Vibration fatigue is the main failure mode of compressor blade. Evaluating the vibration stress of blade that leads to cracking is very useful for analysis of vibration fatigue. In this paper, fatigue stress estimatio...Vibration fatigue is the main failure mode of compressor blade. Evaluating the vibration stress of blade that leads to cracking is very useful for analysis of vibration fatigue. In this paper, fatigue stress estimation methods by quantitative fractography were studied through experimental blade and in-service first-stage compressor blade in order to evaluate the initiation vibration stress of in-service blade. The analysis process of initiation vibration stress was established. The evaluating result of vibration stress of in-service blade subjected to centrifugal force and bending vibration stress agrees with aero engine test result. It is shown that the evaluation method can not only evaluate the equivalent fatigue stresses of different crack depths but also yield the initiation equivalent fatigue stress.展开更多
The fracture surface micromorphology in the near-threshold FCG region was studied in LD-10 aluminum alloy and Ti-6Al-4V allov.The SEM examinations reveal that the frac- ture surface of both alloys at low crack growth ...The fracture surface micromorphology in the near-threshold FCG region was studied in LD-10 aluminum alloy and Ti-6Al-4V allov.The SEM examinations reveal that the frac- ture surface of both alloys at low crack growth rates(1×10^(-7)-1×10^(-5)mm/cycle)takes on a cyclic facet appearance.The typical morphologies were either sawtoothedfacets or terraced facets for LD-10 aluminum alloy and isolated island facets for Ti-6Al-4V alloy.The mech- anism of near-threshold fatigue crack growth is explicated on the basis of experimental ob- servations.展开更多
The effects of pre-stress and bending angle on the flex fatigue lifetimes of para-aramids have been studied choosing the Twaron 2000 high performance filament as the studying subject by use of the self-developed flex ...The effects of pre-stress and bending angle on the flex fatigue lifetimes of para-aramids have been studied choosing the Twaron 2000 high performance filament as the studying subject by use of the self-developed flex fatigue apparatus. The fractography of the fatigue-breaking end of the single filaments has been obtained and the fatigue-breaking mechanisms have been analyzed using the LM and SEM. The differences of the fatigue properties and fractography of a variety of high performance fibers such as Kevlar 129, Kevlar 29 and UHMW PE have been discussed.展开更多
The microfractography of transgranular stress corrosion cracking (TSCC) of 70Cu-30Zn a-brass in ammoniacal solution was studied. The observations indicate that on a very microscale, the crack path of TSCC of or-brass ...The microfractography of transgranular stress corrosion cracking (TSCC) of 70Cu-30Zn a-brass in ammoniacal solution was studied. The observations indicate that on a very microscale, the crack path of TSCC of or-brass follows {111} planes. The crack path very often alternates between {111} Planes to result in 'cleavage-like'facet, the usual average orientation of which is {110} with preferential microscopic crack propagation in (100) and (112) directions. The average orientation of wide secondary facets is often close to {100}. The size of {111} microfacets increases with incrmsing stress intensity K, which indicates that the microscopic crack path follows {111} planes on which some localized slip has occurred. Possible TSCC mechanisms which appear to be consistent with the microfraphic features observed in the present study are also discussed.展开更多
Bulk metallic glasses（BMGs）have attracted considerable attention in the last few decades particularly triggered by their potential applications as novel structural and/or functional materials,owing to their superior...Bulk metallic glasses（BMGs）have attracted considerable attention in the last few decades particularly triggered by their potential applications as novel structural and/or functional materials,owing to their superior strength,large elastic strain limit and relatively low Young′s modulus etc.compared to their crystalline counterparts.Here,a 3Dreconstruction application to the fractography and the morphology of shear bands was reported for a ductile Zr_（56）Co_（28）Al_（16）（at.%）BMG through a Phenom series desktop scanning electron microscope.The results of the 3Dreconstruction and the following contour analysis indicate a typical shear fracture mode for the investigated alloy.It is inferred that the fractography and the morphology of shear bands might be dependent on their composition,structure states,and loading conditions for BMGs.展开更多
The topographical features of fractured tensile, flexural, K<sub>1C</sub>, and impact specimens of monolithic epoxy have been studied and correlated with mechanical properties and surface features of sampl...The topographical features of fractured tensile, flexural, K<sub>1C</sub>, and impact specimens of monolithic epoxy have been studied and correlated with mechanical properties and surface features of samples before fracture. The topographical features studied include waviness (W<sub>a</sub>), roughness average (R<sub>a</sub>), root mean square value (R<sub>q</sub>), and maximum roughness height (R<sub>max</sub> or R<sub>z</sub>). As surface notches generate triaxial state of stress, therefore, the crack propagation is precipitated resulting in catastrophic failure. Although surfaces can be examined before fracture for any deleterious topographical elements, however, fractured surfaces can reveal finer details about the topography. It is because, as discussed in this article, surfaces with specific topography produce fracture patterns of peculiar aesthetics, and if delved deeper, they can further be used to estimate about the topography of surfaces before fracture. In addition, treating the samples with surfaces of specific topography can help improve the mechanical properties of monolithic epoxy.展开更多
