Information about Compressive Strength
Compressive strength is the capacity of a material to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength, e.g. many concrete structures have compressive strengths in excess of 50 MPa, whereas a material such as soft sandstone may have a compressive strength as low as 5 or 10 MPa.
Compare tensile strength.
On an atomic level, the molecules or atoms are forced apart when in tension whereas in compression they are forced together. Since atoms in solids always try to find an equilibrium position and distance between other atoms forces arise throughout the entire material which oppose both tension or compression.
The phenomena prevailing on an atomic level are therefore similar. On a macroscopic scale, these aspects are also reflected in the fact that the properties of materials in tension and compression are quite similar, at least for most materials.
Of course, the major difference between the two types of loading is the strain which would have opposite signs for tension (positive) and compression (negative).
The compressive strength of the material would correspond to the stress at the red point shown on the curve. Even in a compression test, there is a linear region where the material follows Hooke's Law. Hence for this region
where this time E refers to the Young's Modulus for compression.
This linear region terminates at what is known as the yield point. Above this point the material behaves plastically and will not return to its original length once the load is removed.
There is a difference between the engineering stress and the true stress. By its basic definition the uniaxial stress is given by:
where, F = Load applied [N], A = Area [m2]
As we said, the area of the specimen varies on compression. In reality therefore the area is some function of the applied load i.e. A = f(F). Indeed, we can however say that the stress is defined as the force divided by the area at the start of the experiment. This is known as the engineering stress and is defined by,
A0=Original specimen area [m2]
Correspondingly, the engineering strain would be defined by:
where l = current specimen length [m] and l0 = original specimen length [m]
The compressive stress would therefore correspond to the point on the engineering stress strain curve
defined by
where F* = load applied just before crushing and l* = specimen length just before crushing.
The difference in values may therefore be summarized as follows:
Compare tensile strength.
Introduction
When a specimen of material is loaded in such a way that it extends it is said to be in tension. On the other hand if the material compresses and shortens it is said to be in compression.)
Tension
)
Compression
On an atomic level, the molecules or atoms are forced apart when in tension whereas in compression they are forced together. Since atoms in solids always try to find an equilibrium position and distance between other atoms forces arise throughout the entire material which oppose both tension or compression.
The phenomena prevailing on an atomic level are therefore similar. On a macroscopic scale, these aspects are also reflected in the fact that the properties of materials in tension and compression are quite similar, at least for most materials.
Of course, the major difference between the two types of loading is the strain which would have opposite signs for tension (positive) and compression (negative).
Compressive Strength
By definition, the compressive strength of a material is that value of uniaxial compressive stress reached when the material fails completely. The compressive strength is usually obtained experimentally by means of a compressive test. The apparatus used for this experiment is the same as that used in a tensile test. However, rather than applying a uniaxial tensile load, a uniaxial compressive load is applied. As can be imagined, the specimen (Usually cylindrical) is shortened as well as spread . A Stress–strain curve is plotted by the instrument and would look similar to the following:)
The compressive strength of the material would correspond to the stress at the red point shown on the curve. Even in a compression test, there is a linear region where the material follows Hooke's Law. Hence for this region
where this time E refers to the Young's Modulus for compression.
This linear region terminates at what is known as the yield point. Above this point the material behaves plastically and will not return to its original length once the load is removed.
There is a difference between the engineering stress and the true stress. By its basic definition the uniaxial stress is given by:
where, F = Load applied [N], A = Area [m2]
As we said, the area of the specimen varies on compression. In reality therefore the area is some function of the applied load i.e. A = f(F). Indeed, we can however say that the stress is defined as the force divided by the area at the start of the experiment. This is known as the engineering stress and is defined by,
A0=Original specimen area [m2]
Correspondingly, the engineering strain would be defined by:
where l = current specimen length [m] and l0 = original specimen length [m]
The compressive stress would therefore correspond to the point on the engineering stress strain curve
defined by
where F* = load applied just before crushing and l* = specimen length just before crushing.
Deviation of engineering stress from true stress
In engineering design practice we mostly rely on the engineering stress. In reality, the true stress is different from the engineering stress. Hence calculating the compressive strength of a material from the given equations will not yield an accurate result. This is of course due to the fact that the cross sectional area A0 changes and is some function of load A = φ(F).The difference in values may therefore be summarized as follows:
- On compression, the specimen will shorten. The material will tend to spread in the lateral direction and hence increase the cross sectional area.
- In a compression test the specimen is clamped at the edges. For this reason, a frictional force arises which will oppose the lateral spread. This means that work has to be done to oppose this frictional force hence increasing the energy consumed during the process. This results in a slightly inaccurate value of stress which is obtained from the experiment.
)
Barrelling of specimen
See also
References
- Mikell P.Groover, Fundamentals of Modern Manufacturing, John Wiley & Sons, 2002 U.S.A, ISBN 0-471-40051-3
- Callister W.D. Jr., Materials Science & Engineering an Introduction, John Wiley & Sons, 2003 U.S.A, ISBN 0-471-22471-5
Materials are physical substances used as inputs to production or manufacturing. Materials range from man made synthetics such as many plastics to natural materials such as copper or wood.
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Concrete is a construction material that consists of cement (commonly Portland cement) as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel limestone or granite, plus a fine aggregate such as sand or
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MPA is a TLA (three-letter abbreviation) that may mean:
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- Microsoft Product Activation
- Macedonian Press Agency
- Marine Protected Area
- Maritime Patrol Aircraft, like Nimrod, P-3 Orion.
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Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust.
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Tensile strength , or measures the force required to pull something such as rope, wire, or a structural beam to the point where it breaks.
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Explanation
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Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. The opposite of compression is tension.
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Explanation
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atom (Greek ἄτομος or átomos meaning "indivisible") is the smallest particle still characterizing a chemical element.
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Compressive stress is the stress applied to materials resulting in their compaction (decrease of volume). When a material is subjected to compressive stress, then this material is under compression. Usually, compressive stress applied to bars, columns, etc. leads to shortening.
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Hooke's law of elasticity is an approximation that states that the amount by which a material body is deformed (the strain) is linearly related to the force causing the deformation (the stress).
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yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to plastically deform. Prior to the yield point the material will deform elastically and will return to its original shape when the applied
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strain is the geometrical expression of deformation caused by the action of stress on a physical body. Strain is calculated by first assuming a change between two body states: the beginning state and the final state.
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In geometry, a cross section is the intersection of a body in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc. More plainly, when cutting an object into slices one gets many parallel cross sections.
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buckling is a failure mode characterised by a sudden failure of a structural member subjected to high compressive stresses, where the actual compressive stresses at failure are smaller than the ultimate compressive stresses that the material is capable of withstanding.
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In engineering mechanics, deformation is a change in shape due to an applied force. This can be a result of tensile (pulling) forces, compressive (pushing) forces, shear, bending or torsion (twisting). Deformation is often described in terms of strain.
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Strength of materials is materials science applied to the study of engineering materials and their mechanical behavior in general (such as stress, deformation, strain and stress-strain relations).
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