Journal of Failure Analysis and Prevention

, Volume 14, Issue 4, pp 478–490 | Cite as

Probabilistic Failure Prediction of High Strength Steel Rocket Motor Cases

  • A. Krishnaveni
  • T. Christopher
  • K. Jeyakumar
  • D. Jebakani
Technical Article---Peer-Reviewed

Abstract

In traditional deterministic analysis, uncertainties are either ignored or accounted by applying conservative assumptions. In those cases, only the mean values or nominal values are used in the analysis. Currently, the operating pressure of high strength steel rocket motor cases is predicted by arbitrarily assumed safety factor based on experience. This leads to over weight of motor cases and cost. Hence a methodology is required to predict the operating pressure more accurately by considering optimal safety factor. This paper presents the probabilistic failure assessment methodology to predict the safety factor for the specified reliability using various failure pressure prediction equations. In this study, the scatter in the yield strength, ultimate strength, and thickness of the structure is considered. Monte–Carlo simulation method is used to perform the probabilistic failure assessment. A suitable failure pressure prediction equation is identified among thirteen equations using stress–strength interference theory based on the statistical measure of the predicted and literature test failure pressure. The reliability-based safety factor is computed for the specified reliability with the use of identified failure pressure prediction equation. The safe operating pressure of steel rocket motor cases is computed for the specified reliability levels.

Keywords

Failure analysis Structural integrity Monte–Carlo simulation Cylinders Aircraft 

List of symbols

AD

Anderson–darling statistic

e

2.7828183

n

Strain hardening exponent

N

Factor of safety

p

Probability

r

Radius, R i ≤ r ≤ R o (mm)

R

Reliability (%)

s

Predicted failure pressure (MPa)

S

Literature experimental failure pressure (MPa)

t

Thickness of cylinder (mm)

u

Radial displacement (mm)

y

Margin of safety

z

Standard normal variate for the specified reliability

α

Significance level

ε

Strain

κ

R o /R i

Di, Do

Inner and outer diameters of cylinder (mm)

pi

Internal pressure (MPa)

pm

Maximum/failure pressure/burst pressure of unflawed vessel (MPa)

Ri,Ro

Inner and outer radii of cylinder (mm)

VS

Coefficient of variation of experimental failure pressure (%)

Vs

Coefficient of variation of predicted failure pressure (%)

xi

(r + u)/R o

εi

Effective strain at inner surface

εo

Effective strain at outer surface

εu

True strain at ultimate load

εult

Nominal strain at ultimate load

σ0

Material constant in stress–strain equation

σS

Standard deviation of experimental failure pressure

σs

Standard deviation of predicted failure pressure

σu

True stress at ultimate load (MPa)

σult

Ultimate tensile strength (MPa)

σys

Yield strength or 0.2% proof stress (MPa)

μS

Mean of experimental failure pressure (MPa)

μs

Mean of predicted failure pressure (MPa)

po

Operating pressure (MPa)

COV

Coefficient of variation (%)

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Copyright information

© ASM International 2014

Authors and Affiliations

  • A. Krishnaveni
    • 1
  • T. Christopher
    • 1
  • K. Jeyakumar
    • 2
  • D. Jebakani
    • 1
  1. 1.Faculty of Mechanical EngineeringGovernment College of EngineeringTirunelveliIndia
  2. 2.Faculty of Mechanical EngineeringSCAD Engineering CollegeCheranmahadeviIndia

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