Mechanics of air-inflated 3D distance fabric

3D distance fabrics are modern and promising material for lightweight inflatable structures. The applications are used in sport, boats, tents, construction, military etc. Its advantages are large load capacity per unit weight, stiffness dependent on pressurized air, fail-safe structure. However, the mechanics of inflated fabric panel is not still described enough. This paper gives basic theory and its experimental verification about mechanical behaviour of distance fabrics. The mathematical model of air-inflated distance fabric panel is created based on analytical theory of cylindrical bending of plates. Material data of the fabric required for performing computations of the model are determined from tensile tests. The reliability of the analytical model is experimentally verified. For that purpose the air-inflated fabric panel was made and tested. Results obtained both experimentally and analytically are compared and discussed. The experiment proves the validity of the mathematical model and allows us to predict the behaviour of distance fabrics.

Prediction on the Mechanical and Forming Behaviors of Ferrite-Martensite Dual Phase Steels Based on a Flow Model

An innovative flow model incorporating the mixture hardening law, anisotropic yield function, and incremental strain formulations was elaborated and applied to DP590 ferrite-martensite dual phase steel. To verify the flow model, both the macro/micro stress-strain responses and the forming patterns of DP590 steel with different martentite contents were simulated during the processes of the cup deep-drawing and the unconstrained cylindrical bending to evaluate the influence of martensite content on the mechanical and forming behavior of the steel. It was found that maternsite content has a significant impact on the macro/micromechanical and forming behavior of the steel, i.e., the ferrite and steel effective stresses and the effective macro/micro-strain distribution in the cup. Under the unconstrained cylindrical bending, the simulated effective maximum macro/micro-strains were in good agreement with the calculated results from the mixture law-based model. It was concluded that the Buaschinger effect is the main reason for an 8 % error between the simulated and experimental results. The flow model was proved to predict the macro/micro flow and forming behavior of the dual phase steels with a good accuracy.

Springback Characteristics of Cylindrical Bending of Tailor Rolled Blanks

As a new type of variable thickness sheet structure, the TRB (tailor rolled blank) has good prospects for the development of lightweight materials in the automotive industry. However, springback is a key issue in production. Research on TRB springback characteristics has great significance for further applications due to variations in the sheet thickness and gradient distribution of the material mechanical properties. In this study, the springback characteristics of TRBs were investigated by means of the finite element code ABAQUS/USDFLD and experiments taking cylindrical bending as an example. The results showed that the cylindrical bending process of the TRB gradually evolved from three-point bending to four-point bending and, finally, to multipoint bending. At same time, the gradient of the thickness leads to the nonuniform longitudinal distribution of the von Mises stress. On the contrary, larger bending angles can be achieved by reducing R and improving Rd, but t/T has little effect on the bending angles. In terms of the influence of springback, increasing Rd and reducing R and t/T can lead to a smaller springback angle. This project provided an important opportunity to advance the understanding of TRB springback characteristics.

Cylindrical Bending Vibration of Multiple Graphene Sheet Systems Embedded in an Elastic Medium

Based on the Eringen nonlocal elasticity theory and multiple time scale method, an asymptotic nonlocal elasticity theory is developed for cylindrical bending vibration analysis of simply-supported, [Formula: see text]-layered, and uniformly or nonuniformly-spaced, graphene sheet (GS) systems embedded in an elastic medium. Both the interactions between the top and bottom GSs and their surrounding medium and the interactions between each pair of adjacent GSs are modeled as one-parameter Winkler models with different stiffness coefficients. In the formulation, the small length scale effect is introduced to the nonlocal constitutive equations by using a nonlocal parameter. The nondimensionalization, asymptotic expansion, and successive integration mathematical processes are performed for a typical GS. After assembling the motion equations for each individual GS to form those of the multiple GS system, recurrent sets of motion equations can be obtained for various order problems. Nonlocal multiple classical plate theory (CPT) is derived as a first-order approximation of the current nonlocal plane strain problem, and the motion equations for higher-order problems retain the same differential operators as those of nonlocal multiple CPT, although with different nonhomogeneous terms. Some nonlocal plane strain solutions for the natural frequency parameters of the multiple GS system with and without being embedded in the elastic medium and their corresponding mode shapes are presented to demonstrate the performance of the asymptotic nonlocal elasticity theory.

Влияние поверхностных эффектов на изгиб и колебания нанопленок

Static cylindrical bending of nanofilms is considered in linear and nonlinear formulations. The frequency spectrum of bending vibrations and the parametric resonance are determined. In this case, two surface effects are taken into account. The first one is associated with different elastic properties in the surface layer and in the bulk of the material. It is manifested in stretching and bending of nanometer-thick films. The second effect is due to the difference, caused by bending, between the areas of the convex and concave surfaces subjected to gas pressure. The greater the ratio of the mean pressure to the elastic modulus of the material and the ratio of the length of the film to its thickness, the stronger this effect. The loading conditions of the end surfaces of the film are also important, as well as the strain over the film thickness under the action of the mean pressure. A positive mean pressure leads to an increase in effective stiffness, a decrease in deflection, and an increase in natural frequencies. A negative mean pressure reduces stiffness and natural frequencies. It is shown that, in this case, film bending may occur as a result of the longitudinal in stability. Oscillations of the mean pressure lead to a parametric amplification of bending vibrations. These results cannot be obtained on the basis of the classical equations of bending of plates and films.

Transient responses of laminated anisotropic piezothermoelastic plates and cylindrical shells with interfacial diffusion and sliding in cylindrical bending

With aid of the Stroh-type formalism and the state-space approach, a simple and elegant method is presented to obtain an exact solution for the time-dependent problem of a simply-supported laminated anisotropic piezothermoelastic plate in cylindrical bending with interfacial diffusion and sliding. The Stroh-type formalism is used to obtain the general solution of the thermoelectroelastic field in a certain layer. The state-space equation is then constructed for a laminated plate. The relaxation times and the transient thermoelectroelastic response of the laminated plate can be determined by solving the state-space equation via an analysis of a generalized eigenvalue problem. By using a similar method, we also derive an exact solution for a simply-supported laminated anisotropic piezothermoelastic cylindrical shell with interfacial diffusion and sliding under cylindrical bending.