Probabilistic Approach to Damage Tolerance Design of Aircraft Composite Structures

Abstract

A probabilistic approach to determine design parameters for damage-tolerant composite aircraft structures has been developed. The main criterion for acceptance of a structure is a specified probability of failure. The development of this approach is motivated by the increasing use of damage-sensitive composite aircraft structures. The resulting probabilistic model takes into account a probabilistic assessment of in-service accumulated damage, the ability of non-destructive inspection methods to detect such damage, the residual strength degradation of damaged structure, quality of repair and loads/temperatures expected between damage initiation and detection/repair. The special attention has been paid to the availability of input probabilistic data and the possibility to obtain such data at reasonable cost. Computing tools and algorithms for the probabilistic analysis have been developed. The validity of the approach has been demonstrated on several existing structural components. The main result of the study is that the reliability of a damage-tolerable composite structure can be assessed on a quantitative basis, allowing aircraft manufacturers, operators and flight certification authorities to establish the maintenance service guidelines and estimate the reasonable inspection intervals. Engineers can use this methodology in the future as a guide to establish design and inspection criteria while considering structural risk and maintenance cost at the same. = probability of detecting a damage/defect with a size greater than a P f , POF = probability of failure S i = strength through i th interval T° = temperature, K t i = time interval

Probabilistic Design of Wind Turbine Blades with Treatment of Manufacturing Defects as Uncertainty Variables in a Framework

“…However, previous studies 15 on damaged composites have shown that the fatigue life slope remains largely unchanged with damage (Lin and Styuart, 2007).…”

Fatigue crack growth of multiple interacting cracks: Analytical models and experimental validation

“…In this way, millions of different configurations, corresponding to possible fatigue scenarios of the component under investigation, can be simulated to derive the probability of failure as a function of the number of loading cycles. In the field of fatigue design of military aircraft, the USAF has already taken into account the probabilistic methodology 29 and requires a failure probability of less than 10 −7 per flight, although in some cases 30 it has also adopted 10 −8 .…”

Experiments and model predictions for fatigue crack propagation in riveted lap‐joints with multiple site damage

“…At present, USAF requires for the aircraft structure of long‐term military operations a probability of catastrophic failure at or below 10 −7 per flight. In same cases, even a lower probability of failure per flight is assumed, such as 10. −8 So, it is easily understandable that a high number of computer runs are necessary to evaluate the risk of failure by using the Monte Carlo method.…”