TY - CONF A1 - Fischer, G. A1 - Bohse, Jürgen T1 - Observation and analysis of fracture processes in concrete with acoustic emission (AE) and digital image correlation (DIC) N2 - Fracture processes in concrete can be characterized by the formation of a Fracture Process Zone (FPZ), which is a region of the crack extending between the elastic region ahead of the crack tip over the crack bridging zone to the region where the crack opening is sufficiently large to prevent transfer of load across the crack faces. The formation of cracks and the development of the FPZ have typically been documented by Acoustic Emission (AE) methods and important conclusions regarding the nature of the FPZ and the propagation mechanisms of concrete have been drawn to form the basis of current fracture models for concrete. The study presented in this paper focuses on Mode I cracking of concrete using compact tension specimens and is comparing the results of AE measurements to those obtained from documenting the cracking process by Digital Image Correlation (DIC). The findings from this comparison show that distinctly different AE events occur ahead of the crack tip, in the cementitious matrix at the crack tip and in the wake of the crack due to the increasing separation of the crack flanks and further opening of the crack. The DIC measurements indicate that crack initiation occurs with locally corresponding AE signals and furthermore suggest a continuous path of the crack from initiation to eventual transition to the stress-free zone. Based on these comparative measurements the study suggests that crack formation in unreinforced concrete is initiated by an individual, sharp microcrack rather than by a region of diffuse microcracking ahead of the eventual crack tip. Later on sharp crack branches originate from the main macrocrack path. Furthermore, the measurements with AE and DIC result in information on the nature of the deformation mechanisms occurring in distinct regions of the entire cracking process. AE signals detected using wideband sensors show quite different characteristics in time (waveform) and frequency (bandwidth) domain. T2 - 31st Conference of the European working group on acoustic emission (EWGAE) CY - Dresden, Germany DA - 03.09.2014 KW - Concrete KW - Acoustic emission KW - Digital image correlation KW - Signal analysis KW - Fracture process KW - Source mechanisms PY - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-313471 SN - 978-3-940283-63-4 IS - DGZfP-BB 149 SP - Th.3.A.4, 1 EP - 8 PB - BAM / DGZfP AN - OPUS4-31347 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -