Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D ...printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.
This study brings to readers the generalized formulation of three-variable plate theory and an efficient computational approach for analyzing plates. The theory not only has three degree of freedoms ...(DOFs) per node, which complies with three dimensional space of full plate model as classical plate theory (CPT) but also accounts for the effect of shear deformation without any requirement of shear correction factors (SCF). A complete set of strong forms, weak form as well as classical and non-classical boundary conditions (BCs) for linear and geometrically nonlinear analysis are consistently derived in this paper through a variational approach. The strong forms are sixth order differential equations, resulting in the symmetrical fourth order differential weak form. It is known that Isogeometric Analysis (IGA) arguably outweighs classical finite element method in terms of high continuity and high order differentiability. Thanks to its advantage, an IGA framework for the generalized three-variable plate theory is formulated with completely locking-free and only three DOFs per node. The classical BCs are strongly enforced to system equations as usual whilst the non-classical BCs are weakly imposed by a penalty approach. The new plate theory with only three-variable is thereafter used for static linear and nonlinear analysis of isotropic and functionally graded material (FGM) plates to demonstrate its ability. The reliability and accuracy of the present approach are ascertained by comparing the obtained results with other existing ones. Based on a robust formulation devoted in the paper, the proposed approach can be further extended for numerous problems related to the shear deformable effect in the literature.
•We propose a novel theory and isogeometric implementation for linear and nonlinear analysis of isotropic and FG plates.•The new theory has three variables and captures well shear deformable effect.•Strong form of new theory is of sixth order leading to a fourth order differential weak form.•Isogeometric analysis can effectively handle the high order differentiability of the proposed theory.•The numerical results show the reliability and efficiency of the present method.
This work presents a novel design, additive manufacturing and modeling approach of three dimensional voronoi-based composite structures that closely mimic nacre's multilayer composite structure. The ...hierarchical structure of natural nacre is mimicked to produce multilayer composite laminates assembled from three dimensional polygonal tablets bonded with organic adhesives. Furthermore, various complex geometries of the nacreous shells observed from the nature, such as the dome-shaped structure, are developed into three dimensional designs. A novel mapping algorithm is developed to generate complex structures of nacre-like composites that are readily fabricated by unique dual-material 3D printing technology. Preliminary 3D-printed prototypes with complex shapes and material combinations are presented. A novel numerical model of the nacreous composite is proposed, which includes tablet cohesive bonds and interlaminate adhesive layers to mimic the soft organic polymer matrix. The nacreous model is validated against a natural nacre specimen under uniaxial loading. To exemplify a potential application, a scaled model of a nacre-mimetic composite made of Aluminum tablets and Vinylester adhesive is constructed and assessed against blast-induced impulsive loading. The performance of the nacre-like composite panel is investigated in terms of deformation and energy dissipation.
Sandwich panels composed of auxetic cellular cores and metal facets are presented for blast resistance applications. The performance of this hybrid composite structure under impulsive loading is ...numerically studied, taking into account the rate-dependent effects. The Johnson–Cook law is used to model the behaviours of composite materials at high strain rates. Parametric analyses are performed to evaluate the performances of different designs of composite panels and compared with equivalent monolithic panels of identical areal masses in terms of deformations and dissipated plastic energy of the metal facets and auxetic crushable cores. Various design parameters are considered, including the auxetic unit cell effective Poisson’s ratio, material properties, thickness of facet, and diameter of the unit cell truss member. To reduce the computational time, a quarter of the panel is modelled with shell elements for the facets and beam elements for the core. In blast events, auxetic composite panels are found to effectively absorb double the amount of impulsive energy via plastic deformation, and reduce up to 70% of the back facet’s maximum velocity when compared with monolithic ones. The maximum back facet displacement is also noticeably reduced by up to 30% due to the densification and plastic deformation of the auxetic cores.
Protecting building, critical infrastructure and military vehicles from Improvised Explosive Devices (IEDs) has become a critical task. This study aims to examine the performance of a new protective ...system utilizing auxetic honeycomb-cored sandwich panels for mitigation of shock loads from close-in and contact detonations of high explosives. Both field blast tests and drop weight tests were performed using the proposed sandwiches asa shield for concrete panels in combination with conventional steel protective plates. The combined shield was found to be effective in protecting reinforced concrete structures against severe impact and close-in blast loadings. The honeycomb core with re-entrant hexagonal cells shows evident auxetic characteristics which contribute substantially to outstanding force mitigation and blast-resistance performances of such sandwich panels. Numerical simulations showed good agreement with the experimental results. The proposed auxetic panels were found to perform better than conventional honeycomb panels of the same size, areal density and material. Both were found to boost the energy absorption of the monolithic steel plate by a factor of 2.5 by changing its deformation pattern under close-in blast loading. In addition, a combination of the steel plate and an auxetic sandwich panel has aerial specific energy absorption (ASEA) higher than either of them, showing great potential for the development of lightweight blast protection of civil, mining, military, nuclear infrastructure and vehicles.
•The enriched DEM model can describe well the fracture behaviour of foam concrete.•Pore-size and porosity of foam concrete strongly affect its fracture resistance.•The fracture process is triggered ...by a transition state of mortar bonds.
