Identification of process parameters,their effects and contributions to the outcomes of the system using experimental approach could be a daunting,time consuming,and costly course.Using proper statistical methods,i.e....Identification of process parameters,their effects and contributions to the outcomes of the system using experimental approach could be a daunting,time consuming,and costly course.Using proper statistical methods,i.e.,Taguchi method,could significantly reduce the number of required experiments and statistical significance of the parameter can be identified.Friction stir welding is one of those welding techniques with many parameters which have different effects on the quality of the welds.In friction stir welding the tool rotational speed(RPM)and transverse speed(mm/min)influence the strength(i.e.,hardness distribution)of the stirred zone.In this study,these two factors are investigated to determine the effect they will have on the hardness in the stirred zone of the friction stir welds and how the two factors are related to one another for as-cast magnesium alloy AM60 with nominal chemical composition of Mg-(5.5-6.5)Al-(0.24-0.6)Mn-0.22Zn-0.1Si.Experimental data was taken at three different tool rotational speeds and three different transverse speeds.The data obtained was then analyzed using a 32 factorial design to find the contribution of these parameters.It was determined that both tool rotational speed and transverse speed possess significant effects on the stir zone hardness.Also,the interactions between the two factors were statistically assessed.展开更多
Debris avalanches are a major concern due to their high mobility.However,the mechanism of friction weakening in debris avalanches remains poorly understood.This study systematically investigates the friction weakening...Debris avalanches are a major concern due to their high mobility.However,the mechanism of friction weakening in debris avalanches remains poorly understood.This study systematically investigates the friction weakening mechanism of granular flows using rotation drum experiments,large-scale chute experiments,and numerical simulations.Notably,dilation of granular flows is a characteristic feature associated with friction weakening.The results indicate that dilation occurs synchronously with friction weakening during the motion of granular flows,as evidenced by the motion patterns and force interactions of debris avalanches.Collision contacts were identified as the primary driver of particle dilation.An optimal collision strength can induce dilation of granular flows,reducing contact between the sliding body and substrate,thereby leading to friction weakening.The peak collision strength of granular flows during movement is determined by fragment size.The critical condition for triggering friction weakening in debris avalanches is identified as the peak Savage number(Ns,p)greater than 1.06.A mathematical model based on the granular inertial collision-friction coupling equation was developed.This study provides compelling evidence that the fractal dimension of various types of high-speed debris avalanches tends to stabilize within a narrow range.展开更多
Rock-ice granular flows in high-altitude cold regions exhibit extreme mobility and destructive potential,posing severe threats to lives and infrastructure.Basal stress,governing the interaction between the flow and th...Rock-ice granular flows in high-altitude cold regions exhibit extreme mobility and destructive potential,posing severe threats to lives and infrastructure.Basal stress,governing the interaction between the flow and the underlying substrate,is critical for understanding their high mobility and erosion behavior.However,systematic investigations into basal stress fluctuations and their relationship with frictional behavior in rock-ice granular flows remain scarce,particularly regarding the effects of ice content and inclination angle.In this study,a series of flume experiments were conducted with ice contents ranging from 0%to 100%and flume inclination angles of 30°–45°.A triaxial force sensor and high-speed imaging with particle image velocimetry(PIV)were employed to measure basal normal and shear stresses,flow depth,and velocity.The results reveal that both normal and shear basal stresses initially increase slightly at 10%ice content but then decrease progressively as ice content increases further,while both stresses increase monotonically with inclination angle.These variations are attributed to the combined effects of hydrostatic pressure(overburden load and flow depth)and dynamic pressure(particle collisions and flow velocity).Dimensionless normal impulse decreases with ice content,whereas dimensionless tangential impulse increases,indicating enhanced normal interactions but weakened tangential interactions at higher ice concentrations.The maximum stress and standard deviation of stress both scale linearly with the time-mean stress,confirming that stress fluctuations are governed by bulk flow conditions(density,overburden load).The effective friction coefficientμshows a linear decrease with increasing ice content and a negative correlation with the Froude number Fr.Additionally,the normalized standard deviation of normal stress correlates positively withμ,while that of shear stress correlates negatively,suggesting that normal stress fluctuations from particle-substrate collisions enhance basal friction,whereas tangential fluctuations reduce it.These findings provide quantitative insights into the basal stress dynamics of rock-ice granular flows and establish a basis for improved hazard assessment and mitigation strategies in high-altitude mountain regions.展开更多
