Static and free vibration analysis of laminated glass beam on viscoelastic supports

Static behavior and free vibration analysis of laminated glass beam on viscoelastic supports are performed. For the static case, an analytical way is developed for analyzing and optimization of laminated glass beam with general restraints at the boundaries. In the case of free linear vibrations, the modal properties of the glass are determined using a finite element method which is a powerful tool in the design of support damping treatment of a sandwich glass for passive vibration control.     

Mode III fracture behavior of laminated composite with edge crack in torsion

A three-dimensional (3-D) finite element analysis was performed on a [90,(+45/−45)_n,(−45/+45)_n,90]_s class of laminated composites under the edge crack torsion (ECT) test configuration. Finite element delamination models were established and formulas for calculating the Mode III fracture toughness from 3-D finite element models were developed. The relations between the interlaminar fracture behavior and various configuration parameters were investigated and the effects of point loads, ends, geometry, Mode II interference, and friction were evaluated. Results showed that with proper selection of ECT specimen configuration and layup, the delamination could grow in pure Mode III in the middle region of the specimen. Specimen end effect played an important role in the ECT test. A Mode II component occurred in the end regions but it did not interfere significantly with the Mode III delamination state. Specimen dimension ratio, layup, and crack length exhibited significant effect on the interlaminar fracture behavior and the calculated strain energy release rates. However, friction between crackfaces was found to have negligible effect on the interlaminar properties.     

Numerical analysis of convection-diffusion with chemical reaction by combined finite and boundary element methods

A numerical method is presented to analyse a steady convection-diffusion problem with a first-order chemical reaction defined on an infinite region. The present method is based on the combined finite element and boundary element methods. For one- and two-dimensional examples in an infinite region the numerical results by the present method are in excellent agreement with the exact solutions. As a practical application, the simulation of the concentration distribution of the chemical oxygen demand at Kojima Bay is carried out.     

New type of dual bem and Green's-function-library strategy for fracture analysis in complex structures

A new type of dual boundary integral equations (DBIE) is presented first, through which, a smaller system of equations needs to be solved in fracture analysis. Then a non-conforming crack tip element in two-dimensional problems is proposed. The exact formula for the hypersingular integral over the non-conforming crack tip element is given next. By virtue of Green's-function-library strategy, a series of stress intensity factors (SIF) of different crack orientations, locations and/or sizes in a complicated structure can be obtained easily and efficiently. Finally, several examples of fracture analysis in two dimensions are given to demonstrate the accuracy and efficiency of the method proposed. Partially supported by the Aeronautical Science Foundation of China (No. 99C53026)     

A semi-analytical approach for the non-linear large deflection analysis of laminated rectangular plates under general out-of-plane loading

A semi-analytical approach for the geometrically non-linear analysis of rectangular laminated plates with general inplane and out-of-plane boundary conditions under a general distribution of out-of-plane loads is developed. The analysis is based on the elastic thin plate theory with geometrically non-linear von Kármán strains. The solution of the non-linear partial differential equations is reduced to an iterative sequential solution of non-linear ordinary differential equations using the multi-term extended Kantorovich method. The efficiency, accuracy, and convergence of the proposed method are examined through a comparison with other semi-analytical methods and with finite element analyses. The capabilities of the approach and its applicability to the non-linear large deflection analysis of plate structures are demonstrated through various numerical examples. Emphasis is placed on combinations of lamination, boundary, and loading conditions that cannot be analyzed using alternative semi-analytical methods.     

Combining X-ray microtomography with computer simulation for analysis of granular and porous materials

The use of X-ray microtomographic (XMT) methods in analysing particulate systems has expanded rapidly in recent years with the availability of affordable desk-top apparatus. This review presents a summary of the major applications in which computer simulations are explicitly coupled with XMT in the area of granular and porous materials. We envisage two main ways of establishing the coupling between both techniques, based on the transference or exchange of information by using physical or geometrical paramet...     

Cohesive zone laws for void growth — II. Numerical field projection of elasto-plastic fracture processes with vapor pressure

Modeling ductile fracture processes using Gurson-type cell elements has achieved considerable success in recent years. However, incorporating the full mechanisms of void growth and coalescence in cohesive zone laws for ductile fracture still remains an open challenge. In this work, a planar field projection method, combined with equilibrium field regularization, is used to extract crack-tip cohesive zone laws of void growth in an elastic-plastic solid. To this end, a single row of void-containing cell elements is deployed directly ahead of a crack in an elastic-plastic medium subjected to a remote K-field loading; the macroscopic behavior of each cell element is governed by the Gurson porous material relation, extended to incorporate vapor pressure effects. A thin elastic strip surrounding this fracture process zone is introduced, from which the cohesive zone variables can be extracted via the planar field projection method. We show that the material's initial porosity induces a highly convex traction-separation relationship — the cohesive traction reaches the peak almost instantaneously and decreases gradually with void growth, before succumbing to rapid softening during coalescence. The profile of this numerically extracted cohesive zone law is consistent with experimentally determined cohesive zone law in Part I for multiple micro-crazing in HIPS. In the presence of vapor pressure, both the cohesive traction and energy are dramatically lowered; the shape of the cohesive zone law, however, remains highly convex, which suggests that diffusive damage is still the governing failure mechanism.     

