Imperial College London

Dr Ajit Panesar

Faculty of EngineeringDepartment of Aeronautics

Lecturer in Design for Innovative Manufacturing
 
 
 
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Contact

 

+44 (0)20 7594 2202a.panesar

 
 
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Location

 

216City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

32 results found

Plocher J, Panesar A, 2020, Effect of density and unit cell size grading on the stiffness and energy absorption of short fibre-reinforced functionally graded lattice structures, Additive Manufacturing, Pages: 101171-101171, ISSN: 2214-8604

Architectured structures, particularly functionally graded lattices, are receiving much attention in both industry and academia as they facilitate the customization of the structural response and harness the potential for multi-functional applications. This work experimentally investigates how the severity of density and unit cell size grading as well as the building direction affects the stiffness, energy absorption and structural response of additively manufactured (AM) short fibre-reinforced lattices with same relative density. Specimens composed of tessellated body-centred cubic (BCC), Schwarz-P (SP) and Gyroid (GY) unit cells were tested under compression. Compared to the uniform lattices of equal density, it was found, that modest density grading has a positive and no effect on the total compressive stiffness of SP and BCC lattices, respectively. More severe grading gradually reduces the total stiffness, with the modulus of the SP lattices never dropping below that of the uniform counterparts. Unit cell size grading had no significant influence on the stiffness and revealed an elastomer-like performance as opposed to the density graded lattices of the same relative density, suggesting a foam-like behaviour. Density grading of bending-dominated unit cell lattices showcased better energy absorption capability for small displacements, whereas grading of the stretching-dominated counterparts is advantageous for large displacements when compared to the ungraded lattice. The severity of unit cell size graded lattices does not affect the energy absorption capability. Finally, a power-law approach was used to semi-empirically derive a formula that predicts the cumulative energy absorption as a function of the density gradient and relative density. Overall, these findings will provide engineers with valuable knowledge that will ease the design choices for lightweight multi-functional AM-parts.

Journal article

Plocher J, Panesar A, 2020, Mechanical Performance of Additively Manufactured Fiber-Reinforced Functionally Graded Lattices, JOM, Vol: 72, Pages: 1292-1298, ISSN: 1047-4838

Journal article

Bekas DG, Hou Y, Liu Y, Panesar Aet al., 2019, 3D printing to enable multifunctionality in polymer-based composites: A review, COMPOSITES PART B-ENGINEERING, Vol: 179, ISSN: 1359-8368

Journal article

Plocher J, Panesar A, 2019, Review on design and structural optimisation in additive manufacturing: Towards next-generation lightweight structures, Materials & Design, Vol: 183, Pages: 1-20, ISSN: 0264-1275

As the application of additive manufacturing (AM) reaches an unprecedented scale in both academia and industry, a reflection upon the state-of-the-art developments in the design for additive manufacturing (DfAM) and structural optimisation, becomes vital for successfully shaping the future AM-landscape. A framework, highlighting both the interdependencies between these two central aspects in AM and the necessity for a holistic approach to structural optimization, using lightweight strategies such as topology optimization and/or latticing, was established to summarize the reviewed content. Primarily focusing on isotropic material considerations and basic stiffness-optimal problems, these concepts have already found wide application, bridging the gaps between design and manufacturing as well as academia and industry. In pursuit of streamlining the AM-workflow towards digitally print-ready designs, studies are increasingly investigating mathematically-based structural optimization approaches in conjunction with DfAM-specific constraints, providing a portfolio of solutions like generative design, which is gaining traction in industry. Besides an overview on economically-driven to performance-driven design optimizations, insight into commercial AM-specific software is provided, elucidating potentials and challenges for the community. Despite the abundance of AM design methods to-date, computationally inexpensive solutions for common engineering problems are still scarce, which is constituting one of many key challenges for the future.

Journal article

Lee C, Greenhalgh E, Shaffer M, Panesar Aet al., Optimized microstructures for multifunctional structural electrolytes, Multifuctional Materials, ISSN: 2399-7532

Multifunctional structural materials offer compelling opportunities to realize highly efficient products. However, the need to fulfil disparate functions generates intrinsically conflicting physical property demands. One attractive strategy is to form a bi-continuous architecture of two disparate phases, each addressing a distinct physical property. For example, structural polymer electrolytes combine rigid and ion-conducting phases to deliver the required mechanical and electrochemical performance. Here, we present a general methodology, based on topology optimization, to identify optimal microstructures for particular design considerations. The numerical predictions have been successfully validated by experiments using 3D printed specimens. These architectures are directly relevant to multifunctional structural composites whilst the methodology can easily be extended to identify optimal microstructural designs for other multifunctional material embodiments.

