Mechanical testing

Mechanical testing or engineering test is performed to determine various mechanical properties of materials such as strength, hardness, ductility, toughness, brittleness, etc. IDTL works on all the aspects to bring perfect results for Mechanical testing of the material.

IDTL is well equipped to perform the various test given below.

· Tensile Testing

This test provides information such as proof load, 0.2% proof stress, yield strength, ultimate tensile strength or breaking force, percentage elongation, percentage reduction of area, modulus of elasticity, breaking load, etc.

Tensile test is the most elementary type of mechanical test performed on materials. A tensile test measures the resistance of a material to a static or slowly applied force. Information concerning the strength, stiffness, and ductility of a material can be obtained from a tensile test. Tests are performed as per the IS/ BS & ASTM Standards.

A tensile test also known as tension test is performed by holding the test items or test specimens in a suitable equipment. An axial pulling force is applied on the test item or test specimen and its behaviour under force is recorded on a conventional graph or chart or computerised data acquisition method.

This test provides information such as proof load, 0.2% proof stress, yield strength, ultimate tensile strength or breaking force, percentage elongation, percentage reduction of area, modulus of elasticity, breaking load, etc.

Transverse Tensile Test

Transverse tensile test is performed on the test specimen, which is extracted in the transverse direction or across the sample of item such as plate or pipe. This test is performed to measure transverse tensile strength, yield strength, proof stress, elongation and reduction of area. The transverse tensile strength is very important mechanical property in pipes and Hoop’s stress calculation.

All Weld Tensile Test

The all weld metal tensile test is used to determine the tensile properties of weld metal for qualification tests of filler metals and for confirmation of filler metal specifications. The test specimen orientation is parallel to the weld axis and is mechanically removed from the weld metal.

Proof Load Test

A proof load test is performed on various components to ensure that these components can withstand the design load without failure or without yielding (unacceptable deformation). The test is performed by applying force in the range of 1.1 to 1.5 times of the design load or maximum allowable working load (MAWL) for a specified duration.

· Permanent Set Test

Permanent set testing measures the ability of material to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. As the material is compressed over time, it loses its ability to return to its original thickness.

A standard test piece of known length is stretched by a stated percentage for a period of time and is then released. After recovery the length is measured and the change in length (i.e. unrecovered length) is expressed as a percentage of the original length. The lower the percentage, the better the material resists permanent deformation under a given deflection and temperature range

In IDTL Permanent set test is available only for spring washer.

· Bend Test

The bend test is essentially measuring a metal’s ductility. Ductility defines how easily a metal can bend without breaking. The higher the ductility of a 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.

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 by which it is judged and compared to other metals in that group.

Copper and steel are two metals that have a high ductility and do well under pressure.

Root and Face Bend Tests

Root and face bend tests are another simple low cost method of testing. It gives very simple to understand results and will show any signs of poor fusion or weaknesses such as porosity within the weld. There are numerous variations on this method.

Whether the sample piece is bent root up or root down decides whether it is a root or face bend test, with the root on the outside of the bend, in tension that would be a root bend test.

A Face Bend test is performed on a flare-bevel-groove weld specimen with the weld face on the outside of the bend radius.

A Root Bend test is performed on a flare-bevel-groove weld specimen with the side opposite the weld face on the outside of the bend radius.

Side Bend Test

A  Side Bend test is performed on a 3/8″ (10mm) or greater cross-section of a flare-bevel-groove weld. The sectioned specimen in bent transversely to the weld length.

Re Bend Test

The purpose of re-bend test is to measure the effect of strain ageing on steel. Strain ageing has embrittlement effect which takes place after cold deformation by diffusion of nitrogen in steel. Hence, there is limitation stated in some design codes to restrict the nitrogen content of steel to 0.012%.

· Wrap Test

Another measure of ductility is the wrap test, applied to wires in the size range 0.3 – 3.0 mm, in which wire is wrapped eight times around itself.  Again, the ductility requirements are the same for carbon and stainless steel spring wire.  It might reasonably be expected, therefore, that the torsional ductility of both wires would be similar, and sometimes it is, but the point of this Cautionary Tale is that sometimes it is not.

The bench-top wrap tester is designed to test the ductility of spring wire and/or the quality of a metallic coating. The test consists of coiling the wire in a closely spaced helix around a mandrel for a prescribed number of turns. The wire can then be visually inspected for any cracks or fractures.

· Flattening Test

This is usually done on metallic tubes. Tube Flattening testing reveals the compression strength of the tested metallic tube. A pass/fail test, tube flattening is used to determine whether or not the tube will rupture upon flattening.

To perform the test, a section of tubing is flattened under a specific load using the tensile machine. Next a visual inspection is performed, observing the damage evident in the surface of the tube. If there is no visible damage to the surface of the tube, the specimen passes. If the tube shows damage, such as cracking or orange-pealing the specimen fails the test.

