The strength of plants: theory and experimental methods to measure the mechanical properties of stems

From the stems of agricultural crops to the structural trunks of trees, studying the mechanical behaviour of plant stems is critical for both commerce and science. Plant scientists are also increasingly relying on mechanical test data for plant phenotyping. Yet there are neither standardized methods nor systematic reviews of current methods for the testing of herbaceous stems. We discuss the architecture of plant stems and highlight important micro- and macrostructural parameters that need to be controlled and accounted for when designing test methodologies, or that need to be understood in order to explain observed mechanical behaviour. Then, we critically evaluate various methods to test structural properties of stems, including flexural bending (two-, three-, and four-point bending) and axial loading (tensile, compressive, and buckling) tests. Recommendations are made on best practices. This review is relevant to fundamental studies exploring plant biomechanics, mechanical phenotyping of plants, and the determinants of mechanical properties in cell walls, as well as to application-focused studies, such as in agro-breeding and forest management projects, aiming to understand deformation processes of stem structures. The methods explored here can also be extended to other elongated, rod-shaped organs (e.g. petioles, midribs, and even roots).This work is part of a project funded by the Leverhulme Trust (Project title: ‘Natural material innovation’). The project forms a collaboration with the Department of Applied Mathematics and Theoretical Physics, Department of Biochemistry, Department of Chemistry, and Department of Plant Sciences at the University of Cambridge

Design consideration of a multi-function otoacoustic emission measurement system

A new approach for recording otoacoustic emissions (OAEs) is described in the paper. The system is based on a personal computer equipped with INTEL Pentium CPU. A single chip microcomputer INTEL 8096 is developed to be a stimulus generator. Some critical problems and circuit parameters in the design of this system are presented in the paper. The main advantages of the system are (1) it can record three kinds of OAEs which have many clinical applications; (2) it can save raw data for further analysis, as most researchers need; (3) plenty of analysis functions can be developed in this system. With the use of the newly developed system, SOAEs, TEOAEs, and DPOAEs have been successfully measured.published_or_final_versio

Optimising ply orientation in structural laminated bamboo

Currently, only two forms of laminated bamboo are commercially available as structural materials: unidirectional beams and boards, and cross-laminated boards. As a natural quasi-unidirectional composite, the lamination of bamboo into plies with specific orientations would allow the design and manufacture of a family of multi-axial composite laminates with unique properties. In this study, we test the tensile mechanical properties of single- and two-ply laminated bamboo at various off-axis loading angles and laminate configurations. The data is then compared to micro-mechanical models for predicting modulus and strength of composite laminates. On the basis of our analyses, we believe there is significant scope to extend the current range of laminated bamboo products to include angle-ply laminates. Moreover, we demonstrate that composite laminate theory is applicable to this natural composite and may be used for design of products and structures

Thermal conductivity of engineered bamboo composites

Here we characterise the thermal properties of engineered bamboo panels produced in Canada, China, and Colombia. Specimens are processed from either Moso or Guadua bamboo into multi-layered panels for use as cladding, flooring or walling. We utilise the transient plane source method to measure their thermal properties and confirm a linear relationship between density and thermal conductivity. Furthermore, we predict the thermal conductivity of a three-phase composite material, as these engineered bamboo products can be described, using micromechanical analysis. This provides important insights on density-thermal conductivity relations in bamboo, and for the first time, enables us to determine the fundamental thermal properties of the bamboo cell wall. Moreover, the density-conductivity relations in bamboo and engineered bamboo products are compared to wood and other engineered wood products. We find that bamboo composites present specific characteristics, for example lower conductivities – particularly at high density – than equivalent timber products. These characteristics are potentially of great interest for low-energy building design. This manuscript fills a gap in existing knowledge on the thermal transport properties of engineered bamboo products, which is critical for both material development and building design.DUS and MCDB thank Mr Robert Cornell (University of Cambridge) for training on thermal conductivity measurement. Special thanks go to Prof Greg Smith and Dr Kate Semple at the University of British Columbia (Department of Wood Science), working on processing of structural bamboo products. This research has been funded by the EPSRC (Grant EP/K023403/1), a Leverhulme Trust Programme Grant, and the Newton Trust.This is the final version of the article. It was first available from Springer via http://dx.doi.org/10.1007/s10853-015-9610-

Case-control study of stroke and the quality of hypertension control in north west England

