Stiffness design method of Gyroid-based functionally graded lattice structures with variable porosity controlled by load path

Electro-magnetic mass drivers (EMD) are linear payload accelerators at the forefront of multi-physics technology that find use in various applications. In a homopolar variant of EMD, two electrically conductive rails are clamped at a set separation apart in an electrically insulating chamber formed of housing and elastic support. Preloaded bolts and clamping plates are used to minimize the rail deformation during operation. In literature, EMD is treated similarly to a T-shaped, bi-material bolted joint subjected to tensile loading. The difference is that, unlike in a bolted T-joint, two load paths are available during the bolting phase, and bolt preload gets distributed between housing and elastic support. However, during operation, the housing is not subjected to tensile loading. Therefore, the purpose of bolt preload taken up by the housing must be analyzed. This issue has not been addressed in any literature concerned with the design of bolted EMD. The load path in the initial clamping state and that in operation as a function of housing height H and clamp separation distance S is determined. It is observed that stiffness increases from 70.6 MN/m to 231 MN/m as H/S decreases. However, there is a slight decrease in EMD stiffness when the housing carries no preload. Reasons in support of eliminating the housing are provided, and consequences are discussed. The clamp plates suffer adverse bending effects when housing is removed. The EMD section is altered, and the material is aligned in the load path direction to reduce the bending effect of loading. Shape-optimized clamping plates provide improved stiffness while minimizing the peak stress levels by 36%, and EMD section mass is reduced by 10%. The analysis and design method proposed in this paper provides a theoretical basis for designing ultra-stiff and lightweight EMD.

As the typical structure of the large satellite antenna, the hoop-truss deployable antenna with large aperture is in urgent need in the new generation of large communication satellite, the relay satellite and the earth observation satellite. At the same time, the requirement of the antenna aperture size tends to become bigger and bigger. However, with the increase of antenna aperture, the driving force required for deployment of antenna is also increasing rapidly, which leads to the reliability problem in the traditional centralized drive mode with the motor and driving cable. The dynamics simulation model of the large Hoop-Truss deployable antenna was established in this paper firstly, and the dynamics simulation of the deployment of the antenna with the motor and driving cable was carried out, respectively. This paper reveals the problem of the asynchronous synchronization of deployment caused by the friction loss of the motor driving force in the load path. The energy consumption during the process of antenna deployment is analyzed, and the growth trend of motor driving force as the antenna aperture increases. The shortcomings of centralized-driving mode with the motor and driving cable are summarized, which mainly caused by the decreasing of driving cable force due to friction. On the basis, a method of distributed drive deployment based on negative stiffness driving device is presented. The design of negative stiffness driving device is given in the paper. The multi-stage non-circular gear device based is used to realize the negative stiffness joints and the design method of key transmission ratio of multi-stage non-circular gear device is also given in the paper. Finally, numerical example of 25 m antenna is demonstrated to verify the effectiveness of the proposed distributed driving method.

Topology optimization for concurrent design of layer-wise graded lattice materials and structures

Design of nonlinear spring for a designated load path Dein Shaw1 and Chih Ren Huang1 Summary The purpose of this research is to propose a design method for displacement path of a curved nonlinear spring (As shown in Fig. 1). The design method is divided the spring into several nonlinear linear spring segments of coordinates to be determined connecting points (nodal points). The relation between external load and displacement is defined by the request of user. The relation between load and displacement of each line segment of the spring is presented by large deformation theorem. The prior known variables are moment of inertia, cross section area, material property and load path. Those variables can be input to the stiffness equations to get equation of coordinate of the connecting points. After solving the coordinate equation, the coordinate of nodal points obtained. A nonlinear spring is manufactured according to the design coordinates. The large displacement path and rotation angle are measured. Finally, the experiment results are compared with simulation. The verifying results show the feasibility of design method.

