The Experts below are selected from a list of 98403 Experts worldwide ranked by ideXlab platform
Benjamin T Britton - One of the best experts on this subject based on the ideXlab platform.
-
a nanoindentation investigation of Local Strain rate sensitivity in dual phase ti alloys
Journal of Alloys and Compounds, 2016Co-Authors: David E J Armstrong, Benjamin T BrittonAbstract:Abstract Using nanoindentation we have investigated the Local Strain rate sensitivity in dual-phase Ti alloys, Ti–6Al–2Sn–4Zr-xMo (x = 2 and 6), as Strain rate sensitivity could be a potential factor causing cold dwell fatigue. Electron backscatter diffraction (EBSD) was used to select hard and soft grain orientations within each of the alloys. Nanoindentation based tests using the continuous stiffness measurement (CSM) method were performed with variable Strain rates, on the order of 10 −1 to 10 −3 s −1 . Local Strain rate sensitivity is determined using a power law linking equivalent flow stress and equivalent plastic Strain rate. Analysis of residual impressions using both a scanning electron microscope (SEM) and a focused ion beam (FIB) reveals Local deformation around the indents and shows that nanoindentation tested structures containing both α and β phases within individual colonies. This indicates that the indentation results are derived from averaged α/β properties. The results show that a trend of Local rate sensitivity in Ti6242 and Ti6246 is strikingly different; as similar rate sensitivities are found in Ti6246 regardless of grain orientation, whilst a grain orientation dependence is observed in Ti6242. These findings are important for understanding dwell fatigue deformation modes, and the methodology demonstrated can be used for screening new alloy designs and microstructures.
-
Local Strain rate sensitivity of single α phase within a dual phase ti alloy
Acta Materialia, 2016Co-Authors: Zhen Zhang, Giorgio Sernicola, F P E Dunne, Benjamin T BrittonAbstract:Abstract We have performed in-situ micropillar compression to investigate the Local Strain rate sensitivity of single α phase in dual-phase Ti alloy, Ti–6Al–2Sn–4Zr–2Mo (wt%). Electron backscatter diffraction (EBSD) was used to identify two grains, anticipated to primarily activate a slip on the basal and prismatic plane respectively. Comparative micropillars were fabricated within single α laths and load-hold tests were conducted with variable Strain rates (on the order of 10 −2 to 10 −4 s −1 ). Local Strain rate sensitivity exponent (i.e. m value) is determined using two types of methods, constant Strain rate method (CSRM) and conventional stress relaxation method (SRM), showing similar rate sensitivity trends but one order higher magnitude in SRM. We thus propose a new approach to analyse the SRM data, resulting in satisfactory agreement with the CSRM. Significant slip system dependent rate sensitivity is observed such that the prism slip has a strikingly higher m value than the basal. Fundamental mechanisms differing the rate sensitivity are discussed with regards to dislocation plasticity, where more resistance to move dislocations and hence higher hardening gradients are found in the basal slip. The impact of this finding for dwell fatigue deformation modes and the effectiveness of the present methodology for screening new alloy designs are discussed.
Berto Filippo - One of the best experts on this subject based on the ideXlab platform.
