The deformation behavior investigation of a polymers used as a sliding layer in a contact friction unit

The polymers and composites study of is to the present day an actual topic of many research scientists. Experimental studies of antifriction polymer and composite materials are widespread. But analyzing the performance of materials under different conditions does not lose its relevance. This is due to the limited data on the materials behavior in open sources, both statically and dynamically. The article deals with spherical bridge bearing manufactured by “AlfaTech”, Perm, Russia. The bearing includes a steel balancer with a ball segment in contact with the lower steel plate through a spherical protective antifriction layer. The material of the protective layer may vary. Several options for antifriction layer materials both polymer and composite are reviewed in the work. The geometry of structural elements influences its behavior. A particular effect is observed in elements made of plastic. The main part of parameters was considered in this article, such as thickness and physico-mechanical properties of polymer sliding layer. The article considers the value influence of the friction coefficient on the interaction of contact surfaces. It was obtained that the maximum values of contact parameters decrease with increasing sliding layer thickness. The paper deals with the description of viscoelastic behavior of modern polymers and composites used as sliding antifriction layers within.


Introduction
Currently, a large number of polymeric and composite materials are used in various industries, and new modern materials with improved characteristics are being developed [1][2][3].Such materials are used as antifriction sliding layers, protective coverings, etc. in various constructions.Most manufacturers of such constructions think about rational choice of elements geometrical parameters, to ensure its qualitative work.Spherical bridge bearings are a particular case of this construction type.In such constructions it is important to consider the influence of such sliding layer properties as: frictional, physical-mechanical, rheological, thermomechanical, etc.As well as such geometrical parameters as: thickness, depth of embedding into the steel plate, inclination angle of the sliding layer end, location in the upper/lower steel plate, nature of surface treatment, etc.
Researchers strive for a numerical behavior description of polymer/composite materials as close as possible to their behavior in a real structure [4][5][6].Thus, they face an important task of proper selection of the material behavior model depending on the type of contact and loads for the operating structures modes.Elastic or elastoplastic materials behavior is sufficiently studied, but for the description of viscoelastic behavior or rheology, the question of its behavior model proper selection is acute [7][8].Most often various linear models are used to describe the visco-elastic material behavior, such as: the Voigt m., the Kelvin m., the Maxwell m., the Bengam m., etc.In our work we consider the behavior description of polymers and composites using the generalized Maxwell model and Prony series.Also the models application on test problems and in real structures, for example spherical bridge span bearings.

Problem statement
To be able to qualitatively simulate the behavior of polymers and composites in real working conditions, it is necessary to have data on the operation of the real structure.Therefore, it was decided to consider the performance of polymer material in spherical bearing (SB) by "AlfaTex", Perm, Russia.This construction is a plate with spherical segment, a lower steel plate with a cutout and the sliding layer between them.Figure 1 shows its design scheme.

The influence investigation of physical and mechanical sliding layer properties
The article analyzed the influence of antifriction polymers properties on deformation behavior of sliding layer and SB.In particular the settlement of the upper steel plate was considered and comparison of settlement values obtained numerically and experimentally (figure 2) was performed.In the experimental part the SB was considered with wells in the sliding layer from PTFE and with the use of lubricant.The article notes that the results obtained numerically give not a large error with respect to the experimental values of the upper steel plate settlement.The difference of values reaches about ~14 %, but it should be borne in mind that the recesses for lubricant in the sliding layer, as well as lubrication were not taken into account in the numerical model.It follows that the numerical model describes the deformation behavior of the SB and its sliding layer quite well.

The influence investigation of tribological properties on deformation sliding layer behavior
In the second problem the influence of the friction coefficient value on the deformation behavior of sliding layer was considered.On figure 3 is shown the distribution of the plastic deformation intensity of sliding layer from PTFE, with friction coefficient equal to 1 μ =0.04.The frictional properties of the material affect both the minimum values and the maximum values of plastic deformations.The lowest level of plastic deformations we observe at the tabulated friction coefficient, and the highest level of plastic deformations are observed at the experimental friction coefficient with lubrication.Also frictional properties affect the character of plastic strain distribution at the relatively free edge, where stress concentration is observed.Most of the antifriction interlayer works within the elasticity theory.The composite interlayer has the lowest level of stress intensity/plastic deformation for different frictional properties.The other materials have average values.

The influence investigation of introduction depth of sliding layer in lower steel plate
The bridge bearings are critical elements of bridge structures.Previously, in the problems of studying the deformation behavior of spherical bearings, the material model was described in an elastic-plastic formulation.However, in order to obtain better results close to the real work of the structure, it was decided to use viscoelastic model Prony as a description of the material behavior model in numerical calculations.
The paper compared three material behavior models: elastic (model 1), elastic-plastic (model 2), viscoelastic (model 3).In describing model 2, the physical relations presented in more detail in [10] were used.
In the initial phase of the study on the influence of material behavior, a test contact problem was implemented.After selecting the settings and parameters of the viscoelastic material behavior model, the transition to the parameterized model of the real design of spherical bridge bearing was performed [11].

Conclusion
The influence analyze of friction polymer properties is performed in the numerical realization of friction contact interaction of steel plates with spherical segment and spherical cutout of bridge bearing with elastoplastic antifriction sliding layer: on the major contact surfaces The comparative analysis of the materials behavior models of antifriction sliding layer in conditions of contact interaction on deformation of the interlayer is conducted.The problem is considered on the test model, transition to the model of real design of spherical bearing is performed.
Qualitative and quantitative regularities of material influence of antifriction sliding layer and its description in the framework of linear viscoelasticity on deformation behavior of friction units are obtained.

Figure 1 .
Figure 1.Bridge bearing design scheme six materials are considered as antifriction sliding layer: three ultra-high molecular weight polyethylene (UHMWPE) from various producers (mat.1-3); two antifriction composite materials (mat.4-5); Polytetrafluoroethylene (PTFE) (mat.6).Physical and mechanical properties were obtained experimentally at the base of IMSS Ural Branch of the Russian Academy of Sciences, Doctor of Physical and Mathematical Sciences, Professor Adamov A.A. [9].The friction coefficient is equal to 0.04 between the contact surfaces within the framework of the first task realization on the influence study of physical and mechanical properties of materials.At the second stage the influence of different friction coefficients values on the sliding layer behavior is considered.The article considers three different friction coefficients: tabular 1 μ , obtained experimentally without taking into account lubrication 2 μ , and including lubrication 3 μ on the interfeces.Friction coefficients obtained experimentally for the materials UHMWPE produced in Germany, MAK with spherical bronze inclusions, PTFE (table 1

Figure 2 .
Figure 2. The shrinking value of upper stile plate for the standard thickness of sliding layer

Figure 3 .
Figure 3. Plastic strain intensity at the standard thickness of sliding layer from PTFE for tabular friction coefficient

1 C S and 2 CS 3 μ 3 CS
the minimum values of contact parameters are observed at frictional properties of materials (UHMWPE, modified fluoroplastic) with lubrication obtained experimentally.The highest values of parameters are observed for composite material at tabulated friction coefficient.Decrease of contact area connected with divergence of contact surfaces is revealed: for UHMWPE produced in Germany at 2,55 % from the initial contact area.On the relatively free of contact surface of at the lowest level of contact tangential stress the highest level of contact pressure occurs at the experimentally obtained frictional properties of the material with lubrication.It is revealed that at frictional properties obtained experimentally relative to the tabulated friction coefficient the area of distribution of maximum values of stress intensity/plastic deformation has increased.APITECH-V-2023 Journal of Physics: Conference Series 2697 (2024) 012024

Table 1 .
).A static pressure equal to 1000N is applied to the surface Values of friction coefficients 1S .Good quantitative and qualitative results were obtained by solving numerical problems on deformation of SB by static loading at different geometrical parameters, friction coefficients and physico-mechanical materials properties.

Table 2 .
Max values of intension of stress and plastic strain for different friction coefficients.