Design Of Lightweight Structures Research Articles

Approximate postbuckling analysis of shear deformable laminates

AbstractIn the lightweight design of aircraft, spacecraft and marine vessels, often advanced materials are utilised. Advanced materials such as laminated composites made of fibre‐reinforced plastics show transverse shear deformations if they are considered “thick” or possess little transverse shear stiffness. In most cases, the effect of the shear deformations is neglected, and few computational models exist that consider the closed‐form approximate analysis of the postbuckling behaviour. Thus, a new computational model based on high‐order shear deformation theories is introduced. The solution is derived based on the principle of the minimum of the total elastic potential and is evaluated in comparison to finite element analyses. The highly efficient approximate computational model is developed to offer a valuable tool for the preliminary design of lightweight structures utilising shear deformable advanced materials.

Inverse design of multi-material gyroid structures made by additive manufacturing

Additively manufactured gyroid structures have great potential in lightweight structure design, energy absorption, heat transfer, and biomedical applications. The optimization and design of the relative density of gyroid structures have been studied for a decade but mainly focusing on a single material phase. Multi-material Additive Manufacturing brought out the material complexity in structures, which extended the design parameter for gyroid structures from relative density to material distribution. In this research, a data-driven inverse design model was developed for multi-material gyroid structures using machine learning. The structures were fabricated by the material extrusion process with a combination of PLA and TPU materials. The mechanical properties of these structures were studied by compression tests and polynomial interpolations. It was found that the interpolation method can accurately indicate the relationship between relative density, material ratio, and mechanical properties. The interpolation functions were used to randomly generate the training data for machine learning. A well-trained neural network model was developed to find the inverse relationship between the mechanical properties and the design parameters. It is used in the design process to determine the relative density and PLA/TPU ratio by the elastic modulus, energy absorption, and peak stress. Subsequent validation experiments verified the efficacy of the proposed design model, demonstrating its ability to accurately predict the desired properties using the machine learning framework. Consequently, this innovative approach has substantially reduced the complexities associated with designing multi-material gyroid structures.

Structural lightweight design and experimental validation for aerospace sealed cabin

Due to the high specific stiffness, high specific strength, good fatigue resistance and high structural reliability, the integrally stiffened shells are widely applied in the sealed cabins. In order to enhance the detection distance of the deep space and improve the payload detection capability, it is of great significance to carry out lightweight design for the integrally stiffened shells. However, it is challenging to perform optimization for the structures due to the strict loading conditions, complicated structures and short development cycles. In this work, a novel layout design framework for the integrally stiffened shells under complex loading conditions is proposed. The topology optimization method is employed to obtain an innovative layout design of the integrally stiffened shells firstly, and then the mesh-mapping technique is utilized to assist the reconstruction and modeling process of the optimization result. Compared with the traditional design of orthogonal stiffeners, the weight of the optimized configuration of the integrally stiffened shell reduces by 17.1%, demonstrating excellent lightweight design effects. Moreover, a sealed cabin is constructed based on the optimization and numerical analysis result by taking the manufacturing requirement into consideration. With the purpose of assessing the bearing ability of the welded seam and evaluating the airtight performance of the sealed cabin, experimental validations of the hydrostatic test and airtight test are carried out, and the experimental results validate the applicability and effectiveness of the proposed framework.

A review of the multi-dimensional application of machine learning to improve the integrated intelligence of laser powder bed fusion

