Thermal fatigue and fracture mechanics analysis of grey cast iron

Thermal fatigue and fracture mechanics analysis of grey cast iron

crack growth in the plates has been related to the crystallographic texture. The texture, due to its strong influence on the slip behaviour and plasti...

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crack growth in the plates has been related to the crystallographic texture. The texture, due to its strong influence on the slip behaviour and plastic zone size, induces different amounts of roughness-induced closure and slip reversibility, thereby producing the observed anisotropY of the fatigue crack growth properties.

u 0 H. H. N o • ~mith, and Michel,•D. J. J. NucL Mater.

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ni~radietion effects on fatigue crack propagation in alloy 718 at June 1987 148, (1), 109-112

High-temperature structural components in nuclear energy systems experience cyclic or combined cyclic-static loading during irradiation. Studies have shown that the Ni-based precipitation-hardened Alloy 718 is sensitive to heat treatment and heat-to-heat processing variations. Fluences of 0.5-3.0 dpa fast neutron irradiation at 427 °C produced a small decrease in crack propagation rate compared with unirradiated results. A 1 rain hold period in the fatigue cycle significantly increased the crack propagation rate of Alloy 718 at 427 °C. Specimens irradiated to 16-18 dpa at 650 °C showed significantly increased fatigue crack propagation (FCP) rates during cyclic and 1 rain hold time Ioedings. Test specimens were irradiated at 650 ~+5 °C to calculated fast neutron fluences of 6,2 and 7.0 × 1022 n/cmz, > 0.1 MeV. The crack propagation rate increased by a factor of two with cyclic loading and by a factor of ten with 1 min hold time Ioedings. The mode of crack propagation at 650 °C was found to be primarily transgrenular with a crystallographic cleavage character believed to be {100}, The crack propagation rates for unirradiated continuous cycling tests were nearly four times higher in the current test than in previous tests. The test temperature of 650 °C is in excess of the final ageing temperature of the modified heat treatment. This is considered to contribute to the partial dissolution of y" precipitate microstructure leading to higher FCP rates. The differences observed in the crack propagation rates of both heats of Alloy 718 were primarily the result of the influence of different heat treatments. Graphs, photomicrographs. 10 refs.

Contact fatigue resistance of a n e w F e - M n overlaying alloy. Zhang, P.,

Xu, B., klan, W. and Cai, Q. Hanjie Xuebao (Trans. China Weld. Inst.) Sept. 1988 9, (3), 188-194 (in Chinese) The contact fatigue resistance of several overlaying alloys was compared by roiling-sliding tests, and a new Fe-Mn alloy showed the best resistance among the different alloys, The service life of this alloy was found to be a maximum under the condition of ~i = 1560MPa. The mechanism of the good contact fatigue resistance of the alloy was investigated. It is considered that the strain-induced martensitic transformation from ~tto ~' and the precipitation of MaC carbide particles increase the strength of the material effectively, and impede the continuous plastic deformation. As the huge reserve of toughness in the austenite surrounding the martensite can decrease the propagation rate of cracks, the service life is increased. One of the advantages of this overlaying alloy is that the heat treatment for the overlaid surface can be saved because the strength needed can be obviated in the running-in process through effective work-hardening. 13 refs.

Effect of geometric changes on fatigue strength of w e l d e d joints. Kiuchi,

A., Ohtani, O. and Takeuchi, H. Kobe Res. Dev. July 1988 38, (3), 22-25 (in Japanese)

The effect of geometric changes on fatigue strength of welded joints has been investigsted analytically and experimentally. The fatigue strength was found to depend on attachment size (L) and main plate thickness (B). The analytical investigation led to the formulation of equations predicting the fatigue strength for given values of B and L. The predicted fatigue strength agreed well with experimental results. 5 refs.

influence of specimen size on fatigue crack initiation of welded HY100

High-temperature properties of ferritic spheroidal graphite cast iron. Lui, T. S. and Chao, C. G. J. Mater. ScL July 1989 24, (7), 2503-2507

