We have taken a hard look at the loads induced into the corner flexures & tower to evaluate the maximum displacement that can be allowed from the new attachment concept. The results follow:
Analysis: The analysis approach used the detailed FEM of the TKR tower to get bolt forces and sidewall stresses. The side flexures were all unconstrained in this analysis to account for their float during assembly. Three of the four corners were constrained to establish a reference plane. A displacement constraint was applied to the fourth corner equal to 0.001" in the vertical and lateral directions independently (i.e. two separate analyses). The loads extracted from this analysis were scaled to define maximum allowable displacements and superimposed on the launch loads previously defined. Launch loads were scaled back to 24.4 g's to account for the new spectrum with the 3dB notch. Minimum margins were reviewed and evaluated.
Calculated Flexure Loads:
0.001" displacement along the vertical axis ... Fz = 336 N
0.001" displacement along the lateral axis ... Flateral = 192N
Calculated M4 bolt forces:
Vertical axis ... Fz = 92.2 N/0.001" and Flateral = 38.2 N/0.001"
Lateral axis ... Fz = 22 N/0.001" AND Flateral = 8 N/0.001"
Displacements were scaled until a minimum margin of 0.0 was calculated in any location in the load path. The minimum margin of 0 is on the corner flexure. M4 sidewall bolt MS is 0.17, and the sidewall MS is 0.14 using COI material test data (NOT Plyforms).
The analysis assumes that three corner flexures are constrained to establish the reference datum for the fourth flexure positioning. The fourth flexure must be located within 0.004" in the vertical direction and 0.003" in the lateral direction, relative to this reference datum. Machining tolerances will need to be worked out.
Erik A. Swensen
Deputy General Manager, HYTEC Engineering Inc.