Development and capabilities of the NASA Langley Cryogenic Pressure Box

Abstract

A cryogenic pressure box (cryobox) was designed and fabricated for use at NASA Langley Research Center (LaRC) to subject 76 in. x 65 in. curved panels to elevated and cryogenic temperatures and biaxial tensile mechanical loads. The cryobox is capable of testing curved panels down to -423°F (20K) with 52 psig maximum pressure on the concave (internal) surface, and elevated temperatures and atmospheric pressure on the convex (external) surface. The internal surface of the panel is cooled by pressurized helium gas that is cooled to -423°F by liquid helium heat exchangers. An array of twelve independently controlled fans circulate the high pressure gaseous helium to provide uniform cooling on the panel internal surface. A description of the cryobox, design of the load introduction structure, thermal and structural analysis of a checkout panel, control system, and seals are discussed in this report. axial direction of the panel will be applied by means of four hydraulic actuators. The load introduction structure, consisting of four stainless steel load plates and numerous fingers attaching the load plates to the test panel, is designed to introduce loads into the test panel that represent stresses in the actual tank structure. Fingers are used to minimize load interactions between the panel and the load plates. The load plates are trace cooled with liquid nitrogen (LN2) to reduce thermal gradients that may produce bending in the load plates, and thus introduce additional stresses into the test panel. An additional benefit is lower heat loads conducted into the panel. The design and fabrication of the cryobox can be divided into several areas: load introduction structure (including test panel), controls, seals, cryogenic systems, heating system, and support facilities. This report discusses the first three areas (load introduction structure and panels, controls, and seals) which were contracted to AS&M and Lockheed Martin Engineering & Sciences by NASA LaRC. The cryogenic systems were designed and fabricated by Applied Engineering Technologies (AET), Woburn, MA and the heating system and support facilities were designed and fabricated by NASA LaRC and are not discussed in detail here. A brief discussion of the cryobox and its capabilities will be followed by a detailed description of the load introduction structure, checkout panel, controls, and cryogenic seals.