Tab 04 SOW.pdf

High Temperature Ceramic Matrix Composite Accordion Spring Statement of Work

August 2025 NASA Glenn Research Center

Background: NASA seeks to develop high temperature spring preloaders to provide spring back/resiliency for seals and structures anticipated in future vehicle systems. The purpose of the spring preloaders is to ensure that the seals/structures remain engaged with their mating surfaces while not exerting excessive loads that may damage the seals or adjacent walls. It is important that the preloaders do not take on excessive compression set or lose preload at operating temperature. Maintaining preload over the system’s lifetime is essential. The preloaders must minimize compression set and maintain good spring-back and preload at elevated temperatures after repeated load cycling. With the advent of modern ceramic processing and fabrication techniques, flexible ceramic matrix composites (CMCs) are becoming more attractive as a material system for these advanced high temperature preloaders.

Consolidated properly, CMCs have the ability to operate at elevated temperatures in an oxidizing environment without the need of an oxidation resistant coating, which is the limiting technology at these high temperatures for springs made of refractory materials.

Geometry: Figure 1 provides an overview of the spring geometry of interest. The dimensions shown are provided as general guidelines for “keep-in” dimensions for the length, width, and height of the springs so they could be integrated into a seal under development if fabrication trials are successful. The 0.03” flexure thickness is provided as a point of departure for legacy high temperature metallic springs. This dimension can be changed slightly to meet ceramic matrix composite laminate fabrication considerations. However, it is desired that sufficient space is provided between flexures so the spring can be compressed ~20% of its nominal overall height. This thickness can also be adjusted to control the final loads exerted by the spring. If the initial fabrication prototypes are successful, NASA may elect to procure additional springs with different flexure thicknesses for either lower or higher unit loads (i.e., load per linear running inch in the direction shown by “L” in the figure). It is anticipated that multiple springs would be used to preload various lengths of seals ranging from test specimens as short as 4” up to full seal designs as long as 36”.

Figure 1: Spring preloader dimensions

0.45”

0.03”

L =0.90”

0.83”

Prototypes Characteristics:

Springs should be fabricated such that they can withstand temperatures up to 2500F for 10s of hours during a test without loss of structural or material integrity.

Springs should stay within the keep-in geometry shown in Figure 1.

CAD models can be provided if that would help with tooling fabrication.

Materials/Samples of Interest and Desired Quantities:

Springs should be fabricated out of the following flexible CMC materials:

CVD Coated Fabric Specimens o Springs

Length: 4” Quantity: 3 o Flat TGA samples Quantity: 4

SiC Inner-layer Specimens o Springs

Length: 4” Quantity: 3 o Flat TGA samples Quantity: 4

UHT-tape surfaces Specimens o Springs

Length: 4” Quantity: 3 o Flat TGA samples Quantity: 4

PSC-10 Flex Specimens o Flat TGA samples

Quantity: 4

All samples are to be laid up 0/+60/-60 to produce a balanced, 3-ply flex CMC spring. One spring will remain the full 4” length while the other springs will be sectioned into shorter lengths prior to ceramatization. The four flat TGA samples of each configuration will be cut from witness Flex sheets that are to be processed alongside the springs.