The behaviour of fracture mode and intermediate temperature embrittlement of ferritic spheroidal graphite cast iron is influenced by many factors. From the experimental results, intermediate temperature embrittlement can be considered to be dominated by dynamic strain ageing and the triaxial stress field developed in the ferrite matrix amongst the graphite particles. To understand the effect of dynamic strain ageing on high-temperature properties, tensile properties, push-pull lowcycle fatigue properties, rotary bending fatigue properties and creep-rupture properties were investigated from room temperature to 500 °C, It was found that all the properties investigated were influenced by dynamic strain ageing. The intermediate temperature embrittlement of ferritic spheroidal graphite cast iron found in different load conditions is reported. Graphs, photomicrographs. 14 refs. Cyclic deformation pehsviour o f s Cu-1.5 mess% Fe alloy w i t h precipitate iron particles. Kato, M., Nishimura, A., Matsuyama, 7". and Horie, H. Mater. ScL Eng. A M a y 1989 111, 17-25 Three different specimens of Cu-1.5 mass% Fe alloy polycrystals were cyclically deformed: solution-treated specimens (specimens S), aged specimens with coherent "y-Feprecipitate particles (specimens G) and aged, deformed and annealed specimens with incoherent ~-Fe particles (specimens A). In both total-strain-controlled and stress-controlled tests, specimen G had the longest fatigue life. Transmission electron microscopic observation revealed that the formation of dipolar walls or fatigue cells was considerably delayed in specimen G compared with specimens S and A. The deformation-induced ~-~ transformation in the Fe particles in specimen G occurred in the very early stage of cyclic deformation, and the transformation induced the formation of tangled dislocations around the particles. It is concluded that the coexistence of the transformed ~-Fe particles and the tangled dislocations is very effective in preventing the rearrangement of dislocations during cyclic deformation. Graphs, photomicrographs. 29 refs, The phase t r a n s f o r m a t i o n and fatigue characteristics by thermal cycles at / i - N I - u u snspe m e m o r y alloys. Lee, O. Y., Chun, B. S., Nam, K. J.

and Cho, K. H. J. Korean Inst. Met. 1989 27, (2), 103-112 (in Korean)

Martensitic transformation and effects of thermal fatigue cycles on the transformation temperature and shape recovery of Ti-Ni-Cu alloys were investigated by means of electrical resistance measurement, thermal fatigue tests end transmission electron microscopy. Thermo-mechanical treatment at 600 °C for 1 h after cold rolling showed the best shape recovery effect irrespective of Cu concentration. Substitution of a small amount of Cu for Ni in the equistomic composition of Ti-Ni showed the following results: Ms temperature of the Ti-N~-Cu alloy increased slightly with the increase of Cu content: the range of transformation temperature for TisoNJ4oCufa alloy (ie TMf_Af)was reduced to 7 °C. After stress relief treatment at 750 °C for 1 h, the TisoNi4sCus alloy showed a good two-way memory effect. Change of the Ms temperature was observed to a certain number of thermal cycles, and it became nearly constant after a critical number of thermal fatigue cycles. Graphs, photomicrographs. 18 refs.

Joining A study of the fatigue strength of incomplete penetration butt welds.

Li, R. and Zhang, X. Hanjie Xuebao (Trans. China Weld. /nst.) June 1988 9, (2), 119-124 (in

Chinese)

One-side-welded butt welds are widely used in welded structures. The results of tests conducted on Iow-C steel bug welds containing incomplete penetration defects under fluctuating tensile stress are given. As the incomplete penetration defects generally occur at the surface of weld in the case of one-side-welded butt welds, the loss of fatigue strength is more severe compared with that of double-sidewelded butt welds of the same defect ratio. Inclusions existing in the tip of incomplete penetration may intensify the stress concentration in the stress concentration zone. This further lowers the fatigue strength. 4 refs.

Int J Fatigue January 1990

steel. Technical memo. Kreuzer, W, Defence Research Establishment Atlantic Report No AD-A 196 219/O/XAB Jan. 1988

The assumption of a statistical distribution of the flaws in a component leads to a prediction of a correlation between crack initiation life and the size of a fatigue loaded part. The influence of the specimen size on the fatigue crack initiation behaviour was analysed for two series of welded HY100 steel plates of different widths. The weldments were prepared with E12018M2 electrodes, The prediction of the number of cycles to crack initiation and of the allowable stresses for samples of a different size agreed well with the experimental results.

