Improvement for design of beam structures in large vibrating screen considering bending and random vibration

Demand for large vibrating screen is huge in the mineral processing industry. As bending and random vibration are not considered in a traditional design method for beam structures of a large vibrating screen, fatigue damage occurs frequently to affect the screening performance. This work aims to conduct a systematic mechanics analysis of the beam structures and improve the design method. Total motion of a beam structure in screening process can be decomposed into the traditional followed rigid translation(FRT), bending vibration(BV) and axial linear-distributed random rigid translation(ALRRT) excited by the side-plates. When treated as a generalized single-degree-of-freedom(SDOF) elastic system analytically, the BV can be solved by the Rayleigh's method. Stochastic analysis for random process is conducted for the detailed ALRRT calculation. Expressions for the mechanics property, namely, the shearing force and bending-moment with respect to BV and ALRRT, are derived, respectively. Experimental and numerical investigations demonstrate that the largest BV exists at the beam center and can be nearly ignored in comparison with the FRT during a simplified engineering design. With the BV and FRT considered, the mechanics property accords well with the practical situation with the maximum error of 6.33%, which is less than that obtained by traditional method.

Dynamic analysis of spatial parallel manipulator with rigid and flexible couplings

The dynamics of spatial parallel manipulator with rigid and flexible links is explored. Firstly, a spatial beam element model for finite element analysis is established. Then, the differential equation of motion of beam element is derived based on finite element method. The kinematic constraints of parallel manipulator with rigid and flexible links are obtained by analyzing the motive parameters of moving platform and the relationships of movements of kinematic chains, and the overall kinetic equation of the parallel mechanism with rigid and flexible links is derived by assembling the differential equations of motion of components. On the basis of abovementioned analyses, the dynamic mechanical analysis of the spatial parallel manipulator with rigid and flexible links is conducted. After obtaining the method for force analysis and expressions for the calculation of dynamic stress of flexible components, the dynamic analysis and simulation of spatial parallel manipulator with rigid and flexible links is performed. The result shows that because of the elastic deformation of flexible components in the parallel mechanism with rigid and flexible links, the force on each component in the mechanism fluctuates sharply, and the change of normal stress at the root of drive components is also remarkable. This study provides references for further studies on the dynamic characteristics of parallel mechanisms with rigid and flexible links and for the optimization of the design of the mechanism.

Comparison of two theoretical models for electric leak location at landfill

To solve the disability of conventional model used in electrical leak location when measurement electrodes were buried under the liner, a new model of high voltage DC leak detection is developed. For single-liner landfill, the waste material layer, the geomembrane liner and the soil under the liner are simulated with infinite horizontal layers. The leak is regarded as two parts, one being negative current source at the entrance, and the other positive current source of the same size at the exit. Comparisons between the new theoretical model and conventional model show that conventional model is efficient in locating leaks in geomembane liner associating the dipole scanning above the liner but is ineffective when the measurement electrodes were buried under the liner. The new theoretical model data are in excellent agreement with experimental data not only above the liner but also under the liner.

Automatic Extraction Method of Weld Weak Defect Features for Ultra-High Voltage Equipment

To solve the problems of low precision of weak feature extraction,heavy reliance on labor and low efficiency of weak feature extraction in X-ray weld detection image of ultra-high voltage(UHV)equipment key parts,an automatic feature extraction algorithm is proposed.Firstly,the original weld image is denoised while retaining the characteristic information of weak defects by the proposed monostable stochastic resonance method.Then,binarization is achieved by combining Laplacian edge detection and Otsu threshold segmentation.Finally,the automatic identification of weld defect area is realized based on the sequential traversal of binary tree.Several characteristic analysis dimensions are established for weld defects of UHV key parts,including defect area,perimeter,slenderness ratio,duty cycle,etc.The experiment using theweld detection image of the actual production site shows that the proposedmethod can effectively extract theweak feature information ofweld defects and further provide reference for decision-making.

