Mechanical Contact Conditions Research Articles

Finite element software for forming processes of glass containers

AbstractA two‐dimensional (2D) axisymmetric numerical model, based on the finite element method, for glass containers forming processes is presented. Glass forming processes involve coupled thermomechanical phenomena in which heat transfer and viscous flow are dependent, as glass viscosity is highly dependent on temperature. During the overall process glass changes from a molten state to a solid state. Therefore, adequate cooling conditions must be set appropriately. From the numerical point of view, the modeling must be robust so as to adjust to the different sequenced stages. Remeshing techniques requiring adequate data transfer, as well as, different thermal and mechanical contact conditions between glass and molds must be taken into account. Also, effective treatment of the incompressible conditions associated with glass flow must be dealt with. The aim is to set the better process parameters so that the final containers have the required geometrical shape and thickness distribution. A numerical model was conducted addressing all these issues and a thickness distribution comparison with real industrial products was performed.

Determination of Hot Stamping Friction Coefficient of 7075 Aluminum

Aluminum alloy hot stamping technology can improve the formability of materials and obtain parts with high dimensional accuracy. Friction behavior in the hot stamping process is very important for forming quality. Accurate friction coefficient is helpful to improve the prediction accuracy of forming defects. It is hard to obtain the friction coefficient by simple experiments due to the complicated thermal–mechanical coupling and contact conditions during the hot stamping of aluminum alloys. In order to explore the effect of friction behavior on forming quality, hot stamping experiments of 7075 aluminum alloy U-shaped parts with different lubricants were carried out. The influence of different lubricants on the force–displacement curve, material inflow, surface appearance, and thickness distribution of the formed part was analyzed. The results showed that a good lubrication effect could be obtained with the molybdenum disulfide lubricant. The friction coefficient under different lubrication conditions was obtained by using the inverse problem optimization method. Compared with the experimental results, the determined friction coefficients could accurately predict the force–displacement curves and the thickness distributions of formed parts under different lubrication conditions.

Fluid Stiction From a Contact Condition

This paper considers modeling of fluid stiction between two separating plates that start from a mechanical contact condition. Published experimental work on initially contacting plates showed significant variations in stiction force peak values. In order to describe the observed strong force variations with mathematical models, the models should be quite sensitive to some of the input parameters of the stiction problem. The model in this paper assumes that small air bubbles are entrapped between the contact areas of the asperity peaks and that the fluid film flow between the cavitation bubbles is guided by Reynolds equation. The proposed model exhibits high sensitivity to initial bubble size and initial contact force compared to state-of-the art models. A delay of about 1 ms in the simulated stiction force evolution and the experiments was found. Potential causes for this discrepancy are discussed at the end of this paper and an outlook to future work, which can reduce the discrepancy between the model and experimental results is given.

Axisymmetric thermoelastic deformation of a multilayer plate with imperfect thermal contact of its layers

An axisymmetric stationary problem of thermoelasticity for a multilayer plate with imperfect thermal contact between its layers is solved by using the method of compliance functions along with the Hankel transform. It is assumed that the conditions of perfect mechanical contact are satisfied on their common boundaries. The Hankel transforms of displacements, stresses, and temperature at the points of the layer can be represented in the form of the linear combinations of the six auxiliary functions. The auxiliary functions are connected with the Hankel transforms of displacements, stresses, temperature and flow at the points of the upper boundary of the corresponding layer. For the problem considered six auxiliary functions can be found from the boundary conditions. Using the conditions on the common boundaries of the layers and entering a dummy layer the recurrent formulas for finding other auxiliary functions are constructed. The auxiliary functions of each layer are dependence. This dependence is represented in the matrix form using so-called compliance functions. The recurrence relations for the compliance functions of the thermoelastic multilayer plate are constructed. The algorithm for solving the сonsidered problem is formulated. The numerical calculations are made for a two-layer plate subjected to the action of the thermal loads. The influence of the coefficient of thermal resistance on the distribution of temperature at the points of the lower boundary of the upper layer and at the points of the upper boundary of the lower layer is analyzed. Also the influence of this coefficient on the distribution of normal stresses at the common boundary of layers is analyzed.