Journal article

Plocher J, Lee C, Panesar A, 2019, Additive manufacturing of bone-inspired structural-power composites, 22nd International Conference on Composite Materials 2019, Publisher: ICCM

Design for additive manufacturing today – benefitting from unprecedented geometrical freedom – isincreasingly exploiting means of structural optimization, including topology optimization, latticing andby taking inspiration from nature. This paper constitutes a case study, highlighting the added value andpotential of combining these structural design approaches in AM, particularly in terms ofmultifunctionality. A method to obtain bone-inspired structural-power composites, designed for fibre-reinforced additive manufacturing, with both high stiffness-to-weight ratio and ionic conductivity ispresented. For this purpose, a sandwich structure with reinforced shell (compact bone) and lattice core(spongy bone) filled with ionic liquid (bone marrow) is proposed. A finite element analysis andcalculations based on a resistance network model provided insight into the change and trade-off betweenmechanical and electrical performance with increasing shell thickness i.e. level of reinforcement.Investigations into fibre angle assignments following the central difference scheme and the medial axistransformation have shown comparable performance, providing ways of controlling and tailoringdeposition paths to best meet requirements associated with the manufacturing with short and continuousfibre-reinforcements. The model with continuous fibre-reinforcement has shown great potential forimproving the specific stiffness compared to the isotropic functional counterpart used as benchmark,while additionally providing the potential for energy storage, constituting a promising theoreticalapproach as to how AM can serve as means for lightweighting through functional integration. It wasconcluded, that in pursuit of improving the efficient material usage, tailored shell-infill designs shouldbe considered in the future.

Conference paper

Lee C, Greenhalgh E, Panesar A, 2019, Optimised laminated composite ship-structures against wave impact for enhanced dynamic stiffness, Inter-noise 2019, Publisher: International Institute of Noise Control Engineering (I-INCE), ISSN: 0105-175X

Fibre-reinforced laminated composites are increasingly being utilised in marine and offshore structures due to their superior stiffness and strength to weight ratios, such as resistance to corrosion and enhanced toughness over conventional materials like steel and aluminium. A potential application of composites is in the design of wave-breakers on ship structures. These structures absorb the impact energies from a wave slam to ensure vessel serviceability and safety. The inherent anisotropy of composites and the associated dynamic loading characteristics, make the design process for such a structure very challenging. There are limited studies looking at the design optimisation of composite structures under wave impact loads. In particular, dynamic optimisation based on modal vibration characteristics has not been sufficiently studied. In this study, we have optimised a composite wave-breaker to improve the specific dynamic stiffness based on modal vibration characteristics. To tackle this problem, a multi-level optimisation procedure has been adopted; firstly, the minimum thickness of the composite plate has been determined to avoid delamination; subsequently, the stacking sequence has been identified using lamination parameters along with local thickness variation. Importantly, the optimal arrangement of damping materials (sandwiched between plies) has also been investigated to further enhance the dynamic energy dissipation performance.

Conference paper

Lee C, Panesar A, Greenhalgh E, Design of optimised multi-scale structures for multifunctional composites, International conference on composite materials (ICCM-22)

Conference paper

Lee C, Greenhalgh ES, Panesar A, 2019, Optimised laminated composite ship-structures against wave impact for enhanced dynamic stiffness

© INTER-NOISE 2019 MADRID - 48th International Congress and Exhibition on Noise Control Engineering. All Rights Reserved. Fibre-reinforced laminated composites are increasingly being utilised in marine and offshore structures due to their superior stiffness and strength to weight ratios, such as resistance to corrosion and enhanced toughness over conventional materials like steel and aluminium. A potential application of composites is in the design of wave-breakers on ship structures. These structures absorb the impact energies from a wave slam to ensure vessel serviceability and safety. The inherent anisotropy of composites and the associated dynamic loading characteristics, make the design process for such a structure very challenging. There are limited studies looking at the design optimisation of composite structures under wave impact loads. In particular, dynamic optimisation based on modal vibration characteristics has not been sufficiently studied. In this study, we have optimised a composite wave-breaker to improve the specific dynamic stiffness based on modal vibration characteristics. To tackle this problem, a multi-level optimisation procedure has been adopted; firstly, the minimum thickness of the composite plate has been determined to avoid delamination; subsequently, the stacking sequence has been identified using lamination parameters along with local thickness variation. Importantly, the optimal arrangement of damping materials (sandwiched between plies) has also been investigated to further enhance the dynamic energy dissipation performance.

