Culberson, Michael

Dervan, Jared

Pellicciotti, Joseph

Robertson, Brandan

Staab, Lucas

NASA Technical Reports Server

Presenter
JaredDervan
Date
May15,2014
1
Development Testing and 
Subsequent Failure of a Spring 
Strut Mechanism
Jared Dervan (NASA MSFC)
Brandan Robertson (NASA JSC)
Lucas Staab (NASA GRC)
Michael Culberson (LMSSC)
Joseph Pellicciotti (NASA GSFC)
42nd Aerospace Mechanisms Symposium
https://ntrs.nasa.gov/search.jsp?R=20140011056 2019-08-31T19:48:32+00:00Z
Presenter
JaredDervan
Date
May15,2014
 Background & Approach
 Hardware Description
 Development Testing
 Root Cause Investigation
 Failure Scenario Summary and Supporting 
Rationale
 Follow-on Development Testing
 Lessons Learned
 Conclusion
2
Agenda
Presenter
JaredDervan
Date
May15,2014
Background & Approach
3
Spring Strut in Stowed Configuration
Umbilical Separation
• Background
• Commoditiestransferred
betweenCMSMviaexternal
umbilical
• Dualspringloadedstruts
driveumbilicalawayduring
separation
• Novibrationtestingonstrut
developmentunitsscopedin
OrionMultiPurposeCrew
Vehicle(MPCV)program
plan
Presenter
JaredDervan
Date
May15,2014
Background & Approach
4
• Background(contd.)
• ProblemsdiscoveredonotherOrionspringassemblies
duringvibrationtesting(e.g.SpacecraftAdapterFairing
JettisonSpring(SAFJS)Assembly)
SAFJS Assembly
SAFJS Assembly Wear Post Vibration Testing
Presenter
JaredDervan
Date
May15,2014
Background & Approach
5
• Approach
• JointNASAEngineeringandSafetyCenter(NESC)and
LockheedMartin(LM)team
• AssessmentNo.1100747
• PerformdevelopmenttestingonasingleExplorationFlight
Test1(EFT1)springstrutdevelopmentunit
• Testingincludedfunctionalandrandomvibrationtesting
• Preliminaryresultsinformqualificationunitdevelopment
andfollowontesting
Presenter
JaredDervan
Date
May15,2014
CM-SM Umbilical Spring Strut Detail
6
Presenter
JaredDervan
Date
May15,2014
Retention Tool
7
Presenter
JaredDervan
Date
May15,2014
Random Vibration Testing
8
• Two shaker tables utilized 
(uncorrelated)
• Other configurations traded 
(single shaker (correlated); 
grounding one end)
Z-Axis
Successful
X-Axis
Successful
Y-Axis
Failure
Presenter
JaredDervan
Date
May15,2014
Test Failure Observations
9
Presenter
JaredDervan
Date
May15,2014
Test Failure Observations
10
• Rotation of strut forward and aft subassemblies
– Actuator Housing rotates clockwise
– Failure of forward subassembly lockwire
– Counterclockwise rotation of secondary piston ~90 degrees
• Noticeable decrease in noise ~30 seconds after qualification levels 
applied
• Less dynamic response in strut assembly
Presenter
JaredDervan
Date
May15,2014
• Failure of forward lockwire and loosening of 
Forward Lug
• Structural failure of Secondary Piston through 
tooling hole
• Indications of fatigue on opposite tooling hole
• Crack identified as fatigue failure at tooling 
hole
Post-Test Inspection
11
Forward Lug Lockwire Failure
Secondary Piston Failure
Y-axis Post-RV
Presenter
JaredDervan
Date
May15,2014
Post-Test Inspection
12
• External Wear
– Indications of contact at the end fittings and interfacing clevis
– Contact (rotational offset) observed during testing
Presenter
JaredDervan
Date
May15,2014
Fishbone
13
Definitions
Presenter
JaredDervan
Date
May15,2014
Failure Scenario Summary
14
1. Rotational misalignment cause contact at end fittings
2. Inertial forces due to strut C.G. offset result in off-axis contact force 
3. Induced force results in loosening torque
4. Torque exceeds resistive capability of joint
5. Lockwire breaks; rotation until C.G. offset aligns with applied force vector
6. Secondary piston tooling holes placed in maximum bending
7. Fatigue failure at secondary piston tooling hole
Contributors:
1.1.1 Forward Lug 
locking patch design
1.1.6 Joint 
characteristics
1.2.1 Fatigue at tooling 
holes
2.1 Incorrect/incomplete 
stress analysis
Credible:
1.1.3 C.G. offset 
exceeded strut capability
1.1.5 Spring effects
1.4 End fitting rotational 
offset
2.2 Incorrect/Incomplete 
fatigue analysis
3.4 Incorrect test 
constraints
Rotational Misalignment (Aft Cap)
Presenter
JaredDervan
Date
May15,2014
 Due to resource constraints, LM implemented 
corrective actions addressing proximate cause
 NESC continued root cause investigation
 LM 2nd Development Test
 Corrective Actions: larger locking patches; larger 
diameter lockwire and quantity; increase in joint 
preload
