Aluminum Specimens Research Articles

Enhanced Crashworthiness Parameters of Nested Thin-Walled Carbon Fiber-Reinforced Polymer and Al Structures: Effect of Using Expanded Polypropylene Foam

The in-plane loading conditions of carbon fiber/epoxy composite (CFRP) and aluminum nested-tube-reinforced expanded polypropylene (EPP) blocks were empirically examined. This study used crashworthiness metrics to estimate the best design configuration under quasi-static loading rates. The experimental phase began with lateral loading testing of single and nested aluminum and CFRP specimen. In-plane crushing experiments were performed on EPP foam blocks reinforced with nested tubes. Both single and nested aluminum tubes had comparable force–response curves and maintained their load-bearing capacity throughout testing. Despite a load-carrying capacity drop above a particular displacement threshold, the CFRP specimens had superior specific energy absorption (SEA) values due to their lightweight nature. The triple-tube nested specimens with two smaller tubes exhibited the best SEA results (1.72 and 1.88 J/g, respectively, for the aluminum and CFRP nested samples). During concurrent tube deformation, the nested samples showed a synergistic connection that increased energy absorption, especially in the EPP foam blocks with reinforced tubes. The study also examined the effects of building nested specimens with aluminum exterior tubes and CFRP inner tubes, and vice versa. This method showed that CFRP tubes within aluminum outer tubes lowered specimen weight (from 93.1 g to 67.7 g) and energy absorption (from 160.2 J to 153.3 J). However, the weight reduction outweighed the energy absorption, increasing SEA values for certain composite material configurations (from 1.72 J/g to 2.26 J/g).

EddyBot: A multichannel FPGA-based Eddy Current Testing mobile robot

We introduce EddyBot, a novel integration of a multi-channel FPGA-based Eddy Current Testing (ECT) scanner within a mobile robot designed for autonomous non-destructive testing (NDT). EddyBot distinguishes itself by leveraging advanced signal processing, real-time robotics control, and efficient data synchronization to significantly enhance inspection accuracy and efficiency. Our contributions are (i) the deployment of a Zynq-7020 FPGA for fast data acquisition and processing, (ii) alongside the Robot Operating System (ROS) for precise and real-time control with Kalman filtering (KF) sensor fusion for pose estimation. (iii) We further optimize defect detection and localization through a novel data synchronization approach, correlating the robot’s pose with ECT signals to a mean synchronization delay of only 11.77 ms. This allows for precise localization of defects within 0.18 cm, improving the overall reliability. The robot’s performance was evaluated on aluminum and ferromagnetic specimens, highlighting the system’s capability to detect defects with high accuracy.

Low-cost two-dimensional digital image correlation system

A low-cost digital image correlation (DIC) system for measuring two-dimensional displacement fields is described. Using an off-the-shelf camera, lens, and open-source DIC analysis software, displacement fields in aluminum and steel dog-bone tensile specimens were measured. Correction for out-of-plane motion is used to obtain strains from the displacement fields. Proposed DIC strain measurement system is validated using conventional thin-film strain gauges for strains below 1%. Average strain measurements from the DIC system were found to be within 1% of the measurement obtained using strain gauges. For strains between 1% and 10%, strain histories from the DIC systems displayed excellent correlation with strain measurements obtained using an extensometer.

A detailed study on optimizing DMLS process parameters to enhance AlSi10Mg metal component properties

This study investigates the effects of laser power, scan speed, and hatch distance on the features of aluminium specimens produced using direct metal laser sintering (DMLS). By systematically varying these parameters, we identified optimal combinations for producing high-quality metal components. Our findings were validated through reproducible printing processes. Analysis of variance (ANOVA) and grey relational analysis (GRA) were employed to optimize the production parameters further. We found a significant trade-off between laser power, tensile strength, and fatigue resistance, with laser power having the most substantial impact on mechanical properties, microstructure, and surface roughness. Statistical analysis confirmed that higher laser power improves mechanical characteristics but may increase surface roughness. These insights are crucial for enhancing the efficiency and quality of DMLS-produced metal components.

