Parts in this category are classified NFC if documented assessment cited in the FCSR shows they satisfy the specified criteria listed in the item corresponding to the hardware type. Composite and bonded hardware are to satisfy section 6.3 in this NASA Technical Standard in addition to requirements for a specific hardware type.
[FCR 7] To be classified as NFC, each part that is described by a specific hardware type in the following list shall comply with the established approach given in the referenced subsection:
- a. NFC metallic fasteners, rivets, shear pins, and locking devices comply with section 6.1.1 in this NASA Technical Standard.
- b. NFC shatterable components and structures comply with section 6.1.2 in this NASA Technical Standard.
- c. NFC rotating hardware complies with section 6.1.3 in this NASA Technical Standard.
- d. NFC sealed containers comply with section 6.1.4 in this NASA Technical Standard.
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- e. NFC tools, mechanisms, and tethers comply with section 6.1.5 in this NASA Technical Standard.
- f. NFC batteries comply with section 6.1.6 in this NASA Technical Standard.
[Rationale: Parts that can be shown to have no credible catastrophic hazard resulting from a failure of the part caused by a flaw or to have no credible possibility for flaws to cause failure are not fracture critical. These parts can be classified as NFC. To assist this classification process, a number of established approaches have been developed for specific hardware types that are documented in this NASA Technical Standard.]
Use of an alternative approach requires unique rationale and approval by the RFCB as described in section 10 [FCR 26] in this NASA Technical Standard.
6.1.1 NFC Metallic Fasteners, Rivets, Shear Pins, and Locking Devices
To classify a part as an NFC metallic fastener, rivet, shear pin, or locking device, satisfy any of the following items in sections 6.1.1.1 through 6.1.1.6, depending on application, hardware type, and failure modes, to comply with requirement [FCR 7], section 6.1.a in this NASA Technical Standard.
6.1.1.1 NFC Low-Released Mass Fasteners, Rivets, and Shear Pins
To classify a metallic fastener, rivet, or pin as NFC low-released mass, meet the requirements of section 6.2.1 in this NASA Technical Standard.
A metallic fastener, rivet, or pin that has an individual single-point structural failure or a group of fasteners, rivets, or pins where loss of any one fastener, rivet, or pin does not present a catastrophic hazard can be classified in one of these NFC categories.
6.1.1.2 NFC Contained Fasteners, Rivets, and Shear Pins
To classify a metallic fastener, rivet, or pin as NFC contained, meet the requirements of section 6.2.2 in this NASA Technical Standard.
6.1.1.3 NFC Fail-Safe Rivets
To classify metallic rivet applications as NFC fail-safe, meet the requirements in section 6.2.3 in this NASA Technical Standard.
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6.1.1.4 NFC Low-Risk Fasteners
To classify metallic fasteners as NFC low risk, meet the following:
- a. The fastener is in a local pattern of two or more similar fasteners.
- b. The fastener satisfies all of the following general fastener attributes:
- (1) Fasteners are fabricated from a metal with high resistance to stress corrosion cracking, as defined in MSFC-STD-3029, Guidelines for the Selection of Metallic Materials for Stress Corrosion Cracking Resistance in Sodium Chloride Environments.
- (2) Fasteners are fabricated to a military, NAS, or commercial aerospace specification approved by the procuring organization.
- A. The standard and/or associated procurement specification includes tensile, shear, and fatigue testing as part of lot acceptance.
- B. Fasteners with complete traceability are delivered with the Material Test Report or equivalent that includes the following:
- i. The raw material and heat-treat certifications.
- ii. Documentation of applicable testing or processing required in the associated procurement specification.
Fasteners that are manufactured from the following list of ductile materials show a high tolerance for typical fastener defects and flaws. These are typically accepted as low-risk fasteners. Examples of procurement specifications for these commonly accepted low-risk fastener materials are:
- • Iron-based superalloy A286: NAS4003, Fastener, A286 Corrosion Resistant Alloy, Externally Threaded, 160 KSI Ftu, 95 KSI Fsu, 1000 °F; NA0026, Procurement Specification Metric Fasteners, A-286 CRES Externally Threaded, 1100 MPa Tensile, 660 MPa Shear; or equivalent.
