Abstract
The bulk dynamic behaviour of concrete in generally known to be strain rate dependent. However, explanation of the underlying mechanisms has been a subject of debate in the research community. Among other factors, the extent of validity of existing experimental data for concrete-like materials in the high strain rate regime is believed to have further complicated the situation. This paper is concerned about the strain rate limits for dynamic testing of concrete specimens in association with the size requirement for representation of the composite material. The strain rate limits as may be established by elastic theories are discussed firstly. Representative simulation results from numerical experiments using a mesoscale model are then described, and non-uniform distributions of stress and damage under excessively high strain rates are highlighted, and this leads to discussion on the correlation between the externally measured data and the real responses within the sample material. Both dynamic compression and dynamic splitting tension are considered.
Highlights
The apparent strength of concrete-like materials is generally known to increase as the strain rate increases, explanations of the underlying mechanisms may differ
A key requirement for a valid SHPB type of tests is that relative stress uniformity is achieved before the specimen reaches a failure state [1, 2], such that the externally observed strength and deformation at failure may be considered as representative of the bulk material behaviour
While the requirement for the stress uniformity in SHPB tests is understood and generally recognised in the dynamic research community, the need to cater for the heterogeneity often dictates the use of large specimen sizes (e.g. [3,4,5,6]), without always observing a strain rate limit that is associated with guaranteeing stress uniformity
Summary
The apparent strength of concrete-like materials is generally known to increase as the strain rate increases, explanations of the underlying mechanisms may differ. While the requirement for the stress uniformity in SHPB tests is understood and generally recognised in the dynamic research community, the need to cater for the heterogeneity often dictates the use of large specimen sizes We shall take a close look at the response and failure processes of concrete specimens in association with the strain rate limit using numerical experiments for both compression and tension (spit) conditions. In the event of non-compliance with the strain rate limit, appropriate evaluation over the sample structural effect could help extract useful information while avoiding incorrect or misleading interpretation from the recorded data
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