Mechanical damping behavior of Al/C60-fullerene composites with supersaturated Al–C phases

Al-based materials with enhanced mechanical damping properties are of great interest in aerospace and automotive industries as engineering materials for critical components that suffer from severe dynamic environment. In this report, we developed Al/C₆₀-fullerene composites to increase damping capacity by the supersaturated Al–C phases. Carbon atoms, dissolved from individually dispersed C₆₀-fullerenes, are intercalated into the Al interstitial sites, producing Al–C phases with expanded lattice structures. These novel nanostructures exhibit a superior mechanical damping behavior compared to monolithic Al, throughout the temperature range of room temperature to 350 °C. The present approach to control the lattice structure thus represents a new engineering paradigm for atomic-level design of lightweight structural components.     

Deformation behavior of Al–Si alloy based nanocomposites reinforced with carbon nanotubes

Nanocrystalline Al–Si alloy-based composites containing carbon nanotubes (CNTs) were produced by hot rolling ball-milled powders. During the milling process, the grain size was effectively reduced and the Si element was dissolved in the Al matrix. Furthermore, CNTs were gradually dispersed into the aluminum powders, providing an easy consolidation route using a thermo-mechanical process. The composite sheet containing 3 vol.% of CNTs shows ～520 MPa of yield strength with a 5% plastic elongation to failure.     

Microstructure and Mechanical Properties of Rapidly Solidified Hypereutectic Al–Si and Al–Si–Fe Alloys

The microstructure and mechanical properties of rapidly solidified Al–18 wt% Si and Al–18 wt% Si–5 wt% Fe alloys were investigated by a combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, x-ray diffraction, tensile testing, and wear testing. The centrifugally atomized binary alloy powder consisted of the -Al (slightly supersaturated with Si) and Si phases and the ternary alloy powder consisted of the -Al (slightly supersaturated with Si), silicon, and needle-like metastable Al–Fe–Si intermetallic phases. During extrusion the metastable -Al₄FeSi₂ phase in the as-solidified ternary alloy transformed to the equilibrium -Al₅FeSi phase. The tensile strength of both the binary and the ternary alloys decreased with a high-temperature exposure, but a significant fraction of the strength was retained up to 573 K. The specific wear gradually increased with increasing sliding speed but decreased with the addition of 5 wt% Fe to the Al–18 wt% Si alloy. The wear resistance improved with annealing due to coarsening of the silicon particles.     

Structural performance of composite sandwich bridge decks with hybrid GFRP–steel core

This paper presents the static and fatigue performance of composite sandwich bridge decks with hybrid GFRP–steel core. The composite sandwich bridge deck system is comprised of wrapped hybrid core of GFRP grid and multiple steel box cells with upper and lower GFRP facings. Its structural performance under static loading and fatigue loading with a nominal frequency of 5 Hz was evaluated. The responses from laboratory testing were compared with the ANSYS finite element predictions. The failure mode of the proposed composite sandwich bridge deck was more favourable because of the yielding of the steel tube when compared with that of all-GFRP decks. The ultimate failure of the composite sandwich deck panels occurs by shear of the bonded joints between GFRP facings and steel box cells. Results from fatigue load test indicated no loss in stiffness, no signs of de-bonding and no visible signs of deterioration up to 2 million load cycles. The thickness of the composite sandwich deck retaining the similar stiffness may be decreased to some extent when compared with the all-GFRP deck. This paper also presents design of a connection between composite sandwich deck and steel girder.     

Mechanical behavior of pure Al and Al–Mg syntactic foam composites containing glass cenospheres

Glass cenospheres were used as space holders for making aluminum matrix syntactic foams by pressure infiltration technique. The mechanical properties and failure behavior of cenospheres/Al syntactic foams with pure Al and Al–Mg alloys were investigated in the present work. The failure behavior of cenospheres in two syntactic foams was similar. However, the mechanical behavior of these two syntactic foams was different. Under compression process, the cenospheres/pure Al showed discontinuous shear band and drum shape, while cenospheres/Al–Mg exhibited continuous shear band and was divided by main shear zone. At the tensile state, the cenospheres in pure Al matrix syntactic foam debonded from the matrix, while the cenospheres in Al–Mg matrix syntactic foam was well-bonded and appeared to lamellar tearing. It is suggested that the difference of mechanical deformation behavior could be attributed to the matrix ductility and the forming of interfacial reaction product MgAl₂O₄ coatings.     

