Design GoalsDesign GoalsTwo Cases for DesignEquations for DesignActive and Passive Hook DesignMold Design for Active HookMold Design for Passive HookDesign GoalsDesign Goals Function Required Material Parameters Sufficient Young’s modulus High fatigue resistance Ease with installation Safety Failure mode involves deformation and not fracture Allows time for replacement Cost Minimize material cost By using a reasonably inexpensive and widely used material By minimizing volume of material used in each component Simple two-part mold for productionDesign GoalsDesign Goals Function Required Material Parameters Sufficient Young’s modulus High fatigue resistance Ease with installation Safety Failure mode involves deformation and not fracture Allows time for replacement Cost Minimize material cost By using a reasonably inexpensive and widely used material By minimizing volume of material used in each component Simple two-part mold for productionTwo Cases for DesignTwo Cases for Design Two cases where force P causes deflection of the active hook Case 1 – end of hook where deflection is going to be just enough for it to slide past the passive hook Case 2 – person exerts force in the middle region to unhook the latch Case 2 will be where greater force than is needed will often be exerted Design of lock should be based on the force P in Case 2 Beam theory used for designEquations for DesignEquations for Design Inputs Force - P Distance on beam person exerts force - a Distance in deflection - delta Width of active hook - b Modulus of material - E Length of beam - L Outputs bh3lumped parameter - K Height of active hook - h Stress from bending - sigma Equationdelta = (Pa2)(3L-a)/(6EI)where I = bh3/12sigma = My / Iwhere M = Pay = h /2 and I = bh3/12Rearranging to get KK = 2Pa2(3L-a)/(E*delta)Allows you to play with the dimensions b and hActive and Passive Hook DesignActive and Passive Hook Design Optimal inputsP = 15.5 N (a little over 3 lbs.)a = 0.04 mL = 0.06 mE = 2.10E09 Pa (for ABS)delta = 0.008 mb = 0.02 mOutputsK = 4.13E-10 m4h = 0.00274 msigma = 24.7 MPaGood because yield stress for ABS = 41 MPa Good safety factor!Mold Design for Active HookMold Design for Active HookMold Design for Passive HookMold Design for Passive