This study developed a digital twin(DT)and structural health monitoring(SHM)system for a balanced cantilever bridge,utilizing advanced measurement techniques to enhance accuracy.Vibration and dynamic strain measuremen...This study developed a digital twin(DT)and structural health monitoring(SHM)system for a balanced cantilever bridge,utilizing advanced measurement techniques to enhance accuracy.Vibration and dynamic strain measurements were obtained using accelerometers and piezo-resistive strain gauges,capturing low-magnitude dynamic strains during operational vibrations.3D-LiDAR scanning and Ultrasonic Pulse Velocity(UPV)tests captured the bridge's as-is geometry and modulus of elasticity.The resulting detailed 3D point cloud model revealed the structure's true state and highlighted discrepancies between the as-designed and as-built conditions.Dynamic properties,including modal frequencies and shapes,were extracted from the strain and acceleration measurements,providing critical insights into the bridge's structural behavior.The neutral axis depth,indicating stress distribution and potential damage,was accurately determined.Good agreement between vibration measurement data and the as-is model results validated the reliability of the digital twin model.Dynamic strain patterns and neutral axis parameters showed strong correlation with model predictions,serving as sensitive indicators of local damage.The baseline digital twin model and measurement results establish a foundation for future bridge inspections and investigations.This study demonstrates the effectiveness of combining digital twin technology with field measurements for real-time monitoring and predictive maintenance,ensuring the sustainability and safety of the bridge infrastructure,thereby enhancing its overall resilience to operational and environmental stressors.展开更多
Dislocation strengthening,as one of the methods to simultaneously enhance the room temperature strength and ductility of alloys,does not achieve the desired strengthening and plasticity effect during elevated-temperat...Dislocation strengthening,as one of the methods to simultaneously enhance the room temperature strength and ductility of alloys,does not achieve the desired strengthening and plasticity effect during elevated-temperature deformation.Here,we report a novel strategy to boost the dislocation multiplication and accumulation during deformation at elevated temperatures through dynamic strain aging(DSA).With the introduction of the rare-earth element Ho in Mg-Y-Zn alloy,Ho atoms diffuse toward dislocations during deformation at elevated temperatures,provoking the DSA effect,which increases the dislocation density significantly via the interactions of mobile dislocations and Ho atoms.The resulting alloy achieves a great enhancement of dislocation hardening and obtains the dual benefits of high strength and good ductility simultaneously at high homologous temperatures.The present work provides an effective strategy to enhancing the strength and ductility for elevated-temperature materials.展开更多
A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in m...A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in material composition and shape design optimization. In the dynamic strain aging（DSA） temperature regime of gray cast iron, micro-dimples with different dimple depth over diameter and surface area density are fabricated on the material surface by laser peening（LP） which is an LST method. Friction behavior and wear mechanism are investigated to evaluate the effects of surface texturing on the tribological performance of specimens under dry conditions. Through LP impacts assisted by DSA, the friction coefficients of the LPed specimens increase noticeably both at room temperature and elevated temperature in comparison to untreated specimens. Moreover, the coefficient of specimen with dimple depth over diameter of 0.03 and surface area density of 30% is up to 0.351 at room temperature, which dramatically rises up to 1.33 times that of untextured specimen and the value is still up to 0.3305 at 400℃ with an increasing ratio of 35% compared to that of untreated specimen. The surface of textured specimen shows better wear resistance compared to untreated specimen. Wear mechanism includes adhesive wear, abrasive wear and oxidation wear. It is demonstrated that LP assisted by DSA can substantially improve wear resistance, raise the friction coefficient as well as its stability of gray cast iron under elevated temperatures. Heat fade and premature wear can be effectively relieved by this surface modification method.展开更多
This study aims to discover the stress-state dependence of the dynamic strain aging(DSA)effect on the deformation and fracture behavior of high-strength dual-phase(DP)steel at different deformation temperatures(25-400...This study aims to discover the stress-state dependence of the dynamic strain aging(DSA)effect on the deformation and fracture behavior of high-strength dual-phase(DP)steel at different deformation temperatures(25-400°C)and reveal the damage mechanisms under these various configurations.To achieve different stress states,predesigned specimens with different geometric features were used.Scanning electron microscopy was applied to analyze the fracture modes(e.g.,dimple or shear mode)and underlying damage mechanism of the investigated material.DSA is present in this DP steel,showing the Portevin-Le Chatelier(PLC)effect with serrated flow behavior,thermal hardening,and blue brittleness phenomena.Results show that the stress state contributes distinctly to the DSA effect in terms of the magnitude of thermal hardening and the pattern of blue brittleness.Either low stress triaxiality or Lode angle parameter promotes DSA-induced blue brittleness.Accordingly,the damage mechanisms also show dependence on the stress states in conjunction with the DSA effect.展开更多
