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Mechanical Testing of Materials | Mechanical Testing of Metals | Mechanical Testing of Welds

Various Mechanical Testing of Metals or Welds:

What is the difference between various mechanical testing such as tensile testing, compression testing, impact testing, fatigue testing, etc.? What are their applications? How do they differ from each other?

Tensile testing is the most common method of mechanical testing. It measures the force required to stretch or elongate a material. Compression testing is similar to tensile testing except that the load is applied perpendicular to the direction of stretching. Impact testing involves dropping a hammer on a sample of the material to measure its resistance to being crushed. Fatigue testing is done to determine the number of cycles a material can withstand before breaking down.

(1) Tensile testing is used to determine the strength of materials such as metals, plastics, and composites.

(2) Compressive testing is used to determine whether a material has enough strength to support itself.

(3) Impact testing is used to predict the likelihood of damage to a structure.

(4) Fatigue testing is used to determine how long the material can withstand repeated loads without failing.

How often should I test my machine parts or components? How do I know if they are good enough? In this article, I’ll explain some mechanical testing methods and show you how to perform them.

Types of Mechanical Testing

There are two main types of tests that you can perform on machine parts: destructive and non-destructive. Nondestructive tests can reveal information about the part without destroying it (e.g., hardness). Destructive tests destroy the part and give you a more accurate measurement of its properties.

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Tensile Test:

A tensile test, also known as a tension test, tests a material’s strength. It’s a mechanical test where a pulling force is applied to a material from both sides until the sample changes its shape or breaks. It is a common and important test that provides a variety of information about the material being tested, including the elongation, yield point, tensile strength, and ultimate strength of the material. Tensile tests are commonly performed on substances such as metals, plastics, wood, and ceramics.

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Tensile testing systems use a number of different units of measurement. The International System of Units, or SI, recommends the use of either Pascals (Pa) or Newtons per square meter (N/m²) for describing tensile strength. In the United States, many engineers measure tensile strength in kilo-pound per square inch (KSI).

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Tensile test with an electronic extensometer

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This instrument is to be used on tensile or universal testing machines to find out Proof of stress & Young’s modulus values. In the case of many brittle materials, such as high carbon steels, alloy steels, and light aluminum and magnesium alloys, it is difficult to get yield values. For such materials, stress corresponding to a certain allowable amount of plastic deformation is termed “proof stress,” say 0.1% or 0.2% proof stress. The measuring range is up to 5 mm and the resolution is 0.001 mm.

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Tensile testing at elevated temperatures

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High-temperature tensile testing is a procedure to test the properties of a material at above room temperature. It will determine the following parameters:

  • Tensile strength (breaking strength)
  • Yield strength
  • Elongation
  • Reduction of area.

Specialist testing, measurement, and control equipment are required to perform this test. The results of such a test will provide a good indication of the static load-bearing capacity of the material and therefore establishes the suitability of a material for its intended purpose.

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Tensile Test on Tor Steel Bars

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TOR steel is one of the best grades of steel used in concrete reinforcement. It’s a kind of high-adherence steel. Other types of steel are used for less resistant concrete. Thermo-mechanically-treated (TMT) bars are a type of corrosion-resistant steel reinforcing bar used in concrete construction.

Bend test on plates

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A bend test is used to determine whether a specific piece of metal in question will break or fracture under pressure. This is important in the construction of any project using metal, otherwise, the building or the item being made could collapse from the immense pressure exerted on it. Every piece of metal made cannot be tested.

Therefore, certain pieces are tested, and if they pass, the other pieces are made using the same process. The results of a bend test are reported differently depending on the type of material tested. There is no standard method for reporting the durability that applies to all materials, rather each group has its own set of criteria by which it is judged and compared to other metals in that group.

The bend test is essentially a way of measuring a metal’s ductility. Ductility defines how easily a metal can bend without breaking. The higher the ductility of metal, the more it can bend without breaking or becoming deformed from its original shape. This is important because certain metals must handle pressure without snapping yet still be ductile enough to bend slightly and not lose their support or shape. Copper and steel are two metals that have high ductility and do well under pressure.

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Bend test on pipes

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Bending tests are carried out to ensure that metal has sufficient ductility to stand bending without fracturing. A standard specimen is bent through a specified arc and in the case of a strip, the direction of grain flow is noted and whether the bend is with or across the grain.

Bend Test on Tor Steel

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The purpose is to make certain the weld and the base metal are properly fused, and that the weld metal and the heat affected zone (HAZ) have appropriate mechanical properties

Re-Bend test on Tor steel

01wirerodsrebendtestonsteels.jpgThe purpose of the re-bend test is to measure the effect of strain aging on steel. Strain aging has an embrittlement effect that takes place after cold deformation by diffusion of nitrogen in steel. Hence, there is a limitation stated in some design codes to restrict the nitrogen content of the steel to 0.012%.

Nick Break Test

01nickbreaktestweldingfabricationonsheets.jpgThe NICK-BREAK TEST is useful for determining the internal quality of the weld metal. This test reveals various internal defects (if present), such as slag inclusions,  gas pockets,  lack of fusion,  and  oxidized or burned metal. To accomplish the nick-break test for checking a butt weld, you must first flame-cut the test specimens from a sample weld.

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