 Select parts reused from previous test
 Fatigue failure due to life exceedance on Forward 
Lug
 LM 3rd Development Test
 Corrective Actions: integral forward end fitting; aft 
assembly locking patch removed and joint 
adhesively bonded
 Select parts reused from previous test with 
supporting fatigue life analysis
 Y-axis qualification test completed successfully
15
2nd Development Test: Forward Lug 
Fatigue Failure
LM-led Development Testing
Presenter
JaredDervan
Date
May15,2014
Care must be taken in adapting heritage designs 
to new applications.
• Actuator design adapted from another mission
• Obsolete features were retained (forward interface)
Threaded aluminum parts should only be used in 
lightly loaded applications.
• Lower permissible preloads and severe cyclic loads promote 
self loosening
• Galling potential drives uncertainty in locking torque
Lessons Learned
16
1
2
Presenter
JaredDervan
Date
May15,2014
Avoid designs that have the potential to utilize 
fastener thread locking features to react applied or 
induced torque in the higher level assembly.
• Thread locking features resist self loosening
• Applied loads significant relative to capability
Ensure sufficient preloads are obtained to reduce 
the potential for joint loosening.
• Preload much lower than best practice (25% vs. ~70% of tensile 
yield strength)
• Preload primary means to prevent self loosening
Lessons Learned
17
3
4
Presenter
JaredDervan
Date
May15,2014
Conduct machining operations prior to surface 
treatments to reduce the potential for crack 
initiation.
• Machining after anodic coating application promotes crack 
initiation
• Reduction in fatigue life and bending endurance limits
Utilize dedicated tooling for locking patch process 
development.
• Reduces unnecessary cycling of threads (aluminum particularly 
sensitive)
Lessons Learned
18
5
6
Presenter
JaredDervan
Date
May15,2014
Utilize visual movement indicators for threaded 
joints.
• Torque stripping flags relative motion at joints
Conduct testing to determine the required limits on 
running torque for joint designs not conforming to 
available standards and specifications.
• Running torque and preload recommendations dependent on 
joint material and geometry
• Steel fastener recommendations not applicable
• Compliance in joint due to hollow geometry
Lessons Learned
19
7
8
Presenter
JaredDervan
Date
May15,2014
Perform a bounding fatigue analysis in all possible 
orientations on mechanism components that are 
subject to rotation.
• Off-nominal contact conditions
• Joint susceptible to rotation
• Tooling hole fatigue analyzed without worst-case considerations
Review requirements, references, and 
methodologies used in the analyses for design 
applicability.
• Bending not considered in joint separation
• Standards applicable to bolted joints and fasteners
Lessons Learned
20
9
10
Presenter
JaredDervan
Date
May15,2014
Assess the contribution of assumed 
secondary effects to analysis results, and 
perform an analysis and correlation study that 
reflects the major contributors.
• C.Goffsetfoundtoinducesubstantialloadsrelativetojointcapability
• Slidingfits,springbuckling,andassemblytolerancesdriverforC.G.
offset
• Offaxiscontactconditionatclevisesinducedlooseningtorque
Lessons Learned
21
11
Presenter
JaredDervan
Date
May15,2014
 NESC/LM spring strut development testing 
resulted in failure, highlighting design deficiencies
 Root cause investigation conducted and failure 
scenario identified
 Evidence to support failure scenario not definitive
 Demonstration of successful development test by LM 
reduces risk
 Strengthening rationale would require more resources 
with limited benefit to current Orion flight opportunity
 Lessons Learned identified and communicated
22
Summary
Presenter
JaredDervan
Date
May15,2014
 NASA Engineering and Safety Center (NESC)
 Lockheed Martin Space Systems Company
23
Special Thanks
Assessment Team Members and Support
Arthur Brown (NASA MSFC)
Damon Delap (NASA GRC)
Alison Dinsel (NASA JSC)
Michael Dube (NESC/LaRC)
Tina Dunn-Pittman (NESC/LaRC)
Steven Gentz (NESC/MSFC)
Ryan Gordon (LMSSC)
Tom Irvine (Dynamic Concepts, Inc.)
Brent Knight (NASA MSFC)
Ryan Pfeiffer (LMSSC)
Ivatury Raju (NESC/LaRC)
Kyong Song (NASA LaRC)
Philip White (NASA MSFC)
Christina Williams (NESC/LaRC)
Presenter
JaredDervan
Date
May15,2014
24
Development Testing and 
Subsequent Failure of a Spring 
Strut Mechanism
Jared Dervan (NASA MSFC)
Brandan Robertson (NASA JSC)
Lucas Staab (NASA GRC)
Michael Culberson (LMSSC)
Joseph Pellicciotti (NASA GSFC)
42nd Aerospace Mechanisms Symposium
25
Presenter
JaredDervan
Date
May15,2014
Fishbone Element Classification
26
• Definitions
• Most Probable Cause: single event or element that resulted in failure; 
supported by conclusive evidence with allowance for minimal 
reinterpretation
• Contributor: event or element that, when combined with other 
elements, resulted in the failure; evidence, quantitative or qualitative, 
must be conclusive with allowance for minimum reinterpretation
• Credible: event or element that may have contributed to the failure; 
conclusive evidence is not available or multiple interpretations exist 
such that event or element cannot be considered to satisfy the 
definition of ‘Contributor’
• Credible, But Unlikely: event or element that has a potential to 
contribute to the failure; available evidence, while not conclusive, 
suggests event or element’s potential for contribution is unlikely
• Not Credible: event or element, supported by conclusive evidence, 
that did not contribute to failure
Presenter
JaredDervan
Date
May15,2014
Findings Technical Limitations
27
• Unabletoproveexceedanceoftorqueresistivecapabilitywith
linearFEM(onlyspreadsheetcalculations)
• Nophotographicevidenceavailableshowingmisalignmentof
ForwardLugpriortoYaxistest
• ForwardLugweartoindicatelooseninglessevident
• Insufficientinformationonasbuiltassemblyprocess
• Unverifiedlockwiretorquecapability
• C.G.offsetofassemblyunavailable
• Unverifiedspringstatictorquecontribution
Presenter
JaredDervan
Date
May15,2014
 Incorporate non-linear effects (e.g., contact 
conditions) and C.G. offset into FEM to 
measure induced torque at joint interfaces
 C.G. measurement of assembly and additional 
piece parts (Secondary Piston, Spring)
 Lockwire torque test 
 Use empirical methods to sanity check 
environments
 Static compression spring torsion induced 
torque test
28
Activities to Address Technical 
Limitations
Presenter
JaredDervan
Date
May15,2014
Performance Testing
29
• Ensures adequate force margin exists 
after being subjected to qualification 
levels
• Pre-random vibration
• Both ends of strut attached to Instron
through clevis
• ‘Slow’ performance test measuring force 
vs. displacement; data compared to 
analytical prediction
• Wear-in testing performed at deployment 
velocity; 15 cycles
• Post-random vibration
• Secondary piston truncated aft of 1st
development test failure location
• Cupping interface to Instron at 
secondary piston
• Performance test conducted at two 
speeds (slow and deployment)
• Pre- and post-vibration data compared
Pre-RV Post-RV
Presenter
JaredDervan
Date
May15,2014
Performance Testing
30
Nominal
engagement of 
anti-back travel 
latches
Results yielded 
acceptable force 
margin
Presenter
JaredDervan
Date
May15,2014
Assessment Timeline
31
• NESCfundedthefabricationatMSFCofflightlikespringstrutpartsusing
LockheedMartin(LM)drawings
• LMassembledthespringstrutandconfiguredtoflightlengthwithhelpofLM
RetentionTool
• Pre andpostrandomvibrationperformancetestingperformedatLM
MaterialsTechnologyLaboratory(MTL)(PreRV:07/25/2012;PostRV:
08/24/2012)
• RandomvibrationtestingperformedatLMAcousticsVibrationLaboratory
(AVL)(08/1516/2012,08/2021/2012)
• FatiguefailureofSecondaryPistonatYaxisqualificationlevels
• Rootcauseinvestigationinitiated(08/21/2012)
• LMassumedownershipofdevelopmenttestprogramimplementingcorrective
actions
• 2nd DevelopmentTest(fatiguefailure,unrelatedtofirsttest)– (11/28/12)
• 3rd DevelopmentTest(success)– (02/14/13)
• NESCrootcauseinvestigationcompleted(~02/26/13)
• Finalreportcompleted(11/07/13)
Presenter
JaredDervan
Date
May15,2014
Post-Test Inspection
32
• Internal Wear & Particulate Formation
– Borescope inspection between random vibration test axes (insertion through tooling 
hole)
– Larger particulate accumulated at Aft Cap; powder observed throughout 
– Observed existing tooling holes, latch holes, and Forward Cap-to-Secondary 
Piston interface during testing
– Powder most noticeable internal to Secondary Piston


Development Testing and Subsequent Failure Investigation of a Spring Strut Mechanism

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server