M. Amabili, Prabakaran Balasubramanian, Giovanni Ferrari
Damping is largely increasing with the vibration amplitude during nonlinear vibrations of rectangular plates. At the same time, soft materials present an increase of their stiffness with the vibration frequency. These two phenomena appear together and are both explained in the framework of the viscoelasticity. While the literature on nonlinear vibrations of plates is very large, these aspects are rarely addressed. The present study uses the fractional solid model to describe the viscoelastic material behaviour. This allows to capture at the same time (i) the increase in the storage modulus with the vibration frequency and (ii) the frequency-dependent nonlinear damping in nonlinear vibrations of rectangular plates. The solution of the nonlinear vibration problems is obtained through Lagrange equations by deriving the potential energy of the plate and the dissipated energy, both geometrically nonlinear and frequency-dependent. The model is then applied to a silicone rubber rectangular plate tested experimentally. The plate was glued to a metal frame and harmonically excited by stepped sine testing at different force levels and the vibration response was measured by a laser Doppler vibrometer. The comparison of numerical and experimental results was satisfactorily carried out for: (i) nonlinear vibration responses in the frequency and time domain at different excitation levels, (ii) dissipated energy versus excitation frequency and excitation force, (iii) storage energy and (iv) loss factor, which is particularly interesting to evaluate the plate dissipation versus frequency at different excitation levels. Finally, the linear and nonlinear damping terms are compared.
{"title":"Nonlinear Damping in Large-Amplitude Vibrations of Viscoelastic Plates","authors":"M. Amabili, Prabakaran Balasubramanian, Giovanni Ferrari","doi":"10.1115/imece2019-10339","DOIUrl":"https://doi.org/10.1115/imece2019-10339","url":null,"abstract":"\u0000 Damping is largely increasing with the vibration amplitude during nonlinear vibrations of rectangular plates. At the same time, soft materials present an increase of their stiffness with the vibration frequency. These two phenomena appear together and are both explained in the framework of the viscoelasticity. While the literature on nonlinear vibrations of plates is very large, these aspects are rarely addressed. The present study uses the fractional solid model to describe the viscoelastic material behaviour. This allows to capture at the same time (i) the increase in the storage modulus with the vibration frequency and (ii) the frequency-dependent nonlinear damping in nonlinear vibrations of rectangular plates. The solution of the nonlinear vibration problems is obtained through Lagrange equations by deriving the potential energy of the plate and the dissipated energy, both geometrically nonlinear and frequency-dependent. The model is then applied to a silicone rubber rectangular plate tested experimentally. The plate was glued to a metal frame and harmonically excited by stepped sine testing at different force levels and the vibration response was measured by a laser Doppler vibrometer. The comparison of numerical and experimental results was satisfactorily carried out for: (i) nonlinear vibration responses in the frequency and time domain at different excitation levels, (ii) dissipated energy versus excitation frequency and excitation force, (iii) storage energy and (iv) loss factor, which is particularly interesting to evaluate the plate dissipation versus frequency at different excitation levels. Finally, the linear and nonlinear damping terms are compared.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123092627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents a parallelized framework for a multi-scale material analysis method called the generalized method of cells (GMC) model which can be used to effectively homogenize or localize material properties over two different length scales. Parallelization is utlized at two instances: (a) for the solution of the governing linear equations, and (b) for the local analysis of each subcell. The governing linear equation is solved parallely using a parallel form of the Gaussian substitution method, and the subsequent local subcell analysis is performed parallely using a domain decomposition method wherein the lower length scale subcells are equally divided over available processors. The parellization algorithm takes advantage of a single program multiple data (SPMD) distributed memory architecture using the Message Passing Interface (MPI) standard, which permits scaling up of the analysis algorithm to any number of processors on a computing cluster. Results show significant decrease in solution time for the parallelized algorithm compared to serial algorithms, especially for denser microscale meshes. The consequent speed-up in processing time permits the analysis of complex length scale dependent phenomenon, nonlinear analysis, and uncertainty studies with multiscale effects which would otherwise be prohibitively expensive.