Conference paper

Araújo LJP, Panesar A, Özcan E, Atkin J, Baumers M, Ashcroft Iet al., 2019, An experimental analysis of deepest bottom-left-fill packing methods for additive manufacturing, International Journal of Production Research, ISSN: 0020-7543

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. The adoption of Additive Manufacturing (AM) technology requires the efficient utilisation of the avail- able build volumes to minimise production times and costs. Three-dimensional algorithms, particularly the Deepest Bottom-Left-Fill (DBLF) heuristic, have been extensively used to tackle the problem of packing arbitrary 3D geometries within the AM sector. A particularly common method applied to more realistic packing problems is the combination of DBLF and metaheuristics such as Genetic Algorithms (GAs). Through a series of experiments, this paper experimentally investigates the practical aspects, and comparative performance of different DBLF based methods including a brute force algorithm and GA combined with DBLF for AM build volume packing. The insights into the relationship between algorithm efficiency (in terms of volume utilisation), simulation runtime, and practical requirements, in particular geometry rotation constraints are investigated. In addition to providing an increased comprehension of the practical aspects of applying DBLF algorithms in the AM context, this study confirms the limita- tions of traditional DBLF and the requirements for more flexible and intelligent placement strategies while experimentally demonstrating that higher degrees of freedom for part rotation contribute to small improvements in volume density. The resulting additional computational effort discourages this strategy, however.

Journal article

Lee C, Greenhalgh ES, Panesar A, 2019, Optimised laminated composite ship-structures against wave impact for enhanced dynamic stiffness

© INTER-NOISE 2019 MADRID - 48th International Congress and Exhibition on Noise Control Engineering. All Rights Reserved. Fibre-reinforced laminated composites are increasingly being utilised in marine and offshore structures due to their superior stiffness and strength to weight ratios, such as resistance to corrosion and enhanced toughness over conventional materials like steel and aluminium. A potential application of composites is in the design of wave-breakers on ship structures. These structures absorb the impact energies from a wave slam to ensure vessel serviceability and safety. The inherent anisotropy of composites and the associated dynamic loading characteristics, make the design process for such a structure very challenging. There are limited studies looking at the design optimisation of composite structures under wave impact loads. In particular, dynamic optimisation based on modal vibration characteristics has not been sufficiently studied. In this study, we have optimised a composite wave-breaker to improve the specific dynamic stiffness based on modal vibration characteristics. To tackle this problem, a multi-level optimisation procedure has been adopted; firstly, the minimum thickness of the composite plate has been determined to avoid delamination; subsequently, the stacking sequence has been identified using lamination parameters along with local thickness variation. Importantly, the optimal arrangement of damping materials (sandwiched between plies) has also been investigated to further enhance the dynamic energy dissipation performance.

Conference paper

Maskery I, Sturm L, Aremu AO, Panesar A, Williams CB, Tuck CJ, Wildman RD, Ashcroft IA, Hague RJMet al., 2018, Insights into the mechanical properties of several triply periodic minimal surface lattice structures made by polymer additive manufacturing, Polymer, Vol: 152, Pages: 62-71, ISSN: 0032-3861

Three-dimensional lattices have applications across a range of fields including structural lightweighting, impact absorption and biomedicine. In this work, lattices based on triply periodic minimal surfaces were produced by polymer additive manufacturing and examined with a combination of experimental and computational methods. This investigation elucidates their deformation mechanisms and provides numerical parameters crucial in establishing relationships between their geometries and mechanical performance. Three types of lattice were examined, with one, known as the primitive lattice, being found to have a relative elastic modulus over twice as large as those of the other two. The deformation process of the primitive lattice was also considerably different from those of the other two, exhibiting strut stretching and buckling, while the gyroid and diamond lattices deformed in a bending dominated manner. Finite element predictions of the stress distributions in the lattices under compressive loading agreed with experimental observations. These results can be used to create better informed lattice designs for a range of mechanical and biomedical applications.

