Thick Aluminum Plate Research Articles

Experimental study on the ignition mechanism of fuel tanks impacted by reactive material fragment

Abstract Fuel tanks are vital components in military assets, such as aircraft and vehicles, where they play a crucial role in operational safety and functionality. High-velocity impacts from fragments pose significant risks, potentially causing ignition and catastrophic damage. To understand the ignition mechanisms under such extreme conditions, a series of ballistic impact experiments were conducted using tungsten-zirconium (W/Zr) alloy fragments. These experiments simulated impacts on the ullage of a fuel tank made of a 2 mm thick aluminium plate. The experiments revealed that W/Zr alloy fragments create distinct perforations in the fuel tank plates. On the front plate, the fragments produced circular holes matching their diameters. However, on the rear plate, the fragments generated much larger, petal-shaped perforations, approximately three times their diameters. Additionally, the study identified a critical ignition velocity for these impacts. When W/Zr alloy fragments impacted the fuel tank at velocities exceeding 866.9 m/s, consistent ignition was observed. As the impact velocity increased further, the intensity of ignition within the fuel tank intensified. Moreover, the location of the ignition shifted progressively from the rear plate towards the front plate, indicating a complex interaction between fragment velocity and fuel tank response.

Effect of Relative Density on the Lateral Response of Piled Raft Foundation: An Experimental Study

The population surge has led to a corresponding increase in the demand for high-rise buildings, bridges, and other heavy structures. In addition to gravity loads, these structures must withstand lateral loads from earthquakes, wind, ships, vehicles, etc. A piled raft foundation (PRF) has emerged as the most favored system for high-rise buildings due to its ability to resist lateral loads. An experimental study was conducted on three different piled raft model configurations with three different relative densities (Dr) to determine the effect of Dr on the lateral response of a PRF. A model raft was constructed using a 25 mm thick aluminum plate with dimensions of 304.8 mm × 304.8 mm, and galvanized iron (GI) pipes, each 457.2 mm in length, were used to represent the piles. The lateral and vertical load cells were connected to measure the applied loads. It was found that an increase in Dr increased the soil stiffness and led to a decrease in the lateral displacement for all three PRF models. Additionally, the contribution of the piles in resisting the lateral load decreased, whereas the contribution of the raft portion in resisting the lateral load increased. With an increase in Dr from 30% to 90%, the percentage contribution of the raft increased from 42% to 66% for 2PRF, 38% to 61% for 4PRF, and 46% to 70% for 6PRF.

Achieving microstructural homogeneity in the stir zone across thick AA6061 welds using self-reacting bobbin tool friction stir welding

This study focuses into strategizing the usage of self-reacting bobbin tool friction stir welding (SRBT-FSW) to obtain consistent microstructural homogeneity along the thickness of AA6061 aluminium alloy (AA) thick plates during welding. The SRBT-FSW technology, distinguished by its dual-shoulder design, represents a significant step forward in FSW by eliminating the requirement for a backing anvil and promoting balanced heat distribution. This study seeks to address the issues of maintaining uniform microstructural characteristics throughout the weld zone, which is crucial for the mechanical performance and durability of welded joints in structural applications. The experimental study entails the systematic welding of AA6061 plates of 6 mm thickness using a self-reacting bobbin tool under a fixed processing condition. Electron backscatter diffraction (EBSD) was used to characterize the grain structure and phase distribution over the weld. Mechanical parameters like as tensile strength and hardness were determined to establish correlations between microstructure and mechanical performance. The results demonstrated that SRBT-FSW significantly enhances microstructural homogeneity across the weld zone, leading to improved mechanical properties. In the Bottom Zone (BZ), a refined grain structure with an average grain size (AGS) of 3.53 µm and a random or weak texture was observed, contributing to enhanced hardness and mechanical performance, with an ultimate tensile strength (UTS) of 220 MPa. In contrast, the Top Zone (TZ) exhibited a coarser AGS of 4.33 µm with a pronounced {111} crystallographic texture, resulting in a slightly lower UTS of 205 MPa. The Middle Zone (MZ), influenced by the greater heat input from both the TZ and BZ, showed an intermediate AGS of 3.99 µm, predominantly oriented along the {101} plane, and achieved a UTS of 194 MPa, with a slight reduction in ductility. This study highlights the potential of self-reacting bobbin tool friction stir welding as a reliable method for making high-quality, homogeneous welds in thick aluminium plates and paving way for their wider application in the aerospace, automotive, and shipbuilding industries, where homogeneous microstructural qualities are of significant importance.

