Graphical assessment of the linear contact steel on composite material at high temperature and pressure

In this article we have tried to present a graphical assessment of the dry linear contact for composite materials reinforced with glass fibers as well as of the influence of the sliding speed, load and friction coefficient. Perpendicular loads, the contact temperature and the wear of the metal surface were recorded. The wear volume was calculated using the Archard relationship. Using the Archard relationship, the width of trace can be calculated in 3 locations. Numerous experimental trials were performed in connection to the wear of the metal surface, the contact temperature and the value of the friction coefficient. A connection between the evolution of the wear process and the dependency on the contact temperature and friction coefficient can be observed.


Introduction
One of the most sophisticated tribosystems is the one between a polymer polymer with short fibers (SGF) on steel, where the contact is dry. In this case, the input parameters are permanently modified. Based on comprehensive experimental tests, a study for the evolution of wear for a certain duration, as well as for certain loads and contact temperatures. The materials used were composite thermoplastic materials reinforced with glass fiber. The glass fiber content varied from a material to another. The evolution of wear was highlighted depending on the duration, the load, contact pressure and sliding speed. Starting from an extended study, we have tried to come up with a graphical representation of the wear process for a dry contact between polymers reinforced with glass fibers and C120 steel, respectively Rp3 steel. For experimental tests, Archard's relationship for adhesion wear was used. Derjaguin-Muller-Toporov [1] (DMT) model. This model is correct for nanometrically sized bodies, with steel characteristics. The main characteristic of short fiber reinforced polymers (SFRP) is their high level of resistance to rapid loads. This occurs at a relatively low price compared to other materials. Wang, et all, [2] have studied Nylon 1010 composite with MoS 2 filler and short carbon fibers, the study being carried out in a ring-block wear tester, using a dry contact. The following two aspects were observed: by adding the MoS 2 filler, it has led to an increase in wear, while adding the carbon fiber filler has led to a decrease in wear. Chang and Friedrich [3] have noticed that the particles, respectively the nanoparticles do not entirely contribute to the film transfer, thus reducing the adhesion and, as a consequence, also reducing the friction coefficient. Cho and Bahadur [4] have carried out a study on nanosized CuO-filled polyphenylene and on polyphenylene sulfide composites (PPS) reinforced with short carbon fibers (CF) and aramid fibers (Kevlar).
Vos, et all [5][6] have studied polyetheretherketone composites reinforced with short glass fibers and carbon fibers and have shown that the wear rate is influenced by the morphological structure of the matrix of the composite polymer.
Guo, et all [7] have used in their studies composites based on epoxy pitches filled with hybrid particles nano-SiO 2 and short pitches based on carbon fiber. A reduction of the friction coefficient was noticed in the case of hybrid polymers as compared to polymers with added nano-SiO 2 particles U.S. Tewari, J. Bijwe [8] have highlighted the low manufacturing costs achieved through a composite polymer injection. [9] L. Chang, Z. Zhang show that the injection machines suffer from considerable wear due to the glass fibers. Schwartz and Bahadur [10] have studied the transfer of the material film using infrared technology. They have observed the following phenomenon, an increase in the density of the polymer leads to an increase in the cohesion energy.
Li, et all [11] has studied analytically and experimentally the epoxide nano-composites, reinforced with short carbon fibers (SCF), of the nano-TiO 2 particles, of the powder of polytetrafluorethylen (PTFE) and graphite flakes, in order to understand the mechanism for adding filler to modify the wear parameters of the two epoxide nano-composites on metal counterpieces. Chang,et all [12] studies the properties of composite materials, respectively the proprites of polyetheretherketone (PEEK) and polyetherimide (PEI), reinforced with short carbon fibers (CSA). They have determined that by adding submicron particles (TiO 2 and ZnS), for the high contact temperature of the pin-on-disk type tribometer, the wear rate has decreased. L. Capitanu et all [13][14] have highlighted the behaviour of polyamide and polycarbonate reinforced with glass fibers (SGF) in friction on steel surfaces . Kukureka, et all [15] have studied the wear of PA66 in rolling-sliding contact. For the polymer they added glass, carbon or aramid, and both for the glass fibers and for the carbon fibers a drop in the friction coefficient was noticed.
Stachowiak, et all [16] have studied the abrasive effect for the three body abrasion of metal samples, the tests were carried out on two ball-on-flat installations and modified pin-on-disk tribometer. The ball-onflat teste yielded the most significant results. Dwyer-Joyce [17] has noticed that during contact the wear due to contamination with solid compounds of lubricants occurs, the phenomenon closely resembling the abrasion with three bodies No studies regarding the correlation between friction and use concerning the complex friction-wear phenomenon were shown. In our paper we have studied on Timken type couples (with linear contact), in conditions of dry sliding friction, the behavior of glass fiber reinforced composite materials under controlled loads and speeds. We have studied the influence of the percentage of glass fiber, as well as the influence of load and speed on the wear process.

Materials and methods
Wear and friction are analysed from several points of view, such as speed relative to load and stress. The two samples are cylindrical liner and flat sample.

Experimental Method
A Timken type couple with linear friction contact was used as experimental equipment. Thus the normal load and the contact temperature can be controlled. The friction couple is built out of a plastic cylinder which revolves at different speeds. The plastic piece rests on the polished surface of a steel plan disk. The cylinder has a diameter of 22.5 mm and a thickness of 10 mm.
The friction couple is built out of a cylindrical liner (1) and a flat disk (2). The liner is fixed by means of a nut (3) on the driving shaft (4). The disk sample is placed in a hole made in the elastic blade (5) (Figure 1) An electric motor (7), the shaft (4) with rotation movement using trapezoidal belt. Figure 1 shows the functional scheme (a) friction couple (b) and its installation within the experimental equipment (c). The way in which the liner moves against the plane sample is illustrated in Figure 1c. An electric motor (7), the shaft (4) with rotation movement using trapezoidal belt. The friction couple is built of a cylindrical liner (1) a flat disk (2). The liner is fixed by means of a nut (3) on the driving shaft (4). The disk sample is placed in a hole made in the elastic blade (5). An electric motor (7), the shaft (4) with rotation movement using trapezoidal belt transmission (6). The normal and tangential (friction) stresses are measured by means of resistive tensiometers, mounted on the elastic blade (5). The normal load to the elastic blade (5) is applied, through a calibrated spring system (8). The installation can register the friction force on an X-Y recorder. The duration is controlled with a clock and the contact temperature is measured with a miniature thermocouple (9), connected to a millivoltmeter. The installation can also study the wear using other radiometers techniques. For this purpose, the installation has a tank (10) assembled on a base (11) and a tube for collecting the radioactive wear particles (12). (Figure 2) The unidirectional testing is investigations of metal surface wear.

Results and discussion
All the tests were limited to an hour. The volume and wear depth for the wear process were determined. The curves for the volume of the worn metal material (V u ) (Tab.1) and for the depth of the worn metal material (h u ) (Tab.2), as well asa the normal load for each couple were charted. The regression functions and the regression factor were calculated for each couple.
Tab. 1. The regression function between the volume of worn metal material (V u ) and the normal load (N)     Figure 11 Wear evolution as scar wear volume (a) and depth (b) function of the normal load and contact temperature and variation of contact temperature at the sliding speed of 27.85 cm/s for Nylonplast AVE Polyamide + 30% SGF / C120 steel Figure 12 Wear evolution as scar wear volume (a) and depth (b) function of the normal load and contact temperature and variation of contact temperature at the sliding speed of 18.56 cm/s for Nylonplast AVE Polyamide + 30% SGF / Rp3 steel

Conclusion
From the information presented above we can draw some conclusions: -the wear process of metal surfaces in dry friction contact against plastic materials reinforced with short glass fibers evolves over time, depending on loading, moving from the initial abrasive wear caused by glass fibers, at adhesion wear characterized especially by the transfer of plastic material on the metal surface, but also by corrosion; It is difficult to establish a mathematical relationship between the input and output parameters. The linear dry contact between the composite material and steel is highly complex. By changing a single input parameter, all output parameters of the systems will change. For this reason, a graphical representation of the phenomenon may give provide a more suggestive image of these phenomena when they occur, during the dry contact between the composite polymer and the metal surface. The friction coefficient for the composite material and for the C 120 steel samples is higher than the one obtained at the surface of the steel samples. This is due to the differences in hardness between the two types of steel. This phenomenon is so complex that the system evolves while the action of the loads leads from abrasion to adhesion wear and to corrosion. This phenomenon occurs simultaneously with the transfer of thermoplastic material unto the metal surface.