Numerical analysis of layered composite panel behavior with interlaminar defects subject to dynamic loads

The non-linear stability analysis of composite cylindrical panel subjected to concentrated in-plane mechanical and localized thermal loadings are reported here. The buckling of composite panel subjected to concentrated in-plane mechanical loading/ localized thermal loading is solved in two steps as the prebuckling stress distribution within the panel is not known a priori. In the first step, the semi-analytical expressions for the pre-buckling stresses within the composite cylindrical panel under in-plane mechanical/ thermal loadings are developed by solving in-plane elasticity/thermoelasticity problem. Subsequently, using these in-plane stresses within the cylindrical panel, the governing equations for nonlinear stability of layered composite panel are formulated using variational principle. The cylindrical panel is modeled based on Donnell’s shallow shell theory considering higher order shear deformation theory and incorporating von-Karman geometric nonlinearity. The Galerkin’s method is used to solve the non-linear governing partial differential equations. The influence of different types of mechanical and thermal loadings, initial geometric imperfections, and radius of curvature on the postbuckling equilibrium paths is investigated.

Buckling analysis of piezoelectric cylindrical composite panels reinforced with carbon nanotubes

The effect of in-plane stresses on the stability behaviors of constant stiffness and variable stiffness composite panels, exposed to aerodynamic pressure, is studied using the finite element method. The dynamic pressure from the high velocity airflow is evaluated from the first-order piston theory, and the eigenvalue analysis is performed to investigate the flutter or divergence type of instabilities in such composite panels under combined mechanical and aerodynamic loads. Attempt is made to understand the effect of the lamination parameter on the stability characteristics of edge-supported and cantilever composite trapezoidal panels. Finally, the limit cycle oscillation of variable stiffness plates subjected to aerodynamic pressure is investigated.

Finite element analysis of lightweight composite sandwich panels exposed to fire

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. The European Commission project POSICOSS, which lasted from January 2000 to September 2004 and the 4-year follow-up project COCOMAT, which started in January 2004, contribute to this aim [1]. Both projects are under the co-ordination of DLR, Institute of Composite Structures and Adaptive Systems. They reduce structural weight by exploiting considerable reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling and collapse. The POSICOSS team developed fast and reliable procedures for postbuckling analysis of fibre composite stiffened panels, created experimental data bases and derived design guidelines. The COCOMAT project builds up on the POSICOSS results and goes beyond by simulation of collapse. The project improves existing tools as well as design guidelines for stiffened panels taking skin stringer separation and material degradation into account and it creates a comprehensive experimental data base.The improved tools, developed within the POSICOSS and COCOMAT project, have to be validated by test results. Since appropriate test data bases were not available, both projects were constrained to create new experimental data bases for curved stringer stiffend CFRP panels. To that end suitable panels are designed, manufactured, inspected and tested under own project objectives. Each project differentiates between verification panels and industrial panels. The verification panels are designed as to specific limiting aspects of application of the software to be verified, e.g. small or large stiffness reduction in the postbuckling regime. These panels should have a significant postbuckling range up to collapse and have an early onset of degradation. The industrial panels were designed in regard to industrial applications, mainly by existing procedures used in day-to-day industrial design practice.For the analysis of the panels the partners utilized different finite element software tools. This paper focuses on the experience of DLR on the design and analysis of stringer stiffened CFRP panels gained in the frame of the POSICOSS and COCOMAT projects. Geometrical nonlinear computations up to collapse were performed applying the software ABAQUS/Standard. The material was assumed linear elastic. The onset of degradation of the structure and the skin-stringer connection was determined using different failure criteria. Results achieved so far will be presented and an outlook towards future activities will be given.

This paper presents a method of finite element modelling used for the impact analysis of a composite panel. In this research, the composite panel consists of an oxygen mask locking panel of an aircraft. This panel is loaded with one concentrated abuse loading and three uniform distributed abuse loading cases and the stress variation within the composite panel for each load case is determined. In order to assess the impact analysis on the oxygen mask panel of the aircraft, a finite element model is created using Patran as the main application for pre/post-processing and Nastran as the main processor. The paper also presents a comparison between results obtained using the same finite element modelling of the composite panel CAD model of the panel with four load cases with different material types. The results are used to determine the most capable material stresswise.