Estimating the Depths of Normal Surface Notches Using Mode-Conversion Waves at the Bottom Tip.

In this work, a two-parameter inversion problem is analyzed, related to surface crack widths for measuring depths of normal surface notches, based on a laser-based ultrasonic measurement method in the time domain. In determining the depth measurement formulas, the main technique is the time delay between reflected and scattered waves. Scattered waves are generated by two reflections along the bottom and three mode transformations at the surface of the crack tips. Moreover, the scattering angle of the mode-conversion waves is 30°. These two key factors lead to corrected item "2wβ" in the depth measurement formula. A laser-based ultrasonic experimental platform is built to generate and receive surface waves in a non-contact manner on aluminum and steel specimens with surface cracks. The depth measurement method proposed in this paper has been validated through theoretical, simulation, and experimental methods. Finally, in this paper, an effective approach for quantitatively measuring crack depths, based on laser ultrasound, using the time-domain properties of surface wave propagation is provided.

Effects of surface roughness parameters on the shear strength of AA 6061-T6 aluminium alloy in structural adhesive bonding applications

This study aims to investigate the effects of the surface roughness of an aluminium substrate on the adhesive joint strength of aluminium–aluminium specimens prepared using epoxy and methyl methacrylate adhesives for shear strength tests. Aluminium surfaces were mechanically abraded using silicon carbide (SiC) papers with different grit sizes in two different modes. The evaluated bonding performance characteristics included the maximum bonding strength and residual strength of the adhesive joints after their exposure to various environmental conditions. The results demonstrated that excellent adhesion characteristics were obtained at the optimum SiC grit size (grit-80) regardless of the adhesive type. In addition, the topographical and morphological properties of the aluminium surfaces were studied before and after mechanical abrasion via surface profilometry and scanning electron microscopy, respectively. A possible mechanism was proposed to explain the observed shear strength changes and respective modes of fracture after sample exposure to air, de-ionised water, and aqueous salt solutions.

A novel method for stress measurement utilizing the Rayleigh wave virtual superimposed interference spectrum

This study presents a novel stress measurement method utilizing the Rayleigh waves virtual superimposed interference spectrum (RW-VSIS). This method achieves stress measurements by exploiting the effect of stress on the superimposed interference spectrum of two beams of Rayleigh waves. Firstly, the effect of stress on Rayleigh wave velocity is theoretically investigated by partial wave theory and matrix solving algorithm. The theoretical results show that the Rayleigh wave propagation direction versus the stress direction will affect the wave velocity and the time of flight (TOF). Then, a theoretical model of RW-VSIS under pre-stress is derived. It's found that the stress will dominate the first characteristic frequency (FCF). The regulation effects of propagation distance and angle on FCF are discussed. Finally, the feasibility of stress measurement based on the FCF is validated through experiments. The impact of stress on TOF and FCF is comparatively analyzed. The results show a significant improvement of stress measurement by FCF in the superimposed interference spectrum, compared to the TOF in time domain waveform. With a calibration and verification test for the unknow coefficient of an aluminum specimen, the experimental examination of the stress shows a maximum error of less than 4 MPa indicating good measurement accuracy.

Sustainable adhesives: Exploring boronic ester vitrimers containing lignin microparticles

The market of epoxy resin-based adhesives is constantly growing in the automotive, electronics, and healthcare industries thanks to their unique features such as high bonding strength, durability, and corrosion resistance. In this work, alternative sustainable vitrimer adhesives, containing from 20 to 50 wt% of lignin microparticles, were prepared from epoxidized linseed oil (ELO) and a boronic ester dithiol crosslinker (DBEDT), in the absence of solvents and catalysts. The addition of unmodified commercial Kraft lignin to the composites directly influences their thermal and mechanical properties and determines their bonding capacity between several adherent substrates, also affecting the rewelding potential. The lignin-vitrimer composites and the corresponding neat vitrimer matrix exhibited values of lap shear strengths in the range of 9 to 17 MPa, when tested as adhesives with aluminum, stainless steel, and wood specimens, and good to excellent rewelding capability. The amount of lignin microparticles influences the balance between cohesive and adhesive forces during the separation of the adhered aluminum surfaces and the eventual joint failure. In the case of the composites with 20 wt% of lignin, lap shear strength remains constant even after four cycles of rebonding via compression molding, indicating that the best rewelding performance is associated with previous cohesive failure when the adhesive remains on both aluminum sheets' surfaces. In addition, the adhesion was preserved for 83 % of the initial value after 24 h immersed in water. Importantly, biodegradability in both soil and seawater was enhanced by the presence of the lignin filler. In summary, the simple preparation strategy of bio-based vitrimer composites coming from two natural sources could pave the way to green alternatives for industrial applications, such as epoxy-based adhesives.

Modification Of Impact Testing Tools For Research Of Aluminum Alloys Energy Absorption Profile

One of the most popular materials used in industry is aluminum and its alloys. The aluminum manufacturing process is likely to undergo a welding process. Aluminum can be welded by gas or arc welding, but arc welding is more satisfactory. The welding process on aluminum alloys has the potential to present a situation similar to Age hardening. This research was conducted to dig deeper into the impact of welding on the second phase strengthening mechanism in several series of aluminum alloys using impact test equipment with the addition of a modified digital instrumentation device. Modifications were made to the GOTECH impact test equipment model Charpy impact test 0027 by changing the pendulum and adding a plate to the holder to conform to the ASTM E23-02a standard and adding digital instrumentation tools, including load cells, amplifiers, data acquisition, and power supply. The specimens used were aluminum 5052 and 6061 with variations of base metal and TIG welded V 60°. The results of the modified impact test equipment can display a graph of the impact energy absorption of each specimen. Comparison between the manual calculation of absorbed impact energy and digital calculation of 5052 base metal aluminum specimens has an average deviation of 11,716 J, 5052 welded specimens have an average deviation of 1.341 J, 6061 base metal specimens have an average deviation of 0.729 J, and 6061 welded specimens has a mean of 0.845 J.

Effect of hybrid ratio and sintering temperature on hardness properties of hybrid AMCs

The present research work is aimed toward fabrication of hybrid Aluminium matrix composites (AMCs) of different hybrid ratios of Alumina (Al2O3) and Silicon Carbide (SiC) followed by investigation of their microstructure and hardness properties. Hybrid AMCs were fabricated through powder metallurgy process by adding 5 wt% and 10 wt% mixture of Al2O3 and SiC reinforcements of various hybrid ratios (0:1, 1:3, 1:2, 1:1, 3:1, 2:1 and 1:0) with the pure Aluminium powder. The mixture powder were properly mixed by ball milling arrangements for 6 h. The mixture powder were preheated at 500 °C for 2 h in a high temperature programmable tube furnace followed by immediate compaction under a closed die at 1500 psi pressure through automatic hydraulic press. The compacted specimens were then sintered at 350 °C, 500 °C and 650 °C for 2 h in the same furnace. Hardness test of the fabricated hybrid AMCs were carried out by Vickers Micro-hardness testers and hardness values were measured by the integrated software. The hardness properties of hybrid AMCs also were compared with the hardness properties of pure Aluminium specimens fabricated through the same process route and process parameters. It is interestingly observed that hardness of hybrid AMC is more when pure Aluminium powder is reinforced with only SiC of same wt.% for both the cases (5 wt% and 10 wt% reinforce AMCs) and it decreases with decrease of weight fraction of SiC and simultaneously increase of weight fraction of Al2O3 keeping total weight fraction of mixture as constant.