Contact Analysis for Contact Thermoforming of PMMA Sheet

Abstract The ability to produce products with more uniformity in the wall thickness distribution makes contact thermoforming the most suitable optical product processing method. Among all the process parameters, the contact condition significantly affects the structural strength and the optical properties of the product. Thus, it is imperative to investigate the effect of change in the contact conditions on product thickness. Hence, in this study, experimental investigations on contact conditions were performed considering poly(methyl methacrylate) as the sheet material and stainless steel 304 as the punch material. Experiments were conducted to examine the effect of temperature on the coefficient of friction (mechanical contact condition) and the effect of pressure on the thermal contact conductance (thermal contact condition). It was found that the contact conditions change significantly with changes in the operating conditions. Furthermore, numerical simulations were performed, considering isothermal processing and nonisothermal processing with constant and variable contact conditions to identify the effect of the change in contact condition on the product thickness. It was found that the change in contact condition has a considerable effect on the product thickness distribution. This study shows the importance of incorporation of the change in the contact condition for realistic simulations.

Глобально-локальное моделирование односрезных болтовых соединений типа композит — металл и композит — композит в конструктивных силовых элементах самолета

In performing design strength analysis of connection areas of composite — metal and composite — composite types of structural load-bearing wing and empennage elements of the aircraft implemented using mechanical fasteners, it is necessary to considerthe factors determining the local strength of these areas: the conditions of mechanical contact of the body, bolt head and cap with connected elements, the connected elements contact with each other and the effects of friction. These factors can be taken into account only by applying the global-local modeling approach for constructing 3D prediction models of composite — metal and composite — composite joint zones of aircraft caisson structural members. To solve this problem, a method is proposed defining the means and tools of modeling, algorithms for constructing a prediction model and performing calculations, as well as procedures for analyzing the results of calculations.

Effect of Cr-Ni coated Cu-Cr-Zr electrodes on the mechanical properties and failure modes of TRIP800 spot weldments

Resistance spot welding (RSW) is a highly preferred welding process in the automotive and other industries because of its faster and economical processes and also it has higher quality. However, during the joining process, the temperature at the electrode tip reaches the highest value and, in the meantime, electrode tips are deformed. For this reason, the electrode wears down with increasing weld numbers, which changes the thermal, electrical, and mechanical contact conditions at the electrode and sheet interfaces. The coating is generally applied onto the surface of Cu–Cr–Zr electrodes for extended electrode life during RSW process. In this study, the tip surfaces of the electrodes were coated with Cr–Ni filler metal by using electro-spark deposition (ESD) coating method under 40, 80, and 120 V. Consequently, the effects of the coating on electrode characteristics and properties of the TRIP800 resistance spot weldment are investigated. The mechanical behaviors of the joined samples under static load were investigated by applying a tensile shear test and cross tension test. Tensile-shear strength, cross-tension strength was determined, and the failure modes of the samples was investigated. The nugget size was measured by stereo microscope. Microstructure investigations have also been carried out by optic microscope and scanning electron microscopy (SEM).

Behavior of piezoelectric layered composites with mechanical and electrical non-uniform imperfect contacts

In this work, the two scales asymptotic homogenization method (AHM) is applied for determining the effective coefficients of laminated piezoelectric composite with periodic structure under non-uniform electrical and mechanical imperfect contact conditions. The analytical expressions of the local problems and the effective coefficients as result of the AHM are explicitly described. The constituent materials have properties belonging to 2 mm symmetry point group. Numerical values of the effective coefficients are reported and compared with limit cases, where perfect and uniform imperfect contact conditions are considered. Good agreements are found for these comparisons. Hence, the effect of the non-uniform imperfect contact conditions on the effective coefficients can be analyzed.

