{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

MEEM2003_Lecture_Notes_PatrickWong

# MEEM2003_Lecture_Notes_PatrickWong - MEEM2003 Mechanics...

This preview shows pages 1–16. Sign up to view the full content.

MEEM2003 Mechanics Assessment Tasks/Activities: Exam 60% Course work 40% Labs (20%), Case Study (15%), Test (5%). Recommended book: Mechanics of Materials , Beer, Johnston and DeWolf, 4th edition in SI units, McGraw-Hill, 2006. Mechanics of Materials , J.M. Gere, 5th edition, Brooks/Cole, 2001.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Objectives: To provide with the means of analyzing and designing various machines and load-bearing structures. To introduce the fundamental concepts of stress and strain analysis . My part: Mechanics of Materials
Introduction: An engineering design process usually starts with a question, “What do you want?” (A design specification). Example: We want to build a platform or stage being strong enough to support the heaviest student in this class. Specification: able to support maximum mass 100 kg. Items to be thought of: Materials (metal?, wood?, plastic?), Shape, Dimensions…

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
A simple example: We want to know the induced forces in all members
Free body diagram of frame ABC 1. The body ABC 2. All external applied forces 3. Reactions B C 30 kN A A x A y C x C y 0.8 0.6

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Three equilibrium equations: Σ M=0 and take moment @ point C A x (0.6) – (30000) (0.8) = 0 A x = +40 kN (1.1) Σ F x =0; A x + C x = 0 C x = A x = 40 kN (1.2) Σ F y =0 A y + C y – 30000 = 0 A y + C y = +30 kN (1.3) B C 30 kN A A x A y C x C y 0.8 0.6
Free body diagram of member AB 1. The body AB 2. All external applied forces 3. Reactions B 30 kN A A x A y B x B y 0.8 Σ M=0 and take moment @ point B A y (0.8) = 0 A y = 0 (1.4) Put into (1.3) C y = 30 kN

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Free body diagram of frame ABC We found A x = 40 kN A y = 0 C x = 40 kN C y = 30 kN B C 30 kN A A x A y C x C y 0.8 0.6
Free body diagram for member BC B C C x C y 0.8 0.6 C x = 40 kN C y = 30 kN BC is a two-force member. Its own weight can be neglected. Reactions at the end points must be equal and opposite and collinear. F BC = (C x 2 + C y 2 ) = 50 kN

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
B C F BC F’ BC C F BC F’ BC B D F BC F’ BC D D The internal force at different sections on member BC is always F BC (= 50 kN tension).
B C 30 kN A A x C x C y 0.8 0.6 FBD of point B B 30 kN F AB F BC FBD of member AB’ B’ A F AB = A x F’ AB Internal force in member AB is F AB ( = A x = 40 kN compression)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
If the cross sectional area of boom AB is A AB = 30 x 50 mm 2 The induced normal stress in boom AB is σ AB = normal force ÷ cross sectional area = 40x10 3 /(30x50x10 -6 ) = 26.7 MN/m 2
Similarly, the diameter of bar BC is 20 mm and it area is then A BC = π . 20 2 / 4 = 314.2 mm 2 The induced normal stress in bar BC is σ BC = normal force ÷ cross sectional area = 50x10 3 /(314.2x10 -6 ) = 159.1 MN/m 2 120 Brass 216 Carbon Steels Yield Stress (MPa) Material Which material would be the right choice?

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Stress and Strain Analysis Direct stress Stress at section XX A F = = area sectional Cross load Normal σ This assumes that the force is uniformly across the cross section. SECT XX F Tensile F Cross-section area= A F Compression F
If the force is not uniformly distributed over the cross section, Small element of area, dA, carrying load, d F .

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.