Abstract Instability-induced pattern transformations of the architectured multi-phase soft metamaterial under bi-axial compression were explored. The soft metamaterial is composed of two phases: a soft matrix and a reinforcing hexagonal network embedded in the matrix. Equi-biaxial loading is found to induce both micro- and macro- instabilities in the networked architecture. Two types of instability patterns were observed, dependent upon the architecture geometry and the material combination. The critical strain for triggering instability and the two resulting types of patterns was derived, and a theoretical criterion for the transition between the two patterns was determined. Type I patterns retain the original periodicity of the architecture but wrinkles the network walls whereas Type II patterns transform the overall periodicity of the architecture while bending the network walls. Elastic wave propagation analysis was performed for the two distinct patterns under both stressed and stress-free conditions: a change in band gaps is found for both instability-induced pattern transformations, but differs for each type due to their dramatic difference in structure transformation (i.e. Type I wall wrinkling vs. Type II periodicity switching). The distinguished mechanical behavior and the rich properties of this category of multi-phase soft metamaterial can be used to design new smart materials with switchable functionalities controllable by deformation.
As wildfires are of increasing concern in a warming world, there is a need to understand how fire temperatures affect solute concentrations of forest litter and soils in drinking water catchments. In addition, the concentrations are expected to be affected by time since the previous fire. We sampled soil and litter from recently (2 months) and less recently (4.5 years) burnt sites from jarrah forest in SW Australia. The samples were heated at 250°C, 350°C, and 500°C for 30min followed by leaching to determine solute compositions at these temperatures and in unburnt samples. At 250°C–350°C, we found increased concentrations of manganese (Mn), arsenic (As), total phosphorus (TP), phosphate (PO43-), ammonia (NH4+), potassium (K), calcium (Ca), mangesium (Mg), cobalt (Co), barium (Ba), sulphate (SO42-), alkalinity and dissolved organic carbon in soils, as well as of zinc (Zn), As, Ca, Ba, alkalinity, aluminium (Al) and chromium (Cr) in litter. At 350°C–500°C, divalent cations and organic carbon declined, while soils generated very high Al and Cr concentrations. The time following the fire was important, with the more recent fire generating higher concentrations. The elevated concentrations in 250°C–350°C were attributed to a decomposition of organic matter and mineral transformations, including CaCO3 formation. Based on thermodynamics, we propose a couple of burn severity indicators: activities of calcium and carbonates that are calculated from pH, alkalinity and Ca concentration. The indicators do not only show the degree of post-fire transformations, but they also inform on CaCO3 formation. Further studies include: (1) application to field data, (2) association with organic contaminants, and (3) validation in other geographical locations.
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