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Fatigue failure of SUS 304 caused by vibratory cavitation erosion
274
Fatigue Abstracts
Effect of magnesium content on the fatigue of spot-welded aluminium alloys. Krause, A.R., Thornton, P.H. and Davies, R.G. Proc. Conf. Recent Developments in Light Metals, Toronto, Ontario, Canada (20-23 Aug. 1994) 305-314 The bulk thermal and electrical properties of an AI alloy can greatly affect the ability of the alloy to be spot welded and hence can affect the mechanical properties of the spot weld. In this study the fatigue characteristics of spotwelded commercially available alloys varying in Mg content from approx 1 to 4% Mg were determined, both in the as-received condition and after being annealed to the O-temper. These samples were fatigue tested in the overlap shear geometry. The fatigue behaviours were compared on the basis of alloy content, weld nugget shape and failure mode. Graphs, photomicrographs, 11 ref. Fatigue evaluation of aluminum joints. Chernenkoff, R.A. and Krause, A.R. Proc. Conf. Recent Developments in Light Metals, Toronto, Ontario, Canada (20-23 Aug. 1994) 293-303 The cyclic fatigue behaviour of single overlap AI joints (5754-0 and 611 IT4), which have been joined through a variety of processes, has been investigated. Uniaxial tests of spot-welded, weld-bonded and mechanically fastened (clinch and clinch-bonded) joints are compared on the basis of their fatigue performance. The Alcan 5754-0 material, coated with a pretreatment specifically developed for adhesive bonding, is used in conjunction with Ciba-Giegy XD4600 epoxy adhesive to form a structural bonding system. Results show a significant improvement in the fatigue strength of the weld-bonded and clinchbonded joints compared with spot-welded and clinch joints. Graphs, 13 ref.
Mechanism of improving fatigue limit of 16Mn steel weld by explosion shock wave treatment. Chen, L., Zhao, T., Si, C. and Chen, H. Chin. J. Mater. Res. (June 1994) 8 (3), 233-236 (in Chinese) Welding joints of steel 16Mn in the same state of initial microstructure and residual stress were subjected to shock waves with different intensity by changing the distance between the explosive and the sampling location of the specimen. The rotational bending fatigue limits of steel 16Mn welding joints and the ferrite dislocation morphology were studied respectively before and after the explosion treatment within the zones affected by the plastic, elastic and elasto-plastic shock waves, and the mechanism of improving fatigue limits of steel 16Mn weld as a result of the explosion shock wave act was brought out with dislocation tangled and pinned theory. Graphs, photomicrographs, 7 ref.
Surface rolling strengthening of magnesium alloy ZM1. Feng, Z., Z.hang, J. and Chen, X. Acta Metall. Sin. (China) (18 Sept. 1994) 30 (9), A422-A426 (in Chinese) The effect of surface rolling on fatigue strength and fatigue sensitivity to notches of the Mg alloy ZM1 has been studied. The results show that the increase in smooth or notched fatigue limit amounts to 57 or 200% respectively. The fatigue sensitivity to notches may be greatly reduced, and so the q value may become negative. During surface rolling of hcp Mg alloy, the plastic deformation and strengthening may be carried out by the way of slip and twin. The high compressive residual stress is favourable to improving the notched fatigue limit and to modifying the fatigue sensitivity to notches. The plastic deformation strengthening may contribute to developing the beneficial behaviour of the compressive residual stress. Graphs, 12 ref. Improving bearing steel inclusion through Ca-Si deoxidation and acidslag ESR. Zhou, D., Wang, C., Qian, M., Xu, M., Li, Z. and Zhang, Z. Iron Steel (China) (July 1994) 29 (7), 25-28 (in Chinese) The influences of the deoxidizing process of the steel used for ESR electrodes and the slag system used in the ESR process on the non-metals in bearing steel (GCrl5) and the fatigue properties of the steel have been studied. After the ESR process, the slag used in the process is either basic or acidic; the main non-metallic inclusions in the steel are those in the form of brittle AI203, if the aliminium is used as deoxidant in the production of the ESR electrode. If either CA-Si or Ca-Si + Fe-Si is used as deoxidant, the non-metallic inclusions in the steel will be plastic sulphide and silicate after the acidic slag ESR process and will still be brittle AI203 after the basic slag ESR process. Graphs, 7 ref. Fatigue failure of SUS 304 caused by vibratory cavitation erosion. Ahmed, S.M., Hokla'rigawa, K. and Oba, R. Wear (Oct. 1994) 177 (2), 129-137 The mechanism of cavitation erosion is investigated in detail for SUS 304 stainless steel, a typical erosion-resistant material. Systematic observations of eroded surfaces and dislodged particles show that the predominant failure mode in cavitation erosion is fatigue. Characteristic features of such failures include packets of slip bands, cracks that nucleate at regions of high stress (strain) concentrations, cracks that propagate first at an inclination to the surface and then parallel to the surface, fatigue striations, and 'tyre tracks' on the rupture surfaces. These last two features are the most indicative of a fatigue process. It is also deduced that massive voids accompanying pressure shock-rings are the most erosive kind of cavitation. Photomicrographs, 40 ref.
