Global-local multi-field models for the stress analysis of laminated structures.

The present paper presents an innovative numerical model for predicting stress concentrations in composite materials in a multi-physics context. The numerical approach is based on the Carrera unified formulation, a numerical tool able to handle any kinematic model using a unified and compact notation. A general formulation for one-, two- and three-dimensional higher-order models has been presented. Equivalent single-layer and layer-wise models have been considered since they are the most effective in the analysis of composite materials. A hygro-thermo-elastic multi-physics formulation has been considered. The model has been used to investigate stress concentrations considering different configurations. Mechanical, thermal and hygroscopic loads have been considered. An innovative global-local analysis technique has been used to reduce the computational cost preserving the accuracy of the solution. This article is part of the theme issue 'Ageing and durability of composite materials'.

A Variable Kinematic Multifield Model for the Lamb Wave Propagation Analysis in Smart Panels.

The present paper assessed the use of variable kinematic two-dimensional elements in the dynamic analysis of Lamb waves propagation in an isotropic plate with piezo-patches. The multi-field finite element model used in this work was based on the Carrera Unified Formulation which offers a versatile application enabling the model to apply the desired order theory. The used variable kinematic model allowed for the kinematic model to vary in space, thereby providing the possibility to implement a classical plate model in collaboration with a refined kinematic model in selected areas where higher order kinematics are needed. The propagation of the symmetric (S0) and the antisymmetric (A0) fundamental lamb waves in an isotropic strip was considered in both mechanical and piezo-elastic plate models. The convergence of the models was discussed for different kinematics approaches, under different mesh refinement, and under different time steps. The results were compared to the exact solution proposed in the literature in order to assess and further determine the effects of the different parameters used when dynamically modeling a Lamb wave propagating in such material. It was shown that the higher order kinematic models delivered a higher accuracy of the propagating wave evaluated using the corresponding Time Of Flight (TOF). Upon using the appropriate mesh refinement of 2000 elements and sufficient time steps of 4000 steps, the error between the TOF obtained analytically and numerically using a high order kinematics was found to be less than 1% for both types of fundamental Lamb waves S0 and A0. Node-dependent kinematics models were also exploited in wave propagation to decrease the computational cost and to study their effect on the accuracy of the obtained results. The obtained results show, in both the mechanical and the piezo-electric models, that a reduction in the computational cost of up to 50% can be easily attained using such models while maintaining an error inferior to 1%.

Shear horizontal waves in a multiferroic composite semiconductor structure.

Piezoelectric semiconductors (PSs) possess the physical properties of piezoelectric and semiconductor simultaneously. When a piezomagnetic (PM) material is added to the PS, the composite structures will exhibit the comprehensive mageto-electro-semiconductive (MES) coupling effects. In this paper, the propagation characteristics of shear horizontal (SH) waves in a multiferroic composite semiconductor structure are investigated, where a n-type PS thin plate is perfectly bonded to a semi-infinite PM substrate. Based on the three-dimensional macroscopic theory for PS and PM, the dispersion equations are derived analytically. Numerical examples are presented to study the effects of steady-state carrier density, cover thickness, and material properties on the phasevelocity and attenuation of SH wave systematically. The developments of various electromechanical fields through the thickness of the layers are discussed. The results show that initial electron concentration (n0) has an important effect on the distribution of most physical quantities such as displacement, stress, electric potential and electric polarization, but magnetic potential and magnetic flux density are insensitive to n0. The piezoelectric constant e15 and piezomagnetic constant f15 have different effects on the SH wave propagation and magnetic potential distribution. The theoretical results could be helpful for the analysis and design of PS-PM structures or related surface acoustic wave (SAW) devices.

Quasi-static fracture analysis by coupled three-dimensional peridynamics and high order one-dimensional finite elements based on local elasticity.

This work investigates quasi-static crack propagation in specimens made of brittle materials by combining local and non-local elasticity models. The portion of the domain where the failure initiates and then propagates is modeled via three-dimensional bond-based peridynamics (PD). On the other hand, the remaining regions of the structure are analyzed with high order one-dimensional finite elements based on the Carrera unified formulation (CUF). The coupling between the two zones is realized by using Lagrange multipliers. Static solutions of different fracture problems are provided by a sequential linear analysis. The proposed approach is demonstrated to combine the advantages of the CUF-based classical continuum mechanics models and PD by providing, in an efficient manner, both the failure load and the shape of the crack pattern, even for three-dimensional problems.

Accurate Stress Analysis of Variable Angle Tow Shells by High-Order Equivalent-Single-Layer and Layer-Wise Finite Element Models.

New concepts of lightweight components are conceived nowadays thanks to the advances in the manufacture of composite structures. For instance, mature technologies such as Automatic Fibre Placement (AFP) are employed in the fabrication of structural parts where fibres are steered along curvilinear paths, namely variable angle tow (VAT), which can enhance the mechanical performance and alleviate the structural weight. This is of utmost importance in the aerospace field, where weight savings are one of the main goals. For that reason, shell structures are commonly found in the aerospace industry because of their capabilities of supporting external loadings. Straight-fibre composite shell structures have been studied in recent decades and, now, spatially varying composite shells are attracting the attention of manufacturers. This work analyses the mechanical behaviour of VAT composite shells subjected to different external loadings and boundary conditions. The Carrera Unified Formulation (CUF) is employed to obtain the different structural models in a systematic and hierarchic manner. The outcomes of such numerical models are discussed and compared with commercial software Abaqus.

Mechanical characterization of 3D printed mimic of human artery affected by atherosclerotic plaque through numerical and experimental methods.

This paper proposes a novel experimental investigation based on 3D printing to validate numerical models for biomechanics simulations. Soft elastomeric materials have been used in Polyjet multi-material 3D printer to mimicking arteries affected by atherosclerotic plaque. The nonlinear mechanical properties of five digital materials are characterized and used as an input for finite element (FE) modeling. Pressurized air is applied to the internal cavity of the printed model to reproduce the internal blood pressure in the artery. Digital Imaging Correlation is adopted to measure the displacement and deformation. A 1D linear higher-order FE model based on the Carrera Unified Formulation is compared to 3D nonlinear FE solutions.