--- title: Fatigue Analysis for Spaceflight Hardware | Fidelis Aerospace description: Fatigue life analysis for spaceflight hardware, including stress-life, strain-life, cumulative damage, mission spectra, thermal fatigue, and test correlation. --- - Log In [![Fidelis Aerospace - Structural Integrity Engineering](https://www.fidelisaerospace.com/hs-fs/hubfs/Branding/Fidelis%20Aerospace%20Logo%20-%20Structural%20Integrity%20Engineering.png?width=275&height=50&name=Fidelis%20Aerospace%20Logo%20-%20Structural%20Integrity%20Engineering.png "Fidelis Aerospace - Structural Integrity Engineering")](https://www.fidelisaerospace.com?hsLang=en) - [Home](https://www.fidelisaerospace.com) - [Services](https://www.fidelisaerospace.com/services) Show submenu for Services - [Fatigue Analysis](https://www.fidelisaerospace.com/services/fatigue-analysis) - [Fracture Mechanics](https://www.fidelisaerospace.com/services/fracture-mechanics) - [Consulting](https://www.fidelisaerospace.com/consulting) Show submenu for Consulting - [Independent Review](https://www.fidelisaerospace.com/consulting/independent-technical-review) - [Research](https://www.fidelisaerospace.com/research) - [About](https://www.fidelisaerospace.com/about) - [Contact](https://www.fidelisaerospace.com/contact) - [Home](https://www.fidelisaerospace.com) - [Services](https://www.fidelisaerospace.com/services) Show submenu for Services - [Fatigue Analysis](https://www.fidelisaerospace.com/services/fatigue-analysis) - [Fracture Mechanics](https://www.fidelisaerospace.com/services/fracture-mechanics) - [Consulting](https://www.fidelisaerospace.com/consulting) Show submenu for Consulting - [Independent Review](https://www.fidelisaerospace.com/consulting/independent-technical-review) - [Research](https://www.fidelisaerospace.com/research) - [About](https://www.fidelisaerospace.com/about) - [Contact](https://www.fidelisaerospace.com/contact) ## *Spaceflight Fatigue Analysis* # Fatigue analysis and structural life assessment for spaceflight hardware Fidelis Aerospace evaluates how repeated loading affects structural life, which locations and details govern fatigue performance, and how changes in loads, geometry, material, manufacturing, finish, or mission usage affect predicted life. Fatigue analysis supports decisions about design, qualification, testing, mission life, reuse, and additional evidence. The credibility of the result depends on the stress or strain solution, loading spectrum, material data, manufacturing condition, analytical assumptions, and the engineering decision the estimate must support. [Request a Technical Discussion](https://www.fidelisaerospace.com/technical-discussion?hsLang=en) ## When to engage Fidelis for fatigue analysis - A component has a cyclic-life or mission-life requirement. - Repeated mechanical, pressure, thermal, vibration, or combined loading may limit structural life. - The program needs to identify fatigue-critical locations before qualification or flight. - A mission profile, duty cycle, or usage spectrum must be converted into an engineering life assessment. - A design change affects local stress concentration, joint behavior, surface condition, loading, material, or manufacturing state. - Reusable hardware must be evaluated for repeated missions or operating cycles. - A test result or unexpected crack suggests that predicted fatigue behavior does not match the hardware. - The internal engineering team needs specialized fatigue capability, independent review, or additional senior-level support. ## Fatigue analysis capabilities ### Load spectra and cycle characterization Translate mission, operating, qualification, test, or measured loading into cycles and ranges suitable for fatigue assessment. Evaluate cycle counts, loading sequence, spectrum definition, and mission assumptions when they materially affect predicted life. ### Stress-life assessment Use S-N methods to estimate fatigue life where elastic stress methods and appropriate material or detail fatigue data are applicable. Stress-life methods may be used for high-cycle fatigue, preliminary life assessment, design comparison, and other applications where the assumptions of the method are appropriate. ### Strain-life assessment Use strain-life or local-strain methods when significant local cyclic plasticity, low-cycle loading, notch behavior, or highly concentrated local response requires a strain-based approach and suitable material data are available. ### Mean-stress and notch effects Account for mean stress, stress concentration, notch sensitivity, surface condition, size, finish, and other relevant modifiers when supported by the selected fatigue method and available data. ### Cumulative damage Estimate fatigue damage accumulated across variable-amplitude or mission-spectrum loading and identify which cycles, events, or portions of the mission dominate predicted fatigue life. ### Joints and structural details Evaluate fatigue-sensitive holes, lugs, fittings, attachments, transitions, cutouts, joints, fasteners, and other local structural details using appropriate stress, strain, and fatigue methods. ### Thermal and mechanical fatigue Evaluate fatigue driven by repeated thermal loading, mechanical loading, or combined thermal-mechanical response when appropriate stress, temperature, material, and cycle information are available. ### Sensitivity and design improvement Determine how predicted fatigue life changes with loading, geometry, material data, surface condition, manufacturing state, residual stress, stress concentration, spectrum definition, or other important assumptions. Use sensitivity studies to identify the factors that most strongly control life and where design changes, testing, or improved data may provide the most value. ### Test planning and correlation Support fatigue test planning, expected critical locations, loading definition, instrumentation strategy, life prediction, interpretation of observed failures, and comparison between analytical predictions and test behavior. ### Independent review Review client-generated fatigue analyses, including loading spectra, stress or strain solutions, fatigue data, correction factors, cycle counting, cumulative-damage calculations, assumptions, sensitivities, and conclusions. ## Fatigue analysis in practical terms A structure can satisfy static strength requirements and still have inadequate fatigue life. Fatigue analysis asks how repeated loading changes the engineering assessment. The answer may depend on relatively small portions of the overall load history, highly localized stress or strain concentrations, surface or manufacturing conditions, tensile mean stresses, thermal cycling, residual stress, material variability, or details that have