- • Nickel-based superalloy Inconel 718: NASM85604, Bolt, Nickel Alloy 718, Tension, High Strength, 125 KSI Fsu and 220 KSI Ftu, High Temperature, Spline Drive; or equivalent.
- • Cobalt-Chromium-Nickel-based superalloy MP35N: AS7468, Bolts, Cobalt-Chromium-Nickel Alloy, UNS R30035, Tensile Strength 260 Ksi, Procurement Specification; or equivalent.
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B.3 NON-GOVERNMENT DOCUMENTS AIA/ NAS
NA0026, Procurement Specification Metric Fasteners, A-286 CRES Externally Threaded, 1100 MPa Tensile, 660 MPa Shear
NA0271, Metric Fasteners, CRES 300 Series, Externally Threaded, MJ Thread, 500 MPa Ft u and 700 MPa Ft u
NAS4003, Fastener, A286 Corrosion Resistant Alloy, Externally Threaded, 160 KSI Ft u, 95 KSI Fsu, 1000 °F
NASM85604, Bolt, Nickel Alloy 718, Tension, High Strength, 125 KSI Fsu and 220 KSI Ft u, High Temperature, Spline Drive
American Petroleum Institute (API)
API 579-1/ASME FFS-1, Fitness-For-Service
American Society of Mechanical Engineers (ASME)
ASME BPVC-VIII-1, Boiler Pressure Vessel Code, Section VIII, Rules for Construction of Pressure Vessels Division 1
ASME BPVC-VIII-2, Boiler Pressure Vessel Code, Section VIII, Rules for Construction of Pressure Vessels Division 2-Alternative Rules
ASTM International (formerly American Society for Testing and Materials)
ASTM E399, Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic Materials
ASTM E561, Standard Test Method for K-R Curve Determination
ASTM E1681, Standard Test Method for Determining Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials
ASTM E740/E740M, Standard Practice for Fracture Testing with Surface-Crack Tension Specimens
ASTM E1820, Standard Test Method for Measurement of Fracture Toughness
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ASTM E1823, Standard Terminology Relating to Fatigue and Fracture Testing
ASTM E2899, Standard Test Method for Measurement of Initiation Toughness in Surface Cracks Under Tension and Bending
SAE
AS7468, Bolts, Cobalt-Chromium-Nickel Alloy, UNS R30035, Tensile Strength 260 Ksi, Procurement Specification
B.4 OTHER DOCUMENTS
Boyer, R.R.; Spurr, W.F. (January 1978). "Characteristics of Sustained-Load Cracking and Hydrogen Effects in Ti-6Al-4V," Metallurgical Transactions A. Vol. 9A, pp. 23-29.
Lewis, J.C.; Kenny, J.T. (July 1976). Sustained Load Crack Growth Design Data for Ti-6Al-4V Titanium Alloy Tanks Containing Hydrazine. Paper presented at AIAA/SAE 12th Propulsion Conference. Palo Alto, CA.
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- • Austenitic Stainless Steel 300 Series CRES: NA0271, Metric Fasteners, CRES 300 Series, Externally Threaded, MJ Thread, 500 MPa and ; or equivalent.
- (3) Fasteners are not made from any titanium alloy.
Titanium alloys, such as Ti-6Al-4V, cp-Ti, and other titanium alloys are not acceptable in this category because of generic EAC or SLC failure modes, as well as low fracture toughness.
- (4) The fastened joint complies with both of the following from NASA-STD-5020, Requirements for Threaded Fastening Systems in Spaceflight Hardware:
- A. Preload control as detailed in section 6.1 of NASA-STD-5020.
- B. No joint separation in the nominal loading configuration as described in sections 4.3 and 6.5 of NASA-STD-5020.
- (5) Fasteners are subject to the following:
- A. Have rolled threads, with the rolling process occurring after all thermal treatment of the material.
- B. The results of the mandatory lot acceptance fatigue testing are required to establish that the fasteners meet the fatigue requirements in NASA-STD-5001.
- C. For fastener types that do not require fatigue testing as part of lot acceptance, samples from the lot need to be submitted for fatigue testing in accordance with NASM1312-11, Fastener Test Methods, Method 11 Tension Fatigue, and NAM1312-111, Fastener Test Methods, Method 111 Tension Fatigue, or equivalent, to satisfy 6.1.1.4.b.(2) above.
- (6) The fasteners are not made from a low fracture toughness alloy, as defined in section 3.2 in this NASA Technical Standard.
