Finite Element Analysis of Mechanical Properties of 3D Four-directional Rectangular Braided Composites—Part 2: Validation of the 3D Finite Element Model

In the first part of the work, we have established a new parameterized three-dimensional (3D) finite element model (FEM) which precisely simulated the spatial configuration of the braiding yarns and considered the cross-section deformation as well as the surface contact relationship between the yarns. This paper presents a prediction of the effective elastic properties and the meso-scale mechanical response of 3D braided composites to verify the validation of the FEM. The effects of the braiding parameters on the mechanical properties are investigated in detail. By analyzing the deformation and stress nephogram of the model, a reasonable overall stress field is provided and the results well support the strength prediction. The results indicate it is convenient to predict all the elastic constants of 3D braided composites with different parameters simultaneously using the FEM. Moreover, the FEM can successfully predict the meso-scale mechanical response of 3D braided composites containing periodical structures.     

Hashin–Shtrikman Based FE Analysis of the Elastic Behaviour of Finite Random Composite Bodies

This paper demonstrates the effect of non-local interactions in an edge-cracked body made of composite material, in the case that the scale of the body is not large in comparison with the scale of the microstructure, as can occur, for example, in laboratory testing of concrete specimens. Not only are there significant boundary layers in the vicinity of all of the specimen boundaries, but the small size of the body permits their interaction, to alter the value of the mean field globally relative to the value that would be predicted by the use of “ordinary” homogenization, under conditions of “displacement control”. Such an effect would be present even for an uncracked body but the presence of the crack induces strong gradients in the mean field which significantly enhance this effect. The mean strain component tends to become concentrated around the line ahead of the crack in comparison with the prediction of homogenization; there is, in addition, an enhancement of the stress and strain concentrations in the harder phase. The method of analysis is a finite-element implementation of a variational formulation related to the Hashin–Shtrikman variational principle, developed in the context of non-local effective response by the present authors. The present calculations are considered to be more accurate than some previously reported (Luciano and Willis, Journal of the Mechanics and Physics of Solids 53, 1505–1522, 2005) and the conclusions differ correspondingly.     

Fitness Considerations for Contemporary Composite Materials: (Who’s Afraid of the Composite Micro-Crack?)

Avoiding the catastrophic failure of a large structure demands the material’s microstructure be designed in such as a way as to render any crack present innocuous thereby raising the integrity of that structure. Structural integrity of a composite material embraces contributions from: materials science and engineering; processing science; design and fabrication technology. It combines a number of interacting factors: the criticality of the application; the accessibility for and ability to inspect vital parts and components; the intended use including load spectrum and time; the consequences of impact, fatigue, temperature and hostile environment; the nature of inherent flaws; the constituent properties of the material system utilized; and it takes into account human factors.     

Renewed Jeeves’s Mechanical Inversion of the Material Constant of Composite Glass Box Beam via the Cumulative Bayesian Theory*

Strength of Materials - For composite glass box beam, the cumulative Bayesian estimative error function of the material constant of the structure was deduced with the Bayesian theory. Mechanical...     

Building Block Approach’ for Structural Analysis of Thermoplastic Composite Components for Automotive Applications

Advanced thermoplastic prepreg composite materials stand out with regard to their ability to allow complex designs with high specific strength and stiffness. This makes them an excellent choice for lightweight automotive components to reduce mass and increase fuel efficiency, while maintaining the functionality of traditional thermosetting prepreg (and mechanical characteristics) and with a production cycle time and recyclability suited to mass production manufacturing. Currently, the aerospace and automotive sectors struggle to carry out accurate Finite Elements (FE) component analyses and in some cases are unable to validate the obtained results. In this study, structural Finite Elements Analysis (FEA) has been done on a thermoplastic fiber reinforced component designed and manufactured through an integrated injection molding process, which consists in thermoforming the prepreg laminate and overmolding the other parts. This process is usually referred to as hybrid molding, and has the provision to reinforce the zones subjected to additional stresses with thermoformed themoplastic prepreg as required and overmolded with a shortfiber thermoplastic resin in single process. This paper aims to establish an accurate predictive model on a rational basis and an innovative methodology for the structural analysis of thermoplastic composite components by comparison with the experimental tests results.     

Failure Analysis and Finite Element Simulation of Above Ground Oil–Gas Pipeline Impacted by Rockfall

Pipeline is the most important transmission way of oil and gas. Rockfall impact is one of the factors that result in above ground oil–gas pipelines accidents. Deformation of oil–gas pipeline caused by rockfall impacts were investigated using finite element method. Pipeline deformation caused by spherical and cube rockfalls were discussed under radial impact, inclined impact, and eccentric impact. The results show that crater depth of spherical rockfall impact is bigger than the cube rockfall with the same volume. The smaller curvature radius of rockfall’s contact zone has a greater harm to oil–gas pipeline. Angle part impact of irregular rockfall is very harmful for oil–gas pipeline. Under inclined impact, the maximum plastic strain of spherical rockfall impact crater appears when incidence angle α is 45°. Pipeline is prone to rupture when α is small under cube rockfall impact. The plastic strain distribution of the impact crater is more uneven with the increasing of the incidence angle. Plastic strain zone of pipeline decreases with the increasing of eccentricity k under eccentric impact.     

