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 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
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/im ages/HandTools-Jacks.jpg http://www.msha.gov/Accident_Prevention/Tips/im ages/HandTools-Jacks.jpg http://machinedesign.com/article/fe-update- expecting-too-much-from-fea-0710 http://machinedesign.com/article/fe-update- expecting-too-much-from-fea-0710