Additions of reinforced fibres in layered polymers and their effect on wear resistance

. This paper describes a study of layered polymers with the addition of reinforcing fibres. Their advantages are strength and stiffness, lightness and improved chemical resistance. The study deals with a comparative evaluation of the wear resistance of textolite with different reinforcing fibres under sliding friction conditions. A sample of the investigated material, made in the form of a disc, was fixed in the centre of the table surface and driven into rotational motion at a given frequency. A 6 mm diameter ball made of 100 Cr6 steel was used as a control sample, which was rigidly fixed in the end of a cylindrical pin (indenter). A normalised normal load was applied to the indenter, which was resting on the disc at some distance from the centre of rotation. During the tests, the coefficient of friction and the depth of penetration of the ball into the test sample were continuously measured. The tests were carried out with increasing and decreasing of the load with the interval of 2,0 N. The duration of the long-term wear tests for each sample was 21500 m of friction path (about 20 hours). The estimation of fixed changes of the friction coefficient from load at tests on wearability of couplings has been carried out. The results of tests of the investigated materials samples have shown the best indices on the intensity of wear at mating with a sample from textolite PTG compared to oxafen and Kevlar, accordingly, in 2.97 and 5.93 times. Key words: tribotechnical tests, polymeric materials, fibres, textolite, kevlar, oxafen.


Introduction
Layered polymers with added reinforcing fibres are composite materials in which a polymer matrix is combined with reinforcing fibres to improve their mechanical properties.Combining a polymer matrix with reinforcing fibres can create a material that has strength and stiffness, as well as other properties that are rarely achieved by polymers or metals alone [1][2][3].
The advantages of using reinforced layered polymers with added fibres include: 1. Improved strength and stiffness: Reinforcing fibres such as glass fibre, carbon fibre or reinforced fibre reinforce the polymer matrix, increasing its strength and stiffness.This is particularly important in applications where high mechanical strength is required.

Increased cyclic strength:
The fibres help to increase resistance to damage under cyclic loads.They prevent crack propagation and improve resistance to deformation, making laminates with reinforcing fibres ideal for components and parts subjected to cyclic loads.
3. Lightweight: The fibres are relatively lightweight and allow for the creation of lightweight composites.This is particularly important for the aerospace and automotive industries where weight reduction is critical to improve efficiency and reduce energy consumption.
It is important to take into account that the choice of the type of reinforcing fibres and the optimal proportions between matrix and fibres may depend on the specific task and the required performance.
The aim of the work is a comparative assessment of wear resistance of PTH textolite, textolite with kevlar, oxafen fibres working under sliding friction conditions.Comparative tests were carried out in accordance with GOST 23.224-86 [7,8] in Nano-Centre of Federal Scientific Agroengineering Centre VIM on tribometer TRB-S-DE CSMInstruments.

