This paper presents a review of how the ductile diaphragm concept was formulated,evaluated,improved,and implemented over time to achieve seismically resilient bridges.A particular emphasis is placed on the most recent...This paper presents a review of how the ductile diaphragm concept was formulated,evaluated,improved,and implemented over time to achieve seismically resilient bridges.A particular emphasis is placed on the most recent work that has provided a more fully,and more widely applicable,version of the concept.The paper also addresses how to design buckling restrained braces used as energy dissipating elements in the longitudinal di-rection of multi-span bridges(simple spans or continuous bridges)as part of the ductile diaphragm concept.In all cases,the objective of the ductile diaphragm concept is to concentrate ductility demands in steel energy dissi-pating elements located at the ends of the superstructure spans to protect the substructure(and rest of the su-perstructure)from damage,to ensure that the bridge can remain open to full traffic immediately following an earthquake.展开更多
Centrifugal casting of ductile iron pipe is a high-temperature,semi-continuous production process.However,conducting laboratory research on the solidification process of centrifugal casting of ductile iron pipe presen...Centrifugal casting of ductile iron pipe is a high-temperature,semi-continuous production process.However,conducting laboratory research on the solidification process of centrifugal casting of ductile iron pipe presents significant challenges.In this study,a novel research method was introduced for investigating the solidification process of ductile iron pipe,namely thermal simulation of ductile iron pipe.Comparative research was conducted on the microstructure and properties of the thermal simulation sample and the ductile iron pipe.The findings indicate that the thermal simulation sample and ductile iron pipe exhibit good heat transfer similarity and microstructure similarity.The difference of cooling rate between thermal simulation sample and ductile pipe is less than 0.24℃·s^(-1),and the difference of microstructure content of free cementite,ferrite,and pearlite is less than 5%.The tensile strength of annealed ductile iron pipe is 466 MPa,with an elongation of 16.1%and a Brinell hardness of 156.5 HBW.In comparison,the tensile strength of annealed thermal simulation sample is 482.0 MPa,with an elongation of 15.5%and a Brinell hardness of 159.0 HBW.These results suggest that the thermal simulation experimental research method is both scientific and feasible,offering an objective,reliable,and cost-effective approach to laboratory research on ductile iron pipe.展开更多
We present a novel approach for calculating the energy budget components during the progressive failure process in cohesive-frictional geomaterials.The energy supplied through external loading can be either stored as ...We present a novel approach for calculating the energy budget components during the progressive failure process in cohesive-frictional geomaterials.The energy supplied through external loading can be either stored as elastic strain energy and plastic energy storage or dissipated through damage growth and irreversible plastic deformation mechanisms.Analytical functions describing energy budget components are derived based on a thermodynamic formulation in geomaterials fracture.The thermodynamically consistent derivation leads to a non-local ductile damage model,which is solved numerically in a non-linear finite element framework.The proposed model captures geomaterial fractures in three benchmark examples,including tensile and biaxial-compressive shear scenarios and slope stability analysis.The aspects of shear fracture propagation and energy budget mechanisms are elaborately investigated,considering different material properties and stochastic distributions.The numerical results are validated against existing experimental data and other analytical methods.The model provides a physics-based understanding of energy budget in geomaterials fracture,leading to advances in ground improvement and other geotechnical supporting systems.展开更多
Under equivalent stiffness conditions,material substitution based on a thin-walled design is crucial for the lightweight of components.Developing high-performance steels with both high-yield strength and excellent duc...Under equivalent stiffness conditions,material substitution based on a thin-walled design is crucial for the lightweight of components.Developing high-performance steels with both high-yield strength and excellent ductility has become a key focus in fields like aerospace and lowaltitude flight.The novel low-density steel presented here exhibits a yield strength of 1000 MPa,which is 2-3 times higher than conventional low-alloy high-strength steels,while maintaining an elongation of about 18.7%.By combining ex-situ experimental characterization with a phase mechanical response model based on the iso-work theory and the von Mises equivalent method,the role of heterogeneous deformation-induced strengthening was revealed.The calculated values align closely with experimental results.This exceptional performance is attributed to a multiphase heterogeneous microstructure,where fresh martensite,bainite/tempered martensite,and deformation-induced martensite act as hard regions.These regions release micro-stresses through inhomogeneous cooperative deformation with soft ferrite,enabling multiple plastic deformation mechanisms and stress concentration relief.This research offers new insights into optimizing microstructures through mechanical metallurgy,which is crucial for producing high-performance,lightweight components.展开更多
Ductile iron pipes,a staple in global urban water supply systems,face a significant challenge in the form of corrosion,which threatens water quality and pipeline integrity.The deterioration mechanism of shrink-age def...Ductile iron pipes,a staple in global urban water supply systems,face a significant challenge in the form of corrosion,which threatens water quality and pipeline integrity.The deterioration mechanism of shrink-age defects on the passivation behavior of ductile iron in simulated concrete pore solution was investi-gated.The results indicated that shrinkage defects increase donor density and reduce the threshold value of chlorine concentration for rupture of ductile iron passion film(CTV)of ductile iron.Defects reduce CTV from 1-1.1 wt.%to 0.36-0.4 wt.%.Because the matrix/graphite around the defect has a higher Volta potential difference,the shrinkage defect preferentially corrodes and induces local corrosion of the sur-rounding matrix,while no significant corrosion was observed in the region away from the defect.High lattice distortion and Si segregation around the shrinkage defect improve the driving force of corrosion in thermodynamics.Furthermore,shrinkage defects elevate the content of Fe(Ⅲ)compounds in the passive film,without compromising its duplex structure.These defects accelerate the nucleation and growth of the passive film,but generate more cation interstitials.This variation of chemical composition of passive film compromises the film’s integrity and protective properties,attributable to a potential mechanism of micro-environmental acidification and the synergistic effects of shrinkage defect-graphite-matrix multiple micro-galvanic couples.展开更多
