Thin Alloy Research Articles

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.

Numerical simulation of pre-cracked thin aluminum alloy skin repaired with a FRP patch: Pre-crack length studies

The fatigue life of a thin pre-cracked aluminium-alloy panel, repaired with Carbon Fiber Reinforced Plastics (CFRP) patch on one side, is investigated using a numerical model. CFRP plies of different lengths are used to form patch which in turn repair pre-cracked aluminium skin. Numerical studies are performed to determine variation in stress intensity factor (SIF) range and bulging out deflection of specimen subjected to minimum and maximum fatigue load. Patch width to pre-crack and length to pre-crack ratio are kept constant for different pre-crack studies. Numerical simulations are carried out for three different pre-crack length. Three different patch configurations are studied for each pre-crack length. Maximum stress considered is at 50 % yield strength of aluminium skin. The numerical model is simulated by using ANSYS 15.0, a Finite Element Analysis package. The interface behaviour between the skin and the patch is simulated by using cohesive zone material model (CZM). Stress intensity factor (SIF) is determined from J-integral results. Relation between SIF range and crack length can be used to determine fatigue crack propagation by invoking the Paris law. It is found that with increasing the patch length, ΔKI decreased significantly which may result into the increase of the fatigue life.

Comprehensive characterization of AA 2024T3 fiber metal laminate with nanosilica‐reinforced epoxy based polymeric composite panel for lightweight applications

AbstractFiber metal laminates (FMLs) are a hybrid composite material used in aircraft structural parts. They are fabricated by stacking thin aluminum sheets with a fiber‐reinforced polymer composite. In this research work, nanosilica was mixed with epoxy resin in different weight percentages such as 0, 1, 3, 5, and 7 wt% for the preparation of FML. Nanosilica was used as a secondary reinforcement in the epoxy resin to improve the interfacial bonding and mechanical strength of the FML. The morphology and chemical compositions of the cured nanosilica‐dispersed epoxy resin and aluminum were examined using Fourier transform infrared spectroscopy, X‐ray diffraction, field‐emission scanning electron microscope, and energy‐dispersive X‐ray analysis. Thermogravimetric analysis was used to investigate the thermal stability of epoxy before and after the addition of nanosilica. FML was prepared using the hand layup and compression molding processes by sandwiching thin aluminum alloy sheet and E‐glass fiber. The FML specimens were cut using an abrasive water jet machine as per ASTM standards for determining their mechanical characteristics such as tensile strength, flexural strength, and short‐beam strength. Vibrational analysis was undertaken, and the natural frequency and damping factor for the FML specimens were determined. The results revealed that the tensile strength of pure FML was increased by 7% for 3 wt% nanosilica‐dispersed FML. Flexural and interlaminar shear strength was increased by 30.5% and 10.9%, respectively for the 1 wt% nanosilica‐dispersed FML was compared to pure FML.

Characteristics of Thin High Entropy Alloy Films Grown by Pulsed Laser Deposition

Starting from solid-solutions (SS) of AlCoCrFeNix high-entropy alloys (HEAs) that have been produced with high purity constituent elements by vacuum arc remelting (VAR) method varying the nickel molar ratio x from 0.2 to 2.0, we investigated the synthesis of protective thin films of HEAs and high-entropy nitrides (HENs) with the aid of the pulsed laser deposition (PLD) system. The structure of all ten available bulk targets have been examined by means of X-Ray Diffraction (XRD), as well as their elemental composition by means of energy dispersion X-ray spectroscopy (EDS). Three targets with nickel molar composition x = 0.4, 1.2 and 2.0 corresponding to BCC, mixed BCC and FCC, and finally FCC structures were used for thin film depositions using a KrF excimer laser. The depositions were performed in residual low vacuum (10−7 mbar) and under N2 (10−4 mbar) at room temperature (RT~25 °C) on Si and glass substrates. The deposited films’ structure was investigated using grazing incidence XRD, their surface morphology, thickness and elemental composition by scanning electron microscopy (SEM), EDS and X-ray photoelectron spectroscopy (XPS), respectively. A homemade four-point probe (4PP) set-up was applied to determine layers electrical resistance. Besides, a Nanoindentation (NI) was employed to test films’ mechanical properties. XRD results showed that all deposited films, regardless of the initial structure of targets, were a mixture of FCC and BCC structures. Additionally, the quantitative and qualitative EDS and XPS results showed that the elemental composition of films was rather close to that of the targets. The depositions under an N2 atmosphere resulted in the inclusion of several percentage nitrogen atoms in a metallic nitride type compound into films, which may explain their higher electrical resistivity. The Young’s modulus, nanohardness and friction coefficient values showed that the deposited films present good mechanical properties and could be used as protective coatings to prevent damage in harsh environments.

