Corrodible triggering elements for use with subterranean borehole tools having expandable members and related methods

A method of operating an expandable apparatus for use in a subterranean borehole, comprising:

• providing an expandable apparatus for use in a subterranean borehole, comprising:
• a tubular body having a longitudinal bore and at least one opening in a wall of the tubular body;
• at least one member positioned within the at least one opening in the wall of the tubular body, the at least one member configured to move between a retracted position and an extended position;
• and
• a triggering element comprising a composite material, the composite material comprising a discontinuous metallic phase dispersed within a corrodible matrix phase, the metallic phase comprising a metal or metal alloy, a majority of the corrodible matrix phase comprising at least one of a ceramic and an intermetallic compound, a majority of the at least one of the ceramic and the intermetallic compound primarily comprising magnesium and at least one of aluminum and nickel;
• and
• disposing the triggering element in a fluid flow path passing through a longitudinal bore of a tubular body of the expandable apparatus;
• seating the triggering element in a seat formed in the tubular body of the expandable apparatus;
• triggering the expandable apparatus comprising moving at least one member of the expandable apparatus from a retracted position to an extended position;
• at least partially corroding a portion of the triggering element to at least partially remove the triggering element from the seat;
• and
• moving the at least one member of the expandable apparatus from the extended position to the retracted position responsive at least in part to the at least partial removal of the triggering element.

An expandable apparatus for use in a subterranean borehole, comprising:

• a tubular body having a longitudinal bore and at least one opening in a wall of the tubular body;
• at least one member positioned within the at least one opening in the wall of the tubular body, the at least one member configured to move between a retracted position and an extended position;
• a triggering element comprising a core comprising a composite material, the composite material comprising a discontinuous metallic phase dispersed within a corrodible matrix phase, the metallic phase comprising a metal or metal alloy, the corrodible matrix phase comprising a majority of at least one of a ceramic and an intermetallic compound comprising a majority of magnesium and at least one of aluminum and nickel, wherein the triggering element comprises a shell defining an outer surface of the triggering element substantially surrounding the core, wherein the shell is formed from a relatively non-corrodible material as compared to the composite material of the core;
• and
• at least one perforation extending from the outer surface of the triggering element through the shell and exposing a portion of the core.