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S.v. Kamat - One of the best experts on this subject based on the ideXlab platform.
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Dynamic fracture toughness of a near alpha titanium alloy Timetal 834
Journal of Alloys and Compounds, 2009Co-Authors: Kartik Prasad, S.v. KamatAbstract:Abstract The dynamic fracture toughness of Timetal 834 alloy under impact loading was evaluated using fatigue pre-cracked specimens and compared with the fracture toughness under static loading condition evaluated in an earlier study. It was found that the dynamic fracture toughness under impact loading was higher than the fracture toughness value under static loading conditions. This behaviour was attributed to the effect of strain rate on strain hardening exponent and yield strength. The effect of Notch Root Radius on dynamic fracture toughness of this alloy was also studied. It was found that there exists a critical Notch Radius ( ρ 0 ) of ∼150 μm below which the dynamic fracture toughness was independent of Notch Root Radius. Above ρ 0 , the dynamic fracture toughness increased linearly with square Root of Notch Root Radius.
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effect of Notch Root Radius on fracture toughness of ti 18al 8nb alloy
Materials Science and Technology, 2009Co-Authors: Archana Paradkar, A K Gogia, S.v. KamatAbstract:AbstractThe effect of Notch Root Radius on the mode I fracture toughness of Ti–18Al–8Nb alloy in beta solution treated and water quenched condition was investigated. The apparent fracture toughness K IA was found to be independent of the Notch Root Radius below a critical Notch Root Radius ρ 0 and subsequently increase linearly with the square Root of Notch Root Radius ρ1/2 beyond ρ 0. The critical Notch Root Radius in this alloy was found to be ∼50 μm. The results were explained on the basis of strain controlled fracture model.
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effects of Notch Root Radius on crack initiation and growth toughnesses of a cross ply ti6al4v sic composite
Acta Materialia, 1996Co-Authors: S.v. Kamat, J. P. HirthAbstract:Effects of Notch Root Radius on the crack initiation and growth toughnesses of a cross-ply [90{degree}/0{degree}]{sub 2s} Ti-6Al-4V/SiC{sub f} composite have been studied. The initiation toughness was found to be independent of the Notch Root Radius, below a critical value of {rho} {approximately} 50 {micro}m. Beyond this value, the initiation toughness increases linearly with the Notch Root Radius. In contrast, the crack growth toughness was found to be more or less independent of the initial Notch Root Radius. The results are rationalized on the basis of the mechanism of fracture as well as the strain concentrations ahead of the Notch.
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effect of Notch Root Radius on ductile fracture toughness of armco iron
International Journal of Fracture, 1992Co-Authors: M. Srinivas, S.v. KamatAbstract:There are situations when fatigue precracking of fracture toughness test specimens is not feasible. A case in point is when mixed mode fracture toughness is to be evaluated [1]. It, then, becomes necessary to determine the influence of the Notch Root Radius on the fracture toughness of a material. It is well established that Notch Root Radius has a significant influence on the apparent fracture toughness of a material [2-5]." Usually a critical Notch Root Radius, below which fracture toughness is independent of Notch Root Radius, exists and is measured. We present in this communication the results of an investigation of the effect of Notch-Root Radius on mode I fracture toughness (J~o) of Armco iron and a procedure to correct for the same to arrive at the t rue Jic value.
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effect of Notch Root Radius on fracture toughness of an 8090 aluminium lithium alloy
Scripta Metallurgica Et Materialia, 1991Co-Authors: S.v. Kamat, Eswara N PrasadAbstract:Abstract There was no effect of orientation (L-T or T-L) on the variation of apparent fracture toughness with a Notch Root Radius in 8090 type AlLi alloys. The fracture toughness was independent of the Notch Root Radius below a critical Notch Root Radius of approximately 140 μm and increased linearly with the square Root of Notch Root Radius for ϱ greater than 140 μm, for both the test directions. The fracture process in such alloys was strain controlled.
Filippo Berto - One of the best experts on this subject based on the ideXlab platform.
