Overview and Purpose

Our purpose in today\u27s session is to discuss procedures for developing accept/reject criteria for NDE methods of inspection. Many of the methods we will describe this morning are not very familiar to members of the audience, so we have deliberately set the session at a fairly leisurely pace so you can assimilate these concepts as they are presented this morning. We would like the session to be relatively informal so we can ask questions and have a fairly extensive discussion period. Following the talks this morning, and after you have had a chance to assimilate some of the details, there will be a poster session immediately after lunch where we\u27re really asking the question, Are the measurements that are being made in the various labs and institutions in the country really the appropriate measurements to fit within the accept/ reject frame work you will have heard described this morning? Then, finally, after the posters are completed, there will be a general discussion whereby we will all assemble again to ask the question, Are the right measurements being made; if not, what other measurements should be made? and general questions of that nature

Acoustic Emission: A Summary of Current Understanding

Gentlemen, I want to talk in fairly general terms about the acoustic emission technique, which I think you will find is rather different from the other techniques we have heard about thus far in the meeting

A Critical Assessment of Theories of Strain Gradient Plasticity

Theories to extend plasticity to the micron scale have been in existence for over a decade, complemented by a growing body of experimental data. Here, materials and mechanics aspects of two prominent strain gradient theories of plasticity, due to Nix and Gao and to Fleck and Hutchinson, are assessed within the context of simple bending. Differences between the theories are highlighted. The theories predict different trends relative to the size dependence of initial yielding and rate of hardening. The dislocation mechanics underpinning the two theories is addressed. Distinctions between lower-order theories and higher-order theories are also drawn, emphasizing the flexibility of higher-order theories to solve problems for a wide range of boundary conditions, especially those where, locally, the dislocations are blocked (pile up) and the plastic strain is zero.Engineering and Applied Science

A Stretch/Bend Method for In Situ Measurement of the Delamination Toughness of Coatings and Films Attached to Substrates

A stretch/bend method for the in situ measurement of the delamination toughness of coatings attached to substrates is described. A beam theory analysis is presented that illustrates the main features of the test. The analysis is general and allows for the presence of residual stress. It reveals that the test produces stable extension of delaminations, rendering it suitable for multiple measurements in a single test. It also provides scaling relations and enables estimates of the loads needed to extend delaminations. Finite element calculations reveal that the beam theory solutions are accurate for slender beams, but overestimate the energy release rate for stubbier configurations and short delaminations. The substantial influence of residual stress on the energy release rate and phase angle is highly dependent on parameters such as the thickness and modulus ratio for the two layers. Its effect must be included to obtain viable measurements of toughness. In a companion paper, the method has been applied to a columnar thermal barrier coating deposited onto a Ni-based super-alloy.Engineering and Applied Science

VEXAR PLASTIC NETTING TO REDUCE POCKET GOPHER DEPREDATION OF CONIFER SEEDLINGS

In 1976, we began a comprehensive evaluation of Vexar seedling protectors as a means of reducing damage to conifer seedlings by pocket gophers (Thomomys spp.). The protectors are cylinders of plastic netting that gradually decompose in sunlight. The evaluation is being conducted on four national forests in three western states. Three conifer species, lodgepole pine (Pinus contorta), ponderosa pine (P. ponderosa), and Shasta red fir (Abies magnifica var. shastensis), are under study. After two growing seasons, gophers have caused only 5 percent mortality among Vexar -enclosed seedlings compared to 20 percent mortality among unprotected seedlings. In addition, stocking and heights of protected seedlings are better than those of unprotected seedlings. Problems associated with the use of Vexar included compression of the protectors by snow, breakage of the plastic during subfreezing temperatures, and protrusion of seedling terminals through mesh openings; however, these problems have been minor thus far. Information on long-term effectiveness and cost efficiency is still needed before we can recommend operational use of Vexar protectors for pocket gopher damage control

Understanding violence through social media

While social media analysis has been widely utilized to predict various market and political trends, its utilization to improve geospatial conflict prediction in contested environments remains understudied. To determine the feasibility of social media utilization in conflict prediction, we compared historical conflict data and social media metadata, utilizing over 829,537 geo-referenced messages sent through the Twitter network within Iraq from August 2013 to July 2014. From our research, we conclude that social media metadata has a positive impact on conflict prediction when compared with historical conflict data. Additionally, we find that utilizing the most extreme negative terminology from a locally derived social media lexicon provided the most significant predictive accuracy for determining areas that would experience subsequent violence. We suggest future research projects center on improving the conflict prediction capability of social media data and include social media analysis in operational assessments.http://archive.org/details/understandingvio1094556920Major, United States ArmyLieutenant Commander, United States NavyApproved for public release; distribution is unlimited

Tensile and flexural ultimate strength of fiber-reinforced ceramic-matrix composites

International audienceA constitutive equation has been derived for fiber reinforced ceramic-matrix composites, based on fiber breakage and distributed fiber pull-out. Length-dependent and length-independent regimes, governed by the size of the specimen, are differentiated, The constitutive equation is used to predict the ultimate strength of fiber-reinforced ceramic-matrix composites subjected to tensile and flexural loadings