A combined programming and iteration algorithm for finite element analysis of three-dimensional contact problems

Comparing with two-dimensional contact problems, three-dimensional frictional contact problems are more difficult to deal with, because of the unknown slip direction of the tangential force and enormous computing time. In order to overcome these difficulties, a combined PQP (Parametric Quadratic Programming) and iteration method is derived in this paper. The iteration algorithm, which alleviates the difficulty of unknown slip direction, is used along with the PQP method to cut down computing costs. Numerical example is given to demonstrate the validity of the present algorithm. The project supported by the Machinary and Electronics Ministry of China     

A study of the hybrid element methods for stress analysis

A new functional which forms the basis of an improved hybrid element formulation is proposed. The variables for the functional include stresses, strains and displacements, and the displacements and stresses are further decomposed into two parts respectively. The proposed new formulation appears to be particularly suitable for improving conforming models.The relationship between the new hybrid elements and the conventional displacement elements are also explored in this paper.     

Multi-level modeling of woven glass/epoxy composite for multilayer printed circuit board applications

The objective of this paper is to develop a hybrid homogenization method to predict the elastic properties of a common woven glass/epoxy composite substrate for multilayer circuit board applications. Comprehensive high resolution 3D finite element (FE) models of a quarter of the repeated unit cell (RUC) for the woven glass/epoxy composite were developed based on different micromechanical schemes. . Specifically, four different micromechanics schemes were investigated: self-consistent, Mori–Tanaka, three-phase approach and composite cylinder assemblage (CCA). The element based strain concentration matrices were determined and used to obtain the homogenized woven glass/epoxy composite properties via a specially developed MATLAB code. Attention was further devoted to the predictions of the homogenized elastic moduli of the multilayer printed circuit board (PCB). The results from our simulations, based on Mori–Tanaka and CCA, are in good agreement with existing experimental results, indicating that the newly proposed homogenization scheme can be used as a design tool to predict the overall properties of woven composite materials typically used in multilayer PCB applications.     

Simulation of size effects by a phase field model for fracture

In phase field fracture models the value of the order parameter distinguishes between broken and undamaged material. At crack faces the order parameter interpolates smoothly between these two states of the material, which can be regarded as phases. The crack evolution follows implicitly from the time integration of an evolution equation of the order parameter, which is coupled to the mechanical field equations. Among other phenomena phase field fracture models are able to reproduce crack nucleation in initially sound materials. For a 1D setting it has been shown that crack nucleation is triggered by the loss of stability of the unfractured, spatially homogeneous solution, and that the stability point depends on the size of the considered structure. This work numerically investigates to which extend size effects are reproduced by the 2D phase field model. Exemplarily, a finite element study of the hole size effect is performed and the simulation results are compared to experimental data.     

Application of scaled boundary finite element method in static and dynamic fracture problems

The scaled boundary finite element method (SBFEM) is a recently developed numerical method combining advantages of both finite element methods (FEM) and boundary element methods (BEM) and with its own special features as well. One of the most prominent advantages is its capability of calculating stress intensity factors (SIFs) directly from the stress solutions whose singularities at crack tips are analytically represented. This advantage is taken in this study to model static and dynamic fracture problems. For static problems, a remeshing algorithm as simple as used in the BEM is developed while retaining the generality and flexibility of the FEM. Fully-automatic modelling of the mixed-mode crack propagation is then realised by combining the remeshing algorithm with a propagation criterion. For dynamic fracture problems, a newly developed series-increasing solution to the SBFEM governing equations in the frequency domain is applied to calculate dynamic SIFs. Three plane problems are modelled. The numerical results show that the SBFEM can accurately predict static and dynamic SIFs, cracking paths and load-displacement curves, using only a fraction of degrees of freedom generally needed by the traditional finite element methods.The project supported by the National Natural Science Foundation of China (50579081) and the Australian Research Council (DP0452681)The English text was polished by Keren Wang.     