The stiff and fragile structure of thermosetting polymers, such as epoxy, accomplices the innate cracks to cause fracture and therefore the applications of monolithic epoxy are not ubiquitous. However, it is well esta...The stiff and fragile structure of thermosetting polymers, such as epoxy, accomplices the innate cracks to cause fracture and therefore the applications of monolithic epoxy are not ubiquitous. However, it is well established that when reinforced especially by nano-fillers, its ability to withstand crack propagation is propitiously improved. The crack is either deflected or bifurcated when interacting with strong nano-filler such as Multi-Layer Graphene (MLG). Due to the deflection and bifurcation of cracks, specific fracture patterns are observed. Although these fracture patterns seem aesthetically appealing, however, if delved deeper, they can further be used to estimate the influence of nano-filler on the mechanical properties. Here we show that, by a meticulous examination of topographical features of fractured patterns, various important aspects related to fillers can be approximated such as dispersion state, interfacial interactions, presence of agglomerates, and overall influence of the incorporation of filler on the mechanical properties of nanocomposites.展开更多
A combination of hard(SiCP)and soft(fly ash)particulate reinforcements could be a strategy to enhance combination of multiple properties of Magnesium and its alloys which otherwise suffer from low stiffness,low wear r...A combination of hard(SiCP)and soft(fly ash)particulate reinforcements could be a strategy to enhance combination of multiple properties of Magnesium and its alloys which otherwise suffer from low stiffness,low wear resistance,and many other critical properties.However,at present a comprehensive and robust map correlating different properties in particle-reinforced composites is much lacking.In this work,an industrial grade AZ91 magnesium alloy reinforced with hard SiC and soft fly ash particles(with 3 vol.%each),has been prepared using stir casting followed by hot extrusion at 325℃with a ratio of 21.5.Microstructure of the hybrid composite was characterized using optical and scanning electron microscopes.The composite exhibited a reduction in average grain size from 13.6 to 7.1μm,concomitantly an increase in Vickers hardness from 73 to 111 HV.The tension-compression yield asymmetry ratios of the unreinforced alloy and hybrid composite were 1.165 and 0.976,respectively indicating higher yield strength for the composite under compressive load.The composite exhibited 76%improvement in damping capacity under time sweep mode,and 28%improvement at 423 K under temperature sweep mode.The tribological characteristics of the composite under dry sliding conditions at sliding speeds and loads in the range of 0.5 to 1.5 m s^(-1)and 10 to 30 N,respectively showed higher wear resistance than the unreinforced alloy.The composite showed 23%improvement in sliding wear resistance at a load of 20 N and a speed of 1 m s^(-1).Finally,efforts have been made to understand the influence of one property on the other by developing statistical property correlation maps from the properties obtained in this study and from the literature.These maps are expected to help in the design of hybrid Metal Matrix Composites for a variety of targeted applications in different sectors.展开更多
Rotary friction welding is a highly effective solid-state technique for joining dissimilar materials,which offers the potential for significant weight reduction without compromising strength.Traditionally,during rotar...Rotary friction welding is a highly effective solid-state technique for joining dissimilar materials,which offers the potential for significant weight reduction without compromising strength.Traditionally,during rotary friction welding,the severely deformed material,or flash,is expelled from the interface and machined away to achieve the desired joint geometry.However,this work introduces a novel approach:trapping the flash within the joint to improve joint properties.The study investigates two different interface geometry combinationsdflat-flat and flat-taper interfaces.Previous research shows that Ni interlayer between steel and titanium can enhance the joint strength.This study builds on the existing knowledge(effect of Ni interlayer)by examining the influence of interface geometry to further improve the dissimilar joint performance.The experimental results,including tensile testing and microstructural characterization,highlight the superior performance of the flat-taper interface.The modified geometry minimizes flash loss,providing a cavity that retains both the flash and the Ni interlayer within the joint.This retention promotes dynamic recrystallization,resulting in refined grain structures near the interface.Moreover,the trapped Ni interlayer effectively prevents the formation of brittle Fe-Ti intermetallic compounds at the dissimilar material interface.The findings reveal that the flat-taper interface improved joint strength by an impressive 105%compared to the flat-flat interface.This innovative geometry modification demonstrates the potential to enhance mechanical properties of dissimilar joints through better flash and interlayer management.展开更多
Titanium/magnesium alloy bimetal composites show promising prospects for lightweight applications.The Ti/Mg bimetal composite was fabricated in Ti−6Al−4V pyramidal lattice structure via AZ91D melt infiltration.Compara...Titanium/magnesium alloy bimetal composites show promising prospects for lightweight applications.The Ti/Mg bimetal composite was fabricated in Ti−6Al−4V pyramidal lattice structure via AZ91D melt infiltration.Comparative analysis of the tensile and compressive properties was conducted between the composite and its constituent materials(Ti−6Al−4V lattice structure and AZ91D matrix).The tensile strength of the composite(95.9 MPa)was comparable to that of the Ti−6Al−4V lattice structure(94.4 MPa)but lower than that of the AZ91D alloy(120.8 MPa)due to gaps at the bimetal interfaces hindering load transfer during tension.The composite exhibited greater elongation(1.7%)compared to AZ91D(1.4%)alloy but less than the Ti−6Al−4V lattice structure(2.6%).The compressive performance of the composite outperformed that of the Ti−6Al−4V lattice structure,underscoring the significance of the AZ91D alloy in compressive deformation.Fracture analysis indicated that the predominant failure reasons in both the composite and lattice structures were attributed to the breakage of lattice struts at nodes caused by the stress concentration.展开更多
