دكتوراه
الهندسة
University of Bristol
| مجال التميز | بحثي دراسي |
| البحوث المنشورة | |
| البحث (1): | |
| عنوان البحث: | Abnormal stiffness behaviour in artificial cactus-inspired reinforcement materials |
| رابط إلى البحث: | https://iopscience.iop.org/article/10.1088/1748-3190/abc1f2/meta |
| تاريخ النشر: | 24/12/2020 |
| موجز عن البحث: | Cactus fibres have previously shown unusual mechanical properties in terms of bending and axial stiffness due to their hierarchical structural morphology. Bioinspiration from those cactus fibres could potentially generate architected materials with exciting properties. To that end we have built bioinspired artificial analogues of cactus fibres to evaluate their mechanical properties. We have generated 3D printed specimens from rendered models of the cactus structure using two different printing techniques to assess the reproducibility of the structural topology. Bioinspired additive manufactured materials with unusual mechanical properties constitute an ever-evolving field for applications ranging from novel wing designs to lightweight plant-inspired analogues. The cactus-inspired 3D printed specimens developed here demonstrate an unusually high bending to axial stiffness ratios regardless of the manufacturing method used. Moreover, when compared to their equivalent beam analogues the cactus specimens demonstrate a significant potential in terms of specific (weight averaged) flexural modulus. Imaging of the artificial cactus reinforcements has enabled the generation of a one-dimensional reduced order finite element model of the cactus structure, with a distribution of cross sections along the length that simulate the inertia and mechanical behaviour of the cactus topology. The novel bioinspired material structure shows an excellent reproducibility across different manufacturing methods and suggest that the tree-like topology of the cactus fibre could be very suited to applications where high bending to axial stiffness ratios are critical. |
| البحث (2): | |
| عنوان البحث: | Thermoformability characterisation of Flax reinforced polypropylene composite materials |
| رابط إلى البحث: | https://www.sciencedirect.com/science/article/abs/pii/S1359836819335899 |
| تاريخ النشر: | 01/03/2020 |
| موجز عن البحث: | Flax reinforced polypropylene (Flax/PP) composites are currently used as sustainable and recyclable materials in secondary load-bearing applications. This study focuses on the effects of the thermoforming parameters (temperature, dwelling time, pressure and fabricated area parameters) and moisture absorption on the mechanical and aesthetic performance of Flax/PP laminates. The manufacturing and environmental variables have been investigated following a sequential order to identify a cumulative improvement on the performance of the Flax/PP composites. Temperature and dwelling time were the parameters with greatest influence on the aesthetics and mechanical performance of the Flax/PP. The thermoforming pressure and the size of the manufacturing area were the parameters that contributed the less. Although the moisture absorption degraded the Flax/PP mechanical performance, the moisture desorption had however a negligible impact. We therefore conclude that Flax/PP thermoformed parts could be suitably produced and stored in normal room conditions. |
| البحث (3): | |
| عنوان البحث: | Dome-Shape Auxetic Cellular Metamaterials: Manufacturing, Modeling, and Testing |
| رابط إلى البحث: | https://www.frontiersin.org/articles/10.3389/fmats.2019.00086/full |
| تاريخ النشر: | 24/04/2019 |
| موجز عن البحث: | We present in this work the manufacturing, modeling, and testing of dome-shaped cellular structures with auxetic (negative Poisson’s ratio) behavior. The auxetic configurations allow the creation of structures with synclastic (i.e., dome-shaped) curvatures, and this feature is used to evaluate the performance of cellular metamaterials under quasi-static indentation conditions. We consider here different cellular geometries (re-entrant, arrow-head, tri-chiral, hexagonal) and the implications of their manufacturing using 3D printing techniques with PLA material. The dome-shaped configurations are modeled using full-scale non-linear quasi-static and explicit dynamic FE models that represent both the geometry and approximate constitutive models of the PLA filament material derived from tensile tests on dogbone specimens. The cellular metamaterials samples are subjected to indentation tests, with maps of strains obtained through DIC measurements. The correlation between experimental and numerical simulations is good, and shows the peculiar indentation behavior of these cellular structures. We also perform a comparative analysis by simulation of the force/displacement, strain and fracture history during quasi-static loading, and discuss the performance of the different cellular topologies for these dome-shape metamaterial designs. |
| البحث (4): | |
| عنوان البحث: | Meta-tensegrity: Design of a tensegrity prism with metal rubber |
| رابط إلى البحث: | https://www.sciencedirect.com/science/article/abs/pii/S0263822318325029 |
| تاريخ النشر: | 15/12/2018 |
| موجز عن البحث: | A tensegrity structure involves the presence of elements withstanding pure compression, and others under pure tension only. Metal rubber is introduced into a tensegrity prism strut to create a mechanical metamaterial with energy absorption and tuneable dynamic properties. In this work we describe the design and development of the meta-tensegrity structure with particular emphasis on the evaluation of parameters such as the structural size, the metal rubber stiffness, the initial internal force and the external compression load. Prototypes of tensegrity prisms with and without metal rubber inserts have been assembled and subjected to quasi-static loading. The model used to design the meta tensegrity prism has been then modified to take into account specific manufacturing and internal dissipation mechanisms typical of this configuration. The updated model provides a better comparison with the experimental results. Both the theoretical and experimental data show that the introduction of the metal rubber within the tensegrity configuration contributes to improve significantly the energy absorption, and to reduce the stiffness of the whole tensegrity structure. |
| البحث (5): | |
| عنوان البحث: | Tensegrity cell mechanical metamaterial with metal rubber |
| رابط إلى البحث: | https://aip.scitation.org/doi/abs/10.1063/1.5040850 |
| تاريخ النشر: | 20/07/2018 |
| موجز عن البحث: | A tensegrity structure involves the presence of elements withstanding pure compression, and others under pure tension only. Metal rubber is introduced into a tensegrity prism strut to create a mechanical metamaterial with energy absorption and tuneable dynamic properties. In this work we describe the design and development of the meta-tensegrity structure with particular emphasis on the evaluation of parameters such as the structural size, the metal rubber stiffness, the initial internal force and the external compression load. Prototypes of tensegrity prisms with and without metal rubber inserts have been assembled and subjected to quasi-static loading. The model used to design the meta tensegrity prism has been then modified to take into account specific manufacturing and internal dissipation mechanisms typical of this configuration. The updated model provides a better comparison with the experimental results. Both the theoretical and experimental data show that the introduction of the metal rubber within the tensegrity configuration contributes to improve significantly the energy absorption, and to reduce the stiffness of the whole tensegrity structure. |
| البحث (6): | |
| عنوان البحث: | A Kirigami shape memory polymer honeycomb concept for deployment |
| رابط إلى البحث: | https://iopscience.iop.org/article/10.1088/1361-665X/aa6b6d/meta |
| تاريخ النشر: | 19/04/2017 |
| موجز عن البحث: | We present a shape memory polymer (SMP) honeycomb with tuneable and shape morphing mechanical characteristics. Kirigami (Origami with cutting allowed) techniques have been used to design and manufacture the honeycomb. The cellular structure described in this work has styrene SMP hinges that create the shape change and the deployment actuation. To create a large volumetric deployment, the Kirigami open honeycomb configuration has been designed by setting an initial three-dimensional re-entrant auxetic (negative Poisson’s ratio) configuration, while the final honeycomb shape assume a convex (positive Poisson’s ratio) layout. A model was developed to predict the shape change of the structure, and compared to experimental results from a demonstrator honeycomb deployment test. |
