Mechanical Properties of Solids

In this article, students will get to learn and fetch mechanical properties of solids class 11 notes. We are going to discuss the properties that solids have such as elastic behaviour of solids, stress and strain, stress-strain curve, Hooke’s law and elastic moduli.

What are the Mechanical Properties of Solids?

Mechanical properties of solids elaborates the characteristics such as the resistance to deformation and their strength. Strength is the ability of an object to withstand the applied stress, to what extent can it bear the stress. Resistance to deformation is how resistant any object is to the change of shape. If the resistance to deformation is less, the object can easily change its shape and vice versa.

Therefore, some of the mechanical properties of solids include:

1. Elasticity: When we stretch an object, it changes its shape and when we leave, it regains its shape. Or we can say it is the property to regain the original shape once the external force is removed. Example: Spring

2. Plasticity: When an object changes its shape and never comes back to its original shape even when external force is removed. It is the property of permanent deformation. Example: Plastic materials.

3. Ductility: When an object can be pulled in thin sheets, wires or plates, it has the ductile properties. It is the property of being drawn into thin wires/sheets/plates. Example: Gold or Silver

4. Strength: The ability to withstand applied stress without failure. Many categories of objects have higher strength than others.

There are various other properties but in this chapter of class 11 Physics mechanical properties of solids, we will mainly focus on the elasticity of solids. 

Stress and Different Types of Stress

It is the restoring force that develops on an object in the opposite direction; it is measured per unit area. For example, when a rubber ball is applied by an external force with our hands to compress it, at the same time the ball develops an opposite force that restrains it; however, both the forces are equal in magnitude. This restoring force developed by the object or ball is called stress.

Stress = Force/Area 

The S.I. unit of Stress is N/m square or Pascal (Pa)

Different Types of Stress are

1. Longitudinal Stress: Longitude means lengthwise; therefore, it can be defined as the restoring force per unit area when the force applied is normal to the cross-sectional area of the cylindrical body. There is change in the length of the object taking place. Example, when a cylindrical rubber object is tied with a heavy object, there will be longitudinal stress acting upon and the change in the length of the object takes place.

Longitudinal stress is divided into two sub-categories:

Tensile stress: In the above example, it can be said that tensile stress develops when force is applied to stretch the cylinder.

Compressive stress: When force is applied to compress the object.

2. Tangential or Shearing Stress

It is the restoring force per unit area when the force applied is parallel to the cross-sectional area of the body. There is a relative displacement occurring between the opposite faces of the body. 

3. Hydraulic Stress

It is the restoring force per unit area when the force is applied by a fluid like water on the body or object. Suppose, a ball made of rubber (which can be compressed) is dipped inside a river or sea, there is a force acting on the ball from all directions due to the pressure of the water. It results in the minor contraction of the ball. It is an example of hydraulic stress that you can include in the notes of mechanical properties of solids.

Strain and different Kinds of Strain

It is a measure of the deformation that can represent the displacement between particles in the body relative to a reference length. 

Strain is dimensionless quantity. If a rubber object is stretched from both the sides, the change in length represents the strain. 

Different Types of Strain are

1. Longitudinal Strain: It is the change in length to the original length of the body due to the applied longitudinal stress. It is a change in length divided by the original length.

2. Shearing Strain: It is the measure of the relative displacement of the opposite faces of the body due to the shearing stress. Shearing strain can be represented by tan Θ.

3. Volume Strain: It is the ratio of change in volume to the original volume as a result of the hydraulic stress. It is the change in volume divided by the initial or original volume. 

Hooke’s Law

It is named after the scientist Robert Hooke. Hooke’s Law states that stress developed is directly proportional to the strain produced in an object, within elastic limit (if the object is elastic material). An object that can come back to the original shape is its elasticity. Therefore, hooke’s law applies to elastic objects. It doesn’t apply to the plasticity property of solids. 

It can be, therefore, represented as Stress = k * Strain

Where k is the modulus of elasticity

Stress-Strain Curve

A curve drawn between stress and strain is called the stress-strain curve. When stress and stress are drawn along the y-axis and x-axis respectively, a linear graph is formed in the ideal situation of Hooke’s law. However, when actual experiments are drawn, a curve is formed  known as the stress-strain curve as shown below.

