Accession Number:

AD1026465

Title:

A New Approach for Investigating Crystal Stresses that Drive the Initiation of Fatigue-Induced Defects in Structural Alloys

Descriptive Note:

Technical Report,01 Jan 2006,31 Dec 2008

Corporate Author:

Cornell University Ithaca United States

Personal Author(s):

• Dawson,Paul R.
• Miller ,Matthew

Report Date:

2009-03-31

Pagination or Media Count:

15.0

Abstract:

We have developed an approach to investigate crystals stresses during cyclic load by coordinating experiments and simulations at the size scalewhere fatigue induced defects initiate. Our efforts provided new understanding of the stress evolution during cyclic loading through acomplementary process between the experimental measurement of lattice strain and the simulation results. The comparison of the experimental andthe simulated lattice data culminated in a novel picture of how the stress evolves at the crystal scale. Specifically, using the crystal-basedelastoplastic finite element model, we found that for different levels of the single crystal elastic anisotropy, different sets of crystal hkls within aFCC polycrystalline sample evolve differently through the elastic-plastic transition under monotonic tension loading. It is the strength-to-stiffnessratio of these hkls that determines the crystal lattice strain and yield behavior for different values of the single crystal elastic anisotropic ratio.The single crystal elastic anisotropy also causes the hysteresis loops under fully-reversed cyclic loading to contract preferentially. For agiven average grain size and crystallographic texture, an experimental method for measuring a representative volume element RYE in orientation.

Descriptors:

• crystal lattices
• stress strain relations
• mechanical properties
• crystals
• ELASTOPLASTICITY
• alloys

Subject Categories:

• Crystallography

Distribution Statement:

APPROVED FOR PUBLIC RELEASE