tempered at 260°(: the grinding crack tendency will fall to a minimum. The suitable tempering temperature should be in the range of 240-280°C. Graphs. 8 refs. Improving the impact fatigue resistance of WMAoSCr4V2 (M2) high
speed steel. Liu, F. and Chen, Z.-I. Heat Treat. Met. (China) 1989 (4), 20-25 (in Chinese) The infuence of the heat treating process on the impact fatigue behaviour of W6Mo5Cr4V2 (M2) steel was investigated. The results show that the impact fatigue life was decreased linearly with the auatenitizing temperature from 1170-1230°C, especially under the lower level of impact energy. The impact life of this steel reaches maximum after quenching at 1210°C and tempering at 500--560°C. Thus the suitable heat treatment of the steel with optimum impact fatigue resistance is suggested. Graphs, photomicrographs. 12 refs. Effect o f simultaneous B ÷ and N~- implantation on microh•rdness, f a t i g u • lif•, and microstructure in F e - 1 3 C r - 1 5 N l base alloys. Lee, E. H.
and Mansur, L. K.
J. Mater. Res. Nov.-Dec. 1989 4, (6), 1371-1378 M~crohardness and cantilever beam fatigue measurements were conducted on Fe-13Cr-15Ni base austenitic alloys that were implanted with boron and nitrogen ions either singly or simultaneously. The microstructure of the modified surface layer and dislocation slip modes after fatigue tests were investigated by optical and transmission electron microscopy. Both hardness and fatigue life were improved by ion implantation, but the greatest improvement was achieved when B and N were implanted simultaneously. The degree of fatigue life improvement also varied with minor changes in the base alloying compositions: N was detrimental or ineffective in the presence of Ti, and B was much more effective in the presence of Mo. Comparison of slip bend morphology between the compression and tension cycles indicated that implantation improved the reversibility of surface slip and delayed crack initiation. 20 refs.
231