ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Push Rod can be removed from the plunger subassembly without stressing or twisting the sensor leads.  The mechanism is reset by first removing the striker and Front Cap and then the Plunger subassembly is  removed from the housing and the core replaced.  During prototype cover deployment tests, several types of honeycomb were experimented with, for the  goal of reducing cover bounce-back and obtaining the cleanest cover capture. Aluminum core, 3/8-5052-  1 .O, foil thickness 0.01 8 mm (0.0007 in) and crush strength of 172 KPa (25 psi), trimmed to three cells  was found to work well, however the 50.8-mm (2-in) long samples available came close to bottoming out.  New core, 88.9-mm (3.5-in) long, was selected to allow for enough travel with margin (see following  paragraph for more detail). Deployment with this core proved to be the best and the cover bounce back  was limited to approximately 0.04 rad (2.5 deg) (the cover does not rebound off the striker; instead the  Plunger is pulled back to its limit stop). Because of the core’s long length compared to its cross-sectional  area, the core appears to initially buckle uniformly, then folds between the mid-section to base. Crush  tests were conducted with the core and the force required to continue crushing gradually dropped from  the initial buckling. This result corresponded well for this application as the impact force falls off  considerably after some energy is absorbed. See Figure 9 and Figure 10 for before and after cover  deployment images of 50.8-mm (2-in) and 88.9-mm (3.5-in) core respectively.  The kinetic energy of the deployed cover and energy to be absorbed is equal to that of the Hinge  mechanism compression spring’s potential energy at the cover closed position. The average crush load  multiplied by the crushed length gives the energy absorbed, and thus, with some extra length for margin,  defined the length of required core.’ Figure 11 is Hexcel’s honeycomb crush strength curve, which  illustrates the peak load, average crush load, and the energy absorbed. Core used in the Energy  Absorbers were pre-crushed slightly to remove the peak force spike. Crush test data from the three-cell,  88.9-mm (3.5-in) long core is presented in Figure 12.  Housing  Endcap 7  Figure 7. Energy Absorber exploded view  69
Peak Lead  crush load  bsd eMnat.d by precnuhing  Bottomed * I  I  I  I  I  I  I  I 1 out 8 mn.  Area under curve I  energy absorbed  Deflection  Figure 11. Hexcel Honeycomb crush strength curve’  318-5052-,0007, 3 Cell, 3.5in Samples  Displacement vs Force  Sample  -1  -5  Displacement [in]  Figure 12. Force / Displacement graph for 3-cell, 88.9-mm (3.5-in) core  71
Heritage Adoption Lessons Learned  Sufficient review of a heritage design is necessary before adoption as heritage designs may impose  unnecessary limitations, constraints, or failure modes on interacting mechanisms or systems. Additionally,  a flight readiness review of a heritage design is necessary, as it can not be assumed that all necessary  information regarding the design, such as as-built drawings, assembly instructions, test procedures and  test data, are available. Of particular interest are the GALEX heritage adoption lessons learned during the  CDLM technology development.  GALEX cover deploy mechanism was obviously built to a redlined set of drawings; however, these  drawings were not available during this task. As GALEX was an aggressively “faster, better, cheaper”  mission, it is thought that resources were not available to complete the drawing package. Much of any  schedule savings in using the heritage design was exhausted going through more than 70 drawings to  look for, and correct, interference, material, and lubrication issues. Some issues were found only after  fabrication and assembly, necessitating the rework or re-fabrication of built parts. Accurate build and  assembly histories are required to adopt heritage designs.  Very limited test data, such as cover deployment time and cover impact force, was available from GALEX.  The lack of test data necessitated the building of a schedule intensive deployment test fixture and  mockup cover and duplicating cover deployment tests. Fortunately, a spare Latch mechanism and an  engineering model Hinge mechanism were available for testing. An image of the deployment fixture is  shown in Figure 13.  Mockup  cover  Early adoption of the Hinge mechanism restricted the design of the crushable honeycomb Energy  Absorbers. Not until the deployment test fixture and prototype energy absorbers were built and tests run  did it become apparent that the cover impact force was much lower than expected. If the honeycomb  crush strength was too high, the cover would bounce off the Energy Absorbers as the impact force  dropped off during impact. Conversely, the honeycomb had to be strong enough to resist the Plunger  subassembly inertial loads during vibration. It was found during testing that the impact force necessary to  sustain honeycomb crushing, and to effectively keep the cover from rebounding, required the Hinge  torque output to be increased (by the use of larger springs). By increasing the un-dampened Hinge torque  output, the amount of kinetic energy to absorb was also increased. This was further complicated by  adopting the same GALEX composite cover thickness, even though the cover grew substantially in size.  An alternative design, with a stiffer cover, could have placed the crushable honeycomb on brackets close  to the hinge axis where the impact forces would be higher, allowing for a more stable and compact  72
