Amine-functionalized mesoporous UiO-66 aerogel for CO_(2) adsorption

A mesoporous UiO-66-NH_(2) aerogel is prepared via a straightforward sol-gel method without using any binders or mechanical pressures, in which the amine groups are directly introduced into the matrix by using 2-aminoterephthalic acid. The novel UiO-66-NH_(2) aerogel also exhibits high specific surface area and mesopore-dominated structure, implying its highly potential use in CO_(2) adsorption. For ulteriorly investigating the effect of amine loading on the CO_(2) adsorption ability, a series of UiO-66-NH_(2) aerogel with different amino content is fabricated by changing the ligand/metal molar ratio. When the molar ratio is 1.45, the CO_(2) adsorption capacity reaches the optimum value of 2.13 mmol·g^(-1) at 25 ℃ and 0.1 MPa, which is 12.2% higher than that of pure UiO-66 aerogel. Additionally, UiO-66-NH_(2)-1.45 aerogel also has noticeable CO_(2) selectivity against N_(2) and CH_(4) as well as good regeneration stability. Such results imply that it has good application prospect in the field of CO_(2) adsorption, and also contains the potential to be applied in catalysis, separation and other fields.

Multiscale design and biomechanical evaluation of porous spinal fusion cage to realize specified mechanical properties

Backgrou nd Dense titanium(Ti)fusion cages have been commonly used in transforaminal lumbar interbody fusion.However,the stiffness mismatch between cages and adjacent bone endplates increases the risk of stress shielding and cage subsidence.Methods The current study presents a multiscale optimization approach for porous Ti fusion cage development,including microscale topology optimization based on homogenization theory that obtains a unit cell with prescribed mechanical properties,and macroscale topology optimization that determines the layout of framework structure over the porous cage while maintaining the desired stiffness.The biomechanical performance of the designed porous cage is assessed using numerical simulations of fusion surgery.Selective laser melting is employed to assists with fabricating the designed porous structure and porous cage.Results The simulations demonstrate that the designed porous cage increases the strain energy density of bone grafts and decreases the peak stress on bone endplates.The mechanical and morphological discrepancies between the as-designed and fabricated porous structures are also described.Conclusion From the perspective of biomechanics,it is demonstrated that the designed porous cage contributes to reducing the risk of stress shielding and cage subsidence.The optimization of processing parameters and post-treatments are required to fabricate the designed porous cage.The present multiscale optimization approach can be extended to the development of cages with other shapes or materials and further types of orthopedic implants.

Friction behaviors in the metal cutting process:state of the art and future perspectives

Material removal in the cutting process is regarded as a friction system with multiple input and output variables.The complexity of the cutting friction system is caused by the extreme conditions existing on the tool–chip and tool–workpiece interfaces.The critical issue is significant to use knowledge of cutting friction behaviors to guide researchers and industrial manufacturing engineers in designing rational cutting processes to reduce tool wear and improve surface quality.This review focuses on the state of the art of research on friction behaviors in cutting procedures as well as future perspectives.First,the cutting friction phenomena under extreme conditions,such as high temperature,large strain/strain rates,sticking–sliding contact states,and diverse cutting conditions are analyzed.Second,the theoretical models of cutting friction behaviors and the application of simulation technology are discussed.Third,the factors that affect friction behaviors are analyzed,including material matching,cutting parameters,lubrication/cooling conditions,micro/nano surface textures,and tool coatings.Then,the consequences of the cutting friction phenomena,including tool wear patterns,tool life,chip formation,and the machined surface are analyzed.Finally,the research limitations and future work for cutting friction behaviors are discussed.This review contributes to the understanding of cutting friction behaviors and the development of high-quality cutting technology.

