Search

In this study, we analyzed the effect of a single overload fatigue cycle on the efficiency of bonded composite patch repair on a cracked Al 2024 T3 aluminum plate. Experimental and numerical analyses were performed to achieve the objective of the study. In the experimental part of the study, fatigue tests were conducted on a V-notched aluminum plate subjected to a constant amplitude fatigue loading with an overload applied at a relative crack length of 0.06 (a/W = 0.06). The plate was repaired with a carbon/epoxy composite patch. A fatigue life curve (a = f(N)) was plotted for the patched and unpatched specimens using the results of the experimental tests, and scanning electron microscopy images of the fracture surfaces of the failed specimens were observed. In the numerical part, the elastic–plastic finite element method was used to evaluate the plasticity induced by the overload on the patched plate and to analyze the adhesive damage after this overload was applied. The obtained results demonstrate that the patch deposition of the overload can lead to an extended fatigue life, and the adhesive damage after the overload is quite significant, but the risk of total failure of the adhesive layer is not high.

The effect of single overload on the fatigue crack growth in 2024-T3 and 7075-T6 Al alloys was analyzed. Fatigue tests under constant-amplitude loading with overload peak were carried out on V-notched specimens. Fractographic analysis was used as a principal approach to explain the crack growth retardation due to the overload. Scanning electron microscopy (SEM) analyses were conducted on the fractured surface of failed specimens to study the retardation effect. The obtained results show that the overload application generates a plastic zone in both aluminum alloys. The generated plastic zone is three times larger in the case of 2024-T3 compared to 7075-T6, and thus, a significant crack retardation was induced for 2024-T3. The retardation effect due to the overload for 2024-T3 and 7075-T6 lasted for about 10 mm and 1 mm, respectively, from the point of overload application.

This paper presents an experimental study into the comparative response of wiper and round-nose conventional carbide inserts coated with TiCN + AL2O3 + TiN when turning an AISI 4340 steel alloy. The optimal process parameters, as identified by pre-experiments, were used for both types of inserts to determine the machined surface quality, tool wear, and specific cutting energy for different cutting lengths. The wiper inserts provided a substantial improvement in the attainable surface quality compared with the results obtained using conventional inserts under optimal cutting conditions for the entire range of the machined lengths. In addition, the conventional inserts showed a dramatic increase in roughness with an increased length of the cut, while the wiper inserts showed only a minor increase for the same length of cut. A scanning electron microscope was used to examine the wear for both types of inserts. Conventional inserts showed higher trends for both the average and maximum flank wear with cutting length compared to the wiper inserts, except for lengths of 200&ndash, 400 mm, where conventional inserts showed less average flank wear. A higher accumulation of deposited chips was observed on the flank face of the wiper inserts than the conventional inserts. The experimental results demonstrated that edge chipping was the chief tool wear mechanism on the rake face for both types of insert, with more edge chipping observed in the case of the conventional inserts than the wiper inserts, with negligible evidence of crater wear in either case. The wiper inserts were shown to have a higher specific cutting energy than those detected with conventional inserts. This was attributed to (i) the irregular nose feature of the wiper inserts differing from the simpler round nose geometry of the conventional inserts and (ii) a higher tendency of chip accumulation on the wiper inserts.

The technology of bonded composite repair has displayed its effectiveness in increasing the residual fatigue life of cracked aeronautical structures. However, two major phenomena reduce the performance of this technique; the adhesive disbond by the fatigue load and the thermal residual stresses due to the adhesive curing. In this study, the effects of the adhesive disbond and the thermal residual stresses on the fatigue life of repaired cracked aluminum plate were analyzed experimentally and numerically. Fatigue tests were performed on cracked 2024-T3 aluminum alloy specimens repaired using carbon/epoxy patches that have artificial disbonds, to highlight the adhesive disbond effect. Fatigue tests were performed on repaired specimen bonded with elevated temperature cure and ambient temperature cure adhesives to evaluate the effect of the thermal residual stresses. To analyze the effects of the two phenomena, the finite element method was used to compute the stress intensity factor at the front of repaired cracks. The experimental results indicate that fatigue life is significantly reduced by the presence of an initial adhesive disbond and thermal residual stresses. The numerical results are consistent with the experimental observations, and reveal that the stress intensity factor increases with an increase in the disbond width. Moreover, it also increases in the presence of thermal residual stresses.