Solid is one of the four crucial conditions of issue (the others being fluid, gas, and plasma). The atoms in a strong are firmly pressed together and contain minimal measure of active energy. A strong is portrayed by primary inflexibility and protection from a power applied to the surface. Not at all like a fluid, a strong article doesn't stream to assume the state of its holder, nor does it extend to fill the whole accessible volume like a gas. The particles in a strong are bound to one another, either in a customary mathematical cross-section (glasslike solids, which incorporate metals and standard ice), or unpredictably (an indistinct strong, for example, normal window glass). Solids can't be compacted with little strain through gases can be compacted with little tension in light of the fact that the particles in a gas are inexactly pressed.

The part of physical science that arranges with solids is called strong state physical science and is the fundamental part of dense matter physical science (which likewise incorporates fluids). Materials science is essentially worried about the physical and substance properties of solids. Strong state science is particularly worried about the combination of novel materials, just as the study of recognizable proof and substance arrangement.

Microscopic Description

The particles, atoms or particles that make up solids might be set up in a methodical rehashing design, or sporadically. Materials whose constituents are organised in a standard example are known as gems. Now and again, the customary request can proceed solidly over an enormous scope, for instance precious stones, where every jewel is a solitary gem. Strong items that are sufficiently huge to see and deal with are seldom made out of a solitary precious stone, however rather are made of countless single gems, known as crystallites, whose size can shift from a couple of nanometers to a few metres. Such materials are called polycrystalline. Practically all normal metals, and numerous ceramics, are polycrystalline.

In different materials, there is no long-range request in the place of the molecules. These solids are known as shapeless solids; models incorporate polystyrene and glass.

Regardless of whether a strong is glasslike or indistinct relies upon the material in question, and the conditions wherein it was shaped. Solids that are shaped by lethargic cooling will quite often be translucent, while solids that are frozen quickly are bound to be undefined. In like manner, the particular precious stone design embraced by a translucent strong relies upon the material in question and on how it was shaped.

While numerous normal items, for example, an ice solid shape or a coin, are artificially indistinguishable all through, numerous other normal materials include various substances stuffed together. For instance, an average stone is a total of a few unique minerals and mineraloids, with no particular substance piece. Wood is a characteristic natural material consisting essentially of cellulose filaments inserted in a network of natural lignin. In materials science, composites of beyond what one constituent material can be intended to have wanted properties.

Classes of Solids

The powers between the molecules in a strong can take an assortment of structures. For instance, a gem of sodium chloride (normal salt) is composed of ionic sodium and chlorine, which are held together by ionic bonds. In diamond or silicon, the iotas share electrons and structure covalent bonds. In metals, electrons are partaken in metallic bonding. Some solids, especially most natural mixtures, are held along with van der Waals powers coming about because of the polarisation of the electric charge cloud on every atom. The dissimilarities between the sorts of strong outcome from the contrasts between their holding.

Metals

The apex of New York's Chrysler Building, the world's tallest steel-upheld block building, is clad with treated steel.

Metals commonly are solid, thick, and great conduits of both power and hotness. The heft of the components in the intermittent table, those to one side of a corner to corner line attracted from boron to polonium, are metals. Combinations of at least two components in which the significant part is a metal are known as composites.

Individuals have been involving metals for an assortment of purposes since ancient occasions. The strength and dependability of metals has prompted their boundless use in development of structures and different designs, just as in many vehicles, numerous apparatuses and devices, pipes, street signs and railroad tracks. Iron and aluminium are the two most generally utilised primary metals. They are likewise the most bountiful metals in the Earth's covering. Iron is most generally utilised as a combination, steel, which contains up to 2.1% carbon, making it a lot harder than unadulterated iron.

Since metals are great conveyors of power, they are important in electrical apparatuses and for conveying an electric flow over significant distances with little energy misfortune or dissemination. Accordingly, electrical power matrices depend on metal links to convey power. Home electrical frameworks, for instance, are set up with copper for its great leading properties and simple machinability. The high warm conductivity of most metals additionally makes them helpful for burner cooking tools.

The investigation of metallic components and their compounds makes up a critical piece of the fields of strong state science, physical science, materials science and designing.

Metallic solids are held together by a high thickness of shared, delocalized electrons, known as "metallic holding". In a metal, particles promptly lose their peripheral ("valence") electrons, shaping positive particles. The free electrons are spread over the whole string, which is held together solidly by electrostatic cooperations between the particles and the electron cloud. The enormous number of free electrons provides metals with their high upsides of electrical and warm conductivity. The free electrons additionally forestall transmission of noticeable light, making metals hazy, sparkly and glistening.

Further developed models of metal properties consider the impact of the positive particle centres on the delocalised electrons. As most metals have translucent design, those particles are generally organised into an occasional cross section. Numerically, the capability of the particle centres can be treated by different models, the least difficult being the almost free electron model.