Journal article

Panesar A, Abdi M, Hickman D, Ashcroft Iet al., 2018, Strategies for functionally graded lattice structures derived using topology optimisation for Additive Manufacturing, Additive Manufacturing, Vol: 19, Pages: 81-94, ISSN: 2214-8604

A number of strategies that enable lattice structures to be derived from Topology Optimisation (TO) results suitable for Additive Manufacturing (AM) are presented. The proposed strategies are evaluated for mechanical performance and assessed for AM specific design related manufacturing considerations. From a manufacturing stand-point, support structure requirement decreases with increased extent of latticing, whereas the design-to-manufacture discrepancies and the processing efforts, both in terms of memory requirements and time, increase. Results from Finite Element (FE) analysis for the two loading scenarios considered: intended loading, and variability in loading, provide insight into the solution optimality and robustness of the design strategies. Lattice strategies that capitalised on TO results were found to be considerably (∼40–50%) superior in terms of specific stiffness when compared to the structures where this was not the case. The Graded strategy was found to be the most desirable from both the design and manufacturing perspective. The presented pros-and-cons for the various proposed design strategies aim to provide insight into their suitability in meeting the challenges faced by the AM design community.

Journal article

Panesar A, Brackett D, Ashcroft I, Wildman R, Hague Ret al., 2017, Hierarchical re-meshing strategies with mesh mapping for topology optimisation, International Journal for Numerical Methods in Engineering, Vol: 111, Pages: 676-700, ISSN: 0029-5981

This work investigates the use of hierarchical mesh decomposition strategies for topology optimisation using bi‐directional evolutionary structural optimisation algorithm. The proposed method uses a dual mesh system that decouples the design variables from the finite element analysis mesh. The investigation focuses on previously unexplored areas of these techniques to investigate the effect of five meshing parameters on the analysis solving time (i.e. computational effort) and the analysis quality (i.e. solution optimality). The foreground mesh parameters, including adjacency ratio and minimum and maximum element size, were varied independently across solid and void domain regions. Within the topology optimisation, strategies for controlling the mesh parameters were investigated. The differing effects of these parameters on the efficiency and efficacy of the analysis and optimisation stages are discussed, and recommendations are made for parameter combinations. Some of the key findings were that increasing the adjacency ratio increased the efficiency only modestly – the largest effect was for the minimum and maximum element size parameters – and that the most dramatic reduction in solve time can be achieved by not setting the minimum element size too low, assuming mapping onto a background mesh with a minimum element size of 1.

Journal article

Panesar A, Ashcroft I, Brackett D, Wildman R, Hague Ret al., 2017, Design framework for multifunctional additive manufacturing: coupled optimization strategy for structures with embedded systems, Additive Manufacturing, Vol: 16

Journal article

Maskery I, Hussey A, Panesar A, Aremu A, Tuck C, Ashcroft I, Hague Ret al., 2017, An investigation into reinforced and functionally graded lattice structures, Journal of Cellular Plastics

Lattice structures are regarded as excellent candidates for use in lightweight energy-absorbing applications, such as crash protection. In this paper we investigate the crushing behaviour, mechanical properties and energy absorption of lattices made by an additive manufacturing process. Two types of lattice were examined: body-centred-cubic (BCC) and a reinforced variant called BCC z . The lattices were subject to compressive loads in two orthogonal directions, allowing an assessment of their mechanical anisotropy to be made. We also examined functionally graded versions of these lattices, which featured a density gradient along one direction. The graded structures exhibited distinct crushing behaviour, with a sequential collapse of cellular layers preceding full densification. For the BCC z lattice, the graded structures were able to absorb around 114% more energy per unit volume than their non-graded counterparts before full densification, 1371 ± 9 kJ/m3 versus 640 ± 10 kJ/m3. This highlights the strong potential for functionally graded lattices to be used in energy-absorbing applications. Finally, we determined several of the Gibson–Ashby coefficients relating the mechanical properties of lattice structures to their density; these are crucial in establishing the constitutive models required for effective lattice design. These results improve the current understanding of additively manufactured lattices and will enable the design of sophisticated, functional, lightweight components in the future.

Journal article

Aremu AO, Brennan-Craddock J, Panesar A, Ashcroft IA, Hague RJM, Wildman RD, Tuck Cet al., 2017, A voxel-based method of constructing and skinning conformal and functionally graded lattice structures suitable for additive manufacturing, Additive Manufacturing, Vol: 13, Pages: 1-13, ISSN: 2214-8604

Additive Manufacturing (AM) enables the production of geometrically complex parts that are difficult to manufacture by other means. However, conventional CAD systems are limited in the representation of such parts. This issue is exacerbated when lattice structures are combined or embedded within a complex geometry. This paper presents a computationally efficient, voxel-based method of generating lattices comprised of practically any cell type that can conform to an arbitrary external geometry. The method of conforming involves the tessellation and trimming of unit cells that can leave ‘hanging’ struts at the surface, which is a possible point of weakness in the structure. A method of joining these struts to form an external two dimensional lattice, termed a ‘net-skin’ is also described. Traditional methods of manufacturing lattice structures generally do not allow variation of cell properties within a structure; however, additive manufacturing enables graded lattices to be generated that are potentially more optimal. A method of functionally grading lattices is, therefore, also described to take advantage of this manufacturing capability.