Effects of groove clearance size on gap bridging capacity in PWLBW of Ti6Al4V alloy sheet assembled in butt joint configuration: Numerical simulation and experimental assessment

In laser tailor-welding of metal sheets, it is difficult to keep the assembly clearance fixed due to plate specification deviation, tooling error, and thermal deformation. In this paper, the influence of clearance size on gap bridging capacity and in turn the seam appearance quality was investigated for thin Ti6Al4V alloy plates, configured by an improved pulse wave laser beam welding (PWLBW) scheme. The welding experiment and the numerical simulation were performed at 1.2 mm-thick workpieces assembled in a butt joint with a reserved clearance. With the clearance size enlarged from 0.2 mm to 0.4 mm, the gap bridging type changes from bilateral to unilateral, which results in the failure of the keyhole to rebound during the pulse interval, and causes an obvious reduction in metal bridge area at the cross-section. As the clearance increases further, a through-cavity geometry is generated between the weld spots and finally preserved within the solidified weld bead, indicating a poor overlapping effect. The dynamics of the weld pool, including thermal cycle, Marangoni convection, and molten metal flow rate are exquisitely sensitive to the change in clearance size. The clearance size during assembly and welding processes should be controlled below 0.4 mm to attain seam integrity, continuity, and sound tensile property.

The effect of molybdenum (Mo) concentrations on the mechanical and magnetic properties of electrodeposited Co rich ternary CoMoW thin films from citrate electrolytic bath

Cobalt–Molybdenum-Tungsten (CoMoW) alloy thin films were prepared through an induced electroplating route from a citrate bath on the surface of the copper electrode at the controlled value of pH 8. The CoMoW thin films have been prepared by varying the Mo concentrations like 0.1, 0.2, 0.3 and 0.4 M at a deposition time of 30 minutes over a plating current potential of 40 mA / cm2. The electrodeposited CoMoW coatings have been investigated with the help of Field Emission Scanning Electron Microscopy (FESEM), powder crystal X-ray diffraction (XRD), Electrochemical studies (impedance and polarization) and Vibrating Sample Magnetometer (VSM) to reveal its respective microstructure-based information, mechanical and soft magnetic nature of the synthesized CoMoW thin layers. The CoMoW thin films of an HCP crystal structure have been attained. The induced electroplated condition such as Mo concentration has a significant impact on the crystal structure system, surface morphology, and soft magnetic performances. The crystalline size of the CoMoW thin layers has varied from 22.66 nm to 42.87 nm. The synthesized CoMoW thin layers were smooth, without cracks and had uniform morphology. All the electroplated CoMoW films have the highest Co content along with low Mo content (Co content gradually decreased while increasing the Mo content in the deposits) and thickness varied from 10 to 20 μm. Through the electrochemical investigation studies, it is concluded that the corrosion rate of CoMoW thin films was slightly increased by increasing the Mo content and the corrosion resistance varied from 80.2 KΩ to 92.7 KΩ. The CoMoW thin alloy films with higher Co content exhibited a lower coercivity value of 3.69 Oe and the saturation magnetization of 49.049 emu /cm2.

Elucidating the impact of severe oxidation on the powder properties and laser melting behaviors

In this work, commercial 316L stainless steel (SS) powder was used to experimentally determine the impacts of severe oxidation on the powder characteristics and laser powder bed fusion (L-PBF) melting behaviors. The morphology, surface state, and laser absorptivity of both virgin and oxidized powders were systematically characterized. Their impacts on the flowability and powder bed quality were monitored by custom-designed recoating experiments and powder shear tests. The results of an in situ wetting analysis and microstructure evaluation were compared to establish a correlation between the powder characteristics and laser fusion. The powder oxidation enhanced L-PBF processability by improving the homogeneity of powder spreading and the formation of stable, consecutive laser beads. A thin ceramic layer-coated SS alloy reinforced with uniform (Si, Mn)-based oxides was synthesized by the L-PBF processing of severely oxidized powders. The mechanical strength of this alloy was found to be similar to that processed using the virgin powders, whereas the elongation was slightly decreased, likely due to the amorphous oxide feature and the mechanical oxide-Fe interface. This study provides a systematic understanding of powder reuse and new insight into the potential for economically developing high-performance parts by the positive utilization of powder oxidation and the L-PBF process.

