ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Results  Deflections   Table 1 shows the deflection of each part in the linkage from the initial iteration of ADAMS simulation. These deflections are used to compute the stress in each linkage member to classify it as either elastic or  plastic deformation. 

Table 1. Deflections in the DDM for 25.4 mm (1 in) at Door Edge  Location Part (mm) Location Part (deg) Follower 1 5.67E-02 Follower 1 1.63E+00 Rod 1 -3.05E-02 Crank 1 3.09E-01 Rod 2 5.74E-02 Crank 2 -2.54E-01 Door Rod -1.74E-01 Follower 1 1.38E+00Follower 1 4.80E-02 Crank 1 2.59E-01 Rod 1 -2.57E-02 Crank 2 -4.76E-01 Rod 2 1.08E-01 Actuator Crank -2.00E-01 Door Rod -1.48E-01 Actuator Follower 3.15E-01 Actuator Actuator Rod -2.23E-01 Torque Tube Tube -2.64E-01 (positive = tension, negative = compression) (positive = fore [right hand rule])Aft Hinge Fore Hinge ActuatorFore HingeAft HingeLinear Deflections Angular Deflections

Convergence of Equivalent Stiffness   Using the previously outlined process, stress ratios were calculated at iteration 0 and compared to the  predicted stress ratio, calculated as a stiffness ratio. To find this stiffness ratio, the manually calculated  approximate stiffness was used in place of k ds, and a stiffness found directly from a finite element model  (by applying a representative load of 4448 N (1000 lbf) and extracting the displacement) was used in  place of k f. These values are shown in the columns marked “K ratio [0]” in Table 2 and Table 3. Stress  ratio values after one iteration, which should approa ch 1, are shown in the columns marked “/g305 ratio [1]”. 

Table 2. Convergence of Stress Ratios, Links Axially Loaded   Location Part K ratio[0] /g305 ratio[0] /g305 ratio[1] Follower 1 1.016 1.011 Rod 1 0.619 0.636 1.004Rod 2 0.829 0.835 0.997 Door Rod 0.829 0.832 1.009 Follower 1 1.065 1.013 Rod 1 0.619 0.632 1.002 Rod 2 0.829 0.833 0.994 Door Rod 0.829 0.831 1.001 Actuator Rod 1.271 0.996Aft Hinge Fore Hinge

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Table 3. Convergence of Stress Ratios, Links Loaded in Bending   Location Part K ratio[0] /g305 ratio[0] /g305 ratio[1] Follower 1 1.701 1.806 1.061 Crank 1 1.418 1.650 0.999 Crank 2 1.491 1.624 1.005Follower 1 1.701 1.793 1.062 Crank 1 1.418 1.660 1.000 Crank 2 1.491 1.630 1.007Crank 1.577 1.585 1.010 Followe r 1.549 1.415 1.062Aft Hinge Fore Hinge Actuator

Using these results, equivalent stiffnesses can be evaluated for convergence based on stress ratios. If  the stress ratio is equal to 1 then the stiffness values used in ADAMS are equal to the equivalent stiffness  of the part’s finite element model. Therefore, a stress ratio error can be computed by subtracting 1 from  all ratio values. As this stress ratio error approaches zero, the actual ratio will approach 1. Figure 7 and  Figure 8 show the initial stress ratio error values at iteration 0, and the updated stress ratio error values after one iteration. Note that error values greater than 0 signify a part whose stiffness will be increased in  the next iteration, while error values less than zero signify a part whose stiffness will be decreased in the  next iteration.   Linear Springs, Stress Ratio Error -1-0.8-0.6-0.4-0.200.20.40.60.81 Follower 1 Rod 1 Rod 2 Door Rod Follower 1 Rod 1 Rod 2 Door Rod Rod Aft Hinge Fore Hinge Actuator PartRatio Error (SR - 1)Iter 0 Iter 1

Figure 7. Stress Ratio in Parts Represented by Linear Springs 

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Torsional Springs, Stress Ratio Error -1-0.8-0.6-0.4-0.200.20.40.60.81 Follower 1 Crank 1 Crank 2 Follower 1 Crank 1 Crank 2 Crank Follower Aft Hinge Fore Hinge Actuator PartRatio Error (SR - 1)Iter 0 Iter 1