Mechanism and Method of Testing Fracture Toughness and Impact Absorbed Energy of Ductile Metals by Spherical Indentation Tests

To address the problem of conventional approaches for mechanical property determination requiring destructive sampling, which may be unsuitable for in-service structures, the authors proposed a method for determining the quasi-static fracture toughness and impact absorbed energy of ductile metals from spherical indentation tests (SITs). The stress status and damage mechanism of SIT, mode I fracture, Charpy impact tests, and related tests were frst investigated through fnite element (FE) calculations and scanning electron microscopy (SEM) observations, respectively. It was found that the damage mechanism of SITs is diferent from that of mode I fractures, while mode I fractures and Charpy impact tests share the same damage mechanism. Considering the diference between SIT and mode I fractures, uniaxial tension and pure shear were introduced to correlate SIT with mode I fractures. Based on this, the widely used critical indentation energy (CIE) model for fracture toughness determination using SITs was modifed. The quasi-static fracture toughness determined from the modifed CIE model was used to evaluate the impact absorbed energy using the dynamic fracture toughness and energy for crack initiation. The efectiveness of the newly proposed method was verifed through experiments on four types of steels: Q345R, SA508-3, 18MnMoNbR, and S30408.

Research progress of laser cladding self-fluxing alloy coatings on titanium alloys

Laser cladding is a new surface modification technology,and is widely used for fabricating wear and corrosion resistant composites coatings. Self-fluxing alloys have many advantages,such as excellent properties of deoxidizing and slagging,high wear resistance,low melting point and easy cladding,and are often used in laser cladding to improve wear and corrosion resistance of titanium and its alloys. In this paper,the recent development of Ni-based and Co-based self-fluxing alloy coatings which includes the influence of rare earth and ceramic particles in coatings are summarized. Besides,the effects of processing parameters,such as laser power and scanning speed,on coatings are reviewed. Finally,the trend of development in the future is forecasted.

Three‑dimensional Modeling and Simulation of Muscle Tissue Puncture Process

Needle biopsy is an essential part of modern clinical medicine.The puncture accuracy and sampling success rate of puncture surgery can be effectively improved through virtual surgery.There are few three-dimensional puncture(3D)models,which have little significance for surgical guidance under complicated conditions and restrict the development of virtual surgery.In this paper,a 3D simulation of the muscle tissue puncture process is studied.Firstly,the mechanical properties of muscle tissue are measured.The Mooney-Rivlin(M-R)model is selected by considering the fitting accuracy and calculation speed.Subsequently,an accurate 3D dynamic puncture model is established.The failure criterion is used to define the breaking characteristics of the muscle,and the bilinear cohesion model defines the breaking process.Experiments with different puncture speeds are carried out through the built in vitro puncture platform.The experimental results are compared with the simulation results.The experimental and simulated reaction force curves are highly consistent,which verifies the accuracy of the model.Finally,the model under different parameters is studied.The simulation results of varying puncture depths and puncture speeds are analyzed.The 3D puncture model can provide more accurate model support for virtual surgery and help improve the success rate of puncture surgery.

Improving the forming performance of incrementally formed sheet parts with customized heat treatment strategies

Although incremental sheet forming(ISF)is an efficient way to manufacture customized parts,the forming performance and geometric accuracy of formed parts need to be improved to meet industrial application.One feasible solution for these problems is to adopt proper heat treatment strategies for the sheet material both before and during the forming process.In this paper,the effects of heat treatment before forming and heat-assisted forming on the formability and performance of formed parts were experimentally investigated.First,TA1 sheets were heat-treated at different temperatures before forming,and then the sheets were incrementally formed into the target shape with variable angles at different temperatures.After heat treatment,the strength of sheets was decreased due to the occurrence of recrystallization and the growth of grains.Meanwhile,the surface quality of formed parts was also improved with pre-heat treatment before forming.During the heat-assisted forming process,the sheet was softened and the deformation resistance was reduced with the increase of temperature.Therefore,the axial forming force was decreased obviously and the formability of the sheet was increased obviously.Furthermore,by adopting both heat treatment and heat-assisted forming,it was found that the forming force could be further reduced and the formability of the sheet and surface quality could be further improved.As for geometric accuracy,heat treatment has a good effect on improving it,while heat-assisted forming has adverse effect.These findings provide an effective heat treatment strategy for improving the geometric accuracy and surface quality of the incrementally formed parts with lower forming force.

