Accession Number : ADA258931


Title :   Assessment of Helicopter Component Statistical Reliability Computations


Descriptive Note : Final rept.


Corporate Author : ARMY LAB COMMAND WATERTOWN MA MATERIAL TECHNOLOGY LAB


Personal Author(s) : Matthews, William T ; Neal, Donald M


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a258931.pdf


Report Date : Sep 1992


Pagination or Media Count : 29


Abstract : This report identifies potential errors in computing high statistical reliability for a required component fatigue life. The reliability values were determined from application of a joint probability density (JPD) analysis used in an American Helicopter Society round robin safe life problem. In the analysis normal probability density functions (PDFs) were assumed for both the material strength and the spectrum load values. The PDF model parameters were varied and the PDFs were slightly modified (contaminated) in order to examine the sensitivity in computing high statistical reliability when uncertainties exist in assuming the PDF. Lower tails of the PDFs were also modified by truncation, independent of the model contamination, in order to determine the relative influence on reliability from tail modifications as compared with the parameter uncertainties and contamination. The stability of statistical estimates of the extreme tail quantiles and their corresponding probabilities as a function of sample size were examined for a generic distribution. Assuming a PDF to represent load or material strength is a substantially more critical issue than accurate representation of the extreme lower tail of the PDF when computing high reliability. Sampling trials for extreme tail quantiles and reliabilities indicate that unstable values can result from sample sizes of 100. The primary conclusion from these analytic results is that the computation of a high statistical reliability may have little or no association with actual engineering high reliability.


Descriptors :   *COMPUTATIONS , *FATIGUE LIFE , *PROBABILITY DENSITY FUNCTIONS , *STATISTICAL SAMPLES , *ERRORS , *HIGH RELIABILITY , *HELICOPTERS , UNCERTAINTY , ESTIMATES , SAMPLING , TRUNCATION , FLIGHT LOADS , VALUE , FATIGUE , FLIGHT , ENGINEERING , RELIABILITY , MODIFICATION , SENSITIVITY , MODELS , STABILITY


Subject Categories : Helicopters
      Statistics and Probability
      Mfg & Industrial Eng & Control of Product Sys
      Safety Engineering


Distribution Statement : APPROVED FOR PUBLIC RELEASE