{"title":"A Parallelized Generalized Method of Cells Framework for Multiscale Studies of Composite Materials","authors":"Ashwin Rai, T. Skinner, A. Chattopadhyay","doi":"10.1115/imece2019-11529","DOIUrl":"https://doi.org/10.1115/imece2019-11529","url":null,"abstract":"\u0000 This paper presents a parallelized framework for a multi-scale material analysis method called the generalized method of cells (GMC) model which can be used to effectively homogenize or localize material properties over two different length scales. Parallelization is utlized at two instances: (a) for the solution of the governing linear equations, and (b) for the local analysis of each subcell. The governing linear equation is solved parallely using a parallel form of the Gaussian substitution method, and the subsequent local subcell analysis is performed parallely using a domain decomposition method wherein the lower length scale subcells are equally divided over available processors. The parellization algorithm takes advantage of a single program multiple data (SPMD) distributed memory architecture using the Message Passing Interface (MPI) standard, which permits scaling up of the analysis algorithm to any number of processors on a computing cluster. Results show significant decrease in solution time for the parallelized algorithm compared to serial algorithms, especially for denser microscale meshes. The consequent speed-up in processing time permits the analysis of complex length scale dependent phenomenon, nonlinear analysis, and uncertainty studies with multiscale effects which would otherwise be prohibitively expensive.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129005951","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
NinjaFlex is a flexible thermoplastic polyurethane (TPU) material manufactured for use with Fused Deposition Modelling 3D printers. It is widely available, relatively inexpensive, and is useful in various applications including gaskets, wearable electronics, and customized prosthetics because of its great flexibility and strength. The objective of this research was to expand on the limited information available regarding the mechanical characteristics of NinjaFlex and learn how infill density and printing orientation influence those characteristics. An experiment was designed using the ASTM D638-14 standard to evaluate tensile properties of NinjaFlex specimens printed in two different orientations with their longitudinal axis parallel to the printing surface and with their longitudinal axis normal to the printing surface. Four different infill densities were used. Specimens were subjected to tensile loading along their longitudinal axes. A calibrated load cell measured applied force while a camera filmed the experiment for determining the corresponding extension using computer vision methods. The results show that NinjaFlex has sizably greater ultimate strength, elongation, and toughness when loaded parallel to its print layers then when loaded normal to its print layers. The effects of infill density on tensile properties vary depending on loading direction relative to the print layer direction.
{"title":"Identification of the Mechanical Characteristics of 3D Printed NinjaFlex®","authors":"Patrick Messimer, B. O’Toole, M. Trabia","doi":"10.1115/imece2019-11674","DOIUrl":"https://doi.org/10.1115/imece2019-11674","url":null,"abstract":"\u0000 NinjaFlex is a flexible thermoplastic polyurethane (TPU) material manufactured for use with Fused Deposition Modelling 3D printers. It is widely available, relatively inexpensive, and is useful in various applications including gaskets, wearable electronics, and customized prosthetics because of its great flexibility and strength. The objective of this research was to expand on the limited information available regarding the mechanical characteristics of NinjaFlex and learn how infill density and printing orientation influence those characteristics.\u0000 An experiment was designed using the ASTM D638-14 standard to evaluate tensile properties of NinjaFlex specimens printed in two different orientations with their longitudinal axis parallel to the printing surface and with their longitudinal axis normal to the printing surface. Four different infill densities were used. Specimens were subjected to tensile loading along their longitudinal axes. A calibrated load cell measured applied force while a camera filmed the experiment for determining the corresponding extension using computer vision methods.\u0000 The results show that NinjaFlex has sizably greater ultimate strength, elongation, and toughness when loaded parallel to its print layers then when loaded normal to its print layers. The effects of infill density on tensile properties vary depending on loading direction relative to the print layer direction.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116749139","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents a numerical study on nonlinear Lamb wave time reversing for fatigue crack detection. An analytical framework is initially presented, modeling Lamb wave generation, propagation, wave crack linear and nonlinear interaction, and reception. Subsequently, a 3D transient dynamic coupled-field finite element model is constructed to simulate the pitch-catch procedure in an aluminum plate using the commercial finite element software (ANSYS). The excitation frequency is carefully selected, where only single Lamb wave mode will be generated by the Piezoelectric Wafer Active Sensor (PWAS). The fatigue cracks are modelled nucleating from both sides of a rivet hole. In addition, contact dynamics are considered to capture the nonlinear interactions between guided waves and the fatigue cracks, which would induce Contact Acoustic Nonlinearity (CAN) into the guided waves. Then the conventional and virtual time reversal methods are realized by finite element simulation. Advanced signal processing techniques are used to extract the distinctive nonlinear features. Via the Fast Fourier Transform (FFT) and time-frequency spectral analysis, nonlinear superharmonic components are observed. The reconstructed signals attained from the conventional and virtual time reversal methods are compared and analyzed. Finally, various Damage Indices (DIs), based on the difference between the reconstructed signal and the excitation waveform as well as the amplitude ratio between the superharmonic and the fundamental frequency components are adopted to evaluate the fatigue crack severity. The DIs could provide quantitative diagnostic information for fatigue crack detection. This paper finishes with summary, concluding remarks, and suggestions for future work.
