J.H. Dumbleton

The friction and wear behavior of irradiated very high molecular weight polyethylene

Abstract The friction and wear behavior of gamma irradiated very high molecular weight polyethylene has been studied for radiation doses of 20 to 1000 MRad. For tests run at low loads the effect of irradiation is to increase the friction coefficient and the wear factor. As the load is increased the friction coefficient decreases and the wear factor remains constant. At a critical load there is an abrupt increase in the wear factor. However, further increase in the load leads to a decrease in the wear factor to about the original value. This wear behavior is quite different from that shown by unirradiated polyethylene and is connected to changes in structure resulting from the temperatures generated during sliding.

A study of the wear of some materials in connection with total hip replacement

Abstract Failure of total hip prostheses due to wear is examined. It is concluded that wearing out of these devices should not be a problem. However, it is desirable to look for materials of improved wear resistance due to possibilities of long-term response to wear debris. A series of experiments is described to evaluate the wear resistance of candidate materials on an annular wear tester. The results indicate that the wear resistance of ultra high molecular weight polyethylene may be improved by increase in molecular weight, by irradiation or by the use of fillers. Pyrolytic carbon containing silicon is also a good candidate.

The wear behavior of ultrahigh molecular weight polyethylene

Abstract The wear behaviour of ultrahigh molecular weight polyethylene has been studied using a thrust-washer testing machine. The data are examined in the light of findings of other workers and of clinical results. The wear factor exhibits a maximum at about 500 lb in −2 surface pressure for polyethylene samples tested in water. The use of plasma in place of water does not change the wear factor and this indicates that the wear of polyethylene is not sensitive to the type of liquid environment likely to be encountered in a total joint prosthesis.

A comparative evaluation of the wear of ultra-high molecular weight polyethylene abraded by Ti-6Al-4V

Abstract The study was initiated to assess the suitability of Ti-6Al-4V as a metal which articulates against Ultra High Molecular Weight (UHMW) polyethylene in total joint applications. The wear surfaces of Ti alloy were prepared to different levels of surface roughness and the effect of various surface chemical treatments were examined. A specially designed annular contact laboratory wear tester was developed to provide the surface loading and articulation. Comparative tests were also performed using 316 LVM stainless steel and Co-Cr-Mo alloy metallic wear components. All annular contact wear tests were performed in mammalian Ringers solution environments and were evaluated using standard statistical techniques. Scanning electron microscope (SEM) analysis of the wear surfaces indicates the formation of a polyethylene transfer film on all metal surfaces. The surface of the UHMW polyethylene samples after testing was considerably rougher than the original articulating metallic surface; the transfer film on the metal surfaces was responsible for this. It was concluded that Ti-6Al-4V is satisfactory for total joint replacement when used in combination with UHMW polyethylene. Proper surface preparation may allow lower rates of wear than conventional orthopaedic alloys.

A simulator for load bearing joints

Abstract A simulator has been constructed for studying the behaviour of artificial joints. In particular, the present design allows the evaluation of total hip prostheses. Data are presented on the wear behaviour of one type of total hip prosthesis.

The friction and wear behavior of polyoxymethylene in connection with joint replacement

Abstract The wear behavior of polyoxymethylene (Delrin 150) has been studied up to surface pressures of 1200 Ib in −2 using a thrust-washer testing machine. Delrin has the advantages of higher hardness and lower creep than the currently widely used material ultrahigh molecular weight polyethylene (UHMWPE). In contrast to UHMWPE, the wear of Delrin depends on the type of liquid environment used. The wear of Delrin is lower than that of UHMWPE if tests are carried out in plasma; in water the wear of Delrin is much higher than that of UHMWPE.

Wear and its measurement for joint prosthesis materials

Abstract Progress in the measurement of wear with respect to total joint replacement is outlined. The objectives of a wear evaluation are given and test procedures for both laboratory evaluation of wear and wear evaluation on joint-simulating machines are detailed. Information known about the in vivo conditions which a joint prosthesis faces is given, and there is a discussion of the optimum design of a test machine. The role of factors such as load, speed, lubricant and test configuration are described with respect to their influence of wear mechanisms and wear rates. Consideration is given to the techniques available for the measurement of wear both on laboratory testing machines and on joint simulators. Some problems still remaining, including discrepancies in the wear of certain combinations of materials and the role of the test environment, are discussed. Finally an overall programme for the evaluation of the wear behaviour of a new material is described.

The unlubricated adhesive wear resistance of metastable austenitic stainless steels containing silicon

Abstract The unlubricated adhesive wear resistance of metastable austenitic stainless steels can be improved by silicon additions. At low surface temperatures (under the Md temperature) metastability appears helpful in maintaining the alloy in a state of mild wear. Silicon was not found to promote alloy metastability but did tend to strengthen the alloy by solid solution hardening. At lower temperatures the silicon had little effect on the mild wear rates of metastable alloys but did act to lower the severe wear rates of stable alloys. At high surface temperatures (above the Md temperature) the silicon additions (2–4%) were found very beneficial in promoting mild wear rates while metastability had little or no effect. Silicon additions were also found to be beneficial to the oxidation resistance and did not increase the running-in period for the alloys. Improving the oxidation resistance of these alloys is more effective in promoting mild wear than is increasing the hardness through metastability.

The evaluation of a polyimide and a poly(amide-imide) as joint replacement materials

Abstract The possibility of using some high temperature materials in total hip replacement was evaluated, with special attention to the acetabular cup of this joint. Two commercially available materials, Torlon were studied using a thrust-washer type wear tester. The results indicate that the wear resistance of both materials is excellent in dry conditions. The use of water or blood plasma as lubricants, especially water, decreases the wear resistance of both materials. A scanning electron microscope study revealed that specimens tested in water or plasma conditions suffer severe three-body abrasion, while those tested dry evidently undergo a mild adhesive and/or delaminative type of wear.

Wear behavior of high-pressure melamine-formaldehyde laminates

Abstract The wear process of melamine-formaldehyde resin reinforced with α-cellulose paper was studied using a ball and disc apparatus. The wear behavior was followed optically and the various stages were photographed. Three stages of wear were noted: 1. (1) the initial failure consisted of cracking and chipping most often above the point of intersection of the paper fibers with the laminate surface. Lines which formed the envelope of these failure points defined the boundaries of the wear track in stage 2. (2) which consisted of continued chip ejection until the entire surface of the track had been pitted. At that point the ball was seated in the track and in stage 3. (3) continued to cut a groove.