little effect on a conventional static-strength calculation. For spaceflight hardware, fatigue may be driven by launch and ascent environments, pressurization cycles, repeated mechanism operation, thermal cycling, ground testing, reusable missions, propulsion-system operation, or other recurring load events. The objective is not simply to calculate a number of cycles. It is to understand what controls structural life and whether the available analysis and evidence are sufficient to support the program decision. ## Information commonly needed - Geometry and local detail definition at potential fatigue-critical locations. - Nominal, local, analytical, or finite-element-derived stress or strain histories. - Mission profiles, operating cycles, qualification loads, test spectra, or measured loading. - Material fatigue data appropriate to the material condition, heat treatment, temperature, environment, and manufacturing process. - Surface condition, finish, machining, additive manufacturing, residual stress, and other process-related information where relevant. - Joint, fastener, interference, preload, contact, and load-transfer assumptions where applicable. - Life requirement, mission count, operating cycles, reliability or scatter treatment, acceptance criteria, and intended use of the result. - Existing test data, prior fatigue analyses, observed cracks, failures, or other relevant evidence. ## Potential outputs Depending on scope, outputs may include: - Fatigue-analysis plans. - Mission-spectrum and cycle definitions. - Cycle-count summaries. - Stress or strain extraction. - Fatigue-critical-location screening. - Stress-life or strain-life calculations. - Cumulative-damage assessments. - Mission-life or cycle-life predictions. - Sensitivity and uncertainty studies. - Design comparisons. - Fatigue-test predictions. - Analysis-test correlation. - Independent-review findings. - Design or analysis recommendations. - Technical memoranda or engineering reports. ## Fatigue analysis versus fracture mechanics Fatigue analysis generally evaluates structural life under repeated loading before a crack is explicitly represented. Typical fatigue methods use stress, strain, loading cycles, material fatigue behavior, and cumulative-damage relationships to estimate life or identify fatigue-critical locations. Fracture mechanics begins with an assumed or existing flaw and evaluates quantities such as crack-driving force, fatigue crack growth, critical flaw size, residual strength, and remaining structural life. The two disciplines answer different but related questions. A fatigue assessment may ask: **How long can this hardware withstand repeated loading before fatigue becomes limiting?** A fracture mechanics assessment may ask: **If a crack or crack-like flaw exists, how will it behave and when could it become critical?** Some structural-life problems require both approaches. [Explore Fracture Mechanics](https://www.fidelisaerospace.com/services/fracture-mechanics?hsLang=en) ## Interpreting a fatigue-life result A calculated fatigue life is not an inherent property of a component. It is the result of a defined engineering model of geometry, loading, local stress or strain, material behavior, manufacturing condition, environment, cycle definition, and failure criterion. Changes in any of these inputs can materially change the predicted life. Fidelis documents the assumptions, identifies the dominant life drivers, evaluates important sensitivities, and communicates how the analysis can appropriately support the engineering decision. ### Need to understand how repeated loading affects your hardware? Share a non-sensitive summary of the hardware, mission or life requirement, loading environment, available stress or strain results, material and manufacturing condition, and the engineering decision the fatigue assessment must support. Fidelis can help determine the appropriate fatigue-analysis approach and the information needed to establish a defensible life assessment. [Request a Technical Discussion](https://www.fidelisaerospace.com/technical-discussion?hsLang=en) ## Frequently Asked Questions ### What is fatigue analysis? Fatigue analysis evaluates how repeated loading affects structural life. Depending on the application, the analysis may use stress-life, strain-life, cumulative-damage, detail-based, test-supported, or other appropriate methods to estimate life and identify the locations or conditions most likely to govern fatigue performance. ### What types of loading can contribute to fatigue in spaceflight hardware? Fatigue may result from repeated mechanical loading, launch and vibration environments, pressurization cycles, thermal cycling, mechanism operation, propulsion-system cycles, ground testing, reusable missions, or combinations of these events. The relevant loading depends on the hardware and mission. ### What data are needed for fatigue analysis? Typical inputs include geometry, local stress or strain, mission or operating cycles, material fatigue data, manufacturing and surface condition, environment, temperature, mean stress, structural-detail information, life requirements, and relevant test evidence. The exact inputs depend on the selected fatigue method and the engineering decision being supported. ### Can fatigue life be predicted without testing? An analytical fatigue-life estimate can be developed without a dedicated component fatigue test when suitable loading, stress or strain solutions, material data, and analytical methods are available. Confidence in the prediction generally improves when the methods and inputs are supported by representative material, coupon, element, component, or system-level test evidence. ### What can cause low predicted fatigue life? Common drivers include high local stress or strain concentration, severe cyclic loading, tensile mean stress, surface condition, manufacturing effects, residual stress, joint behavior, material variability, temperature, environment, and assumptions that do not accurately represent the actual hardware or mission.  ### Does Fidelis perform fatigue crack-growth analysis? Yes, but fatigue crack growth is treated as a fracture-mechanics problem because the analysis begins with an assumed or existing crack. Fidelis provides fatigue crack-growth analysis as part of its fracture mechanics services. ### Does Fidelis perform finite element analysis for fatigue problems? Yes. Finite element analysis may be used when needed to establish the local stress, strain, temperature, or structural response required for a fatigue assessment. FEA is used as a supporting analytical method rather than offered as a standalone general-purpose service. 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