Laser powder bed fusion (LPBF) as one of the most promising additive manufacturing (AM) technologies, has been widely used to produce metal parts and applied in fields such as medical and aerospace. However, the full development of LPBF is still limited by the existence of a limited variety of materials suitable for LPBF, a single structure of printed components, defects in the processing, and complex post-processing. Machine learning (ML), as the core of artificial intelligence (AI), is expected to be an effective tool for LPBF related researches due to its ability to find latent relationships among numerous research issues. This paper provides a newly comprehensive review of ML applications to LPBF. The ML-assisted three stages of LPBF, including the pre-processing, in-situ processing and post-processing, are systematically reviewed. In the pre-processing phase, the application of ML in designing lightweight structures as well as high-performance materials are analyzed in detail. The optimization on the identification of the process and real-time monitoring during the in-situ processing stage are thoroughly discussed. In the post-processing stage, the material-structure-performance (MSP) relationship and their optimization are summarized. Based on the comprehensive review, challenges and perspectives for ML multiscale application development are eventually envisaged. This work contributes a great help to utilize ML to AM and suggests meaningful guidelines for future ML applications to manufacturing work.

Finite element analysis of the mechanical properties of sheet- and skeleton-gyroid Ti6Al4V structures produced by laser powder bed fusion

Additive manufacturing, and laser powder bed fusion (L-PBF) in particular, can produce complex geometric components with high resolution, and is very suitable for manufacturing lightweight triple periodic minimal surface (TPMS) structures to achieve lightweight. With regard to the two forms of the same structure, most of the previous studies focused on sheet-TPMS, but lacked the understanding of the difference between skeleton-TPMS and sheet-TPMS structures. In order to explore the characteristics of these two structures and provide theoretical support for the development of lightweight structure design, this paper compares the manufacturing performance and defect distribution of skeleton-gyroid (GSK) and sheet-gyroid structures (GSH). It employs high-precision finite element analysis (FEA) prediction and experimental verification to compare comprehensively the mechanical properties, failure behavior and energy absorption characteristics of the two structures. The results show that, compared to GSK, the larger specific surface area of GSH leads to more unmelted powder and draping adhesion, without affecting its higher stiffness and strength. Moreover, the more stable failure mode of GSH leads to more gentle stress platform stage and superior energy absorption performance. The results predicted by simulation are highly consistent with the experimental results. This improved understanding allows better prediction of the mechanical properties of the specimens using the Gibson–Ashby theory, which can reduce the experimental cost and time, and improve the resource consumption of TPMS structural performance research. This study can open new possibilities for the design and application of TPMS structures.

Investigations on the fatigue behaviour of welded cover plates with extended weld seams

AbstractNowadays the necessity to design lightweight structures and reducing the use of resources is more important than ever. Normally, cover plates are used as a local strengthening for an optimised load bearing in all kind of steel structures like steel bridges. Under cyclic loading, this notch detail exhibits a worse fatigue behaviour due to the geometrically induced notch factor at the end of the cover plate. By using extended weld seams the stress concentration of this detail can be reduced by a continuous and smooth transition between the ground and the cover plate and thus the fatigue strength can be improved. By using different post weld treatment methods, the fatigue strength could be raised further. Unfortunately, there are almost no experimental results in literature dealing with extended weld seams for any notch detail, even when this type of detail is already used for different construction machines.Within this paper systematic experimental research on possible influencing factors for extended weld seams will be presented.

Numerical Approach to Optimize the Dynamic Behaviour of Structures Considering Structural Durability

In the design of lightweight structures, both the dynamics and durability must be taken into account. In this paper, a methodology for the combined optimization of structural dynamics, lightweight design, and lifetime with discrete vibration engineering measures is developed and discussed using a demonstration structure. A two-sided welded bending beam is excited at the centre and optimal parameters for tuned mass dampers (TMD) are searched, satisfying the requirements for the dynamic behaviour, the overall mass, and the lifetime of the weldings. It is shown that the combination of a reduced order model with the implementation of the structural stress approach at critical welds enables an efficient evaluation of certain design concepts in the time domain. Using this approach, multi-criterial optimization methods are used to identify the best set of parameters of the TMD to reduce the structural vibrations and enhance the durability.

