# Strain ε ௦ ௦ ࢤ బ where ઢ l change in

• No School
• AA 1
• 87

This preview shows page 63 - 68 out of 87 pages.

Strain ( ε )= ஼௛௔௡௚௘௜௡ௗ௜௠௘௡௦௜௢௡ ை௥௜௚௜௡௔௟ௗ௜௠௘௡௦௜௢௡ = ࢤࡸ Where L = change in length ܮ = Original length Example Calculate the tensile strain in a member of a strut 2m long, which extends by 0.03cm when under a load. Solution Strain ( ε ) = ࢤࡸ L = 0.03cm ܮ = 2m x 100 200cm ε = ࢤࡸ = ଴.଴ଷ௖௠ ଶ଴଴௖௠ = 1.5x10 4
Prepared By: ChilesheMwenyaMporokoso Page 63 THERMAL STRAIN Change in temperature in a material gives rise to a thermal strain. The extension in a bar of length L is given by; L = α ܮ θ Where = α = Coefficient of linear expansion ܮ = original length θ = change in temperature ε = ࢤࡸ = ஑௅ ୼஘ = α θ ε = α θ HOOKE’S LAW Many objects such as a coiled spring or a metal rod exhibit a property called elasticity. When stretched or compressed by an applied force, they tend to return to their original length when a force is removed provided the elastic limit is not exceeded. Beyond the elastic limit, they material loses its elasticity. HOOKE’S LAW states that when an object is distorted, the amount of distortion is linearly proportional to the distortion provided the elastic limit is not exceeded. From hooke’s law Stress Strain Stress = E x Strain
Prepared By: ChilesheMwenyaMporokoso Page 64 E = ௌ்ோாௌௌ ௌ்ோ஺ூே Where E = Young’s Modulus Example A 2.6kg mass is attached to the end of a vertical wire of length 2m and diameter 2mm. If the wire extended by 0.08mm, Calculate ; Solution F = W = mg = 2.6x9.81 = 2.506N ܮ = 2m = 2000mm L = 0.08mm r = = 1mm = 1mmx ଵ௠ ଵ଴଴଴௠௠ = 1.0 x 10 3 A = π r 2 = π (1.0 x 10 3 ) 2 = 3.142 x 10 6 m 2 (a) σ = ி = ଶ.ହ଴଺ ଷ.ଵସଶ௫ ଵ଴ షల = 8.11x10 6 N/m 2 (b) ε = ࢤࡸ = ଴.଴଼௠௠ ଶ଴଴଴௠௠ = 4.0 x 10 5 (c)E = = ଼.ଵଵ ௫ ଵ଴ ସ.଴ ௫ ଵ଴ షఱ = 2.027 x 10 11 N/m 2 ULTIMATE TENSILE STRESS ( U.T.S) This is the ratio if the maximum load to the original cross sectional area ( U.T.S) = ெ௔௫௜௠௨௠ ௟௢௔ௗ ௢௥௜௚௜௡௔௟ ௖௥௢௦௦ି௦௘௖௧௜௡௔௟ ௔௥௘௔
Prepared By: ChilesheMwenyaMporokoso Page 65 FACTOR OF SAFETY This is the ratio of the ultimate tensile stress to the working stress Example An aluminium wire with an initial length L= 25m and diameter d = 2m is used to lift a 10kg load. Determine (i)The length of the wire (ii)working stress in the wire (iii)Strain in the wire (iv)The factor of safety (v)The maximum load that the wire can support [Young’s modulus for aluminium ε = 7.0 x 10 10 N/m 2 , ultimate tensile strength (U.T.S) for aluminium is 1.4 x 10 8 Pa]. UNIT 2.0: HEAT AND TEMPERATURE Heat is a form of energy which is transmitted between two bodies at different temperatures. Temperature is the degree of hotness and coldness of an object. INSTRUMENTS USED FOR MEASURING TEMPERATURE A thermometer is a device used for measuring temperature The principle of operation of the thermometer is based on some of effects such as; i. Expansion ii. Increase in pressure iii. Electrical changes i. The following are some of the common types of thermometers. LIQUID IN GLASS THERMOMETER
Prepared By: ChilesheMwenyaMporokoso Page 66 ii. These depend on the expansion of the liquid (mercury or alcohol) used.

#### You've reached the end of your free preview.

Want to read all 87 pages?

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern