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Failure in extrusion tooling, causes and methods of avoiding failures
Gong. Z.,
describing fatigue crack initiation and early crack growth in cyclically loaded resistance spot welds. SAE960X steel is discussed. Graphs. 32 rats.
Results from acoustic emission (AE) monitoring of 36 steel railroad bridges are presented. The demonstrated successes of using AE to find new cracks, to identify active cracks, to validate the effectiveness of repairs, and to provide damage assessments to assist with repair prioritization are discussed. The challenges presented in using AE for fatigue-life estimation; for the assessment of pins, hangers, and complex weldments; and for crack assessment of severely corroded members are outlined. Finally, new ideas for refined monitoring and enhanced data analysis are presented. Graphs. 15 rats.
A s t u d y of t h e strength of single s p o t - w e l d e d Joint o f a WP 370 steel.
Acoustic emission m o n i t o r i n g
o f steel railroad bridges.
Nyborg, E,D. and Dommen, G. Mater. Eval. July 1992 50, (7), 883-887
Effect o f shot peening on fatigue behavior in a l u m i n u m alloys. Wagner,
L. and Mueller, C. Mater. Menuf. Prec. 1992, 7, (3), 423-440
The individual contributions of residual compressive stresses, high dislocation densities, and surface roughness that are induced by shot peening to the improvement of fatigue life of A12024 are assessed. Stress amplitudes to number of fatigue cycles (S-N) curves and microcrack propagation (da/dN--AKcurves) are determined for both under-aged (T3) and peak-aged (T6) conditions. The fatigue beheviour of the electropolished (which is also the reference condition), shot peened, shot peened and stress relieved, shot peened and polished, and shot peened, stress relieved, and polished condition are evaluated in fatigue teats. Graphs, photomicrographs. 10 rats. The microstructure t r a n s f o r m a t i o n and fatigue fracture analysis of coldw o r k i n g die steel LD in the subzero t r e a t m e n t . Huang, G. and Guo, B. Heat Treat, Met. (China) Jan. 1992 (1), 27-31 (in Chinese) The microatructure transformation and fatigue fracture of steel LD(7CrTMo2V2Si), after treatment by various processes, have been investigated. The result shows that martensite decomposed and precipitated a lot of fine carbide in the subzero process after quenching, the twin line of twinned martensites is banded and some of the retained auatenite transforms to martensite. The fatigue fracture by various processes is transgranular quasi-cleavage fracture. Photomicrographs, diffraction patterns. 5 rats. Fatigue strength o f laser beam surface treated structural steels. Merrien,
P., Lieurede, H.P., Theobalt, M., Baudry, G., Puig, T. and Leroy, F. Surface Eng. 1992 8, (1), 61-65
An industrial advantage of laser processing is that it permits local treatment of mechanical components on those specific areas subject to high stress levels. The way in which this type of laser treatment enhances structural steel properties has been studied. The 42CD4 and XC42 steel specimens were notched to create a stress concentration factor identical to that observed for gears. The work involved optimizing three parameters: the laser beam itself, ie the beam energy-time of interaction couple; specimen preparation, ie selection of the best laser beam-specimen coupling medium (phosphating gave the best emissivity coefficient while avoiding specimen contamination); the metallurgical heat treatment, designed to obtain both high toughness and good ductility. Specimens tempered at various temperatures before the laser treatment were fatigue tested. The results enabled the selection of an intermediate tempering temperature resulting in the highest fatigue limit. They also showed that, in regard to fatigue behaviour, laser surface treatment compared fevourebly with thermochemicel carbonitriding. Photomicrographs, graphs. 9 rats. ~aconsistencies in design code rules f o r fatigue in the presence o f w e l d
ws - a case study. Socie, D. and Marriott, D.L. Int. J. Pressure Vessels and Piping 1992 50, (1-3), 291-296 A failure in an A312-specified austenitic stainless stall fuel delivery piping system revealed some inconsistencies in existing design rules for fatigue. It was discovered that piping manufactured to one set of standards combined with design to a seemingly compatible design code contains a deficiency whereby weld flaws can be formed, remain undetected by hydrotesting and NDE, but still be large enough to propagate in service to the point of leaking. A brief description of this failure is given, as is a more general discussion of welded piping systems containing weld flaws.
Feng.M., Nan, S., Zhang, D. and Dang, Z. Mater. Mech. Eng. (China) Apr. 1991 15, (2), 6-10, 56 (in Chinese) The spot weldability and the strength of a single spot-welded joint of a Chinese steel WP 370 were investigated, and the effects of welding parameters were also tested. It was found that the weldability of WP 370 is satisfactory and the mechanical properties of the joints in the centre of the weldebility zone are better than those near the boundary. The static and fatigue strengths of spot-welded joints of WP 370 are much higher compared with those of SPCE, a Japanese steel which is similar to 08AI. This can be explained by an increase in strength of the base metal. Numerical data, graphs, photomicrographs. 6 refs.
