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In order to connect a fiberglass composite structure to a steel structure, a hybrid composite made of glass and steel fibers has been studied. The hybrid composite has one end section with all glass fibers and the opposite end section with all steel fibers. As a result, it contains a transition section in the middle of the hybrid composite changing from glass fibers to steel fibers. The purpose of this paper is to examine interface strength at the glass to steel fiber transition section, in order to evaluate the effectiveness of the hybrid composite as a joining technique between a polymer composite structure and a metallic structure.

The present micromechanical study considers two types of glass to steel fiber joints: butt and overlap joints. For the butt joint, the end shape of the steel fiber is also modified to determine its effect on interface strength. The interface strength is predicted numerically based on the virtual crack closure technique to determine which joint is the strongest under various loading conditions such as tension, shear and bending. Numerical models include resin layers discretely. A virtual crack is considered inside the resin, at the resin/glass‐layer interface, and at the resin/steel‐layer interface. The crack is located at the critical regions of the joints.

Overall, the butt joint is stronger than the overlap joint regardless of loading types and directions. Furthermore, modification of an end shape of the middle fiber layers in the butt joint shifts the critical failure location.

The paper describes one of a few studies which investigated the interface strength of the hybrid joint made of fiberglass and steel‐fiber composites. This joint is important to connect a polymeric composite structure to a metallic structure without using conventional mechanical joints.

The purpose of this paper is to study theoretically the ability of the prestressed foam core composite sandwich Split Cantilever Beam (SCB) for generating mixed-mode II/III crack loading conditions (the mode II fracture was provided by prestressing the beam using imposed transverse displacements).

The concepts of linear-elastic fracture mechanics were used. The fracture behavior was studied in terms of the strain energy release rate. For this purpose, a three-dimensional finite element model of the prestressed sandwich SCB was developed. The virtual crack closure technique was applied in order to analyze the strain energy release rate mode components distribution along the crack front.

It was found that the distribution is non-symmetric. The analysis revealed that a wide mixed-mode II/III ratios range can be generated by varying the magnitude of the imposed transverse displacement. The influence of the sandwich core material on the mixed-mode II/III fracture behavior was investigated. For this purpose, three sandwich beam configurations with different rigid cellular foam core were simulated. It was found that the strain energy release rate decreases when the foam core density increases.

For the first time, a mixed-mode II/III fracture study of foam core composite sandwich beam is performed.

This study provides an analysis of patch repair for cracked aircraft structures. Delamination is a type of damage that affects the patch's behavior. The purpose of this study is to assess the influence of delamination on repair performance.

An analytical and numerical study using the finite element method was conducted for a cracked plate repaired with a patch containing a pre-existing delamination defect. The method for defining the contact pair surfaces and modeling the delamination interaction within the patch interface is specified using the virtual crack closure technique (VCCT) approach.

The efficiency of the repair is measured in terms of the J-integral. The effects of delamination initiation, mechanical loading, crack length and patch stacking sequences are presented. It is noted that in mode I, delamination propagation is only significant at node A. The numerical results are in good agreement with those of the analytical solution found in the literature. It is observed that the patch's behavior is strongly dependent on loading, crack size and stacking sequences in terms of reducing the structure's lifespan, especially in the presence of delamination.

The numerical modeling presented by the VCCT approach is highly valuable for studying delamination evolution. The influence of loading, crack size and stacking sequences on repair performance is discussed in this work.

Failure of the materials occurs once the stress intensity factor (SIF) overtakes the material fracture toughness. At this level, the crack will grow rapidly resulting in unstable crack growth until a complete fracture happens. The SIF calculation of the materials can be conducted by experimental, theoretical and numerical techniques. Prediction of SIF is crucial to ensure safety life from the material failure. The aim of the simulation study is to evaluate the accuracy of SIF prediction using finite element analysis.

The bootstrap resampling method is employed in S-version finite element model (S-FEM) to generate the random variables in this simulation analysis. The SIF analysis studies are promoted by bootstrap S-version Finite Element Model (BootstrapS-FEM). Virtual crack closure-integral method (VCCM) is an important concept to compute the energy release rate and SIF. The semielliptical crack shape is applied with different crack shape aspect ratio in this simulation analysis. The BootstrapS-FEM produces the prediction of SIFs for tension model.

