How to measure the strength of TMT bars?

The materials used in construction projects play a significant role in determining the success and durability of the finished project. TMT bars, in particular, are known for their high tensile strength, ductility, and corrosion resistance, which makes them a popular choice among architects, construction engineers, and builders. However, before selecting TMT bars it is necessary to ensure that the bars are strong and suitable for your project. As one of the best TMT brands in India, we share with you some of the useful insights on measuring the strength of TMT bars: 

Methods to Measure TMT Bar Strength:

• Tensile Strength

The tensile strength test is one of the most common methods to measure the strength of TMT bars. The test involves preparing a sample of the TMT bar as per standards and placing it in a Universal Testing Machine (UTM) where a concentrated force is applied until the bar fractures. The maximum force applied and the actual cross-sectional area of the TMT bar are used to calculate the ultimate tensile strength (UTS). Yield strength is detected by selecting a point on the stress-strain curve where the TMT bar no longer remains elastic and becomes plastic. Both ultimate tensile strength and yield strength are crucial measurements for assessing the strength and flexibility of TMT bars.

The tensile strength of S-E-L Tiger TMT bars is measured using a universal testing machine (UTM)- it is designed to apply a controlled amount of force to a sample of the material to determine its mechanical properties, such as tensile strength, 0.2% proof stress, percentage of elongation, and total elongation. The UTM is equipped with a load cell, which measures the force applied to the sample, and a crosshead, which moves up and down to apply the force. The results obtained from the UTM can help to determine the suitability of the material for a specific application, and ensure that it meets the required standards and specifications.

Sampling & test piece preparation :

i) A sample (600 mm Approx. ) is collected from the cooling bed / lot. Sample surface should be defect free

ii) For deformed steel bar (IS 1786)/ steel round bar(IS 2062), sample is cut 0.5mtr (min)

iii) For other national or international standards, the sample is prepared as per the specification.

YS/0.2% proof stress, UTS, and elongation can be determined by following these steps:

• The sample’s mass per metre can be determined by weighing the sample and measuring its length, and then dividing the mass by the length to obtain Mass/mtr in Kg/Mtr. Section weight (SW) can be obtained by measuring the sample’s length (L) and weight (W), and then dividing the SW by 0.00785 to obtain the cross-sectional area (Ae)
• The specimen should be subjected to a hard punch according to the cross-sectional area (5.65√So or 5D) to determine its IGL
• Depending on the sample thickness, the upper and lower head jaw should be fixed, with 0 to 22mm Grip for 8 to 20mm, 10 to 30mm Grip for 25mm, and 30 to 50mm Grip for 32 & 36mm
• The software should be opened and the type of sample to be tested should be selected.
• The required data, such as Diameter, Length, weight, IGL, etc., should be entered.
• For analogue testing, the load range should be selected by the “Load regulator” according to the area of the test piece (trained operators only can operate the Universal testing machine).
• The upper end of the test piece should be fully gripped in the jaw rack of the upper crosshead, and the lower end of the specimen should be fully gripped between the lower jaw rack of the lower crosshead by moving the lover crosshead up (By up/Down button).
• The UTM should be started by pressing the Start button.
• The left control valve (Hydraulic Control valve) should be closed.
• For analogue testing, the load pointer should be adjusted to zero by adjusting the aluminium rack knob. For electronic testing, the load should be tared, and then the test should be started.
• The control valve on the right side of the panel should be turned slowly to the open position until the desired loading rate is achieved.
• The lower crosshead should be locked.
• The yield point should be noted by reading the load of the load pointer where it is stopped slightly. For electronic testing, it will be automatically calculated after feeding Final gauge length.
• The ultimate load should be read from the dial gauge.
• Loading should be continued until the test piece fractures.
• The right control valve should be closed, and the left control valve should be opened. The broken pieces should be removed.
• The broken pieces should be re-joined, and the extended distance between two punch points (FGL) should be measured.

• Bending  test

The flexibility and bending strength of TMT bars are examined in a bending test, where the bar is subjected to a specified bending radius or diameter until it cracks or fractures. The TMT bar is bent in a device and visually inspected for fractures and cracks. The bending strength is calculated by dividing the maximum stress exerted on the bar during the bending test by the distance between the neutral axis and the outer surface of the bent bar. Higher bending strength indicates better ductility and elasticity of the TMT bar.

For S-E-L Tiger TMT bars, the bending test is conducted as per IS 1599 and using appropriately sized mandrels as specified in IS 1786. 

Sampling & test piece preparation :

• The sample preparation involves rounding the edges of the tensile surface of the test piece and flattening the bend zone.
•  The processing can be done by machining or grinding (except for HSDS Bar), with appropriate precautions taken to avoid superficial hardness increase. 
• The testing can be conducted in a press or by bending over rollers. The capacity of the equipment must be appropriate to complete the bending.

Procedure: 

• The specimen is cut as per the required length. (The length of the bend specimen depends upon the sample diameter and bending apparatus/engagement.)
• The appropriate mandrel is set in the UTM arrangement (The free length between two rollers should be Mandrel Length + 3 x Material Dia)
• The specimen, mandrel, and the roller fixtures are adjusted as required such that the load should be drawn in the middle portion of the specimen.
• Load is applied through the mandrel until its edges become parallel.
• The specimen is drawn out and checked for any crack or rupture on the bent portion.
• If no rupture or cracks are visible to a person of normal or corrected vision on the bent portion, the specimen shall be considered to have passed the test.
  

• Re-bend test:

The rebend test is carried out to verify that the TMT bar has enough ductility to withstand bending and rebending without cracking or breaking. The re-bend test is important to ensure that the TMT bars meet the required standards and specifications for use in construction.

For S-E-L Tiger TMT bars, the bending test is conducted as per the guideline and appropriately sized mandrels as specified in IS 1786.

Procedure:

• The specimen is cut to the required length.
• The appropriate mandrel is set in the UTM arrangement.
• The specimen, mandrel, and roller fixtures are adjusted as required such that load should be drawn in the middle portion of the specimen.
• The test piece is bent to an included angle of 135o.
• The bent piece is kept in boiling water for 30 min.
• The test piece is taken out and allowed to cool.
• After cooling, it is bent back at an angle of 157.5o by reverse pressure.

The specimen shall be considered to have passed the test if no rupture or cracks are visible to a person of normal or corrected vision on the rebent portion.

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Looking for the best TMT brand in India for your construction project?

Explore  S-E-L Tiger TMT bars. The size range of the S-E-L Tiger TMT Rebar is from 5.5 mm to 32 mm. We operate two state-of-the-art integrated steel plants to fulfil the modern construction demands with the best quality TMT bars. Our TMT bars are widely known for their strength, durability, and versatility across India. The perfect blend of carbon and manganese endows the bars with endurance, making them resistant to fire, corrosion, and earthquakes.

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