Effect of Microstructural Anisotropy on Mechanical Behavior of a High-Strength Al–Mg–Si Alloy

The mechanical behavior of an extruded aluminum alloy pipe has been investigated after repeated failures in an oil and gas industry. The pipe failures occurred by longitudinal cracking, and the mechanical properties of the pipe were blamed for the failure. The relevant critical properties of the pipe including basic tests of hardness, tensile, and impact behavior were measured, and extended fatigue testing of the material was conducted. Microstructural examination revealed a recrystallized grain structure and clusters of constituent particles aligned in the direction of extrusion. Tensile testing in both the longitudinal and circumferential directions showed virtually identical yield and tensile strengths. However, the material exhibited higher toughness in the longitudinal direction. Impact test showed that the energy absorbed during fracture was four times higher in the longitudinal direction. Fatigue testing displayed a shorter fatigue life in the transverse direction. The study showed that the microstructure after extrusion and the distribution of the constituent particles have a pronounced effect on the mechanical behavior of the extruded pipe and induced anisotropy in the material performance. Performance of the material can be improved by choosing the proper extrusion ratio to control the microstructure and by controlling the density and distribution of the constituent particles.     

Numerical simulation and validation of impact response of axially-restrained steel–concrete–steel sandwich panels

Steel–concrete–steel (SCS) sandwich panels are an effective means for protecting personnel and infrastructure facilities from the effects of external blast and high-speed vehicle impact. In conventional SCS construction, the external steel plates are connected to the concrete infill by welded shear stud connectors. This paper describes a programme of research in which the non-composite SCS panels with axially restrained connections were studied experimentally and numerically. High fidelity finite element models for axially restrained steel–concrete–steel panels subjected to impact loading conditions were developed using LS-DYNA. The simulation results were validated against the dynamic testing experimental results. The numerical models were able to predict the initial flexural response of the panels followed by the tensile membrane resistance at large deformation. It was found that the strain rate effects of the materials and the concrete material model could have significant effect on the numerically predicted flexural strength and tensile membrane resistance of the panels.     

In-situ EBSD study of deformation behavior of Al–Si–Cu alloys during tensile testing

This study deals with the microstructural aspects of the deformation behavior in Al–Si–Cu alloy A380. This has been carried out with in-situ tensile testing coupled with EBSD analysis. The alloy specimens having different microstructures with two different secondary dendrite arm spacing (SDAS) of 9 μm and 27 μm were produced by the unique gradient solidification method. The study of misorientation distribution and texture evolution was performed with different tools in EBSD analysis. The texture was not significantly affected by deformation in both types of alloy specimens. With increase in the deformation, the microstructures are characterized by degradation of EBSD patterns and generation of substructures including low angle boundaries (LABs) and high angle boundaries (HABs). In both the microstructures with low and high SDAS, the boundaries were concentrated around eutectic phases; however this behavior was more pronounced at higher SDAS. The increase in the fraction of LABs with deformation was much higher in the microstructure with higher SDAS than with lower SDAS. This localized strain concentration was especially attributed to the large and elongated eutectic Si particles and Fe-rich intermetallics. The lower mechanical properties obtained at higher SDAS are the result of inhomogeneous strain distribution in the microstructure.     

Compressive and impression creep behavior of a cast Mg–Al–Zn–Si alloy

Creep behavior of an Mg–6Al–1Zn–0.7Si cast alloy was investigated by compression and impression creep test methods in order to evaluate the correspondence of impression creep results and creep mechanisms with conventional compression test. All creep tests were carried out in the temperature range 423–523 K and under normal stresses in the range 50–300 MPa for the compression creep and 150–650 MPa for impression creep tests. The microstructure of the AZ61–0.7Si alloy consists of β-Mg₁₇Al₁₂ and Mg₂Si intermetallic phases in the α-Mg matrix. The softening of the former at high temperatures is compensated by the strengthening effect of the latter, which acts as a barrier opposing recovery processes. The impression results were in good agreement with those of the conventional compressive creep tests. The creep behavior can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring, depending on the test temperature, around 0.009 < (σ/G) < 0.015 and 0.021 < (σ_imp/G) < 0.033 for the compressive and impression creep tests, respectively. Based on the steady-state power-law creep relationship, the stress exponents of about 4–5 and 10–12 were obtained at low and high stresses, respectively. The low-stress regime activation energies of about 90 kJ mol⁻¹, which are close to that for dislocation pipe diffusion in the Mg, and stress exponents in the range of 4–5 suggest that the operative creep mechanism is pipe-diffusion-controlled dislocation viscous glide. This behavior is in contrast to the high-stress regime, in which the stress exponents of 10–12 and activation energies of about 141 kJ mol⁻¹ are indicative of a dislocation climb mechanism similar to those noted in dispersion strengthening mechanisms.     