Digital shearography for NDT: Study on a novel experiment based method for removing global deformation✰

Fringe patterns are typically produced as the results of traditional optical Nondestructive Evaluation (NDE) employing digital shearography. Structural flaws affect the response of the surrounding material to a certain loading, resulting in unique fringe patterns that are related to the local deformation. Smaller defect information, however, can be easily lost in the fringe pattern caused by global deformation during the flaw detection procedure. In order to improve the flaw detection capabilities of this technology, it is important to streamline the inspection process and to simplify the interpretation of the results. This study proposes a practical and effective methodology that experimentally removes fringe patterns caused by global deformation in digital shearography and only retains the defect information. For shearographic Non-Destructive Testing (NDT), two sets (3 or 4 images) of temporal phase-shifted interferograms under different loads P1 and P2 are recorded. This novel approach involves recording one additional set of temporal phase-shifted interferograms at a load between P1 and P2, e.g. P1’. Two phase maps of shearograms can be generated using the phase shift technique, corresponding to the two loads Δ2 = (P1’-P1) and Δ1 = (P2-P1), respectively. Because of the nondestructive nature of the testing, the magnitude of the loads P1 and P2 is small, and the 1st derivative of global deformation in the shearing direction of the test part is assumed to be linear. Therefore, a linear coefficient C based on the two shearograms can be determined. The information from global deformation is then removed by subtracting the shearogram generated with the small load Δ2 multiplied by the correlation coefficient C from the one obtained with the relatively large load Δ1. This technique is further improved by calculating a complete surface linear coefficient Cij, which improves the detail processing of the deformation of samples with complex geometry and mechanical properties. This technique is shown to effectively assess a wide range of structures, including aluminum specimens with prepared flaws and intricate composite laminates. The experimental findings demonstrate that the suggested technique improves the non-destructive testing capabilities of digital shearography, thereby simplifying defect detection and visualization.

Sintering of 3D-printed aluminum specimens from the slurry-based binder jetting process

This work investigates a novel method of producing complex-shaped aluminum parts by slurry-based binder jetting and sintering. In this process, a green body is built up by layer-wise deposition of an aqueous aluminum suspension and selective powder bonding by ink-jet printing. The powder bulk generated from the suspension shows an increased density compared to powder-based binder jetting and, thus, a high initial density for the subsequent densification step. This allows for higher final densities and reduced shrinkage. Aluminum is of special interest as it is widely available and of low density but challenging to sinter due to an oxide skin surrounding every particle. The research in this paper investigates the effects of the sintering atmosphere and sintering additives on the microstructure of powder compacts produced by slurry-based binder jetting. The incorporation of magnesium as an additive during the sintering process of aluminum has been found to substantially improve densification during sintering in an argon atmosphere.

Experimental and numerical analysis of the behavior of rehabilitated aluminum structures using chopped strand mat GFRP composite patches

PurposeThis paper comprehensively addresses the influence of chopped strand mat glass fiber-reinforced polymer (GFRP) patch configurations such as geometry, dimensions, position and the number of layers of patches, whether a single or double patch is used and how well debonding the area under the patch improves the strength of the cracked aluminum plates with different crack lengths.Design/methodology/approachSingle-edge cracked aluminum specimens of 150 mm in length and 50 mm in width were tested using the tensile test. The cracked aluminum specimens were then repaired using GFRP patches with various configurations. A three-dimensional (3D) finite element method (FEM) was adopted to simulate the repaired cracked aluminum plates using composite patches to obtain the stress intensity factor (SIF). The numerical modeling and validation of ABAQUS software and the contour integral method for SIF calculations provide a valuable tool for further investigation and design optimization.FindingsThe width of the GFRP patches affected the efficiency of the rehabilitated cracked aluminum plate. Increasing patch width WP from 5 mm to 15 mm increases the peak load by 9.7 and 17.5%, respectively, if compared with the specimen without the patch. The efficiency of the GFRP patch in reducing the SIF increased as the number of layers increased, i.e. the maximum load was enhanced by 5%.Originality/valueThis study assessed repairing metallic structures using the chopped strand mat GFRP. Furthermore, it demonstrated the superiority of rectangular patches over semicircular ones, along with the benefit of using double patches for out-of-plane bending prevention and it emphasizes the detrimental effect of defects in the bonding area between the patch and the cracked component. This underlines the importance of proper surface preparation and bonding techniques for successful repair.Graphical abstract

A novel impact indentation technique with dynamic calibration method for measurement of dynamic mechanical properties

