Design Of Lightweight Structures Research Articles

Bicontinuous Nanoporous Design Induced Homogenization of Strain Localization in Metallic Glasses

Bi-continuous nano-porous metallic glasses (MG) synergize the outstanding properties of MGs and open-cell nano-porous materials. The low-density and high-specific-surface-area of bi-continuous nano-porous structures have the potential to enhance the applicability of MGs in catalysis, sensors, and lightweight structural designs. Here, we report molecular dynamics simulations of tensile loading deformation and failure of bi-continuous nano-porous Cu64Zr36 MG with 55% porosity and 4.4 nm ligament size. Results indicate an anomalous mechanical behavior featuring delocalized plastic deformation preceding ductile failure. The deformation follows two mechanisms: i) Necking of ligaments aligned with the loading direction and ii) progressive alignment of randomly oriented ligaments. Failure occurs at 0.16 strain, following successive necking and rupture events. This work indicates that a bi-continuous nano-porous design is able to effectively delocalize strain localization in a MG due to a combination of size effect on the ductility of MGs resulting in nano-ligaments necking and progressive asynchronous alignment of ligaments.

Dependence of the Joint Strength on Different Forming Steps and Geometry in Hybrid Compound Forging of Bulk Aluminum Parts and Steel Sheets

Hybrid compound forging of aluminum bulk parts and steel sheet metals is a combination of material lightweight design and structural lightweight design. During this process, an aluminum bulk part and a steel sheet metal are combined and formed simultaneously. A material joint is generated by deforming, using zinc as solder material. This prevents the generation of brittle intermetallic Fe-Al-Phases as well as contact corrosion. The zinc layer is applied to the aluminum bulk part by hot dipping. To create a material locking connection by forming, suitable parameters such as the forming temperature are identified in first experimental trials. Microsections showed that the zinc layer is still intact after forming. In this paper the investigation of the effects of different steps of forming and different geometries of the aluminum bulk part surface on the joint strength are described. The forming tests show that a further forming of the aluminum part, resulting in a bigger deformation, leads to a stronger connection between both joining partners. But there is a limit to the forming since the applied forces can transfer to the steel sheet leading to an unintended deformation. The generated hybrid parts are tested for their ability for further forming. Therefore, the joined hybrid parts are undertaken a deep drawing process to see if the joint withstands further forming of the hybrid part.

Frequency-selective-surface based sandwich structure for both effective loadbearing and customizable microwave absorption

Multifunctional composite structure with unique mechanical and physical characteristics is essential for the lightweight design of engineering structures. Here, we develop a multifunctional sandwich structure for both effective loadbearing and customizable microwave absorption by employing glass fiber reinforced plastic, polyvinyl chloride foam, carbon fiber reinforced plastic, and frequency selective surfaces. The resultant sandwich structures are endowed with effective specific flexure stiffness (up to 130 N/mm), benefiting from the efficiency in material distribution configuration. Moreover, the proposed structures also show highly customizable microwave absorbing capacity in both bandwidth (from 2 GHz to 18 GHz) and band depth (from −10 dB to −15 dB), due to the flexible design ability of multiple interfaces, electromagnetic loss artificial film. The optimized structures highlight a tradeoff among microwave absorption, flexure stiffness, and surface density and thus are promising a smart stage on which high-performance customizable properties can be envisaged.

Effect of Relative Density on Compressive Load Response of Crumpled Aluminium Foil Mesh.

In recent years, a large number of metal foams and porous metals have been developed. Due to the high cost of these materials alternative manufacturing methods for cellular metallic materials are being explored. Crumpled metallic foil meshes, manufactured via die compression techniques, are evolving as a potential alternative method. However, the non-availability of sufficient data on their load response is limiting their uptake. Uniaxial compressive load response of crumpled aluminium foil meshes (CAFMs) of varying densities, forged by open and closed die compression, are studied. A 0.05 mm thick aluminium sheet mesh, manufactured by the expanded metal process is used. X-ray computed micro-tomography is employed to image the CAFM’s internal cellular structure. The stress-strain relation demonstrates that the CAFMs produce identical load response profile irrespective of their relative density. Power law functions and define the relationships between real Young’s Modulus and effective yield strength, . The study provides new knowledge on the effect of relative density on the compressive properties of CAFMs which have applications across lightweight structural design.

