Introduction: Types of Strengths
The strength of a material is simply its ability to withstand load before it becomes deform or breaks. Metals have different types of strength which need to be carefully analyzed for determining their strength and hardness and their suitability for specific applications. Normally we use a hardness tester to test the hardness of an object.
Some materials are suited more for a specific type of applications than other materials due to their hardness and strength. Understanding the strength of materials helps to ensure safety and high-quality of the end product which will in compliance with the different regulatory compliances. The different types of strength for metals are discussed below:
The compressive strength of a material is the maximum amount of force it can withstand before getting compressed or squeezed.
Compressive strength of material resists the applied force for compression. Different materials react differently upon reaching their compressive strength limit. Some materials fracture at this point while others may deform irreversibly.
Compressive strength is measured using a universal testing machine and is calculated by dividing the maximum load by the cross-sectional area of the specimen.
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Compressive strength is a popular and key indicator used for determining the suitability of materials in the construction sector. The measurement of compressive strength may be affected by test methods and testing environment.
Tensile strength is the maximum amount of stress or force which a material can withstand before it can be pulled apart or breaks. It is calculated by dividing the total force by the original cross-sectional area of the specimen.
It is generally represented as pounds per inch (psi). The SI unit for tensile strength is Pascal (Pa).
Tensile strength of a specimen is measured by pulling the specimen with a tensometer at a constant strain till it breaks. Some materials break sharply without any plastic deformation and this is known as a brittle failure.
Other materials which are more ductile undergo a small amount of plastic deformation and then neck out before breaking. Tensile strength is an important measurement of metal strength for assessing their suitability for a different type of applications.
Impact strength of a material is its ability to absorb sudden force or impact before it breaks. It is expressed in terms of energy- the amount of mechanical energy absorbed by the material in the process of deformation and fracture.
The impact strength of a material is an important indicator which is used to determine whether it will act in a brittle or ductile manner. It gives a fair idea of the toughness of the material.
Bending impact test is commonly used for determining the impact strength of a specimen. On lowering the temperature, a drastic drop in the impact strength of the specimen indicates the brittle temperature of the material. Reliable estimates of the impact strength of a specimen are possible only at temperatures above the brittle temperature.
Factors affecting the impact strength of materials include its volume, modulus of elasticity, yield strength, and distribution of forces through the material section.
Yield strength helps to determine the extent to which a material is stubborn or ductile. The point at which a material becomes completely plastic and it yields is known as its yield point.
Yield strength is the amount of stress at which permanent deformation of the specimen occurs. Before reaching the yield point, the material will deform elastically and return back to its original shape. However, once the yield point is reached, the deformation is plastic and irreversible.
The yield strength is indicative of the limit of elastic behavior of a material. Ductile metals like iron have higher yield strength than plastics. Yield strength is used by the engineers for determining the suitability of use in construction and civil works.
Details of Strongest Materials in the World
The details of some of the strongest materials in the world are provided below:
Steel is not a pure metal but an alloy made from the combination of iron, carbon, and of some other elements. Iron is heated in the furnace and its impurities are removed and this is followed by adding carbon to it. Adding other elements like manganese, niobium, and vanadium adds more strength to steel.
Steel is one of the most commonly used metals in the world. It has different applications and is used predominantly in transportation, infrastructure, construction, etc.
Most contemporary buildings and other structures make heavy use of steel which helps to keep it together. There are different types of steel alloy.
Stainless steel is a rust and corrosion-free steel alloy which is manufactured by adding at least 11% chromium to the regular steel. Maraging steel is made by adding nickel and other elements. It has low carbon content and is very strong which makes it ideal for advanced applications like manufacturing of rockets and missiles skin, fencing blades, etc.
Titanium is a silver-colored metal which is lightweight and has high tensile strength. It is abundantly found on Earth mostly as oxides in ingenious rocks. Though it is a hard metal, it is not as hard as some of the heat-treated steel. It is also not as strong or as hard as a diamond.
However, its tensile strength to density ratio is higher than even tungsten but it ranks lower on the Mohs scale of hardness compared to tungsten.
One of the distinct advantages of using titanium over steel is that it is lightweight. Titanium is blended with different other metals like iron, aluminum, vanadium, etc. to form stronger and harder alloys.
These titanium alloys are versatile, lightweight, and extremely durable and find a wide variety of applications in the automotive, aerospace, aviation, and other industrial applications.
It is commonly used for manufacturing of aircraft parts. Titanium is also highly resistant to corrosion and rust which makes it popular for different applications.
Tungsten is a rare metal discovered by Carl Scheele in the year 1781. It has a very high melting point and has an ultimate strength of 1510 Megapascals, making it one of the hardest metals on Earth.
It is metallic gray in color and when refined to its purest form, it is stronger than many types of steels. Among all the pure metals, tungsten has the highest melting point, lowest vaporization point, and highest tensile strength.
It is also known to have the lowest coefficient of thermal expansion among all the pure metals. Most of the tungsten is commercially used for manufacturing of hard materials especially tungsten carbide.
