Apparatus and Method for Fatigue Testing of a Material Specimen in a High-Pressure Fluid Environment

An apparatus for applying a load to a material specimen in a pressurized fluid environment comprising:

• a vessel having an interior surface defining a volume for holding a pressurized fluid, said interior surface including a specimen receiver configured to accept a first end of a specimen;
• a piston assembly disposed in said vessel, said piston assembly having a specimen receiver configured to accept a second end of a specimen and having an exterior surface that cooperates with the vessel's interior surface to form a seal that partitions the volume into a tensile chamber and a compression chamber;
• a tension branch conduit for conveying the fluid from a source into the tensile chamber at a first pressure (P1);
• a compression branch conduit for conveying the fluid from the source into the compression chamber at a second pressure (P2);
• a pressure controller for regulating the pressures of the fluid in the tension and compression branch conduits;
• and
• wherein said piston assembly is movable in relation to the vessel when acted upon by the pressurized fluid and the specimen receivers move away from one another when the fluid pressure (P1) in the tension chamber is greater than the fluid pressure (P2) in the compression chamber, and the specimen receivers move toward one another when the fluid pressure (P2) in the compression chamber is greater than the fluid pressure (P1) in the tension chamber.