In this study, austenitic stainless steel(ASS) was additively fabricated by an arc-based direct energy deposition(DED) technique. Macrostructure, microstructure, mechanical characteristics at different spatial orienta...In this study, austenitic stainless steel(ASS) was additively fabricated by an arc-based direct energy deposition(DED) technique. Macrostructure, microstructure, mechanical characteristics at different spatial orientations(0°, 90°, and 45°), and wear characteristics were evaluated at the deposited structure top, middle, and bottom regions. Results show that austenite(γ) and delta-ferrite(δ) phases make up most of the microstructure of additively fabricated SS316LSi steel. Within γ matrix, δ phase is dispersed both(within and along) grain boundaries, exhibiting a fine vermicular morphology. The bottom, middle,and top regions of WAAM deposited ASS exhibit similar values to those of wrought SS316L in the tensile and impact test findings. Notably, a drop in hardness values is observed as build height increases. During SEM examinations of fractured surfaces from tensile specimen, closed dimples were observed, indicating good ductility of as-built structure. Wear test findings show signs of mild oxidation and usual adhesive wear. By depositing a mechanically mixed composite layer, an increase in the oxidation percentage was discovered to facilitate healing of worn surfaces. The findings of this study will help in design, production and renovation of products/components that are prone to wear. WAAM-deposited ASS has remarkable strength and ability to withstand impacts;it can be used in the production of armour plates for defence applications, mainly military vehicles and aircraft.展开更多
The effect of platinum(a rare metal)-aluminide coating parameters on the tensile properties of nickel-based superalloy Rene■80 was evaluated at 871℃.For this purpose,initial layers of platinum with different thickne...The effect of platinum(a rare metal)-aluminide coating parameters on the tensile properties of nickel-based superalloy Rene■80 was evaluated at 871℃.For this purpose,initial layers of platinum with different thicknesses(2,4,6 and 8μm)were coated on tensile samples Then,low-temperature high-activity(LTHA)and hightemperature low-activity(HTLA)processes were used for aluminizing.Results of microstructural evaluations using scanning electron microscope(SEM)and phase analysis by X-ray diffraction(XRD)showed a three-layer structure coating for different platinum layer thicknesses and both aluminizing processes.Increasing the thickness of the platinum layer from 2 to 8μm led to the improvement in the final coating thickness from 91.6 to 102.1μm in HTLA.This increase was from 128.1 to 148.6μm in LTHA.The results of hot tensile tests at 871℃ showed a decrease in strength properties of the coated samples compared to the uncoated ones.However,HTLA and high thicknesses of the initial platinum layer showed an intense reduction.The results of fractographic evaluations abou uncoated samples showed a ductile fracture.On the other hand,coated samples showed a simultaneous ductile and brittle fracture failure mechanism.But the main fracture morphology was brittle cleavage fracture which was for the HTLA.展开更多
The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4,11)Al(wt.%)low-density steels.Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum(Al)alloyi...The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4,11)Al(wt.%)low-density steels.Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum(Al)alloying control.Meanwhile,microstructure evolution and fracture morphology were investigated by X-ray diffraction(XRD),a scanning electron microscope(SEM)equipped with electron backscatter diffraction(EBSD),a transmission electron microscope(TEM),and a stereo-optical microscope(OM).It is found that the Al addition obviously promotes the dislocation planar slipping,resulting in cleavage and brittle impact fracture in 11wt.%Al steel.Besides,the microband-induced plasticity(MBIP)mechanism is found in 4wt.%Al containing steel,introducing considerable work hardening capacity and impact toughness of 156.8±17.4 J.The present study provides a direct illustration of the relationship between work hardening and impact toughness behaviors of these two low-density steels for potential application as impact-resistant components.展开更多
A comprehensive understanding of the failure behavior and mechanism of coal is a prerequisite for dealing with dynamic problems in mining space.In this study,the failure behavior and mechanism of coal under uniaxial d...A comprehensive understanding of the failure behavior and mechanism of coal is a prerequisite for dealing with dynamic problems in mining space.In this study,the failure behavior and mechanism of coal under uniaxial dynamic compressive loads were experimentally and numerically investigated.The experiments were conducted using a split Hopkinson pressure bar(SHPB)system.The results indicated that the typical failure of coal is lateral and axial at lower loading rates and totally smashed at higher loading rates.The further fractography analysis of lateral and axial fracture fragments indicated that the coal failure under dynamic compressive load is caused by tensile brittle fracture.In addition,the typical failure modes of coal under dynamic load were numerically reproduced.The numerical results indicated that the axial fracture is caused directly by the incident compressive stress wave and the lateral fracture is caused by the tensile stress wave reflected from the interface between coal specimen and transmitted bar.Potential application was further conducted to interpret dynamic problems in underground coal mine and it manifested that the lateral and axial fractures of coal constitute the parallel cracks in the coal mass under roof fall and blasting in mining space.展开更多
Gigacycle fatigue behavior of 60Si2CrVA high strength spring steel was investigated by ultrasonic fatigue test machine. Fatigue fractography was observed by scanning electron microscopy （SEM）. Maximum inclusion size...Gigacycle fatigue behavior of 60Si2CrVA high strength spring steel was investigated by ultrasonic fatigue test machine. Fatigue fractography was observed by scanning electron microscopy （SEM）. Maximum inclusion sizes and fatigue strength in different volumes were estimated by statistics of extreme values （SEV） and generalized Pareto distribution （GPD） methods. The results showed that S N curves of 60Si2CrVA spring steels for two rolling processes were not horizontal asymptotes but a gradient in a regime of 109 cycles, and traditional fatigue limits were eliminated. Surface machined topography and inclusions in steel were major factors that led to elimination of fatigue limit for 60Si2CrVA spring steel. The SEV and GPD methods could effectively predict size of the maximum inclusion and fatigue strength in different volumes of 60Si2CrVA spring steel. Predicted fatigue strength was in accordance with experimental results by ultrasonic fatigue testing.展开更多
