Engineering procedure for evaluating the load-bearing capacity and life of a defective structure

A piece of rocket and space hardware may consist of tens of thousands of parts. Virtually every as-built piece of hardware has some non-conformances to the design documentation. Manufacturing defects often occur or are discovered during the final stages of the vehicle assembly or pre-launch processing. In such cases, removal of the non-conformance is either impossible or is too difficult and costly. The procedure described in the paper makes it possible to evaluate the degree of impact of a typical defect on the load-bearing capacity, strength, leak integrity, and life of a structure under its operating conditions. Sections of the procedure include description of operations involving non-destructive testing, determining loads on the vehicle and other operating conditions, stress-strain analysis, experimental determination of the material properties, prediction of the crack kinetics from the standpoint of fracture mechanics. The procedure gives a structural analyst an algorithm for solving the complex problem of estimating the service life, which consists of a sequence of specific tasks: developing the finite element model, classifying the defect, constructing the loading block, analyzing stress-strain behavior, predicting the behavior of the initial defect. Introducing the procedure into engineering practice will make it possible to increase validity of the estimate of the load bearing capacity and life, and, therefore, of the reliability and safety of the vehicle operation.