A novel bio-inspired microstructure for improved compressive performance of multidirectional CFRP laminates

In this work, we design, manufacture, test and discuss the first bio-inspired microstructural concept to enhance longitudinal compressive performance of multidirectional (MD) Carbon Fibre Reinforced Polymer (CFRP) laminates. To do so, we take inspiration from biologically occurring layered materials; one remarkable example being the anchoring spicula of the deep-sea glass sponge Monoraphis chuni. We designed numerically various concepts and then devised a strategy to reproduce, in a MD CFRP laminate, the characteristic alternation of stiff and soft regions observed in this material, followed by a bespoke procedure to manufacture the laminate. We evaluated their performances by means of small-scale notched compression tests and direct comparison with an industrially relevant baseline laminate. Our results show that the proposed concept led to a statistically significant increase in the failure load and in the average ligament specific stress at failure. Furthermore, the designed microstructure showed potential to delay damage initiation from a stress concentration and to arrest damage propagation. We conclude that the presented microstructural concept is potentially of great value for the design of lightweight structures undergoing compression loading.

Efficient manufacturing techniques and connection failure analysis of CFRP lifting lug for main bearing structure

Complex lifting lug connection structures often hinder the integral molding of main load-bearing components in automotive, aerospace, construction, and other fields, thus limiting the potential for lightweight structural design. In this paper, a method of forming web-reinforced sandwich composite lifting lug structure of the new energy vehicle by thermal expansion molding process (TEMP) is proposed, and connection failure analysis model is established to verify the process-structure-performance relationship. First, compression tests and failure analysis confirmed that the web-reinforced structure significantly improved the strength and stiffness of the lifting lugs. Then, the hybrid connection mode of the steel sleeve through the thermal expansion film and glass fiber reinforced plastics (GFRP) was designed, and the reliability of the steel sleeve interface connection was verified by the axial press out test. Finally, the lifting lug was simulated to be mounted on the vehicle body, and the comprehensive connection performance was verified by connection compression test, finite element analysis (FEA) and macroscopic failure mode. This study determined that the web-reinforced structure increased the initial failure load of the lifting lug by 65%, surpassing 60 kN compared to the pure foam sandwich structure. The maximum pressure load of the steel sleeve reaches 11.24 kN, and the comprehensive connection strength can meet the static load of the battery box more than 6000 kg. The TEMP technology has the potential to integrate and scale up main bearing components with complex web reinforcement structures.

Optimization of brazing process and structure lightweight design for diamond microchannel

The application of diamond material significantly improves the heat dissipation capability of liquid cooling microchannels, solving the bottleneck problem of heat dissipation for highly integrated electronic components and thus promoting the development of a new generation of military electronic equipment. In this study, diamond microchannels with ultra-high heat flux density were reliably vacuum-brazed by using AgCuTi filler metal in a high vacuum furnace. Microstructure and properties of diamond brazing joints were studied and effect of brazing temperature and time was analyzed. The optimal brazing process parameters were obtained as follows: a vacuum level of <1×10−5 Pa, brazing temperature of 840°C, brazing pressure of 0.5–3 bars and holding time of 10 min. Following vacuum-brazing experiment, the brazing residual stress and working stress of the diamond microchannel were analyzed by finite element simulation. The wall thickness of the diamond microchannel was optimized. The minimum wall thickness, which was 0.4 mm, was obtained for the diamond microchannel with dimensions of 14 mm × 10 mm × 1.3 mm. On that basis, the influence of brazing pressure on the brazing filler overflow in the diamond microchannel brazing process was studied. It was showed that when the pressure was below 1 bar, the overflow of brazing filler from the brazing seam could be controlled to a minimum, especially suitable for brazing precision. The formation of residues in the diamond microchannel was thereby avoided basically, and a diamond microchannel heat sink with good performance was obtained.

Topological Design of a Hinger Bracket Based on Additive Manufacturing.

