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Filippo Berto - One of the best experts on this subject based on the ideXlab platform.
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Assessment of tensile and fatigue behavior of PEEK specimens in a physiologically relevant environment
Gruppo Italiano Frattura, 2019Co-Authors: Mirco Peron, Jan Torgersen, Filippo BertoAbstract:In the last decades the necessity of implant devices is continuously increasing. The researchers have thus focused their attentions on the development of new biocompatible materials, in particular polymers. Among them, polyetheretherketone (PEEK) has gained wide interest in loadbearing applications such as spinal cages due to its yielding behavior and its superior corrosion resistance. Since such applications are characterized by notches and other stress concentrators weakening the implant resistance, a design tool for assessing their tensile and fatigue behavior, in the presence of such discontinuities, is highly claimed. To this aim, tensile and fatigue data available in literature related to neat and differently notched PEEK samples, experimentally tested in a phosphate-buffered saline (PBS) at 37 �C have been analyzed using the strain energy density (SED) approach. The method is shown to provide accurate results regardless of the different notch geometries, both in terms of tensile and fatigue behavior. Concerning the former, the tensile strength was in fact estimated with an error lower than �10%, whereas for the latter the SED approach was able to summarize the experimental fatigue data in a single narrow Scatter Band, independently from the notch geometr
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assessment of tensile and fatigue behavior of peek in a physiologically relevant environment
Frattura ed Integrità Strutturale, 2018Co-Authors: Mirco Peron, Jan Torgersen, Filippo BertoAbstract:In the last decades the necessity of implant devices is continuously increasing. The researchers have thus focused their attentions on the development of new biocompatible materials, in particular polymers. Among them, polyetheretherketone (PEEK) has gained wide interest in load-bearing applications such as spinal cages due to its yielding behavior and its superior corrosion resistance. Since such applications are characterized by notches and other stress concentrators weakening the implant resistance, a design tool for assessing their tensile and fatigue behavior in the presence of such discontinuities is highly claimed. To this aim, tensile and fatigue data available in literature of neat and differently notched PEEK samples (circumferentially cracked and U-notched specimens with different notch radii) experimentally tested in a phosphate-buffered saline (PBS) at 37 °C have been analyzed using the strain energy density (SED) approach. The method is shown to provide accurate results regardless of the different notch geometries, both for tensile and fatigue data. Concerning the former, the tensile strength was in fact estimated with an error lower than ±10%, regardless of the strain rate, while for the latter the SED approach was able to summarize the fatigue data with a single narrow Scatter Band independently from the notch geometry
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application of the strain energy density approach in comparing different design solutions for improving the fatigue strength of load carrying shear welded joints
International Journal of Fatigue, 2017Co-Authors: Filippo Berto, Alexey Vinogradov, S FilippiAbstract:Abstract In the present paper two types of load carrying shear welded joints are considered and analyzed numerically and experimentally. Fatigue tests have been carried out on two specific design solutions proposed and aimed to improve the fatigue strength of the joints. By employing three-dimensional models, the Strain Energy Density (SED) over a control volume surrounding the most critical point has been determined. All the experimental results have been summarized in terms of SED showing that all the data fall within the Scatter Band previously proposed in the literature for welded structural steel.
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analysis of multiaxial low cycle fatigue of notched specimens for type 316l stainless steel under non proportional loading
Theoretical and Applied Fracture Mechanics, 2017Co-Authors: Pasquale Gallo, Takahiro Morishita, Stefano Bressan, Filippo BertoAbstract:Abstract The paper analyzes multiaxial low cycle fatigue tests of notched specimens under proportional and non-proportional loading conditions. Strain controlled multiaxial low cycle fatigue tests were carried out using circumferentially notched round-bar specimens of type 316L stainless steel, with different stress concentration factors. The experimental results show that the crack initiation site is shifted from the notch tip. Based on this finding, a new model for life evaluation is proposed by taking into account the strain gradient in the proximity of the notch tip and the effective maximum strain range. The new model allows evaluating the fatigue life in a narrow Scatter Band.
