Inconel 718(IN718)alloy is widely applied to fabricate high temperature resistant or corrosion resistant parts due to its excellent mechanical performance.However,the machining of IN718 alloy is difficult as it may ca...Inconel 718(IN718)alloy is widely applied to fabricate high temperature resistant or corrosion resistant parts due to its excellent mechanical performance.However,the machining of IN718 alloy is difficult as it may cause serious tool wear and poor surface quality(SQ)of the workpiece.In this work,grinding experiments on IN718 alloy at different speeds were conducted by using a CBN grinding wheel.The relationship between grinding speed,SQ and subsurface damage(SSD)was well studied.With increasing grinding speed,surface roughness decreased,and SQ was greatly improved.Meanwhile,the microhardness of the grinding surface declined as the grinding speed increased.The SSD depth was almost unchanged when the grinding speed was lower than 15 m/s,then it decreased with higher grinding speeds.It was attributed to the mechanical-thermal synergistic effect in the grinding process.The results indicated that increasing grinding speed can effectively improve the SQ and reduce the SSD of IN718 alloy.The conclusion in the work may also provide insight into processing other hard-to-machining materials.展开更多
Fatigue properties are crucial for critical aero-engine components in extreme serviceenvironments,which are significantly affected by surface integrity(SI)indexes(especially surface topography,residual stressσ_(res),...Fatigue properties are crucial for critical aero-engine components in extreme serviceenvironments,which are significantly affected by surface integrity(SI)indexes(especially surface topography,residual stressσ_(res),and microhardness)after machining processes.Normal-direction ultrasonic vibration-assisted face grinding(ND-UVAFG)has advantages in improving the machinability of Inconel 718,but there is a competitive relationship between higher compressiveσ_(res)and higher surface roughness R_(a)in affecting fatigue strength.The lack of a quantitative relationship between multiple SI indexes and fatigue strength makes theindeterminacy of a regulatory strategy for improving fatigue properties.In this work,a model of fatigue strength(σ_f)_(sur)considering multiple SI indexes was developed.Then,high-cycle fatigue tests were carried out on Inconel 718 samples with different SI characteristics,and the influence of ND-UVAFG process parameters on SI was analyzed.Based on SI indexes data,the(σ_f)_(sur)distribution in the grinding surface layer for ND-UVAFG Inconel 718 samples was determined using the developed model,and then the fatigue crack initiation(FCI)sites were furtherpredicted.The predicted FCI sites corresponded well with the experimental results,therebyverifying this model.A strategy for improving the fatigue life was proposed in this work,which was to transfer the fatigue source from the machined surface to the bulk material by controlling the SI indexes.Finally,a critical condition of SI indexes that FCI sites appeared on the surface or in bulk material was given by fitting the predicted results.According to the critical condition,an SI field where FCI sites appeared in the bulk material could be obtained.In this field,thefatigue life of Inconel 718 samples could be improved by approximately 140%.展开更多
High-speed machining(HSM) has been studied for several decades and has potential application in various industries, including the automobile and aerospace industries. However,the underlying mechanisms of HSM have not ...High-speed machining(HSM) has been studied for several decades and has potential application in various industries, including the automobile and aerospace industries. However,the underlying mechanisms of HSM have not been formally reviewed thus far. This article focuses on the solid mechanics framework of adiabatic shear band(ASB) onset and material metallurgical microstructural evolutions in HSM. The ASB onset is described using partial differential systems. Several factors in HSM were considered in the systems, and the ASB onset conditions were obtained by solving these systems or applying the perturbation method to the systems. With increasing machining speed, an ASB can be depressed and further eliminated by shock pressure. The damage observed in HSM exhibits common features. Equiaxed fine grains produced by dynamic recrystallization widely cause damage to ductile materials, and amorphization is the common microstructural evolution in brittle materials. Based on previous studies, potential mechanisms for the phenomena in HSM are proposed. These include the thickness variation of the white layer of ductile materials. These proposed mechanisms would be beneficial to deeply understanding the various phenomena in HSM.展开更多
This study is concerned with the surface integrity of Inconel 738LC parts manufactured by selective laser melting(SLM)followed by high-speed milling(HSM).In the investigation process of surface integrity,the study emp...This study is concerned with the surface integrity of Inconel 738LC parts manufactured by selective laser melting(SLM)followed by high-speed milling(HSM).In the investigation process of surface integrity,the study employs ultradepth three-dimensional microscopy,laser scanning confocal microscopy,scanning electron microscopy,electron backscatter diffractometry,and energy dispersive spectroscopy to characterize the evolution of material microstructure,work hardening,residual stress coupling,and anisotropic effect of the building direction on surface integrity of the samples.The results show that SLM/HSM hybrid manufacturing can be an effective method to obtain better surface quality with a thinner machining metamorphic layer.High-speed machining is adopted to reduce cutting force and suppress machining heat,which is an effective way to produce better surface mechanical properties during the SLM/HSM hybrid manufacturing process.In general,high-speed milling of the SLM-built Inconel 738LC samples offers better surface integrity,compared to simplex additive manufacturing or casting.展开更多
