Ductile Aluminum Research Articles

A successful combination of the equivalent material concept and the averaged strain energy density criterion for predicting crack initiation from blunt V-notches in ductile aluminum plates under mixed mode loading

Crack initiation from blunt V-notch borders in ductile A16061-T6 plates is investigated experimentally and theoretically under mixed mode I/II loading. Experimental observations with naked eye during loading indicated large plastic deformations around the notch tip at the onset of crack initiation, demonstrating large-scale yielding failure regime for the aluminum plates. To theoretically predict the experimentally obtained value of the maximum load that each plate could sustain, i.e. the load-carrying capacity, without performing elastic-plastic failure analyses, the equivalent material concept (EMC) is combined with a well-known brittle fracture criterion, namely the averaged strain energy density (ASED) criterion. It is shown that the combined EMC-ASED criterion could successfully predict the experimental results for various V-notch angles and radii.

Opening-mode micro-cracking in brittle coatings on ductile wires/rods

A simplified two-dimensional model is presented to simulate periodically distributed micro-cracking in a thin coating fully bonded to an elastoplastic aluminum wire/rod. The alumina coating which is generated by anodic oxidation is treated as an elastic material, while the ductile aluminum wire substrate is characterized by a bi-linear elastoplastic hardening model. An elastoplastic shear lag model is applied to transfer the shearing stress from the substrate layer to the thin coating. When the coated structure is subjected to different applied load, the system will undergo different stress levels and exhibit different cracking stages. Accordingly, explicit solutions corresponding to different loading stages are presented based on a generalized axisymmetric formulation. Finite element simulation is employed to verify the present elastic solution when the applied load is relatively small and the whole system is in the elastic state. Experimental characterization is conducted to validate the present elastoplastic solution when the substrate or interlayer undergoes large deformation. A versatile high-fidelity optical microscope is utilized to check the micro structure of the coating and continuously monitor the fracture development in the coating layer, through which valuable detailed micro-cracking information, such as critical applied load corresponding to crack initiation, crack pattern and crack spacing, is obtained. It shows that the presented fracture model is able to accurately capture the stress and strain distribution in the coated structure and predict the fracture initiation, infilling, and saturation in the thin coating layer.

Mechanical properties of an innovative shear-clinching technology for ultra-high-strength steel and aluminium in lightweight car body structures

Comfort- and safety-related requirements lead to weight increase of automotive structures. Modern constructions in automotive body in white (BIW) production confront this upward weight spiral with multi-material design. This restricts conventional thermal joining technologies. The basic idea of mechanical joining technologies is a force- and form-fitting joint. Clinching technologies create a joint only by plastic deformation. The formability of the joining partners limits this technology, especially when joining ultra-high-strength steels (UHSS) in multi-material design. State of the art to realise this is multi-stage clinching with pre-hole. Industrial applications in BIW are, e.g. the brackets for mouldings in the upper windscreen frame of Daimler’s S-class and the battery holder of Daimler’s M-class. Innovative shear-clinching enables joining by forming hot formed UHSS and ductile aluminium in a single-stage process. The spherical punch-sided tool set prevents any harm of the punch-sided ductile material. The cutting die initialises a crack in the die-sided material with limited formability. This paper presents detailed studies on the mechanical behaviour of state of the art multi-stage clinching with cylindrical and tapered pre-hole under quasistatic and fatigue testing methods to evaluate the influence of the interlock. These results were compared to the single-stage shear-clinching technology to derive further recommendations.

Discontinuously reinforced aluminum MMC extrusions

What do you do when you need to design energy or weight saving part for an aerospace, marine, automotive or robotics system and the perfect material is not available? Desirable properties not normally found in an off the shelf material. Properties for example low density, high strength, high modulus and low coefficient of thermal expansion (CTE). One answer is to select several materials that have the desired properties and mix them together to produce an engineered material with the combination of desired properties. This is primarily how composites are designed, including metal matrix composites (MMCs). One lightweight MMC system specifically aluminum-SiC MMCs is described in this article which combine a low density moderate strength ductile aluminum matrix with a low CTE, high strength silicon carbide reinforcement.