In the present study, an Al/Cu/Mg multi-layered composite was produced by accumulative roll bonding(ARB) through seven passes, and its microstructure and mechanical properties were evaluated. The microstructure invest...In the present study, an Al/Cu/Mg multi-layered composite was produced by accumulative roll bonding(ARB) through seven passes, and its microstructure and mechanical properties were evaluated. The microstructure investigations show that plastic instability occurred in both the copper and magnesium reinforcements in the primary sandwich. In addition, a composite with a perfectly uniform distribution of copper and magnesium reinforcing layers was produced during the last pass. By increasing the number of ARB cycles, the microhardness of the layers including aluminum, copper, and magnesium was significantly increased. The ultimate tensile strength of the sandwich was enhanced continually and reached a maximum value of 355.5 MPa. This strength value was about 3.2, 2, and 2.1 times higher than the initial strength values for the aluminum, copper, and magnesium sheets, respectively. Investigation of tensile fracture surfaces during the ARB process indicated that the fracture mechanism changed to shear ductile at the seventh pass.展开更多
A high performance thermosetting epoxy resin crosslinkable at room temperature was obtained via directly moulding diglycidyl ether of bisphenol A（DGEBA） and flexibleα,ω-bisamino（n-alkylene）phenyl terminated poly...A high performance thermosetting epoxy resin crosslinkable at room temperature was obtained via directly moulding diglycidyl ether of bisphenol A（DGEBA） and flexibleα,ω-bisamino（n-alkylene）phenyl terminated poly（ethylene glycol）.The influences of the n-alkylene inserted in aminophenyl of flexible amino-terminated polythers（ATPE） on the mechanical properties,fractographs and curing kinetics of the ATPE-DGEBA cured products were studied.The results show that the insertion of n-alkylene group into the aminophenyl group of the ATPE,on one hand,can significantly increase the strain relaxation rate and decrease glass transition temperature of the ATPE-DGEBA cured products,resulting in slight decrease of the Young’s modulus and tensile strength,and significant increase of the toughness and elongation of the ATPE-DGEBA cured products.On the other hand,it can remarkably enhance the reactivity of amine with epoxy,much accelerating the curing rate of the ATPE-DGEBA systems.The activation energy of DGEBA cured by BAPTPE,BAMPTPE and BAEPTPE was 53.1,28.5 and 25.4 kJ·mol;,respectively.The as-obtained ATPE-DGEBA cured products are homogeneous, transparent,and show excellent mechanical properties including tensile strength and toughness.Thus they are promising to have important applications in structure adhesives,casting bulk materials,functional coatings,cryogenic engineering, damping and sound absorbing materials.展开更多
Magnesium alloy(AZ91D)composites reinforced with silicon carbide particle with different volume percentage were fabricated by two step stir casting process.The effect of changes in particle size and volume fraction of...Magnesium alloy(AZ91D)composites reinforced with silicon carbide particle with different volume percentage were fabricated by two step stir casting process.The effect of changes in particle size and volume fraction of SiC particles on physical and mechanical properties of composites were evaluated under as cast and heat treated(T6)conditions.The experimental results were compared with the standard theoretical models.The results reveal that the mechanical properties of composites increased with increasing SiC particles and decrease with increasing particle size.Distribution of particles and fractured surface were studied through SEM and the presence of elements is revealed by EDS study.展开更多
As promising light-weight and high-performance structure components, large-diameter thin-walled （LDTW） Ti 6Al^4V titanium alloy （TC4） bent tubes are needed most urgently in many industries such as aviation and aer...As promising light-weight and high-performance structure components, large-diameter thin-walled （LDTW） Ti 6Al^4V titanium alloy （TC4） bent tubes are needed most urgently in many industries such as aviation and aerospace. Warm bending may be a feasible way for manufacturing these components. Understanding their temperature and strain rate dependent tensile behavior is the foundation for formability improvement and warm bending design. In this paper, uniaxial ten- sile tests were conducted at elevated temperatures ranging from 298 K to 873 K at tensile velocities of 2, 10, 15 mm/min. The main results show that the tensile behavior of LDTW TC4 tubes is dif- ferent from that of TC4 sheets. The typical elongation of TC4 tubes at room temperature is 10% lower than that of TC4 sheets. The flow stress of TC4 tubes decreases greatly by about 50% with the temperature rising to 873 K. At temperatures of 573-673 K, the hardening exponent is at its highest value, which means the deformation mechanism changes from twining to more dislocation movement by slipping. The fracture elongation of TC4 tubes fluctuates with increasing temperature, which is associated with changes in the deformation mechanism and with the blue brittleness. The fractography of TC4 tubes at various temperatures, especially at 673 K, shows that second phases and impurities significantly influence fracture elongation. By considering the characteristics of the tensile behavior and by properly choosing the die material, the warm bending for TC4 tubes can be achieved at temperatures of 723-823 K.展开更多
基金financially supported by Equipment Advance Research Fund of China (No. 9140A1211HK51)
文摘Vibration fatigue is the main failure mode of compressor blade. Evaluating the vibration stress of blade that leads to cracking is very useful for analysis of vibration fatigue. In this paper, fatigue stress estimation methods by quantitative fractography were studied through experimental blade and in-service first-stage compressor blade in order to evaluate the initiation vibration stress of in-service blade. The analysis process of initiation vibration stress was established. The evaluating result of vibration stress of in-service blade subjected to centrifugal force and bending vibration stress agrees with aero engine test result. It is shown that the evaluation method can not only evaluate the equivalent fatigue stresses of different crack depths but also yield the initiation equivalent fatigue stress.