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advanced materials for applications at high temperature fatigue assessment by means of local strain energy density
Advanced Engineering Materials, 2016Co-Authors: Pasquale Gallo, Filippo BertoAbstract:The interest on fatigue assessment of steel and other alloys at high temperature has increased continuously in the last years. However, high cycle fatigue of notched components at high temperature has not been deeply investigated experimentally and theoretically. The present paper investigates the accuracy of Strain Energy Density (SED) averaged over a control volume approach when applied to high-temperature fatigue data from notched components. In the present work, a large bulk of high-temperature fatigue data, taken from the literature and regarding notched components made of different advanced materials, is reanalyzed. In detail: C45 carbon steel at 250 °C, Inconel 718 at 500 °C, and directionally solidified superalloy DZ125 at 850 °C are considered. The main advantage of SED averaged over a control volume is that different geometries can be summarized in a single narrow Scatter Band. From an industrial viewpoint, the use of a geometry-independent parameter (and fatigue curve) leads to a considerable advantage in terms of time and cost.
Giovanni Meneghetti - One of the best experts on this subject based on the ideXlab platform.
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analysis of dissipated energy and temperature fields at severe notches of aisi 304l stainless steel specimens
Frattura ed Integrità Strutturale, 2018Co-Authors: Daniele Rigon, Mauro Ricotta, Giovanni MeneghettiAbstract:In the last years, a large amount of fatigue test results from plain and bluntly notched specimens made of AISI 304L stainless steel were synthetized in a single Scatter Band by adopting the specific heat loss per cycle (Q) as a damage parameter. During a fatigue test, the Q parameter can be evaluated measuring the cooling gradient at a point of the specimens after having suddenly stopped the fatigue test. This measurement can be done by using thermocouples; however, due to the high stress concentration at the tip of severely notched components analysed in the present paper, an infrared camera achieving a much improved spatial resolution was adopted. A data processing technique is presented to investigate the heat energy distribution close to the notch tip of hot-rolled AISI 304L stainless steel specimens, having notch tip radii equal to 3, 1 and 0.5 mm and subjected to constant amplitude cyclic loads. A thermal finite element analysis was also performed by assigning heat generation in the appropriate region close to the notch tip. Then the numerical temperature values were compared with the experimental measurement.
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a two parameter heat energy based approach to analyse the mean stress influence on axial fatigue behaviour of plain steel specimens
International Journal of Fatigue, 2016Co-Authors: Giovanni Meneghetti, Mauro Ricotta, B AtzoriAbstract:Abstract Recently, fatigue data generated from fully reversed stress- and strain-controlled tests on plain and notched stainless steel specimens were rationalised in a single Scatter Band by using the specific heat energy per cycle as fatigue damage index. In this paper, the energy approach is extended to analyse the mean stress influence on the axial fatigue behaviour of un-notched bars made of cold drawn AISI 304L stainless steel or hot rolled quenched and tempered C45 steel. In view of this, stress controlled fatigue tests at different load ratios R were carried out. A new two-parameter, energy-based approach is defined to account for the R -ratio effects, which combines the specific heat loss and the thermoelastic temperature corresponding to the maximum stress of the load cycle. Such parameters can be readily evaluated at a point of a specimen or a component undergoing a fatigue test by means of temperature measurements, while controlling or monitoring the thermal boundary conditions of the tests is unnecessary. The new two-parameter approach was able to rationalise the stress ratio effect observed experimentally.
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the heat energy dissipated in a control volume to correlate the fatigue strength of bluntly and severely notched stainless steel specimens
Procedia structural integrity, 2016Co-Authors: Giovanni Meneghetti, Mauro Ricotta, B AtzoriAbstract:Abstract In previously published papers by the authors, the specific heat energy loss per cycle (the Q parameter) was used to rationalize about 120 experimental results generated from constant amplitude, push-pull, stress- or strain-controlled fatigue tests on plain and notched hot rolled AISI 304 L stainless steel specimens as well as from cold drawn un-notched bars of the same steel, tested under fully-reversed axial or torsional fatigue loadings. It has been shown that Q can be estimated starting from the cooling gradient measured at the critical point immediately after the fatigue test has been stopped. Concerning notched specimens, it was noted that a 3 mm notch tip radius was close to the limitation of applicability of the adopted temperature sensor, consisting in 0.127-mm-diameter thermocouples, because of the 1.5-to-2 mm diameter spot of the glue which prevented to measure the maximum temperature level. In this paper, the fatigue-damage-index effectiveness of Q parameter was investigated, carrying out fully reversed axial fatigue tests on 4-mm-thick AISI 304L specimens, having 3, 1 and 0.5 mm notch tip radii. The cooling gradients were measured by using an infrared camera, characterized by a 20 μm/pixels spatial resolution. As a result, all new fatigue data could be rationalized using the same Scatter Band published previously by the authors.