Environmental evaluation of repairs to fuselage lap joints. Molent, L., Bridgford, N., Rees, D. and Jones, R. Composite Struct. (1992) 21, (2), 121-130 The results of a fatigue test programme undertaken to investigate repairs to multisite damage in aircraft fuselage lap joints made of 2024-T3 plate are presented. It is demonstrated that a boron/epoxy composite doubler bonded over the joint should significantly increase the fatigue life of the structure and that environmental effects are negligible. Graphs. 6 rats. Valve spdng w i r e w i t h e x t r a - l o w o x y g e n and w i t h shaved surface - a real need. Rosa, J.A.C., Barcelos, E. Costa, M.L., Hayakawa, M.O. and
Ce, J.C. Wire J. Int. Apr. 1992 25, (4), 59-64
The production of valve spring steels with very low O (8 ppm) which uses vacuum reduction of sulfur and oxygen (VRSO) refining process is described. It involves melting in an electric arc furnace (EAF) using a highly reducing slag to reduce S, followed by ladle metallurgy and vacuum degassing (VD) prior to ingot casting under Ar protection. The hot-rolled wire rod (7.94 mm gauge) is treated to remove rolling-in flaws by a peeling process which uses a rotating tool for machining followed by the 'shavelite' method of peeling the wire by passing through a specialgeometry die. Both O content and level of microinclusioos are lower with improved fatigue strength of the wire thus manufactured compared with that of the wire produced by the conventional method. Failure in extrusion tooling, causes and methods of avoiding failures.
Kortmann, W.A. Prec. Fifth Aluminum Extrusion Technology Sam., Chicago, Illinois, USA, 19-22 May 1992, Vol I (The A l u m i n i u m Association, Washington,
DC, USA, 1992) pp 219-231 Presented are examples of failed tools and dies and components in AI extrusion. A material selection and recommendations for heat treatment, manufacture and use of tools and dies in production are presented. Tool steels for AI extrusion include 6F2, 6F3, H l l , H12 and H13. Effect of surface defects in light press a l u m i n u m extrusions on aerospace manufacturing. Sorenson, E.
Prec. Fifth International Aluminum Extrusion Technology Sere., Chicago,
Illinois, USA, 19-22 May 1992, V e i l (The A l u m i n u m Washington, DC, USA, 1992) pp 521-525
Association,
Extruded AI alloy series 7XXX and 2XXX are prone to surface defects such as blistering, hot tearing, and corrosion pitting. These defects can negatively affect the service life of an airframe and are indeed considered to be undesirable. A recent study by the Boeing Company has shown that the rework and scrap coats associated with receiving extrusions containing these defects, fabricating airframe components and then finding the extrusion defects during the final part inspection are large and unacceptable. The Boeing Company has initiated a cooperative programme with a number of AI extrusion producers to define its needs more clearly and implement a system for minimizing these problems. The programme strives to define rajecteble surface conditions better, improve visual inspection at the producers, and delineate cases in which rework is permitted. The programme is being carefully coordinated with the producer participants to assure that all terms are mutually agreeable.
Fatigue behavior o f (BS 1470 Na-0) a l u m l n l u m alloy end (BS 1501-510) nickel steel double-fillat and t e e - b u t t w e l d s (subject to handing). White, G.C ASTM J. Test. Eval. M a y 1992 20, (3), 180-189
Tempera.l u r e effects on the mesttanism of t i m e independent hydrogen assisted fatigue craCK propagation in steels. Marrow, T.J., King, J.E.
The shell-to-bess welds of liquefied natural gas (LNG) tanks are normally double fillet welds, although in some tanks tee-butt welds are used. The fatigue beheviour of these welds has been examined by testing 134 full-size specimens. The testing examined the low-cycle, high-strain performance of the welds in air at +20°C and in liquid nitrogen at -196 °C. The results have shown that double fillet weld and tee-butt weld fatigue performance are comparable. The low-temperature fctigue performance matched or exceeded that under equivalent ambient conditions. The shell-to-bottom welds used in British Gas LNG tanks have fatigue lives well in excess of that required for operational duty. BS 1470 N8-O and BS 1501-510 are discussed. Photomicrographs, graphs. 1 ref.
