2. Acceptable wear patterns are observed on shear ties. Acceptable wear is defined as wear  showing a galled area of less than 6.45 mm2. The acceptable galling area is calculated by finding  the area of a perfectly welded joint that would prevent separation, and dividing by three (Safety factor of three against failure to self-separate). Test article Although the entire LLA assembly was used as a test article for this test, only the wearing parts were  considered test specimens. All of the wearing parts were made from Ti-6Al-4V, Solution Treated and  Aged, coated with Tiodize type 2, and over-coated with Tiolube 460. The test specimens were fabricated to flight drawings and standards. A total of 3 sets of the wearing parts were tested. Three test specimen pairs were used to provide a reasonable idea of the variations in coating performance that might occur in a given lot.  After each wear test regimen was completed, the wearing parts were inspected and replaced with the next set. Shear Tie specimens were preloaded to 28.9 kN ± 222 N (6500 lb ± 50 lb), which corresponds to a maximum Hertzian contact stress of 665 MPa (96.4 ksi).  Test Overview Figure 4 shows a diagram of the test setup. A photograph of the test setup is shown in Figure 5. The  primary wear mode for the LLA is a rocking mode about the shear tie center of rotation. This rocking mode occurs in two axes, so the resultant displacement was applied in one rotation axis. There is a third rotation mode on the flight article, a rotation about the central axis of the shear ties. This mode is small in  magnitude, and was not enveloped by this test. The spacecraft side of the test article was mounted to a base plate, which was mounted to the ram of a  servohydraulic Instron machine. The “payload-wing” side of the test article (the bolt-catcher bracket), was grounded to the Instron load cell by a linkage that was connected to a steel block mounted to the bolt catcher bracket. As the base plate moved up and down, the shear ties were forced to rotate, introducing the desired wear mode.  Rocking motions were measured using two extensometers, one in line with the clevis, and another placed  6.35 cm inboard of the clevis. The purpose here was to provide a measurement of the rotation angle that would be somewhat independent of the deflections in the test fixture. The actual rocking angle applied during each test was found using the extensometer data, using the formula below.  /g84tan1/g16d1d2/g16 R/g167/g168 /g169/g183 /g185 Where d 1 and d 2 are the extensometer displacements, R is the distance between the extensometers, and  /g84 is the rotation angle.  Uncontrolled rotations were monitored using an autocollimator, which was set up to stare at a mirror flat  mounted to the clevis mount (Figure 4). The rotations measured by this autocollimator were not recorded  during testing – the purpose for this measurement was to monitor these rotations and verify that they were not affecting the shear tie wear during the test. The autocollimator readings were monitored during  testing by personnel who were instructed to halt the test if more than 5000 /g80rad (0.3 degree) of rotation  was observed in the non-controlled axis.  The test was conducted in three phases. The first phase, or “LLA Stiffness Characterization” phase, was  performed to verify that the load limits set for each run would not be tripped during testing. The second  phase was the actual wear test, and the third phase was the separation test.  Phase 1 Test During phase 1, the Instron was controlled using its built-in position transducer. This was done as a  safety measure, since the extensometers have a tendency to slip at higher frequencies. The loading cases for the test are shown in Table 3. Each test run was controlled using displacement control, with load limits set per Table 3. Prior to testing, the range of motion for the test article was measured at ±5.1 mm. In order to protect the test article from damage, displacement limits were set at ±4.4 mm. Phase 1  163