MIL-HDBK-1530B(USAF)
5.2.4 will be used to develop design flight-by-flight stress/environment spectra as appropriate to support the various analyses and test tasks described herein.
5.2.4 Design chemical/thermal environment spectra. Detail guidance for design chemical/thermal environment spectra is in JSSG-2006. These environmental spectra should characterize the intensity, duration, frequency of occurrence, etc.
5.2.5 Stress analysis. A stress analysis should consist of the analytical determination of the stresses, deformation, and margins-of-safety which result from the external loads and temperatures imposed on the airframe. In addition to verification of strength, the stress analysis should be used as a basis for durability and damage- tolerance analyses, selection of critical structural components for design development tests, material review actions, and selection of loading conditions to be used in the structural strength tests. The stress analysis is also used as a basis to determine the adequacy of structural changes throughout the life of the air vehicle and to determine the adequacy of the structure for new loading conditions which result from increased performance or new mission requirements. The stress analysis should be revised to reflect any major changes to the airframe or to the loading conditions applied to the airframe.
5.2.6 Damage tolerance analysis. Detail guidance for damage tolerance analysis is contained in the requirement and verification for Damage tolerance (3.12 and 4.12) in JSSG-2006. The purpose of this analysis is to substantiate the ability of the structural components to comply with the detail requirements for damage tolerance. The design flight-by-flight stress/environment spectra based on the requirements of 5.2.3 and 5.2.4 should be used
in the damage growth analysis and verification tests. The calculations of critical flaw sizes, residual strengths, safe crack growth periods, and inspection intervals should be based on existing fracture test data and basic fracture allowables data generated as a part of the design development test program. The effect of variability in fracture properties on the analytical results should be accounted for in the damage tolerance design.
5.2.7 Durability analysis. Detail guidance for durability is contained in the requirement and verification for Durability (3.11 and 4.11) in JSSG-2006. The purpose of this analysis is to substantiate the ability of the structure to comply with the detail requirements for durability. The design flight-by-flight stress/environment spectra based on the requirements of 5.2.3 and 5.2.4 should be used in the durability analysis and verification tests. The analysis approach should account for those factors which affect the time for cracks or equivalent damage to reach sizes large enough to cause uneconomical functional problems, repair modification, or replacement. These factors should include initial quality and initial quality variations, chemical/thermal environment, load sequence and environment interaction effects, material property variations, and analytical uncertainties. In addition to providing analytical assurance of a durable design, the durability analysis will provide a basis for development of test load spectra to be used in the design development and full-scale durability tests.
5.2.8 Aeroacoustic durability analysis. Utilize the verification guidance for Vibration and aeroacoustics, Aeroacoustic disability, Structures, and Analyses (4.4.3, 4.5, 4.5.1, and 4.5.1.1; respectively) in JSSG-2006 to comply with the requirements for sonic durability of the contract. The objective of the sonic durability analysis is to ensure the airframe is resistant to sonic durability cracking throughout the design service goal. The analysis should define the intensity of the acoustic environment from potentially critical sources and should determine the dynamic response, including significant thermal effects. Potentially-critical sources include but are not limited to powerplant noise, aerodynamic noise in regions of turbulent and separated flow, exposed cavity resonance, and localized vibratory forces.
5.2.9 Vibration analysis. Utilize the verification guidance for Ramps, Vibration, and Analyses (4.3.3, 4.6, and 4.6.1; respectively) in JSSG-2006 to comply with the requirements for vibration analysis specified in the contract. The analysis should predict the resultant environment in terms of vibration levels in various areas of the
air vehicle such as the crew compartment, cargo areas, equipment bays, etc. The vibration analyses, in conjunction with the durability analyses of 5.2.7, should show that the structure in each of these areas is resistant to cracking due to vibratory loads throughout the design service goal. In addition, the analyses should show that the vibration levels are suitable for the reliable performance of personnel and equipment throughout the design-life of the air vehicle.
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