6061-T6 Plates Research Articles

Enhancing strength performance of laser welded 7075 aluminum alloy joints with TiC nanoparticle-mixed filler powder

Precipitation-strengthened 7075 aluminum alloy (AA 7075) is a crucial structural material widely utilized in the aerospace industry. Nevertheless, the achievement of highly strengthened joints of this alloy remains a challenge because of its susceptibility to composition dilution and defect formation during welding. In this study, the method of powder-filled laser welding was employed to weld AA 7075-T6 plates, utilizing both AA 7075 powder and a mixed powder of AA 7075 and 5 wt % TiC nanoparticles as the filler. To investigate the impact of the filler on the mechanical properties of the welded joints, their microstructure, phase constitution and tensile strength were measured and analyzed. Moreover, the transient temperature and the forming process of the joints during laser welding were captured. The results indicate that the joints are heat-treatable when the filler contains the AA 7075 powder. The ultimate tensile strength (UTS) of the joints can reach 500 MPa as a result of the η′ phase precipitated during heat treatment. The incorporation of TiC nanoparticles into the AA 7075 powder led to a refinement of grains, a reduction in porosity within the joints and an increase in the UTS by up to 540 MPa, which is 91.5 % of the base metal. Further theoretical estimation suggests that Orowan strengthening as well as grain size strengthening due to the Hall-Petch effect are the main strengthening mechanisms for the improved tensile performance. The powder-filled laser welding method also provides a flexible approach for designing compositions of filler material.

Guidline to Asses Geometrical Intolerance of Thin-Walled Blanks After Burnishing Process

AbstractApplication of lightweight material like aluminum alloy is increasing its importance in various industries due to effective reduction of structure weight and sequential advantages like reduction of greenhouse gas emission and carbon footprint. However, deflection of aluminum thin-walled blank during production by machining is a challenge that merits further studies. Burnishing as a non-metal removal finish-machining process is usually used as a final treatment in the production chain of samples. However, in burnishing of thin-walled structure, machining-induced residual stress causes dimensional and geometrical distortion followed by problems in manufacturing accuracy and mismatch in assembly. Therefore, to minimize the consequence of the abovementioned errors, the source of the distortion should be identified and minimized during machining since usually no further operation is placed in the production chain after burnishing. To effectively tackle this challenge, in the present study an analytical model is developed to find how the burnishing process factors i.e. pass number and static force together with initial blank size impact the distortion of thin-walled 6061-T6 plates. The curvatures which were derived from analytical model were compared to those of burnished samples measured by coordinate measuring machine. It was found from the results that the burnishing pass number because of its impact on work hardening and regeneration of stress together with blank size play crucial role on determining the sample’s distortion. It was obtained that with 2 pass burnishing results in minimizing the distortion of material. Moreover, the blank’s length to width ratio due to its impact on material stiffness in corresponding direction significantly impacts the deformation after unclamping. The results which were derived from analytical model were compatible well with experimental values in term of final distribution of residual stress and maximum height of distorted parts.

Enhancing aircraft crack repair efficiency through novel optimization of piezoelectric actuator parameters: A design of experiments and adaptive neuro-fuzzy inference system approach

This study addressed the critical problem of repairing cracks in aging aircraft structures, a safety concern of paramount importance given the extended service life of modern fleets. Utilized a finite element (FE) method enhanced by the design of experiments (DOE) and adaptive neuro-fuzzy inference system (ANFIS) approaches to analyze the efficacy of piezoelectric actuators in mitigating stress intensity factors (SIF) at crack tips—a novel integration in structural repair strategies. Through simulations, we examined the impact of various factors on the repair process, including the plate, actuator, and adhesive bond size and characteristics. In this work, initially, the SIF estimation used the FE approach at crack tips in aluminum 2024-T3 plate under the uniform uniaxial tensile load. Next, numerous simulations have been performed by changing the parameters and their levels to collect the data information for the analysis of the DOE and ANFIS approach. The FE simulation results have shown that changing the parameters and their levels will result in changing of SIF. Several DOE and ANFIS optimization cases have been performed for the depth analysis of parameters. The current results indicated that optimal placement, size, and voltage applied to the piezoelectric actuators are crucial for maximizing crack repair efficiency, with the ability to significantly reduce the SIF by a quantified percentage under specific conditions. This research surpasses previous efforts by providing a comprehensive parameter optimization of piezoelectric actuator application, offering a methodologically advanced and practically relevant pathway to enhance aircraft structural integrity and maintenance practices. The study innovation lies in its methodological fusion, which holistically examines the parameters influencing SIF reduction in aircraft crack repair, marking a significant leap in applying intelligent materials in aerospace engineering.