Dynamic strain aging （DSA） effect on SA508-III reactor pressure vessel （RPV） steel was investigated. The SA508-III RPV steel was subjected to tension tests at different strain rates （1.1× 10-5 s-1 and 6.6...Dynamic strain aging （DSA） effect on SA508-III reactor pressure vessel （RPV） steel was investigated. The SA508-III RPV steel was subjected to tension tests at different strain rates （1.1× 10-5 s-1 and 6.6× 10-5 s-1） and different temperatures （500 and 550 ℃） to evaluate the influence of strain rate and temperature on the serrated flow behavior, which is the repetitive and discontinuous yielding phenomenon on the stress-strain curves. The higher temperature leads to the higher density of precipitates, M23C6 carbides and needle-like Mo2C carbides. It was found that the samples under tension test of 6.6 × 10-5 s-1 and 500 ℃ possess superior mechanical properties and mainly show A-type serrations on the tension test curves. Then, the local regress method was used to filter the DSA curves, thus to show the real trend of the curves. It has been found that the less time of interaction between dislocations and precipitates under higher strain rates leads to a higher strength of the sample. The more tiny-stress drops on the 550 ℃ serration curve can be attributed to the hardening phase, M23C6 carbides and needle-like Mo2C carbides. The higher percentage of the small stress drops on the serration curves represents the higher mechanical strength.展开更多
The dynamic strain aging(DSA) behavior was investigated in GH4169 alloy during tensile deforming with electric-pulse current(EPC) at 750 ℃.The results show that DSA is restrained in the alloy when deformed with 40 Hz...The dynamic strain aging(DSA) behavior was investigated in GH4169 alloy during tensile deforming with electric-pulse current(EPC) at 750 ℃.The results show that DSA is restrained in the alloy when deformed with 40 Hz-EPC.The size ofγ " phase inner grains increases obviously and δ phase is facilitated to precipitate on grain boundary in the alloy applied with EPC,due to the promotion effect of EPC on the diffusion and segregation of atoms.Transmission electron microscopy(TEM)results indicate that dislocations can cut through small γ" precipitate with the size of less than 10 nm,while dislocations can only bypass dislocations when γ " precipitate grow up over 20 nm.The growth of precipitates consumes large amounts of atoms as well as the velocity of dislocation increase,which makes dislocations difficult to be pinned.Therefore,when γ" precipitates grow up to a large size more than the critical size of dislocation pinning,DSA is significantly restrained in the alloy after necking deformed with EPC.展开更多
In this paper,a series of static/dynamic tensile tests are performed for glass fiber reinforced plastic(GFRP)composites.Using the combination of high-speed photography and digital image correlation(DIC)technology,true...In this paper,a series of static/dynamic tensile tests are performed for glass fiber reinforced plastic(GFRP)composites.Using the combination of high-speed photography and digital image correlation(DIC)technology,true stress-strain curves in different directions and strain rates are obtained.We also obtained the dynamic failure strain of the material in different directions,which are used to accurately describe the dynamic tensile and failure behavior of the material.The experimental results show that there is a stiffness change point N in three directions under different strain rate(10-3 s-1,10 s-1,100 s-1)tensile conditions.The stiffness before and after N point is recorded as Einitial and Echanged respectively.The values of Echanged in weft direction and warp direction are about 30%to 50%of Einitial,while Echanged in tilt direction is only about 10%of Einitial.The fiber has the highest strength in the weft direction and the tilt direction has the lowest strength.With the combination of high-speed photography and DIC technology,the dynamic failure parameters of different directions under the strain rate of 100 s-1 are obtained.The dynamic failure strains in three directions are 0.245,0.373 and 0.341,respectively.The parameters are verified by impact three-point bending test.These works can more accurately describe the dynamic mechanical behavior of glass fiber reinforced plastic(GFRP)composites and provide reference for the design of GFRP structures.展开更多
Studies were made of the symmetric tensile-compressive low cycle fatigue behaviour and the influence of dynamic strain aging(DSA)pre-treatment of 18-8 austenitic stainless steel. Within the testing amplitude range of ...Studies were made of the symmetric tensile-compressive low cycle fatigue behaviour and the influence of dynamic strain aging(DSA)pre-treatment of 18-8 austenitic stainless steel. Within the testing amplitude range of strain.±0.5 % to±1.5 %,the three processes of cyclic hardening,cyclic saturation and cyclic softening were observed.In the same amplitude of strain,the peak stress of the samples pre-treated by DSA is higher than that of solid-solu- tion and cold working pre-treatment,but no remarkable differences of the fatigue lives of them were found.TEM observation shows that the uniform and stable dislocation networks with high density form after DSA pre-treatment,which increases the cyclic peak stress.The cyclic softening results from the low dislocation density and elongated cell structure with low energy.展开更多
Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The result...Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The results show that the morphology of the β-Mg17Al12 phases during forging process dynamically precipitates and aging process（statically precipitation） exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg17Al12 phases but the grain is still coarse where there is no Mg17Al12 phases. During the aging process, the morphology of newly formed β-Mg17Al12 phases depends on the structural character of the forged sample. The newly precipitated β-Mg17Al12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated β-Mg17Al12 phases are fine granular and needle-like in the area with fine grain.展开更多
Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high...Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization展开更多
In order to investigate the damage and deformation mechanism of large scale steel fixed-roof oil-storage tanks under the combustible gas explosion, a series of explosion experiments of scaled models are conducted. Th...In order to investigate the damage and deformation mechanism of large scale steel fixed-roof oil-storage tanks under the combustible gas explosion, a series of explosion experiments of scaled models are conducted. The l： 25 scaled numerical models of oil-storage tanks with a capacity of 5 000 m3 are also set up by ANSYS/LS-DYNA software, and their damage processes under the blast impact are numerically simulated. Both the experimental results and the numerical simulations show that the blast loading curve displays a pressure jump instantaneously at the moment of contact with the experimental models, and the overpressure peaks at the stagnation area of the outer surface on the blast side. The yield range first appears at the stagnation area and then propagates to the neighboring parts, and the irregular plastic hinge circle obviously appears around the deformation area, which results in the concaved buckling of the tank inner surface. During the whole process, the inner liquid not only impacts on the structures, but also absorbs and consumes part of the blast energy.展开更多
Dynamic strain aging (DSA) is an important phenomenon in solutehardened metals and seri- ously affects the mechanical properties ofmetals. DSA is generally induced by the interaction between themoving dislocations and...Dynamic strain aging (DSA) is an important phenomenon in solutehardened metals and seri- ously affects the mechanical properties ofmetals. DSA is generally induced by the interaction between themoving dislocations and the mobile solute atoms. In this paper, onlythe interaction between moving disloca- tions and mobile solute atomsin a dislocation core area (core atmosphere) will be taken intoaccount. To es- tablish the constitutive model which can describe theDSA phenomenon, we improved the Zerilli-Armstrongdislocation-mechanics-based thermal viscoplastic constitutiverelation, and added the effect of the interaction between the movingdislocations and core atmosphere.展开更多
Application of digital image correlation(DIC) method to determination of in-situ dynamic strain is presented in this study. Firstly, an integrative software is programmed based on the DIC algorithms and pointwise leas...Application of digital image correlation(DIC) method to determination of in-situ dynamic strain is presented in this study. Firstly, an integrative software is programmed based on the DIC algorithms and pointwise least-squares fitting technique. Then, simulated speckle images are generated to study the computational accuracy of this software. The experimental setup and procedures for measuring in-situ dynamic strain through both DIC and strain gauge are proposed. The DIC results are close to those measured by strain gauge. This fact reveals that DIC is a practical and effective tool for in-situ dynamic strain measurement. Finally, the full-field in-situ dynamic strain of another specimen is measured by DIC, and the overall distribution of the strain in the measurement area is clearly shown.展开更多
Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed ...Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.展开更多
The effects of Cu on stacking fault energy,dislocation slip,mechanical twinning,and strain hardening in Fe–20Mn–1.3C twinning-induced plasticity（TWIP） steels were systematically investigated.The stacking fault ene...The effects of Cu on stacking fault energy,dislocation slip,mechanical twinning,and strain hardening in Fe–20Mn–1.3C twinning-induced plasticity（TWIP） steels were systematically investigated.The stacking fault energy was raised with an average slope of 2 mJ/m2 per 1 wt% Cu.The Fe–20Mn–1.3C–3Cu steel exhibited superior tensile properties,with the ultimate tensile strength reached at 2.27 GPa and elongation up to 96.9% owing to the high strain hardening that occurred.To examine the mechanism of this high strain hardening,dislocation density determination by XRD was calculated.The dislocation density increased with the increasing strain,and the addition of Cu resulted in a decrease in the dislocation density.A comparison of the strain-hardening behavior of Fe–20Mn–1.3C and Fe–20Mn–1.3C–3Cu TWIP steels was made in terms of modified Crussard–Jaoul（C–J） analysis and microstructural observations.Especially at low strains,the contributions of all the relevant deformation mechanisms—slip,twinning,and dynamic strain aging—were quantitatively evaluated.The analysis revealed that the dislocation storage was the leading factor to the increase of the strain hardening,while dynamic strain aging was a minor contributor to strain hardening.Twinning,which interacted with the matrix,acted as an effective barrier to dislocation motion.展开更多
The complexity of the loads acting on the offshore wind turbines （OWl＇s） structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model ...The complexity of the loads acting on the offshore wind turbines （OWl＇s） structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model are also summarized. The model is supported on monopile, subjected to different types of dynamic loading using an innovative out of balance mass system to apply cyclic/dynamic loads. The test results show the natural frequency of the wind turbine structure increases with the number of cycles, but with a reduced rate of increase with the accumulation of soil strain level. The change is found to be dependent on the shear strain level in the soil next to the pile which matches with the expectations from the element tests of the soil. The test results were plotted in a non-dimensional manner in order to be scaled to predict the orototvoe conseouences usin~ element tests of a soil usin~ resonant column aoDararus.展开更多