-
Local Strain energy based fatigue assessment of cruciform welded joints: experimental data analysis and influence of hot-dip galvanization
'EDP Sciences', 2018Co-Authors: Viespoli, Luigi Mario, Mutignani Francesco, Gulyas Gabor, Remes Heikki, Berto FilippoAbstract:Performing the fatigue assessment of a welded joint using the Notch Stress Intensity Factors [1] presents two major challenges. The first is the necessity of a precise reconstruction of the stress field around the notch tip, thus needing an extremely refined discretization with an evident computational cost. The other, is that the dimensions of the N-SIFs and so their critical values, vary accordingly to the William’s solution [2] depending on the notch-opening angle. Consequence of this is that the mechanical properties necessary for the assessment vary as a function of the geometry treated. The research to overcome this issue has led to the use of the Local Strain Energy Density [3]. The power of this parameter, used as a tool to perform fatigue assessment, consists of having a very low mesh refinement sensitivity [4], being the energy computed directly from nodal displacements and stiffness matrix [5], and having constant dimensions, so constant critical value for a given class of materials. In this paper, the Local energetic method is applied to the analysis of the results of a series of tests performed on cruciform load carrying and non-load carrying specimens realized by S235 JRG2 structural steel plates. If load carrying, the fillet welded joints are made of S355 J2+N structural steel. The fatigue testing has been performed in atmosphere at room temperature in as welded condition both with and without the corrosion protective zinc layer. Particularly, the interest is focused on the influence of the zinc layer of the fatigue properties of the joint and on the capability of the Local energetic approach, confronted with the classic nominal stress approach, to accurately predict the fatigue failure. To conclude, the investigation of the tests executed reveals no significant difference in the fatigue life for the coated samples, compared with the uncoated specimens and the predictions according to the IIW recommendations [6]
-
Local Strain energy based fatigue assessment of cruciform welded joints
'EDP Sciences', 2018Co-Authors: Viespoli, Luigi Mario, Mutignani Francesco, Gulyas Gabor, Remes Heikki, Berto FilippoAbstract:Performing the fatigue assessment of a welded joint using the Notch Stress Intensity Factors [1] presents two major challenges. The first is the necessity of a precise reconstruction of the stress field around the notch tip, thus needing an extremely refined discretization with an evident computational cost. The other, is that the dimensions of the N-SIFs and so their critical values, vary accordingly to the William's solution [2] depending on the notch-opening angle. Consequence of this is that the mechanical properties necessary for the assessment vary as a function of the geometry treated. The research to overcome this issue has led to the use of the Local Strain Energy Density [3]. The power of this parameter, used as a tool to perform fatigue assessment, consists of having a very low mesh refinement sensitivity [4], being the energy computed directly from nodal displacements and stiffness matrix [5], and having constant dimensions, so constant critical value for a given class of materials. In this paper,the Local energetic method is applied to the analysis of the results of a series of tests performed on cruciform load carrying and non-load carrying specimens realized by S235 JRG2 structural steel plates. If load carrying, the fillet welded joints are made of S355 J2+N structural steel. The fatigue testing has been performed in atmosphere at room temperature in as welded condition both with and without the corrosion protective zinc layer. Particularly, the interest is focused on the influence of the zinc layer of the fatigue properties of the joint and on the capability of the Local energetic approach, confronted with the classic nominal stress approach, to accurately predict the fatigue failure. To conclude, the investigation of the tests executed reveals no significant difference in the fatigue life for the coated samples, compared with the uncoated specimens and the predictions according to the IIW recommendations [6].Peer reviewe
-
Local Strain energy based fatigue assessment of cruciform welded joints: experimental data analysis and influence of hot-dip galvanization
