Patch Thicknesses Research Articles

Determination of an optimum patch configuration in the repair of a center crack in thin aluminum sheet using polymer composite patch

AbstractThe formation of cracks and their growth is an issue of concern in structural applications incorporating thin metal sheets. Adhering cracked region with a patch of composite material has proved effective in repairing cracks. Determining an optimum configuration of composite patch is still a challenge as a shorter patch may not be effective and a larger patch leads to wastage of resources. An appropriate methodology is required for specifying an optimum patch configuration in terms of its length, width, and thickness. The work presented prescribes a methodology for obtaining an appropriate combination of geometrical parameters of the composite patch. The computational tools like finite element analysis and response surface method have been incorporated. This is an extensive work consisting of a number of iterations of numerical analyses carried out for different combinations of the length and width of the patch. The results were also obtained for three different patch thicknesses in which the number of plies were increased from a single ply to three plies. The optimum size was obtained for each of the three patch thicknesses. Finally, a methodology for obtaining the most appropriate patch configuration based on the practical constraint of a small available area is prescribed.Highlights The crack repair in a thin structural sheet using fiber reinforced polymer composite patch separates at the interface. The optimum size of the patch needs to be used for an effective repair. The work consists of a combination of experiments and numerical simulations using finite element analysis. Response surface methodology is employed in this optimization study.

Effects of Patch Properties of Submerged Vegetation on Sediment Scouring and Deposition

Vegetation plays a key role in trapping sediments and further controlling pollutants. However, few studies were conducted to clarify the erosion and deposition laws of sediments and the influence factors caused by vegetation patch properties, which is not conducive to the revelation of riverbank protection and erosion prevention. Therefore, this study investigated the change in scouring and deposition characteristics around submerged vegetation patches of nine kinds of typical configurations and their influencing factors. Vegetation patches were assembled from three vegetation densities (G/d = 0.83, 1.3, and 1.77, representing dense, medium, and sparse, respectively), and three vegetation patch thicknesses (dn = 170, 400, and 630, representing narrow, usual, and wide, respectively), to measure vegetation patch property influences. Flow velocity, scouring, and deposition characteristics under nine patches were determined by a hydraulic flume experiment, three-dimensional acoustic Doppler velocimetry (ADV), and three-dimensional laser scanner, and then ten geometry and morphology indices were measured and calculated based on the results of laser scanning. Results showed that both vegetation patch density and thickness were positively related to the turbulence kinetic energy (TKE) above the vegetation canopy, and only vegetation patch density was negatively related to the flow velocity above the vegetation canopy. The relation between the product of density and vegetation patch thickness and erosion area in planform (EA) showed a power function (R2 = 0.644). Both density and vegetation patch thickness determined the scouring degree, but deposition location and amount did not rely on each one simply. On average, medium density showed the smallest maximum erosion length (MEL), EA, deposition area in planform (DA), and average deposition length (ADL) and a minimum of the above parameters also occurred at narrow vegetation patch thickness. The shape factor of the erosion volume (SFEV), the shape factor of the deposition volume (SFDV), ADL, and MEL of medium density and narrow thickness vegetation patch (G/d = 1.3, dn = 170) were significantly smaller than that of other types of patches. DA and equivalent prismatic erosion depth on the erosion area (EPED) were significantly linearly related (R2 = 0.766). Consequently, most sediment was deposited close to the vegetation patch edge. It is suggested that vegetation patch thickness and density should be given to control sediment transport. In particular, natural vegetation growth changes vegetation patch density and then alters vegetation patch thickness. Management and repair need to be first considered. The results of this study shed light on riparian zone recovery and vegetation filter strip mechanism.

PDMS-embedded wearable FBG sensors for gesture recognition and communication assistance.

This study introduces fiber Bragg grating (FBG) sensors embedded in polydimethylsiloxane (PDMS) silicone elastomer specifically engineered for recognizing intricate gestures like wrist pitch, finger bending, and mouth movement. Sensors with different PDMS patch thicknesses underwent evaluation including thermal, tensile strain, and bending deformation characterization, demonstrating a stability of at least four months. Experiments revealed the FBG sensors' accurate wrist pitch recognition across participants after calibration, confirmed by statistical metrics and Bland-Altman plots. Utilizing finger and mouth movements, the developed system shows promise in assisting post-stroke patients and individuals with disabilities, enhancing their interaction capabilities with the external surroundings.