Metallic materials,although composed of metallic bonds,exhibit a wide range of mechanical properties:some are ductile and deformable,while others undergo a pronounced ductile-to-brittle transition(DBT),displaying cera...Metallic materials,although composed of metallic bonds,exhibit a wide range of mechanical properties:some are ductile and deformable,while others undergo a pronounced ductile-to-brittle transition(DBT),displaying ceramic-like brittle behavior once below a critical temperature.For decades,the dominant mechanism driving the ductile-to-brittle transition of metals-whether dislocation nucleation or dislocation slip-has been a topic of ongoing debate.A new concept of dislocation source efficiency,however,suggests that both processes are complementary and essential for overall ductile deformation.The relative mobility of screw versus edge dislocations dictates the efficiency of dislocation sources,which in turn governs dislocation multiplication and ultimately the material’s ability to plastic deformation.Furthermore,we developed a new model that incorporates factors affecting dislocation activities,such as the initial dislocation density and the number of dislocation sources,offering promising toughening strategies for both metallic structural alloys and ceramics.展开更多
Ductile iron represents an optimal solution for saving material and costs in producing large heavy-section castings in the energy sector.It aimed to investigate the influence of very long solidification time(3,10 and ...Ductile iron represents an optimal solution for saving material and costs in producing large heavy-section castings in the energy sector.It aimed to investigate the influence of very long solidification time(3,10 and 20 h)in different casting zones(casting center and transition zone)on the microstructure and mechanical properties of non-standard heavy-section ferritic ductile iron(EN-GJS-400-15)castings.The different solidification conditions significantly influenced the microstructure(graphite and ferrous matrix).The extent of phenomena such as degenerate graphite,solidification defects,hard carbides,and intergranular pearlitic areas and the microstructural coarsening were proportional to the solidification time and attributable to the combined effect of limited undercooling,solid solution diffusion mechanisms,and segregation phenomena.For comparable solidification time,the transition zone was characterized by larger nodules,comparable nodularity,and lower nodule count than the casting center due to more effective diffusion phenomena during cooling.Moreover,the lower segregation phenomena in the transition zone reduced the amount of pearlite and carbides in the intercellular zones.Hardness was only slightly influenced by the different solidification conditions and did not represent a reliable indicator of the microstructural inhomogeneities.These results are essential to refine casting simulations for producing large ferritic ductile iron castings,considering the wide microstructural variability within non-standard heavy-section castings caused by significantly different solidification conditions.展开更多
This study systematically investigated the effects of graphite nodule parameters,including count,average diameter,and nodularity,on microstructure and mechanical properties of austempered ductile irons(ADIs).The ADI s...This study systematically investigated the effects of graphite nodule parameters,including count,average diameter,and nodularity,on microstructure and mechanical properties of austempered ductile irons(ADIs).The ADI specimens with graphite nodule counts of 212±11 mm^(-2),308±9 mm^(-2),415±10 mm^(-2),and 589±13 mm^(-2) were designated as G-200,G-300,G-400,and G-600,respectively.Results indicate a progressive refinement of graphite with an increase in nodule counts.Specifically,the average nodule diameter decreases from 33.3±1.3μm for G-200 to 17.0±0.7μm for G-600.The nodularity of all samples is above 90%.Furthermore,the nodularity exhibits a corresponding increasing trend with the rise of graphite nodule count in ADIs.Additionally,the volume fraction of the austenite phase in ADIs decreases with an increase in graphite nodule count.The graphite nodule count changes the tensile strength and elongation of ADIs.The specimen G-400 exhibits the ultimate tensile strength of 897±11 MPa and an elongation of 9.8%±0.6%,representing 5.3%and 44.1%improvements respectively compared to G-200.To explore the wear resistance of ADIs with different graphite nodule counts,dry sliding friction and wear test of different samples was carried out at room temperature.At a high load of 25 N,G-400 exhibits superior wear resistance,achieving a 42%reduction in worn volume compared to G-200.Worn micromorphology identifies three primary wear mechanisms:microcutting-dominated abrasive wear,adhesive wear,and fatigue wear.展开更多
In the present research, TTT curve of bainitic ductile iron under the condition of controlled cooling was generated. The cooling rate of grinding ball and its temperature distribution were also measured at the same ti...In the present research, TTT curve of bainitic ductile iron under the condition of controlled cooling was generated. The cooling rate of grinding ball and its temperature distribution were also measured at the same time. It can be concluded that the bainitic zone of TTT curve is separated from the pearlitic zone. As compared to the water-quenching condition, more even cooling rate and temperature distribution can be achieved in the controlled cooling process. The controlled cooling can keep away from pearlitic zone in the high temperature cooling stage and produce similar results to the process of traditional isothermal cooling with a low cooling rate in the low temperature cooling stage.展开更多
As one of the principal failures,ductile fracturing restricts metal forming process.Cockcroft-Latham type fracture criterion is suited for ductile fracture in bulk metal-forming simulation.Finding a way to evaluate th...As one of the principal failures,ductile fracturing restricts metal forming process.Cockcroft-Latham type fracture criterion is suited for ductile fracture in bulk metal-forming simulation.Finding a way to evaluate the ductile fracture criterion（DFC） and identify the relationship between DFC and deformation conditions for a strain-softening material,7075 aluminum alloy;however,it is a non-trivial issue that still needs to be addressed in a greater depth.An innovative approach is brought forth that the compression tests and numerical simulations provide mutual support to evaluate the ductile damage cumulating process and determine the DFC diagram.One of the results shows that for a fixed temperature,the maximum cumulated damage decreases regularly with increasing strain rate.The most important result shows that DFC of 7075 aluminum alloy at temperatures of 573-723 K and strain rates of 0.01-10 s-1 is not a constant but a change in a range of 0.255-0.453,thus it has been defined with varying ductile fracture criterion（VDFC） and characterized by a function of strain rate and temperature.According to VDFC diagram,the exact fracture moment and position during various forming processes will be predicted conveniently,in addition to which,the deformation domains with lower fracture risk corresponding to higher VDFC can be identified.展开更多
