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Hole-making for Carbon Fiber Reinforced Plastics (CFRP)/Ti-6Al-4 V stacks is crucial for the assembling strength of aircraft structure parts. This work carried out experimental work for helical milling (HM) of the stacks with sustainable cooling/lubrication (dry, MQL and cryogenic) conditions. Cutting forces and temperatures at the CFRP layer, Ti-6Al-4 V layer and the interface of stacks were obtained by a developed measuring system. The temperatures in CFRP machining at cryogenic condition varied from −167 °C to −94 °C, which were much lower than those at dry and MQL conditions. The maximum temperature near the interface of stacks for the ninth hole was higher than 240 °C due to heat conduction from Ti-6Al-4 V layer. The hole quality, hole diameter and tool wear mechanism at different cooling/lubrication conditions were presented and discussed. MQL condition generated mainly extrusion fracture for the fibers, due to the reduced friction effect compared with dry condition. MQL was helpful to reduce the feed mark at the hole surface of Ti-6Al-4 V alloy. The flank wear of cutting edge at MQL condition was better than those at dry and cryogenic conditions. Cryogenic cooling contributed to better CFRP surface with smaller delamination and hole entrance damage due to the increased resin strength and fiber brittleness. The damage near the entrance of CFRP were analyzed by the contact state of cutting edges and fibers. Additionally, hole diameters near the exit of CFPR layer were larger than other test positions. This work provided feasible processes for improving hole quality and tool life in hole-making of CFRP/Ti-6Al-4 V stacks.

In order to study the friction and wear properties of cast iron in free grinding environment under the condition of line contact. This paper presented a new method to calculate the friction coefficient by measuring the friction torque. Through the self-developed free abrasive grinding experimental device in line contact condition, this work carried out friction and wear experiment with relative speed, load, abrasive particle diameter and abrasive mass fraction as process parameters, and studied the evolution rules of friction coefficient and wear amount of cast iron materials under different process parameters. Based on the response surface method Box-Behnken experimental design, the significance of the experimental results was analyzed, and the prediction model of the friction coefficient and wear amount of cast iron material was established. According to the significance of the prediction model, the influence degree of each process parameter on the friction coefficient and wear amount was revealed. The results showed that under the action of free abrasive, the friction coefficient of cast iron material in line contact with GCr15 is between 0.18 and 0.35. When the experimental time is 1.5h, the removal amount of cast iron material is between 20mg and 65mg. Which is significantly increased compared with that without abrasive and the wearing capacity of cast iron increases with the increase of relative speed, load, abrasive particle diameter and abrasive mass fraction. The friction coefficient had a negative correlation with relative speed, and a positive correlation with abrasive particle diameter and abrasive mass fraction, With the increase of load, the change of friction coefficient decreased first and then increased. The influence degree of each process parameter on the friction coefficient and wear amount of cast iron material: the particle diameter and relative velocity of abrasive were relatively significant, the abrasive mass fraction was the second, and the load was the smallest. Through random experiments, the prediction model of friction coefficient and wearing capacity were verified to be highly accuracy, and could be used to predict the friction and wear performance parameters of cast iron materials in the process of free grinding under the condition of line contact. It provided a certain theoretical basis for the friction and wear behavior of cast iron as a grinding tool material in the grinding process.

Among ceramic matrix composites (CMCs), carbon fiber-reinforced silicon carbide matrix (C/SiC) composites are widely used in numerous high-temperature structural applications because of their superior properties. The fiber–matrix (FM) interface is a decisive constituent to ensure material integrity and efficient crack deflection. Therefore, there is a critical need to study the mechanical properties of the FM interface in applications of C/SiC composites. In this study, tensile tests were conducted to evaluate the interfacial debonding stress on unidirectional C/SiC composites with fibers oriented perpendicularly to the loading direction in order to perfectly open the interfaces. The characteristics of the material damage behaviors in the tensile tests were successfully detected and distinguished using the acoustic emission (AE) technique. The relationships between the damage behaviors and features of AE signals were investigated. The results showed that there were obviously three damage stages, including the initiation and growth of cracks, FM interfacial debonding, and large-scale development and bridging of cracks, which finally resulted in material failure in the transverse tensile tests of unidirectional C/SiC composites. The frequency components distributed around 92.5 kHz were dominated by matrix damage and failure, and the high-frequency components distributed around 175.5 kHz were dominated by FM interfacial debonding. Based on the stress and strain versus time curves, the average interfacial debonding stress of the unidirectional C/SiC composites was approximately 1.91 MPa. Furthermore, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to observe the morphologies and analyze the chemical compositions of the fractured surfaces. The results confirmed that the fiber was completely debonded from a matrix on the fractured surface. The damage behaviors of the C/SiC composites were mainly the syntheses of matrix cracking, fiber breakage, and FM interfacial debonding.

High-speed cutting (HSC) and ultra-high-speed cutting (u-HSC) (6.07–32.7 m/s) tests of Ti-6Al-4V alloy were developed based on an improved Split Hopkinson Pressure Bars (SHPB) system. Specific cutting energy was calculated and scaling effect was observed in HSC with different uncut chip thicknesses (20–200 μm). Considering time-dependent (in situ and ex situ) microstructure and mechanical parameters, chip morphology, adiabatic shear band (ASB), chip-free surface, material separation characteristic at chip-workpiece interface, and surface integrity were investigated. The micro-hardness within ASB was 25% higher than that outside of the ASB. Ultra-fine grains (77% grain sizes less than 330 nm) and micro-texture were observed by electron backscattering diffraction (EBSD) test. Grain refinement in ASB was explained by rotation dynamic recrystallization. The maximum shear strain and the range of shear strain rate in ASB at the condition of v = 10 m/s and t1 = 100 μm were approximately 17 and 6.44 × 106 s−1–8.5 × 106 s−1, respectively. Severe plastic deformation was observed by the dimples at ductile fracture surface along ASB. Mechanism of parabolic and ellipsoid dimples caused by shear and tensile stresses was explained for HSC of Ti-6Al-4V alloy. Additionally, the micro-hardness of machined subsurface and the ASB (ex situ parameter) exhibits a relationship with specific energy (in situ parameter), which can provide an effective way to control the formation of ASB and surface integrity by the control of in situ parameters in HSC and u-HSC conditions.

