Design of Bistable Composite Laminates for Shape Morphing Applications

Composite materials, specifically Laminated Fibre Reinforced Polymers / Plastics (FRP), are versatile material systems which have become a part of everyday life. These are no longer considered “space age” materials, but are also being used in aircraft/military, automotive/transportation and construction/civil infrastructure applications. The major reasons behind these materials gaining prominence are that they are light weight, they have high strength to weight ratio and tailored properties. In the recent past, 35 years back, an entirely new research area in the field of composite materials had begun called “Bistable Composites”. These composites, as the name suggests, have two stable shapes and a snap through / snap back phenomenon between these two shapes, which makes them suitable materials for use in “Adaptive Structures”. Bistable composites are unsymmetric laminated FRPs that exhibit bistability because of the unsymmetric laminate stacking sequence about the middle surface. In this research, the possibility of obtaining desired shapes in both stable states of any given geometry is explored using Finite Element (FE) simulations and experimental validation. The methodology followed is as follows: the given geometry is tessellated and several iterations are carried out to find the combination of symmetric and unsymmetric laminates for which the desired shapes are achievable. To decide on the proper tessellation and carry out the iterations efficiently, two major topics are addressed initially. They are the behavior of individual unsymmetric laminates and the behavior of the combination of symmetric and unsymmetric laminates. In the individual unsymmetric laminates, the effects of geometry and fibre orientation on the snap through and snap back loads are studied, to identify the parameters that controls the critical load at which the shape changes. In the combination of symmetric and unsymmetric laminates, various standard geometries are split into smaller geometries, each of those are made into symmetric or unsymmetric laminates and different combinations of those symmetric and unsymmetric laminates are studied to find the various bistable shapes that are possible in each standard geometry. An experimental setup is built to measure the snap through and snap back loads of the individual rectangular unsymmetric laminates. The simulation results obtained are validated by fabricating those laminates and conducting experiments to confirm the data obtained numerically

Multiscale computational first order homogenization of thick shells for the analysis of out-of-plane loaded masonry walls

This work presents a multiscale method based on computational homogenization for the analysis of general heterogeneous thick shell structures, with special focus on periodic brick-masonry walls. The proposed method is designed for the analysis of shells whose micro-structure is heterogeneous in the in-plane directions, but initially homogeneous in the shell-thickness direction, a structural topology that can be found in single-leaf brick masonry walls. Under this assumption, this work proposes an efficient homogenization scheme where both the macro-scale and the micro-scale are described by the same shell theory. The proposed method is then applied to the analysis of out-of-plane loaded brick-masonry walls, and compared to experimental and micro-modeling results.Peer ReviewedPostprint (author's final draft

Multiple length/time-scale simulation of localized damage in composite structures using a Mesh Superposition Technique

A Mesh Superposition Technique (MST) for the progressive transition between differently-discretized subdomains is proposed and implemented in an FE code. The interfaces between these subdomains are replaced by transition regions where the corresponding meshes are superposed. The MST is applied to the multiple length/time-scale analysis of a low-velocity impact of a projectile on a composite plate. Unlike using a sudden discretization-transition approach, the use of the MST eliminates the undesirable stress disturbances at the interface between differently-discretized subdomains and, as a result, it correctly captures the impact-induced damage pattern at a lower computational cost. Finally, the MST is coupled with an implicit/explicit co-simulation technique for a multiple time/length-scale analysis. The results indicate that, if the length-scale transition is performed using the proposed MST instead of a sudden discretization-transition, the CPU time can be nearly halved

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

A proposed segmented precast concrete spherical cap: geometry, structural stability and construction

This study proposes the design and construction of a concrete spherical cap composed of uniformly-shaped precast doubly-curved panels based on spherical division techniques. A numerical structural analysis is conducted to study the failure behavior of the segmented structure and the capacity of the joints by using finite element modeling techniques to model the concrete material behavior, boundary conditions and intermediate joints of the precast panels. An experimental analysis is conducted to verify the capacity of the structure and the reliability of the modeling techniques, and to study the feasibility of the proposed panel prefabrication and assembly method. The results of this study demonstrate that the proposed precast system and connection design perform efficiently when compared to the monolithically-cast counterpart, particularly under uniform loading conditions. Additional insights on the properties and solution parameters of finite element modelling of concrete shell structures are presented based on the structural analysis of this work. The study concludes the ability of the proposed geometric design and construction method to enhance the prefabrication and construction efficiency with little effect on the structural capacity within the context of the selected geometry and conducted load tests, and recommends further parameters to study for design and construction optimization

