Wear Test Apparatus Research Articles

Temperature considerations in the study of surfaces using a four-ball wear apparatus

The evolution and distribution of temperature have been studied theoretically for an idealized model of a four-ball wear-test apparatus which can be used to study macroscopic effects of surfaces interacting under frictional conditions. The finite-difference method was used to solve the coupled equations of heat generation, conduction, and cooling. Parameters were chosen to represent two types of material, a typical steel with relatively good thermal conductivity, and a ceramic with relatively poor thermal conductivity. Two values for the coefficients of friction were used to simulate dry and lubricated surfaces. A significant dependence on thermal conductivity was found.

An apparatus for the study of wear under dynamic loading conditions

A multipurpose wear testing apparatus has been designed, constructed and calibrated. The apparatus is primarily an impact wear testing device, but it may also be used for vibratory and oscillatory wear experimentation. The system utilizes a versatile displacement- and force-controlled device, which allows accurate control and measurement of the load cycles and their frequencies and the relative normal and transverse velocities between the wear surfaces as well as their time of contact. Features of this design permit testing at elevated frequencies and investigation of the effect of individual parameters on the wear process. These features include a facility to manipulate the system stiffness, the ability to control the impact and rotational velocities independently, feedback to maintain a constant nominal stress parameter, the ability to use spherical or cylindrical wear specimens and a method of applying the load and relative transverse motion in a constant, random or prescribed manner. The design facilitates modifications to include lubrication and environmental control, measurement of friction forces and fretting wear capabilities. Some initial results are included.

Wear and Friction of Nitrogen Ion Implanted Steel

A pin on disk wear test apparatus was used to evaluate wear and friction properties for nitrogen ion implanted and non-ion implanted steel disks in the presence of a lubricant. Both AISI/1018 mild steel and 304 stainless steel were examined. Typical fluence levels for ion implantation were above 1017 ions/cm2. In this paper disk wear is measured directly by a Talysurf profilometer tracing of the disk wear scar. By varying the contact area of the pin it was possible to evaluate wear behavior of both unimplanted and implanted disks over a wide range of contact pressures. It is shown that stainless steel disk wear can be decreased by nitrogen ion implantation, provided that contact pressures remain less than the yield strength of the substrate material. No significant wear improvements were observed for 1018 steel. To evaluate improvements in hardness due to nitrogen ion implantation, very low penetration depth microhardness measurements were made and the indentation diagonals were measured in a scanning electron microscope. These results and their limitations are also presented.

Transfer of semicrystalline polymers sliding against a smooth steel surface

The interrelationships between transfer and wear in polymers were studied using a pin-disk-type wear testing apparatus. The wear rates of polymers except polytetrafluoroethylene (PTFE) were high for up to about the first 100 revolutions of the disk and decreased gradually until the steady low wear rates which generally occurred after about 2000 revolutions. However, PTFE exhibited an almost constant high wear rate throughout the wear process. The thickness of transferred polymer increased rapidly with increasing number of revolutions in the initial wear stage but after about several hundred revolutions remained constant. A coherent transfer film was formed in most parts of the friction track after about 100 revolutions. It was found that polymer wear could occur in polymers sliding on a transferred polymer layer. All polymers except PTFE exhibited smaller wear rates when sliding on the transferred layer. The load dependence of the thickness was very small compared with that of the wear rate. PTFE produced a very dense and coherent transferred layer compared with that of other polymers. However, there was no clear relationship between friction and the thickness of the transferred polymer layer.

