Bend Test for Steel bars | E-bend Test | Steel bar test

Bend Test for Metal Products

 

Aim

1. To ascertain the qualitative degree of formability or ductility of steel products, typically reinforcing steel, by bend test.

2. To ascertain the ageing effect on rebar by rebend test

 

Uses of Bend Test

Bending test is related to mechanical testing of steel products; This is done by subjecting the model of the object to a measured distortion, which is likely to be subject to service/use. Indicates sufficient quantity or otherwise testing of the material subject to the required decomposition without fracture or yield.

To strengthen the concrete structures, the rebar is bent into different shapes. To ensure that the material is bent without losing significant strength, the curve test specimen is tested by rotating it around a mandrel or at 90 ° or 180 angles. Sometimes, a three-point curve test is used as a quality control test to confirm the design of the bar.

 

Theory and Scope of Bend Test

Bending tests are carried out according to IS: 1599-1985, which ensures that the metal is thin enough to bend without fracture. A standard sample at room temperature is bent to the inner diameter and inspected for large (specific) cracks on the outside of the curved area, as indicated by the applicable product specifications. In the case of a metal bar, the direction of grain flow is indicated by whether the curve is with the grain or across it. Bending speed is usually not a major factor.

 

Apparatus

Rebar bending test jig or fixture: The mechanism for a typical Bend Test Fixture is shown in the Figure below

 

Procedure

Preparation of test specimen

The bend test is carried out on a specimen made from finished steel product from each lot. The number of tests is one for every 20 tonnes of material or part thereof, rolled continuously

Typical bend testing fixture with a test specimen loaded and ready to be tested

 

The test pieces are cut lengthwise or widthwise from plates and strips, and lengthwise from sections, flats and bars. When section permits, these shall be not less than 40 mm wide. If so desired the round, square, hexagonal, flat bars and structural sections shall be bent in the full section as rolled.

In all bend test pieces, the rough edge arising from shearing is removed by filing or grinding or machining but the test pieces shall receive no other preparation. The test pieces shall not be annealed or otherwise subjected to heat treatment unless the material from which these are taken is similarly treated.

 

Bend Test

Procedure

Step 1: Select mandrel of required diameter as per Table below for the bend test and install it on the testing jig.

Mandrel diameter for bend test (Adapted from IS: 1599-1985)

Note: φ is the nominal size of the test specimen in mm

 

Step 2: Bend the specimen first by 90° about the mandrel of appropriate diameter selected in Step 1; examine the specimen for cracks in the bent portion.

 

Step 3: Bend the specimen by an additional 90° about the mandrel to make a total bend angle of 180°C.

 

Step 4: Examine the specimen carefully for cracks in the bent portion.

 

Observations

Source ____________

Date of sampling __________

Use of material __________

 

Result

Test specimen _______ Passed/ failed.

(To pass the bend test, the test specimen at room temperature shall withstand bending through 180 to an internal diameter not greater than that of mandrel without cracking).

 

E-bend Test

Theory and Scope

The purpose of the re-bend test is to measure the effect of strain ageing on steel. Strain ageing 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 per cent.

 

Procedure

Step 1: Select a mandrel of the required diameter as per Table 14.7 and install it on the testing jig. Bend the specimen by 45°, i.e., to an included angle of 135° using a mandrel of appropriate diameter.

Approximate mandrel diameter for re-bend test

Note: is the nominal size of test specimen in mm

 

Step 2: Keep the bent test specimen in boiling water, i.e., 100°C for 30 minutes.

 

Step 3: Remove the test specimen from boiling water and allow it to cool to room temperature.

 

Step 4: Bend back the test specimen by 22½° to have an included angle of 157½° as illustrated in Figure below

 

Step 5: Examine the specimen carefully for cracks in the bent portion.

 

Step 6: Discuss the experimental results and give conclusions.

 

Observations

 

Result

Test specimen _________ Passed/ failed.

(The sample specimen is considered to have passed the test if there is no fracture in the bend portion).

 

Precautions

1. For proper results, careful preparation of test specimens and selection of the appropriate mandrel should be done prior to bend testing.

 

2. The key to bending is to gradually (continuously) bend the test specimen without bending it around the pin or mandrel.

 

Formative Comments

For this test, the sample should generally be bent at 90 ° or 180 angles and visually inspected for cracks on any surface. International standards specify the pin diameter, degree of the bend, and requirements for support spacing. In addition, most rebar standards require the bend test to be completed in one consecutive test stroke.