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Rupture Predictions of Notched Ti-6Al-4V Using Local Approaches
MDPI AG, 2018Co-Authors: Mirco Peron, Jan Torgersen, Filippo BertoAbstract:Ti-6Al-4V has been extensively used in structural applications in various engineering fields, from naval to automotive and from aerospace to biomedical. Structural applications are characterized by geometrical discontinuities such as Notches, which are widely known to harmfully affect their tensile strength. In recent years, many attempts have been done to define solid criteria with which to reliably predict the tensile strength of materials. Among these criteria, two local approaches are worth mentioning due to the accuracy of their predictions, i.e., the strain energy density (SED) approach and the theory of critical distance (TCD) method. In this manuscript, the robustness of these two methods in predicting the tensile behavior of Notched Ti-6Al-4V specimens has been compared. To this aim, two very dissimilar Notch geometries have been tested, i.e., semi-circular and blunt V-Notch with a Notch Root Radius equal to 1 mm, and the experimental results have been compared with those predicted by the two models. The experimental values have been estimated with low discrepancies by either the SED approach and the TCD method, but the former results in better predictions. The deviations for the SED are in fact lower than 1.3%, while the TCD provides predictions with errors almost up to 8.5%. Finally, the weaknesses and the strengths of the two models have been reported
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Notched plates in mixed mode loading i ii a review based on the local strain energy density and the cohesive zone mode
Engineering Solid Mechanics, 2017Co-Authors: Filippo Berto, G GomezAbstract:Two procedures to evaluate fracture resistance of Notched components are proposed in this contribution: the Strain Energy Density (SED) over a control volume and the Cohesive Zone Model (CZM). With the aim to simplify the application of the two fracture criteria, the concept of the ‘equivalent local mode I’ is presented. The control volume of the SED criterion and the cohesive crack of the CZM, have been rotated along the Notch edge and centered with respect to the point where the elastic principal stress is maximum. Numerical predictions are compared with experimental results from U and V shaped Notches under three point bending with Notch Root Radius ranging from 0.2 to 4.0 mm. In parallel the loading conditions vary, from pure mode I to a prevailing mode II. All specimens were made of PMMA and tested at -60°C. The good agreement between theory and experimental results adds further confidence to the proposed fracture criteria.
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local strain energy density to assess the multiaxial fatigue strength of titanium alloys
Fracture and Structural Integrity, 2016Co-Authors: Filippo Berto, Alberto Campagnolo, Torgeir WeloAbstract:The present paper investigates the multiaxial fatigue strength of sharp V-Notched components made of titanium grade 5 alloy (Ti-6Al-4V). Axisymmetric Notched specimens have been tested under combined tension and torsion fatigue loadings, both proportional and non-proportional, taking into account different nominal load ratios (R = -1 and 0). All tested samples have a Notch Root Radius about equal to 0.1 mm, a Notch depth of 6 mm and an opening angle of 90 degrees. The fatigue results obtained by applying multiaxial loadings are discussed together with those related to pure tension and pure torsion experimental fatigue tests, carried out on both smooth and Notched specimens at load ratios R ranging between -3 and 0.5. Altogether, more than 250 fatigue results (19 S-N curves) are examined, first on the basis of nominal stress amplitudes referred to the net area and secondly by means of the strain energy density averaged over a control volume embracing the V-Notch tip. The effect of the loading mode on the control volume size has been analysed, highlighting a wide difference in the Notch sensitivity of the considered material under tension and torsion loadings. Accordingly, the control Radius of the considered titanium alloy (Ti-6Al-4V) is found to be strongly affected by the loading mode.
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Fatigue strength of Notched specimens made of 40CrMoV13.9 under multiaxial loading
Materials & Design (1980-2015), 2014Co-Authors: Filippo Berto, Paolo Lazzarin, C. MarangonAbstract:Abstract The work deals with multiaxial fatigue strength of Notched round bars made of 40CrMoV13.9 steel and tested under combined tension and torsion loading, both in-phase and out-of-phase. The axis-symmetric V-Notches present a constant Notch Root Radius, 1 mm, and a Notch opening angle of 90°; the Notch Root Radius is equal to 4 mm in the semi-circular Notches where the strength in the high cycle fatigue regime is usually controlled by the theoretical stress concentration factor, being the Notch Root Radius large enough to result in a Notch sensitivity index equals to unity. In both geometries the diameter of the net transverse area is 12 mm. The results from multi-axial tests are discussed together with those obtained under pure tension and pure torsion loading from Notched specimens with the same geometry. Altogether more than 120 new fatigue data are summarised in the present work, corresponding to a one-year of testing programme. All fatigue data are presented first in terms of nominal stress amplitudes referred to the net area and then re-analysed in terms of the mean value of the strain energy density evaluated over a given, crescent shape volume embracing the stress concentration region. For the specific steel, the Radius of the control volume is found to be independent of the loading mode.
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local strain energy density applied to martensitic steel plates weakened by u Notches under mixed mode loading
Theoretical and Applied Fracture Mechanics, 2012Co-Authors: K Taghizadeh, Filippo Berto, Ehsan BaratiAbstract:Abstract The averaged value of the strain-energy density over a well-defined volume is used to assess the static strength of U-Notched specimens under mixed mode loading (I + II). The volume is centered in relation to the maximum principal stress present on the Notch edge, by rigidly rotating the crescent-shaped volume already used in the literature to analyze U- and V-shaped Notches under mode I loading. In total 96 new tests have been carried out on specimens made of structural steel with a martensite phase weakened by U-Notches. The Notch Root Radius varies from 0.2 to 2.0 mm while the Notch depth is equal to 5, 7.5, 10 and 15 mm, respectively. In addition, for the lowest value of the Notch depth (5 mm), some data from cracked specimens are summarized in the paper. Good agreement was found between experimental results and theoretical assessment based on the averaged strain energy density criterion under mixed mode loading.
R Danzer - One of the best experts on this subject based on the ideXlab platform.
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Polished Notch modification of SENB-S fracture toughness testing
Journal of the European Ceramic Society, 1997Co-Authors: R Damani, Ch. Schuster, R DanzerAbstract:Abstract In fracture toughness testing it is common for reasons of simplicity and reproducibility to use Notches to approximate sharp cracks. However, a dependence of measured fracture toughness (KIc) on Notch-Root Radius is observed. This can be explained as a consequence of the interaction of a distorted stress field with material flaws in front of a Notch. A relationship to quantify this effect is presented and examined. It is shown that to measure true fracture toughness sharp Notches of the size of microstructural features are required. A simple method to make very sharp Notches is presented. Fracture toughness values determined with sharp-Notched samples are compared with the results of experiments with conventional sawn-in Notches. It is shown that sharp Notches deliver considerably lower, more accurate and reproducible values of KIc for materials with fine microstructures. These values are thought to lie at the beginning of any R-curve.
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critical Notch Root Radius effect in senb s fracture toughness testing
Journal of The European Ceramic Society, 1996Co-Authors: R Damani, R Gstrein, R DanzerAbstract:Abstract The brittle behaviour of ceramic materials makes imperative the development of accurate and reproducible methods of measuring their resistance to fracture. To this end, a European round robin was set up to investigate the relative merits of five different methods of fracture toughness testing. Of these the single edge Notch bend — saw cut (SENB-S) method seemed to deliver the most reproducible results, both within and between laboratories. However, it has been observed empirically that if Notches are cut too thick, the values of fracture toughness determined are systematically too high. An explanation and a theoretically based relationship to describe this behaviour are presented. It is suggested that this effect results from the interaction of the stress field around the Notch tip and defects related to the microstructure or machining damage. Measured data from a number of materials seem to correlate well with the theory. It is shown that if correct values of fracture toughness are to be determined with the SENB-S method, the Notch width must be of the order of the size of the relevant microstructural or machining-induced defects (e.g. large pores and weak grain boundaries).