During high speed machining in the field of manufacture,chip formation is a severe plastic deformation process including large strain,high strain rate and high temperature.And the strain rate in high speed cutting pro...During high speed machining in the field of manufacture,chip formation is a severe plastic deformation process including large strain,high strain rate and high temperature.And the strain rate in high speed cutting process can be achieved to 105 s^（-1）.30CrMnSiNi2Asteel is a kind of important high-strength low-alloy structural steel with wide application range.Obtaining the dynamic mechanical properties of30CrMnSiNi2Aunder the conditions of high strain rate and high temperature is necessary to construct the constitutive relation model for high speed machining.The dynamic compressive mechanical properties of30CrMnSiNi2Asteel were studied using split Hopkinson pressure bar（SHPB）tests at 30-700°C and3000-10000s^（-1）.The stress-strain curves of 30CrMnSiNi2Asteel at different temperatures and strain rates were investigated,and the strain hardening effect and temperature effect were discussed.Experimental results show that 30CrMnSiNi2Ahas obvious temperature sensitivity at 300°C.Moreover,the flow stress decreased significantly with the increase of temperature.The strain hardening effect of the material at high strain rate is not significant with the increase of strain.The strain rate hardening effect is obvious with increasing the temperature.According to the experimental results,the established Johnson-Cook（J-C）constitutive model of 30CrMnSiNi2Asteel could be used at high strain rate and high temperature.展开更多
Intermediate temperature embritttement （ITE） is a general phenomenon in Ni alloys and recently was interpreted by dynamic strain aging （DSA）. The relationship between ITE and DSA was studied by a binary Ni-Bi allo...Intermediate temperature embritttement （ITE） is a general phenomenon in Ni alloys and recently was interpreted by dynamic strain aging （DSA）. The relationship between ITE and DSA was studied by a binary Ni-Bi alloy. The experimental alloy of well-controlled purity was produced by vacuum induction inching and then heat-treated properly. Tensile tests were performed at various tensile temperatures, and the elongation at fracture was used to indicate the ductility. In order to identify the mechanisms of fracture and ITE, fracture morphologies of the samples of low ductility were observed by scanning electron microscopy. According to the tensile ductility, Ni-Bi alloy shows an obvious embrittlement behavior in the intermediate temperature range （700--750℃ ）. However, the stress strain curves of Ni-Bi alloy and the fracture morphologies indicate that DSA does not exist over the whole temperature range. Based on the experimental results and literatures, the interpretation of DSA was then discussed and proved to be invalid for elucidating the general feature of ITE in Ni-Bi alloy and Ni-based superalloys.展开更多
Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated f...Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated flow in the tensile stress-strain curves was observed in the temperature range from 300 ℃ to 500 ℃. Normal DSA behavior was found at temperatures ranging from 300 ℃ to 350 ℃, while inverse DSA behavior was observed at temperatures ranging from 400 ℃ to 500 ℃. The yield strength, ultimate tensile strength, elongation, work hardening index, and fracture features were not affected by temperature and strain rates in DSA regime. Negative strain-rate sensitivity of flow stress was observed in DSA regime. The analysis suggests that the ordering of the substitutional solutes around some defects like mobile dislocations and stacking faults due to the thermal activated process may cause the serrations on the tensile curves.展开更多
The dynamic strain aging behavior during tensile tests of K40S alloy has been investigated in the temperature range of 25-1100℃ with the strain rate range from 10-4 to 10-3s-1. The results show that four different ty...The dynamic strain aging behavior during tensile tests of K40S alloy has been investigated in the temperature range of 25-1100℃ with the strain rate range from 10-4 to 10-3s-1. The results show that four different types of serration, identified as A, B, C and E type serration were observed in the temperature range of 300-600℃. The strain exponents for onset of the serrated flow were calculated as 1.21, 2.19 and 1.61, and the activation energies as 121, 40 and 67kJ/mol for E, B and C type serration respectively. The main mechanism for dynamic strain aging discussed in light of the strain exponent and the activation energy.展开更多
基金funded by the Thailand Science Research and Innovation Fund,Chulalongkorn University(BCG_FF_68_165_2100_027)The first author(Tidarut Jirawattanasomkul)also gratefully acknowledges support from the Grants for Development of New Faculty Staff,Ratchadaphiseksomphot Fund,Chulalongkorn University.The corresponding author(Supasit Srivaranun)acknowledges the Research and Innovation Funding from National Research Council of Thailand(No.N84A680208)+2 种基金the Research Grant from Faculty of Engineering,Kasetsart University(No.67/05/CE)The fourth author(Suched Likitlersuang)acknowledges Thailand Science Research and Innovation Fund Chulalongkorn University(DISF68210001)the National Research Council of Thailand(NRCT):Grant No.N42A670572.