Reducing Stress Concentration Around a Hole in a Thin-Wall Cylinder Subjected to Internal Pressure Using Piezoelectric Patches

Decreasing stress in a part or piece of equipment especially in a stress concentration point without increasing thickness or using stronger material is always an interesting issue for design engineers. In this paper, piezoelectric patches were used for stress concentration reduction around various hole sizes in thin-walled cylindrical shells subjected to internal pressure. Applied voltage to piezoelectric patches induces strain on both patch and part and alters stress flow on the part, leading to new distribution of stresses. Three dimensionless effective parameters that include hole and shell diameters as well as shell and piezo patch thicknesses were selected in this investigation. Ant colony optimization was utilized, and attachment of optimal arrangements of piezoelectric patches was derived for various numbers of piezoelectric patches. Using finite element analysis, it was shown that various combinations of these dimensionless parameters (R/t, tp/t and d/D) have different effects on reducing the maximum stress around the hole and up to 20% reduction on maximum stress was achieved during this research. Experimental tests were finally performed to verify finite element results.

The Impact Degrees of Basic Parameters on Repair Performance in Composite Patch Applications

In this study, for composite patch repairs, the impact degrees of patch configuration and patch sizes on repair performance were determined and compared with each other. First, stress intensity factor (SIF) values were calculated by using the Finite Element Method for tensile loading in an aluminum plate with center cracks, in unpatched situation. In this model, the repair was made by forming single and double sided patches and adhesive volumes too. The SIF values are recalculated for different patch thicknesses, widths, and crack lengths. The criterion that determines the impact degrees of the examined parameters was accepted to be the reduction rate in the SIF values. The results show that even the most disadvantageous patch application contributes significantly to the repair performance and that the application itself is the most effective factor. The second most effective parameter is patch configuration; the patch sizes have much less impact degree

Improved quantitative circuit model of realistic patch-based nanoantenna-enabled detectors

Improving the sensitivity of infrared detectors is an essential step for future applications, including satellite- and terrestrial-based systems. We investigate nanoantenna-enabled detectors (NEDs) in the infrared, where the nanoantenna arrays play a fundamental role in enhancing the level of absorption within the active material of a photodetector. The design and optimization of nanoantenna-enabled detectors via full-wave simulations is a challenging task given the large parameter space to be explored. Here, we present a fast and accurate fully analytic circuit model of patch-based NEDs. This model allows for the inclusion of real metals, realistic patch thicknesses, non-absorbing spacer layers, the active detector layer, and absorption due to higher-order evanescent modes of the metallic array. We apply the circuit model to the design of NED devices based on Type II superlattice absorbers, and show that we can achieve absorption of ∼70% of the incoming energy in subwavelength (∼λ/5) absorber layers. The accuracy of the circuit model is verified against full-wave simulations, establishing this model as an efficient design tool to quickly and accurately optimize NED structures.

Effect of Patch Thickness on the Repair Performance of Bonded Composite Repair in Cracked Aluminum Plate

Bonded composite patch repair of cracked components and weakened aerospace structures has gained high acceptance and demand. It offers significant advantages over traditional repair methods. These advantages permit a significant increase in fatigue life. In this study, we investigated experimentally the fatigue crack behavior of V- notched Aluminum 2024-T3 plates, of 2mm thickness, bonded with single side carbon composite patch configuration. This include the study of the repair efficiency and fatigue life of cracked samples patched with three different patch thicknesses consisting of 4, 6 and 8 layers, subjected to fatigue loading. However, to compare and calculate the efficiency of bonding, we studied the behavior of unrepaired configurations. The experimental results showed that the fatigue life increases with increase in patch thickness. Maximum fatigue life was obtained for specimen repaired with 8 plies patch which was about 3 folds compared to unrepaired one.