Initiation and growth of fatigue cracks in sheets with U-shaped notches in the first and mixed modes of fracture

Initiation and growth of fatigue cracks in sheets with U-shaped notches in the first and mixed modes of fracture

Enhancing joint performance in friction stir welding through tailored double-butt-lap geometry

The study investigates the effectiveness of a novel joint configuration, the double-butt-lap (DBL), in friction stir welding (FSW) to join 6-mm-thick AA 6061-T6 plates. Four welds, including a simple square butt (SSB) configuration and three DBL variations (with UB to LB ratios of 1:2, 1:1, and 2:1), were executed. Using consistent parameters, the investigation evaluates the force distribution, macrostructure, and mechanical properties of the joints. Results show varied force profiles; spindle torque and Z-force decrease notably in DBL configurations compared to SSB, while X-force decreases overall for all DBL variations. Macrostructural analysis indicates increased weld area and finer microstructures in DBL joints. A correlation between peak temperature, grain size, and hardness highlights larger grain sizes at higher temperatures, influencing joint hardness. The DBL configuration with a 2:1 ratio exhibits the highest joint efficiency (83.76%). Fractographic analysis indicates ductile failure in all samples. Bend testing reveals increased flexural strength and bend angles in two DBL-configured joints compared to SSB. The results indicate that using a 2:1 ratio for joining 6-mm AA6061-T6 plates through FSW is viable, providing valuable insights into enhancing mechanical properties by optimizing joint geometry.

Analysis of water absorption on the efficiency of bonded composite repair of aluminum alloy panels

Abstract Carbon fiber-reinforced polymer (CFRP) exhibits aging effects over time that can degrade its mechanical properties. In this study, a systematic investigation was carried out to investigate the effect of distilled water aging on the mechanical properties of CFRP composite patch bonded on Al 2024-T3 plates. We built a finite element model to analyze the effect of water absorption by the composite and the adhesive on the effectiveness of the composite patch repair. Using the experimentally evaluated mechanical properties of CFRP and Araldite adhesive subjected to distilled water immersion, finite element simulations were validated. The experimental observations deduce that there was a negligible effect of moisture absorption on the bulk mechanical properties of CFRP and adhesive over time. However, a significant effect of moisture absorption was observed on the elasto-plastic behavior of both CFRP and adhesive. Consequently, the numerical simulations suggest that the moisture absorption reduces the bonded composite patch repair efficiency attributed to an increase in the plasticity around the crack front and accordingly increases the damage in the adhesive layer. This study attempts to provide guidelines on the severity of damage caused by water absorption on the performance of structures repaired with composite patches.

Machine Learning-Based predictions of crack growth rates in an aeronautical aluminum alloy

Recent advancements in computational capabilities have made data-driven approaches increasingly valuable for accurately simulating complex engineering phenomena. These approaches provide mathematical approximations that serve as surrogate models, replacing complex explicit mathematical relationships with significantly reduced computational demands. In this study, we propose the development of a surrogate model to predict the crack growth behavior of aluminum 7075-T6, a commonly used material in the aviation industry. The crack growth behavior of this alloy is complex and challenging to describe with explicit mathematical equations due to multiple influencing factors. Notably, the “waviness” behavior observed in the linear Paris law region, coupled with the significant impact of the R-ratio and specimen thickness, complicates crack growth predictions. To address this complexity, four different machine learning regression algorithms are studied: Random Forest (RF), Gaussian Process Regression (GPR), K-Nearest Neighbors (KNN), and Kernel Regression (KR). Their performance is evaluated and the most promising algorithm is selected to predict a crack growth benchmark problem of a central crack in aluminum 7075-T6 plate under various fatigue stress spectra.

