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Crack growth rate estimation on a three-point bend specimen during low-cycle fatigue
Fatigue behaviour o f corrugated roofing under cyclic w i n d loading.
Mahendran, M. Trans. Inst. Eng. Australia, Civil Eng. Trans. Dec. 1990 CE32, (4), 219-226
Low-cycle fatique cracking of light-gauge metal roofing was investigated by testing a number of two-span corrugated roofing assemblies with different spans and fastening systems under cyclic uplift windloading. Fatigue results correlated quite well with the corresponding static results reported earlier, and revealed the dependence of the fatigue behaviour on the type of fastening system used. A comparison was made of one type of fastening system with the other regarding the fatigue performance. The fatigue behaviour was dependent on the load at which local plastic deformations occurred under the fastener heads for roofing fastened at alternate crests, and it was found that a few cycles of preloading above this load caused a significant reduction in fatigue life. The fatigue characteristics in the form of two matrices of cycles to failure for various combinations of range and mean level of loading for the most common types of roofing systems were developed in order to be used in the on-going investigation to review the current standard fatigue tests. 14 refs. O r t h o t r o p i c bridge decks: fatigue behaviour. Caramelli, S., Croce, P.,
Fro~i, M. and Sanpaolesi, L. Costruz. Mattall. Nov.-Dec. 1990 42, (6), 375-394 (in Italian) Orthotropic-steel bridge decks, directly subjected to traffic loads, are very sensitive to fatigue, aa is shown by the cracks that have appeared recently in some European bridges. The improvement in knowledge of the fatigue behaviour of welded connections in orthotroplc decks and the study of finer details obviously influences the design and the concept of these structures. For this purpose, the EEC have'" promoted end financed a large research programme in which seven laboratories from six European countries have participated. The most important theoretical and experimental results are given and discussed in the paper.
Non-I]nuer a n a l y M I o f infllled frames unde¢ m o n o t o n i c and cyclic
loading. May, I.M. and Naji, J.H. Comput. Struct. 1991 38, (2), 149-160 A non-linear finltsiement programme to simulate the behaviour of steel frames infilled with concrete panels is described. The infilled frame may be subjected to monotonic or cyclic loading. The steel frame is modelled es a strain hardening plastic material, and in the tnfill concrete model cracking, yielding and crushing are comlldared. Separation, sliding, and the opening ilnd clOSing of initial gaps at the interface between the frame end the inffil penal= are accounted for by adjueting the properties of the interface elements. NomeriCat examples to demomm~te the capabilities and limitations of the programme are dacribed. Graphs. 22 refs.
General A 14:udy o f OOlTosk)n ~
which has superior stress rupture properties, was used in the rim region, and TMP3, which has good tensile properties and a low-cycle fatigue life, was used in the bore region. A 400 mm diameter dual-property disc was successfully produced through double-stepped HIP treatment and suparplestic forging, in which gasatomized powders composed of the above alloys were consolidated into a welldesigned preformed structure. After heat treatment, the microstructure of the product was very fine and homogeneous in the bore region, and coarse grains were obtained in the rim region. The mechanical properties were of such a high quality as to enable applications to, for example, turbine discs. 9 refs.
PSB observation in copper fatigued at one half the melting temperature.