Helical milling (HM), axial ultrasonic vibration helical milling (A-UVHM) and longitudinal and torsional ultrasonic vibration helical milling (LT-UVHM) were developed for hole-making of Carbon Fiber Reinforced Plastic (CFRP) composites. Cutting trajectory, cutting speed, acceleration and effective rake angle of peripheral edge in HM and UVHM processes were modeled. Compared with HM, axial forces with UVHM processes were reduced by 9.0 %–35.7 %. The burrs at entrance and exit with UVHM were also reduced. In A-UVHM and LT-UVHM processes, an effect of shear with variable direction which is good to fracture fibers was presented, according to the relative movement of peripheral edge and fibers. Additionally, the variations of cutting speed and acceleration in A-UVHM and LT-UVHM are also helpful to fracture fibers, due to the wide range of speed and impact effect. Smooth surface with regular fiber fracture morphology and tiny fragments was generated in UVHM due to the effect of shear along variable direction. Compared with HM, the maximum effective rake angle of peripheral edge in UVHM was increased by 112.1 %–192.6 %, which is helpful to fracture fibers by sharper cutting edge.

The requirement of high-speed and high-precision contouring with NURBS tool path to the CNC machining process is increasing. The calculation of the contouring error (CE) of the NURBS tool path to real time is necessary for the advanced contour control like the cross-coupled controller (CCC). Based on the complexity of the CE calculation of NURBS, most studies use estimating methods to approximate the real CE in the controller. However, when the cutter is at the large curvature zones in the high-speed machining, the difference between the estimated the CE and the real one becomes large. To solve this problem, an algorithm to calculate the exact CE of NURBS tool path to real time is proposed. The calculation model of the CE of NURBS is derived. Also, the numerical calculation algorithm from Brent’s method is given to solve the CE model. Multiple solutions of CE model is discussed and real-time solution tracking method is developed to determine the intervals of the candidate solutions for numerical calculation. Contour error for control (CCE) is proposed for controller design to improve the stability of contour control, which is different from the definition of conventional control error for measurement (MCE). The proposed algorithm is validated for both the simulation and the experiment on the X–Y table. Experimental results show the effectiveness of the proposed algorithm and the actual CE is reduced significantly compared with other methods.

Implant-associated infections are generally difficult to cure owing to the bacterial antibiotic resistance which is attributed to the widespread usage of antibiotics. Given the global threat and increasing influence of antibiotic resistance, there is an urgent demand to explore novel antibacterial strategies other than using antibiotics. Recently, using a certain surface topography to provide a more persistent antibacterial solution attracts more and more attention. However, the clinical application of biomimetic nano-pillar array is not satisfactory, mainly because its antibacterial ability against Gram-positive strain is not good enough. Thus, the pillar array should be equipped with other antibacterial agents to fulfill the bacteriostatic and bactericidal requirements of clinical application. Here, we designed a novel model substrate which was a combination of periodic micro/nano-pillar array and TiO2 for basically understanding the topographical bacteriostatic effects of periodic micro/nano-pillar array and the photocatalytic bactericidal activity of TiO2. Such innovation may potentially exert the synergistic effects by integrating the persistent topographical antibacterial activity and the non-invasive X-ray induced photocatalytic antibacterial property of TiO2 to combat against antibiotic-resistant implant-associated infections. First, to separately verify the topographical antibacterial activity of TiO2 periodic micro/nano-pillar array, we systematically investigated its effects on bacterial adhesion, growth, proliferation, and viability in the dark without involving the photocatalysis of TiO2. The pillar array with sub-micron motif size can significantly inhibit the adhesion, growth, and proliferation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Such antibacterial ability is mainly attributed to a spatial confinement size-effect and limited contact area availability generated by the special topography of pillar array. Moreover, the pillar array is not lethal to S. aureus and E. coli in 24 h. Then, the X-ray induced photocatalytic antibacterial property of TiO2 periodic micro/nano-pillar array in vitro and in vivo will be systematically studied in a future work. This study could shed light on the direction of surface topography design for future medical implants to combat against antibiotic-resistant implant-associated infections without using antibiotics. Keywords: Titanium dioxide, Micro/nano-structured surface, Topographical bacteriostatic activity, Photocatalytic bactericidal property, Non-invasive treatment

Surface quality of workpiece could be significantly improved by ELID grinding. However, ELID grinding bearing outer ring raceway with small inner diameter has small space, which limits installation of electrode. In this work, ELID grinding bearing outer ring raceway acting as cathode is proposed. But electric spark discharge will occur in ELID grinding with workpiece-cathode, which affects grinding quality. The purpose of this work is to investigate formation mechanism of electric spark discharge and influence of oxide layer on grinding quality. A novel experimental method is proposed to study state of oxide layer (mainly thickness and compactness) in ELID grinding bearing outer ring raceway with workpiece-cathode. Experimental results show that electric spark discharge occurs with thick oxide layer (characterized by control current), resulting in corroded pits on surface of oxide layer and workpiece in ELID grinding with workpiece-cathode. With increased control current, surface of oxide layer becomes smooth. Moreover, grinding force increases with increased control current. When control current is 0.5 A, surface roughness of workpiece is the largest. And surface roughness of workpiece increases with increased control current, as control current is greater than or equal to 1 A. The results are helpful to apply ELID to grind bearing outer ring raceway and improve ELID grinding performance.