Thin Wire Casting Using Twin Wheel Caster Equipped with Horizontal Wheels

solidification, process shortening and energy saving. A twin-wheel caster equipped with two additional horizontal wheels was proposed to cast thin aluminum alloy wire at higher speed. In the proposed twin-wheel caster, a groove was machined on the lower wheel. Two small horizontal wheels were positioned between the molten-metal-pouring launder and the upper wheel to assist the solidification of poured molten metal and to prevent burr formation. The alignment of the horizontal wheel sensitively affected the occurrence of wire defects. An Al-1.2%Fe wire with a cross section of 6.2 mm2 was cast at 15 m/min. Thinner wires without burring could be cast at a speed higher than that of the twin-wheel caster without the horizontal wheels. The surface condition of the as-cast wire cast by the twin-wheel caster equipped with horizontal wheels was worse than that of the casting using the twin-wheel caster without horizontal wheels.

Suitable CFRP Patches to Arrest Crack Growth in Thin Alloy Aluminium Panels

Suitable CFRP Patches to Arrest Crack Growth in Thin Alloy Aluminium Panels

Effect of structural relaxation at bellow crystallization temperature on internal stress of Ni–Nb–Zr thin film amorphous alloys diaphragm for micro electromechanical systems sensors

In this paper, the effect of structural relaxation at temperatures below crystallization on internal stress of Ni–Nb–Zr thin film amorphous alloy (including thin film metallic glass: TFMG) diaphragms was investigated. We fabiricated the Ni–Nb–Zr diaphragm samples with four compositions. Before fabrication of diaphragm structure by etching, Ni–Nb–Zr thin films on Si substrate were annealed at a temperature below crystallization (473, 523, and 573 K) for structural relaxation. By performing bulge tests on annealed Ni–Nb–Zr diaphragms, we were able to determine their mechanical properties. As the result, Young’s modulus of all samples increased slightly with increasing annealing temperature because of the decrease of the free volumes during structural relaxation. Based on the results of internal stress, structural relaxation of all samples occurred below 473 K. Moreover, the effects of annealing temperature on internal stress differed by compositions. They were thought to be caused by the rate of structural relaxation.

Comparison of quantitative elemental depth distribution analyses of Ni and Ti in co-sputtered Ni-Ti alloy thin films using MCs+ and M+ secondary ions

Compositional uniformity in Ni-Ti thin alloy films, both at the surface and in the depth, significantly enhances their performance in various engineering applications. Quantitative depth distributions of Ni and Ti in magnetron co-sputtered Ni-Ti thin alloy films of various composition and thickness, were determined through an effective depth profiling technique. Secondary ion mass spectrometry (SIMS) was utilized to determine the qualitative elemental depth distribution of Ni and Ti in the films using MCs+-SIMS (Cs+ primary ion beam; MCs+ secondary ions, 'M' is the element of interest) and M+-SIMS (O2+ primary ion beam) approaches. The qualitative depth profiles were converted to quantitative depth profiles using the relative sensitivity factor values determined from the elemental concentrations obtained through energy dispersive x-ray spectroscopy analysis of one of the Ni-Ti thin film taken as reference. Thickness of the deposited films determined by x-ray reflectivity was used for depth scale calibration of SIMS raw profile. A comparison of the analytical capabilities of MCs+-SIMS and M+-SIMS approaches for determining the mean concentration and quantitative depth distribution of elements Ni and Ti in deposited Ni-Ti thin films has been presented.

Effects of processing parameters on residual stress fields of 2024-T351 alloy blade subjected to massive double-sided laser peening treatment

Double-sided laser shot peening (DSLSP) is a promising technique for improving mechanical properties for thin-section components. Residual stress (RS) field induced in the thin 2024-T351 alloy blade by DSLSP was investigated through experiments and finite element simulation. The effects of key parameters, such as pulse scanning patterns, overlapping rates, and DSLSP modes, on the RS field were analyzed. The model was validated by comparing the simulation results with experiment data. The results revealed that the scanning patterns advertently influenced the RS distribution, and compressive residual stresses were found to exist inside the curved thin-section blade. The overlapping rate of 70% could drive the tensile stress (TS) distributed at the near-surface into a fully compressed state, while it could also cause a large-scale TS concentration at the edge of the blade. Moreover, the mechanism of shock wave reflection-coupling on RS distribution with two DSLSP modes was also clearly revealed. The alternate double-sided laser peening mode would greatly limit the edge stress concentration and result in a better RS distribution.

