A three-dimensional numerical model for delaminations, transverse crack or debonding in composite sandwich plates with piezoelectric sensors

An Extended Layerwise/Solid-Element (XLW/SE) method is developed based on the Extended Layerwise method (XLWM) and eight-node solid element method for the static analysis of damaged composite sandwich structures with piezoelectric sensor. In this method, the XLWM is used to model the facesheets and piezoelectric sensors, and the eight-node solid element is used for the lattice. Based on the equilibrium conditions of displacement and internal force of the overlapped joints at the facesheet/sensors and facesheet/lattice interfaces, the general governing equation is established. In the numerical examples, the proposed method is verified by comparing with the 3D elasticity model developed in the commercial finite element software, and composite sandwich plates with delamination and/or transverse crack and/or debonding are analyzed.

Extension of the unsymmetric 8-node hexahedral solid element US-ATFH8 to geometrically nonlinear analysis

Purpose The purpose of this paper is to extend a recent unsymmetric 8-node, 24-DOF hexahedral solid element US-ATFH8 with high distortion tolerance, which uses the analytical solutions of linear elasticity governing equations as the trial functions (analytical trial function) to geometrically nonlinear analysis. Design/methodology/approach Based on the assumption that these analytical trial functions can still properly work in each increment step during the nonlinear analysis, the present work concentrates on the construction of incremental nonlinear formulations of the unsymmetric element US-ATFH8 through two different ways: the general updated Lagrangian (UL) approach and the incremental co-rotational (CR) approach. The key innovation is how to update the stresses containing the linear analytical trial functions. Findings Several numerical examples for 3D structures show that both resulting nonlinear elements, US-ATFH8-UL and US-ATFH8-CR, perform very well, no matter whether regular or distorted coarse mesh is used, and exhibit much better performances than those conventional symmetric nonlinear solid elements. Originality/value The success of the extension of element US-ATFH8 to geometrically nonlinear analysis again shows the merits of the unsymmetric finite element method with analytical trial functions, although these functions are the analytical solutions of linear elasticity governing equations.

Computational modeling of carbon nanofibers reinforced composites: A comparative study

The carbon nanotubes/nanofibers reinforced composites (CNRC) show great mechanical properties. There are several methods to simulate the mechanical properties of composites. Among the modeling techniques, embedded region (ER) shows the possibility for direct multi-scale simulation. A comparative study among beam element embedded model, solid element embedded model, as well as common solid element model is carried out. Programs developed in Matlab are utilized to generate geometric configurations, and finite element models are obtained from MSC.Patran with a script written in the Patran command language (PCL). Besides, a set of parametric studies are performed to investigate the influence of the aspect ratios of nanofibers and load cases on the mechanical properties of CNRC. The result shows that the ER technique is reliable to represent composites though neglecting the localized stress concentration, and beam element embedded models are trustworthy only for nanofibers with a large aspect ratio.

Modeling of Welded Joints in a Pyramidal Truss Sandwich Panel Using Beam and Shell Finite Elements

Pyramidal truss sandwich panels (PTSPs) are widely used in engineering structures and their face sheets and core parts are generally bonded by the welding process. A large number of solid elements are usually required in the finite element (FE) model of a PTSP with welded joints to obtain its accurate modal parameters. Ignoring welded joints of the PTSP can save many degrees of freedom (DOFs), but significantly change its natural frequencies. This study aims to accurately determine modal parameters of a PTSP with welded joints with much fewer DOFs than those of its solid element model and to obtain its operational modal analysis results by avoiding missing its modes. Two novel methods that consider welded joints as equivalent stiffness are proposed to create beam-shell element models of the PTSP. The main step is to match stiffnesses of beam and shell elements of a welded joint with those of its solid elements. Compared with the solid element model of the PTSP, its proposed models provide almost the same levels of accuracy for natural frequencies and mode shapes for the first 20 elastic modes, while reducing DOFs by about 98% for the whole structure and 99% for each welded joint. The first 14 elastic modes of a PTSP specimen that were measured without missing any modes by synchronously capturing its two-faced vibrations through use of a three-dimensional scanning laser vibrometer (SLV) and a mirror experimentally validate its beam-shell element models created by the two proposed methods.

