Digby D. Symons

Characterisation of indentation damage in 0/90 lay-up T300/914 CFRP

High- and low-speed impact tests and quasi-static indentation tests have been conducted on CFRP laminated plates. The resulting damage has been characterised and compared by the use of ultrasonic C-scanning, optical microscopy and X-ray computer microtomography. Repeated quasi-static indentation tests are used to investigate modes of energy absorption in the impact event.

Fatigue testing of impact-damaged T300/914 carbon-fibre-reinforced plastic

Abstract Fatigue tests have been conducted on impact damaged coupons of T300/914 carbon-fibre-reinforced plastic. Two damage levels were used to represent BVID (barely visible impact damage) and VID (visible impact damage). Fatigue tests were conducted at a frequency of 5 Hz and a load ratio of R =−1. Progression of fatigue damage was monitored by ultrasonic C-scan, measurement of changes in the coupon modulus and measurement of hysteresis in the impact damaged coupons.

The imperfection sensitivity of isotropic two-dimensional elastic lattices

The imperfection sensitivity of the effective elastic properties is numerically explored for three planar isotropic lattices: fully triangulated, the Kagome grid, and the hexagonal honeycomb. Each lattice comprises rigid-jointed, elastic Euler-Bernoulli beams, which can both stretch and bend. The imperfections are in the form of missing bars, misplaced nodes, and wavy cell walls. Their effect on the macroscopic bulk and shear moduli is numerically investigated by considering a unit cell containing randomly distributed imperfections, and with periodic boundary conditions imposed. The triangulated and Kagome lattices have sufficiently high nodal connectivities that they are stiff, stretching dominated structures in their perfect state. In contrast, the perfect hexagonal honeycomb, with a low nodal connectivity of 3, is stretching dominated under pure hydrostatic loading but is bending dominated when the loading involves a deviatoric component. The high connectivity of the triangulated lattice confers imperfection insensitivity: Its stiffness is relatively insensitive to missing bars or to dispersed nodal positions. In contrast, the moduli of the Kagome lattice are degraded by these imperfections. The bulk modulus of the hexagonal lattice is extremely sensitive to imperfections, whereas the shear modulus is almost unaffected. At any given value of relative density and level of imperfection (in the form of missing bars or dispersed nodal positions), the Kagome lattice has a stiffness intermediate between that of the triangulated lattice and the hexagonal honeycomb. It is argued that the imperfections within the Kagome lattice switch the deformation mode from stretching to a combination of stretching and bending. Cell-wall waviness degrades the moduli of all three lattices where the behavior of the perfect structure is stretching dominated. Since the shear response of the perfect hexagonal honeycomb is by bar bending, the introduction of bar waviness has a negligible effect on the effective shear modulus.

Actuation of kagome lattice structures

The kagome lattice has been shown to have promise as the basis of active structures, whose shape can be changed by linear actuators that replace some of the bars of the lattice. As a preliminary examination, this paper examines the effect of the actuation of a single bar in a large two-dimensional kagome lat- tice. Previous work has shown that interesting properties of the kagome lattice depend on the bars that are co-linear with the actuated bar being straight, but has also shown that actuation causes these bars to bend; this paper therefore explores the geometrically non-linear response of the structure. Numerical re- sults show that due to geometrically non-linear effects, the actuation stiffness is reduced from that predicted by linear models, while the peak elastic strain in the structure is increased. Individual actuators replace some of the members of the truss: altering the length of these actuators changes the macroscopic shape of the structure. In two dimensions, the kagome truss (Fig. 1) has been shown to be a promising solution for these structures. 3 It has been shown to be one of the few periodic, planar, single length scale lattice topologies that has optimal passive stiffness. At the same time, if considered as pin-jointed, any bar can be actuated without resistance. Although practical micro-scale structures will necessarily be rigid-jointed, the additional resistance to actuation from bar bending is small providing that the members are slender. The rigid- jointed planar Kagome lattice therefore has the required properties for use in high authority shape morphing structures; namely passive stiffness and low resistance to actuation. As a preliminary investigation, this paper will examine the effect of the actuation of a single bar in a large two-dimensional kagome lattice, and will consider how the stockiness, s, of the members affects the response. The stockiness is a non-dimensional measure of the aspect ratio of each bar, defined as the ratio of the in-plane radius of gyration of the cross-section, k, to the length of the member, L. Practical structures have s in the range from 0.005 to 0.05, which is the range investigated here. Previous work 4 has examined the energy required to actuate a single bar in a large two-dimensional lattice by considering various linear analytical and computational models. However, the special properties of the kagome lattice are dependent on its geometry, and actuation imposes large geometric deformations. This paper therefore builds on the previous work by considering the geometrically non-linear response of the structure. The resistance of the structure to actuation will be considered, as well as the limitation on actuation imposed by material yield; the limiting actuation strain will be calculated for various values of material yield strain. The paper is structured as follows. Section II will describe the computational model used, and Section III will describe some generic features of the response of the kagome lattice to the actuation of a single bar. Section IV then goes on to explore the build-up of force in the actuated member as the bar is actuated. Section V explores the peak elastic strain anywhere in the structure due to the imposed actuation, and shows how the actuation strain is limited by yielding of the structure for varying values of stockiness and yield strain.