In order to understand the epidemic characteristics of major viral infectious diseases of pig farms in Guangxi from 2019 to 2022,the PCR and RT-PCR methods were applied to detect the pathogens of 1046 samples suspecte...In order to understand the epidemic characteristics of major viral infectious diseases of pig farms in Guangxi from 2019 to 2022,the PCR and RT-PCR methods were applied to detect the pathogens of 1046 samples suspected CSFV(swine fever virus),PRRSV(porcine reproductive and respiratory syndrome virus),PCV-2(porcine circovirus virus type 2),PCV-3(porcine circovirus virus type 3),PRV(pseudorabies virus),TGEV(transmissible gastroeneritis of pigs virus),PEDV(porcine epidemic diarrhea virus)and PoRV(porcine rotavirus)infections in recent four years,and epidemiological analysis was carried out.The results showed that positive rates of CSFV,PRRSV,PCV-2,PCV-3,PRV,TGEV,PEDV and PoRV were 3.91%(21/537),20.46%(143/699),29.90%(116/388),16.10%(81/503),27.75%(121/436),2.10%(8/381),28.50%(61/214)and 13.74%(18/131).The infection rates of PCV-2 and PEDV were decreasing year by year,while the infection rate of TGEV was increasing year by year.In single infection,the infection rates of PRV and PEDV were higher,with an average infection rate of 13.53%and 18.22%.In the mixed infection,the infection rate of PRRSV and PCV-2 was the highest,with an average infection rate of 11.34%.The second mixed infection rate was PEDV and PoRV,and the average infection rate was 8.05%.The infection rate of PCV-3 and PEDV was higher in spring,with 18.80%and 40.00%respectively.The infection rate of PRRSV,PCV-2,PRV,TGEV and PoRV was higher in winter,with 24.40%,40.57%,37.30%,3.23%and 19.44%respectively.The results showed that PRRSV,PCV-2,PRV and PEDV were the main viral diseases with serious damage to pig farms in Guangxi.It was necessary to strengthen pathogen monitoring and improve comprehensive prevention and control ability,in order to reduce the incidence of disease and economic losses.展开更多
Defect formation is a common problem in selective laser melting （SLM）. This paper provides a review of defect formation mechanisms in SLM. It sum- marizes the recent research outcomes on defect findings and classifi...Defect formation is a common problem in selective laser melting （SLM）. This paper provides a review of defect formation mechanisms in SLM. It sum- marizes the recent research outcomes on defect findings and classification, analyzes formation mechanisms of the common defects, such as porosities, incomplete fusion holes, and cracks. The paper discusses the effect of the process parameters on defect formation and the impact of defect formation on the mechanical properties of a fabri- cated part. Based on the discussion, the paper proposes strategies for defect suppression and control in SLM.展开更多
Subsurface damage is easily induced in machining of hard and brittle materials because of their particular mechani?cal and physical properties. It is detrimental to the strength,performance and lifetime of a machined ...Subsurface damage is easily induced in machining of hard and brittle materials because of their particular mechani?cal and physical properties. It is detrimental to the strength,performance and lifetime of a machined part. To manu?facture a high quality part,it is necessary to detect and remove the machining induced subsurface damage by the subsequent processes. However,subsurface damage is often covered with a smearing layer generated in a machining process,it is rather di cult to directly observe and detect by optical microscopy. An e cient detection of subsur?face damage directly leads to quality improvement and time saving for machining of hard and brittle materials. This paper presents a review of the methods for detection of subsurface damage,both destructive and non?destructive. Although more reliable,destructive methods are typically time?consuming and confined to local damage infor?mation. Non?destructive methods usually su er from uncertainty factors,but may provide global information on subsurface damage distribution. These methods are promising because they can provide a capacity of rapid scan and detection of subsurface damage in spatial distribution.展开更多
Single-crystal silicon is an important material in the semiconductor and optical industries.However,being hard and brittle,a silicon wafer is vulnerable to subsurface cracks(SSCs)during grinding,which is detrimental t...Single-crystal silicon is an important material in the semiconductor and optical industries.However,being hard and brittle,a silicon wafer is vulnerable to subsurface cracks(SSCs)during grinding,which is detrimental to the performance and lifetime of a wafer product.Therefore,studying the formation of SSCs is important for optimizing SSC-removal processes and thus improving surface integrity.In this study,a statistical method is used to study the formation of SSCs induced during grinding of silicon wafers.The statistical results show that grinding-induced SSCs are not stochastic but anisotropic in their distributions.Generally,when grinding with coarse abrasive grains,SSCs form along the cleavage planes,primarily the{111}planes.However,when grinding with finer abrasive grains,SSCs tend to form along planes with a fracture-surface energy higher than that of the cleavage planes.These findings provide a guidance for the accurate detection of SSCs in ground silicon wafers.展开更多
New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance.This study comprehensively investigated the effect of influencing fa...New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance.This study comprehensively investigated the effect of influencing factors includ-ing excitation frequency,lift-off distance,defect depth and size,residual heat,and surface roughness on the defect EC signals of an Inconel 738LC alloy produced by selective laser melting(SLM).The experimental investigations recorded the impedance amplitude and phase angle of EC signals for each defect to explore the feasibility of detecting sub-surface defects by merely analyzing these two key indicators.Overall,this study revealed preliminary qualitative and roughly quantitative relationships between influencing factors and corresponding EC signals,which provided a prac-tical reference on how to quantitively inspect subsurface defects using eddy current testing(ECT)on SLMed parts,and also made solid progress toward on-line ECT in additive/subtractive hybrid manufacturing(ASHM)for fabricating SLMed parts with enhanced quality and better performance.展开更多
