F. Benyahia

Elliptical and circular bonded composite repair under mechanical and thermal loading in aircraft structures

In this study, the three-dimensional finite element method is used to achieve a comparison between the semi circular and semi elliptical patch repairs in aircraft structures. The comparison was done by the analysis of : the mechanical and thermal stress intensity factors (SIF and TSIF) at the tip of repaired crack and the distribution of the adhesive stresses for the two patch shapes. The obtained results show that the semi circular shape of the patch presents lower stress intensity factor at the crack tip, which is beneficial for the fatigue life and lower adhesives stresses, which is beneficial for the repair durability. In addition the circular patch is subjected to less significant thermal residual stresses compared to the elliptical shapes.

Mass Gain Estimation Between Double and Single-Bonded Composite Repairs for Inclined Cracks in Aircraft Structures

Repair of cracked components by an adhesively bonded composite patch has gained acceptance in aerospace structures. The advantages of the double symmetric repair compared to the single one are well known. These advantages permit a significant reduction of the stress intensity near the repaired defect. In this study, a new approach was used to determine the advantage of the double symmetric patch: it is the determination of the mass gain obtained by the use of the double patch if the two techniques (single and double patches) give the same stress intensity at the crack tip. The mass gain was estimated numerically using the three-dimensional finite element method for repaired inclined cracks. The obtained results show that the mass gain eventually obtained by the use of the double patch can be very significant.

Effect of temperature on the mechanical properties of polypropylene–talc composites:

In this study, the effect of the temperature and talc concentration on the mechanical properties of the polypropylene (PP) + talc composite is analysed. Tensile, impact, bending and dynamic mechanical tests were carried out to evaluate the mechanical properties of PP + talc composite and to analyse the effect of temperature variation on these properties. The obtained results show that the temperature increase has a very negative effect on the mechanical strength of the PP–talc composite but it can be significantly reduced by the augmentation of the talc content.

Analysis of Thermal Residual Stresses Distribution in Circular and Elliptical Bonded Composite Repair of Metallic Cracked Structures

In this study, the distribution of the thermal residual stresses due to the adhesive curing in elliptical and circular bonded composite repairs is analyzed using the finite element method. The computation of these stresses comprises all components of the structures: cracked plate, composite patch and adhesive layer. In addition, the influence of these residual stresses on the repair performance is highlighted by analyzing their effect on the stress intensity factor at the crack tip. The obtained results show that the normal thermal stresses in the plate and the patch are significant.. The presence of the thermal stresses increases the stress intensity factor at the crack tip which reduce the repair efficiency.

Computation of the stress intensity factor for repaired cracks with bonded composite wrap in pipes under traction effect

In this article, the analysis of the behavior of cracked pipeline repaired with bonded composite wrap subjected to traction effect is performed using three-dimensional finite element methods. The stress intensity factor at the crack front was used as the fracture criteria. The stress intensities at the internal and external positions of repaired crack were compared. The effects of the mechanical and geometrical properties of the adhesive layer and the composite wrap on the variation of the stress intensity factor at the crack front were analyzed. The obtained results show that the presence of the bonded composite repair reduces significantly the stress intensity factor, which can improve the life span of the pipe.

Interaction between adherend plasticity and adhesive damage in metal/composite joints: application to bonded composite repair of metallic structures

The plasticity in the crack region is a great influence on the fatigue life of aircraft structures, and the adhesive damage has negative effects on the durability of bonded joints. In this paper, the interaction effect between the crack tip’s plasticity and adhesive damage in a bonded composite repair of cracked metallic panels was analyzed using the three-dimensional finite element (FE) method. A damage criterion was implemented in the FE model to evaluate the damaged zone in the adhesive layer, and the plastic strain around the crack was extracted from the FE calculations. In this research, we have demonstrated that the applied load has very significant effects both on crack plasticity and adhesive damage, but the ductility of the repaired material has no significant effect on adhesive failure. Fatigue tests and SEM observations were performed to validate the numerical results.

Fatigue crack propagation in aluminum plates with composite patch including plasticity effect

In this paper, we analyzed experimentally and numerically the behavior of fatigue crack in aluminum plates repaired with bonded composite patch. We studied the behavior of repaired crack in AA 2024 T3 and AA 7075 T6 under two levels of applied fatigue stresses: maximal stresses of 70 and 120 MPa at a load ratio of 0.1. In the experimental part, the fatigue life of unrepaired and repaired notched specimens were determined. In the numerical part, the J integral around repaired and unrepaired crack tips was calculated. The numerical and the experimental results were used to plot the crack velocity (da/dN) as a function of the J integral. The analysis was completed with scanning electron microscopic observations on fracture surfaces of repaired and unrepaired specimens. It was found that patch improves the fatigue life but this improvement is considerably reduced with the increase in the applied fatigue load. The Al 2024 T3 presents better resistance to fatigue crack propagation in both repaired and unrepaired cases.

Effects of Voids Growth on the Damage of Polypropylene/Talc Micro-composite

AbstractIn this study, the effect of the voids growth on the damage of PP/talc micro-composite was analyzed using experimental and numerical approaches. Pure PP was filled with four proportions of treated talc: 5, 10, 40 and 50%. Tensile tests were performed on specimens manufactured from this composite. The Gurson–Tvergaard–Needleman model was implemented in FE model to predict the damage of the PP/talc. The predicted results were compared to the experimental ones. There is a good agreement between the numerical and the experimental results for pure PP, PP + 40% of talc and the PP + 50% of talc. We noted a significant divergence between the experimental and the numerical results for the PP reinforced with 5 and 10% of talc.

Bonded Composite Repairs of Aluminum Alloy 2024T3 Cracked Plates

In this study, the behavior of repaired cracks, located in aluminum alloy sheets 2024T3, with bonded composite patch is analyzed experimentally and numerically. The experimental study has been conducted through fatigue tests on aluminum cracked plate repaired with Carbon/epoxy patch. In the numerical analysis, the stress intensity factor at the crack front is computed using three-dimensional finite element method. The obtained results show that the stress intensity factor at the crack front is highly reduced by the presence of the patch repair. Therefore, the fatigue life of the damaged structure can be significantly improved especially if the patch repair is applied at small crack lengths.© 2014 ASME

J Integral Computation for Repaired Cracks with Bonded Composite Patch in Aircraft Structures

In this study, the three-dimensional and nonlinear finite element method is used to estimate the performances of bonded composite repairs of metallic cracked aircraft structures by analyzing the J integral and at the crack tips of repaired cracks for single and double symmetric patches. Several calculations have been realized to extract the plasticized elements around the crack tip. The obtained results show that composite repair reduces significantly the J integral at the crack tip which can improve the fatigue life of aircraft structures. It was also shown that the double symmetric patch has a considerable beneficial effect on the repair performance compared to the single patch.