What are the best practices and standards for fatigue and fracture analysis of spacecraft structures?

1 Material selection

One of the first steps in fatigue and fracture analysis is to select the appropriate material for the spacecraft structure, based on its intended function, loading, and environment. The material should have adequate strength, stiffness, ductility, toughness, and resistance to corrosion, creep, and fatigue. Moreover, the material should be compatible with the manufacturing process and the joining techniques, such as welding or bonding. Some of the common materials used for spacecraft structures are aluminum alloys, titanium alloys, steel alloys, composites, and ceramics.

2 Stress analysis

The next step is to perform a stress analysis to determine the stress distribution and the critical locations in the spacecraft structure under various loading scenarios. The stress analysis can be done using analytical methods, numerical methods, or experimental methods, depending on the complexity and accuracy required. The stress analysis should consider both static and dynamic loads, as well as thermal loads and pressure loads. The stress analysis should also account for stress concentrations, stress gradients, and stress singularities, which can increase the risk of fatigue and fracture.

3 Fatigue life prediction

The fatigue life prediction is the process of estimating the number of cycles or the duration of time that a spacecraft structure can withstand before it fails due to fatigue. The fatigue life prediction is based on the stress analysis results and the material fatigue properties, such as the S-N curve or the strain-life curve. The fatigue life prediction can be done using various methods, such as the stress-life method, the strain-life method, the crack growth method, or the damage tolerance method. The fatigue life prediction should also consider the effects of mean stress, load sequence, load spectrum, load interaction, and load history.

4 Fracture mechanics

The fracture mechanics is the branch of mechanics that deals with the initiation and propagation of cracks in a material or a structure. The fracture mechanics is based on the concept of fracture toughness, which is a measure of the resistance of a material or a structure to crack growth under a given stress intensity factor. The fracture mechanics can be used to evaluate the critical crack size, the crack growth rate, and the residual strength of a spacecraft structure. The fracture mechanics can also be used to assess the effects of crack closure, crack tip plasticity, crack branching, crack coalescence, and crack interaction.

5 Testing and validation

The testing and validation is the process of verifying and validating the results of the fatigue and fracture analysis using experimental data or field data. The testing and validation can be done at different levels, such as material level, component level, subsystem level, or system level. The testing and validation can involve various types of tests, such as tensile tests, fatigue tests, fracture toughness tests, crack growth tests, or full-scale tests. The testing and validation should also consider the effects of environmental factors, such as temperature, humidity, pressure, radiation, or corrosion.

6 Standards and guidelines

The standards and guidelines are the documents that provide the best practices and recommendations for fatigue and fracture analysis of spacecraft structures. The standards and guidelines are developed by various organizations, such as NASA, ESA, ASTM, ISO, or AIAA. The standards and guidelines cover various aspects and topics of fatigue and fracture analysis, such as material selection, stress analysis, fatigue life prediction, fracture mechanics, testing and validation, design criteria, safety factors, inspection methods, maintenance procedures, or failure reporting. The standards and guidelines are intended to ensure the quality, reliability, and safety of spacecraft structures.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?