Example 2
The stiffness of a polyurethane based filament was increased by overlaying a shell of a similar monomer chemistry over the core material. The elastomeric core was Tecothane TT-1077A having a flexural modulus of 1,100 psi and the shell material was Tecoplast TP-470 having have a flexural modulus of 300,000 psi. The filament was assumed to have a diameter of 0.12 inches and the core was assumed to have a diameter of 0.11 inches.
The area of the shell was calculated to be 0.0018 in.2 and the area of the core was calculated to be 0.0095 in.2. The area moment of inertia for the shell was calculated to be 2.99e−6 and the area moment of inertia for the core was calculated to be 1.76e−8. The area moment of inertia for a cylindrical filament of elastomeric material was calculated to be 1.02e−5.
The calculated stiffness of the shell was 0.897 and the stiffness of the core was calculated to be 0.00002, resulting in the core-shell elastomer filament having a composite stiffness of 0.897. In comparison, the stiffness of a neat elastomeric filament was calculated to be 0.011 lbf per in2.
As such, adding 16 volume percent of the shell material increases the stiffness by a factor of over 80.