文摘The fracture surface micromorphology in the near-threshold FCG region was studied in LD-10 aluminum alloy and Ti-6Al-4V allov.The SEM examinations reveal that the frac- ture surface of both alloys at low crack growth rates(1×10^(-7)-1×10^(-5)mm/cycle)takes on a cyclic facet appearance.The typical morphologies were either sawtoothedfacets or terraced facets for LD-10 aluminum alloy and isolated island facets for Ti-6Al-4V alloy.The mech- anism of near-threshold fatigue crack growth is explicated on the basis of experimental ob- servations.
文摘The effects of pre-stress and bending angle on the flex fatigue lifetimes of para-aramids have been studied choosing the Twaron 2000 high performance filament as the studying subject by use of the self-developed flex fatigue apparatus. The fractography of the fatigue-breaking end of the single filaments has been obtained and the fatigue-breaking mechanisms have been analyzed using the LM and SEM. The differences of the fatigue properties and fractography of a variety of high performance fibers such as Kevlar 129, Kevlar 29 and UHMW PE have been discussed.
文摘The microfractography of transgranular stress corrosion cracking (TSCC) of 70Cu-30Zn a-brass in ammoniacal solution was studied. The observations indicate that on a very microscale, the crack path of TSCC of or-brass follows {111} planes. The crack path very often alternates between {111} Planes to result in 'cleavage-like'facet, the usual average orientation of which is {110} with preferential microscopic crack propagation in (100) and (112) directions. The average orientation of wide secondary facets is often close to {100}. The size of {111} microfacets increases with incrmsing stress intensity K, which indicates that the microscopic crack path follows {111} planes on which some localized slip has occurred. Possible TSCC mechanisms which appear to be consistent with the microfraphic features observed in the present study are also discussed.
基金supported by National Natural Science Foundation of China(51301078,51461026and51671120)the Specialized Research Fund for the Doctoral Program of Higher Education of China(20135314120002)+1 种基金the Scientific Research Foundation of Department of Education,Yunnan(2017YJS059)the Young Talents Support Program of Faculty of Materials Science and Engineering,Kunming University of Science and Technology(20140102)
文摘Bulk metallic glasses（BMGs）have attracted considerable attention in the last few decades particularly triggered by their potential applications as novel structural and/or functional materials,owing to their superior strength,large elastic strain limit and relatively low Young′s modulus etc.compared to their crystalline counterparts.Here,a 3Dreconstruction application to the fractography and the morphology of shear bands was reported for a ductile Zr_（56）Co_（28）Al_（16）（at.%）BMG through a Phenom series desktop scanning electron microscope.The results of the 3Dreconstruction and the following contour analysis indicate a typical shear fracture mode for the investigated alloy.It is inferred that the fractography and the morphology of shear bands might be dependent on their composition,structure states,and loading conditions for BMGs.
文摘The topographical features of fractured tensile, flexural, K<sub>1C</sub>, and impact specimens of monolithic epoxy have been studied and correlated with mechanical properties and surface features of samples before fracture. The topographical features studied include waviness (W<sub>a</sub>), roughness average (R<sub>a</sub>), root mean square value (R<sub>q</sub>), and maximum roughness height (R<sub>max</sub> or R<sub>z</sub>). As surface notches generate triaxial state of stress, therefore, the crack propagation is precipitated resulting in catastrophic failure. Although surfaces can be examined before fracture for any deleterious topographical elements, however, fractured surfaces can reveal finer details about the topography. It is because, as discussed in this article, surfaces with specific topography produce fracture patterns of peculiar aesthetics, and if delved deeper, they can further be used to estimate about the topography of surfaces before fracture. In addition, treating the samples with surfaces of specific topography can help improve the mechanical properties of monolithic epoxy.