Material transport phenomena in the impact wear of titanium alloys

Results are presented from compound impact wear studies performed with titanium alloys of different β phase content and morphology. The “material pair” consisted of a 17-4 PH stainless steel counterface and a flatended titanium alloy specimen. Each material pair was exposed to variations in relative transverse sliding velocity and number of repetitive load cycles. Testing was conducted primarily at a single level of nominal peak normal impulsive stress. Both optical and scanning electron microscopy were used to monitor changes in worn surface and subsurface regions. Energy-dispersive X-ray studies of the initial and worn surfaces comprising the material pair clearly indicated the nature of the material transport between the opposing surfaces. Wear debris were studied by optical microscopy and by powder X-ray techniques. Utilizing the reciprocating impact wear testing apparatus, it was determined that material transport appears to be a controlling factor. The type of transport ( i.e. material passing from specimen to counterface or vice versa) was found to vary under differing test conditions. Such findings may contribute to the understanding of wear for systems other than those characterized by repetitive impulsive contact. Material removal is minimal at particular levels of relative transverse sliding velocity, and these levels are not necessarily affected by the magnitude of the nominal level of stress. It appears that the nature and quantity of the constituents (α, β) in the titanium alloys are critical in establishing wear behavior for the material pairs investigated.

Design and statistical evaluation of a sliding wear test apparatus for in vitro evaluation of dental restoratives

A five-station sliding wear apparatus of the pin-on-disc type has been constructed and evaluated for statistical reproducibility. The results, which are based on the wear of polymeric materials, demonstrate that wear rates can be determined with a precision of 9.5% at the 95% level of confidence.

Techniques in the study of impact and sliding wear of Zircaloy-4

A wear test apparatus has been designed to conduct detailed measurements of the contact forces and motion during impact and sliding (and combinations of the two). After carrying out pure impact and sliding tests on Zircaloy-4 couples in air at room temperature, it appears that the test apparatus has acceptable dynamic characteristics for wear studies. In pure impact, the wear rate of Zircaloy-4 was primarily influenced by the initial impact force which was measured dynamically. Secondary vibrations had a minimal effect on the wear rate. The wear rate in pure sliding was dependent upon the characteristics of the apparatus, such as its compliance, and the test conditions. Consequently the sliding amplitude should be monitored continuously throughout the test. In general, sliding wear was more severe than impact wear and good correlation between the average sliding amplitude and weight loss was observed. An indication of the relative motion between the wear specimens was given by the magnitude and form of the coefficient of friction which tended to increase with weight loss.

Reciprocating impact wear testing apparatus

A reciprocating impact wear testing apparatus has been developed for studies of wear occurring between solid materials undergoing repetitive impulsive loading. Such loading may be purely normal or may include simultaneous transverse sliding. The apparatus is designed to allow measurement of the impact load pulse and to provide for the maintenance of repeatable force pulses for the duration of a prolonged series of impacts (millions of cycles). When utilized with a flat-nosed impacting specimen, the time-invariant impulse waveform results in repeatable surface and subsurface stress cycling of materials undergoing wear. This paper describes the testing apparatus and procedures and includes results from a preliminary series of tests on two polymeric materials.

The Measurement of the Coefficient of Friction of Polymer Pellets Under Extruder Conditions

Abstract A modification of a friction and wear test apparatus is described which permits measurement of the coefficient of friction (COF) of polymer pellets at conditions comparable to those in the solids feed section of an extruder. A specimen holder containing three pellet-filled cylinders is rotated against a stationary plate under prescribed conditions; the effects of pressure, velocity, temperature, roughness, and surface cleanliness can be investigated. The device is connected to an electronic load cell and recorder so that a continuous record of COF versus time is obtained. The utility of the apparatus is demonstrated by measuring the change in the COF of thermoplastic pellets as a function of several test parameters.

On Fretting Corrosion : Part 1, Nature of Fretting Corrosion

A special wear testing apparatus is designed in which the slider with spherical surface reciprocates axially on the surface of rotating cylinder. Amplitude of the reciprocation of slider can be varied from 0.5 to 2.0 mm, and its frequency from 100 to 2400 cpm. The cylinder can be rotated at a low speed of 0.003 rpm. The cylinder surface can be heated up to 150°C by electric heater under the surface. Effects of load, velocity, amplitude, frequency, temperature, humidity and other factors on the volume of the wear are studied, and the relation [numerical formula] is obtained experimentally, where L is the volume of the worn away material and W the load.