Minerals

Minerals are normally happening solids framed through different land processes under high tensions. To be named a genuine mineral, a substance should have a precious stone construction with uniform actual properties all through. Minerals range in organisation from unadulterated components and basic salts to extremely complex silicates with a huge number of known structures. Interestingly, a stone example is an arbitrary total of minerals or potentially mineraloids, and has no particular substance organisation. By far most of the stones of the Earth's covering comprise of quartz (glasslike SiO₂), feldspar, mica, chlorite, kaolin, calcite, epidote, olivine, augite, hornblende, magnetite, hematite, limonite and a couple of different minerals. A few minerals, similar to quartz, mica or feldspar are normal, while others have been found in a couple of areas around the world. The biggest gathering of minerals by a long shot is the silicates (most shakes are ≥95% silicates), which are made to a great extent out of silicon and oxygen, with the expansion of particles of aluminium, magnesium, iron, calcium and different metals.

Ceramics

Si3N4 clay bearing parts

Clay solids are made out of inorganic mixtures, normally oxides of substance components. They are synthetically inactive, and frequently are fit for enduring compound disintegration that happens in an acidic or scathing climate. Earthenware production for the most part can endure high temperatures going from 1000 to 1600 °C (1800 to 3000 °F). Special cases incorporate non-oxide inorganic materials, like nitrides, borides and carbides.

Conventional artistic unrefined substances incorporate earth minerals, for example, kaolinite, later materials incorporate aluminium oxide (alumina). The cutting edge ceramic materials, which are named progressed earthenware production, incorporate silicon carbide and tungsten carbide. Both are esteemed for their scraped area opposition, and henceforth observe use in such applications as the wear plates of devastating hardware in mining activities.

Most clay materials, like alumina and its mixtures, are framed from fine powders, yielding a fine grained polycrystalline microstructure that is loaded up with light-dispersing focuses similar to the frequency of noticeable light. In this manner, they are for the most part hazy materials, rather than straightforward materials. Ongoing nanoscale (for example sol-gel) innovation has, notwithstanding, made conceivable the creation of polycrystalline straightforward ceramics, for example, straightforward alumina and alumina compounds for such applications as high-power lasers. Progressed earthenware production is likewise utilised in the medication, electrical and hardware enterprises.

Earthenware designing is the science and innovation of making strong state artistic materials, parts and gadgets. This is done either by the activity of hotness, or, at lower temperatures, utilising precipitation responses from compound arrangements. The term incorporates the decontamination of natural substances, the review and creation of the synthetic mixtures concerned, their development into parts, and the investigation of their design, synthesis and properties.

Precisely talking, clay materials are fragile, hard, solid in pressure and feeble in shearing and strain. Weak materials might display critical elasticity by supporting a static burden. Durability demonstrates how much energy a material can ingest before mechanical disappointment, while break strength (signified KIc ) depicts the capacity of a material with inborn microstructural defects to oppose crack by means of break development and proliferation. Assuming a material has an enormous worth of break strength, the essential standards of crack mechanics propose that it will probably go through malleable crack. Weak break is exceptionally normal for generally artistic and glass-ceramic materials that regularly display low (and conflicting) upsides of KIc.

For an illustration of uses of ceramics, the outrageous hardness of zirconia is used in the production of blade sharp edges, just as other modern cutting devices. Ceramics, for example, alumina, boron carbide and silicon carbide have been utilised in tactical armour carriers to repulse enormous type rifle shoot. Silicon nitride parts are utilised in clay metal rollers, where their high hardness makes them wear safe. As a general rule, earthenware production is synthetically safe and can be utilised in wet conditions where steel orientation would be helpless to oxidation (or rust).

As one more illustration of artistic applications, in the mid 1980s, Toyota investigated the creation of an adiabatic clay motor with a working temperature north of 6000 °F (3300 °C). Artistic motors don't need a cooling framework and subsequently permit a significant weight decrease and along these lines more prominent eco-friendliness. In a regular metallic motor, a large part of the energy let out of the fuel should be dispersed as waste hotness to forestall an emergency of the metallic parts. Work is additionally being done in creating artistic parts for gas turbine motors. Turbine motors made with ceramics could work all the more productively, giving aeroplanes more prominent reach and payload for a limited measure of fuel. Such motors are not underway, notwithstanding, in light of the fact that the assembling of clay parts in the adequate accuracy and toughness is troublesome and expensive. Handling strategies regularly bring about a wide conveyance of minute blemishes that often assume an inconvenient part in the sintering system, bringing about the multiplication of breaks, and extreme mechanical disappointment.