Verification of Bolt Pre-Load

摘要

Bolt pre-load verification is critical for space flight applications due to the large launch loads that must be sustained during lift off. In addition to these large structural loads, which can exceed 10g's, flight payloads are also subjected to significant in-orbit thermal loading due to solar and electronic heating sources. Typical temperature cycles can vary from ambient at launch to very cold space environment temperatures of-60 degrees F. In orbit temperatures also, can vary from -60 to well over 100 degrees F due to solar and electronic heating. For these reasons, bolt pre-load specification is extremely important and must be verified to insure that flight payload structural connections remain tight over projected loading due to mechanical and thermal life cycles. To this end, a bolt pre-load measuring instrument has been developed and successfully used at the Goddard Space Flight Center to verify pre-load application of critical spacecraft bolted connections. This instrument has been successfully used for bolt pre-load verification testing on the Tropical Rain Measuring Mission (TRMM) and the CAPL Flight Experiment. For these projects, specified torque levels were verified by fastener testing as follows: 1. Each fastener type and size was tested in a flight like test setup. 2. A minimum five fasteners (each size) were tested and average measured torque values were then used for flight payload assembly. Typical data from a recently completed Fastener Test Program performed for the Naval Research Center for Space Technology is presented and discussed below.