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.

In this study, the effect of a single overload on the fatigue life of cracked aluminum 2024-T3 alloy repaired with a bonded composite patch were studied. Special consideration was given to the load history, sequence of the bonded patch repair and the overload application (repair-overload and overload-repair). The two cases were compared to a reference case involving a single overload on unrepaired specimen. Fatigue tests were performed on V-notched repaired and unrepaired specimens naturally pre-cracked under constant amplitude loading. Fractographic analysis on the failed specimens was carried out to analyze the obtained fatigue results. It was found that when the crack is repaired before the overload application, the retardation effect due to the overload is attenuated by the patch. Nonetheless, when the patch precedes the overload, very high fatigue life extension of about 38.9 times is observed due to a cumulative retardation effect of the two events (patching and overload).

In 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.

Under real working conditions, structures are subjected to variable and peak loads. It is well known that cracks growth rate is load history dependent. Overloads generate crack growth retardation while underloads produce acceleration in crack growth. The effect of load history on patch repair is not covered so far. In this work, we investigated experimentally, how a single overload peak affects the performance of a bonded composite patch repair in cracked Al 2024-T3 and 7075-T6 samples fatigued under a cyclic loading. We studied the effect of three overload peaks; 9, 12 and 14 kN, applied just before and soon after the bonded composite repair. The fatigue lives and retardation cycle numbers exhibited that subjecting the test sample to overload before the repair will cause more retardation of the crack growth, while the reverse will result in less retardation, yet still better than that subjected to an overload alone. We carried out SEM observations to analyse the fractographs of failed specimens subjected to overloads and observed mixed mode fracture type.

This study analyzes the effect of the patch length the repair performance of bonded composite repair. Experimental and numerical approaches are used. In the experimental part of the study, fatigue tests with a constant amplitude were performed on notched specimens of 2024 T3 and 7075 T6 aeronautical aluminum alloys. Two stress ratios of R = 0 and R=0.1 were applied. The value of the patch length was varied to highlight its effect on the fatigue life. In the numerical part, the stress intensity factor and adhesive stresses were computed for different sizes of the patch length. The experimental results show that the fatigue life of repaired plates is significantly reduced with increases in patch length irrespective of the type of aluminum alloy and the stress ratio. The numerical results show that the stress intensity factor increases with increases in the patch length, and this is in agreement with the experimental results. This effect is explained by the presence of a secondary bending moment generated by the application of a single sided composite patch.

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.

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.

In this work, an extensive analysis has been presented and discussed to study the effectiveness of using different cooling and lubrication techniques when turning AISI 1045 steel. Three different approaches have been employed, namely dry, flood, and minimum quantity lubrication based nanofluid (MQL-nanofluid). In addition, three multi-objective optimization models have been employed to select the optimal cutting conditions. These cases include machining performance, sustainability effectiveness, and an integrated model which covers both machining outputs (i.e., surface roughness and power consumption) and sustainability aspects (carbon dioxide emissions and total machining cost). The results provided in this work offer a clear guideline to select the optimal cutting conditions based on different scenarios. It should be stated that MQL-nanofluid offered promising results through the three studied cases compared to dry and flood approaches. When considering both sustainability aspects and machining outputs, it is found that the optimal cutting conditions are cutting speed of 147 m/min, depth of cut of 0.28 mm and feed rate of 0.06 mm/rev using MQL-nanofluid. The three studied multi-objective optimization models obtained in this work provide flexibility to the decision maker(s) to select the appropriate cooling/lubrication strategy based on the desired objectives and targets, whether these targets are focused on machining performance, sustainability effectiveness, or both. Thus, this work offers a promising attempt in the open literature to optimize the machining process from the performance&ndash, sustainability point of view.

