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The determination of stress intensity factors (SIF) is of fundamental importance in prediction of brittle failure using linear elastic fracture mechanics. The presence of a crack in the vicinity of another crack induces an interaction effect. The purpose of this paper is to determine the SIF for an orthotropic lamina subjected to uniaxial loading and containing two cracks. The solution is obtained for one crack being horizontal and located in the centre of lamina while the other crack is inclined to first one. The effect of angle of the second crack, fibre angle is studied. Also, for the case of two parallel cracks, effect of eccentricity in x and y directions is observed.

Boundary collocation method is used and stress functions satisfying governing equations in the domain and ensuring stress singularity at the crack tips are defined. The boundary condition on the edges of lamina and the crack is satisfied to determine the complex coefficients in the stress functions.

For the given fibre angle, orientations of second crack which result in increase/decrease in the SIF at the most dangerous crack tip are found out.

Boundary collocation method which is simple and efficient is extended for studying two crack problem in orthotropic materials.

The purpose of this study is to confirm that the stiffness of fused filament fabrication (FFF) three-dimensionally (3D) printed fiber-reinforced thermoplastic (FRP) materials can be predicted using classical laminate theory (CLT), and to subsequently use the model to demonstrate its potential to improve the mechanical properties of FFF 3D printed parts intended for load-bearing applications.

The porosity and the fiber orientation in specimens printed with carbon fiber reinforced filament were calculated from micro-computed tomography (µCT) images. The infill portion of the sample was modeled using CLT, while the perimeter contour portion was modeled with a rule of mixtures (ROM) approach.

The µCT scan images showed that a low porosity of 0.7 ± 0.1% was achieved, and the fibers were highly oriented in the filament extrusion direction. CLT and ROM were effective analytical models to predict the elastic modulus and Poisson’s ratio of FFF 3D printed FRP laminates.

In this study, the CLT model was only used to predict the properties of flat plates. Once the in-plane properties are known, however, they can be used in a finite element analysis to predict the behavior of plate and shell structures.

By controlling the raster orientation, the mechanical properties of a FFF part can be optimized for the intended application.

Before this study, CLT had not been validated for FFF 3D printed FRPs. CLT can be used to help designers tailor the raster pattern of each layer for specific stiffness requirements.

In the design of anisotropic materials, such as advanced fibre‐reinforced composites, the failure envelope has a crucial role. A geometrical representation of the envelope is of particular value to investigate the highly anisotropic nature of the strength of the material. This provides the design engineer with a visualization of the failure envelope by graphically representing it using a CAD package. Use is made of both stress‐based and strain‐based polynomial failure criteria and examples are given of changes in the failure envelope due to changes in fibre orientation for a high strength graphite/epoxy composite lamina.

The architecture of 3D-printed parts made through fused deposition modelling (FDM) with raster infill resembles that of composite laminates. Classical lamination theory (CLT), the simplest model for composite laminates, has been proved successful for describing the stiffness properties of FDM parts, while strength modeling so far has been limited to unidirectional lay-ups. The aim of this paper is to show that CLT can be used to predict also FDM part failure.

Wood flour-filled polyester has been chosen as a model material. Unidirectional specimens oriented at 0°, 90° and ± 45° have been first characterized in simple tension to obtain the properties of the single layer. Next, two quasi-isotropic lay-ups, possessing different layer sequences, have been tested again in simple tension for CLT validation.

The measured properties are in good agreement with theoretical predictions, both for stiffness and strength, and an even better agreement can be achieved if a correction for taking the contour lines into account is implemented.

The paper shows that also the tensile strength of FDM parts can be predicted by using a mathematical model based on CLT. This opens up the possibility of using CLT for studying optimization of raster filled lay-ups, for example in terms of the best raster angles sequence, to better resist applied external loads.

To provide a basis for making assessment of the safety of adhesively bonded joints after they have been de‐painted by a dry abrasive method or a wet chemical method.

Stress analysis by a finite element method has been conducted for metal/composite and composite/composite joints in a single lap configuration. The effects of degradation of composite and adhesive, separately or combined, on the stresses in the adhesive layer bonding the two components are studied. Effects of wet and dry conditions of de‐painting are included in the study. It is assumed that in the composite these conditions affect only the laminae close to the surface from which the paint coating is removed.

The locations and values of the maximum peel and shear stresses in the adhesive are determined for both joints under different assumed conditions of degradation caused by de‐painting.

Experimental data indicating the extent of surface damage caused by de‐painting is not available.

Extensive literature study did not show any investigation of composite surface damage and adhesive property degradation on integrity of adhesively bonded joints. Results reported here will be of use in assessing effects of de‐painting on the structural performance of adhesively bonded joints.

Determining fiber orientations around geometric discontinuities is challenging and simultaneously crucial when designing laminates against failure. The purpose of this paper is to present an approach for selecting the fiber orientations in the vicinity of a geometric discontinuity; more specifically round holes with edge cracks. Maximum stresses in the discontinuity region are calculated using Classical Lamination Theory (CLT) and the stress concentration factor for the aforementioned condition. The minimum moment to cause failure in a lamina is estimated using the Tsai–Hill and Tsai–Wu failure theories for a symmetric general stacking laminate. Fiber orientations around the discontinuity are obtained using the Tsai–Hill failure theory.

The current research focuses on a general stacking sequence laminate under three-point bending conditions. The laminate material is S2 fiber glass/epoxy. The concepts of mode I stress intensity factor and plastic zone radius are applied to decide the radius of the plastic zone, and stress concentration factor that multiplies the CLT stress distribution in the vicinity of the discontinuity. The magnitude of the minimum moment to cause failure in each ply is then estimated using the Tsai–Hill and Tsai–Wu failure theories, under the aforementioned stress concentration.

The findings of the study are as follows: it confirms the conclusions of previous research that the size and shape of the discontinuity have a significant effect on determining such orientations; the dimensions of the laminate and laminae not only affect the CLT results, but also the effect of the discontinuity in these results; and each lamina depending on its position in the laminate will have a different minimum load to cause failure and consequently, a different fiber orientation around the geometric discontinuity.

This paper discusses an important topic for the manufacturing and design against failure of Glass Fiber Reinforced Plastic (GFRP) laminated structures. The topic of introducing geometric discontinuities in unidirectional GFRP laminates is still a challenging one. This paper addresses these issues under 3pt bending conditions, a load condition rarely approached in literature. Therefore, it presents a fairly simple approach to strengthen geometric discontinuity regions without discontinuing fibers.

The purpose of this paper is to present several two‐dimensional plate elements for the analysis of shear actuated laminate.

The limitations of the classical formulations based on the principle of virtual displacements in depicting the peculiar behavior of the transverse and normal stresses of multilayered structures have been easily overcome by using the mixed variational theorem proposed by Reissner (Reissner mixed variational theorem). In the framework of a unified formulation (UF), the assumptions of the unknowns is made through a common expansion leading both to global and layerwise description of the assumed unknowns. In addition, the possibility to choose the order of the expansion between one and four allows to be derived and compared 22 different plate models. The performances of the proposed elements have tested on application for whom an exact solution is available in open literature.

The obtained results complain quite well with the exact ones even if the need of advanced plate models come to evidence.

This paper describes how the capabilities of the UF to accurately analyze multilayered structures exploiting the shear mode actuation have been tested and states that in order to extend the capabilities of the UF, further efforts should be made toward the assumptions of discontinuous electric fields (potential and normal displacement). The paper confirms the need for advanced higher order plate models in modeling of adaptive laminate.

The purpose of this paper is to develop an analytical approach to evaluate the influence of material uncertainties on cross‐sectional stiffness properties of thin walled composite beams.

Fuzzy arithmetic operators are used to modify the thin‐walled beam formulation, which was based on a mixed force and displacement method, and to obtain the uncertainty properties of the beam. The resulting model includes material uncertainties along with the effects of elastic couplings, shell wall thickness, torsion warping and constrained warping. The membership functions of material properties are introduced to model the uncertainties of material properties of composites and are determined based on the stochastic behaviors obtained from experimental studies.

It is observed from the numerical studies that the fuzzy membership function approach results in reliable representation of uncertainty quantification of thin walled composite beams. The propagation of uncertainties is also demonstrated in the estimation of structural responses of composite beams.

This work demonstrates the use of fuzzy approach to incorporate uncertainties in the responses analytically, in turn improving computational efficiency drastically as compared to the Monte‐Carlo method.

The purpose of this paper is to analyse the nonlinear flexural behaviour of laminated curved panel under uniformly distributed load. The study has been extended to analyse different types of shell panels by employing the newly developed nonlinear mathematical model.

The authors have developed a novel nonlinear mathematical model based on the higher order shear deformation theory for laminated curved panel by taking the geometric nonlinearity in Green-Lagrange sense. In addition to that all the nonlinear higher order terms are considered in the present formulation for more accurate prediction of the flexural behaviour of laminated panels. The sets of nonlinear governing equations are obtained using variational principle and discretised using nonlinear finite element steps. Finally, the nonlinear responses are computed through the direct iterative method for shell panels of various geometries (spherical/cylindrical/hyperboloid/elliptical).

The importance of the present numerical model for small strain large deformation problems has been demonstrated through the convergence and the comparison studies. The results give insight into the laminated composite panel behaviour under mechanical loading and their deformation behaviour. The effects of different design parameters and the shell geometries on the flexural responses of the laminated curved structures are analysed in detailed. It is also observed that the present numerical model are realistic in nature as compared to other available mathematical model for the nonlinear analysis of the laminated structure.

A novel nonlinear mathematical model is developed first time to address the severe geometrical nonlinearity for curved laminated structures. The outcome from this paper can be utilized for the design of the laminated structures under real life circumstances.

The purpose of this paper is to study the nonlinear forced vibration responses of delaminated composite shells in hygrothermal environments.

Finite element method using an eight-noded C0 continuity, isoparametric quadrilateral element is employed. The theoretical formulations are based on the first order shear deformation theory and von Kármán type nonlinear kinematics. For modeling the delamination, multipoint constraint algorithm is incorporated in the finite element code.

The effect of delaminations on the nonlinear transient response of delaminated composite shells is dependent not only on the size but also on the location of the delaminations and hygrothermal environments.

The present study is limited to cylindrical and spherical shells having rectangular planform containing single delamination. Studies on different shell forms having non rectangular planforms containing multiple delaminations can be taken up for future research.

Nonlinear transient response of delaminated shells in hygrothermal environments is studied for the first time. It will assist researchers of nonlinear dynamic behavior of elastic systems.