文摘The stiff and fragile structure of thermosetting polymers, such as epoxy, accomplices the innate cracks to cause fracture and therefore the applications of monolithic epoxy are not ubiquitous. However, it is well established that when reinforced especially by nano-fillers, its ability to withstand crack propagation is propitiously improved. The crack is either deflected or bifurcated when interacting with strong nano-filler such as Multi-Layer Graphene (MLG). Due to the deflection and bifurcation of cracks, specific fracture patterns are observed. Although these fracture patterns seem aesthetically appealing, however, if delved deeper, they can further be used to estimate the influence of nano-filler on the mechanical properties. Here we show that, by a meticulous examination of topographical features of fractured patterns, various important aspects related to fillers can be approximated such as dispersion state, interfacial interactions, presence of agglomerates, and overall influence of the incorporation of filler on the mechanical properties of nanocomposites.
文摘A combination of hard(SiCP)and soft(fly ash)particulate reinforcements could be a strategy to enhance combination of multiple properties of Magnesium and its alloys which otherwise suffer from low stiffness,low wear resistance,and many other critical properties.However,at present a comprehensive and robust map correlating different properties in particle-reinforced composites is much lacking.In this work,an industrial grade AZ91 magnesium alloy reinforced with hard SiC and soft fly ash particles(with 3 vol.%each),has been prepared using stir casting followed by hot extrusion at 325℃with a ratio of 21.5.Microstructure of the hybrid composite was characterized using optical and scanning electron microscopes.The composite exhibited a reduction in average grain size from 13.6 to 7.1μm,concomitantly an increase in Vickers hardness from 73 to 111 HV.The tension-compression yield asymmetry ratios of the unreinforced alloy and hybrid composite were 1.165 and 0.976,respectively indicating higher yield strength for the composite under compressive load.The composite exhibited 76%improvement in damping capacity under time sweep mode,and 28%improvement at 423 K under temperature sweep mode.The tribological characteristics of the composite under dry sliding conditions at sliding speeds and loads in the range of 0.5 to 1.5 m s^(-1)and 10 to 30 N,respectively showed higher wear resistance than the unreinforced alloy.The composite showed 23%improvement in sliding wear resistance at a load of 20 N and a speed of 1 m s^(-1).Finally,efforts have been made to understand the influence of one property on the other by developing statistical property correlation maps from the properties obtained in this study and from the literature.These maps are expected to help in the design of hybrid Metal Matrix Composites for a variety of targeted applications in different sectors.
文摘Rotary friction welding is a highly effective solid-state technique for joining dissimilar materials,which offers the potential for significant weight reduction without compromising strength.Traditionally,during rotary friction welding,the severely deformed material,or flash,is expelled from the interface and machined away to achieve the desired joint geometry.However,this work introduces a novel approach:trapping the flash within the joint to improve joint properties.The study investigates two different interface geometry combinationsdflat-flat and flat-taper interfaces.Previous research shows that Ni interlayer between steel and titanium can enhance the joint strength.This study builds on the existing knowledge(effect of Ni interlayer)by examining the influence of interface geometry to further improve the dissimilar joint performance.The experimental results,including tensile testing and microstructural characterization,highlight the superior performance of the flat-taper interface.The modified geometry minimizes flash loss,providing a cavity that retains both the flash and the Ni interlayer within the joint.This retention promotes dynamic recrystallization,resulting in refined grain structures near the interface.Moreover,the trapped Ni interlayer effectively prevents the formation of brittle Fe-Ti intermetallic compounds at the dissimilar material interface.The findings reveal that the flat-taper interface improved joint strength by an impressive 105%compared to the flat-flat interface.This innovative geometry modification demonstrates the potential to enhance mechanical properties of dissimilar joints through better flash and interlayer management.
基金the financial support from the National Natural Science Foundation of China(Nos.51875062,52205336)。
文摘Titanium/magnesium alloy bimetal composites show promising prospects for lightweight applications.The Ti/Mg bimetal composite was fabricated in Ti−6Al−4V pyramidal lattice structure via AZ91D melt infiltration.Comparative analysis of the tensile and compressive properties was conducted between the composite and its constituent materials(Ti−6Al−4V lattice structure and AZ91D matrix).The tensile strength of the composite(95.9 MPa)was comparable to that of the Ti−6Al−4V lattice structure(94.4 MPa)but lower than that of the AZ91D alloy(120.8 MPa)due to gaps at the bimetal interfaces hindering load transfer during tension.The composite exhibited greater elongation(1.7%)compared to AZ91D(1.4%)alloy but less than the Ti−6Al−4V lattice structure(2.6%).The compressive performance of the composite outperformed that of the Ti−6Al−4V lattice structure,underscoring the significance of the AZ91D alloy in compressive deformation.Fracture analysis indicated that the predominant failure reasons in both the composite and lattice structures were attributed to the breakage of lattice struts at nodes caused by the stress concentration.