Fluoridated hydroxyapatite (FHA) [Ca10(PO4)6Fx(OH)2−x, x = 0–2] is believed to be a promising calcium phosphate (CaP) to replace pure hydroxyapatite (HA) for next-generation implants, owing to its better biocompatibility, higher antibacterial activity, and lower solubility. Notably, the shape and size of the CaP crystals play key roles in their performance and can influence their applications. One-dimensional (1D) FHA nanorods are important CaP materials which have been widely used in regenerative medicine applications such as restorative dentistry. Unfortunately, the traditional synthesis methods for FHA nanorods either employ surfactants or take a relatively long time. In this study, we aimed to propose a facile synthesis route to fabricate FHA nanorods without any surfactants using an electrochemical deposition method for the first time. This study focused on preparing FHA nanorods without the assistance of any surfactant, unlike the traditional synthesis methods, to avoid chemical impurities. FHA nanorods with lengths of 124–2606 nm, diameters of 28–211 nm, and aspect ratios of 4.4–21.8 were synthesized using the electrochemical method, followed by a heat treatment. For the as-synthesized FHA nanorods, the Ca/P ratio was 1.60 and the atomic concentration of F was 2.06 at.%. An ultrastructure examination revealed that each FHA nanorod possessed long-range order, good crystallinity, and a defect-free lattice with a certain crystallographic plane orientation along the whole rod. In short, we propose a novel, surfactant-free, cost-saving, and more efficient route to synthesize FHA nanorods which can be widely applied in multiple biomedical applications, including drug delivery, bone repair, and restorative dentistry.

Compared with conventional hole-making process, rotary ultrasonic machining (RUM) is commonly believed to improve the cutting performance, such as low cutting force, good hole quality, long tool life, and high material removal rate. However, this work proposes an interesting observation on hole-making process using longitude-torsional ultrasonic assisted helical milling (LT UAHM). Due to the special kinematic motion in LT UAHM, the trajectory of the cutting tool has complex characteristics which may generate a negative effect on machining performance. In this study, a comparative experiment between LT UAHM and conventional helical milling (HM) was carried out. The results showed that the axial cutting force is not always reduced, the machined hole quality is also not improved consistently in LT UAHM. To comprehend the cutting mechanism of LT UAHM incisively, a kinematic trajectory model was proposed. By the theoretical kinematic trajectory model, LT UAHM can generate the ultrasonic elliptical cutting in the process, and the phase shift is a critical factor that can affect the elliptical trajectory shape even the vibration cutting direction of the tool’s cutting edge. The equivalent cutting angle and direction of friction between the rake face and chip in processing change accordingly. As a result, the magnitude of cutting force and machined hole quality in terms of burr height in this process will be significantly affected.

Currently, the characteristics of solid-state phase transformation corresponding to octacalcium phosphate (OCP) sintering is still not completely understood. Although it was known that Ca-deficient (Ca-def) hydroxyapatite (HA) is usually unstable at high temperature, the thermal stability and sintering behavior of OCP have been rarely reported. The objective of this study is to systematically investigate the thermal stability and sintering behavior of OCP powders by comprehensive characterization techniques including in-situ high temperature X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA) and scanning electron microscopy (SEM). In-situ XRD results showed that the “collapsed OCP”, Ca-def HA and β-tricalcium phosphate (TCP) crystal structures formed by heating OCP at 200–250 °C, 300–600 °C and 800–900 °C, respectively. Furthermore, DTA analysis revealed that the peak temperatures of the phase transitions of OCP to Ca-def HA and Ca-def HA to β-TCP were ∼170 °C and ∼720 °C, respectively. SEM examination indicated that a large number of pores were introduced during sintering OCP powders due to the release of structurally contained water at 200–250 °C. Therefore, a porous β-TCP ceramic can be directly prepared by sintering OCP powders at 900 °C. This phase transition induced foaming method may be extended for preparing porous bioceramics by sintering calcium phosphate phases as long as they contain crystalline water, which could provide guidelines for better utilizing the phase transformations of calcium phosphate to produce special bioceramics for biomedical applications.

As one of the ceramic matrix composites (CMCs), carbon fiber-reinforced silicon carbide matrix (C/SiC) composites are promising materials used in various engineering applications owing to their superior properties. Precision surface grinding has been widely applied in the machining of CMC composites; however, the material removal mechanisms of C/SiC composites have not been fully elucidated yet. To reveal the material removal mechanisms in the grinding of chemical vapor infiltration-fabricated C/SiC composites, novel single-abrasive scratch tests were designed and conducted in two typical cutting directions. The experimental parameters, especially the cutting speed, conformed to the actual grinding process. The results show that the grinding parameters (feed rate, spindle speed, depth of cut, and cutting direction) have significant influences on the grinding forces, surface integrity, and affected subsurface region. The tangential force is in general larger than the normal force at the same cutting depth. Furthermore, both the tangential and normal forces in the longitudinal cutting direction are larger than those in the transverse cutting direction. The impacts and abrasive actions at the tool tip mainly caused the material removal. The predominant material removal mode is brittle fracture in the grinding of unidirectional C/SiC composites, because the damage behaviors of the C/SiC composites are mainly the syntheses of matrix cracking, fiber breakage, and fiber/matrix interfacial debonding. These results are rationalized based on the composite properties and microstructural damage features.

Cutting simulation technology is widely used to predict the micro-scale and instantaneous information in cutting and can be used to reduce the manufacturing costs in industry. Material constitutive models characterize the deformation behaviors involved in cutting and are the key factors affecting the simulation accuracy. In this work, different plastic constitutive models, JC model, JCM model and KHL models were used to simulate the segmented chip formation in Ti-6Al-4V alloy orthogonal cutting. Meanwhile, the JC damage initiation as well as energy-density based damage evolution criteria were applied in cutting simulation. A VUMAT subroutine was developed to characterize the stable plastic and damage constitutive model. The simulated chip morphology using different constitutive models was compared with the experimental results. The plastic models and the ductile failure model can characterize the flow softening behavior during segmented chip formation. The influence of plastic model on the principle cutting force and the segmented chip morphology at different cutting conditions was discussed.