Conclusion  Heritage designs offer projects an attractive means of reducing cost and schedule. However, without a  through review and investigation of the state of readiness, a heritage design may impose unnecessary  limitations and restrictions, in addition to cost and schedule impacts. It is recommended that trade studies  be completed of designs similar in function to that of the proposed heritage design prior to adoption. Only  then, potential shortcomings of the heritage design may become apparent.  Before adopting a heritage design:  Perform trade studies of designs similar in function to that of the heritage hardware. Look for best  solution.  Thoroughly review heritage drawing package for completeness  Verify the heritage design will meet project requirements  Review heritage test data and test plans and verify they meet current projects requirements. If  they do not, study impact and feasibility of revised testing.  Review heritage design for failure modes. It can not be assumed that all modes were found, or  that new modes will not be introduced.  Perform all prototype testing with as flight-like hardware configurations as possible  Acknowledgements  The research described in this paper was performed by the Jet Propulsion Laboratory, California Institute  of Technology, under contract with the National Aeronautics and Space Administration.  The author gratefully acknowledges the contributions of JPL team members: Mark Baker, Kevin Burke,  Keith English, Ted Iskenderian, Mike Johnson, Ellyn McCoy, Doug Packard, Don Sevilla, and Brad  Swenson.  References  1. “HexWeb Honeycomb Energy Absorption Systems, Design Data”, Hexcel Corporation, March 2005.  74
Problems and Product Improvements in a Qualified, Flight Heritage Product  Chuck Lazansky’ and Scott Christiansen*  Abstract  This paper will discuss improvements to an existing, qualified, flight heritage launch restraint and release  mechanism. The changes made to the design are the result of customer feedback, test failures, and  optimization of performance margins. Specific test failures and their resolutions will be discussed. Impacts  to field units, process controls, product heritage, and qualification status will be summarized. Conclusions  and lessons learned will include aspects of what “qualified product” means and insights around what is  required to improve a product based on lessons learned through production and customer use.  Introduction  A Launch restrainthelease device must meet a demanding set of requirements to be reliable and robust.  Most importantly, the device must never release prior to command (during ground handling,  transportation, launch, etc.) and must always release when properly commanded. A combination of  redundancy and robust design features are typically used in pursuit of meeting these demanding  requirements. The QWKNUT has been designed with these goals in mind, and has been shown through  qualification and flight use to meet these requirements.  Figure 1. Gen 1 QWKNUT Mechanism  Product Description  The QWKNUT is a device which utilizes a segmented nut to maintain and release an axial preload. The  device accepts a standard, hardened, %-28 bolt to carry the nominal 13345-N (3000-lbf) load. Preload is  released when the four nut segments are opened by activating the mechanism. Release of the device is  initiated by a redundant pair of shape-memory alloy (SMA) wires within the QWKNUT, which are linked  directly to the latch. The QWKNUT requires an electrical pulse (3-5 Amps, -10-75 msec) similar to that  used for pyrotechnic release devices. The pulse causes resistive heating of the SMA wire above its  transition temperature, resulting in a strain of the wire and release of the latch.  Functionally, the mechanism can be separated into two parts: the preload-bearing part, and the latch-  release part. The preload-bearing part consists of four nut segments (Figure 3). Axial load from the bolt  exerts a radial load on these nut segments, which are retained radially by a set of rollers and a bearing  outer race. This outer race has slots which correspond to each roller, such that rotation of the race allows  the rollers to drop into these slots, allowing the nut segments to open and release the bolt. The outer race  is preloaded with redundant coil springs acting to rotate the race and release the device.  Starsys Research Corporation, Boulder, CO  Proceedings of the 3d’ Aerospace Mechanisms Symposium, Langley Research Center, May 17- 19,2006  75