Fracture toughness of steel weldments containing lack of penetration

defects, (Dissertation). Byaruhanga, J. K. Diss. Abstr. Int. M a y 1988 48, (11)

The fracture resistance of weldments containing flaws in the as-welded state was studied. The major considerations which prompted this investigation were: (a) the suspicion that the use of standard notches to generate fracture toughness data for assessing real flaws in weldments might be unduly pessimistic; and (b) the fact that workmanship codes and specifications seldom distinguish between welding processes and procedures when nominating allowable defects in weldrnents. Therefore, the major aims were the investigation of the possibility of fracture toughness testing using real defects such as )ack of penetration as opposed to machined and fatigue cracked notches, the effects of welding process and procedure on fracture toughness, and the effects of factors such as notch geometry and angular distortion on the fracture toughness of weldments. The results of these investigations revealed the following: (i) lack of penetration defects and fatigue cracks gave similar fracture resistance values over a range of temperatures; (ii) specimens with shallow notches gave better fracture resistance values than those with standard notches; (iii) different welding processes and procedures gave different fracture resistance data; and I)v) specimens made with a restraining weld had better resistance to fracture than those allowed to distort during welding. The maior implications include: since lack of penetration defects and fatigue cracks gave similar fracture resistance values, the simpler lack of penetration defect could be used to generate fracture toughness data for the assessment of a range of welded structures using fracture mechanics. The fracture resistance of weldments is dependent on notch geometry since the results showed that the critical crack tip opening displacement for shallow notches was much greater than that for deep notches. The fracture resistance of weldments is dependent on the welding process and procedure, a factor not covered in workmanship codes. The reduction of angular distortion in weldments leads to significantly improved fracture resistance.

Mechanical properties Fatigue/creep interaction fracture map at various temperstums. Zhang, H., ~u, Z. and Chen, G. Acta Metal/. Sin, (China) Dec. 1988 24, ('6), A439-A442 lin Chinese) The relative ratio of fatigue resistance to creep resistance of materials varies with test temperature. As the temperature decreases, the creep resistance, since it is a thermal activation process, becomes relatively larger than the fatigue resistance. The fatigue damage therefore becomes predominant, and results in expansion of the fatigue fracture region (F region) and shrinkage, or even complete elimination of the creep fracture region (C region). This phenomenon could be understood on the basis of an integrated model of competitive and cumulative models of fatigue/ creep interaction. A material parameter, Q, can be used to estimate the temperature at which the creep fracture region is completely depressed. 5 refs. cTI~.ormsl fatigue and fracture mechanics analysis o f grey cast iron. Guo,

and Zhou, W. Acta Metal/. Sin. (China) Dec. 1988 24, (6), A419-A425 (in Chinese) The in-phase and out-of-phase thermal fatigue and the C-P type and P-C type isothermal fatigue of grey cast iron were experimentally studied. The fatigue life was evaluated analytically by using the elastic-plastic fracture mechanics method (mainly J integral). The results of experiments and calculations showed that the life times of in-phase and C-P type fatigue are longer than those of out-of-phase end P-C type fatigue respectively within the same strain range. This is in contrast to

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the results for other materials, such as low-carbon steel. On the other hand, the predicted lifetimes are consistent with experimental results. This suggests the J integral as a mechanics parameter for characterizing the thermal fatigue strength of grey cast iron. The mechanics model and calculation method developed here are efficient. A parameter &Wt was proposed from an energy aspect to characterize the capacity of crack propagation. The isothermal fatigue life is the same as the thermal fatigue life for identical &Wt values. 7 refs.

Mechanical properties of austempered ductile iron. lio, Y., Yoshino, S. and Ogino, Y. Kubota Tech. Rep. Apr. 1988 (20), 1-6 (in Japanese) Non-alloyed austempered ductile iron with less than 10 mm wall thickness was studied. The relationship between austempering treatment and the mechanical properties against the various total carbon contents was investigated. Total C was changed to three marks, 2.5, 3.0 and 3.6%. In order to get the effect of the total C contents accurately, purified Fe (obtained by lowering Mn, phosphorus and minor elements) was used as a raw material. The maximum tensile strength was obtained at 2.5% of the total C, and maximum elongation, impact value and fatigue strength were obtained at 3% of the total C. 2 refs.

Radiographic line width and surface rupture density as wear criteria. Schilh'ng, A., Reinhold, C., Stemmler, D. and Wuttke, W. Schmierungstechnik 1989 20, (3), 86-88 (in German) The relation between wear-induced surface damage, determined by scanning electron microscopy and lattice strain measured as line width, is demonstrated by taking high-cycle fatigue wear as an example. The stochasticity of straining and real structural development are discussed as causes of the lattice strain variations, which are dependent upon the number of cycles. In addition, the removal of heavily deformed zones of materials is discussed. 13 refs,

Notch effect on fatigue and creep/fatigue interaction properties of GH132 disc superalloy. Xio, X., Chen, G. and Jiang, H. J. Univ. Sci. Technol. Beijing 1989 11, (2), 130-135 (in Chinese) The iron-base disc superalloy GH132 is susceptible to LCF notch sensitivity, though it has no stress rupture notch sensitivity at elevated temperature. The creep/fatigue interaction lives to fracture of GH132 for notch and smooth specimens both exhibit 'nose' curves with maximum lives to fr3cture. In the regime above the 'nose', the alloy is susceptible to notch sensitivity. Below and near the 'nose' regime, lives to fracture of notch specimens are longer than in smooth specimens. For turbine disc alloy development it is necessary both to raise the strength and to improve the ductility. 3 refs.