 

This test helps to determine the shape or dilution, but it cannot be considered as a quantitative means of predicting service performance in bending operations. The intensity of the bend test is primarily a function of the angle of bend and the internal diameter at which the specimen is bent and the cross-section of the specimen. These conditions vary depending on the location and orientation of the test sample and the chemical composition, tensile properties, hardness, type and fuel quality.

 

The bend test is usually performed to measure the flexural strength and modulus of all types of materials and products.

 

NATIONAL STANDARDS

1. IS: 2-1960 (revised): Rules for Rounding off Numerical Values.

2. IS 432 (Parts 1 and 2)–1982: Specification for Mild Steel and Medium Tensile Steel Bars and Hard-Drawn Steel Wire for Concrete Reinforcement, Part I: Mild Steel and Medium Tensile Steel Bars; Part 2: Hard-Drawn Steel Wire

3. IS 961–1975: Structural Steel (High Tensile).

4. IS 1499:1977 (RA-2009) (1st revision): Method for Charpy impact test (U-notch) for metals

5. IS 1500:2005 (3rd revision)/ ISO 6506-1:1999; Metallic materials—Brinell hardness test—Test method

6. IS 1501:2002 (3rd revision) / ISO 6507-1:1997: Method for Vickers Hardness Test for Metallic Materials.

7. IS 1586:2000 (3rd revision): Method for Rockwell Hardness Test for Metallic Material.

8. IS 1598:1977 (RA-2009) (1st revision): Method for Izod Impact Test of Metals.

9. IS 1599:1985 (RA-2011)/ ISO 7438:2005 (2nd revision): Method for Bend Test for Steel Products Other.

10. IS 1608-2005 (RA-2011)/ ISO 6892:1998 (3rd revision): Metallic Materials—Tensile Testing at Ambient Temperature.

11. IS 1716:1985 (RA-2001) (2nd revision): Method for Reverse Bend Test for Metallic Wire

12. IS:1730-1989 (2nd revision): Steel Plates Sheets, Strips and Flats for Structural and General Engineering Purposes.

13. IS: 1732-1989 (1st revision): Dimensions for Round and Square Steel Bbars for Structural and General Engineering Purposes.

14. IS 1754:2002 (3rd revision) / ISO 6507-2:1997; Method for verification of Vickers hardness testing machines

15. IS 1757:1988 (RA-2009) (2nd revision): Method for Charpy Impact Test (V- notch) for Metallic Material.

16. IS 2281:2005 (RA-2011) (3rd revision)/ISO 6506-2:1999: Method for Verification of Brinell Hardness Testing Machines.

17. IS 2854:1990 (RA-2001) (1st revision): Determination of Young’s Modulus, Tangent Modulus and Chord Modulus—Test Method.

18. IS 4258:1982(RA-2003) (1st revision): Hardness Conversion Tables for Metallic Materials

19. IS 5069:1982 (RA-2003) (1st revision): Glossary of Terms Relating to Methods of Mechanical Testing of Metals.

20. IS 5074:1969 (RA-2001): Method for Axial Load Fatigue Testing of Steel.

21. IS 5075:1985 (RA-2001) (1st revision):  Method of Rotating Bar Bending Fatigue Testing of Metals.

22. IS 5242:1979 (RA-2006) (1st revision): Method of Test for Determining Shear Strength of Metals

23. IS 10588:1983 (RA-2001); Tables of Brinell Hardness Values for Use in Test Made on Flat Surfaces

24. IS 12514:1988 (RA-2003): Method for Torsional Stress Fatigue Testing.

25. IS 13780:1993 /ISO 4506:1979: Hard Metals—Compression Test

26. IS 13838:1993 (RA-2001): Mechanical Testing of Metals—Determination of Poisson’s Ratios.

27. ISO 178: Plastics—Determination of Flexural Properties

 

REFERENCES

1. AASHTO M31M/M 31-02: Specifications for Deformed and Plain Billet-Steel Bars for Concrete Reinforcement

2. ASTM E8 -Vol. 3.01: Test Methods for Tension Testing of Metallic Materials

3. ASTM E606 Standard Practice for Strain-Controlled Fatigue Testing

4. ASTM E855—08: Standard Test Methods for Bend Testing of Metallic Flat Materials for Spring Applications Involving Static Loading.

5. Gambhir, M. L., Fundamentals of Solid Mechanics, PHI Learning Private Limited, 2010.

6. Gambhir, M. L. and Neha Jamwal, Building Materials: Products, Properties and Systems, McGraw-Hill Education (India), 2011.