RESUMEN
This study describes analytically the behaviour of bamboo culms subjected to bending, and predicts the failure load and stiffness loss after the linear-elastic stage. Basis of the failure load prediction is the identification of the critical failure mechanisms. The study examines analytically four distinct failure mechanisms: Brazier instability, longitudinal tension/compression, tension perpendicular to the fibres and shear parallel to the fibres. It concludes that, for the three bamboo species examined (Moso, Guadua and Kao Jue), critical failure mechanisms are tension perpendicular to the fibres (with potential tension-shear interaction) and longitudinal compression. Which of the two mechanisms occurs first depends on the case-specific material properties and culm radius-to-thickness ratio. Regarding stiffness loss, the main cause is longitudinal splitting. The extent of the stiffness loss depends on crack length, crack number and crack location along the culm circumference. Secondary causes are nonlinear geometric effects at the large deflection stage. Assuming a parabolic deformed shape, a single equation can describe the stiffness loss induced by nonlinear geometric effects, regardless of material properties and culm geometry. Comparing the analytical results with pertinent experimental data, the proposed equations are sufficiently accurate in their prediction of failure load and stiffness loss, although they tend to underestimate both.
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PoaceaeRESUMEN
We report on the design and realization of an x-ray imaging system for quantitative phase-contrast microscopy at high x-ray energy with laboratory-scale instrumentation. Phase and amplitude were separated quantitatively at x-ray energies up to 80 keV with micrometric spatial resolution. The accuracy of the results was tested against numerical simulations, and the spatial resolution was experimentally quantified by measuring a Siemens star phase object. This simple setup should find broad application in those areas of x-ray imaging where high energy and spatial resolution are simultaneously required and in those difficult cases where the sample contains materials with similar x-ray absorption.