[FCR 10] Parts shall be classified as fracture critical unless one of the following is met:
- a. There is no credible possibility for a flaw in the part to cause failure during the lifetime of the part.
- b. Part failure does not result in a credible catastrophic hazard.
[Rationale: Parts that do not meet one of the above criteria require mitigation to preclude catastrophic failure. Classification as fracture critical denotes the need for knowledge of the sensitivity of the part to flaws or damage, an adequate screening of parts for flaws or damage
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and protection from damage, and traceability to assure a high-quality aerospace part is produced.]
Parts that are fracture critical require risk mitigation activities to provide assurance that flaw or damage sensitivity is understood relative to flaw screening or qualification and acceptance testing and material processing parameters.
The methods in this section are based on NASA’s experience base, established approaches, industry standards, or aerospace standards. Any deviations or omissions of elements in the activities or approaches described in this section constitute an alternative approach that is to satisfy the requirements in section 10 [FCR 26] in this NASA Technical Standard.
In addition to assessments discussed in the subsequent subsections, fracture critical parts are subject to flaw screening, traceability, and material selection requirements in accordance with section 8 in this NASA Technical Standard. Documentation of the approaches to implementation and the results of implementation activities are discussed in section 9 of this NASA Technical Standard for the FCP and FCSR requirements.
- a. Parts are fracture critical unless one of the following is met:
- (1) The part is exempt in accordance with section 5 in this NASA Technical Standard.
- (2) The part is NFC in accordance with section 6 in this NASA Technical Standard.
- b. Fracture critical parts are to comply with one of the following applicable items:
- (1) Established approaches for the specific hardware types in accordance with section 7.2 in this NASA Technical Standard.
- (2) General approach for fracture critical metallic parts assessment in accordance with section 7.3 in this NASA Technical Standard.
- (3) General approach for fracture critical composite or bonded hardware assessment in accordance with section 7.4 in this NASA Technical Standard.
- (4) Optional approaches for fracture critical parts in accordance with section 7.5 in this NASA Technical Standard.
- (5) Satisfy requirements in section 10 in this NASA Technical Standard for an alternative approach.
- c. Fracture critical parts are also to comply with the following items:
- (1) Satisfy flaw screening, traceability, and material requirements in section 8 in this NASA Technical Standard.
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- (2) Satisfy documentation requirements in section 9.1 in this NASA Technical Standard.
- d. A part should always be classified as fracture critical if there is doubt or concern to establish that it is not fracture critical.
- e. Parts that are often determined to be fracture critical include but are not limited to: rotating hardware that does not satisfy this NASA Technical Standard's section 6.1.3 requirements, hazardous fluid containers, pressure systems that contain hazardous fluids (such as liquid rocket engine systems), and pressurized structures (such as propellant tank structures), primary thrust structure (unpressurized), solid rocket motor cases and nozzles, and habitable modules.
- f. Pressure vessels, as defined in section 3.2 of this NASA Technical Standard, are fracture critical.
- g. Fracture critical parts receive additional attention beyond the standard structural and quality assurance assessments normally given to spaceflight hardware. These additional activities include the following:
- (1) Either an approved set of prescribed activities deemed to be sufficient to mitigate the risk of failure because of a flaw (established approaches and optional approaches) or a damage tolerance assessment (analysis, test, or both) to show life requirements are met in the presence of flaws.
- (2) Screening of parts for flaws.
- (3) Traceability of the parts.
- (4) Material requirements.
- (5) Documentation of the assessment and hardware implementation process.