Boehme, F., Hidaka, K. and Weertman, J.R. Scr. Metal/. Mater. Dec. 1990 24, (12), 2341-2346
Studies of single-crystal Cu fatigued at 678 K show that persistent slip bands (PSBs) form in a ladder structure. The PSBs are unstable at high temperatures, transforming to a cell structure within a few minutes after the cessation of cycling. An extremely high cooling rate is essential for the preservation down to room temperature of the dislocation structure produced during elevated-temperature cycling. Graphs, photomicrographs. 10 refs. Crack g r o w t h rate estimation on a three-point bend specimen during low-cyCle fatigue. Tryding, J. Exp. Mech. Mar. 1991 31, (1), 4 2 - 4 6 The ratio of the change of the clip-gauge measured crack-opening displacement of a three-point bend specimen to the change of the displacement at the point of application of (e.g., oxg12E) the cyclic load is shown to vary linearly with the ratio of the crack length to the specimen height. With the aid of this relation, the crack growth rate is obtained by numerical differentiation of the crack length with respect to the number of load cycles. A clip-gauge correction factor is introduced to compensate for the use of external edges, which position the clip-gauge during experiments. Graphs. 9 refs. I m p r o v e m e n t o f fatigue life of T I - 6 A I - 4 V alloy by carbon ion Implantation. Zhang, D., Yu, W. and Wang, Z, Acts Metall. Sinica (China) Oct. 1990 26, (5), A351-A355 (in Chinese) The fatigue limit of Ti-6AI-4V alloy could be improved by over 28% by implantation of a dose of 3 x 1017 ions/cm 2 of C st 80 keV under a strees-controlled zero-tension condition. The microatrucure of the surface layer, whether implanted or not end before or after fatiguing, as well as the concentration distribution of implanted ions along the depth of the surface layer, were examined by SEM, TEM and SIMS. A great deal of radiation damage and • good many fine TiC particles are found in the implanted layer. The fatigue cracking origins, implanted or not, occur in subsurfaces under lower stress and longer fatigue lives. The implanted species diffuse into the substrata under cyclic loading. Photomicrographs, graphs. 8 refs. Fatigue softening behllviour and its threshold of cold-strained poly-
bel~lviour o f anodi=~ed luld u n d m o d i z ~
20a4-1r~ Mumklum alley. Tu, G.C., Hwang, R. Y. and Chen, I. 7". J. Mater. Sci. Mar. 1991 26, (5), 1375-1382 The corrosion fatigue (CF) beheviour, under constant deflection-bending conditions with a pulsating tension atrmm form, of 2024-T3 AI alloy, uuenodised and anodized to form a thick porous film, in 3.5% NaCI solution has been investigated. It was found that Ecorr varies very little until specimen fracture under low-frequency CF conditions, whereas Ecmr drops rapidly when approaching the later fracturing stage of the CF process under high-frequency conditions for unenodized specimens. However, a slow drop in ~ was detected from the commencement of the CF process, and lasted up to a much more rapid drop at a later fracturing stage for the anodized specimen. This behaviour presumably can be explained by the cracking of the anodic film and the theory of imperfect recovery of the surface film. It is suggested that the Ecorr monitoring technique may be useful for determining the remnant of CF life for existing structural parts of this alloy or other AI alloys, regardless of whether or not they are anodized. Furthermore, the "1"3temper provides • microstructure that may retard main-crack formation and penetration in the CF process of the anodized alloy, thus partly mitigating the negative effect of the readily crsckable enodic film. Graphs, photomicrographs. 5 refs. The influemm o f ondercuts on t h e fatigue stbrength o f w e l d s - - a Iitaraturo
survey. Patershagen, H. Weld. World 1990 26, (7-8), 114-125 (in English and French) A survey is presented on the influence of the dimensions of undercut (depth or ratio depth/width) on fatigue strength, particularly in the case of butt welds in steel and AI. In spite of the lack of available data, it ia thought that the conventional method of evaluating fatigue life can also be used for welds with undercuts. Graphs. 43 refs.
¢Wstalllne copper. Fan, Q., Chai, H. and Tong, M. Acts Matell. Sin. (China) Oct. 1990 26, (5), A368-A373 (in Chinese) Symmetrical push-pull fatigue tests in load control were carried out for prestrained polycwstalline Cu. The change in mechanical behaviour during cycling was recorded in detail and the effects of various degrees of preatrsining on the saturated beheviour end the dislocation structure were compared. The results show that the cyclic saturation state is still dependent on history at low stress amplitudes and the dislocation structure after fatigue has an 'inheritance'. The amount of softening has been calculated at various load amplitudes and a softening threshold of approximately 0.43-0.45 of the flow stress, which is the same as that for low-carbon steel, is obtained by the extrapolating method. These stages of the cyclic process and their mechanisms have been described. 5 rofs. Precticol application of modifkld susforming t o production o f tapered
leaf springs. Ohmori, M., Tanaka, C., Saitoh, 7". and Tanaka, D. Netsu Shori (J. Japan Soc. Heat Treat.) Apr. 1990 30, (2), 99-103 (in Japanese) A modified ausforming method has been proposed for the development of lighter tapered steel springs for trucks. In the process the temperature range for hotworking was selected in the metesteble auatenite range, from the conventional austenitizing temperature to approximately 700 °C. The allowable elapsed time for air cooling after heating was investigated in relation to the working temperature and the degree of work hardening. The roll stands for the modified ausforming process were designed. The process was very much simplified as compared with the conventional quenching and tempering process. A 31-36% weight reduction was achieved end the fatigue life was extended. Graphs. 9 refs.
