Engineering topics

Yun, H. M.

Publications and source records attributed to Yun, H. M..

21 records · Page 2

NASA NTRS1993

Preliminary evaluation of tensile and stress-rupture behavior of W + 24 at. pct Re + 0.4 at. pct HfC wire

Results are presented of an evaluation of tensile properties and stress-rupture bahavior of a small-diameter W24ReHfC (W-24Re-0.4(HfC)) wire, which is considered to be an excellent reinforcing fiber candidate for a variety of metal-matrix composites. The results were compared to data of Petrasek (1972) on W4ReHfC (W-4Re-0.4(HfC)) wire. It was found that the room-temperature (RT) tensile strength of the W24ReHfC wire was about 3250 MPa, higher than that of the W4ReHfC (3160 MPa) and WHfC (2250 MPa) wires. Above 1366 K, the W4ReHfC wire had both a greater tensile strength and the stress rupture strength than the W24ReHfC wire.

Yun, H. M.↗

NASA NTRS1992

Tensile strain-rate sensitivity of tungsten/niobium composites at 1300 to 1600 K

The tensile behavior of continuous tungsten fiber reinforced niobium composites (W/Nb), fabricated by an arc-spray process, was studied in the 1300 to 1600 K temperature range. The tensile properties of the fiber and matrix components as well as of the composites were measured and were compared to rule of mixtures (ROM) predictions. The deviation from the ROM was found to depend upon the chemistry of the tungsten alloy fibers, with positive deviations for ST300/Nb (i.e., stronger composite strength than the ROM) and negative or zero deviations for 218/Nb.

Yun, H. M.↗

NASA NTRS1988

On the cyclic stress-strain behaviour of a Ni-base superalloy at room temperature

The cyclic stress-strain behavior of Nimonic alloy PE16 was studied at room temperature and at different aging conditions to determine whether the plateau in the cyclic stress-strain curve (CSSC) reported by Arbuthnot (1982) is typical of the room temperature behavior and/or some specific initial microstructural states. Specimen blanks were heat-treated in batches in Ar/H2 (98/2) atmosphere to produce gamma-prime precipitates of different average sizes, but with the volume fraction of gamma-prime precipitates kept constant at about 7 percent at all the heat-treatment conditions. Total axial strain controlled LCF tests were conducted under fully reversed loading (R = -1) at a constant strain rate of 0.004/s, using a servohydraulic machine. The load response in tension and compression was recorded continually, and stress-strain hysteresis loops were recorded at frequent intervals. In the present investigation, the CSSCs of the P16 alloy at room temperature did not display the plateaus reported by Arbuthnot.

Singh, Vakil↗