DESIGN PHASEWhat kind of analysis you need to do? MIME Senior Design Projects - Spring 2013
Overview • Design/Analysis Requirements • Common Design Issues • Welds • Fatigue • Safety • Quality
Design Requirements • What type of analyses do I need?
Design Requirements • Measure twice, cut once • Make sure you do adequate calculations and analysis • Tendency to build first, design later • Works if you’re right the first time • Costs material, effort, and time if you’re wrong • Anticipate use • Anticipate misuse!
Design/Analysis • FREE BODY DIAGRAM • FEA • Approximate Design/Calculations • Is it a beam or a plate?
Design/Analysis - FEA • Quality of input determines quality of output • “Magic” Black Box • Factors • Solid model quality • Correct boundary conditions • Load accuracy • Proper material selection • Mesh quality • Correct Failure Criteria
Design/Analysis - FEA • Solid Model Quality • Balance simplicity/accuracy • Use your intuition to include features that will increase stresses • Exclude trivial features • Correct Boundary Conditions • Make sure your restraints accurately represent real conditions • Check degrees of freedom • Check fastener/mating conditions in assemblies
Design/Analysis - FEA • Load Accuracy • What type of loading? point load? distributed load? • Am I missing loads? thermal? centripedal? • What is the magnitude? 10lbs? 500lbs? 1,000,000lbs? • Rationalize with intuition • Determine with testing • Material Selection • Did I select the correct material? • Are my properties in the correct units?
FEA – What to expect?http://machinedesign.com/article/fe-update-expecting-too-much-from-fea-0710
Design/Analysis - FEA • Mesh Quality • Make sure it is fine enough to accurately depict features • Affects processing time
Design/Analysis - FEA • Correct Failure Criteria • Stress based: yielding or fracture? • Excessive displacement • Loss of function • Corrosion • Thermal degradation • Fatigue Remember that ductile and brittle materials fail differently and have different failure criteria!
Design/Analysis • When in doubt, do some hand calculations • Mathcad and Matlab are very useful • Shigley is very useful • DANotes is a good resource as well: • http://www.mech.uwa.edu.au/DANotes/ • Your basic calculations and FEA should support each other • If they don’t, you should know why
Welds • Strength of welds • Location- sharp corners? • Loading- stress state of weld? • Size • Quality of weld! • Fatigue
Fatigue • Are their cyclic loads? • Do fatigue analysis • S/n approach used in Shigley
Safety • Pinch points? • Sanitation? • Exposed wiring? • Warnings?
Quality • Deliverables should function well • Make sure products are durable • Double-check safety
References • References: • What Kind of Analysis do you Need for your Project?, Dr. Kramer, MIME Dept. • Photo Credits: • http://www.msha.gov/Accident_Prevention/Tips/images/HandTools-Jacks.jpg • http://machinedesign.com/article/fe-update-expecting-too-much-from-fea-0710