The Ti6Al4V parts produced by the existing selective laser melting(SLM)are mainly confronted with poor surface finish and inevitable interior defects,which substantially deteriorates the mechanical properties and perf...The Ti6Al4V parts produced by the existing selective laser melting(SLM)are mainly confronted with poor surface finish and inevitable interior defects,which substantially deteriorates the mechanical properties and performances of the parts.In this regard,ultrasonically-assisted machining(UAM)technique is commonly introduced to improve the machining quality due to its merits in increasing tool life and reducing cutting force.However,most of the previous studies focus on the performance of UAM with ultrasonic vibrations applied in the tangential and feed directions,whereas few of them on the impact of ultrasonic vibration along the vertical direction.In this study,the effects of feed rate on surface integrity in ultrasonically-assisted vertical milling(UAVM)of the Ti6Al4V alloy manufactured by SLM were systemically investigated compared with the conventional machining(CM)method.The results revealed that the milling forces in UAVM showed a lower amplitude than that in CM due to the intermittent cutting style.The surface roughness values of the parts produced by UAVM were generally greater than that by CM owing to the extra sinusoidal vibration textures induced by the milling cutter.Moreover,the extra vertical ultrasonic vibration in UAVM was beneficial to suppressing machining chatter.As feed rate increased,surface microhardness and thickness of the plastic deformation zone in CM raised due to more intensive plastic deformation,while these two material properties in UAVM were reduced owing to the mitigated impact effect by the high-frequency vibration of the milling cutter.Therefore,the improved surface microhardness and reduced thickness of the subsurface deformation layer in UAVM were ascribed to the vertical high-frequency impact of the milling cutter in UAVM.In general,the results of this study provided an in-depth understanding in UAVM of Ti6Al4V parts manufactured by SLM.展开更多
This paper proposes the‘skin effect’of the machining-induced damage at high strain rates.The paper first reviews the published research work on machining-induced damage and then identifies the governing factors that...This paper proposes the‘skin effect’of the machining-induced damage at high strain rates.The paper first reviews the published research work on machining-induced damage and then identifies the governing factors that dominate damage formation mechanisms.Among many influential factors,such as stress-strain field,temperature field,material responses to loading and loading rate,and crack initiation and propagation,strain rate is recognized as a dominant factor that can directly lead to the‘skin effect’of material damage in a loading process.The paper elucidates that material deformation at high strain rates(>103 s−1)leads to the embrittlement,which in turn contributes to the‘skin effect’of subsurface damage.The paper discusses the‘skin effect’based on the principles of dislocation kinetics and crack initiation and propagation.It provides guidance to predicting the material deformation and damage at a high strain-rate for applications ranging from the armor protection,quarrying,petroleum drilling,and high-speed machining of engineering materials(e.g.ceramics and SiC reinforced aluminum alloys).展开更多
Material embrittlement is often encountered in machining,heat treatment,hydrogen and lowtemperature conditions among which machining is strain-rate related.More strain-rate evoked embrittlement is expected in material...Material embrittlement is often encountered in machining,heat treatment,hydrogen and lowtemperature conditions among which machining is strain-rate related.More strain-rate evoked embrittlement is expected in material loading processes,such as in high-speed machining and projectile penetration.In order to understand the fundamental mechanisms of the strain-rate evoked material embrittlement,this study is concerned with the material responses to loading at high strain-rates.It then explores the strain-rate evoked material embrittlement and fragmentation during high strain-rate loading processes and evaluates various empirical and physical models from different researchers for the assessment of the material embrittlement.The study proposes strain-rate sensitivity for the characterization of material embrittlement and the concept of the pseudo embrittlement for material responses to very high strain-rates.A discussion section is arranged to explore the underlying mechanisms of the strain-rate evoked material embrittlement and fragmentation based on dislocation kinetics.展开更多
The management of diabetic wounds remains a critical therapeutic challenge. Platelet-rich plasma (PRP) gel, PRP-derived exosomes (PRP-Exos), and mesenchymal stem cell-derived exosomes (MSC-Exos) have demonstrated ther...The management of diabetic wounds remains a critical therapeutic challenge. Platelet-rich plasma (PRP) gel, PRP-derived exosomes (PRP-Exos), and mesenchymal stem cell-derived exosomes (MSC-Exos) have demonstrated therapeutic potential in wound treatment. Unfortunately, their poor mechanical properties, the short half-lives of growth factors (GFs), and the burst release of GFs and exosomes have limited their clinical applications. Furthermore, proteases in diabetic wounds degrade GFs, which hampers wound repair. Silk fibroin is an enzyme-immobilization biomaterial that could protect GFs from proteases. Herein, we developed novel dual-crosslinked hydrogels based on silk protein (SP) (sericin and fibroin), including SP@PRP, SP@MSC-Exos, and SP@PRP-Exos, to