The effects of temperature on hydrogen-assisted fatigue crack propagation are investigated in three steels in the low-to.medium strength range: a low alloy structural steal (4360 Gr.50EE), a super duplex stainless steel (Zeron 100), and a super ferritic stainless steel (E-brite). Significant enhancement of crack growth rates is observed in H gas at atmospheric pressure in all three materials. Failure occurs via a mechanism of time-independent, transgranular, cyclic cleavage over a frequency range of 0.1-5 Hz. Increasing the temperature in H up to 80 °C markedly reduces the degree of embrittlement in the structural and superferritic steels. No such effect is observed in the duplex stainless steel until the temperature exceeds 120 °C. The temperature response may be understood by considering the interaction between absorbed H and microstructurel traps, which are generated in the zone of intense plastic deformation ahead of the fatigue crack tip. Photomicrographs. graphs, diffraction patterns. 49 refs.
Fatigue life estimation in rssistance spot w e l d s : initiation and early g r o w t h phase. Sheppard, S.D. and Strange, M. Fatigue Fract. Eng. Mater. Struct. June 1992 15, (6), 531-649 The main objective is to develop a model of fatigue crack initiation and early crack growth in resistance spot welds that is specimen independent. This objective is achieved by examining the stress state around a resistance spot weld. A general expression for the structural stress around the weld is formulated that is dependent only on the loading immediately surrounding the weld. As such, it is specimen independent. An additional objective is to explore the feasibility of applying this fatigue crack initiation model of life estimation using structural response data from finite element analysis (FEA). This numerical technique is often used for evaluating structural integrity of assemblies. Limited verification examples show that the structural stress range as calculated from FEA reaction load data is capable of
Int J Fatigue July 1993
and Cotterill, P.J. Acta Metal/. Mater. Aug. 1992 40, (8), 2059-2068
Frectographic analysis of fatigue cracking in spheroidal graphite cast irons. Bulloch, J.H. Theor. Appl. Fract. Mech. Apr. 1992 17, (1), 19-45 An attempt is made to describe a fairly intense fractogrephic analysis which was performed on the fatigue fracture surfaces of two spheroidal graphite cast iron microstructurse subjected to fatigue loading at various R-ratio values in an ambient air environment. A significem amount of intergranular failure was evident In both microstructurse at low to intermediate AK levels; this failure mode attained maxima at specific &K levels which correspond to the condition when the reversed plsetlc zone size approached the structural parameter (grain) size. The extent or amount
343
describing fatigue crack initiation and early crack growth in cyclically loaded resistance spot welds. SAE960X steel is discussed. Graphs. 32 rats.
Results from acoustic emission (AE) monitoring of 36 steel railroad bridges are presented. The demonstrated successes of using AE to find new cracks, to identify active cracks, to validate the effectiveness of repairs, and to provide damage assessments to assist with repair prioritization are discussed. The challenges presented in using AE for fatigue-life estimation; for the assessment of pins, hangers, and complex weldments; and for crack assessment of severely corroded members are outlined. Finally, new ideas for refined monitoring and enhanced data analysis are presented. Graphs. 15 rats.
A s t u d y of t h e strength of single s p o t - w e l d e d Joint o f a WP 370 steel.
Acoustic emission m o n i t o r i n g
o f steel railroad bridges.
Nyborg, E,D. and Dommen, G. Mater. Eval. July 1992 50, (7), 883-887
Effect o f shot peening on fatigue behavior in a l u m i n u m alloys. Wagner,
L. and Mueller, C. Mater. Menuf. Prec. 1992, 7, (3), 423-440
The individual contributions of residual compressive stresses, high dislocation densities, and surface roughness that are induced by shot peening to the improvement of fatigue life of A12024 are assessed. Stress amplitudes to number of fatigue cycles (S-N) curves and microcrack propagation (da/dN--AKcurves) are determined for both under-aged (T3) and peak-aged (T6) conditions. The fatigue beheviour of the electropolished (which is also the reference condition), shot peened, shot peened and stress relieved, shot peened and polished, and shot peened, stress relieved, and polished condition are evaluated in fatigue teats. Graphs, photomicrographs. 10 rats. The microstructure t r a n s f o r m a t i o n and fatigue fracture analysis of coldw o r k i n g die steel LD in the subzero t r e a t m e n t . Huang, G. and Guo, B. Heat Treat, Met. (China) Jan. 1992 (1), 27-31 (in Chinese) The microatructure transformation and fatigue fracture of steel LD(7CrTMo2V2Si), after treatment by various processes, have been investigated. The result shows that martensite decomposed and precipitated a lot of fine carbide in the subzero process after quenching, the twin line of twinned martensites is banded and some of the retained auatenite transforms to martensite. The fatigue fracture by various processes is transgranular quasi-cleavage fracture. Photomicrographs, diffraction patterns. 5 rats. Fatigue strength o f laser beam surface treated structural steels. Merrien,
