Oblique Cutting Based Mechanical Model for Insertion Torque of Dental Implant

The insertion torque of a dental implant is an important indicator for the primary stability of dental implants.Thus,the preoperative prediction for the insertion torque is crucial to improve the success rate of implantation surgery.In this present research,an alternative method for prediction of implant torque was proposed.First,the mechanical model for the insertion torque was established based on an oblique cutting process.In the proposed mechanical model,three factors,including bone quality,implant geometry and surgical methods were considered in terms of bone-quality coefficients,chip load and insertion speeds,respectively.Then,the defined bone-quality coefficients for cancellous bone with the computed tomography(CT)value of 235–245,345–355 and 415–425 Hu were obtained by a series of insertion experiments of IS and ITI implants.Finally,the insertion experiments of DIO implants were carried out to verify the accuracy of developed model.The predicted insertion torques calculated by the mechanical model were compared with those acquired by insertion experiments,with good agreement,the relative error being less than 15%.This method allows the insertion torque for different implant types to be quickly established and enhances prediction accuracy by considering the effects of implants’geometries and surgical methods.

3D bioprinting of complex biological structures with tunable elastic modulus and porosity using freeform reversible embedding of suspended hydrogels

Three-dimensional(3D)bioprinting has been used widely for the construction of hard tissues such as bone and cartilage.However,constructing soft tissues with complex structures remains a challenge.In this study,complex structures characterized by both tunable elastic modulus and porosity were printed using freeform reversible embedding of suspended hydrogels(FRESHs)printing methods.A mixture of alginate and gelatin was used as the main functional component of the bioink.Rheological analysis showed that this bioink possesses shear thinning and shear recovery properties,supporting both cryogenic and FRESH printing methods.Potential printing capabilities and limitations of cryogenic and FRESH printing were then analyzed by printability tests.A series of complex structures were printed by FRESH printing methods which could not be realized using conventional approaches.Mechanical tests and scanning electron microscopy analysis showed that the printed structure is of excellent flexibility and could be applied in various conditions by adjusting its mechanical modulus and porosity.L929 fibroblast cells maintained cell viability in cell-laden-printed structures,and the addition of collagen further improved the hydrogels’biocompatibility.Overall,all results provided useful insight into the building of human soft tissue organ blocks.

Error Compensation of Thin Plate-shape Part with Prebending Method in Face Milling

Low weight and good toughness thin plate parts are widely used in modem industry, but its flexibility seriously impacts the machinability. Plenty of studies locus on the influence of machine tool and cutting tool on the machining errors. However, few researches focus on compensating machining errors through the fixture. In order to improve the machining accuracy of thin plate-shape part in face milling, this paper presents a novel method for compensating the surfacc errors by prebending the workpiece during the milling process. First, a machining error prediction model using finite element method is formulated, which simplifies the contacts between the workpiece and fixture with spring constraints. Milling fbrces calculated by the micro-unit cutting force model arc loaded on the error prediction model to predict the machining error. The error prediction results are substituted into the given formulas to obtain the prebending clamping forces and clamping positions. Consequently, the workpiece is prebent in terms of the calculated clamping forces and positions during the face milling operation to reduce the machining error. Finally, simulation and experimental tests are carried out to validate the correctness and efficiency of the proposed error compensation method. The experimental measured flatness results show that the flatness improves by approximately 30 percent through this error compensation method. The proposed mcthod not only predicts the machining errors in face milling thin plate-shape parts but also reduces the machining errors by taking full advantage of the workpiece prebending caused by fixture, meanwhile, it provides a novel idea and theoretical basis for reducing milling errors and improving the milling accuracy.

Effects of Temperature and Pressure on Stress Corrosion Cracking Behavior of 310S Stainless Steel in Chloride Solution

310S is an austenitic stainless steel for high temperature applications, having strong resistance of oxidation, hydrogen embrittlement and corrosion. Stress corrosion cracking（SCC） is the main corrosion failure mode for 310S stainless steel. Past researched about SCC of 310S primarily focus on the corrosion mechanism and influence of temperature and corrosive media, but few studies concern the combined influence of temperature, pressure and chloride. on SCC of 310S stainless steel, prepared samples are investigated via For a better understanding of temperature and pressure＇s effects slow strain rate tensile test（SSRT） in different temperature and pressure in NACE A solution. The result shows that the SCC sensibility indexes of 310S stainless steel increase with the rise of temperature and reach maximum at 10MPa and 160~C, increasing by 22.3% compared with that at 10 MPa and 80 ℃. Instead, the sensibility decreases with the pressure up. Besides, the fractures begin to transform from the ductile fracture to the brittle fracture with the increase of temperature. 310S stainless steel has an obvious tendency of stress corrosion at 10MPa and 160℃ and the fracture surface exists cleavage steps, river patterns and some local secondary cracks, having obvious brittle fracture characteristics. The SCC cracks initiate from inclusions and tiny pits in the matrix and propagate into the matrix along the cross section gradually until rupture. In particular, the oxygen and chloride play an important role on the SCC of 310S stainless steel in NACE A solution. The chloride damages passivating film, causing pitting corrosion, concentrating in the cracks and accelerated SSC ultimately. The research reveals the combined influence of temperature, pressure and chloride on the SCC of 310S, which can be a guide to the application of 310S stainless steel in super-heater tube.

