Structural Component Failures

Most structural failures are due to fatigue (cyclic stress) rather than static loading. A combination of several analysis methods aid in defining the “root cause” of a structural failure. A combination of several analysis methods will aid in defining the “root cause” of a structural failure.

Analyses of structural failures can include:

• Metallurgical examination of the surfaces and material properties
• Calculation of stress or deformation from applied loads
• Knowledge of dynamic characteristics of the failed components
• Non-Destructive Testing (NDT)

Metallurgical examinations can define the conditions which caused the failure: overload, high-cycle fatigue, corrosion, stress risers, etc. A metallurgical investigation can determine whether environmental conditions (corrosion, hydrogen embrittlement, etc.) reduced the component’s strength below its design condition.

In addition to metallurgical examination, engineering analyses of the component should also consider dynamic characteristics (resonant frequencies) which can amplify dynamic loads. Determination of the load sufficient to produce a stress in excess of the material endurance stress or yield stress can help identify abnormal load conditions which would have caused the failure. A well-designed component will usually survive under “design load conditions”, however, an unexpected or transient condition may occur which leads to failure. These analysis methods complement each other to form a complete scenario leading to the failure.

Non Destructive Testing (NDT) of remaining components within the machine or on identical machines in the same operating system can be performed in lieu of dynamic analyses. Actual testing is usually more pertinent when identical components are available. As an example see Summary of Turbine Wheel Test.

EDI can perform all types of NDT and operating tests to document resonant frequencies, vibration and stress. EDI has an affiliation with metallurgical engineers and a test laboratory to perform all types of fractographic and corrosion examinations, chemical analyses, and mechanical property tests to complement to the failure analysis.