A novel approach to minimizing material loss for computer numerical control flank-regrinding of worn end mills

Flanks of end mills are prone to wear in a long machining process.Regrinding is widely used in workshops to restore the flank to an original-like state.However,the traditional method involves material waste by trial and error and dramatically decreases the potential regrinding.Moreover,over-cut would happen to the flutes of worn cutters in the regrinding processes because of improper wheel path.This study presented a new approach to planning the wheel path for regrinding worn end mills to minimize material loss and recover the over-cut.In planning,a scaling method was developed to determine the maximum size of the new cutter according to the similarity of cutter shapes before and after regrinding.Then,the wheel path is first generated by envelope theory to regrind the worn area with a four-axis computer numerical control grinder according to the new size of cutters.Moreover,a second regrinding strategy is applied to recover the flute shape over-cut in the first grinding.Finally,the proposed method is verified by an experiment.Results showed that the proposed approach could save 25%of cutter material compared with the traditional method and ensure at least three regrinding times.This work effectively provides a general regrinding solution for the worn flank with maximum material-saving and regrinding period.

Effects of FDM-3D printing parameters on mechanical properties and microstructure of CF/PEEK and GF/PEEK

Fused deposition modeling(FDM)has unique advantages in the rapid prototyping of thermoplastics which have been developed in diverse fields.However,although great efforts have been made to optimize FDM process,the mechanical properties of printed parts are limited by the weak interlamination bonding as well as the poor performance of raw filaments used,such as acrylonitrile butadiene styrene(ABS),polylactic acid(PLA).Adding fibers into thermoplastic matrix and preparing high-performance filaments have been indicated to enhance the properties of fabricated parts.Recently,heat-resistant polyetheretherketone(PEEK)and its fiber reinforced composites were proposed for FDM process due to overcoming the limitation of equipment and process.However,few researches have been reported on the effects of FDM-3 D printing parameters on the mechanical properties of fiber reinforced PEEK composites.Therefore,5 wt%carbon fiber(CF)and glass fiber(GF)reinforced PEEK composite filaments were prepared respectively in this study.The effects of various printing parameters including nozzle temperature,platform temperature,printing speed and layer thickness on the mechanical properties(including tensile strength,flexural strength and impact strength)were surveyed.To analyze the microstructure and failure reasons of printed CF/PEEK and GF/PEEK samples,the tensile fractured surfaces were investigated via scanning electron microscope(SEM).

The influence of ultrasonic vibration on parts properties during incremental sheet forming

The integration of ultrasonic vibration into sheet forming process can significantly reduce the forming force and bring benefits including the enhancement of surface quality,the enhancement of formability and the reduction of spring-back.However,the influencing mechanisms of the high-frequency vibration on parts properties during the incremental sheet forming(ISF)process are not well known,preventing a more efficient forming system.This paper comprehensively investigates the effects of different process parameters(vibration amplitude,step-down size,rotation speed and forming angle)on the micro-hardness,minimum thickness,forming limit and residual stress of the formed parts.First,a series of truncated pyramids were formed with an experimental platform designed for the ultrasonic-assisted incremental sheet forming.Then,microhardness tests,minimum thickness measurements and residual stress tests were performed for the formed parts.The results showed that the surface micro-hardness of the formed part was reduced since the vibration stress induced by the ultrasonic vibration within the material which eliminated the original internal stress.The superimposed University,Beijing 100083,People’s Republic of China ultrasonic vibration can effectively uniform the residual stress and thickness distribution,arid improve the forming limit in the case of the small deformation rate.In addition,through the tensile fracture analysis of the formed part,it is shown that the elongation of material is improved and the elastic modulus and hardening index are decreased.The findings of the present work lay the foundation for a better integration of the ultrasonic vibration system into the incremental sheet forming process.