Optimization of damage repair with piezoelectric actuators using the Taguchi method

Over the last two decades, piezoelectric actuators have emerged as a promising solution for structural repair. In this work, initially the stress intensity factor (SIF) estimation using the finite element (FE) approach at crack tips in aluminium 2024-T3 plates. Based on Taguchi’s L9 orthogonal array the FE simulation has been conducted. Later, this study uses the optimization method via the design of experiments to systematically evaluate the effect of various dimensions and material qualities, especially under the conditions of Mode-I crack propagation. It also investigated the complex interaction of factors impacting adhesive bonds, piezoelectric actuators, and aluminium plates, The study not only analyses the parameter relationships but also examines their controls, identifying those best aligned with primary objectives. This sensitivity enhances the piezoelectric actuator's efficacy and quality. The research determines an optimal parameter combination, developing active repair performance and establishing an essential SIF benchmark. This research explores the complex world of piezoelectric actuator-assisted repairs, providing a road map for better structural rehabilitation.

Effect of pin geometry, rotational speed, and dwell time of tool in dissimilar joints of low-carbon galvanized steel and aluminum 6061-T6 by friction stir spot welding

In this study, aluminum 6061-T6 plates were joined with low-carbon galvanized steel using friction stir spot welding. Three conical pins with varying lengths (short, medium, and long) were utilized, along with different dwell times and rotation speeds of the tool. The objective of this research was to compare the simultaneous effects of several important process parameters on mechanical and welding properties. The results indicate that the use of short conical pins significantly increased the microhardness in the upper aluminum plate. Conversely, increasing the pin length led to higher microhardness in the lower steel plate. Tensile shear loading was greater for short pins compared to medium pins, attributed to the influence of the tool shoulder. However, with increasing pin length, failure loading reached its highest value due to the dispersion of particles in the weld. The failure mode for short pins exhibited a mixed pattern, which transitioned to a ductile shape in all conditions as pin length increased. Overall, the most influential parameter was the tool penetration depth, which positively affected the obtained properties. The rotational speed of the tool was the second most significant parameter, followed by the dwell time.

Fatigue crack initiation life prediction using different plasticity models in cold expanded AL-alloy plates utilized in double shear lap joints

Cold expansion of fastener holes is a recognized technique for enhancing the fatigue life of holed plates utilized in detachable joints. This method involves introducing compressive residual stress around the holes, which has proven to be effective in improving the structural integrity and longevity of such components. In this research, the role of using different plasticity models in finite-element simulations of cold expansion (CE) in determining residual stress distribution and predicting the fatigue life of lap joints was investigated. Finite-element simulations were conducted to analyze the distribution of residual stress in cold-expanded Al-alloy 2024-T3 plates utilized in double-shear lap joints. Three time-independent plasticity models, specifically multilinear kinematic hardening, multilinear isotropic hardening (M.L.I.H) based on monotonic tensile tests, and nonlinear combined hardening models derived from saturated hysteresis stress and strain loops, were employed in the simulations. These models allowed for an accurate determination of the residual stress distribution in the plates. In finite-element simulations, two CE sizes of 1.5% and 4.7% were employed to create residual stresses. In the simulations, after creating residual stress by CE, remote sinusoidal loads are applied to the joints corresponding to the previously conducted fatigue tests in order to obtain stress and mechanical strain distributions. In order to predict the fatigue life, four different multiaxial fatigue criteria (Smith–Watson–Topper, Glinka, Kandil–Brown–Miller, and Fatemi–Socie) were employed, using the stress and strain distributions obtained from the finite element simulations with the different plasticity models. The simulations yielded varying stress and strain distribution results for the multilinear kinematic and M.L.I.H models, while the results of the nonlinear combined hardening model fell between the other two models. Notably, the fatigue life prediction based on the nonlinear combined hardening plasticity model closely matched the experimentally observed fatigue lives, with an absolute percentage deviation of 24.8%.