Topology optimization technology is often used in the design of lightweight structures under the condition that mechanical performance should be guaranteed, but a topology-optimized structure is often complicated and difficult to process using traditional machining technology. In this study, the topology optimization method, with a volume constraint and the minimization of structural flexibility, is applied to the lightweight design of a hinge bracket for civil aircraft. A mechanical performance analysis is conducted using numerical simulations to obtain the stress and deformation of the hinge bracket before and after topology optimization. The numerical simulation results show that the topology-optimized hinge bracket has good mechanical properties, and its weight was reduced by 28% compared with the original design of the model. In addition, the hinge bracket samples before and after topology optimization are prepared with additive manufacturing technology and mechanical performance tests are conducted using a universal mechanical testing machine. The test results show that the topology-optimized hinge bracket can satisfy the mechanical performance requirements of a hinge bracket at a weight loss ratio of 28%.

Multi‐material topology optimization method for transient thermal structure with constraint on permissible temperatures

AbstractExcessive temperature may lead material to performance degradation, ablation, and phase change. Thus, controlling the maximum temperature of used material within a safe range is of great significance to the safe operation of thermal structures. In this article, a density‐based multi‐material topology optimization method for transient thermal structures is proposed, in which the maximal temperature for each material is controlled not greater than its permissible temperature. In this method, a projection algorithm based on the PDE (partial differential equation) filter and Heaviside projection is set up and used to identify the domains occupied by each material. The maximal temperature of each specific material occupying domain is approximately expressed by the condensed integrals in the time and space domains. The permissible temperature constraint is satisfied by controlling the condensed integrals not great than a specific threshold value (depending on the corresponding material's permissible temperature). Several examples illustrate that the permissible temperature plays an important role in the selection and the distribution scheme of the candidate materials for the design of multi‐material thermal structures. The proposed method can effectively control the maximal temperature of each material within its constraint range, and achieve the rational design for multi‐material thermal structures. In addition, different thermal loading time may also lead to different material selection of structure. This work has potential applications in the lightweight design of thermal insulation structures.

Application of column buckling theory to steel aluminium foam sandwich panels

In steel structures, a lot of attention is paid to lightweight structures, i.e. reduction of dead load without compromising structural safety, integrity and performance. Thanks to modern steel aluminium foam sandwich panel manufacturing technology a new possibility became available for lightweight structural design. Assessment and understanding of the behaviour of this sandwich panel under in-plane compression or flexure is crucial before its application in steel structures. Column buckling theory is considered and applied to the steel aluminium foam sandwich panel to evaluate its behaviour under in-plane compressive load. In this work, various assumptions are made to generalise Euler’s buckling formula. The generalisation requires modification of the buckling stiffness expression to account for sandwich panel composite properties. The modified analytical expression is verified with finite element simulation employing various material models specific to steel face-plates and aluminium foam as well as various geometric imperfections. Based on this study, it can be concluded that Euler’s buckling formula can be successfully modified and used in the prediction of the load-carrying capacity of a sandwich panel.

Koch Hierarchical Honeycomb: A Fractal-Based Design for Enhanced Mechanical Performance and Energy Absorption.

A novel energy-absorbing structure, the Koch hierarchical honeycomb, which combines the Koch geometry with a conventional honeycomb structure, is proposed in this work. Adopting a hierarchical design concept using Koch has improved the novel structure more than the honeycomb. The mechanical properties of this novel structure under impact loading are studied by finite element simulation and compared with the conventional honeycomb structure. To effectively verify the reliability of the simulation analysis, quasi-static compression experiments were conducted on 3D-printed specimens. The results of the study showed that the first-order Koch hierarchical honeycomb structure increased the specific energy absorption by 27.52% compared to the conventional honeycomb structure. Furthermore, the highest specific energy absorption can be obtained by increasing the hierarchical order to 2. Moreover, the energy absorption of triangular and square hierarchies can be significantly increased. All achievements in this study provide significant guidelines in the reinforcement design of lightweight structures.

