The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Solveig Melin - One of the best experts on this subject based on the ideXlab platform.
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Numerical modeling of short Crack behavior in a thermal barrier coating upon thermal shock loading
Journal of Thermal Spray Technology, 2004Co-Authors: Christer Persson, Solveig MelinAbstract:The behavior of microstructurally short inherent Cracks within a preoxidized thermal barrier coating system upon thermal shock loading is considered. A thin alumina oxide layer holding residual stresses was induced at the ceramic/metal interface to simulate thermally grown oxide on the bond coat. Undulation of the oxidized bond coat was modeled as a sinusoidal surface. The variations of the stress-intensity factors of inherent centrally located Cracks and of edge Cracks were calculated during the thermal cycling. The instant Crack shapes during the first thermal cycle and at steady state were investigated. It was found that oxide layer thickness, Crack Tip location, as well as interfacial undulation are factors influencing the risk of Crack propagation. It was also found that an edge Crack constitutes a greater threat to the coating durability than a central Crack. The propagation of an edge Crack, if it occurs, will take place during the first load cycle, whereas for a central Crack, Crack Tip Position decides the risk of Crack propagation.
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Fracture mechanics analysis of microCracks in thermally cycled thermal barrier coatings
Journal of Thermal Spray Technology, 2004Co-Authors: Christer Persson, Solveig MelinAbstract:The effects from thermal shock loading on pre-existing microCracks within thermal barrier coatings (TBCs) have been investigated through a finite element based fracture mechanical analysis. The TBC system consists of a metallic bond coat and a ceramic top coat. The rough interface between the top and bond coats holds an alumina oxide layer. Stress concentrations at the interface due to the interface roughness, as well as the effect of residual stresses, were accounted for. At the eventual closure between the Crack surfaces, Coulomb friction was assumed. To judge the risk of fracture from edge Cracks and centrally placed Cracks, the stress intensity factors were continuously monitored during the simulation of thermal shock loading of the TBC. It was found that fracture from edge Cracks is more likely than from centrally placed Cracks. It was also concluded that the propagation of an edge Crack is already initiated during the first load cycle, whereas the Crack Tip Position of a central Crack determines whether propagation will occur.
Philip J. Withers - One of the best experts on this subject based on the ideXlab platform.
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In situ through-thickness analysis of Crack Tip fields with synchrotron X-ray diffraction
International Journal of Fatigue, 2019Co-Authors: Pablo Lopez-crespo, J.v. Peralta, Joe Kelleher, Philip J. WithersAbstract:Abstract In this work a novel approach to estimate in situ the stress intensity factor (SIF) through the thickness of metal specimens is presented. It is based on a hybrid methodology that combines powerful synchrotron X-ray diffraction data with an elastic analytical model describing the strain field around the Crack Tip. A sensitivity analysis is conducted to understand the largest sources of error and their impact on the estimated SIF values. The accuracy in locating the Crack Tip Position was found to affect the quality of the SIF estimation. Accordingly a procedure is developed to help locate the Crack Tip Position. The methodology is tested on ultra-fine grained aluminium alloy 5091 and on a bainitic steel. It is recommended that an area of interest having a size at least 3 times larger than the plane strain plastic zone is mapped, providing good SIF estimations (within 8%) for all cases studied.
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Obtaining the J-integral by diffraction-based Crack-field strain mapping
Procedia structural integrity, 2016Co-Authors: S.m. Barhli, Philip J. Withers, Luis Saucedo-mora, Christopher Simpson, Thorsten Becker, Mahmoud Mostafavi, Thomas James MarrowAbstract:Abstract The analysis by diffraction of polycrystalline materials can determine the full tensor of the elastic strains within them. Point-by-point maps of elastic strain can thus be obtained in fine-grained engineering alloys, typically using synchrotron X-rays or neutrons. In this paper, a novel approach is presented to calculate the elastic strain energy release rate of a loaded Crack from two-dimensional strain maps that are obtained by diffraction. The method is based on a Finite Element approach, which uses diffraction data to obtain the parameters required to calculate the J-integral via the contour integral method. The J integral is robust to uncertainties in the Crack Tip Position and to poor definition of the field in the Crack vicinity, and does not rely on theoretical assumptions of the field shape. A validation of the technique is presented using a synthetic dataset from a finite element model. Its experimental application is demonstrated in an analysis of a synchrotron X-ray diffraction strain map for a loaded fatigue Crack in a bainitic steel.