It is used to make knives, drills, lathes, etc. It is also commonly used in electrical and military applications. The toughness of tungsten can be drastically improved by alloying it with steel.
Inconel is a nickel-chromium superalloy which was first developed in the 1940s. though the exact composition of Inconel alloys varies considerably, they are all nickel combined with chromium as the second element. It is oxidation and corrosion-resistant alloy and is ideal for usage in extreme environments which are subjected to high pressure and kinetic energy.
Inconel is characterized by high strength, which is not affected even at high temperatures. This makes it perfect for being used in applications involving extremely high temperatures in which aluminum and steel would otherwise succumb to the heat.
Considering that Inconel is an extremely hard alloy that can withstand extreme working conditions, it is commonly used in industries like aerospace and automotive. It is also commonly used in gas turbine blades, well motor pump shafts, chemical processing plants, nuclear-pressurized water reactors, etc.
Diamond is the hardest mineral found on the Earth. It is an allotrope of carbon and is the hardest naturally-occurring mineral. It is the least compressible and best thermal conductor among all the natural materials.
The hardness of a diamond is the highest level of Mohs scale-10. It is 1000 times harder than quartz and 150 times harder than corundum.
On the Rockwell scale, diamond’s hardness is 98.07 HRC while titanium measures 36 HRC on the same scale in terms of hardness.
Due to being the hardest known mineral in the world, diamond is extensively used in making drilling bits, rock drill cutters, cutting tool inserts, extrusion dies, optical grinding tools, coatings for ball bearings, etc.
Diamond also has excellent semiconductor properties due to which it is also commonly used for manufacturing high power transistors, high temperature integrated circuits, piezoelectric devices, etc. It is also used in hardness testing as an indenter.
Chromium is the hardest known metal on the Earth and it measures 8.5 on the Mohs scale. It also has a high melting point. It shows antiferromagnetic properties at room temperature, however, above 30 degree Celsius, it transforms to paramagnetic material.
It has a high specular reflection due to which it is used for coating for reflective purposes.
It is also very resistant to corrosion and rust which makes it popular as a coating material on outer surfaces to protect against corrosion. It is for this reason that it is mixed with steel to form stainless steel alloy which is free from corrosion and rust.
It is also used for coating of automotive parts which protect them from corrosion and also enhance its visual appeal. It is estimated that nearly 85% of chromium is used for producing metal alloys and the remaining are used in dye and paints, wood preservative, tanning, refractory material, a catalyst for producing hydrocarbons, etc.
Boron Nitride is a compound of boron and nitrogen. It exists in many crystalline forms. The wurtzite form of boron nitride is rare and is considered to be even harder than diamond. Based on the results of a simulation, this form of boron nitride is supposed to be 18% harder than diamond.
However, as only a very small amount of this mineral exists, it has not been extensively tested to verify the claim experimentally.
Boron nitride depicts a very high degree of chemical and thermal stability. It is used in cosmetics, paints, dental cement, pencil leads, etc.
Due to its exceptional thermal and chemical stability, it is also used in manufacturing parts of high-temperature equipment. It can be added in different metals, ceramics, plastics, rubber, etc. to impart self-lubricating properties to them. These materials are then ideal for the construction of ball bearings and manufacturing steel.
Lonsdaleite is an allotrope of carbon with a hexagonal lattice due to which it is also commonly called as the hexagonal diamond. It occurs naturally when meteorites containing graphite strike the Earth.
The extreme heat and pressure of the meteorite impact convert the graphite into diamond but it retains the hexagonal crystal lattice which is a key characteristic of Lonsdaleite.
It was first discovered in 1967 during the Canyon Diablo meteorite strike. Since then, it has also been manufactured in a laboratory set up by compressing and heating graphite or by chemical vapor deposition.
Lonsdaleite is a translucent and brownish-yellow in color and its hardness is considered to be 58% more than that of a diamond. It is also known to resist indentation pressures of 152 Gpa, while diamond is supposed to break at 97 Gpa. Lonsdaleite is also stronger than boron nitride as the carbon-carbon bonds in it are much stronger than the boron-nitrogen bonds in boron nitride.
Graphene is an allotrope of carbon which exists in a two-dimensional and hexagonal lattice form.
Graphene has many significant properties and it is known to be at least 100 times stronger than the strongest form of steel. It is nearly transparent and an excellent conductor of heat and electricity. Graphene has a tensile strength of 130 Gpa which makes it one of the strongest materials ever discovered.
In addition to it being extremely strong, Graphene is also remarkably light. It weighs about 0.77 mg per square meter which is 1000 times lighter than the weight of 1 square meter of paper.
Graphene is known to have some amazing properties and many new features are still being discovered. It is being commonly used in domains like biological engineering, optical electronics, development of water filtration systems, etc. In the future, it is expected that graphene will be used for creating composite materials which will be many times stronger and lighter than presently being used metals and alloys.