- (7) Fasteners are not reworked or custom made unless the application is approved by the RFCB.
6.1.1.5 NFC Fail-Safe Fasteners
To classify metallic fasteners as NFC fail-safe, meet the following:
-
a. The fasteners meet the fail-safe requirements in section 6.2.3 in this NASA Technical Standard.
-
b. The fastener satisfies all of the following general fastener attributes:
-
(1) Fasteners are fabricated from a metal with high resistance to stress corrosion cracking as defined in MSFC-STD-3029.
-
(2) Fasteners are fabricated, procured, and inspected in accordance with NASA-STD-8739.14, NASA Fastener Procurement, Receiving Inspection, and Storage Practices for Spaceflight Hardware, and an equivalent military standard, NAS, proprietary, or commercial aerospace specification approved by the procuring organization.
-
(3) The fastened joint complies with NASA-STD-5020 without joint separation in the nominal configuration.
-
(4) Fasteners have rolled threads and are assessed to establish that they meet the fatigue requirements in NASA-STD-5001.
-
(5) The fasteners are not made from a low fracture toughness alloy as defined in section 3.2 in this NASA Technical Standard.
-
(6) Fasteners are not reworked or custom made unless the application is approved by the RFCB.
-
(7) Fasteners manufactured from titanium alloys require additional considerations for this classification, including risk mitigation and assessment that are approved by the RFCB. Titanium alloys, such as Ti-6Al-4V (including annealed and STA conditions), cp-Ti, and other titanium alloys, have potential generic EAC or SLC failure modes that are not mitigated by the fail-safe requirements. Additional risk mitigation is needed for their use in this classification with an assessment that establishes that there is no credible risk of generic fastener failures related to flaws or under applied load. The assessment should include credible initial fastener defects/crack size, the largest credible preload, and maximum service life loading and should compare the Critical Stress Intensity Factor to KSLC and KEAC lower bound values determined from tests of flawed fasteners in applicable service life environments.
6.1.1.6 NFC Locking Devices
To classify metallic locking devices to prevent fastener or connector backout, including wires, tangs, or other methods, as NFC locking devices, NFC hardware is to meet the requirements of section 6.2.1 in this NASA Technical Standard.
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6.1.2 NFC Shatterable Components and Structures
To classify parts as NFC shatterable components or structures, satisfy one of the items listed below in section 6.1.2.1 or section 6.1.2.2 in this NASA Technical Standard, depending on application and hardware type, to meet requirement [FCR 7], section 6.1.b in this NASA Technical Standard.
6.1.2.1 NFC Internal Shatterable Components
Shatterable components and structures are classified as NFC by one of the following:
- a. For shatterable components and structures inside habitable volumes, meet the following:
- (1) Requirements in section 6.2.2 in this NASA Technical Standard.
- (2) The particulate containment requirements in NASA-STD-5018, Strength Design and Verification Criteria for Glass, Ceramics, and Windows in Human Space Flight Applications.
- b. For shatterable components and structures inside non-habitable volumes, meet the requirements in sections 6.2.1, 6.2.2, 6.2.3, 6.2.4, or 6.2.6 in this NASA Technical Standard.
6.1.2.2 NFC External Shatterable Components
To classify parts as NFC shatterable components or structures located on the external surface of a spacecraft that are manufactured from a material with limited ductility such that it is prone to brittle failures when cracked and/or subjected to impact, meet 6.1.2.2.a, 6.1.2.2.b, and 6.1.2.2.c below:
- a. A DTA and IDMP are developed to mitigate credible catastrophic impacts from vehicle loss of external surface mass, crew exposure, micrometeoroid and orbital debris (MMOD), extravehicular activity (EVA), inadvertent contacts, and EVA tool impact hazards.
- b. The design has sufficient structural integrity such that the loss of a primary member does not result in catastrophic loss of spaceflight hardwate function or required strength that prevents the hardware from safely completing the mission.
- c. Any mass released from these components meets the low-released mass requirements of section 6.2.1 in this NASA Technical Standard.
Refer to section 7.4.1 for DTA and 7.4.2 for IDMP.
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6.1.3 NFC Rotating Hardware
Satisfy one of the following items to classify a part as NFC rotating hardware to meet requirement [FCR 7], section 6.1.c in this NASA Technical Standard:
- a. The rotating hardware is computer equipment, such as computer data storage disks and computer cooling fans.