Flow of Damp Powder in a Rotating Impervious Cone

A one dimensional analytical model is developed for the steady state, axisymmetric flow of damp powder within a rotating impervious cone. The powder spins with the cone but migrates up the wall of the cone (along a generator) under centrifugal force. The powder is treated as incompressible and Newtonian viscous, while the shear traction at the interface is taken to be both velocity and pressure dependent. A nonlinear second order ordinary differential equation is established for the mean through-thickness velocity as a function of radius in a spherical coordinate system, and the dominant nondimensional groups are identified. For a wide range of geometries, material parameters, and operating conditions, a midzone exists wherein the flow is insensitive to the choice of inlet and outlet boundary conditions. Within this central zone, the governing differential equation reduces to an algebraic equation with an explicit analytical solution. Furthermore, the bulk viscosity of the damp powder does not enter this solution. Consequently, it is suggested that the rotating impervious cone is a useful geometry to measure the interfacial friction law for the flow of a damp powder past an impervious wall.

Optimizing the Entrainment Geometry of a Dry Powder Inhaler: Methodology and Preliminary Results

PurposeFor passive dry powder inhalers (DPIs) entrainment and emission of the aerosolized drug dose depends strongly on device geometry and the patient’s inhalation manoeuvre. We propose a computational method for optimizing the entrainment part of a DPI. The approach assumes that the pulmonary delivery location of aerosol can be determined by the timing of dose emission into the tidal airstream.MethodsAn optimization algorithm was used to iteratively perform computational fluid dynamic (CFD) simulations of the drug emission of a DPI. The algorithm seeks to improve performance by changing the device geometry. Objectives were to achieve drug emission that was: A) independent of inhalation manoeuvre; B) similar to a target profile. The simulations used complete inhalation flow-rate profiles generated dependent on the device resistance. The CFD solver was OpenFOAM with drug/air flow simulated by the Eulerian-Eulerian method.ResultsTo demonstrate the method, a 2D geometry was optimized for inhalation independence (comparing two breath profiles) and an early-bolus delivery. Entrainment was both shear-driven and gas-assisted. Optimization for a delay in the bolus delivery was not possible with the chosen geometry.ConclusionsComputational optimization of a DPI geometry for most similar drug delivery has been accomplished for an example entrainment geometry.

Frictional flow of damp granular material in a conical centrifuge

An analysis is given of velocity and pressure-dependent sliding flow of a thin layer of damp granular material in a spinning cone. Integral momentum equations for steady state, axi-symmetric flow are derived using a boundary layer approximation. These reduce to two coupled first-order differential equations for the radial and circumferential sliding velocities. The influence of viscosity and friction coefficients and inlet boundary conditions is explored by presentation of a range of numerical results. In the absence of any interfacial shear traction the flow would, with increasing radial and circumferential slip, follow a trajectory from inlet according to conservation of angular momentum and kinetic energy. Increasing viscosity or friction reduces circumferential slip and, in general, increases the residence time of a particle in the cone. The residence time is practically insensitive to the inlet velocity. However, if the cone angle is very close to the friction angle then the residence time is extremely sensitive to the relative magnitude of these angles.

Comparison of theoretical and numerical buckling loads for wind turbine blade panels

Theoretical and finite element (FE) methods for predicting buckling of wind turbine blades are compared. The theoretical method considers the blade skin as separate panels (idealised as cylindrically curved, simply-supported, and under uniform axial compression); established theory provides the critical load. This approach is compared to FE models of individual panels and representative aerofoils. The FE calculation for an idealised panel agrees with the theory (within 10%). Idealising the panel curvature as cylindrical makes little difference to the critical load (<5%). Adoption of a more realistic load distribution over the length of a blade has greater influence: the buckling strain at the root of a blade under a cubically varying bending moment distribution (e.g. flap-wise bending of a tapered blade under uniform incident wind pressure) is 15% higher than that for an idealised panel. The idealised panel method is therefore a conservative method suitable for preliminary design.

The effects of forward rotation of posture on computer-simulated 4-km track cycling: Implications of Union Cycliste Internationale rule 1.3.013.:

The aim of this research was to indicate improvements in 4-km cycling performance that may be gained as a function of reduced frontal surface area (A) when Union Cycliste Internationale rule 1.3.013 is contravened. In 10 male cyclists age 26 ± 2 (mean ± standard deviation) years, height 180 ± 5 cm and body mass 71 ± 6 kg, entire cycling posture was rotated forward from where the nose of the saddle was 6 cm rearward of the bottom bracket spindle (P6) to 4, 2 and 0 cm (P4, P2 and P0); contravening Union Cycliste Internationale rule 1.3.013. Using computerised planimetry, A was estimated and a forward integration model was compiled to simulate 4-km track cycling end time (T4km) when a fixed power profile was applied. At P2, there was a significant but non-meaningful reduction compared to P6 (p < 0.05, d < 0.02). There were small but significant reductions in A and T4km between P6 and P0; −0.007 ± 0.004 m2 and −1.40 ± 0.73 s, respectively (p < 0.001, d = −0.259). There were no significant differences between P4 and P6 for A and T4km. These results suggest that at the most forward position (P0), a small but significant increase in 4-km performance can be expected compared to the legal position (P6). Moreover, the mean difference in T4km between P6 and P0 is greater than the winning margin at the Union Cycliste Internationale 4-km pursuit world championships four times in the previous 10 years.

Measurement of Fluid Flow Thickness Within a Rotating Cone

© 2015 by ASME. This paper reports experimental measurements of film thickness for continuous fluid flow on the internal surface of a cone rotating about a vertical axis. Measurements were obtained via an optical method based on photographing the displacement of a grid projected onto the surface of the flow within the cone. Results are compared to analytical theory for axisymmetric, steady state, free-surface laminar flow of a Newtonian fluid in a spinning cone. The theory assumes that the flow is thin but takes account of gravity. The theoretical model is found to be in good agreement with the experimental results.