Petal failure models of thin aluminum alloy plate penetrated by conical projectile nose

Petal failure models of thin aluminum alloy plate penetrated by conical projectile nose

Effects of a thermal-ultrasonic stress relaxation process on the residual stress, mechanical properties and microstructures of C19400 copper alloy strips

With the development of 5G communication, more demanding requirements have been specified for copper alloy strips applied in lead frames. Thin copper alloy strips with high residual stress always warp during the etching process, so they do not meet the requirements of industry. Therefore, it is essential to reduce the residual stress in these strips. In this work, a novel effective technique suitable for thin strips, the thermal-ultrasonic stress relaxation (TUSR) method, which integrates conventional thermal stress relaxation (TSR) and ultrasonic stress relaxation (USR), is proposed. The equipment used to conduct TUSR and TSR experiments on C19400 copper alloy was produced in this laboratory. The residual stress evolution was investigated using X-ray diffraction (XRD). The microstructure evolution of the strips was analyzed by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The mechanism of the relaxation of residual stress was revealed. The maximum residual stress relaxation values in the transverse and rolling directions after TUSR treatment were 80.56 and 89.39%, respectively, which were better than the results obtained after TSR treatment. After TUSR treatment, the grain sizes were smaller, and the percentage of low-angle grain boundaries (LAGBs) was higher than that before the treatment. The dislocation morphology was converted to ordered dislocation cells and dislocation walls and macroscopic plastic deformation of the grains released elastic strain energy, which was the main reason for residual stress relaxation in the C19400 alloy strips. In addition, the increase in tensile strength was mainly due to the enhancement of a precipitate pinning effect and grain refinement. These findings can provide guidance for future work related to the relaxation of residual stress in copper alloy strips for lead frames.

Investigation on graphene addition on the quasi-static and dynamic responses of carbon fibre-reinforced metal laminates

In this paper, graphene nanoplatelets (GnPs) were used with carbon fibre/epoxy composite to enhance the mechanical performance of fibre metal laminates (FMLs). The designed FMLs are composed of thin aluminium alloy layers alternating with carbon-fibre epoxy/GnP composite plies with a chemical treatment performed on the aluminium laminate to promote adhesion strength with the epoxy composite. Two different configurations of FMLs were investigated (i) composite plies with unidirectional carbon fibres (U-FMLs) and (ii) composite plies with plain carbon woven (W-FMLs). Samples were tested under dynamic loading (Charpy impact) and quasi-static loading (three-point flexure). The experimental results showed that FMLs with 0.3 wt% GnPs logged the best impact performance; the impact strength of W-FMLs and U-FMLs are respectively 18.2% and 25.2% higher than FMLs without GnPs. FMLs with 0.5 wt% GnPs recorded the highest enhancement in flexural strength, fracture strain and flexural modulus recording increments 23.1%, 19.3% and 48% for the W-FMLs, and 60.3%, 34.5% and 61.4% for the U-FMLs, respectively. Also, an in-depth microscopic analysis was conducted to understand the reinforcing mechanism of GnPs into FMLs. Moreover, a numerical model of a three-point flexural test was developed to show the ability of numerical tools to predict material behaviour at optimized costs. Johnson–Cook and Hashin damage models were used respectively for aluminium alloy and carbon fibre epoxy/GnP composite to accurately predict their deformation and damage modes.

Novel Fabrication Routes of Metallic Micromembranes for In Situ Mechanical Testing

A methodology to miniaturize mechanical tests of metal alloys based on membrane deformation was developed in this investigation. The buildup of this new path for miniaturization tests requires small amounts of material for testing. This is of particular interest for irradiated structural nuclear materials. Micrometric metallic circular membranes were fabricated starting from thin alloy foils and using two different paths. Serial fabrication of microspecimens was performed by means of successive focused ion beam (FIB) steps. On the other hand, high-throughput parallel fabrication was achieved by differential sputtering (DS) based on reactive ion etching followed by a final fine FIB polishing to flatten the membranes and straighten the mechanical response. Micro-punch tests were performed using spherical tips and the in situ load–displacement curves were recorded while monitoring the test in a scanning electron microscope. The values reached after testing of the DS membranes were more reliable than those of FIB samples, showing a large stretching section and higher values of maximum force (64 mN) and displacement (22.2 μm). The micro-punch testing methodology developed in this work combines the advantage of facilitating the interpretation of the mechanical response, by producing a bi-axial stress distribution during membrane stretching, while being amenable to high-throughput microspecimen fabrication.

