Results of the Round Robin on opening-load measurement conducted by ASTM Task Group E24.04.04 on Crack Closure Measurement and Analysis

An experimental Round Robin on the measurement of the opening load in fatigue crack growth tests was conducted on Crack Closure Measurement and Analysis. The Round Robin evaluated the current level of consistency of opening load measurements among laboratories and to identify causes for observed inconsistency. Eleven laboratories participated in the testing of compact and middle-crack specimens. Opening-load measurements were made for crack growth at two stress-intensity factor levels, three crack lengths, and following an overload. All opening-load measurements were based on the analysis of specimen compliance data. When all of the results reported (from all participants, all measurement methods, and all data analysis methods) for a given test condition were pooled, the range of opening loads was very large--typically spanning the lower half of the fatigue loading cycle. Part of the large scatter in the reported opening-load results was ascribed to consistent differences in results produced by the various methods used to measure specimen compliance and to evaluate the opening load from the compliance data. Another significant portion of the scatter was ascribed to lab-to-lab differences in producing the compliance data when using nominally the same method of measurement

Evaluating Air Force Civil Engineer\u27s Current Automated Information Systems

Almost every organization has some form of information system where data is captured and stored for later use. The Air Force civil engineering organization is no exception and is in the process of transitioning from the Interim Work Information Management System (WIMS) to the Automated Civil Engineer System (ACES). This research focused on users perceptions of both database and data importance to determine if significant differences existed between various user sub-groups. The research also attempted to identify the most frequently reported problems regarding system usage. The methods of analysis of variance and content analysis were used to answer the research questions using survey responses from a sample size of 814. The results indicate that civil engineers slightly agree that their database and the data it collects are important. However, significant differences in perception levels were found between men and women, between some major commands (MAJCOMS), between users of different systems, and between personnel of different rank. Content analysis of comments in response to open-ended questions found that users are generally satisfied with their current system. However, areas of concern included slow system speed, lack of a user-friendly report writing feature, and poor reliability

An Experimental Study of Fatigue Crack Growth in Aluminum Sheet Subjected to Combined Bending and Membrane Stresses

An experimental study was conducted to determine the effects of combined bending and membrane cyclic stresses on the fatigue crack growth behavior of aluminum sheet material. The materials used in the tests were 0.040-in.- thick 2024-T3 alclad and 0.090-in.-thick 2024-T3 bare sheet. In the tests, the membrane stresses were applied as a constant amplitude loading at a stress ratio (minimum to maximum stress) of 0.02, and the bending stresses were applied as a constant amplitude deflection in phase with the membrane stresses. Tests were conducted at ratios of bending to membrane stresses (B/M) of 0, 0.75, and 1.50. The general trends of the results were for larger effects of bending for the higher B/M ratios, the lower membrane stresses, and the thicker material. The addition of cyclic bending stresses to a test with cyclic membrane stresses had only a small effect on the growth rates of through-thickness cracks in the thin material, but had a significant effect on the crack growth rates of through-thickness cracks in the thick material. Adding bending stresses to a test had the most effect on the initiation and early growth of cracks and had less effect on the growth of long through-thickness cracks

Measurements of fuselage skin strains and displacements near a longitudinal lap joint in a pressurized aircraft

Strains and displacements in a small area near a longitudinal lap joint in the fuselage skin of a B737 aircraft were measured during a pressurization cycle to a differential pressure of 6.2 psi while the aircraft was on the ground. It was found that hoop strains were higher than longitudinal strains at each location; membrane strains in the unreinforced skin were higher than in the joint; membrane strains in the hoop direction, as well as radial displacements, tended to be highest at the mid-bay location between skin reinforcements; significant bending in the hoop direction occurred in the joint and in the skin near the joint, and the bending was unsymmetrically distributed about the stringer at the middle of the joint; and radial displacements were unsymmetrically distributed across the lap joint. The interpretation of the strain gage data for locations on the bonded and riveted lap joint assumed that the joint did not contain disbonded areas

Neglecting plant–microbe symbioses leads to underestimation of modeled climate impacts

The extent to which terrestrial ecosystems slow climate change by sequestering carbon hinges in part on nutrient limitation. We used a coupled carbon–climate model that accounts for the carbon cost to plants of supporting nitrogen-acquiring microbial symbionts to explore how nitrogen limitation affects global climate. To do this, we first calculated the reduction in net primary production due to the carbon cost of nitrogen acquisition. We then used a climate model to estimate the impacts of the resulting increase in atmospheric CO2 on temperature and precipitation regimes. The carbon costs of supporting symbiotic nitrogen uptake reduced net primary production by 8.1 Pg C yr−1, with the largest absolute effects occurring in tropical forest biomes and the largest relative changes occurring in boreal and alpine biomes. Globally, our model predicted relatively small changes in climate due to the carbon cost of nitrogen acquisition with temperature increasing by 0.1 ∘C and precipitation decreasing by 6 mm yr−1. However, there were strong regional impacts, with the largest impact occurring in boreal and alpine ecosystems, where such costs were estimated to increase temperature by 1.0 ∘C and precipitation by 9 mm yr−1. As such, our results suggest that carbon expenditures to support nitrogen-acquiring microbial symbionts have critical consequences for Earth\u27s climate, and that carbon–climate models that omit these processes will overpredict the land carbon sink and underpredict climate change