Figure 8. Stress Ratio in Parts Represented by Torsional Springs 

Stress Analysis   The stress results for each component after one iteration (used to find the “/g305 ratio[1]” values in Table 2  and Table 3) are shown below in Table 4 and Table 5. These values represent the predicted stress induced by a 25.4 mm (1 in) forced movement of the door’s outboard edge, with the DDM actuator crank  fixed. To calculate factor of safety (FS) values, an allowable stress of 703 MPa (102 ksi) was used based  on A286 stainless steel [4].   Table 4. Stress Results After 1 Iteration, Parts in Bending  Location Part Deflection (deg) M (N·m) F (N) FEA /g305 (MPa) FS FEA /g305 (MPa) FS Follower 1 1.85E+00 2.34E+04 1.01E+05 1.44E+03 0.49 1.36E+03 0.52 1.19E+03 0.59 1.12E+03 0.63 1.00E+03 0.70 9.93E+02 0.71 9.51E+02 0.74 8.96E+02 0.781.061 1.806 Crank 1 3.83E-01 2.27E+03 1.56E+04 5.12E+02 1.37 5.12E+02 1.37 0.999 1.650Crank 2 -3.15E-01 -2.38E+03 -2.45E+04 5.38E+02 1.31 5.36E+02 1.31 1.005 1.624Follower 1 1.52E+00 1.92E+04 8.32E+04 1.062 1.793 Crank 1 3.11E-01 1.84E+03 1.26E+04 4.16E+02 1.69 4.16E+02 1.69 1.000 1.660 Crank 2 -5.87E-01 -4.43E+03 -4.56E+04 1.007 1.630Crank -2.48E-01 -1.80E+03 -2.47E+04 6.52E+02 1.08 6.46E+02 1.09 1.010 1.585Follower 3.91E-01 2.71E+03 3.35E+04 1.062 1.415Actuator/g305 ratio[i] /g305 ratio[i-1] Aft HingeDisplacement LBC Force LBC Fore Hinge

