Torsion Testing

Topics: Shear stress, Elasticity, Force Pages: 7 (1601 words) Published: November 24, 2012
Table of Contents
1.0 Introduction3
2.0 Experiment Design4
2.1 Apparatus5
2.2 Methods5
2.3 Procedure6
3.0 Results and Discussion7
4.0 Error Analysis13
5.0 Conclusion and Recommendation13
6.0 References14

In this torsion testing experiment, the torsion test was evaluated as a system for calculating the torsional rigidity (GJ), modulus of rigidity (G) and the shear yield stress (τ) for aluminium, mild steel and brass. The both ends of the cylindrical specimen are tightened to hexagonal sockets, which one is fixed to a torque shaft and another is fixed to an input shaft. By turning the input handwheel, the twisting moment has applied to produce the torque until the specimen fails. In the end of the experiment, it shows that the comparison of the behaviour of ductile and brittle materials under torsion.

1.0 Introduction

The responses of metals were deal by mechanical testing to applied forces. This testing includes torsion, tension, hardness, fatigue, creep and stress rupture, and impact tests. Torsion occurs when any shaft is subjected to a torque. The torque causes the shaft to twist. This makes one of the ends to rotate relative to the other; shear stress is induced on any cross section. Besides that, torsion testing is made on materials to determine modulus of elasticity in shear, torsion yield strength and the modulus of ruptures. The shearing stress at any point on a transverse cross section varies directly proportional as the distance from the centre of the shaft, when a simple circular solid shaft is twisted. Therefore, during twisting, the cross section is initially planar remains a plane and rotates only about the axis of the shaft.

2.0 Experiment Design

Figure 7: 360 degree protractor scale
Figure 6: Three specimen mild steel (top), brass (middle), and aluminium (bottom) after experiment. Figure 5: Three specimen mild steel (top), brass (middle), and aluminium (bottom) before experiment.

Figure 2: Torque meter
Figure 3: Deflection arm, dial gauge, levelling handwheel and linear potential meter Figure 4: Input handwheel with 6 degree protractor scale
Figure 1: Torsion testing machine

2.1 Apparatus
There were only few apparatus and materials involved in this experiment, such as: 1) 3 pieces of specimens (Aluminium, brass and mild steel) 2) Vernier Caliper
3) Torsion Testing Equipment

2.2 Methods
Firstly the apparatus was set up as shown in Figure 1. The torque meter was switched on to allow the reading appear on the screen which connected to the torsion testing machine. Three specimens was carried out, mild steel, brass and aluminium. Each specimen was placed at the hexagonal sockets and it was tightened with the deflection arm. The handwheel was turn 90 degree each time to take the reading for angle of twist from the 360 protractor scale and torque from the torque meter of each specimen. Therefore, 12 readings were taken and evenly distributed. After taking the 12 readings, the handwheel was continuously turned until the specimen was fracture. By the time the specimen was fractured, this shows that the maximum torque and the maximum angle of twist of the specimen. All the readings were recorded in a table form and calculations were done using the equations shown at section Results and Discussion.

2.3 Procedure
1. The specimen as shown in figure 2 below was used for testing. The mild steel specimen was mounted on the torsion testing machine at position no.4. 2. It was made sure that on the specimen there was no preload. Before starting the experiment, the hand wheel at the input of the worm gear was turned when necessary until the read out of the amplifier is zero. There was still zero error on the amplifier. 3. Both the indicators at the input and output shaft of the worm gear was set to zero. 4. The dial gauge of the compensation unit was set to zero. 5. The revolution counter was reset.

6. The hand...

References: 1) “Laboratory Handbook”, Taylor’s University, 2012/2013.
2) J.L.Meriam and L.G.Kraige, 2006, Engineering Mechanics Statics. 6th Ed.
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