Details of Grant 

EPSRC Reference:	GR/K91248/01
Title:	MODELLING BRITTLE-TO-TOUGH TRANSITION MECHANISMS IN TOUGH PLASTICS
Principal Investigator:	Leevers, Dr P
Other Investigators:
Researcher Co-Investigators:
Project Partners:	Afg Corporate Services Ltd BP Uponor Aldyl Ltd
Department:	Mechanical Engineering
Organisation:	Imperial College London
Scheme:	Standard Research (Pre-FEC)
Starts:	31 March 1997	Ends:	29 September 2000	Value (£):	235,460
EPSRC Research Topic Classifications:	Materials Characterisation
EPSRC Industrial Sector Classifications:	Manufacturing
Related Grants:
Panel History:
Summary on Grant Application Form
Crystalline thermoplastics (e.g. polyethylenes used for gas and water distribution pipe) generally show very high ductility and toughness under slowly applied loads. Under impact, however, brittle cracks can initiate at low stresses, and may continue to propagate at even lower ones. Impact tests results are, therefore, widely used to index plastics; but they cannot be used as material data for design. Impact tests are better used to identify a thickness-dependent 'brittle-tough transition temperature', above which ductility appears on the brittle fracture surface, invades it, and abruptly increases fracture resistance. A new model allows resistance to brittle impact crack initiation and propagation to be predicted from basic property data, for a given geometry and impact speed. The aim of this programme is to extend the model to ductile tearing mechanisms, so that the brittle-tough transition temperature itself can be explained quantitatively. The model will be based on micrographic evidence and on analytical models for adiabatic shear banding (self-concentration of shear due to associated thermal softening) and for isothermal void growth (which, in plastics, produces a strong, sponge-like 'craze' at a crack tip). The ultimate objective is a model to predict impact crack resistance and its dependence on temperature and specimen geometry.
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