Instrumented indentation testing in materials research and development

Every so often a conference manages to attract a truly representative cross-section of key workers in a field. This issue captures the results of just such an event, the majority of papers being taken from presentations at the ECI (Engineering Conferences International, Inc.) Conference Instrumented Indentation Testing in Materials Research and Development held at the Fodele Beach Hotel, Crete during 9–14th October 2005.

Over the last 25 years, instrumented indentation testing has grown and developed to become a widely accepted tool for acquiring material property data, particularly from small volumes of material. Indeed, the technique has been encapsulated in an international standard, ISO 14577 1, which provides procedures covering instrumented indentation at forces from zero to 30 kN, reflecting the expansion of applications into both larger and smaller length and force scales since the early days of nanoindentation.

Developments of the technique continue apace. Improved calibration, traceable to SI units, and a better understanding of the uncertainties involved have resulted in the ability to distinguish even small differences between experimental results and contact mechanics predictions. This is driving a fusion of modelling and experimentation, which promises both to improve our understanding of contact mechanics and to unlock new areas of application for indentation, such as the capability of acquiring true stress versus true strain relationships and resulting tensile property data. Closely linked is the ability to characterize length-scale effects, which has the potential to provide design rules for obtaining enhanced material properties purely by nano-scale structuring. Finally, the quasi-static testing cycles used for hard materials are inadequate for determining the properties of time-dependent materials. Dynamic mechanical analysis is available for bulk testing and the application of similar methodologies to create dynamic indentation techniques is one possible route to the measurement of visco-elastic material properties in the frequency domain. Also of interest are pseudo-quasi-static techniques, which use improved modelling and data analysis to determine time-dependent properties in the time domain of creep relaxation.

This issue represents a snapshot of the present state of instrumented indentation testing by focusing on some currently hot topics within the instrumented indentation community. If the final open discussion session of the conference is any guide, the hottest topic is, perhaps, the understanding of the length-scale dependency of plasticity, since this has fundamental implications for both nano-structures and the determination of constitutive properties by indentation.

The editors wish to thank the Editors of Philosophical Magazine, in particular Professor A. L. Greer and Professor E. A. Davis, for agreeing to undertake this special issue. We especially thank the editorial office staff, Brenda Radcliffe and Anne Chippindale, for their able and willing assistance at all stages of this project. Finally, we would like to express our heartfelt thanks to all the authors and reviewers who contributed so much to the quality and timeliness of this issue.

Nigel M. Jennett

National Physical Laboratory, Teddington, Middlesex, UK

George M. Pharr

The University of Tennessee, Knoxville, Tennessee, USA

& Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA

Carl J. MCHargue

University of Tennessee, Knoxville, Tennessee, USA