Dynamic interaction of a thin metallic inclusion with a piezoceramic matrix

A mathematical model of dynamic behavior of a thin metallic inclusion or a layer in a piezoelectric medium subjected to longitudinal shear load is constructed. At the boundary of inclusion and matrix, the conditions of perfect mechanical contact and zero electric potential are prescribed. Modeling is performed using the apparatus of the theory of singular perturbations. Cite as: Yu. I. Maksymiv, Yu. V. Porokhovsky, R. V. Rabosh, V. O. Mishchenko, Ya. I. Kunets, “Dynamic interaction of a thin metallic inclusion with a piezoceramic matrix,” Prykl. Probl. Mekh. Mat. , Issue 17, 134–138 (2019) (in Ukrainian), https://doi.org/10.15407/apmm2019.17.134-138

Antiplane Shear of an Elastic Body with Elliptic Inclusions Under the Conditions of Imperfect Contact on the Interfaces

We study the problem of аntiplane shear of an elastic body containing a finite array of arbitrarily located and oriented elliptic inclusions under the conditions of imperfect mechanical contact on the interfaces. The analytic solution of the problem is obtained by the method of multipole expansions with the use of the technique of complex potentials. By expanding the disturbances of the field of displacements caused by inclusions in a series in the system of elliptic harmonics and using the formulas for their reexpansion and exact validity of all contact conditions, we reduce the boundary-value problem of the theory of elasticity to an infinite system of linear algebraic equations. It is also proved that the reduction method is applicable to the indicated system, the rate of convergence of the solution is investigated, and the accumulated results are compared with the data available from the literature. The presented numerical results of parametric investigations reveal the presence of a strong dependence of stress concentration on the conditions of contact on the interfaces, as well as on the sizes, shapes, and relative positions of the inclusions.

Bimetallic diffusion modeling and temperature regulation during ball milling

This work establishes a computationally efficient model of temperature and diffusion dynamics in ball milled bimetallic Ni-Al particulates. Mechanical contact conditions between adjacent bimetallic domains and temperature fields generated upon impact define the diffusive fluxes through the domains' interfaces. The concentration distributions are studied via Green's function methods, by defining mirror images which reflect the boundary diffusive resistance conditions. Predictions of the model are validated against experimental open-loop scanning electron micrographs and X-ray diffraction spectra at steady-state. Dynamic models of diffusion saturation and internal temperature are developed for the design of closed-loop controller via simulation. This feedback controller is implemented on a laboratory device, equipped with infrared thermometry for external vial temperature measurement, as a self-tuning regulator. The controller adapts an efficiency parameter of the model that thus serves as a real-time observer for internal temperature and diffusion saturation, which are physically inaccessible during processing. Experimental open-loop results are employed to set thresholds of diffusion penetration to avoid early exothermic reaction during fabrication. By controlling the process duration, the regulation system successfully reproduces the material composition of the open-loop reference tests, to ensure desired thermodynamic properties of the ball milled products and safety of the operation.

Support Stiffness Monitoring of Cylindrical Structures Using Magnetostrictive Transducers and the Torsional Mode T(0,1).

In this paper, a support stiffness monitoring scheme based on torsional guided waves for detecting loss of rigidity in a support of cylindrical structures is presented. Poor support performance in cylindrical specimens such as a pipeline setup located in a sloping terrain may produce a risky operation condition in terms of the installation integrity and the possibility of human casualties. The effects of changing the contact forces between support and the waveguide have been investigated by considering variations in the load between them. Fundamental torsional mode is produced and launched by a magnetostrictive collar in a pitch-catch configuration to study the support effect in the wavepacket propagation. Several scenarios are studied by emulating an abnormal condition in the support of a dedicated test bench. Numerical results revealed ultrasonic energy leakage in the form of bulk waves when a mechanical coupling between the cylindrical waveguide and support is yielded. Experimental results showed that the rate of ultrasonic energy leakage depends on the magnitude of the reaction forces between pipe and support; so different levels of attenuation of mode will be produced with different mechanical contact conditions. Thus, it is possible to relate a measured attenuation to variations in the supports condition. Results of each scenarios are presented and discussed demonstrating the feasibility and potential of tracking of the amplitude of the as an indicator of abnormal conditions in simple supports.