Dissimilar unbeveled aluminum to steel butt joint achieved by laser-arc hybrid welding-brazing

In this study, unbeveled butt joints of 2 mm thick steel and aluminum plates were welded using a laser-arc hybrid process. The influence of welding speed and wire feed speed on joint weld formation, microstructures, and mechanical properties were investigated. The results indicate that using a laser-arc hybrid heat source enables good weld formation of steel/aluminum dissimilar metals without groove preparation, even under high welding speed conditions. The steel side interface formed Fe₂(Al,Si)₅ near the steel and Fe(Al,Si)₃ near the aluminum. As the welding heat input decreased, the thickness of the intermetallic compounds gradually reduced. With an increase in welding speed or wire feed speed, the tensile strength of the joint first increased and then decreased, reaching a maximum of 104.47 MPa. Cracks propagated rapidly along the intermetallic compound region, resulting in brittle fracture characteristics. The three-point bending test showed a maximum longitudinal bending angle of 53.82° and a maximum transverse bending angle of 36.54°.

Stepwise double-sided friction stir welding: an alternative for root defect mitigation in aluminium plates with lower gauge numbers

Penetration-induced fractional unbonded defects and flow-induced root flaws are part of the discontinuities of the conventional friction stir welded (FSW’ed) aluminium alloys with limited impact assessment/clarification in literature. The novelty of this study lies in the attempt to eliminate penetration-aided root defect via a stepwise double-sided welding process as well as identify its impact on loadbearing. As a result, the stepwise double-sided FSW welding of a thick aluminium plate (6 mm) was carried out while the microstructure, strength, and fracture modes of the ensuing welds were compared with the conventional (single-sided) friction stir welded counterparts. The stepwise double-sided FSW-welded joint demonstrated better tensile strength relative to the single-sided FSW-welded counterparts owing to its material flow consolidation (two-side deformation) and elimination of penetration-induced fractional unbonded region/root defect. The welding processes do not have a noteworthy influence on the fracture location of the welds as failure ensued via the stir zones of the respective welds. Transient breaking/brittle appearance, and ductile fracture modes were noticed in the single-sided and stepwise double-sided FSW-welded samples respectively. The stepwise double-sided FSW process is recommended as a better choice for thick workpieces relative to conventional FSW to improve the weld’s loadbearing resistance.

Experimental and Numerical Evaluation of Calcium-Silicate-Based Mineral Foam for Blast Mitigation

Cellular materials such as aluminum and polyurethane foams are recognized for their effectiveness in energy absorption. They commonly serve as crushable cores in sacrificial cladding for blast mitigation purposes. This study delves into the effectiveness of autoclaved aerated concrete (AAC), a lightweight, porous material known for its energy-absorbing properties as a crushable core in sacrificial cladding. The experimental set-up features a rigid frame made of steel measuring 1000 × 1000 × 15 mm3 with a central square opening (300 × 300 mm2) holding a 2 mm thick aluminum plate representing the structure. The dynamic response of the aluminum plate is captured using two high-speed cameras arranged in a stereoscopic configuration. Three-dimensional digital image correlation is used to compute the transient deformation fields. Blast loading is achieved by detonating 20 g of C4 explosive set at 250 mm from the plate’s center. The study assesses the mineral foam’s absorption capacity by comparing out-of-plane displacement and mean permanent deformation of the aluminum plate with and without the protective solution. Six foam configurations (A to F) are tested experimentally and numerically, varying in the foam’s free space for expansion relative to its total volume. Results show positive protective effects, with configuration F reducing maximum deflection by at least 30% and configuration C by up to 70%. Foam configuration influences energy dissipation, with an optimal lateral surface-to-volume ratio (ζ) enhancing protective effects, although excessive ζ leads to non-uniform foam crushing. To address the influence of front skin deformability, a non-deformable front skin has been adopted. The latter demonstrates an increased effectiveness of the sacrificial cladding, particularly for ζ values above the optimal value obtained when using a deformable front skin. Notably, using a non-deformable front skin increases maximum deflection reduction and foam energy absorption by up to approximately 30%.