High-strength steel plates for offshore platform for deep and cold sea. Bessyo, K., Arimochi, K,, Tsukamoto, M., Konda, N. and Fujimoto, M. Sumitomo Search Nov. 1988 (37), 13-28 New explorations for offshore oil and gas fields are tending to move from shallow seas to deep and cold seas. Therefore, platforms are becoming very large and heavy, and the adoption of HT60 steel plates in place of conventional HTS0 steel plates is being explored as a way to reduce the total weight of the structure, HT60 steel plates with superior low-temperature toughness properties have been developed using the quench-tempering and DAC (dynamic accelerated cooling) processes. The base metal properties, weLdability, welded joint properties, fracture toughness and fatigue properties of these newly developed steel plates were investigated. The results showed superior properties for all test items. It was confirmed that these new steel plates could be applied to structures in deep and cold sea fields with welding procedures equivalent to those of conventional normalized HT50 steels. L o w cycle fatigue damage in turboengine discs. Guedou, J. Y. and

Honnorat, Y. Mater. Tech. (Paris) Jan.-Feb. 1989 77, (1-2), 49-56 (in French) In modern turboengines, discs are the most critical parts due to the high thermal and mechanical Ioadings they are subjected to. The damage processes of these parts are correlated to engine working cycles, generating low-frequency and highamplitude cyclic loads: the life of discs is therefore mainly limited by low-cycle fatigue, possibly associated with environmental effects (time, temperature) and high-frequency low-amplitude cycles superimposition (due to interference in rotating machines). Disc design is based on laboratory test results, which permits the quantification of damage models used in calculations, The reliability of those methods, as well as the accurate knowledge of physical damaging mechanisms in disc alloys, makes it possible to give 'safe lives' to those parts, which are however checked by spin pit tests on modules or whole engines. Nevertheless, the recent trend towards 'damage tolerance concepts', in which material defects are taken into account, need more intensive studies of crack propagation and damage mechanics, including complex phenomena such as spectrum fatigue. Therefore, the improvement of more and more sophisticated laboratory mechanical tests (short crack propagation, thermomechanical fatigue, complex fatigue) seems mandatory to meet those requirements. 15 refs.

High strength, high carbon grey irons containing vanadium and their resistance to thermal fatigue cracking. Dawson, J. V. and Sage, A. M. Foundry Trade J. Int. June 1989 12, (2), 36, 38, 48 The development of high strength, high-C grey irons containing V is described. It is suggested that the higher thermal conductivity arising from the increased C content can provide enhanced heat dissipation, especially in those cases where castings are subjected to rapid thermal cycfing. Amongst possible applications are heavy-duty brake drums and discs. 4 refs.

Fatigue crack propagation in AI-Sn bearing alloys. Busby, A, K. and Martin, J. W. Mater. Sci. Technol. July 1989 5, (7), 689-698 Fatigue crack propagation has been studied in a series of AI-Sn bearing alloys as a function of microstructure and environment at stress intensity ratios R of 0.7 and 0.1. Fatigue thresho]ds of Sn-containing alloys increased with a reduction in content

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and in continuity of the Sn-phase in laboratory air. This is interpreted in terms of crack closure, crack growth along the AI/Sn interface, and crack tip blunting mechanisms. Mechanisms that retard fatigue crack growth through the AI phase leg by an increase in the reversibility of slip or by an increase in the size of the reverse plastic zone) were found to increase fatigue thresholds. When tested in dry air, the AI/Sn interface shows reduced embrittlement. The consequence of this for fatigue thresholds is complex: at R = 0.7, fatigue thresholds increase with a decrease in Sn content, while the thresholds are constant at R - 0.1. 10 refs.

Investigation of die stresses and die deflections in forging axisymmetric parts. Hirt, G. and Allan, T. Steel Res. 1989 60, (6), 255-262 In this study, two examples were investigated. The first was cold coining of a thin circular disc where the effect of elastic die deflections upon the tolerances of the formed part was evaluated, in the second example, the die stresses and die deflections were estimated for the upper die in hot closed-die forging of a flangeshaft type part. The predicted results in the first example showed good agreement with experimental data. Thus, it was illustrated that the methods used and discussed in this study are reliable to estimate die stresses and deflections. It is expected that additional work is necessary to develop a practical procedure for predicting the failure and fatigue life of cold and hot forging dies. 16 refs.

