Design 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 production Design 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 production Two 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 design Equations 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 bh3 lumped parameter K Height of active hook h Stress from bending sigma Equation delta Pa2 3L a 6EI where I bh3 12 sigma My I where M Pa y h 2 and I bh3 12 Rearranging to get K K 2Pa2 3L a E delta Allows you to play with the dimensions b and h Active and Passive Hook Design Optimal inputs P 15 5 N a little over 3 lbs a 0 04 m L 0 06 m E 2 10E09 Pa for ABS delta 0 008 m b 0 02 m Outputs K 4 13E 10 m4 h 0 00274 m sigma 24 7 MPa Good because yield stress for ABS 41 MPa Good safety factor Mold Design for Active Hook Mold Design for Passive Hook