Modeling and Simulation of Missile Launcher System Wear During Captive Carry
Type of Degreethesis
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Across the branches of the United States and foreign militaries, missiles are used for a variety of missions. Many of these missiles mount to their respective vehicles by means of a rail system. While the service life of an as-designed rail system in a laboratory or other well-defined environment is generally known, the wear rates of manufactured systems at the upper and lower limits of specified clearance, and under varied vibrational loads in arbitrary environments has not been well established. By leveraging multibody vibrational simulation and mathematical wear models, a given rail system has been assessed for its robustness to a variety of parameters. This was done by developing a modification of the commonly used Archard wear model, and by developing a wear prediction plugin for the multibody simulation software package, MSC.ADAMS. The parameters for the wear model were first generated using a simple laboratory test on a Friction and Wear tester, where 3 aluminum samples were fretted against a square coupon to generate experimental wear mass data points. Using these data points, a wear model was developed, and then validated for the simulation of wear in rattling contacts with a simple shaker table fixture of a square tube with a free-floating cube inside it. This fixture was vibrated for a period of time and the experimental wear mass of the cube was compared to the predicted wear mass from ADAMS. Finally, a multi-body simulation of a Hellfire missile launcher system was developed in order that generalized relationships could between system configurations and total service life could be found. This simulation model was validated with another shaker table experiment in which an instrumented missile system was vibrated in each axis at key frequencies found in the MIL-810G standard for accelerated vibration testing of military hardware. The experiment consisted of 4 sine tones in each of the three axes, and through an iterative tuning process, the ADAMS model's prediction of the frequency spectrum of the bulk missile motion was matched closely to the experimental spectra. After the model's dynamics were validated, a third and final validation experiment was conducted to validate the wear predictions for 2 critical components of the system. In this experiment a full missile system was mounted to a shaker table and vibrated to create wear on the mid and rear shoes. This experimental wear was compared to predictions from ADAMS to finally validate the model. The errors of the two wear mass predictions were 6.50\% and 3.35\% respectively. Once the multibody simulation wear prediction model was validated, a missile launcher systems of various dimensions and under varied vibration loads were simulated, and their wear rates were compared to the reference configuration upon which the stated service life and maintenance schedules are based. With this information a service life penalization methodology was proposed to more effectively schedule replacement of missile launcher rails in the field.