Planar cellular lattice structures subject to axial compression may undergo elastic bending or buckling of the unit cells. If sufficient compression is applied, the columns of adjacent cells make contact. This changes the topology of the lattice by establishing new load paths. This topology change induces a corresponding shift in the effective stiffness characteristics of the lattice — in particular, the shear modulus undergoes a step-change. The ability to embed adaptive stiffness characteristics through a topology change allows structural reconfiguration to meet changing load/operational requirements efficiently. The concept, of topological reconfiguration, can be exploited across a range of length scales, from (meta-)materials to components. Here we focus on macroscopic behaviour presenting results obtained from finite element analysis that shows excellent correlation with the observed response of 3D-printed PLA lattices. Through a parametric study, we explore the role of key geometric and stiffness parameters and identify desirable regions of the design space. The non-linear responses demonstrated by this topology morphing lattice structure may offer designers a route to develop bespoke elastic systems.

Design of heterogeneous mesoscale structure for high mechanical properties based on force-flow: 2D geometries

The loading path is one of the most important design parameters for the success of a tube hydroforming process. Wrinkles, necking, and cracking may occur if the internal pressure and feeding are not correct. In this paper, we propose an adaptive loading path design method using fuzzy logic theory. The fuzzy logic controller is based on the properties of the tube hydroforming process, for asymmetric parts in particular. We investigated symmetric and asymmetric test cases to verify the proposed technique using the finite element method, and the results were consistent with our practical experiment.

Graded lattice structures have garnered significant attention for their ability to combine lightweight properties with superior mechanical performance. Their tailored structures/properties under in-plane loading make them ideal for impact resistance and energy absorption (EA) applications in aerospace, automotive, and biomedical engineering. Despite the research advances in this field, research into out-of-plane of graded lattice structures is relatively limited. This study investigates the out-of-plane EA performance of three common lattice structures, namely, hexagonal honeycomb (HEX), auxetic re-entrant (REE), and double arrowhead (DAH). Unique grade patterns including bottom thick (BOT), mid thick (MID), and ends thick (EDG), were introduced in the lattices’ out-of-plane direction and their mechanical behavior was examined under quasi-static compression conditions using both experimental and finite element analysis. Parametric investigations were conducted to examine the effects of grade ratio, cell wall thickness, and grade patterns, aiming to optimize mechanical EA and crashworthiness of each structure. Results show that the specific energy absorption (SEA) of all structures follows the trend MID > EDGE > BOT > UNI and HEX_MID demonstrated the highest SEA value amongst all designs. On the other hand, all graded lattice structures demonstrated significantly enhanced crash force efficiency, with HEX_BOT, REE_EDGE, and DAH_EDGE approaching ∼90% of the maximum performance, showcasing their potential for efficient EA.

Crashworthiness improvements of multi-cell thin-walled tubes through lattice structure enhancements

Stiffness design of a multilayer arbitrary BCC lattice structure with face sheets

The lack of reliable tying methods for the design of low and medium-rise mass timber buildings with regard to progressive collapse constitutes a strong limitation for the timber structural engineering community. In this context, the current work aims to validate and apply a recently developed rational tying force method for robustness design of post-and-beam timber buildings falling in low and medium consequence classes. This rational tying force method, which considers the requisite resistance via tying to the loss of a load-bearing member, preserves the simplicity of the prescriptive rules present in some current standards, while utilising a mechanical basis similar to that considered in alternative load path analysis. An extended example of the application of the new tying force method to a post-and-beam timber structure is reported in this work. The example highlights several critical aspects for achieving a robust design of post-and-beam timber structures. The results presented in this work show that the new tying force method represents a promising and practical strategy for robustness design of post-and-beam timber buildings.

Purpose The purpose of this paper is to describe a novel design method to construct lattice structure computational models composed of a set of unit cells including simple cubic, body-centered cubic, face-centered cubic, diamond cubic and octet cubic unit cell. Design/methodology/approach In this paper, the authors introduce a new implicit design algorithm based on the computation of volumetric distance field (VDF). All the geometric components including lattice core structure and outer skin are represented with VDFs in a given design domain. This enables computationally efficient design of a computational model for an arbitrarily complex lattice structure. In addition, the authors propose a hybrid method based on the VDF and parametric solid models to construct a conformal lattice structure, which is oriented in accordance with the geometric form of the exterior surface. This method enables the authors to design highly complex lattice structure, computational models, in a consistent design framework irrespective of the complexity in geometric representations without sacrificing accuracy and efficiency. Findings Experimental results are shown for a variety of geometries to validate the proposed design method along with illustrative several lattice structure prototypes built by additive manufacturing techniques. Originality/value This method enables the authors to design highly complex lattice structure, computational models, in a consistent design framework irrespective of the complexity in geometric representations without sacrificing accuracy and efficiency.

