Properties Of Metallic Materials
Mechanical properties are defined as the properties of a material that reveal its elastic andinelastic (plastic) behaviour when force is applied, thereby indicating its suitability formechanical applications, for example, modulus of elasticity, tensile strength, elongation,hardness, and fatigue limit. Other mechanical properties, not mentioned specifically above, areyield strength, yield point, impact strength, and reduction of area, to mention a few of the morecommon terms. In general, any property relating to the strength characteristics of metals isconsidered to be a mechanical property. Physical properties relate to the physics of a metal suchas density, electrical properties, thermal properties, magnetic properties and the like. These andother properties will be described here in slightly more detail.
Elasticity and plasticity
When stress or force is applied to a metal, it changes shape. For example a metal under acompressive stress will shorten and metal in tension will lengthen. This change in shape is calledstrain. The ability of metal to strain under load and then return to its original size and shape whenunloaded is called elasticity. The elastic limit (proportional limit) is the greatest load a materialcan withstand and still spring back into its original shape when the load is removed. Within theelastic range stress is proportional to strain and this is known as Hooke’s law.
The relationshipbetween applied stress or load and the consequent strain or change in length is shown in Figure1.14. The end of the straight line portion is known as the elastic limit. A point on the curveslightly higher than the elastic limit is known as the yield point or yield strength. The allowable orsafe load for a metal in service should be well below the elastic limit. If higher loads are applied,however, the range of elasticity or elastic deformation is exceeded and the metal is nowpermanently deformed. Now it will not return to its original dimensions even when the load isremoved. For this reason, the area of the stress strain curve beyond the elastic limit is called theplastic range. It is this property that makes metals so useful. When enough force is applied byrolling, pressing or hammer blows, metals can be formed, when hot or cold, into useful shapes. Ifthe application of load is increased in the plastic region a stage comes when the material fractures.
A very important feature of the stress-strain curve must be pointed out. The straight-line or elastic part of the stress-strain curve of a given metal has a constant slope. That is, it cannot be changed by changing the microstructure or heat treatment. This slope, called the modulus of elasticity, measures the stiffness of the metal in the elastic range. Changing the hardness or strength does not change the stiffness of the metal. There is only one condition that changes the stiffness of any given metal, that is temperature. The stiffness of any metal varies inversely with its temperature; that is, as temperature increases, stiffness decreases, and vice versa.
Strength
The strength of a metal is its ability to resist change in shape or size when external forces are applied. There are three basic types of stresses namely tensile, compressive, and shear. When we consider strength, the type of stress to which the material will be subjected must be known.
Steel has equal compressive and tensile strength, but cast iron has low tensile strength and high compressive strength. Shear strength is less than tensile strength in virtually all metals. The tensile strength of a material can be determined by dividing the maximum load by the original cross-sectional area before testing. Thus
Metals are “pulled” on a machine called a tensile tester. A specimen of known dimensions is placed in the tensile testing machine and loaded slowly until it breaks. Instruments are sometimes used to make a continuous record of the load and the amount of strain (proportional change in length). This information is put on a graph called a stress-strain diagram. A stress-strain diagram can be made for any metal.
Hardness
The hardness of a metal is its ability to resist being permanently deformed. There are three ways that hardness is measured; resistance to penetration, elastic hardness, and resistance to abrasion. Hardness varies considerably from material to material. This variation can be illustrated by making an indentation in a soft metal such as aluminium and then in a hard metal such as alloy tool steel. The indentation could be made with an ordinary centre punch and a hammer, giving a light blow of equal force on each of the two specimens. In this case just by visual observation one can tell which specimen is harder. Of course, this is not a reliable method of hardness testing, but it does show one of the principles of hardness testers; measuring penetration of the specimen by an indenter or penetrator, such as a steel ball or diamond point.
Rockwell, Vicker and Brinell hardness testers are the most commonly used types of hardness testers for industrial and metallurgical purposes. Heat treaters, inspectors, and many others in industry often use these machines. The Rockwell hardness test is made by applying two loads to a specimen and measuring the difference in depth of penetration in the specimen between the minor load and the major load.
The Brinell hardness test is made by forcing a steel ball, usually 10 millimetres (mm) in diameter, into the test specimen by using a known load weight and measuring the diameter of the resulting impression. A small microscope is used to measure the diameter of the impressions.
Various loads are used for testing different materials, for example, 500 kilograms (kg) for soft materials such as copper and aluminium and 3000 kg for steels and cast irons.
Generally the harder the material is, the greater its tensile strength will be, that is, its ability
to resist deformation and rupture, when a load is applied.
The fracture toughness in metallic materials is described by the plain strain value of The properties of composite materials are susceptible to changes
http://esmat.esa.int/SME/SME1-_Metallic_Materials.ppt
Properties of Non-Metallic Materials
Properties of non-metallic materials used in RAF products.
http://www.rafhdwe.com/nonmetmatl.htm
Metal – Wikipedia, the free encyclopedia
The large number of free electrons in any typical metallic solid (element or Metallurgy is a domain of materials science that studies the physical
http://en.wikipedia.org/wiki/Metal
Synthesis, Microstructure and Properties of Metallic
Synthesis, Microstructure and Properties of Metallic Materials with Nanoscale Growth Synthesis, Microstructure and Properties of Metallic Materials with
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA481202&Location=U2&doc=GetTRDoc.pdf
ASTM E2448 – 08 Standard Test Method for Determining the
E2448 – 08 Standard Test Method for Determining the Superplastic Properties of Metallic Sheet Materials , constant strain rate, metallic materials, m value, SPF,
http://www.astm.org/Standards/E2448.htm
Nanohetero Metallic Materials Project
Properties of metallic materials are controlled by microstructures. Magnetic properties and other functional properties of metallic materials are also
http://www.nims.go.jp/apfim/apfim/nanohetero_aim.html
Scitopia : Topic Page for: metallic materials
By nature of thin and closely-spaced metallic sections, electronic components are prone properties of metallic surfaces with different metal materials, we
http://www.scitopia.org/topicpages/m/metallic+materials.html
Other articles you might like;
- Radiographic Indications for Castings
- Hydrogen contribution in Welding
- Welding Tools and Supplies: Your Global Market
- URANUS 45N METALLURGY
tags: materials, Materials Properties, metal, metallic, Metallic Materials, strength
Properties Of Metallic Materials Welding Materials
Metallic Materials Physical Mechanical and Corrosion Properties
Properties of Non Metallic Materials RAF Electronic Hardw
Metal Wikipedia the free encyclopedia
Material properties requirements for metallic materials
Properties Of Non Metallic Materials Welding Materials
Metallic Materials Physical Mechanical and Corrosion Properties