P., Lieurede, H.P., Theobalt, M., Baudry, G., Puig, T. and Leroy, F. Surface Eng. 1992 8, (1), 61-65
An industrial advantage of laser processing is that it permits local treatment of mechanical components on those specific areas subject to high stress levels. The way in which this type of laser treatment enhances structural steel properties has been studied. The 42CD4 and XC42 steel specimens were notched to create a stress concentration factor identical to that observed for gears. The work involved optimizing three parameters: the laser beam itself, ie the beam energy-time of interaction couple; specimen preparation, ie selection of the best laser beam-specimen coupling medium (phosphating gave the best emissivity coefficient while avoiding specimen contamination); the metallurgical heat treatment, designed to obtain both high toughness and good ductility. Specimens tempered at various temperatures before the laser treatment were fatigue tested. The results enabled the selection of an intermediate tempering temperature resulting in the highest fatigue limit. They also showed that, in regard to fatigue behaviour, laser surface treatment compared fevourebly with thermochemicel carbonitriding. Photomicrographs, graphs. 9 rats. ~aconsistencies in design code rules f o r fatigue in the presence o f w e l d
ws - a case study. Socie, D. and Marriott, D.L. Int. J. Pressure Vessels and Piping 1992 50, (1-3), 291-296 A failure in an A312-specified austenitic stainless stall fuel delivery piping system revealed some inconsistencies in existing design rules for fatigue. It was discovered that piping manufactured to one set of standards combined with design to a seemingly compatible design code contains a deficiency whereby weld flaws can be formed, remain undetected by hydrotesting and NDE, but still be large enough to propagate in service to the point of leaking. A brief description of this failure is given, as is a more general discussion of welded piping systems containing weld flaws.
Feng.M., Nan, S., Zhang, D. and Dang, Z. Mater. Mech. Eng. (China) Apr. 1991 15, (2), 6-10, 56 (in Chinese) The spot weldability and the strength of a single spot-welded joint of a Chinese steel WP 370 were investigated, and the effects of welding parameters were also tested. It was found that the weldability of WP 370 is satisfactory and the mechanical properties of the joints in the centre of the weldebility zone are better than those near the boundary. The static and fatigue strengths of spot-welded joints of WP 370 are much higher compared with those of SPCE, a Japanese steel which is similar to 08AI. This can be explained by an increase in strength of the base metal. Numerical data, graphs, photomicrographs. 6 refs.
Environmental evaluation of repairs to fuselage lap joints. Molent, L., Bridgford, N., Rees, D. and Jones, R. Composite Struct. (1992) 21, (2), 121-130 The results of a fatigue test programme undertaken to investigate repairs to multisite damage in aircraft fuselage lap joints made of 2024-T3 plate are presented. It is demonstrated that a boron/epoxy composite doubler bonded over the joint should significantly increase the fatigue life of the structure and that environmental effects are negligible. Graphs. 6 rats. Valve spdng w i r e w i t h e x t r a - l o w o x y g e n and w i t h shaved surface - a real need. Rosa, J.A.C., Barcelos, E. Costa, M.L., Hayakawa, M.O. and
Ce, J.C. Wire J. Int. Apr. 1992 25, (4), 59-64
The production of valve spring steels with very low O (8 ppm) which uses vacuum reduction of sulfur and oxygen (VRSO) refining process is described. It involves melting in an electric arc furnace (EAF) using a highly reducing slag to reduce S, followed by ladle metallurgy and vacuum degassing (VD) prior to ingot casting under Ar protection. The hot-rolled wire rod (7.94 mm gauge) is treated to remove rolling-in flaws by a peeling process which uses a rotating tool for machining followed by the 'shavelite' method of peeling the wire by passing through a specialgeometry die. Both O content and level of microinclusioos are lower with improved fatigue strength of the wire thus manufactured compared with that of the wire produced by the conventional method. Failure in extrusion tooling, causes and methods of avoiding failures.
Kortmann, W.A. Prec. Fifth Aluminum Extrusion Technology Sam., Chicago, Illinois, USA, 19-22 May 1992, Vol I (The A l u m i n i u m Association, Washington,
DC, USA, 1992) pp 219-231 Presented are examples of failed tools and dies and components in AI extrusion. A material selection and recommendations for heat treatment, manufacture and use of tools and dies in production are presented. Tool steels for AI extrusion include 6F2, 6F3, H l l , H12 and H13. Effect of surface defects in light press a l u m i n u m extrusions on aerospace manufacturing. Sorenson, E.
