Fatigue crack growth prediction for spectrum loadings using neural networks

Fatigue crack growth prediction for spectrum loadings using neural networks

Abstracts provide excellent correlation for the R-dependence of the present AKin data. Graphs, 33 ref. A new damage variable for low-cycle fatigue of ...

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Abstracts provide excellent correlation for the R-dependence of the present AKin data. Graphs, 33 ref. A new damage variable for low-cycle fatigue of metallic materials. Cheng, G.X., Lou, Z.-W. and Kuang, Z.-B. Eng. Fract. Mech. (May 1994) 48 (2), 281-287 Experimental results show that the inherent ductility in a material is deflected after cycle loading. Based on the concept of ductility deflection, a new fatigue damage variable D , for low-cycle fatigue is recommended in this paper. This new damage variable D , has definite physical meaning and can be measured with a simple experimental procedure. It can be connected directly with the usual mechanical properties of materials. D , increases slowly at the initial stage of cycle loading, but it increases rapidly after a definite cycle where the macroscale crack is formed. We define the turning point on the D~-N curve as the critical damage value D , and its corresponding cycle number N is the fatigue life Nt. 16MnR is mentioned. Graphs, 10 ref. Fatigue strength assessment by using a nonlinear finite element technique. Chen, C.-N. Eng. Fract. Mech. (May 1994) 48 (2), 247-256 An elastic-plastic finite element procedure considering nonlinear deformation behaviour is used to evaluate the fatigue strength of ductile structures. Few cycles of statically cyclic response analysis are needed to reach a steady-state response with which the local deformation-related post-finite-element results are used to evaluate the ductile crack initiation cycles through the use of an S-N curve obtained from uniaxial tests. The consideration of using this type of fracture parameter is based on the objective of being able to solve general ductile fatigue problems without regard to the degree of plastic deformation that exists in the structure being solved. Mechanical models of both linear and nonlinear deformations are solved separately and the results are compared using a model of the mild steel JIS HT80. Graphs, 7 ref. Fatigue strength of high manganese non-magnetic steel and its microscopic characteristics. Nishida, S.. Hattori, N. and Shimada, T. J. Soc. Mater. Sci. Jpn (Mar. 1994) 43 (486), 324-328 (in Japanese) Fatigue behaviour of high-Mn non-magnetic austenitic steel (HM steel, Fe-0.178C-23.77Mn-2.05Cr-0.23Ni-0.23Si) was studied through rotating bending fatigue tests using plain specimens with a partial shallow notch by means of the successively taken replica method. This behaviour was compared with that of an austenitic stainless steel (SUS 304). The experimental results showed that the fatigue limit of HM steel was the same as that of SUS 304. and a distinct knee point was observed in the S-N curve of both materials. It was found that the fatigue cracks of these materials initiated at grain boundaries or in their neighbourhood. It was apparently observed that some non-propagating micro-cracks existed in the slSecimen surface of HM steel subjected to the stress cycling of fatigue limit by 107 cycles, while no microcrack existed in the specimen of SUS 304 subjected to the same stress condition. Graphs, photomicrographs, 5 ref. Fatigue threshold in steels-mean stress and microstructure influences. Bulloch, J.H. Int. J, Pressure Vessels Piping (1994) 58 (1), 103-127 The effect of R-ratio on a large variety of microstructures commonly found in low-carbon steels was investigated and the predictability of a selection of approaches or models which deal specifically with R-ratio effects on threshold

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fatigue stress intensity range values, AKth, were assessed. Essentially the extent of the R-ratio response on AKth was found to be significantly microstructure-dependent but the trends were by no means simple. Generally the predictions of the various models dealing with R-ratio-AKth trends exhibited poor commonality with the experimentally determined AKth values. Marked complex yield strength try effects on AKth were observed at low Rratio levels (R approx = 0): (a)AKth levels initially increased with try, (b) attained a maximum AK~h value of 9 MPa m It2 which remained constant with increasing try level over the range 300-500 MPa and (c)above o~v approx = 600 MPa AKtt, decreased with try. Graphs, photomicrographs, 35 ref. Fatigue crack growth prediction for spectrum Ioadings using neural networks. Pidaparti, R.M.V. and Palakal. M. (Purdue University) Proc. 34th AIAAIASMEIASCEIAHS/ASC Structures, Structural Dynamics, and Materials Conference; AIAAIASME Adaptive Structures Forum V, La Jolla, California, USA (19-22 Apr. 1993) 2654-2660 An artificial neural network method is developed to represent the fatigue crack growth and cycle relationships under different spectrum loadings. The method utilizes load cycle spectrum using available flight data and experimental data for growth vs. cycles as input. The trained network is able to predict the relationship between the crack growth and loading cycles in centrecracked panel specimens of 7075 aluminium alloy. The neural network is able to generalize the crack growth-cycle behaviour for different variations in the loading spectrums. The result predicted by the neural network model seems reasonable and the model is capable of representing crack growth behaviour for arbitrary Ioadings. Graphs, 7 ref. Grain-boundary participation in high-temperature deformation: an historical review. Gifkins, R.C. Mater. Charact. (Mar. 1994) 32 (2), 59-77 A personal and historical approach is used to frame this review of the development of understanding of the role of grain boundaries in hightemperature deformation of, e.g. brass, steels, aluminium, nitrogen, zinc alloys and lead alloys. Power-law creep, creep ductility, diffusion creep, superplasticity, and high-temperature fatigue are included in the survey, as is a brief discussion of models for the grain boundary itself. Some of the principal features described are subgrains, grain-boundary sliding, cavity nucleation and growth, various kinds of localized diffusion creep, grain* boundary migration, and the core and mantle concept. Photomicrographs, graphs, 61 ref, Evaluation of fatigue damage under random stress sequences on the view point of plastic strain. Seki, H., lida, 7"., Oda, A. and lkai, Y. J. Soc. Mater. Sci. Jpn (Feb. 1994) 43 (485), 197-202 (in Japanese) Fatigue damage evaluation is one of the most important processes for the integrity of a machine or a structure. Although many trials have been made for fatigue damage evaluation, few methods can be used to deal with a wide range of stress or strain conditions of fatigue tests. The fatigue damage evaluation methods were examined with respect to plastic strain ranging from small to large amplitudes of strain repetition for a given stress sequence. Then, a new fatigue damage rule was proposed in terms of strain condition. The new rule showed agreement with the theoretical estimations for various experimental conditions. A technique was developed to obtain the stress-strain behaviour of a sample material for a given stress sequence. This showed a good applicability for fatigue damage estimation. Graphs, 5 ref.