MEC424 LAB Content Torsion PDF

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Summary

Table of Contents ABSTRACT............................................................................................................................................. 1 INTRODUCTION.........................................................................................................................

Description

Table of Contents ABSTRACT.............................................................................................................................................. 2 1.0

INTRODUCTION......................................................................................................................... 3

2.0

OBJECTIVES................................................................................................................................4

3.0

THEORY......................................................................................................................................5

4.0

EXPERIMENTAL PROCEDURE......................................................................................................7

4.1

Apparatus and Equipment.....................................................................................................7

4.2

Procedure of The Experiment................................................................................................8

5.0

RESULTS.....................................................................................................................................9

6.0

DISCUSSION.............................................................................................................................10

7.0

CONCLUSION...........................................................................................................................11

8.0 REFERENCES...................................................................................................................................12

ABSTRACT The following experiment outlines the proper procedure for determining the shear modulus for a material. The experiment conducted is to determine the torsion properties subjected to pure torque loading, identify Types of fracture surface under pure torque and to validate the data between experimental and theoretical values. During this experiment, mild steel was used as samples to demonstrate how materials behave during testing conditions. By measuring the applied torque with respect to the angle of twist, the shear modulus, shear stress at the limit of proportionality, and failure conditions can be found. We can conclude that not all deformation is elongational or compressive. The concept of stress and strain can be extended to inclined shearing or distortional effects. In solid mechanics, torsion is the twisting of an object due to an applied torque. Torsion test are made on materials to determine such properties as the modulus elasticity in shear, the torsion yield strength and the modulus of rupture. It is often used for testing brittle materials and can be tested in full-sized parts, i.e., shafts, axles and twist drills which are subjected to torsion loading in service.

Figure 1: Application of torsion test

1.0 INTRODUCTION In many areas of engineering applications, materials are sometimes subjected to torsion in services, for example, drive shafts, axles and twisted drills. Moreover, structural applications such as bridges, springs, car bodies, airplane fuselages and boat hulls are randomly subjected to torsion. The materials used in this case should require not only adequate strength but also be able to withstand torque in operation.

Figure 1.1: Torsion test

Many products and components are subjected to torsional forces during their operation. Products such as shaft, switches, fasteners, and automotive steering columns are just a few devices subject to such torsional stresses. By testing these products in torsion, manufacturers can simulate real life service conditions, check product quality, verify designs, and ensure proper manufacturing techniques. A torsion test can be conducted on most materials to determine the torsional properties of the material. These properties are modulus of elasticity in shear, yield shear strength, ultimate shear strength, and modulus of rupture in shear and ductility. The torsion test generates the "torque versus angle" diagram that looks very similar to a "stress versus strain" curve in a tensile test. They are not the same however they are analogous to properties that can be determined during a tensile test. This experiment is designed to determine the modulus of rigidity. Utilizing test specimens with a known geometry, specimens can be twisted with the values for torque simultaneously measured. With the sample secured and clamped within the Torsion Test Machine, the specimen can be twisted by applying a rotational torque to one end, while the opposing end is kept straight.

2.0 OBJECTIVES

Upon completion of this experiment, students should be able to; 

Determine the torsion properties subjected to pure torque loading



Identify types of fracture surface under pure torque



Validate the data between experimental and theoretical values

3.0 THEORY In solid mechanics, torsion is the twisting of an object due to an applied torque. It is expressed in newton meters (Nm). In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius. Torsion occurs when any shaft is subjected to a torque. The shaft is rotating such as drive shafts on engines, motors and turbines or stationary such as with a bolt or screw. The torque makes the shaft twist and one end rotates relative to the other inducing shear stress on any cross section. Failure might occur due to shear alone or because the shear is accompanied by stretching or bending. For shafts of uniform cross-section, the torsion is:

T is the applied torque or moment of torsion in Nm. T is the maximum shear stress at the outer surface. JT is the torsion constant for the section. It is identical to the second moment of area Jzz for concentric circular tubes or round solid shafts only. For other shapes, J must be determined by other means. For solid shafts, the membrane analogy is useful, and for thin-walled tubes of arbitrary shape, the shear flow approximation is fairly good, if the section is not re-entrant. For thick-walled tubes of arbitrary shape, there is no simple solution, and finite element analysis (FEA) may be the best method. r is the distance between the rotational axis and the farthest point in the section (at the outer surface). L is the length of the object the torque is being applied to or over. θ is the angle of twist in radians. G is the shear modulus or more commonly the modulus of rigidity and is usually given in gigapascals (GPa),The product JT G is called the torsional rigidity wT. The shear stress at a point within a shaft is:

Note that the highest shear stress occurs on the surface of the shaft, where the radius is maximum. High stresses at the surface may be compounded by stress concentration such as

rough spots. Thus, shafts for use in high torsion are polished to a fine surface finish to reduce the maximum stress in the shaft and increase their service life. The angle of twist can be found by using:

Consider a cylindrical bar subjected to a torsional moment at one end. The twisting moment is resisted by shear stresses set up in the cross section of the bar. zero at centre, max at surface

τ = shear stress, Pa MT = torsional moment, Nm r = radial distance measured from centre of bar, m J = polar moment of inertia, m 4

For the shear stress, The maximum shear stress at the surface of the bar is

For a tubular specimen, the shear stress on the outer surface is

Where D1 = Outside diameter of tube D2 = Inside diameter of tube

Both equation of stress is applied only for a linear relationship.

4.0 EXPERIMENTAL PROCEDURE 4.1

Apparatus and Equipment Vernier Caliper

Torque Meter

Figure 4.1.1: Vernier Caliper

Worm Gear

Figure 4.1.3: Worm Gear

Figure 4.1.2: Torque Meter

Mild Steel Sample

Figure 4.1.4: Mild steel sample

Torsion Test Machine

Figure 4.1.2: Torsion test machine

4.2 1.

Procedure of The Experiment Measure the specimen size and overall length

Figure 4.2.1: Specimen

2. Put the specimen and fix it at the end on the machine chuck and set zero reading.

Figure 2.2.2: Shifting Sample holder

3. The handwheel is needed to be turn on clockwise direction to provide the applied load

Figure 4.2.3: Worm Gear

4. For the rotation, first, it increments is a quarter rotation ( 90° ) and the second and third rotation ( 180° ) and for the forth up to 10 rotations of one rotation ( 360° ). 5. For the reading, turn the handwheel at the position first or second or other then the dial gauge is needed to set to be initial value as 0 and from that the reading of torque will display at torque meter.

Figure 4.2.4: Torque Meter

6. Record the data that obtain from the torque meter and the rotation of handwheel and plot the graph from the given data.

5.0

6.0

7.0

8.0 REFERENCES 1. R. C. Hibbeler, Mechanics of Material Eight Edition in SI Unit, United States of America: Prentice Hall, 2010.

2. Torsion

Test.

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3. Engineering, M. (1970, January 01). Mechanical Engineering. Retrieved May

7,

2018,

from

https://pursuitengineering.blogspot.my/2016/03/torsion-testing.html

4. TORSION

TEST.

(n.d.).

Retrieved

May

7,

2018,

from

http://www.learneasy.info/MDME/MEMmods/MEM23061A/Torsion/Tor sion.html

5. G. Dahlberg, "Materials Testing Machines Investigation of error sources and

determination

of measurement

Corporation, Eden Prairie, USA.

uncertainty,"

MTS

Systems...