Available online
Description
The programme examines the problem of corrosion fatigue in artificial hip replacement joints.
The programme examines the problem of corrosion fatigue in artificial hip replacement joints.
| Module code and title: | T351, Materials under stress |
|---|---|
| Item code: | T351; 11 |
| First transmission date: | 14-08-1976 |
| Published: | 1976 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:30 |
| + Show more... | |
| Producer: | Ted Smith |
| Contributors: | John Scales; Graham Weaver; Keith Williams |
| Publisher: | BBC Open University |
| Keyword(s): | Corrosion fatigue; Design; Electro-chemical behaviour; Hip replacement joints; Implant failures; Materials; Steel in saline |
| Footage description: | Brief film shots of a Wimbledon ladies singles match in progress. Keith Williams introduces the programme. Shots of a human skeleton (mainly pelvis and leg bones). Prof. John Scales, Royal National Orthopaedic Hospital, points out, on a model of the human femur and several x-rays, what can go wrong with the ball and hip joint and how this condition can be alleviated by joint replacement. Scales goes on to explain the conditions under which materials for joint replacement must operate. He lists materials currently available for use. Scales uses a split femur and a model femur to demonstrate some of the characteristics of this bone. He then examines a femur which has had a prosthesis mounted in it and explains how this was done. Scales next looks at artificial hip sockets. He shows specimens of a metal socket and then a plastic socket of the type now used. Scales explains the advantages of using plastic rather than metal sockets. He goes on to discuss some of the problems which may occur with a prosthesis during its life. Shot of x-ray of a ball joint stem inside a femur showing fatigue fracture. Keith Williams looks at the fracture surface of a broken ball stem. He then examines a bone with a ball stem in place in order to explain how a crack in the cement holding the stem might cause a fracture to develop in the stem. Graham Weaver, with a device which measures corrosion current through a metal explains how the apparatus works. He performs an experiment of passing a current through a stainless steel specimen in a slightly alkaline solution but with chloride added. Weaver compares the resulting trace with one performed earlier in the alkaline solution without chloride. In order to minimise the risk of corrosion fracture of the ball stem in patients, Weaver discusses the problem of obtaining optimum ion concentrations around the stem cement. Williams compares plots of fatigue curves for stainless steel specimens in air and in saline solutions. He then uses an animation to re-cap how a fatigue crack develops in passive materials protected by an oxide film. Williams looks at a graph which plots crack velocity against stress intensity. He explains how, in a cyclical stress situation, corrosive environment is supplied continuously to the crack area. An animation shows the process. Williams examines a graph of fatigue tests on stainless steel specimens in water solutions and in vacuum. The results appear to confirm the hypothesis illustrated in the animation above. Williams sums up. |
| Master spool number: | 6HT/72168 |
| Production number: | 00525_5262 |
| Videofinder number: | 1422 |
| Available to public: | no |
