The manufacture of honeycomb cores using Fused Deposition Modeling

Sandwich panels are used in many industries for the advantageous properties of high stiffness, good strength to weight ratio, and impact resistance. This paper investigates properties of thin-walled cores manufactured through Fused Deposition Modeling (FDM); a process which, through a wider design space, could improve the functionality of sandwich panels. The bond strength between the layers of thin walls manufactured through FDM was evaluated through tensile testing. To measure the effect of modified manufacturing speeds, wall thicknesses were varied through the flow rate and nozzle speed. Honeycomb cores using FDM were produced with different toolpaths, and compared with an example of an industry standard Nomex honeycomb core. During tensile testing, thick-walled FDM components exhibited a more ductile failure with a lower yield point when compared to thinner specimens. The ultimate tensile stress remained constant across samples within each of the tested ABS and PLA polymers used. Honeycomb cores produced using FDM were found to have a higher compressive failure force than Nomex honeycomb, and a lower specific strength. The force–displacement curves of compressive failure show a ductile response for thick specimens, consistent with the previous result. These results, combined with the increased flexibility of additive manufacture technologies, could provide a method of manufacturing high strength cores with complex geometry

The manufacture of honeycomb cores using Fused Deposition Modeling

Sandwich panels are used in many industries for the advantageous properties of high stiffness, good strength to weight ratio, and impact resistance. This paper investigates properties of thin-walled cores manufactured through Fused Deposition Modeling (FDM); a process which, through a wider design space, could improve the functionality of sandwich panels. The bond strength between the layers of thin walls manufactured through FDM was evaluated through tensile testing. To measure the effect of modified manufacturing speeds, wall thicknesses were varied through the flow rate and nozzle speed. Honeycomb cores using FDM were produced with different toolpaths, and compared with an example of an industry standard Nomex honeycomb core. During tensile testing, thick-walled FDM components exhibited a more ductile failure with a lower yield point when compared to thinner specimens. The ultimate tensile stress remained constant across samples within each of the tested ABS and PLA polymers used. Honeycomb cores produced using FDM were found to have a higher compressive failure force than Nomex honeycomb, and a lower specific strength. The force–displacement curves of compressive failure show a ductile response for thick specimens, consistent with the previous result. These results, combined with the increased flexibility of additive manufacture technologies, could provide a method of manufacturing high strength cores with complex geometry

A comparison of FDM structural layouts and implementation of an open-source arm-based system

Fused Deposition Modelling (FDM) is a manufacturing process to build components in a layer-by-layer approach through extrusion of polymers from a movable nozzle, allowing for significantly higher degrees of complexity over machined parts. Current FDM systems typically use actuation provided through a gantry or delta structural layout, operating through depositing successive planar layers in a 2.5D process; it has been shown in numerous studies the bonding between layers has significantly lower strength than the homogeneous material or in-plane properties - an issue which can be mitigated through the deposition of curved layers. This paper compares four differing structural layouts of FDM systems (gantry, delta, Stewart Platform, and arm-based) to identify the key advantages of an arm-based method as the increased workspace and manipulability enabling “Additive Finalisation” of components, and suitability for curved layer FDM. Details are then presented of the open-source implementation and evaluation of a 6 degree-of-freedom arm-based FDM printer at the University of Bristol

Characteristics of interannual variability in space-based XCO2_2 global observations