Analysis of Frequency Characteristics and Sensitivity of Compliant Mechanisms

Based on a modified pseudo-rigid-body model,the frequency characteristics and sensitivity of the large-deformation compliant mechanism are studied.Firstly,the pseudo-rigid-body model under the static and kinetic conditions is modified to enable the modified pseudo-rigid-body model to be more suitable for the dynamic analysis of the compliant mechanism.Subsequently,based on the modified pseudo-rigid-body model,the dynamic equations of the ordinary compliant four-bar mechanism are established using the analytical mechanics.Finally,in combination with the finite element analysis software ANSYS,the frequency characteristics and sensitivity of the compliant mechanism are analyzed by taking the compliant parallel-guiding mechanism and the compliant bistable mechanism as examples.From the simulation results,the dynamic characteristics of compliant mechanism are relatively sensitive to the structure size,section parameter,and characteristic parameter of material on mechanisms.The results could provide great theoretical significance and application values for the structural optimization of compliant mechanisms,the improvement of their dynamic properties and the expansion of their application range.

Natural frequencies analysis of a composite beam consisting of Euler-Bernoulli and Timoshenko beam segments alternately

Present investigation is concerned with the free vibration property of a beam with periodically variable cross-sections.For the special geometry characteristic,the beam was modelled as the combination of long equal-length uniform Euler-Bernoulli beam segments and short equal-length uniform Timoshenko beam segments alternately.By using continuity conditions,the hybrid beam unit(ETE-B) consisting of Euler-Bernoulli beam,Timoshenko beam and Euler-Bernoulli beam in sequence was developed.Classical boundary conditions of pinned-pinned,clamped-clamped and clamped-free were considered to obtain the natural frequencies.Numerical examples of the equal-length composite beam with 1,2 and 3 ETE-B units were presented and compared with the equal-length and equal-cross-section Euler-Bernoulli beam,respectively.The work demonstrates that natural frequencies of the composite beam are larger than those of the Euler-Bernoulli beam,which in practice,is the interpretation that the inner-welded plate can strengthen a hollow beam.In this work,comparisons with the finite element calculation were presented to validate the ETE-B model.

A novel explosion-proof walking system: Twin dual-motor drive tracked units for coal mine rescue robots

A new explosion-proof walking system was designed for the coal mine rescue robot(CMRR) by optimizing the mechanical structure and control algorithm. The mechanical structure innovation lies mainly in the dual-motor drive tracked unit used, which showed high dynamic performance compared with the conventional tracked unit. The control algorithm, developed based on decision trees and neural networking, facilitates autonomous switching between "Velocity-driven Mode" and "Torquedriven Mode". To verify the feasibility and effectiveness of the control strategy, we built a self-designed test platform and used it to debug the control program; we then made a robot prototype and conducted further experiments on single-step, ramp, and rubble terrains. The results show that the proposed walking system has excellent dynamic performance and the control strategy is very efficient, suggesting that a robot with this type of explosion-proof walking system can be successfully applied in Chinese coal mines.

Rock Breaking Performance of a Pick Assisted by High-pressure Water Jet under Different Configuration Modes

In the process of rock breaking, the conical pick bears great cutting force and wear, as a result, high-pressure water jet technology is used to assist with cutting. However, the effect of the water jet position has not been studied for rock breaking using a pick. Therefore, the models of rock breaking with different configuration modes of the water jet are established based on SPH combined with FEM. The effect of the water jet pressure, distance between the jet and the pick bit, and cutting depth on the rock breaking performance as well as a comparison of the tension and compression stress are studied via simulation; the simulation results are verified by experiments. The numerical and experimental results indicate that the decrease in the rates of the pick force obviously increases from 25 MPa to 40 MPa, but slowly after 40 MPa, and the optimal distance between the jet and the pick bit is 2 mm under the JFP and JSP modes. The JCP mode is proved the best, followed by the modes of JRP and JFP, and the worst mode is JSP. The decrease in the rates of the pick force of the JCP, JRP, JFP, and JSP modes are up to 30.96%, 28.96%, 33.46%, 28.17%, and 25.42%, respectively, in experiment. Moreover, the JSP mode can be regarded as a special JFP model when the distance between the pick-tip and the jet impact point is 0 mm. This paper has a dominant capability in introducing new numerical and experimental method for the study of rock breaking assisted by water jet and electing the best water jet position from four different configuration modes.