Edge surface grinding has been widely applied in achieving functional surfaces and repairing the damage surfaces of carbon fiber–reinforced plastic (CFRP) composites especially with complex three-dimensional features. The conventional surface grinding (CSG) usually generates surface damages, leading to reduced service life and load-carrying capability of the parts. Therefore, there is a critical need to develop a surface grinding process of CFRP composites in a high-quality and high-efficiency way. Rotary ultrasonic machining (RUM) surface grinding has been proven to be such a process. In addition, RUM edge surface grinding can be conducted by up surface grinding or down surface grinding. However, the difference between up surface grinding and down surface grinding with RUM has not been reported. In this paper, the comparison between up surface grinding and down surface grinding with RUM is studied for the first time. The effects of the grinding parameters on machining performance, including cutting force, surface roughness, and surface morphology characteristics, are experimentally studied. The results show that the cutting forces in up grinding are obviously larger than those in down grinding. Lower surface roughness is generated by down grinding when grinding parameters are kept unchanged. The reasons for the differences of cutting forces and surface integrity are discussed. Surface morphologies suggest clearly that brittle fracture is the predominant material removal mode in grinding of CFRP composites. The chip size of the resin, the fracture size of the carbon fiber, and the material removal scale are smaller in down grinding. Furthermore, compared with CSG, the advantages of RUM surface grinding are presented. This investigation will provide useful guidance for surface grinding of CFRP composites.

Ductile damage behavior of Ti-6Al-4V alloy was characterized by the evolution of flow curves and deformed specimens in compression tests at high strain rates and various temperatures. Cracks along the shear bands of deformed specimens were observed at lower temperatures (20 °C and 100 °C) and high strain rates (2500–10,000 s−1). The failure initial strains (FIS) during crack generation were calculated according to the measured flow stresses at the transition from stable plastic to damage evolution stage. Special emphasis is placed on the influence of strain rate and temperature on the ductile failure initiation. The failure initiation parameters of Johnson-Cook (JC) damage model were obtained by genetic algorithm (GA) optimization using a combined experimental–numerical approach. That is, the ductile damage parameters were optimized according to the measured FIS and the simulated stress triaxiality, equivalent strains, stresses and temperatures, using compression simulation without damage model. At lower temperatures (T

The material removal processes generate interesting surface topographies, unfortunately, that was usually considered to be surface defects. To date, little attention has been devoted to the positive applications of these interesting surface defects resulted from laser ablation to improve C/SiC surface wettability. In this study, the formation mechanism behind surface defects (residual particles) is discussed first. The results showed that the residual particles with various diameters experienced regeneration and migration, causing them to accumulate repeatedly. The effective accumulation of these residual particles with various diameters provides a new method about fabricating bionic microstructures for surface wetting control. The negligible influence of ablation processes on the chemical component of the subsurface was studied by comparing the C-O-Si weight percentage at the C/SiC subsurface. A group of microstructures were fabricated under different laser trace and different laser parameters. Surface wettability experimental results for different types of microstructures were compared. The results showed that the surface wettability increased as the laser scanning speed decreased. The surface wettability increased with the density of the laser scanning trace. We also demonstrated the application of optimized combination of laser parameters and laser trace to simulate a lotus leaf’s microstructure on C/SiC surfaces. The parameter selection depends on the specific material properties.

Many advantages make electrolytic in-process dressing (ELID) grinding desirable for cutting hard and brittle material with high surface requirements. The self-electrolytic in-process dressing property in ELID grinding is also largely responsible for the shorter wear life and lower forming accuracy of the grinding wheel. In ELID grinding, except for traditional mechanical wear, the electrolytic oxidation wear also adds more uncertainties to the wear velocity of the grinding wheel. To date, few investigations focused on the grinding wheel wear life characterization in ELID cut-in grinding of ball bearing raceway. In this study, the wear life characterization of the grinding wheel during ELID grinding was quantitatively simulated by a moving normal distribution curve of the grit state variation. As all types of cutting grits wear out, so did the normal distribution curve, showing movement towards the grinding wheel center. With the normal distribution curve moving towards the grinding wheel center, a local acceleration and local deceleration in moving velocities occurred. It is the diversity of the moving speed of the normal distribution curve that provides a quantitative description to understand the wear life characterization of the ELID grinding wheel. Some experimental results can easily explain this new proposed perspective. This new perspective can also be extended to predict the forming accuracy and surface topography of the bearing raceway during ELID grinding.

Many of the advantages that make C/SiC functional materials desirable are also largely responsible for the machining difficulties encountered. The time-lag of water droplet adsorption (WDA) arised from the complex fabricated carbon fiber precast body may cause cooling condition deterioration in near dry machining of C/SiC, which then gives rise to a lower machinability with respect to the surface integrity. However, little attention has been devoted to the fiber induced time-lag of WDA on C/SiC surfaces. In this study, theoretical models of WDA of two typical C/SiC surfaces, namely, pillar fiber ending and circle fiber ending C/SiC surfaces, were first established. Uni-directional C/SiC was fabricated to experimentally simulate the WDA process on these two typical surfaces. The complete WDA process on a single sample was analyzed first. Considering the stochastic shape of the flow channel, WDA experiments conducted on two typical C/SiC surfaces were repeated 2000 times. The frequency occurrence of the water droplet adsorption time (WDAT) of these 2000 experiments was fitted using the normal distribution function. The statistical evaluation methods indicated that the WDAT of a pillar fiber ending C/SiC surface lagged behind the WDAT of a circle fiber ending C/SiC surface. Furthermore, the time-lags were dependent on both the volume of the water droplet volume and increase in temperature. A critical discussion was conducted regarding the prevention of the WDA time-lag on C/SiC surfaces, and it is suggested that reducing the tiny droplet diameter of cooling mists and spray mists in advance and properly improving the cutting heat can limit, to some extent, the fiber induced time-lag of the WDA of C/SiC surfaces, which is an important factor for optimizing the cooling supply of near dry machining of C/SiC composites.

