Growth Cone Pathfinding: a competition between deterministic and stochastic events

BACKGROUND: Growth cone migratory patterns show evidence of both deterministic and stochastic search modes. RESULTS: We quantitatively examine how these two different migration modes affect the growth cone's pathfinding response, by simulating growth cone contact with a repulsive cue and measuring the resultant turn angle. We develop a dimensionless number, we call the determinism ratio Ψ, to define the ratio of deterministic to stochastic influences driving the growth cone's migration in response to an external guidance cue. We find that the growth cone can exhibit three distinct types of turning behaviors depending on the magnitude of Ψ. CONCLUSIONS: We conclude, within the context of these in silico studies, that only when deterministic and stochastic migration factors are in balance (i.e. Ψ ~ 1) can the growth cone respond constructively to guidance cues

Considering the healthcare needs of older people with multimorbidity: managing Alice

Editoria

Design and analysis of strut-based lattice structures for vibration isolation

This paper presents the design, analysis and experimental verification of strut-based lattice structures to enhance the mechanical vibration isolation properties of a machine frame, whilst also conserving its structural integrity. In addition, design parameters that correlate lattices, with fixed volume and similar material, to natural frequency and structural integrity are also presented. To achieve high efficiency of vibration isolation and to conserve the structural integrity, a trade-off needs to be made between the frame’s natural frequency and its compressive strength. The total area moment of inertia and the mass (at fixed volume and with similar material) are proposed design parameters to compare and select the lattice structures; these parameters are computationally efficient and straight-forward to compute, as opposed to the use of finite element modelling to estimate both natural frequency and compressive strength. However, to validate the design parameters, finite element modelling has been used to determine the theoretical static and dynamic mechanical properties of the lattice structures. The lattices have been fabricated by laser powder bed fusion and experimentally tested to compare their static and dynamic properties to the theoretical model. Correlations between the proposed design parameters, and the natural frequency and strength of the lattices are presented

Compressive failure modes and energy absorption in additively manufactured double gyroid lattices

Lattice structures are excellent candidates for lightweight, energy absorbing applications such as personal protective equipment. In this paper we explore several important aspects of lattice design and production by metal additive manufacturing, including the choice of cell size and the application of a post-manufacture heat treatment. Key results include the characterisation of several failure modes in double gyroid lattices made of Al-Si10-Mg, the elimination of brittle fracture and low strain failure by the application of a heat treatment, and the calculation of specific energy absorption under compressive deformation (16x106 J m-3 up to 50% strain). These results demonstrate the suitability of double gyroid lattices for energy absorbing applications, and will enable the design and manufacture of more efficient lightweight parts in the future

Selective laser melting of aluminium alloys

Metal additive manufacturing (AM) processes, such as selective laser melting, enable powdered metals to be formed into arbitrary 3D shapes. For aluminium alloys, which are desirable in many high-value applications for their low density and good mechanical performance, selective laser melting is regarded as challenging due to the difficulties in laser melting aluminium powders. However, a number of studies in recent years have demonstrated successful aluminium processing, and have gone on to explore its potential for use in advanced, AM componentry. In addition to enabling the fabrication of highly complex structures, selective laser melting produces parts with characteristically fine microstructures that yield distinct mechanical properties. Research is rapidly progressing in this field, with promising results opening up a range of possible applications across scientific and industrial sectors. This paper reports on recent developments in this area of research as well as highlighting some key topics that require further attention

Measurement of internal surfaces of additively manufactured parts by X-ray computed tomography

Recent advances in X-ray computed tomography (XCT) have allowed for measurement resolutions approaching the point where XCT can be used for measuring surface topography. These advances make XCT appealing for measuring hard-to-reach or internal surfaces, such as those often present in additively manufactured parts. To demonstrate the feasibility and potential of XCT for topography measurement, topography datasets obtained using two XCT systems are compared to those from more conventional non-contact optical surface measurement instruments. A hollow Ti6Al4V part produced by direct metal laser sintering is used as a measurement artefact. The artefact comprises two component halves that can be separated to expose the internal surfaces. Measured surface datasets are compared by various qualitative and quantitative means, including the computation of ISO 25178-2 areal surface texture parameters. Preliminary results show that XCT can provide surface information comparable with more conventional surface measurement technologies, thus representing a viable alternative to more conventional measurement, particularly appealing for hard-to-reach and internal surfaces