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).

Effectiveness of a Passive-active Vibration Isolation System with Actuator Constraints

In the prediction of active vibration isolation performance, control force requirements were ignored in previous work. This may limit the realization of theoretically predicted isolation performance if control force of large magnitude cannot be supplied by actuators.The behavior of a feed-forward active isolation system subjected to actuator output constraints is investigated. Distributed parameter models are developed to analyze the system response, and to produce a transfer matrix for the design of an integrated passive-active isolation system. Cost functions comprising a combination of the vibration transmission energy and the sum of the squared control forces are proposed. The example system considered is a rigid body connected to a simply supported plate via two passive-active isolation mounts. Vertical and transverse forces as well as a rotational moment are applied at the rigid body, and resonances excited in elastic mounts and the supporting plate are analyzed. The overall isolation performance is evaluated by numerical simulation. The simulation results are then compared with those obtained using unconstrained control strategies. In addition, the effects of waves in elastic mounts are analyzed. It is shown that the control strategies which rely on tmconstrained actuator outputs may give substantial power transmission reductions over a wide frequency range, but also require large control force amplitudes to control excited vibration modes of the system. Expected power transmission reductions for modified control strategies that incorporate constrained actuator outputs are considerably less than typical reductions with unconstrained actuator outputs. In the frequency range in which rigid body modes are present, the control strategies can only achieve 5-10 dB power transmission reduction, when control forces are constrained to be the same order of the magnitude as the primary vertical force. The resonances of the elastic mounts result in a notable increase of power transmission in high frequency range and cannot be attenuated by active control. The investigation provides a guideline for design and evaluation of active vibration isolation systems.

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 influenee 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.

In-situ Fabricated TiB_2 Particle-whisker Synergistically Toughened Ti(C,N)-based Ceramic Cutting Tool Material

The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers.However,the process of adding whiskers or nanoparticles has the disadvantages of high cost and health hazard as well as the agglomeration;although a new in-situ two-step sintering process can solve the above problems to some extent,yet the problems of low conversion ratio of the raw materials and the abnormal grain growth exist in this process.In this paper,an in-situ one-step synthesis technology is proposed,which means the growth of whiskers or nanoparticles and the sintering of the compact can be accomplished by one time in furnace.A kind of Ti（C,N）-based ceramic cutting tool material synergistically toughened by TiB_2 particles and whiskers is fabricated with this new process.The phase compositions,relationships between microstructure and mechanical properties as well as the toughening mechanisms are analyzed by means of X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The composite which is sintered under a pressure of 32 MPa at a temperature of 1700℃in vacuum holding for 60 min can get the optimal mechanical properties.Its flexural strength,fracture toughness and Vickers hardness are 540 MPa,7.81 MPa·m（1/2）and 20.42 GPa,respectively.The composite has relatively high density,and the in-situ synthesized TiB_2 whiskers have good surface integrity,which is beneficial for the improvement of the fracture toughness.It is concluded that the main toughening mechanisms of the present composite are whiskers pulling-out and crack deflection induced by whiskers,crack bridging by whiskers/particles and multi-scale particles synergistically toughening.This study proposes an in-situ one-step synthesis technology which can be well used for fabricating particles and whiskers synergistically toughened ceramic tool materials.

滚珠丝杠预紧用环状磁致伸缩致动器的设计与特性研究（英文）

为实现双螺母滚珠丝杠副预紧力的自动调整,提出一种磁致伸缩滚珠丝杠副预紧系统。以中空的超磁致伸缩材料(GMM)为核心,完成了新型环状超磁致伸缩致动器(CGMA)的结构设计;通过测试数据确定了CGMA的预压力;利用磁路分析法对穿入丝杠后致动器内部磁场进行了分析计算;为抑制发热对磁致伸缩输出的影响,提出了直接冷却发热源的油冷散热方法。对自行研制的预紧用致动器输出的位移和力进行了实验研究,结果表明,偏置磁场可以消除CGMA的倍频效应,改善线性度;油冷散热可有效减小热变形影响,使CGMA磁致伸缩输出特性稳定;穿入滚珠丝杠后致动器的输出减小,但在工作区间内输出位移可达26μm、输出力超过6200 N,满足所选滚珠丝杠副预紧系统设计要求。新型CGMA的研制为双螺母滚珠丝杠副预紧力的自动调整提供一种新的方法。

