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Fluoridated hydroxyapatite (FHA) [Ca 10 (PO 4) 6 F x (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. [ABSTRACT FROM AUTHOR]

Abstract High quality hole-making technology in the aviation industry is urgently needed due to the application of difficult-to-cut materials, such as titanium alloy, composite materials and the stacks in aircraft fuselage skins. To improve the hole-making quality, an ultrasonic vibration helical milling (UVHM) technology was developed for machining of Ti 6Al 4V alloy, meanwhile, comparison experiments were conducted between UVHM and conventional helical milling (HM) processes. Material removal mechanism of UVHM was investigated by modeling of cutting trajectories and the analysis of tool-workpiece contact behavior for bottom and peripheral cutting edges. The actual vibration frequency in UVHM was also determined by a theoretical-experimental combined method. Due to the vibration in UVHM, the bottom cutting edges generate discontinuous contact with workpiece. Unit forces considering material removal were modeled and applied to analyze the axial force reduction. The axial cutting forces of UVHM were reduced by 38–64% compared with HM at different cutting speeds. The cutting speed of peripheral cutting edge changes periodically. The cutting edges can separate with chips due to axial vibration, which will contribute to reducing the cutting forces and improving heat dissipation. Meanwhile, a friction effect was generated by the peripheral cutting edge which can improve the micro-scale surface roughness. Due to the effects of periodical friction and compression by ultrasonic vibration, UVHM increases the surface compressive stresses by 85% and 99% at the hole surface for axial and circumferential directions, respectively. Highlights • Ultrasonic vibration helical milling process was developed for machining of Ti 6Al 4V alloy. • The actual vibration frequency was calculated by the cutting trajectories generated by bottom cutting edge. • The trajectories and the cutting speeds of the bottom and peripheral edges were modeled. • The axial cutting forces are reduced up to 64% due to the interrupted cutting effect in UVHM. • Surface roughness and compressive residual stress were improved by periodic friction and compression in UVHM. [ABSTRACT FROM AUTHOR]

• Damage occurred at high strain rate and low temperature in Ti-6Al-4V SHPB tests. • Damage parameter was determined by measured FIS and SHPB simulation without damage. • A coupling JCM plastic and energy density based damage model were presented. • Damage behaviors were further validated at higher temperature (T ≥ 300 °C) conditions. • Energy density method was effective to keep the flow stress of damage evolution. 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 < 300 °C), the failure parameters were used to simulate the flow stresses and deformation of specimen by the JC plastic and damage models. To further validate the failure parameters, at higher temperatures (T ≥ 300 °C), a coupling modified JC (JCM) plastic and energy density based damage model was proposed to characterize the flow curves at damage evolution stage by compression simulation using a subroutine program. The predicted flow stresses and the deformed specimens were consistent with the experimental results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Temperature generates in micro-scale cutting process has a great effect on cutting performance due to centralized heat generation. In this study, a set of micro-cutting experiments (8μm/r≤f≤50μm/r) were carried out to measure temperatures in micro-cutting process with high accuracy. A fast-response thermocouple with a property of self-renewing was installed in a cylinder workpiece to measure the temperatures of workpiece and tool tip simultaneously. In each test, temperature of the workpiece surface is obtained just before the hot junction of thermocouple is machined. When the hot junction is machined, the tested maximum temperature is recognized as the temperature of tool tip. In parallel, an energy density-based ductile failure material model is developed to simulate the micro-cutting process by finite element method. In simulation, when mesh distribution is changed, the predicted forces with same energy density G ε are closer to the forces at original mesh distribution than those predicted by same energy G f . Consequently, the energy density-based ductile failure material model can reduce mesh dependence in different mesh distribution conditions. Under new mesh distribution, Temperatures of the workpiece surface and tool tip are identified in the predicted micro-cutting temperature field. The predicted micro-cutting temperatures of workpiece surface and tool tip are very close to the experimental results. Further, the variation of temperature and its relationship with chip curling are also discussed. [Copyright &y& Elsevier]

This work introduces a novel ring-type lapping method for precision machining of tapered rollers. In contrast to the conventional centerless grinding, this method allows for the simultaneous machining of a group of tapered rollers. The stable rotation of the tapered rollers during the lapping process is a prerequisite for achieving a high manufacturing accuracy. Therefore, an investigation is conducted to examine the criteria for achieving a stable rotation of the tapered rollers. First, the equilibrium equation for the tapered rollers in the lapping process was established. The stable rotation region for the tapered rollers was determined according to the stable rotation criteria. The impacts of the included angle of straight groove and the contact force of lapping sleeve on the stable rotation region were examined. The results demonstrated that the tapered roller's stable rotation can only be realized when a specific parameter combination was satisfied. Subsequently, to expand the stable rotation region, the electromagnetic driving force was introduced to enhance the lapping process. An electromagnetic lapping sleeve structure was designed according to the critical electromagnetic force required for the tapered roller's lapping process. Furthermore, the structure of the electromagnetic lapping sleeve was optimized by electromagnetic simulation in order to improve the uniformity of the electromagnetic driving force exerted on each tapered roller. Finally, the rotation movement of the tapered rollers and the critical electromagnetic forces exerted on the tapered rollers were validated on a ring-type tapered roller lapping platform. The results demonstrated that the stable rotation of the bearing rollers in the lapping process can be achieved throughout a wide range of processing parameters. The roundness of the tapered rollers was significantly improved from 0.83 μm to 0.47 μm on the stable rotation condition. This study established a solid foundation for the precision machining of tapered rollers. • A novel ring-type lapping method for tapered rollers was proposed. • The rotation stability of the tapered roller in the novel ring-type lapping method was analyzed. • Electromagnetic field was introduced to expand the rotation region of the tapered rollers. • The roundness of the tapered roller was significantly improved from 0.83 μm to 0.47 μm. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]