Thermo-mechanical behavior of the Al–Si alloy coated hot stamping boron steel

Hot tensile tests of boron steels with and without an Al–Si coating were performed using a Gleeble 3500 test system, at temperatures of 700–850 °C and strain rates of 0.01–1/s. The phase and microstructure of the coating in as-coated and press-hardened conditions were observed under scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis and X-ray diffraction (XRD). Experimental results indicate that the Al–Si coating gave an unignorable influence on the thermo-mechanical properties of the boron steels. The ultimate tensile strength (UTS) of the Al–Si coated boron steel was almost equal to that of the uncoated under the lower strain rate at the same deformation temperature. At a higher strain rate, the UTS value appeared to be lower than that of the uncoated. Moreover, the UTS difference increased with the decreasing deformation temperature. The ductility of the Al–Si coated steel was lower than that of the uncoated under the described test conditions. Following the tensile tests, extensive cracks were visible in the Al–Si coating layer. SEM observation showed that microcracks and voids appeared after austenization, which may act as nucleation sites for the cracks. The cracks first propagated in the direction perpendicular to the coating/substrate interface and were identified as Type I cracks. The propagation was hindered by the substrate when these cracks reached the coating/substrate interface. This occurred because the interfacial bonding strength between the coating and the substrate was lower than the substrate strength. Following this initial failure, the cracks turned to propagate paralleled to the coating/substrate interface. In addition with the shear stress resulting from the substrate yielding, Type II cracks formed. Eventually, the cracked coatings were accompanied by interface decohesion from the substrate. The width and density of the cracks were found to increase with the decreasing deformation temperature and rising stain rate.     

Effect of stamping deformation on microstructure and properties evolution of an Al–Mg–Si–Cu alloy for automotive panels

The effect of 5 % tensile deformation, which simulates the stamping process of Al–Mg–Si–Cu automotive outer panels, on the microstructural evolution during age strengthening, has been investigated. In addition, its benefit on key mechanical properties including hardness, yield strength, ductility, and corrosion resistance has been linked to the microstructural features. It was found that the aging precipitation sequence, SSSS → clusters and G.P. zones → β″ → β′ + Q′ → Q, was not influenced by the dislocations introduced through the stamping deformation prior to aging. On the other hand, stamping deformation could promote the formation of precipitates and refine the precipitates because of the enhanced heterogeneous nucleation and the accelerated precipitation kinetics, leading to superior strength of the alloy at the early stage. Meanwhile, the larger amount of Cu incorporated into nanoprecipitates leads to better intergranular corrosion resistance of the stamped alloy compared with the unstamped one. Due to the reduction in free Si amount at grain boundaries, the formation of fine subgrain structures and the increase of dislocation accumulation, the ductility of the stamped alloy was increased.     

Monotonic and cyclic deformation behavior of the Al–Si–Cu–Mg cast alloy with micro-additions of Ti,V and Zr

Monotonic and cyclic tests were used to assess the influence of micro-additions of Ti, V and Zr on the deformation behavior of the Al–7Si–1Cu–0.5Mg (wt.%) alloy in as-cast and T6 heat treated conditions and to compare the results with alloys of similar chemistry described in the literature. The microstructure of the as-cast alloy consisted of α-Al, eutectic Si, and Cu, Mg and Fe based phases Al_2.1Cu, Al_8.5Si_2.4Cu, Al_7.2Si_8.3Cu₂Mg_6.9 and Al₁₄Si_7.1FeMg_3.3. In addition, the micro-size Zr–Ti–V-rich phases Al_21.4Si_4.1Ti_3.5VZr_3.9, Al_6.7Si_1.2TiZr_1.8, Al_2.8Si_3.8V_1.6Zr and Al_5.1Si_35.4Ti_1.6Zr_5.7Fe were present in the as-cast state. During solution treatment, Cu based phases were completely dissolved, while the eutectic silicon, Fe- and Zr–Ti–V-rich intermetallics experienced only partial dissolution. The monotonic test results showed that the T6 heat treated alloy achieved a tensile strength of 343 MPa and a compressive strength of 418 MPa. Also, the cyclic yield stress of the studied alloy in the T6 temper condition was higher than the monotonic value and reached 335 MPa. The fatigue life of the studied alloy was substantially longer than that of the reference alloy with the same base but lower additions of V, Zr and Ti, reported in the literature. The fractography revealed the tensile crack propagation through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features of the plate-shape Zr–Ti–V-rich intermetallics with a presence of fatigue striations on the latter, indicating their ductile nature. It is believed that the intermetallic precipitates containing Zr, Ti and V improve the fatigue life of the studied alloy in the T6 condition.     