The effect o f the sheet rigidity on strength of the s p o t w e l d tension
#near joint. Li, C.-Z. and Wang, Y.-H. Acta Mechanica Sofida Sinica 1990 3, (4), 403-416 Some test and analysis results for a spot-welded joint of Fe-O.34C-0.26Mn-0.O73N-O.O44AI steel sheet subjected to tensile and alternate loads are presented. The effect of sheet rigidity on the tensile strength and fatigue life of the spot-welded joint is studied by using the stress intensity factors KI, KII, Kill and an 'effective stress intensity factor' r-~emaxcalculated by the finitHlement method for cracks around the nugget, The results show that the 'effective stress intensity factor" r-~.emaxis an essential parameter for estimating the fetigua life of the spot-welded joint. Graphs. 6 rofs. Pt-c~ell:ies of P/M nidud.blmed SUlBeralioy d u a l - p r o p e r t y d i m s p r o d u c o d Impeq)lcotlc forging. Tsuda, 0., Kanarnaru, N., Furuta, S., Tekigawa,
and Iwai, K. Kobelco Technol. Rev. Oct. 1990 (9), 38-42
A manufacturing process for dual-structured turbine discs made from P/M Ni-beesd suparalloys has been developed. The discs are composed of two materials: AF115.
502
Joining Orientation IXofmence and f i r u t a l character of short fatigue cracks in
a welding metal. Hong, Y., Lu, Y. and Zheng, Z. J. Mater. Sci. Apr. 1991 26, (7), 1821-1826
The short-fatigue-crack behaviour in • welding metal (Fe-O.12C-O.55Si-O.g7Mn) has been investigated. The Schmid factor and the fractal dimension of short cracks on leo-stress specimens subjected to reversed bending have been determined and then applied to account for the distribution and orientation characteristics of short fatigue cracks. The result indicates that the orientation preference of short cracks is attributed to the large values of Schmid factor at relevant grains. The Schmid factors of most slip systems, which produced short cracks, are at most 0.4. Crack length measurements reveal that a short-crack path, compared with that of a long crack, possesses a more stable and relatively larger value of the fractal dimension. This is regarded as one of the typical features of short cracks. Graphs, photomicrographs. 12 rofs.
Int J Fatigue November 1991
Mahendran, M. Trans. Inst. Eng. Australia, Civil Eng. Trans. Dec. 1990 CE32, (4), 219-226
Low-cycle fatique cracking of light-gauge metal roofing was investigated by testing a number of two-span corrugated roofing assemblies with different spans and fastening systems under cyclic uplift windloading. Fatigue results correlated quite well with the corresponding static results reported earlier, and revealed the dependence of the fatigue behaviour on the type of fastening system used. A comparison was made of one type of fastening system with the other regarding the fatigue performance. The fatigue behaviour was dependent on the load at which local plastic deformations occurred under the fastener heads for roofing fastened at alternate crests, and it was found that a few cycles of preloading above this load caused a significant reduction in fatigue life. The fatigue characteristics in the form of two matrices of cycles to failure for various combinations of range and mean level of loading for the most common types of roofing systems were developed in order to be used in the on-going investigation to review the current standard fatigue tests. 14 refs. O r t h o t r o p i c bridge decks: fatigue behaviour. Caramelli, S., Croce, P.,
Fro~i, M. and Sanpaolesi, L. Costruz. Mattall. Nov.-Dec. 1990 42, (6), 375-394 (in Italian) Orthotropic-steel bridge decks, directly subjected to traffic loads, are very sensitive to fatigue, aa is shown by the cracks that have appeared recently in some European bridges. The improvement in knowledge of the fatigue behaviour of welded connections in orthotroplc decks and the study of finer details obviously influences the design and the concept of these structures. For this purpose, the EEC have'" promoted end financed a large research programme in which seven laboratories from six European countries have participated. The most important theoretical and experimental results are given and discussed in the paper.
Non-I]nuer a n a l y M I o f infllled frames unde¢ m o n o t o n i c and cyclic
loading. May, I.M. and Naji, J.H. Comput. Struct. 1991 38, (2), 149-160 A non-linear finltsiement programme to simulate the behaviour of steel frames infilled with concrete panels is described. The infilled frame may be subjected to monotonic or cyclic loading. The steel frame is modelled es a strain hardening plastic material, and in the tnfill concrete model cracking, yielding and crushing are comlldared. Separation, sliding, and the opening ilnd clOSing of initial gaps at the interface between the frame end the inffil penal= are accounted for by adjueting the properties of the interface elements. NomeriCat examples to demomm~te the capabilities and limitations of the programme are dacribed. Graphs. 22 refs.