文摘This study developed a digital twin(DT)and structural health monitoring(SHM)system for a balanced cantilever bridge,utilizing advanced measurement techniques to enhance accuracy.Vibration and dynamic strain measurements were obtained using accelerometers and piezo-resistive strain gauges,capturing low-magnitude dynamic strains during operational vibrations.3D-LiDAR scanning and Ultrasonic Pulse Velocity(UPV)tests captured the bridge's as-is geometry and modulus of elasticity.The resulting detailed 3D point cloud model revealed the structure's true state and highlighted discrepancies between the as-designed and as-built conditions.Dynamic properties,including modal frequencies and shapes,were extracted from the strain and acceleration measurements,providing critical insights into the bridge's structural behavior.The neutral axis depth,indicating stress distribution and potential damage,was accurately determined.Good agreement between vibration measurement data and the as-is model results validated the reliability of the digital twin model.Dynamic strain patterns and neutral axis parameters showed strong correlation with model predictions,serving as sensitive indicators of local damage.The baseline digital twin model and measurement results establish a foundation for future bridge inspections and investigations.This study demonstrates the effectiveness of combining digital twin technology with field measurements for real-time monitoring and predictive maintenance,ensuring the sustainability and safety of the bridge infrastructure,thereby enhancing its overall resilience to operational and environmental stressors.
基金supported by the National Key Research and Development Project(2023YFA1609100)the NSFC Funding(U2141207,52171111,52001083)+6 种基金Natural Science Foundation of Heilongjiang(YQ2023E026)China Postdoctoral Science foundation(2024M754149)Postdoctoral Fellowship Program of CPSF(GZC20242192)support from the National Science Foundation(DMR-1611180 and 1809640)with the program directors,DrsHKU Seed Fund for Collaborative Research(#2207101618)support by Croucher Senior Research Fellowship and City U Project(Project No.9229019)Shenzhen Science and Technology Program(Project No.JCYJ20220818101203007)。
文摘Dislocation strengthening,as one of the methods to simultaneously enhance the room temperature strength and ductility of alloys,does not achieve the desired strengthening and plasticity effect during elevated-temperature deformation.Here,we report a novel strategy to boost the dislocation multiplication and accumulation during deformation at elevated temperatures through dynamic strain aging(DSA).With the introduction of the rare-earth element Ho in Mg-Y-Zn alloy,Ho atoms diffuse toward dislocations during deformation at elevated temperatures,provoking the DSA effect,which increases the dislocation density significantly via the interactions of mobile dislocations and Ho atoms.The resulting alloy achieves a great enhancement of dislocation hardening and obtains the dual benefits of high strength and good ductility simultaneously at high homologous temperatures.The present work provides an effective strategy to enhancing the strength and ductility for elevated-temperature materials.
基金Supported by National Natural Science Foundation of China(Grant No.51175236)Research Fund for the Doctoral Program of Higher Education of China(Grant No.20123227110022)+1 种基金Industrial Science and Technology Project of Jiangsu Province,China(Grant No.BE2013097)Jiangsu Provincial Innovation Program of Graduated Student of China(Grant No.1011110008)
文摘A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in material composition and shape design optimization. In the dynamic strain aging（DSA） temperature regime of gray cast iron, micro-dimples with different dimple depth over diameter and surface area density are fabricated on the material surface by laser peening（LP） which is an LST method. Friction behavior and wear mechanism are investigated to evaluate the effects of surface texturing on the tribological performance of specimens under dry conditions. Through LP impacts assisted by DSA, the friction coefficients of the LPed specimens increase noticeably both at room temperature and elevated temperature in comparison to untreated specimens. Moreover, the coefficient of specimen with dimple depth over diameter of 0.03 and surface area density of 30% is up to 0.351 at room temperature, which dramatically rises up to 1.33 times that of untextured specimen and the value is still up to 0.3305 at 400℃ with an increasing ratio of 35% compared to that of untreated specimen. The surface of textured specimen shows better wear resistance compared to untreated specimen. Wear mechanism includes adhesive wear, abrasive wear and oxidation wear. It is demonstrated that LP assisted by DSA can substantially improve wear resistance, raise the friction coefficient as well as its stability of gray cast iron under elevated temperatures. Heat fade and premature wear can be effectively relieved by this surface modification method.
基金The authors gratefully acknowledge the valuable comments by Prof.Sebastian Münstermann from Steel Institute(IEHK),RWTH Aachen University,Germany.The work has been supported by the European Commission Research Fund for Coal and Steel(No.709711).Wenqi Liu is grateful to Shujing Li and Guangming Zeng from IEHK for data processing.