Objective: To examine the risk of stroke in relation to quality of hypertension control in routine general practice across an entire health district. Design: Population based matched case-control study. Setting: East Lancashire Health District with a participating population of 388,821 aged < or = 80. Subjects: Cases were patients under 80 with their first stroke identified from a population based stroke register between 1 July 1994 and 30 June 1995. For each case two controls matched with the case for age and sex were selected from the same practice register. Hypertension was defined as systolic blood pressure > or = 160 mm Hg or diastolic blood pressure > or = 95 mm Hg, or both, on at least two occasions within any three month period or any history of treatment with antihypertensive drugs. Main outcome measures: Prevalence of hypertension and quality of control of hypertension assessed by using the mean blood pressure recorded before stroke) and odds ratios of stroke (derived from conditional logistic regression). Results: Records of 267 cases and 534 controls were examined; 61% and 42% of these subjects respectively were hypertensive. Compared with non-hypertensive subjects hypertensive patients receiving treatment whose average pre-event systolic blood pressure was controlled to or = 160 mm Hg) or untreated had progressively raised odds ratios of 1.6, 2.2, 3.2, and 3.5 respectively. Results for diastolic pressure were similar; both were independent of initial pressures before treatment. Around 21% of strokes were thus attributable to inadequate control with treatment, or 46 first events yearly per 100,000 population aged 40-79. Conclusions: Risk of stroke was clearly related to quality of control of blood pressure with treatment. In routine practice consistent control of blood pressure to below 150/90 mm Hg seems to be required for optimal stroke prevention

Spider silk inspired damping fibres drawn from a supramolecular hydrogel composite at room temperature - A step closer to sustainable fibre technology

We report the aqueous self-assembly of hierarchical supramolecular polymer-colloidal hydrogels consisting of functionalized polymer-grafted silica nanoparticles, a hydroxyethyl cellulose derivative and cucurbit[8]uril. The resulting material (98 wt% water) can be drawn into uniform (6 μm) ‘supramolecular fibres’ at room temperature. They exhibited better tensile strength and superior stiffness to natural fibres such as viscose, protein-based silks, and human and animal hair, while cyclic loading tests illustrated their remarkable damping capacity (60–70%). These supramolecular hydrogels represent a new class of hybrid supramolecular composites, opening a window into fibre technology through low-energy manufacturing from a broad range of sustainable materials.Leverhulm

Thermal relaxation of laminated bamboo for folded shells

Laminated bamboo is emerging as a novel material in design and construction. As a natural fibre composite, it has unique mechanical properties that allow for innovations that are not possible in other materials. Here, we discuss one new application of those properties: the development of a novel bending technique using high temperature, and we explore its implications for design. We have explored the fundamental properties of laminated bamboo and its thermal relaxation asit passes the glass transition temperatures of its constituent polymers.By mechanically thinning engineered bamboo material, score lines allow precise, controlled and localised heating that promotes limited but essential elasto-plastic behaviour. Concentrated heating above the glass transition temperature induces property evolution and structural morphology changes, which results in thermal relaxation with minimal recovery and full set upon cooling.This original technology is then deployed in the design and construction of a folded plate helical shell composed of thin laminated bamboo sheets.The presented work is supported by a Leverhulme Trust Programme Grant, and EPSRC Grant EP/K023403/1

Fast tracking of evoked potential variations using correlated scale function designed by multiresolution analysis

Fast tracking of evoked potential variations is of great importance in clinical operation. The paper describes a method whereby an ensemble averaged signal is used as the prototype of the scale function and designs a correlated scale function based on multiresolution analysis. Hence, an effective low pass digital filter having powerful tracking capability is obtained. Results show that the filter designed filters out the noise more effectively than that using general wavelet filtering, and the tracking of the peak of evoked potential is easily obtained.published_or_final_versio

Relationship of structure and stiffness in laminated bamboo composites

Laminated bamboo in structural applications has the potential to change the way buildings are constructed. The fibrous microstructure of bamboo can be modelled as a fibre-reinforced composite. This study compares the results of a fibre volume fraction analysis with previous experimental beam bending results. The link between fibre volume fraction and bending stiffness shows that differences previously attributed to preservation treatment in fact arise due to strip thickness. Composite theory provides a basis for the development of future guidance for laminated bamboo, as validated here. Fibre volume fraction analysis is an effective method for non-destructive evaluation of bamboo beam stiffness