Pyramidal ceramic armor ability to defeat projectile threat by changing its trajectory

Abstract This paper presents a numerical study of a multilayer composite panel impacted by an AP (Armor Piercing) 14.5×114 mm B32 projectile. The composite consists of alternating layers of hard ceramic and a ductile aluminum alloy. While the alloy layer consists of typical plate, ceramics confront projectiles in the form of ceramic pyramids. The studied models are compared with a reference structure, which is a standard double layer panel. The problem has been solved with the usage of modeling and simulation methods as well as a finite elements method implemented in LS-DYNA software. Space discretization for each option was built with three dimensional elements ensuring satisfying accuracy of the calculations. For material behavior simulation, specific models including the influence of the strain rate and temperature changes were considered. A steel projectile and aluminum plate material were described by the Johnson-Cook model and a ceramic target by the Johnson-Holmquist model. The obtained results indicate that examined structures can be utilized as a lightweight ballistic armor in certain conditions. However, panels consisting of sets of ceramic prisms are a little easier to penetrate. Despite this fact, a ceramic layer is much less susceptible to overall destruction, making it more applicable for the armor usage. What is most important in this study is that significant projectile trajectory deviation is detected, depending on the impact point. Such an effect may be utilized in solutions, where a target is situated relatively far from an armor.

Potentials of Snailshell as a Reinforcement for Discarded Aluminum Based Materials

Snailshells and discarded aluminium based alloys have low economic values and are mostly considered as environmental pollutants. However, recycling them for further application in material processing can create significant economic value. Snailshell particles are known for their hardness, and thus useful as good alloying element for aluminium based pistons. In this paper, the potential of snailshell particles as reinforcement agent in Al/snailshell particulate composites is reported. Snailshell particles of weight fraction ranging from 16 to 48 wt.% and size of 200, 400 and 600 μm were added to aluminium obtained from discarded aluminum pistons during casting. The microstructures of the composites were examined under optical metallurgical microscope. The tensile strength and hardness were measured based on the experiments conducted using Box Behnken design. The results showed that, at 48 wt.% and 600 μm particle size, the tensile strength and hardness are maximum (236 MPa and 48.3 HRF, respectively) compared to the tensile strength of 92.4 MPa and hardness of 29.2 HRF for the unalloyed samples. These increments are attributed to the uniform distribution of snailshells in the ductile aluminum matrix. It is concluded that both the tensile strength and hardness are significantly enhanced, and snailshells can be used as a low-cost reinforcement for engineering applications.

Properties of aluminum matrix Nano composites prepared by powder metallurgy processing

Pure aluminum Nano composite reinforced with Nano titanium dioxide was produced by powder metallurgy route. Measurements of tensile strength, hardness, and density showed that the porosity and the tensile strength of composites increased with an increase in volume fraction of nanoparticles; however ductility of aluminum was decreased. Wear test revealed that composites offer superior wear resistance compared to alloy.

Toward Demystifying the Mohs Hardness Scale

Today, the Mohs scale is used profusely throughout educational systems without any persuasive understanding of the fundamental principles. Why one mineral has a scratch hardness over the next culminating in a scale of 1 (chalk) to 10 (diamond) has no atomistic or structure‐sensitive basis that explains this outcome. With modern computationally based atomistic and multiscale models, there is increasing promise of defining the pressure and rate‐dependent parameters that will allow a fundamental understanding of the Mohs scale. This study principally addresses the combined fracture and plasticity parameters that qualitatively affect fracture at the nanoscale. A physical model wherein the crack tip under a scratch is shielded by dislocations is supported by molecular dynamics (MD) simulations in both ductile aluminum and brittle silicon carbide. Next, this model is applied to nanoindentation data from the literature to produce a ranking of Mohs minerals based on their fundamental properties. As such, what is presented here is a first step to address the flow and fracture parameters ultimately required to provide a figure of merit for scratch hardness and thus the Mohs scale.

