Non-stationary oscillations of sandwich plates under local dynamic loading

The paper addresses the elastic response of composite sandwich panels to local\ud dynamic loading. The plane and axisymmetric formulations are considered; no\ud overall bending is assumed. The governing equations are derived using the static\ud Lamé equations for the core and the plate Kirchoff-Love dynamic theory for the\ud faces. The closed form solutions for the non-stationary excitation are obtained\ud using integral transformations technique. The solutions allow to predict the stressstrain state of the structure and are in good agreement with finite element analysis

Internal geometry of structurally stitched NCF preforms

Internal geometry of a textile reinforcement is an important factor of the reinforcement performance during the composite manufacturing and service life. In this article, generalized geometrical models of structural stitching loops are presented for the sewing, tufting, and dual-needle stitching methods. The term 'structural' presumes here that the stitching yarn does not only consolidate the plies (as the non-structural one does) but forms also a through-the-thickness (3D) reinforcement. The models account for the general features of the yarn loop geometry and are believed to allow for enough precise modelling on the meso-scale (textile unit cell) level. The modelling approach is validated with experimental data

Multilevel modelling of mechanical properties of textile composites: ITOOL Project

The paper presents an overview of the multi-level modelling of textile composites in the ITOOL project, focusing on the models of textile reinforcements, which serve as a basis for micromechanical models of textile composites on the unit cell level. The modelling is performed using finite element analysis (FEA) or approximate methods (method of inclusions), which provide local stiffness and damage information to FEA of composite part on the macro-level

Stability of the face layer of sandwich beams with sub-interface damage in the foam core

This paper addresses the effect of local indentation/impact damage on the bearing capacity of foam core sandwich beams subjected to edgewise compression. The considered damage is in a form of through-width zone of crushed core accompanied by a residual dent in the face sheet. It is shown that such damage causes a significant reduction of compressive strength and stiffness of sandwich beams. Analytical solutions estimating the Euler’s local buckling load are obtained for two typical modes of damage. These solutions are validated through experimental investigation of three sandwich configurations. The results of the analytical analysis are in agreement with the experimental data

Compression strength of sandwich panels with sub-interface damage in the foam core

This paper addresses the effect of a local quasi-static indentation or a low-velocity impact on the residual strength of foam core sandwich panels subjected to edgewise compression. The damage is characterized by a local zone of crushed core accompanied by a residual dent in the face sheet. Experimental studies show that such damage can significantly alter the compressive strength. Theoretical analysis of the face sheet local bending is performed for two typical damage modes (with or without a face–core debonding). The solutions allow estimation of the onset of (a) an unstable dent growth (local buckling) or (b) a compressive failure in the face sheet. The theoretical results are in agreement with the test data for two considered sandwich configurations

Effect of Physical Nonlinearity on Local Buckling in Sandwich Beams

This article deals with experimental, theoretical, and FE characterization of the local buckling in foam-core sandwich beams. In the theoretical approach, this phenomena is considered in a periodic formulation (unbounded wrinkle wave); a nonlinear stress—strain response of the face material is accounted for. In the FE approach, nonlinearity of the core material is also modeled. Full-field strain measurement is employed in the tests showing that the commonly used edgewise compression set-up can cause premature waviness of the faces, and therefore, nonlinear local deformations in the core layer

Residual dent in locally loaded foam core sandwich structures – Analysis and use for NDI

This paper addresses the residual denting in the face sheet and corresponding core damage in a locally loaded flat sandwich structure with foam core. The problem is analytically considered in the context of elastic bending of the face sheet accompanied by non-linear deformation of the crushed foam core. The plane and axisymmetric formulations are studied. The obtained solutions allow for the estimation of the magnitude of the residual face dent through the size of the crushed core zone (or vice versa). Thus, the analytical background is proposed for a non-destructive inspection of locally indented/impacted sandwich structures. The solutions are verified experimentally

Residual In-plane Mechanical Properties of Transversely Crushed Structural Foams

The mechanical properties of structural polymer foams are investigated after crushing in the rise direction (out-of-plane axis of a foam material block). The crushed foams are loaded in uniaxial compression, tension, or shear. All tests are performed in the plane of the foam block, i.e., perpendicular to the crushing direction. For comparison, virgin foams are also characterized. The results are discussed featuring the properties of crushed foams, which can be important for the damage tolerance analysis of a foam core sandwich structure

The inelastic quasi-static response of sandwich structures to local loading

The paper addresses the inelastic quasi-static response of sandwich beams and panels with foam core to localized loads. The plane and axisymmetric formulations for local indentation or local low-velocity impact by a rigid body are considered; no overall bending is assumed. The governing equations for the face are derived using the Kirchhoff–Love static theory under the assumption that the core crushing follows elastic–ideally-plastic behavior. Analytical solutions are constructed on the basis of the principle of minimum work. The solutions allow predicting the face deflection, size of crushed core area and contact force. In general, the solutions are in good agreement with experimental data and finite element analysis