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A physical model to simulate the mesoscale morphology evolution of carbon fiber is established to characterize the thermal mechanical erosion behavior of C/C composite in high temperature and high pressure gas flow. The process of mechanical erosion of single carbon fiber is calculated by the DSMC method. The fracture criteria and mesoscale mechanical erosion model of carbon fiber are developed by theory of mechanics of materials. Finally, an engineering method for prediction of mesoscale mechanical erosion is formulated, and the predictions agree well with the experiment results. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper deals with such a kind of surface crack problem with a same depth (called a liked-plane crack problem for short). Based on the previous investigations on an internal rectangular crack and a surface rectangular crack in an infinite solid in tension and the hybrid displacement discontinuity method, a numerical approach for the liked-plane crack problem is presented. Numerical examples are given to illustrate the numerical approach is simple, yet accurate for calculating the stress intensity factors (SIFs) of the liked-plane crack problem. Specifically, SIFs of a pair of cracks emanating from a surface square hole in an infinite body in tension are investigated in detail. [ABSTRACT FROM AUTHOR]

The present work reported the intrinsic mechanical behavior of vanadium dioxide (VO2) thin film deposited on a SiO2 substrate using a combination of nanoindentation tests and a theoretical model. The effect of phase transition on mechanical parameters was studied by adjusting the test temperature. A new model that can simultaneously extract the elastic modulus and hardness was derived by introducing a dimensional analysis. The results showed that the thin film exhibits a hardness of 9.43 GPa and a Young's modulus of about 138.5 GPa at room temperature, compared with the values of 5.71 GPa and 126.9 GPa at a high temperature, respectively. It can be seen that the intrinsic mechanical parameters decrease to a certain extent after a phase transition. Finally, the numerical simulation results were consistent with those of the experiments, which verified the effectiveness of the new method. In addition, this study also provided useful guidance for mechanical tests on other ultra-thin films. [ABSTRACT FROM AUTHOR]

The buckling, de-lamination, and cracking of the thin film/substrate system caused by thermal stress is the main obstacle for functional failure. Moreover, the thermal stress of vanadium dioxide (VO2) thin film may be more complicated due to the stress re-distribution caused by phase transition. Therefore, the thermal stress of VO2 thin films deposited on four substrates with different materials (fused silica, silicon slice, sapphire, and glass) has been studied by finite element method in the present work. The influences of external temperature, substrate, and interlayer on thermal stress were analyzed. It was found that the substrates can greatly affect the thermal stresses, which were mainly caused by the mismatch of coefficient of thermal expansion (CTE). The thermal stress had a linear relationship with the external temperature, but this tendency would be redistributed or even change direction when phase transition occurred. The simulated results were in tandem with the analytical method. Meanwhile, the radial stress and shear stress distribution under the influence of phase transition were calculated. In addition, the reduction of thermal stress and shear stress showed that the appropriate interlayer can enhance the adhesive strength effectively. [ABSTRACT FROM AUTHOR]

By using a hybrid displacement discontinuity method and a generalization of Bueckner’s principle, the interactions of two collinear square-hole cracks in an infinite plate in tension are investigated in this paper. Numerical examples are included to illustrate that the numerical approach is very effective for analyzing multiple-hole cracks in an infinite plate in tension. Many numerical results are given and discussed. It is found that a square hole has a shielding effect on crack(s) emanating from the hole. The finding perhaps has an important meaning in engineering. [ABSTRACT FROM AUTHOR]

Abstract: By using a hybrid displacement discontinuity method, the interactions of two collinear circular hole cracks in infinite plate subjected to internal pressure are investigated in this paper. Numerical examples are included to illustrate that the numerical approach is very simple and effective for calculating the stress intensity factors (SIFs) of crack problems. In particular, the interaction problem of two collinear circular hole cracks is investigated in detail. Many numerical results are given and discussed. It is found that a circular hole has a shielding effect on the SIFs of crack(s) emanating from the hole. The finding perhaps has an important meaning in engineering. [Copyright &y& Elsevier]

[Display omitted] • We demonstrate the use of polymer additive to promote deposition of PANI with smooth and dense morphology. • The mechanism of polymer additive regulating the growth morphology of PANI film has been deeply analyzed. • The infrared electrochromic device exhibits wonderful durability and can achieve large emissivity modulation. • The thermal management capability of the device was evaluated by the transient thermal field analysis. Infrared electrochromic device based on polyaniline (PANI) possesses the ability to regulate infrared radiation, which has a great application prospect in the field of satellite intelligent thermal control. However, it is still challenging to efficiently fabricate uniform and dense PANI functional layer with excellent infrared electrochromic properties. Here, we demonstrate the use of polymer additive to promote deposition of PANI with smooth and dense morphology by inducing uniform electrochemical deposition rate on the electrode surface and inhibiting the growth of PANI in three-dimensional direction through adsorption mechanism. By adding a low concentration of poly(styrene sulfonate) (PSS) to the electrodeposition solution, the PANI film with uniform and compact micromorphology was prepared with excellent infrared electrochromic property, which can realize the modulation of emittance more than 0.4 and 0.45 in the range of 8 ∼ 14 μm and 2.5 ∼ 25 μm, respectively. Furthermore, the infrared electrochromic device that employ the optimized PANI functional film and adsorbing ionic liquid porous gel electrolyte was constructed. Through high and low temperature cycle test (1000 cycles) and vacuum environment test, the device exhibits wonderful durability and can achieve large emissivity modulation in the wavelength range of 2.5 μm ∼ 25 μm (Δε = 0.38). Meanwhile, the transient thermal analysis of the heat dissipating plate attached with the infrared electrochromic device exhibits that the device has an excellent potential for the purposes of efficient thermal management of the satellite. [ABSTRACT FROM AUTHOR]