文摘This study aims to discover the stress-state dependence of the dynamic strain aging(DSA)effect on the deformation and fracture behavior of high-strength dual-phase(DP)steel at different deformation temperatures(25-400°C)and reveal the damage mechanisms under these various configurations.To achieve different stress states,predesigned specimens with different geometric features were used.Scanning electron microscopy was applied to analyze the fracture modes(e.g.,dimple or shear mode)and underlying damage mechanism of the investigated material.DSA is present in this DP steel,showing the Portevin-Le Chatelier(PLC)effect with serrated flow behavior,thermal hardening,and blue brittleness phenomena.Results show that the stress state contributes distinctly to the DSA effect in terms of the magnitude of thermal hardening and the pattern of blue brittleness.Either low stress triaxiality or Lode angle parameter promotes DSA-induced blue brittleness.Accordingly,the damage mechanisms also show dependence on the stress states in conjunction with the DSA effect.
文摘Dynamic strain aging （DSA） effect on SA508-III reactor pressure vessel （RPV） steel was investigated. The SA508-III RPV steel was subjected to tension tests at different strain rates （1.1× 10-5 s-1 and 6.6× 10-5 s-1） and different temperatures （500 and 550 ℃） to evaluate the influence of strain rate and temperature on the serrated flow behavior, which is the repetitive and discontinuous yielding phenomenon on the stress-strain curves. The higher temperature leads to the higher density of precipitates, M23C6 carbides and needle-like Mo2C carbides. It was found that the samples under tension test of 6.6 × 10-5 s-1 and 500 ℃ possess superior mechanical properties and mainly show A-type serrations on the tension test curves. Then, the local regress method was used to filter the DSA curves, thus to show the real trend of the curves. It has been found that the less time of interaction between dislocations and precipitates under higher strain rates leads to a higher strength of the sample. The more tiny-stress drops on the 550 ℃ serration curve can be attributed to the hardening phase, M23C6 carbides and needle-like Mo2C carbides. The higher percentage of the small stress drops on the serration curves represents the higher mechanical strength.
基金financially supported by the Open Project of State Key Laboratory of Advanced Special Steel,Shanghai Key Laboratory of Advanced Ferrometallurgy,the Shanghai University and the Science and Technology Commission of Shanghai Municipality(No.19DZ2270200)the Open fund of Key Laboratory of Fundamental Science for National Defense of Aeronautical Digital Manufacturing Process(No.SHSYS202003)。
文摘The dynamic strain aging(DSA) behavior was investigated in GH4169 alloy during tensile deforming with electric-pulse current(EPC) at 750 ℃.The results show that DSA is restrained in the alloy when deformed with 40 Hz-EPC.The size ofγ " phase inner grains increases obviously and δ phase is facilitated to precipitate on grain boundary in the alloy applied with EPC,due to the promotion effect of EPC on the diffusion and segregation of atoms.Transmission electron microscopy(TEM)results indicate that dislocations can cut through small γ" precipitate with the size of less than 10 nm,while dislocations can only bypass dislocations when γ " precipitate grow up over 20 nm.The growth of precipitates consumes large amounts of atoms as well as the velocity of dislocation increase,which makes dislocations difficult to be pinned.Therefore,when γ" precipitates grow up to a large size more than the critical size of dislocation pinning,DSA is significantly restrained in the alloy after necking deformed with EPC.
基金the National Department of Science and Technology(Grant 2016YFB1200505).
文摘In this paper,a series of static/dynamic tensile tests are performed for glass fiber reinforced plastic(GFRP)composites.Using the combination of high-speed photography and digital image correlation(DIC)technology,true stress-strain curves in different directions and strain rates are obtained.We also obtained the dynamic failure strain of the material in different directions,which are used to accurately describe the dynamic tensile and failure behavior of the material.The experimental results show that there is a stiffness change point N in three directions under different strain rate(10-3 s-1,10 s-1,100 s-1)tensile conditions.The stiffness before and after N point is recorded as Einitial and Echanged respectively.The values of Echanged in weft direction and warp direction are about 30%to 50%of Einitial,while Echanged in tilt direction is only about 10%of Einitial.The fiber has the highest strength in the weft direction and the tilt direction has the lowest strength.With the combination of high-speed photography and DIC technology,the dynamic failure parameters of different directions under the strain rate of 100 s-1 are obtained.The dynamic failure strains in three directions are 0.245,0.373 and 0.341,respectively.The parameters are verified by impact three-point bending test.These works can more accurately describe the dynamic mechanical behavior of glass fiber reinforced plastic(GFRP)composites and provide reference for the design of GFRP structures.