A modified MK model combined with ductile fracture criterion（DFC-MK model） is proposed to compute the forming limit diagrams（FLDs） of 5A06-O aluminum alloy sheet at different temperatures.The material constant（C...A modified MK model combined with ductile fracture criterion（DFC-MK model） is proposed to compute the forming limit diagrams（FLDs） of 5A06-O aluminum alloy sheet at different temperatures.The material constant（C） of ductile fracture criterion and initial thickness imperfection parameter（f0） at various temperatures are determined by using a new computing method based on wide sheet bending test.The FLDs at 20 and 200 °C are calculated through the DFC-MK model.The DFC-MK model,which includes the influence of through-thickness normal stress,is written into the subroutine VUMAT embedded in Abaqus/ Explicit.The cylindrical cup hydroforming tests are carried out to verify the model.The results show that compared with experimental observations,the predicted FLDs based on DFC-MK model are more accurate than the conventional MK model;the errors between the simulations and experiments in warm hydroforming are 8.23% at 20 °C and 9.24% at 200 °C,which verify the effectiveness of the proposed model.展开更多
A numerical analysis of mechanical behavior of aluminum alloy sheet under cyclic plastic deformation was investigated.Forming limit at fracture was derived from Cockcroft-Latham ductile damage criterion.The strain pat...A numerical analysis of mechanical behavior of aluminum alloy sheet under cyclic plastic deformation was investigated.Forming limit at fracture was derived from Cockcroft-Latham ductile damage criterion.The strain path of bending center of incremental roller hemming could be accepted as a kind of plane strain bending deformation process.Incremental rope roller hemming could be used to alleviate ductile fracture behavior by changing the stress state of the hemming-effected area.SEM observation on the fracture surface indicates that cyclic plastic deformation affects ductile fracture mechanism.展开更多
In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and ...In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and time） on microstructure and mechanical properties of LZQT500-7 ductile iron dense bars with 172 mm in diameter which were produced by horizontal continuous casting （HCC）. The results show that the major factors influencing the hardness of austempered ductile iron （ADI） are austenitizing temperature and austempering temperature. The fraction of retained austenite increases as the austenitizing and austempering temperatures increase. When austenitizing temperature is low, acicular ferrite and retained austenite can be efifciently obtained by appropriately extending the austenitizing time. The proper austmepering time could ensure enough stability of retained austenite and prevent high carbon austenite decomposition. The optimal mechanical properties of ADI can be achieved with the fol owing process parameters： austenitizing temperature and time are 866 ＆#176;C and 135 min, and austempering temperature and time are 279 ＆#176;C and 135 min, respectively. The microstructure of ADI under the optimal austempering process consists of ifne acicular ferrite and a smal amount of retained austenite, and the hardness, tensile strength, yield strength, elongation and impact toughness of the bars are HBW 476, 1670 MPa, 1428 MPa, 2.93%and 25.7 J, respectively.展开更多
Consistent mechanical and machining properties are essential in many applications where ductile irons offer the most cost-effective way to produce structural parts.In the production of hydraulic rotators,dimensional t...Consistent mechanical and machining properties are essential in many applications where ductile irons offer the most cost-effective way to produce structural parts.In the production of hydraulic rotators,dimensional tolerances are typically 20μm to obtain designated performance.For castings where intermediate strength and ductility is required,it is common knowledge that conventional ferritic-pearlitic ductile irons such as ISO 1083/500-7 show large hardness variations.These are mainly caused by the notoriously varying pearlite content,both at different locations within a part and between parts in the same or different batches.Cooling rate variations due to different wall thickness and position in the molding box,as well as varying amounts of pearlite-stabilizing elements,all contribute to detrimental hardness variations.The obvious remedy is to avoid pearlite formation,and instead obtain the necessary mechanical properties by solution strengthening of the ferritic matrix by increasing silicon content to 3.7wt%-3.8wt%.The Swedish development in this field 1998 resulted in a national standardization as SS 140725,followed in 2004 by ISO 1083/ JS/500-10.Indexator AB decided 2005 to specify JS/500-10 for all new ductile iron parts and to convert all existing parts.Improvements include reduction by 75%in hardness variations and increase by 30%in cutting tool life,combined with consistently better mechanical properties.展开更多
In order to accurately simulate the fine-blanking process, a suitable ductile fracture is significant.So an evaluation strategy based on experimental and corresponding simulation results of tensile, compression, torsi...In order to accurately simulate the fine-blanking process, a suitable ductile fracture is significant.So an evaluation strategy based on experimental and corresponding simulation results of tensile, compression, torsion and fine-blanking test is designed to evaluate five typical ductile fracture criteria, which are widely-used in metal forming process.The stress triaxiality and ductile damage of each test specimen are analyzed.The results show that none of these five criteria is sufficient for all tests.Furthermore, an improved fracture criterion based on Rice and Tracey model, taking the influence of both volume change and shape change of voids into account, is proposed.The characterization of this model for fine-blanking process is easily done by the tensile test and the prediction result shows good.展开更多
A foundry research project has been recently initiated at RTIT in order to better understand the fabrication of as-cast heavy section DI parts meeting high impact energy requirements at low temperatures.The experiment...A foundry research project has been recently initiated at RTIT in order to better understand the fabrication of as-cast heavy section DI parts meeting high impact energy requirements at low temperatures.The experimental castings have the following dimensions 180 mm x 180 mm x 190 mm.The achieved as-cast Charpy impact strengths were as follows:17 J (RT),16 J (-20℃) and 11 J (-40℃).The foundry process,the chemical composition and the microstructure of this experimental casting are compared to the ones of various examples in order to show the detrimental effects of residual elements,microshrinkage and microcarbide on the impact properties.Finally,quality index empirical models (based on casting chemical compositions) are used to analyse the impact tests results.This paper illustrates that an adequate nodule count can contribute to reducing the detrimental effects of the residual elements and microsegregation.展开更多