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an hysteresis energy based synthesis of fully reversed axial fatigue behaviour of different polypropylene composites
Composites Part B-engineering, 2014Co-Authors: Giovanni Meneghetti, Mauro Ricotta, Giovanni Lucchetta, Simone CarmignatoAbstract:Abstract In this paper the hysteresis energy density per cycle was considered as fatigue damage index to rationalise in a single Scatter Band the fatigue behaviour of short glass fibre reinforced polypropylene (30 wt% 1-mm-long glass fibre), long glass fibre reinforced polypropylene (30 wt% 10-mm-long glass fibre) and 42 wt% calcium carbonate filled polypropylene. Moreover the nature of such a mechanical energy was investigated to establish to which extent dissipation is due to creep strains and it was found that hysteresis energy dissipated in a unit volume of material per cycle due to visco-elasticity is negligible with respect to the total hysteresis energy.
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The specific heat loss combined with the thermoelastic effect for an experimental analysis of the mean stress influence on axial fatigue of stainless steel plain specimens
Frattura ed Integrità Strutturale, 2014Co-Authors: Giovanni Meneghetti, Mauro Ricotta, Bruno AtzoriAbstract: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 un- notched 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.
Pasquale Gallo - One of the best experts on this subject based on the ideXlab platform.
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analysis of multiaxial low cycle fatigue of notched specimens for type 316l stainless steel under non proportional loading
Theoretical and Applied Fracture Mechanics, 2017Co-Authors: Pasquale Gallo, Takahiro Morishita, Stefano Bressan, Filippo BertoAbstract:Abstract The paper analyzes multiaxial low cycle fatigue tests of notched specimens under proportional and non-proportional loading conditions. Strain controlled multiaxial low cycle fatigue tests were carried out using circumferentially notched round-bar specimens of type 316L stainless steel, with different stress concentration factors. The experimental results show that the crack initiation site is shifted from the notch tip. Based on this finding, a new model for life evaluation is proposed by taking into account the strain gradient in the proximity of the notch tip and the effective maximum strain range. The new model allows evaluating the fatigue life in a narrow Scatter Band.
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advanced materials for applications at high temperature fatigue assessment by means of local strain energy density
Advanced Engineering Materials, 2016Co-Authors: Pasquale Gallo, Filippo BertoAbstract:The interest on fatigue assessment of steel and other alloys at high temperature has increased continuously in the last years. However, high cycle fatigue of notched components at high temperature has not been deeply investigated experimentally and theoretically. The present paper investigates the accuracy of Strain Energy Density (SED) averaged over a control volume approach when applied to high-temperature fatigue data from notched components. In the present work, a large bulk of high-temperature fatigue data, taken from the literature and regarding notched components made of different advanced materials, is reanalyzed. In detail: C45 carbon steel at 250 °C, Inconel 718 at 500 °C, and directionally solidified superalloy DZ125 at 850 °C are considered. The main advantage of SED averaged over a control volume is that different geometries can be summarized in a single narrow Scatter Band. From an industrial viewpoint, the use of a geometry-independent parameter (and fatigue curve) leads to a considerable advantage in terms of time and cost.
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extension of linear elastic strain energy density approach to high temperature fatigue and a synthesis of cu be alloy experimental tests
Engineering Solid Mechanics, 2015Co-Authors: Filippo Berto, Pasquale GalloAbstract:Article history: Received October 6, 2014 Accepted 28 January 2015 Available online 29 January 2015 The present paper summarizes the results from uniaxial-tension stress-controlled fatigue tests performed at different temperatures up to 650°C on Cu-Be specimens. Two geometries are considered: hourglass shaped and plates weakened by a central hole (Cu-Be alloy). The motivation of the present work is that, at the best of authors’ knowledge, only a limited number of papers on these alloys under high-temperature fatigue are available in the literature and no results deal with notched components. The Cu-Be specimens fatigue data are re-analyzed in terms of the mean value of the Strain Energy Density (SED) averaged over a control volume. Thanks to the SED approach it is possible to summarize in a single Scatter-Band all the fatigue data, independently of the specimen geometry. © 2015 Growing Science Ltd. All rights reserved.
