Development Of On Structure Stress Gages

Development of On-structure Stress Gages

The report describes the development of three types of on-structure stress (OSS) gages (the IF and FS soil-pressure gages and the M-1 airblast gage) based upon the load column principle. The OSS gage design is based upon the assumption (backed by theory and experiment) that if the gage is made much stiffer than the soil, the over-registration of the gage approaches a constant value. A brief discussion of some of the unique problems of measurement of soil pressures is presented. Six OSS gages (four IF, one FS, and one M-1) were statically tested and evaluated with respect to linearity, hysteresis, resolution, thermal sensitivity, and strain sensitivity. Dynamic tests were performed in a laboratory shock tube and blast load simulator facilities. The OSS gages are concluded to be adequate for soil-pressure measurements on certain types of rigid structures and for airblast measurements, even in explosive atmospheres. They successfully measured dynamic gas pressure up to 5,000 psi in the firing tubes of the laboratory blast simulator device. Additional research is recommended to evaluate the gage performance more completely in static and dynamic soil tests. A range of soil types from coarse dry sand to moist fat clays should be investigated. Future research on gages for measuring soil pressures on structures should be concentrated on development of small gages for use with models and thin-walled structures. (Author).

Evaluation of the Crack Growth Gage Concept as an Individual Aircraft Tracking Device

An analytical and experimental program was conducted to evaluate the crack growth gage concept for application as an individual aircraft tracking device. Three gage designs were evaluated. Volume I discusses the evaluation of two versions of a stepped thickness gage and a stepped width gage. Volume II discusses the evaluation of a side-grooved constant thickness gage. An analytical evaluation of the change in transfer function corresponding to gage design parameter changes was performed to determine the configuration of the gages to be tested. Initial spectrum tests were conducted on the first stepped gage design to determine the ranking ability of the gage. Then constant amplitude tests were conducted on the second stepped gage design. A modification of the gage was made to improve spectrum test response. The modified gage was subjected to both constant amplitude testing and spectrum testing. The analytically derived crack growth rates were compared to the test data. In general, the analysis predicted slightly higher growth rates than observed.

Technical Abstract Bulletin