The wear resistances of austempered ductile iron （ADI） were improved through intxoduction of a new phase （carbide） into the ma- txix by addition of chromium. In the present investigation, low-caxbon-equivalent duc...The wear resistances of austempered ductile iron （ADI） were improved through intxoduction of a new phase （carbide） into the ma- txix by addition of chromium. In the present investigation, low-caxbon-equivalent ductile iron （LCEDI） （CE = 3.06%, and CE represents cax- bon-equivalent） with 2.42% chromium was selected. LCEDI was austeintized at two difl＇erent temperatures （900 and 975~C） a^ld soaked for 1 h and then quenched in a salt bath at 325~C for 0 to 10 h. Samples were analyzed using optical microscopy and X-ray diffraction. Wear tests were carded out on a pin-on-disk-type machine. The efl＇ect of austenization temperature on the wear resistance, impact strength, and the mi- crostructure was evaluated. A stxucture-property correlation based on the observations is established.展开更多
The Tianshan range could have been built by both late Early Paleozoicaccretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture ismarked by Ordovician ophiolitic melange and a Silu...The Tianshan range could have been built by both late Early Paleozoicaccretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture ismarked by Ordovician ophiolitic melange and a Silurian flysch sequence, high-pressure metamorphicrelics, and mylonitized rocks. The Central Tianshan belt could principally be an Ordovician volcanicarc; whereas the South Tianshan belt, a back-arc basin. Macro- and microstructures, along withunconformities, provide some kinematic and chronological constraints on 2-phase ductile deformation.The earlier ductile deformation occurring at ca. 400 Ma was marked by north-verging ductileshearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-facies ductiledeformation, and the later deformation, a dextral strike-slip tectonic process, occurred during theLate Carboniferous-Early Permian. Early Carboniferous molasses were deposited unconformably onpre-Carboniferous metamorphic and ductilely sheared rocks, implying the end of the early orogeny.The large-scale ductile strike-slip along the Aqqikkudug-Weiya zone was possibly caused by thesecond tectonic event, the Hercynian collision between the northern Tarim block and the southernSiberian block. Late Paleozoic granitic magmatism and superimposed structures overprinted this EarlyPaleozoic deformation belt. Results of geometric and kinematic studies suggest that the primaryframework of the Southern-Central Tianshan belt, at least the eastern part of the Tianshan belt, wasbuilt by these two phases of accretion events.展开更多
Abstract The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the ...Abstract The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the Central Tianshan belt in Xinjiang, NW China and is composed of mylonitized Early Palaeozoic greywacke, volcanic rocks, ophiolitic blocks as a mélange complex, HP/LT-type bleuschist blocks and mylonitized Neoproterozoic schist, gneiss and orthogneiss. Nearly vertical mylonitic foliation and sub-horizontal stretching lineation define its strike-slip feature; various kinematic indicators, such as asymmetric folds, non-coaxial asymmetric macro- to micro-structures and C-axis fabrics of quartz grains of mylonites, suggest that it is a dextral strike-slip ductile shear zone oriented in a nearly E-W direction characterized by “flower” strusture with thrusting or extruding across the zone toward the two sides and upright folds with gently plunging hinges. The Aqqikkudug-Weiya zone experienced at least two stages of ductile shear tectonic evolution: Early Palaeozoic north vergent thrusting ductile shear and Late Carboniferous-Early Permian strike-slip deformation. The strike-slip ductile shear likely took place during Late Palaeozoic time, dated at 269±5 Ma by the40Ar/39Ar analysis on neo-muscovites. The strike-slip deformation was followed by the Hercynian violent S-type granitic magmatism. Geodynamical analysis suggests that the large-scale dextral strike-slip ductile shearing is likely the result of intracontinental adjustment deformation after the collision of the Siberian continental plate towards the northern margin of the Tarim continental plate during the Late Carboniferous. The Himalayan tectonism locally deformed the zone, marked by final uplift, brittle layer-slip and step-type thrust faults, transcurrent faults and E-W-elongated Mesozoic-Cenozoic basins.展开更多
A high-angle ductile thrusting deformation with top-to-the-north movement penetratively developed in the Proterozoic-Early Paleozoic metamorphic rocks along the Central East Kunlun belt. The deformed rocks suffered ep...A high-angle ductile thrusting deformation with top-to-the-north movement penetratively developed in the Proterozoic-Early Paleozoic metamorphic rocks along the Central East Kunlun belt. The deformed rocks suffered epidote-amphibolite facies metamorphism. On the basis of our previous study, we present more data in this paper to further support that the ducdle thrust deformation occurred in the later Caledonian and more detailed information about the deformation. A zircon U-Pb concordant age of 446±2.2 Ma of a deformed granodiorite in the ductile thrust zone was obtained and can be interpreted as the lower limit of the deformation. A syntectonically crystallized and also strongly deformed hornblende Ar/ Ar dating gives an Ar/Ar plateau age of 426.5±3.8 Ma, which represents the deformation age. A strongly orientated muscovite gives an Ar/Ar plateau age of 408±1.6Ma, representing the cooling age after the peak temperature, constraining the upper limit of the ductile thrust deformation. This ductile thrust deformation can be interpreted as the result of the closing of the Central East Kunlun archipelago ocean. To the north, Ar/Ar plateau ages of 382.9±0.2 Ma and 386.8±0.8 Ma of muscovite in the deformed Xiaomiao Group represent the uplift cooling ages of deeper rocks after the thrusting movement. The original thrusting foliation has a low angle. A rotation model was put forward to explain the development of the foliation from the original low-angle to present high-angle dipping.展开更多
文摘This paper presents a review of how the ductile diaphragm concept was formulated,evaluated,improved,and implemented over time to achieve seismically resilient bridges.A particular emphasis is placed on the most recent work that has provided a more fully,and more widely applicable,version of the concept.The paper also addresses how to design buckling restrained braces used as energy dissipating elements in the longitudinal di-rection of multi-span bridges(simple spans or continuous bridges)as part of the ductile diaphragm concept.In all cases,the objective of the ductile diaphragm concept is to concentrate ductility demands in steel energy dissi-pating elements located at the ends of the superstructure spans to protect the substructure(and rest of the su-perstructure)from damage,to ensure that the bridge can remain open to full traffic immediately following an earthquake.
