Width Of Contact Area Research Articles

Fretting Fatigue Life Prediction of Dovetail Structure Based on Plastic Effect and Sensitivity Analysis of Influencing Factors.

Micro relative sliding exists on the contact surface of the main primary equipment's surface structures, resulting in serious fretting fatigue. The plastic effect causes serious fatigue to the structure under alternating loads. Existing fatigue life prediction models fail to fully consider the shortcomings of fretting and plastic effects, which causes the prediction results to be significantly different to real-lifeworld in engineering situations. Therefore, it is urgent to establish a fretting damage fatigue life prediction model of contact structures which considers plastic effects. In this study, a plastic fretting fatigue life prediction model was established according to the standard structural contact theory. The location of dangerous points was evaluated according to a finite element simulation. The cyclic load maximum stress value was compared with the fretting fatigue test data to confirm the error value, and the error between the proposed fretting fatigue life model and the test value was within 15%. Concurrently, we combined this with mass data analysis and research, as it is known that the contact zone parameters have an impact on fretting fatigue and affect the structural lifespan. With the help of ABAQUS, the fretting numerical calculation of the dovetail tenon model was carried out to analyze the sensitive factors affecting the fretting fatigue life of the dovetail tenon structure. By keeping the fretting load unchanged, the contact area parameters such as contact surface form, contact area width and friction coefficient were changed in order to calculate the fretting stress value, σfretting and the dovetail structure was improved to extend its fretting fatigue life. Finally, it was concluded that fretting fatigue was most sensitive to the width and contact form of the contact area. In actual engineering design, multiple factors should be considered comprehensively to determine a more accurate and suitable width and form of the contact area. For the selection of friction coefficient, on the premise of saving costs and meeting the structural strength requirements, the friction coefficient should be as small as possible, and the problem can also be solved through lubrication during processing.

Analysis of Smile Aesthetic Changes With Fixed Orthodontic Treatment.

The mouth and teeth are vital in facial aesthetics and the face as a whole is the most critical individual component determining one's physical look. As dentists, we need to be aware that this might significantly alter the care given to a patient since the patient's and the dentist's ideas of beauty may be quite different. This study sought to ascertain how the general public, general dental specialists, and orthodontics all rated the attractiveness of patients who had received orthodontic treatment using a visual scale, as well as how the facial reference could be used to gauge the improvement in smiles. The attractiveness of 80 continuously treated patients was assessed by comparing their pre- and post-treatment posed grin images. The attractiveness of participants' smiles was evaluated using the Visual Simple Scale, which measures affect, and the Graph of Facial Stylish Reference, which measures objectively. "Making a Jazzy Face Chart" -The analysts were able to fairly evaluate changes in elements such as the symmetry of the smile twist, the position of the gingival peak of the front teeth relative to each other, the height of the incisal edges of the front teeth, the width of the connector band of the front six teeth, and the general tip of the front teeth by referring to photographs taken during treatment. We put the Visual Basic Scale to the test by having five male orthodontists, five male general dental specialists, and five male laypeople rate how much of an improvement they noticed between the before and after photos of a patient's smile. According to the findings of the first section of the research, orthodontic treatment generally leads to an increase in all indicators. Some instances, however, demonstrated worsening in characteristics such as grin arc consonance, gingival zenith location relative to each other, and incisal edge height. The second half of this research revealed that the opinions of orthodontic specialists, general dentists, and the general public varied with regard to the beauty of a smile. Based on this research, we can say the following: Orthodontic treatment led to improvements in many of the variables that contribute to smile attractiveness, factors include the interproximal width of contact area, the height of the incisal margins of the front teeth, and the location of the gingival zenith in relation to one another, to name a few. The results of this research support the idea that the aesthetics of the smile should be assessed at the last stages of orthodontic treatment when fine adjustments are being made.