Heat treatment optimization for tensile properties of 8011 Al/15% SiCp metal matrix composite using response surface methodology

Abstract In this study, a mathematical model was developed to optimize the heat treatment process for maximum tensile strength and ductility of aluminum (8011) silicon carbide particulate composites. The process parameters are solutionizing time, aging temperature, and aging time. The experiments were performed on an universal testing machine according to centre rotatable design matrix. A mathematical model was developed with the main and interactive effects of the parameters considered. The analysis of variance technique was used to check the adequacy of the developed model. The optimum parameters were obtained for maximum tensile strength. Fractographic examination shows the cracks and dimples on the fractured surfaces of heat-treated specimen.

The effect of Nb–B inoculation on binary hypereutectic and near-eutectic LM13 Al–Si cast alloys

Hyper-eutectic Al–Si alloys are used for wear-resistant components, such as pistons, because their microstructure is composed by ductile aluminium dendrites and hard primary silicon particles. In this study the effect of Nb–B inoculation on the microstructural features of binary hyper-eutectic and near-eutectic LM13 Al–Si alloys is assessed. It is found that the inoculation with Nb-based compounds (i.e. NbB2 and Al3Nb) leads to the refinement of the microstructural features (i.e. finer and more homogeneous distribution of the eutectic phase as well as smaller primary Si particles as secondary effects). The study also demonstrates that the addition of Nb–B inoculants do not interfere with additions of strontium (used to modify the morphology of the eutectic phase) or phosphorous (added to nucleate primary Si particles).

OS0802-137 アルミニウム合金の損傷発生とミクロ組繊形態の3Dイメージベース解析

Recently, Toda et al. have performed X-ray microtomography using synchrotron radiation to observe the ductile fracture process of a 2024 aluminum alloy, revealing that the ductile fracture in its material does not occur through a conventional ductile fracture process (i.e. growth and coalescence of voids nucleated at inclusions/particles) but through the simple catastrophic linkage of hydrogen pores. Hence, if one is able to control the size/shape/distribution of those hydrogen pores, it is highly possible for an aluminum alloy to attain an unprecedented high-ductility. We therefore attempt to find an optimum microstructure through R4ME, pursuing a ductile aluminum alloy.

Adaptive Hierarchical-Concurrent Multiscale Modeling of Ductile Failure in Heterogeneous Metallic Materials

This article addresses two topics on multiscale modeling of heterogeneous metals and alloys. The first topic focuses on developing an adaptive hierarchical-concurrent multilevel modeling framework for ductile fracture. The microstructure of aluminum alloys, for example, is characterized by a dispersion of heterogeneities such as silicon and intermetallics in a ductile aluminum matrix. The multilevel model invokes two-way coupling, viz. hierarchical models for homogenized constitutive modeling and concurrent models with scale transition in regions of localization and damage. Adaptivity is necessary for evolving microstructural deformation and damage. A macroscopic analysis in regions homogeneity incorporates homogenization-based continuum plasticity-damage models. A microscopic analysis using locally enhanced-Voronoi cell finite-element method is required for regions of high macroscopic gradients caused by underlying localized plasticity and damage. Coupled macroscopic and microscopic analysis is conducted concurrently. Physics-based level change criteria are developed to improve accuracy and efficiency. The second topic discusses a nested dual-stage homogenization method for microstructure-based homogenized continuum plasticity models for cast aluminum alloys with large secondary dendrite arm spacing. Two distinct statistically equivalent representative volume elements are identified and used in the asymptotic expansion-based homogenization and self-consistent homogenization processes, respectively. The two-stage homogenization enables an evaluation of the overall homogenized model of a cast alloy from limited experimental data, as well as material properties of constituents like interdendritic phase and pure aluminum matrix.

High-temperature deformation behavior of carbon nanotube (CNT)-reinforced aluminum composites and prediction of their high-temperature strength

The high-temperature deformation behavior of aluminum matrix composites reinforced by carbon nanotubes (CNTs), in which the CNTs broken during the ball milling process were randomly dispersed in the interiors of the grains, were studied at elevated temperatures. The addition of 1vol.% of CNTs simultaneously improved the strength and ductility of aluminum over a wide strain rate range between 10−4 and 10−1s−1 at 523K. The tensile ductility of the composite increased as the strain rate increased, which was attributed to the higher strain rate sensitivity at higher strain rates. The deformation mechanisms of the CNT/Al composites and the matrix materials at high temperatures were analyzed and, based on the results of the analysis, the constitutive equations capable of predicting the strength of the CNT/Al composite at elevated temperatures was proposed.