Ice friction is influenced by multiple interconnected parameters between the sliding body and ice,making it a challenging research area in tribology.The motivation for this review lies in the need to understand the pa...Ice friction is influenced by multiple interconnected parameters between the sliding body and ice,making it a challenging research area in tribology.The motivation for this review lies in the need to understand the parameters affecting ice friction and its relevance to the fields of sport,safety,and various industrial applications.The existing literature on ice friction only partially describes the test methods used.Thus,the comparability of the results and the drawing of conclusions are more challenging.This review addresses this issue by analyzing factors affecting ice friction,including properties of the ice,liquid-like layer,sliding body,and experimental methods.Small-scale rotary,linear,and large-scale laboratory and on-field setups are reviewed,and advantages and limitations are highlighted.The main results indicate that laboratory setups tend to provide more precise control over measurements but may not replicate real-world conditions.On the other hand,large-scale and on-field setups are closer to the actual conditions,but the control over experiments,reproducibility,and implementation is more challenging.The review concludes that future research should focus on comparing different test methods with the possibility of developing standardized protocols and improving large-scale experimental setups.The study aims to enhance the reliability of ice friction research and its practical applications,which should lead to improved safety and performance in the fields where ice friction plays a crucial role.展开更多
A systematic approach was presented to develop the empirical model for predicting the ultimate tensile strength of AA5083-H111 aluminum alloy which is widely used in ship building industry by incorporating friction st...A systematic approach was presented to develop the empirical model for predicting the ultimate tensile strength of AA5083-H111 aluminum alloy which is widely used in ship building industry by incorporating friction stir welding(FSW) process parameters such as tool rotational speed,welding speed,and axial force.FSW was carried out considering three-factor five-level central composite rotatable design with full replications technique.Response surface methodology(RSM) was applied to developing linear regression model for establishing the relationship between the FSW process parameters and ultimate tensile strength.Analysis of variance(ANOVA) technique was used to check the adequacy of the developed model.The FSW process parameters were also optimized using response surface methodology(RSM) to maximize the ultimate tensile strength.The joint welded at a tool rotational speed of 1 000 r/min,a welding speed of 69 mm/min and an axial force of 1.33 t exhibits higher tensile strength compared with other joints.展开更多
Five kinds of 45# steel samples with concave features on the surface were manufactured using Laser Texturing Technology (LTT). Optimum design theory was used to design the experiment, and a two-level orthogonal table-...Five kinds of 45# steel samples with concave features on the surface were manufactured using Laser Texturing Technology (LTT). Optimum design theory was used to design the experiment, and a two-level orthogonal table-L 16 (2 15 ) design was adopted . Micro-wear and micro-friction experienced by samples with concave surface features and samples with smooth surfaces were compared experimentally. The wear resistance of samples with concave surface features was increased most, and different surface morphologies had different effects on friction and wear properties.展开更多
Aluminium alloys generally present low weldability by traditional fusion welding process. Development of the friction stir welding （FSW） has provided an alternative improved way of producing aluminium joints in a fa...Aluminium alloys generally present low weldability by traditional fusion welding process. Development of the friction stir welding （FSW） has provided an alternative improved way of producing aluminium joints in a faster and reliable manner. The quality of a weld joint is stalwartly influenced by process parameter used during welding. An approach to develop a mathematical model was studied for predicting and optimizing the process parameters of dissimilar aluminum alloy （AA6351 T6-AA5083 Hlll）joints by incorporating the FSW process parameters such as tool pin profile, tool rotational speed welding speed and axial force. The effects of the FSW process parameters on the ultimate tensile strength （UTS） of friction welded dissimilar joints were discussed. Optimization was carried out to maximize the UTS using response surface methodology （RSM） and the identified optimum FSW welding parameters were reported.展开更多
