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
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 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
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.
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 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.