{"title":"Numerical Investigation of Nonlinear Lamb Wave Time Reversing for Fatigue Crack Detection","authors":"Junzhen Wang, Yanfeng Shen","doi":"10.1115/imece2019-10881","DOIUrl":"https://doi.org/10.1115/imece2019-10881","url":null,"abstract":"\u0000 This paper presents a numerical study on nonlinear Lamb wave time reversing for fatigue crack detection. An analytical framework is initially presented, modeling Lamb wave generation, propagation, wave crack linear and nonlinear interaction, and reception. Subsequently, a 3D transient dynamic coupled-field finite element model is constructed to simulate the pitch-catch procedure in an aluminum plate using the commercial finite element software (ANSYS). The excitation frequency is carefully selected, where only single Lamb wave mode will be generated by the Piezoelectric Wafer Active Sensor (PWAS). The fatigue cracks are modelled nucleating from both sides of a rivet hole. In addition, contact dynamics are considered to capture the nonlinear interactions between guided waves and the fatigue cracks, which would induce Contact Acoustic Nonlinearity (CAN) into the guided waves. Then the conventional and virtual time reversal methods are realized by finite element simulation. Advanced signal processing techniques are used to extract the distinctive nonlinear features. Via the Fast Fourier Transform (FFT) and time-frequency spectral analysis, nonlinear superharmonic components are observed. The reconstructed signals attained from the conventional and virtual time reversal methods are compared and analyzed. Finally, various Damage Indices (DIs), based on the difference between the reconstructed signal and the excitation waveform as well as the amplitude ratio between the superharmonic and the fundamental frequency components are adopted to evaluate the fatigue crack severity. The DIs could provide quantitative diagnostic information for fatigue crack detection. This paper finishes with summary, concluding remarks, and suggestions for future work.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128525024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study addresses the crack surfaces closure effects of a cracked cantilever beam subjected to transverse force applied at its free end under static loading. A crack closure method is developed as needed to account for crack surface contact in regions wherein the linear solutions predict physically inadmissible crack surface inter penetration. An efficient finite element algorithm is developed accordingly to solve the static problem of the beam containing a fully embedded sharp crack in a linear, elastic, homogeneous and isotropic system. Emphasis is placed on the comparison between the near-tip fracture characteristics estimates, e.g. the normalized energy release rate, Mode I and Mode II stress intensity factors (SIF), and mode mixity, with closure effects and those without closure effects reported elsewhere. The crack length, orientation, and crack center location appear as the studied model parameters of a beam of fixed beam aspect ratio. In addition, based on the study observations of pure Mode II crack, a case study on the beam with an embedded vertical crack in the compressive regime is reported to show the deformed profiles due to full crack surfaces closure during loading. The curvature profile of the cracked beam with and without closure effects are compared to those of the healthy beam for the application of closure effects in improving the results accuracy.