The micro-scale heat dissipation fins significantly contribute to cool off a brake system. However, micro-scale heat dissipation fins will change the surface wetting and then change the humidity of components in the brake system. A higher humidity is helpful for improving the thermal conductivity coefficient of the C/SiC component, which aids in further improving the cooling performance. To the best knowledge of the authors, little attention has been devoted to improving the humidity of the C/SiC brake lining by micro-scale fins. The aim of this study is mainly to discuss the surface wetting of the porous C/SiC brake lining with micro-scale heat dissipation fins to facilitate heat dissipation in the brake system by increasing the humidity. In this study, micro-scale heat dissipation fins with various intervals were fabricated by a laser on three typical C/SiC surfaces. Surface wetting was characterized by the spreading time of the water droplets. The theoretical model of the water droplet spreading time was established by a Washburn-type equation. Both the experimental and theoretical results indicated that: (1) a hydrophilic C/SiC surface could be achieved by fabricating micro-scale heat dissipation fins on a circular fibre-ending surface compared with a pillar fibre-ending surface; (2) wetting control of the C/SiC surface is not obvious by changing of the micro-fin interval on the order of micrometers; and (3) the surface wetting of the pillar fibre-ending C/SiC surface was more sensitive to increased repetitions of laser scanning. In the current stage, the experimental results presented a stochastic surface wetting. In this regard, more details on the irregularity of micro-scale heat dissipation fins resulting from a laser process are discussed. The conclusions can be extended to optimize the heat dissipation fin arrangement of the C/SiC brake lining and optimize the overall cooling performance of the brake system.

As a relatively new grinding technology, ELID (electrolytic in-process dressing) is widely used in some businesses. The oxide layer plays an important role in ELID grinding performance. The purpose of this work is to investigate the state of the oxide layer on ELID grinding wheel surfaces based on workpiece-cathode and tool-cathode. The thickness and surface topography of the oxide layer were measured from ELID grinding experiments based on workpiece-cathode and tool-cathode in different controlled dressing current. The normal grinding force was also compared in ELID grinding with workpiece-cathode and tool-cathode. According to the results, there are some caves on the surface of the oxide layer in ELID grinding with workpiece-cathode. With increasing controlled dressing current, the surface of the oxide layer becomes discontinuous in ELID grinding with workpiece-cathode. And the surface of the oxide layer becomes smoother with increasing controlled dressing current in ELID grinding with tool-cathode. Meanwhile, it was found that the oxide layer in ELID grinding with workpiece-cathode is thicker than that in ELID grinding with tool-cathode. Moreover, the normal grinding force in ELID grinding with workpiece-cathode is smaller than that in ELID grinding with tool-cathode. The results are helpful to improve the ELID grinding performance and apply ELID grinding technology with workpiece-cathode to abroad industrial applications.

In this work, the orthogonal cutting experiments on Ti-6Al-4V alloy were conducted at different cutting speeds(10—160 m/min)and feed rates(20—160 μm/rev). The tool-chip contact length was measured by the track of tool rake face; meanwhile, the chip morphology caused by the localized and overall chip deformation was characterized by the degree of segmentation and the chip compression ratio, respectively. These parameters were analyzed and calculated according to the segmented chip morphology. In addition, three modified models considering the overall chip deformation and the localized deformation of adiabatic shear band were proposed, and the constants of the models were calculated by the genetic algorithm optimization. Considering the overall and localized chip deformation, the value and variation trend of the tool-contact length predicted by these three models agreed well with the experimental results.

Implant-associated infections are generally difficult to cure owing to the bacterial antibiotic resistance which is attributed to the widespread usage of antibiotics. Given the global threat and increasing influence of antibiotic resistance, there is an urgent demand to explore novel antibacterial strategies other than using antibiotics. Recently, using a certain surface topography to provide a more persistent antibacterial solution attracts more and more attention. However, the clinical application of biomimetic nano-pillar array is not satisfactory, mainly because its antibacterial ability against Gram-positive strain is not good enough. Thus, the pillar array should be equipped with other antibacterial agents to fulfill the bacteriostatic and bactericidal requirements of clinical application. Here, we designed a novel model substrate which was a combination of periodic micro/nano-pillar array and TiO2 for basically understanding the topographical bacteriostatic effects of periodic micro/nano-pillar array and the photocatalytic bactericidal activity of TiO2. Such innovation may potentially exert the synergistic effects by integrating the persistent topographical antibacterial activity and the non-invasive X-ray induced photocatalytic antibacterial property of TiO2 to combat against antibiotic-resistant implant-associated infections. First, to separately verify the topographical antibacterial activity of TiO2 periodic micro/nano-pillar array, we systematically investigated its effects on bacterial adhesion, growth, proliferation, and viability in the dark without involving the photocatalysis of TiO2. The pillar array with sub-micron motif size can significantly inhibit the adhesion, growth, and proliferation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Such antibacterial ability is mainly attributed to a spatial confinement size-effect and limited contact area availability generated by the special topography of pillar array. Moreover, the pillar array is not lethal to S. aureus and E. coli in 24 h. Then, the X-ray induced photocatalytic antibacterial property of TiO2 periodic micro/nano-pillar array in vitro and in vivo will be systematically studied in a future work. This study could shed light on the direction of surface topography design for future medical implants to combat against antibiotic-resistant implant-associated infections without using antibiotics., Graphical abstract Image 1, Highlights • TiO2 periodic micro/nano-pillar array was fabricated by “photolithography + RF magnetron sputtering + thermal oxidation”. • It is a model substrate for investigating the topographical bacteriostatic and TiO2 photocatalytic bactericidal effects. • Systematically investigated its effects on bacterial adhesion, growth, proliferation, and viability in the dark. • Such antibacterial ability mainly attributes to a spatial confinement size-effect generated by the special topography. • Different from conventional topographical antibacterial surfaces, it was prepared with a bioactive biomaterial (TiO2).