Performance Evaluation of ANCF Tetrahedral Elements in the Analysis of Liquid Sloshing

The performance of the absolute nodal coordinate formulation (ANCF) tetrahedral element in the analysis of liquid sloshing is evaluated in this paper using a total Lagrangian nonincremental solution procedure. In this verification study, the results obtained using the ANCF tetrahedral element are compared with the results of the ANCF solid element which has been previously subjected to numerical verification and experimental validation. The tetrahedral-element model, which allows for arbitrarily large displacements including rotations, can be systematically integrated with computational multibody system (MBS) algorithms that allow for developing complex sloshing/vehicle models. The new fluid formulation allows for systematically increasing the degree of continuity in order to obtain higher degree of smoothness at the element interface, eliminate dependent variables, and reduce the model dimensionality. The effect of the fluid/container interaction is examined using a penalty contact approach. Simple benchmark problems and complex railroad vehicle sloshing scenarios are used to examine the performance of the ANCF tetrahedral element in solving liquid sloshing problems. The simulation results show that, unlike the ANCF solid element, the ANCF tetrahedral element model exhibits nonsmoothness of the free surface. This difference is attributed to the gradient discontinuity at the tetrahedral-element interface, use of different meshing rules for the solid- and tetrahedral-elements, and the interaction between elements. It is shown that applying curvature-continuity conditions leads, in general, to higher degree of smoothness. Nonetheless, a higher degree of continuity does not improve the solution accuracy when using the ANCF tetrahedral elements.

Refined Vehicle-Bridge Interaction Analysis Using Incompatible Solid Finite Element for Evaluating Stresses and Impact Factors

The vehicle-bridge interaction can induce bridge vibration and consequently fatigue, durability deterioration, local damage, and even collapse of bridge structure. In this paper, a solid vehicle-bridge interaction (VBI) analysis method is developed to provide refined analysis on the bridge responses including displacement and local stress under vehicle loads. The incompatible solid finite element (FE) is introduced to model the bridge, where the element shear locking is alleviated by incompatible displacement modes without sacrificing the computational efficiency. Benchmark example shows the incompatible solid element has superior computational efficiency compared to the conventional solid element. By virtue of the mass-spring-damper vehicle model, the interaction between vehicle and bridge is simulated with point-to-point contact assumption and the coupled dynamic equations are solved via nonlinear iteration. A case study on a simply supported T-girder bridge is conducted to validate the developed solid VBI analysis method and then the dynamic impact factor (DIF) of the bridge is evaluated based on the computed stress results and compared to code values. Results show that the solid VBI analysis method yields more accurate time-history bridge responses including displacement and stress under moving vehicles than the grillage method despite higher computational cost. Particularly, it can simulate realistic stress distribution and concentration along any concerned sections as well as in local components, which can provide detail information on the bridge behavior under dynamic loads. On the other hand, the DIF based on the computed stress result generally agrees well with the code values except for heavy vehicles where the stress-based DIF is slightly higher than the value in Chinese code while lower than that of AASHTO, suggesting the value specified by Chinese code may underestimate the DIF of heavy vehicles in certain circumstances to which more attention should be paid.

The Progressive Failure Analysis of Uni-Directional Fibre Reinforced Composite Laminates

ABSTRACTThe three dimensional standard damage model developed by Lavedeze et.al [9, 13] for uni-directional fibre reinforced ply is implemented into the nonlinear solution of NX Nastran within composite solid element to analyze the progressive damage process and ultimate failure of fibre reinforced composite laminates. This ply level meso-damage-constitutive-model takes into account main damage mechanisms including fibre breaking, matrix transverse cracking, and fibre/matrix de-bonding; also considers contributions like plasticity coupling, damage delay effects, and elastic nonlinearity in fibre compression. Dissipated energy and damage status are also introduced to reflect the damage condition on the macrostructural-level. Using the implemented code, simulation is carried out on the uniaxial tension of a [±45]2s laminate with IM6/914 material, wherein the predicted ply shear rupture stress matches the experimental results very well and better than the theoretical predictions in literature. Moreover, a [-45/0/45/90] holed laminate loaded in tension is simulated to show the complex behavior of subcritical damage evolution and failure process in the composite structure. The composite solid element with damage model supported in NX Nastran is shown to be a reliable tool to analyze the progressive failure of uni-directional fibre reinforced composite laminates.