Cyclic strength of cyanided steels designed for heavily loaded machine components. Geshelin, V.G., Polunin, V.I. and Akhant'ev, V.P. Met. Sci. Heat Treat. (Russia) (July 1994) 36 (1-2), 8-13 In order to provide high strength to cyclic loads for structural steels; methods of surface hardening by thermochemical treatment are widely applied. Among them, the processes of cyaniding and case hardening are efficient under the conditions of large-batch mass production. However, the data available in the literature are insufficient to choose efficiently materials and process characteristics ensuring high cyclic strength and reliability of heavily loaded components. The present work is devoted to studying the effect of the structure, method of treatment, depth of hardening, core and surface hardness and other factors on the cyclic strength of structural steels 14KhGN, 19KhGN, 20KhGNM, 40KhGNM, and 30KhM. Graphs, photomicrographs.
The low-cycle fatigue properties of weldable Al-Zn-Mg-Mn alloy and aliuminium 7039 in various environments. Cho, H.S. and Nam, S.W. J. Korean Inst. Met. Mater. (July 1994) 32 (7), 765-770 (in Korean) The strain-controlled low-cycle fatigue properties of recently developed weldable A I - Z n - M g - M n (AI4.3Zn-2.8Mg-0.68Mn) alloy and commercial AI 7039 alloy were studied in air, distilled water, and 3.5 wt% NaCI solution. While the tensile strength of the A I - Z n - M g - M n is greater than that of 7039 alloy, the fatigue life of the A I - Z n - M g - M n alloy is found comparable to those of the AI 7039 alloy at the condition of the same total strain range in all the environments tested. However, the fatigue life of the A I - Z n - M g - M n alloy appears longer than that of the AI 7039 in terms of the dissipated energy/cycle in the specimen. These results are considered to be caused by the difference in cyclic deformation behaviour between the weldable A I - Z n - M g - M n alloy and A1 7039 alloy. Graphs, photomicrographs, 11 ref.
Fatigue life and crack growth prediction methodology. Newman, J.C., Phillips, E.P. andEverett, R.A. Gov. Res. Announce. Index (Mar. 1994) 13 pp The paper reviews the capabilities of a plasticity-induced crack-closure model and life-prediction code to predict fatigue crack growth and fatigue lives of metallic materials. Crack-tip constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (AKaf) under constant-amplitude loading. Some modifications to the AKcff rate relations were needed in the near threshold regime to fit small-crack growth rate behaviour and endurance limits. The model was then used to calculate small- and large-crack growth rates, and in some cases total fatigue lives, for several ahiminium and titanium alloys under constant-amplitude, variable-amplitude, and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks. Results from the tests and analyses agreed well.
