Chapter 10 - Structural Integrity, Safety and Design精品.pdfVIP

Chapter 10 Structural Integrity, Safety and Design A central issue in the design of composite structures is damage tolerance. Composite structures are often in a critical state when ‘ large’ damage is present, loss of damage tol- erance integrity constituting an ‘ unsafe state ’ inevitably leading to failure if not detected and corrected. The distribution of ‘ operating ’ internal loads is an elusive quantity, such loads varying from location to location; many similarities with stress fatigue spectra can be seen and the best way to deal with this situation might be in terms of criteria. Existing practices are not uniform, and future regulations need a baseline of struc- tural safety. This could be approached through the following equation, which describes the probability of an unsafe state: P (S ) P (A X D B H ) P (A | X D B H ) P (H | X D B ) n t 5T LT T n t 5T LT T T T 5T LT P (B || D X ) P (D | X } P (X ) (10.1) LT 5T t 5T t t An : Failure after n flights X t : Damage present since time t H T : Damage not detected at time T BLT : Residual strength less than requirement at time T D5T : Damage size in region D5 at time T . Numerical values with a realistic chance of satisfying the safety requirements yield P (A S ) (1 pn ) 108 P (B | D X ) n T s LT 5T t There is not a consistent practice for residual strength allowable values. If we adopt, for background, the ultimate allowable practice we get the following equation: P (A S ) (1 pn ) 103 P (B | D X S S ) P (D | X )