This study investigates the influences of pore-structure and mortar properties on the fracture behaviour of geopolymer foamed concrete. The discrete element method (DEM) is utilised to explicitly describe the internal pore-structure, while the mortar phase is modelled at the micro/meso-scale using a cohesive-frictional model. Numerical tests are conducted on numerous DEM foam concrete specimens with various porosities and pore-size distributions. The numerical results show that the pore-size can have a profound effect on the material’s fracture resistance. A decrease in pore size results in higher compressive strength and this influence is more significant for foam concrete with lower porosity. However, the elastic modulus seems to be less sensitive to the pore size variation. Further looking at the fracture process of the foam concrete at the micro-scale shows a gradual transition contact bonds from compressive to tensile modes, which is triggered by the breakage of contact bonds persisting as the loading continues. The study also demonstrates that the pore size distribution mainly affects the empirical power exponent of Balshin’s equation of compressive strength-porosity relationship, while the mortar properties have a profound influence on the strength of the material at zero porosity.
Sandwich panels with auxetic lattice cores confined between metallic facets are proposed for localised impact resistance applications. Their performance under localised impact is numerically studied, ...considering the rate-dependent effects. The behaviour of the composite structure material at high strain rates is modelled with the Johnson-Cook model. Parametric analyses are conducted to assess the performance of different designs of the hybrid composite structures. The results are compared with monolithic panels of equivalent areal mass and material in terms of deformations and plastic energy dissipation. Design parameters considered for the parametric analyses include the auxetic unit cell effective Poisson’s ratio, thickness of the facet, material properties and radius of the unit cell’s struts. Significant reduction in computational time is achieved by modelling a quarter of the panel, with shell elements for facets and beam elements for the auxetic core. With projectile impacts up to 200 m/s, the auxetic composite panels are found to be able to absorb a similar amount of energy through plastic deformation, while the maximum back facet displacements are reduced up to 56% due to localised densification and plastic deformation of the auxetic core.
This study evaluates the potential use of discarded plasterboard paper as fibers from buildings to reinforce concrete. Various concentrations of wastepaper fibers (0.5%, 1%, 1.5%, 2%, and 2.5% by ...weight of the binder) were investigated in this research. To mitigate the water absorption effect of the paper fibers, metakaolin was employed as a partial cement replacement. The results demonstrate that the inclusion of the wastepaper fiber enhances the mechanical and durability performance of the concrete. The optimal fiber proportion was identified as 1%, leading to a 29% increase in the compressive strength, a 38% increase in the splitting tensile strength, a 12% decrease in the water absorption, and a 23% decrease in the drying shrinkage with respect to the concrete containing 20% metakaolin. However, exceeding this optimal fiber content results in decreased mechanical and durability properties due to the fiber agglomeration and non-uniform fiber distribution within the concrete matrix. Based on the microstructural analysis, the improved performance of the concrete is ascribed to decreased porosity, more refined pore structure, and reduced propagation of microcracks within the concrete matrix in the presence of wastepaper fiber. According to the results, concrete containing 20% metakaolin and 1% wastepaper fiber exhibits durability and mechanical properties comparable to those of the traditional concrete. This finding highlights the significant promise of reducing dependency on conventional cement and incorporating suitable recycled materials, such as discarded plasterboard, and secondary by-products like metakaolin. Such a strategy encourages the preservation of resources, reduction in carbon dioxide emissions, and a decrease in the ecological footprint resulting from concrete production.
Composite materials such as glass fibre reinforced polymers (GFRPs) possess the advantages of high strength and stiffness, as well as low density and highly flexible tailoring; therefore, their ...potential in replacing conventional materials (such as concrete, aluminium and steel) in building façade has become attractive. This paper addresses one of the major issues that hinder the extensive use of composite structures in the high-rise building industry, which is the fire resistance. In this study, a fire performance enhancement strategy for multilayer composite sandwich panels, which are comprised of GFRP composite facets and polyethylene foam core, is proposed with the addition of environmentally friendly, fire retardant unsaturated polyester resins and gel-coats. A series of burning experimental studies including thermo-gravimetric analysis (TGA) and single burning item (SBI) are carried out on the full scale composite sandwich as well as on single constituents, providing information regarding heat release rate, total heat release, fire growth rate, and smoke production. Experimental results are compared with fire safety codes for building materials to identify the key areas for improvements. A fire dynamic numerical model has been developed in this work using the Fire Dynamics Simulator (FDS) to simulate the burning process of composite structures in the SBI test. Numerical results of heat production and growth rate are presented in comparison with experimental observations validating the computational model and provide further insights into the fire resisting process. Parametric studies are conducted to investigate the effect of fire retardant additives on the fire performance of the composite sandwich panel leading to optimum designs for the sandwich panel.
The key nanostructural changes occurring in a series of alkali-activated materials (AAM) based on blends of slag and fly ash precursors during exposure to temperatures up to 1000 °C are investigated. ...The main reaction product in each AAM is a crosslinked sodium- and aluminium-substituted calcium silicate hydrate (C-(N)-A-S-H)-type gel. Increased alkali content promotes the formation of an additional sodium aluminosilicate hydrate (N-A-S-(H)) gel reaction product due to the structural limitations on Al substitution within the C-(N)-A-S-H gel. Heating each AAM to 1000 °C results in the crystallisation of the disordered gels and formation of sodalite, nepheline and wollastonite. Increased formation of N-A-S-(H) reduces binder structural water content after thermal treatment and correlates closely with previous observations of improved strength retention and reduced microcracking in these AAM after heating to 1000 °C. This provides new insight into thermally induced changes to gel atomic structure and thermal durability of C-(N)-A-S-H/N-A-S-H gel blends which are fundamental for the development of new fire-resistant construction materials.
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