Partial Surface Damper to Suppress Vibration for Thin Walled Plate Milling

The material removal rate and required work- piece surface quality of thin-walled structure milling are greatly limited due to its severe vibration, which is directly associated with the dynamic characteristics of the system. Therefore, the suppression of vibration is an unavoidable problem during milling. A novel partial surface damping method is proposed to modify the mode of the thin walled cantilever plate and to suppress vibration during milling. Based on classical plate theory, the design criterion is analyzed and configuration of the partial surface damper is introduced, in which viscoelastic plate and constraining plate are attached to the surface of the plate to increase the system＇s natural frequency and loss factor. In order to obtain the energy expression of the cutting system, the Ritz method is used to describe the unknown displacements. Then, with Lagrange＇s equation, the natural frequency and loss factor are calculated. In addition, the plate is divided into a finite number of square elements, and the regulation of treated position is studied based on theoretic and experimental analysis. The milling tests are conducted to verify its damping performance and the experimentalresults show that with treatment of partial surface damper, the deformation of the hare plate is reduced from 0.27 mm to 0.1 mm, while the vibration amplitude of the bare plate is reduced from 0.08 mm to 0.01 mm. The proposed research provides the instruction to design partial surface damper.

3D Cohesive Finite Element Minimum Invasive Surgery Simulation Based on Kelvin‑Voigt Model

Minimally invasive surgery is an important technique used for cytopathological examination.Recently,multiple studies have been conducted on a three-dimensional(3D)puncture simulation model as it can reveal the internal deformation state of the tissue at the micro level.In this study,a viscoelastic constitutive equation suitable for muscle tissue was derived.Additionally,a method was developed to define the fracture characteristics of muscle tissue material during the simulation process.The fracture of the muscle tissue in contact with the puncture needle was simulated using the cohesive zone model and a 3D puncture finite element model was established to analyze the deformation of the muscle tissue.The stress nephogram and reaction force under different parameters were compared and analyzed to study the deformation of the biological soft tissue and guide the actual operation process and reduce pain.

Three‑dimensional Modeling and Simulation of Muscle Tissue Puncture Process

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

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

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

Arbitrarily polarized bound states in the continuum with twisted photonic crystal slabs

Arbitrary polarized vortex beam induced by polarization singularity offers a new platform for both classical optics and quantum entanglement applications.Bound states in the continuum(BICs)have been demonstrated to be associated with topological charge and vortex polarization singularities in momentum space.For conventional symmetric photonic crystal slabs(PhCSs),BIC is enclosed by linearly polarized far fields with winding angle of 2π,which is unfavorable for high-capacity and multi-functionality integration-optics applications.Here,we show that by breakingσz-symmetry of the PhCS,asymmetry in upward and downward directions and arbitrarily polarized BIC can be realized with a bilayer-twisted PhCS.It exhibits elliptical polarization states with constant ellipticity angle at every point in momentum space within the vicinity of BIC.The topological nature of BIC reflects on the orientation angle of polarization state,with a topological charge of 1 for any value of ellipticity angle.Full coverage of Poincarésphere(i.e.,-π/4≤X≤4 and-π/2≤ψ≤π/2)and higher-order Poincarésphere can be realized by tailoring the twist angles.Our findings may open up new avenues for applications in structured light,quantum optics,and twistronics for photons.

制造业杠杆、企业异质性与银行系统性风险

金融安全是经济平稳健康发展的重要基础,防范化解系统性风险是金融工作的根本性任务。本文基于2008-2018年我国16家上市银行、制造业企业等相关数据,对制造业杠杆、企业异质性和银行系统性风险之间的关系进行实证分析,结果表明:第一,制造业杠杆对银行系统性风险具有明显的正向影响,但传导机制并不单一,且较为复杂;第二,制造业杠杆对银行系统性风险的影响存在明显的企业异质性,主要表现为国有企业和民营企业整体杠杆率对银行系统性风险的影响方式和传导路径差别较大;第三,银行流动性监管指标在一定程度上缓解了制造业杠杆对银行系统性风险的不利影响,并且这种缓释作用主要表现在国有企业。因此,应加强银行系统性风险的源头治理,推动制造业企业降低债务杠杆,促进债务杠杆由非金融企业部门向政府部门和居民部门进行有序适度转移,以更好地实现整体制造业的转型升级和金融体系的健康稳定发展。

经济政策不确定性与商业银行资产避险

本文基于中国银行业的数据,研究了经济政策不确定性对商业银行资产避险行为的影响。研究发现:随着经济政策不确定性的增强,商业银行从信贷投放、债券投资、现金资产持有三方面调整资产结构,将高风险资产向低风险资产转移进行资产避险。经济政策不确定性的增强导致商业银行资产流动性囤积效应,降低了商业银行的资产收益率,不利于实体经济融资和货币政策的有效传导。本文的研究发现对于商业银行经营管理和货币政策实施具有重要启示。

A novel stability prediction approach for thin-walled component milling considering material removing process

The milling stability of thin-walled components is an important issue in the aviation manufacturing industry, which greatly limits the removal rate of a workpiece. However, for a thin-walled workpiece, the dynamic characteristics vary at different positions. In addition, the removed part also has influence on determining the modal parameters of the workpiece. Thus,the milling stability is also time-variant. In this work, in order to investigate the time variation of a workpiece＇s dynamic characteristics, a new computational model is firstly derived by dividing the workpiece into a removed part and a remaining part with the Ritz method. Then, an updated frequency response function is obtained by Lagrange＇s equation and the corresponding modal parameters are extracted. Finally, multi-mode stability lobes are plotted by the different quadrature method and its accuracy is verified by experiments. The proposed method improves the computational efficiency to predict the time-varying characteristics of a thin-walled workpiece.

Constrained layer damping treatment of a model support sting

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

Agent-Based Simulation of Rumor Propagation on Social Network Based on Active Immune Mechanism

To simulate the rumor propagation process on online social network during emergency, a new rumor propagation model was built based on active immune mechanism. The rumor propagation mechanisms were analyzed and corresponding parameters were defined. BA scale free network and NW small world network that can be used for representing the online social network structure were constructed and their characteristics were compared. Agent-based simulations were conducted on both networks and results show that BA scale free network is more conductive to spreading rumors and it can facilitate the rumor refutation process at the same time. Rumors paid attention to by more people is likely to spread quicker and broader but for which the rumor refutation process will be more effective. The model provides a useful tool for understanding and predicting the rumor propagation process on online social network during emergency, providing useful instructions for rumor propagation intervention.

Novel metasurface phase-modulation mechanism

Science,373(6559),1133–1137,(2021)https://doi.org/10.1126/science.abj3179 The past few years have witnessed exciting developments in non-Hermitian physics,showing unconventional phenomena and unique features associated with exceptional points(EPs).EPs exist in many open systems,leading to a spectral singularity.The research team from CNRS-CRHEA in France collaborating with the University of California,Berkeley in US utilizes the topological feature around an EP to introduce a novel design in metasurface to achieve a new wavefront phase encoding technique.