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Crack monitoring around a hole under mixed mode (I+II) loading by image correlation
2013Co-Authors: Pablo Lopez-crespo, Philip J. Withers, Anton Shterenlikht, John R. Yates, A. Patterson, Richard L. BurgueteAbstract:Fastening holes are critical in the aircraft industry from a structuralintegrity viewpoint. This is because they act as stress concentrators from which Cracksoften grow. In this work the image correlation technique has been used to measuredisplacements near a Crack Tip under mixed mode (I+II) stress field on Al 7010 samples.The Crack Tip Position was deduced from the shape of the displacement fields. Thenanalytical displacement fields have been fitted to the experimental data by combiningMuskhelishvili's complex function approach with conformal mapping and mulTiple pointover-deterministic method to infer SIFs. The mode I experimentally calculated SIFsoverall agree well with the theoretical applied values, with the maximum difference lessthan 10%. The agreement for the mode II SIF was not as good as for mode I, althoughthe differences between calculated and nominal values are comparable to thoseobtained for mode I. Probably the signal to noise ratio is the main reason for thisdiscrepancy, as in all the cases nominal KI were several times bigger than KII.
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Real-time acquisition of fatigue Crack images for monitoring Crack-Tip stress intensity variations within fatigue cycles
Journal of Strain Analysis for Engineering Design, 2008Co-Authors: F. Yusof, Philip J. WithersAbstract:Digital images of fatigue Crack behaviour have been acquired in real time at high cycle fatigue rates (77 Hz) using a high-speed camera at 1000 frames/s. Digital image correlation has then been used to determine the Crack-Tip Position and stress intensity variations (KI and KII) within selected cycles. This has been achieved for a pre-Cracked aluminium compact tension (CT) specimen subjected to constant load amplitude fatigue Crack cycling. The Crack-Tip displacement field has been determined at 14 points within each cycle. In this proof of concept study, despite noise in the inferred displacement fields, by least squares fitting the displacement field rather than the strain field to the Muskhelishvili's form Crack-Tip stress field, the Crack-Tip stress intensity inferred from the measured Crack-Tip displacement field was found to good accuracy (around 0.2 MPa m1/2). Furthermore, the observed sinusoidal variation was in excellent agreement with the nominal ΔK obtained from the applied fatigue amplitude co...
V. Valle - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of fracture properties of cancellous bone tissues using digital image correlation/wedge splitting test method
Journal of the mechanical behavior of biomedical materials, 2020Co-Authors: P. Bokam, Alexis Germaneau, T. Vendeuvre, P Rigoard, V. ValleAbstract:The fracture mechanics (FM) parameters of cancellous bone tissues are very important from a clinical point of view especially for the bone cement augmentation. From the literature review, one can observe that the experimental determination of fracture mechanic parameters of cancellous bone are still lacking. This can be due to the conditions associated with the unstable Crack propagation in the cancellous bone and lack of tools to extract and measure the parameters (like Crack opening displacement (COD) and Crack length) in the course of fracture tests, which are necessary to evaluate the fracture properties. To address above mentioned, a platform was developed integrating an optical measurement technique like digital image correlation (DIC) with classical wedge splitting test (WST) method to extract precise and real Crack Tip Positions, Crack opening displacement (COD) at each load step. These indeed used for the evaluation of the fracture mechanic properties (fracture toughness, specific fracture energy ()) of the cancellous bone. Two approaches were used to evaluate the fracture mechanic properties of the bone. The first method is based on the global approach, which was widely used in the literature and the second method is based on the local approach. In this local approach, the local fracture energy () during the course of the test was evaluated, which give access to local fracture mechanics. The results evaluated by both the methods were in good accordance and compared with available literature. In addition, an attempt made to retrieve the real Crack Tip Position at each load step during the test.