文摘Studies were made of the symmetric tensile-compressive low cycle fatigue behaviour and the influence of dynamic strain aging(DSA)pre-treatment of 18-8 austenitic stainless steel. Within the testing amplitude range of strain.±0.5 % to±1.5 %,the three processes of cyclic hardening,cyclic saturation and cyclic softening were observed.In the same amplitude of strain,the peak stress of the samples pre-treated by DSA is higher than that of solid-solu- tion and cold working pre-treatment,but no remarkable differences of the fatigue lives of them were found.TEM observation shows that the uniform and stable dislocation networks with high density form after DSA pre-treatment,which increases the cyclic peak stress.The cyclic softening results from the low dislocation density and elongated cell structure with low energy.
基金supported by the National Natural Science Foundation of China (Nos.51204053,51674078 and 51374067)the Fundamental Research Fund for Central Universities (Nos.N160913002,N130409005 and N130209001)A Project supported by Scientific Research Fund of Liaoning Province (No.2015022003)
文摘Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The results show that the morphology of the β-Mg17Al12 phases during forging process dynamically precipitates and aging process（statically precipitation） exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg17Al12 phases but the grain is still coarse where there is no Mg17Al12 phases. During the aging process, the morphology of newly formed β-Mg17Al12 phases depends on the structural character of the forged sample. The newly precipitated β-Mg17Al12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated β-Mg17Al12 phases are fine granular and needle-like in the area with fine grain.
文摘Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization
基金The National Natural Science Foundation of China(No. 51078115)
文摘In order to investigate the damage and deformation mechanism of large scale steel fixed-roof oil-storage tanks under the combustible gas explosion, a series of explosion experiments of scaled models are conducted. The l： 25 scaled numerical models of oil-storage tanks with a capacity of 5 000 m3 are also set up by ANSYS/LS-DYNA software, and their damage processes under the blast impact are numerically simulated. Both the experimental results and the numerical simulations show that the blast loading curve displays a pressure jump instantaneously at the moment of contact with the experimental models, and the overpressure peaks at the stagnation area of the outer surface on the blast side. The yield range first appears at the stagnation area and then propagates to the neighboring parts, and the irregular plastic hinge circle obviously appears around the deformation area, which results in the concaved buckling of the tank inner surface. During the whole process, the inner liquid not only impacts on the structures, but also absorbs and consumes part of the blast energy.
基金the Chinese Academy of Sciences and the High Technical Project.
文摘Dynamic strain aging (DSA) is an important phenomenon in solutehardened metals and seri- ously affects the mechanical properties ofmetals. DSA is generally induced by the interaction between themoving dislocations and the mobile solute atoms. In this paper, onlythe interaction between moving disloca- tions and mobile solute atomsin a dislocation core area (core atmosphere) will be taken intoaccount. To es- tablish the constitutive model which can describe theDSA phenomenon, we improved the Zerilli-Armstrongdislocation-mechanics-based thermal viscoplastic constitutiverelation, and added the effect of the interaction between the movingdislocations and core atmosphere.
基金the National Natural Science Foundation of China(Nos.51575347,51405297 and 51204107)
文摘Application of digital image correlation(DIC) method to determination of in-situ dynamic strain is presented in this study. Firstly, an integrative software is programmed based on the DIC algorithms and pointwise least-squares fitting technique. Then, simulated speckle images are generated to study the computational accuracy of this software. The experimental setup and procedures for measuring in-situ dynamic strain through both DIC and strain gauge are proposed. The DIC results are close to those measured by strain gauge. This fact reveals that DIC is a practical and effective tool for in-situ dynamic strain measurement. Finally, the full-field in-situ dynamic strain of another specimen is measured by DIC, and the overall distribution of the strain in the measurement area is clearly shown.
基金National Natural Science Foundation of China under Grant Nos.51622803 and 51878103China Postdoctoral Science Foundation under Grant No.2021M692689。
文摘Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.
基金financially supported by the Major Project for Industry-University-Research of Fujian Province,China (No.2011H6012)the Natural Science Foundation of Fujian Province,China (No.2011J01292)the Key Project of Fujian Provincial Department of Science and Technology (No.2011H0001)
文摘The effects of Cu on stacking fault energy,dislocation slip,mechanical twinning,and strain hardening in Fe–20Mn–1.3C twinning-induced plasticity（TWIP） steels were systematically investigated.The stacking fault energy was raised with an average slope of 2 mJ/m2 per 1 wt% Cu.The Fe–20Mn–1.3C–3Cu steel exhibited superior tensile properties,with the ultimate tensile strength reached at 2.27 GPa and elongation up to 96.9% owing to the high strain hardening that occurred.To examine the mechanism of this high strain hardening,dislocation density determination by XRD was calculated.The dislocation density increased with the increasing strain,and the addition of Cu resulted in a decrease in the dislocation density.A comparison of the strain-hardening behavior of Fe–20Mn–1.3C and Fe–20Mn–1.3C–3Cu TWIP steels was made in terms of modified Crussard–Jaoul（C–J） analysis and microstructural observations.Especially at low strains,the contributions of all the relevant deformation mechanisms—slip,twinning,and dynamic strain aging—were quantitatively evaluated.The analysis revealed that the dislocation storage was the leading factor to the increase of the strain hardening,while dynamic strain aging was a minor contributor to strain hardening.Twinning,which interacted with the matrix,acted as an effective barrier to dislocation motion.
