The size effect is a phenomenon where the strength and the ductility of a material depend on the size of the structure. Investigating size effects and related crack formation in brittle materials requires advanced monitoring methods. The aim of this research is to experimentally investigate the impact of size effect with the acoustic emission (AE) technique. Brazilian splitting tests with AE monitoring were performed on cement-based mortar cylinders of three sizes. It was found that in addition to the size, the boundary condition affects the final strength. When adopting similar boundary conditions in samples with different sizes, the larger samples had the lowest tensile splitting strength. For the larger samples, initially, there were fewer AE activities. However, there was a surge of high-amplitude AE events near the peak load. This indicates that as size increases, there is a lack of micro-cracking before macro-crack propagation, and the material fails in a more brittle manner. The width of the fracture process zone was quantified with AE and increased with sample size. A further analysis of the AE amplitude distribution demonstrated a change in the distribution in the pre-peak phase for the larger samples and for the smaller samples in the post-peak phase, signifying the brittle to ductile failure transition that occurs as size decreases.

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Determining the crack mode in structures made of brittle materials, such as concrete and masonry, is important for structural analysis and failure prediction. Fractures monitored with the acoustic emission technique (AE) are commonly classified into different modes using Rise angle (RA) – Average Frequency (AF) analysis, the simplified Green's functions for moment tensor analysis (SiGMA), and frequency spectrum analysis. However, the classification limits are dependent on the material, the test setup, and the monitoring condition. Hence, this study defines these limits by comparing the three AE-based fracture mode analysis methods on AE data collected from three test types on mortar specimens. In a direct tensile test, the peak frequencies of most of the AE events were higher ( >60 kHz). While almost all of the AE events in a friction test had significantly lower peak frequency (

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Fatigue loading in brittle materials introduces damage at a micro-scale. These micro-fractures can accumulate and cause a significant reduction in material stiffness or even lead to structural failure. Deformation-based monitoring techniques can be inadequate when detecting damage at a micro-level. Hence, here is where advanced nondestructive testing (NDT) methods such as acoustic emission (AE) and digital image correlation (DIC) can play a great role. The paper aims to combine AE and DIC for advanced fatigue damage analysis on a cylindrical sample subjected to a fatigue Brazilian splitting test. The damage progress quantified from cumulative AE event count, and horizontal displacement measured with DIC showed a very good correlation. The damaged region was identified with an AE localization plot and with a DIC displacement field plot, the damaged area was well represented by both techniques. When a material goes through an irreversible change, part of the released energy will generate an elastic wave. The wave will propagate through the material and the whole phenomenon is termed an acoustic emission. By using AE sensors on the surface of the sample, these waves are captured and analyzed to better understand the source of the emission. Its high sensitivity to micro-changes makes it an ideal technique to use for fatigue damage investigation. Digital image correlation relates sequentially taken images to determine displacement and strain measurements. While DIC analyzes material evolution using surface deformation measurements, AE on the other hand is capable of monitoring damage inside the volume of material. Hence, their combination provides an efficient test setup for monitoring fatigue micro-fracture. The paper aims to combine AE and DIC for advanced fatigue damage analysis on cylindrical samples that are subjected to monotonic and fatigue Brazilian splitting tests. The analysis will use damage progress under monotonic loading as a reference to further understand fatigue fracture. Methods of AE data filtering and AE source localization are discussed and evaluated for their use in fracture analysis. The utilization of DIC to track the material stiffness evolution is investigated. In addition, the paper compares fracture process zones quantified by AE and DIC. From the experimental analysis, it was found that both methods captured the fatigue damage patterns, yet provided complementary information for damage evaluation.