Experimental Research on the Mechanical Behavior of the Cracked Aluminum Plate Bonded by the Graphite/Epoxy Composite Patch

The effect of the graphite/epoxy composite patch parameters on the static and fatigue strength of the cracked aluminum plate was investigated experimentally. A series of specimens repaired by six types of composite patches including four different patch lengths and two different patch thicknesses were tested on the material tester. Specimens single-sided repaired and double-sided repaired by the same composite patches were also tested. The experiment results show that composite patches can provide an improvement in static and fatigue strength of the cracked aluminum plate, double-sided repair is more effective than single-sided repair, if the thickness and the length were selected properly, the composite patches can significantly enhance the strength of the repaired specimens.

Finite element fatigue propagation of induced cracks by stiffeners in repaired panels with composite patches

Fatigue crack growth analyses of aluminum panels with stiffeners repaired by composite patches have been rarely investigated. Generally, cracks may occur around the rivets which are capable to propagate under cyclic loadings. A composite patch can be used to stop or retard the crack growth rate. In this investigation, finite element method is used for the crack propagation analyses of stiffened aluminum panels repaired with composite patches. In these analyses, the crack-front can propagate in 3-D general mixed-mode conditions. The incremental 3-D crack growth of the repaired panels is automatically handled by a developed ANSYS Parametric Design Language (APDL) code. Effects of rivets distances and their diameters on the crack growth life of repaired panels are investigated. Moreover, the obtained crack-front shapes at various crack growth steps, crack trajectories, and life of the unrepaired and repaired panels with various glass/epoxy patch lay-ups and various patch thicknesses are discussed.

Determination of Mechanical Properties of Double-Strap Adhesive Joints with an Embedded Patch

In this study, stress analysis of double-strap joints used to fasten parts, particularly in aircraft and automotive industries and in the repair of damaged parts, was done using the finite element method. In classical double-strap adhesive joints, patch parts are bonded to the outer surface and these parts resist air flow. To decrease this effect and for constructive and aesthetic requirements, patch parts were embedded into the adherends. The effects of embedded patch parts on failure loads and stress distributions were investigated experimentally and numerically. For this purpose, AA 2024-T3 aluminum adherends with four different thicknesses (4.8, 5.6, 6.4 and 7.2 mm) were bonded as double patches with 0.4, 0.8 and 1.2 mm spring steel patch thicknesses and 20, 40 and 60 mm overlap lengths. The stress analyses were done under plain strain assumption. To verify the finite element model, experiments were carried out. The results show that adherends and patch thicknesses as well as overlap length all have considerable influence on failure loads and stress distributions.

Fatigue and fracture analysis of aluminum plate with composite patches under the hygrothermal effect

In this paper, fatigue life of the repaired cracks in 2024-T 3 aluminum with bonded patches made of unidirectional composite plates has been investigated experimentally and numerically for hygrothermal effect. The problem is handled in plane stress and Mode I condition. In the experimental study the mechanical properties of the aluminum plate and patch materials are determined and fatigue experiments are conducted. The results obtained from these experiments and numerical solutions are compared. Thus the reliability of the numerical solution has been proven. For all conditions, numerical solutions have been made and stress intensity factor (KI) and fatigue life are calculated. Different plate and patch thicknesses are also considered in the experiments.

Tensile behaviour of three-dimensional carbon-epoxy adhesively bonded single- and double-strap repairs

An experimental and numerical study of the tensile behaviour of three-dimensional carbon-epoxy adhesively bonded strap repairs is presented. Experimentally, the failure mode, elastic stiffness and strength were evaluated for different overlap lengths and patch thicknesses. The numerical simulations, performed in ABAQUS ®, allowed obtaining the elastic stiffness and the patch debonding load, used to understand the repairs behaviour. The adhesive layer was simulated with cohesive elements including a mixed-mode cohesive damage model with trapezoidal traction-separation laws in pure modes I and II, to account for the ductile behaviour of the adhesive used. These laws were determined by an inverse method, which consists on the estimation of the cohesive parameters with a fitting procedure of the experimental and numerical load–displacement curves of the respective fracture characterization test. The pure mode III cohesive law was equalled to the pure mode II one. This numerical methodology was found adequate to reproduce the experimentally observed behaviour of these repairs.