Umberto Galietti - One of the best experts on this subject based on the ideXlab platform.
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Automatic procedure for evaluating the Paris Law of martensitic and austenitic stainless steels by means of thermal methods
Engineering Fracture Mechanics, 2016Co-Authors: F. Ancona, R. De Finis, Davide Palumbo, Giuseppe Pompeo Demelio, Umberto GaliettiAbstract:Abstract Determination of the Paris Law constants implies the knowledge of both Stress Intensity Factor (SIF) and the Crack growth rate (da/dN). In this regard, the Crack length and the SIF values can be measured using various methods suggested by literature and proposed by Standards, but most of them require an off-line measurement of the Crack with consequent high testing time and cannot be applied on actual structural components. In this work, the Thermoelastic Stress Analysis (TSA) technique is used for the monitoring of fatigue Crack growth during fracture mechanics tests on four stainless steels: AISI 422 and ASTM A182 grade F6NM with martensitic lattice and CF3M and CF8M with austenitic lattice. In particular, an automatic procedure based on the TSA technique was proposed for the continuous evaluation of the Crack Tip Position and the SIF value. Advantages with respect to classical methods can be obtained in terms of reduction of: testing time, experimental set-up, data processing and data report.
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Crack Growth Monitoring in Stainless Steels by Means of TSA Technique
Procedia Engineering, 2015Co-Authors: F. Ancona, R. De Finis, Davide Palumbo, Umberto GaliettiAbstract:Abstract In this work, the Thermoelastic Stress Analysis (TSA) technique was used for the monitoring of fatigue Crack growth during fracture mechanics tests on stainless steel. In this regards, different methods are used in literature but most of them cannot be applied on real components since they require an off-line measurement of the Crack. An automatic procedure based on TSA technique was proposed for the continuous evaluation of the Crack Tip Position. Advantages with respect to classical methods can be obtained in terms of reduction of testing time, experimental set-up, data processing and data report.
Christer Persson - One of the best experts on this subject based on the ideXlab platform.
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Numerical modeling of short Crack behavior in a thermal barrier coating upon thermal shock loading
Journal of Thermal Spray Technology, 2004Co-Authors: Christer Persson, Solveig MelinAbstract:The behavior of microstructurally short inherent Cracks within a preoxidized thermal barrier coating system upon thermal shock loading is considered. A thin alumina oxide layer holding residual stresses was induced at the ceramic/metal interface to simulate thermally grown oxide on the bond coat. Undulation of the oxidized bond coat was modeled as a sinusoidal surface. The variations of the stress-intensity factors of inherent centrally located Cracks and of edge Cracks were calculated during the thermal cycling. The instant Crack shapes during the first thermal cycle and at steady state were investigated. It was found that oxide layer thickness, Crack Tip location, as well as interfacial undulation are factors influencing the risk of Crack propagation. It was also found that an edge Crack constitutes a greater threat to the coating durability than a central Crack. The propagation of an edge Crack, if it occurs, will take place during the first load cycle, whereas for a central Crack, Crack Tip Position decides the risk of Crack propagation.
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Fracture mechanics analysis of microCracks in thermally cycled thermal barrier coatings
Journal of Thermal Spray Technology, 2004Co-Authors: Christer Persson, Solveig MelinAbstract:The effects from thermal shock loading on pre-existing microCracks within thermal barrier coatings (TBCs) have been investigated through a finite element based fracture mechanical analysis. The TBC system consists of a metallic bond coat and a ceramic top coat. The rough interface between the top and bond coats holds an alumina oxide layer. Stress concentrations at the interface due to the interface roughness, as well as the effect of residual stresses, were accounted for. At the eventual closure between the Crack surfaces, Coulomb friction was assumed. To judge the risk of fracture from edge Cracks and centrally placed Cracks, the stress intensity factors were continuously monitored during the simulation of thermal shock loading of the TBC. It was found that fracture from edge Cracks is more likely than from centrally placed Cracks. It was also concluded that the propagation of an edge Crack is already initiated during the first load cycle, whereas the Crack Tip Position of a central Crack determines whether propagation will occur.