General A 14:udy o f OOlTosk)n ~
which has superior stress rupture properties, was used in the rim region, and TMP3, which has good tensile properties and a low-cycle fatigue life, was used in the bore region. A 400 mm diameter dual-property disc was successfully produced through double-stepped HIP treatment and suparplestic forging, in which gasatomized powders composed of the above alloys were consolidated into a welldesigned preformed structure. After heat treatment, the microstructure of the product was very fine and homogeneous in the bore region, and coarse grains were obtained in the rim region. The mechanical properties were of such a high quality as to enable applications to, for example, turbine discs. 9 refs.
PSB observation in copper fatigued at one half the melting temperature.
Boehme, F., Hidaka, K. and Weertman, J.R. Scr. Metal/. Mater. Dec. 1990 24, (12), 2341-2346
Studies of single-crystal Cu fatigued at 678 K show that persistent slip bands (PSBs) form in a ladder structure. The PSBs are unstable at high temperatures, transforming to a cell structure within a few minutes after the cessation of cycling. An extremely high cooling rate is essential for the preservation down to room temperature of the dislocation structure produced during elevated-temperature cycling. Graphs, photomicrographs. 10 refs. Crack g r o w t h rate estimation on a three-point bend specimen during low-cyCle fatigue. Tryding, J. Exp. Mech. Mar. 1991 31, (1), 4 2 - 4 6 The ratio of the change of the clip-gauge measured crack-opening displacement of a three-point bend specimen to the change of the displacement at the point of application of (e.g., oxg12E) the cyclic load is shown to vary linearly with the ratio of the crack length to the specimen height. With the aid of this relation, the crack growth rate is obtained by numerical differentiation of the crack length with respect to the number of load cycles. A clip-gauge correction factor is introduced to compensate for the use of external edges, which position the clip-gauge during experiments. Graphs. 9 refs. I m p r o v e m e n t o f fatigue life of T I - 6 A I - 4 V alloy by carbon ion Implantation. Zhang, D., Yu, W. and Wang, Z, Acts Metall. Sinica (China) Oct. 1990 26, (5), A351-A355 (in Chinese) The fatigue limit of Ti-6AI-4V alloy could be improved by over 28% by implantation of a dose of 3 x 1017 ions/cm 2 of C st 80 keV under a strees-controlled zero-tension condition. The microatrucure of the surface layer, whether implanted or not end before or after fatiguing, as well as the concentration distribution of implanted ions along the depth of the surface layer, were examined by SEM, TEM and SIMS. A great deal of radiation damage and • good many fine TiC particles are found in the implanted layer. The fatigue cracking origins, implanted or not, occur in subsurfaces under lower stress and longer fatigue lives. The implanted species diffuse into the substrata under cyclic loading. Photomicrographs, graphs. 8 refs. Fatigue softening behllviour and its threshold of cold-strained poly-
bel~lviour o f anodi=~ed luld u n d m o d i z ~
20a4-1r~ Mumklum alley. Tu, G.C., Hwang, R. Y. and Chen, I. 7". J. Mater. Sci. Mar. 1991 26, (5), 1375-1382 The corrosion fatigue (CF) beheviour, under constant deflection-bending conditions with a pulsating tension atrmm form, of 2024-T3 AI alloy, uuenodised and anodized to form a thick porous film, in 3.5% NaCI solution has been investigated. It was found that Ecorr varies very little until specimen fracture under low-frequency CF conditions, whereas Ecmr drops rapidly when approaching the later fracturing stage of the CF process under high-frequency conditions for unenodized specimens. However, a slow drop in ~ was detected from the commencement of the CF process, and lasted up to a much more rapid drop at a later fracturing stage for the anodized specimen. This behaviour presumably can be explained by the cracking of the anodic film and the theory of imperfect recovery of the surface film. It is suggested that the Ecorr monitoring technique may be useful for determining the remnant of CF life for existing structural parts of this alloy or other AI alloys, regardless of whether or not they are anodized. Furthermore, the "1"3temper provides • microstructure that may retard main-crack formation and penetration in the CF process of the anodized alloy, thus partly mitigating the negative effect of the readily crsckable enodic film. Graphs, photomicrographs. 5 refs. The influemm o f ondercuts on t h e fatigue stbrength o f w e l d s - - a Iitaraturo
survey. Patershagen, H. Weld. World 1990 26, (7-8), 114-125 (in English and French) A survey is presented on the influence of the dimensions of undercut (depth or ratio depth/width) on fatigue strength, particularly in the case of butt welds in steel and AI. In spite of the lack of available data, it ia thought that the conventional method of evaluating fatigue life can also be used for welds with undercuts. Graphs. 43 refs.
