Mechanical engineering - LIGHTWEIGHT DESIGN OF MECHANICAL STRUCTURES

Oral exam

Titolo presentazionesottotitoloMilano, XX mese 20XXMoreschiniChiaraMaterial replacement of KAFO side barsLightweightdesign of mechanical structuresAA 2022/23 Nome_Laureando1, Nome_Laureando2OutlineChiara Moreschini11)Description of the part chosen for material replacement2)Working conditions analyzed of the part chosen 3)The new part: material and design method 4)FE model: setup and results5)More complex working conditions: proposed solution6)Discussion 7)Conclusions Nome_Laureando1, Nome_Laureando21) Descriptionof the part chosenfor metal replacementChiara MoreschiniKAFO (Knee-Ankle-Foot Orthosis)Bear part of the body weight leaving to the bones and the joints less load to sustain and improving their healing, for example in case of bone fractures, joints pathologies, etc...Lateral bars usually made of metallic materials: -AISI304stainlesssteel-AISI1020carbonsteel-Aluminumalloy705-T6 Nome_Laureando1, Nome_Laureando21) Descriptionof the part chosenfor metal replacementChiara MoreschiniØAs light as possible ØBiocompatible with the skin ØCapable of bearing the body weight during daily life activities ØCorrosion resistant §Maximum deflection (avoid joint’s excessive displacement)§Resistance to static and dynamic load§Resistance to buckling §Fixed dimensions depending on patient’s characteristics Design requirements:Constraints: Nome_Laureando1, Nome_Laureando22) Consideredworkingconditionof KAFO Chiara MoreschiniWorking conditions considered:Static standing position withfull extension of the knee (femur and tibia aligned)Patient’s characteristics: Average Italian male (age 18-35)Hight: 175 cm Weight: 70 kg We neglect: Flexion of the kneeDynamic loads Nome_Laureando1, Nome_Laureando23) The new part Chiara MoreschiniSimplified shape showed in the figure; side bars with rectangular cross sectionVertical load equal to ¼ total weight of the patient (= 200 N) on each side bar (static standing position without knee flexion)ØComposite single lamina of T300/Epoxy unidirectionalØComposite laminatewith 4 plies of T300/EpoxyAim: weight reduction½ W¼ WShape: Load: Material replacement: Nome_Laureando1, Nome_Laureando23.1) The new part: materialChiara MoreschiniContinuous fibers reinforced polymer:T300 carbon reinforced epoxy Elastic modulus in fiber direction:E1= 181 GPaElastic modulus in matrix direction:E2= 10,3 GPaIn-plane shear modulus: G12= 7,17 GPaPoisson’s ratio:nu12= 0,28111222333Single ply of thickness t1: fiber direction 2: matrix direction 3: out-of-plane direction Nome_Laureando1, Nome_Laureando23.2) The new part: design methodChiara MoreschiniThe most critical constraint in this problem is the deflection, so the dimensions of the part were chosen in order to satisfy this constraint ABC100mm200mm100mm30mmLength fixed by patient’s height Cross section’s dimensions TBDwtDimensions Nome_Laureando1, Nome_Laureando23.2) The new part: design methodChiara MoreschiniAxial loadCBA6000 NmmFlexion momentCBAShear loadCBA---200 N200 N197,8 N29,7 N!!!"¼ W=200NABCDisplacement of segment AB onlyDisplacement of segment BC onlyDimensions Nome_Laureando1, Nome_Laureando23.2) The new part: design methodChiara Moreschini!!!"!#$%,"=!"+!!==$'%()3'*(+++$'%()*+*)+,,,$--%((2'*(+++,,%)(2'*(++¼ W=200NBendingcontrib. of $'Shearcontrib.Bendingcontrib.!#$%,"./$≤!./#,"=522→!"#$%&#"'%()!*=1,5ABBendingcontrib. of ,,,$--CDisplacement of segment AB onlyDisplacement of segment BC onlyDimensions4*=522)=4022%789:; Nome_Laureando1, Nome_Laureando23.2) The new part: design methodChiara MoreschiniAxial loadCBA6000 NmmFlexion momentCBAShear loadCBA---Maximum deflection:/(('%)B(3_(−3_+1)==187('%)(+('%)*=47807,AYThickness of the plies chosen to have the same maximum lateral deflection of the previous configuration!#$%,"≅2,922→*B=2224 plies of same thickness OC Nome_Laureando1, Nome_Laureando25.2) FE model: resultsChiara Moreschini