Biaxial high-cycle fatigue life assessment of ductile aluminium cruciform specimens

Several results of experimental high-cycle fatigue tests carried out on a new biaxial in plane testing system are presented, covering a wide range of biaxial stress states, including proportional and non-proportional, performed on cruciform specimens machined from ductile aluminium (A1050-H14) sheet plate with 3mm thickness. A specially designed cruciform specimen for crack initiation and low capacity test machines was used to perform fatigue tests. This specimen was optimized for the test machine in order to achieve the maximum uniform stress at the centre gauge area, while keeping the remaining stresses at least 20% lower than the stress at centre. Several of the most common multiaxial fatigue criteria were used to determine an equivalent uniaxial fatigue damage parameter for all the specimens that were tested experimentally and to determine which criteria provide a better correlation to the experimental results. From the results it was shown that most of the criteria provide non-conservative estimations. In overall, better results were found by the Minimum Circumscribed Ellipse criterion and also when using the damage parameter related with the shear stress computed by the Minimum Circumscribed Ellipse in the modified non-linear criterion proposed by Carpinteri and Spagnoli.

Microstructure and Mechanical Properties of Ductile Aluminium Alloy Manufactured by Recycled Materials

The present paper introduces the microstructure and mechanical properties of the Al-Mg-Si-Mn alloy made by recycled materials, in which the impurity levels of iron are mainly concerned. It is found that the increased Fe content reduces the ductility and yield strength but slightly increases the UTS of the diecast alloy. The tolerable Fe content is 0.45wt.%, at which the recycled alloys are still able to produce castings with the mechanical properties of yield strength over 140MPa, UTS over 280MPa and elongation over 15%.The Fe content is steadily accumulated in the alloy with the increase of recycle times. However, after 13 cycles, the recycled alloys are still able to produce ductile alloys with satisfied mechanical properties.

Multiaxial fatigue evaluation of laserbeam-welded magnesium joints according to IIW-fatigue design recommendations

Under non-proportional multiaxial loading, welded magnesium joints show a decrease of fatigue life compared to combined proportional loading as is also observed for welded ductile steels and aluminium alloys. The investigated laserbeam-welded overlapped tube-tube joints of the wrought magnesium alloys AZ31 and AZ61 were tested under combined in- and out-of-phase axial loading and torsion. The IIW-Recommendations for the evaluation of multiaxial stress states with constant and with changing principal stress directions describe, on the safe side, the results obtained for fully reversed loading R = −1 and the probability of survival P s = 50 %. The comparisons of the experimental results with the allowable values for P s = 97.7 % and R = 0.5 are quite conservative. However, as, at present, relatively few multiaxial fatigue investigations with magnesium alloys in the welded state are available, the suggested IIW procedure, the Gough-Pollard Equation with the multiaxial damage parameters D MA = 1.0 and 0.5, should be retained.

Influence of fly ash particles on tensile and impact behaviour of aluminium (Al/3Cu/8.5Si) metal matrix composites

AbstractThe present work aimed to study the tensile and impact behaviour of fly ash particle reinforced aluminium matrix composites. Fly ash particles reinforced aluminium (Al/3Cu/8.5Si) matrix composites were fabricated by the stir casting technique. Three different size ranges of fly ash particles (50–75, 75–103 and 103–150 μm) were used. The composites were subjected to tensile and impact tests. The tensile and impact fracture surfaces of the aluminium alloy and composites were investigated using a scanning electron microscope to characterise the fracture mechanism of the composites. The tensile strength of composites increased, while the ductility and impact strength of composites decreased with an increase in fly ash particle content. The fracture surface of the unreinforced material was characterised by uneven distribution of a large number of dimples resulting in ductile failure. In the case of composites, the presence of hard and brittle reinforcement particles in the ductile aluminium matrix places constraints on the plastic flow of the matrix leading to brittle failure with an increase in fly ash particles.

Production and properties of a precision-cast bio-inspired composite

The article presents the production and investigation of a bio-inspired metal–metal-composite inspired by the pomelo peel. The pomelo fruit is able to withstand a fall externally undamaged, even from heights of over 10 m most likely due to the hierarchical structuring of its foamy peel, which represents a complex composite structure. Especially the foam’s struts, which are cells from the biological point of view, consisting of liquid-filled cores and shells (cell walls) with relatively high strength, give point to a technical adaptation. With the objective to make use of the pomelo’s ability to absorb impact energy, the design of a pomelo strut is abstracted and transferred to aluminium/aluminium–silicon-alloy (A356) composite tensile specimens. Testing results show that the properties of the individual materials can successfully be combined. After fracture of the outer high strength, but less ductile A356-shell, the applied stress can still be absorbed by deformation of the inner highly ductile pure aluminium. As a result, the ductility of a bio-inspired composite is significantly higher compared with an A356 tensile specimen. By varying the mould and casting temperatures, the relationship between the production parameters and the quality of the composite is shown. A reduced mould and casting temperature lowers the dendrite arm spacing in the A356 outer shell of the composite material thus leading to an increased tensile strength. The detected metal bond between the two materials is mainly influenced by the interaction between the casting and the mould temperature.

Adaptive concurrent multi-level model for multi-scale analysis of ductile fracture in heterogeneous aluminum alloys

This paper creates a novel adaptive multi-level modeling framework for rate-dependent ductile fracture of heterogeneous aluminum alloys with non-uniform microstructures. The microstructure of aluminum alloys is characterized by a dispersion of brittle heterogeneities such as silicon and intermetallics in a ductile aluminum matrix. These microstructural heterogeneities affect their failure properties like ductility in an adverse manner. The multi-level model invokes two-way coupling, viz. homogenization for upscaled constitutive modeling, and top-down scale-transition in regions of localization and damage. Adaptivity is necessary for incorporating continuous changes in the computational model as a consequence of evolving microstructural deformation and damage. The macroscopic finite element analysis in regions of homogeneity incorporates homogenization-based continuum rate-dependent plasticity-damage (HCPD) models. Transcending scales is required in regions of high macroscopic gradients caused by underlying localized plasticity and damage. Complete microscopic analysis using the LE-VCFEM is conducted in these regions, which follow the growth of microscopic voids and cracking to cause local ductile fracture. The macroscopic and microscopic simulations are done concurrently in a coupled manner. Physics-based level change criteria are developed to improve the accuracy and efficiency of the model. Numerical simulations are conducted for validations and ductile fracture in a real microstructure is demonstrated.

Comparative analysis of the effect of mechanical activation in an attritor on the structure and behavior of β-RuAl and β-NiAl alloy powder mixtures during reactive sintering

The structure of Ni + Al (two ductile fcc metals) and Al + Ru (ductile aluminum and hard-to-deform hcp ruthenium) powder mixtures subjected to short-term (≤16 h) mechanical activation (MA) is studied. During MA of a 50Ni + 50Al mixture, the powder particles undergo multiple compressive and shear deformation, and large layered granules form due to contact welding and flattening of the layers of both metals. The related increase in the internal stresses, the increase in the dislocation density in particles of both metals, and the decrease in the coherent domain size (CDS) lead to the fracture and fragmentation of the powder particles. In a 49Ru + 48Al + 3Re mixture, aluminum particles are deformed and “spread” over “rigid” ruthenium particles. The formed granules consist of disperse undeformable ruthenium particles connected by an Al binder. The work hardening of ruthenium occurs due to a decrease in CDS. An increase in the contact area between metal particles and a decrease in the diffusion path lengths (aluminum in nickel and ruthenium) cause a decrease in the temperature of the onset of interaction with the participation of liquid aluminum, the activation of solid-phase interaction, and the formation of aluminum-rich nickel (ruthenium) aluminide NiAl (RuAl). Nevertheless, unreacted nickel (ruthenium) particles are retained. A microhomogeneous distribution of the basic and alloying elements and phases in a compacted material is achieved Annealing at temperatures ≥0.8T m is required to complete reactive alloy formation.