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COMPONENT FAILURE MUSEUM

The main sections of the museum are listed below;

Metal Fatigue
Manufacturing Faults
Bicycle Components
Corrosion
Polymers
Composite Materials

Tools of the trade, some ways to investigate problems;
Photoelasticity
Dye penetrant testing

Glossary
of materials engineering terms


Glossary of materials engineering terms - 3

SEM- Scanning Electron Microscope;

Method for examination of material surfaces using a high cost microscope with a focused electron beam for imaging. Can produce a high magnification, large depth of field image which allows detailed exploration of fracture surfaces. Non-conducting materials such as ceramics, glasses and polymers usually need coating with a thin conductive layer (e.g. gold or carbon) to prevent static build-up. (Picture of a SEM)

Stress corrosion;

When there is an unfavourable combination of susceptable microstructure, suitable environment and a local stress then cracks and pits can propogate at higher rates than expected. The precise mechanisms are complex.

Stress relaxation;

When components are subjected to a constant displacement they contain an internal stress. It is possible for atomic or molecular reorganisation to occur to reduce this internal stress, eventually to zero. This may be by creep mechanisms in metals and ceramics and viscoelastic strain in polymers. The component then takes the shape of its displaced form even when the load is removed. An opposite displacement is required to return it to its original shape.

Striations;

Surface markings associated with an advance of a fatigue crack in a single load cycle. Not usually visible to the naked eye. Their absence at high magnification does not exclude a fatigue mechanism.

Viscoelastic strain;

Many polymeric materials have strain responses that have classical elastic components and an additional viscous flow component that is time dependant. The imposed strain creates a initial stress similar to that generated in a material that obeys Hooke's Law. However over time this stress will reduce due to internal rearrangement by viscous flow.

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© 2005 Materials Engineering - Page last modified 18-Dec-2007