The coefficient of thermal conductivity was influenced by the wetting state of material. The wetting state usually depends on the surface wettability. C/SiC is a promising ceramic composites with multi-components. The wettability of C/SiC composites is hard to resort to the classical wetting theory directly. So far, few investigations focused on C/SiC surface wettability diversity after different material removal processes. In this investigation, comparative studies of surface wettability of ground C/SiC surface and laser-ablated C/SiC surface were carried out through apparent contact angle (APCA) measurements. The results showed that water droplets easily reached stable state on ground C/SiC surface; while the water droplets rappidly penetrated into the laser–ablated C/SiC surface. In order to find out the reason for wettability distinctions between the ground C/SiC surface and the laser–ablated C/SiC surface, comparative studies on the surface micro-structure, surface C–O–Si distribution, and surface C–O–Si weight percentage were carried out. The results showed that (1) A large number of micro cracks in the fuzzy pattern layer over laser-ablated C/SiC surfaces easily destoried the surface tension of water droplets, while only a few cracks existed over the ground C/SiC surfaces. (2) Chemical components (C, O, Si) were non-uniformly distributed on ground C/SiC surfaces, while the chemical components (C, O, Si) were uniformly distributed on laser-ablated C/SiC surfaces. (3) The carbon weight percentage on ground C/SiC surfaces were higher than that on laser-ablated C/SiC surfaces. All these made an essential contribution to the surface wettability diversity of C/SiC surface. Although more investigations about the quantitative influence of surface topography and surface chemical composition on composites wettability are still needed, the conslusion can be used in application: the wettability of C/SiC surface can be controlled by different material removal process without individual following up surface modification process.

A constitutive model is critical for the prediction accuracy of a metal cutting simulation. The highest strain rate involved in the cutting process can be in the range of 104–106 s–1. Flow stresses at high strain rates are close to that of cutting are difficult to test via experiments. Split Hopkinson compression bar (SHPB) technology is used to study the deformation behavior of Ti-6Al-4V alloy at strain rates of 10–4–104s–1. The Johnson Cook (JC) model was applied to characterize the flow stresses of the SHPB tests at various conditions. The parameters of the JC model are optimized by using a genetic algorithm technology. The JC plastic model and the energy density-based ductile failure criteria are adopted in the proposed SHPB finite element simulation model. The simulated flow stresses and the failure characteristics, such as the cracks along the adiabatic shear bands agree well with the experimental results. Afterwards, the SHPB simulation is used to simulate higher strain rate(approximately 3×104 s–1) conditions by minimizing the size of the specimen. The JC model parameters covering higher strain rate conditions which are close to the deformation condition in cutting were calculated based on the flow stresses obtained by using the SHPB tests (10–4–104 s–1) and simulation (up to 3×104 s–1). The cutting simulation using the constitutive parameters is validated by the measured forces and chip morphology. The constitutive model and parameters for high strain rate conditions that are identical to those of cutting were obtained based on the SHPB tests and simulation.

Functional micro-structures on laser-ablated carbon fibre reinforced composites surfaces exhibit distinct advantages. A variety of fibre endings with different orientations may coexist on the C/SiC sectional plane, the anisotropic nature of C/SiC (carbon fibre reinforced silicon carbide) composites present a new challenge to the laser ablation process. However, few reports describing the influence of the fibre ending orientations on the laser-ablated C/SiC surface topography could be found. In this investigation, micro-ridges were established on three typical C/SiC surfaces by laser ablation, and a comparative study was performed to identify the topography variations on these laser-ablated C/SiC surfaces. The results showed that C/SiC surfaces with different fibre ending orientations present distinct surface characters ( Sz , Sq ) after laser ablation. Although all of the laser ablation processes are similar in nature, the fibre ending variation made the laser and material interaction different greatly. Attention should be devoted to the influence of the fibre ending orientation on surface topography formation before performing the laser ablation of carbon fibre reinforced composite materials. Finally, some typical surface defects on these laser-ablated surfaces were also discussed.

The compression mechanical behaviors of 7050-T7451 alloy over a wide range of strain rates were studied. The quasi-static and dynamic uniaxial compression tests were presented over a wide range of strain rates (0.0001 s −1 , 0.01 s −1 , 2500 s −1 , 4000 s −1 , 7500 s −1 and 10,000 s −1 ) and temperatures (20 °C, 100 °C, 200 °C and 270 °C). The work hardening behavior changes from work hardening to flow softening with the increase of plastic strain at dynamic conditions. In addition, the dynamic recrystallization (DRX), grain refining and phase transition were observed from the microstructures of the cross-section of the compressed specimens. The microstructure evolution at dynamic condition leads to a smaller work hardening rate than that at most of the quasi-static conditions, indicating a coupling effect of the work hardening and strain rate for 7050-T7451 alloy. Besides, the calculated average thermal softening rate decreases with the increase of logarithmic strain rate, which indicates a coupled effect of thermal softening and strain rate. Based on the calculated work hardening and thermal softening behaviors, a modified Johnson Cook (JC) model was developed to incorporate the coupled effects into the items of work hardening and thermal softening. Most of the average absolute relative errors ( AARE ) between the predicted and measured flow stresses were less than 5%. In addition, the prediction accuracy of the proposed constitutive model was further evaluated by a loading condition jump test.

The machining mechanism of woven ceramic matrix composites is one of the most challenging problems in composite application. To elucidate the grinding mechanism of the woven ceramic matrix composites, a new model material consisting of unidirectional CVI-C/SiC was prepared and ground. The composite was ground in three typical directions and the experimental investigation of the surface grinding process for this composite is described. In addition, the micro structural characteristics and grinding mechanism of the composite were analyzed. The result shows that brittle fracture is the dominant removal mechanism for grinding of the C/SiC composites, and the destroy form of the composites is mainly the syntheses of the matrix cracking, fiber fracture, and interfacial debonding. The grinding force follows the order: Normal > Longitudinal > Transverse, and the surface roughness follows: Longitudinal > Normal > Transverse. The grinding parameters (feed speed, cut depth, grinding speed) have great influence on the grinding force and surface roughness. Based on the findings, the grinding force and surface integrity of the woven ceramic matrix composites can be predicted. Furthermore, it is expected to provide a useful guideline for the design, evaluation and optimal application of the C/SiC composites.