GEOMETRICAL ANALYSIS OF LIGHT-EMITTING DIODE FOR ENHANCING EXTRACTION EFFICIENCY

A non-uniform current spreading in the current spreader can greatly reduce the efficiency of the light-emitting diode (LED). The effects of the electrode contact area to the spreading layer towards extraction efficiency of LED chips is analysed in analytical simulations. Length of current spreading and light extraction efficiency is analysed for variation of contact area. The contact area value is varied by changing the shape of the electrode and the value of width of contact area. The increase in contact area decreases light extraction efficiency as more light are absorbed by the bottom electrode surface. The effective current spreading length for Indium Tin Oxide (ITO) of thickness 300nm is 36.44µm. The 6 strips ‘fork’ design is the most optimum. The design has the most area for photons produced in active region to escape without reducing the area cover with current density. This enables the chip to has more extraction efficiency with more uniform current spreading.

Refined Zigzag Theory: an appropriate tool for the analysis of CLT-plates and other shear-elastic timber structures

Cross laminated timber (CLT), as a structural plate-like timber product, has been established as a load bearing product for walls, floor and roof elements. In a bending situation due to the transverse shear flexibility of the crossing layers, the warping of the cross section follows a zigzag pattern which should be considered in the calculation model. The Refined Zigzag Theory (RZT) can fulfill this requirement in a very simple and efficient way. The RZT, founded in 2007 by A. Tessler (NASA Langley Research Center), M. Di Sciuva and M. Gherlone (Politecnico Torino) is a very robust and accurate analysis tool, which can handle the typical zigag warping of the cross section by introducing only one additional kinematic degree of freedom in case of plane beams and two more in case of biaxial bending of plates. Thus, the RZT-kinematics is able to reflect the specific and local stress behaviour near concentrated loads in combination with a warping constraint, while most other theories do not. A comparison is made with different methods of calculation, as the modified Gamma-method, the Shear Analogy method (SA) and the First Order Shear Deformation Theory (FSDT). For a test example of a two-span continuous beam, an error estimation concerning the maximum bending stress is presented depending on the slenderness L/h and the width of contact area at the intermediate support. A stability investigation shows that FSDT provides sufficiently accurate results if the ratio of bending and shear stiffness is in a range as stated in the test example. It is shown that by a simple modification in the determination of the zigzag function, the scope can be extended to beams with arbitrary non-rectangular cross section. This generalization step considerably improves the possibilities for the application of RZT. Furthermore, beam structures with interlayer slip can easily be treated. So the RZT is very well suited to analyze all kinds, of shear-elastic structural element like CLT-plate, timber-concrete composite structure or doweled beam in an accurate and unified way.

Study of Wire Deformation Characterization and Size Effects during the Micro-Flat-Rolling Process

A comprehensive research on the flat rolling deformation characterization of microwire has been conducted systematically through finite element simulation and testified by the results from the experimental analysis. The obtained results are compared in terms of lateral spread, geometrical characteristic, contact area width and surface roughness considering the effects of pass reduction and initial wire diameter. The size effect has been identified and surface layer modeling has been set up based on surface grain share and grain size distribution. The numerical method combined with varied flow stress has been verified by experimental value with a maximum difference of 3.7% for the 1.5 mm wire. With the increase of the height reduction, the curvature radius is decreased while the lateral spread and contact area width are increased. Surface roughness evolution in the range of 0.52–0.85 µm for the rolled wire has also been investigated.

Deformation Behaviors of Flat Rolled Wire in Twinning-Induced Plasticity Steel

The influence of room temperature flat rolling on microstructure, mechanical properties, and shape change in twinning-induced plasticity (TWIP) steel wire has been investigated to understand the deformation behaviors of flat rolled wire in TWIP steel and to apply TWIP steels to flat rolled wire products. Numerical simulation, hardness test, and EBSD techniques were used to analyze the distribution of strain, mechanical properties, and microstructure of flat rolled TWIP steel wire. The shape of flat rolled TWIP steel wire was also evaluated and compared with plain carbon steels having low strain hardening rate. A very different behavior of hardness, strain, twinning, and KAM value was observed with area of flat rolled wire due to the different stress state and strain with area of wire. The center area had the maximum twin density, KAM value, effective strain, and hardness; whereas free surface area had the minimum values. The hardness inhomogeneity factor (HIF) along the horizontal direction was much higher in comparison with that of the vertical direction. The maximum HIF value occurred at the specific reduction in height, i.e., 27%. This means HIF value gradually increased and then decreased with reduction in height, which is inconsistent with the results of plain carbon steel and Cu wire. The lateral spread and width of contact area of flat rolled TWIP steel wire were lower than those of plain carbon steels, indicating that material properties such as strain hardening exponent are crucial parameters that influence the shape of flat rolled wire products.

A comparison investigation of the contact models for contact and vibration features of cylindrical roller bearings

PurposeThe purpose of this study is to investigate the contact models for contact and vibration features of cylindrical roller bearings (CRBs). CRBs are important parts of rotating machinery. The contact deformation between the roller and the raceway is an essential research topic for the CRBs. The contact deformation between the roller and the raceway can greatly affect vibration characteristics and fatigue life of the CRBs. In this investigation, six different methods are adopted to calculate the contact deformation, contact area width and contact stress between the roller and raceways of a CRB.Design/methodology/approachIn this paper, the contact deformations and the contact stiffnesses between the roller and the raceway of a CRB obtained by various well-known empirical methods (Lundberg’s, Palmgren’s, Houpert’s, Cheng’s and Hertzian methods) are directly compared with those by the finite element (FE) method. A two degree-of-freedom (2 DOF) dynamic model of the CRB is applied to investigate the effects of the contact stiffness obtained by different line contact deformation calculation methods on the vibration characteristics, such as the root mean square (RMS), the peak to peak (PTP), the crest factor and the kurtosis of the displacement, velocity and acceleration of the inner raceway.FindingsThe computational results show that different calculation methods for the contact deformations between rollers and raceways have significant effects on the vibrations of the CRB. It is found that that the differences of computational results obtained by Palmgren’s and Lundberg’s models with respect to the FE method are smaller than those by the other three methods, i.e. Houpert’s, Cheng’s and Hertzain models. The amplitude and peak frequency of the frequency response functions from Palmgren’s method are much more similar to those from the finite element method. The above results indicate that Palmgren’s method is a better calculation method for predicting the contact deformations and dynamics of the CRBs.Originality/valueThis work adopts six different methods to calculate the contact deformation, contact area width and contact stress between the roller and raceways of a CRB. Moreover, a vibration model of a CRB is used to investigate the effect of contact stiffness obtained by the above methods on the vibrations of the CRB. The works can give some guidance for the accurate analytical method for calculating the contact deformations between rollers and raceways and the vibrations of the CRB.

Contact Analysis of the Two Dimensional Wheel-Rail Based on Finite Element Method

Wheel-rail contact mechanics is one of the fundamental areas for studying wheel-rail relationship, therefore, the study of wheel/rail contact is of great significance to solve related problems. In this paper, simplified two dimensional rigid wheel-rail and resilient wheel-rail contact finite element models are established, and the reliability of the established models is verified by comparison of the finite element method and Hertz theory results. In the vicinity of the rail joint, the contact conditions do not satisfy the relevant hypothesis of Hertz theory, so the finite element method is used to investigate the wheel/rail contact analysis in rail joint. The results show that wheel-rail contact pressure, maximum equivalent stress, the plastic deformation areas, and δ x of the rail increases with the distance decreasing of the contact point to the rail joint. By comparing rigid wheel and resilient wheel, we also can find that the contact pressure, the maximun equivalent stress and δ x of the resilient wheel-rail are less than the rigid wheel-rail, and width of contact area is basically same as rigid wheel-rail. Therefore, the use of resilient wheel can reduce the wear between wheel and rail and reduce the collapse of rail joint.