{"title":"The Mechanical Response of a Cantilever Beam With an Embedded Crack With Non-Linear Crack Surface Closure Effects","authors":"X. Fang, P. Charalambides","doi":"10.1115/imece2019-11018","DOIUrl":"https://doi.org/10.1115/imece2019-11018","url":null,"abstract":"\u0000 This study addresses the crack surfaces closure effects of a cracked cantilever beam subjected to transverse force applied at its free end under static loading. A crack closure method is developed as needed to account for crack surface contact in regions wherein the linear solutions predict physically inadmissible crack surface inter penetration. An efficient finite element algorithm is developed accordingly to solve the static problem of the beam containing a fully embedded sharp crack in a linear, elastic, homogeneous and isotropic system. Emphasis is placed on the comparison between the near-tip fracture characteristics estimates, e.g. the normalized energy release rate, Mode I and Mode II stress intensity factors (SIF), and mode mixity, with closure effects and those without closure effects reported elsewhere. The crack length, orientation, and crack center location appear as the studied model parameters of a beam of fixed beam aspect ratio. In addition, based on the study observations of pure Mode II crack, a case study on the beam with an embedded vertical crack in the compressive regime is reported to show the deformed profiles due to full crack surfaces closure during loading. The curvature profile of the cracked beam with and without closure effects are compared to those of the healthy beam for the application of closure effects in improving the results accuracy.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131566302","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The CCR (Continuous Catalytic Reforming) Platforming™ process is Honeywell UOP’s technology to convert low octane naphtha to high octane fuel or petrochemical feedstock such as aromatics. It is accomplished in a hydrogen atmosphere at elevated temperature and pressure across a platinum containing catalyst. The process flow is routed through heaters, blowers and coolers between reactors to maintain the heat of reaction. This article captures the procedure of selecting a suitable expansion joint for absorbing thermal movement between two important pieces of CCR equipment — the regeneration cooler and regeneration blower. It shows the design calculations of a universal hinged expansion joint operating at 0.14 MPa and 593°C in a pipe of 762mm diameter. The joint contains 5 single-ply INCOLOY 800H bellows with unreinforced convolutions. Design calculations of the expansion joint have been carried out using formulae prescribed in the Expansion Joints Manufacturers Association (EJMA) standard. Since it is difficult to quantify stresses using a movement test, the EJMA calculations have been verified against finite element analysis results of the bellows.
{"title":"Analysis of CCR Expansion Joints","authors":"S. Kaul, R. Gohil, Parul Bisharia, Apoorva Roy","doi":"10.1115/imece2019-10559","DOIUrl":"https://doi.org/10.1115/imece2019-10559","url":null,"abstract":"\u0000 The CCR (Continuous Catalytic Reforming) Platforming™ process is Honeywell UOP’s technology to convert low octane naphtha to high octane fuel or petrochemical feedstock such as aromatics. It is accomplished in a hydrogen atmosphere at elevated temperature and pressure across a platinum containing catalyst. The process flow is routed through heaters, blowers and coolers between reactors to maintain the heat of reaction. This article captures the procedure of selecting a suitable expansion joint for absorbing thermal movement between two important pieces of CCR equipment — the regeneration cooler and regeneration blower. It shows the design calculations of a universal hinged expansion joint operating at 0.14 MPa and 593°C in a pipe of 762mm diameter. The joint contains 5 single-ply INCOLOY 800H bellows with unreinforced convolutions. Design calculations of the expansion joint have been carried out using formulae prescribed in the Expansion Joints Manufacturers Association (EJMA) standard. Since it is difficult to quantify stresses using a movement test, the EJMA calculations have been verified against finite element analysis results of the bellows.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114936226","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid Expandable Tubular Technology (SETT) finds its extensive applications in the oil and gas industries where it is used for well completion and remediation. The purpose of his work is to investigate the material behavior upon expansion and to optimize the parameters that are relevant to the expansion process. Tube expansion tests have been performed using a newly designed experimental setup. Seamless stainless steel (AISI 304) tubes have been deformed and monitored using a Digital Image Correlation (DIC) system to measure the full field displacement. A parametric study has been performed in order to study the effect of key expansion parameters such us mandrel geometry (angle), expansion ratio, mandrel-tube friction on the tube expansion and its buckling. The commercial code VIC-3D has been used to process the strain and displacement data obtained by the charge-coupled device (CCD) cameras. Moreover, the tests have been modeled numerically using the Finite Element Method (FEM) to gain further insight into the stress and strain distributions during metal forming. A good correlation has been observed between the numerical and experimental results.