LABORATORY BASED PARAMETRIC STUDY ON THE SWELL RESPONSES IN EXPANSIVE VERTOSOLS

Expansive grey Vertosols are predominant in Australia, especially in Queensland. These soils induce a significant amount of swell strain on the lightweight structures founded on/in these soils when soil moisture changes due to climatic influence. According to AS2870: Residential slab and footing design code (AS2870, 2011) and available literature, active zone depth which contributes to the climate induced-soil displacement in Queensland can be up to 5m. To design lightweight structures founded within the active zone depth, it is imperative to understand swelling behavior of expansive grey Vertosols. The resultant swell strain of these expansive soils is primarily a function of initial water content or initial soil suction and overburden pressure (surcharge). However, there is an extremely limited amount of data available for unsaturated swelling characteristics of expansive soils in Queensland. In this study, a series of conventional oedometer tests were conducted to investigate the effect of the initial water content, initial soil suction and the surcharge on the swelling behavior of expansive grey Vertosol that is predominant in South-East Queensland. The swell strain of expansive grey Vertosol displayed greater sensitivity to surcharge when compared to initial water content or suction. Developed relationship between swell strain per unit change in volumetric water content and surcharge depicted statistically strong (R2 = 0.89) agreement. The application of the knowledge gathered from this study will benefit the decision making in semi-arid regions when building lightweight structures on grey Vertosol.

Reinforcement learning based compliance control of a robotic walk assist device

ABSTRACTMillions of people around the globe have to deal with walking disability. Robotic walk assist devices can help people with walking disabilities, especially those with weak legs. However, safety, cost, efficiency and user friendliness are some of the key challenges. For robotic walk assist devices, light weight structure and energy efficient design as well as optimal control are vitally important. In addition, compliance control can help to improve the safety of such devices as well as contribute to their user friendliness. In this paper, an optimal adaptive compliance control is proposed for a Robotic walk assist device. The suggested scheme is based on bio-inspired reinforcement learning. It is completely dynamic-model-free scheme and employs joint position and velocity feedback as well as sensed joint torque (applied by user during walk) for compliance control. The efficiency of the controller is tested in simulation on a robotic walk assisting device model.

A Lightweight Design of Tree-shaped Support Structures for SLM Additive Manufacturing

A Lightweight Design of Tree-shaped Support Structures for SLM Additive Manufacturing

Design Method of Function-Structure Integrated Lattice Structure

Structure lightweight has always been a hot topic in the field of engineering. Lattice structure has characteristics of light weight, high specific stiffness and high specific strength because of its high porosity and low relative density. It has been widely used in structural lightweight design. In addition, lattice structure has broad application prospects in advanced industrial equipment, due to the potential of anti-vibration, anti-impact, heat transfer and heat dissipation, zero/negative thermal expansion, electromagnetic wave absorption, sound absorption and noise reduction. In this paper, a design method of function-structure integrated lattice structure is proposed, topology optimization and variable density lattice filling technology are studied, the research methods of multi- functional characteristics of lattice structures are discussed, and the related simulation and experimental methods are introduced, which is of certain reference significance to the development of technology in this field.

Conceptual design of a new thermal‐electric conversion device in lightweight concentrating solar thermal power system

AbstractConcentrating solar thermal power (CSTP) technology has become a hot issue in the present research because of its high conversion efficiency. However, traditional schemes cannot be widely applied due to their complex structure, low power density, and high cost. In view of this, based on a new type of lightweight cable mesh reflector structure and the Rankine cycle, a new conceptual design of thermal‐electric conversion device in CSTP system is proposed. The process of thermal‐electric conversion is actualized through smart and lightweight structural design; the performance estimation of the device is carried out through focusing performance analysis and thermodynamic analysis; the cycling feasibility is verified through multifield coupling simulation analysis. Compared with the existing thermal‐electric conversion devices, the device proposed in this paper has higher power‐to‐weight ratio. And the power generation system that combines the proposed device with the flexible cable net reflector has the characteristics of lightweight, portability, and small land area, which has a great significance for the popularization and application of distributed layout CSTP system.

An Analytic Verification on Fracture Behavior of Adhesion Exfoliation with Out-plane Shear Mode due to Tapered Angles of 6°and 8° at TDCB Made of Unidirectional Laminated CFRP

Because of environmental issues, the regulations on gas emission from fossil fuels become stricter. Some investigations are being carried out actively to change the fossil fuel power into electrical power. Researches on the reduction of weight in the transportation machine is also executed. Weight reduction is one of the methods of reducing the gas emission and increasing the range of electrically powered machines. The method of weight reduction includes the development of light weight material and light weight structure design method. FRP is the most representative light weight material. Among various FRP materials, (CFRP) has the highest specific strength. Light weight structure design method includes the method of designing the structure by converting the bonding method with bolts and rivets to adhesion method with the use of adhesives. In order to pursue the research on the adhesive structure design method, the research on adhesion exfoliation by using CZM needs to be carried out. There are the researches with various methods in accordance with the style of adhesion exfoliation load and material designs. In this study, the adhesion exfoliation on the tearing fracture of tapered double cantilever beam configuration was applied to the research. Research model was composed by applying the gradient angles of 6° and 8° to TDCB. The model with the gradient angle of 8° has less fracture due to adhesion than that of 8°. The basic data on structural design of adhesion structure were provided by comparatively analyzing the research models. This research was carried out by using finite element analysis method in this study. Finite element analysis method has the advantage of reducing the cost and time taken for experiments in researches. Therefore, the finite element analysis program, ANSYS, was used in this study.

