EG 1003 Introduction to Engineering and Design Boom

EG 1003: Introduction to Engineering and Design Boom Construction

Overview Ø Objectives Ø Background Ø Materials Ø Procedure Ø Rules of the Competition Ø Report / Presentation Ø Closing

Objectives Ø What is a boom? Ø How and why do materials fail? Ø Stress and strain Ø Design light-weight boom to hold significant load Ø Understand factors engineers consider when designing a boom Ø Construct and test boom

Boom Lifts and moves heavy objects Ø Objects usually much heavier than the boom Examples Ø Construction cranes Ø Computer monitor arms Ø Cantilever bridges Ø Rotating bridges

Common Structural Modes of Failure Ø Corrosion Ø Thermal cycling Ø Thermal Shock Ø Breakage under load Ø Instant fracture Ø Delayed response (fatigue)

Corrosion Ø Exposure to caustic chemicals for extended periods Ø Acids Ø Water (rust) Ø Salt Ø Air (oxidation) Ø Substances and material react ØMaterial weakened by being “eaten away” Ø Examples ØIron rusting (exposing iron to water) ØWind blowing sand on rocks, bridges, etc

Thermal Cycling Ø Material’s temperature changes continuously over time Ø Material cracks or shatters due to stresses created by expansion/contraction Ø Example: ØElastic in clothes cracks once removed from clothes dryer

Thermal Shock Ø Material undergoes extreme temperature changes in a short time period Ø Mixed temperatures throughout material cause compression/expansion resulting in cracks Ø Example: Ø Hot glass bottle placed into ice cold water, bottle would explode and shatter

Breakage Under Load Ø Maximum load supported by material is exceeded Ø Material cracks/crumbles (ie. Thermal shock) Ø Over usage ØToo many load cycles

Breakage Under Load Ø Maximum load supported by material is exceeded Ø Material cracks/crumbles (ie. Thermal shock) Ø Over usage Ø Too many load cycles

Stress and Strain Ø Stress: measure of internal force that keeps material together Ø Resists form change of body Ø Strain: measure of deformation (elongation/compression) of material Ø Change from original dimension Ø Examples Ø Stretching of rope while pulling Ø Car tire under load

Stress-Strain Figure • Stress (s) = F A • Strain (e) = DL Lo Fixed Support Cross-sectional area of bar D L Lo Load F F= Applied force DL=Change in length A = Cross-sectional area Lo=Original length

Stress-Strain Graph U. T. S. Ø Key points/regions Stress (s) ØU. T. S. (Ultimate Tensile {P} [psi] Strength) ØFracture Stress ØElasticity Region {E} ØPlasticity Region {P} {E} Fracture Stress Strain (e) [in/in]

Stress-Strain Graph U. T. S. Stress (s) {P} [psi] Ø Greatest amount of stress material will withstand without failing Ø Plastic instability occurs when past U. T. S. {E} Fracture Stress Strain (e) [in/in] Ø U. T. S. = Pmax Ao Ø Pmax = Applied force Ø Ao= Cross-sectional Ø area

Stress-Strain Graph U. T. S. Ø Stress at which the material completely fails Stress (s) {P} [psi] {E} Fracture Stress Strain (e) [in/in]

Stress-Strain Graph U. T. S. Stress (s) {P} [psi] {E} ØStrain will disappear when stress is removed ØStress and strain vary linearly, obeying Hooke’s Law s e ØStiffness of material found by Young’s Modulus of Elasticity: Fracture Ø E= s/e (slope of elastic region) Stress Strain (e) [in/in]

Stress-Strain Graph U. T. S. Stress (s) {P} [psi] {E} Ø Strain will NOT disappear when stress is removed Ø Permanent deformation Ø Range of plasticity: Ø Ductile materials deform considerably before fracture Ø Brittle materials do Fracture not deform much and Stress failure occurs suddenly Strain (e) [in/in]

Stress-Strain Example The Plastic Pen Cap and Nervous Student 1. Elastic Region - Student applies force, bending tip of pen cap back. When force is removed, tip of cap returns to original position. 2. Plastic Region - Student twists and bends tip of cap. When force is removed, the tip of cap stays mangled. 3. U. T. S. - Student bends cap some more. Cap still in one piece, but certain areas are very weak and on the verge of breaking. 4. Fracture Stress - Student bends cap one more time. The cap finally breaks into 2 pieces. 1 2 3 4

Materials for Lab Ø 2 thin dowels (5/16” dia. x 48”) Ø 2 thick dowels (7/16” dia. x 48”) Ø 6 12” bamboo skewers Ø Cellophane Tape Ø Kevlar string

Setup for Testing

Assignment: Presentation Ø Unadjusted Ratio Ø Adjusted Ratio

Assignment: Presentation • Design Specifications • Disqualifications • Declaration of winners Ø Design specifications ØTA initials and dates sketches of design before materials are distributed ØMaterials may be cut and arranged in any way ØBoom must extend a horizontal distance of at least 1. 5 m after mounting ØConstruction must be completed in time allotted ØNo more than 2 minutes to anchor boom ØWeight will be added until boom deflects 0. 2 m

Assignment: Presentation Ø Disqualifications • Design Specifications • Disqualifications • Declaration of winners Ø Design is less than 1. 5 m horizontally when mounted Ø Exceed 2 minute max time for anchoring boom Ø Boom must only touch anchor Ø (4” dia. pipe)

Assignment: Presentation • Design Specifications • Disqualifications Ø Declaration of winners Ø Design with highest adjusted ratio wins competition Ø Decision of TA is FINAL • Declaration of winners

Assignment: Presentation Boom design • Boom Design • Test • Post-Test Ø Observe provided materials Ø Brainstorm design strategy with team members Ø Note design decisions and necessary design changes Ø Sketch proposed design Ø Have TA initial sketch and notes Ø Build boom according to sketch

Assignment: Presentation • Boom Design • Test • Post-Test ØTA will create a spreadsheet to record competition results ØWeigh boom and announce value to TA ØWhen instructed, fasten boom to anchor ØAnnounce when “DONE!”, to record time ØTA measures length from tip of anchor to weight mounting point on boom ØMust meet 1. 5 m requirement ØAdd weights until boom deflects 0. 2 m vertically, or fails

Assignment: Presentation • Boom Design • Test • Post-Test Ø TA announces winner of competition Ø Team with largest adjusted ratio Ø Copies of spreadsheet available to all teams on eg. poly. edu Ø TA initials and scans original data

Assignment: Report Ø Team Lab Report Ø Title Page Ø Discussion topics in the manual Ø Include class results and photo of boom

Assignment: Presentation Ø Team presentation Ø State rules of competition Ø Describe your design and its concepts Ø Include table of class results, sketches, photo/video of boom Ø How could your current design be improved?

Closing Ø Think Safety! Be careful not to poke classmates with the dowels Ø Have all original data signed by TA Ø Submit all work electronically Ø Clean up workstations Ø Return all unused materials to TA GOOD LUCK!