The outer race is prevented from turning by two latch pawls (called “toggles”) that engage the OD of the  race. The latch-release paH of the mechanism consists of a lever-arm which reacts the radial load from  the toggles, and retains them in the outer race (Figure 2). Nominally, the lever arm is held against a stop  feature, in the latched position, by a retention spring. The lever arm is acted on directly by the SMA wire,  which upon activation rotates the lever arm and frees the toggles, causing release of the mechanism.  REDUNDANT COMPRESSIMJ  SPRINGS =ATE TCRQUE  TO ROTATE OUTER RAE  ROTATES OUTER RACE  LATCHED RELEASED  Figure 2. Latch-Release Section Detail  OUTER RACE  ROLLERS DROP  INTO NOTCHES  NUT SEGMENTS ARE  SEGMENTED NUT FREE TI7 OPEN  LATCHED RELEASED  Figure 3. Preload-Bearing Section Detail  A key feature of the QWKNUT is that it is fully resettable. The reset procedure entails using a small tool to  rotate the outer race back towards its latched position. The reset process is the exact reverse of the  release sequence. Once the outer race is rotated, the rollers move radially inward closing the nut  segments. The toggles then re-engage the outer race, and the lever arm, which is spring loaded, moves  over both toggles to latch the mechanism. The straightforward reset process and multiple use capability is  an attractive feature in a release device, allowing a “test as you fly” approach to ground verification. For  additional ease of ground use, the original version of the QWKNUT contains cutoff switches, which  discontinue power to the SMA circuits once release occurs. The switches are not rated for Flight use, and  additional lead wires are included which bypass the cutoff switches for Flight.  76
showed relatively low inertial forces on the lever, which could not overcome the lever retention spring and  drive the lever in the direction of release.  Tests were developed to assess latch performance. The lever retention spring force was measured, and  also the net force required to release the lever arm from the toggles (force-to-release, or FTR). The  results of the testing were that some units showed low lever spring force (up to 50% below nominal), and  this was strongly correlated to vibration failure at 35 Grms. All units which failed in vibration showed  spring force below nominal values. The low spring force was traced to yielding of the spring caused by  installation damage, as well as overstress during manual releases. Though low spring retention force was  strongly correlated to vibration failure, it did not explain the physical cause of the lever motion under  vibration.  The true root cause was elusive. Driven in part by the need to resume production, the vibration  performance was initially addressed by increasing latch retention spring force. This was accomplished  with the addition of a second retention spring. The dual-spring design provided strong margin for load-  holding under vibration, and was not vulnerable to handling damage. Validation testing of the proposed  change supported the assertion that release margins and vibration margins were better balanced with the  second spring, and that cycle life was not impacted. A formal Delta-Qualification test program of the new  configuration was planned in parallel with production. The latch performance tests were also added to the  production process as additional screens. However, when production resumed, the in-process testing  showed inconsistent results for FTR screening. There was variability within a single mechanism that could  not be explained. Production was stopped, and the investigation resumed with the focus on the dry-film  lubrication layer at the latch interface. The lubrication was to be removed from the lever of a production  unit to determine the source of the inconsistent FTR measurements.  Drive springs (2X) provide bias  torque for Flywheel  ! ! !  ! !  ! !  ! ! !  i  Section through latch area of QWKNUT “%._. ,,...- During launch Lever  :’ Spring preloads Lever On orbit SMA wire  pulls Lever Arm off  Lever Arm creates  &/;&n force n Toggle of is Lever  perpe dicular to the Lever  Toggle Pivot  reacts torque  to the Body t  Figure 4. Latch-Toggle Section Detail  Failure Mechanism  The physical cause of the failure was discovered when lubrication was removed from the critical latch  surface on the lever. The shape of the surface did not meet the intent of the design. The curved surfaces  contained “flat” areas approximately 0.76 mm (0.030 in) in width, at each end (Figure 5). These flats were  not easily seen with the dry-film lubrication present. The presence of the flats immediately explained the  78
;MA Wire Fc  EL== 3  Figure 7. QWKNUT in Partially Released State  Failure Mechanism  The tilted lever arm in the failed unit had been stroked about 1.78 mm (0.070 in) from its stop. Previous  testing had shown that only 1.02 mm (0.040 in) of lever travel will release the mechanism. It was  determined that the addition of the second spring changed the force balance on the lever arm during  actuation. The result was the observed tilting motion of the lever during release, which extended the  nominal latch release point from 1.02 mm (0.040 in) to over 1.78 mm (0.070 in). Figure 8 shows how  forces acting on the lever, including the added spring force, contribute to the anomalous tilting motion.  The extended release point is only part of the failure mechanism.  The SMA wire stroke expected from analysis and early development tests was 2.29 mm (0.090 in). It was  unclear why the unit had not released even with the extended release point. This led us to measure  actual SMA wire strokes for the entire lot using high-speed video. Measurement of the 7 units in the failed  lot showed a mean stroke of 1.85 mm (0.073 in) and a variation of k0.305 mm (0.01 2 in), well below the  expected 2.29 mm (0.090 in). The unit which failed had the lowest recorded stroke in the lot (1.55 mm, or  0.061 in). If the failed unit had the expected SMA stroke it would have released, but the stroke was not  available. The extended release point in combination with reduced SMA wire stroke produced the failure.  Both are required for a partial release to occur. This failure is essentially one of low performance margins.  