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•3D specimens printed with cementitious materials are orthotropic.•Mechanical properties and failure depend on inter-layer and inter-strip bonds.•Stress–strain relationship and ...failure criterion proposed for 3D printed materials.•Behavior of 3D printed structures depends strongly on the printing direction.
The three dimensional (3D) printing technology has undergone rapid development in the last few years and it is now possible to print engineering structures. This paper presents a study of the mechanical behavior of 3D printed structures using cementitious powder. Microscopic observation reveals that the 3D printed products have a layered orthotropic microstructure, in which each layer consists of parallel strips. Compression and flexural tests were conducted to determine the mechanical properties and failure characteristics of such materials. The test results confirmed that the 3D printed structures are laminated with apparent orthotropy. Based on the experimental results, a stress–strain relationship and a failure criterion based on the maximum stress criterion for orthotropic materials are proposed for the structures of 3D printed material. Finally, a finite element analysis was conducted for a 3D printed shell structure, which shows that the printing direction has a significant influence on the load bearing capacity of the structure.
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•Bi-DCB specimens were designed and manufactured by the vacuum bag method, and bistable deformation processes of Bi-DCB specimens were achieved.•Based on the Tsai-Hill and maximum ...stress criteria, two nonlinear explicit finite element models were established for predicting the folding stable state of the Bi-DCB.•Numerical results of two finite element models were compared with experiments, and the three were in good agreement.
The bistable deployable composite boom (Bi-DCB) can realize the bistable function by storing and releasing strain energy, which has a good application prospect in the aerospace field. In this paper, the folding stable state of the Bi-DCB was investigated using experimental and numerical approaches. Using the vacuum bag method, six Bi-DCB specimens were prepared. Bistable experiments of Bi-DCB specimens were conducted and linear fitting with Archimedes’ helix was performed to determine the folding stable configuration. In addition, two Finite Element Models (FEMs) were established for predicting the folding stable state of the Bi-DCB. Two classical failure criteria were utilized to analyze the stress level of the folding stable state of the Bi-DCB. Numerical results of two FEMs agreed well with experimental results, including the bistable deformation process and the folding stable state.
In the present study authors have studies the mechanical behavior of the hexagonal boron nitride nanoribbon (BNNR) filled polyethylene (PE) nanocomposites using classical mechanics based approach. ...Reaction force field in conjunction with L-J potentials are used to model the bonded and non-bonded interaction between PE and BNNR. In order to calculate the mechanical properties of the polyethylene based nanocomposites uniaxial tensile testing was applied on the PE/BNNR nanocomposites. Maximum stress, elastic modulus and strain at failure were calculated at the strain rate of 109 s−1 and compared with the corresponding pristine PE value. It was predicted that, 4% BNNR in polyethylene significantly enhance the maximum stress and elastic modulus. This study gives deep insight of the load transfer mechanism in case of the nanofiller reinforced polymer nanocomposites.
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•A new multi-material topology optimisation framework for design of periodic micro-composites is developed.•The effects of weight ratios assigned to the property and stress objectives ...are investigated.•Evaluation indices are proposed with decision-making approaches to obtain the optimal solution for competing objectives.
This study develops a new multi-material topology optimisation framework for design of periodic micro-composites with optimal functional performance and reduced stress concentration. First, multi-material topology optimisation is developed based on the alternating active phase algorithm and inverse homogenisation method with the sensitivity analysis derived for specific property objective i.e., negative Poisson's ratio (NPR) or maximum effective bulk modulus (EBM) and (p-norm macroscopic) stress objective. Then, the effects of initial material distribution and weight ratio (w1, w2 assigned to the property and stress objectives, respectively) are investigated, and the evaluation indices are also developed to obtain the optimal solution. Further, two cases related to the design of micro-composites for maximised either NPR or EBM with reduced maximum stress are performed. The results show that when designing the multi-material NPR micro-composites, the decrease of w1/w2 contributes to a general decease of both NPR and maximum stress. While in designing the maximum EBM, decreasing w1/w2 leads to the reduced maximum stress and simultaneously reduced EBM; hereby, a decision-making method as well as the proposed evaluation index are both applied and compared for acquiring the optimal result. This study provides new methods and solutions to multi-material micro-composites design for future industrial applications.