The characterization of interfaces in woven ceramic matrix composites is one of the most challenging problems in composite application. In this investigation, a new model material consisting of the chemical vapor infiltration unidirectional C/SiC composites with PyC fiber coating were prepared and evaluated to predict the interfacial mechanic properties of woven composites. Single fiber push-out/push-back tests with the Berkovich indenter were conducted on the thin sliced specimens using nano-indentation technique. To give a detailed illustration of the interfacial crack propagation and failure mechanism, each sector during the push-out process was analyzed at length. The test results show that there is no detectable difference between testing a fiber in a direct vicinity to an already tested fiber and testing a fiber in vicinity to not-pushed fibers. Moreover, the interface debonding and fiber sliding mainly occur at the PyC coating, and both the fiber and surrounding matrix have no plastic deformation throughout the process. Obtained from the load-displacement curve, the interfacial debonding strength (IDS) and friction stress (IFS) amount to, respectively, 35 ± 5 MPa and 10 ± 1 MPa. Based on the findings, the interfacial properties with PyC fiber coating can be predicted. Furthermore, it is expected to provide a useful guideline for the design, evaluation and optimal application of CVI-C/SiC.

Surface integrity of hole-making for Ti-6Al-4 V alloy is very important due to its application in aviation industry. Geometrical and mechanical behaviors of machined holes by helical milling (HM) and ultrasonic vibration helical milling (UVHM) were investigated. The textures of machined holes by the two processes were analyzed and the distances of adjacent textures were calculated according to the movement of peripheral edges. Due to the different surface geometrical textures, the hole-diameter error and surface roughness in UVHM are smaller than those of HM. A plastic deformation layer with thickness of 4–6 μm was observed by the distorted β phase in the cross-section of hole-surface in UVHM by SEM results. Compared with HM process, UVHM generates larger hardness at the subsurface of machined holes (20–200 μm) due to the material deformation caused by ultrasonic vibration. Compared with HM, the compressive residual stress of hole surface was increased larger than 63.5% by UVHM. The compressive stresses in UVHM are larger than 150 MPa at the depth less than 10 μm, which is consistent with the microstructure evolution caused by mechanical deformation.

The plastic deformation behaviors of Ti–6Al–4V alloy over wide ranges of strain rate (from 10−4 to 104 s−1) and temperature (from 20 to 900 °C) are investigated by the quasi-static and dynamic uniaxial compression tests. The microstructure evolution of Ti–6Al–4V alloy at different temperatures is discussed. Material generates higher ductility and formability when temperature is higher than 500 °C, which leads to the decrease of work hardening rate. The true stress–strain responses are modeled with the JC, modified JC, KHL and modified KHL models. In detail, a temperature dependent work hardening function is introduced into the original JC and KHL models. The parameters of the four models for Ti–6Al–4V alloy are calculated by GA optimization method. The average standard deviations between the experimental and calculated flow stresses range from 4% to 13%, which validates the accuracy of the models. In addition, comparison of flow stresses at dynamic (10,000 s−1), the work hardening rates at dynamic (7500 s−1), as well as the quasi-static jump experiments were proposed to further validate the models. The modified JC and modified KHL models could characterize the temperature dependent work hardening effect for Ti–6Al–4V alloy over large strain rate and temperature ranges. Keywords: Ti–6Al–4V alloy, Constitutive behavior, Work hardening, Deformation mechanisms, Flow stress

Nickel-based alloys have been extensively used as critical components in aerospace industry, especially in the key section of aeroengine. In general, these sections are manufactured by milling process because most of them have complex forms. However, surface defects appear frequently in milling due to periodic impact force, which leads to the deterioration of the fatigue life. We conducted milling experiments under different cutting conditions and found that four kinds of defects, i.e., tear, cavity, build up edge (BUE) and groove, commonly appear on the machined surface. Based on the observed results, the morphology and generation regime of these defects are analyzed and the carbide particle cracking is discussed to explain the appearance of the nickel alloy defects. To study the effect of the cutting parameters on the severity of these surface defects, two qualitative indicators, which are named as average number of the defects per field and average area ratio of the defects per field, are presented and the influence laws are summarized based on the results correspondingly. This study is helpful for understanding the generation mechanism of the surface defects during milling process of nickel based super alloy.

The groove profile of ball-bearing raceway is of vital importance to ensure the bearing transmission accuracy. It is an attempt to apply electrolytic in-process dressing (ELID) groove grinding for the ball-bearing raceway finishing process. The wear rate of the grinding wheel is directly related to the profile accuracy of the bearing raceway. In order to maintain a high-forming accuracy, the interrupt truing has to be performed at the grinding interval. However, how to rationally plan the grinding interval for high-forming accuracy is hard to resort to the general concept of the wear of the grinding wheel. This study recorded the raceway profile variation on axial direction and radial direction by monitor points. The results show that the raceway profile variation (monitor points) on the axial direction could be omitted, because it is far less than the profile variation (monitor points) on radial direction. An evaluation method was proposed to plan the interrupt truing based on the raceway profile variation (monitor points) on radial direction. Finally, the feasibility of the proposed evaluation method was verified by the experimental results. The evaluation method of forming accuracy could provide a reference for selecting the truing interruption during ELID groove grinding process. The approach that incorporates the interrupt truing with the ELID groove grinding enriches bearing manufacturing method. The ELID groove grinding has a great potential for application in precision machining of ball bearing ring raceway.

Anisotropic wettability characterizes the surfaces of the carbon fiber reinforced carbon and silicon carbide dual matrix composites (C/C–SiC), because the surfaces are composed of different fiber endings. The aim of this investigation is to establish control over the anisotropic wettability on C/C–SiC surfaces. The influence of the groove density on the droplet contact angles (surface wettability) was investigated both on the circle fiber ending surfaces and on the pillar fiber ending surfaces. Based on the groove density, the 14 specimens were divided into 7 groups. Each group was composed of a circle ending surface and a pillar ending surface. Comparison of the droplet contact angles was also established within each group. The results showed that the droplet contact angles were decreased after laser treatment. The droplet contact angles also decrease with the increase of the groove density. The differential of the droplet contact angles within each group was narrowed after laser treatment. The hypothesized explanations were proposed for the observed phenomenon. Some fibers initially covered by the SiC matrix were re-exposed on the groove side wall. The variety of the fiber ending distribution on the groove side wall could possibly introduce a more efficient control over the surface wettability. This method can be extended to optimize the surface wettability and to eliminate the anisotropic effects of the fiber reinforced composites.

