during vibration are in the 70 percent Fty range [2]. Preload was applied to the joint by tightening to a  predetermined torque range. Galling, typical for threaded aluminum joints, would have added to the resistive torque measured during application of a final assembly torque and resulted in a reduced asassembled preload. Additionally, the profile of the forward lug and aft cap could have contributed to  lower preload values given the end fittings were hollow and more susceptible to flexure and joint relaxation. The requirements and analysis methods utilized in the assessment of joint preload [3, 4] did not consider bending as a potential source of joint separation and are primarily focused on typical  bolted joints and fasteners, the definitions of which are not completely applicable to the spring strut  joints.   4.Strut Retention Design and Fatigue Analysis : The retention tool utilized to hold the spring strut in a  compressed state interfaces with secondary piston tooling holes and clamps onto the actuator  housing body just aft of the actuator housing-to-forward cap interface. The two tooling holes were  machined as a part of the spring strut assembly process whereupon the forward lug is fastened to the secondary piston, the location of the tooling holes relative to this subassembly are identified, and the forward lug is removed and holes machined. Since this machining operation occurs during the  assembly phase, the tooling holes did not have the surface treatment that was applied to the rest of the secondary piston.   Prior stress and fracture analyses did not include the tooling holes, and the secondary piston was not  considered fracture critical. Large structural margins in this analysis deemed the secondary piston satisfied the definition of a ‘low risk’ component and were subsequently classified as non-fracture critical. These prior analyses were based on flight load factors found to be inadequate and inconsistent with the EFT-1 flight configuration. After the secondary piston failure, an updated fatigue  analysis was performed accounting for the off-nominal secondary piston rotation to quantify the Cumulative Damage Index (CDI) using Rayleigh’s distribution and Miner’s Rule for response to the  base input Power Spectral Density (PSD). In summary, the analysis results showed exceedance of  the secondary piston fatigue life capability at the tooling hole (CDI = 1.519 > 1.0) when subjected to Y-axis qualification levels in a maximum bending condition. After the failure, the spring strut was evaluated by LM and Marshall Space Flight Center (MSFC) failure analysis groups with both groups  concluding the structural failure occurred at the aft-most secondary piston tooling hole initiated in fatigue followed by ductile overload. The opposite side of the failed tooling hole also showed the beginnings of fatigue cracking. 5.CG Offset : Through hardware inspection and as-designed tolerance limitations on select dimensions,  the spring strut center of gravity (CG) could be approximated as 1.09 mm (0.043 in) offset for the  forward assembly (i.e., secondary piston, forward lug, actuator spring, and piston) and 0.76 mm  (0.030 in) offset for the aft assembly (i.e., aft cap, actuator housing, forward cap, damper module assembly, latch, retention spring, and fasteners) in the Z-axis. With random vibration loads applied to  the strut, the CG offset in the forward assembly could contribute to a moment being applied in the direction of rotation of the secondary piston during the Y-axis random vibration testing. Other factors that may have contributed to the applied torque on secondary piston are the static, induced torque  from compression of the actuator spring and the instrumentation mass offset from the strut centerline, neither of which was incorporated into the pre-test analysis.   Application of recorded time history data permitted an across-the-board comparison of applied torque  versus estimated torque capability as a function of CG offset. It was shown that the required torque to  overcome the forward lug-to-secondary piston secondary locking feature’s capability would have  been exceeded given a 3- and 4-/g305/g3 /g79/g82/g68/g71/g3 /g68/g81/g71/g3 1.09-mm (0.043-in) CG offset. Similarly, reasonably  attainable CG offsets would have resulted in significant induced torques relative to the predicted capability of the joint for a 3-/g305/g3/g79/g82/g68/g71/g17 Therefore, the CG offset in the forward assembly could have led  to induced torques capable of overcoming the torque-resistive capability of the forward strut interfacewith reasonable assumptions, known input environments, and predicted dynamic responses. Note  that no such reasonably attainable CG offset would have induced significant enough torque to  399