Structural and thermal performances of topological optimized masonry blocks

Structural topology optimization is the most fundamental form of structural optimization and receives an increasing attention from engineers and structural designers. The method enables the exploration of the general topology and shape of structural elements at an early stage of the design process and gives rise to inspiring and innovative improvements. In this paper, topology optimization as a principle is used to design new types of insulating masonry blocks. Two main objectives are addressed: maximizing the structural stiffness and minimizing the thermal transmittance. The first part of this paper uses these objectives to create new block topologies. A general problem is formulated and the influences of boundary conditions, external loading, and filter value on the resulting geometry are discussed. In general, maximizing the stiffness is in strong contrast to minimizing the thermal transmittance. This causes problems not encountered in conventional topology optimization. Nevertheless, by adjusting the interpolation schemes and adding multiple load groups, convergent solutions are found. An isotropic material model with an enforced solid-or-empty distribution is considered as the primary method. The optimized block topologies are then thoroughly analyzed to review their structural and thermal performance using the commercial finite element software Abaqus. The direct compressive strength of the block is a measure of the structural performance and the equivalent thermal conductivity gives an indication of the thermal performance. The second part then gives some thoughts on three-dimensional optimization and the incorporation of mesostructures in the design

Behaviour of Reinforced Concrete Conical Tanks under Hydrostatic Loading

Reinforced concrete conical tanks are used in municipalities and industrial applications as liquid containing vessels. Such tanks can be ground supported tanks or elevated on a supporting shaft. Although most design codes provide guidelines for rectangular and cylindrical tanks, no guidance is provided in such codes for conical tanks. Therefore, this thesis is motivated to study the behaviour and design of this type of tanks. In the current study, the accuracy of a design approach based on the provisions of Portland Cement Association (PCA-CCTWP) code for cylindrical tanks combined with an equivalent cylindrical approach provided by the American Water Works Association AWWA-D100 (2005) is assessed. This assessment is done by comparing the internal forces resulting from this method with those obtained from a linear finite element analysis model built in-house. It is noticed that in some of the studied tanks, the PCA-CCTWP approach combined with the equivalent cylinder method is found to be unsafe. As such, and due to the complexity of analysing these conical tanks, a simplified design approach in the form of design charts is provided in this study. This set of charts can be easily used for the analysis and design of reinforced concrete conical tanks subjected to hydrostatic pressure and having a constant wall thickness. This approach is developed using the results obtained from finite element analysis of a wide range of reinforced concrete conical tanks having different configurations combined with code requirements. This simplified approach is then utilized to investigate the economics of reinforced concrete conical tanks versus steel counterparts. A cost analysis is conducted for several conical tanks having different capacities and different construction materials by including both construction and life-cycle costs. In addition to the cost analysis, a general study of the effect of tank dimensions on its cost is illustrated

Nonlinear probabilistic finite element models of laminated composite shells

A probabilistic finite element analysis procedure for laminated composite shells has been developed. A total Lagrangian finite element formulation, employing a degenerated 3-D laminated composite shell with the full Green-Lagrange strains and first-order shear deformable kinematics, forms the modeling foundation. The first-order second-moment technique for probabilistic finite element analysis of random fields is employed and results are presented in the form of mean and variance of the structural response. The effects of material nonlinearity are included through the use of a rate-independent anisotropic plasticity formulation with the macroscopic point of view. Both ply-level and micromechanics-level random variables can be selected, the latter by means of the Aboudi micromechanics model. A number of sample problems are solved to verify the accuracy of the procedures developed and to quantify the variability of certain material type/structure combinations. Experimental data is compared in many cases, and the Monte Carlo simulation method is used to check the probabilistic results. In general, the procedure is quite effective in modeling the mean and variance response of the linear and nonlinear behavior of laminated composite shells

The Effect of Ply Orientation on the Vibration Characteristics of ‘T’ Stiffen Composites Panel: A Finite Element Study

This is an open access article, distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/Aircraft producers have extensively adopted the use of T-shaped stiffened fibre reinforced composite panels in the thin walled structures such as the fuselage and wings. The composite materials present the advantage of high specific strength and stiffness ratios, coupled with weight reduction compare to traditional materials. This report presents a numerical study about the free-free vibration analysis of T-stiffened carbon fibre reinforced epoxy composite panels with surface and identical ply orientations of 0°, 15°, 30°, 45°, 60°, 75° and 90° using ANSYS 17 finite element code. These changes has effect on the element stiffness matrix and hence the dynamic characteristics of the panels. The fundamental frequencies increase to a peak and then decrease taking the form a half sine curve. The dynamic analysis was realized using the Lanczos tool to extract the mode shapes and natural frequencies.Peer reviewedFinal Published versio

Parallel adaptive fluid-structure interaction simulations of explosions impacting on building structures

We pursue a level set approach to couple an Eulerian shock-capturing fluid solver with space–time refinement to an explicit solid dynamics solver for large deformations and fracture. The coupling algorithms considering recursively finer fluid time steps as well as overlapping solver updates are discussed. Our ideas are implemented in the AMROC adaptive fluid solver framework and are used for effective fluid–structure coupling to the general purpose solid dynamics code DYNA3D. Beside simulations verifying the coupled fluid–structure solver and assessing its parallel scalability, the detailed structural analysis of a reinforced concrete column under blast loading and the simulation of a prototypical blast explosion in a realistic multistory building are presented