¢Wstalllne copper. Fan, Q., Chai, H. and Tong, M. Acts Matell. Sin. (China) Oct. 1990 26, (5), A368-A373 (in Chinese) Symmetrical push-pull fatigue tests in load control were carried out for prestrained polycwstalline Cu. The change in mechanical behaviour during cycling was recorded in detail and the effects of various degrees of preatrsining on the saturated beheviour end the dislocation structure were compared. The results show that the cyclic saturation state is still dependent on history at low stress amplitudes and the dislocation structure after fatigue has an 'inheritance'. The amount of softening has been calculated at various load amplitudes and a softening threshold of approximately 0.43-0.45 of the flow stress, which is the same as that for low-carbon steel, is obtained by the extrapolating method. These stages of the cyclic process and their mechanisms have been described. 5 rofs. Precticol application of modifkld susforming t o production o f tapered
leaf springs. Ohmori, M., Tanaka, C., Saitoh, 7". and Tanaka, D. Netsu Shori (J. Japan Soc. Heat Treat.) Apr. 1990 30, (2), 99-103 (in Japanese) A modified ausforming method has been proposed for the development of lighter tapered steel springs for trucks. In the process the temperature range for hotworking was selected in the metesteble auatenite range, from the conventional austenitizing temperature to approximately 700 °C. The allowable elapsed time for air cooling after heating was investigated in relation to the working temperature and the degree of work hardening. The roll stands for the modified ausforming process were designed. The process was very much simplified as compared with the conventional quenching and tempering process. A 31-36% weight reduction was achieved end the fatigue life was extended. Graphs. 9 refs.
The effect o f the sheet rigidity on strength of the s p o t w e l d tension
#near joint. Li, C.-Z. and Wang, Y.-H. Acta Mechanica Sofida Sinica 1990 3, (4), 403-416 Some test and analysis results for a spot-welded joint of Fe-O.34C-0.26Mn-0.O73N-O.O44AI steel sheet subjected to tensile and alternate loads are presented. The effect of sheet rigidity on the tensile strength and fatigue life of the spot-welded joint is studied by using the stress intensity factors KI, KII, Kill and an 'effective stress intensity factor' r-~emaxcalculated by the finitHlement method for cracks around the nugget, The results show that the 'effective stress intensity factor" r-~.emaxis an essential parameter for estimating the fetigua life of the spot-welded joint. Graphs. 6 rofs. Pt-c~ell:ies of P/M nidud.blmed SUlBeralioy d u a l - p r o p e r t y d i m s p r o d u c o d Impeq)lcotlc forging. Tsuda, 0., Kanarnaru, N., Furuta, S., Tekigawa,
and Iwai, K. Kobelco Technol. Rev. Oct. 1990 (9), 38-42
A manufacturing process for dual-structured turbine discs made from P/M Ni-beesd suparalloys has been developed. The discs are composed of two materials: AF115.
502
Joining Orientation IXofmence and f i r u t a l character of short fatigue cracks in
a welding metal. Hong, Y., Lu, Y. and Zheng, Z. J. Mater. Sci. Apr. 1991 26, (7), 1821-1826
The short-fatigue-crack behaviour in • welding metal (Fe-O.12C-O.55Si-O.g7Mn) has been investigated. The Schmid factor and the fractal dimension of short cracks on leo-stress specimens subjected to reversed bending have been determined and then applied to account for the distribution and orientation characteristics of short fatigue cracks. The result indicates that the orientation preference of short cracks is attributed to the large values of Schmid factor at relevant grains. The Schmid factors of most slip systems, which produced short cracks, are at most 0.4. Crack length measurements reveal that a short-crack path, compared with that of a long crack, possesses a more stable and relatively larger value of the fractal dimension. This is regarded as one of the typical features of short cracks. Graphs, photomicrographs. 12 rofs.
Int J Fatigue November 1991