Honing is a material removal process widely used in manufacturing of engine cylinders, compressors, valves, bearings, and hydraulic cylinders. The surface topography generated by honing has a profo...

This paper introduces the potential feasibility that ELID (electrolytic in-process dressing) grinding replaces superfinishing in bearing manufacturing, but ELID grinding will bring new challenges. Different regions present distinguish surface profile due to the non-uniform contact in ELID groove grinding. However, few reports explaining the non-uniform contact are available. This article explores the mechanisms of the non-uniform contact during ELID groove grinding. Experiments on the non-uniform contact between bearing raceway and grinding wheel have been carried out under different conditions. The results show that non-uniform contact exists in ELID groove grinding process and it exerts influence on the profile of the raceway surface. Non-uniform contact influences the Rsk and Rku value all the time, but it influences the Ra value occasionally. Improvement strategies of eliminating the non-uniform contact are also discussed based on the experimental study.

s Material flow stress in cutting is difficult to measure experimentally due to the complex deformation behavior involved. In this work, a finite element (FE) simulation of cutting and a theoretical flow stress model including plastic and failure criteria were developed to determine the flow stress during aluminum alloy (7075-T6) cutting process. In a stable plastic stage, the Johnson–Cook model considering the adiabatic temperature rise (ATR) was proposed to calculate the plastic flow stress, and the relative errors of the calculated and FE simulated stresses were less than 4%. In the ductile failure stage, an improved failure initiation criterion in terms of temperature, pressure and strain rate was proposed to determine the failure initiation strain in cutting. In addition, an energy-density based ductile failure criterion was used to predict the flow stress in the failure stage. By combining the proposed theoretical model results and the FE simulation results, the entire flow stress during cutting was obtained. The influence of the failure initiation strain of the chip layer on cutting performance was also discussed. In addition, a set of aluminum alloy (A2024-T351) orthogonal cutting simulations were performed to validate the effect of the failure initiation strain on the cutting process. The predicted variation trends of the failure initiation strain for the two types of aluminum alloys were similar, and the predicted forces and tool–chip contact lengths were compared with the measured values in Atlati et al. [9]. Finally, the prediction of the failure initiation strain and its influence on tool–chip contact behavior were validated indirectly.

Better prediction about the temperature distribution of workpiece has a great significance for improving performance of cutting process, especially relating to the workpiece of carbon fiber reinforced plastics (CFRP). In this paper, a heat transfer model is developed to investigate the temperature distribution of CFRP workpiece in helical milling process. Depending on characteristics of helical milling, two kinds of heat sources have been presented, the geometrical shapes of which are modeled as semicircle arc and line. The complex trajectory of each heat source relative to the stable workpiece has been studied. Based on the analysis, unsteady state three-dimensional governing equation of heat transfer in CFRP workpiece with adiabatic boundary condition is proposed. The solution procedure of this nonhomogeneous heat transfer equation consists of two steps: it is transformed into homogeneous equation according to the heat transfer theory firstly; and then the homogeneous equation is solved using the separation of variables. Basing on the solution of the homogeneous equation, the temperature distribution resulting from the moving semicircle arc heat source and the line heat source has been studied detailedly. In order to calculate the heat generation in the helical milling process, a cutting force model is presented and the heat partition transferring into the CFRP workpiece is solved using the Conjugate Gradient Method. A series of tests of helical milling for CFRP are conducted, and the experiment results agree well with the results calculated by the predicted model. This model can be extended to optimize the cutting condition and restrain the thermal damage of the CFRP workpiece.

The present article established empirical models of tool life, residual stress, and surface roughness according to titanium alloy milling parameters. The empirical models were utilized for optimization of production cost and surface quality. As the effects of milling parameters on production cost and surface quality are conflicting in nature, the multiobjective optimization problem in titanium alloy milling was proposed. Considering different industrial demands, two optimization objectives were established, optimization objective I aims to minimize the production time per piece and the number of consumed tools, the objective II aims to minimize the production time per piece, surface roughness, and absolute value of residual stress. In addition, the coupling of the two optimization objectives is considered to optimize the production cost and surface quality simultaneously. Nondominated sorting genetic algorithm-II (NSGA-II) was adopted to solve the multiobjective optimization problem and the optimized results were obtained by the Pareto-optimal solutions. These pareto-optimal solutions were used to conduct the verification experiments. Comparison of experimental and optimized results shows that the relative errors of tool life, surface roughness, and residual stress are less than 5, 7, and 5 %, respectively. The achieved results can provide the beneficial guidelines for the engineering applications depending upon industrial demands.

This paper represented a three-dimensional heat transfer model which describes the temperature distribution with the time variation in solid with conduction-convection boundary during the helical milling process. On the basis of the kinematic mechanisms of helical milling, two types of heat sources were presented; one was the first heat source (FTHS) resulting from the peripheral cutting edge, and the other one was the second heat source (STHS) resulting from the bottom cutting edge. Both effects of the FTHS and the STHS on the temperature distribution of the workpiece were investigated. The FTHS was defined as one semicircle which acted on a helical path; the STHS was defined as one straight line and the movements of which consisted of three ways: rotating around the axis of the tool, turning around the center of the hole, and moving along the axial direction. In order to accurately study the heat transfer model, a stationary coordinate established in the hole and a moving coordinate established in the heat source were developed. The transformation of coordinates and the trajectory of the moving coordinate had been illustrated. Under the two coordinates, a nonhomogeneous partial differential equation (PDE) containing heat source term was derived and was solved using the Green function approach. The heat source term was depicted using the Dirac delta function. A series of experimental tails for Ti-6Al-4V were organized. The experimental results agreed well with the data calculated using the model. The effects of different cutting parameters on the temperature rise were also investigated.