Prec. Fifth International Aluminum Extrusion Technology Sere., Chicago,
Illinois, USA, 19-22 May 1992, V e i l (The A l u m i n u m Washington, DC, USA, 1992) pp 521-525
Association,
Extruded AI alloy series 7XXX and 2XXX are prone to surface defects such as blistering, hot tearing, and corrosion pitting. These defects can negatively affect the service life of an airframe and are indeed considered to be undesirable. A recent study by the Boeing Company has shown that the rework and scrap coats associated with receiving extrusions containing these defects, fabricating airframe components and then finding the extrusion defects during the final part inspection are large and unacceptable. The Boeing Company has initiated a cooperative programme with a number of AI extrusion producers to define its needs more clearly and implement a system for minimizing these problems. The programme strives to define rajecteble surface conditions better, improve visual inspection at the producers, and delineate cases in which rework is permitted. The programme is being carefully coordinated with the producer participants to assure that all terms are mutually agreeable.
Fatigue behavior o f (BS 1470 Na-0) a l u m l n l u m alloy end (BS 1501-510) nickel steel double-fillat and t e e - b u t t w e l d s (subject to handing). White, G.C ASTM J. Test. Eval. M a y 1992 20, (3), 180-189
Tempera.l u r e effects on the mesttanism of t i m e independent hydrogen assisted fatigue craCK propagation in steels. Marrow, T.J., King, J.E.
The shell-to-bess welds of liquefied natural gas (LNG) tanks are normally double fillet welds, although in some tanks tee-butt welds are used. The fatigue beheviour of these welds has been examined by testing 134 full-size specimens. The testing examined the low-cycle, high-strain performance of the welds in air at +20°C and in liquid nitrogen at -196 °C. The results have shown that double fillet weld and tee-butt weld fatigue performance are comparable. The low-temperature fctigue performance matched or exceeded that under equivalent ambient conditions. The shell-to-bottom welds used in British Gas LNG tanks have fatigue lives well in excess of that required for operational duty. BS 1470 N8-O and BS 1501-510 are discussed. Photomicrographs, graphs. 1 ref.
The effects of temperature on hydrogen-assisted fatigue crack propagation are investigated in three steels in the low-to.medium strength range: a low alloy structural steal (4360 Gr.50EE), a super duplex stainless steel (Zeron 100), and a super ferritic stainless steel (E-brite). Significant enhancement of crack growth rates is observed in H gas at atmospheric pressure in all three materials. Failure occurs via a mechanism of time-independent, transgranular, cyclic cleavage over a frequency range of 0.1-5 Hz. Increasing the temperature in H up to 80 °C markedly reduces the degree of embrittlement in the structural and superferritic steels. No such effect is observed in the duplex stainless steel until the temperature exceeds 120 °C. The temperature response may be understood by considering the interaction between absorbed H and microstructurel traps, which are generated in the zone of intense plastic deformation ahead of the fatigue crack tip. Photomicrographs. graphs, diffraction patterns. 49 refs.
Fatigue life estimation in rssistance spot w e l d s : initiation and early g r o w t h phase. Sheppard, S.D. and Strange, M. Fatigue Fract. Eng. Mater. Struct. June 1992 15, (6), 531-649 The main objective is to develop a model of fatigue crack initiation and early crack growth in resistance spot welds that is specimen independent. This objective is achieved by examining the stress state around a resistance spot weld. A general expression for the structural stress around the weld is formulated that is dependent only on the loading immediately surrounding the weld. As such, it is specimen independent. An additional objective is to explore the feasibility of applying this fatigue crack initiation model of life estimation using structural response data from finite element analysis (FEA). This numerical technique is often used for evaluating structural integrity of assemblies. Limited verification examples show that the structural stress range as calculated from FEA reaction load data is capable of
Int J Fatigue July 1993
and Cotterill, P.J. Acta Metal/. Mater. Aug. 1992 40, (8), 2059-2068
Frectographic analysis of fatigue cracking in spheroidal graphite cast irons. Bulloch, J.H. Theor. Appl. Fract. Mech. Apr. 1992 17, (1), 19-45 An attempt is made to describe a fairly intense fractogrephic analysis which was performed on the fatigue fracture surfaces of two spheroidal graphite cast iron microstructurse subjected to fatigue loading at various R-ratio values in an ambient air environment. A significem amount of intergranular failure was evident In both microstructurse at low to intermediate AK levels; this failure mode attained maxima at specific &K levels which correspond to the condition when the reversed plsetlc zone size approached the structural parameter (grain) size. The extent or amount
343