· Drift Expansion Test

This test is also called ‘Flare’ testing. This is a robust test to measure the ductility of Steel tubes. The end of a typical steel tube is expanded until a specific diameter is achieved that corresponds to a specific angle of drift. A steel tube is considered to have passed the Drift Testing if it shows no sign of cracks, splits or other stress marks at the end of this test.

· Weld Fracture Test – Nick Break

Weld fracture test is performed to reveal embedded imperfections such as lack of fusion, incomplete penetration, cracking due to inadequate width to height ratio, slag inclusions and porosity.

An artificial notch or a groove is intentionally introduced by a hacksaw or a cutting disc on the weld face, along the primary axis of the weld to facilitate fracture in the center line of the weld. The depth of the notch is approximately 2 to 3mm depending on the thickness of the weld. In thin materials, the depth of the notch may be less than 2mm. The weld specimen is then mechanically bent to fracture along the weld center line and the cross section is visually examined for imperfections.

·  Impact Test – Izod & Charpy

Impact or toughness strength is very important mechanical property for structures or components subject to shock loading and especially in shipping industry, offshore industry, aviation industry, pressure vessels and bridges in the cold and stormy conditions.

There are primarily 2 types of impact test – Charpy impact test and Izod impact test.

Both tests involves fracturing a notched specimen of standard dimension and measuring the amount of energy absorbed to fracture the specimen.

The absorbed energy is a measuring unit of a materials toughness or impact strength which is used to derive temperature dependent ductile to brittle transition or fracture point.

These tests can also be used to determine critical crack or notch depth.

Izod Impact Test

Izod Impact Test is a single point test that measures a materials resistance to impact from a swinging pendulum.

Izod impact is defined as the kinetic energy needed to initiate fracture and continue the fracture until the specimen is broken. Izod specimens are notched to prevent deformation of the specimen upon impact.

This test can be used as a quick and easy quality control check to determine if a material meets specific impact properties or to compare materials for general toughness.

Charpy Impact Test

In the Charpy test, the test specimens are subjected to stress in a set-up similar to the three-point loading test and broken as soon as they are sufficiently brittle. Notched test specimens must be used in order to produce a break in ductile materials. The test is possible within a temperature range from –193°C to +23°C.

· Hardness Test

Hardness is a mechanical property of material which refers to resistance to plastic deformation by indentation under applied force.

Hardness is very common terminology used by almost every engineering person to describe materials behaviour in terms of hard, soft, machinability, strength, etc.

Hardness values are used as a reference to determine materials machinability, ductility, elasticity, malleability, brittleness, toughness, strength in various modes and wear resistance.

Hardness test is also used to measure hardened case ( effective case depth and total case depth) on case carburised and hardened or induction or flame hardened ( surface hardening).

There are several types of hardness tests.

Brinell Hardness Test

A Brinell hardness test is performed by forcing a Tungsten Carbide indenter of specified diameter under the application of known force to produce an indentation in the material. The indenter diameter can be 1mm to 10mm and the test force can be 1kgf to 3000kgf. The diameter of the indentation is measured after removal of the force and the hardness is calculated. Most of the modern machines can indicate direct hardness values without a need of manual measurement of indentation.

The Brinell hardness test can be performed up to only 650HBW. The BHN – Brinell Hardness Number can be used to relate hardness to other hardness measuring units.

Rockwell Hardness Test

Rockwell hardness test is performed by forcing an indenter of specified material, size and shape under the application of known force to produce an indentation in the material. The most common test loads are 60kgf, 100kgf and 150kgf. The depth of indentation is proportional to the hardness of material. The hardness testing machine indicates direct value of hardness by measuring depth of indentation under preliminary test force.

·  Adhesion Testing

Measuring the adhesion strength of coatings such as paint, glue, varnish etc. is necessary to ensure the coating has bonded well to the substrate and is performing satisfactory.   A variety of adhesion testing methods are available to determine how well the coating is bonding to the zinc coated iron & steel articles.

· Twist Test

A portion of the washer is gripped in the jaws and then an equal portion is gripped in wrench jaws. Edges of the wrench jaws shall be sharp and parallel to the vice jaws. The wrench shall then be rotated in a direction that increases the free height of the spring lock washer till the washer is twisted through an angle of 90 degrees. The washer shall show no sign of fracture.

· Macro Examination

Macro Examination is mostly used for determination of weld defect in plates, pipes, etc.

Standards used are relevant IS/ BS /ASTM & ASME SEC IX.

 

  • Tensile Test
  • Permanent Set Test
  • Strength Test
  • Bend Test
  • Wrapping Test
  • Flattening Test
  • Drift Expansion Test
  • Weld Fracture Test
  • Impact Test
  • Hardness Test
  • Adhesion Test
  • Twist Test
  • Macro Examination