Search NASA⌕ Search

Engineering topics

Johnson, S. A.

Publications and source records attributed to Johnson, S. A..

5 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Effect of mission cycling on the fatigue performance of SiC-coated carbon-carbon composites

The effects of thermal and pressure cycling on the fatigue performance of carbon-carbon composites, and the influence of mission cycling on these effects, were investigated by subjecting both virgin and mission-cycled two-dimensional specimens of SiC-coated carbon-carbon composites to fatigue tests, conducted at room temperature in three-point bending, with a stress ratio of 0.2 and a frequency of 1 Hz. It was found that the fatigue strength of C-C composites is high (about 90 percent of the ultimate flexural strength), but decreased with the mission cycling. The lowering of the fatigue strength with mission cycling is attributed to the increase in interfacial bond strength due to thermal and pressure cycling of the material. The already high sensitivity of C-C composites to stress during cyclic loading increases further with the amount of mission cycling. Results of NDE suggest that the damage growth in virgin C-C, in the high-cycle range, is slow at the initial stage of the cyclic life, but propagates rapidly after certain threshold cycles of the fatigue life.

Mahfuz, H.↗
NASA NTRS1983

Aeroelastic analysis for propellers - mathematical formulations and program user's manual

Mathematical development is presented for a specialized propeller dedicated version of the G400 rotor aeroelastic analysis. The G400PROP analysis simulates aeroelastic characteristics particular to propellers such as structural sweep, aerodynamic sweep and high subsonic unsteady airloads (both stalled and unstalled). Formulations are presented for these expanded propeller related methodologies. Results of limited application of the analysis to realistic blade configurations and operating conditions which include stable and unstable stall flutter test conditions are given. Sections included for enhanced program user efficiency and expanded utilization include descriptions of: (1) the structuring of the G400PROP FORTRAN coding; (2) the required input data; and (3) the output results. General information to facilitate operation and improve efficiency is also provided.

Bielawa, R. L.↗
NASA NTRS1983

Practical preventive reliability using matrix forms

This paper describes a practical new tool to improve the reliability of equipment. It uses a matrix form to help monitor anticipated component faults precisely. The tool provides the practical measures necessary to generate matrix tables that accurately display all causes of failure and all planned programmatic analyses, tests, processes, and inspections. When completed, the matrix tables give users in-depth visibility of the degree of protection against component failure that is provided by the program's preventive measure plans. The matrix form is an excellent technique for tracking, and thereby influencing, the reliability of nonelectronic spacecraft subsystems or components. No electronic applications have been tried, but the procedure can be useful in the electronics field, e.g., in integrated circuit production planning, and perhaps in process control, inspection or test lines for other electronic components. The drawing of forms, and the recording/manipulation of the data can be computerized.

Johnson, S. A.↗