This paper reports stick-slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention （NIED）, Tsuk...This paper reports stick-slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention （NIED）, Tsukuba, Japan. The apparatus consists of the existing shaking table as the shear-loading device up to 3,600 kN, the main frame for holding two large rectangular prismatic specimens with a sliding area of 0.75 m^2 and for applying normal stresses an up to 1.33 MPa, and a reaction force unit holding the stationary specimen to the ground. The shaking table can produce loading rates v up to 1.0 m/s, accelerations up to 9.4 m/s^2, and displacements d up to 0.44 m, using four servocontrolled actuators. We report results from eight preliminary experiments conducted with room humidity on the same gabbro specimens at v = 0.1-100 mm/s and an = 0.66-1.33 MPa, and with d of about 0.39 m. The peak and steady-state friction coefficients were about 0.8 and 0.6, respectively, consistent with the Byerlee friction. The axial force drop or shear stress drop during an abrupt slip is linearly proportional to the amount of displacement, and the slope of this rela- tionship determines the stiffness of the apparatus as 1.15 × 10^8 N/m or 153 MPa/m for the specimens we used. This low stiffness makes fault motion very unstable and the overshooting of shear stress to a negative value was recognized in some violent stick-slip events. An abrupt slip occurred in a constant rise time of 16-18 ms despite wide variation of the stress drop, and an average velocity during an abrupt slip is linearly proportional to the stress drop. The use of a large-scale shaking table has a great potential in increasing the slip rate and total displacement in biaxial friction experiments with large specimens.展开更多
Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch an...Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.展开更多
The nucleation process of stick-slip instability was analyzed based on the experimental measurements of strain and fault slip on homogeneous and non-homogeneous faults. The results show that the nucleation process of ...The nucleation process of stick-slip instability was analyzed based on the experimental measurements of strain and fault slip on homogeneous and non-homogeneous faults. The results show that the nucleation process of stick-slip on the homogeneous fault is of weak slip-weakening behavior under constant loading point velocity. The existence of a short "weak segment" on the fault makes slip-weakening phenomenon in nucleation process more obvious, while the existence of a long "weak segment" on the fault makes the nucleation process changed. The nucleation is characterized by accelerating slip in a local region and rapid increase of shear stress along the fault in this case, which is more coincident with the rate and state friction law. During the period when fault is locked, increasing of shear stress causes lateral elastic dilation near the fault, and the rebound of the dilation at the time of instability causes an instantaneous increase of normal stress in the fault plane, which is an important factor making fault be rapidly locked and its strength recovered.展开更多
The aluminium alloy AA2219(Al—Cu—Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance.Welding is main fabrication method of AA2219 al...The aluminium alloy AA2219(Al—Cu—Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance.Welding is main fabrication method of AA2219 alloy for manufacturing various engineering components.Friction stir welding(FSW) is a recently developed solid state welding process to overcome the problems encountered in fusion welding.This process uses a non-consumable tool to generate frictional heat on the abutting surfaces.The welding parameters,such as tool pin profile,rotational speed,welding speed and axial force,play major role in determining the microstructure and corrosion resistance of welded joint.The main objective of this work is to develop a mathematical model to predict the corrosion resistance of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters.In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions.Dynamic polarization testing was carried out to determine critical pitting potential in millivolt,which is a criteria for measuring corrosion resistance and the data was used in model.Further the response surface method(RSM) was used to develop the model.The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the friction stir welded AA2219 aluminium alloy joints.展开更多
The present study focuses on the development of polymeric friction composites with short carbon fiber, micron and nano-sized fillers, additives with varying weight% in phenol formaldehyde (PF) matrix using hot compres...The present study focuses on the development of polymeric friction composites with short carbon fiber, micron and nano-sized fillers, additives with varying weight% in phenol formaldehyde (PF) matrix using hot compression moulding process. The composites prepared with fillers viz. Molybdenum disulfide or Molykote (MK) and multi walled carbon nanotubes (MWCNTs) in carbon fiber reinforced PF matrix is designated as Set-I composites. Inclusion of graphite and nano-clay in carbon fiber reinforced PF matrix is designated as Set-II composites. The prepared composites are tested in Dry sand rubber wheel abrasion wear test rig, following ASTM standards for evaluating the abrasive wear behaviour. From the routine experiments, it was observed that the presence of combined micro and nanofillers i.e. 11.5 wt% MK + 0.5 wt% MWCNTs of Set-I, has shown superior abrasion resistance among the study group. The test results of the Set-I and Set-II composites are analyzed using Taguchi experimental design followed by analysis of variance (ANOVA) to understand the contributions of wear control factors affecting the abrasive wear characteristics. Further, worn surface of selected samples is analyzed using scanning electron micrographs.展开更多