Domain decomposition algorithms for problems of thermomechanical contact between several elastic bodies

We consider a thermoelastic multibody contact problem for finite bodies with unilateral mechanical and imperfect thermal contact conditions. Using a penalty method, we obtain a weak formulation of this problem in the form of a system of linear and nonlinear variational equations in Hilbert space. To solve this variational system, we propose a class of iterative Robin type domain decomposition algorithms. In each iterative step of these algorithms one have to solve two linear variational equations for each of the bodies, which correspond to heat conduction problem with Newton boundary conditions on the possible contact areas and linear elasticity problem with additional volume forces and Robin boundary conditions respectively. The program implementation of proposed algorithms is made for plane thermoelastic contact problems with the use of linear and quadratic finite element approximations on triangles. The numerical analysis is performed for one-body and two-body thermoelastic contact problems.

Innovative seismic isolation of masonry infills using cellular materials at the interface with the surrounding RC frames

In this study an innovative concept is proposed to isolate – at low and moderate storey drifts – infill panels from the surrounding reinforced concrete (RC) frame, using thin layers of cellular materials. The concept is verified experimentally through testing of three fully infilled (i.e. at full height) and two partially infilled (i.e. at reduced height) RC frames with different infill-to-frame interface contact conditions under in-plane cyclic loading. The shear strength, hysteretic behavior, damage evolution and stiffness degradation of conventionally infilled RC frames is compared with the respective properties of frames with isolated infills. The experimental results show that fully infilled test specimens exhibit much more severe damage than the isolated ones, leading to the conclusion that the proposed isolation system significantly preserves the integrity of infill panels at moderate storey drifts and increases shear strength and lateral stiffness of the infilled frames at higher deformations. Additional tests on frames with infills at partial height show that cellular material joints at the sides of infills decrease the adverse effects of the infill-frame interaction. Finally, it is demonstrated that mechanical properties, contact conditions and joint thickness of the cellular material influence the overall hysteretic behavior of the specimens. A simple analytical model is developed, combining single-strut elements for the infills with nonlinear springs for the cellular material joints. The model, implemented in OpenSees, is in good agreement with test results. The concept is demonstrated through parametric analyses in full scale RC structures. Overall, it is concluded that the proposed technique has a high potential in reducing infill-frame interactions – hence damage of the infills – up to moderate drifts, whereas full interaction – hence increased capacity – is still in place when drifts are large.

Analysis of mechanical and electrical imperfect contacts in piezoelectric composites

The problem of a heterogeneous piezoelectric composite with mechanical and electrical imperfect contact conditions is studied by means of the asymptotic homogenization method. As an illustrative example, in order to provide a benchmark for the numerical validation of theoretical models, a one-dimensional two-phase periodic laminate piezoelectric composite is considered with imperfect adhesion. Numerical examples show the effect of interface imperfections on the effective properties. Reductions in the effective Young’s modulus, the piezoelectric coupling and the dielectric permittivity under the effect of the imperfect contact conditions are reported herein.

Analysis of hot cracking during lap joint laser welding processes using the melting state-based thermomechanical modeling approach

Although lap joint laser welding is in great demand in practice, very limited numerical studies have been performed to investigate the hot cracking behavior in this welding configuration. This is because the traditional numerical methods are ineffective in simulating lap joint welding processes, which requires consideration of the discontinuous thermomechanical fields across the metal sheet interface prior to joining and the complicated contact conditions that evolve with material phase transitions during the welding process. The aim of the present study is to introduce a new irreversible melting state variable into the thermomechanical coupled computational model to account for the melting state effects on the mechanical and thermal properties at the welding interfaces. Under this framework, the calculation of thermal conductance and frictional coefficient depends on both temperature and the melting state variable. This allows the proper thermal and mechanical contact conditions to be captured at various melting states during the whole welding process. The proposed melting state-based model has been applied to the simulation of lap joint laser welding for the numerical investigation of the critical crack initiation location as well as the influence of various processing parameters on the cracking susceptibility and the cracking mechanism during heating-cooling processes.