In this study, the effects of patch shape on the performance of bonded composite repairs on aircraft structures are investigated using experimental and numerical approaches. Fatigue tests under constant amplitude loading, with a positive stress ratio, are performed on V-notch cracked specimens using two aluminum alloys, 2024-T3 and 7075-T6 that are repaired with bonded carbon/epoxy patches. Three composite patch shapes are used: rectangular, trapezoidal, and triangular. Left- and right-oriented triangular patch shapes are used to analyze the effects of the patch orientation on the repair efficiency. Numerical models are built with these patch shapes and orientations. The stress intensity factors and adhesive stresses are computed to numerically evaluate the repair performances obtained with the different patch shapes and orientations. The experimental results demonstrate that rectangular patches provide the most efficient repair, whereas the triangular shape with a left-orientation may lead to catastrophic results, particularly with the 2024-T3 aluminum alloy. The numerical results concur with the experimental observations.

In this study, the fatigue behavior of aluminum alloy 2024T3 v-notched specimens repaired with composite patch under block loading was analyzed experimentally. Two loading blocks were applied: increasing and decreasing at two stress ratio: R = 0 and R = 0.1. Failed samples were examined under scanning electron microscope at different magnifications to analyze their fractured surfaces. The obtained results show that under increasing blocks, the crack growth is accelerated for both repaired and unrepaired specimens. This is attributed to the increase of the loading amplitude in the second block. A retardation effect was observed for decreasing blocks loading in unrepaired specimens. However, this retardation effect is attenuated by the presence of the patch which lead to lower fatigue life for repaired specimens.

The oxidation of aluminum machining chips retards the successful recycling through the conventional remelting route. A promising approach to overthrow this problem is the utilization of solid state recycling in converting aluminum machining chips directly into semifinished products to eliminate the cost of the remelting process and reduce CO2 emissions. Therefore, in recent work, chips of aluminum alloy (AA6061) were recycled by compaction and then extrusion conducted at 500°C, followed by equal channel pressing (ECAP) to study the resultant material properties and its microstructure. Moreover, the present investigation explores the influence of ECAP after hot extrusion on the corrosive behaviour of the recycled samples in saline solution (NaCl) by electrochemical impedance spectroscopy (EIS) and linear polarization (LP). The results demonstrated a remarkable enhancement of the recycled chips’ properties subjected to hot extrusion followed by the ECAP process. Furthermore, the successive ECAP passes leads to increased film thickness and decreased corrosion rate Deanship of Scientific Research, King Saud University | Ref. RGP-1440-101

In this study, experimental and numerical investigations were carried out in order to compare the performances of composite and metallic patches for repairing aircraft structures. In the experimental part, an accelerating aging of the composite was realized by the immersion of the composite patch in distilled water. The fatigue lives of notched plates repaired with aged composite patch, non-aged composite patch and aluminum patch were measured. The obtained results show that the composite patch is more beneficial than the aluminum patch if there is no significant water absorption by the composite. In the numerical part, the stress intensity factor at the crack tip was computed for aged and non-aged composite patches and for aluminum patches. The numerical results confirm the experimental ones, the reduction of the stress intensity factor by the composite patch is more significant than the aluminum patch but the water absorption reduces significantly the repair efficiency.

In this study, we analyzed the fatigue behavior of a V-notch crack in an aluminum alloy 7075-T6 plate repaired with bonded composite patch under constant and stepped variable amplitude loading. The effect of adhesive disbond on the repair performance was analyzed. The obtained results confirm the need of repairing cracks at their early creation for a maximum repair performance and showed that the increases in the disbond width and the stress ratio have a large negative effect on the repair efficiency. The latter is low for increasing loading blocks but significantly high for decreasing blocks.