Micromechanisms governing fatigue behaviour of lithium-containing a l u m i n i u m alloys. Srivatsan, 7. S. and Coyne, Jr, E. J. Mater. Sci. Technol. June 1989 5, (6), 548-555 The emergence of Li-containing AI alloys as potential light metals for aircraft structures has engendered an unprecedented widespread interest aimed at improving their mechanical properties and studying their cyclic fatigue characteristics. The phenomenon of fatigue is environment sensitive and the alternating moisture conditions experienced by this candidate airframe material can be a handicap when designing for enhanced fatigue resistance. In this paper the fatigue properties, deformation characteristics and cyclic stress response of the commercial AI-Li-Cu-Mn and the experimental AI-Li-Mn and AI-Li-Cu-Mg-Zr alloys cycled to failure are compared over a range of plastic strain amplitudes in various environments, spanning the inert to the very aggressive. Abnormal plastic strain-fatigue life behaviour was observed for all the alloy systems and is attributed to differences in the distribution of deformation as a function of plastic strain amplitude and to change in the relative amounts of intergranular and transgranular fracture as a function of strain amplitude. Cyclic deformation was also observed to produce softening in the three alloys for most of their fatigue life. The softening is due to progressive loss of ordering contributions to hardening and is a mechanical and not an environmental effect. 43 refs.

Structure and properties of A I - L i - - C u - M g - Z r alloy AA 2091 in sheet form. Smith, P. F. Mater. Sci. Technol. June 1989 5, (6), 533-641 The structure and properties of AI-Li-Cu-Mo-Zr alloy AA 2091 in sheet form have been studied. Static and dynamic behaviour of material aged to the 'damage tolerant' category has been found to be at least equivalent to current BS L109 (AA2024-T3) sheet while re-solution heat treatment did not appear to degrade properties. In contrast, although static strength parameters of stretched material aged to the 'medium strength' category were comparable to those of BS L157 (AA2014-T6), re-solution heat treatment effected a noticeable decrease, with a failure to achieve 0.2% PS levels. Mechanical properties and subsequent fracture behaviour were correlated with submicrostructure throughout the investigation. 23 refs.

Code rules for fatigue analysis of crack-like discontinuities and small cracks, Roche, R. L. Int. J. Pressure Vessels Piping 1989 37, (1-4), 201-218 Practical application of code rules for preventing fatigue crack initiation in geometrical discontinuities having the appearance of cracks is discussed. Attention is given to the RCC-MR specific rules for fatigue analysis of crack-like discontinuities. These rules are based on the 'd-concept', that is to say that the strain range is computed at some finite distance d below the surface, this distance d being characteristic of the material. This strain range and the conventional fatigue design curves are then utilized as usual for fatigue analysis. Experimental validation of these rules is discussed and several examples of practical application are given. In addition it is shown this rule can be applied to avoid fatigue crack initiation from small cracks. Steel 316L is included in the analysis. Graphs. 32 refs.

Derivation of design curves for the elevated-temperature fatigue endurance of type 316 stainless steels. Wood, D. S., Wynn, J. and Williamson, K. Int. J. Pressure Vessels Piping 1989 37, (1-4), 171-188 Elevated4emperature low-cycle continuous cycling fatigue data on type 316 steel have been collected and statistically analysed using a multiple linear regression method. Average fatigue curves between 102-105 cycles have been produced over the temperature range RT-650 °C. The data curves have been translated into design curves and compared with published fatigue design curves in ASME Code Case N47 and the French RCC-MR design code. At 550 °C and low strain range, a condition very relevant to some fast reactor structures, it is shown that the existing codes are too conservative. Graphs. 23 refs. Simplified elastoplastic f a t i g u e analysis. Autrusson, B., Acker, D. and

Hoffmann, A. Int. J. Pressure Vessels Piping 1989 37, (1-4), 157-169 In design by analysis, the rules to avoid unacceptable fatigue damage require the true local strain range to be determined conservatively. A review of simplified methods to estimate the local strain range by the Ke factor and also of experimental results is presented. For each test, the results are the maximum strain range in the notch. In addition, those results have been compared with predictions. The results vary greatly, depending on the tests, because the simplified rules are established for particular cases and then generalized afterwards. Finally, a simplified elastoplastic method based on finite element codes is tested. The calculated strains are very

Int J Fatigue January 1990