{"title":"Analysis of Tube Expansion Using 3D Digital Image Correlation and Numerical Modeling","authors":"F. Abbassi, F. Ahmad, A. Karrech, Md.S. Islam","doi":"10.1115/imece2019-10035","DOIUrl":"https://doi.org/10.1115/imece2019-10035","url":null,"abstract":"\u0000 Solid Expandable Tubular Technology (SETT) finds its extensive applications in the oil and gas industries where it is used for well completion and remediation. The purpose of his work is to investigate the material behavior upon expansion and to optimize the parameters that are relevant to the expansion process. Tube expansion tests have been performed using a newly designed experimental setup. Seamless stainless steel (AISI 304) tubes have been deformed and monitored using a Digital Image Correlation (DIC) system to measure the full field displacement. A parametric study has been performed in order to study the effect of key expansion parameters such us mandrel geometry (angle), expansion ratio, mandrel-tube friction on the tube expansion and its buckling. The commercial code VIC-3D has been used to process the strain and displacement data obtained by the charge-coupled device (CCD) cameras. Moreover, the tests have been modeled numerically using the Finite Element Method (FEM) to gain further insight into the stress and strain distributions during metal forming. A good correlation has been observed between the numerical and experimental results.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"306 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122699704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Since the operating condition of thermal power plants has become harsher for minimizing the emission of CO2, Ni-based superalloys, such as Alloy 617 and 625, have been used in the plants to replace the conventional ferritic materials. Unfortunately, the increase of coefficient of thermal expansion compared with conventional steels is a concern. In addition, Ni-based superalloys have to suffer creep-fatigue random loading because thermal power plants have to compensate the random output of various renewable energies. It was found that the lifetime of Ni-based superalloys under creep-fatigue loading was much shorter than that under simple fatigue or creep loading. Thus, it has become very important to clarify the crack mechanism and establish the quantitative theory for estimating their lifetime under various loading conditions at elevated temperatures. Thus, the elucidation of the initial damage mechanism of Alloy 625 under various loading is indispensable. Hence, the initial cracking mechanism of Alloy 625 at grain boundaries under creep loading was investigated experimentally. The creep test was applied to small specimens in Argon atmosphere. The change of the micro texture during the creep test was observed by using SEM. It was confirmed that all the initial cracks appeared at certain grain boundaries. The change of the crystallinity was observed by EBSD (Electron Back-Scatter Diffraction) analysis quantitatively. It was found that the local accumulation of dislocations at the cracked grain boundaries caused the initial cracks at those grain boundaries. The initiation of cracks appeared clearly between two grains which had difference of KAM (Kernel Average Misorientation) values larger than 0.2. Therefore, dislocations were accumulated at one side of the grain boundary. By measuring the KAM values near grain boundaries, the appearance of initial cracks can be predicted approximately.
{"title":"Grain Boundary Cracking of Nickel-Based Alloy 625 Under Creep Loadings at Elevated Temperatures","authors":"Yan Liang, Yifan Luo, Ken Suzuki, H. Miura","doi":"10.1115/imece2019-11186","DOIUrl":"https://doi.org/10.1115/imece2019-11186","url":null,"abstract":"\u0000 Since the operating condition of thermal power plants has become harsher for minimizing the emission of CO2, Ni-based superalloys, such as Alloy 617 and 625, have been used in the plants to replace the conventional ferritic materials. Unfortunately, the increase of coefficient of thermal expansion compared with conventional steels is a concern. In addition, Ni-based superalloys have to suffer creep-fatigue random loading because thermal power plants have to compensate the random output of various renewable energies. It was found that the lifetime of Ni-based superalloys under creep-fatigue loading was much shorter than that under simple fatigue or creep loading. Thus, it has become very important to clarify the crack mechanism and establish the quantitative theory for estimating their lifetime under various loading conditions at elevated temperatures.\u0000 Thus, the elucidation of the initial damage mechanism of Alloy 625 under various loading is indispensable. Hence, the initial cracking mechanism of Alloy 625 at grain boundaries under creep loading was investigated experimentally. The creep test was applied to small specimens in Argon atmosphere. The change of the micro texture during the creep test was observed by using SEM. It was confirmed that all the initial cracks appeared at certain grain boundaries. The change of the crystallinity was observed by EBSD (Electron Back-Scatter Diffraction) analysis quantitatively. It was found that the local accumulation of dislocations at the cracked grain boundaries caused the initial cracks at those grain boundaries. The initiation of cracks appeared clearly between two grains which had difference of KAM (Kernel Average Misorientation) values larger than 0.2. Therefore, dislocations were accumulated at one side of the grain boundary. By measuring the KAM values near grain boundaries, the appearance of initial cracks can be predicted approximately.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"63 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132795246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper describes preliminary experiments carried in a wind tunnel to study the effect of different turbulence intensities (nominally Tu = 0.6, 0.8 and 1.0%) on the dynamics of a flexible silicone filament (length to diameter ratio L/D = 83) hanging in crossflow in the range of reduced velocities of 7 < U* < 108. The turbulence intensity inside the wind tunnel was modified by employing two different grids (porosity β = 0.563 and 0.026). At low reduced velocities the filament was statically reconfigured but remained mostly rectilinear along its length. As the reduced velocity was further increased the filament started vibrating, and beyond a certain critical reduced velocity large-amplitude limit-cycle oscillation motions were observed. It is suggested that the turbulence intensity (shear velocity) affects the onset of the flapping motions and the amplitude of these. However, this behavior also depends on the turbulence integral length scale.