In this study, a finite element analysis of the crack repair with composite wrap of circumferential through cracks in pipes subjected to bending moment is presented. Also, the evaluation of the long-term performance of composite repair systems has been addressed. The stress intensity factor is utilized as a fracture criterion. Finally, an attempt was made to provide industry with an overview of the current state of the art in composite repair technology and how the integrity of pipeline systems is being restored using composite materials. The obtained results show that the presence of the bonded composite repair reduces significantly the stress intensity factor, which can improve the residual fatigue life of the pipe. However, the main disadvantage of the technique of bonded composite repair in pipe is the impossibility to bond double sided composite wrap in order to equilibrate the stress transfer between the internal and external crack tip

In this study, the performances of aged bonded composite repair of aircraft structures have been evaluated by conducting experimental and numerical investigations. The accelerating aging of the patch was realized by immersion in water for 120 days. The performance of aged and non-aged bonded composite patches in the repair of cracked structures was evaluated. The experimental results showed that the fatigue life of the aircraft structures can be significantly improved with the patch repair. The patch aging reduces the repair performances because of the reduction of the composite rigidity by humidity absorption. Numerical results show that the stress intensity factor at the crack tip is significantly reduced by the presence of the patch. The humidity absorption increases the stress intensity factor at the crack tip and decreases the adhesive stresses. Nevertheless, the repair durability cannot be improved by the humidity absorption because it leads to a reduction of the mechanical resistance of the adhesive.

AISI 1045 has been widely used in many industrial applications requiring good wear resistance and strength. Surface roughness of produced components is a vital quality measure. A suitable combination of machining process parameters must be selected to guarantee the required roughness values. The appropriate parameters are generally defined based on ideal lab conditions since most of the researchers conduct their experiments in closed labs and ideal conditions. However, when repeating these experiments in industrial workshops, different results are obtained. Imperfect conditions such as the absence of a turning tool with definite specifications as shown in know-how “tool nose radius 0.4 mm” and its replacement with the closest existence tool “tool nose radius 0.8 mm” as well as the interruption of cutting fluid during work as a result of sudden failure in the coolant pump lead to the mentioned different lab-industrial conditions. These complications are common among normal problems that happened during the metal cutting process in realistic conditions and are called noise factors. In this paper, Taguchi robust design is used to select the optimum combination of the cutting speed, depth of cut, and feed rate to enhance the surface roughness of turned AISI 1045 steel bars while minimizing the effects of the two noise factors. The optimum parameters predicted by the developed model showed good agreement with the experimental results.

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.

In this study, the mechanical properties of the aged adhesive Adekit A140 epoxy were used in a finite element model to evaluate the effect of water absorption on the adhesive damage in bonded composite repair of aircraft structures. The damage zone theory was implemented in the finite element code in order to achieve this objective. In addition, the effect of the water absorption, by the adhesive, on the repair efficiency was analyzed by computing the stress intensity factor at the crack tip. The obtained results show that, when the water absorption increases the adhesive loses its rigidity, which reduces the repair durability. Besides, it leads to the increase of the stress intensity factor at the crack tip indicating a reduction in the repair efficiency.

In this study, the adhesive damage in bonded composite repair of aircraft structures is analyzed using a three dimensional finite element method. Four different patch shapes were chosen to analyze the adhesive damage: rectangular, trapezoidal, circular and elliptical. The modified damage zone theory was implemented in the FE code to evaluate the adhesive damage. The obtained results show that the rectangular shape is beneficial for the repair durability but it presents a disadvantage for the repair efficiency. The elliptical patch is found the optimal whereas the trapezoidal patch represents the worst shape among the four types analyzed in this paper.

In this paper, we studied the fatigue behavior of a crack emanating from v-notched aluminum (7075-T6) plate. To analyze the fatigue life of notched specimens we applied variable cyclic block-loading sequences, including increasing (L-H) and decreasing (H-L) blocks. We also analyzed the effect of the stress ratio(R) on the fatigue life of aluminum specimen subjected to stepped variable cyclic loading. The obtained results show that the effect of stress ratio on the fatigue life is significant. The patch repair efficiency is found to be limited for increasing (L-H) loading blocks but is significantly high for decreasing (H-L) cyclic loading blocks.

