China
Africa
Explore chapters and articles related to this topic
Ceramic Armour
Published in Paul J. Hazell, Armour, 2023
For polycrystalline ceramics, as with metals, plastic deformation occurs by the motion of dislocations. One of the reasons why ceramic materials tend to be hard and brittle is the difficulty of these materials to accommodate slip (or dislocation motion). This is true for both ionic and highly covalently bonded ceramics. Consequently, it is often difficult to measure plastic deformation in ceramics at room temperature before fracture. However, it is possible to use a Vickers or a Knoop indenter (Chapter 2) to incur local plastic deformation in the sample. These methods can be used to establish the hardness of ceramic materials. Typical Knoop hardness values of ceramics are provided in Table 8.3.
Microscopic Aspects of Fracture
Published in Ashok Saxena, Advanced Fracture Mechanics and Structural Integrity, 2019
Figure 6.6 shows a schematic representation of how cleavage fracture conditions can occur due to the presence of microcracks ahead of the main crack. Here, the crack tip stress is further amplified by the presence of the microcracks raising it to levels that exceed the theoretical cohesive strength. Microcracks can form to accommodate strain inhomogeneity in neighboring grains. This is frequently observed in brittle materials such as ceramics and in intermetallics, both of which have limited slip systems.
Ceramic Materials
Published in Fred D. Barlow, Aicha Elshabini, Ceramic Interconnect Technology Handbook, 2018
The mechanical properties of ceramic materials are strongly influenced by the strong interatomic bonds that prevail. Dislocation mechanisms, which create slip mechanisms in softer metals, are relatively scarce in ceramics, and failure may occur with very little plastic deformation. Ceramics also tend to fracture with little resistance.
On humble technologies: containers, care, and water infrastructure in northwest Madagascar, 1750s-1960s
Published in History and Technology, 2021
By the late nineteenth century, clay jugs were ubiquitous. These jugs, referred to in northern and northwestern Madagascar as sajoa (or sadjoa in French transliteration), were commonly found in Malagasy homes where they were used to conserve freshwater for daily consumption.54 Pottery and vessel-production had been present in the region for several centuries, and practiced by Malagasy groups in various regions of the Island. Ceramic fragments from the ninth or tenth century reveal that potters used a red slip to reinforce impervious surfaces and as a decorative element, and this technique persisted for centuries.55 Travelers to northwest Madagascar in the seventeenth century observed that women fabricated pots of clay, of varying sizes up to ‘five gallons’ of capacity.56 Once formed, they were dried and hardened by sunlight exposure, and artisans then coated them in a protective covering of rice husks, and set them upon the open fire to cure for a ‘day and half, till they think they are baked enough’.57 These vessels were evidently used for cooking and preparing rice, but were also critical for transporting water.
Preparation of modified silicon carbide powder with high dispersibility for slip casting
Published in Journal of Dispersion Science and Technology, 2020
Youxing Liu, Jiaxiang Liu, Tianyu Yang
Slip casting is one of the common methods for the preparation of ceramic materials.[7,8] The key step of slip casting is the preparation of SiC slurry with high solid content and low viscosity using modified SiC powder with high dispersibility.[9] So far, Saint-Gobain's modified SiC (SG SiC) powder has achieved the requirements of slip casting. SiC powders are very prone to agglomeration and show poor dispersibility in water due to their high surface energy.[10] To breakdown the agglomeration of particles and improve the dispersibility of particles in water, the technology of surface modification, as an effective method, is commonly used.[11,12] Surface modification methods for SiC powder can be divided into two classes: physical and chemical.[13,14]
Effect of annealing ambient conditions on crack formation mechanisms of bulk Bi-2212 ceramic systems
Published in Journal of Asian Ceramic Societies, 2021
U. Erdem, B. Akkurt, A.T. Ulgen, Y. Zalaoglu, T. Turgay, G. Yildirim
Mechanical performance of a material is in association with the response to the load and resulting deformation depending on the motions of internal omnipresent flaws, pores, voids, interior cracks and dislocations in the crystal system. Thus, the mechanical performance is one of the most important parameters affecting the economic service lifetime of materials. It is well known that the internal omnipresent flaws, dislocations and interior cracks are naturally introduced in the entire specimen during the basic processes: plastic deformation, solidification, and rapid cooling leading to the thermal stresses throughout the crystal structure. In case a load resulting in the irreversible deformation in the system is applied to the compound, 95% of deformation energy is dissipated as heat along the body. The remaining part of energy is stored internally, and the majority of energy retained is conserved into the strain energy for the internal omnipresent flaws, dislocations and interior cracks. Additionally, the flaws and dislocations move with the different difficulty level through the crystallographic directions and planes. Hence, the flaws and dislocations move along the slip system consisting of specific slip directions and planes. The inner term is related to the most closely packed (greatest linear density) directions with atoms when the latter one is attributed to the densest atomic packing (highest planar density) plane. The number of possible slip systems in the crystal matrix is a measure of plastic deformation. On this basis, the ceramic materials exhibit high brittleness nature due to intrinsic few active slip systems. In the current work, hardness test method is used to determine the general mechanical performance quantities.