Fatigue-Life Prediction Methodology Using Small-Crack Theory

This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using 'small-crack theory' for various materials and loading conditions. Crack-tip constraint factors, to account for three-dimensional state-of-stress effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (delta K(eff)) under constant-amplitude loading. Some modifications to the delta k(eff)-rate relations were needed in the near-threshold regime to fit measured small-crack growth rate behavior and fatigue endurance limits. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens made of two aluminum alloys and a steel under constant-amplitude and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks for the aluminum alloys and steel for edge-notched specimens. An equivalent-initial-flaw-size concept was used to calculate fatigue lives in other cases. Results from the tests and analyses agreed well

The 2016 Revision of ISO 1 – Standard Reference Temperature for the Specification of Geometrical and Dimensional Properties

This paper discusses the changes in the 2016 (third edition) of International Standard ISO 1. While the value of the standard reference temperature remains unchanged at 20 °C, the important definitions for the “reference temperature” and “standard reference temperature,” absent in prior editions, are now defined, with the latter exclusively reserved for the assignment of the internationally agreed upon temperature of 20 °C. The scope of the revised Standard has been carefully refined and made more explicit. This, together with other clarifications and improvements, has eliminated the ambiguities associated with specifications at non-standard reference temperatures and allows, if needed, different reference temperatures to be associated with different properties of a workpiece. The relationship between ISO 1 and dimensional measurements is also discussed and clarified. In this paper, we discuss the motivation for these changes and present several issues debated during the revision process for the benefit of future standards committees that might study this topic

Myeloid DAP12-associating lectin (MDL)-1 regulates synovial inflammation and bone erosion associated with autoimmune arthritis.

DNAX adaptor protein 12 (DAP12) is a trans-membrane adaptor molecule that transduces activating signals in NK and myeloid cells. Absence of functional Dap12 results in osteoclast defects and bone abnormalities. Because DAP12 has no extracelluar binding domains, it must pair with cell surface receptors for signal transduction. There are at least 15 known DAP12-associating cell surface receptors with distinct temporal and cell type-specific expression patterns. Our aim was to determine which receptors may be important in DAP12-associated bone pathologies. Here, we identify myeloid DAP12-associating lectin (MDL)-1 receptor (also known as CLEC5A) as a key regulator of synovial injury and bone erosion during autoimmune joint inflammation. Activation of MDL-1 leads to enhanced recruitment of inflammatory macrophages and neutrophils to the joint and promotes bone erosion. Functional blockade of MDL-1 receptor via Mdl1 deletion or treatment with MDL-1-Ig fusion protein reduces the clinical signs of autoimmune joint inflammation. These findings suggest that MDL-1 receptor may be a therapeutic target for treatment of immune-mediated skeletal disorders

Population genetic estimation of the loss of genetic diversity during horizontal transmission of HIV-1

BACKGROUND: Genetic diversity of the human immunodeficiency virus type 1 (HIV-1) population within an individual is lost during transmission to a new host. The demography of transmission is an important determinant of evolutionary dynamics, particularly the relative impact of natural selection and genetic drift immediately following HIV-1 infection. Despite this, the magnitude of this population bottleneck is unclear. RESULTS: We use coalescent methods to quantify the bottleneck in a single case of homosexual transmission and find that over 99% of the env and gag diversity present in the donor is lost. This was consistent with the diversity present at seroconversion in nine other horizontally infected individuals. Furthermore, we estimated viral diversity at birth in 27 infants infected through vertical transmission and found there to be no difference between the two modes of transmission. CONCLUSION: Assuming the bottleneck at transmission is selectively neutral, such a severe reduction in genetic diversity has important implications for adaptation in HIV-1, since beneficial mutations have a reduced chance of transmission

Measuring enjoyment of physical activity in older adults: invariance of the physical activity enjoyment scale (paces) across groups and time

The purpose of this study was to validate the Physical Activity Enjoyment Scale (PACES) in a sample of older adults. Participants within two different exercise groups were assessed at two time points, 6 months apart. Group and longitudinal invariance was established for a novel, 8-item version of the PACES. The shortened, psychometrically sound measure provides researchers and practitioners an expedited and reliable instrument for assessing the enjoyment of physical activity