Microcompression high cycle fatigue tests up to 10 million cycles

Nanomechanical tests are moving beyond hardness and modulus to encompass host of different mechanical properties like strain rate sensitivity [1, 2], stress relaxation [3], creep, and fracture toughness [4] by taking advantage of focused ion beam milled geometries. Adding high cycle fatigue to this list will be useful to extend the gamut of properties studied at the micro/nanoscale. However, this presents inherent challenges like low oscillation frequencies, long duration of tests and large thermal drift when attempted with standard indenters. This presentation will report, for the first time, the development of micropillar compression-compression high cycle fatigue tests going up to 10 million cycles. This has been made possible by the development of a novel piezo-based nanoindentation technique that allows accessing extremely high strain rates (\u3e104 s-1) and high oscillation frequencies (up to 10 kHz). The associated instrumentation and technique development, design of the fatigue tests at the micron scale, data analysis methodology, experimental protocol and challenges will be discussed. Validation data on single crystal silicon, a reference material, will be presented to demonstrate the reliability of the designed high cycle fatigue tests. Finally, case studies of compression-compression high cycle micropillar fatigue on nanostructured materials will be presented and their results will be discussed in light of existing literature data, particularly the operative deformation mechanism(s). The convolution of time dependent plasticity in such tests will also be addressed. It is hoped that this study will pave way for routine high cycle fatigue tests of metals at the micron scale and provide clues for designing a similar indentation fatigue test. [1] Mohanty G, Wheeler JM, Raghavan R, Wehrs J, Hasegawa M, Mischler S, et al. Elevated temperature, strain rate jump microcompression of nanocrystalline nickel. Philosophical Magazine 2015;95:1878-95. [2] Wehrs J, Mohanty G, Guillonneau G, Taylor AA, Maeder X, Frey D, et al. Comparison of In Situ Micromechanical Strain-Rate Sensitivity Measurement Techniques. Jom 2015;67:1684-93. [3] Mohanty G, Wehrs J, Boyce BL, Taylor AA, Hasegawa M, Philippe L, et al. Room temperature stress relaxation in nanocrystalline Ni measured by micropillar compression and miniature tension. Journal of Materials Research 2016;In press. [4] Sebastiani M, Johanns K, Herbert EG, Carassiti F, Pharr G. A novel pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings. Philosophical Magazine 2015;95:1928-44

General Report Session 7: Stability of Slopes and Earth Dams Under Earthquakes

The papers received for this session may be classified into five general topic areas; the number of papers in each subtopic area is shown in parentheses. 1. Slope stability analysis incorporating dynamic loading analysis methods (3) dynamic effects on soil properties (2) case study (1) 2. Dynamic response of embankment dams analysis methods (5) case studies (2) 3. Dynamic deformation analysis analysis methods adapted for a specific case (3) comparison of analysis methods (1) 4. Dynamic deformation or stability analysis incorporating pore pressure development or liquefaction considerations analysis methods (3) analysis methods developed for a specific case (2) case history of remediation (1) 5. Special studies hillside stability monitoring system (1) analysis of response of numerous dams to earthquake loading (1) A brief synopsis of each of the papers will be provided in the order indicated above, followed by an analysis and commentary on the significance of the papers

Grand Coulee Riverbank Stabilization – Case History of the Design of Remedial Measures

Planned peaking operations at Grand Coulee Dam will cause river fluctuations of up to 1 feet daily for the authorized plant and up to 38 feet daily for a proposed plant expansion. Treatment of the historically unstable riverbanks was required to offset the destabilizing effect of the peaking operations. Consideration of the geologic history of the bank materials, estimation of future pore pressure conditions, formulation of the stabilization criteria, and the success in reducing pore pressure levels in varved clays in the bank were some of the important aspects of this project

Comparison of wind velocity in thunderstorms determined from measurements by a ground-based Doppler radar and an F-106B airplane

As a part of the NASA Storm Hazards Program, the wind velocity in several thunderstorms was measured by an F-106B instrumented airplane and a ground-based Doppler radar. The results of five airplane penetrations of two storms in 1980 and six penetrations of one storm in 1981 are given. Comparisons were made between the radial wind velocity components measured by the radar and the airplane. The correlation coefficients for the 1980 data and part of the 1981 data were 0.88 and 0.78, respectively. It is suggested that larger values for these coefficients may be obtained by improving the experimental technique and in particular by slaving the radar to track the airplane during such tests