High strain rates and continuous real-time data acquisition are difficult to balance in existing impact indentation techniques. Meanwhile, the inaccuracy of the testing P-h curves limits the development of quantitative applications for dynamic testing of mechanical properties at micro region. This article develops a momentum exchange impact indentation testing method, which extends the testing range of strain rate to above 105 s−1, and at the same time avoids secondary impact. Impact indentation tests are conducted on single-crystal aluminum specimens with impact velocity from 76.9 to 176 mm/s. Based on calibrated data, the comparison of calculation methods for dynamic hardness is carried out. The dynamic elastic modulus is obtained by means of the Oliver-Pharr method, which increases from 71.9 to 89.4 GPa with increasing impact velocity. A multi-dimensional data analysis method is proposed based on the obtained experimental data to quantitatively study the damping and stiffness characteristics of materials. This testing method is particularly useful for quantitatively obtaining the micro region dynamic mechanical properties of solid materials at high strain rates.

Damage detection of thin plates by fusing variational mode decomposition and spectral entropy

This paper presents a new approach for damage detection in thin plates by fusing variational mode decomposition and spectral entropy (VMD-SE). In this method, after the received signal is decomposed into some intrinsic mode functions (IMFs) by variational mode decomposition (VMD), the spectral entropy ratio of the first and last IMFs is calculated for optimizing the VMD’s parameters and improving its decomposition performance. Moreover, the cross-correlation coefficient between the decomposed IMFs and the reference signal is computed to separate the desired IMF, which contains more damage information. Finally, the spectral entropy of the obtained IMF is calculated as an indicator for assessing the damage’s severity. The comparative analysis of the simulated signal clearly shows that only the proposed method can successfully separate the damage-related and reference signals. To verify the VMD-SE method, damage detection of two different types of damage on aluminum and composite fiber-reinforced polymer (CFRP) plates is conducted by using this new approach. The experimental results demonstrate that the parameters of VMD affect greatly its decomposition performance, and the best parameters are selected. The results also indicate that the normalized spectral entropy monotonically increases when the diameter of the through-hole or the length of the scratch increases. In addition, the correlation coefficients of the fitting lines of the plates are larger than 0.998. The experimental results of aluminum specimens demonstrate that the damage’s location has an influence on the normalized spectral entropy. At last, based on the linear relationship, the severity of damage in the fourth specimen is identified. The identification results demonstrate that the relative error of the aluminum and CFRP plates is less than 7.34%, which indicates that this new algorithm by fusing VMD and spectral entropy can detect the damage size in thin plates accurately and efficiently.

Investigating a defect width identification based on half-peak width for LDC-based eddy current testing

ABSTRACT The eddy current testing (ECT) technology based on the Inductance-to-Digital Converter (LDC) has the advantages of low power consumption and simple signal conditioning circuitry, which contributes to the miniaturisation of the instrument and low power consumption design. Existing defect identification methods primarily focus on the conventional Analog-to-Digital Converter (ADC)-based ECT. These methods rely on complex analytical models to analyze the phase and amplitude information of voltage signal. However, these approaches do not apply to the LDC-based ECT. The paper proposes a method to identify defects employing the R p -Inductance 2D plane, and use the half-peak width of the inductance signal to evaluate the defect width for symmetric slots. Using finite element simulation and experimental verification, the half-peak widths of the inductive signal wave crests at the defects are the same for the four slots with 1 mm width and different depths on the aluminum specimen; for four wire-cut slots with 4 mm depth and different widths, the half-peak widths are positively correlated with the defect widths. These experimental results demonstrate that the relationship between crack width, wave crest, and half-peak width can serve as the foundation for width identification and classification. This also offers a fresh perspective for further quantifying crack widths.

Study on fatigue crack growth property of abrasive waterjet peened aluminum alloy

Abrasive waterjet peening is a favorable surface treatment method for improving the fatigue resistance of metal materials. An insight into the fatigue crack growth properties of AWJ peened specimens is meaningful for obtaining better strengthening performance. In present work, a numerical model of AWJ peening was established and experimentally validated for investigating the fatigue crack growth characteristics of Aluminum specimens. The effect of peening and loading conditions on the fatigue performance was also analyzed. The results indicated that the stress intensity factor at the peened region was enhanced and the crack propagation was significantly inhibited by the compressive residual stress. The influence of compressive residual stress on the effective stress factor range is greater under lower external load and higher loading ratio. The fatigue life for reaching the crack length of 40 mm is increased by 37%, 60% and 98% after peening by using the intensity of 0.6 mmA, 0.8 mmA and 1 mmA, respectively.

An application of machine learning for material crack diagnosis using nonlinear ultrasonics

Crack diagnosis in non-destructive testing often requires reference data from the structure before damage or a considerable amount of response data. Also, detecting compression cracks is challenging. In this study, a machine learning-based method is proposed for diagnosing cracks in structures under compression. The method consists of convolutional neural networks (CNN) and fully connected networks (FCN). The CNN extracts features from nonlinear ultrasonic signal data, and the features determine the occurrence of fatigue cracks in a target specimen. Four types of input data are defined in accordance with the number of input frequency combinations. The performance of the proposed method is investigated using each data type to secure efficiency and accuracy in diagnosing aluminum specimens under various compression conditions. As a result, the F1 score, a measure of accuracy, of the proposed method depends on the number of input frequency combinations. The method detects high-compression cracks with high accuracy compared to the present technology specialized for compression cracks in a certain data type. A high accuracy of more than 96% is achieved with less computation time. The proposed method will provide an accurate crack diagnosis for compression cracks with reduced time and effort.

Effect of microtexture morphology on the tribological properties of PI/EP-PTFE-WS2 coating under starved oil and dry sliding wear

The limited wear resistance of aluminum alloys constrained their applications and longevity. Surface microtexture combined with polymer coating technology can prolong the service life of aluminum alloy materials under extreme conditions of aerospace. A370 aluminum specimens were textured with three types of microtexture surfaces including circular pits, rectangular grooves and cross grids. A PI/EP-PTFE/WS2 coating was designed and prepared on the surfaces of these textures by liquid spraying to improve the tribological properties of A370 aluminum under starved oil and dry sliding wear. The influences of different micro-texture morphology on the tribological performances of these coatings were experimented. The results indicated that the surface qualities of the micro-textures are improved by coating deposition on their surfaces. The friction coefficients of the coated surfaces on all micro-texture are effectively reduced under the relatively stable wear stage compared to the sample without micro-texture coating. The coating on the pitted texture exhibits superior performance in friction tests, reducing average coefficients and wear rate by 13.58% and 35.34% in dry sliding wear, and by 16.18% and 83.98% under the starved oil lubrication compared to the non-textured substrate, respectively. This is followed by the coating on cross-mesh texture and the rectangular groove texture. The reason is that the pitted texture facilitates the local stress release of coating during the process of coating deposition due to its smaller spacing between pits and higher density of pits per unit area. The bearing capacity of the pitted texture is highest and its deformation is the lowest. The wear debris created in the friction process is more easily accumulated in the pit units, which results in a reduction in wear.

Residual Stresses in a Wire and Arc-Directed Energy-Deposited Al–6Cu–Mn (ER2319) Alloy Determined by Energy-Dispersive High-Energy X-ray Diffraction

In order to enable and promote the adoption of novel material processing technologies, a comprehensive understanding of the residual stresses present in structural components is required. The intrinsically high energy input and complex thermal cycle during arc-based additive manufacturing typically translate into non-negligible residual stresses. This study focuses on the quantitative evaluation of residual stresses in an Al–6Cu–Mn alloy fabricated by wire and arc-directed energy deposition. Thin, single-track aluminum specimens that differ in their respective height are investigated by means of energy-dispersive high-energy X-ray diffraction. The aim is to assess the build-up of stresses upon consecutive layer deposition. Stresses are evaluated along the specimen build direction as well as with respect to the lateral position within the component. The residual stress evolution suggests that the most critical region of the specimen is close to the substrate, where high tensile stresses close to the material’s yield strength prevail. The presence of these stresses is due to the most pronounced thermal gradients and mechanical constraints in this region.