glenn research center at lewis field 1 standardization efforts for mechanical testing and design of...

1Glenn Research Center at Lewis Field

STANDARDIZATION EFFORTS FOR MECHANICAL TESTING AND DESIGN OF ADVANCED

CERAMICS AND COMPONENTS

NES Working Group Meeting

September 2004NASA GRC

Jon Salem NASA GRC


OUTLINE

Standards Being Developed Under NTSP: - Machining Practices for Ceramics - Determination of Slow Crack Growth Parameters

Motivations: - Failure of a leading edge - Failure of a sapphire solar concentrator - Test specimens for a combustion facility window

Status & Related Standardization Efforts in ASTM C28, ISO TC206, and NASA GRC


FAILURE OF A LEADING EDGE

Sharp Leading Edges are Needed :

- maneuverability - aerodynamics - Re-entry vehicles - airframes Issues : - higher edge temperatures

- more oxidation, etc.

Candidate Materials are UHTC’s

(Ultra-High Temperature Ceramics)



Testing of UHTC Edge Segments Resulted in Failures:

Failed test component showing thermocouple hole.

Bad design or a more basic issue?

2 mm



Fractographic investigations indicate that the thermocouple hole was poorly machined:

Crack network on inside walls of the thermocouple hole. Could standards have prevented the failure?

10 mm



Holes were made via electro-discharge machining.

EDM results in localized surface damage.

No EDM guidelines for ceramics.

Machining techniques in current standards are test specimen specific (e.g. flexure beams).

Literature indicates that other techniques with follow-up treatment could eliminate machining damage.

Need for machining guidelines.


TEST SPECIMENS FOR A COMBUSTION FACILITY WINDOW

Space Station Fluids and Combustion Facility

Combustion Integrated Rack:

Mission - Supports a wide

range of microgravity

combustion investigations.


BACKGROUNDCombustion Chamber and Subsystems

Fuel/OxidizerManagement

Assembly (FOMA)• Gas Distribution

• Exhaust Vent

OpticsBench

CombustionChamber

Rack ClosureDoor**

SAMSRTS**

Active RackIsolation

Subsystem(ARIS)*

Environmental Control (ECS)• Air Thermal Control**

• Fire Detection* & Suppression**• Water Thermal Control**

• Gas Interfaces (GN2, VES, VRS)**

Input/OutputProcessor(IOP)**Experiment Specific

Chamber Insert

OpticsBench Slides**

Window Section

4”



Window is required to transmit 1 to 5 micron IR.

Candidate material is sapphire.

Two sets of test specimens were made according to commonly used scratch-dig specification.

Testing indicated minimal scatter in one test set and substantial scatter in the other set.



Strength and crack growth test results:

Too much scatter to determine crack growth parameters.R-plane set A-plane set

Stress Rate, , MPa/s Stress Rate, , MPa/s



X-ray topography indicate subsurface damage and a “short finish” in one test sets:

Could standards have reduced the scatter?

4 mm

0.20 mm



Scratch-dig specifications do not require removal of damage created during previous polishing stage.

Sufficient removal reduces damage from the early polishing stages:

Guidelines requiring stages of removal should help! Also, a standard for SCG parameters is needed.


STATUS

SCG Parameters Standard:- Balloted in spring (ASTM)

- Re-ballot in November

Machining Guide:- draft completed

- Needs to be put in the new format


NASA-RELATED STANDARDS for ADVANCED CERAMICS

ASTM Standards NASA Helped Develop:

C1212 - 98 Practice for Fabricating Ceramic Reference Specimens Containing Seeded Voids

C1239 – 95 Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters

C1368 - 01 Test Method for Determination of Slow Crack Growth Parameters by Constant Stress-Rate Testing

C1421- 01 Test Methods for the Determination of Fracture Toughness of Advanced Ceramics

C1499 - 01 Test Method for Monotonic Equibiaxial Flexural Strength Testing Of Advanced Ceramics

Above Standards used for SSME bearings, FEANICS windows, FCF windows.


Potential Future Work

Standards of Interest to NASA & ASTM: Determination of the inert strength.

Determination of elevated temperature fracture toughness (proposed).

Determination of elevated temperature monotonic equibiaxial strength.

Equibiaxial strength of very thin plates (fuel cells and substrates).


SUMMARY

Many NASA missions use advanced ceramic materials (ISS, SSME, RSC).

Standards for advanced ceramics have been and are being developed by NASA, ASTM, and ISO.

A need exists for the development of new standards for advanced ceramics and ceramic composites.

glenn research center at lewis field 1 standardization efforts for mechanical testing and design of...

Documents