Final answer:
Restricting dislocation motions in materials makes them brittle, meaning they break instead of deforming plastically. Brittleness occurs when materials fracture upon reaching their tensile strength without significant deformation beforehand. Elasticity is the ability of a material to return to its original shape, while plasticity denotes permanent deformation.
Step-by-step explanation:
Restricting or hindering dislocation motions in a material typically renders the material brittle. Brittleness is a property of materials that do not deform plastically before fracturing; they rather break or shatter upon reaching their tensile strength. An example of this is observed in ionic compounds, where the application of force causes like-charged ions in the crystal to come too close to one another, leading to a shattering of the crystal structure. Conversely, ductile materials, like metals, allow dislocation motions to a larger extent, characterized by a gradual decrease in stress with increased strain, making them more malleable. When discussing the behavior of materials under load, it's essential to understand that the elasticity of materials is defined by their ability to return to their original shape after the load is removed. However, when the stress exceeds the elastic limit, permanent deformation occurs, indicating plastic behavior.The elasticity limit is the maximum stress that can be applied to a material before it yields to permanent deformation. Materials with a high elastic modulus require a large load to achieve significant strain. This terminology is critical when analyzing stress-strain diagrams and understanding the differences between elastic and plastic regions. In the plastic region, the material does not return to its original shape when the stress is removed, signifying permanent deformation, which continues until the stress reaches the fracture point, where the material ultimately breaks.