1. Laboratory 6 Boom Construction Competition General Engineering Department Polytechnic University

2. Outline  Review  Breakage Under Load  Ultimate Tensile Stress  Fracture Stress  Elasticity  Plasticity  Materials  Procedure  Testing  Weighted and Unweighted Ratios  Test Data (Excel)  Rules of the Competition  Recitation Topics  Report Questions  Closing

3. Review  Stress  Strain  Minimal Design

4. Breakage Under Load  Some areas of material weaker than others  Fracturing results from continuous loading and unloading  Crack expands due to plastic deformation  Cross-sectional area reduced  Material unable to contain stresses and fails  Fatigue caused by change in microstructure associated with cyclic loading

5. Ultimate Tensile Stress (  m )  Greatest amount of stress the material will withstand without failing  Plastic instability occurs when pass U.T.S. U.T.S. = P max A 0 P = Applied Force A 0 = Cross Sectional Area

6.  Stress at which the material fails  Calculated from the following formula: Fracture = P f Stress A 0 P = Applied Force A 0 = Cross Sectional Area Fracture Stress (  f )

7. Elasticity  Strains produced by stress disappear if stress removed  Stress is proportional to strain Hooke’s Law    e  = E * e E = Young’s Modulus of Elasticity (slope ofgraph in elastic region) measures stiffness of material and is constant for given material

8. Plasticity  Plastic deformation occurs when a material is loaded to a point beyond elastic region  When material is un- loaded, it would return along a line parallel to that of elastic region (slope E) to a non-zero value of e, resulting in permanent deformation

9. Materials  2 - thin dowels (5/16” diam. X 48”)  2 - thick dowels (7/16” diam. X 48”)  Foam board (3/16” x 15” x 20”)  6 - 13” bamboo skewers  Tape  Kevlar string

10. Procedure  Discuss strategy  Record reasons that led to design and choice of materials  Draw sketches of boom design  Build boom according to sketches  During competition: –Weigh boom –Fasten boom to anchor –Record maximum weight supported prior to boom failure

11. Testing

12. Unweighted and Weighted Ratios Unweighted Ratio Weighted Ratio

13. Test Data (Excel) 1st DISQUALIFIED 2nd 3rd

14. Rules of the Competition  Instructor will initial sketches of design before competition  Materials can be cut, drilled, and arranged in any way  Weight supported by boom must extend at least 1.5 m  Add one min to construction time for each min over  Do not record # weights held; take reading of total weight  Boom only supported at one end by anchor (4-in dia pipe)  Two min max time for anchoring boom plus any time over  Add weights until weights slip off or boom deflects.2 m  Team with highest ratio wins

15. Recitation Topics  Standards  Design failure  Criteria considered in design  Minimal design / over-design  Reasons for choice of materials  Weighted ratio formula: largest and smallest factor

16. Report Questions  Describe rules of competition  Strategy/Criteria used in design  Reasons for choice of materials  Boom performance, include unweighted ratio  Reason boom failed and improvements  Ratio contributing most to large/small weighted ratio

17. Closing

23.  Safety: –Wear goggles when using power tools –Use power tools on the work benches  Original data: –Sketches including dimensions –Readings recorded on Excel during competition along with weighted ratio –Reasons that led to design and choice of materials