Materials and methods
Armide fibres are a class of high-modulus and high-strength fibres that have outstanding mechanical properties.In materials science, reinforced fibres are used to create composite materials with reinforced structures.They can be used in composite panels, rods, tubes and other parts where high strength and stiffness are required.Various materials are used as such fibres.Studies have been carried out with the following materials: Textolite is a high strength and insulating material widely used in industry.It is a composite material which consists of layers of glass fabric impregnated with epoxy resin and heat treated.Due to the layers of glass fibre, textolite has high strength and resistance to mechanical stress, it can withstand high temperatures without deformation or loss of properties.The epoxy resin used in textolite has chemical resistance, which makes it resistant to various chemicals [6,9].
Kevlar is an armide fibre that was originally developed for use in body armour.However, kevlar has found wide applications in various industries including mechanical engineering, automotive, aerospace and others.The main characteristics of Kevlar are its high strength and stiffness with relatively light weight.Kevlar fibres have a crystalline structure that provides them with high mechanical strength and tensile strength.This property makes Kevlar an ideal material for use in products where high strength and mechanical resistance are required [1,4,5,10].
Oxafens are a class of chemical compounds that contain a heterocyclic ring that includes oxygen and nitrogen atoms.Oxafens can be used in various fields and material science.They can be used as components to create polymeric materials with desired mechanical, thermal or electrical properties.They can be incorporated into a polymer matrix to improve its stability, strength or other characteristics [10,11].
Circular motion tests on a TRB-S-DE tribometer were performed to investigate the surface properties and wear resistance of a disc-shaped specimen (specimen-disc) in interaction with a ball-shaped control sample (ball indenter).This type of test simulates sliding conditions on the surface of a rotating disc in the absence of lubrication, i.e., dry friction.
During the tests, a normalised load was applied to the specimens to measure the friction forces generated between the disc specimen and the ball indenter.By performing circular trajectory motion, friction occurs along the radius of the sample disc, and this method provides an estimate of the coefficient of friction and wear resistance of the materials.
Unlubricated tests provide information on the behaviour of materials under dry friction conditions, which can be critical in many industrial processes and applications.Wear and friction under dry friction conditions can be more intense and lead to increased wear and deterioration of surface properties.
Such tests on the TRB-S-DE tribometer provide data on friction, wear and other surface properties of materials under conditions that are as close as possible to actual operating conditions.This data can be useful for optimising design and material selection in a variety of applications such as automotive, mechanical engineering, and industrial applications.
Several key parameters are recorded and analysed during testing on the TRB-S-DE tribometer.Some of these include: 1 Creating friction curves: During testing, friction force data is recorded as a function of time or number of cycles passed, allowing friction curves to be plotted.Analysing these curves can provide information on the durability and stability of friction during testing.
2 Wear: Wear on a specimen can be determined from visual observations or physical measurements such as measuring the depth of a mark or the amount of material wiped off.Wear can indicate a material's resistance to mechanical action and can be used to compare different materials.
3 Tribological properties: Testing on the TRB-S-DE Tribometer can also provide information on other important properties such as seizure and sliding tendencies and surface changes after testing.
A disc-shaped sample of the material under test was fixed in the centre of the table surface and driven in rotational motion at a specified frequency.A 6 mm diameter ball made of 100 Cr6 steel was used as a control sample, which was rigidly fixed in the end of a cylindrical pin (indenter).A normalised normal load was applied to the indenter, which was resting on the disc at some distance from the centre of rotation.During the tests, the coefficient of friction and the depth of ball penetration into the test specimen were continuously measured.The parameters and data obtained from TRB-S-DE tribometer tests in "circular motion" without lubrication allow the evaluation of surface properties and wear resistance of materials under dry friction conditions.This information is essential for the development of new materials, design optimisation and material selection decisions in various industrial and technical applications.

Results
Friction and wear tests for three investigated samples were carried out with increase and decrease of load applied to the tribometer indenter with the interval of 2.0 N. The results of change of friction coefficient at tests on wearability of investigated mating are presented in Table 2. Evaluation of the parameters of wearability and selection of parameters for long-term wear tests of the studied couplings are presented in Figure 1 and Table 3.The results of testing of samples of investigated materials in mating for wear and wearability are summarised in Table 3.The duration of the long-term wear tests for each specimen was 21500 m of friction path (about 20 hours).
The results of wear tests are presented in Table 4.

Conclusions
Since the samples with the addition of reinforcing fibres were taken for testing, characterised by rather high mechanical strength, resistance to deformation, friction, the results of tribotechnical tests showed high results for the three samples taken.The samples withstand loads of about 20...22 N and 4.5-5.1 units.But the sample made of textolite RTN showed the best result out of the three.When comparing the samples submitted, the following results were obtained.In the study of the wear resistance of materials through friction on a tribometer, samples of PT textolite showed high results in terms of wear resistance.Compared to oxafen, the wear resistance of textolite is higher by a factor of 2.97, compared to kevlar it is higher by a factor of and 5.93.
This data was obtained as a result of one rather short study for such samples, but can be the basis for determining the qualitative characteristics of the presented materials.These characteristics should be taken into account depending on the purpose and method of use of materials in applied activities.

Table 1 .
Parameters of samples and control samples

Table 2 .
Step test results

Table 3 .
Results of coupling wearability tests

Table 4 .
Results of wear tests of the investigated material samples