基金Science&Engineering Research Board(SERB),DST,for its financial assistance received from the project(vide sanction order no.SPG/2021/003383)。
文摘In this study, austenitic stainless steel(ASS) was additively fabricated by an arc-based direct energy deposition(DED) technique. Macrostructure, microstructure, mechanical characteristics at different spatial orientations(0°, 90°, and 45°), and wear characteristics were evaluated at the deposited structure top, middle, and bottom regions. Results show that austenite(γ) and delta-ferrite(δ) phases make up most of the microstructure of additively fabricated SS316LSi steel. Within γ matrix, δ phase is dispersed both(within and along) grain boundaries, exhibiting a fine vermicular morphology. The bottom, middle,and top regions of WAAM deposited ASS exhibit similar values to those of wrought SS316L in the tensile and impact test findings. Notably, a drop in hardness values is observed as build height increases. During SEM examinations of fractured surfaces from tensile specimen, closed dimples were observed, indicating good ductility of as-built structure. Wear test findings show signs of mild oxidation and usual adhesive wear. By depositing a mechanically mixed composite layer, an increase in the oxidation percentage was discovered to facilitate healing of worn surfaces. The findings of this study will help in design, production and renovation of products/components that are prone to wear. WAAM-deposited ASS has remarkable strength and ability to withstand impacts;it can be used in the production of armour plates for defence applications, mainly military vehicles and aircraft.
文摘The effect of platinum(a rare metal)-aluminide coating parameters on the tensile properties of nickel-based superalloy Rene■80 was evaluated at 871℃.For this purpose,initial layers of platinum with different thicknesses(2,4,6 and 8μm)were coated on tensile samples Then,low-temperature high-activity(LTHA)and hightemperature low-activity(HTLA)processes were used for aluminizing.Results of microstructural evaluations using scanning electron microscope(SEM)and phase analysis by X-ray diffraction(XRD)showed a three-layer structure coating for different platinum layer thicknesses and both aluminizing processes.Increasing the thickness of the platinum layer from 2 to 8μm led to the improvement in the final coating thickness from 91.6 to 102.1μm in HTLA.This increase was from 128.1 to 148.6μm in LTHA.The results of hot tensile tests at 871℃ showed a decrease in strength properties of the coated samples compared to the uncoated ones.However,HTLA and high thicknesses of the initial platinum layer showed an intense reduction.The results of fractographic evaluations abou uncoated samples showed a ductile fracture.On the other hand,coated samples showed a simultaneous ductile and brittle fracture failure mechanism.But the main fracture morphology was brittle cleavage fracture which was for the HTLA.
基金This work was financially supported by the Guangdong Province Key Area R&D Program(Grant No.2020B0101340004)the International Science and Technology Cooperation Project of Guangdong Province(Grant No.2021A0505030051)+2 种基金the Innovation and Technology Fund(ITF)(Grant No.ITP/020/21AP)the Young Talent Support Project of Guangzhou Association for Science and Technology(Grant No.QT20220101075)the GDAS'Project of Science and Technology Development(Grant No.2022GDASZH-2022010103).
文摘The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4,11)Al(wt.%)low-density steels.Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum(Al)alloying control.Meanwhile,microstructure evolution and fracture morphology were investigated by X-ray diffraction(XRD),a scanning electron microscope(SEM)equipped with electron backscatter diffraction(EBSD),a transmission electron microscope(TEM),and a stereo-optical microscope(OM).It is found that the Al addition obviously promotes the dislocation planar slipping,resulting in cleavage and brittle impact fracture in 11wt.%Al steel.Besides,the microband-induced plasticity(MBIP)mechanism is found in 4wt.%Al containing steel,introducing considerable work hardening capacity and impact toughness of 156.8±17.4 J.The present study provides a direct illustration of the relationship between work hardening and impact toughness behaviors of these two low-density steels for potential application as impact-resistant components.
基金supports for this work,provided by the Natural Science Foundation of Anhui Province(No.1908085QE187,1808085ME161)the Open Research Program of Key Laboratory of Safety and High-efficiency Coal Mining(No.JYBSYS2019202)the Open Research Program of State Key Laboratory Cultivation Base for Gas Geology and Gas Control(No.WS2019B09)are gratefully acknowledged.
文摘A comprehensive understanding of the failure behavior and mechanism of coal is a prerequisite for dealing with dynamic problems in mining space.In this study,the failure behavior and mechanism of coal under uniaxial dynamic compressive loads were experimentally and numerically investigated.The experiments were conducted using a split Hopkinson pressure bar(SHPB)system.The results indicated that the typical failure of coal is lateral and axial at lower loading rates and totally smashed at higher loading rates.The further fractography analysis of lateral and axial fracture fragments indicated that the coal failure under dynamic compressive load is caused by tensile brittle fracture.In addition,the typical failure modes of coal under dynamic load were numerically reproduced.The numerical results indicated that the axial fracture is caused directly by the incident compressive stress wave and the lateral fracture is caused by the tensile stress wave reflected from the interface between coal specimen and transmitted bar.Potential application was further conducted to interpret dynamic problems in underground coal mine and it manifested that the lateral and axial fractures of coal constitute the parallel cracks in the coal mass under roof fall and blasting in mining space.