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high temperature fatigue tests of a cu be alloy and synthesis in terms of linear elastic strain energy density
Key Engineering Materials, 2014Co-Authors: Filippo Berto, Pasquale Gallo, Pierina LazzarinAbstract:The present paper summarises the results from uniaxial-tension stress-controlled fatigue tests performed at different temperatures up to 650°C on Cu-Be specimens. Two geometries are considered: hourglass shaped and plates weakened by a central hole (Cu-Be alloy). The motivation of the present work is that, at the best of authors’ knowledge, only a limited number of papers on these alloys under high-temperature fatigue are available in the literature and no results deal with notched components.The Cu-Be specimens fatigue data are re-analyzed in terms of the mean value of the Strain Energy Density (SED) averaged over a control volume. Thanks to the SED approach it is possible to summarise in a single Scatter-Band all the fatigue data, independently of the specimen geometry.
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High temperature fatigue tests of un-notched and notched specimens made of 40CrMoV13.9 steel
Materials & Design, 2014Co-Authors: Filippo Berto, Pasquale Gallo, Pierina LazzarinAbstract:Abstract The present paper summarizes data from uniaxial-tension stress-controlled fatigue tests on specimens made of 40CrMoV13.9 steel. Tests are performed varying temperature, from room temperature up to 650 °C. This steel is commonly employed for hot-rolling of metals and it is subjected, in service, to a combination of mechanical and thermal loadings. Two geometries are considered: plain specimens and plates weakened by symmetric V-notches, with opening angle and tip radius being equal to 90 degrees and 1 mm, respectively. The present work is motivated by the fact that, at the best of authors’ knowledge, only a limited number of works dealing with high-temperature fatigue are reported in the literature for the medium/high cycle fatigue regime; in particular, no results seem to be available for 40CrMoV13.9 steel when tested at elevated temperature in the presence of notch effects. After a brief review of the recent literature, the experimental procedure is described in detail and the new data from un-notched and notched specimens are summarized in terms of stress range, at the considered temperatures, for a total of 60 new experimental data. Finally, fatigue data from un-notched and notched specimens are re-analyzed by means of the mean value of the strain energy density (SED), employed here as the critical fatigue parameter, able to summarize in the same Scatter Band data from different temperatures.
B Atzori - One of the best experts on this subject based on the ideXlab platform.
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a two parameter heat energy based approach to analyse the mean stress influence on axial fatigue behaviour of plain steel specimens
International Journal of Fatigue, 2016Co-Authors: Giovanni Meneghetti, Mauro Ricotta, B AtzoriAbstract:Abstract Recently, fatigue data generated from fully reversed stress- and strain-controlled tests on plain and notched stainless steel specimens were rationalised in a single Scatter Band by using the specific heat energy per cycle as fatigue damage index. In this paper, the energy approach is extended to analyse the mean stress influence on the axial fatigue behaviour of un-notched bars made of cold drawn AISI 304L stainless steel or hot rolled quenched and tempered C45 steel. In view of this, stress controlled fatigue tests at different load ratios R were carried out. A new two-parameter, energy-based approach is defined to account for the R -ratio effects, which combines the specific heat loss and the thermoelastic temperature corresponding to the maximum stress of the load cycle. Such parameters can be readily evaluated at a point of a specimen or a component undergoing a fatigue test by means of temperature measurements, while controlling or monitoring the thermal boundary conditions of the tests is unnecessary. The new two-parameter approach was able to rationalise the stress ratio effect observed experimentally.