Validation of Hole-Drilling Residual Stress Measurements in Workpieces of Various Thickness

BackgroundA recent revision to the ASTM E837 standard for near-surface residual stress measurement by the hole-drilling method describes a new thickness-dependent stress calculation procedure applicable to “thin” and “intermediate” workpieces for which strain versus depth response depends on workpiece thickness. This new calculation procedure differs from that of the prior standard, which applies only to thick workpieces with strain versus depth response independent of thickness.ObjectiveHerein we assess the new calculation procedures by performing hole-drilling residual stress measurements in samples with a range of thickness.MethodsNear-surface residual stress is measured in a thick aluminum plate containing near-surface residual stress from a uniform shot peening treatment, and in samples of different thickness removed from the plate at the peened surface. A finite element (FE) model is used to assess consistency between measured residual stress across the range of sample thickness.ResultsMeasured residual stress varies with sample thickness, with thinner samples exhibiting smaller near-surface compressive stress and a larger gradient of subsurface stress. These trends are consistent with both observed bending (curvature) of the removed samples and the trend in FE-calculated expected residual stress. The measured and expected residual stresses are in good agreement for samples of intermediate thickness, but the agreement decreases with sample thickness. Measured residual stress is invariant with gage circle diameter.ConclusionThe new thickness-dependent stress calculation procedure for hole-drilling provides meaningful improvement compared to thick-workpiece calculations.

Focused Electromagnetic Acoustic Transducers for Lamb Wave Inspection

Abstract Ultrasonic inspection of conductive samples can be performed using electromagnetic acoustic transducers (EMATs). These allow generation of guided waves, such as Lamb waves, in thin plates. Lamb waves are used for defect screening as they can travel long distances with relatively little attenuation. However, large wavelengths are used, which results in poor sensitivity to subwavelength sized defects. This work presents methods for using Lamb waves to detect smaller defects. Curved, geometrically focused EMATs were used to generate and detect Lamb waves in a 1 mm thick aluminum plate. The focal spot of these EMATs is investigated and the dependence of the focal spot dimensions and locations on the wavelength of the generation signal are presented. An array of geometrically focused detection EMATs was used to measure a 10×10×0.5mm square machined defect, simulating wall thinning. Perturbations in the pulse transmission in the region of the defect were detected, along with reflections, with each detector in the array sensitive to different defect features. B-scans and C-scans are presented utilizing these perturbations and reflections to locate, size, and image the machined defect. Analysis of data from the B-scan is shown to accurately size the defect width to within ±0.73mm. Very good agreement is shown between the C-scan images and the known location and orientation of the defect. Data fusion techniques are presented to combine data sets from different receiver EMATs and increase the defect detection capability, accuracy, and precision, with the potential for full defect sizing demonstrated.