Topology optimization of UAV structure based on homogenization of honeycomb core

In this paper, a new optimization design strategy is explored to achieve a rapid design of lightweight structures for unmanned aerial vehicles (UAVs) using honeycomb sandwich panels. Based on the existing performance equivalent method of honeycomb core material, an effective mechanical property homogenization model of honeycomb material is proposed and applied to finite element analysis. A finite element model is established to analyze the mechanical response of honeycomb sandwich panels under different bending loads, and the rationality of the model is verified by mechanical tests. The error between the simulation results and the experimental results is about 10%. Based on the variable density method and rational approximation of material properties interpolation method, a topology optimization model with the minimum structural flexibility as the objective is constructed. By comparing with the experiment-based design scheme, it is found that the optimized design scheme has a more reasonable structure and better performance. The optimized design can effectively reduce the structural weight and improve the load transfer path while ensuring structural stiffness. In this way, the influence of stress concentration and large deformation on the structure is avoided, which is of great significance for the design of UAV structures.

Study to analyze the mechanical strength of composite glass fiber laminated with resin epoxy, resin polyester, and PVC foam under tensile loading conditions by numerically using finite element analysis via Ansys

With the development of material sciences, different kinds of materials are being developed and studied continuously. In order to significantly reduce weight and reduce emissions, composite materials are employed in aerospace, automobile, mechanical, and wind industries all over the world. Advanced polymer composites, which generally consist of continuous fibers inside a polymer matrix, give greater material qualities than metals and provide for the achievement of lightweight structural designs. Additionally, it is expensive and time-consuming to prepare samples and carry out studies with these materials. Therefore, finite element analysis and simulation have been chosen as the method for failure analysis in order to understand the complicated failure behavior of polymer matrix composite material. The primary goal of this study is to investigate the mechanical strength of glass fiber/resin epoxy, glass fiber/resin polyester, and glass fiber/PVC foam at the laminate level and lamina level under tensile loading conditions in Ansys and Ansys ACP. After analysis, this study has revealed that glass fiber laminated with resin epoxy composite has a higher life cycle and high stress-bearing capacity compared to glass fiber/resin polyester, and glass fiber/PVC foam.

Effects of thermomechanical treatments on Cu–Al–Mn Shape Memory Alloys

In this paper, the authors, building on the established state-of-the-art knowledge, explore the effects of thermomechanical treatments on the Shape Memory Effect (SME) and damping performance of the Cu–Al–Mn Shape Memory Alloys (SMA). Specifically, to explore the potential of application of this SMA in the form of sheets, for the purpose of designing lightweight structures with high damping performance. The casting and the thermomechanical treatment process were fully laid out in the paper. The characterization of the material in terms of chemical composition and microstructure was performed through optical microscopy and SEM coupled with EDX analysis. The temperature-induced phase transformation behavior of the alloy was explored using DSC. The damping performance was quantified through the loss factor which was measured at different levels of static tensile preload using a DMA machine. The alloy has shown significant workability which permits the fabrication of sheets. However, the material displays high sensitivity to oxidation due to a combined effect of impurities and the hot-rolling process necessary for obtaining thin SMA sheets. Nonetheless, the alloy shows competitive damping performance with respect to commercially available NiTi SMA.

Flow behaviour of Ti-6Al-4V alloy in a wide range of strain rates and temperatures under tensile, compressive and flexural loads