- b. The rotating hardware meets the conditions in section 6.2.5 in this NASA Technical Standard.
- c. The rotating hardware is within an enclosure and meets the following:
- (1) In the event of a rotor fracture caused by flaws, a conservative assessment of credible rotor fragments shows the fragments are contained within the enclosure in accordance with section 6.2.2 in this NASA Technical Standard.
- (2) The structural mounts for the rotating hardware and the enclosure are evaluated as standard structure and meet fracture control requirements.
- (3) The mount assessments include credible loads from a sudden stop of the rotor, unless it is established that either of the following are satisfied:
- A. The rotating hardware does not have a credible sudden stop catastrophic hazard during the service life that has resulted from a structural failure of the rotating hardware or adjacent structure caused by flaws.
- B. The rotating hardware has design features and monitoring with safety controls that make a sudden stop a non-credible event.
6.1.4 NFC Sealed Containers
Satisfy all of the following to classify a part as an NFC sealed container, e.g., a sealed electronics box that is not part of a pressure system and is not a pressure vessel, to meet requirement [FCR 7] section 6.1.d in this NASA Technical Standard:
- a. The container meets the following:
- (1) Does not contain a hazardous material.
- (2) Loss of pressure or fluid from the container does not result in a catastrophic hazard.
- (3) Container supports meet fracture control requirements.
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Note that supports may either be integral to the container or separate parts, such as brackets. If the supports are integral to the container and are fracture critical, further discussion with the RFCB is necessary for classification of the container. Separate support parts should be classified independent of the container.
- b. The part is manufactured from metal alloys typically used for commercially available sealed containers procured to an aerospace standard or equivalent that are not susceptible to crack extension related to EAC or SLC.
- c. The container satisfies the LBB definition in this document at MDP.
- d. The container does not have an impervious barrier or coating that inhibits leakage on either the interior or exterior surfaces.
- e. A container is subject to the following:
- (1) Inspected for leaks before repressurization.
- (2) Re-flight containers are inspected for leaks before being re-flown.
- f. The container stored fluid energy is less than 19,307 J (14,240 ft-lb) based on adiabatic expansion of a perfect gas.
- g. If the MDP of the container is 152 kPa (22 psi, 1.5 atm) or less, no additional assessment for items h and i below is required.
- h. If the MDP of the container is greater than 152 kPa (22 psi, 1.5 atm) and no more than 304 kPa (44 psi, 3 atm), satisfy one of the following:
- (1) An analysis shows that the container has a positive margin against burst when a factor of 2.5 on MDP is used.
- (2) The container is proof tested to a minimum of 1.5 times the MDP.
- i. If MDP is greater than 304 kPa (44 psi, 3 atm), the sealed container may not be classified in this category.
The container portion of an NFC sealed container does not require NDE to screen for flaws. The container supports may require NDE, depending on their individual fracture control classification. The guidance on LBB assessment provided in section 6.2.4 in this NASA Technical Standard is also applicable to this section. Proof tests are usually performed in the operational environment, or the test levels are adjusted via an ECF.
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Inertial load effects (including attach points) may necessitate additional assessments beyond the items in this category.
6.1.5 NFC Tools, Mechanisms, and Tethers
Satisfy either of the following to classify a part as an NFC tool, mechanism, or tether to meet requirement [FCR 7] section 6.1.e in this NASA Technical Standard:
- a. To classify tools, mechanisms, and tethers as NFC during storage and usage, meet the requirements in sections 6.2.1 or 6.2.5 in this NASA Technical Standard.
- b. To classify tools, mechanisms, and tethers as NFC during storage, meet the requirements in sections 6.2.2 or 6.2.3 in this NASA Technical Standard.
6.1.6 NFC Batteries
Satisfy one of the following to classify parts as NFC battery cells/cases to meet requirement [FCR 7] section 6.1.f in this NASA Technical Standard:
- a. Meet the NHLBB requirements in section 6.2.4 in this NASA Technical Standard.
- b. Meet the sealed container requirements in section 6.1.4 in this NASA Technical Standard.
Small batteries in common use, such as button cells of 200 mA-hr or less and carbon-zinc or zinc-air batteries of size F or smaller are exempt from fracture control.