On the cutoff, reappearance, and persistence of subsonic leaky A0 Lamb waves

Abstract Subsonic leaky A0 Lamb waves, whose phase speeds are lower than the fluid’s sound speed, exhibit several peculiar behaviours. In this work, we investigate three such behaviours: Cutoff, where the A0 branch cuts off at some point in the subsonic domain, reappearance, where the cut-off A0 branch reappears at lower frequencies, and persistence, where the A0 branch is never cut off at all. From the literature, we take the case of a 1 mm thick aluminium plate immersed in air of varying density. We then analyse its exact leaky A0 wave solutions by means of a sound radiation model that takes energy conservation into account. This analysis explains these peculiar behaviours by connecting them with the conditions that allow sound-radiating subsonic leaky A0 Lamb waves.

All-fiber 3 kW LP02 laser output based on long-period fiber grating for precise welding

An innovative all-fiber mode converter specifically designed for high-power fiber lasers is introduced. The mode converter relies on the coupling theory of long-period fiber gratings (LPFGs) and involves the fabrication of a LPFG, where the performance is meticulously studied by examining various fabrication parameters. The LPFG is integrated into a high-power fiber laser system to achieve efficient conversion from the LP01 mode to the LP02 mode with a conversion ratio of 90 % and a low transmission loss of only 0.088 dB. Under a 3.03 kW laser output, the LP02 fiber laser exhibits a remarkable laser-to-raman peak intensity ratio, which is 15.98 dB higher than that of the signal-mode fiber laser. Furthermore, during the welding process of a thick aluminum plate, the LP02 fiber laser demonstrates a significant increase of 1.2 times in the depth of the weld pool morphology compared to the signal-mode fiber laser, particularly evident when operating at a laser welding head speed of 100 mm/s. The mode converter with LPFG exhibits lower insertion loss, enhanced power-handling capacity, making it ideal for diverse high-power fiber laser applications with promising practical prospects.

Ultrasonic Through-Metal Communication Based on Deep-Learning-Assisted Echo Cancellation.

Ultrasound is extremely efficient for wireless signal transmission through metal barriers due to no limit of the Faraday shielding effect. Echoing in the ultrasonic channel is one of the most challenging obstacles to performing high-quality communication, which is generally coped with by using a channel equalizer or pre-distorting filter. In this study, a deep learning algorithm called a dual-path recurrent neural network (DPRNN) was investigated for echo cancellation in an ultrasonic through-metal communication system. The actual system was constructed based on the combination of software and hardware, consisting of a pair of ultrasonic transducers, an FPGA module, some lab-made circuits, etc. The approach of DPRNN echo cancellation was applied to signals with a different signal-to-noise ratio (SNR) at a 2 Mbps transmission rate, achieving higher than 20 dB SNR improvement for all situations. Furthermore, this approach was successfully used for image transmission through a 50 mm thick aluminum plate, exhibiting a 24.8 dB peak-signal-to-noise ratio (PSNR) and a about 95% structural similarity index measure (SSIM). Additionally, compared with three other echo cancellation methods-LMS, RLS and PNLMS-DPRNN has demonstrated higher efficiency. All those results firmly validate that the DPRNN algorithm is a powerful tool to conduct echo cancellation and enhance the performance of ultrasonic through-metal transmission.

Detection of a Submillimeter Notch-Type Defect at Multiple Orientations by a Lamb Wave A0 Mode at 550 kHz for Long-Range Structural Health Monitoring Applications.

The early detection of small cracks in large metal structures is a crucial requirement for the implementation of a structural health monitoring (SHM) system with a low transducers density. This work tackles the challenging problem of the early detection of submillimeter notch-type defects with a semielliptical shape and a groove at a constant width of 100 µm and 3 mm depth in a 4.1 mm thick aluminum plate. This defect is investigated with an ultrasonic guided wave (UGW) A0 mode at 550 kHz to investigate the long range in thick metal plates. The mode selection is obtained by interdigital transducers (IDTs) designed to operate with a 5 mm central wavelength. The novel contribution is the validation of the detection by pulse-echo and pitch and catch with UGW transducers to cover a distance up to 70 cm to reduce the transducers density. The analysis of scattering from this submillimeter defect at different orientations is carried out using simulations with a Finite Element Model (FEM). The detection of the defect is obtained by comparing the scattered signals from the defect with baseline signals of the pristine laminate. Finally, the paper shows that the simulated results are in good agreement with the experimental ones, demonstrating the possible implementation in an SHM system based on the efficient propagation of an antisymmetric mode by IDTs.