文摘Identification of process parameters,their effects and contributions to the outcomes of the system using experimental approach could be a daunting,time consuming,and costly course.Using proper statistical methods,i.e.,Taguchi method,could significantly reduce the number of required experiments and statistical significance of the parameter can be identified.Friction stir welding is one of those welding techniques with many parameters which have different effects on the quality of the welds.In friction stir welding the tool rotational speed(RPM)and transverse speed(mm/min)influence the strength(i.e.,hardness distribution)of the stirred zone.In this study,these two factors are investigated to determine the effect they will have on the hardness in the stirred zone of the friction stir welds and how the two factors are related to one another for as-cast magnesium alloy AM60 with nominal chemical composition of Mg-(5.5-6.5)Al-(0.24-0.6)Mn-0.22Zn-0.1Si.Experimental data was taken at three different tool rotational speeds and three different transverse speeds.The data obtained was then analyzed using a 32 factorial design to find the contribution of these parameters.It was determined that both tool rotational speed and transverse speed possess significant effects on the stir zone hardness.Also,the interactions between the two factors were statistically assessed.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2240221 and 52379105)the National Key R&D Program of China(Grant No.2022YFC3080100).
文摘Debris avalanches are a major concern due to their high mobility.However,the mechanism of friction weakening in debris avalanches remains poorly understood.This study systematically investigates the friction weakening mechanism of granular flows using rotation drum experiments,large-scale chute experiments,and numerical simulations.Notably,dilation of granular flows is a characteristic feature associated with friction weakening.The results indicate that dilation occurs synchronously with friction weakening during the motion of granular flows,as evidenced by the motion patterns and force interactions of debris avalanches.Collision contacts were identified as the primary driver of particle dilation.An optimal collision strength can induce dilation of granular flows,reducing contact between the sliding body and substrate,thereby leading to friction weakening.The peak collision strength of granular flows during movement is determined by fragment size.The critical condition for triggering friction weakening in debris avalanches is identified as the peak Savage number(Ns,p)greater than 1.06.A mathematical model based on the granular inertial collision-friction coupling equation was developed.This study provides compelling evidence that the fractal dimension of various types of high-speed debris avalanches tends to stabilize within a narrow range.
基金financial support from the National Key Research and Development Program of China(Project No.2023YFC3008300,2023YFC3008302)the National Natural Science Foundation of China(Grant No.U22A20603).
文摘Rock-ice granular flows in high-altitude cold regions exhibit extreme mobility and destructive potential,posing severe threats to lives and infrastructure.Basal stress,governing the interaction between the flow and the underlying substrate,is critical for understanding their high mobility and erosion behavior.However,systematic investigations into basal stress fluctuations and their relationship with frictional behavior in rock-ice granular flows remain scarce,particularly regarding the effects of ice content and inclination angle.In this study,a series of flume experiments were conducted with ice contents ranging from 0%to 100%and flume inclination angles of 30°–45°.A triaxial force sensor and high-speed imaging with particle image velocimetry(PIV)were employed to measure basal normal and shear stresses,flow depth,and velocity.The results reveal that both normal and shear basal stresses initially increase slightly at 10%ice content but then decrease progressively as ice content increases further,while both stresses increase monotonically with inclination angle.These variations are attributed to the combined effects of hydrostatic pressure(overburden load and flow depth)and dynamic pressure(particle collisions and flow velocity).Dimensionless normal impulse decreases with ice content,whereas dimensionless tangential impulse increases,indicating enhanced normal interactions but weakened tangential interactions at higher ice concentrations.The maximum stress and standard deviation of stress both scale linearly with the time-mean stress,confirming that stress fluctuations are governed by bulk flow conditions(density,overburden load).The effective friction coefficientμshows a linear decrease with increasing ice content and a negative correlation with the Froude number Fr.Additionally,the normalized standard deviation of normal stress correlates positively withμ,while that of shear stress correlates negatively,suggesting that normal stress fluctuations from particle-substrate collisions enhance basal friction,whereas tangential fluctuations reduce it.These findings provide quantitative insights into the basal stress dynamics of rock-ice granular flows and establish a basis for improved hazard assessment and mitigation strategies in high-altitude mountain regions.