EDP Sciences, 2018Co-Authors: Viespoli, Luigi Mario, Mutignani Francesco, Gulyas Gabor, Remes Heikki, Berto FilippoAbstract:Performing the fatigue assessment of a welded joint using the Notch Stress Intensity Factors [1] presents two major challenges. The first is the necessity of a precise reconstruction of the stress field around the notch tip, thus needing an extremely refined discretization with an evident computational cost. The other, is that the dimensions of the N-SIFs and so their critical values, vary accordingly to the William’s solution [2] depending on the notch-opening angle. Consequence of this is that the mechanical properties necessary for the assessment vary as a function of the geometry treated. The research to overcome this issue has led to the use of the Local Strain Energy Density [3]. The power of this parameter, used as a tool to perform fatigue assessment, consists of having a very low mesh refinement sensitivity [4], being the energy computed directly from nodal displacements and stiffness matrix [5], and having constant dimensions, so constant critical value for a given class of materials. In this paper, the Local energetic method is applied to the analysis of the results of a series of tests performed on cruciform load carrying and non-load carrying specimens realized by S235 JRG2 structural steel plates. If load carrying, the fillet welded joints are made of S355 J2+N structural steel. The fatigue testing has been performed in atmosphere at room temperature in as welded condition both with and without the corrosion protective zinc layer. Particularly, the interest is focused on the influence of the zinc layer of the fatigue properties of the joint and on the capability of the Local energetic approach, confronted with the classic nominal stress approach, to accurately predict the fatigue failure. To conclude, the investigation of the tests executed reveals no significant difference in the fatigue life for the coated samples, compared with the uncoated specimens and the predictions according to the IIW recommendations [6].publishedVersion© The Authors, published by EDP Sciences, 2018. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
-
A criterion based on the Local Strain energy density for the fracture assessment of cracked and V-notched components made of incompressible hyperelastic materials
'Elsevier BV', 2015Co-Authors: Berto FilippoAbstract:The present contribution is devoted to the theoretical and numerical study of the elasto-static fields at a vertex notch under mode I loading. The analysis is based on the plane deformation hyperelasticity theory for an incompressible Mooney-Rivlin material. While for cracked components some contributions can be found in the recent and past literature, studies on V-notched components are instead very limited. The aim of this paper is to partially fill this lack, providing a fracture criterion for the assessment of components weakened by sharp V-notches. In the first part of the paper, a brief description of the analytical frame available for V-notches in hyperelastic material is reported. A Williams' type diagram reporting the degree of singularity for a material obeying a Mooney-Rivlin behavior is present. The asymptotic stress field and the Local Strain energy density are investigated by means of non-linear finite element analyses. In the second part of the paper, a criterion based on the Local energy is proposed and successfully applied to a set of experimental data taken from the literature. Future works are surely necessary to validate the criterion considering more sets of data from sharp and blunt V-notches
Dierk Raabe - One of the best experts on this subject based on the ideXlab platform.
-
the impact of grain scale Strain Localization on Strain hardening of a high mn steel real time tracking of the transition from the γ e α transformation to twinning
Acta Materialia, 2020Co-Authors: Dirk Ponge, I Souza R Filho, Aniruddha Dutta, D R Almeida, M J R Sandim, H R Z Sandim, Dierk RaabeAbstract:Abstract Strain partitioning and Localization were investigated in a high-Mn steel (17.1 wt.% Mn) during tensile testing by a correlative probing approach including in-situ synchrotron X-ray diffraction, micro- digital image correlation (μ-DIC) and electron microscopy. By combining Warren's theory with the μ-DIC analysis, we monitored the formation of planar faults (stacking faults and mechanical twins) and correlated them with the Local Strain partitioning behavior within the microstructure. Starting with an initial microstructure of austenite (γ) and athermally formed e- and α’-martensite, Strain accumulates preferentially near the γ/e interfaces during tensile Straining. The Local microscopic von Mises Strain (evM) maps obtained from μ-DIC probing show that these Local Strain gradients produce Local Strain peaks approximately twice as high as the imposed macroscopic engineering Strain (e), thus Locally triggering formation of e-martensite already at early yielding. The interior of the remaining austenite, without such interfacial Strain peaks, remained nearly devoid of planar faults. The Local Strain-driven growth of the e-domains occurs concomitantly with the α’-martensite formation. At intermediate macroscopic applied Strains, austenite grain size is considerably reduced to a few nanometers and the associated γ/e interfacial microscopic Strain peaks increase in magnitude. This scenario favors twinning to emerge as a competing Strain hardening mechanism at engineering Strain levels from e = 0.075 onwards. At large tensile Strains, the γ → e → α’ transformation rates tend to cease making both twinning and SFs formation to operate as the main Strain hardening mechanisms. The findings shed light on the transformation micro-mechanisms in multiphase Mn-TRIP steels by revealing how Strain Localization among the constituents can directly influence the kinetics of the competing Strain hardening mechanisms.
