ME 323 – Mechanics of Materials

Lecture 0: Class OverviewJoshua Pribe

Fall 2019

General Information

• Instructor• Josh Pribe, jpribe@purdue.edu

• Office hours:• Tuesday, 2 – 3 PM and Thursday, 1 – 2 PM

• ME 2nd floor common area (at the circular tables)

• Lectures• Monday, Wednesday, Friday; 4:30 – 5:20 PM; ME 2061

• TA office hours in ME 2134 (Tutoring room 1):• Sunday, 1 – 5 PM

• Monday, 4:30 – 8:30 PM

• Tuesday, 3:30 – 6:30 PM

• Wednesday, 8:30 AM – 12:30 PM and 6 – 9 PM

• Friday, 1 – 3 PM2

Resources

• Textbooks• Required: ME 323 Lecture Book (2019-20 Academic Year), University bookstore

• Optional: Mechanics of Materials, R. R. Craig, Wiley, 3rd Edition, 2011

• Course website• www.purdue.edu/freeform/me323: homework assignments, discussion forum, lecture

notes, numerous worked and un-worked examples• Also includes links to homework submission (Gradescope) and pre-week videos/quizzes

• Other resources• web.mst.edu/~mecmovie/: “Mec Movies”, useful for visualizing concepts and

derivations

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Assignments and Grading

• Grading• Homework and quizzes (20%)

• Average score on two midterm exams (55% or 25%)

• Final exam (55% or 25%)

• Homework• Posted on Wednesdays; due the following Wednesday on Gradescope at 11:59 PM

• You can discuss the problems with classmates, but the work must be your own

• No late homework; if you have a legitimate excuse, email me ASAP and attach a PDF of your homework

• Must have clear and easy-to-follow structure

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Assignments and Grading

• Quizzes• Pre-lecture quizzes: due each Monday by noon (12 PM)

• Based on a video describing concepts and derivations relevant to each week’s lectures

• You get two attempts on each quiz and up to 30 minutes to finish the quiz

• Links to videos and quizzes are on the course website

• In-class quizzes: usually on Fridays (no make-up quizzes)• Open notes, open book, work together

• My goal is to grade and post these on Gradescope by Monday, so we can do any additional examples as necessary in class on Monday

• Exams• Closed book and closed notes, but you’re given a formula sheet

• Midterm exams: Wednesday, 10/2/19, 8 – 10 PM and Wednesday, 11/6/19, 8 – 10 PM

• Final exam: TBA

• The average of the two midterms OR the final (whichever is higher) = 55% of your grade5

Assignments and Grading

• Regrade requests must be submitted on Gradescope within a week of receiving your grade• Include a detailed description of what you think was graded incorrectly

• Academic Integrity• In short: don’t copy someone else’s work• Details on the syllabus; email me if you have further questions

• Calculator policy: only TI-30XIIS is allowed

• Students with disabilities: contact the Disability Resource Center and email me ASAP with any accommodations you will need

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Lectures

• Before class• Mondays: watch pre-lecture video(s) and complete quiz by noon (12 PM)

• Read through the relevant material in the lecture book

• Email me if you need to miss class

• During class• Slides will have key concepts, review of important equations, and diagrams

• They will be posted the day before class on the course website on our section’s page

• Lots of examples (the best way to learn material in this course)

• Highly encouraged to bring your lecture book and take notes

• #1 rule: avoid disrupting your classmates

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Emergencies

• Evacuation route for this classroom is easy:

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Schedule

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Schedule

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Schedule

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ME 323 – Mechanics of Materials

Lecture 1: Review of Static Equilibrium

Lecture Book: Chapter 1

Joshua Pribe

Fall 2019

Objectives

• Introduce Mechanics of Materials

• Review concepts from Statics (ME 270)• Free-body diagrams (FBDs)

• External forces and support reactions

• Equilibrium equations

• Internal resultants (very important in ME 323!)

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ME 323 Introduction

External loads

Internal resultants

Stress, deformation, possibly failure

Goal: take a complicated physical situation (structure, machine, etc.), and break it down into components we can describe with a mechanical model

Trusses, beams, tension/compression members

Pressure vessels

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ME 323 Introduction

• Real-world design codes are based on Mechanics of Materials• Simplified mechanical model → calculate stresses and strains in a material

• Make corrections based on experiments or finite element calculations

• Helps to diagnose the problem when failures occur

Walkway collapse:

Uncontained engine failure:

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https://www.ntsb.gov/investigations/pages/dca18ma142.aspxhttps://ethics.tamu.edu/hyatt-regency-photos/

ME 323 Introduction

ME 323 at Purdue Other relevant topics

ME 270 (Statics)

ME 323 (Mechanics of Materials)

ME 274 (Dynamics)

Half of ME 352 (Machine Design I)

Half of ME 352 (Machine Design I)

ME 452 (Machine Design II)

• Micromechanics and composites

• Fracture mechanics

• Vibrations and acoustics

• Finite element methods

• Elasticity theory and continuum mechanics

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Free-body diagrams

• FBD: start of almost every problem we will solve

• Procedure:• Isolate the body or structure from its supports and connections

• Sketch a coordinate system and all loads acting on the body

• Apply the equilibrium equations

• Typically drawn for each body in a structure

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Equilibrium

0F = ( ) 0O

M =

Force and moment equilibrium In 3-D Cartesian coordinate form

0

0

0

x

y

z

F

F

F

=

=

=

( )

( )

( )

0

0

0

O

O

O

x

y

z

M

M

M

=

=

=

Apply the equilibrium equations with an FBD to determine unknown forces and moments 18

Internal resultants

• Equivalent forces and moments within a member to maintain equilibrium• Key part of this course: finding stress distributions associated with internal resultants

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Internal resultants

• Internal resultants on one side of a cut are equal and opposite to the internal resultants on the other side of the cut

• Internal resultants may depend on the location of the cut

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Example 1.2

The truss shown below is used to support a rigid container with weight W. Complete the FBDs of the full truss and the truss section shown below.

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Example 1.8

Member BCD is loaded with a line load p0 (force/length) over section CD. Ends B and D are connected to the ground by roller and pin connections, respectively.

(a) Determine the external reactions on member BCD at ends B and D.

(b) Determine the internal shear force, axial force, and bending moment acting on the left face of a cut through the member at E. 1.25 L

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Example 1.9

Find the internal resultant forces and moments at the center of cross section B for bar HCO.

The forces at H and D are parallel to the z axis. The force P at K is parallel to the z axis, and the force 2P at K is parallel to the x axis.

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Summary

• Statics procedure• Draw FBD(s)

• Use equilibrium equations

• Solve for unknowns

• Make a “cut” in a member to find the internal resultants

• Next time: relate internal resultants with stress and strain in a material

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