Verification of ball-on-ring test using finite element analysis

This sheet deals with analysis of the oblique impact system, which is composed of the golf-ball and club. The impact system is modeled by both a nonlinear spring and a nonlinear dashpot using Hertz's contact theory. This model is applied to the oblique impact system of ball. The characteristics of the oblique impact were obtained by using this model. In previous studies,the validity of the normal model was confirmed, validity of tangential model was not confiemed. Therefore, reconsider the tangential model. The result is improved accuracy of the model. Also.examined the characteristics of oblique impacts of changes in coefficient of friction from experiments and analysis.

This sheet deals with characteristics of the oblique impact system, which is composed of the ball and flat surface. The impact system is modeled by both a nonlinear spring and a nonlinear dashpot using Hertz's contact theory. This model is applied to the oblique impact system of ball. The characteristics of the oblique impact were obtained by using this model. The results show that the spin rate increased in proportion to the angle of incidence and impact velocity. Also, in the case of increase the tangential stiffness, the spin rate was decreased and the angel of reflection was increased.

Problems connected with a shock interaction of a thin elastic cylindrical bar and an elastic sphere with an Uflyand-Mindlin plate of a finite size are considered. In enumerated problems, an impact process is accompanied by material local deformations and propagation of wave surfaces of a strong or weak discontinuity in elastic bodies coming in contact. The local deformations are taken into account in terms of the Hertz's contact theory, but the dynamic deformations behind the fronts of incident and reflected waves are determined by means of truncated power series with variable coefficients (what is known as ray series). These two types of deformations are mated on the contact region boundary. As the truncated ray series, as a rule, are not uniformly applicable in the whole region of the wave solution existence, then for their improvement the method of “forward-area” regularization is used which is based on a combination of the recurrent equations of the ray method with the method of multiple scales. The method of power series (ray method) allows one to find the main characteristics of the impact theory in an analytical form.

In this paper, photoelastic experimental hybrid method using external traction free boundary condition and using the relative equation of two stress functions in contact problems are developed. Their validities are confirmed through experiments and discussions Hertz's contact theory and two photoelastic experimental hybrid methods explained above are applied to the stress analysis of O-ring under 10% or 20% squeeze rate. Among them, the photoelastic experimental hybrid method using the relative equation of two stress functions in contact problems is most effective. When squeeze rates of O-ring are 20%, Maximum of absolute σ_x is greater than maximum of absolute σ_y by little. But they are almost equal to each other. Maximums of absolute τ_<xy> are 1/5 of absolute σ_x when squeeze rate of O-ring is 20%.

Our sense of touch is spatially focused and has a far lower bandwidth in comparison with visual sense that has the largest bandwidth. While most haptic studies utilize point interactions, resulting in a conflict between this low information bandwidth and relative complexity of virtual scene. In this paper, we investigate a novel multi-resolution force evaluation scheme of hybrid virtual models in a unified haptic interaction framework. Force contact model of tool-object interaction based on Hertz's contact theory is integrated in our work. Physical properties with different object materials expressed by Poisson's Ratio and Young's Modulus are involved to investigate most realistic perception during multi-resolution haptic interaction. The hierarchical impostor representation of surface and volumetric models are constructed, and the optimal performance based on cost and benefit evaluation at run time is employed to meet both the visual and hapic perceptual qualities. During this multi-resolution haptic interaction, our scheme adaptively determines the rendering mode using graphics and haptics impostors represented in the virtual environments. Our experimental results have demonstrated the satisfactory performance of proposed multi-resolution haptic interaction framework applicable for hybrid virtual models.

