Allowables-Based Flow Curves for Nonlinear Finite-Element Analysis
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Allowables-Based Flow Curves for Nonlinear Finite-Element Analysis J. D. Pratt
Received: 4 December 2006 / Accepted: 15 February 2007 / Published online: 28 April 2007 ASM International 2007
Abstract A methodology for developing allowablesbased stress versus strain relationships for metal alloys is presented. The approach incorporates Federal Aviation Administration/Department of Defense (FAA/DoD) Metallic Materials Property Development and Standardization (MMPDS) statistically derived material properties for tensile yield and ultimate strengths to derive flow curves at room or elevated temperature with an A-, B-, or S-Basis probability. The resulting flow curves may be used for new designs to comply with Federal Air Regulations as well as for forensic investigations and failure analysis. Keywords Materials allowables Finite-element analysis Material properties MMPDS Cozzone method Fictitious stress
Notation c Distance from neutral axis to extreme fiber e Engineering strain ep Plastic strain ePL Strain at the proportional limit eF Strain at failure eU Strain at maximum load eY Strain at 0.2%-offset E Elastic modulus f0 Fictitious stress F Allowables-based stress FF Allowables-based stress at failure FM Maximum allowable stress FPL Allowables-based stress at the proportional limit J. D. Pratt (&) Argos Engineering, 44 Argos, Laguna Niguel, CA 92677, USA e-mail: [email protected]
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FTU FTY I M P Q S SF SPL SU SY e eF ep ePL eU eY r rF rPL rU rY
Allowables-based stress at maximum load Allowables-based stress at 0.2%-offset Moment of inertia Moment Load Reduction of area at failure Engineering stress Engineering stress at failure Engineering stress at the proportional limit Engineering stress at maximum load Engineering stress at 0.2%-offset True strain True strain at failure True plastic strain True strain at the proportional limit True strain at maximum load True strain at 0.2%-offset True stress True stress at failure True stress at the proportional limit True stress at maximum load True stress at 0.2%-offset
Introduction Component design is typically accompanied by yield and ultimate load stress analyses to guard against premature failure and ensure compliance with specifications. Most linear analyses are readily performed using well established closed-form equations, whereas the more difficult ultimate analyses oftentimes rely on nonlinear finiteelement methods. Failure analysis and accident reconstruction may also employ limit and ultimate stress analysis to gain insight as to the nature of the failure and sensitivity
J Fail. Anal. and Preven. (2007) 7:144–151
to possible flaws in workmanship. Unfortunately, flow curves of nonlinear material behavior are not readily available to analysts, especially for elevated temperatures. Statistically based flow curves are even rarer. This paper describes a procedure for the analytical development of flow curves for metallic materials. These flow curves are suitable for nonlinear analysi
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