Engineering topics

Wolak, J.

Publications and source records attributed to Wolak, J..

7 records

NASA NTRS1985

Metallurgical and mechanical phenomena due to rubbing of titanium against sintered powder Nichrome

Metallurgical and mechanical changes occurring during high-speed rubbing of Ti-6Al-4V blade specimens against an abradable Nichrome aircraft engine seal material were studied using optical microscopy, electron microscopy, and microhardness techniques. Evidence of temperatures above the beta transus of Ti-6Al-4V (1000 C) and of thermal hardening was found on blade tips that exhibited undesirable abrading characteristics resulting in high forces of interaction, high temperatures, and smearing. The material within the layer of the corresponding seals was found to be work-hardened to a depth of about 0.1 mm and showed evidence of densification extending to a depth of about 0.5 mm below the rubbed surface. Wear particles produced by rub interactions that generated cleanly abraded seal surfaces were found to be several times larger than those produced during interactions which showed evidence of surface smearing and seal densification.

Zenas, R.↗

NASA NTRS1984

Blade tip geometry - A factor in abrading sintered seal material

Experimental results are presented for the case of titanium blade tip specimens of various geometrical configurations rubbing at 100 m/s against specimens of nickel-chromium sintered powder metal seal material, the latter being fed toward the rotating blades at an incursion rate of 0.0254 mm/s. Blade tips in the form of orthogonal cutting tools with about 85 deg negative rake angles exhibited desirable abrading capabilities, as measured by the tear-free appearance of the grooves they generated in the seal material, little wear of blade tips, low forces of interaction and low seal densification. Similar results have been obtained for blade specimens with tips of small radius of curvature, as well as for square-ended and slanted blade tips that are plasma-sprayed with abrasive particles. The relationship between the size of these particles and their abrading effectiveness is considered.

Wolak, J.↗

NASA NTRS1983

An experimental investigation and numerical prediction of thermomechanical phenomena in high speed rotor tip rubbing

A thermomechanical study of the intermittent rubbing of a rotor blade tip and a casing seal is carried out taking into account the existence of thermal contact resistance. The effect of the thermal properties of a plasma sprayed coating on the blade tip is studied. The influence of a variable heat generation and variable thermal contact resistance at the blade tip as it passes along the path of rubbing is also discussed.

Emery, A. F.↗

NASA NTRS1982

Preliminary results on the abradability of porous, sintered seal material

Preliminary results are presented for the case of titanium blade specimens, with bare tips (or covered with wear resistant, plasma sprayed materials) rubbing at 100 m/s against specimens of abradable nickel-chromium seal material moving toward the rotating blades at 0.0125 mm/s or at 0.025 mm/s. Using a two component dynamometer, the normal force of the rub interaction was measured and the shear component estimated. The elastoplastic properties of the seal material have been determined and those parameters as well as the rigidity of the rub tester system are considered in conjunction with those affecting the accuracy of the measurement of the forces arising at the blade-seal interface. The average and the 'local instantaneous' temperatures of the seal specimen and the temperature of the blade tip surface during rubbing are presented as functions of time. A seal densification factor is defined and its functional relationships with contact force components, temperature, wear ratio and blade tip abrading capability are indicated.

Wolak, J.↗

NASA NTRS1982

An experimental investigation of interfacial temperatures in blade-seal material rubbing of aircraft compressors

Results are presented for the rubbing of rotating (100 m/s) titanium blade specimens, with different plasma-sprayed tip coating, against an abradable porous seal material at two different incursion rates. In general, there was a good correspondence between the average transverse force of rubbing and the seal specimen surface temperature. Instantaneous seal surface temperature measurement showed a significant temperature jump before and after each rubbing with a high rate of cooling during each revolution and a high overall temperature level. Numerical predictions of both blade and seal temperature agreed well for the bare blade tip experiments but were consistently high for the coated blades. This suggests that the thermal properties of the coatings may significantly affect the temperatures and hence the wear characteristics of the system.

Emery, A. F.↗

NASA NTRS1981

Interfacial temperatures and surface heat fluxes during a blade-seal rubbing process

A thermal analysis was made of a blade-seal configuration to determine the effects of thermal contact resistance, blade speed, and thermal properties upon the interfacial temperature. The analysis disclosed that while the thermal properties of the blade or the seal specimen strongly affect the temperatures in their respective parts, the factors which control the overall temperature field are the contact resistance and the heat generated at the interface.

Emery, A. F.↗

NASA NTRS1981

Effects of geometric variables on rub characteristics of Ti-6Al-4V

Experiments simulating rub interactions between Ti-6Al-4V blade tips and various seal materials were conducted. The number of blade tips and the blade tip geometry were varied to determine their effects on rub forces and on wear phenomena. Contact was found to be quite unsteady for all blade tip geometries except for those incorporating deliberately rounded blade tips. The unsteady contact was characterized by long periods of rubbing contact and increasing blade tip that terminated in sudden rapid metal removal, sometimes accompanied by tearing and disruption of porous seal material under the rub surface. A model describing the blade tip loading is proposed and is based on the propagation of an elastic stress wave through the seal material as the seal material is dynamically compressed by the blade tip leading edge.

Bill, R. C.↗