Adhesives play important roles in bonded composite repair as it ensures the transfer of load between the composite patch and the cracked aluminum component. Also, it holds the two structures together. The damage of the adhesive can thus reduce significantly the efficiency and the durability of the bonded composite repair. The adhesive damage models using critical zone have proven their effectiveness due to simplicity and applicability of the damage criteria in these models. The scope of this study is the estimation of the adhesive damage and failure in bonded composite repair of aircraft structures using modified damage zone theory. The effect of this damage on the repair efficiency was analyzed. In order to achieve these objectives, non-linear finite element analyses of adhesive joints considering the material nonlinearity of the adhesive layer were performed. The obtained results show that adhesive damage is principally located at the free edges of the patch and over the crack region. The damage zone ratios depends on the applied load, it affects the repair efficiency when its value approaches the critical value of 0.22.

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.

The determination of the stress intensity factor at the crack tip is one of the most widely used methods to predict the fatigue life of aircraft structures. This prediction is more complicated for repaired cracks with bonded composite patch. This study was performed in order to establish an analytical model for the stress intensity factor for repaired crack emanating from central holes. The model was developed by modifying that of Kujawski initially developed for cracks emanating from notch without repair. The obtained results were compared with those calculated with the finite element method and the model of Jones et al. It was found that our model gives a good approximation of the stress intensity factor for repaired crack emanating from central elliptical and circular holes if the results of the finite element analysis are taken as references.

International audience; The proposed work will be consecrated to the study of positive pre-breakdown currents triggered in mineral transformer oil under 50 Hz alternating overvoltage. Since negative currents are recorded in low rates and for higher voltage levels than positive ones, only the latter will be prior taken into consideration. Both streamer propagation and arc discharge current types are identi ed and are used in the training process of an arti cial neural network and the multi-linear regression line of these currents in order to develop a complementary diagnosis tool that can serve as an on-line transformer protection. More successful results than those obtained by other developed techniques are expected.

Composite materials have been used to structurally repair piping and other facilities for many years. However, the original use of composite materials was for repairing corroded pipelines where the intent was to restore strength to the damaged section of the pipeline. In addition to repairing corrosion, composite materials have successfully been used to repair dents, wrinkle bends, induction bends, and pipe fittings including elbows and tees as well as repair of offshore risers. In this study, the behavior of circumferential through cracks in repaired pipe with bonded composite wrap subjected to bending moment is investigated using three-dimensional finite-element analysis. The stress intensity factor (SIF) is utilized as a fracture criterion. The effects of the mechanical and geometrical properties of the adhesive on the variation of the SIF at the crack front were also analyzed. The obtained results show that the presence of the bonded composite repair significantly reduces the SIF, which can improve the residual lifespan of the pipe. Meanwhile, the SIF is also reduced as the elastic and the geometrical wrap properties are improved, particularly when the Young's modulus of the adhesive and the wrap thickness are increased.

In this study the three-dimensional nonlinear finite element method is used to determine the J integral variation along the front of repaired crack with bonded composite patch in aircraft structures. It is known that several parameters influence the repair quality such as the size and the intrinsic properties of the adhesive, the patch and the plate. The experimental design method is used to investigate the effects of patch dimensions (length, width and thickness) in order to achieve an optimisation of the repair operation. This optimisation allows us to determine the most influencing parameters on the repair performances. One can thus help the patch designers to improve the repair quality and durability.

In this study, the effects of the adhesive disband on the efficiency of bonded composites repair in aircraft structures were analyzed. The three-dimensional finite element method was used to achieve the objectives of the study. The stress intensity factor at the crack tip was chosen as fracture criteria. The analysis was extended to the single and double symmetric bonded composite patches. The obtained results show that the repair efficiency is negatively influenced if the adhesive disband growths perpendicularly to the crack. In the case of double symmetric patch, the presence of double adhesive disband highly decreases the repair efficiency and increases the risk of adhesion failure between the composite patch and the cracked aluminum structures.

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.