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Failure of the Trailing Umbilical System Disconnect Actuator on the International Space Station  Adam Gilmore*, Chris Schmitt**, Laura Merritt*, and VJ Bolton** Abstract  In December of 2005, one of two trailing umbilical cables used on the International Space Station (ISS)  Mobile Transporter (MT) was inadvertently severed by an internal cutter system designed to free a  snagged cable or jammed reel while transporting hazardous payloads. The mechanism’s intended means  of actuation is electrical; however, troubleshooting revealed a mechanical actuation occurred. The  investigation of the failed component revealed several lessons learned in developing hardware  requirements, understanding and following the rationale behind the requirements throughout the design life cycle, understanding the impacts of gaps and tolerances in a mechanism, and the importance of  identifying critical steps during assembly.  Introduction  On December 16, 2005, a power switch on the ISS was tripped by a short circuit. Video of the MT and  Trailing Umbilical System (TUS) cable revealed the cable routed to Interface Umbilical Assembly (IUA) 2  on the nadir side of the MT had been inadvertently severed (see Figure 1). When the cable was severed  the live wire tips contacted metal causing a short, leading to a tripped power switch. Commanded actuation requires three independent power switch closures to the TUS Disconnect Actuator (TDA), and  telemetry analysis indicated no possible electrical cause. The only remaining cause of the severed cable  was a mechanical failure of the TDA.  A team was formed to evaluate the failure, understand the impact of operating the MT with a single TUS  cable in the near term, and implement the recovery plan based on an extensive failure investigation. This paper will describe the high level system, the lower level mechanism design and failure, the design and  assembly errors, along with the implemented changes, and current operating configuration. As the  investigation proceeded, it was clear that not only did the mechanism fail, but that the need for the  mechanism was outdated for the current ISS requirements.   Figure 1.  Severed TUS Cable on IUA 2  * NASA, Johnson Space Center, Houston, Texas  ** Boeing, Houston, Texas  Proceedings of the 39th Aerospace Mechanisms Symposium, NASA Marshall Space Flight Center, May 7-9, 2008  IUA 2  Nominal Cable  Location Severed Cable  259
Hardware Description  System Description The ISS MT moves along the Integrated Truss Segment rail, and in conjunction with the Mobile Base  System (MBS) and Space Station Remote Manipulator System (SSRMS), are used to transport payloads.  When the MT is latched down at a worksite, the Umbilical Mating Assembly (UMA) provides the  necessary power to the MBS and SSRMS. The MBS, SSRMS, and other payloads will now be generically referred to as the MT payloads. The TUS cable provides both power and data at any point along the truss  to the MT, but only data and video to payloads. Ther efore, the MT payload s do not receive power  between MT worksites. The capability to remotely free a stranded MT can be critical to the survivability of the payload and also provides a way to prevent a catastrophic hazard.   The TUS consists of two parallel cables, one on each side of the MT. Each cable in this redundant  system is on a retractable reel stored within the S0 truss segment (see Figure 2). The Interface Umbilical  Assembly (IUA) is the interaction point between the MT and the TUS. The MT also has two IUAs, one for each TUS cable. Contained within the IUA is the TDA which allows the crew or ground to remotely sever  the TUS cable and free the MT in the case of a TUS reel jam or failure during translation. The ability to  remotely cut the TUS cable was a feature added early in the ISS Program to prevent catastrophic hazards due to moving hazardous materials along the truss rails.  Figure 2.  MT Schematic  TUS Cable  TUS Reel Assembly Mobile Transporter  TUS Interface Umbilical Assembly  260
TDA Mechanism The TDA is a low shock, fast acting guillotine cable cutting mechanism. A cross section is shown in Figure  3, omitting the Release Plunger Compression Springs and the Restraining Wire that is wrapped around  the Split Spool 15 times. The Primary Compression Springs load the T-plunger, which drives the blade that cuts the TUS cable (not shown). There is a compression spring under the Release Plunger, which  pushes the Actuator Plunger into the Split Spool. The two halves of the Split Spool are held together with  a Restraining Wire and connected to a fuse wire at the end (not shown). The fuse wire holds the restraining wire in place.  Figure 3.  Actuation of the TUS Disconnect Actuator  TDA Actuation To actuate the mechanism, current is passed through the fuse wire, causing it to weaken and break under  load. The Restraining Wire is then free to uncoil; thus it quickly unwinds from the Split Spool (see Figure 4). With the Restraining Wire out of the load path, the spring under the Release Plunger pushes the  Actuator Plunger, splitting the two halves of the Split Spool apart as the Actuator Plunger moves upwards.  With the Release Plunger clear, the Retaining Pins are forced outward by the T-plunger. Without the Retaining Pins in the load path, the Primary Compression Springs are able to release their stored energy,  pushing the T-plunger through the assembly, and driving the cutting blade into the TUS cable. See the  actuation sequence in Figure 3.                                                 Figure 4.  TDA X-Rays  Primary  Compression  Springs T-PlungerRetaining  PinsRelease  PlungerActuator PlungerCover Housing Cutting DirectionFULLY LOCKEDPARTIAL ACTUATIONFULL ACTUATION Restraining  BoltSplit Spool Uncoiled Restraining Wire  Actuator Plunger has  moved upwards ActuatorPlunger Restraining Wire  Locked Actuated 261
