Digital image correlation applied to in situ evaluation of surface cracks upon curing of MgO-containing refractory castables

Abstract

MgO particles are added to high-alumina castables to provide in situ spinel formation at high temperatures. However, the MgO hydration upon curing may damage the material because of localized volumetric expansion. Usually, the damage is evaluated by the ex situ overall measurement of Young's modulus changes during processing via Impulse Excitation Techniques. In this paper, an experimental setup was designed to use Digital Image Correlation (DIC) as an in situ alternative to evaluate the damage. Tomographic scans highlighted that all cracks initiated on the sample surfaces, and propagated in the bulk in an intergranular mode. Crack initiation and growth were assessed, for different temperatures, via Surface Crack Density (SCD) measurements, and Mean Crack Opening Displacement (MCOD) fields. They provided important insights into heterogeneous expansion phenomena and crack network quantification; for example, the SCD flattened out while the overall damage was still increasing. The results attested the usefulness of DIC for in-situ quantification of ceramics cracking during the processing.

Modal characterization of crack network development in an MgO containing refractory castable

“…The detailed composition is presented in Ref. 9 The material was prepared in a castable rheometer, and the resulting mix was cast under vibration into silicone molds of size 70 × 70 × 70 mm 3 to produce cubic specimens (Figure 1(a)). The edge size of the cube (70 mm) was selected to be over 10 times the average diameter of the largest aggregates (≈6 mm).…”

On the benefits of correcting brightness and contrast in global digital image correlation: Monitoring cracks during curing and drying of a refractory castable

“…More details about the specimen production and the climatic chamber used in the experimental set-up can be found in Ref. [48].…”

“…The case study discussed herein consists of monitoring and quantifying cracks induced by curing and drying. Therefore, the maximum principal strain field is one of the essential quantities to analyze since it can be related to the crack opening displacement [45,48]. With the selected elements (i.e., T3), the strains are uniform over each element.…”

“…The latter erases spurious gray level variations caused by the pores. However, they may lead to higher strain levels, which would be considered as cracks in some analyses, such as the crack density [48], and thereby reduce the accuracy of the damage evaluation.…”

Pyramidal adaptive meshing for Digital Image Correlation dealing with cracks

“…MgO hydrates during curing and drying, which may damage the material. In previous works, a climatic chamber was developed to evaluate such mechanism using DIC [66]. A cubic specimen was kept in the climatic chamber at 50°C and 50% relative air humidity (Fig-…”