Deployable structures can realize the transformation from a folded configuration to a deployed configuration to satisfy the requirements of applications. They have been widely used in aerospace ...structures, civil temporary components, medical devices, transformable robotics and other engineering applications. A large amount of research has been carried out on the structural design ranging from rigid, rigid-flexible to flexible structures and the performance analysis including the static loading properties and structural stability, as well as the dynamics during deployment and in the deployed configuration. However, to date, there are no mature systematic approaches for the design and analysis of deployable structures due to diverted application demands. Therefore, in this review, efforts are made to find a common methodology from most existing successful cases and to propose the major challenges for the future applications of deployable structures.
The working mechanism is an important part of a wheel loader. It is used to accomplish the shoveling, loading, lifting, and dumping tasks. Usually, the working mechanism is a Z-bar linkage and the ...dimensional design of the linkage directly affects the loader’s service performance, such as dumping clearance and dumping height. As there are many other performance indexes and various field requirements for the loader, comprehensive optimum, and adaptable design methodology with full-parameterized kinematic model attracts engineers’ research interests. Focusing on the multi-objective and multi-variable problems, this paper firstly establishes an accurate and simplified kinematic model of the Z-bar linkage with deduced expression of the basic parameters, and then investigates the performance indexes including mechanism transmission ratio, lifting stationary, dumping angle in any position, bucket flat setting, and extreme transmission angle, etc. With the full-parameterized kinematic model and the optimum algorithm, modified complex method, a comprehensive and adaptable design platform is built to solve the multi-objective and multi-variable problems of the Z-bar linkage. A case study with two optimization schemes as “full variables design” and “partial variable design” is conducted. The simulation results show that both schemes are better than the original one. The methodology and platform in this paper are of importance in generating user requirement oriented linkage design schemes with enough consideration and optimization of multiple performance indexes.
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•Accurate shape memory alloys (SMA) constitutive models considering incomplete phase transformation are proposed.•The model parameters are easy to obtain by experiments, and the ...constitutive models are more applicable in engineering.•Differences between shape memory effect SMA and super elasticity SMA are fully considered in the constitutive model.•Tensile tests and loading-unloading cycles experiments verified the constitutive models’ results.
The current shape memory alloys (SMA) constitutive models have the problems of complicated calculation, inaccurate results, measuring difficult parameters, and inconvenient application, which brings about challenges for designing, analyzing, and simulating SMA’s macroscopic behavior in engineering. This paper proposed practical SMA constitutive models for accurate engineering calculation, which apply to both the single loading-unloading process and the multiple loading-unloading cycles. The more accurate SMA theoretical tensile curve and temperature-stress phase transformation diagram is introduced to derive the constitutive model. The more accurate calculation method of elastic modulus, phase transformation modulus, and critical phase transformation stress is proposed in this paper. The proposed constitutive model considers the incomplete phase transformation phenomenon and the variation of critical phase transformation stress under multiple loading and unloading conditions. It can accurately evaluate the critical phase transformation stress and stress-strain relationships at various temperatures. Tensile tests under various working conditions were conducted. The results demonstrated that the proposed constitutive model could well simulate the SMA’s macroscopic mechanical behavior at various temperatures, loads, and multiple loading-unloading cycles with accuracy, practicality, and efficiency.
Warping is conventionally regarded as a drawback of asymmetrical sheet rolling caused by speed mismatch-induced cross-shear straining. But, in this paper, by utilizing the warping effect, we ...developed a novel roll bending process, named cross-shear roll bending (CSRB), for the manufacturing of tubular sections. In the process, the metal sheet is rolled and bended under cross-shear straining by mismatched circumferential speeds of two rollers. The process is capable of manufacturing continuously changeable curvature tubular sections with minimized springback and straight ends and also with increased strength through strain hardening. Experiments show that the CSRB process is effective in forming the tubular sections by the following aspects. (1) The curvature radius decreases as the circumferential speed differential rate increases, but it loses its sensitivity to a relatively larger circumferential speed differential rate. (2) The curvature radius evolves along with the change of thickness reduction rate of the sheet in a V-shape manner, which indicates the existence of a minimum curvature radius. (3) The change of radius ratio poses little effect on the curvature radius. Therefore, by exclusively regulating the circumferential speed differential rate and the thickness reduction rate, the curvature of the sections can be controlled.