Figure 5.  Gap Illustrations  This movement was confirmed on-orbit when the Restraining Bolt required higher than expected torque  during removal due to the load being applied to the bolt from the Release Plunger.  This was seen again  when the Restraining Bolt would not re-engage during failure troubleshooting years later, since the  Release Plunger had shifted and created interference. When the gap is closed, the TDA is placed into a partially actuated state that changes the load path within the mechanism. After the failed TDA was  returned to the ground, a CAD model was created using the as-flown component dimensions. This model  further illustrated the gap and clearly showed a discrepancy in the design assembly drawing.  Ground Investigation Upon return of the failed TDA, disassembly and non-destructive evaluations were performed. The first  was an x-ray of the TDA Housing and internal components to determine whether or not the Restraining  Wire and Fuse Wire were still intact. In addition, a detailed survey was performed of the exterior of the  TDA Housing and Cover. Since the TDA mechanism was actuated and disassembled from the IUA on-orbit, the T-plunger and spring dimensions and surfaces could also be inspected. The x-ray of the TDA  Housing clearly showed the Restraining Wire and Fuse Wire were still intact and did not cause the failure.  When the outer covering tape was removed from th e top portion of the TDA Cover, a non-uniform gap  nearly 1.02 mm (0.04 in) tall was found between the Cover and Housing, in dicating an assembly error.  This gap was also confirmed by a subsequent review of the x-ray. The markings on the removed tape were consistent with a gap that had been present from initial Cover installation.   Figure 6. Failed TDA External View (tape removed) & X-Ray TDA CAD Model Partially Actuated  (Restraining Bolt released, Release  Plunger shifted, gap closed) Modified TDA Assembly Drawing  (Modified to show gap) TDA Assembly Drawing  GapRestraining  Bolt ReleasePlunger ShiftActuator PlungerSplit Spool  Cover  Housing Cover  Housing As Assembled Gap   Cover   Housing  263
Upon inspection of the T-plunger, yielding was found where it contacted the Retaining Pins. Prior to  obtaining the failed TDA, a series of ground tests were performed to support the planned on-orbit repair  strategy. These tests included both a slow mechanical release of the Actuator Plunger and a near  instantaneous release of the Actuator Plunger. Mechanical actuation was achieved by slowly backing out the fasteners that hold the Cover and Split Spool to the Housing, thus allowing the Release Plunger to  shift and release the T-plunger. This test resulted in three findings that were significant to the failure  investigation: 1) The T-plunger release required significantly less travel than expected (~0.965 mm (0.038 in) actual vs. ~4.75 mm (0.187 in) expected), 2) The edge of the T-plunger notch was mechanically  yielded at the Release Pin interface, 3) The Split Spool was damaged at the Actuator Plunger interface.  Post flight inspection of the failed TDA T-plunger indicated similar notch yielding at the Retaining Pin interface. The travel required to mechanically actuate the TDA was similar to the gap that was seen  between the Cover and the Housing on the failed TDA. This indicates the TDA was very close to  actuating when the Restraining Bolt was first removed on-orbit.  Figure 7. T-Plungers Post Actuation  Electrically Actuated Mechanically Actuated On-orbit Failed TDA 264
The Split Spool and Restraining Wire were in spected via x-ray and visually after initial disassembly. The  Restraining Wire was intact and did not allow the Split Spool to separate. The Split Spool was then  separated by removing the Restraining Wire to allow a detailed inspection of the Split Spool halves. The  inspection revealed the Release Plunger had compressively yielded the interior of the Split Spool. This finding was consistent with the damage seen during the mechanically actuated ground test. This damage  is caused by an increased force transferred to the Actuator Plunger from the Primary Compression  Springs during a slow release actuation. As the Release Plunger travels upward the Primary Compression Springs force the Restraining Pins outward. This outward force is then transmitted to the  Release Plunger and subs equently to the Split Spool.  When the TDA is electrically actuated the Split  Spool is free to separate and thus does not compressively yield (see Figure 8).  Figure 8.  Split Spool Details  Review of our findings from the ground testing, analysis, disassembly, and inspection of the failed unit  revealed the failure was caused by a combination of the as-built gap, the gap created during assembly, and overstress of the T-plunger and Split Spool. The gaps caused by design tolerances and an assembly  error put the mechanism in a position that was near firing. This position put the T-plunger and Split Spool  in a loading configuration that was not consistent with the validated design and exceeded their structural capability. Test TDA Split Spool After  Electrical Actuation Failed TDA Split Spool 265
Implemented Repair  The ISS Program was tasked with developing a forward plan for the IUAs on-orbit and the remaining  spare on the ground while maintaining MT capability for continued assembly. Consideration was required for both controlling hazardous transportations as well as the loss of power to payloads in a stranded MT  case. The ISS Program no longer plans to transport hazardous cargo; and therefore, determined the TDA  and cutting capability is not presently necessary. There is still the open issue of losing critical payloads in  the MT stranded case, but that was being addressed by the ISS Program and not a requirement that the  repair team had to solve.  In the weeks after the TUS 2 cable sever, the team was concerned with the possibility of a second TDA  failure on IUA 1 leading to a TUS 1 cable sever. In early February 2006 during Russian Extravehicular  Activity (EVA) 15, the TUS 1 cable was routed outside of the TDA to prevent it from being cut until a long  term repair could be implemented. The configuration of the MT leading up to the removal of the failed  system was the TUS 1 cable was severed (IUA 1 failed) and the TUS 2 cable was routed outside of the TDA. The team prepared a repair to regain full MT redundancy in one Shuttle Flight, STS-121 (ISS  Mission ULF1.1), in July of 2006. One requirement was to fly a spare TUS Reel containing a fully intact  cable with connectors. In addition, the blade blocker (see Figure 9) was designed and tested on the ground to be installed EVA onto IUA 1 to prevent the TDA from cutting the cable in the case it too  mechanically failed. The repair allowed for IUA 1 to be fixed in place in one short EVA task.  Figure 9. Blade Blocker Details  BladeBolt 2 Bolt 1 Blade Blocker  Cut Away Showing Bolt 1  Engaged Blade Blocker Installed  266