Effects of process parameters on periodic impact force exerting on cutting tool in ultrasonic vibration-assisted oblique turning

During ultrasonic vibration-assisted machining,the large impact force induced by tool-workpiece reengagement(TWR)is an important factor that affects tool chipping.However,mechanical analysis into process factors that affect the impact force and their influencing mechanisms are insufficient.Herein,a prediction model for the instantaneous cutting force during both TWR and the stable turning process,which depends on the process parameters and material properties,is firstly proposed based on the kinematic and dynamic analysis of ultrasonic vibration-assisted oblique turning(UVAOT).The results calculated using the developed cutting force model agree well with the experimental results presented in the literature.Next,the linear change law of the instantaneous cutting force with cutting time during the actual TWR is clarified using the proposed model.The effect of the UVAOT process parameters on the average impact force during the periodic TWR process is discussed,and the influence mechanism is analyzed from the perspective of mechanics.A positive linear correlation is discovered between the feed speed and average impact force.The ultrasonic amplitude and cutting speed do not significantly affect the average impact force of the new sharp cutting tools.These findings are consistent with the experimental observations of tool chipping and are applicable to select process parameters for reducing tool chipping during UVAOT.

Investigation of mini-hydrocyclone performance in removing small-size microplastics

Large amounts of microplastics(MPs)have been found in rivers and oceans,bringing great harm to aquatic animals,plants,even human beings.However,the effective removal method of MPs,especially those with small sizes(5-20 μm)is still lacking.This work presents mini-hydrocyclones to remove 10 μm(average size)diameter MPs.The removal performance of nine mini-hydrocyclones with different diameters of spigot and vortex finder is examined experimentally and numerically.The performance of the designed cyclones is evaluated in terms of recovery,water split,concentration ratio and pressure drop.The results show that mini-hydrocyclones are applicable to removing small-size MPs with the maximum concentra-tion ratio at 2.16 and the particle recovery at 51%.The flow characteristics inside the mini-hydrocyclones are analyzed in detail.It is shown that the distributions of water axial velocity and radial velocity could collectively affect the behaviors of small-size MPs in mini-hydrocyclones.Specifically,a larger amount of water split could entrain more fine particles to underflow.Meanwhile,a less frequent alternation of radial velocity between the positive and negative directions on the same side of the cyclone should benefit the removal of small-size MPs.

Modal parameter determination and chatter prediction for blade whirling: a comparative study based on symmetric and asymmetric FRF

Whirling has been adopted for the cost-effective machining of blade-shape components in addition to traditional end milling and flank milling processes.To satisfy the requirements of rotary forming in the blade whirling process,the workpiece must be clamped at both ends in suspension and rotated slowly during machining,which complicates the dynamics.This study aims to identify the dynamic characteristics within the blade whirling operation and present strategies for stability prediction.In this study,the dynamic characteristics of a whirling system are modeled by assuming symmetric and asymmetric parameters.Theoretical prediction frequency response function(FRF)results are compared with experimental results.Moreover,semi-discretization stability lobe diagrams(SLDs)obtained using the dynamic parameters of these models are investigated experimentally.The results show that the asymmetric model is more suitable for describing the whirling system,whereas the symmetric model presents limitations associated with the frequency range and location of measuring points.Finally,a set of airfoil propeller blade whirling operations is conducted to verify the prediction accuracy.

Influences of processing parameters and heat treatment on microstructure and mechanical behavior of Ti-6Al-4V fabricated using selective laser melting

Selective laser melting(SLM)has provided an alternative to the conventional fabrication techniques for Ti-6Al-4V alloy parts because of its flexibility and ease in creating complex features.Therefore,this study investigated the effects of the process parameters and heat treatment on the microstructure and mechanical properties of Ti-6Al-4V fabricated using SLM.The influences of various process parameters on the relative density,tensile properties,impact toughness,and hardness of Ti-6Al-4V alloy parts were studied.By employing parameter optimization,a high-density high-strength Ti-6Al-4V alloy was fabricated by SLM.A relative density of 99.45%,a tensile strength of 1188 MPa,and an elongation to failure of 9.5%were achieved for the SLM-fabricated Ti-6Al-4V alloy with optimized parameters.The effects of annealing and solution aging heat treatment on the mechanical properties,phase composition,and microstructure of the SLM-fabricated Ti-6Al-4V alloy were also studied.The ductility of the heat-treated Ti-6Al-4V alloy was improved.By applying a heat treatment at 850℃ for 2 h,followed by furnace cooling,the elongation to failure and impact toughness were found to be increased from 9.5%to 12.5%,and from 24.13 J/cm^(2)to 47.51 J/cm^(2),respectively.

