Burst Containment Means

Abstract

The invention relates to a means for containing burst fragments generated when very high speed machinery, particularly gas turbines, rupture. The containment means is a winding of tape over the machinery housing and radially aligned along the expected path of travel of part fragments. The winding is formed from lightweight material having high strength and high elongation properties providing unusual energy absorbing capabilities which tends to contain the impact of burst fragments primarily by deflection rather than high yield stresses.

Description

The containment means described is used for the purpose of containing burst fragments within a localized area in the event the rotor of a very high speed machine ruptures. The invention has immediate application to the compressor section of gas turbines and can be further extended to the turbine section following the development of a high temperature and high elongation plastic fiber such as a high temperature nylon known as "Norel" for example.

In the past a metal, usually steel, in a single mass, laminated or woven form has been used. In one respect steel would appear to be an excellent candidate. In practice, particularly in aviation gas turbine applications, it is practically useless for a rather unusual reason, to be demonstrated.

It is an object of the invention to provide a burst containment means for high energy fragments which (i) avoids the limitations and disadvantages of prior art devices, (ii) is lightweight and compact, (iii) made from material which is capable of absorbing at least twice as much kinetic energy as steel of the same weight, (iv) is constructed from a nylon tape material having a high strength to failure ratio, and (v) comprises a winding of at least 15 turns of tape.

In accordance with the invention a burst containment means comprises a housing, a winding made up of at least 15 overlying turns of a tape formed from a material having a specific energy absorbing capability of at least 200,000 (IN-LB/LB).

The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a partial cross-sectional representation of a burst containment means embodying the principles of the present invention;

FIG. 2 is a schematic representation of the winding comprising a portion of the burst containment means;

FIG. 3 is an expanded segmented view of the burst containment means showing structural details; and

FIG. 4 is a pictorial representation of the invention in the act of restraining high kinetic energy fragments.

The energy absorbing capability of a material is determined by reference to a standard stress-strain curve of the material where stress is specified in LB/IN.sup.2 and the strain in IN/IN. The energy absorbing capability of a material is determined by calculating the area under the stress-strain curve.

In tests conducted on a nylon ballistic cloth material the energy absorbing capability of the material was determined to be 8,000 (IN-LB/IN.sup.3). The energy absorbing capability of steel that was considered suitable for fragment containment was determined to be 35,000 (IN-LB/IN.sup.3). It would appear from the foregoing that steel is much more suited for fragment containment than the nylon cloth. The fact of the matter is, however, that it is, from a practical point of view, much worse. For one thing, steel, because it has a high modulus of elasticity, tends to resist an impact with negligible deflection and consequently it tends to shatter rather than absorb energy.

Another very serious limitation of steel is its weight. For example, the specific energy absorbing capability, i.e. the energy that a material can absorb per pound of material, of steel is 121,000 (IN-LB/LB.) The specific energy absorbing capability of nylon, on the other hand, is 204,000 (IN-LB/LB) and is in fact a preferred candidate material.

The low strength material is utilized to its fullest capability when it is wound into a coil or winding containing at least 15 turns for reasons that will be explained hereinafter.

Referring to FIG. 1 of the drawings there is illustrated in cross section the pertinent elements of a gas turbine compressor assembly 10. The assembly includes a hub 11 on the circumference of which are fastened a plurality of compressor blades 12. Surrounding and spaced from the compressor blades 12 is a housing 13 formed from any suitable metal material.

Lapped around the housing 13 is a winding 14 comprising at least 15 turns 16.

The turns 16 are formed from a continuous length of a material having a specific energy absorbing capability of 200,000 (IN-LB/LB) or greater. A nylon ballistic cloth as defined and identified in the Mill Standard specification Mil-C123690 is the preferred material to use in making up the winding of 14.

FIG. 2 is a schematic representation showing the use of a continuous tape in making up the winding 14. It also represents schematically that there are no means for bonding or fastening the adjacent turns 16 of the winding 14 to each other or to the housing 13.

FIG. 3 is another representation of the winding structure providing additional detail.

FIG. 4 of the drawings serves to illustrate why it is important to (1) provide a plurality of turns 16 preferably a minimum of 15 turns, and (2) provide a winding where adjacent turns are free to move relative to each other. FIG. 4 illustrates the winding 14 in the process of absorbing three high energy fragments from an exploding mechanical member. The housing 11 has been completely shattered and is no longer a factor in containing the fragments. The configuration of the winding 14 has changed into an optimum configuration for the type of impact it is resisting. The wide center portion 19 of the three legs of the winding indicate that a number of turns 16 of the winding 14 have failed in tension. The high density of turns 16 adjacent to the outside of the winding 14 indicate that a substantial number of turns 16 are compressed and absorbing the energy applied to the winding by the fragments.

It is clear that the amount of energy that is to be contained will vary with the speed and the configuration of the high energy fragments. The primary use of the housing relates to its function in connection with the gas turbine compressor. Its very presence causes it to absorb some of the energy from fragments; but because it is made of metal and because its thickness is determined by the gas turbine performance, it is not a good energy absorber and in fact the major portion of the energy contained in a fragment is absorbed by the winding 14. On occasion it has been noted that the housing upon rupturing creates secondary high energy fragments but generally these do not pose a serious problem.

A number of tests have been made by preparing a 3 -inch wide winding over an 18 -inch diameter housing. Each turn was one thirty-second inch thick and 331/3 turns were used to make up the complete winding. This particular design has successfully resisted impact up to and including 83,500 IN-lbs. Up to 40 percent of the turns experienced one or more breaks. These breaks were examined and were determined to be tension breaks. The "intact" turns underwent appreciable elongation. High energy fragments were completely contained in the windings.

Claims

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims:

1. A burst containment means comprising the combination of a housing about a rotated bladed structure, a winding on said housing consisting essentially of at least 15 overlapping turns of a tape formed from a nylon ballistic material having a specific energy absorbing capability of at least 200,000 (IN-LB/LB).

2. A burst containment means as defined in claim 1 in which the winding is formed from a woven tape of a nylon ballistic material.