ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Torque Tension Testing of Fast eners used for NASA Flight   Hardware Applications Ed Hemminger*, Alan Posey* and Michael Dube*  Abstract The effect of various lubricants and other compounds on fastener torque-tension relationships is  evaluated. Testing was performed using a uni que test apparatus  developed by Po sey at the NASA  Goddard Space Flight Center. A description of the test methodology, including associated data collection and analysis will be presented. Test results for 300 series CRES and A286 heat resistant fasteners, torqued into various types of inserts will be presented. The primary objective of this testing was to obtain torque-tension data for use on NASA flight projects.   Introduction Threaded fasteners are used extensively in flight hardware assembly at the Goddard Space Flight  Center. The reliability and safety of the assembly is dependent primarily on the preload which is applied  by trained and certified technicians using a calibrated torque wrench of the proper size. It has been  shown that most of the applied torque is used in overcoming the head bearing and thread friction leaving only a small fraction for fastener elongation or tension resulting in joint pre-load application. The torque tension relationship is therefore highly dependent on the friction coefficients and lubrication applied to the threads and washer-to-bolt head bearing surfaces. Even the most reliable torque application methods  have been shown to result in wide scatter and do not accurately predict the joint preload. This can result in premature joint or fastener failure due to over or under estimation of the applied preload. Typical failure  mechanisms are vibration loosening, fastener fatigue due to insufficient preload, or joint failure due to  excessive preload. Alan Posey has developed a new bolt preload measurement system which incorporates three miniature  load cells and an instrumented torque wrench for measurement of applied torque and joint preload (see Figures 1 and 2).  Figure 1. Bolt Preload Test Fixture & Test Plate *NASA Goddard Space Flight Center, Greenbelt, MD /g51/g85/g82/g70/g72/g72/g71/g76/g81/g74/g86/g3/g82/g73/g3/g87/g75/g72/g3/g23/g21/g81/g71/g3/g36/g72/g85/g82/g86/g83/g68/g70/g72/g3/g48/g72/g70/g75/g68/g81/g76/g86/g80/g86/g3/g54/g92/g80/g83/g82/g86/g76/g88/g80/g15/g3/g49/g36/g54/g36/g3/g42/g82/g71/g71/g68/g85 /g71/g3/g54/g83/g68/g70/g72/g3/g41/g79/g76/g74/g75/g87/g3/g38/g72/g81/g87/g72/g85/g15/g3/g48/g68/g92/g3/g20/g23/g16/g20/g25/g15/g3/g21/g19/g20/g23/g3 Test Plate with  Keenserts®Test Fixture 231
Figure 2. Bolt Preload Measurement System In the past, one load washer was typically used for torque tension testing but this was not practical for the  smaller #0 (1.5-mm) to #6 (3.5-mm) size fasteners as load washers this size were not available. The  system consists of three load cells mounted in a high-strength steel fixture plate in an equilateral triangle  configuration. A counter-bored bushing, sized for the fastener being tested, is centered in this triangular  pattern. The system is connected to a laptop computer with LabVIEW and MATLAB software for data  collection and analysis (Figure 3). Fasteners from size #0 (1.5-mm) to ¼-in (6.3-mm) diameter have been  tested using this system. Figure 3. Bolt Analyzer Interface 232