When the propulsion change was made, the risk posed by a system failure should have been reexamined  more thoroughly. A near instant response method was no longer necessary, and slower acting  alternatives to the TDA could have become viable options. A detailed reexamination of requirements after  each major design change would screen for impacts such as this. A new trade study at that point may have changed the requirements for disconnection greatly. A different approach, like a quick disconnect,  could mitigate the destructive aspects of a cable disconnection and reduce the severity of an actuator  failure to the overall system.  Tolerances and Drawing Cross sections of the TDA assembly drawing show a close fit between the Split Spool and the Actuator  Plunger and a gap between the Restraining Bolt and Release Plunger. As-built assembly indicated a gap  at the Split Spool and a closed gap at the Restraining Bolt to Release Plunger interface, as seen in Figure  5, leaving the TDA partially actuated and changing the load path.  Creating a gap between the Actuator Plunger and the Split Spool allows a partial actuation of the TDA  when the Restraining Bolt is removed. The effect of creating that gap is movement of the Retaining Pins  along the slope of the T-plunger, as shown in Figure 10. When this loading condition is created, the high  force from the Primary Compression Springs is concentrated on a sig nificantly smaller area within the  TDA. The designed line contact reduces greatly as it approaches a point contact as shown in Figure 10.  Any yielding at that point exacerbates the problem and further actuates the TDA.  Figure 10. Change in Load Condition at Retaining Pin A detailed design study and resting state review considering the impacts of spring forces would point out  the possibility of these issues and their impact to loading within the mechanism. Defining critical  dimensions for Split Spool and Actuator Plunger heig ht to ensure the Restraining Pins would remain fully  seated could prevent a gap and the associated high loading condition.  T-Plunger has Moved Down  DesignedLine ContactPlanned Actual T-Plunger Contact Area Direction of Decreasing Contact Area Direction of Decreasing Contact Area  Actual Reduced Line Contact  268
Mandatory Inspection Point Selection During disassembly of the failed TDA, a significant 1.02 mm (0.04 in) gap was found between the Cover  and the Housing. This additional gap exacerbated the design gap at the interface, worsened the partial  actuation state, and increased the load concentration.  Cover installation drawings called out a torque requirement for the bolts used to attach the Cover, but did  not require any dimensional inspection or verification that the two parts were in solid contact. As a result, if the bolts reached their minimum installation torque before the parts were fully seated, a new gap could  be created between the Split Spool and the Actuator Plunger.  Adding a mandatory inspection of the gap between the Cover and the Housing would prevent creating a  gap from incomplete seating between the parts. Required inspection for both fastener torque and seating  should be considered whenever an interface is critical to the load path of your mechanism.  Heritage Design Disassembly of the Cover portion of the TDA assembly  revealed deformation and yielding of the Split  Spool (see Figure 11). Torlon Split Spools of this type had been used previously in switches for power  systems.   Figure 11. Split Spool Deformation In other applications, Torlon was highly desirable because of its electrical insulating properties. For the  TDA, electrical properties were irrelevant. Structure focused requirements for this portion of the TDA  would have weighted strength as far more important than electrical resistance. Torlon would not be as  robust as steel for this application. Since electrical resistance was irrelevant, a steel Split Spool would be a more desirable choice for a compressively loaded structural member.  Where mechanical and strength properties are the main requirement, they should be weighted more  heavily than flight history or other concerns. If the Split Spool was never overloaded, polymer selection  would not have been a problem. In this case, other issues led to structural members experiencing loads in excess of design loads and failed by yielding. Caution should be used whenever adapting heritage  designs that were developed for other applications.  Conclusions  Evidence indicates the TDA was in a partially actuated state from the moment it was activated on orbit,  thus fundamentally changing the load within the mechanism and creating an unforeseen failure mode.  This investigation discovered several is sues that should be mitigated in future designs: 1) Ensure that the  requirements driving your mechanism design are still valid and are properly weighted in trade studies. 2) Verify that the as built components of the assembly will produce a mechanism that will function as  intended both structurally and kinematically. 3) Inspect dimensions that control the kinematics and load  path of the mechanism, checking both torque and seating of assemblies. 4) Lastly, focus material selection requirements on each specific application and exercise caution when reusing heritage design. A  TDA with these issues corrected wo uld not experience the failure seen on-orbit.  269