Multi-objective analysis of solid-state joints: Effect of tool pin shoulder clearance on thick dissimilar aluminum plates

ABSTRACT Friction stir welding is a well-established technique developed extensively over the past two decades for various applications. This study investigates the effect of repositioning the tool pin shoulder (0.18 mm) above the surface of a 12 mm thick dissimilar aluminum alloy (AA6063-AA5083) on tensile strength, welding temperature, and micro-hardness. Trials were conducted according to the L9 Taguchi method and further simulated using ABAQUS software. The input parameters spindle speed, tool pin length, and traversing speed were each tested at three levels. The impact of these parameters on weld quality was analyzed using ANOVA. Optimization of the process to achieve the desired temperature and tensile strength was carried out using grey relational analysis for both experimental and simulated results. Mathematical models were generated using the multi-variable regression method and the response surface method (RSM). Predicted data from the RSM model were compared to experimental outcomes, revealing a maximum deviation of 8.69% for temperature and 5.17% for tensile strength. Furthermore, the study demonstrated that ABAQUS accurately simulates the friction stir welding process with an accuracy of up to 93.71%.

Machining-Induced Distortion during Peripheral Milling of High Strength Aluminum Parts

In the aerospace and automotive industries aluminum sheet metal components are often produced by forming and post-machining. Due to the change in the complex stress state during manufacturing, part distortion is a major challenge. The overall objective of this work is to streamline the process chain to minimize production costs. For this, a determination of the material properties and analysis of the machining process parameters and their influence on the resulting distortion are required.First, tensile tests of the aluminum alloy EN AW-7075-T651 were performed. Subsequently, a series of machining tests were conducted to examine the effect of the machining process on the resulting part distortion. This paper presents machining-induced part distortion depending on the variation of the process parameters for down milling operations of thick aluminum plate material. It was found that the radial depth of cut and the cutting speed have a high impact on the resulting distortion, while the feed rate has a small influence.

Cutting thick aluminum plates using laser fusion cutting enhanced by dynamic beam shaping

Cutting thick plates is affected not only by the laser power but also by the cut kerf width and the melt flow dynamics that determine the ejection of the molten material. Employing the same laser beam intensity distribution for various thicknesses is the limiting factor when cutting thicker plates. This paper investigates fiber laser fusion cutting of 25 mm thick aluminum with dynamic beam shaping (DBS). While both static and longitudinal dynamic intensity distributions fail to cut this thickness with a 4 kW laser power, a cut through is achieved using annular and elliptical intensity distributions. However, an improvement of 45% in cutting speed can be achieved using an elliptical intensity distribution compared to an annular one. In order to understand the effect of the beam shape, an infrared thermal camera is used to study lateral heat propagation when using different process parameters. Moreover, to analyze the melt flow when changing the DBS frequency, high-speed imaging is utilized to observe the molten material inside the cut kerf. Finally, the cut edge quality is investigated for different cutting conditions.

A single crystal Lamb wave sensing array

This paper reports on a multi-element relaxor ferroelectric single crystal (RFSC) based acoustic emission (AE) sensor called LAMDA (linear array for modal decomposition and analysis). This sensor is being developed foracoustic-signature detection applications, including for AE-based damage detection on space-based and undersea platforms. RFSC [011] Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (or PIN-PMN-PT) was machined into 200 μm thick × 1 mm long × 4 mm wide elements, with 16 of these elements arranged on a flexible-polyimide-carrier to form a LAMDA. This sensor was bonded to a 1.6 mm thick aluminium plate with dimensions 600 mm x 600 mm. Acoustic emissions consisting of Lamb waves (e.g., A0, S0) were generated in the plate using both piezoceramic (Pz26) disk-actuators and pencil lead breaks (PLBs). LAMDA measurements and one-dimensional laser-vibrometry were undertaken on the plate and compared with two-dimensional multi-physics model predictions. The plane-strain model geometry comprised a rectangular-section 1.6 mm thick and 600 mm long with a LAMDA located centrally. An AE, being a 5.5-cycle Hann-windowed function with centre-frequencies 300–1000 kHz, was introduced 150 mm from the LAMDA via point loading perpendicular to the surface. The Lamb wave dispersion-curves generated from the model showed good agreement with the experimental curves determined from LAMDA and laser-vibrometry.