Test Objectives The primary objective was to obtain torque-tension data for use of various lubricants such as Braycote  601EF and compounds such as Arathane and Super Koropon. Arathane has been used as a thread locking compound to replace worn out locking features on helical-wire inserts and Super Koropon is used  as a corrosion inhibitor/sealer on threaded fasteners and inserts as specified in NASA/JSC PRC-4004,  “/g54/g72/g68/g79/g76/g81/g74/g3/g82/g73/g3/g45/g82/g76/g81/g87/g86/g3/g68/g81/g71/g3/g41/g68/g92/g76/g81/g74/g3/g54/g88/g85/g73/g68/g70/g72/g86/g180 . Some secondary objectives of this testing were to identify the  effect of the following variables on torque coefficient (or nut factor) and running torque:  /g120Multiple cycling of locking inserts.  /g120Fastener and washer replacement in multiple cycling of inserts. /g120The use of multiple lot and or multiple type inserts of a given size.  /g120The use of ultrasonic cleaning in isopropyl alcohol (IPA) of all hardware as compared to use in as  received, un-cleaned condition.  Small Fastener Testing (#2, #4 & #6) (2.2 mm, 2.8 mm & 3.5 mm) Torque-tension testing of A286 and 300-series CRES fasteners threaded into free running phosphor  bronze and silver-plated CRES helical-wire inserts was performed using the system developed by Posey.  Fastener testing was performed both with a low outgassing flight-approved lubricant (Braycote 601EF) and dry insertion.   Torque-tension measurements were taken up to 65% of the fastener yield strength which represents the  standard preload currently used at Goddard. Both torque and preload were measured at five equally spaced increments up to the target preload. All hardware was ultrasonically cleaned and handled with  gloves using flight hardware processes. Each fastener tested was torque cycled three times while each insert was cycled six times. After three  torque cycles into a given insert, the fasteners and washers were replaced with new hardware and relubricated. Separate test plates were used for dry and Braycote lubricated samples. Lubrication was  applied to the threads and under the fastener head. The fasteners were torqued at a rate of  approximately 6 rpm until the target preload was reached. The data tables and plots below provide a summary of the statistics for the torque coefficient (K) for fasteners installed both lubricated and dry into two different types of helical-wire inserts (Silver-Plated CRES and Phosphor Bronze). The standard  deviation of the torque coefficient was calculated for each grouping and also combined for all groups. The B-Basis tolerance limit factors of Kmax and Kmin were also calculated based on the sample size and are given in the tables below. Running torque was included in all measured torque values. Small Fastener Test Results and Conclusions  Table 1 and Figures 4 and 5 provide a summary of the statistics for the torque coefficient (K) for each of  the types of fasteners into the different types of inserts (Silver-Plated CRES and Phosphor Bronze).  233
Figure 4. Unlubricated Cyclic M ean Torque Coefficients Example Figure 5. Lubricated Cyclic Mean Torque Coefficients Example  0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.450  1 2 3 4 5 6 TORQUE COEFFICIENT 

TORQUE CYCLES Mean Torque Coefficients  for Ag/Cres & Ph/Bz  #4-40 (2.8 mm) Locking Helicoils, IPA Cleaned, Un-lubricated Combined  Mean Torque  Coeff Ag/Cres Mean  Torque Coeff Ph/Bro Mean Torque Coeff 0.000 0.050 0.100 0.150 0.200 0.250  1 2 3 4 5 6 TORQUE COEFFICIENT 

TORQUE CYCLES Mean Torque Coefficients vs Cycles for Ag/Cres & Ph/Bz #4-40 (2.8 mm) Locking Helico ils IPA Cleaned & Lubricated Combined  Mean Torque  Coeff Ag/Cres  Mean Torque  Coeff Ph/Bro Mean  Torque Coeff 234
