Engineering topics

Baker, Dean M.

Publications and source records attributed to Baker, Dean M..

3 records

NASA NTRS2011

Metal-Matrix/Hollow-Ceramic-Sphere Composites

A family of metal/ceramic composite materials has been developed that are relatively inexpensive, lightweight alternatives to structural materials that are typified by beryllium, aluminum, and graphite/epoxy composites. These metal/ceramic composites were originally intended to replace beryllium (which is toxic and expensive) as a structural material for lightweight mirrors for aerospace applications. These materials also have potential utility in automotive and many other terrestrial applications in which there are requirements for lightweight materials that have high strengths and other tailorable properties as described below. The ceramic component of a material in this family consists of hollow ceramic spheres that have been formulated to be lightweight (0.5 g/cm3) and have high crush strength [40.80 ksi (.276.552 MPa)]. The hollow spheres are coated with a metal to enhance a specific performance . such as shielding against radiation (cosmic rays or x rays) or against electromagnetic interference at radio and lower frequencies, or a material to reduce the coefficient of thermal expansion (CTE) of the final composite material, and/or materials to mitigate any mismatch between the spheres and the matrix metal. Because of the high crush strength of the spheres, the initial composite workpiece can be forged or extruded into a high-strength part. The total time taken in processing from the raw ingredients to a finished part is typically 10 to 14 days depending on machining required.

Baker, Dean M.↗

NASA NTRS1992

Fatigue and flexural response of advanced carbon-carbon composites at room and elevated temperatures

The flexural response of SiC-coated carbon-carbon composites (ACC-4) at room and elevated temperatures is presented. Three-point bending tests were performed on virgin and mission-cycled specimens, and the variation in flexural strength is examined. The load-deflection behavior of the material at various temperatures is investigated, and the Weibull (1939) analysis of the strength data is performed. Micrographs of various cross sections in the damaged zone were taken, and the failure mechanisms are discussed. Fatigue tests were conducted under flexural loads, and the S-N diagram with the corresponding Weibull analysis are presented. Untested as well as fractured specimens under static and dynamic loading were C-scanned to identify the damaged zone and visualize the extent of the damage. Failure analyses are presented for both static and cyclic loading on the basis of NDE, the micrographs, and the experimental data.

Mahfuz, Hassan↗

NASA NTRS1992

Fatigue characterization of advanced carbon-carbon composites

Response of quasi-isotropic laminates of SiC coated Carbon-Carbon (C/C) composites under flexural fatigue are investigated at room temperature. Virgin as well as mission cycled specimens are tested to study the effects of thermal and pressure cycling on the fatigue performance of C/C. Tests were conducted in three point bending with a stress ratio of 0.2 and frequency of 1 Hz. Fatigue strength of C/C has been found to be considerably high - approximately above 85 percent of the ultimate flexural strength. The fatigue strength appears to be decreasing with the increase in the number of mission cycling of the specimens. This lower strength with the mission cycled specimens is attributed to the loss of interfacial bond strength due to thermal and pressure cycling of the material. C/C is also found to be highly sensitive to the applied stress level during cyclic loading, and this sensitivity is observed to increase with the mission cycling. Weibull characterization on the fatigue data has been performed, and the wide scatter in the Weibull distribution is discussed. Fractured as well as untested specimens were C-scanned, and the progressive damage growth during fatigue is presented.

Mahfuz, Hassan↗