Crack severity index of monitored load spectra. Dejong, J.B. Gov. Res. Announce. Index (Mar. 1994) 5pp To assess the consequences with regard to fatigue and damage tolerance of changes in operational usage, a simple means to quantify the relative severity of recorded load spectra is required. The paper describes the development and validation of the crack severity index (CSI) as a means to express the relative damage in terms of a crack growth potential of stress spectra. The CSI is based on a crack-closure crack growth model and takes account of interaction effects by considering the shape of the spectrum. It is shown that the CSI concept is a reasonably accurate method for comparing the relative severity of manoeuvre-dominated spectra in aluminium alloy structures.
Growth of artificially and naturally initiating notch root cracks under FALSTAFF spectrum loading. Sunder, R., Prakash, R.V. and Mitchenko, E.I. Gov. Res. Announc. Index (Mar. 1994) 12 pp The paper describes an experimental study of notch lOOt fatigue crack growth under FALSTAFF spectrum loading in an aiuminium-copper alloy. Crack growth rates were measured from crack size as small as 20 p,m using optical fractography and replication techniques. Fractographic measurements indicate similar scatter levels between notch root short crack and long growth rate data. This is in contrast to surface-replica-based measurements, which are indicative of large scarer. Growth rate variation was noticed between multiple cracks initiating after different periods of natural crack formation. This is attributed to the influence of larger existing cracks on smaller cracks that appear later. In contrast, identical artificially initiating cracks grew at a similar rate.
Creep-fatigue failure of SAF 2205 and 316 stainless steels in AR+3% SOz environment at 700°C. Aghion, E. and Molaba, C.A. J. Mater. Sci (1 Apr. 1994) 29 (7), 1758-1764 The creep-fatigue behaviour of SAF 2205 duplex stainless steel and 316 austenitic stainless steel was studied under a sulphur-containing environment of an AR + 3% SO 2 atmosphere at 700°C. The cyclic loading employed creeptension and plastic compression following the creep-plasticity (cp)-mode of the strain-range partitioning life-prediction method. The results showed that a premature failure was obtained with both SAF 2205 and 316 stainless steels under the combination of creep-fatigue loading and an SO2-bearing atmosphere. However, SAF 2205 was significantly more resistant than 316 as far as the
Fatigue Abstracts
Effect of magnesium content on the fatigue of spot-welded aluminium alloys. Krause, A.R., Thornton, P.H. and Davies, R.G. Proc. Conf. Recent Developments in Light Metals, Toronto, Ontario, Canada (20-23 Aug. 1994) 305-314 The bulk thermal and electrical properties of an AI alloy can greatly affect the ability of the alloy to be spot welded and hence can affect the mechanical properties of the spot weld. In this study the fatigue characteristics of spotwelded commercially available alloys varying in Mg content from approx 1 to 4% Mg were determined, both in the as-received condition and after being annealed to the O-temper. These samples were fatigue tested in the overlap shear geometry. The fatigue behaviours were compared on the basis of alloy content, weld nugget shape and failure mode. Graphs, photomicrographs, 11 ref. Fatigue evaluation of aluminum joints. Chernenkoff, R.A. and Krause, A.R. Proc. Conf. Recent Developments in Light Metals, Toronto, Ontario, Canada (20-23 Aug. 1994) 293-303 The cyclic fatigue behaviour of single overlap AI joints (5754-0 and 611 IT4), which have been joined through a variety of processes, has been investigated. Uniaxial tests of spot-welded, weld-bonded and mechanically fastened (clinch and clinch-bonded) joints are compared on the basis of their fatigue performance. The Alcan 5754-0 material, coated with a pretreatment specifically developed for adhesive bonding, is used in conjunction with Ciba-Giegy XD4600 epoxy adhesive to form a structural bonding system. Results show a significant improvement in the fatigue strength of the weld-bonded and clinchbonded joints compared with spot-welded and clinch joints. Graphs, 13 ref.
