Detecting the fracture process zone in concrete using scanning electron microscopy and numerical modelling using the nonlocal isotropic damage model

Abstract

This paper deals with two aspects of the characterization of the fracture process zone (FPZ) in quasi-brittle materials such as concrete. An overview is given of the possibility of using a destructive technique, such as the scanning electron microscope, and a numerical model, such as the nonlocal isotropic damage model (NLIDM), to detect FPZ characteristics, e.g., length and width of the FPZ. The fracture of concrete requires the consideration of progressive damage, which is usually modelled by a constitutive law and can be studied by a numerical method. The object-oriented finite element method (OOFEM) has recently been used in damage studies, and thus the FPZ is calculated on the basis of one of the damage models (the NLIDM). The results obtained from the experimental investigation are similar to those obtained using the NLIDM, which has proven to be a useful tool for analysis of the cracking process.Key words: object-oriented finite element method, nonlocal isotropic damage model, fracture process zone, scanning electron microscope.

Tension softening curves of plain concrete

“…Zhang and Wu [3], who indicated that the saturated FPZ moved ahead and shrank as the crack extended; thus, the length of the FPZ decreased after saturation. The maximum length of the fully developed FPZ was approximately 90 mm, which is in excellent agreement with the results of Hadjab et al, who used acoustic emission [6] and scanning electron microscopy [56]. However, the length of the FPZ may be dependent on size and geometry [3] and may also be influenced by aggregate characteristics [15].…”

Mesoscopic investigation of size effect in notched concrete beams: The role of fracture process zone

“…Due to the important role of FPZ during fracture process in concrete, it is significant to be able to measure the size of the FPZ and on this basis to investigate the role of the FPZ in the size dependence of fracture parameters. Recently various measurement techniques are already employed to track the fracture process in concrete experimentally, for example the holographic interferometry method [8], the scanning electron microscopy method [9,10], acoustic emission (AE) techniques [11] and digital image correction (DIC) method [12][13][14][15][16].…”

Damage Zone Size Limit During the Crack Propagation

“…Dislocations or microcracks are crystalline defects and are easily detected by an electronics device such as a high resolution microscope [8,9]. These defects can affect the macro crack by amplifying or reducing the stress field around a crak-tip.…”