Composite pyramidal-truss core sandwich panels, in which the lattice core is strengthened by reinforced frames between dispersive nodes, were manufactured via water-jet cutting and interlocking assembly. The coefficients of thermal expansion and outgassing (mass loss) ratios of the composite laminates were determined. Subsequently, the effect of vacuum thermal cycling on the compression and shear performance of the composite sandwich panels with pyramidal-truss cores was studied using theoretical and experimental methods. In particular, the out-of-plane compression stiffness and strength, as well as the shear stiffness and strength of the structures subjected to vacuum thermal cycling, were predicted using theoretical equations. The compression and shear performance improved initially and then deteriorated with an increase in the vacuum thermal cycling-time. The observed failure modes depended on the number of vacuum thermal cycles. In addition, the catastrophic response of the composite sandwich panels with pyramidal-truss cores was investigated, and their possible failure modes (including the crushing and localized buckling of composite struts) were complemented with results of analytical modeling. The truss cores collapsed mainly due to crushing and localized-buckling processes, caused by matrix outgassing and debonding of the interface between the carbon fibers and epoxy resin, after prolonged thermal cycling. [ABSTRACT FROM AUTHOR]

• The coupling element-based peridynamics and finite element method are developed. • The coupling model is proposed to solve the elastic-plastic deformation and failure problems. • A reducing elements scheme for EBPD is proposed to improve computational efficiency. • The coupling model can eliminate the surface effect in EBPD. An element-based peridynamics (EBPD) and finite element method (FEM) coupling model is proposed to solve the elastic-plastic deformation and failure problems. The FEM and EBPD are used in the boundary region and the interior elastic-plastic crack growth region, respectively. A scheme is proposed to improve the computation efficiency of EBPD by deleting the bad quality elements in the horizon of each PD node. EBPD has the non-local stress and non-local strain concepts to conveniently describe the yield stress and equivalent plastic strain, and does not have instability problems. The elastic-plastic computation framework is used in the coupling model solved by the incremental method to calculate the elastic-plastic deformation and failure process. The coupling model can calculate the elastic-plastic problem with the linear and nonlinear hardening laws. A 2D elastic-plastic crack propagation process is also simulated by the proposed coupling model. [Display omitted] [ABSTRACT FROM AUTHOR]

An element-based peridynamic (EBPD) model is developed to represent the Euler-Bernoulli beam. The force density is described by the two-node beam elements with three displacement and three rotation freedom degrees. The dynamic and static problems of the EBPD beam model are derived from Lagrangian formalism and variation principle, respectively. The Newmark and Gauss elimination methods are used to solve dynamic and static problems. The damage criterion expressed by the critical strain energy density is extended to the EBPD beam. Moreover, two different schemes of boundary conditions are discussed. Finally, various benchmark cases subjected to different loading and boundary conditions are used to validate the proposed EBPD beam model. • A 3D element-based peridynamic (EBPD) Euler-Bernoulli beam model is proposed. • A new scheme for applying boundary conditions in EBPD model for beam structures is proposed. • The damage criterion is expressed by the critical strain energy density. [ABSTRACT FROM AUTHOR]

A new method has been proposed and verified to measure the viscoelastic properties of polymers by nanoindentation tests. With the mechanical response of load–displacement curves at different loading rates, the parameters of creep compliance and relaxation modulus are calculated through the viscoelastic contact model. Dynamic thermomechanical analysis (DMA) tests are conducted to compare the results by the proposed technique. The results show that the correlation coefficients between DMA tests and the new method are above 0.9 in the entire range, which verified the feasibility of the method. The loading curves fitted by the model are identical to the experimental curves within the discrete points and so it shows that this technique is more suitable for general linear viscoelastic materials. Numerical creep tests are carried out to examine the effectiveness of the proposed method by input the Prony series calculated by the three-element Maxwell model and the viscoelastic contact model. The good agreement shows that the proposed technique can be applied in practice. • A new method to measure the viscoelastic properties by nanoindentation is proposed. • Parameters can be calculated directly by the condition of different loading rates. • The correlation coefficients are all above 0.9 compared with the traditional test. • The method is suitable for linear viscoelastic materials. • Results of creep simulation by input Prony series coincide with the experimental. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO 2 ) thin films of different thicknesses were prepared by regulating the deposition time (2, 2.5, 3, and 3.5 h). The impact of deposition time on the microstructure, surface morphology, and cross-section morphology was investigated. The results showed that the grain size increased with the film thickness. Meanwhile, the influence of film thickness on the residual stress was evaluated by X-ray diffraction. The phenomenon of "compressive-to-tensile stress transition" was illustrated as the thickness increased. The change of dominant mechanism for residual stress was used for explaining this situation. First, the composition of residual stress indicates that growth stress play a key role. Then, the effect of "atomic shot peening" can be used to explain the compressive stress. Lastly, the increased grain size, lower grain boundary density, and "tight effect" in the progress of film growth cause tensile stress.