Determining the Elastic Constants of Isotropic Materials by Measuring the Phase Velocities of the A0 and S0 Modes of Lamb Waves.

In this study, a new method for determining the elastic constants of isotropic plates using Lamb wave fundamental modes is presented. This method solves the inverse problem, where the elastic constants (Young's modulus and Poisson's ratio) of the plate were estimated by measuring the phase velocities of the Lamb wave using the Rayleigh-Lamb equations to find the solution and determining the phase velocities of the A0 and S0 modes using a new method. The suitability of the proposed method for determining the elastic constants was evaluated using simulated and experimental signals propagating on an aluminum plate. The theoretical modeling on the aluminum 7075-T6 plate shows that the proposed method allows the determination of the Poisson ratio with a relative error not exceeding 2% and Young's modulus with a relative error not exceeding 0.5%. The experimental measurements of an aluminum plate of known thickness (2 mm) and density (2685 kg/m3) confirmed the suitability of the proposed method for the measurements of elastic constants. In the proposed method, the processing of ultrasonic signals can be performed in real-time, and the values of the elastic constants can be obtained immediately after scanning the required distance.

Prediction of surface crack growth life for AA7075-T6 under nonproportional loading

The growth direction and growth rate of fatigue cracks initiated from the surface of an aluminum alloy 7075-T6 plate were investigated under six sets of nonproportional loadings produced by combined axial-torsion loading. A digital image correlation method was simultaneously applied to measure the crack opening displacements around the crack tip during the fatigue tests. The effective stress intensity factor ranges were determined on the basis of the measured crack opening displacements and applied to arrange the crack growth rate. Results showed that fatigue crack tended to propagate orthogonally to the direction in which the resultant normal stress in the nonproportional loading cycle was maximized, suggesting that the maximum resultant normal stress dominates crack growth under nonproportional loadings. When the effective stress intensity factor range based on the maximum resultant normal stress was used to arrange the crack growth rates, all data collapsed into a single narrow scatter band. The growth lifetime until the surface crack penetrates the plate could be estimated within a relative error of about ± 20 % based on a modified Paris-type equation through numerical integration.

Fatigue life of thin pre-cracked aluminum alloy panel repaired with CFRP patch at elevated temperature

The fatigue life of a thin pre-cracked aluminum alloy panel, repaired with CFRP patches was investigated. Aluminum alloy 6061-T6 plate having a center crack (20 mm) was repaired by varying no. of CFRP patches made of several UD CFRP plies. Asymmetrically bonded CFRP patched specimen were prepared using VARTM (Vacuum Assisted Resin Transfer Moulding). Different configurations of CFRP plies were tested with changes in stiffness ratio and environment temperature mainly at 80°C and room temperature. Using a computerized axial fatigue test machine the specimens were loaded under tension – tension fatigue load. Fatigue testing was carried out at 50% of yield strength of skin made of Al 6061-T6 alloy. Frequency of 9 Hz and Stress ratio, R = 0.1 were maintained throughout the experimentation. A set of three specimens under each temperature condition and patch configuration were tested and results were recorded. Fatigue crack propagation cycles till final failure, Nf of the specimen was monitored. The numerical simulations were carried out to find SIF at various crack lengths. The results were compared with experimental results. The tested specimens at elevated temperature showed an increase in fatigue cycles compared to room temperature specimens.

Investigation of the effect of sloping head fault in solid riveting on the strength of the joint