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critical Notch Root Radius effect in senb s fracture toughness testing
Journal of The European Ceramic Society, 1996Co-Authors: R Damani, R Gstrein, R DanzerAbstract:Abstract The brittle behaviour of ceramic materials makes imperative the development of accurate and reproducible methods of measuring their resistance to fracture. To this end, a European round robin was set up to investigate the relative merits of five different methods of fracture toughness testing. Of these the single edge Notch bend — saw cut (SENB-S) method seemed to deliver the most reproducible results, both within and between laboratories. However, it has been observed empirically that if Notches are cut too thick, the values of fracture toughness determined are systematically too high. An explanation and a theoretically based relationship to describe this behaviour are presented. It is suggested that this effect results from the interaction of the stress field around the Notch tip and defects related to the microstructure or machining damage. Measured data from a number of materials seem to correlate well with the theory. It is shown that if correct values of fracture toughness are to be determined with the SENB-S method, the Notch width must be of the order of the size of the relevant microstructural or machining-induced defects (e.g. large pores and weak grain boundaries).
P. Lazzarin - One of the best experts on this subject based on the ideXlab platform.
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Generalised stress intensity factors for rounded Notches in plates under in-plane shear loading
International Journal of Fracture, 2011Co-Authors: P. Lazzarin, M. Zappalorto, F. BertoAbstract:The Notch Stress Intensity Factors (NSIFs) quantify the intensities of the asymptotic linear elastic stress distributions of sharp (zero Radius) V-shaped Notches. When the Notch tip Radius is different from zero, the singular sharp-Notch field diverges from the rounded-Notch solution in the close neighborhood of the Notch tip. Nevertheless the NSIFs might continue to be parameters governing fracture if the Notch Root Radius is small enough. Otherwise they can be seen simply as stress field parameters useful in quantifying the stress distributions ahead of the specific Notch. Taking advantage of some analytical formulations which are able to describe stress distributions ahead of parabolic, hyperbolic and V-shaped Notches with end holes, the paper discusses the form and the significance of the NSIFs with reference to in-plane shear loading, considering explicitly the role played by the Notch opening angle and the Notch tip Radius. These parameters quantify the stress redistribution due to the Root Radius with respect to the sharp Notch case to which they should naturally tend for decreasing values of the Notch Radius.
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a generalised Notch stress intensity factor for u Notched components loaded under mixed mode
Engineering Fracture Mechanics, 2008Co-Authors: F J Gomez, Filippo Berto, M Elices, P. LazzarinAbstract:Abstract A novel Notch stress intensity factor (NSIF) for U-Notched specimens loaded under mixed mode is examined in this article. The concept is based on the averaged strain energy density criterion, or alternatively on the cohesive zone model, as well as the equivalent local mode approach. To a certain extent, it is a generalisation of Glinka’s NSIF for mode I, where σtip is replaced by σmax. The applicability of a fracture criterion based on this new NSIF is checked against 171 fracture tests with PMMA (at −60 °C) performed on U-Notched specimens, with different Notch Root radii and loaded under mixed mode. The asymptotic behaviour of the new NSIF as the Notch becomes a crack (when the Notch Root Radius tends to zero) or when the Notch disappears (when the Notch Root Radius tends to infinity) is also discussed.
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a generalized stress intensity factor to be applied to rounded v shaped Notches
International Journal of Solids and Structures, 2006Co-Authors: P. Lazzarin, S FilippiAbstract:Abstract In the presence of sharp (zero Radius) V-shaped Notches the Notch stress intensity factors (N-SIFs) quantify the intensities of the asymptotic linear elastic stress distributions. They are proportional to the limit of the mode I or II stress components multiplied by the distance powered 1 − λ i from the Notch tip, λ i being Williams’ eigenvalues. When the Notch tip Radius is different from zero, the definition is no longer valid from a theoretical point of view and the characteristic, singular, sharp-Notch field diverges from the rounded-Notch solution very next to the Notch. Nevertheless, N-SIFs continue to be used as parameters governing fracture if the Notch Root Radius is sufficiently small with respect to the Notch depth. Taking advantage of a recent analytical formulation able to describe stress distributions ahead of rounded V-Notches, the paper gives a generalized form for the Notch stress intensity factors, in which not only the opening angle but also the tip Radius dimension is explicitly involved. Such parameters quantify the stress redistribution due to the Root Radius with respect to the sharp Notch case.