Mechanical Analysis and Performance Optimization for the Lunar Rover’s Vane-Telescopic Walking Wheel

It is well-known that optimizing the wheel system of lunar rovers is essential. However, this is a difficult task due to the complex terrain of the moon and limited resources onboard lunar rovers. In this study, an experimental prototype was set up to analyze the existing mechanical design of a lunar rover and improve its performance. First, a new vane-telescopic walking wheel was proposed for the lunar rover with a positive and negative quadrangle suspension, considering the complex terrain of the moon. Next, the performance was optimized under the limitations of preserving the slope passage and minimizing power consumption. This was achieved via analysis of the wheel force during movement. Finally, the effectiveness of the proposed method was demonstrated by several simulation experiments. The newly designed wheel can protrude on demand and reduce energy consumption; it can be used as a reference for lunar rover development engineering in China.     

Unified Analysis of the Hybrid Form of Mixed Finite Elements for Second Order Elliptic Problems

In this paper we systematically analyze the hybrid form of two mixed methods, the Raviart= Thomas and Brezzi-Douglas-Marini methods, for second order elliptic equations. We directly show that the hybrid form of the mixed methods is stable with respect to the usual Sobolev norms by means of the abstract stability theory for mixed methods, and thus error estimates in these norms can be obtained in a simple manner. We also introduce a new postprocessing method for improving the scalar variable as an alternative to the usual postprocessing methods.     

Development of methods and instruments of the Russian service for determination of the Earth’s orbital parameters

The state and future outlook of research to determine the Earths orbital parameters, i.e., Universal Time and the coordinates of the pole, carried out by the State Time and Frequency Service and in calculations of the Earths orbital parameters are described.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 24–27, January, 2005.     

Analysis of the division of labor in China’s high-quality life sciences research

Scientometrics - International cooperation has always been a popular subject in academic research. Recently, with the rise of “Author Contributions,” quantitative research using the...     

Research on Pantograph and Overhead Contact System′s Simulation of High Speed Railway and Comparison of Three Calculation Methods by Finite Element Method

This study relies on the project about Jining to Tongliao railway electrification reconstruction project. The dynamic simulation model of the pantograph-OCS(overhead contact system) suitable for Jitong project is designed, according to the corresponding numerical calculation method and workflow. Firstly, We establish the pantograph and catenary′s BIM models, and the parameters related to the dynamic simulation of the pantograph system are attached to the BIM model. Then, the BIM model is transformed into a mechanical analysis model, which is input into the dynamic simulation software of pantograph-OCS. The rationality of the design scheme of the pantograph system is verified through simulation.     

Simulation of the motion and destruction of bolides in the Earth’s atmosphere

Issues of high-temperature interaction of bolides with the Earth’s atmosphere are considered. As an example, the motion and destruction of the Chelyabinsk (Chebarkul) meteorite are studied. The calculation results are compared with data of observations.     

Hill’s lemma for the average-field theory of Cosserat continuum

There are two typical definitions for the macroscopic average couple stress tensor in the literature, which brings confusion and difficulty to the establishment of Hill’s lemma for heterogeneous Cosserat continuum. Besides, some boundary conditions on the representative volume element (RVE) commonly used in the homogenization method cannot be properly determined by the existing version of Hill’s lemma of Cosserat continuum. To deal with these issues, Hill’s lemma for micro-macro homogenization modeling of Cosserat continuum is further investigated in the frame of the average-field theory in this paper. An intermediate form of Hill’s lemma is constructed in which the micromechanically based definition of the average couple stress tensor is not specified. By substituting two existing definitions of the average couple stress tensor into the presented intermediate form, not only the previous version of Hill’s lemma is derived, but also a new version of Hill’s lemma is obtained. According to the new version of Hill’s lemma, more versatile RVE boundary conditions in the strong form can be properly given, and the periodic RVE boundary conditions in the weak form are also constructed.     

Effect of Hot Pressing Conditions on the Microstructure and Optical Properties of MgO–Y2O3 Composite Ceramics

Inorganic Materials - We have studied the effect of hot pressing conditions on the microstructure and optical characteristics of Y2O3–MgO composite ceramics. The hot pressing conditions have...     

Mechanical Characterisation of Interface for Steel/Polymer Composite Using Pull-out Test： Shear-Lag and Frictional Analysis

Fibre-matrix interface is known to have contribution to the mechanical performance of fibre-reinforced composite by its potential for load transfer between the fibre and the matrix. Such load transfer is of great importance in dentistry when a post is used for fixing a ceramic crown on the tooth. In this study, a pull-out test was carried out to analyse the interfacial properties of a steel fibre embedded in a polyester and epoxy matrices. It was found that the fibre-matrix interface is debonded on the whole embedded length when the fibre stress reached the debonding stress. Then, the fibre stress fell down to the initial extraction stress required to pulling out the debonded fibre from the matrix. Both debonding stress and initial extraction stress initiated a linear increase with the implantation length after the debonding stress reached horizontal asymptotes. To analyse the fibre-matrix load transfer before debonding, an analytical shear-lag model was adopted to in this test conditions. Fitting the experimental results with the analytical model provided the interfacial shear strength. By considering the Coulomb friction at the fibre-matrix interface during the fibre extraction process, an analytical model which considers Poisson＇s effects on both fibre and matrix, was developed. In this model, knowledge of the initial extraction stress of the fibre provides the residual normal stress at the fibre-matrix interface.