Prof. Nigel Jennett
Surprise....size matters! Probing the fundamental size dependence of material strength – Continuum mechanics R.I.P.
Guest speaker: Professor Nigel Jennett
Abstract: Three reasons why developers of nano-crystalline materials urgently need to stop depending on continuum mechanics and use a length-scale dependent approach to plasticity: the stress-strain curve for <metal X> cannot be “taken from the literature”, hardness is not constant (even for a constant indentation strain) and FEA cannot be used to validate/predict the strength/deformation of an engineering design using nano-enabled materials.
Ask someone to define the yield stress or strength of a material and the odds are that they will draw you a stress-strain curve. FEA packages typically use a continuum mechanics approach and define the properties of a material as: a Young’s modulus, a Poisson’s ratio, and a stress-strain curve. These properties are assumed to be length-scale independent. In real life, however, they are not. and (subconsciously at least) Engineers know this! Cold working or annealing a sample changes the microstructure and dislocation density and also the stress-strain response. Consequently FEA cannot model plastically deforming materials or predict the strength of nano-enabled materials.
This talk will show why this is and describe new research at Coventry to define material constitutive properties in a length-scale enabled way.
Biography: Professor Nigel Jennett has a Chair in Materials, Mechanics and Measurement at Coventry University, in the Materials division of the Institute for Future Transport and Cities. Previously Nigel worked for 23 years at the UK National Physical Laboratory, where he led a research group focused on surfaces, coatings and nano-mechanical test methods.
Nigel now has 30 years' experience of coating fabrication, materials characterisation and developing nano-mechanical test methods. Among other roles, Nigel chairs VAMAS Technical working area 22, the British Standards Institute indentation hardness committee, and leads the UK delegation for a number of ISO working groups drafting standards for indentation-based test methods; of particular relevance, Nigel is co-author of ISO14577 and ISO/TR 29381.
Click here to see Prof. Nigel Jennett’s biography and profile.