Engineering topics

Uppaluri, B.

Publications and source records attributed to Uppaluri, B..

6 records

NASA NTRS1979

Reusable solid rocket motor case - Optimum probabilistic fracture control

A methodology for the reliability analysis of a reusable solid rocket motor case is discussed in this paper. The analysis is based on probabilistic fracture mechanics and probability distribution for initial flaw sizes. The developed reliability analysis can be used to select the structural design variables of the solid rocket motor case on the basis of minimum expected cost and specified reliability bounds during the projected design life of the case. Effects on failure prevention plans such as nondestructive inspection and the material erosion between missions can also be considered in the developed procedure for selection of design variables. The reliability-based procedure that has been discussed in this paper can easily be modified to consider other similar structures of reusable space vehicle systems with different fracture control plans.

Hanagud, S.↗

NASA NTRS1977

Probabilistic Fracture Mechanics and Optimum Fracture Control Analytical Procedures for a Reusable Solid Rocket Motor Case

A methodology for the reliability analysis of a reusable solid rocket motor case is discussed. The analysis is based on probabilistic fracture mechanics and probability distribution for initial flaw sizes. The developed reliability analysis is used to select the structural design variables of the solid rocket motor case on the basis of minimum expected cost and specified reliability bounds during the projected design life of the case. Effects of failure prevention plans such as nondestructive inspection and the material erosion between missions are also considered in the developed procedure for selection of design variables. The reliability-based procedure can be modified to consider other similar structures of reusable space vehicle systems with different failure prevention plans.

Hanagud, S.↗

NASA NTRS1977

Probabilistic fracture mechanics and optimum fracture control of the solid rocket motor case of the shuttle

Development of a procedure for the reliability analysis of the solid rocket motor case of the space shuttle is described. The analysis is based on probabilistic fracture mechanics and consideration of a probability distribution for the initial flaw sizes. The reliability analysis can be used to select design variables, such as the thickness of the SRM case, projected design life and proof factor, on the basis of minimum expected cost and specified reliability bounds. Effects of fracture control plans such as the non-destructive inspections and the material erosion between missions can also be considered in the developed methodology for selection of design variables. The reliability-based procedure can be easily modified to consider other similar structures and different fracture control plans.

Hanagud, S.↗

NASA NTRS1976

A reliability-based cost effective fail-safe design procedure

The authors have developed a methodology for cost-effective fatigue design of structures subject to random fatigue loading. A stochastic model for fatigue crack propagation under random loading has been discussed. Fracture mechanics is then used to estimate the parameters of the model and the residual strength of structures with cracks. The stochastic model and residual strength variations have been used to develop procedures for estimating the probability of failure and its changes with inspection frequency. This information on reliability is then used to construct an objective function in terms of either a total weight function or cost function. A procedure for selecting the design variables, subject to constraints, by optimizing the objective function has been illustrated by examples. In particular, optimum design of stiffened panel has been discussed.

Hanagud, S.↗

NASA NTRS1975

Stochastic model for fatigue crack size and cost effective design decisions

This paper describes a methodology for making cost effective fatigue design decisions. The methodology is based on a probabilistic model for the stochastic process of fatigue crack growth with time. The development of a particular model for the stochastic process is also discussed in the paper. The model is based on the assumption of continuous time and discrete space of crack lengths. Statistical decision theory and the developed probabilistic model are used to develop the procedure for making fatigue design decisions on the basis of minimum expected cost or risk function and reliability bounds. Selections of initial flaw size distribution, NDT, repair threshold crack lengths, and inspection intervals are discussed.

Hanagud, S.↗

NASA NTRS1975

Reliability-based optimum inspection and maintenance procedures

The development of reliability-based optimum inspection and maintenance schedules for engines needs an understanding of the fatigue behavior of the engines. Critical areas of the engine structure prone to fatigue damage are usually identified beforehand or after the fleet has been put into operation. In these areas, fatigue cracks initiate after several flight hours, and these cracks grow in length until failure takes place when these cracks attain the critical lengths. Crack initiation time and its growth rate are considered to be random variables. Usually, the inspection (fatigue) or test data from similar engines are used as prior distributions. The existing state-of-the-art is to ignore the different lengths of cracks obserbed at various inspections and to consider only the fact that a crack existed (or did not exist) at the time of inspection. In this paper, a procedure has been developed to obtain the probability of finding a crack of a given size at a certain time if the probability distributions for crack initiation and rates of growth are known. Application of the developed stochastic models to devise optimum procedures for inspection and maintenance are also discussed.

Nanagud, S.↗