An armored face conveyor（AFC） is a key piece of equipment for a fully mechanized long-wall mining system and is currently the only means for transporting bulk material in hard coal mines. To date, ...the AFC power train design has mainly been based on heuristics obtained via experience, coupled with simple calculations, which cannot take the dynamic behaviors and coupling effects of the components into consideration. Therefore, model-based and simulation-driven design is preferred. In this paper, a new design and analysis methodology for an AFC power train is presented to achieve the optimal dynamic characteristics and transmission performance. A preliminary design procedure for a power train is first introduced. Then, a system-level hydro-mechatronic model of the power train is built to evaluate and optimize the preliminary scheme. Sub-models, including those for the motors, fluid couplers, gearboxes, and chain, are obtained according to their individual disciplines and assembled to form the system-level model. The chain sub-system is discretized into multiple finite elements. Governing equations are established for each element based on the Newton Euler approach and assembled according to the topological structure of the chain system. In order to make the new approach applicable for engineers, a design and analysis software is developed, with a graphical user interface that involves the whole design process. MATLAB/SIMULINK is used as the computational engine, and Visual C＋＋ is adopted to develop the interactive software framework. Simulations for the SGZ1000/2000 type AFC are provided as an illustrative case study to validate the effectiveness and practicality of the model and software package.
The objective of this research is to characterize the structure–property relationship of a heat-treatable Al–Mg–Si aluminum alloy that is subjected to various straining and heat treatments. The ...effects of paint bake cycle (PBC), pre-straining and annealing on mechanical tensile properties were investigated. Pre-straining combined with rapid, high temperature annealing can noticeably improve ductility and increase formability. While pre-straining by itself does not change the hardening behavior of the as-received material, combining pre-straining with rapid, high temperature annealing does alter the hardening behavior and decreases the final post-PBC yield strength. It is well documented that PBC increases the yield stress in Al–Mg–Si alloys by precipitation of the β″ phase. The reduction in precipitation hardening after pre-straining and annealing is caused by the high temperature annealing treatment that promotes over-aging and conversion of the β″ phase to β′ and β precipitates, even with a short annealing time. The yield stress after PBC can be increased if the pre-strained and annealed material is strained a second time after annealing, although this increase may not reach the strength levels of the alloy without the annealing step. Hence, the intermediate annealing and forming technology is most useful for age hardenable alloys if applied locally to complex areas of a panel where increased formability is more important than high strength.
PurposeDue to the structural layout, mining process, and working environment, curved chains such as horizontal and vertical bends inevitably exist in the armoured face conveyor (AFC). With the ...increasing power, conveying capacity, and distance of the AFC, the dynamic influence of these curved chains should be highly emphasized. This paper establishes a dynamic model of the AFC by multi-body system theory and finite segment method, in which the curved chains can be fully considered.Design/methodology/approachThe scraper chains are firstly grouped into the straight, horizontal bend, vertical convex and concave bend sections. Each bend section running in a circle is simplified as an ideal arc. Through solving its differential equilibrium equation and using Newton's second law, its running resistance is derived. Then the grouped chains are discretized into finite control elements according to the Kelvin model, and the governing equation of each control element is established. The dynamic model of the AFC is obtained by assembling these equations, and the corresponding simulation model is developed by using MATLAB/Simulink.FindingsCase studies with real scenarios are provided, and simulations are carried out. The results show that the running resistance contributed by the curved chains is larger than the traditional empirical value.Originality/valueThe work in this paper helps the dynamic performance design of AFC, with a deep understanding of the curved chains.
•Cable-truss interaction is captured for cable-truss structural system.•Long-term mesh reflector antenna creep phenomenon is analysed.•Time-related tangent stiffness matrix is deduced for static ...solution.•Proper pre-tension can compensate for surface accuracy deterioration.