promote diabetic wound healing synergistically. SP@PRP was prepared from PRP and SP using calcium gluconate/thrombin as agonist, while SP@PRP-Exos and SP@MSC-Exos were derived from exosomes and SP with genipin as crosslinker. SP provided improved mechanical properties and enabled the sustained release of GFs and exosomes, thereby overcoming the limitations of PRP and exosomes in wound healing. The dual-crosslinked hydrogels displayed shear-induced thinning, self-healing, and eradication of microbial biofilms in a bone-mimicking environment. In vivo, the dual-crosslinked hydrogels contributed to faster diabetic wound healing than PRP and SP by upregulating GFs expression, down-regulating matrix metalloproteinase-9 expression, and by promoting an anti-NETotic effect, angiogenesis, and re-epithelialization. Hence, these dual-crosslinked hydrogels have the potential to be translated into a new generation of diabetic wound dressings.展开更多
Many chemical processes can be modeled as Wiener models, which consist of a linear dynamic subsystem followed by a static nonlinear block. In this paper, an effective discrete-time adaptive control method is proposed ...Many chemical processes can be modeled as Wiener models, which consist of a linear dynamic subsystem followed by a static nonlinear block. In this paper, an effective discrete-time adaptive control method is proposed for Wiener nonlinear systems with uncertainties. The parameterization model is derived based on the inverse of the nonlinear function block. The adaptive control method is motivated by self-tuning control and is derived from a modified Clarke criterion function, which considers both tracking properties and control efforts. The uncertain parameters are updated by a recursive least squares algorithm and the control law exhibits an explicit form. The closed-loop system stability properties are discussed. To demonstrate the effectiveness of the obtained results, two groups of simulation examples including an application to composition control in a continuously stirred tank reactor(CSTR) system are studied.展开更多
As a big rapeseed （Brassica napus L.） producing and consuming country, China provides more and more rapeseea oil year by year. With the development of demand for rapeseed and import of edible oil, rapeseed breeding ...As a big rapeseed （Brassica napus L.） producing and consuming country, China provides more and more rapeseea oil year by year. With the development of demand for rapeseed and import of edible oil, rapeseed breeding and production is fac- ing a great challenge. New situation has proposed higher requirements to yield, oil quality and safety, etc. In the review, some aspects about rapeseed breeding in China were reported, including breeding of high-oil content rapeseed, breeding of extremely early-maturing rapeseed, development of mechanization and development of chemical emasculation. Some prospects and expec- tations were also proposed.展开更多
Rabies is a serious public health problem in Asia and Africa.Approximately 99%of cases result from a bite by an infected dog.The high rabies risk countries are generally characterized by rapid urbanization;however,the...Rabies is a serious public health problem in Asia and Africa.Approximately 99%of cases result from a bite by an infected dog.The high rabies risk countries are generally characterized by rapid urbanization;however,the prevalence and risk factors for rabies in urban dogs in developing countries remain unclear.Beijing,the capital of China,has been undergoing rapid urbanization,and implemented compulsory rabies immunization for dogs on October 1,2014.We evaluated the effects of this immunization policy and investigated the dynamics and determinants of the spread of dog rabies virus(RABV)in Beijing.Between 2013 and 2018,the positive rate of rabies in biting dogs declined significantly;79.6%of these were stray dogs.Reconstructed spatiotemporal diffusion for RABV presents a more central distribution within Beijing and a surrounding dissemination of virus lineage toward suburban areas,indicating that rabies is self-sustaining in Beijing.Continuous RABV phylogeographic reconstructions and logistic regression analysis of rabies cases revealed that rabies tended to remain in commercial areas,high-rise residences,demolition areas,and high-GDP,high-population and high-accessibility areas.Demolition areas,where many residents have abandoned their pets,are recognized as high-risk areas for rabies.Our findings reveal that the implementation of the immunization policy in Beijing has been effective in prevention and control of canine rabies,and because the prevalence of canine rabies results from multiple factors,emphasize the important role of multi-sectoral cooperation in rabies prevention and control.展开更多
In a recent study published in Science,Zhang et al.discovered that tripartite motif-containing(TRIM)protein 11(TRIM11)exhibited strong inhibition on tau aggregation,which is a pathological characteristic of tauopathie...In a recent study published in Science,Zhang et al.discovered that tripartite motif-containing(TRIM)protein 11(TRIM11)exhibited strong inhibition on tau aggregation,which is a pathological characteristic of tauopathies including Alzheimer’s disease(AD).1 This makes TRIM11 a promising novel target for the treatment of AD and other tauopathies.展开更多
The success of the Beijing Winter Olympics and Paralympics epitomized the vision of a community with a shared future for humankind.Various robots and artificial intelligence technologies were used in various games and...The success of the Beijing Winter Olympics and Paralympics epitomized the vision of a community with a shared future for humankind.Various robots and artificial intelligence technologies were used in various games and events,such as assisting in parades,logistics,and security inspections.The integration of unmanned robotic systems into torch relays was one of the highlights of the Winter Olympics.展开更多
基金Supported by Shenzhen Municipal Science and Technology Innovation Commission of China(Grant Nos.KQTD20190929172505711,JSGG20210420091802007,GJHZ20210705141807023).