Determination of SIF for patched crack in aluminum plates by the combined finite element and genetic algorithm approach

ABSTRACTIn this paper, the finite element method is used to analyze the behaviour of repaired cracks in 2024‐T3 aluminum with bonded patches made of unidirectional composite plates. The problem is considered in Mode I condition. First the KI stress intensity factor (SIF) is calculated by the finite element method using displacement correlation technique. Different plate and patch thicknesses and crack lengths are considered in the analyses. Then an equation is determined by using genetic algorithms for the calculation of stress intensity factor without any further finite element analysis. The equation gives reasonably accurate results.

Numerical analysis for the determination of the stress intensity factors and crack opening displacements in plates repaired with single and double composite patches

In this study, the numerical behaviour of centrally cracked aluminium panels repaired with single and double sided composite graphite/epoxy patches and subjected to uni-axial loading is investigated. The stress intensity factors are computed for panels repaired with 12 ply and 14-ply repair patches and having different adhesive thicknesses. It is shown that there are considerable differences between the stress intensity factors and crack opening displacements for two patch thicknesses and various adhesive thicknesses.

Integrated experimental screening of bonded composites patch repair schemes to notched aluminum-alloy panels based on static and fatigue strength concepts

This paper seeks to outline an experimental screening procedure for a bonded composites patch repair scheme for cracked aluminum-alloy panels based on static and fatigue strength concepts. The materials used in this investigation comprised LY12 aluminum-alloy as a substrate, SY-24C as the adhesive system and T300/3234, G803/3242 and SW220/2322 fibre/epoxy prepregs as the patch materials. Static and fatigue behaviour of the specimens with serious patch materials and thicknesses was investigated experimentally. The experiments showed that the effects of repair of a notched panel with an asymmetric composite patch on the static strength and fatigue life of the repaired panel vary depending on the thicknesses of the patch and the fibre/epoxy prepreg materials. Because of the reduction of stress concentration caused by repairing, there is an improvement in the residual strength of the repaired specimens; thus the tensile residual strengths of repaired specimens are greater than those of un-repaired notched specimens.

Comparison of Human Ice Detection Capabilities and Ground Ice Detection System Performance under Post Deicing Conditions

Currently, after deicing operations, the presence of residual ice on an aircraft's wing is determined by a human deicer from a deicing ground crew via visual and tactile inspections. One method proposed to overcome some of the safety and physical concerns associated with human inspections is to use Ground Ice Detection Systems (GIDS). However, before regulatory authorities can consider GIDS for operational use, their performance had to be compared to human ice detection capabilities. In August 2005, the Federal Aviation Administration (FAA) William J. Hughes Technical Center's (WJHTC) Simulation and Analysis Group conducted a study sponsored by the FAA Office of Aviation Research, Flight Safety Branch (WJHTC), and Transport Canada's Transportation Development Centre to compare human ice detection performance using current visual and tactile techniques with the performance of two different GIDS under post deicing inspection scenarios. Nine male deicers from Globe Ground at Toronto Pearson Airport and Aero Mag 2000 Montreal performed post deicing inspections using three methods: the current method (Visual inspections and Tactile inspections), the GIDS1 method, and the GIDS2 method. Three separate post-deicing scenarios were presented each day for three days: a wing with 12 ice patches (High Contamination), three ice patches (Low Contamination), and a clean wing (No Contamination). Accuracy data, false detection data, and time to complete an inspection were collected and analyzed for each condition. The results from the study consistently indicated that overall GIDS1 was superior to human visual and tactile inspections and GIDS2 inspections in terms of accuracy, false detections, and stability in performance. Participants using GIDS1 were able to detect all patch sizes and thicknesses with the greatest accuracy while the other methods' accuracy improved as a function of patch size and thickness. In addition, inspections completed by the GIDS1 manufacturer throughout the study suggest that, with time and experience, performance could further improve.