Analytical model of tilted driver–pickup coils for eddy current nondestructive evaluation

A driver-pickup probe possesses better sensitivity and flexibility due to individual optimization of a coil. It is fre- quently observed in an eddy current （EC） array probe. In this work, a tilted non-coaxial driver-pickup probe above a multilayered conducting plate is analytically modeled with spatial transformation for eddy current nondestructive evalua- tion. Basically, the core of the formulation is to obtain the projection of magnetic vector potential （MVP） from the driver coil onto the vector along the tilted pickup coil, which is divided into two key steps. The first step is to make a projection of MVP along the pickup coil onto a horizontal plane, and the second one is to build the relationship between the pr, ojected MVP and the MVP along the driver coil. Afterwards, an analytical model for the case of a layered plate is established with the reflection and transmission theory of electromagnetic fields. The calculated values from the resulting model indicate good agreement with those from the finite element model （FEM） and experiments, which validates the developed analytical model.

Bond strength analysis of the bone cement-stem interface of hip arthroplasties

Objective:To study and establish the preliminary linear and modified models for the interface shear mechanics performance between implant and bone cement and to explore its damage significantce.Method:The loosening research between artificial hip joint prosthesis stem and bone cement interface performance can be evaluated by the push-in test.Based on the debondittg perforntance test,the analytical expressions of the average load and displacement from the debottdiftg failure and splitting failure process were deduced and determined.The correlations of the expressions of the average load-displacement and statistical experimental data were analyzed.Results:It demonstrated that the interface debonding failure mechanical model could be characterisied as interface bond strength mechanical performance.Based on analysis of models and experimental data by the three statistical analysis methods,the results indicated the modified model could be better represented by the interfacial debonding strength properties.The bond stress(?)and relative sliding s distribution along the embedment regional were coupling affected by both pressure arch effect and shear lag effect in bone cement.Two stress peaks of implant have been found at the distance from 0.175L_0 loading tip to 0.325L_0 free tip,which also verified the early loosening clinical reports for the proximal and latter region.As the bone cement arch effect,the bond stress peak tend to move to the free tip when the debonding failure would be changed into the splitting failure,which presents a preliminary study on the mechanism of early delmnding failure for the stem-cement interface.Conclusions:Functional models of the stembone cement interfacial debonding failure are developed lo analyze the relevant mechanism.The different lotcational titanium alloy stress,and the interfacial bond stress and the relative slides are evaluated to acquire a guide of the different positions of interfacial damage.The coupling;effect which is original from the pressure arch and the interfacial shear hysteresis cumulative effect has influence on the interfacial debonding and damage process.

Synthesis of a Novel TiO_(2)@Ag_(3)PO_(4)Core-Shell Structure with Enhanced Photocatalytic Performance

Ag_(3)PO_(4)exhibits a high photocatalytic activity if exposed to visible light,however,it displays bottlenecks such as poor cycle-stability and mediocre ability to degrade methyl orange(MO)because of limited adsorption of MO molecules onto its surface.In this study,nano TiO_(2)prepared by a one-step method was combined with Ag_(3)PO_(4)to form a TiO_(2)@Ag_(3)PO_(4)heterojunction in order to improve this material both in terms of photocatalysis and photostability.After adding a KH-570 silane coupling agent,the photocatalytic performance of TiO_(2)@Ag_(3)PO_(4)could be improved even further,with the degradation rate of MO maintained at more than 90%after three cycles of visible in light.

Application of 3D Projection Profilometry in the High Speed Impaction Surface Deformation Measurement Research

In order to study the strength of the composite material plate problems, need to adopt a nondestructive testing method to obtain the specimen surface under the effect of high-speed impact regularity of shape. The projection profilometry was used to measure the surface profile or the full field deformation. Furtherly, by using the Fourier transform algorithm, there is only one frame of captured image which is needed in the measurement, so that it can be introduced into the high speed impaction procedure measurement. An experimental system, which was contained with an impact setup and the projection profilometry measurement part, was constructed for the impaction action characteristic research. The metallic impact object can be launched by a gas gun or a spin fan, respectively. The detected object is manufactured by composite materials. In order to increase the surface deformation measurement accuracy, the calibration method and the error was discussed with different calibration specimen. And then, the proposed profilometry measurement method is proved by the gas gun and spin fan projectile test. The surface deformation of the manufactured composite plates and fan case are measured in the impaction procedure. So that the impact action details can be described much more clearly than the traditional video monitoring method.