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some expressions for the strain energy in a finite volume surrounding the Root of blunt v Notches
International Journal of Fracture, 2005Co-Authors: P. Lazzarin, Filippo BertoAbstract:The paper gives some closed form expressions for the strain energy averaged in a finite size volume surrounding the Root of blunt V-shaped Notches under Mode I loading. The control volume, reminiscent of Neuber’s concept of elementary structural volumes, is thought of as dependent on the ultimate tensile strength and the fracture toughness KIC in the case of brittle or quasi-brittle materials subjected to static loads. Expressions for strain energy density under plane strain conditions and Mode I loading have been derived from an analytical frame recently reported in the literature, which matches Williams and Creager-Paris’ solutions in the particular cases of plates weakened by sharp V-Notches or blunt cracks (U-Notches), respectively. In order to validate a local-strain-energy based approach, a well-documented set of experimental data recently reported in this journal by Gomez and Elices has been used. Data refer to blunt and sharp V-specimens of PMMA subjected to static tension loads and characterised by a large variability of Notch Root Radius (from 0 to 4.0 mm) and Notch angle (from 0° to 150°). Critical loads obtained experimentally have been compared with the theoretical ones, estimated here by keeping constant the mean value of the strain energy in a well-defined small size volume.
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fatigue crack initiation and propagation phases near Notches in metals with low Notch sensitivity
International Journal of Fatigue, 1997Co-Authors: P. Lazzarin, R Tovo, Giovanni MeneghettiAbstract:Abstract The paper summarizes the results of experimental work carried out in order to analyse the initiation and propagation of fatigue cracks on plates in a deep drawing steel and in a cast aluminium alloy. The plates were characterized by lateral V and U-shape symmetric Notches, with a Notch Root Radius ranging from 0.1 to 10 mm, the Notch depth being 10 mm and the plate thickness 2 mm for the steel and 5 mm for the light alloy. In order to estimate the crack initiation life two new parameters are proposed; they are no longer based on the peak values of strain and stress, but on the averaged values of such quantities in the neighbourhood of the Notch tip. The dimension of the process-zone is correlated to the intrinsic crack length of the material. The estimates need an elastoplastic approach and a numerical solution. Experimantal data and expected values are compared.
Gerold A Schneider - One of the best experts on this subject based on the ideXlab platform.
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influence of finite Notch Root Radius and optically determined crack length on the measured fracture toughness of brittle materials
Journal of The European Ceramic Society, 2010Co-Authors: Hüseyin Özcoban, Hans Jelitto, Gerold A SchneiderAbstract:Abstract When measuring the fracture toughness of ceramics, for instance with the Single Edge V-Notched Beam (SEVNB) method, a known problem is given by the finite Notch Root Radius. If this Radius is larger than a certain small value of a few micrometers, the measured stress intensity factor is higher than the true intrinsic value. Another problem is that due to technical and physical reasons the optically measured crack length at stable crack growth is smaller than the true crack length, which might lead to an underestimation of the fracture toughness. In the given paper an experimental approach is presented to register these effects quantitatively with stable crack advance and to finally obtain the correct fracture toughness. This is achieved by applying a new computer aided automatic control system for stable crack advance and by analyzing the results in force–displacement and crack length–force diagrams. The used material is zirconia-toughened alumina.
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r curve determination for the initial stage of crack extension in si3n4
Journal of the American Ceramic Society, 2008Co-Authors: Theo Fett, Hans Jelitto, Stefan Funfschilling, Michael J Hoffmann, Rainer Oberacker, Gerold A SchneiderAbstract:In experimental R-curve investigations crack development usually starts from Notches. The validity of R-curves depends on the size of the Notch Root Radius. This influence is ignored in many cases. In this study it will be shown how the Notch Radius affects the formally computed crack resistance curve and how the initial true R-curve can be obtained from the same data. The tests were performed on a silicon nitride with 5 wt% Y2O3 and 2 wt% MgO. The evaluation of load versus displacement measurements during fracture showed a very steep R-curve with the saturation reached even after about 10 μm crack extension.