文摘Inconel 718(IN718)alloy is widely applied to fabricate high temperature resistant or corrosion resistant parts due to its excellent mechanical performance.However,the machining of IN718 alloy is difficult as it may cause serious tool wear and poor surface quality(SQ)of the workpiece.In this work,grinding experiments on IN718 alloy at different speeds were conducted by using a CBN grinding wheel.The relationship between grinding speed,SQ and subsurface damage(SSD)was well studied.With increasing grinding speed,surface roughness decreased,and SQ was greatly improved.Meanwhile,the microhardness of the grinding surface declined as the grinding speed increased.The SSD depth was almost unchanged when the grinding speed was lower than 15 m/s,then it decreased with higher grinding speeds.It was attributed to the mechanical-thermal synergistic effect in the grinding process.The results indicated that increasing grinding speed can effectively improve the SQ and reduce the SSD of IN718 alloy.The conclusion in the work may also provide insight into processing other hard-to-machining materials.
基金support from the National Science Fund of China(52325506)the National Science and Technology Major Project(2017-VII-0002-0095)Fundamental Research Funds for the Central Universities(DUT22LAB501)。
文摘Fatigue properties are crucial for critical aero-engine components in extreme serviceenvironments,which are significantly affected by surface integrity(SI)indexes(especially surface topography,residual stressσ_(res),and microhardness)after machining processes.Normal-direction ultrasonic vibration-assisted face grinding(ND-UVAFG)has advantages in improving the machinability of Inconel 718,but there is a competitive relationship between higher compressiveσ_(res)and higher surface roughness R_(a)in affecting fatigue strength.The lack of a quantitative relationship between multiple SI indexes and fatigue strength makes theindeterminacy of a regulatory strategy for improving fatigue properties.In this work,a model of fatigue strength(σ_f)_(sur)considering multiple SI indexes was developed.Then,high-cycle fatigue tests were carried out on Inconel 718 samples with different SI characteristics,and the influence of ND-UVAFG process parameters on SI was analyzed.Based on SI indexes data,the(σ_f)_(sur)distribution in the grinding surface layer for ND-UVAFG Inconel 718 samples was determined using the developed model,and then the fatigue crack initiation(FCI)sites were furtherpredicted.The predicted FCI sites corresponded well with the experimental results,therebyverifying this model.A strategy for improving the fatigue life was proposed in this work,which was to transfer the fatigue source from the machined surface to the bulk material by controlling the SI indexes.Finally,a critical condition of SI indexes that FCI sites appeared on the surface or in bulk material was given by fitting the predicted results.According to the critical condition,an SI field where FCI sites appeared in the bulk material could be obtained.In this field,thefatigue life of Inconel 718 samples could be improved by approximately 140%.
基金support of the Shenzhen Science and Technology Innovation Commission under Project Numbers KQTD20190929172505711,JSGG20210420091802007, and JCYJ20210324115413036Guangdong Provincial Department of Science and Technology under Project Number K22333004。
文摘High-speed machining(HSM) has been studied for several decades and has potential application in various industries, including the automobile and aerospace industries. However,the underlying mechanisms of HSM have not been formally reviewed thus far. This article focuses on the solid mechanics framework of adiabatic shear band(ASB) onset and material metallurgical microstructural evolutions in HSM. The ASB onset is described using partial differential systems. Several factors in HSM were considered in the systems, and the ASB onset conditions were obtained by solving these systems or applying the perturbation method to the systems. With increasing machining speed, an ASB can be depressed and further eliminated by shock pressure. The damage observed in HSM exhibits common features. Equiaxed fine grains produced by dynamic recrystallization widely cause damage to ductile materials, and amorphization is the common microstructural evolution in brittle materials. Based on previous studies, potential mechanisms for the phenomena in HSM are proposed. These include the thickness variation of the white layer of ductile materials. These proposed mechanisms would be beneficial to deeply understanding the various phenomena in HSM.
基金Shenzhen Municipal Science and Technology Innovation Commission Projects(Grant Nos.Y01336107,JCYJ20180504165824643,GJHZ20180411143506667,JC YJ20170817111811303 and KQTD20190929172505711)。
文摘This study is concerned with the surface integrity of Inconel 738LC parts manufactured by selective laser melting(SLM)followed by high-speed milling(HSM).In the investigation process of surface integrity,the study employs ultradepth three-dimensional microscopy,laser scanning confocal microscopy,scanning electron microscopy,electron backscatter diffractometry,and energy dispersive spectroscopy to characterize the evolution of material microstructure,work hardening,residual stress coupling,and anisotropic effect of the building direction on surface integrity of the samples.The results show that SLM/HSM hybrid manufacturing can be an effective method to obtain better surface quality with a thinner machining metamorphic layer.High-speed machining is adopted to reduce cutting force and suppress machining heat,which is an effective way to produce better surface mechanical properties during the SLM/HSM hybrid manufacturing process.In general,high-speed milling of the SLM-built Inconel 738LC samples offers better surface integrity,compared to simplex additive manufacturing or casting.