Impact localization on structures using remote sensors

Acoustic waves provide a wealth of information about their source and the environment in which they propagate. For large structures, it is sometimes desirable to use acoustic remote sensing methods to collect structure-borne sound because the microphone array and structure can then be maintained separately. Traditional time-of-flight array signal processing techniques used to localize acoustic sources are ill-suited for structures due to the potential for complicated propagation paths, the dispersive propagation of acoustic waves in structures, and the coupling of the vibrating structure and surrounding medium. Thus, source localization experiments were conducted using Matched Field Processing for a 6.4-mm thick circular aluminum plate excited by the impact of a 12.7-mm-diameter stainless-steel ball bearing dropped from 76-mm above the plate. This impulsive excitation of the plate contained frequencies between 0 and 5 kHz, resulting in wave speeds in the plate up to approximately 550 m/s. A linear array of 14 microphones with 51-mm spacing located 90-mm above the plate was placed in a random location such that it was not centered over the plate. Source localization results in both a quiet environment and an environment with additive white Gaussian noise are presented. [Sponsored by a SMART Scholarship, and the NEEC.]

Combination of Aluminum Plates of Different Thicknesses to Increase the Homogeneity of Radiation Treatment by Accelerated Electrons

Combination of Aluminum Plates of Different Thicknesses to Increase the Homogeneity of Radiation Treatment by Accelerated Electrons

The DISCS method for perforation simulation of thin metallic plates by a rigid projectile

The DISCS method had been developed for penetration analysis of an axisymmetric projectile with a slender nose into a semi-infinite medium. Recently, the authors developed an approximate approach to assess perforation of concrete slabs of finite thickness, using the DISCS method. The present paper extends the approximate model to the perforation analysis of ductile metallic thin plates and determines the key parameters of the projectile residual velocity, the target perforation limit, and the ballistic limit. The present investigation focuses on thin metallic plates, the thickness of which is considerably smaller than that of the concrete slabs and smaller in comparison to the projectile nose length. The method is rather simple, easy to implement and provides a fast solution. An idealized target is characterized by a set of discs of small thickness responding in the plate plane, disregarding the local damage around the penetration ductile hole. The in-plane response of the discs during penetration and perforation of an idealized target are calculated. The Residual Velocity upon perforation of the Idealized Target (RVIT) is lower than the residual velocity of the real plate since it disregards the local damage, hence, the RVIT is the lower bound of the true residual velocity of the real perforated thin plate. Therefore, a positive RVIT for the thin plate with a given thickness indicates right away that the real target will be perforated. Using the RVIT parameter, the proposed DISCS method turns into a series of RVIT-perforation problems of plates with thicknesses that are smaller than the real thickness, to determine the decreasing RVIT with increasing thickness, until the full thickness is considered. The analysis is carried out using the modified (hybrid) DISCS method, that aims at analyzing penetration depth into a thick target. The analysis is based on the theoretical field equations and the constitutive equations of the plate material. The proposed method is based on a theoretical model and on engineering insight. Neither empirical constants nor any calibrations are required. Validation of the proposed method is carried out thorough comparisons with numerous test data on ductile aluminum and steel plates of different thicknesses that are struck by rigid projectiles at different impact velocities. All the comparisons demonstrate very good correspondence between the proposed method predictions and the test data.

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.