Numerical and experimental fatigue crack growth analysis in mode-I for repaired aluminum panels using composite material

Abstract Crack-front shape is an important parameter influencing the stress intensity factor and crack propagation rate in asymmetric repaired panels. In this study, the numerical and experimental fatigue crack growth behaviour of centrally cracked aluminum panels in mode-I condition repaired with single-side composite patches are investigated. It is shown that the crack growths non-uniformly from its initial location through the thickness of a single-side repaired panel. There is a good agreement between the propagated crack-front shapes obtained from finite element analysis with those obtained from the experiments for various repaired panels with different patch thicknesses. Furthermore, effects of plate and patch thickness on the crack growth life of the repaired panels are investigated. The experimental results show that the crack growth life of thin panels may increase up to 236% using a 16 layers patch. However, for thick panels, the life may extend about 21–35% using a 4 layers patch. Implementing of 8 and 16 layers patches has not a significant effect on the life extension of thick panels with respect to the 4 layers patch life.

Experimental fatigue crack growth and crack-front shape analysis of asymmetric repaired aluminium panels with glass/epoxy composite patches

In this study, we investigate the experimental fatigue crack-growth behaviour of centrally cracked aluminium panels in mode-I condition which have been repaired with single-side composite patches. It shows that the crack growths non-uniformly from its initial location through the thickness of the single-side repaired panels. The propagated crack-front shapes are preformed for various repaired panels with different patch thicknesses. It is shown that there are considerable differences between the crack-front shapes obtained for thin repaired panels with various patch thicknesses. However, the crack-front shapes of thick repaired panels are not significantly changed with various patch thicknesses. Furthermore, effects of patch thickness on the crack growth life of the repaired panels are investigated for two typical thin and thick panel thicknesses. It shows that the crack growth life of thin panels may increase up to 236% using a 16 layers patch. However, for thick panels, the life may extended about 21–35% using a 4 layers patch, and implementing 8 and 16 layers patches has not a significant effect on the life extension with respect to the 4 layers patch life.

Mixed-mode fracture analysis of aluminium repaired panels using composite patches

Three-dimensional analyses are conducted to study the fatigue crack growth of panels containing mixed-mode cracks, reinforced with composite patches. A procedure is developed to obtain the crack trajectories using dynamic mesh generation for repaired panels in both mode-I and mixed-mode conditions. It is shown that the fatigue crack growth life obtained using mid-plane fracture parameters of the repaired panels in mode-I condition are almost compatible with the experimental results, however, they are non-conservative in some cases. The calculated fatigue crack growth life using un-patched surface fracture parameters are too conservative. It is shown that in both mode-I and mixed-mode crack loading conditions the J-integral values at mid-plane of the cracked plates are reduced with increasing the patch thickness; however, they depend on the patch thickness at un-patched surface at the crack-tip. The crack propagation path may be changed by the amount of about 10% due to the various fibers orientations of the patch. It is also shown that the patch thickness has not a considerable effect on the crack propagation path. Furthermore, there are considerable differences between the life obtained using un-patched surface and mid-plane fracture parameters for various patches thicknesses and layers angles of the repaired panels. The optimum patch layer angle considering maximum fatigue crack growth life of the repaired panels with an inclined crack angel of 45° is also obtained. Finally, a simple formulation is presented to justify the trend of finite element results obtained for single-sided repaired panels with various patch thicknesses.

Fatigue of Cracked Plates Repaired with Single-Sided Composite Patches

Fatigue of cracked plates repaired with single-sided composite patches is studied via both analytical and experimental approaches. A finite element model, which considers out-of-plane bending effects induced by asymmetric repair, is presented to determine the crack tip opening displacements of the repaired plates subjected to in-plane loading. The modified crack closure technique is used to calculate the stress intensity factor of the repaired plates. Fatigue life of the repaired plates is studied via the use of Paris law for crack propagation. The effects of cracked plate and composite patch thicknesses on the fatigue crack propagation of repaired plates containing different types of cracks are investigated. Fatigue tests of aluminum C-T specimens repaired with single-sided composite patches are performed, and the test data are used to validate the analytical approach. It has been shown that the repair of a cracked plate with a single-sided composite patch may have beneficial or adverse effects on the fatigue life of the repaired plate depending on the thicknesses of the patch and the cracked plate. .