Tactile perception of textile fabrics based on friction and brain activation

Tactile perception plays a critical role in the interaction of humans and environment.It begins with the mechanical stimulation induced by friction and is processed in the somatosensory cortex.To quantify the tactile perceptions of textile fabrics,the mechanical properties of fabrics and the features extracted from the friction and vibration signals were correlated with the subjective sensation rated by questionnaires.Meanwhile,the technique of functional magnetic resonance imaging(fMRI)was used to identify the brain areas responsible for the tactile perception of textile fabrics.The results showed that during the tactile perception of textile fabrics,the coefficient of friction increased with the increasing normal load,indicating that the deformation mechanism of skin was relevant to the friction of skin against fabrics.The features of spectral centroid(SC),coefficient of friction,and diameter and critical buckling force of fiber had a strong correlation with the perceived fineness,slipperiness,and prickliness of fabrics,respectively.The postcentral gyrus,supramarginal gyrus,and precentral gyrus,with the corresponding functional regions of the primary somatosensory cortex(SI),secondary somatosensory cortex(SII),primary motor cortex(MI),and secondary motor cortex(MII),were involved with the perceptions of fabric textures.The fiber properties and fabric surface structures that caused the multidimensional feelings tended to induce the large area,intensity,and percent signal change(PSC)of brain activity.This study is meaning for evaluating the tactile stimulation of textile fabrics and understanding the cognitive mechanism in the tactile perception of textile fabrics.

Wear mechanism and debris analysis of PEEK as an alternative to CoCrMo in the femoral component of total knee replacement

The polyetheretherketone(PEEK)-highly cross-linked polyethylene(XLPE),all-polymer knee prosthesis has excellent prospects for replacing the traditional metal/ceramic-polyethylene joint prosthesis,improving the service life of the joint prosthesis and the quality of patients’life.The long-term wear mechanism of PEEK-XLPE knee joint prosthesis is comprehensively evaluated from wear amount,wear morphology,and wear debris compared to that of CoCrMo-XLPE joint prosthesis.After 5 million cycles of in vitro wear,the wear loss of XLPE in PEEK-XLPE(30.9±3.2 mg)is lower than that of XLPE in CoCrMo-XLPE(32.1±3.1 mg).Compared to the XLPE in CoCrMo-XLPE,the plastic deformation of XLPE in PEEK-XLPE is more severe in the early stage,and the adhesive peeling and adhesion are lighter in the later stage.The size distribution of XLPE wear debris in PEEK-XLPE is relatively dispersed,which in CoCrMo-XLPE is relatively concentrated.Wear debris is mainly flake and block debris,and the wear mechanism of XLPE was abrasive wear.The wear volume per unit area of PEEK femoral condyle(10.45×10^(5)μm^(3)/mm^(2))is higher than that of CoCrMo(8.32×10^(5)μm^(3)/mm^(2)).The PEEK surface is mainly furrows and adhesions,while the CoCrMo surface is mainly furrows and corrosion spots.The PEEK wear debris is mainly in flakes and blocks,and the CoCrMo wear debris is mainly in the shape of rods and blocks.The wear mechanism of PEEK is abrasive wear and adhesion,and that of CoCrMo is abrasive wear and corrosion.