Table 1. Phosphor Bronze Data Summary Phosphor Bronze Inserts FastenerWet Lubrication DryMean Torque  Coefficient K STD Dev No. Samples Tolerance Limit  Factor B-Basis Limits  K-Low B-Basis Limits    K-High Mean Torque  Coefficient K STD Dev No. Samples Tolerance Limit  Factor B-Basis Limits  K-min B-Basis Limits    K-max A286 0.169 0.024 48 1.654 0.129 0.210 0.373 0.084 46 1.664 0.233 0.513 300 CRES 0.174 0.022 36 1.725 0.136 0.211 0.339 0.028 36 1.725 0.290 0.387 NAS1352N   A2860.182 0.032 18 1.974 0.119 0.244 0.401 0.102 17 2.002 0.198 0.605 NAS1101   A2860.167 0.016 18 1.974 0.135 0.198 0.375 0.071 18 1.974 0.236 0.514 NAS8100/1   A2860.154 0.017 12 2.21 0.117 0.192 0.326 0.056 11 2.275 0.199 0.453 NAS 1352C   300 CRES0.170 0.018 18 1.974 0.133 0.206 0.333 0.028 18 1.974 0.278 0.389 MS51957   300 CRES0.181 0.025 18 1.974 0.132 0.231 0.344 0.028 18 1.974 0.289 0.399 Silver Plated Inserts    FastenerWet Lubrication DryMean Torque  Coefficient K STD Dev No. Samples B-Basis  Tolerance Limit  Factor B-Basis Limits KLow B-Basis Limits    K-High Mean Torque  Coefficient K STD Dev No. Samples Tolerance Limit  Factor B-Basis Limits KLow B-Basis Limits    K-High A286 0.165 0.019 48 1.654 0.134 0.197 0.422 0.098 45 1.664 0.259 0.585 300 CRES 0.180 0.025 36 1.725 0.137 0.224 0.413 0.081 36 1.725 0.273 0.552 NAS1352N   A2860.173 0.022 18 1.974 0.129 0.216 0.432 0.072 17 2.002 0.287 0.577 NAS1101   A2860.160 0.013 18 1.974 0.134 0.187 0.444 0.106 18 1.974 0.234 0.653 NAS8100/1   A2860.162 0.017 12 2.210 0.125 0.199 0.225 0.021 10 2.355 0.175 0.275 NAS 1352C   300 CRES0.174 0.028 18 1.974 0.119 0.230 0.429 0.074 18 1.974 0.283 0.575 MS51957   300 CRES0.186 0.021 18 1.974 0.145 0.227 0.396 0.086 18 1.974 0.226 0.566 Conclusions and Observations based on the results shown in Table 1:  1. For dry un-lubricated cases, the torque coefficient was found to increase with cycles, whereas for  the lubricated cases the reverse was true.  2. The dispersion (standard deviation) of the torque coefficient for all the groups of fasteners was  much greater for the dry installation versus the lubricated installation. The smaller dispersion for  lubrication make it a better choice (when acceptable to the project) than installing dry since there  235
Figure 6. Arathane and Braycote Torque Coefficient Comparison A typical plot of torque coefficients for individual torque application cycles is shown in Figure 7 for #10-32  size fasteners. Cycles 1-10 are Braycote wear cycles, cycle 11 is for a new fastener and washer used in the worn insert with Arathane and cycle 12 for a new fastener and washer used in a new insert with  Arathane. The Kmax and Kmin torque coefficients are based on B-basis calculations similar to those used for small fasteners.   Figure 7. Cyclic Torque Coefficients, Braycote (1-10), Arathane (11-12) The variation curve in Figure 7 is based on data scatter or difference from Kmean and was calculated as  follows: Variation = (Kmax-Kmin)/(2*Kmean) 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4  1 2 3 4 5 6 7 8 9 10 11 12 TORQUE COEFFICIENT &  VARIATION VALUES  TORQUE CYCLES TORQUE COEFFICIENTS & % VARIATION vs CYCLES FOR #10-32 ARATHANE TESTING Ave Torque  Coeff Plots  Max Torque Coeff Plots  Min Torque Coeff Plots  % Variation  237
Table 3. Data Summary Tables for A286 Fasteners FastenerBraycote Lubrication Phosphor Bronze Insert (Worn) Mean  Torque  Coefficient KmeanSTD  DevNo.  SamplesTolerance  Limit  FactorBBasis  Limits  KminBBasis  Limits   Kmax%  Below  mean%  Above  mean #8 - 0.25 in  (4.2 – 6.3 mm)0.182 0.039 300 1.417 0.127 0.238 30.5 30.5 Fastener Arathane Installati on Phosphor Bronze Insert (Worn) #8 - 0.25 in  (4.2 – 6.3 mm) IPA & HFE  Clean0.304 0.028 30 1.777 0.254 0.355 16.5 16.5 FastenerArathane and Braycote Comparison  New Phosphor Bronze Insert Mean  Torque  Coefficient  KmeanSTD  DevNo.  