Thermoelastic Equilibrium of a Three-Layer Circular Hollow Cylinder Weakened by a Crack

We solve plane problems of stationary heat conduction and thermoelasticity for a hollow three-layer cylinder weakened by a crack by the method of singular integral equations. The cross section of the cylinder is a circular concentric ring with similar rings of a different material inserted into this ring. The inner ring contains an edge radial crack. The surfaces of the cylinder are free of loads and temperature conditions of the first kind are satisfied on these surfaces. On the interface of the media, we impose the conditions of perfect thermal and mechanical contact. The numerical solution is obtained for the case where unequal constant temperatures are given on the inner and outer surfaces of the cylinder. The stress intensity factors at the tip of an edge crack are found for different values of thermal and mechanical parameters of the components of the cylinder.

Transient Vibrations of an Elastic Cylinder Inserted in the Elastic Medium

Abstract Using method of Laguerre polynomials we have obtained the solution of the dynamic problem of the theory of elasticity for elastic cylinder inserted into massive body modeled as a space. The source of non-stationary processes in composite is high intensity force load of the inner surface of the cylinder. On the surface separation of materials of space and cylinder the conditions of ideal mechanical contact are satisfied. The solution is obtained as series of Laguerre polynomials, which coefficients are found from recurrent relations. The results of numerical analysis of transient stress-strain state in elastic space with cylindrical insertion might be used for the technological process of hydraulic fracturing during shale gas extraction.

Numerical and experimental investigation of (de)lithiation-induced strains in bicontinuous silicon-coated nickel inverse opal anodes

A volume expansion of up to ∼310% occurs upon the lithiation of silicon in Si-coated nickel inverse opal anodes, which causes (de)lithiation-induced mismatch stresses and strains between the Si and Ni during battery cyclical (dis)charging. These (de)lithiation-induced mismatch strains and stresses are modeled via sequentially coupled diffusion- and stress-based finite element (FE) analysis, which takes the mechanical contact between the Si and Ni phases into account, as well as the complex geometry and material properties of the Si-coated Ni inverse opal anode system. During lithiation, compressive strains up to 0.2% are developed in the Ni scaffold since the Si active layer expands. A rapid recovery of these lithiation-induced mismatch strains occurs during subsequent delithiation, though full recovery is not achieved. Strain histories upon multiple (de)lithiation cycles vary with the choice of various mechanical contact conditions employed between the two phases, since the mechanical contact properties determine how the contacted phases interact mechanically. The numerically predicted strains are compared with experimental strain data collected in operando using X-ray diffraction. The simulated strain histories agree with the measured data, enabling the possibility of predicting mechanical performance and eventual degradation using only numerical modeling. In particular, the FE model indicates that plastic deformation occurs first in the lithiated Si active layer, then in the Ni scaffold.

The role of tribo-pairs in modifying the tribological behavior of the MoS2/Ti composite coating

Mechanical contact conditions and the shear strength of the interface are the two independent factors that control the friction behavior of the MoS2 coating. Although ZrO2 and GCr15 had similar mechanical contact conditions, they showed rather different friction behaviors. Therefore, the shear strength of the interface was prominent in determining the friction behavior of the MoS2/Ti composite coating, particularly in the initial stage of friction. The strong interfacial shear strength between GCr15, WC and MoS2/Ti resulted in the high friction coefficient in air and short wear life in vacuum. Furthermore, we found that the interfacial shear strength was affected by the Ti content in the MoS2/Ti coatings, and the adhesive behavior of Ti and GCr15 was responsible for the high friction coefficient and high wear rate. The shear strength between the two sliding materials was amplified with the increase in the vacuum degree. These results benefit us to tailor or select the MoS2-based composite coatings and the corresponding tribo-pairs for vacuum operating conditions.