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

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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