What is the primary cause of structural failure in aircraft under stress?

The primary cause of structural failure in aircraft under stress is material fatigue due to repeated loading. Aircraft structures endure various loads throughout their operational life, including aerodynamic forces, pressure changes, and temperature fluctuations. Over time, the constant cycling of these stresses can lead to microscopic cracks in the material, which may grow and ultimately result in structural failure. This fatigue is a critical factor in the longevity and safety of aircraft, as even well-designed structures can succumb to this issue if not properly monitored.

While excessive weight during takeoff can certainly impose additional stress on the airframe, it is not the primary cause of structural failure; rather, it is more of a contributing factor that can exacerbate existing issues. Similarly, poor aircraft design can lead to vulnerabilities, but many designs are thoroughly tested to meet safety standards, making systematic fatigue a more prevalent concern. Insufficient maintenance checks can also lead to undetected fatigue issues or material degradation, but again, the inherent material properties and behavior under repeated stress is the fundamental cause of failure. Thus, material fatigue is recognized as the principal concern in the structural integrity of aircraft under stress.