时域自适应算法求解弹性地基薄板的动力问题

为更精确地求解弹性地基薄板的动力响应,发展了一种分段时域自适应算法,通过变量在离散时段内的展开,将时空耦合的初边值问题转化为一系列递推的基于有限元(FEM)的空间问题求解,通过自适应计算保持稳定的计算精度。数值算例表明:本文解与解析解相比最大相对误差不超过3.59%;当步长较大时四阶Runge-Kutta法和Newmark法均失效,本文所提算法仍可得到满意的计算结果。     

Discrete element method analysis of single wheel performance for a small lunar rover on sloped terrain

The purpose of this study is to analyze the performance of a lugged wheel for a lunar micro rover on sloped terrain by a 2D discrete element method (DEM), which was initially developed for horizontal terrain. To confirm the applicability of DEM for sloped terrain locomotion, the relationships of slope angle with slip, wheel sinkage and wheel torque obtained by DEM, were compared with experimental results measured using a slope test bed consisting of a soil bin filled with lunar regolith simulant. Among the lug parameters investigated, a lugged wheel with rim diameter of 250 mm, width of 100 mm, lug height of 10 mm, lug thickness of 5 mm, and total lug number of 18 was found, on average, to perform excellently in terms of metrics, such as slope angle for 20% slip, power number for self-propelled point, power number for 15-degree slope and power number for 20% slip. The estimation of wheel performance over sloped lunar terrain showed an increase in wheel slip, and the possibility exists that the selected lugged wheel will not be able to move up a slope steeper than 20°.     

Interfacial stress analysis and prediction of debonding for a thin plate bonded to a curved substrate

This paper focuses on the analytical and numerical modeling of the interface between a rigid substrate with simple constant curvature and a thin bonded plate. The interfacial behavior is modeled by independent cohesive laws in the normal and tangential directions, coupled with a mixed-mode fracture criterion. The newly developed analytical model determines the interfacial shear and normal stress distributions as functions of the substrate curvature, during the various behavioral stages of the interface prior to the initiation of debonding. The model is also able to predict the debonding load and the effective bond length. In the numerical model the interface is modeled by zero-thickness node-to-segment contact elements, in which both the geometrical relationships between the nodes of the discretized problem and the interface constitutive laws are suitably defined. Numerical results and comparisons between the predictions of the two models are presented.     

MODEL AND METHOD OF WELL TEST ANALYSIS FOR WELLS WITH VERTICAL FRACTURE

NomenclatureB———volumecoefficientofformationfluid,dimensionless;C———wellborestoragecoefficient,m3 MPa;Cft ———comprehensivecompressioncoefficientoffluidinfracture ,1 MPa;Ct ———comprehensivecompressioncoefficientofformationfluid,1 MPa ;h———heightofformation ,m ;K———formationpermeability ,μm2 ;Kf ———fracturepermeability ,μm2 ;KfWf ———fractureconductivity ,μm2 ·cm ;Lf ———halfoffracturelength,m ;N———thetotalnumberofselectedtimepoint,dimensionless;P———for…     

Parametric analysis of lugged wheel performance for a lunar microrover by means of DEM

The purpose of this study was to develop a numerical tool to simulate the performance of lugged wheels designed for a lunar microrover. The performance was analyzed using a Discrete Element Method (DEM) whose accuracy was validated for interactions between lugged wheels and soil. DEM analysis indicated that, on flat horizontal lunar surfaces, wheels with 18 10-mm-high lugs would provide less net traction than would wheels with 36 5-mm-high lugs.     

Coupled thermal/mechanical analysis for the fracture of functionally graded materials under transient thermal loading

A comprehensive treatment of fracture of functionally graded materials (FGMs) is provided. It is assumed that the material properties depend only on the coordinate perpendicular to the crack surfaces and vary continuously along the crack faces. By using a laminated composite plate model to simulate the material non-homogeneity, an algorithm for solving the system based on Laplace transform and Fourier transform techniques is presented. Unlike earlier studies that considered certain assumed property distributions and a single crack problem, the current investigation studies multiple crack problem in the FGMs with arbitrarily varying material properties. Transient thermal stresses are presented. Project supported by the National Natural Science Foundation of China (Nos 10102004 and 19902003).     

复合材料结构力学分析CAE软件现状

复合材料结构分析软件是用以分析、设计复合材料结构的重要工具,常用的复合材料结构分析软件包括基于CAD软件发展而来的复合材料分析工具、通用有限元软件自带复合材料分析工具和以Digimat等为代表的专业化复合材料结构分析软件。本文对常用的复合材料分析软件进行了综述,介绍其主要功能,从学术、应用等多方面探讨相关产品的优点及不足;论述了专业化复合材料结构分析软件的特点及功能;分析了复合材料结构分析软件的现状和发展趋势;探讨了复合材料结构力学分析CAE软件在国产化方面所需进一步解决的问题。     

Symmetric-Galerkin boundary element analysis of the dynamic T-stress for the interaction of a crack with an auxetic inclusion

In this work, the symmetric-Galerkin boundary element method (SGBEM) for 2-D elastodynamics in the Laplace-space frequency domain (Laplace domain) is employed to study the dynamic stress intensity factors (DSIFs) and the dynamic T-stress (DTS) during the interaction between a crack and an auxetic inclusion under impact loading conditions. It is found that, while the auxeticity has virtually no effect on the DSIFs, its influence on the DTS is noticeable. This finding is particularly important as it implies the imperative need of fracture criteria based on both the DSIFs and DTS for predicting crack growth in composite materials with auxetic phases.