Dynamic compressive response of additively manufactured AlSi10Mg alloy hierarchical honeycomb structures

Periodic honeycombs have been used for their high strength, low weight and multifunctionality. The quasi-static and dynamic compressive responses of three types of additively manufactured AlSi10Mg honeycomb structures, specifically a single-scale honeycomb and two hierarchical honeycombs with two and three levels of hierarchy, respectively, have been investigated using experimental measurement and finite element (FE) simulations. The validated FE simulation has been employed to investigate the effects of relative density of the honeycombs and the key experimental parameters. The following failure modes of the three types of honeycombs have been observed both under quasi-static and dynamic compression: (1) the single-scale honeycomb experienced a transition of failure mechanism from local plastic buckling of walls to local damage of the parent material without buckling with the increase of the relative density of the honeycomb; (2) the hierarchical honeycombs all failed with parent material damage without buckling at different relative densities. For both quasi-static and dynamic compression, the hierarchical honeycombs offer higher peak nominal wall stresses compared to the single-scale honeycomb at low relative density of ; the difference is diminished as relative density increases, i.e. the three types of honeycombs can achieve similar peak wall stresses when Numerical results have suggested the hierarchical honeycombs can offer better energy absorption capacity than the single-scale honeycomb. The two-scale and three-scale hierarchical honeycombs achieved similar peak nominal wall stresses for both quasi-static and dynamic compression, which may suggest that the structural performance under out-of-plane compression is not sensitive to the hierarchical architecture. This work indicates that the structural advantage of hierarchical honeycombs can be utilised to develop high performance lightweight structural components

X-ray computed tomography of additively manufactured metal parts: the effect of magnification and reconstruction sampling on surface topography measurement

X-ray computed tomography (XCT) has recently become recognised as a viable method of surface topography measurement for additively manufactured (AM) metal parts [1–5]. AM is capable of producing internal features that are inaccessible to other surface topography measurement instruments [6,7], which makes XCT topography measurement particularly interesting to the AM community. A rigorous assessment of the ability of XCT systems to measure surface topography is, however, yet to be performed, and represents a complex challenge that must account for the large number of control variables involved in XCT measurement (e.g. voltage, current, magnification, computational corrections, filtering and surface determination). The aim of this study is to investigate the sensitivity of XCT topography measurement to some such control variables. More specifically, the effects of varying magnification (i.e. the ratio between source-to-detector distance and source-to-object distance [8]) and reconstruction sampling (i.e. the resolution of the volumetric grid filled during reconstruction [9]) are investigated. These variables have been chosen for their influence on the voxel size of the volumetric dataset, which in turn affects the extracted topography, and any subsequent texture assessment. In this work, the internal top surface of a hollow Ti6Al4V cubic artefact with an external size of (10 × 10 × 10) mm, fabricated via laser powder bed fusion (LPBF) is considered (see figure 1). Measurements are performed with geometric magnification (the first control variable) set at 5×, 10×, 20× and 50×, aligned with typical magnifications used during optical surface topography measurement. The effects of super- and sub-sampling in the volume reconstruction phase (the second control variable) are investigated using Nikon software (CT Pro). Texture parameters and reconstructed topography profiles obtained as a result of XCT measurements are investigated and compared to measurements by coherence scanning interferometry (CSI) and focus variation (FV). Datasets are bandwidth-matched [10] between instruments for the quantitative comparison of texture parameters. For profile comparison, CSI, FV and XCT areal topographies are relocated with geometric registration methods. Initial results indicate that, for selected combinations of magnification and sampling reconstruction, XCT surface topography is in agreement with topography obtained by CSI, FV and stylus measurements. The authors expect this study to provide information about how these control variables can be optimised, (with the purpose of decreasing measurement complexity and time) without significantly altering the quality of the topographic result