Tension Test on Steel Rod


Objective: For the assessment of properties of mild steel, tore steel and high tensile steel under tension and ascertain the Young’s Modulus, Ultimate strength, and percentage elongation

Tool and Equipment

  1. Punching Tools
  2. Scale Venire Calipers
  3. Extensometer
  4. UTM

The machine mainly comprises of 2 main parts which are the loading unit and the control panel.

Loading Unit

It comprises of a tough and strong base. The chief hydraulic cylinder is connected in the core of the foundation. A geared motor is connected to the foundation and the chain and sprocket regulated by the motor rotate the two screwed columns strongly clamped in the base. The lower table is joined with main piston with the help of a ball and seat joint. This joint makes sure of axial loading.

Control Panel

The control panel comprises of a hydraulic power pack which includes the hydraulic oil. Oil level sight glass is strongly clasped to the oil tank to monitor the oil tank. A positive movement kind piston pump is given to make sure of a constant high pressure non- pulsating oil flow for the efficient presentation of the load on the sample. A pendulum dynamometer is connected to compute and show the force which is being exerted on the specimen. A big size load showing dial connected with a glass cover is joined on the sides of the control panel. The range showing dial (indicated at the back side of the load showing dial) is to be regulated for the particular range chosen.

Principle and Theory

The chosen sample is exposed to factors like the tensile load and after that the extension is marked against the load with in the elastic limit. Loads at, Yield point, breaking point and Ultimate point are marked down. With these, stress-strain graph is plotted and the results are computed.

Modulus of Elasticity = Stress (with in the elastic limit)/Strain.

Yield stress = (Load at yield point /original c/s area)

Ultimate stress = (Ultimate Load/ original c/s area.)

Nominal Wreaking Stress = (Breaking load / Nominal Breaking Stress)

Actual Breaking Stress = (Breaking load / neck area)

Percentage elongation = (Change in Length/ Original length) x 100

Percentage reduction in area= (Change in Length/Original area) x100

Procedure

First of all, clean the chosen rod meticulously with help of sand paper. Assess the diameter of the rod. Compute the gauge length utilizing the formula image  . Note down the gauge length (for example: 20mm) on the rod. The markings are done by punching. With the assumption of a tensile stress, compute the greatest expected load on the chosen range of the device. Regulate the ram manually for the range. Strongly clasp the upper end of the sample by manually operating the handle once again. The left valve is put completely in shut position and the right valve in regular open position. Open the right valve and shut it after the lower table is partially raised. Regulate the load pointer to nil with the zero adjusting knobs. By the means of operating the handle, raise the lower cross head chuck up and clasp strongly the lower part of the sample. Clasp the jaws.Connect the extensometer on the sample and mark the reading to nil. Turn on the right control valve slightly to open spot to achieved required loading rate. When the sample is under load, unfastening the locking handle. Mark down the extension at an appropriate load augmentation. Extensometer has to be detached prior to reaching the result point. Once again, apply the load. At a specific point, the load pointer will become still. Load corresponding to this shows result point. Exert the load once again and mark down the final load prior to the point where pointer goes backward and sample breaks at a specific load. Mark down the breaking load. Shut the right control valve, detach the broken piece. Now, turn open the left control valve to pump the oil back. Maximum capacity of sample could be indicated against the red pointer. Compute the diameter of the sample at the neck.

Range Calculation

Assuming working stress = 140N/mm^2.

Factor of safety = 3.

ie Ultimate stress = 140×3 = 420N\mm^2.

Ultimate load = 420 x area of c\s.

From the ultimate load, range to be utilized

Graph

image

Result

1. Young’s Modulus = ______ N/mm^2

2. Yield stress= ______ N/mm^2

3. Ultimate stress = ______ N/mm^2

4. Nominal Breaking stress= ______ N/mm^2

5. Actual breaking stress = ______ N/mm^2

6. % Elongation = ______

7. %reduction for Area= = ______

Important Questions

1. Explain why testing machine is known as Universal Testing Machine?

2. Write the maximum capacity of UTM in the laboratory?

3. Name the possible ranges in the UTM. Name the corresponding least count?

4. Explain the process of changing the loading capacity of the UTM?

5. Explain the process to grip the sample for tension test?

6. Explain the process to find set the load pointer to zero in UTM?

7. What is the use of dummy pointer?

8. Name the device which is utilized for measuring elongation of the specimen in tension test.

9. What do you mean by gauge length? Explain its importance in brief.

10. What is the gauge length utilized for tension test.

11. Before you mount a specimen on the testing machine for any test, what are the preliminaries you must complete?

12. Identify the moving cross head in UTM.

13. Explain the terms ductility and brittleness with example/

14. Differentiate between elastic limit and yield point.

15. State differences between elastic limit and proportional limit.

16. Explain the purpose of calculating percent4ge elongation and percentage reduction in area in tension test.

17. Define an isotropic material.

18. When is the neck formed in tension test.

19. Explain why breaking load is less than the maximum load.

20. Define true stress-strain curve.

21. Explain the process to find the area of cross-section of deformed bar.