AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS & MANUFACTURING DIR METALS CERAMICS & NONDESTRUCTIVE EVALUATION DIV/NONDESTRUCTIVE EVALUATION BRANCH

Vacuum Levels Needed to Simulate Internal Fatigue Crack Growth in Titanium Alloys and Nickel-base Superalloys: Thermodynamic Considerations

01 Mar 2012

20 pages

Authors: V Sinha; J M Larsen; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS & MANUFACTURING DIR METALS CERAMICS & NONDESTRUCTIVE EVALUATION DIV/NONDESTRUCTIVE EVALUATION BRANCH

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Prior studies have examined fatigue growth of surface cracks in vacuum to simulate sub-surface growth in Ti-alloys and Ni-base superalloys. Even with the highest vacuum level attained using state-of-the-artpumps, it is unclear if conditions of internal crack growth are truly simulated. We consider thermodynamics of the oxidation process to help answer this question. This consideration helps explain a previously reported anomalous behavior of longer life in air than in vacuum ...

Quantitative Evaluation for Two-Dimensional Electromagnetic Propagation in a Dielectric Medium using Markov Chain Monte Carlo Method (Preprint)

Feb 2012

8 pages

Authors: Jeremy S Knopp; Fumio Kojima; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS & MANUFACTURING DIR METALS CERAMICS & NONDESTRUCTIVE EVALUATION DIV/NONDESTRUCTIVE EVALUATION BRANCH

The motivation of this work is to quantify the degradation of aging electrical cables. The dielectric material parameter of insulation can be correlated with degradation. In this paper, the forward problem is posed as a microwave nondestructive evaluation (NDE) problem. A 2D finite difference time domain (FDTD) was used to evaluate the forward problem. The inverse problem is solved via a Bayesian approach. The Bayesian formulation describes the solution as ...

Three-dimensional Crack Depth Profile Assessment using Near-Field Surface Acoustic Wave Signal Response (Postprint)

Feb 2012

6 pages

Authors: James L Blackshire; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS & MANUFACTURING DIR METALS CERAMICS & NONDESTRUCTIVE EVALUATION DIV/NONDESTRUCTIVE EVALUATION BRANCH

A method for determining the three-dimensional depth profile of a surface-breaking crack-like feature is presented based on near-field surface acoustic wave signal responses. Three-dimensional finite element models were used to study the forward problem, where the characteristic near-field scattering of a surface acoustic wave incident on a surface breaking crack was investigated. Experimental validation of the modeling predictions was accomplished using a wedge transducer for surface wave generation and a ...

Protocol and Demonstrations of Probabilistic Reliability Assessment for Structural Health Monitoring Systems (Preprint)

Nov 2011

12 pages

Authors: Eric A Lindgren; Charles F Buynak; Jeremy S Knopp; John C Aldrin; Enrique A Medina; Jose Santiago; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS & MANUFACTURING DIR METALS CERAMICS & NONDESTRUCTIVE EVALUATION DIV/NONDESTRUCTIVE EVALUATION BRANCH

This paper will describe the development of a protocol for probabilistic reliability assessment for SHM systems as well as present an experimental demonstration for a vibration-based structural damage sensing system. The results of the full validation study highlight the general protocol feasibility, emphasize the importance of evaluating key application characteristics prior to the POD study, and demonstrate an approach to quantify varying sensor durability on the POD performance. Challenges remain ...

Demonstration Study for Reliability Assessment of SHM Systems Incorporating Model-Assisted Probability of Detection Approach (Preprint)

Nov 2011

10 pages

This paper presents the results of a demonstration featuring the application of a validation protocol to a vibration-based structural damage sensing system. The results of the full validation study highlight the general protocol feasibility, emphasize the importance of evaluating key application characteristics prior to the POD study, and demonstrate an approach to quantify varying sensor durability on the POD performance. Challenges remain to properly address long time-scale effects with accelerated ...

Observations on the Role of Hydrogen in Facet Formation in Near-alpha Titanium (Preprint)

May 2011

71 pages

Authors: A L Pilchak; J C Williams; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS & MANUFACTURING DIR METALS CERAMICS & NONDESTRUCTIVE EVALUATION DIV/NONDESTRUCTIVE EVALUATION BRANCH

Faceted features are frequently observed on the fracture surfaces of titanium alloys that have failed by static loading, continuous cycling, dwell fatigue loading, and stress corrosion cracking. Although the facets formed under different loading conditions appear qualitatively similar, there are significant differences in the spatial and crystallographic orientations of the facets as well as subtle differences in facet surface topography. The present study compares and contrasts facets in the Ti-8Al-1Mo-1V ...