Numerical Study on Silver Diffusion Joints of Coated Conductors by Finite-Element Method

Given the length limitations of commercial coated conductors, joint is very important for their practical applications. Silver diffusion joints are regarded to be promising in the superconducting applications without operation in persistent current mode. This paper presents a 3-D numerical model of silver diffusion joints. The current distributions in the contact layers and their effect on the joint resistance are systematically studied by varying silver layer thickness, length, and width of contact area. It is investigated that the width of the contact area has an inverse proportion to the simulated joint resistances in the range of 2-12 mm like a normal conductor. However, the relationship between the contact length and the simulated joint resistance has an evident deviation from the inverse proportion, because the current distribution in silver layers is highly nonuniform and gives rise to a smaller “silver usage ratio” when the contact length is longer. Based on the hypothesis that the sheet resistivity of ReBCO-Ag and Ag-Ag interfaces is uniformly distributed and is affected by the “silver usage ratio” to the same extent as the bulk resistance of the silver layers, the joint resistances derived from our model are in good agreement with the experimental results.

Tire–Pavement Contact Stress With 3D Finite-Element Model—Part 2: All-Steel Tire on Heavy Vehicles

Abstract Heavy vehicles increase on highways in China year by year. Heavy loads are among the most important factors causing pavement distresses. The distribution of contact stresses between tires and pavement surface greatly influences the initiation and propagation of pavement distresses, especially for the top-down cracking. Therefore, to accurately and precisely describe pavement responses, the distribution of contact stresses should be first investigated thoroughly. This study focuses on simulating the contact stresses between all-steel tires on heavy vehicles and the pavement surface. A 3D finite-element model was proposed and used to simulate the distribution of contact stresses in different conditions of tires, including standstill, free rolling, accelerating rolling, and decelerating rolling conditions. This model was validated by previous study of the authors. There were three loading levels used in this study, including 20 kN, 40 kN, and 60 kN. In the standstill condition, the maximum pressures on pavement surface were simulated as 1.2 MPa, 1.2 MPa, and 2.4 MPa in 20 kN, 40 kN, and 60 kN loading levels, respectively, which were much higher than 0.7 MPa, the standard contact pressure in pavement design specification in China. An interesting phenomenon was observed that when the load passed a certain value, the width of contact area kept constant, whereas the length of contact area was prolonged. And the length of the contact area prolonged linearly with the increase of load. Based on this phenomenon, the Hertz contact theory was applied to simplify the traditional 3D finite-element model. In the simplified model, the complicated 3D all-steel tire was simplified to an equivalent medium. The 3D finite-element model and the simplified model were compared with the analytic method. This indicates that the simplified model can simulate the contact stress of all-steel tires closely to the analytic results (no more than 10 % difference) and greatly improves the calculation efficiency.

Predicted tyre–soil interface area and vertical stress distribution based on loading characteristics

The upper boundary condition for all models simulating stress patterns throughout the soil profile is the stress distribution at the tyre–soil interface. The so-called FRIDA model (Schjønning et al., 2008. Biosyst. Eng. 99, 119–133) treats the contact area as a superellipse and has been shown to accurately describe a range of observed vertical stress distributions. Previous research has indicated that such distributions may be predicted from tyre and loading characteristics. The objective of this study was to establish a stepwise calculation procedure enabling accurate predictions from readily available data. We used multiple regression to identify equations for predicting the FRIDA model parameters from measured loading characteristics including tyre carcass volume (VT), wheel load (FW), tyre deflection (L), and an expression of tyre inflation pressure (Kr) calculated as the natural logarithm of the actual to recommended inflation pressure ratio. We found that VT and Kr accounted for nearly all variation in the data with respect to the contact area. The contact area width was accurately described by a combination of tyre width and Kr, while the superellipse squareness parameter, n, diminished slightly with increasing Kr. Estimated values of the contact area length related to observed data with a standard deviation of about 0.06m. A difference between traction and implement tyres called for separate prediction equations, especially for the contact area. The FRIDA parameters α and β, reflecting the tyre’s ability to distribute the stress in the driving direction and in the transversal direction, respectively, increased with increases in the relevant contact area dimension (length or width). The α-parameter was further affected by FW, while Kr and L added to model performance for the β-parameter. The prediction accuracy of our models was tested on an independent data set and through a range of case studies. We found satisfactory small root mean square errors and effectively no bias in the comparisons. Further studies are needed, though, to quantify effects of topsoil consistencies deviating from those tested in this study.

