CROSSLINK DENSITY MEASUREMENT BY THE DYNAMIC MICRO-INDENTATION METHOD
Abstract
The prediction and assessment of SRM service life estimate (SLE) based on measurement of propellant properties using samples from dissected in-service or companion motors is recognized to be a time-consuming and costly endeavor. The measurement of crosslink density using a dynamic micro-indenter was investigated because it may offer a way to eventually measure crosslink density changes in-situ in a solid rocket motor. Inert propellant slabs, prepared under contract by Northrop Grumman Innovation Systems for crosslink density measurements, were stored in an oven set at 140 F and withdrawn at the prescribed time intervals. Each test specimen was tested at 20 C, 40 C and 60 C using the dynamic micro-indenter method. The indenter frequency was swept between 1 Hz and 100 Hz in seven equal increments in log frequency space over a minimum of seven test locations on the specimen at each temperature. Statistical analyses showed that there were storage modulus differences among the 0 day, 7 day, 15 to 20 day, 40 to 100 day and 120 day accelerated aging datasets. The inert propellant hardened from 0 to 100 days aging and then softened at 120 days of aging. The crosslink density calculations based on the measured storage moduli determined the crosslink density at 20 C at 0 day aging was 508 mol/m3. After 7 days of accelerated aging, the crosslink density increased to 632 mol/m3. The crosslink density increased to 769 to 824 mol/m3 after 15 to 20 days of aging. After 40 to 100 days of aging, the crosslink density increased further to 892 to 947 mol/m3. The crosslink density decreased to 824 mol/m3 after 120 days of aging. It is recommended that equilibrium swelling measurements or traditional dynamic mechanical analysis be used to confirm these crosslink density results.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2021
- Accession Number
- AD1142609
Entities
People
- Franklin C. Wong