Prediction of temperature field in machined workpiece surface during the cutting of Inconel 718 coated with surface-active media

The heat generated and accumulated on the machined surface of an Inconel 718 workpiece causes thermal damage during the cutting process.Surface-active media with high thermal conductivity coated on the workpiece to be machined may have the potential to reduce the generation of cutting heat.In this study,a theoretical model for predicting the instantaneous machined surface temperature field is proposed for surface-active thermal conductive medium(SACM)-assisted cutting based on the finite element and Fourier heat transfer theories.Orthogonal cutting experiments were performed to verify the results predicted using the proposed surface-temperature field model.Three SACMs with various thermal conductivities were used to coat Inconel 718 surface to be machined.Thermocouples embedded into the workpiece were used to measure the cutting temperature at different points on the machined workpiece surface during the cutting process.The experimental results were in agreement with the predicted temperatures,and the maximum error between the experimental results and predicted temperatures was approximately 9.5%.The cutting temperature on the machined surface decreased with an increase in the thermal conductivity of the SACM.The graphene SACM with high thermal conductivity can effectively reduce the temperature from 542℃ to 402℃,which corresponds to a reduction of approximately 26%.The temperature reduction due to SACM decreases with an increase in the distance between the temperature prediction point and machined workpiece surface.In conclusion,the cutting temperatures on the machined workpiece surface can be reduced by coating with SACM.

Fiber orientation effects on grinding characteristics and removal mechanism of 2.5D C_(f)/SiC composites

Carbon fiber reinforced silicon carbide(C_(f)/SiC)composites are widely used in aerospace for their excellent mechanical properties.However,the quality of the machined surface is poor and unpredictable due to the material heterogeneity induced by complex removal mechanism.To clarify the effects of fiber orientation on the grinding characteristics and removal mechanism,single grit scratch experiments under different fiber orientations are conducted and a three-phase numerical modelling method for 2.5D C_(f)/SiC composites is proposed.Three fiber cutting modes i.e.,transverse,normal and longitudinal,are defined by fiber orientation and three machining directions i.e.,MA(longitudinal and normal),MB(longitudinal and transverse)and MC(normal and transverse),are selected to investigate the effect of fiber orientation on grinding force and micro-morphology.Besides,a three-phase cutting model of 2.5D C_(f)/SiC composites considering the mechanical properties of the matrix,fiber and interface is developed.Corresponding simulations are performed to reveal the micro-mechanism of crack initiation and extension as well as the material removal mechanism under different fiber orientations.The results indicate that the scratching forces fluctuate periodically,and the order of mean forces is MA>MC>MB.Cracks tend to grow along the fiber axis,which results in the largest damage layer for transverse fibers and the smallest for longitudinal fibers.The removal modes of transverse fibers are worn,fracture and peel-off,in which normal fibers are pullout and outcrop and the longitudinal fibers are worn and push-off.Under the stable cutting condition,the change of contact area between fiber and grit leads to different removal modes of fiber in the same cutting mode,and the increase of contact area results in the aggravation of fiber fracture.

Probing the intriguing frictional behavior of hydrogels during alternative sliding velocity cycles