基金financially supported by the National Natural Science Foundation of China(52130109)。
文摘Centrifugal casting of ductile iron pipe is a high-temperature,semi-continuous production process.However,conducting laboratory research on the solidification process of centrifugal casting of ductile iron pipe presents significant challenges.In this study,a novel research method was introduced for investigating the solidification process of ductile iron pipe,namely thermal simulation of ductile iron pipe.Comparative research was conducted on the microstructure and properties of the thermal simulation sample and the ductile iron pipe.The findings indicate that the thermal simulation sample and ductile iron pipe exhibit good heat transfer similarity and microstructure similarity.The difference of cooling rate between thermal simulation sample and ductile pipe is less than 0.24℃·s^(-1),and the difference of microstructure content of free cementite,ferrite,and pearlite is less than 5%.The tensile strength of annealed ductile iron pipe is 466 MPa,with an elongation of 16.1%and a Brinell hardness of 156.5 HBW.In comparison,the tensile strength of annealed thermal simulation sample is 482.0 MPa,with an elongation of 15.5%and a Brinell hardness of 159.0 HBW.These results suggest that the thermal simulation experimental research method is both scientific and feasible,offering an objective,reliable,and cost-effective approach to laboratory research on ductile iron pipe.
基金supported by the National Natural Science Foundation of China(Grant No.52179128)the Sand Hazards and Opportunities for Resilience,Energy,and Sustainability(SHORES)Center,funded by Tamkeen under the NYUAD Research Institute Award CG013.
文摘We present a novel approach for calculating the energy budget components during the progressive failure process in cohesive-frictional geomaterials.The energy supplied through external loading can be either stored as elastic strain energy and plastic energy storage or dissipated through damage growth and irreversible plastic deformation mechanisms.Analytical functions describing energy budget components are derived based on a thermodynamic formulation in geomaterials fracture.The thermodynamically consistent derivation leads to a non-local ductile damage model,which is solved numerically in a non-linear finite element framework.The proposed model captures geomaterial fractures in three benchmark examples,including tensile and biaxial-compressive shear scenarios and slope stability analysis.The aspects of shear fracture propagation and energy budget mechanisms are elaborately investigated,considering different material properties and stochastic distributions.The numerical results are validated against existing experimental data and other analytical methods.The model provides a physics-based understanding of energy budget in geomaterials fracture,leading to advances in ground improvement and other geotechnical supporting systems.
基金funded by the National Natural Science Foundation of China(No.51974134)the Innovation Ability Promotion Plan Project of Hebei Province,China(No.24461002D)。
文摘Under equivalent stiffness conditions,material substitution based on a thin-walled design is crucial for the lightweight of components.Developing high-performance steels with both high-yield strength and excellent ductility has become a key focus in fields like aerospace and lowaltitude flight.The novel low-density steel presented here exhibits a yield strength of 1000 MPa,which is 2-3 times higher than conventional low-alloy high-strength steels,while maintaining an elongation of about 18.7%.By combining ex-situ experimental characterization with a phase mechanical response model based on the iso-work theory and the von Mises equivalent method,the role of heterogeneous deformation-induced strengthening was revealed.The calculated values align closely with experimental results.This exceptional performance is attributed to a multiphase heterogeneous microstructure,where fresh martensite,bainite/tempered martensite,and deformation-induced martensite act as hard regions.These regions release micro-stresses through inhomogeneous cooperative deformation with soft ferrite,enabling multiple plastic deformation mechanisms and stress concentration relief.This research offers new insights into optimizing microstructures through mechanical metallurgy,which is crucial for producing high-performance,lightweight components.
基金financially supported by the National Natural Science Foundation of China(Nos.52104319 and 52374323).
文摘Ductile iron pipes,a staple in global urban water supply systems,face a significant challenge in the form of corrosion,which threatens water quality and pipeline integrity.The deterioration mechanism of shrink-age defects on the passivation behavior of ductile iron in simulated concrete pore solution was investi-gated.The results indicated that shrinkage defects increase donor density and reduce the threshold value of chlorine concentration for rupture of ductile iron passion film(CTV)of ductile iron.Defects reduce CTV from 1-1.1 wt.%to 0.36-0.4 wt.%.Because the matrix/graphite around the defect has a higher Volta potential difference,the shrinkage defect preferentially corrodes and induces local corrosion of the sur-rounding matrix,while no significant corrosion was observed in the region away from the defect.High lattice distortion and Si segregation around the shrinkage defect improve the driving force of corrosion in thermodynamics.Furthermore,shrinkage defects elevate the content of Fe(Ⅲ)compounds in the passive film,without compromising its duplex structure.These defects accelerate the nucleation and growth of the passive film,but generate more cation interstitials.This variation of chemical composition of passive film compromises the film’s integrity and protective properties,attributable to a potential mechanism of micro-environmental acidification and the synergistic effects of shrinkage defect-graphite-matrix multiple micro-galvanic couples.
