Civil Engineering

Understanding compressive strength

Compressive strength is a constrained level of compressive stress that causes ductile failure (infinite theoretical yield) or brittle failure in a material (rupture as the result of crack propagation, or sliding along a weak plane). On materials, parts, and structures, compressive strength is measured. The amount of uniaxial compressive stress attained when a material totally fails is, by definition, its ultimate compressive strength.

The particular test procedures and measurement conditions have an impact on compressive strength measurements. Typically, compression strengths are provided in accordance with a particular technical standard.

Contrary to materials with strong tensile strengths, concrete and ceramics often have substantially higher compressive strengths. Tensile strengths are frequently higher than compressive strengths in composite materials like glass fiber epoxy matrix composite.

Compressive-Strength-of-Concrete-Cubes

Read more: Different types of material mechanical properties

In this article, you’ll get answers to the following questions:

  • What is compressive strength?
  • What is the formula for compressive strength?
  • Which material has the highest or lowest compressive strength?
  • Which materials require high or low compressive strength?
  • Engineering stress vs true stress

 

What is compressive strength?

The ability of a material or structure to endure loads that tend to reduce size is known as compressive strength or compression strength in mechanics. To put it another way, tensile strength resists tension, whereas compressive strength resists compression. Tensile strength, compressive strength, and shear strength can all be examined separately when studying a material’s strength.

A material or structural element’s capacity to endure loads that, when applied, cause them to shrink in size is referred to as their compressive strength. A test sample is subjected to a force at its top and bottom until it breaks or deforms. Fracturing happens when materials like rock and concrete are tested for compressive strength because this method is frequently used to analyze these materials.

Compressive strength tests can be performed on materials like steel, and deformation is frequently seen with ductile materials. A ductile material will initially adapt to the applied load by changing the internal organization of its structure—a process known as plastic flow.

The plastic flow ceases when the deformation is concentrated in one place, and the material breaks. Tensile strength is typically the chosen indication for measuring and comparing ductile metals. This is due to the fact that tensile stress, which is better suited to the plastic flow phenomena, gauges the forces required to pull a material apart.

Read more: Understanding Brittleness of materials

What is the formula for compressive strength?

The formula to calculate compressive strength is F = P/A, where:

  • F=The compressive strength (MPa)
  • P=Maximum load (or load until failure) to the material (N)
  • A=A cross-section of the area of the material resisting the load (mm2)

 

Which material has the highest or lowest compressive strength?

Materials like rock often have higher compressive strengths of 140 MPa under the brittle material category. Sandstone and other softer varieties often have compressive strengths of 60 MPa or less. For the majority of structural applications, ductile materials like mild steel have a compressive strength of about 250 MPa.

Contrary to materials with strong tensile strengths, concrete and ceramics often have substantially higher compressive strengths. Tensile strengths are frequently higher than compressive strengths in composite materials like glass fiber epoxy matrix composite.

Typically, tension-resistant materials are used to strengthen concrete. Compressive strength is frequently employed for concrete quality assurance and specification requirements. The objective tensile (flexural) requirements are known to engineers, and they express these needs in terms of compressive strength.

For residential concrete, compressive strength needs might range from 2,500 psi to 4,000 psi and more for commercial constructions. For some applications, higher strengths up to and surpassing 10,000 psi are required.

The compressive strength is typically much larger than the tensile strength for both brittle and ductile materials. Fiber-reinforced composites, such as fiberglass, which are robust in tension but easily crushed, are an exception to this rule. But because concrete, a particle-reinforced composite, is much stronger in compression than tension, it must be reinforced with steel rods if it is going to be subjected to tensile stresses.

Read more: Understanding the non-traditional machining process

Which materials require high or low compressive strength?

In terms of concrete, ultra-high-strength concrete can be used to build buildings like highway bridges that must be able to bear tremendous loads and strains, whereas the concrete can have a lesser compressive strength of 30 MPa for standard, domestic paving use.

Watch the video below to learn more about compressive strength:

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Engineering stress vs true stress

Professionals mostly use engineering stress in the practice of engineering design. True stress differs from engineering stress in reality. As a result, using the above formulae to calculate the material’s compressive strength will not produce an accurate answer. This is due to the fact that the cross-sectional area A0 varies and is somewhat dependent on the load A =. (F).

Therefore, the value discrepancy can be summed up as follows:

The specimen will become shorter upon compression. The material has a tendency to stretch out laterally, which expands the cross-sectional area.

The specimen is clamped at the edges during a compression test. Because of this, a frictional force develops that will work against the lateral spread. This implies that effort is required to counteract this frictional force, increasing the amount of energy used in the process. As a result, the experiment’s measurement of stress is somewhat off.

For the whole cross-section of the specimen, the frictional force is not constant. A minimum is found in the center, away from the clamps, while a maximum is found towards the margins where the clamps are. As a result, the specimen takes on a barrel-like form, a phenomenon known as barreling.

Read more: Understanding Hardness, strength, and toughness of materials

In summary

A material or structural element’s capacity to endure loads that, when applied, cause them to shrink in size is referred to as their compressive strength. A test sample is subjected to a force at its top and bottom until it breaks or deforms. That is all for this article, where the following questions are being discussed:

  • What is compressive strength?
  • What is the formula for compressive strength?
  • Which material has the highest or lowest compressive strength?
  • Which materials require high or low compressive strength?
  • Engineering stress vs true stress

I hope you learn a lot from the reading, if so, kindly share with others. Thanks for reading, see you around!