The brittle-ductile transition of tungsten single crystals at the micro-scale

The process zone or plastic zone around a loaded crack tip can significantly influence the fracture behavior of a material. Especially in micro-scale specimens, the plastic zone size may make out a large share of the sample volume and lead to a different fracture behavior than the one usually observed for macroscopic samples of the same material. Furthermore, the theoretical description of the plastic zone according to Irwin is not valid for single crystals. Therefore, a characteristic elastic-plastic fracture behavior is observed depending on crystallographic sample orientation and slip system activation. It is the aim of the study to understand the fracture process and behavior in micro-scale specimens in the presence of crack tip plasticity. Notched micro-cantilevers were prepared by focused ion beam (FIB) milling in a tungsten single crystal. This material has nearly perfect elastic isotropy, a limited amount of activated slip systems and detailed knowledge of the macroscopic fracture behavior is available [1]. The cantilevers have dimensions of 25 µm in length, 5-7 µm in thickness and crack length to thickness ratios a/w of ca. 0.4. Loading rate and temperature are known to influence the fracture behavior decisively in bcc metals. Therefore displacement-controlled fracture tests were performed inside a scanning electron microscope in the temperature range between -150°C and 500°C. Applying the recently presented J-Integral technique [2] to plot continuous crack resistance curves, the fracture toughness and brittle-to-ductile transition (BDT) temperatures, which depend on the applied loading rate, were determined. This allows a thorough investigation of the activation energy of the BDT at the micro-scale. Crack tip plasticity before and during crack growth was investigated by high-resolution electron backscatter diffraction measurements (HR-EBSD) on FIB cross-sections of the micro-cantilevers after mechanical testing. Plastic zones, which are strongly depending on the activated slip systems, and plastic strain gradients in terms of geometrically necessary dislocations were quantified and linked with the observed BDT behavior. Transmission electron microscopy was used to confirm the EBSD results and to provide dislocation analysis. [1] P. Gumbsch, J. Riedle, A. Hartmaier, H.F. Fischmeister, Controlling Factors for the Brittle-to-Ductile Transition in Tungsten Single Crystals, Science. 282 (1998) 1293–1295. [2] J. Ast, B. Merle, K. Durst, M. Göken, Fracture toughness evaluation of NiAl single crystals by microcantilevers - a new continuous J-integral method, Journal of Materials Research. 31 (2016) 3786–3794

Adverse weather impact on aviation safety, investigation and oversight

A brief review of the weather factors that effect aviation safety with respect to U.S. Coast Guard operations is presented. Precise meteorological information is an absolute necessity to the Coast Guard which must conduct life saving and rescue operations under the worst of weather conditions. Many times the weather conditions in which they operate are the cause of or a contributing factor to the predicament from which they must execute a rescue operation

Impact of changing US cigarette smoking patterns on incident cancer: Risks of 20 smoking-related cancers among the women and men of the NIH-AARP cohort

Background: Historically, US women started smoking at a later age than men and had lower relative risks for smoking-related cancers. However, more recent birth cohorts of women and men have similar smoking histories and have now reached the high-risk age for cancer. The impact of these changes on cancer incidence has not been systematically examined. Methods: Relative risks (RR), 95% confidence intervals (CI) and attributable fractions were calculated for cigarette smoking and incidence of 20 smoking-related cancers in 186 057 women and 266 074 men of the National Institutes of Health-AARP cohort, aged 50 to 71 years in 1995 and followed for 11 years. Results: In the cohort, which included participants born between 1924 and 1945, most women and men started smoking as teenagers. RRs for current vs never smoking were similar in women and men for the following cancers: lung squamous-cell (RR women: 121.4, 95% CI: 57.3–257.4; RR men:114.6, 95% CI: 61.2–214.4), lung adenocarcinoma (RR women: 11.7, 95% CI: 9.8–14.0; RR men: 15.6, 95% CI: 12.5–19.6), laryngeal (RR women: 37.0, 95% CI: 14.9–92.3; RR men: 13.8, 95% CI: 9.3–20.2), oral cavity-pharyngeal (RR women:4.4, 95% CI: 3.3–6.0; RR men: 3.8, 95% CI: 3.0–4.7), oesophageal squamous cell (RR women: 7.3, 95% CI: 3.5–15.5; RR men: 6.2, 95% CI: 2.8–13.7), bladder (RR women: 4.7, 95% CI: 3.7–5.8; RR men: 4.0, 95% CI: 3.5–4.5), colon (RR women: 1.3, 95% CI: 1.2–1.5; RR men: 1.3, 95% CI: 1.1–1.4), and at other sites, with similar attributable fractions. Conclusions: RRs for current smoking and incidence of many smoking-related cancers are now similar in US women and men, likely reflecting converging smoking patterns