What is aircraft structure fatigue?

Fatigue is a common occurrence among all metal airframes. Due to the repeated flight cycles and frequent use, the metal elements of planes become weakened over time, and they will eventually require attention and repair. This weakness manifests in cracks, which are microscopic at first.

What is life in fatigue analysis?

Fatigue analysis itself usually refers to one of two methodologies: either the Stress-Life (S-N) or S-N method, commonly referred to as Total Life since it makes no distinction between initiating or growing a crack, or the Local Strain or Strain-Life (e-N) method, commonly referred to as the Crack Initiation method …

What governs the ultimate fatigue life of an aircraft?

“Aircraft lifespan is established by the manufacturer,” explains the Federal Aviation Administration’s John Petrakis, “and is usually based on takeoff and landing cycles.

What is structural failure in aircraft?

Defective Design, Unsafe Aircraft, Overstressed Frame. An aircraft’s structural failure in midair is a frightening and often fatal experience. Bad design, improper maintenance, careless construction and retrofitted parts are among many causes of structural failure which lead to aircraft crashes.

Which method can be selected to monitor the fatigue cracks in components of aerospace and transport systems?

Eddy current tests are important test & widely used method within the broad field of Nondestructive materials & evaluation. This method is particularly well suited for the detection of service induced cracks usually caused either by fatigue or by stress corrosion.

What is fatigue life of a component?

Fatigue life is defined as the number of cycles that lead to the failure of structural system [19].

What determines an airplane’s lifespan?

The lifespan of aircraft is determined by the manufacturer. The age is calculated based on pressurization cycles. As a rule of thumb, each cycle involves “takeoff/landing.” Fuselage and wings suffer stress from pressurization, including on “short hauls.”

What are the three main aspects of damage tolerance?

Damage tolerance analysis stresses in the structure (both fatigue and operational maximum stresses) that cause crack growth from the damaged condition. geometry of the material which intensifies or reduces the stresses on the crack tip.

What is damage tolerant in aviation?

Damage tolerance is the ability of an aircraft structure to sustain damage, without catastrophic failure, until such time that the component can be repaired or replaced.

What are the three reasons for structural deterioration of an aircraft?

Structural Fatigue

• in internal load-bearing airframe structural components which can develop stress ‘hot spots’;
• in load bearing skins of large aircraft in which the skin itself carries a significant structural load;

What are the most common fatigue failures of aircraft structural components?

The most common fatigue failures arise from sharp edges, notch sensitive areas and necked down sections in the structural parts. In this chapter, two case studies about failure of aircraft structural components are discussed.

What is aircraft fatigue and why does it occur?

While aircraft fatigue is a natural part of flight, both visible cracks and cracks invisible to the eye mean failure is a real possibility. Why Does Aircraft Fatigue Occur? Much like any metal vehicle, heavy use and wear weaken aircraft over long periods. Any time an aircraft is flown, it endures fatigue.

How do we demonstrate fatigue service life for composites?

Current regulations require airframes to demonstrate fatigue service life by testing and/or analysis. This requirement is identical for both metals and composites. As composites exhibit higher scatter than metals, extensive scatter analysis was conducted by Northrup/Grumman using several material databases.

Structural failure occurs when aircraft fatigue is not detected early enough or is left untended. Since most fatigue cracks are invisible to the eye initially, it makes them particularly challenging to detect. These cracks are what directly cause large-scale damage and danger.