The thin-walled tubular deployable composite boom (DCB) can realize folding and deploying functions, and it has a good application prospect in space field. This paper investigates the folding ...behaviour of the tubular DCB by analytical modeling. Based on the Archimedes’ helix, the geometrical model of the DCB was established. By combining equilibrium equation and energy principle, an analytical model to predicted the folding moment versus rotational displacement of the DCB was presented. The failure indices in the equal-sense and opposite-sense folding processes were calculated utilizing Tsai‐Hill and maximum stress criteria. Analytical results agreed well with experimental and numerical results. At last, the influence of geometric parameters (i.e., radius, central angle and thickness of cross-section) on the folding behaviour of the DCB was further studied using the analytical model.
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•An analytical model is presented to predict the folding behaviour of the deployable composite boom (DCB).•Failure indices are calculated using two criteria in equal-sense and opposite-sense folding processes.•The analytical model is validated against experimental and numerical results, showing good prediction accuracy.•Geometric parameters (radius, central angle, and thickness) significantly affect the folding behavior of the DCB.
Thin-walled tubular deployable composite boom (DCB) has gained significant attention due to its lightweight, simple structure and high packaging efficiency. The experimental and numerical simulation ...methods were employed in this paper to investigate the folding behavior of the DCB. Using T700/epoxy unidirectional reinforced prepreg as raw material, DCB specimens were prepared by the vacuum bag method. To complete the folding experiments of DCB specimens, a folding mechanism was designed and manufactured. Folding experiments of DCB specimens were conducted and folding moment versus rotational displacement curves were measured. In addition, a Finite Element Model (FEM) was established to predict the folding behavior of the DCB. Different failure criteria were considered in the numerical analysis, including the Tsai‐Hill criterion and maximum stress criterion. Prediction results using the FEM were compared with experimental results, and both sets of results were in good agreement. It is shown that the DCB can achieve the folding function without failure. The research results in this paper are of great significance to the practical engineering application of the DCB.
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•Six tubular deployable composite boom specimens and a precise folding mechanism were designed and prepared.•Folding experiments were conducted to measure the folding moment and rotational displacement curves.•A finite element model for predicting the folding behavior of the tubular deployable composite boom was established.
•Maximum stress effect incorporated into low cycle fatigue damage accumulation.•Non-linear summation approach was used to consider creep–fatigue interacted effect.•Crack growth behavior and damage ...evolution was revealed in creep–fatigue regime.•Crack growth relation in creep–fatigue regime greatly depended on dwell time.
In this paper, a novel creep–fatigue interaction damage model was proposed to evaluate damage evolution and crack growth behavior in creep–fatigue regime. The model incorporated the maximum stress effect into the low cycle fatigue damage accumulation and utilized the non-linear summation approach to consider the creep–fatigue interacted effect. The model could predict the relation between (da/dt)avg against (Ct)avg in creep–fatigue interacted environment and demonstrate the crack growth behavior under pure fatigue condition, which respectively matched well the corresponding experimental results. In addition, the crack growth rate was greatly dependent on the dwell time in creep–fatigue regime. The crack growth rate (da/dt)avg was increased with decreasing the hold time at the same (Ct)avg values. During crack growth process, the creep damage accounted for a larger portion compared with the fatigue damage. Furthermore, in creep–fatigue regime, the effect of the initial crack depth on crack growth behavior was dependent on the hold time while the applied initial stress factor range had slight effect on the crack growth behavior.
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Molecular dynamics simulations are used to study the mechanical properties of α-graphyne and α2-graphyne. The square and rectangular α-graphyne and α2-graphyne with different dimensions are modelled. ...It is seen that for both of the considered nanosheets, Young's modulus is smaller than along the armchair direction than along the zigzag direction. Similarly, zigzag α-graphyne has larger fracture strain than the armchair one. For the α2-graphyne, however, the fracture strain along the armchair direction is larger than zigzag direction. Besides, it is observed that Young's modulus of the α-graphyne is smaller than α2-graphyne for both of the armchair and zigzag structures. However, the α-graphyne possesses larger fracture strain than α2-graphyne. It is also seen that Young's modulus of the square α-graphyne and α2-graphyne nanosheet is not dependent on the nanosheet dimension. However, fracture strain and maximum stress of these nanosheets decrease by increasing the nanosheet size. Finally, the Poisson's ratio of the α-graphyne and α2-graphyne is obtained as large as 0.9 for some sizes.
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•MD simulations are used to study the mechanical properties of α-graphyne and α2-graphyne.•The square and rectangular α-graphyne and α2-graphyne with different dimensions are modelled.•For both α-graphyne and α2-graphyne, Young’s modulus along the armchair direction is smaller than zigzag direction.•Zigzag α-graphyne has larger fracture strain than the armchair one.•Fracture strain along the armchair α2-graphyne is larger than zigzag one.
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