An effective method for calculating elasto-plastic contact pressure and contact patch size under elliptical, circular and line contact conditions

In industrial plants and pressurized equipment, leakage control and prevention are key tasks in preventive maintenance programs. The most critical element in these types of equipment is the seals. Several types of seals are used and the most popular are flat seals and O-rings. Two conditions affect the proper functioning of the seals: the mounting configuration and the initial loading parameters during operation. In this work, the analysis of the mechanical and leakage behaviour of the O-ring seal, when installed either in a cylindrical concave groove or in a rectangular one, is presented. Two finite element models were developed with Ansys software to study the behaviour of the assemblies in both cases when the clamping load is applied and when the assembly is pressurized. The results of the numerical models are compared to the analytical approach based on Hertz's contact theory. This study shows that the use of a cylindrical concave groove for mounting elastomeric O-rings can improve sealing in pressurized systems.

This sheet deals with characteristics of the oblique impact system, which is composed of the golf ball and elastic supported clubface. The impact system is modeled by both a nonlinear spring and a nonlinear dashpot using Hertz's contact theory. This model is applied to the oblique impact system of golf ball and elastic supported clubface. The characteristics of the oblique impact were obtained by using this model. The results show that the spin rate increased in proportion to the angle of incidence and impact velocity and a coefficient of friction. Also, in the case of increase the tangential stiffness, the spin rate was decreased.

We report on the results of extensive computer simulation of the effect of deformation on the morphology of a porous medium and its fluid flow properties. The porous medium is represented by packings of spherical particles. Both random and regular as well as dense and nondense packings are used. A quasistatic model based on Hertz's contact theory is used to model the mechanical deformation of the packings, while the evolution of the permeability with the deformation is computed by the lattice-Boltzmann approach. The evolution of the pore-size and pore-length distributions, the porosity, the particles' contacts, the permeability, and the distribution of the stresses that the fluid exerts in the pore space are all studied in detail. The distribution of the pores' lengths, the porosity, and the particles' connectivity change strongly with the application of an external strain to the porous media, whereas the pore-size distribution is not affected as strongly. The permeability of the porous media strongly reduces even when the applied strain is small. When the permeabilities and porosities of the random packings are normalized with respect to their predeformation values, they all collapse onto a single curve, independent of the particle-size distribution. The porosity reduces as a power law with the external strain. The fluid stresses in the pore space follow roughly a log-normal distribution, both before and after deformation.

For determining die strength, there are a couple of tests available in the literature, such as three-point and four-point bending, ball breaker, ball-on-the-ring, ring-on-the-ring, and recently proposed ball-on-elastic- pad (BoEP) and ball-on-the-hole (BoH) tests. It's well known that the test data reduction with theoretical formulations is more convenient and useful than that with numerical simulation results. However, those theoretical formulations have to be validated either by numerical simulation or experiments, before their applications. The objective of this study is to reevaluate and thus improve the existing BoEP and BoH tests for die strength using Hertzian contact theory, plate theories and finite element method (FEM). In this paper, the FEM analysis with ¿contact element¿ successfully has been verified with Hertzian contact theory and further proved that Hertzian contact theory can be employed to estimate the contact area for calculating die strength in both methods. The results indicate that the consistency between the theoretical formulation and FEM simulation for both tests exist only at the relatively large radius of ball and high applied loading, because the feasibility of the theoretical formulations requires large contact radius(> 0.06 mm) or area. For the BoEP test, the elastic moduli of elastic pad and ball have no obvious effect on the difference of maximum die stress between theoretical and FEM results. The theoretical solutions associated with contact radius determined by Hertzian contact theory are successfully proved for improving BoEP and BoH tests for die strength determination, and for better accuracy of die strength the ball with radius ranging from 2 mm to 4 mm is suggested.

Critical loads and load-carrying capacities for steel scaffolds used as shoring systems were compared using computational and experimental methods in Part I of this paper. In that paper, a simple 2-D model was established for use in evaluating the structural behavior of scaffold-shoring systems. This 2-D model was derived using an incremental finite element analysis (FEA) of a typical complete scaffold-shoring system. Although the simplified model is only two-dimensional, it predicts the critical loads and failure modes of the complete system. The objective of this paper is to present a closed-form solution to the 2-D model. To simplify the analysis, a simpler model was first established to replace the 2-D model. Then, a closed-form solution for the critical loads and failure modes based on this simplified model were derived using a bifurcation (eigenvalue) approach to the elastic-buckling problem. In this closed-form equation, the critical loads are shown to be function of the number of stories, material properties, and section properties of the scaffolds. The critical loads and failure modes obtained from the analytical (closed-form) solution were compared with the results from the 2-D model. The comparisons show that the critical loads from the analytical solution (simplified model) closely match the results from the more complex model, and that the predicted failure modes are nearly identical.