Atmospheric carbon dioxide (CO$_2$) accounts for the largest radiative forcing among anthropogenic greenhouse gases. There is, therefore, a pressing need to understand the rate at which CO$_2$ accumulates in the atmosphere, including the interannual variations (IAVs) in this rate. IAV in the CO$_2$ growth rate is a small signal relative to the long-term trend and the mean annual cycle of atmospheric CO$_2$, and IAV is tied to climatic variations that may provide insights into long-term carbon–climate feedbacks. Observations from the Orbiting Carbon Observatory-2 (OCO-2) mission offer a new opportunity to refine our understanding of atmospheric CO$_2$ IAV since the satellite can measure over remote terrestrial regions and the open ocean, where traditional in situ CO$_2$ monitoring is difficult, providing better spatial coverage compared to ground-based monitoring techniques. In this study, we analyze the IAV of column-averaged dry-air CO$_2$ mole fraction (XCO$_2$) from OCO-2 between September 2014 and June 2021. The amplitude of the IAV, which is calculated as the standard deviation of the time series, is up to 1.2 ppm over the continents and around 0.4 ppm over the open ocean. Across all latitudes, the OCO-2-detected XCO$_2$ IAV shows a clear relationship with El Niño–Southern Oscillation (ENSO)-driven variations that originate in the tropics and are transported poleward. Similar, but smoother, zonal patterns of OCO-2 XCO2 IAV time series compared to ground-based in situ observations and with column observations from the Total Carbon Column Observing Network (TCCON) and the Greenhouse Gases Observing Satellite (GOSAT) show that OCO-2 observations can be used reliably to estimate IAV. Furthermore, the extensive spatial coverage of the OCO-2 satellite data leads to smoother IAV time series than those from other datasets, suggesting that OCO-2 provides new capabilities for revealing small IAV signals despite sources of noise and error that are inherent to remote-sensing datasets

The Icebreaker Life Mission to Mars: A Search for Biomolecular Evidence for Life

The search for evidence of life on Mars is the primary motivation for the exploration of that planet. The results from previous missions, and the Phoenix mission in particular, indicate that the ice-cemented ground in the north polar plains is likely to be the most recently habitable place that is currently known on Mars. The near-surface ice likely provided adequate water activity during periods of high obliquity, ~ 5 Myr ago. Carbon dioxide and nitrogen is present in the atmosphere, and nitrates may be present in the soil. Perchlorate in the soil together with iron in basaltic rock provides a possible energy source for life. Furthermore, the presence of organics must once again be considered, as the results of the Viking GCMS are now suspect given the discovery of the thermally reactive perchlorate. Ground-ice may provide a way to preserve organic molecules for extended periods of time, especially organic biomarkers. The Mars Icebreaker Life mission focuses on the following science goals: 1. Search for specific biomolecules that would be conclusive evidence of life. 2. A general search for organic molecules in the ground ice. 3. Determine the processes of ground ice formation and the role of liquid water. 4. Understand the mechanical properties of the Mars polar ice-cemented soil. 5. Assess the recent habitability of the environment with respect to required elements to support life, energy sources, and possible toxic elements. And 6. Compare the elemental composition of the northern plains with mid-latitude sites. The Icebreaker Life payload has been designed around the Phoenix spacecraft and is targeted to a site near the Phoenix landing site. However, the Icebreaker payload could be supported on other Mars landing systems. Preliminary studies of the SpaceX Dragon lander show that it could support the Icebreaker payload for a landing either at the Phoenix site or at mid-latitudes. Duplicate samples could be cached as a target for possible return by a Mars Sample Return mission. If the samples were shown to contain organic biomarkers interest in returning them to Earth would be high

A high-resolution map of human evolutionary constraint using 29 mammals.

The comparison of related genomes has emerged as a powerful lens for genome interpretation. Here we report the sequencing and comparative analysis of 29 eutherian genomes. We confirm that at least 5.5% of the human genome has undergone purifying selection, and locate constrained elements covering ∼4.2% of the genome. We use evolutionary signatures and comparisons with experimental data sets to suggest candidate functions for ∼60% of constrained bases. These elements reveal a small number of new coding exons, candidate stop codon readthrough events and over 10,000 regions of overlapping synonymous constraint within protein-coding exons. We find 220 candidate RNA structural families, and nearly a million elements overlapping potential promoter, enhancer and insulator regions. We report specific amino acid residues that have undergone positive selection, 280,000 non-coding elements exapted from mobile elements and more than 1,000 primate- and human-accelerated elements. Overlap with disease-associated variants indicates that our findings will be relevant for studies of human biology, health and disease