Modeling of 3D brick-and-mortar structures using cohesive zone finite elements

Nacre-inspired brick-and-Mortar composite structures exhibit exceptional combinations of properties as well as a highly tuneable mechanical response, due to their large range of design parameters. Understanding the effect of these parameters on the response is essential to optimally design these structures and can be guided by modeling. Traditional models only consider 2D geometries and limited attempts at modeling 3D geometric designs exist. Herein, 3D brick-and-mortar structures using a finite element in conjunction with an experimentally calibrated cohesive zone model to represent the layers are proposed. The model is successfully validated against experimental results for a nonplanar brick assembly using so-called osteomorphic bricks. The capabilities of the model are further demonstrated through a parametric study, where the effect of brick shape, number of bricks, and soft layer material properties on the structure mechanical properties (elastic modulus, yield strength and toughness) are investigated. Numerical results show that toughness is significantly increased by transitioning from a “two-peak” failure mechanism to a “peak-plateau-peak,” which is controlled by the brick shape. It is also shown that 3D structures may exhibit significant out-of-plane deformation involving the cooperative motion of many bricks, which may contribute to their improved toughness compared to 2D structures

Design, microstructure and mechanical characterization of Ti6Al4V reinforcing elements for cement composites with fractal architecture

This paper presents a study on the design, and microstructural and mechanical characterization of additively manufactured reinforcing elements for composite materials exhibiting fractal geometry, with a focus on the flexural reinforcement of cement-matrix composites. The examined elements are manufactured via an additive process, electron beam melting, from the Ti6Al4V titanium alloy, using a Koch curve construction ruled by three complexity parameters. Koch fibers and meshes are designed, additively manufactured and experimentally tested, through the use of the proposed fractal design procedure. Laser scanning tests illustrate the correspondence between the CAD objects and the additively manufactured samples. The experimental characterization of the surface properties of the Koch fibers is conducted through optical microscopy and contact angle tests, while their mechanical performance is analyzed through Vickers hardness and bending tests on a fiber-reinforced reinforced mortar. The given mechanical tests highlight that reinforcing fibers with fractal architecture significantly enhance the first crack strength and the residual loading capacity of cement mortar specimens subject to three-point bending tests. This is due to the relevant interlocking mechanisms acting at the interface between the matrix and the ribs of such reinforcing elements, which delay the macroscopic cracking of the mortar

Computational Homogenization of Architectured Materials

Architectured materials involve geometrically engineered distributions of microstructural phases at a scale comparable to the scale of the component, thus calling for new models in order to determine the effective properties of materials. The present chapter aims at providing such models, in the case of mechanical properties. As a matter of fact, one engineering challenge is to predict the effective properties of such materials; computational homogenization using finite element analysis is a powerful tool to do so. Homogenized behavior of architectured materials can thus be used in large structural computations, hence enabling the dissemination of architectured materials in the industry. Furthermore, computational homogenization is the basis for computational topology optimization which will give rise to the next generation of architectured materials. This chapter covers the computational homogenization of periodic architectured materials in elasticity and plasticity, as well as the homogenization and representativity of random architectured materials

From Architectured Materials to Large-Scale Additive Manufacturing

The classical material-by-design approach has been extensively perfected by materials scientists, while engineers have been optimising structures geometrically for centuries. The purpose of architectured materials is to build bridges across themicroscale ofmaterials and themacroscale of engineering structures, to put some geometry in the microstructure. This is a paradigm shift. Materials cannot be considered monolithic anymore. Any set of materials functions, even antagonistic ones, can be envisaged in the future. In this paper, we intend to demonstrate the pertinence of computation for developing architectured materials, and the not-so-incidental outcome which led us to developing large-scale additive manufacturing for architectural applications

Design, fabrication and characterisation of topological interlocking structures utilising additive manufacturing

This thesis explores a particular class of architectured hybrid materials based on the concept of topological interlocking. In this approach, a structural component is tessellated in identical, discrete elements, which are held in place owing to their specially designed geometry and arrangement. This distinct form of segmentation allows interlocking to occur in three dimensions, providing the structure with an ability to retain its shape, even if some components are fully displaced. In this work, a range of mechanical properties of topologically interlocked assemblies are characterised to provide a greater understanding of the complex deformation mechanisms of these new structures

Effect of angled layers on failure regimes in brick-and-mortar structures

Brick-and-Mortar structures can exhibit exceptional combinations of properties, such as high strength and toughness. The properties are highly dependent on the failure regime, namely the ability to distribute damage prior to failure. In our recent work on rectangular Brick-and-Mortar structures, we have identified a transition from localised damaged (called ‘two-peak’ failure) to distributed damage (called ‘peak-plateau-peak’ failure), depending on the brick aspect ratio and the relative normal and shear layer material properties. However, the effect of non-rectangular brick shapes on these failure regimes has not yet been explored. In this work we predict with semi-analytical modelling, and validate with experiments, that introducing an angle into the ‘shear’ layers of the Brick-and-Mortar structure to create ‘diamond’ and ‘inverse diamond’ brick shapes results in a transition from ‘two-peak’ to ‘peak-plateau-peak’ failure for low aspect ratios. It is further shown that the angle required to transition to ‘peak-plateau-peak’ failure decreases with increasing aspect ratio, and that introducing an out of-plane angled layer in the form of an osteomorphic brick shape can further decrease the angle required for the transition. Our work demonstrates that the transition from ‘two-peak’ to ‘peak-plateau-peak’ failure significantly increases the toughness of the structure, without compromising strength or stiffness, highlighting the importance of understanding and controlling the parameters that affect the failure regimes

Controlling failure regimes in Brick-and-Mortar structures

Brick-and-Mortar structures have a highly tunable mechanical response, offering the possibility to achieve exceptional combinations of properties such as strength and toughness. These properties markedly depend on the failure mechanism. However, the effect of geometric and material parameters on failure is not fully understood. In this work we report the existence of a ‘two-peak’ and a ‘peak-plateau-peak’ failure regime, differing in the ability of the structure to distribute damage in the layers prior to failure. A transition from the ‘two-peak’ to ‘peak-plateau-peak’ regime is observed in 3D-printed Brick-and-Mortar structures by increasing the aspect ratio (brick width over height) in the lower “layer failure” aspect ratio range. Further control of the two regimes is investigated with the help of a semi-analytical model of finite-sized structures. Theoretical predictions suggest that the failure regime can be controlled by tuning the relative shear and normal layer materials. This is confirmed experimentally by testing Brick-and-Mortar structures made with different materials for the shear and normal layers. Our work demonstrates that the transition from the ‘two-peak’ to the ‘peak-plateau-peak’ failure regime significantly increases the toughness, without compromising strength or stiffness of the structure, highlighting the importance of controlling these regimes

Deformation mechanics of non-planar topologically interlocked assemblies with structural hierarchy and varying geometry

Abstract Structural hierarchy is known to enhance the performance of many of Nature’s materials. In this work, we apply the idea of hierarchical structure to topologically interlocked assemblies, obtained from measurements under point loading, undertaken on identical discrete block ensembles with matching non-planar surfaces. It was demonstrated that imposing a hierarchical structure adds to the load bearing capacity of topological interlocking assemblies. The deformation mechanics of these structures was also examined numerically by finite element analysis. Multiple mechanisms of surface contact, such as slip and tilt of the building blocks, were hypothesised to control the mechanical response of topological interlocking assemblies studied. This was confirmed using as a model a newly designed interlocking block, where slip was suppressed, which produced a gain in peak loading. Our study highlights the possibility of tailoring the mechanical response of topological interlocking assemblies using geometrical features of both the element geometry and the contact surface profile