Mechanical behavior of thin CoCrFeNi high-entropy alloy sheet under laser shock peening

It is a challenge to optimize the mechanical performance of high entropy alloys (HEAs). Here, we obtain yield strength enhancement along with considerable tensile ductility of CoCrFeNi HEA by laser shock peening (LSP). The surface hardness of the material is also increased significantly by 40% after LSP. Based on microstructure analysis, it is observed that the grain refinement and the mixed deformation mode of dislocation slip and deformation twin are the main strengthening mechanisms after being treated by LSP. This study demonstrates an effective method for tailoring the mechanical properties of HEAs.

Fatigue assessment of 5059 aluminum alloy thin plate welded joint accounting for welding deformation and residual stress

ABSTRACT Compared with the traditional 5083 or 6082 aluminum alloy, 5059 has better mechanical properties and corrosion resistance. The traditional fatigue class curve is no longer suitable for fatigue strength evaluation of 5059 marine aluminum alloy structures. Meanwhile, the welding structure of thin aluminum alloy has bigger initial welding defects, resulting in more obvious stress concentration effect at the corner. Large welding deformation brings great challenges to the precision evaluation of stress concentration effect and fatigue strength near corners. Therefore, in order to accurately consider the influence of welding defects, the welding temperature field and stress field of 5059 aluminum alloy structures were simulated and analyzed systematically. In addition, considering the influence of welding deformation and residual stress, the fatigue assessment of 5059 aluminum alloy welded joints based on hot spot stress was carried out, and the fatigue class curve suitable for thin plate cruciform joint of 5059 was renewed.

Bending analysis and residual stress measurement of thin stainless-steel alloy

LPF (laser peen forming) is a non-contact sheet metal forming technology that uses a laser detonated shockwave to bend, shape, and fix engineering components accurately. To understand the bending behavior of SS-304 steel samples in the form of thin sheets of various thicknesses (0.3, 0.5, and 0.8 mm), laser peening at various power densities (3, 6, and 9 GW /cm2) was used. After the peening process, laser peened samples show convex and concave bending. The bending that occurs as a result of residual stress distribution across the sample's cross section during the laser peening process. As a result, to better understand the role of residual stress in LPF, the residual stress was studied using the usual X-ray based cos approach. The significance of these findings for a possible laser forming process known as laser peen forming are also investigated.

Potentiodynamic corrosion behavior and microstructural features of gas tungsten constricted arc (GTCA)-welded superalloy 718 joints

Abstract The gas tungsten constricted arc welding (GTCAW) process was used to join thin Su-718 alloy sheets to minimize alloying segregation and Laves phase precipitation in the fusion zone (FZ). The potentiodynamic corrosion behavior of GTCAW Su-718 alloy joints was studied and correlated to the microstructural features of welds. The potentiodynamic corrosion test was done in a 3.56 wt.-% NaCl solution to determine the corrosion rate of Su-718 alloy joints. The optical microscopy (OM) technique was used to analyze the microstructure of corroded weldments. The scanning electron microscopy (SEM) technique was used to study the Laves phase development in FZ. The SEM X-ray energy dispersive spectroscopy (EDS) technique was used to for elemental mapping of FZ. The corrosion resistance of Su-718 joints is inversely proportional to the precipitation of Laves phase in FZ. The GTCA welded Su-718 alloy joints disclosed superior corrosion resistance for the joints with lower Laves phase precipitation. It is correlated to the refining of FZ microstructure, which aids in minimizing the Laves phase precipitation. The joints with higher Laves phase precipitation revealed inferior corrosion resistance. It is attributed to coarsening of FZ microstructure, which raises the alloying segregation and leads to depletion of alloying elements in FZ. The dendritic core regions showed severe corrosion compared to the interdendritic regions. The corrosion resistance of GTCA welded Su-718 joints is better than that of CC-GTAW and PC-GTGAW joints and comparable to that of EBW and LBW joints. It refers to the arc constriction and high frequency current pulsation.