基金supported by the National Natural Science Foundation of China(Grant Nos.51971170 and 51922082)。
文摘Metallic materials,although composed of metallic bonds,exhibit a wide range of mechanical properties:some are ductile and deformable,while others undergo a pronounced ductile-to-brittle transition(DBT),displaying ceramic-like brittle behavior once below a critical temperature.For decades,the dominant mechanism driving the ductile-to-brittle transition of metals-whether dislocation nucleation or dislocation slip-has been a topic of ongoing debate.A new concept of dislocation source efficiency,however,suggests that both processes are complementary and essential for overall ductile deformation.The relative mobility of screw versus edge dislocations dictates the efficiency of dislocation sources,which in turn governs dislocation multiplication and ultimately the material’s ability to plastic deformation.Furthermore,we developed a new model that incorporates factors affecting dislocation activities,such as the initial dislocation density and the number of dislocation sources,offering promising toughening strategies for both metallic structural alloys and ceramics.
文摘Ductile iron represents an optimal solution for saving material and costs in producing large heavy-section castings in the energy sector.It aimed to investigate the influence of very long solidification time(3,10 and 20 h)in different casting zones(casting center and transition zone)on the microstructure and mechanical properties of non-standard heavy-section ferritic ductile iron(EN-GJS-400-15)castings.The different solidification conditions significantly influenced the microstructure(graphite and ferrous matrix).The extent of phenomena such as degenerate graphite,solidification defects,hard carbides,and intergranular pearlitic areas and the microstructural coarsening were proportional to the solidification time and attributable to the combined effect of limited undercooling,solid solution diffusion mechanisms,and segregation phenomena.For comparable solidification time,the transition zone was characterized by larger nodules,comparable nodularity,and lower nodule count than the casting center due to more effective diffusion phenomena during cooling.Moreover,the lower segregation phenomena in the transition zone reduced the amount of pearlite and carbides in the intercellular zones.Hardness was only slightly influenced by the different solidification conditions and did not represent a reliable indicator of the microstructural inhomogeneities.These results are essential to refine casting simulations for producing large ferritic ductile iron castings,considering the wide microstructural variability within non-standard heavy-section castings caused by significantly different solidification conditions.
基金supported by the Science and Technology Project of Hebei Education Department(Grant No.BJK2023075)the Science and Technology Project of Tianjin Education Department(Grant No.2022K1087)the Chunhui Project Foundation of the Education Department of China(Grant No.HZKY20220264).
文摘This study systematically investigated the effects of graphite nodule parameters,including count,average diameter,and nodularity,on microstructure and mechanical properties of austempered ductile irons(ADIs).The ADI specimens with graphite nodule counts of 212±11 mm^(-2),308±9 mm^(-2),415±10 mm^(-2),and 589±13 mm^(-2) were designated as G-200,G-300,G-400,and G-600,respectively.Results indicate a progressive refinement of graphite with an increase in nodule counts.Specifically,the average nodule diameter decreases from 33.3±1.3μm for G-200 to 17.0±0.7μm for G-600.The nodularity of all samples is above 90%.Furthermore,the nodularity exhibits a corresponding increasing trend with the rise of graphite nodule count in ADIs.Additionally,the volume fraction of the austenite phase in ADIs decreases with an increase in graphite nodule count.The graphite nodule count changes the tensile strength and elongation of ADIs.The specimen G-400 exhibits the ultimate tensile strength of 897±11 MPa and an elongation of 9.8%±0.6%,representing 5.3%and 44.1%improvements respectively compared to G-200.To explore the wear resistance of ADIs with different graphite nodule counts,dry sliding friction and wear test of different samples was carried out at room temperature.At a high load of 25 N,G-400 exhibits superior wear resistance,achieving a 42%reduction in worn volume compared to G-200.Worn micromorphology identifies three primary wear mechanisms:microcutting-dominated abrasive wear,adhesive wear,and fatigue wear.
文摘In the present research, TTT curve of bainitic ductile iron under the condition of controlled cooling was generated. The cooling rate of grinding ball and its temperature distribution were also measured at the same time. It can be concluded that the bainitic zone of TTT curve is separated from the pearlitic zone. As compared to the water-quenching condition, more even cooling rate and temperature distribution can be achieved in the controlled cooling process. The controlled cooling can keep away from pearlitic zone in the high temperature cooling stage and produce similar results to the process of traditional isothermal cooling with a low cooling rate in the low temperature cooling stage.
基金Project(2012ZX04010081) supported by the National Key Technologies R & D Program of ChinaProject(cstc2009aa3012-1) supported by the Science and Technology Committee of Chongqing,ChinaProject(CDJZR11130009) supported by the Fundamental Research Funds for the Central Universities,China
文摘As one of the principal failures,ductile fracturing restricts metal forming process.Cockcroft-Latham type fracture criterion is suited for ductile fracture in bulk metal-forming simulation.Finding a way to evaluate the ductile fracture criterion（DFC） and identify the relationship between DFC and deformation conditions for a strain-softening material,7075 aluminum alloy;however,it is a non-trivial issue that still needs to be addressed in a greater depth.An innovative approach is brought forth that the compression tests and numerical simulations provide mutual support to evaluate the ductile damage cumulating process and determine the DFC diagram.One of the results shows that for a fixed temperature,the maximum cumulated damage decreases regularly with increasing strain rate.The most important result shows that DFC of 7075 aluminum alloy at temperatures of 573-723 K and strain rates of 0.01-10 s-1 is not a constant but a change in a range of 0.255-0.453,thus it has been defined with varying ductile fracture criterion（VDFC） and characterized by a function of strain rate and temperature.According to VDFC diagram,the exact fracture moment and position during various forming processes will be predicted conveniently,in addition to which,the deformation domains with lower fracture risk corresponding to higher VDFC can be identified.