Experimental investigation of the yielding process of a ductile polycarbonate cylinder subjected to line loading using digital image correlation

The yielding formation and propagation of a ductile polycarbonate cylinder subjected to line loading, which corresponds to the global behavior of the structure, was experimentally studied and evaluated by measuring the strain fields on the end of the cylinder using Digital Image Correlation. The global behavior of the structure is expressed by a relationship between the average stress (load divided by contact area) and the equivalent strain (ratio of half width of contact area to radius of the cylinder); the contact area was measured in the same experiment by analyzing the images of the compressed pressure film captured through a transparent plate below the cylinder. A correspondence between the yielding state and the nonlinearity of the global behavior was constructed and, as loading was increased, the cylinder was found to first yield at a specific point after which a yielding core formed and propagated. Before the yielding core propagated to the surface of the cylinder, the global behavior of the structure remained linear, although the cylinder was no longer homogeneous and the material was nonlinear. After the yielding core propagated to the surface of the cylinder, the propagation was accelerated and the global behavior became nonlinear. The correspondence constructed in the paper will be helpful to understand the failure process and to evaluate the carrying capacity of a ductile polycarbonate cylinder subjected to line loading.

Experimental and Finite Element Investigation of Roll Drawing Process

In this research, the wire drawing process with flat roller dies is investigated. A prototypal apparatus is developed to conduct experimental tests on such a process and analyze the influence of main roll drawing parameters (e.g., incoming wire diameter, forming rolls diameter, thickness reduction, and friction conditions) on geometrical characteristics of flattened wires. A finite element model (FEM) is developed to simulate the deformation of the wire during the process. Within the entire range of experiments, a good agreement between experimental data and numerical results is found which allows validating the FE model. A further observation from the experimental program and numerical simulations is that a complicated dependence of the lateral spread of wire and width of contact area on process parameters exists during wire drawing with roller dies.

Numerical and Experimental Investigation of Process Parameters Effect of Low Carbon Steel Wire Produced with Roll Drawing Process

The effect of roll drawing process parameters on geometrical characteristics of flat roll draw wires is analyzed. Low carbon steel wires AISI 1010 are used in the experimental tests to assess the final geometry, mainly characterized by the width of flat wires, varying among several experimental levels the main process parameters i.e., initial wire dimensions, height reduction and lubrication conditions. Design of experiment technique was used to define the experimental plan and statistical techniques, such as analysis of mean (ANOM) and variance (AVOVA), were used to evaluate the effective influence of previous cited process parameters on final geometry of wire. A finite element model is developed to investigate a further process parameter i.e. the working rolls dimensions. In order to validate the finite element model, a campaign of experimental tests was conducted and the geometrical predictions of FE model were compared with experimental mea-surements with particular attention to final wire width, width of contact area and wire elongation. A linear regression analysis was performed and an empirical formulation to forecast the lateral spread of wire according to the main process parameters was developed.

Stresses in hard coating due to a rigid spherical indenter on a layered elastic half-space

The axisymmetrical contact problem of elasticity connected with an indentation of a rigid spherical indenter in an elastic semi-space covered by an elastic layer is considered. Stress tensor components in interior points of the non-homogeneous half-space by numerical calculation of some integrals was obtained. Detailed analysis of the maximal tensile stress distributions and Huber-von Mises reduced stress distributions produced by contact pressure is presented. The dependence between these stresses and the ratio between the layer thickness and contact area width is explored. The obtained results for stresses are compared with results obtained for half-space loaded by the Hertz pressure.