基金Sponsored by National Basic Research Program(973 Program)of China(2004CB619100)
文摘Gigacycle fatigue behavior of 60Si2CrVA high strength spring steel was investigated by ultrasonic fatigue test machine. Fatigue fractography was observed by scanning electron microscopy （SEM）. Maximum inclusion sizes and fatigue strength in different volumes were estimated by statistics of extreme values （SEV） and generalized Pareto distribution （GPD） methods. The results showed that S N curves of 60Si2CrVA spring steels for two rolling processes were not horizontal asymptotes but a gradient in a regime of 109 cycles, and traditional fatigue limits were eliminated. Surface machined topography and inclusions in steel were major factors that led to elimination of fatigue limit for 60Si2CrVA spring steel. The SEV and GPD methods could effectively predict size of the maximum inclusion and fatigue strength in different volumes of 60Si2CrVA spring steel. Predicted fatigue strength was in accordance with experimental results by ultrasonic fatigue testing.
文摘In the present study, an Al/Cu/Mg multi-layered composite was produced by accumulative roll bonding(ARB) through seven passes, and its microstructure and mechanical properties were evaluated. The microstructure investigations show that plastic instability occurred in both the copper and magnesium reinforcements in the primary sandwich. In addition, a composite with a perfectly uniform distribution of copper and magnesium reinforcing layers was produced during the last pass. By increasing the number of ARB cycles, the microhardness of the layers including aluminum, copper, and magnesium was significantly increased. The ultimate tensile strength of the sandwich was enhanced continually and reached a maximum value of 355.5 MPa. This strength value was about 3.2, 2, and 2.1 times higher than the initial strength values for the aluminum, copper, and magnesium sheets, respectively. Investigation of tensile fracture surfaces during the ARB process indicated that the fracture mechanism changed to shear ductile at the seventh pass.
基金supported by the National 863 Plan(No.2006AA03A209)New Century Excellent Talent Plan (No.NECT-05-0660) from Ministry of EducationDefense Basic Research Item(No.D1420061057)
文摘A high performance thermosetting epoxy resin crosslinkable at room temperature was obtained via directly moulding diglycidyl ether of bisphenol A（DGEBA） and flexibleα,ω-bisamino（n-alkylene）phenyl terminated poly（ethylene glycol）.The influences of the n-alkylene inserted in aminophenyl of flexible amino-terminated polythers（ATPE） on the mechanical properties,fractographs and curing kinetics of the ATPE-DGEBA cured products were studied.The results show that the insertion of n-alkylene group into the aminophenyl group of the ATPE,on one hand,can significantly increase the strain relaxation rate and decrease glass transition temperature of the ATPE-DGEBA cured products,resulting in slight decrease of the Young’s modulus and tensile strength,and significant increase of the toughness and elongation of the ATPE-DGEBA cured products.On the other hand,it can remarkably enhance the reactivity of amine with epoxy,much accelerating the curing rate of the ATPE-DGEBA systems.The activation energy of DGEBA cured by BAPTPE,BAMPTPE and BAEPTPE was 53.1,28.5 and 25.4 kJ·mol;,respectively.The as-obtained ATPE-DGEBA cured products are homogeneous, transparent,and show excellent mechanical properties including tensile strength and toughness.Thus they are promising to have important applications in structure adhesives,casting bulk materials,functional coatings,cryogenic engineering, damping and sound absorbing materials.
基金This work was supported by Department of Science and Technology,Government of India,under Grant No:RP02197.
文摘Magnesium alloy(AZ91D)composites reinforced with silicon carbide particle with different volume percentage were fabricated by two step stir casting process.The effect of changes in particle size and volume fraction of SiC particles on physical and mechanical properties of composites were evaluated under as cast and heat treated(T6)conditions.The experimental results were compared with the standard theoretical models.The results reveal that the mechanical properties of composites increased with increasing SiC particles and decrease with increasing particle size.Distribution of particles and fractured surface were studied through SEM and the presence of elements is revealed by EDS study.
基金support of the National Natural Science Foundation of China(No.51275415 and No.50905144)the program for New Century Excellent Talents in University+2 种基金the Natural Science Basic Research Plan in Shaanxi Province(No.2011JQ6004)of Chinathe fund of the State Key Laboratory of Solidification Processing in NWPU of Chinathe 111 Project(No.B08040)of China
文摘As promising light-weight and high-performance structure components, large-diameter thin-walled （LDTW） Ti 6Al^4V titanium alloy （TC4） bent tubes are needed most urgently in many industries such as aviation and aerospace. Warm bending may be a feasible way for manufacturing these components. Understanding their temperature and strain rate dependent tensile behavior is the foundation for formability improvement and warm bending design. In this paper, uniaxial ten- sile tests were conducted at elevated temperatures ranging from 298 K to 873 K at tensile velocities of 2, 10, 15 mm/min. The main results show that the tensile behavior of LDTW TC4 tubes is dif- ferent from that of TC4 sheets. The typical elongation of TC4 tubes at room temperature is 10% lower than that of TC4 sheets. The flow stress of TC4 tubes decreases greatly by about 50% with the temperature rising to 873 K. At temperatures of 573-673 K, the hardening exponent is at its highest value, which means the deformation mechanism changes from twining to more dislocation movement by slipping. The fracture elongation of TC4 tubes fluctuates with increasing temperature, which is associated with changes in the deformation mechanism and with the blue brittleness. The fractography of TC4 tubes at various temperatures, especially at 673 K, shows that second phases and impurities significantly influence fracture elongation. By considering the characteristics of the tensile behavior and by properly choosing the die material, the warm bending for TC4 tubes can be achieved at temperatures of 723-823 K.