Journal article

Panesar A, Rennick-Egglestone S, Pujari A, Ashcroft I, Benford S, Goodridge Ret al., 2016, Anthropomorphic design using advanced manufacturing

Conference paper

Panesar A, 2016, Advancing prosthetics through innovative manufacturing

Other

Panesar A, Ashcroft I, Wildman R, Hague Ret al., 2016, A method for bi-directional coupling of structure and system in the optimization of multi-functional components

Conference paper

Panesar A, Brackett D, Ashcroft I, Wildman R, Hague Ret al., 2015, Design framework for multifunctional additive manufacturing: placement and routing of three-dimensional printed circuit volumes, Journal of Mechanical Design – An Additive Manufacturing Special Issue, Vol: 137, Pages: 1-10, ISSN: 1050-0472

A framework for the design of additively manufactured (AM) multimaterial parts with embedded functional systems is presented (e.g., structure with electronic/electrical components and associated conductive paths). Two of the key strands of this proposed framework are placement and routing strategies, which consist of techniques to exploit the true-3D design freedoms of multifunctional AM (MFAM) to create 3D printed circuit volumes (PCVs). Example test cases are presented, which demonstrate the appropriateness and effectiveness of the proposed techniques. The aim of the proposed design framework is to enable exploitation of the rapidly developing capabilities of multimaterial AM.

Journal article

Panesar A, Brackett D, Ashcroft I, Wildman R, Hague Ret al., 2015, Design optimization for multifunctional 3D printed structures with embedded functional systems

Conference paper

Panesar A, Brackett D, Ashcroft I, Wildman R, Hague Ret al., 2014, Design optimization strategy for multifunctional 3D printing, Pages: 1179-1193

An optimization based design methodology for the additive manufacture of multi-functional parts (for example, a structure with embedded electronic/electrical systems and associated conductive paths) is presented. This work introduces a coupled optimization strategy where Topology Optimization (TO) is combined with an automated placement and routing approach that enables determination of an efficient internal system configuration. This permits the effect of the incorporation of the internal system on the structural response of the part to be taken into account and therefore enables the overall optimization of the structure-system unit. An example test case is included in the paper to evaluate the optimization strategy and demonstrate the methods effectiveness. The capability of this method allows the exploitation of the manufacturing capability under development within the Additive Manufacturing (AM) community to produce 3D internal systems within complex structures.

Conference paper

Panesar A, Brackett D, Ashcroft I, Wildman R, Hague Ret al., 2014, Design optimisation strategy for multifunctional 3D printing

Conference paper

Brackett D, Panesar A, Aremu A, Ashcroft I, Wildman R, Hague Ret al., 2014, Adaptive mesh decomposition strategies for topology optimization for multi-functional additive manufacture

Conference paper

Brackett D, Panesar A, Aremu A, Brennan-Craddock J, Ashcroft I, Wildman R, Hague Ret al., 2013, An optimisation based design framework for multifunctional 3D printing, Pages: 592-605

Conference paper

Panesar A, Weaver P, 2012, Optimisation of blended bistable laminates for a morphing flap, Composite Structures, Vol: 94, Pages: 3092-3105, ISSN: 0263-8223

Journal article

Panesar A, Hazra K, Weaver P, 2012, Investigation of thermally induced bistable behaviour for tow-steered laminates, Composites Part A: Applied Science and Manufacturing, Vol: 43, Pages: 926-934, ISSN: 1359-835X

Journal article

Panesar AS, Weaver PM, 2010, Optimization of blended bistable laminate for morphing flap, ISSN: 0273-4508

Multistable composite structures offer a potential platform for the development of morphing flight vehicles. The recent advance in tow-placement technology has enabled the blending of multistable sections with major structural components thereby enhancing the overall structural performance of the flight vehicle. The use of ant colony systems as an optimization concept has been implemented by incorporating the feedback from the finite element analysis on a blended bistable laminate for a morphing flap application.

Conference paper

Panesar A, Weaver P, 2010, Optimization of blended bistable laminates for morphing control surfaces, Publisher: American Institute of Aeronautics and Astronautics

Conference paper

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