A Means of Assessing the Effects of Periodic Proof Testing and NDE on the Reliability of Cyclically Loaded Structures

A technique is presented that allows the effect of periodic proof testing and nondestructive evaluation (NDE) on the reliability of cyclically loaded structures to be calculated. This technique combines the initial defect size and nondestructuve inspection detection probability with fracture mechanics calculations of fatigue crack growth and final fracture to predict the failure probability of a cyclically loaded structure as a function of the number of cycles of load application. The influence of part geometry, stress levels, material properties, inspection procedures and inspection interval enter into the analysis. The results of an example problem are presented which indicates that the benefits of proof testing are restricted to a fairly short period immediately following the proof test. The length of this period can be extended significantly by acoustic emission monitoring of the proof test. The benefits of an in-service inspection can be large or small, depending on the inspection interval, detection probabilities, and stress level. The capability of the techniques presented to quantitatively assess the influence of the many parameters involved should make these procedures useful in a wide variety of applications.