Modeling the formation of internal boundaries in an unidirectional fiber strand compacted in plastic state

The formation of internal boundaries in a unidirectional fiber strand during isostatic and uniaxial pressing in plastic state is studied. The process is modeled using the finite-element method (FEM). An ideal contact elastoplastic problem for a hexagonal fiber strand undergoing plane deformation is solved taking into account friction at the boundaries. For angles of 0°, 30°, 60°, and 90° between the normal to the contact area and the pressing direction, the contact area width, change in the contact area slope, and the radius vector of the cross-sectional boundary of the fiber inside the pore channel as functions of density are determined for the friction coefficient at the boundaries of fibers equal to 0 and 0.5.

垂直円柱壁面に付着した液滴の転落体積(熱工学,内燃機関,動力など)

The critical volume of liquid droplet (CV) was investigated when the droplet starts to slide on the wall of a vertical cylinder. The critical condition was theoretically considered from the force balance between the gravitational force and the resultant of surface tension acting on the three-dimensionally curved contact line. The results show that the critical condition can be simplified to the similar one for the droplets on the inclined plates treated in the previous reports, and CV can be estimated from the maximum width of the contact area on the cylinder. The maximum width was calculated based on the energy minimum condition for the droplets in a similar manner to the inclined plate. CV was experimentally measured for each combination between two kinds of test liquids and polypropylene with different roughness. The results fairly agree with those of theory within 10% deviation. CV increases with the cylinder diameter and approaches the value for the plate asymptotically. This is due to the fact that the volume of droplets increases with the curvature under the same width of contact area.

A study on the cross-sectional profile of flat rolled wire

In this research the cross-sectional profile of flattened wires after flat rolling are calculated for different reductions. The empirical formulation, analytical formulation and numerical method have been used to predict the cross-sectional profile. Also, the theoretical results are compared with the experimental data. It has been found that the numerical method is able to predict the lateral spread, the width of contact area, and the curvature radius in all ranges of the reduction in height with a good accuracy, while the other methods exhibit a reasonable accuracy only for a limited range of height reduction. All results of the methods show that with increasing the reduction in height, the lateral spread and width of contact area are increased and the curvature radius is decreased. The appropriate ranges of height reductions for each method are recommended.

Contact problem for elastic layer and rigid cylinder with friction forces

The contact problem for the elastic layer of an arbitrary thickness and the rigid cylinder with friction forces acting in the contact area is solved and the solution is analyzed. Domains of applicability of the widely used solutions, i.e. the solution for a rigid cylinder and elastic half-space and the solution for a thin elastic layer, are determined for the contact under consideration. It is shown that for coatings from composite materials with a low elastic modulus both solutions can result in a significant error. Typical modes of the elastic displacement of the layer surface are given for different contact area width, Poisson’s ratio, and friction coefficient. The example of the calculation of the particular contact for the layer of the polymer composite with a low elastic modulus is presented.

Applicability of the FSEM for analyzing wire flat rolling process

PurposeThe purpose of this paper is to present an assessment of the ability of combined finite and slab element method (FSEM) for analyzing the wire flat rolling process.Design/methodology/approachUsing the FSEM, the effective strain field of flat rolled wire is predicted for different reductions in height and frictional conditions. The validity of the method is assessed by performing the Vickers microhardness measurements on the flattened wire cross section. Also, the creation of macroscopic shear bands in cross section of the flat rolled wire is investigated and confirmed by microhardness and metallographic examinations. Moreover, the lateral spread and width of contact area are predicted by the FSEM for different reductions in height and frictional conditions.FindingsThe FSEM and microhardness results show the minimum and the maximum effective strains at the round edge and center of the flattened wire, respectively. Also, the results show the bands of maximum effective strain at cross section of the flattened wire, i.e. macroscopic shear bands.Practical implicationsThis paper can be useful in rolling industries to produce electronic parts, various springs, trolley cables, piston rings, and guide rails.Originality/valueThe paper shows the applicability of the FSEM for calculating the effective strain field and geometry of wire after wire flat rolling process.