The mean of BootstrapS-FEM is calculated from 100 samples by the resampling method. The bounds are computed based on the lower and upper bounds of the hundred samples of BootstrapS-FEM. The prediction of SIFs is validated with Newman–Raju solution and deterministic S-FEM within 95 percent confidence bounds. All possible values of SIF estimation by BootstrapS-FEM are plotted in a graph. The mean of the BootstrapS-FEM is referred to as point estimation. The Newman–Raju solution and deterministic S-FEM values are within the 95 percent confidence bounds. Thus, the BootstrapS-FEM is considered valid for the prediction with less than 6 percent of percentage error.

The bootstrap resampling method is employed in S-FEM to generate the random variables in this simulation analysis.

This paper aims to study the benefits of use of bi-adhesive (combination of two different adhesives) over conventional single adhesive in bonded lap joints. Characterise damage severity due to cohesive and adherent failure as feedback for operating load levels that assist in developing damage tolerance design of the adhesively bonded joints.

Single lap joint where the adherent plate is made up of aluminium alloy joined together with bi-adhesives is analysed. The nature of adhesives ranges from brittle, elastic-plastic, moderately ductile to largely ductile. Numerical analysis is performed considering the material and geometric non-linear behaviour of the joint. The optimum bond ratio of bi-adhesives and the effect of the location of adhesive on the stress distribution are studied. The cohesive zone modelling (CZM) is adopted to account for the cohesive failure of the joint. The adherent plate failure is also addressed by modelling and studying the behaviour of the crack at different locations in the plate using modified virtual crack closure integral (MVCCI).

The results obtained from the stress analysis show some important characteristic behaviour of the bi-adhesive joint. Although bi-adhesive is expected to result in improved joint strength, the purpose gets defeated if a brittle adhesive is used at the corners and ductile adhesive at the middle. The joint strength based on CZM, evaluated for a single adhesive, is in good comparison with the experimental results from the literature. Also, the location of the crack in the adherent plate plays a significant role in the failure of the joint.

Estimating joint strength for the bi-adhesive model using CZM and evaluating damage severity in the presence of de-bond and crack in the bi-adhesive lap joint model assists in developing robust damage tolerance design models of such joints.

In this work, the cohesive zone model (CZM) developed by some of the authors to simulate the propagation of fatigue defects in two dimensions is extended in order to simulate the propagation of defects in 3D. The paper aims to discuss this issue.

The procedure has been implemented in the finite element (FE) solver (Abaqus) by programming the appropriate software-embedded subroutines. Part of the procedure is devoted to the calculation of the rate of energy release per unit, G, necessary to know the growth of the defect.

The model was tested on different joint geometries, with different load conditions (pure mode I, mode II pure, mixed mode I/II) and the results of the analysis were compared with analytical solutions or virtual crack closure technique (VCCT).

The possibility to simulate the growth of a crack without any re-meshing requirements and the relatively easy possibility to manipulate the constitutive law of the cohesive elements makes the CZM attractive also for the fatigue crack growth simulation. However, differently from VCCT, three-dimensional fatigue de-bonding/delamination with CZM is not yet state-of-art in FE softwares.

The fuselage riveted lap-joints are susceptible to multiple site damage (MSD) and should be considered in damage tolerance analysis. This paper aims to investigate the stress intensity factor (SIF) and crack growth simulation for lap-joints based on three-dimensional (3D) finite element analysis.

The 3D finite element model of lap-joints is established by detailed representation of rivets and considering the rivet clamping force and friction. Numerical study is conducted to investigate the SIF distribution along the thickness direction and the effect of clamping force. A predictive method for the cracks propagation of MSD is then developed, in which an integral mean is adopted to quantify the SIF at crack tips, and the crack closure effect is considered. For comparison, a fatigue test of a lap-joint with MSD cracks is conducted to determine the cracks growth live and measure the cracks growth.