Sample s Tolerance  Limit  FactorBBasis  Limits  KminBBasis  Limits   Kmax%  Below  mean%  Above  mean Arathane  #8 - 0.25 in  (4.2 – 6.3 mm)0.322 0.024 30 1.777 0.278 0.365 13.5 13.5 Braycote  #8 - 0.25 in  (4.2 – 6.3 mm)0.205 0.044 30 1.777 0.128 0.283 37.7 37.7 The following conclusions were noted based on the above test results and Figure 8 for combined  Arathane and Small Fastener Testing which were both based on similar A286, 160-ksi (1.1-MPa) strength fasteners installed into Braycote 601EF lubricated phosphor bronze inserts. 1. For both worn and new inserts, the torque coefficient for Arathane installed fasteners was  significantly higher than the same size fastener lubricated with Braycote. 2. For worn inserts, the Arathane torque coefficient was ~71% higher than Braycote (K: 0.304 vs.  0.178). It is recommended that for worn inserts the torque should be based on a torque coefficient of 0.30 when Arathane is used. 3. For new inserts, the Arathane torque coefficient was ~57% higher than Braycote (K: 0.322 vs.  0.205). It is recommended that for new wire inserts the torque should be based on a torque coefficient of 0.32 when Arathane is used.  4. There was not an appreciable difference of the Arathane torque coefficient for those inserts  cleaned with IPA vs. HFE7100.  5. The torque coefficient was lowest for the #8 (4.2-mm) fasteners and highest for the 0.25-in (6.3mm) diameter fasteners.  6. If all the data are combined the resulting average torque coefficient is 0.180. As previously noted, the Goddard torque spec tables in 540-PG-8072.1.2 specify a torque coefficient of 0.150 for  lubricated fasteners. The data show that for a very commonly used (@ GSFC) combination of  238
A286/160 ksi (1.1 MPa) fasteners installed with Braycote 601EF into phosphor bronze wire  inserts, a change to the Goddard Mechanical Systems Division torque spec should specify a torque coefficient of 0.18  7. Also, the B-Basis scatter of the Torque coefficient is ±30%. Typically a torque coefficient range of  ±25% is commonly used at GSFC.  Figure 8. Combined Torque Coefficients Arathane & Small Fastener Testing “ORION” Super Koropon Testing ORION is a manned spacecraft proposed for beyond low Earth orbit that is being designed and built  jointly by Lockheed Martin for NASA and the European Space Agency. Two phases of torque-tension  testing were performed for ORION. Phase I (6) cycle testing was performed to determine if as-received and un-cleaned fasteners, inserts and washers could be used for assembly of flight hardware. All inserts  were received with molybdenum disulfide dry film lubricant applied to the threads by the manufacturer.  The fastener and insert combinations tested are shown in Table 4. In addition to the different insert typesand cleanliness, various lot numbers for each size and type were also tested to determine the effect on torque coefficient. Table 4. Test Hardware Phase I & II Fasteners/Inserts & Washers Fasteners Washers 1 #10-32 Hex Head A286   NAS6703U12 LMC21D5AC3C/A286  CS 2 1/4-28 Hex Head A286   NAS6704U12 LMC21D5AC3C/A286  CS Keensert Type HD EXHD LW 1 #10-32 MS51831CA201L MS51832CA201L MS51830CA201L 2 1/4-28 MS51831CA202L MS51832CA202L 239
