Ultra high speed full-field deformation measurements on concrete spalling specimens and stiffness identification with the Virtual Fields Method

摘要: For one decade, spalling techniques based on the use of a metallic Hopkinson bar in contact with concrete sample have been widely employed to characterise dynamic tensile strength at strain rates ranging from few tens hundreds s-1. However, processing method velocity profile measured rear free surface (Novikov formula) remains quite basic. In particular, identification whole softening behaviour material is currently out reach. present paper, new technique proposed virtual fields (VFM). First, digital ultra-high-speed camera used record pictures grid bonded onto specimen. Then, images recorded by are processed obtain full-field axial displacement maps Finally, specific field has defined VFM equation acceleration map as an alternative ‘load cell’. This applied three tests different impact parameters allowed Young’s modulus during test. It was shown that this constant initial compressive part test and decreases when microdamage exists. also such simple inertial test, it possible reconstruct average stress profiles using only data. then construct local stress–strain curves derive value.