PurposeThe purpose of this study is to investigate how the sloping head fault in solid riveting affects the strength of the joint and to develop an efficient system for the solution of the problem.Design/methodology/approachFor rivet joints, 1.2-mm thick 2024-T3 plates were used. AD 2117 T4 solid rivets with a diameter of 3.2 mm were chosen for the joints. A new riveting mechanism has been created unmatched in the literature for solid rivets. In the riveting process, the bucking bar surface is positioned at a right angle to the riveting process axis. Alternative 5°, 10° and 15° fault angles were obtained. During the riveting process, a total of eight different test samples were produced, four for each of the tension-shear and cross-tension joints, by making 0°, 5°, 10° and 15° angles to the bucking bar. To determine the mechanical properties of the prepared samples, cross-tensile and linear tensile-shear tests were performed on a universal tensile testing machine. Special apparatus has been designed and produced for cross-tensile tests.FindingsAs a result of the tensile-shear tests, the decrease in the joint at 15° was 25% compared to the joint at 0°. There is no systematic change in elongation. As a result of the cross-tensile tests, there was a decrease in the cross-tensile force toward the sample with an error of 15°. Compared to the 0° joint, this decrease was approximately 14.5% in the 10° joint, while the decrease in the 15° faulty joint was 25.8%. It has been understood that riveting with an angle of 0° affects the strength very much.Originality/valueA new riveting mechanism has been created unmatched in the literature for solid rivets. Experimentally, it has been shown that forged rivets can be made very economically and properly. It has been experimentally proven how much the rivet head shape formed in the wrong forged rivet application changes the result.

Enhancement of tensile strength in AA 6061-T6 plates joined by gas tungsten arc welding using high entropy alloy filler sheet

This work has focused on enhancing the tensile strength of AA 6061-T6 plates by gas tungsten arc welding (GTAW) using an AA 1100-O sheet embedded with a high entropy alloy (HEA, Cr0.14Fe0.13Al0.26Cu0.11Si0.25Zn0.11) as a filler metal. HEA filler sheets were prepared by accumulative roll bonding (ARB). The prepared (AA 1100-O)-HEA filler metal was used to join the AA 6061-T6 plates. Phase formation and microstructural evaluations were carried out using an x-ray diffractometer and advanced electron microscopy in the (AA 6061-T6)-HEA weldment. The phase evaluation results revealed the presence of HEA with Al peaks and unveiled FCC phase formations and disappearance of the BCC phase owing to the incorporation of more FCC elements and less solid dissolution. The major FCC phase is attributed to the atomic radius mismatch among the incorporated metallic elements. The retention of the HEA phase after welding indicated thermal stability and sluggish diffusion behaviour. (AA 6061-T6)-10 wt.% HEA welded plates exhibited higher strength and plasticity due to the presence of nanocrystalline HEA, superior interfacial bonding between AA 6061-T6 and HEA elements, and the involvement of solid solution (178 MPa), dislocation (152 MPa), and grain boundary strengthening (27 MPa) towards the total strength (357 MPa).

A High-Pressure Shear Testing Approach to Measure Flow Stresses Near a Friction Stir Welding Tool

Abstract A new approach for measuring flow stresses near a spinning friction stir welding (FSW) tool is evaluated on AA 6061-T6 plate. The test consists of plunging a cylindrical tool with a flat face into the plate at different rotational speeds, using a variety of constant vertical loads. A viscosity-based model of the shear layer created under the tool is employed to estimate local flow stresses. The flow stresses measured by this approach exhibited an inverse relationship with temperature and a positive dependence on the pressure imposed by the spinning flat-faced tool. Compared to hot compression and hot torsion results, estimated flow stress levels in high-pressure shear were lower by 20–68 %, for similar temperatures and strain rates, owing to grain refinement induced by continuous dynamic recrystallization. This high-pressure shear approach could be used to characterize material behavior near a rapidly spinning FSW tool, leading to improved process model predictions.

Applicability of unique scarf joint configuration in friction stir welding of AA6061-T6: Analysis of torque, force, microstructure and mechanical properties

