A computational lifetime prediction of a thermal shock experiment. Part II: discussion on difference fatigue criteria (original) (raw)
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Fatigue & Fracture of Engineering Materials & Structures, 2006
The SPLASH experiment has been designed in 1985 by the CEA to simulate thermal fatigue due to short cooling shocks on steel specimens and is similar to the device reported by Marsh in Ref. [1]. The purpose of this paper is to discuss the mechanical and the fatigue analysis of the experiment using results from FEM computations. The lifetime predictions are obtained using a modified dissipated energy with a maximal pressure term and agree with the experimental observations. The numerical analysis of the mechanical state shows an important evolution of the triaxiality ratio during the loading cycle. Further comparisons and discussions of the fatigue criteria are provided in the second part of the paper (Part II)2.
The specific heat loss combined with the thermoelastic effect for an experiment.PDF
The energy dissipated to the surroundings as heat in a unit volume of material per cycle, Q, was recently proposed by the authors as fatigue damage index and it was successfully applied to correlate fatigue data obtained by carrying out fully reversed stress-and strain-controlled fatigue tests on AISI 304L stainless steel plain and notched specimens. The use of the Q parameter to analyse the experimental results led to the definition of a scatter band having constant slope from the low-to the high-cycle fatigue regime. In this paper the energy approach is extended to analyse the influence of mean stress on the axial fatigue behaviour of unnotched cold drawn AISI 304L stainless steel bars. In view of this, stress controlled fatigue tests on plain specimens at different load ratios R (R=-1; R=0.1; R=0.5) were carried out. A new energy parameter is defined to account for the mean stress effect, which combines the specific heat loss Q and the relative temperature variation due to the thermoelastic effect corresponding to the achievement of the maximum stress level of the stress cycle. The new two-parameter approach was able to rationalise the mean stress effect observed experimentally. It is worth noting that the results found in the present contribution are meant to be specific for the material and testing condition investigated here.
Computer methods in applied mechanics and engineering 19 (1979) no. 3
Computer Methods in Applied Mechanics and Engineering, 1979
The performance of singular crack elements including the behavior of associated field derivatives dealing with multiple cracking in composite thick walled cylinders subjected to blasting is investigated. Transient opening mode thermal stress intensity factors of multiple radial cracks emanating from the bore of autofrettaged, internally plated, thick-walled cylinders. subjected to thermal shock and internal pressurization, are evaluated. Quasistatic thermoelasticity problem is solved using the well-known boundary-only element method, in conjunction with the subregion technique, where= the singular behavior of temperature/displacement and flux/stress fields in the vicinity of the crack-tip is modeled through the traction-singular quarter-point element. Results obtained during thermomechanical shocks in chromium-plated composite tubes, illustrate the considerable influence of the plating thickness as well as the autofrettage process on thermal stress intensity factors. 0 1998 Elsevier Science S.A. All rights reserved.
Comparison of Experimental Results with Numerical Solution of Thermal Stress Analysis
Communications - Scientific letters of the University of Zilina
This paper presents experimental measurement of the first stress invariant on the plate with hole at fatigue testing machine due to adiabatic elastic deformation. The theoretical part is concentrated on the theory of thermal stress analysis focusing on thermoelastic analysis. The experimental part is dedicated to the postprocessing of the measured data including analytical and numerical solutions for the plate with hole using finite element method (FEM).
The thermal shock resistance of solids
Acta Materialia, 1998
ÐThe thermal shock resistance of a brittle solid is analysed for an orthotropic plate suddenly exposed to a convective medium of dierent temperature. Two types of plate are considered: (i) a plate containing a distribution of¯aws such as pores, for which a stress-based fracture criterion is appropriate, and (ii) a plate containing a single dominant crack aligned with the through-thickness direction, for which a critical stress intensity factor criterion is appropriate. First, the temperature and stress histories in the plate are given for the full range of Biot number. For the case of a cold shock, the stress ®eld is tensile near the surface of the plate and gives rise to a mode I stress intensity factor for a pre-existing crack at the surface of the plate. Alternatively, for the case of hot shock, the stress ®eld is tensile at the centre of the plate and gives rise to a mode I stress intensity factor for a pre-existing crack at the centre of the plate. Lower bound solutions are obtained for the maximum thermal shock that the plate can sustain without catastrophic failure according to the two distinct criteria: (i) maximum local tensile stress equals the tensile strength of the solid, and (ii) maximum stress intensity factor for the pre-existing representative crack equals the fracture toughness of the solid. Merit indices of material properties are deduced, and optimal materials are selected on the basis of these criteria, for the case of a high Biot number (high surface heat transfer) and a low Biot number (low surface heat transfer). The relative merit of candidate materials depends upon the magnitude of the Biot number, and upon the choice of failure criterion. The eect of porosity on thermal shock resistance is also explored: it is predicted that the presence of porosity is generally bene®cial if the failure is dominated by a pre-existing crack. Finally, the analysis is used to develop merit indices for thermal fatigue.
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.
Effect of Constitutive Model on Thermomechanical Fatigue Life Prediction
Procedia Engineering, 2015
In this paper, thermomechanical fatigue life (TMF) prediction is performed on an automotive exhaust manifold using in-house postprocessor code (Hotlife) with four different constitutive models: elastoplastic model with kinematic hardening, two-layer viscoplastic model, and two unified elasto-viscoplastic models based on the equations proposed by Sehitoglu and Chaboche, respectively. Commercial FEA software Abaqus has been used for the analysis. The first two models are already available in Abaqus; the Chaboche and Sehitoglu models were implemented using a user material subroutine (UMAT, available in Abaqus). The stress and strain histories calculated by these four models are output to Hotlife for post-processing. The results from the prediction are then compared to the experimental TMF life obtained from a component thermal fatigue bench test. Result show the Hotlife calculations based on the two implemented elasto-viscoplastic models yield better correlation with test results.