The vocal folds are subject to repeated collision during phonation. The resulting contact pressure is often considered to play an important role in vocal fold injury, and has been measured in many experimental studies. In this study, vocal fold contact pattern and contact pressure during phonation were numerically investigated and compared to Hertzian contact theory. The results show that vocal fold contact in general occurs within a horizontal strip on medial surface, first appearing at the inferior medial surface and propagating upward. Because of the localized and traveling nature of vocal fold contact, sensors of a finite size may significantly underestimate the peak vocal fold contact pressure (by about as large as 80% for a sensor diameter of 2 mm), particularly for vocal folds of low transverse stiffness or thick medial surface. In general, the contact pressure increases with the size and curvature of the contact area, as predicted from Hertzian contact theory, indicating the possibility of estimating vocal fold contact pressure from medial surface kinematics. However, deviations from Hertzian theory were also observed, which need to be taken into consideration in estimating vocal fold contact pressure.

Ultra-high molecular weight polyethylene (UHMWPE) was modified on purpose to enhance the wear resistance. The modification was done either by crosslinking the amorphous region of the surface using difunctional monomers or by crosslinking the bulk in the melt state using peroxide. The changes in thermal and tensile properties indicated that the modifications were effected. The volumetric wear rate, determined on a pin-on-disk wear tester, was suppressed by the modifications. The correlation between the tensile properties and the wear rates was sought. Any single tensile property or tensile rupture energy did not correlate well with the observed wear rate. Instead, the ratio of maximum contact stress calculated by the Hertz's contact theory to yield stress appeared to correlate well with volumetric wear rate.

This study investigates the effect of the defect width on the burst capacity of corroded pipelines repaired with fiber reinforced polymer composite. Parametric finite element analyses are carried out to evaluate the burst capacities of composite-repaired pipes containing localized and full-circumferential corrosion defects. The analysis results indicate that burst capacities of composite-repaired pipes containing localized defects can be markedly lower than those of composite-repaired pipes with full-circumferential defects. The burst capacity model derived from the design equation recommended in the ASME PCC-2 code is found to be nonconservative for composite-repaired pipes with localized defects based on the parametric finite element analyses. An empirical equation for the defect width correction factor is then developed and shown to be highly effective in improving the predictive accuracy of the PCC-2 burst capacity model.

Atomic force microscopy (AFM) is a crucial tool for nanoscale material characterization of soft materials. However, AFM data is easily convoluted by many real, non-ideal artifacts. Researchers have identified some of them and developed techniques to deconvolute AFM data. Yet, several effects remain poorly understood. One of these effects has been identified as destructive AFM indentation. In particle-matrix composites, hard particle inclusions are responsible for varying degrees of stiffness across the sample, making nondestructive AFM indentation challenging. This paper utilizes finite element analysis (FEA) and AFM to study the impact of polymer matrix damage caused by destructive indentation on AFM data. AFM indentation is simulated on a polymer matrix FE model at varying depths. The Derjaguin-Muller-Toporov (DMT) contact model is validated for the FE geometry and applied to probe-matrix interactions for small indentation depths. Experimental data from AFM performed on PNCs reinforced with 0.5 wt.% multi-walled carbon nanotube (MWCNT) and CNT buckypaper (BP) is used to supplement FEA. Force-displacement data obtained through FEA is used to determine the indentation force and yield strength at the nanoscale following Hertzian contact theory and Tresca’s yield criterion. Subsequent destructive indentations are simulated to study their effect on force-displacement data.