-
joint investigation of Strain partitioning and chemical partitioning in ferrite containing trip assisted steels
Acta Materialia, 2020Co-Authors: Dirk Ponge, Wenjun Lu, Yunbo Xu, Huansheng He, Di Wu, Dierk RaabeAbstract:Abstract We applied two types of hot-rolling direct quenching and partitioning (HDQ&P) schemes to a low-C low-Si Al-added steel and obtained two ferrite-containing TRIP-assisted steels with different hard matrix structures, viz, martensite or bainite. Using quasi in-situ tensile tests combined with high-resolution electron back-scattered diffraction (EBSD) and microscopic digital image correlation (µ-DIC) analysis, we quantitatively investigated the TRIP effect and Strain partitioning in the two steels and explored the influence of the Strain partitioning between the soft and hard matrix structures on the TRIP effect. We also performed an atomic-scale analysis of the carbon partitioning among the different phases using atom probe tomography (APT). The results show that the Strain mainly Localizes in the ferrite in both types of materials. For the steel with a martensitic hard-matrix, a strong Strain contrast exists between ferrite and martensite, with the Local Strain difference reaching up to about 75% at a global Strain of 12.5%. Strain Localization bands initiated in the ferrite rarely cross the ferrite/martensite interfaces. The low Local Strain (2%-10%) in the martensite regions leads to a slight TRIP effect with a transformation ratio of the retained austenite of about 7.5%. However, for the steel with bainitic matrix, the ferrite and bainite undergo more homogeneous Strain partitioning, with an average Local Strain in ferrite and bainite of 15% and 8%, respectively, at a global Strain of 12.5%. The Strain Localization bands originating in the ferrite can cross the ferrite/bainite (F/B) interfaces and increase the Local Strain in the bainite regions, resulting in an efficient TRIP effect. In that case the transformation ratio of the retained austenite is about 41%. The lower hardness difference between the ferrite and bainite of about 178 HV, compared with that between the ferrite and martensite of about 256 HV, leads to a lower Strain contrast at the ferrite/bainite interfaces, thus retarding interfacial fracture. Further microstructure design for TRIP effect optimization should particularly focus on adjusting the strength contrast among the matrix structures and tuning Strain partitioning to enhance the Local Strain partitioning into the retained austenite.
N Swaminathan - One of the best experts on this subject based on the ideXlab platform.
-
effects of lewis number on the reactive scalar gradient alignment with Local Strain rate in turbulent premixed flames
Proceedings of the Combustion Institute, 2009Co-Authors: Nilanjan Chakraborty, N SwaminathanAbstract:Abstract The effects of Lewis number Le on the reactive scalar gradient alignment with the Local Strain rate have been studied using Direct Numerical Simulation data of freely propagating statistically planar turbulent premixed flames with Le ranging from 0.34 to 1.2. The alignment characteristics of the reaction progress variable gradient are explained using the statistics of dilatation rate, and flame normal and tangential Strain rates. The strength of dilatation rate is shown to increase with decreasing Le and this effect becomes particularly strong for the flames with Le Le close to unity, contrary to the alignment of scalar gradient with the most compressive principal Strain rate in turbulent passive scalar transport. However, stronger dilatation rate effects in Le ≪ 1 flames (e.g. Le = 0.34) gives rise to the preferential alignment of the reactive scalar gradient with the most extensive principal Strain rate for the major portion of the flame-brush. The scalar gradient alignment with Local Strain rate plays an important role in the transport of scalar dissipation rate and the flame surface density. The observed alignment with the most extensive principal Strain rate destroys the scalar gradient and the magnitude of this sink is found to increase with decreasing Lewis number for a given turbulent Reynolds number and Damkohler number.
-
effects of lewis number on the reactive scalar gradient alignment with Local Strain rate in turbulent premixed flames
Proceedings of the Combustion Institute, 2009Co-Authors: Nilanjan Chakraborty, M Klein, N SwaminathanAbstract:The effects of Lewis number Le on the reactive scalar gradient alignment with the Local Strain rate have been studied using Direct Numerical Simulation data of freely propagating statistically planar turbulent premixed flames with Le ranging from 0.34 to 1.2. The alignment characteristics of the reaction progress variable gradient are explained using the statistics of dilatation rate, and flame normal and tangential Strain rates. The strength of dilatation rate is shown to increase with decreasing Le and this effect becomes particularly strong for the flames with Le < 1 because of thermo-diffusive instability. The dilatation rate is shown to be responsible for the preferential alignment of the reactive scalar gradient with the most extensive principal Strain rate in the reaction zone for flames with Le close to unity, contrary to the alignment of scalar gradient with the most compressive principal Strain rate in turbulent passive scalar transport. However, stronger dilatation rate effects in Le ≪ 1 flames (e.g. Le = 0.34) gives rise to the preferential alignment of the reactive scalar gradient with the most extensive principal Strain rate for the major portion of the flame-brush. The scalar gradient alignment with Local Strain rate plays an important role in the transport of scalar dissipation rate and the flame surface density. The observed alignment with the most extensive principal Strain rate destroys the scalar gradient and the magnitude of this sink is found to increase with decreasing Lewis number for a given turbulent Reynolds number and Damkohler number.