基金supported by VPP-IZM-Sports-2023/1-0001 innovations,methodologies,and recommendations for the development and management of the sports sector in Latviafunded by the Austrian COMET-Program(project InTribology2,No.906860,project coordinator AC2T research GmbH).
文摘Ice friction is influenced by multiple interconnected parameters between the sliding body and ice,making it a challenging research area in tribology.The motivation for this review lies in the need to understand the parameters affecting ice friction and its relevance to the fields of sport,safety,and various industrial applications.The existing literature on ice friction only partially describes the test methods used.Thus,the comparability of the results and the drawing of conclusions are more challenging.This review addresses this issue by analyzing factors affecting ice friction,including properties of the ice,liquid-like layer,sliding body,and experimental methods.Small-scale rotary,linear,and large-scale laboratory and on-field setups are reviewed,and advantages and limitations are highlighted.The main results indicate that laboratory setups tend to provide more precise control over measurements but may not replicate real-world conditions.On the other hand,large-scale and on-field setups are closer to the actual conditions,but the control over experiments,reproducibility,and implementation is more challenging.The review concludes that future research should focus on comparing different test methods with the possibility of developing standardized protocols and improving large-scale experimental setups.The study aims to enhance the reliability of ice friction research and its practical applications,which should lead to improved safety and performance in the fields where ice friction plays a crucial role.
文摘A systematic approach was presented to develop the empirical model for predicting the ultimate tensile strength of AA5083-H111 aluminum alloy which is widely used in ship building industry by incorporating friction stir welding(FSW) process parameters such as tool rotational speed,welding speed,and axial force.FSW was carried out considering three-factor five-level central composite rotatable design with full replications technique.Response surface methodology(RSM) was applied to developing linear regression model for establishing the relationship between the FSW process parameters and ultimate tensile strength.Analysis of variance(ANOVA) technique was used to check the adequacy of the developed model.The FSW process parameters were also optimized using response surface methodology(RSM) to maximize the ultimate tensile strength.The joint welded at a tool rotational speed of 1 000 r/min,a welding speed of 69 mm/min and an axial force of 1.33 t exhibits higher tensile strength compared with other joints.
基金The authors are grateful for the financial support provided by the National High Technology Research and Development Program of China(863 Program)(No.2002AA331180)Trans-Century Training Program Foundation for the Talents by the Chinese Ministry of Education(No.20030720)+1 种基金the Foundation for Distin-guished Young Scholars of Jilin Province(Grant No.20040104)the Natural Science Foundation of Jilin Province(No.2002628-2).
文摘Five kinds of 45# steel samples with concave features on the surface were manufactured using Laser Texturing Technology (LTT). Optimum design theory was used to design the experiment, and a two-level orthogonal table-L 16 (2 15 ) design was adopted . Micro-wear and micro-friction experienced by samples with concave surface features and samples with smooth surfaces were compared experimentally. The wear resistance of samples with concave surface features was increased most, and different surface morphologies had different effects on friction and wear properties.
文摘Aluminium alloys generally present low weldability by traditional fusion welding process. Development of the friction stir welding （FSW） has provided an alternative improved way of producing aluminium joints in a faster and reliable manner. The quality of a weld joint is stalwartly influenced by process parameter used during welding. An approach to develop a mathematical model was studied for predicting and optimizing the process parameters of dissimilar aluminum alloy （AA6351 T6-AA5083 Hlll）joints by incorporating the FSW process parameters such as tool pin profile, tool rotational speed welding speed and axial force. The effects of the FSW process parameters on the ultimate tensile strength （UTS） of friction welded dissimilar joints were discussed. Optimization was carried out to maximize the UTS using response surface methodology （RSM） and the identified optimum FSW welding parameters were reported.