전과정평가에 의한 복합소재 선체구조 경량화 효과의 환경영향 분석

전과정평가에 의한 복합소재 선체구조 경량화 효과의 환경영향 분석

Concurrent topology optimization with uniform microstructure for minimizing dynamic response in the time domain

This paper aims to develop an efficient concurrent topology optimization approach for minimizing the maximum dynamic response of two-scale hierarchical structures in the time domain. Compared with statics problems, the dynamic response problems usually involve many time steps, which may lead to intensive computational burdens in both dynamic response and sensitivity analyses. This study thus proposes an enhanced decoupled sensitivity analysis method for concurrent topology optimization of the time-domain dynamic response problems. The mode acceleration method is incorporated for efficient dynamic response analysis. The three-field density-based approach is employed for topology optimization of macrostructure and microstructure. A previously proposed aggregation functional is employed to approximate the maximum dynamic response of the structure. The method of moving asymptotes (MMA) is employed to update the design variables. Three numerical examples are presented to demonstrate the effectiveness of the proposed approach. Some discoveries regarding the concurrent topology optimization for dynamics problems are presented and discussed. Furthermore, the potential of the concurrent topology optimization formulation for designing lightweight structures under dynamic loads is also demonstrated.

Research on the Lightweight Design of Body-Side Structure Based on Crashworthiness Requirements

Crashworthiness is the most significant variable during lightweight design of vehicle structures. However, crashworthiness studies using the single substructure-based method are limited due to the negligence of interactions among substructures. Thus, a whole structure-based study was conducted for the lightweight design of a body-side structure. In this study, a full finite element model was firstly created and then modified into a simplified model for structural improvements, where the major load-carrying subassemblies were improved from the perspectives of crashworthiness and manufacturing costs. Finally, sensitivity analyses were conducted to further optimize the strength distribution, based on which an adaptive response surface method was employed for thickness optimization of the structure. It is found that through the structural improvements and optimizations, the weight of the structure was significantly reduced even when its crashworthiness was improved. This indicates that the whole structure-based method is effective for lightweight design of vehicle structures.

Research on Lightweight Design of Inertia Vibrator

The lightweight structure design of the inertia vibrator is one the core tasks for subgrade vibration. This paper describes the relationship of the dynamic test parameters, including the vibrator weight, the vibration frequency, the vibration displacement, the landing time, and the impact force. By analysis and simulation, the influences of the static weight and the frequency on the vibrator performance are present, which is valuable for the optimal calculation of impact force.

An efficient technique for simultaneous local and overall buckling analysis of stiffened panels

The overall buckling and local buckling of stiffened panels are two possible failure modes and thus should be concerned by engineers in the preliminary design of lightweight structures. In this paper, an efficient technique is proposed to solve the local and overall buckling problem of stiffened panels simultaneously. A weak form quadrature plate element with stiffeners located anywhere in the plates other than along the nodal lines of the plate element is formulated. Explicit formulations with an arbitrary number of nodes are given. Improvement of solution accuracy can be easily done by increasing the number of element nodes if necessary. A convergence study is performed. Several numerical examples are given. Results are compared with either existing analytic solutions or finite element data for verification. It is shown that high accuracy can be achieved with a small number of nodes. In addition, the proposed method can allow a quick analysis of simultaneous overall and local buckling behavior of stiffened panels and thus may be suitable for optimization routines in preliminary design of stiffened panels.

Study on lightweight structural optimization design system for gantry machine tool

In order to improve the efficiency and effectiveness of the lightweight design of the gantry machine tool, a lightweight structural optimization design system for the gantry machine tool was constructed. Serialized gantry machine tools were parametrically modeled, and a load model with multiple operating conditions was established. A twice optimization design method integrating zero-order optimization, parameter rounding, and structural re-optimization was proposed. Using the proposed method, a lightweight structural optimization design system for gantry machine tool with parametric design, lightweight design, and other functions was developed. The developed gantry machine tool lightweight structural optimization design system was applied to complete the lightweight structural optimization design of gantry frame of a certain gantry machine tool, so the structural parameters of the gantry frame were optimized. Although the maximum stress and the maximum deformation of the gantry frame increases within the allowable range, the experimental comparison before and after the optimization shows that the mass of the whole gantry frame is reduced by 9.24%, which is beneficial to save the manufacturing cost. The research results show that the constructed lightweight structural optimization design system of the gantry machine tool has high engineering practicality.