The stroke margin on the failed unit was less than zero.  In addition, the partial release behavior was only displayed when the mechanism was under preload.  However, the process screenings were all performed with no applied preload, and the anomaly was not  detected until test. All units in the failed lot displayed the partial release behavior during screening once  preload was applied. In addition, the forces required to release the latch increased significantly with the  presence of preload. A majority of units in the lot showed unacceptably low actuation force margin.  The described anomaly was present only on units with the dual return springs. Single spring units were  not affected. Fortunately, though we did not have the margins we expected in the dual-spring design,  acceptable margins were confirmed in the single spring units. This limited the scope of affected units in  the field.  81
-1 SMA Wire FO - I- -  Figure 8. Forces Acting on Lever Arm  Root Cause  The change to the dual spring design created an anomalous lever motion during release. The tilting  motion that was introduced to the lever required significantly more stroke from the SMA wire than the  single spring design. The motion of the lever arm was not properly constrained in the design, but until the  second spring was added, there was no impact to performance. The tolerances in the latch assembly  allowed for the anomalous tilting motion, and this was a root cause of the failure.  The other root cause was variability in the manufacturing process. SMA wire stroke was found to be  lower, and more variable, than expected by previous test results and analysis. Wire stroke measurement  was not part of the manufacturing process for the QWKNUT. There was inherent process variability that  had not been characterized. The wire setting process had also drifted with ongoing production lots and  different operators since its development. Without in-process measurement of stroke, the drift was not  detected.  Finally, a contributing cause was that the in-process latch screening tests were not performed under load.  An assumption was made that load bearing part of the mechanism performed independently of the latch  portion, which was not correct. Preloading the mechanism for the screening tests takes more time, and  adds cycles, but it is necessary. In designing screening tests, care must be taken to ensure the tests  accurately represent true operating conditions.  Corrective Actions  Corrective actions for the Release Anomaly were:  1.  2.  3. A stabilizing washer was added to control lever arm release motion and eliminate "tilt" and the  partially released state.  The SMA wire setting process was improved to increase the mean stroke and reduce variation  (was reduced by 30%). Actual SMA wire stroke was to be measured on each unit.  New process controls were added to measure latch release point and SMA wire stroke, and  determine actual performance margins present in each flight unit. Existing process controls were  now to be performed with the mechanism under nominal preload, which better reflects true  operating conditions.  82
pins”) on the main drive element broke. The life test is a 200 cycle test, to support a 100 cycle life rating  for the device. The failure occurred at a thread relief on the pins in both units. The fracture surface  displayed characteristic signs of a low-cycle fatigue failure. This type of failure had not been seen before  in previous life tests.  r 4  Figure 9. Flywheel Pins in QWKNUT  Failure Mechanism  The flywheel pins in the QWKNUT transmit force from the main drive springs to the outer race (or  “flywheel”). They also serve to limit travel of the outer race following release,-andare subject to an impact  load with each cycle (Figure 9). The initial investigation steps were to measure the corner radii and  estimate the total number of impact cycles seen by the pins. Sample pins taken from the failed lot showed  that the corner radius at the point of failure was undersized, and measured between 0.000 and 0.051 mm  (.OOO and .002 in). The pin drawing controlled the corner radius only by block tolerance to a minimum of  0.076 mm (0.003 in), and the parts were therefore discrepant per the drawing.  When the number of cycles on the failed units was counted, we found they had over 450 documented  releases, and an indeterminate number of un-documented manual releases. This inordinately large  number of cycles was due to all the activities from the previous two investigations. This included in-  process checks, multiple rebuilds and confidence tests, and finally, the qualification cycles. When number  of impact cycles and the undersized radius were considered in a fatigue analysis, the failure should have  been expected. The physical cause of the failure was a classic combination of stress concentration and  cyclic loading.  A total of 5 lots of flywheel pins were procured since product inception, and only the most recent lot had a  corner radius below the block tolerance of .076 mm (.003 in). Analysis showed that yith a radius of > .089  mm (.0035 in), the mechanisms would have a predicted cycle life of at least 10 , which confined the  hardware affected by the failure to the current lot.  Spring Force (-14 lbf) (62 N)  Impact Reaction  at PEEKBody - Flange bent ”up”, here  Failure initiation at  thread relief  Figure 10. Force Balance on Flywheel Pin  84