The design and analysis of lightweight structures subjected to impact loads require detailed understanding of impact phenomena, and dynamic responses of the selected materials for their safety and reliability. Titanium alloys are in demand for such structures due to high strength to weight ratio, high toughness, and the ability to withstand extreme temperatures. Therefore, this paper investigates the flow behaviour of the titanium alloy Ti-6Al-4V under tensile, compressive and flexural loads at different strain rates and temperatures. Quasi-static tests are performed under tension and compression at strain rates 0.0001–0.1 s−1 while flexural (three-point bending) tests at crosshead speeds 1–100 mm/min are conducted for 90–150 mm span lengths with varying specimen orientations (flat and transverse) on electromechanical universal testing machine (UTM) at room temperature 25 °C. High temperature (300–700 °C) experiments are performed on this UTM under tensile strain rate 0.001s−1 where, the effects of soaking time (5–25 min) and heating rate (10–50 °C/min) are studied. Superplastic behaviour of the alloy is observed at temperature 700 °C with maximum engineering strain nearly 200%. High strain rate experiments on split Hopkinson tension bar (SHTB) and split Hopkinson pressure bar (SHPB) setups are conducted under tension with strain rates 850–1150 s−1, and compression with strain rates 1100–2300 s−1, respectively at room temperature. Ductility and toughness (energy dissipation) are determined at different loading rates. The dependency of the material properties is observed on specimen geometry. Fractography analysis is done for fractured tensile specimens by scanning electron microscope (SEM), and thereafter, existing Cowper-Symonds (CS) and Johnson-Cook (JC) material models are evaluated for the alloy based on the experimental data obtained at different loading conditions.

Crash topology optimization for front-end safety parts of battery electric vehicle using an improved equivalent static loads method

Crash topology optimization is a typical nonlinear dynamic response structural topology optimization problem, which is one of the most difficult problem in the structural design field. The equivalent static load method (ESLM) provides a well-defined pattern to solve such difficult problems, which can convert a nonlinear dynamic response optimization into multi-load steps optimization problem with the equivalent static loads (ESLs). However, due to the large deformation in the crash condition and nodal characteristics of the ESLs, it is hard to solve the crash topology optimization directly using the standard ESLM. To expand the application scope of the ESLM, an improved ESLs calculation method is proposed by using the model order reduction method and energy principle, which only acting on some nodes and can be scaled adaptively. Correspondingly, to enrich the connotation of topology optimization, a crash topology optimization method is proposed by using the improved ESLs, which can solve the numerical problems in the design domain by guaranteeing the topology optimization with the improved ESLs perform in the linear rang. First, the principle of the standard ESLM is introduced, and corresponding problems and deficiencies in solving the crash topology optimization are summarized. Then, to solve the above problems, the improved ESLs calculation method is proposed. Meanwhile, the corresponding crash topology strategy is proposed based on the improved ESLs. Finally, to verify the effectiveness and engineering application value of the proposed crash topology optimization method, a test-verified frontal crash simulation model of the BEV front-end is established, and their safety parts are redesigned by using the proposed method. The results show that, the proposed method can effectively solve the crash topology optimization of thin-walled structures under large deformation crash condition. This method also provides a new idea and practical method for the crashworthiness and lightweight design of automobile structures.

Risk-Based Hybrid Light-Weight Ship Structural Design Accounting for Carbon Footprint

The study aims to develop an integrating risk-based formulation and cost-benefit analysis for identifying an optimal ship hull structural design solution where the steel cargo holds aluminium honeycomb sandwich panels to replace inner side shells. The risk of progressive structural failure includes hazards related to environmental pollution due to accidental fuel and oil spills, possible loss of cargo, crew members and ship during operations, and air pollution during shipyard construction and ship voyages. The structural failure incorporates progressive time-dependent structural degradation coupled with ship hull load-carrying capacity in predicting structural integrity during the service life. The ship hull structural failure and associated risk are estimated over the ship’s service life as a function of the design solution. The carbon footprint and cost to mitigate the impact for the entire steel and hybrid ship hull structural solution implemented as a sustainable life cycle solution are analysed where the steel ship hull structure is built through primary construction. The cost of structural measures accounts for redesigning the ship structure and implementing aluminium honeycomb composite panels instead of steel plates, reducing steel weight, environmental pollution and cost and increasing the transported cargo and corrosion degradation resistance. It has been found that design solutions AHS1 and AHS2, in which aluminium honeycomb panels replace the inner steel shell plates, enhance the corrosion degradation resistance, and reduce the ship hull’s lightweight, reflecting a better beta-reliability index at the time of the first repair with a lower repair cost and more transported cargo. The cost of the ship associated with the design solutions AHS1 and AHS2 is about 11% lower than the steel solutions.