• A modified Tsai-Hill stress interpolation model for lattices is proposed. • Multiscale lattice structure topology optimization under stress constraints for static and dynamic loads is addressed. • Full-scale analysis and experimental validation of the optimized structures are conducted. This study presents a topology optimization method for heterogeneous lattice structures subject to stress constraints. The proposed approach extends the ordered SIMP (Solid Isotropic Material with Penalization) framework to incorporate a composite material failure criterion. Specifically, a modified Tsai–Hill yield criterion is employed to characterize the anisotropic yielding behavior of the heterogeneous lattice, which is subsequently integrated into the optimization as a stress constraint. To address the variation in yield strength across different lattice configurations, a normalization strategy is applied to the stress field. Additionally, a P-norm aggregation scheme is introduced to efficiently handle local stress constraints while reducing computational cost. The equivalent elastic tensor and yield strength of each lattice configuration are obtained using a representative volume element (RVE) based on homogenization theory. The effectiveness of the proposed method is demonstrated through a series of 2D cases, achieving lightweight structural designs that satisfy stress constraints. Finally, full-scale mechanical analysis and 3D printing experimental validation further confirm the strength reinforcement of the optimized results.

Evaluation of dynamic loads on a skew box girder continuous bridge Part II: Parametric study and dynamic load factor

: The objective of this program was to develop design procedures and durability validation methods for curved metal and composite panels designed to operate in the postbuckling range under the action of combined compression and shear loads. This research and technology effort was motivated by the need to develop design and life prediction methodologies for such structures.

Mode II- delamination modeling in multi-directional laminates using cohesive zone methodology under static and dynamic loading

This article discusses the design of airborne dye-sensitized solar cell (DSSC) panel integrated in the airplane composite panel which is subjected to mechanical dynamic loading so that the DSSC will function continuously as airborne energy harvester. This article consists of two parts, first synthesis of more rubut DSSC, and then its integration into a composite panel with durability demonstrated.

Blast response study of the sandwich composite panels with 3D chiral auxetic core

3D printing is recently gaining attention, yet only few researchers address underlying design principles such as minimal thickness to shape ratio; even though they are essential to industrial applications. The authors outline an optimization and verification approach considering structural aspects such as stiffness and strength as well as producibility and structural performance. This multitude of disciplines brought forth objectives, being diametral to each other. An example is giving by simultaneous mass reduction by increasing the part’s strength performance. So as to harmonize all of those objectives to an optimal compromise, topology optimization has been used in tandem with consultations of design and structural experts. Additionally, an aerospace part, namely a 3D printed titanium insert was built and glued into an aluminium sandwich panel with carbon fiber reinforced plastic face sheets. This composite panel was then subjected to actual flight loads of the METimage satellite campaign. During all mechanical and thermal tests, cracks are captured via acoustic monitoring. Studying all test results revealed, that the approach brought forth multiple advances such as; reduced weight, increased mass-specific effective stiffness and lower mechanical bonding stresses, which increased overall structural strength.

Post-buckling finite element analysis of composite cylindrical panels in axial compression

The present study deals with the dynamic stability of laminated composite pre-twisted cantilever panels. The effects of various parameters on the principal instability regions are studied using Bolotin's approach and finite element method. The first-order shear deformation theory is used to model the twisted curved panels, considering the effects of transverse shear deformation and rotary inertia. The results on the dynamic stability studies of the laminated composite pre-twisted panels suggest that the onset of instability occurs earlier and the width of dynamic instability regions increase with introduction of twist in the panel. The instability occurs later for square than rectangular twisted panels. The onset of instability occurs later for pre-twisted cylindrical panels than the flat panels due to addition of curvature. However, the spherical pre-twisted panels show small increase of nondimensional excitation frequency.