The effects of carbonaceous inclusions and their distributions on dynamic failure processes in boron carbide ceramics

Abstract

Commercially available boron carbide ceramics typically have heterogeneous microstructures that contain distributions of processing‐induced inclusions. The inclusions that are rich in carbon (i.e., carbonaceous) govern the underlying mechanisms of brittle fracture through wing crack formation, and thus dictate the mechanical response of the ceramic. In this study, we investigate the dynamic failure of five boron carbide ceramic materials with different inclusion populations. All of the materials were prepared by hot‐pressing; four of these boron carbides contained different sizes and concentrations of carbonaceous inclusions, while one contained no carbonaceous inclusions. The heterogeneity distributions were characterized in some detail for statistical analysis using scanning electron microscopy and quantitative image analysis. A modified compression Kolsky bar setup with in situ ultra‐high‐speed microscopic imaging (10 million frames per second) was then used to study the influence of the inclusion distributions on the dynamic failure processes in these materials, at nominal high strain rates of 102–103 s−1. The in situ ultra‐high‐speed microscopy highlighted the link between micro and macroscale failure processes and demonstrated that the carbonaceous inclusions are indeed the preferential sites for nucleation of wing cracks, as previously hypothesized based on post‐mortem observations. The relative orientation of an inclusion with respect to the compression axis was shown to affect the likelihood that it would participate in crack nucleation. All of the ceramics were also found to have orientation‐dependent peak compressive stress, regardless of the presence of carbonaceous inclusions, suggesting that grain orientation distributions are also important.

Progress in the study of the constitutive relationship of porcelain casing materials under different strain rate loading

“…Most of the domestic research for transparent Al2O3 ceramics focuses on the preparation and optical properties, and the research tools for Al2O3 ceramics have been perfected. Kato [4] summarized that the research progress of transparent Al2O3 ceramics mainly includes three aspects: submicron transparent alumina, grain oriented transparent alumina, and alumina single crystals obtained by solid state grain growth method; Zhang Xiaoqing et al [5] conducted a simple test on the dynamic mechanical properties of single-crystal alumina by using Hopkinson compression rod technique to obtain its stress-strain curve, the modulus of elasticity as well as the compressive strength and strain to failure at high strain rate; Liu Qingfeng et.al [6] investigated the dynamic mechanical properties of A12O3 ceramics by using the improved SHPB experimental method, and obtained the dynamic stress-strain curves of the material, which showed that the dynamic stress-strain relationship of the ceramic material has a strain-rate effect in the range of higher strain rates; Gao et al [7] investigated that the mechanism of increasing dynamic properties of A12O3 ceramics is different from that of metallic materials in that it lacks plastic deformation, and its destruction is crack generation and extension until brittle fracture, and the dynamic properties of ceramics are more strongly correlated with their elastic resistance than their static properties; Tan Rui et al [8] investigated the macroscopic mechanical response and damage mechanism of Al2O3 ceramics, revealing that there are significant differences in the crack nucleation and extension modes under dynamic and static loading, and the change in the damage mode ultimately leads to a significant increase in the strain sensitivity of ceramic materials at high strain rates; Heard and Cline [9] conducted quasi-static confinement experiments on three different ceramic materials as early as 1980 and found that the peak strength increased with increasing confinement pressure; Cheng Y [10] and Zare A [11] performed dynamic compression tests on glass-ceramics under peripheral pressure conditions using the modified SHPB test technique and found that the damage of the material under high peripheral pressure (230MPa) conditions occurs as a brittle to ductile transition phenomenon; Feng Xiaowei et al [12] pointed out that the formation and propagation mechanism of damage wave in ceramics is mainly controlled by the fine-scale mechanical behaviour, and further constructed a mechanical model based on the microscopic scanning images of Al2O3 ceramics containing finescale features such as crystalline phases, glass phases, etc., which showed that the formation of damage array in ceramics mainly relies on the rapid nucleation and expansion process of primary micro-defects under the impact loading, and the propagation characteristics of which satisfy the diffusion process.…”