Effect of Machined Surface Integrity on Fatigue Performance of Metal Workpiece:A Review

Fatigue performance is a serious concern for mechanical components subject to cyclical stresses,particularly where safety is paramount.The fatigue performance of components relies closely on their surface integrity because the fatigue cracks generally initiate from free surfaces.This paper reviewed the published data,which addressed the effects of machined surface integrity on the fatigue performance of metal workpieces.Limitations in existing studies and the future directions in anti-fatigue manufacturing field were proposed.The remarkable surface topography(e.g.,low roughness and few local defects and inclusions)and large compressive residual stress are beneficial to fatigue performance.However,the indicators that describe the effects of surface topography and residual stress accurately need further study and exploration.The effect of residual stress relaxation under cycle loadings needs to be precisely modeled precisely.The effect of work hardening on fatigue performance had two aspects.Work hardening could increase the material yield strength,thereby delaying crack nucleation.However,increased brittleness could accel-erate crack propagation.Thus,finding the effective control mechanism and method of work hardening is urgently needed to enhance the fatigue performance of machined components.The machining-induced metallurgical structure changes,such as white layer,grain refinement,dislocation,and martensitic transformation affect the fatigue performance of a workpiece significantly.However,the unified and exact conclusion needs to be investigated deeply.Finally,different surface integrity factors had complicated reciprocal effects on fatigue performance.As such,studying the comprehensive influence of surface integrity further and establishing the reliable prediction model of workpiece fatigue performance are meaningful for improving reliability of components and reducing test cost.

Numerical Investigation of Lid-Driven Deep Cavity with Local Grid Refinement of MRT-LBM

In the case of lid-driven deep cavity flow, the effects of different resolutions of local grid refinement have been studied in the frame of multiple relaxation times (MRT) lattice Boltzmann method (LBM). In all the cases, the aspect ratio and Reynolds number are set as 1.5 and 3.200, respectively. First, the applied method is validated by comparing it with two reported works, with which agreements are reached. Then, six separate degrees of local grid refinement at the upper left corner, i.e. purely coarse grid, including 1/64, 1/32, 1/16, 1/8, 1/4 refinements of the lattice number in the width direction have been studied in detail. The results give the following indications:① The refinement degrees lower than 1/8 produce similar results;② For single corner refinement, 1/4 refinement is adequate for clearing the noises in the singularity zone to a large extent;③ New noise around the interface between coarse and fine zones are introduced by local grid refinement. Finally, refinement of entire subzone neighboring the lid is examined to avoid introducing new noises and it has been found effective.

Adaptive Change Detection for Long-Term Machinery Monitoring Using Incremental Sliding-Window

Detection of structural changes from an opera- tional process is a major goal in machine condition moni- toring. Existing methods for this purpose are mainly based on retrospective analysis, resulting in a large detection delay that limits their usages in real applications. This paper presents a new adaptive real-time change detection algorithm, an extension of the recent research by combin- ing with an incremental sliding-window strategy, to handle the multi-change detection in long-term monitoring of machine operations. In particular, in the framework, Hil- bert space embedding of distribution is used to map the original data into the Re-producing Kernel Hilbert Space （RK_HS） for change detection; then, a new adaptive threshold strategy can be developed when making change decision, in which a global factor （used to control the coarse-to-fine level of detection） is introduced to replace the fixed value of threshold. Through experiments on a range of real testing data which was collected from an experimental rotating machinery system, the excellent detection performances of the algorithm for engineering applications were demonstrated. Compared with state-of- the-art methods, the proposed algorithm can be more suitable for long-term machinery condition monitoring without any manual re-calibration, thus is promising in modern industries.

A new modeling approach for stress-strain relationship taking into account strain hardening and stored energy by compacted graphite iron evolution