Cartilage-bone inspired the construction of soft-hard composite material with excellent interfacial binding performance and low friction for artificial joints

Inspired by the cartilage-bone structure in natural joints,soft-hard integrated materials have received extensive attention,which are the most promising candidates for artificial joints due to their combination of excellent load-bearing properties and lubricating properties.The latest progress showed that the combination of hydrogel and titanium alloy can realize a bionic natural joint lubrication system on the surface of titanium alloy.However,obtaining a tough interface between the hydrogel(soft and wet)and the titanium substrate(hard and dry)is still a great challenge.Here,we designed a"soft(hydrogel)-hard(Ti6Al4V)"integrated material with outstanding combination,which simulates the structure and function of cartilage-bone in the natural joint.The load-bearing properties,binding performance,and tribological behaviors for different forms of the soft-hard integrated materials were investigated.The results showed that the hydrogel layer and Ti6Al4V substrate possess ultra-high interfacial toughness(3,900 J/m^(2)).In addition,the combination of the hydrogel layer and Ti6Al4V substrate provided a good lubrication system to endow the"soft(hydrogel)-hard(Ti6Al4V)"integrated material with high load-bearing and excellent tribological properties.Therefore,this study provided an effective strategy for prolonging the service life of Ti6Al4V in the biomedical field.

Pulsed Eddy Current Non-destructive Testing and Evaluation:A Review

Pulsed eddy current （PEC） non-destructive test- ing and evaluation （NDT＆E） has been around for some time and it is still attracting extensive attention from researchers around the globe, which can be witnessed through the reports reviewed in this paper. Thanks to its richness of spectral components, various applications of this technique have been proposed and reported in the lit- erature covering both structural integrity inspection and material characterization in various industrial sectors. To support its development and for better understanding of the phenomena around the transient induced eddy currents, attempts for its modelling both analytically and numeri- cally have been made by researchers around the world. This review is an attempt to capture the state-of-the-art development and applications of PEC, especially in the last 15 years and it is not intended to be exhaustive. Future challenges and opportunities for PEC NDT＆E are also presented.

Backfill support＇s backfill and operation properties and evaluation

充填采煤液压支架是充填采煤技术实现充采一体化的核心设备,其性能的可靠性是实现致密充填的关键。为评价充填采煤液压支架的充填性能,本文提出充填运转特性的概念,并从结构特性、支护特性、夯实特性、力学响应特性及地质适应特性5个方面阐述其内涵,具体通过支护强度、夯实空顶距等14个指标综合体现。选择其中7个独立的评价指标,采用多指标综合评价方法,构建了基于充填运转特性的充填采煤液压支架设计方案评价体系,给出了评价的方法与流程,以及充填运转特性工程控制措施。运用该体系评价了翟镇矿ZC5200/14.5/30型充填采煤液压支架的11个优化方案,评选出的10#最佳方案在夯实离顶距等充填运转特性指标上具有明显优势,验证了评价体系的合理性。基于此构建了"初始方案设计、设计方案优化、评价指标优选、优化方案评价、运转特性控制"的充填采煤液压支架研究框架,为深入研究充填采煤液压支架控顶性能提供借鉴。

Research on Containment Relationships between Rapid Prototyping Part and CAD Model

Aiming at the geometrical features of different containment relationships in Rapid Prototyping （RP）, a general method of achieving the RP layer＇s cusp distribution of the positive, negative and mixed tolerance is proposed to meet the part＇s different applications. The procedure is executed by projecting the current and the next section of the CAD model onto a horizontal plane, computing the union and the intersection of the sections to get the outer and the inner boundary, and then blending the boundaries using a rotary vector through a proper inner point in the intersection to achieve the current layer＇s scanning contour. The method can realize the layer＇s cusp distribution of the mixed tolerance with unequal cusp height, expanding the connotation of the mixed tolerance.

Characteristics of pressure fluctuations and fine coal preparation in gas-vibro fluidized bed

To improve the separation efficiency of air dense medium fluidized beds tor dry coal preparation, a gasvibro fluidized bed has been proposed in which magnetic powder is used as the heavy medium. Pressure fluctuations in the gas-vibro fluidized bed were investigated using time- and frequency-domain analysis methods. The relationship between pressure fluctuations, bubble behavior, and separation efficiency was established. The low amplitude of the standard deviation, the power spectral density （PSD）, the incoherent-output PSD, and the high amplitude of the coherent-output PSD, which corresponds to the bubble behavior in the bed, were improved for coal preparation. The coal ash content was reduced from 42.5570 to 16.54% by using the gas-vibro fluidized bed.