In this study, the effects of hygrothermal aging of composite patches and adhesives on the plasticity ahead of repaired crack with bonded composite patch were analyzed. The finite element method was used to compute the size and the shape of the plastic zone for cracks repaired with bonded hygrothermal aged composite patches and adhesives. The obtained results show that moisture absorption has a negative effect on the repair performance. Indeed, the size of plastic zone increases with an increase in the rate of water absorption whether in composite patches or in adhesives. The reduction of the composite patches and adhesive strength by the water absorption leads to a reduction of the repair performances.

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.

The optimization of the patch shape of bonded composite repair in aircraft structures is a good way to improve the repair performance. In this study, the three-dimensional finite element method is used to compare the repair performance of patches with rectangular and trapezoidal shapes in aircraft structures. The comparison is done by analysing the stress intensity factor (SIF) at the tip of repaired crack and the distribution of the adhesive stresses for the two patch shapes. The obtained results show that, when the crack length is ranged from 5 to 20 mm, the trapezoidal shape 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. These advantages disappear when the crack length reaches the value of 40 mm. It is also shown that the use of the trapezoidal shape reduce the mass of the patch, which can reduce the repair cost.

The validation of the diametral disk compression test with a small flat ground and soft pad utilization has been established. The stress distribution was determined by the finite element analysis for a range of loading conditions. The results showed that for the case of a point load, the fracture is due to shear and compressive stresses at the loading point. The application of the diametral disk test for a flat ground, as well as the use of soft pads at loading regions were proposed and tested. The results showed that both grounds, flat areas and soft pads, have a significant effect on the stress distribution patterns and values in the compression disk test. The stress distributions obtained in both cases, as loading continued, are found to deviate immediately from the assumed ideal point load condition. The obtained results and data, particularly at the disk center, were manipulated in order to obtain a correction equation. Thus, the maximum tensile stress variations, at the center, with the different loading conditions over a wide range ratio of the width of the loading area to the diameter of 0.5 were recorded. Consequently, the stress differences from the ideal case (i.e., the point loading condition) were calculated and fitted with a correction equation. The use of this correction equation can be used to obtain accurate results of the diametral compression test.

In this study the finite element method is used to analyse the effect of the thermal residual stresses resulting from adhesive curing on the performances of the bonded composite repair in aircraft structures. The stress-intensity factor at the crack tip is chosen as fracture criterion in order to estimate the repair performances. The obtained results show that the presence of the thermal residual stresses reduces considerably the repair performances and consequently decreases the fatigue life of cracked structures. The effects of the curing temperature, the adhesive properties and the adhesive thickness on the stress-intensity factor (SIF) variation with thermal stresses are also analysed.

In this study, a new approach is applied to compare the performances of single sided and double-sided symmetric composite patch with circular shape for repairing cracked aircraft structures. This is an approach that consists to evaluate the mass gain eventually obtained by the use of double symmetric composite patch if the two patch configurations give the same stress intensity factor at the crack tip. The three-dimensional finite elements method is used to compute the stress intensity factor. The obtained results show that the use of the double patch technique leads to a significant reduction of the stress intensity at the crack tip. The mass gain eventually given by the double patch technique can be very significant and this gain depends on the patch shape and the adhesive properties.

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.

The use of composite systems as a repair methodology in the pipeline industry has grown in recent years. In this study, the analysis of the behavior of circumferential through cracks in repaired pipe with bonded composite wrap subjected to internal pressure is performed using three-dimensional finite element analysis. The fracture criterion used in the analysis is the stress intensity factor (SIF). The obtained results show that the bonded composite repair reduces significantly the stress intensity factor at the tip of repaired cracks in the steel pipe, which can improve the residual lifespan of the pipe.

Plein texte : http://joam.inoe.ro/download.php?idu=3357; International audience; This paper presents a survey of positive pre-breakdown and breakdown currents in transformer mineral oil submitted to 50 Hz alternating voltage. The streamer positive currents are classified according to their possibility to lead towards breakdown. The data constituting the current vectors are collected in real time and smoothed by the use of arithmetic and geometric averages in order to serve as a fast and reliable diagnosis element.