{"title":"Effect of Grid-Generated Turbulence on the Dynamics of a Flexible Filament Hanging in Cross-Flow","authors":"Jorge Silva-Leon, A. Cioncolini","doi":"10.1115/imece2019-10404","DOIUrl":"https://doi.org/10.1115/imece2019-10404","url":null,"abstract":"\u0000 This paper describes preliminary experiments carried in a wind tunnel to study the effect of different turbulence intensities (nominally Tu = 0.6, 0.8 and 1.0%) on the dynamics of a flexible silicone filament (length to diameter ratio L/D = 83) hanging in crossflow in the range of reduced velocities of 7 < U* < 108. The turbulence intensity inside the wind tunnel was modified by employing two different grids (porosity β = 0.563 and 0.026). At low reduced velocities the filament was statically reconfigured but remained mostly rectilinear along its length. As the reduced velocity was further increased the filament started vibrating, and beyond a certain critical reduced velocity large-amplitude limit-cycle oscillation motions were observed. It is suggested that the turbulence intensity (shear velocity) affects the onset of the flapping motions and the amplitude of these. However, this behavior also depends on the turbulence integral length scale.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130172765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To enable real-time monitoring of the physical condition of the drilling equipment such as drill collars, a methodology for efficiently predicting the fatigue life of ports subjected to variable-amplitude cyclic bending or torsional loads is needed. In this paper, such a method is reported, which involves several steps. Firstly, elastic finite element analysis (FEA) of a collar port was performed to determine the elastic stress states with unit loads. Secondly, the unit load-based linear elastic solutions with the loading history were superimposed to produce a time history of the stress tensor. Thirdly, the previously established pseudo-elastic stress states were transformed into the true elastoplastic stress and strain states with a cyclic plasticity model and a notch correction rule. Finally, the cumulative fatigue damage was computed with the rainflow counting algorithm and a damage accumulation rule. The resulting fatigue life predictions for the ports were found to agree favorably with the experimental measurements from full-scale fatigue tests of port-containing collar samples with variable-amplitude loads. This newly developed method can be used to predict the remaining useful life of a port in real time with the loads resulting from downhole measurements or a drill string dynamics simulation code.
{"title":"Efficiently Predicting Fatigue Life of Drill Collars With Ports Subjected to Variable-Amplitude Bending or Torsional Loads","authors":"F. Song, Ke Li, S. Ossia","doi":"10.1115/imece2019-11066","DOIUrl":"https://doi.org/10.1115/imece2019-11066","url":null,"abstract":"\u0000 To enable real-time monitoring of the physical condition of the drilling equipment such as drill collars, a methodology for efficiently predicting the fatigue life of ports subjected to variable-amplitude cyclic bending or torsional loads is needed. In this paper, such a method is reported, which involves several steps. Firstly, elastic finite element analysis (FEA) of a collar port was performed to determine the elastic stress states with unit loads. Secondly, the unit load-based linear elastic solutions with the loading history were superimposed to produce a time history of the stress tensor. Thirdly, the previously established pseudo-elastic stress states were transformed into the true elastoplastic stress and strain states with a cyclic plasticity model and a notch correction rule. Finally, the cumulative fatigue damage was computed with the rainflow counting algorithm and a damage accumulation rule. The resulting fatigue life predictions for the ports were found to agree favorably with the experimental measurements from full-scale fatigue tests of port-containing collar samples with variable-amplitude loads. This newly developed method can be used to predict the remaining useful life of a port in real time with the loads resulting from downhole measurements or a drill string dynamics simulation code.","PeriodicalId":375383,"journal":{"name":"Volume 9: Mechanics of Solids, Structures, and Fluids","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129953113","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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