基金supported by the NIED research project titled‘‘Development of the Earthquake Activity Monitoring and Forecasting,’’the JSPS KAKENHI Grant No.23340131the State Key Laboratory of Earthquake Dynamics,Institute of Geology,CEA(LED2014A06)
文摘This paper reports stick-slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention （NIED）, Tsukuba, Japan. The apparatus consists of the existing shaking table as the shear-loading device up to 3,600 kN, the main frame for holding two large rectangular prismatic specimens with a sliding area of 0.75 m^2 and for applying normal stresses an up to 1.33 MPa, and a reaction force unit holding the stationary specimen to the ground. The shaking table can produce loading rates v up to 1.0 m/s, accelerations up to 9.4 m/s^2, and displacements d up to 0.44 m, using four servocontrolled actuators. We report results from eight preliminary experiments conducted with room humidity on the same gabbro specimens at v = 0.1-100 mm/s and an = 0.66-1.33 MPa, and with d of about 0.39 m. The peak and steady-state friction coefficients were about 0.8 and 0.6, respectively, consistent with the Byerlee friction. The axial force drop or shear stress drop during an abrupt slip is linearly proportional to the amount of displacement, and the slope of this rela- tionship determines the stiffness of the apparatus as 1.15 × 10^8 N/m or 153 MPa/m for the specimens we used. This low stiffness makes fault motion very unstable and the overshooting of shear stress to a negative value was recognized in some violent stick-slip events. An abrupt slip occurred in a constant rise time of 16-18 ms despite wide variation of the stress drop, and an average velocity during an abrupt slip is linearly proportional to the stress drop. The use of a large-scale shaking table has a great potential in increasing the slip rate and total displacement in biaxial friction experiments with large specimens.
基金Supported by the National Natural Science Foundation of China(11472093 and21276056)
文摘Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.
文摘The nucleation process of stick-slip instability was analyzed based on the experimental measurements of strain and fault slip on homogeneous and non-homogeneous faults. The results show that the nucleation process of stick-slip on the homogeneous fault is of weak slip-weakening behavior under constant loading point velocity. The existence of a short "weak segment" on the fault makes slip-weakening phenomenon in nucleation process more obvious, while the existence of a long "weak segment" on the fault makes the nucleation process changed. The nucleation is characterized by accelerating slip in a local region and rapid increase of shear stress along the fault in this case, which is more coincident with the rate and state friction law. During the period when fault is locked, increasing of shear stress causes lateral elastic dilation near the fault, and the rebound of the dilation at the time of instability causes an instantaneous increase of normal stress in the fault plane, which is an important factor making fault be rapidly locked and its strength recovered.
文摘The aluminium alloy AA2219(Al—Cu—Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance.Welding is main fabrication method of AA2219 alloy for manufacturing various engineering components.Friction stir welding(FSW) is a recently developed solid state welding process to overcome the problems encountered in fusion welding.This process uses a non-consumable tool to generate frictional heat on the abutting surfaces.The welding parameters,such as tool pin profile,rotational speed,welding speed and axial force,play major role in determining the microstructure and corrosion resistance of welded joint.The main objective of this work is to develop a mathematical model to predict the corrosion resistance of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters.In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions.Dynamic polarization testing was carried out to determine critical pitting potential in millivolt,which is a criteria for measuring corrosion resistance and the data was used in model.Further the response surface method(RSM) was used to develop the model.The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the friction stir welded AA2219 aluminium alloy joints.
文摘The present study focuses on the development of polymeric friction composites with short carbon fiber, micron and nano-sized fillers, additives with varying weight% in phenol formaldehyde (PF) matrix using hot compression moulding process. The composites prepared with fillers viz. Molybdenum disulfide or Molykote (MK) and multi walled carbon nanotubes (MWCNTs) in carbon fiber reinforced PF matrix is designated as Set-I composites. Inclusion of graphite and nano-clay in carbon fiber reinforced PF matrix is designated as Set-II composites. The prepared composites are tested in Dry sand rubber wheel abrasion wear test rig, following ASTM standards for evaluating the abrasive wear behaviour. From the routine experiments, it was observed that the presence of combined micro and nanofillers i.e. 11.5 wt% MK + 0.5 wt% MWCNTs of Set-I, has shown superior abrasion resistance among the study group. The test results of the Set-I and Set-II composites are analyzed using Taguchi experimental design followed by analysis of variance (ANOVA) to understand the contributions of wear control factors affecting the abrasive wear characteristics. Further, worn surface of selected samples is analyzed using scanning electron micrographs.
