Journal of Mechanics of Materials and Structures最新文献

Inflated membranes are a kind of flexible structure with the enveloping membrane supported by the inflating air. A change in the pressure of the inflating air resulting from the deformation of the enveloping membrane will induce a change in the stress state and stiffness of the enveloping membrane, and hence influence the mechanical behavior of inflated membranes. This paper studies the effect of inflating air on the static behavior of inflated membranes via the geometrically nonlinear analysis of square ETFE (ethylene-tetrafluoroethylene) cushions under a uniformly distributed load on the top membrane. Three different models are adopted in the analysis, in which the inflating air is treated respectively as the traction boundary conditions of the enveloping membrane, a kind of fluid satisfying the ideal gas equation and a potential-based fluid. The results obtained from the models are compared to investigate their accuracies and the effect of inflating air. Based on the actual variation of the internal pressure with the deformation, a new model with correct treatment of the influence of inflating air is then proposed and its validity and accuracy for different influencing parameters, e.g., initial internal pressure, membrane thickness, side length, rise-to-span ratio, etc., are further investigated. The results show that: (a) The effect of inflating air is characterized by the air-membrane interaction, and it makes the top and bottom membranes work together as a whole. (b) The inflating air has a significant influence on the mechanical behavior of a cushion with less deformation. (c) The effect of inflating air can be approximated by a linear function with respect to the ratio of its pressure to the density. (d) The proposed model of the inflating air is accurate for different influencing factors, and it can be used as an efficient approach to the effect of inflating air without any effort to deal with the fluid-structure interaction in the computation. The present research facilitates the accurate understanding of the effect of inflating air and the mechanical behavior of inflated membranes for rational design and reliable engineering application.

Forming mechanics of a twin-roll cast AA1100/409L clad sheet after annealing and cold rolling was investigated by tensile and three-point bending tests. The effect of mechanical properties of the base metals and bonding strength on the strength and ductility of the clad sheet was investigated based on the mixed rule. The clad sheet’s strength obeys the mixed rule only when the bonding strength is as high as 15 N/mm. The negative correlation between strength and ductility and the synergistic effect also exist in the TRC SS/Al clad sheet only when the bonding strength is as high as 15 N/mm. Because of the too small thickness and much higher strength of the steel layer than that of the Al layer, tensile stress dominates during bending of the TRC clad sheet. The deformation and failure process of the clad sheet was analyzed and the processing route for a better formability was proposed.

Multistable structures have a promising potential in a wide range of engineering and scientific applications, such as shock absorption, soft robotics, superelastic structures, vibration mitigation, foldable structures, configurable structures, programmable materials, and tunable shape-memory structures. In addition, they are directly relevant to the study of materials undergoing martensitic phase transformations, macromolecular networks, and the development of new metamaterials. In this paper, we study the quasistatic behavior of 2-D bistable lattices subjected to shear, with emphasis on the multitude of equilibrium configurations, overall stress-strain relation, sequence of phase transition, and statistics of stress jumps. In particular, the influence of material (properties of the individual bistable interaction) and microstructure geometry (architecture of the lattice) on the above mentioned characteristics of the overall behavior is investigated. To this end, we perform extensive numerical simulations with four different periodic lattice geometries. We find that, for the same loading conditions, different lattice geometries or different material (bistable) properties of the building block may result in fundamentally different overall (macro) behaviors. This is manifested both in the overall stress-strain relation and also in the evolution of the phase-transition patterns. Also, hysteresis, which is a macroscopic manifestation of the energy dissipated during change of configuration, is significantly affected by the lattice architecture. Similar effects of geometrical incompatibility, but at the level of the atomic lattice, have been observed in shape-memory alloys. Our results also reproduce stress peaks, associated with nucleation of a new phase. The magnitude of these nucleation peaks, their location, and number is dictated by the geometry of the lattice and boundary effects that lead to stress concentrations.

Structures that have thin cross-sections and are prone to compressive loads may buckle suddenly at critical load values. To calculate the critical buckling load, researchers have reported many analytical solutions which are related mainly to the deterministic approach. However, the important geometric and material parameters highly affect critical buckling loads of structures and they should be considered as uncertain in order to obtain realistic estimations. This is due to the fact that imperfections in the geometry and material properties may occur during the production stages of a component or under operational conditions. In the present study, which is based on first-order shear deformation theory (FSDT), in the first step the deterministic buckling equation of symmetric sandwich composite plates consisting of two identical carbon/epoxy skins and a foam core between the skins is formulated considering the uncertainties which can occur in the nondeterministic state. In the next step, closed-form analytical buckling equations including the geometric and material uncertainties are derived using the convex modeling and Lagrange multiplier method and based on the worst-case scenario leading to the lowest buckling loads. Sensitivity analysis is also conducted to understand which uncertain parameters have the most negative effect on the critical buckling load. Finite element analysis (FEA) is implemented to validate the derived equations. It is seen that even minor variations in the material properties and geometric dimensions lead to considerable variations in the critical buckling load. The significance of involving the uncertainty in the analysis is explained both qualitatively and quantitatively.