The Phase I (6) cycle test sequence was as follows: /g120One half of the fasteners/inserts and washers were cleaned in IPA and the other half were tested  as received and un-cleaned. /g120Super Koropon, an epoxy-polymide corrosion inhibitor/sealer for threaded assemblies, was  applied to the fastener and washer bearing surfaces of all Koropon installed samples. Fastener  threads were not lubricated with Koropon. /g120Some cleaned and un-cleaned/as received sample sets were also tested dry without Super  Koropon applied to fastener and washer bearing surface.  /g120 All inserts were torqued to 65% fastener yield for total of six cycles with fastener and washer  replacement after the third cycle. Phase II (10) cycle testing was performed to determine the effect of ten cycles on running torque and also  if additional benefit could be derived by lubrication of fastener threads with Braycote. All hardware wastested as received and un-cleaned. Super Koropon was applied to fastener and washer bearing surfaces of Koropon samples with some sample sets also being tested dry, without Koropon. Some fastener threads were also lubricated with Braycote to determine the effect on torque coefficient. Two types of Braycote lubricant were tested, Type 601 for anti-rust and Type 602EF with moly disulfide for anti-galling.  Phase II test sequence was as follows: /g120As received dry film lubricated inserts with no additional Braycote lubrication.  /g120As received dry film lubricated inserts with fastener threads lubricated with Braycote 601. /g120As received dry film lubricated inserts with fastener threads lubricated with Braycote 602EF.  /g120Fasteners were replaced only if running torque was less than 3 in-lb (0.3 N-m).  Phase I and Phase II Test Results  The data plots and tables below provide a summary of the statistics for Phase I and II testing. Figure 9  and Table 5 summarize the Phase I (6) cycle test results. Figure 10 and Table 6 summarize the Phase II  (10) cycle results. Koropon Lubricated Samples: /g120Lower Kmean. /g120Cleaning has little effect.  /g120Kmean decrease vs. size. No Koropon Lubrication: /g120Higher Kmean. /g120Cleaning has some effect. /g120Kmean increase vs. size.   Figure 9. Kmean with and without Koropon Lube  0.00000.10000.20000.30000.40000.50000.6000 12Kmean  #10 & 1/4" Fastener Size   Kmean No  Koropon &   un-clean  Kmean No  Koropon &   Cleaned  Kmean No  Koropon  combined  Kmean  Koropon  Lube & un-clean  240
Table 5. Phase I (6) Cycle Statistics for #10-32 (4.8 mm) & 1/4-28 (6.3 mm) Fasteners Koropon Lube cleaned and un-cleaned Koropon/un-clean Koropon/cleaned Koropon/Combined Size #10 1/4" #10 1/4" #10 1/4" Kmean 0.217 0.167 0.221 0.175 0.219 0.170 Kmax 0.273 0.203 0.270 0.214 0.268 0.208 Kmin 0.161 0.132 0.172 0.137 0.169 0.132 Variation 0.259 0.212 0.223 0.219 0.226 0.223 N=cycles 60 96 48 90 108 186 No Koropon Lube #10,  cleaned and un-cleaned No Koropon/un-clean No Koropon/cleaned No Koropon/Combined Size #10 1/4" #10 1/4" #10 1/4" Kmean 0.289 0.432 0.293 0.478 0.292 0.445 Kmax 0.393 0.554 0.390 0.632 0.384 0.568 Kmin 0.186 0.309 0.196 0.325 0.200 0.322 Variation 0.359 0.284 0.331 0.321 0.316 0.277 N=cycles 30 30 54 12 84 42 Additional Braycote Lubrication applied to  fastener threads is beneficial for smaller  size #10-32 (4.8 mm) fasteners but less so for larger size 1/4-28 (6.3 mm)fasteners. For larger size fasteners, the head-towasher bearing surface becomes more dominant and thread friction is less of a factor. Use of Braycote 601 or 602EF are  equally effective with respect to Kmean. Figure 10. Kmean for Koropon with and without Braycote Lube For Fastener Statistics in Table 5 for (6) cycle test results and Table 6 for (10) cycle test results, the data  variation was calculated as follows: Variation = (Kmax-Kmin)/(2*Kmean)0 0.020.040.060.080.10.120.140.160.18 1 2 Kmean #10 & 1/4" Dia. Fastener/insertKmean   Braycote  601 Kmean  Braycote  602 No  Braycote 241