文摘In order to understand the epidemic characteristics of major viral infectious diseases of pig farms in Guangxi from 2019 to 2022,the PCR and RT-PCR methods were applied to detect the pathogens of 1046 samples suspected CSFV(swine fever virus),PRRSV(porcine reproductive and respiratory syndrome virus),PCV-2(porcine circovirus virus type 2),PCV-3(porcine circovirus virus type 3),PRV(pseudorabies virus),TGEV(transmissible gastroeneritis of pigs virus),PEDV(porcine epidemic diarrhea virus)and PoRV(porcine rotavirus)infections in recent four years,and epidemiological analysis was carried out.The results showed that positive rates of CSFV,PRRSV,PCV-2,PCV-3,PRV,TGEV,PEDV and PoRV were 3.91%(21/537),20.46%(143/699),29.90%(116/388),16.10%(81/503),27.75%(121/436),2.10%(8/381),28.50%(61/214)and 13.74%(18/131).The infection rates of PCV-2 and PEDV were decreasing year by year,while the infection rate of TGEV was increasing year by year.In single infection,the infection rates of PRV and PEDV were higher,with an average infection rate of 13.53%and 18.22%.In the mixed infection,the infection rate of PRRSV and PCV-2 was the highest,with an average infection rate of 11.34%.The second mixed infection rate was PEDV and PoRV,and the average infection rate was 8.05%.The infection rate of PCV-3 and PEDV was higher in spring,with 18.80%and 40.00%respectively.The infection rate of PRRSV,PCV-2,PRV,TGEV and PoRV was higher in winter,with 24.40%,40.57%,37.30%,3.23%and 19.44%respectively.The results showed that PRRSV,PCV-2,PRV and PEDV were the main viral diseases with serious damage to pig farms in Guangxi.It was necessary to strengthen pathogen monitoring and improve comprehensive prevention and control ability,in order to reduce the incidence of disease and economic losses.
基金Supported by National Natural Science Foundation of China(Grant No.51605077)Science Challenge Project(Grant No.CKY2016212A506-0101)Science Fund for Creative Research Groups of NSFC(Grant No.51621064)
文摘Defect formation is a common problem in selective laser melting （SLM）. This paper provides a review of defect formation mechanisms in SLM. It sum- marizes the recent research outcomes on defect findings and classification, analyzes formation mechanisms of the common defects, such as porosities, incomplete fusion holes, and cracks. The paper discusses the effect of the process parameters on defect formation and the impact of defect formation on the mechanical properties of a fabri- cated part. Based on the discussion, the paper proposes strategies for defect suppression and control in SLM.
基金Supported by National Natural Science Foundation of China(Grant No.51575084)the Science Fund for Creative Research Groups of NSFC(Grant No.51621064)the Science Challenge Project(Grant No.JCKY2016212A506–0101)
文摘Subsurface damage is easily induced in machining of hard and brittle materials because of their particular mechani?cal and physical properties. It is detrimental to the strength,performance and lifetime of a machined part. To manu?facture a high quality part,it is necessary to detect and remove the machining induced subsurface damage by the subsequent processes. However,subsurface damage is often covered with a smearing layer generated in a machining process,it is rather di cult to directly observe and detect by optical microscopy. An e cient detection of subsur?face damage directly leads to quality improvement and time saving for machining of hard and brittle materials. This paper presents a review of the methods for detection of subsurface damage,both destructive and non?destructive. Although more reliable,destructive methods are typically time?consuming and confined to local damage infor?mation. Non?destructive methods usually su er from uncertainty factors,but may provide global information on subsurface damage distribution. These methods are promising because they can provide a capacity of rapid scan and detection of subsurface damage in spatial distribution.
基金Financial supports from the National Natural Science Foundation of China (Grants No.51575084)the Science Fund for Creative Research Groups of NSFC (Grants No.51621064) are gratefully acknowledged
文摘Single-crystal silicon is an important material in the semiconductor and optical industries.However,being hard and brittle,a silicon wafer is vulnerable to subsurface cracks(SSCs)during grinding,which is detrimental to the performance and lifetime of a wafer product.Therefore,studying the formation of SSCs is important for optimizing SSC-removal processes and thus improving surface integrity.In this study,a statistical method is used to study the formation of SSCs induced during grinding of silicon wafers.The statistical results show that grinding-induced SSCs are not stochastic but anisotropic in their distributions.Generally,when grinding with coarse abrasive grains,SSCs form along the cleavage planes,primarily the{111}planes.However,when grinding with finer abrasive grains,SSCs tend to form along planes with a fracture-surface energy higher than that of the cleavage planes.These findings provide a guidance for the accurate detection of SSCs in ground silicon wafers.
基金Supported by Basic Research Project of Science and Technology Plan of Shenzhen(Grant No.JCYJ20170817111811303).
