Evaluation of the Sensitivity of Various Reinforcement Patterns for Structural Carbon Fibers to Open Holes during Tensile Tests

This paper is devoted to the experimental study of polymeric composite specimens, with various types of reinforcement, in order to evaluate the breaking strength of specimens with open holes when undergoing uniaxial compression and tensile tests. Four types of interlaced 3D woven preforms were considered (orthogonal, orthogonal combined, with pairwise inter-layer reinforcement, and with pairwise inter-layer reinforcement and a longitudinal layer), with a layered preform used for comparison. Tensile tests of solid specimens without a hole, under ASTM D 3039, and of specimens with an open hole, under ASTM D 5766, were carried out using the Instron 5989 universal electromechanical testing system. Movements and strains on the specimen surface were recorded using a Vic-3D contactless optical video system and the digital images correlation method (DIC). For all the series of carbon fiber tension specimens, strain and stress diagrams, mechanical characteristics, and statistical processing for 10 specimens were obtained. The paper evaluated deformation fields for certain points in time; the obtained fields showed an irregular distribution of deformation and dependency on types of reinforcing fibers. A coefficient of strength variation is introduced, which is defined as a ratio of the ultimate stress limits obtained on solid samples with and without open holes. Within the framework of ASTM D 5766, when calculating the ultimate stress, the hole is not taken into account, and the paper shows that for certain structures a hole cannot be excluded. The hole size must not be neglected when calculating the ultimate stress.

Environmental Audit Committee Call for Evidence: “Sustainability of the Built Environment”

The Centre for Natural Material Innovation in the Department of Architecture at the University of Cambridge is a cross-disciplinary centre, bringing together people and research in plant sciences, biochemistry, chemistry, fluid dynamics, engineering, and architecture. Through innovative research and experimentation, we aim to transform the way we build to achieve zero carbon emissions. Our work enables the substitution of artificial materials such as concrete and steel with nature-based materials such as timber and bamboo, and replacement of structural carbon fibre and glass fibre with hemp and flax-based biocomposites. We collaborate with other leading research institutions globally, including in the USA, China, Australia, Uruguay and others.

Investigation of the physical and mechanical characteristics of the applied corrosion-resistant powder coating

This article presents the results of experimental work on the development of a laser complex for micro-and nanomodification of metal surfaces using hybrid technologies. As an alloying material, a corrosion-resistant composite powder of the national brand was chosen, which is used in industry to prevent the occurrence of corrosion formations on the working surfaces of the executive parts of machines. One of the most used national grades of structural carbon steels was chosen as the substrate. The parameters of the laser radiation varied in two parameters: scanning speeds in the range of 12-15 mm/sec and radiation power in the range of 3-5 kW. As a result of the work carried out under various power modes, prototypes were obtained. On their basis, tabular data on the obtained values of microhardness, wear resistance and friction coefficients are compiled. The description of the obtained results is given and the direction of further work is indicated.

Establishing the Relationship between Cutting Speed and Output Parameters in Belt Grinding on Steels, Aluminum and Nickel Alloys: Development of Recommendations

This paper presents the research results of one of the main technological parameters of belt grinding, i.e., the cutting speed while machining corrosion- and heat-resistant, structural carbon and structural alloy steels, aluminum, and heat-resistant nickel alloys. Experimental and analytical methods are used to establish the dependence of the output parameters of surface belt grinding on the cutting speed and tool characteristics. An analytical model, considering the physical and mechanical properties of the grinding belt (strength depending on the base and bond; the thermal conductivity; the type of grinding operation) and the machined material, is created to determine the belt grinding speed. The output parameters, such as the arithmetic mean of the surface roughness (Ra) and the material removal rate (MRR) during the belt grinding of steels, heat-resistant and light alloys, have been studied. Based on the empirical dependencies of the belt grinding parameters, the model was developed for the selection and setting of the cutting speed of belt grinding for the aforementioned alloys, taking into account the type of operation, the type of the machined material, and the main characteristics of the sanding belt.

Quantifying whole tree non-structural carbon dynamics under long-term experimental drought using radiocarbon

<div> <div> <div> <p>Under increasingly frequent, persistent, and severe drought events, predicting future forest carbon dynamics necessitates quantitative understanding of the physiological processes leading to tree mortality and physiological impairment. The responses of non-structural carbon (NSC; primarily sugars and starch) pools in mature trees is particularly important, as dynamics in NSC interact with hydraulic damage to perturb future tree growth. However, NSC concentration measurements alone are not suUcient to understand the stress responses of tree NSC pools formed over years to decades. Thus, we are using radiocarbon (14C) to quantify the age of NSC stored within, and used by, piñon pine trees exposed to either severe or long-term drought stress at the Sevilleta LTER, in New Mexico, USA. Measuring the age of NSC allows inference on the storage history of a tree, and how different NSC pools may be altered by drought. Experimental plots are subjected to either 0% (control) or 90% reduction in precipitation. A 45% precipitation reduction plot has also been in place since 2009, offering a chance to study the impacts of a decade of drought. We are measuring Δ14C of NSC in twigs, bole sapwood, and coarse roots, as well as in CO2 respired from the bole and branches. Our goal is to quantify the role of different-aged NSC pools across tree organs in driving whole-tree physiological responses to drought. Preliminary results show that the long-term droughted trees store and respire on average younger NSC than control trees. Ongoing drought treatments and sampling will provide additional information on how NSC dynamics in these trees are influenced by drought.</p> </div> </div> </div>

Seasonal dynamics of non-structural carbon pools and their relationship to growth in two boreal conifer tree species

In an attempt to comprehensively study the dynamics of non-structural carbon compounds (NCC), we measured the seasonal changes of soluble sugars, starch, lipids, and sugar alcohols in the leaves, branches, stem, and roots of the fast-growing Pinus contorta (pine) and slow-growing Picea glauca (spruce) trees growing in a boreal climate. In addition to measuring seasonal concentrations of these compounds, the relative contribution of these compounds to the total NCC pool within organs of trees (~8 m tall) was estimated and compared across different phenological and growth stages. Both species showed large seasonal shifts from starch to sugars from spring to fall in nearly all organs and tissues; most likely an adaptation to the cold winters. For both species the total fluctuation of sugar + starch across the year (i.e., the difference between the minimum and maximum observed across collection times) was estimated to be between 1.6 kg and 1.8 kg for all NCCs. The fluctuation, however, was 1.40 times greater than the minimum reserves in pine while only 0.72 times the minimum reserves in spruce. By tissue type, NCC fluctuations were greatest in the roots of both species. Roots showed a large build-up of reserves in late spring, but these reserves were depleted over summer and fall. Storage reserves in needles and branches declined over the summer and this decline may be linked to the sink strength of the stem during diameter growth. Some notable highlights of this holistic study: a late winter build-up of sugars in the stem xylem of both species but especially spruce; an increase in sugar alcohols in the bark of spruce in very late winter which could indicate mobilization to support early growth in spring; high lipid reserves in the bark of pine, that appeared not to be impacted by seasonal changes between summer and winter. Collectively, these observations point towards a more conservative NCC reserve strategy in spruce compared to pine which is consistent with its stress tolerance and greater longevity.