Fiber-reinforced polymer (FRP) composites offer several advantages in relation to traditional materials, such as high specific strength, good corrosion resistance, low thermal conductivity and rapid component installation. Despite the great potential of these materials, two major disadvantages limit their acceptance in civil engineering applications: their lack of inherent ductility and the fact that their fibrous and anisotropic character makes the joining of structural components difficult. The purposes of this research are to develop ductile structures using brittle all-FRP materials and to provide a corresponding design method assuring robustness and structural safety. The proposed concept for all-FRP structures incorporates system ductility through the use of ductile, adhesively-bonded joints and redundant (statically indeterminate) structural systems. The concept envisages adhesives with an initially elastic behavior sufficiently stiff to meet short- and long-term serviceability requirements. When serviceability and ultimate loads are exceeded, however, adhesive behavior should change and become plastic, or at least highly non-linear inelastic, with much lower stiffness. The ductile connections effect a favorable redistribution of internal and external forces in the redundant system in the same way as plastic hinges in statically indeterminate systems with ductile materials. In case of joint failure, the redundant system allows the creation of alternative load paths and redistribution of section forces preventing structural collapse. Numerical and experimental investigations of adhesively-bonded double-lap joints demonstrate that using an appropriate bilinear adhesive is more advantageous than using a traditional structural and stiff epoxy adhesive. These investigations show that ductile adhesives generate a linear axial strain distribution and consequently a constant shear stress distribution along the overlap. Numerical and analytical modelings are validated with experimental results. The numerical modeling allows evaluation of the effect of ductile adhesive behavior on joint behavior and establishment of recommendations for the selection of adhesive mechanical properties, according to serviceability and failure limit state requirements. Based on numerical modeling results, joints can also be classified according to stiffness (stiff or flexible). An analytical model, based on numerical and experimental results, is developed for predicting joint stiffness when using ductile adhesives, assuming that the adhesive deforms only and uniformly in shear and that adherends deform only in tension. The design method is developed in accordance with the new structural concept and Eurocode design philosophy. It is based on both numerical and analytical model results for adhesively-bonded double-lap joints. A case study illustrating the adhesively-bonded joint design and appropriate adhesive selection is carried out on continuous beams with adhesively-bonded joints at mid-support. Corresponding bending experiments on beams with ductile, adhesively-bonded connections demonstrate the new structural concept's feasibility and validate the proposed design method. An energy factor defined as the ultimate strength to serviceability limit state energy ratio is proposed to quantify and compare the robustness and safety of structures built from both ductile and brittle materials.

Bionic design is considered a promising approach to improve the performance of lattice structures. In this work, bamboo-inspired cubic and honeycomb lattice structures with graded strut diameters were designed and manufactured by 3D printing. Uniform lattice structures were also designed and fabricated for comparison. Quasi-static compression tests were conducted on lattice structures, and the effects of the unit cell and structure on the mechanical properties, energy absorption and deformation mode were investigated. Results indicated that the new bionic bamboo structure showed similar mechanical properties and energy absorption capacity to the honeycomb structure but performed better than the cubic structure. Compared with the uniform lattice structures, the functionally graded lattice structures showed better performance in terms of initial peak strength, compressive modulus and energy absorption.

Lattice structures are increasingly used in lightweight designs due to the advances of additive manufacturing. The overall performance of the lattice structures highly depends on the lattice cell arrangement. Previous studies show that body-centered cubic with z-axis reinforcement (BCCz) lattice has higher stiffness and strength compared to regular body-centered cubic (BCC) lattice subject to unidirectional compression. In this report, a load path-based methodology for the design of BCCz lattice sandwich structure with variable reinforcement directions is presented. A homogenization model of the sandwich structure with a specified volume fraction is developed first. Load path analysis is then conducted on the homogenization model to calculate the pointing stress vectors, which are lastly used to determine the orientations of BCCz cells. Based on the numerical simulations of a cantilever sandwich structure, the proposed lattice design has superior specific stiffness over the designs based on BCC or uniformly oriented BCCz unit cells.