Tensile Test

Tensile testing is a fundamental mechanical test where a standard specimen is loaded in a uniaxial tension manner while measuring the applied load and the elongation of the specimen over some distance. Tensile tests are used to determine the Ultimate Tensile Strength, Yield Strength, Elongation, Reduction in Area, Modulus of Elasticity and other tensile properties. The main product of a tensile test is a load versus elongation curve which is then converted into a stress versus strain curve. Ultimate Tensile Strength can be obtained by dividing the load and area of specimen geometry under test.

NUSATEK provides tensile testing in a wide range of test loads from 1kN up to 2000kN and is capable to perform at ambient temperature & elevated temperatures up to +300ºC in accordance with customer specifications as well as the following international and industry standards. Typical types of test products are:

  • Raw metallic material (plate, pipe, beam, equal angle, ingot and etc.)
  • Welded Metallic material (Butt weld, stud weld and etc.)
  • Reinforcement Bar/ Rebar (Various sizes)
  • Bolts & Nuts (Various sizes)

 

Type Of Tensile Test:

  • Longitudinal Tensile Test
  • Transverse Tensile Test
  • Through Thickness Tensile Test (z-direction)
  • All Weld Metal Tensile Test
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    Tensile Testing

    As mentioned earlier the tensile test is used to provide information that will be used in design calculations or to demonstrate that a material complies with the requirements of the appropriate specification - it may therefore be either a quantitative or a qualitative test.

    The test is made by gripping the ends of a suitably prepared standardized test piece in a tensile test machine and then applying a continually increasing uni-axial load until such time as failure occurs, refer Figure 1. Test pieces are standardized in order that results are reproducible and comparable as shown in Figure 2

     

    Figure 1: Typical Tensile Testing Arrangement

     

    Figure 2: Typical Standard Specimen of Tensile Test

     

    Tensile strength, also known as the ultimate tensile strength and define as the load at failure divided by the original cross sectional area where the ultimate tensile strength (U.T.S.),  σmax = maximum load /cross section area.

    Yield point is the stress at which deformation changes from elastic to plastic behaviour ie below the yield point unloading the specimen means that it returns to its original length, above the yield point permanent plastic deformation has occurred,  Yield stress , σy = load at the yield point/cross section area.

    By reassembling the broken specimen, the percentage elongation (El%) can be determine,  El% = (L f - L 0 /L o ) x100 where Lf = gauge length at fracture and L0 = original gauge length.

    The percentage reduction of area, how much the specimen has necked or reduced in diameter at the point of failure where R of A% =(A 0- A f /A 0 ) x 100 where A f = cross sectional area at site of the fracture.

    The slope of the elastic portion of the curve, essentially a straight line, will give Young's Modulus of Elasticity, a measure of how much a structure will elastically deform when loaded. A low modulus means that a structure will be flexible, a high modulus a structure that will be stiff and inflexible.

    To produce the most accurate stress-strain curve an extensometer should be attached to the specimen to measure the elongation of the gauge length. A less accurate method is to measure the movement of the cross-head of the tensile machine.

    The stress-strain curve in Fig.3 shows a material that has a well pronounced yield point but only annealed carbon steel exhibits this sort of behavior. Metals that are strengthened by alloying, by heat treatment or by cold working do not have a pronounced yield and some other method must be found to determine the 'yield point'.

    Figure 3: Typical Stress- Strain Curve (Graph)

     

     

    The other method to determine yield strength is done by measuring the proof stress (offset yield strength in American terminology), the stress required to produce a small specified amount of plastic deformation in the test piece.

    The proof stress is measured by drawing a line parallel to the elastic portion of the stress/strain curve at a specified strain, this strain being a percentage of the original gauge length, hence 0.2% proof, 1% proof (see Fig.4)

    Figure 4: Typical Method of Proof stress Determination

     

     

     

    Types of Tensile Tests

    Longitudinal Tensile Test

     

    Longitudinal tensile test is performed on the test specimen, which the sample is extracted parallel to the rolling or forging direction. Longitudinal tensile test is the most common tensile test performed on all types of materials.

     

     

    Transverse Tensile Test

     

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

     

     

    Through Thickness Tensile Test (z-direction)

     

    Through thickness tensile test also known as z-direction tensile test is performed to evaluate mechanical properties in steel. The test involves applying tensile forces on a test specimen whose axis is perpendicular to the rolled surfaces of steel plate. The primary purpose of the test is to measure resistance to lamellar tearing by determining reduction of area and ultimate tensile strength in z-direction. Lamellar tearing is a particular type of cracking that occurs under the weld of a steel plate weldment. It is generally caused by strain induced in the thickness direction resulting from shrinkage of the weld deposit and by the restraint imposed by the components that comprise the weldment. High restraint increases the possibility of lamellar tearing. However, lamellar tearing is not solely confined to highly restrained weldments. Lamellar tearing may also result from loads on the plate surface. (ASTM A770)

     

     

    All Weld Metal Tensile Test

     

    The all weld metal tensile test is performed to determine the tensile properties of weld metal for qualification tests of filler metals and for conformation of filler metal specifications. The test specimen orientation is parallel to the weld axis and extracted from the weld metal portion.

     

     

    Type of Tensile Specimens

                (a) Rectangular Tensile specimen

                (b) Round Tensile Specimen

                (c) Full-Section Tensile Specimen