文摘New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance.This study comprehensively investigated the effect of influencing factors includ-ing excitation frequency,lift-off distance,defect depth and size,residual heat,and surface roughness on the defect EC signals of an Inconel 738LC alloy produced by selective laser melting(SLM).The experimental investigations recorded the impedance amplitude and phase angle of EC signals for each defect to explore the feasibility of detecting sub-surface defects by merely analyzing these two key indicators.Overall,this study revealed preliminary qualitative and roughly quantitative relationships between influencing factors and corresponding EC signals,which provided a prac-tical reference on how to quantitively inspect subsurface defects using eddy current testing(ECT)on SLMed parts,and also made solid progress toward on-line ECT in additive/subtractive hybrid manufacturing(ASHM)for fabricating SLMed parts with enhanced quality and better performance.
基金Supported by Shenzhen Municipal Science and Technology Innovation Commission of China(Grant Nos.Y01336107,GJHZ20180411143506667,JCYJ20170817111811303).
文摘The Ti6Al4V parts produced by the existing selective laser melting(SLM)are mainly confronted with poor surface finish and inevitable interior defects,which substantially deteriorates the mechanical properties and performances of the parts.In this regard,ultrasonically-assisted machining(UAM)technique is commonly introduced to improve the machining quality due to its merits in increasing tool life and reducing cutting force.However,most of the previous studies focus on the performance of UAM with ultrasonic vibrations applied in the tangential and feed directions,whereas few of them on the impact of ultrasonic vibration along the vertical direction.In this study,the effects of feed rate on surface integrity in ultrasonically-assisted vertical milling(UAVM)of the Ti6Al4V alloy manufactured by SLM were systemically investigated compared with the conventional machining(CM)method.The results revealed that the milling forces in UAVM showed a lower amplitude than that in CM due to the intermittent cutting style.The surface roughness values of the parts produced by UAVM were generally greater than that by CM owing to the extra sinusoidal vibration textures induced by the milling cutter.Moreover,the extra vertical ultrasonic vibration in UAVM was beneficial to suppressing machining chatter.As feed rate increased,surface microhardness and thickness of the plastic deformation zone in CM raised due to more intensive plastic deformation,while these two material properties in UAVM were reduced owing to the mitigated impact effect by the high-frequency vibration of the milling cutter.Therefore,the improved surface microhardness and reduced thickness of the subsurface deformation layer in UAVM were ascribed to the vertical high-frequency impact of the milling cutter in UAVM.In general,the results of this study provided an in-depth understanding in UAVM of Ti6Al4V parts manufactured by SLM.
基金The authors would like to acknowledge the supports by the National Natural Science Foundation of China(Grant No.51575084)and the Peacock Program of Shenzhen(Grant No.KQJSCX20180322152221965).
文摘This paper proposes the‘skin effect’of the machining-induced damage at high strain rates.The paper first reviews the published research work on machining-induced damage and then identifies the governing factors that dominate damage formation mechanisms.Among many influential factors,such as stress-strain field,temperature field,material responses to loading and loading rate,and crack initiation and propagation,strain rate is recognized as a dominant factor that can directly lead to the‘skin effect’of material damage in a loading process.The paper elucidates that material deformation at high strain rates(>103 s−1)leads to the embrittlement,which in turn contributes to the‘skin effect’of subsurface damage.The paper discusses the‘skin effect’based on the principles of dislocation kinetics and crack initiation and propagation.It provides guidance to predicting the material deformation and damage at a high strain-rate for applications ranging from the armor protection,quarrying,petroleum drilling,and high-speed machining of engineering materials(e.g.ceramics and SiC reinforced aluminum alloys).
基金The authors would like to acknowledge the supports by the National Natural Science Foundation of China(Grant No.51575084)the Peacock Program of Shenzhen(Grant No.KQJSCX20180322152221965).
文摘Material embrittlement is often encountered in machining,heat treatment,hydrogen and lowtemperature conditions among which machining is strain-rate related.More strain-rate evoked embrittlement is expected in material loading processes,such as in high-speed machining and projectile penetration.In order to understand the fundamental mechanisms of the strain-rate evoked material embrittlement,this study is concerned with the material responses to loading at high strain-rates.It then explores the strain-rate evoked material embrittlement and fragmentation during high strain-rate loading processes and evaluates various empirical and physical models from different researchers for the assessment of the material embrittlement.The study proposes strain-rate sensitivity for the characterization of material embrittlement and the concept of the pseudo embrittlement for material responses to very high strain-rates.A discussion section is arranged to explore the underlying mechanisms of the strain-rate evoked material embrittlement and fragmentation based on dislocation kinetics.
基金supported by the National Natural Science Foundation of China(51973076)the Fundamental Research Funds for Central Universities(2020kfyXJJS035).