We describe a mass spring system (MSS), which is also referred as lattice model in the literature, predicting the load-displacement curve of the orthotropic materials. We have developed the MSS model of a double cantilever beam to capture the energy release rate in a mode I fracture of the orthotropic materials using two different formulations: maximum strain energy and maximum strain. Further, we have considered determination of fracture energy of cortical bone, as a case study, using the compliance based beam method (CBBM). This method avoids monitoring of crack length during fracture and provides the complete R-curve along with the plateau, which is the fracture energy. We have also obtained the R-curve from the load-displacement curve predicted by the MSS model and determined the fracture energy of cortical bone. As the maximum percentage error in fracture energy predicted by the MSS model for dehydrated and hydrated bone is 1.02 per cent and 1.15 per cent, respectively, the results are in good agreement with the experimental results. Thus, we have shown the ability of the MSS model to produce quantitative results as well in comparison to the models presented in the literature for simulation of a fracture, which give essentially qualitative results. We have used the validated MSS model for characterizing the load-displacement behavior of cortical bone for increasing mineralization and porosity.

Cracks with unstable paths will appear in the glass during quenching. For different quenching speeds and temperatures, there will be linear, oscillatory and bifurcated crack paths. In this work, the phase-field cohesive zone model (PF-CZM) is adopted as the prototype model to address the problem of crack path instabilities in a quenched glass plate. Substituting the temperature field model into the phase field model, the thermal-mechanical coupling fracture problem is solved. The model accurately predicts different crack patterns in the quenched glass under different thermal shock densities. The variation of the crack tip positions and the crack propagating velocity are obtained. Several typical crack morphologies are simulated and analyzed, including linear, sinusoidal, semicircular and bifurcated cracks. The thresholds for crack propagation morphological variations are distinguished. Comparison with experimental data shows the efficiency and accuracy of the used phase-field model applied to thermal shock problems.

Common stress recovery methods usually cannot introduce the stress boundary conditions. The general mixed finite element method can only solve the whole model and its calculation requires large memory resources. A stress recovery method using generalized mixed elements in a local model is proposed in this paper. The elements surrounding some nodes where stress results are required are selected to construct a local noncompatible generalized mixed element model, which is used to introduce the stress boundary conditions in the local model. For the problem of composite structures, the modified generalized mixed variational principle is used to obtain the solution equation of out-plane stress, and then the local models for the linear system of in-plane stress are constructed according to different material layers. The continuous results of in-plane stress in each layer of material can be obtained, and the discontinuity of in-plane stress at the interface of each material layer is ensured at the same time. Numerical examples show that this method can obtain objective and more accurate stress results. Compared with the mixed finite element method for whole model, the present method greatly improves the computational efficiency.

The interlayer tearing of a plate viscoelastic (VE) damper is an important issue, which may cause failure of the damper. In this work, two new interfacial reinforced damper structures are proposed, which can effectively enhance the working ability of the VE damper. Dynamic performance tests are carried out on the reinforced VE dampers with a series of temperatures, frequencies and displacement amplitudes. The experimental results show that the proposed VE dampers have great energy dissipation capacity, and a damper with a baffle structure has better performance. The finite element method (FEM) is used to investigate the impact of structure optimization on the performance improvement of the VE dampers. The simulation results demonstrate that the baffle structure significantly enhances the stiffness of the damper, which is consistent with the experimental findings. In order to characterize the influence of frequency, temperature and displacement amplitude on the VE dampers, a modified fractional-derivative Burgers model is proposed, which introduces internal variable theory and a temperature-frequency equivalent principle to explain the amplitude and temperature effect, respectively. The comparison between theoretical and experimental results reveals little discrepancies, thereby affirming the precision of the mathematical model.

The study of wave propagation in chiral elastic systems has important potential applications in areas such as controlling vibrations and wave filtering. Although the behaviour of elastic waves in traditional elastic media is well understood, how elastic waves behave in chiral materials is still to be further explored. We present an analytical study of elastic waves in a new continuous chiral elastic material, focusing on (i) the development of the new continuum model based on a class of discrete elastic metamaterials and (ii) the study of dispersion behaviour of elastic waves in this new chiral material. The effective material developed is isotropic and characterized by both elastic moduli and coupling parameters, associated with chirality. The dispersion relation and the corresponding waveforms are studied to evaluate the general behaviour of wave propagation in this new chiral medium. Different from the property of waves in traditional isotropic elastic media, generally no independent longitudinal or transverse waves can be observed in the new chiral medium except for cases at specific frequencies. The analytical findings are accompanied by illustrative numerical examples to show the general property of the dispersion and wave modes.

The Hamiltonian system is utilized to establish an accurate buckling solution model for piezoelectric material cylindrical shells with stepped thickness. The critical loads and nonuniform buckling modes are obtained by finding the symplectic eigenvalues and eigensolutions of the Hamiltonian equation. The results show that the transition between local buckling and global buckling can be controlled by an applied voltage. These findings can provide a novel method to control the buckling deformation range and symmetry of cylindrical shells.