ICM method for topology optimization of multimaterial continuum structure with displacement constraint

A new topology optimization method is formulated for lightweight design of multimaterial structures, using the independent continuous mapping (ICM) method to minimize the weight with a prescribed nodal displacement constraint. Two types of independent topological variable are used to identify the presence of elements and select the material for each phase, to realize the interpolations of the element stiffness matrix and total weight. Furthermore, an explicit expression for the optimized formulation is derived, using approximations of the displacement and weight given by first- and second-order Taylor expansions. The optimization problem is thereby transformed into a standard quadratic programming problem that can be solved using a sequential quadratic programming approach. The feasibility and effectiveness of the proposed multimaterial topology optimization method are demonstrated by determining the best load transfer path for four numerical examples. The results reveal that the topologically optimized configuration of the multimaterial structure varies with the material properties, load conditions, and constraint. Firstly, the weight of the optimized multimaterial structure is found to be lower than that composed of a single material. Secondly, under the precondition of a displacement constraint, the weight of the topologically optimized multimaterial structure decreases as the displacement constraint value is increased. Finally, the topologically optimized multimaterial structures differ depending on the elastic modulus of the materials. Besides, the established optimization formulation is more reliable and suitable for use in practical engineering applications with structural performance parameters as constraint.

Selective polishing method to increase precision in large format lightweight machine tools working with petrous material

In this article two complementary methods are developed. Firstly, a method to add precision in large machine tools with modular lightweight structures (APLM), which performs the compensation of geometrics and dynamics errors using embedded intelligence, and secondly, an alternative polishing method called selective polishing (SP). This systematic process comprehends measurement tools and algorithm resources. Phenomena occurred in the machine structure, due to interaction between the cutting tools and the petrous materials in the grinding and polishing processes are modeled mathematically. Using validated flatness models, the variables and parameters were discretized to determine the errors with respect to the Z axis. To validate the method, a test machine of 3m 2 workspace with a multi-body lightweight structure design was built. The geometrical errors were determined using precision instruments and those were compared with a pattern surface. A higher flatness is achieved through a combined grinding-traditional polishing and selective polishing process using the same machine. This method saves time and energy consumption.

Experimental and numerical investigations of penetration resistance of ultra-high strength concrete protected with ceramic balls subjected to projectile impact

Ceramic materials characterized by high hardness, high inherent strength, low density and excellent dimensional stability have been extensively applied in the design of high-performance and lightweight protective structures to resist the high-speed projectile impact. In order to study the anti-penetration capability of ceramic balls protected ultra-high strength concrete (CB-UHSC), high-speed projectile impact tests were conducted at striking velocities of 545 m/s, 679 m/s, and 809 m/s to investigate the impact performance of ceramic balls, projectiles, and the protected UHSC. The experimental results indicated the effectiveness and economy of ceramic balls in resisting the high-speed projectile impact. Numerical studies were then conducted to reproduce the projectile penetration process within CB-UHSC targets with the assistance of LS-DYNA. Based on the validated numerical models, impact resistance and ballistic deviation of projectiles, as well as the energy evolution between projectiles and targets, were further investigated to comprehensively understand the impact performance of this newly designed protective structure under projectile penetration.

Homogenization driven design of lightweight structures for additive manufacturing

The diffusion of design tools suitable for regular lattice structures was recently stimulated by the spread of additive manufacturing technologies that enable the fabrication of complex geometries, exceeding the limits of traditional manufacturing methods. Fillet radii play a fundamental role in the design of lattice materials, reducing the stress concentration and improving fatigue life. However, only simplified beam and 2D models are available in the literature, which are unable to capture the actual stiffness and stress concentrations in the cell nodes of the 3-D beam based lattice structures with fillets. In this paper, four types of polyamide 12 cells, fabricated by selective laser sintering technology, based on cylindrical elements, are studied by finite element (FE) analysis, evaluating the influence of struts and fillet radii on the mechanical properties. In order to study a single cell, specific boundary conditions, simulating the presence of adjacent cells, were adopted in FE analysis. As a result, a model describing mechanical properties as a function of geometrical characteristics is obtained. By this model, it is possible to replace the complex shape of a lattice structure with its boundary, simplifying numerical analyses. This approach, called homogenization, is very useful in the design process of lightweight structures and can be adopted in optimization strategies. Numerical outcomes show that the effect of fillet radius is not negligible, especially in cells having a large number of struts. Moreover, experimental tests were also carried out showing a good agreement with the numerical analysis. Finally, an interactive design process for lattice structures based on experimental and numerical outcomes is proposed.