The numerical study shows that the through-thickness crack at riveted hole in lap-joints can be treated as mode I crack. The distribution of SIF along the thickness direction is inconstant and nonmonotonic. Besides, the increase in clamping force will lead to more frictional load transfer at the faying surfaces. The multiple crack growth simulation results agreed well with the experimental data.

The novelty of this work is that the SIF distribution along the thickness direction and the MSD cracks growth simulation for lap-joints are investigated by 3D finite element analysis, which can reflect the secondary bending, rivet clamping, contact and friction in lap-joints.

The purpose of this paper is to analyze the repair of a straight and angular crack in the structure using a piezoelectric material under thermo-mechanical loading by the extended finite element method (XFEM) approach. This provides a general and simple solution for the modeling of crack in the structure to analyze the repair.

The extended finite element method is used to model crack geometry. The crack surface is modeled by Heaviside enrichment function while the crack front is modeled by branch enrichment functions.

The effectiveness of the repair is measured in terms of stress intensity factor and J-integral. The critical voltage at which patch repair is most effective is evaluated and presented. Optimal patch shape, location of patch, adhesive thickness and adhesive modulus are obtained for effective repair under thermo-mechanical loading environment.

The presented numerical modeling and simulation by the XFEM approach are of great benefit to analyze crack repair in two-dimensional and three-dimensional structures using piezoelectric patch material under thermo-mechanical loading.

The purpose of this paper is to investigate on the behaviour of a delaminated stiffened panel; the delamination growth is simulated via fracture elements implemented in B2000++® code based on the Modified Virtual Crack Closure Technique (MVCCT), matrix cracking and fibre failure have been also taken into account.

In order to correctly apply the MVCCT on the delamination front a very fine three-dimensional (3D) mesh is required very close to the delaminated area, while a 2D-shell model has been employed for the areas of minor interest. In order to couple the shell domain to the solid one, shell-to-solid coupling elements based on kinematic constraints have been used.

Results obtained with the global/local approach are in good correlation with those obtained with experimental results.

The global/local approach based on kinematic coupling elements in conjunction with fracture elements allows to investigate and predict the behaviour of a stiffened delaminated composite panel in an efficient and effective way.

Lug joints with fasteners play a crucial role in connecting many major components of the aircraft. Most of the failures in the past were credited to the damages initiating and progressing from these types of joints. Ensuring the structural integrity of these fastener joints is a major issue in many engineering structures, especially in aerospace components, which would otherwise lead to fatal failure. The purpose of this paper is to adopting the prognostic approach for analysing these lug joints with fasteners subjected to off-axis loading by estimating the crack initiation and crack growth life of these joints. This data will be useful to estimate the remaining life of these joints at any given stage of operations, which is mandatory in structural health monitoring (SHM).

Straight and tapered lug joints are modelled using the finite element method in MSC PATRAN and analysed in MSC NASTRAN. These lug joints are analysed with a push fit fastener. The contact/separation regions at the pin–lug interface are carefully monitored throughout the analysis for various loading conditions. Critical locations in these lug joints are identified through stress analysis. Fatigue crack initiation and fatigue crack growth analysed is carried out at these locations for different load ratios. A computational method is proposed to estimate the cycles to reach crack initiation and cycles at which the crack in the lug joint become critical by integrating several known techniques.

Analysis carried out in this paper describes the importance of tapered lug joints, particularly when subjected to non-conventional way of loading, i.e. off-axis loading. There is a partial loss of contact between pin and lug upon pin loading, and this does not change further with monotonically increasing pin load. But during load reversals, there is a change in contact/separation regions which is effectively handled by inequality constraints in the boundary conditions. Crack growth in these lug joints pertains to mixed-mode cracking and is computed through the MVCCI technique.

Most of the earlier works were carried out on in-plane pin loading along the axis of symmetry of the lug. The current work considers the off-axis pin loading by loading the lug joints with transverse and oblique pin load. The significance of taper angle under such loading condition is brought in this paper. The results obtained in this paper through prognostic approach are of direct relevance to the SHM and damage tolerance design approach where the safety of the structural components is of foremost priority.