文摘The management of diabetic wounds remains a critical therapeutic challenge. Platelet-rich plasma (PRP) gel, PRP-derived exosomes (PRP-Exos), and mesenchymal stem cell-derived exosomes (MSC-Exos) have demonstrated therapeutic potential in wound treatment. Unfortunately, their poor mechanical properties, the short half-lives of growth factors (GFs), and the burst release of GFs and exosomes have limited their clinical applications. Furthermore, proteases in diabetic wounds degrade GFs, which hampers wound repair. Silk fibroin is an enzyme-immobilization biomaterial that could protect GFs from proteases. Herein, we developed novel dual-crosslinked hydrogels based on silk protein (SP) (sericin and fibroin), including SP@PRP, SP@MSC-Exos, and SP@PRP-Exos, to promote diabetic wound healing synergistically. SP@PRP was prepared from PRP and SP using calcium gluconate/thrombin as agonist, while SP@PRP-Exos and SP@MSC-Exos were derived from exosomes and SP with genipin as crosslinker. SP provided improved mechanical properties and enabled the sustained release of GFs and exosomes, thereby overcoming the limitations of PRP and exosomes in wound healing. The dual-crosslinked hydrogels displayed shear-induced thinning, self-healing, and eradication of microbial biofilms in a bone-mimicking environment. In vivo, the dual-crosslinked hydrogels contributed to faster diabetic wound healing than PRP and SP by upregulating GFs expression, down-regulating matrix metalloproteinase-9 expression, and by promoting an anti-NETotic effect, angiogenesis, and re-epithelialization. Hence, these dual-crosslinked hydrogels have the potential to be translated into a new generation of diabetic wound dressings.
基金Supported by the National Natural Science Foundation of China(61473072)
文摘Many chemical processes can be modeled as Wiener models, which consist of a linear dynamic subsystem followed by a static nonlinear block. In this paper, an effective discrete-time adaptive control method is proposed for Wiener nonlinear systems with uncertainties. The parameterization model is derived based on the inverse of the nonlinear function block. The adaptive control method is motivated by self-tuning control and is derived from a modified Clarke criterion function, which considers both tracking properties and control efforts. The uncertain parameters are updated by a recursive least squares algorithm and the control law exhibits an explicit form. The closed-loop system stability properties are discussed. To demonstrate the effectiveness of the obtained results, two groups of simulation examples including an application to composition control in a continuously stirred tank reactor(CSTR) system are studied.
基金Supported by Earmarked Fund for Modern Agro-industry Technology Research System of China(CARS-13)National Key Research and Development Plan(JFYS2016ZY03002156)+6 种基金Ministry of Agriculture Experimental Observation of the Upper Reaches of the Yangtze River Oil Crop Science Station(09203020)Sichuan Crop Breeding CommunityInnovation Ability Promotion Project of Sichuan Provincial Finance(2016zypz-013)Sichuan Province Innovation Team FundingNatural Science Foundation of China(NSFC31360262)Science and Technology Achievements Transformation Project of Sichuan Province(2017CC0052)SAAS Modern Agricultural Technology Special Fund(2015JSCX-012)
文摘As a big rapeseed （Brassica napus L.） producing and consuming country, China provides more and more rapeseea oil year by year. With the development of demand for rapeseed and import of edible oil, rapeseed breeding and production is fac- ing a great challenge. New situation has proposed higher requirements to yield, oil quality and safety, etc. In the review, some aspects about rapeseed breeding in China were reported, including breeding of high-oil content rapeseed, breeding of extremely early-maturing rapeseed, development of mechanization and development of chemical emasculation. Some prospects and expec- tations were also proposed.
文摘Rabies is a serious public health problem in Asia and Africa.Approximately 99%of cases result from a bite by an infected dog.The high rabies risk countries are generally characterized by rapid urbanization;however,the prevalence and risk factors for rabies in urban dogs in developing countries remain unclear.Beijing,the capital of China,has been undergoing rapid urbanization,and implemented compulsory rabies immunization for dogs on October 1,2014.We evaluated the effects of this immunization policy and investigated the dynamics and determinants of the spread of dog rabies virus(RABV)in Beijing.Between 2013 and 2018,the positive rate of rabies in biting dogs declined significantly;79.6%of these were stray dogs.Reconstructed spatiotemporal diffusion for RABV presents a more central distribution within Beijing and a surrounding dissemination of virus lineage toward suburban areas,indicating that rabies is self-sustaining in Beijing.Continuous RABV phylogeographic reconstructions and logistic regression analysis of rabies cases revealed that rabies tended to remain in commercial areas,high-rise residences,demolition areas,and high-GDP,high-population and high-accessibility areas.Demolition areas,where many residents have abandoned their pets,are recognized as high-risk areas for rabies.Our findings reveal that the implementation of the immunization policy in Beijing has been effective in prevention and control of canine rabies,and because the prevalence of canine rabies results from multiple factors,emphasize the important role of multi-sectoral cooperation in rabies prevention and control.
基金support from the National Key Research and Development Program of China(2022YFA1302901 to B.Z.)the National Natural Science Foundation of China(32271210 to B.Z.).
文摘In a recent study published in Science,Zhang et al.discovered that tripartite motif-containing(TRIM)protein 11(TRIM11)exhibited strong inhibition on tau aggregation,which is a pathological characteristic of tauopathies including Alzheimer’s disease(AD).1 This makes TRIM11 a promising novel target for the treatment of AD and other tauopathies.
基金This study was supported by the National Natural Science Foundation of China(U22A2067,62103406,61821005,61925307,and 62333007)。
文摘The success of the Beijing Winter Olympics and Paralympics epitomized the vision of a community with a shared future for humankind.Various robots and artificial intelligence technologies were used in various games and events,such as assisting in parades,logistics,and security inspections.The integration of unmanned robotic systems into torch relays was one of the highlights of the Winter Olympics.