Mechanism of improving fatigue limit of 16Mn steel weld by explosion shock wave treatment. Chen, L., Zhao, T., Si, C. and Chen, H. Chin. J. Mater. Res. (June 1994) 8 (3), 233-236 (in Chinese) Welding joints of steel 16Mn in the same state of initial microstructure and residual stress were subjected to shock waves with different intensity by changing the distance between the explosive and the sampling location of the specimen. The rotational bending fatigue limits of steel 16Mn welding joints and the ferrite dislocation morphology were studied respectively before and after the explosion treatment within the zones affected by the plastic, elastic and elasto-plastic shock waves, and the mechanism of improving fatigue limits of steel 16Mn weld as a result of the explosion shock wave act was brought out with dislocation tangled and pinned theory. Graphs, photomicrographs, 7 ref.
Surface rolling strengthening of magnesium alloy ZM1. Feng, Z., Z.hang, J. and Chen, X. Acta Metall. Sin. (China) (18 Sept. 1994) 30 (9), A422-A426 (in Chinese) The effect of surface rolling on fatigue strength and fatigue sensitivity to notches of the Mg alloy ZM1 has been studied. The results show that the increase in smooth or notched fatigue limit amounts to 57 or 200% respectively. The fatigue sensitivity to notches may be greatly reduced, and so the q value may become negative. During surface rolling of hcp Mg alloy, the plastic deformation and strengthening may be carried out by the way of slip and twin. The high compressive residual stress is favourable to improving the notched fatigue limit and to modifying the fatigue sensitivity to notches. The plastic deformation strengthening may contribute to developing the beneficial behaviour of the compressive residual stress. Graphs, 12 ref. Improving bearing steel inclusion through Ca-Si deoxidation and acidslag ESR. Zhou, D., Wang, C., Qian, M., Xu, M., Li, Z. and Zhang, Z. Iron Steel (China) (July 1994) 29 (7), 25-28 (in Chinese) The influences of the deoxidizing process of the steel used for ESR electrodes and the slag system used in the ESR process on the non-metals in bearing steel (GCrl5) and the fatigue properties of the steel have been studied. After the ESR process, the slag used in the process is either basic or acidic; the main non-metallic inclusions in the steel are those in the form of brittle AI203, if the aliminium is used as deoxidant in the production of the ESR electrode. If either CA-Si or Ca-Si + Fe-Si is used as deoxidant, the non-metallic inclusions in the steel will be plastic sulphide and silicate after the acidic slag ESR process and will still be brittle AI203 after the basic slag ESR process. Graphs, 7 ref. Fatigue failure of SUS 304 caused by vibratory cavitation erosion. Ahmed, S.M., Hokla'rigawa, K. and Oba, R. Wear (Oct. 1994) 177 (2), 129-137 The mechanism of cavitation erosion is investigated in detail for SUS 304 stainless steel, a typical erosion-resistant material. Systematic observations of eroded surfaces and dislodged particles show that the predominant failure mode in cavitation erosion is fatigue. Characteristic features of such failures include packets of slip bands, cracks that nucleate at regions of high stress (strain) concentrations, cracks that propagate first at an inclination to the surface and then parallel to the surface, fatigue striations, and 'tyre tracks' on the rupture surfaces. These last two features are the most indicative of a fatigue process. It is also deduced that massive voids accompanying pressure shock-rings are the most erosive kind of cavitation. Photomicrographs, 40 ref.
Cyclic strength of cyanided steels designed for heavily loaded machine components. Geshelin, V.G., Polunin, V.I. and Akhant'ev, V.P. Met. Sci. Heat Treat. (Russia) (July 1994) 36 (1-2), 8-13 In order to provide high strength to cyclic loads for structural steels; methods of surface hardening by thermochemical treatment are widely applied. Among them, the processes of cyaniding and case hardening are efficient under the conditions of large-batch mass production. However, the data available in the literature are insufficient to choose efficiently materials and process characteristics ensuring high cyclic strength and reliability of heavily loaded components. The present work is devoted to studying the effect of the structure, method of treatment, depth of hardening, core and surface hardness and other factors on the cyclic strength of structural steels 14KhGN, 19KhGN, 20KhGNM, 40KhGNM, and 30KhM. Graphs, photomicrographs.