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the heat energy dissipated in a control volume to correlate the fatigue strength of bluntly and severely notched stainless steel specimens
Procedia structural integrity, 2016Co-Authors: Giovanni Meneghetti, Mauro Ricotta, B AtzoriAbstract:Abstract In previously published papers by the authors, the specific heat energy loss per cycle (the Q parameter) was used to rationalize about 120 experimental results generated from constant amplitude, push-pull, stress- or strain-controlled fatigue tests on plain and notched hot rolled AISI 304 L stainless steel specimens as well as from cold drawn un-notched bars of the same steel, tested under fully-reversed axial or torsional fatigue loadings. It has been shown that Q can be estimated starting from the cooling gradient measured at the critical point immediately after the fatigue test has been stopped. Concerning notched specimens, it was noted that a 3 mm notch tip radius was close to the limitation of applicability of the adopted temperature sensor, consisting in 0.127-mm-diameter thermocouples, because of the 1.5-to-2 mm diameter spot of the glue which prevented to measure the maximum temperature level. In this paper, the fatigue-damage-index effectiveness of Q parameter was investigated, carrying out fully reversed axial fatigue tests on 4-mm-thick AISI 304L specimens, having 3, 1 and 0.5 mm notch tip radii. The cooling gradients were measured by using an infrared camera, characterized by a 20 μm/pixels spatial resolution. As a result, all new fatigue data could be rationalized using the same Scatter Band published previously by the authors.
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a synthesis of the push pull fatigue behaviour of plain and notched stainless steel specimens by using the specific heat loss
Fatigue & Fracture of Engineering Materials & Structures, 2013Co-Authors: Giovanni Meneghetti, Mauro Ricotta, B AtzoriAbstract:The energy dissipated to the surroundings as heat in a unit volume of material per cycle, Q, was recently proposed as fatigue damage index, and it was successfully applied to rationalise fatigue data obtained by carrying out stress-controlled and strain-controlled fatigue tests on AISI 304 L stainless steel plain and hole specimens. In this paper, it is shown that the Q parameter is independent on thermal and mechanical boundary conditions occurring during experiments. After that, additional stress-controlled fatigue tests on plain and notched specimens characterised by smaller notch tip radii than those tested previously have been performed. Present data have been compared with previous ones, and it was found that all available results can be synthesised in terms of the energy parameter Q into a unique Scatter Band, independently on the testing conditions (stress-controlled or strain-controlled) and on the specimens' geometry (plain or notched). About 100 data were included in the statistical analysis to characterise the energy-based Scatter Band of the material. Finally, some limitations of applicability of the experimental technique adopted in the present paper are discussed.
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a synthesis of the fatigue behavior of stainless steel bars under fully reversed axial or torsion loading by using the specific heat loss
Key Engineering Materials, 2013Co-Authors: Giovanni Meneghetti, Mauro Ricotta, L. Negrisolo, B AtzoriAbstract:In previous papers, the energy dissipated to the surroundings as heat in a unit volume of material per cycle, Q, has been successfully applied to correlate experimental data generated from push-pull, stress- or strain-controlled fatigue tests on AISI 304 L stainless steel plain and notched specimens. In this paper the fatigue behaviour of AISI 304 L un-notched bars under fully-reversed axial or torsional loading was investigated. By using the Q parameter it was found that the experimental data collapse into the same energy-based Scatter Band previously determined with the push-pull tests. The results found in the present contribution are meant to be specific for the material investigated.
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fatigue strength assessment of welded joints from the integration of paris law to a synthesis based on the notch stress intensity factors of the uncracked geometries
Engineering Fracture Mechanics, 2008Co-Authors: B Atzori, P Lazzarin, Giovanni MeneghettiAbstract:In the welded joints, the conventional welding procedures result in a small value of the weld toe and the weld root radius. By assuming such a radius equal to zero, the paper demonstrates the effectiveness of the Notch-stress intensity factor approach in summarising a number of experimental data from failures occurring at the weld toe. Then it is shown that fatigue data from failures originated from both weld roots and weld toes can be summarised in a single Scatter Band by using the mean value of the strain energy density in a well defined volume (area) surrounding the critical points. Finally, a simplified application of the NSIF approach based on finite element analyses carried out with coarse meshes is presented.
Mauro Ricotta - One of the best experts on this subject based on the ideXlab platform.
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analysis of dissipated energy and temperature fields at severe notches of aisi 304l stainless steel specimens
Frattura ed Integrità Strutturale, 2018Co-Authors: Daniele Rigon, Mauro Ricotta, Giovanni MeneghettiAbstract:In the last years, a large amount of fatigue test results from plain and bluntly notched specimens made of AISI 304L stainless steel were synthetized in a single Scatter Band by adopting the specific heat loss per cycle (Q) as a damage parameter. During a fatigue test, the Q parameter can be evaluated measuring the cooling gradient at a point of the specimens after having suddenly stopped the fatigue test. This measurement can be done by using thermocouples; however, due to the high stress concentration at the tip of severely notched components analysed in the present paper, an infrared camera achieving a much improved spatial resolution was adopted. A data processing technique is presented to investigate the heat energy distribution close to the notch tip of hot-rolled AISI 304L stainless steel specimens, having notch tip radii equal to 3, 1 and 0.5 mm and subjected to constant amplitude cyclic loads. A thermal finite element analysis was also performed by assigning heat generation in the appropriate region close to the notch tip. Then the numerical temperature values were compared with the experimental measurement.
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a two parameter heat energy based approach to analyse the mean stress influence on axial fatigue behaviour of plain steel specimens
International Journal of Fatigue, 2016Co-Authors: Giovanni Meneghetti, Mauro Ricotta, B AtzoriAbstract:Abstract Recently, fatigue data generated from fully reversed stress- and strain-controlled tests on plain and notched stainless steel specimens were rationalised in a single Scatter Band by using the specific heat energy per cycle as fatigue damage index. In this paper, the energy approach is extended to analyse the mean stress influence on the axial fatigue behaviour of un-notched bars made of cold drawn AISI 304L stainless steel or hot rolled quenched and tempered C45 steel. In view of this, stress controlled fatigue tests at different load ratios R were carried out. A new two-parameter, energy-based approach is defined to account for the R -ratio effects, which combines the specific heat loss and the thermoelastic temperature corresponding to the maximum stress of the load cycle. Such parameters can be readily evaluated at a point of a specimen or a component undergoing a fatigue test by means of temperature measurements, while controlling or monitoring the thermal boundary conditions of the tests is unnecessary. The new two-parameter approach was able to rationalise the stress ratio effect observed experimentally.
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the heat energy dissipated in a control volume to correlate the fatigue strength of bluntly and severely notched stainless steel specimens
Procedia structural integrity, 2016Co-Authors: Giovanni Meneghetti, Mauro Ricotta, B AtzoriAbstract:Abstract In previously published papers by the authors, the specific heat energy loss per cycle (the Q parameter) was used to rationalize about 120 experimental results generated from constant amplitude, push-pull, stress- or strain-controlled fatigue tests on plain and notched hot rolled AISI 304 L stainless steel specimens as well as from cold drawn un-notched bars of the same steel, tested under fully-reversed axial or torsional fatigue loadings. It has been shown that Q can be estimated starting from the cooling gradient measured at the critical point immediately after the fatigue test has been stopped. Concerning notched specimens, it was noted that a 3 mm notch tip radius was close to the limitation of applicability of the adopted temperature sensor, consisting in 0.127-mm-diameter thermocouples, because of the 1.5-to-2 mm diameter spot of the glue which prevented to measure the maximum temperature level. In this paper, the fatigue-damage-index effectiveness of Q parameter was investigated, carrying out fully reversed axial fatigue tests on 4-mm-thick AISI 304L specimens, having 3, 1 and 0.5 mm notch tip radii. The cooling gradients were measured by using an infrared camera, characterized by a 20 μm/pixels spatial resolution. As a result, all new fatigue data could be rationalized using the same Scatter Band published previously by the authors.
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an hysteresis energy based synthesis of fully reversed axial fatigue behaviour of different polypropylene composites
Composites Part B-engineering, 2014Co-Authors: Giovanni Meneghetti, Mauro Ricotta, Giovanni Lucchetta, Simone CarmignatoAbstract:Abstract In this paper the hysteresis energy density per cycle was considered as fatigue damage index to rationalise in a single Scatter Band the fatigue behaviour of short glass fibre reinforced polypropylene (30 wt% 1-mm-long glass fibre), long glass fibre reinforced polypropylene (30 wt% 10-mm-long glass fibre) and 42 wt% calcium carbonate filled polypropylene. Moreover the nature of such a mechanical energy was investigated to establish to which extent dissipation is due to creep strains and it was found that hysteresis energy dissipated in a unit volume of material per cycle due to visco-elasticity is negligible with respect to the total hysteresis energy.
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The specific heat loss combined with the thermoelastic effect for an experimental analysis of the mean stress influence on axial fatigue of stainless steel plain specimens
Frattura ed Integrità Strutturale, 2014Co-Authors: Giovanni Meneghetti, Mauro Ricotta, Bruno AtzoriAbstract: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 un- notched 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.