The present research introduces a unique concept of scarf joint technique in friction stir welding (FSW) of aluminum alloy AA 6061-T6 plates and an investigation on weld quality. A new joint configuration with two distinct scarf angles (75° and 60°) was considered in this study. The various aspects of welding were compared with contemporary simple square butt (SSB) joint configuration. Welding was carried out at a constant tool rotation speed (TRS), tool traverse speed (TTS) and tool tilt angle of 1100 rpm, 2 mm/s and 2°, respectively. The results are analyzed in terms of force and torque distribution, microstructure, macrostructure, and mechanical property perspective for different joint configurations. The study reveals the minimum amount of force and torque at 60° scarf angle joint configuration compared to that of square butt joint configuration. Macro study shows that all the joints were defect-free, and a prominent onion ring was present in the lower portion of the weld nugget (WN). Fine equiaxed grains with a minimum average grain size diameter of 6.82 μm were obtained in the WN of scarf joint configuration (SJC). The maximum ultimate tensile strength (UTS) and maximum average NZ hardness of 267 MPa and 83.82 HV0.1 were obtained in SJC3 at a scarf angle of 60°. It has been observed from the investigation that the joint efficiency increases from 72.5% (SSB) to 86% (SJC3) at a 60° scarf angle. This unique characteristic may lay an impetus on probable joint strength enhancement technique without increasing the production cost.

Fatigue Life Improvement of Cracked Aluminum 6061-T6 Plates Repaired by Composite Patches.

Bonded patches are widely used in several industry sectors for repairing damaged plates, cracks in metallic structures, and reinforcement of damaged structures. Composite patches have optimal properties such as high strength-to-weight ratio, easiness in being applied, and high flexibility. Due to recent rapid growth in the aerospace industry, analyses of adhesively bonded patches applicable to repairing cracked structures have become of great significance. In the present study, the fatigue behavior of the aluminum alloy, repaired by a double-sided glass/epoxy composite patch, is studied numerically. More specifically, the effect of applying a double-sided composite patch on the fatigue life improvement of a damaged aluminum 6061-T6 is analyzed. 3D finite element numerical modeling is performed to analyze the fatigue performance of both repaired and unrepaired aluminum plates using the Abaqus package. To determine the fatigue life of the aluminum 6061-T6 plate, first, the hysteresis loop is determined, and afterward, the plastic strain amplitude is calculated. Finally, by using the Coffin-Manson equation, fatigue life is predicted and validated against the available experimental data from the literature. Results reveal that composite patches increase the fatigue life of cracked structures significantly, ranging from 55% to 100% for different applied stresses.

Effect of bolt tightening on the fatigue behavior of GLARE double shear lap joints

In this paper, the effect of bolt torque tightening has been investigated on the fatigue behavior of GLARE in double shear lap configuration. To do so, experimental fatigue tests were conducted using GLARE3-5/4-0.4 specimens with applied torques of 0 (finger tightened), 2 and 4 Nm at different cyclic longitudinal load ranges to achieve the stress-life (S-N) curves. The results revealed that applying and increasing the clamping force enhances the fatigue life of the GLARE specimens. Furthermore, comparison of fatigue test results of GLARE and available monolithic aluminum alloy 2024-T3 plates indicated when the applied load range is low, the effect of clamping force is more noticeable in GLARE specimens due to longer fatigue crack growth life of GLARE. Also, the occurrence of fretting fatigue didn’t reduce the fatigue life of GLARE specimens considerably in contrary to aluminum sheets because of the laminated structure of GLARE. The obtained results can provide insights in designing bolted GLARE joints with superior fatigue in-service performance.

Experimental and numerical investigation on the fretting fatigue behavior of cold expanded Al-alloy 2024-T3 plates

In this paper, fretting fatigue behavior of the cold expanded plates have been studied both numerically and experimentally. For this purpose, fretting fatigue testing fixture has been designed and fabricated for simulating fretting condition on the holed plates. The test specimens were cut from aluminum alloy 2024-T3 plate and have been cold expanded at two sizes of 1.5% and 4.7% before fretting fatigue tests. Two values of cyclic longitudinal load and normal contact force were applied to the specimens. The results of the experiments revealed that applying high level of cold expansion affects the frictional force on the contact interface. Moreover, cold expansion makes the fretting fatigue phenomenon to be likely to occur at locations away from the hole. The obtained numerical results indicated that tensile residual stress would be generated at areas away from the hole edge by cold expanding the holes. During fatigue loading, the tensile residual stress is superimposed to the tensile fatigue load which intensifies the stress severity and reduces the fretting fatigue life. The intensity of the tensile residual stress increases by increasing the level of cold expansion. As a result, lower fretting fatigue life is expected on higher size cold expanded plates.