Precipitation of iron-rich intermetallics and mechanical properties of Al–Si–Mg–Fe alloys with Al–5Ti–B

Effects of added Al–5Ti–B master alloys on precipitation of iron-rich intermetallics and mechanical properties of A356 cast alloys with high Fe content (1.5?wt-%) were investigated using image analysis, scanning electron microscopy, and tensile testing. Results show that added Al–5Ti–B has apparent refinement on α (Al) grain size of A356 alloys that have high Fe content. 12?wt-% Al–5Ti–B is beneficial for improving mechanical properties of A356 cast alloys with high Fe content. Improved mechanical properties can be attributed to refined microstructure, the proper amounts of TiB₂ and Ti(AlSi)₃, and decreased porosity. An excessive amount of Al–5Ti–B deteriorates mechanical properties of alloys because it leads to the formation of large secondary intermetallics and increased porosity.     

A study on the mechanochemical behavior of TiO2–Al–Si system to produce Ti5Si3–Al2O3 nanocomposite

In the present study Ti₅Si₃–Al₂O₃ nanocomposite was synthesized by a displacement reaction between Al and TiO₂ in ball milling of TiO₂, Al and Si powders. The effect of milling time and heat treatment temperatures were also investigated. The structural changes of powder particles during mechanical alloying were investigated by X-ray diffraction (XRD). Morphology and microstructure of powders were characterized by scanning electron microscopy (SEM). It was found that after 10 h of MA, the reaction between Al and TiO₂ initiated in a gradual mode and after about 45 h of milling, the reaction was successfully completed. The final product consisted of Ti₅Si₃ intermetallic compound with a crystallite size of 13 nm and amorphous Al₂O₃. Heat treatment of this structure at 1050 °C led to the crystallization of Al₂O₃ and ordering of Ti₅Si₃. The crystallite size of Ti₅Si₃ and Al₂O₃ after annealing at 1050 °C for 1 h remained in nanometer scale. So the final product appeared to be stable upon annealing.     

Thermomechanical behavior of Fe–Mn–Si–Cr–Ni shape memory alloys modified with samarium

The deformation and training behavior of Fe–14Mn–3Si–10Cr–5Ni (wt.%) shape memory alloys containing samarium addition has been studied in the iron-based shape memory alloys. It is noticed that thermomechanical treatment (training) has significant influence on proof stress, critical stress and shape memory behavior of the alloys. The improvement in shape memory behavior can be attributed to the decrease in the proof stress and critical stress which facilitates the formation of ? (hcp martensite). It is also observed that alloy 2 containing samarium undergoes less softening as compared to alloy 1 with training which inhibits the formation of ? (bcc martensite) and thus enhances the shape memory behavior. The excessive thermomechanical treatment with increase in the training cycle has led to the formation of ? (bcc martensite) along with ? (hcp martensite) in the alloy 1 which appeared to have decline in the shape memory effect. This has been demonstrated by the examination of microstructure and identification of ? (bcc martensite) martensite in the alloy 1 as compared to alloy 2.     

Mechanical properties of Ir–Nb–Pt–Al quaternary alloys

Ir–Nb–Pt–Al quaternary alloys had exhibited suitable microstructure for high-temperature usage in the previous study. In this work, investigations were made of the mechanical properties of these quaternary alloys. Compression tests at 1200 °C were carried out for five samples, and compression creep test at 1400 °C under 100 MPa was conducted for one sample. These alloys showed high strength and good creep resistance.     

Simulation of delamination–migration and core crushing in a CFRP sandwich structure

Following the onset of damage caused by an impact load on a composite laminate structure, delaminations often form propagating outwards from the point of impact and in some cases can migrate via matrix cracks between plies as they grow. The goal of the present study is to develop an accurate finite element modeling technique for simulation of the delamination–migration phenomena in laminate impact damage processes. An experiment was devised where, under a quasi-static indentation load, an embedded delamination in the facesheet of a laminate sandwich specimen migrates via a transverse matrix crack and then continues to grow on a new ply interface. Using data from this test for validation purposes, several finite element damage simulation methods were investigated. Comparing the experimental results with those of the different models reveals certain modeling features that are important to include in a numerical simulation of delamination–migration and some that may be neglected.