A new methodology to predict damage tolerance based on compliance via global-local analysis

Over the years several design philosophies to fatigue developed in order to combine structural safety and economy to manufacturing and operating aircraft process. The safe-life approach, which consists of designing and manufacturing a safe aeronautical structure throughout its useful life, results in factors that oversize the structural elements, preventing the possibility of failure and evidently leading to high design costs. On the other hand, the approach based on the damage tolerance concept, in which it is assumed that the structure, even whether damaged, is able to withstand the actions for which it was designed until the detection of a crack due to fatigue or other defects during its operation. Here, we propose a new methodology to the damage tolerance problem in which two-dimensional global-local analysis at different levels of external requests will be made by means of compliance, aimed at finding a relationship between fatigue life and the Paris constant. Moreover, the BemCracker2D program for simulating two-dimensional crack growth is used. This methodology has been proved to be an efficient and applied alternative in the damage tolerance analysis.

Aircraft repair damage tolerance analysis

Modern air travel has become a perpetual evolution both from a practical and scientific point of view. However, it is also becoming increasingly common to fly in an airplane with little or no regard for the immense engineering involvement that goes into making air travel as safe and efficient as possible. This report considers the problems of aircraft fatigue and how it translates to inspectability for safety in order to predict problems and solve them before they actually occur. The most common aircraft repair is a crack in a pressurized skin panel. This report evaluates the structural integrity of a particular panel that is assumed to have failed in service and thus been repaired by the addition of a doubler. Damage tolerance analysis is used to evaluate a conservative crack growth scenario for a typical business jet with a structural economic life of 15,000 flight hours. The step shown follow the guidelines approved by the regulating aviation bodies of both Canada and the United States (Transport Canada and the FAA respectively). Structural inspections are a common practice for aircraft at their half lives; in this case it would be 7,500 flights. The report determines that this particular scenario defines a threshold inspection interval of 8,414 flights and a repeat of 2,944 flights thereafter. In comparison with an actual test aircraft, having experienced an almost identical failure and repair program, the test aircraft experienced failure at 9,963 flights. Therefore, the intervals presented herein provide adequate clearance for the detection and repair of such damage. The purpose of this report is to introduce the underlying principals of damage tolerance analysis to the reader and illustrate the analytical process with a real world example. Such is the job of an aerospace stress engineer.

Aircraft repair damage tolerance analysis

Modern air travel has become a perpetual evolution both from a practical and scientific point of view. However, it is also becoming increasingly common to fly in an airplane with little or no regard for the immense engineering involvement that goes into making air travel as safe and efficient as possible. This report considers the problems of aircraft fatigue and how it translates to inspectability for safety in order to predict problems and solve them before they actually occur. The most common aircraft repair is a crack in a pressurized skin panel. This report evaluates the structural integrity of a particular panel that is assumed to have failed in service and thus been repaired by the addition of a doubler. Damage tolerance analysis is used to evaluate a conservative crack growth scenario for a typical business jet with a structural economic life of 15,000 flight hours. The step shown follow the guidelines approved by the regulating aviation bodies of both Canada and the United States (Transport Canada and the FAA respectively). Structural inspections are a common practice for aircraft at their half lives; in this case it would be 7,500 flights. The report determines that this particular scenario defines a threshold inspection interval of 8,414 flights and a repeat of 2,944 flights thereafter. In comparison with an actual test aircraft, having experienced an almost identical failure and repair program, the test aircraft experienced failure at 9,963 flights. Therefore, the intervals presented herein provide adequate clearance for the detection and repair of such damage. The purpose of this report is to introduce the underlying principals of damage tolerance analysis to the reader and illustrate the analytical process with a real world example. Such is the job of an aerospace stress engineer.

Crack Growth in a Range of Additively Manufactured Aerospace Structural Materials

The aerospace industry is now beginning to adopt Additive Manufacturing (AM), both for new aircraft design and to help improve aircraft availability (aircraft sustainment). However, MIL-STD 1530 highlights that to certify airworthiness, the operational life of the airframe must be determined by a damage tolerance analysis. MIL-STD 1530 also states that in this process, the role of testing is merely to validate or correct the analysis. Consequently, if AM-produced parts are to be used as load-carrying members, it is important that the d a / d N versus ΔK curves be determined and, if possible, a valid mathematical representation determined. The present paper demonstrates that for AM Ti-6Al-4V, AM 316L stainless steel, and AM AerMet 100 steel, the d a / d N versus ΔK curves can be represented reasonably well by the Hartman-Schijve variant of the NASGRO crack growth equation. It is also shown that the variability in the various AM d a / d N versus Δ K curves is captured reasonably well by using the curve determined for conventionally manufactured materials and allowing for changes in the threshold and the cyclic fracture toughness terms.