Compacted graphite iron(CGI)is considered to be an ideal diesel engine material with excellent physical and mechanical properties,which meet the requirements of energy conservation and emission reduction.However,knowledge of the microstructure evolution of CGI and its impact on flow stress remains limited.In this study,a new modeling approach for the stress–strain relationship is proposed by considering the strain hardening effect and stored energy caused by the microstructure evolution of CGI.The effects of strain,strain rate,and deformation temperature on the microstructure of CGI during compression deformation are examined,including the evolution of graphite morphology and the microstructure of the pearlite matrix.The roundness and fractal dimension of graphite particles under different deformation conditions are measured.Combined with finite element simulation models,the influence of graphite particles on the flow stress of CGI is determined.The distributions of grain boundary and geometrically necessary dislocations(GNDs)density in the pearlite matrix of CGI under different strains,strain rates,and deformation temperatures are analyzed by electron backscatter diffraction technology,and the stored energy under each deformation condition is calculated.Results show that the proportion and amount of low-angle grain boundaries and the average GNDs density increase with the increase of strain and strain rate and decreased first and then increased with an increase in deformation temperature.The increase in strain and strain rate and the decrease in deformation temperature contribute to the accumulation of stored energy,which show similar variation trends to those of GNDs density.The parameters in the stress–strain relationship model are solved according to the stored energy under different deformation conditions.The consistency between the predicted results from the proposed stress–strain relationship and the experimental results shows that the evolution of stored energy can accurately predict the stress–strain relationship of CGI.

Sampled-data extended state observer for uncertain nonlinear systems

In this paper, we present a sampled-data nonlinear extended state observer （NLESO） design method for a class of nonlinear systems with uncertainties and discrete time output measurement. To accommodate the inter-sample dynamics, an inter-sample output predictor is employed in the structure of the NLESO to estimate the system output in the sampling intervals, where the prediction is used in the proposed observer instead of the system output. The exponential convergence of the sampled-data NLESO is also discussed and a sufficient condition is given by the Lyapunov method. A numerical example is provided to illustrate the performance of the proposed observer.

A beam flexure-based nanopositioning stage supporting laser direct-write nanofabrication

A nanopositioning system of both millimetric stroke and nanometric tracking accuracy is a key component for nanofabrication in many applications. In this paper, a novel bi-axial beam-flexure nano servo stage is proposed to support a direct writing system for femtosecond laser nanofabrication. The important features of the stage lie in: a mirror symmetric instead of rotational symmetric configuration is adopted to restrict cross axis coupling, and a novel Z-shaped guidance module is proposed to achieve relative large linear stiffness range, in addition a redundant constraints module is introduced to increase off-axis stiffness of the stage. Mechanical analysis and system identification are provided, with which a feedback control algorithm demonstrates the tracking capability for laser fabrication purposes. Based on the fabricated XY nano-stage, real time control and measurements are deployed, demonstrating the millimetric operating workspace and 77.8 nm(RMS) error of tracking a circular trajectory.

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.

Prediction of cutting power and surface quality, and optimization of cutting parameters using new inference system in high-speed milling process

During the actual high-speed machining process,it is necessary to reduce the energy consumption and improve the machined surface quality.However,the appropriate prediction models and optimal cutting parameters are difficult to obtain in complex machining environments.Herein,a novel intelligent system is proposed for prediction and optimization.A novel adaptive neuro-fuzzy inference system(NANFIS)is proposed to predict the energy consumption and surface quality.In the NANFIS model,the membership functions of the inputs are expanded into:membership superior and membership inferior.The membership functions are varied based on the machining theory.The inputs of the NANFIS model are cutting parameters,and the outputs are the machining performances.For optimization,the optimal cutting parameters are obtained using the improved particle swarm optimization(IPSO)algorithm and NANFIS models.Additionally,the IPSO algorithm as a learning algorithm is used to train the NANFIS models.The proposed intelligent system is applied to the high-speed milling process of compacted graphite iron.The experimental results show that the predictions of energy consumption and surface roughness by adopting the NANFIS models are up to 91.2%and 93.4%,respectively.The NANFIS models can predict the energy consumption and surface roughness more accurately compared with other intelligent models.Based on the IPSO algorithm and NANFIS models,the optimal cutting parameters are obtained and validated to reduce both the cutting power and surface roughness and improve the milling efficiency.It is demonstrated that the proposed intelligent system is applicable to actual high-speed milling processes,thereby enabling sustainable and intelligent manufacturing.

Novel intelligent reasoning system for tool wear prediction and parameter optimization in intelligent milling

Accurate intelligent reasoning systems are vital for intelligent manufacturing.In this study,a new intelligent reasoning system was developed for milling processes to accurately predict tool wear and dynamically optimize machining parameters.The developed system consists of a self-learning algorithm with an improved particle swarm optimization(IPSO)learning algorithm,prediction model determined by an improved case-based reasoning(ICBR)method,and optimization model containing an improved adaptive neural fuzzy inference system(IANFIS)and IPSO.Experimental results showed that the IPSO algorithm exhibited the best global convergence performance.The ICBR method was observed to have a better performance in predicting tool wear than standard CBR methods.The IANFIS model,in combination with IPSO,enabled the optimization of multiple objectives,thus generating optimal milling parameters.This paper offers a practical approach to developing accurate intelligent reasoning systems for sustainable and intelligent manufacturing.