In-situ X-ray Differential Micro-tomography for Investigation of Water-weakening in Quasi-brittle Materials Subjected to Four-point Bending

Abstract

Several methods, including X-ray radiography, have been developed for the investigation of the characteristics of water-saturated quasi-brittle materials. Here, the water content is one of the most important factors influencing their strength and fracture properties, in particular, as regards to porous building materials. However, the research concentrated on the three-dimensional fracture propagation characteristics is still significantly limited due to the problems encountered with the instrumentation requirements and the size effect. In this paper, we study the influence of the water content in a natural quasi-brittle material on its mechanical characteristics and fracture development during in-situ four-point bending by employing high-resolution X-ray differential micro-tomography. The cylindrical samples with a chevron notch were loaded using an in-house designed four-point bending loading device with the vertical orientation of the sample. The in-house designed modular micro-CT scanner was used for the visualisation of the specimen’s behaviour during the loading experiments. Several tomographic scans were performed throughout the force-displacement diagrams of the samples. The reconstructed 3D images were processed using an in-house developed differential tomography and digital volume correlation algorithms. The apparent reduction in the ultimate strength was observed due to the moisture content. The crack growth process in the water-saturated specimens was identified to be different in comparison with the dry specimens.

Experimental Investigation of the Dynamic Tensile Properties of Naturally Saturated Rocks Using the Coupled Static–Dynamic Flattened Brazilian Disc Method

“…The weakening effects of water have been widely researched and recognized with respect to the physical and mechanical properties of rock materials [9][10][11][12][13]. The softening coefficient (K) was introduced to evaluate the weakening effect of water on the dynamic tensile strength of sandstone under various external forces, while k is delimited as the specific value of the tensile strength of the naturally saturated sandstone relative to that of the natural sandstone: in the saturated pores [34,42], which is induced by pore water under external loads, further promotes the propagation of microcracks, leading to a reduction in tensile strength, as shown in Figure 11a.…”

“…Rocks in deep engineering are not only subjected to static loads caused by gravity stress and tectonic stress, but also affected by dynamic loads, generally induced by earthquakes, excavation, blasting, and drilling [6][7][8][9]. There is a general consensus that the water evidently weakens the mechanical properties of rocks, which may pose potential hazards to rock engineering [10][11][12][13]. Moreover, rocks are quite vulnerable to tensile loads, and their tensile strength is exceedingly low compared to their compressive strength [14,15].…”

Research on mechanical properties and acoustic emission characteristics of rock beams with different lithologies and thicknesses

“…In lab experiments, three-point (Dong et al 2017;Stavrakas et al 2016) and four-point (Ayatollahi et al 2013;Efimov 2011;Koudelka et al 2020) loading are generally used to provide bending loads for rock beams. AE (Acoustic Emission) test is a very effective method to study the fracture of rock beams.…”

A Method for Evaluation the Fatigue Microcrack Propagation in Human Cortical Bone Using Differential X-ray Computed Tomography

“…To achieve the best possible quality of the CT reconstruction suitable for the investigation of the linear microcracks even without synchrotron radiation, it is necessary to use an enhanced methodology of the time-lapse XCT imaging and post-processing protocol. This comprises the in situ fatigue loading of the sample, X-ray source focal spot movement correction, and the post-processing of the dataset using a differential tomography approach coupled with a digital volume correlation (DVC) as a basis for the volume registration procedure [ 17 , 18 , 19 ]. DVC is an extension of the digital image correlation procedure to three dimensions, which can be effectively used for two different purposes.…”