Nilanjan Chakraborty - One of the best experts on this subject based on the ideXlab platform.
-
Statistics of vorticity alignment with Local Strain rates in turbulent premixed flames
European Journal of Mechanics B-fluids, 2014Co-Authors: Nilanjan ChakrabortyAbstract:Abstract The instantaneous alignment of the vorticity vector with Local principal Strain rates is analysed for statistically planar turbulent premixed flames with different values of heat release parameter and global Lewis number spanning different regimes of combustion. It has been shown that the vorticity vector predominantly aligns with the intermediate principal Strain rate in turbulent premixed flames, irrespective of the regime of combustion, heat release parameter and Lewis number. However, the relative alignment of vorticity with the most extensive and compressive principal Strain rates changes based on the underlying combustion conditions. Detailed physical explanations are provided for the observed behaviours of vorticity alignment with Local principal Strain rates. It has been shown that heat release due to combustion significantly affects the alignment of vorticity with Local principal Strain rates. However, the mean contribution of the vortex-stretching term in the transport equation of enstrophy remains positive for all cases considered here, irrespective of the nature of the vorticity alignment.
-
effects of lewis number on the reactive scalar gradient alignment with Local Strain rate in turbulent premixed flames
Proceedings of the Combustion Institute, 2009Co-Authors: Nilanjan Chakraborty, N SwaminathanAbstract:Abstract The effects of Lewis number Le on the reactive scalar gradient alignment with the Local Strain rate have been studied using Direct Numerical Simulation data of freely propagating statistically planar turbulent premixed flames with Le ranging from 0.34 to 1.2. The alignment characteristics of the reaction progress variable gradient are explained using the statistics of dilatation rate, and flame normal and tangential Strain rates. The strength of dilatation rate is shown to increase with decreasing Le and this effect becomes particularly strong for the flames with Le Le close to unity, contrary to the alignment of scalar gradient with the most compressive principal Strain rate in turbulent passive scalar transport. However, stronger dilatation rate effects in Le ≪ 1 flames (e.g. Le = 0.34) gives rise to the preferential alignment of the reactive scalar gradient with the most extensive principal Strain rate for the major portion of the flame-brush. The scalar gradient alignment with Local Strain rate plays an important role in the transport of scalar dissipation rate and the flame surface density. The observed alignment with the most extensive principal Strain rate destroys the scalar gradient and the magnitude of this sink is found to increase with decreasing Lewis number for a given turbulent Reynolds number and Damkohler number.
-
effects of lewis number on the reactive scalar gradient alignment with Local Strain rate in turbulent premixed flames
Proceedings of the Combustion Institute, 2009Co-Authors: Nilanjan Chakraborty, M Klein, N SwaminathanAbstract:The effects of Lewis number Le on the reactive scalar gradient alignment with the Local Strain rate have been studied using Direct Numerical Simulation data of freely propagating statistically planar turbulent premixed flames with Le ranging from 0.34 to 1.2. The alignment characteristics of the reaction progress variable gradient are explained using the statistics of dilatation rate, and flame normal and tangential Strain rates. The strength of dilatation rate is shown to increase with decreasing Le and this effect becomes particularly strong for the flames with Le < 1 because of thermo-diffusive instability. The dilatation rate is shown to be responsible for the preferential alignment of the reactive scalar gradient with the most extensive principal Strain rate in the reaction zone for flames with Le close to unity, contrary to the alignment of scalar gradient with the most compressive principal Strain rate in turbulent passive scalar transport. However, stronger dilatation rate effects in Le ≪ 1 flames (e.g. Le = 0.34) gives rise to the preferential alignment of the reactive scalar gradient with the most extensive principal Strain rate for the major portion of the flame-brush. The scalar gradient alignment with Local Strain rate plays an important role in the transport of scalar dissipation rate and the flame surface density. The observed alignment with the most extensive principal Strain rate destroys the scalar gradient and the magnitude of this sink is found to increase with decreasing Lewis number for a given turbulent Reynolds number and Damkohler number.
