Tension Test on Steel Rod – Procedure and Results

The purpose of conducting a tension test on mild steel, tor steel, and high tensile steel is to determine their properties such as Young’s modulus, ultimate strength, and percentage elongation. The test is performed by subjecting a steel rod to tension load using a Universal Testing Machine (UTM). The entire process and equipment arrangement for conducting the tension test on a steel rod are explained in great detail in this article.

Equipment for Tension Test on Steel

The tension test is a common mechanical test used to determine the tensile strength of a material. To conduct this test, certain equipment is required, including a Universal Testing Machine (UTM) which applies a tensile force to the material until it reaches its breaking point.

In addition to the UTM, an extensometer is also needed. This device is used to measure the amount of deformation or strain that the material undergoes as it is subjected to the tensile force. The results obtained from the extensometer are critical in determining the material’s elastic properties.

Furthermore, a Scale Vernier Caliper is essential in obtaining accurate measurements of the dimensions of the test specimen before and after the test. This instrument can measure the diameter and gauge length of the specimen to determine its cross-sectional area, which is used in calculating the material’s tensile strength.

Lastly, punching tools are also used in the preparation of the test specimen. These tools are used to cut the material into the required shape and size to fit into the UTM. The preparation of the specimen is crucial in ensuring accurate and reliable test results.

Universal Testing Machine(UTM)

UTM consists of two primary components, which are the loading unit and the control panel. The loading unit is responsible for handling the loading and unloading of materials, while the control panel is responsible for managing and regulating the operations of the UTM. These two units work together to ensure the smooth and efficient functioning of the UTM system. The loading unit handles the physical aspects of material handling, such as loading materials onto the UTM and unloading them after processing. On the other hand, the control panel manages the various settings and parameters of the UTM, such as speed, temperature, and pressure, to ensure optimal performance. Together, the loading unit and control panel play a critical role in the overall operation of the UTM, working in tandem to ensure the system operates effectively and efficiently.

Fig.1.Universal Testing Machine (UTM)

The loading unit, shown in the figure above, is responsible for applying the load to the specimen during testing. It consists of three crossheads: the upper head, middle head, and lower head, which are used depending on the type of load (tensile, compressive, or shear) being applied to the specimen. For tensile testing, the upper and lower crossheads are used.

The control panel is an integral part of the loading unit and is used to facilitate the application of load to the specimen. This is achieved through the use of hydraulic pressure. A pendulum dynamometer is fitted to the control panel, which measures and indicates the force being applied to the specimen. A large-sized load indicating dial, covered by a glass cover, is mounted on the side of the control panel. The range indicating dial is adjusted to the specific range selected for the test.

Theory

In this experiment, a steel rod is placed under a constant tension load, and the extension caused by the load is measured within the elastic limit. The load values at the yield point, breaking point, and ultimate point are carefully noted.

Using the obtained data, the stress and strain values are calculated and plotted on a graph. The Modulus of Elasticity, E, is calculated within the elastic limit by taking the ratio of stress to strain. The slope of the stress-strain curve provides the modulus of elasticity.

Other important parameters obtained from the experiment include the Yield Stress, which is calculated by dividing the load at the yield point by the original cross-sectional area of the rod. The Ultimate Stress is calculated by dividing the ultimate load by the original cross-sectional area of the rod.

The Nominal Breaking Stress is calculated by dividing the breaking load by the nominal cross-sectional area of the rod. The Actual Breaking Stress is calculated by dividing the breaking load by the neck area of the rod.

The percentage elongation is calculated by dividing the change in length by the original length of the rod and multiplying the result by 100. Similarly, the percentage reduction in the area is calculated by dividing the change in area by the original area of the rod and multiplying the result by 100.

Procedure for Tension Test on Steel Rod

Fig.2. Tension Test on Steel Rod Arrangement on UTM

The preparation of the steel rod specimen involves cleaning it and marking the gauge length using a punching tool, which is calculated using a formula. The range for the tensile stress test is determined based on the assumed ultimate stress, working stress, and factor of safety. The ultimate load is calculated using the ultimate stress and the cross-sectional area of the specimen.

To place the specimen in the Universal Testing Machine (UTM), the handle is operated to secure the specimen to the top base. The valves on the UTM are adjusted accordingly, with the left valve closed and the right valve open. The load pointer is set to zero using the zero adjusting knobs. The lower crosshead chuck is lifted to grip the lower part of the specimen, and the jaws are locked.

An extensometer is fixed on the specimen and set to zero for measuring the extension during the test. Load is applied by slowly turning the right control valve to the desired loading rate. The locking handle is slowly unclamped while noting the extension at convenient load increments. The extensometer must be removed before reaching the yield point. The left valve is used to release the load on the specimen.

Important load points during the test are observed, including the yield point where the load pointer remains stationary, indicating the point of yielding in the material. The ultimate load is reached when the specimen breaks after the load goes beyond the ultimate stress. Necking, which is a reduction in the cross-sectional area of the steel rod, starts to form after the load crosses the ultimate stress, as shown in Figure-4.

Fig.3.Necking of Steel Rod Under Tension Load

To begin the repair process, the right control valve should be closed, and the broken piece must be carefully removed. Once this is done, the left control valve should be opened to allow the oil to be pumped back into the system. The maximum capacity of the specimen can be determined by observing the reading against the red pointer. To obtain accurate measurements, the diameter of the specimen at the neck should be measured. The change in length can be calculated by recording the readings from the extensometer. This change in length is used to calculate the strain, which is the ratio of the change in length to the original length of the specimen. Additionally, the stress at different values of strains can be determined by dividing the load by the area, which gives the stress. By collecting data on stress and strain at various points, a stress-strain graph can be plotted to better understand the behavior of the specimen under different conditions.

Fig.4.Stress-Strain Graph for Tension Test on Steel Rod

Results From Tension Test on Steel Rod

1. Young’s Modulus = ______ N/mm² 2. Yield stress = ______ N/mm² 3. Ultimate stress = ______ N/mm² 4. Nominal Breaking stress = ______ N/mm² 5. Actual breaking stress = ______ N/mm² 6. % Elongation = ______ 7. % reduction for Area =  ______

Viva Questions – Do you know?

1. The testing machine is called the Universal Testing Machine (UTM) because it can perform a wide range of mechanical tests on various materials, including tension, compression, bending, and shear tests.
2. The maximum capacity of the UTM in a laboratory depends on the specific machine, but it can range from a few hundred pounds to several hundred thousand pounds.
3. The possible ranges in the UTM depend on the specific machine, but the corresponding least count is usually in the order of 1/10,000 to 1/100,000 of the maximum load capacity.
4. The loading capacity of the UTM can be changed by adjusting the hydraulic or electric power source, depending on the specific machine.
5. The specimen for tension test is typically gripped by jaws that are attached to the UTM. The grip must be secure enough to prevent the specimen from slipping during the test, but not so tight that it causes deformation or failure at the grip location.
6. To set the load pointer to zero in the UTM, the load cell is unloaded and adjusted to read zero, typically with the use of a dummy specimen.
7. A dummy pointer is used to calibrate the UTM, allowing for more accurate readings of the load cell and reducing errors in testing.
8. The device used for measuring the elongation of the specimen in a tension test is typically an extensometer, which can measure changes in length with high precision.
9. The gauge length is the length of the specimen over which the strain is measured. It is an important parameter in tensile testing, as it affects the accuracy of the results.
10. The gauge length is typically specified by the testing standard or protocol being used, and is usually a few inches long for standard specimens.
11. Before mounting a specimen on the UTM for any test, it is important to ensure that the machine is calibrated, that the grips are secure and properly aligned, and that the specimen is properly prepared and marked.
12. The moving crosshead in the UTM is the part of the machine that moves relative to the stationary crosshead, and is typically used to apply the load to the specimen.
13. Ductility refers to a material’s ability to deform under load without fracturing, while brittleness refers to a material’s tendency to fracture without significant deformation. An example of a ductile material is copper, while an example of a brittle material is glass.
14. The elastic limit is the point at which a material begins to deform elastically under load, while the yield point is the point at which a material begins to deform plastically under load.
15. The elastic limit and proportional limit both refer to the point at which a material begins to deform elastically under load, but the proportional limit specifically refers to the point at which the stress-strain curve becomes linear.
16. The percentage elongation and percentage reduction in area are used to quantify the ductility and formability of a material, and are important parameters for assessing the suitability of a material for various applications.
17. An isotropic material is one that exhibits the same properties in all directions, regardless of orientation. This is in contrast to an anisotropic material, which exhibits different properties in different directions.
18. The neck is formed in a tension test when the material begins to deform locally at a point of stress concentration, resulting in a reduction in cross-sectional area.
19. The breaking load is typically less than the maximum load due to the presence of defects or imperfections in the material, which can cause premature failure or reduce the material’s strength.
20. The true stress-strain curve takes into account the change in cross-sectional area of the specimen as it deforms, resulting in a more accurate representation of the material’s behavior under load.