基金supported by the National Natural Science Foundation of China(51109184,51209183,and 51325901)
文摘The complexity of the loads acting on the offshore wind turbines （OWl＇s） structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model are also summarized. The model is supported on monopile, subjected to different types of dynamic loading using an innovative out of balance mass system to apply cyclic/dynamic loads. The test results show the natural frequency of the wind turbine structure increases with the number of cycles, but with a reduced rate of increase with the accumulation of soil strain level. The change is found to be dependent on the shear strain level in the soil next to the pile which matches with the expectations from the element tests of the soil. The test results were plotted in a non-dimensional manner in order to be scaled to predict the orototvoe conseouences usin~ element tests of a soil usin~ resonant column aoDararus.
基金supported by the National High Technology Research and Development Program of China(2014AA041504)the National Natural Science Foundation of China(51605161)
文摘During high speed machining in the field of manufacture,chip formation is a severe plastic deformation process including large strain,high strain rate and high temperature.And the strain rate in high speed cutting process can be achieved to 105 s^（-1）.30CrMnSiNi2Asteel is a kind of important high-strength low-alloy structural steel with wide application range.Obtaining the dynamic mechanical properties of30CrMnSiNi2Aunder the conditions of high strain rate and high temperature is necessary to construct the constitutive relation model for high speed machining.The dynamic compressive mechanical properties of30CrMnSiNi2Asteel were studied using split Hopkinson pressure bar（SHPB）tests at 30-700°C and3000-10000s^（-1）.The stress-strain curves of 30CrMnSiNi2Asteel at different temperatures and strain rates were investigated,and the strain hardening effect and temperature effect were discussed.Experimental results show that 30CrMnSiNi2Ahas obvious temperature sensitivity at 300°C.Moreover,the flow stress decreased significantly with the increase of temperature.The strain hardening effect of the material at high strain rate is not significant with the increase of strain.The strain rate hardening effect is obvious with increasing the temperature.According to the experimental results,the established Johnson-Cook（J-C）constitutive model of 30CrMnSiNi2Asteel could be used at high strain rate and high temperature.
基金Item Sponsored by National Natural Science Foundation of China(51001011)Fundamental Research Funds for the Central Universities of China(FRF-TP-12-042A)Fok Ying Tong Education Foundation(141043)
文摘Intermediate temperature embritttement （ITE） is a general phenomenon in Ni alloys and recently was interpreted by dynamic strain aging （DSA）. The relationship between ITE and DSA was studied by a binary Ni-Bi alloy. The experimental alloy of well-controlled purity was produced by vacuum induction inching and then heat-treated properly. Tensile tests were performed at various tensile temperatures, and the elongation at fracture was used to indicate the ductility. In order to identify the mechanisms of fracture and ITE, fracture morphologies of the samples of low ductility were observed by scanning electron microscopy. According to the tensile ductility, Ni-Bi alloy shows an obvious embrittlement behavior in the intermediate temperature range （700--750℃ ）. However, the stress strain curves of Ni-Bi alloy and the fracture morphologies indicate that DSA does not exist over the whole temperature range. Based on the experimental results and literatures, the interpretation of DSA was then discussed and proved to be invalid for elucidating the general feature of ITE in Ni-Bi alloy and Ni-based superalloys.
基金partly supported by "Hundred of Talents Projects"the National Basic Research Program (973 Program) of China under grant No. 2010CB631206the National Natural Science Foundation of China (NSFC) under Grant Nos. 51171179, 51128101 and 51271174
文摘Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated flow in the tensile stress-strain curves was observed in the temperature range from 300 ℃ to 500 ℃. Normal DSA behavior was found at temperatures ranging from 300 ℃ to 350 ℃, while inverse DSA behavior was observed at temperatures ranging from 400 ℃ to 500 ℃. The yield strength, ultimate tensile strength, elongation, work hardening index, and fracture features were not affected by temperature and strain rates in DSA regime. Negative strain-rate sensitivity of flow stress was observed in DSA regime. The analysis suggests that the ordering of the substitutional solutes around some defects like mobile dislocations and stacking faults due to the thermal activated process may cause the serrations on the tensile curves.
文摘The dynamic strain aging behavior during tensile tests of K40S alloy has been investigated in the temperature range of 25-1100℃ with the strain rate range from 10-4 to 10-3s-1. The results show that four different types of serration, identified as A, B, C and E type serration were observed in the temperature range of 300-600℃. The strain exponents for onset of the serrated flow were calculated as 1.21, 2.19 and 1.61, and the activation energies as 121, 40 and 67kJ/mol for E, B and C type serration respectively. The main mechanism for dynamic strain aging discussed in light of the strain exponent and the activation energy.
