Energy Dissipation in Medium and High Cycle Fatigue of Metallic and Composite Materials (original) (raw)
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International Journal of Fatigue, 2000
By analysing the temperature of the external surface during the application of cyclic loading, it is possible to evaluate the dynamic behaviour of an element and to determine the fatigue limit. The methodology (Risitano method) does not need any particular testing machine and allows reliable results to be obtained using a very limited number of specimens in a very short time. This methodology also yields information on the energy retained by the specimen and mechanical components. The results of 15 years of research into a new methodology for the determination of the fatigue limit of materials or mechanical components are reported.
Thermographic applications for the rapid estimation of fatigue limit
Procedia Structural Integrity, 2019
The AIAS group studying Energetic Methods for Experimental Analysis, MEAS, is performing round robin experimental tests for the rapid determination of fatigue limit on steels by different thermographic techniques. This work is part of the project and describes the experimental activity performed at Politecnico di Milano, based on stepwise cyclic tests. Thermograms are processed in terms of: 1) amplitude of the first order harmonic, in-phase with respect to the loading signal; 2) amplitude of the second harmonic, out-of-phase; 3) slope of the thermal signal with respect to the number of cycles. These values typically show bilinear trends, allowing to define a breakup point and a corresponding stress which is the thermographic estimation of the fatigue limit. The paper presents and discusses the results of tests with different stress ratios, i.e. fully reversed cycling with R=-1 and tensiletensile cycling with R=0.1.
Energy analysis of fatigue damage by thermographic technique
2002
The main aims of this paper are to describe the thermographic methodologies currently used in Italy for the rapid evaluation of the fatigue limit and to describe the local energy approach actually under development by the authors. Thermographic methodologies currently used in Italy for the rapid evaluation of the fatigue limit were applied to two stainless steels (AISI 304 and AISI 409). All the experimental results here obtained are in good agreement with the respective values reported in literature. An experimental program for the local energy approach is under development: its main characteristic consists in doing, besides the usual thermal measurements made by thermography, mechanical measurements in order to evaluate the mechanical energy locally dissipated inside the material. This experimental research is part of an interuniversity research program and it is made on stainless steel (AISI 304) notched specimens.
Energy analysis of fatigue damage by thermographic technique
Thermosense XXIV, 2002
The main aims of this paper are to describe the thermographic methodologies currently used in Italy for the rapid evaluation of the fatigue limit and to describe the local energy approach actually under development by the authors. Thermographic methodologies currently used in Italy for the rapid evaluation of the fatigue limit were applied to two stainless steels (AISI 304 and AISI 409). All the experimental results here obtained are in good agreement with the respective values reported in literature. An experimental programme for the local energy approach is under development: its main characteristic consists in doing, besides the usual thermal measurements made by thermography, mechanical measurements in order to evaluate the mechanical energy locally dissipated inside the material. This experimental research is part of an interuniversity research programme and it is made on stainless steel (AISI 304) notched specimens.
Rapid evaluation of fatigue limit on thermographic data analysis
International Journal of Fatigue, 2017
Based on infrared thermography, the graphic methods such as Luong's method and Risitano's method are proved to be rapid and efficient for fatigue limit determination comparing to conventional methods. However, the determination procedure involves visual inspection so contains man-made uncertainties, which restricts their usage. In the present paper, we propose three new treatment methods in terms of relation curve between experimental temperature response (or dissipated energy) and the applied stress amplitude so as to determine the fatigue limit with uniqueness. Those three methods were all evaluated by applying to the experimental data from literature and the error of results were discussed and analyzed. In addition, numerical experiments were carried out to investigate the influence of loading stepped length and random error on each new treatment method.
Temperature evolution during fatigue damage
Intermetallics, 2005
Fatigue damage is closely related to plastic deformation and heat dissipation, which affect the temperature of the materials. In the current research, a state-of-the-art infrared-thermography camera has been used as a nondestructive evaluation (NDE) method to investigate the temperature evolutions in both crystalline and amorphous materials during fatigue experiments. Fatigue-damage processes, such as the Lüders band growth in reactor-pressure-vessel (RPV) steels and shear-band evolution in bulk metallic glasses (BMGs), have been observed in situ and analyzed by thermography. Theoretical models combining fracture mechanics and thermodynamics have been formulated to quantify the temperature-evolution processes during fatigue. Specifically, the plastic work in RPV steel during low-cycle fatigue has been calculated and the fatigue life has been predicted from the observed temperature. The prediction matches the experimental data quite well. q
Mechanical Engineering Journal, 2019
The rapid evaluation technique of fatigue limit using infrared thermography has been developed during the past 30 years. In this technique, the fatigue limit is evaluated on the basis of the temperature evolution associated with cyclic loading. However, this technique is still not reliable enough because the temperature evolution has not been verified quantitatively very well. In previous studies, the authors conducted numerical analysis to simulate the temperature evolution. The results of fatigue limit evaluation were compared fairy well with experimental ones. However, the temperature evolution was significantly larger compared to experimental results due to adiabatic assumption. In this paper, heat conduction within the specimen is taken into account in order to conduct more realistic simulation of temperature evolution. The results are compared quantitatively to those obtained in experiment. The fatigue limit obtained from simulation is compared with those determined by Wöhler method and thermography experiment.
Journal of Solid Mechanics and Materials Engineering, 2012
The technique for rapid evaluation of fatigue limit using infrared thermography has been developed and paid much attention recently. However, the enhancement of reliability of this technique is demanded for practical application in industries. This study is conducted to verify the effect of stress concentration on fatigue limit evaluation through numerical simulation. Temperature evolutions of stainless steel specimens with different notches are simulated by 3D elasto-plastic finite element analysis. It has been shown that the fatigue limit evaluation based on the temperature evolution is essentially explained by plastic energy dissipation, and that the temperature evolution should be measured after a sufficiently large number of cycles so that plastic shakedown is achieved. It has been remarked that the fatigue limit is overestimated if the spatial resolution of infrared thermography is not fine enough to measure the temperature evolution at the stress concentration site.
The Journal of Strain Analysis for Engineering Design, 2008
This paper presents the first results provided by an experimental set-up developed to estimate locally the terms of the energy balance associated with the high-cycle fatigue (HCF) of DP 600 steel. The experimental approach involves two quantitative imaging techniques: digital image correlation and infrared thermography. First, a variational method is used to derive stress fields from the displacement fields. Patterns of deformation energy per cycle can then be determined on the basis of stress and strain data. Second, a local form of the heat equation is used to derive separately the thermoelastic and dissipative sources accompanying HCF. Energy balances show that around 50 per cent of the deformation energy associated with the mechanical hysteresis loop is dissipated while the rest corresponds to stored energy variations.
Fatigue limit evaluation of structure materials based on thermographic analysis
Procedia structural integrity, 2017
During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.