International audience; This paper is aimed at the analysis of positive pre-breakdown currents triggered in mineral transformer oil submitted to 50 Hz alternating overvoltages. Different shapes of streamer currents and electrical discharges have been recorded to develop a discrimination technique based on an Artificial Neural Network (ANN) and Wavelet analysis of these currents. This enables us to address a complementary diagnosis tool that can serve as an online transformer monitoring and protection.

For the further development of CCS (Carbon Capture and Storage) an integrated approach is needed to optimize the full chain from capture, via transport to application. For the near future, carbon dioxide will be one of the largest commodities. In order to manage the captured CO2 it is anticipated that for different cases, like for example different sources of the CO2 and geographic location, different options will apply. The potential of various options for CO2 utilization are discussed in this paper. An overview will be given of a number of possible applications where CO2 is used as feedstock. For different applications the operational boundaries and the specific requirements will be addressed.

Background: The mechanisms of late asthmatic reactions provoked in atopic asthmatics by allergen-derived T-cell peptide epitopes remain unclear. Previous studies showed no changes in airway eosinophils or mast cell products after peptide challenge. In the present study our aim was to measure calcitonin gene-related peptide (CGRP), neurokinin (NK)-A, and substance P (SP) in bronchoalveolar lavage fluid and bronchial biopsies (BB) after inhalation of allergen-derived T-cell peptide epitopes since these neuropeptides (NP) had not previously been evaluated in this chronic asthma model. Methods: Bronchoscopy, with BB and bronchoalveolar lavage (BAL), was performed in 24 cat-allergic subjects 6 h after inhalation of Fel d 1-derived peptides. Neuropeptides were measured in BAL by enzyme-linked immunosorbent assay and CGRP expression in the airways was assessed by immunohistochemistry and confocal microscopy. Results: Twelve subjects (termed ‘responders’) developed isolated late reactions. Calcitonin gene-related peptide, but not NK-A or SP, was significantly elevated in BAL in responders only. Biopsy studies showed that in virtually all responders peptide challenge induced marked increases in CGRP immunoreactivity in bronchial epithelial cells, infiltrating submucosal cells and in association with airway smooth muscle. Double immunostaining indicated that CGRP colocalized predominantly to CD3+/CD4+ and CD68+ submucosal inflammatory cells. Conclusion: Calcitonin gene-related peptide, a potent vasodilator, is markedly up-regulated in the airways of atopic asthmatics during late-phase reactions provoked by inhalation of allergen-derived T-cell peptides.

Rationale We previously demonstrated the induction of IgE-independent, MHC-restricted, isolated late asthmatic reactions (LARs) by intradermal (i.d.) administration of T-cell peptide epitopes derived from the major cat allergen, Fel d 1 (J Exp Med 1999;189:1885-94). A bronchoscopy study investigating i.d. peptide-induced LARs found neither cellular infiltration nor elevated concentrations of inflammatory mediators. We subsequently observed that inhalation of Fel d 1 peptides induced isolated LARs with associated sputum eosinophilia, suggesting that local peptide delivery might lead to more superficial changes. Methods A randomized, placebo-controlled, crossover study was performed involving bronchial biopsies and bronchoalveolar lavage fluids from 12 subjects who developed LARs 6 hours after Fel d 1 peptides inhalation (responders) and 12 subjects who showed no clinical response (non-responders). Histamine PC 20 was performed at baseline and 1 week after each challenge. Results Peptide-induced LARs were associated with a significant elevation in bronchial biopsy CD4+ count (p=0.034), whereas there was no change in non-responders. A trend towards increased total CD3+ cells was also observed (p=0.052), that was significantly different (p=0.005) from the non-responder group. A trend for increased eosinophils was noted in responders with Congo Red stain (p=0.064) and anti-MBP (p=0.067). No differences in cell numbers in BALF were identified. A significant increase in airway hyperreponsiveness was identified in responders 7 days after peptide challenge compared with diluent (p=0.001002), that was not seen in nonresponders (p=0.85). Conclusion Thus, inhalation of T-cell epitope peptides induces isolated LARs, associated with bronchial infiltration of CD4+ T-cells, and increased airway hyperresponsiveness, but only modest eosinophilia.