The low-cycle fatigue properties of weldable Al-Zn-Mg-Mn alloy and aliuminium 7039 in various environments. Cho, H.S. and Nam, S.W. J. Korean Inst. Met. Mater. (July 1994) 32 (7), 765-770 (in Korean) The strain-controlled low-cycle fatigue properties of recently developed weldable A I - Z n - M g - M n (AI4.3Zn-2.8Mg-0.68Mn) alloy and commercial AI 7039 alloy were studied in air, distilled water, and 3.5 wt% NaCI solution. While the tensile strength of the A I - Z n - M g - M n is greater than that of 7039 alloy, the fatigue life of the A I - Z n - M g - M n alloy is found comparable to those of the AI 7039 alloy at the condition of the same total strain range in all the environments tested. However, the fatigue life of the A I - Z n - M g - M n alloy appears longer than that of the AI 7039 in terms of the dissipated energy/cycle in the specimen. These results are considered to be caused by the difference in cyclic deformation behaviour between the weldable A I - Z n - M g - M n alloy and A1 7039 alloy. Graphs, photomicrographs, 11 ref.
Fatigue life and crack growth prediction methodology. Newman, J.C., Phillips, E.P. andEverett, R.A. Gov. Res. Announce. Index (Mar. 1994) 13 pp The paper reviews the capabilities of a plasticity-induced crack-closure model and life-prediction code to predict fatigue crack growth and fatigue lives of metallic materials. Crack-tip constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (AKaf) under constant-amplitude loading. Some modifications to the AKcff rate relations were needed in the near threshold regime to fit small-crack growth rate behaviour and endurance limits. The model was then used to calculate small- and large-crack growth rates, and in some cases total fatigue lives, for several ahiminium and titanium alloys under constant-amplitude, variable-amplitude, and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks. Results from the tests and analyses agreed well.
Crack severity index of monitored load spectra. Dejong, J.B. Gov. Res. Announce. Index (Mar. 1994) 5pp To assess the consequences with regard to fatigue and damage tolerance of changes in operational usage, a simple means to quantify the relative severity of recorded load spectra is required. The paper describes the development and validation of the crack severity index (CSI) as a means to express the relative damage in terms of a crack growth potential of stress spectra. The CSI is based on a crack-closure crack growth model and takes account of interaction effects by considering the shape of the spectrum. It is shown that the CSI concept is a reasonably accurate method for comparing the relative severity of manoeuvre-dominated spectra in aluminium alloy structures.
Growth of artificially and naturally initiating notch root cracks under FALSTAFF spectrum loading. Sunder, R., Prakash, R.V. and Mitchenko, E.I. Gov. Res. Announc. Index (Mar. 1994) 12 pp The paper describes an experimental study of notch lOOt fatigue crack growth under FALSTAFF spectrum loading in an aiuminium-copper alloy. Crack growth rates were measured from crack size as small as 20 p,m using optical fractography and replication techniques. Fractographic measurements indicate similar scatter levels between notch root short crack and long growth rate data. This is in contrast to surface-replica-based measurements, which are indicative of large scarer. Growth rate variation was noticed between multiple cracks initiating after different periods of natural crack formation. This is attributed to the influence of larger existing cracks on smaller cracks that appear later. In contrast, identical artificially initiating cracks grew at a similar rate.
Creep-fatigue failure of SAF 2205 and 316 stainless steels in AR+3% SOz environment at 700°C. Aghion, E. and Molaba, C.A. J. Mater. Sci (1 Apr. 1994) 29 (7), 1758-1764 The creep-fatigue behaviour of SAF 2205 duplex stainless steel and 316 austenitic stainless steel was studied under a sulphur-containing environment of an AR + 3% SO 2 atmosphere at 700°C. The cyclic loading employed creeptension and plastic compression following the creep-plasticity (cp)-mode of the strain-range partitioning life-prediction method. The results showed that a premature failure was obtained with both SAF 2205 and 316 stainless steels under the combination of creep-fatigue loading and an SO2-bearing atmosphere. However, SAF 2205 was significantly more resistant than 316 as far as the