During the in-orbit service, mesh reflector antennas inevitably withstand the long-term creep behavior, resulting in changes in material properties and loss of cable tensions, thus decreasing the structural stiffness and surface accuracy. Pretension design plays an important role for mesh reflector antennas in achieving high surface accuracy, and different levels of pretension also affect the antenna’s creep behavior in the time dimension, which can be actively utilized to improve stability of the antenna surface accuracy. In this paper, we present an anti-creep pretension determination method for mesh reflector antennas to improve the surface accuracy stability. The creep model in the discretized time domain is adopted to describe the cable creep behavior. The time-related nonlinear equilibrium equation of the mesh reflector antenna is established with the force density method. The time-related tangent stiffness matrix is derived and adopted to solve the nonlinear equilibrium equation by the Newton-Raphson method, providing an effective way to analyze the antenna creep phenomenon in the discretized time domain. Aiming to minimize the long-term peak value of the time-variant surface error, the pretension schemes are generated and optimized. Finally, this approach is effectively applied to a thirty-unit mesh reflector antenna and its feasibility and effectiveness are verified.
•Considering the compatible deformation between the cable network and supporting truss, the equilibrium state of the mesh antenna is solved by the DR method.•The problem of compatible deformation ...between a 3 degree-of-freedom cable and a 6 degree-of-freedom Euler-Bernoulli beam is solved in the DR method.•A novel pretension design method to obtain both high surface accuracy and uniform tension distribution is proposed.•This method does not require the assembly of the structural stiffness matrix and is easy to program with good computational stability and high computational efficiency.
Cable truss structures are widely used in large satellite antennas with ultrahigh electromagnetic performance. The electromagnetic performance is directly determined by the mesh reflector's surface accuracy, which triggers research on the pretension design. In this paper, a novel pretension design method for both high surface accuracy and uniform tension distribution is proposed based on the dynamic relaxation (DR) method. In this approach, members of the cable network are regarded as string elements with 3 degrees of freedom to resist the axial tensile force, and members of the supporting truss are regarded as Euler-Bernoulli beams with 6 degrees of freedom to resist the axial and transverse forces and the bending and torsion moments. The DR method is adopted to find the static equilibrium of the whole mesh antenna, including both the cable mesh and the supporting truss. Thus, the deformation of the cables and rods and their interactive effects are fully captured. Then, to find an expected high-precision mesh surface with a uniform tension distribution, the inverse iteration algorithm (IIA) is adopted to adjust the original cable lengths of the cable network in each DR calculation cycle until the convergence criterion is met. Finally, this approach is effectively applied to the pretension design of symmetric and asymmetric mesh antennas, and the results indicate that the method is effective in obtaining both high surface accuracy and uniform tension distribution with high computational efficiency.
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Mesh reflector antennas have been widely used in space satellites for their characteristics of large aperture, low levels of total mass, stowed volume, surface distortion, etc. The antenna turns from ...a stowed state to a fully deployed configuration and finally forms a required functional surface, and this deployment process affects the performances of antennas on orbit. The dynamic modeling and analysis for the deployment of mesh reflector antennas considering the rigid body rotation of rods, the geometric nonlinearity of the cable net, and the rigid-flexible coupling of the truss and the cable net are presented in this paper. Instead of the previous lumped mass model, the mass of hinges is concentrated on their centroids and the longerons, battens, and diagonals are regarded as homogeneous rods in the study. By this model, the rigid body motion of rods can be well considered in the calculation of kinetic energies rather than be ignored in previous researches. Then, the cable net is discretized into multiple cable elements that are modeled by springs. The slacked and tensioned state of cable elements during deployment are captured by updating the stiffness matrix real-timely. The elastic energy of the cable net is derived by solving systematic equilibrium equations. The dynamic model is established by using Lagrange equation, and then the driving force under the predesigned motion is derived. The “ideal deployment motion” and “feasible deployment motion” are proposed and discussed through several numerical examples. Simulation results match well with experimental data in previous literature.
