The properties of solids and their structure have a definite geometric shape and size, are compressible, and don’t easily flow into surroundings. But there are several particular properties of solutes, like mechanical properties, melting point, elasticity, hardness, and resistivity that differ greatly for every solid. A mechanical property of a solid is the way a solid body moves when a force acts on it. Elasticity and hardness are included among the mechanical properties of solids because they change with some changes in the relative pressure and temperature.
Mechanics of solids is often used to determine the strength of materials. There are two classifications of mechanical properties of solids that are relevant to strength analysis – tensile strength and compressive strength. The former refers to the ability of a solid system to withstand mechanical forces of different values. On the other hand, compressive strength measures the ability of a solid material to deform in response to indentation and torsion.
Among all types of mechanical properties of solids, hardness is perhaps one of the most important, since it affects nearly all mechanical properties of solids. Since most mechanical stresses occur at high temperatures, hardness is important for a variety of applications. For instance, diamond is considered a ductile crystal, meaning that it is extremely hard, so engineers use diamond as a tool in construction and other industries. Other hard crystals like garnet, sapphire, ruby, amethyst, emerald, and titanium are also included in hardness classification.
All the crystalline solids exhibit one or more mechanical properties. Bulk hardness, which is a measure of the stiffness of a solid mass, can be measured using a variety of techniques. It is a measure of the amount of stretch, where a material is stretched without the container being broken, such as during the process of shipping. Another mechanical property is grain hardness, which is a measure of the coarseness of the crystalline structures.
All the mechanical properties of solids can be affected by several external factors. These include external temperature, outside chemical reaction to the solutes in the solid materials, mechanical damage, mechanical deformity, rate of cooling, the level of bonding stress, bonding effect, molecular weight, mechanical disorder, and mechanical hardness. External temperature can affect both the hardness and the softness of solid materials, but it is the rate of cooling of the crystal structures that govern their mechanical properties most directly. Outside chemical reactions can have an indirect influence on mechanical properties of solids through chemical reactions that alter the solute structure, alter the bonding potential of the substances, modify the stability of the solid, or alter the hardness of the solid.
Bulkiness, rigidity, homogeneity, homogenous structure, chemical makeup, translucency, porosity, and cleavage are some of the physical properties of solids that can be associated with one another. They all depend upon external factors. If the external factor is temperature, then mechanical properties of solids can change depending on changes in temperature. If the external factor is a decrease in density of crystalline solids, then hardness will increase because of less internal friction.
The relationship between mechanical properties of solids and thermal conductivity of the solid is complicated. Often when mechanical properties of solids are studied, one finds that they are negatively correlated to one another. The mechanical properties of solids do become greater when temperatures are high, but once the temperatures decrease to below the critical point, mechanical conduction stops, thus stopping the mechanical properties of solids from changing.
The relationship between hardness and mechanical conduction is best illustrated by way of an example. Take a block of wood that has been completely machined, which has removed any external roughness, compressed it into a stubby block, and then placed that stubby block in an oven to heat it up. Once the wood begins to burn, you will notice that its internal structure changes, becoming less smooth with increasing temperatures. The wood’s hardness will decrease at an increasing rate until it reaches a new critical point where mechanical conduction stops and the wood returns to its crystal form.