Patent Application
20140082912
The subject matter disclosed herein relates to the art of turbomachines and, more particularly, to a turbomachine having a crack arrestment system and method of arresting cracks formed in a turbomachine member.
Many turbomachines include a compressor portion linked to a turbine portion through a common compressor/turbine shaft or rotor and a combustor assembly. The compressor portion guides compressed air flow through a number of sequential stages toward the combustor assembly. In the combustor assembly, the compressed air flow mixes with a fuel to form a combustible mixture. The combustible mixture is combusted in the combustor assembly to form hot gases. The hot gases are guided to the turbine portion through a transition piece. The hot gases expand through the turbine portion rotating turbine blades to create work that is output, for example, to power a generator, a pump, or to provide power to a vehicle. In addition to providing compressed air for combustion, a portion of the compressed airflow is passed through the turbine portion for cooling purposes. Generally the compressor portion includes a compressor casing and the turbine portion includes a turbine casing. During normal use, cracks may develop in one, the other, or both of the compressor casing and the turbine casing. Cracks may also develop in other portions of the turbomachine.
According to one aspect of the exemplary embodiment, a turbomachine includes a member formed from a material having a first coefficient of thermal expansion. The member includes a crack. A crack arrestment system is provided in the member. The crack arrestment system includes at least one crack arresting element provided at the crack. The at least one crack arresting element has a second coefficient of thermal expansion that is distinct from the first coefficient of thermal expansion. The at least one crack arresting element is configured and disposed to exert a compressive force on the member at the crack to substantially arrest crack propagation.
According to another aspect of the exemplary embodiment, a method of arresting cracks formed in a turbomachine member includes securing at least one crack arresting element to the turbomachine member adjacent a crack, and applying a compressive force to the turbomachine member adjacent to the crack through the at least one crack arresting element to substantially arrest crack propagation.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
A turbomachine in accordance with an exemplary embodiment is indicated generally at 2 in
During operation, casing assembly 4 is subjected to thermal load cycles. Occasionally, the thermal load cycles may lead to development of fissures or cracks. As best shown in
In accordance with an exemplary embodiment, crack arrestment system 70 includes a first crack arresting element 80 and a second crack arresting element 84. First crack arresting element 80 takes the form of a first plug 90 that is embedded in strut member 12 alongside crack 50. Second crack arresting element 84 takes the form of a second plug 94 embedded in strut member 12 on an opposing side of crack 50. First and second plugs 90 and 94 are arranged adjacent to second end 55 of crack 50. As will be discussed more fully below, first and second plugs 90 and 94 selectively exert a compressive force on crack 50 to prevent or at least substantially limit movement of second end 55 over strut member 12.
As first plug 90 and second plug 94 are shown as being generally similar, a detailed description will follow with reference to
First plug 90 is formed from a material having a second coefficient of thermal expansion that is distinct from the first coefficient of thermal expansion. More specifically, first plug 90 is formed from a second or “high alpha” material having a coefficient of thermal expansion that is greater than the first coefficient of thermal expansion of the first material. With this arrangement, first and second plugs 90 and 94 are installed in openings (not separately labeled) formed in strut member 12 adjacent to crack 50. Once installed, operation of turbomachine 2 causes strut member 12 to be heated. First and second plugs 90 and 94 are also heated and begin to expand at a rate that is faster than a rate of expansion of strut member 12. Expansion of first and second plugs 90 and 94 exerts a compressive force on crack 50 that substantially limits crack propagation when strut member 12 is exposed to thermal load cycles during the turbomachine operation.
In accordance with another aspect of the exemplary embodiment, first and second plugs 90 and 94 are formed from a shaped memory alloy configured to expand at a rate greater than the first material so as to exert a compressive force on crack 50. In accordance with still another aspect of the exemplary embodiment, the shaped memory alloy takes the form of a nickel/titanium alloy or Nitinol. When using shaped memory alloys, openings (not separately labeled) are formed in strut member 12 adjacent crack 50. First and second plugs 90 and 94 are adjusted from a first size that is greater than size of the openings to a second size that allows installation into the openings. When heated, plugs 90 and 94 attempt to return to the first size resulting in a compressive force being applied to crack 50.
At this point it should be understood that the exemplary embodiments provide a system for arresting cracks in a turbomachine. The crack arrestment system employs one or more plugs that are installed alongside a crack formed in a base material. The plugs are formed from a material that is designed to grow at a rate greater than the base material when exposed to heat. In this manner, the plugs may exert a compressive force on the crack to prevent or at least substantially arrest crack propagation. It should also be understood, that while shown and described as having a generally cylindrical cross-section, the geometry of the plugs may vary. Also, while shown as using two plugs to create the compressive force, the number of plugs may vary. In certain instances, a single plug may be all that is needed, in other instances, more than two plugs may be desirable. Finally, while shown and described as being a shaped memory alloy, the plugs may be formed from a wide variety of materials.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