Table 6. Phase II Kmean for Koropon with and without use of Braycote  EXHD & HD Keenserts Koropon Lube Applied Braycote 601 Braycote 602 Combined No Braycote  Size #10 1/4" #10 1/4" #10 1/4" #10 1/4" Kmean 0.108 0.143 0.114 0.146 0.111 0.144 0.143 0.153 STDVA 0.013 0.031 0.024 0.022 0.019 0.027 0.025 0.028 Kmax 0.137 0.204 0.168 0.191 0.149 0.195 0.193 0.210 Kmin 0.078 0.082 0.059 0.102 0.072 0.094 0.092 0.097 Variation 0.274 0.427 0.480 0.305 0.351 0.351 0.356 0.369 N 2 05 02 04 04 09 04 05 0 Figure 11. Cyclic Kmean for Un-lubricated and Lubricated Samples The following generalized conclusions can be drawn based on the six and ten cycle testing:  1. For Dry/no-Koropon, Kmean and Variation were found to increase with fastener size. The reverse  was true for use of Koropon.  2. There was little difference in Kmean for cleaned and un-cleaned test samples.3. Removal of running torque was found to reduce Kmean by as much as 20%, refer to corrected  plots, Figure 11.  4. The Kmean vs. cycles for un-lubricated samples was found to increase. For lubricated samples,  the trend was reversed (refer to Figure 11). Replacement of fastener, washer and re-lubrication  after third cycle is beneficial in reducing Kmean. 5. For cycles 1-6 into the same insert without Koropon, there was a large change in torque  coefficients. With Koropon use, there was little change. 6. Running Torque was reduced significantly after first torque application but remained above a  minimum of 3 in-lb (0.3 N-m) in all but (3) sample sets, Figure 12. 0 0.05 0.1 0.15 0.2 0.25 0.3  1 2 3 4 5 6 TORQUE COEFICIENT 

TORQUE CYCLES   KOROPON LUBRICAT ED #10-32 AVE  TORQUE COEFFICIENTS VS CYCLES  Un-Clean  Clean  Combined   Combined  Corrected 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4  1 2 3 4 5 6 TORQUE COEFICIENT 

TORQUE CYCLES   DRY UNLUBRICATED #10-32 AVE  TORQUE COEFFICIENTS VS CYCLES  Unclean Clean Combined  Combined  Corrected 242
With Braycote Lubrication    Running Torque 8 in-lb (0.9 N-m) max. Is 30% less than 12 in-lb (1.4 N-m) for  no Braycote lube.       Follow-on cycles are also lower due to the lubrication effect but remain above  minimum required 3 in-lb (0.3 N-m).  Figure 12. Typical Running Torque Plot for (10) Cycles, Koropon + Braycote Lube References [1] Bickford, J. H., and Nassar, S. A., 1998, “ /g43/g68/g81/g71/g69/g82/g82/g78/g3/g82/g73/g3/g37/g82/g79/g87/g86/g3/g68/g81/g71/g3/g37/g82/g79/g87/g72/g71/g3/g45/g82/g76/g81/g87/g86 ”, Marcel Dekker, Inc.,  New York. /g3 [2] Bickford, J. H., 1997, “ /g36/g81/g3/g44/g81/g87/g85/g82/g71/g88/g70/g87/g76/g82/g81/g3/g87/g82/g3/g87/g75/g72/g3/g39/g72/g86/g76/g74/g81/g3/g68/g81/g71/g3/g36/g81/g68/g79/g92/g86/g76/g86/g3/g82/g73/g3/g37/g82/g79/g87/g72/g71/g3/g45/g82/g76/g81/g87/g86 ”, third edition,  Marcel Dekker, /g3/g44/g81/g70/g17/g15/g3 New York. /g3 [3) Alan Posey, August 20, 2008, “Small Bolt Torque/Tension Report”, NASA Goddard Space Flight  Center, Greenbelt, Maryland. (4) Alan Posey, March 24, 2010, “ /g36/g85/g68/g87/g75/g68/g81/g72/g3/g37/g82/g79/g87/g3/g55/g82/g85/g84/g88/g72/g18/g55/g72/g81/g86/g76/g82/g81/g3/g53/g72/g83/g82/g85/g87/g180/g15/g3 NASA Goddard Space Flight  Center, Greenbelt, Maryland. (5) Edgar Hemminger, July 2012, Chris McLeod and John Peil, NASA/CR-2012-217587 “ /g50/g85/g76/g82/g81/g3/g177/g3/g54/g88/g83/g72/g85/g3 /g46/g82/g85/g82/g83/g82/g81/g3/g55/g82/g85/g84/g88/g72/g18/g55/g72/g81/g86/g76/g82/g81/g3/g53/g72/g83/g82/g85/g87/g180/g15/g3 NASA Goddard Space Flight Center, Greenbelt, Maryland. (6) Edgar Hemminger and Ray Burkhardt, April 30, 2000, /g179/g57/g72/g85/g76/g73/g76/g70/g68/g87/g76/g82/g81/g3/g82/g73/g3/g37/g82/g79/g87/g3/g51/g85/g72/g16/g47/g82/g68/g71/g180/g15 NASA Goddard  Space Flight Center, Greenbelt, Maryland. (7) NASA/JSC PRC-4004, “ /g54/g72/g68/g79/g76/g81/g74/g3/g82/g73/g3/g45/g82/g76/g81/g87/g86/g3/g68/g81/g71/g3/g41/g68/g92/g76/g81/g74/g3/g54/g88/g85/g73/g68/g70/g72/g86/g180 . 243