Understanding the friction behavior of hydrogels is critical for the long-term stability of hydrogelrelated bioengineering applications.Instead of maintaining a constant sliding velocity,the actual motion of bio-components(e.g.,articular cartilage and cornea)often changes abruptly.Therefore,it is important to study the frictional properties of hydrogels serving under various sliding velocities.In this work,an unexpected low friction regime(friction coefficientμ<10^(-4) at 1.05×10^(-3) rad/s)was observed when the polyacrylamide hydrogel was rotated against a glass substrate under alternative sliding velocity cycles.Interestingly,compared with the friction coefficients under constant sliding velocities,the measuredμdecreased significantly when the sliding velocity changed abruptly from high speeds(e.g.,105 rad/s)to low speeds(e.g.,1.05×10^(-3) rad/s).In addition,μexhibited a downswing trend at low speeds after experiencing more alternative sliding velocity cycles:the measuredμat 1.05 rad/s decreased from 2×10^(-2) to 3×10^(-3) after 10 friction cycles.It is found that the combined effect of hydration film and polymer network deformation determines the lubrication and drag reduction of hydrogels when the sliding velocity changes abruptly.The observed extremely low friction during alternative sliding velocity cycles can be applied to reduce friction at contacted interfaces.This work provides new insights into the fundamental understanding of the lubrication behaviors and mechanisms of hydrogels,with useful implications for the hydration lubrication related engineering applications such as artificial cartilage.

Constrained layer damping treatment of a model support sting

In transonic wind tunnel tests,the pulsating airflow is prone to induce the first order resonance of the sting support system.The resonance limits the wind tunnel test envelope,makes the test data inaccurate,and brings potential security risks.In this paper,a model support sting with constrained layer damping(CLD)treatment is proposed to reduce the first order resonance response.The CLD treatment mainly consists of material selection and geometric optimization processes.The damping performance of the optimized CLD sting is compared with an AISI 1045 steel sting with the identical diameter in laboratory.The frequency response curves of the CLD sting support system and the AISI 1045 steel sting support system are obtained by sine sweep tests.The test results show that the first order resonance response of the CLD sting support system is 37.3%of that of the AISI 1045 steel sting support system.The first order damping ratios are calculated from the frequency response curves by half power point method.It is found that the first order damping ratio of the CLD sting support system is approximately 2.6 times that of the AISI 1045 steel sting support system.

Surface integrity evolution of machined NiTi shape memory alloys after turning process

Owing to their shape memory effect and pseudoelasticity,NiTi shape memory alloys(SMAs)are widely used as functional materials.Mechanical processes particularly influence the final formation of the product owing to thermal softening and work-hardening effects.Surface integrity is an intermediate bridge between the machining parameter and performance of the product.In this study,experiments were carried out on turning NiTi SMAs at different cutting speeds,where surface integrity characteristics were analyzed.The results show that a higher cutting speed of 125 m/min is required to turn NiTi SMAs based on the evaluation of surface integrity.The degree of work hardening is higher at 15 m/min.Consequently,as a primary effect,work hardening appears on the plastic deformation of the machined samples,leading to dislocations and defects.As the cutting speed increases,the thermal softening effect exceeds work hardening and creates a smoother surface.A stress-induced martensitic transformation is considered during the turning process,but this transformation is reversed to an austenite from the X-ray diffraction(XRD)results.According to the differential scanning calorimetry(DSC)curves,the phase state and phase transformation are less influenced by machining.Subsequently,the functional properties of NiTi-SMAs are less affected by machining.

Damage mechanism and evaluation model of compressor impeller remanufacturing blanks:A review

The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program“Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing”are reviewed in this work.Large centrifugal compressor impeller blanks were used as the study object.The materials of the blanks were FV520B and KMN.The mechanism and evaluation model of ultra-high cycle fatigue,erosion wear,and corrosion damage were studied via theoretical calculation,finite element simulation,and experimentation.For ultra-high cycle fatigue damage,the characteristics of ultra-high cycle fatigue of the impeller material were clarified,and prediction models of ultra-high cycle fatigue strength were established.A residual life evaluation technique based on the“b-HV-N”(where b was the nonlinear parameter,HV was the Vickers hardness,and N was the fatigue life)double criterion method was proposed.For erosion wear,the flow field of gas-solid two-phase flow inside the impeller was simulated,and the erosion wear law was clarified.Two models for erosion rate and erosion depth calculation were established.For corrosion damage,the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated.KISCC(critical stress intensity factor)and da/dt(crack growth rate,where a is the total crack length and t is time)varied with H2S concentration and temperature,and their variation laws were revealed.Through this research,the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multi-strength field and cross-scale were solved.The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.