Simple DesignBuildTest Experiences

1
Simple Design-Build-Test Experiences

• Cecil G Armstrong
• School of Mechanical Manufacturing Engineering
• Ashby Building, Stranmillis Road
• Belfast BT9 5AH
• c.armstrong_at_qub.ac.uk

2
Stage 2 Strength of Materials

• THE DESIGN, CONSTRUCTION AND TESTING OF A GLUED
  MDF BEAM
• Contribution to CDIO Goals
• How to CDIO a simple engineering system in a
  team-based environment
• Deeper working knowledge of technical
  fundamentals
• Objectives
• Design and build a glued fibreboard beam with
  highest load at failure/mass ratio under three
  point bending
• Compare the strength and mode of failure with
  predictions based on beam theory
• Based on an exercise from the University of
  Auckland, developed with JF Orr PJ Martin

3
Beam Specification
500
500
P
60 mm
100 mm
BEAM
1220
4
Design Constraints

• Space envelope (to eliminate complex modes of
  failure e.g. bending-torsion buckling)
• No cutouts
• Ease of manufacturing
• Beam equations for stressing
• Cheap, easily-worked homogeneous materials
• 3 mm fibreboard, PVA glue, cardboard for concepts
• Students given hints on where to find theory to
  assess likely failure modes bending stress,
  shear failure of glue, local buckling

5
Laboratory Schedule

• Week 1
• Test concepts with aid of cardboard models
• Week 2
• Final design specification and marking out
• Week 3
• Assembly of beam
• End of semester
• Testing of all beams

6
Assessment

• Total marks available 100
• Max Load/weight 60
• Prediction of Max Load 20
• Design/construction 20
• Performance determines group mark
• Peer assessment moderates group mark
• Competition increases motivation!

7
Previous Similar Designs

• Previous years designs
• Failure mode visible but failure load not
  provided
• Promotes
• critical assessment
• awareness of other similar structures e.g. in
  Ulster Museum

8
Design Philosophy

• Before testing
• 2 minute overview by students
• critique by staff
• After testing
• Informal analysis of failure mode
• Reflection on performance and accuracy of
  predictions

9

• Video

10
Conclusions

• Very little extra staff effort
• Can be incorporated into conventional lab program
• Performance determines marks
• But result is only 10 of total mark for course
• Promotes
• Teambuilding and group ethos
• Deeper understanding of basic structural theory
• Appreciation of design optimisation
• Deliberately limited in scope
• Several similar D-B-T experiences 1 keystone
  project?

11
The Instrumented Bench

• Live update
• Strain gt Bending Moment
• Strain gradient gt Shear Force
• Shear Force gt Weight position

12
Conclusions

• Enhanced student enjoyment motivates academic
  staff
• Simple Design-Build-Test projects
• Provide opportunity for quick successes with
  minimal resources
• Build case for systematic adoption of CDIO