基金Project(51175024)supported by the National Natural Science Foundation of China
文摘A modified MK model combined with ductile fracture criterion（DFC-MK model） is proposed to compute the forming limit diagrams（FLDs） of 5A06-O aluminum alloy sheet at different temperatures.The material constant（C） of ductile fracture criterion and initial thickness imperfection parameter（f0） at various temperatures are determined by using a new computing method based on wide sheet bending test.The FLDs at 20 and 200 °C are calculated through the DFC-MK model.The DFC-MK model,which includes the influence of through-thickness normal stress,is written into the subroutine VUMAT embedded in Abaqus/ Explicit.The cylindrical cup hydroforming tests are carried out to verify the model.The results show that compared with experimental observations,the predicted FLDs based on DFC-MK model are more accurate than the conventional MK model;the errors between the simulations and experiments in warm hydroforming are 8.23% at 20 °C and 9.24% at 200 °C,which verify the effectiveness of the proposed model.
基金Project(2010CB731703) supported by the National Basic Research Program of China Project(0804) supported by the Shanghai Automotive Industry Corporation Foundation,ChinaProject(MSV-2010-03) supported by State Key Laboratory of Mechanical System and Vibration,Shanghai Jiao Tong University,China
文摘A numerical analysis of mechanical behavior of aluminum alloy sheet under cyclic plastic deformation was investigated.Forming limit at fracture was derived from Cockcroft-Latham ductile damage criterion.The strain path of bending center of incremental roller hemming could be accepted as a kind of plane strain bending deformation process.Incremental rope roller hemming could be used to alleviate ductile fracture behavior by changing the stress state of the hemming-effected area.SEM observation on the fracture surface indicates that cyclic plastic deformation affects ductile fracture mechanism.
基金financially supported by the fund of the Key Projects of Shaanxi Provincial International Technology Cooperation Plan(2013KW16)the Scientific Research Program funded by Shaanxi Provincial Education Department(2013JK0914)+2 种基金the State Key Laboratory of Solidifi cation Processing in NWPU(SKLSP201115)the Scientific Research Project of Xi'an University of Technology(2013CX004)the fund of the Key Laboratory of Electrical Materials and Infi ltration Technology of Shaanxi Province,China(2014)
文摘In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and time） on microstructure and mechanical properties of LZQT500-7 ductile iron dense bars with 172 mm in diameter which were produced by horizontal continuous casting （HCC）. The results show that the major factors influencing the hardness of austempered ductile iron （ADI） are austenitizing temperature and austempering temperature. The fraction of retained austenite increases as the austenitizing and austempering temperatures increase. When austenitizing temperature is low, acicular ferrite and retained austenite can be efifciently obtained by appropriately extending the austenitizing time. The proper austmepering time could ensure enough stability of retained austenite and prevent high carbon austenite decomposition. The optimal mechanical properties of ADI can be achieved with the fol owing process parameters： austenitizing temperature and time are 866 ＆#176;C and 135 min, and austempering temperature and time are 279 ＆#176;C and 135 min, respectively. The microstructure of ADI under the optimal austempering process consists of ifne acicular ferrite and a smal amount of retained austenite, and the hardness, tensile strength, yield strength, elongation and impact toughness of the bars are HBW 476, 1670 MPa, 1428 MPa, 2.93%and 25.7 J, respectively.
文摘Consistent mechanical and machining properties are essential in many applications where ductile irons offer the most cost-effective way to produce structural parts.In the production of hydraulic rotators,dimensional tolerances are typically 20μm to obtain designated performance.For castings where intermediate strength and ductility is required,it is common knowledge that conventional ferritic-pearlitic ductile irons such as ISO 1083/500-7 show large hardness variations.These are mainly caused by the notoriously varying pearlite content,both at different locations within a part and between parts in the same or different batches.Cooling rate variations due to different wall thickness and position in the molding box,as well as varying amounts of pearlite-stabilizing elements,all contribute to detrimental hardness variations.The obvious remedy is to avoid pearlite formation,and instead obtain the necessary mechanical properties by solution strengthening of the ferritic matrix by increasing silicon content to 3.7wt%-3.8wt%.The Swedish development in this field 1998 resulted in a national standardization as SS 140725,followed in 2004 by ISO 1083/ JS/500-10.Indexator AB decided 2005 to specify JS/500-10 for all new ductile iron parts and to convert all existing parts.Improvements include reduction by 75%in hardness variations and increase by 30%in cutting tool life,combined with consistently better mechanical properties.
基金the National Natural Science Foundation of China (No. 50505027)the Research Fund forthe Doctoral Program of Higher Education of China(No. 20070248056)
文摘In order to accurately simulate the fine-blanking process, a suitable ductile fracture is significant.So an evaluation strategy based on experimental and corresponding simulation results of tensile, compression, torsion and fine-blanking test is designed to evaluate five typical ductile fracture criteria, which are widely-used in metal forming process.The stress triaxiality and ductile damage of each test specimen are analyzed.The results show that none of these five criteria is sufficient for all tests.Furthermore, an improved fracture criterion based on Rice and Tracey model, taking the influence of both volume change and shape change of voids into account, is proposed.The characterization of this model for fine-blanking process is easily done by the tensile test and the prediction result shows good.
文摘A foundry research project has been recently initiated at RTIT in order to better understand the fabrication of as-cast heavy section DI parts meeting high impact energy requirements at low temperatures.The experimental castings have the following dimensions 180 mm x 180 mm x 190 mm.The achieved as-cast Charpy impact strengths were as follows:17 J (RT),16 J (-20℃) and 11 J (-40℃).The foundry process,the chemical composition and the microstructure of this experimental casting are compared to the ones of various examples in order to show the detrimental effects of residual elements,microshrinkage and microcarbide on the impact properties.Finally,quality index empirical models (based on casting chemical compositions) are used to analyse the impact tests results.This paper illustrates that an adequate nodule count can contribute to reducing the detrimental effects of the residual elements and microsegregation.
文摘The wear resistances of austempered ductile iron （ADI） were improved through intxoduction of a new phase （carbide） into the ma- txix by addition of chromium. In the present investigation, low-caxbon-equivalent ductile iron （LCEDI） （CE = 3.06%, and CE represents cax- bon-equivalent） with 2.42% chromium was selected. LCEDI was austeintized at two difl＇erent temperatures （900 and 975~C） a^ld soaked for 1 h and then quenched in a salt bath at 325~C for 0 to 10 h. Samples were analyzed using optical microscopy and X-ray diffraction. Wear tests were carded out on a pin-on-disk-type machine. The efl＇ect of austenization temperature on the wear resistance, impact strength, and the mi- crostructure was evaluated. A stxucture-property correlation based on the observations is established.
基金the supports from the National 973 Project on Westemn China (No.2001CB409804)the National Natural Science Foundation of China (grants 49772151 , 49832040)
文摘The Tianshan range could have been built by both late Early Paleozoicaccretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture ismarked by Ordovician ophiolitic melange and a Silurian flysch sequence, high-pressure metamorphicrelics, and mylonitized rocks. The Central Tianshan belt could principally be an Ordovician volcanicarc; whereas the South Tianshan belt, a back-arc basin. Macro- and microstructures, along withunconformities, provide some kinematic and chronological constraints on 2-phase ductile deformation.The earlier ductile deformation occurring at ca. 400 Ma was marked by north-verging ductileshearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-facies ductiledeformation, and the later deformation, a dextral strike-slip tectonic process, occurred during theLate Carboniferous-Early Permian. Early Carboniferous molasses were deposited unconformably onpre-Carboniferous metamorphic and ductilely sheared rocks, implying the end of the early orogeny.The large-scale ductile strike-slip along the Aqqikkudug-Weiya zone was possibly caused by thesecond tectonic event, the Hercynian collision between the northern Tarim block and the southernSiberian block. Late Paleozoic granitic magmatism and superimposed structures overprinted this EarlyPaleozoic deformation belt. Results of geometric and kinematic studies suggest that the primaryframework of the Southern-Central Tianshan belt, at least the eastern part of the Tianshan belt, wasbuilt by these two phases of accretion events.
文摘Abstract The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the Central Tianshan belt in Xinjiang, NW China and is composed of mylonitized Early Palaeozoic greywacke, volcanic rocks, ophiolitic blocks as a mélange complex, HP/LT-type bleuschist blocks and mylonitized Neoproterozoic schist, gneiss and orthogneiss. Nearly vertical mylonitic foliation and sub-horizontal stretching lineation define its strike-slip feature; various kinematic indicators, such as asymmetric folds, non-coaxial asymmetric macro- to micro-structures and C-axis fabrics of quartz grains of mylonites, suggest that it is a dextral strike-slip ductile shear zone oriented in a nearly E-W direction characterized by “flower” strusture with thrusting or extruding across the zone toward the two sides and upright folds with gently plunging hinges. The Aqqikkudug-Weiya zone experienced at least two stages of ductile shear tectonic evolution: Early Palaeozoic north vergent thrusting ductile shear and Late Carboniferous-Early Permian strike-slip deformation. The strike-slip ductile shear likely took place during Late Palaeozoic time, dated at 269±5 Ma by the40Ar/39Ar analysis on neo-muscovites. The strike-slip deformation was followed by the Hercynian violent S-type granitic magmatism. Geodynamical analysis suggests that the large-scale dextral strike-slip ductile shearing is likely the result of intracontinental adjustment deformation after the collision of the Siberian continental plate towards the northern margin of the Tarim continental plate during the Late Carboniferous. The Himalayan tectonism locally deformed the zone, marked by final uplift, brittle layer-slip and step-type thrust faults, transcurrent faults and E-W-elongated Mesozoic-Cenozoic basins.
文摘A high-angle ductile thrusting deformation with top-to-the-north movement penetratively developed in the Proterozoic-Early Paleozoic metamorphic rocks along the Central East Kunlun belt. The deformed rocks suffered epidote-amphibolite facies metamorphism. On the basis of our previous study, we present more data in this paper to further support that the ducdle thrust deformation occurred in the later Caledonian and more detailed information about the deformation. A zircon U-Pb concordant age of 446±2.2 Ma of a deformed granodiorite in the ductile thrust zone was obtained and can be interpreted as the lower limit of the deformation. A syntectonically crystallized and also strongly deformed hornblende Ar/ Ar dating gives an Ar/Ar plateau age of 426.5±3.8 Ma, which represents the deformation age. A strongly orientated muscovite gives an Ar/Ar plateau age of 408±1.6Ma, representing the cooling age after the peak temperature, constraining the upper limit of the ductile thrust deformation. This ductile thrust deformation can be interpreted as the result of the closing of the Central East Kunlun archipelago ocean. To the north, Ar/Ar plateau ages of 382.9±0.2 Ma and 386.8±0.8 Ma of muscovite in the deformed Xiaomiao Group represent the uplift cooling ages of deeper rocks after the thrusting movement. The original thrusting foliation has a low angle. A rotation model was put forward to explain the development of the foliation from the original low-angle to present high-angle dipping.
