Ductile Matrix Research Articles

Crack Initiation and Propagation in Dual-phase Steels Through Crystal Plasticity and Cohesive Zone Frameworks

Ferrite-martensite dual-phase (DP) steels have become popular in weight-reduced automotive components due to their straightforward thermomechanical processing and excellent mechanical properties. Even though it has been a popular and productive area of research, there are still many open questions related to their interesting microstructure. Being composed of brittle martensitic clusters dispersed in a ductile ferrite matrix, DP steels benefit from the properties of both phases, which induce interesting failure mechanisms at the same time. The microstructural parameters such as martensite volume fraction, grain size, carbon content, martensite/ferrite morphology, ferrite grain size, and texture, as well as micro and mesoscale segregation, make them difficult to analyze. However these aspects have to be studied in order to link the underlying microstructural influence to macroscopic behaviour. Therefore, the modelling techniques at the microstructure scale should be utilized for physical understanding. In this work, a multi scale modeling strategy is followed for the analysis of plastic deformation and failure in DP steels. A rate-dependent crystal plasticity framework and the isotropic J2 plasticity model are employed for the simulation of the plastic deformation in ductile ferrite phase and in the hard martensite phase respectively at the RVE scale. Moreover, the intergranular cracking is studied by the incorporation of a cohesive zone model at the ferrite-martensite grain boundaries and the failure in martensite phase is addressed through a ductile failure model. The effect of microstructural parameters on both plastic and fracture behaviour is analyzed under axial loading conditions.

Деформації зони насуву між скибами Зелем’янка і Парашка Скибового покриву Українських Карпат (Гребенівський кар’єр)

In the article, based on own field observations, the deformation structures into the thrust zone of the Zelemianka Skyba (=thrust-sheet) onto the Parashka Skyba (the Ukrainian Carpathian Skyba Nappe) are described. They are exposed in the Hrebeniv quarry located in the Opir River basin (Lviv Region, Skole district). The tectonically disintegrated Stryi Formation (Upper-Cretaceous–Paleocene flysch) characterized by the rigid sandstone blocks (formed mainly as a result of boudinage) placed in a ductile clay matrix is represented in the Hrebeniv quarry. This formation is proposed to be classified as a “broken formation”, which is strongly tectonized, but retain their lithological and stratigraphic identity. It is a transitional element between the weakly deformed strata and tectonic mélange. Their characteristic features are: linearity of the distribution zone; significant monomictic composition and absence of exotic formations; the presence of an intensively tectonized matrix with clastolites (blocks) of less tectonized rocks of the same lithostratum (formation, series); the presence of newly formed hydrothermal minerals in clastolite cracks; the upper and lower contacts limiting the broken formation have a tectonic nature. An intensely tectonized matrix and a weakly tectonized rigid blocks belong to the same stratigraphic unit in a broken formation. The structural features suggest a brittle deformations in the studied rocks. Tectonic processes occurred in the completely lithified deposits. Thrust processes were accompanied by the formation of the duplexes, including antiformal stack duplexes, which are well expressed in the quarry. Duplexes are observed in different parts of the quarry, and the most representative ones are developed in its central section. Horses in the duplexes are characterized by a size of 1 to 3 meters here. They are generally subparallel, which is consistent with monoclinal bedding, however, they sometimes acquire an antiform appearance as a result of tectonic thrusting.

Laser cladding as a flexible exploration tool for the design of cobalt-free hardfacing coatings made of high entropy materials

Significant research efforts have been undertaken over the past forty years to replace the StelliteTM cobalt-based alloys, which boast outstanding performances when used as hardfacing coatings, but proved problematic especially in radioactive environments. This work's purpose is to contribute to this effort by coming up with viable substitutes made of Complex Concentrated Alloys (CCAs). Previous work evidenced the (CrFeNi)90Mo5Ti5 alloy as a promising base that relies on the formation of intermetallic phases within a ductile matrix for an increase in hardness and an improved tribological behaviour. In this particular framework, the in situ alloying capabilities of the DED (Direct Energy Deposition) process were used for further explorations around this composition. Compositionally graded samples were successfully made despite the especially high brittleness of the alloys of interest. Coupled with an extensive use of the CALPHAD method, this combinatorial strategy dramatically speeds up material development compared to what the more conventional ways can achieve. The present paper emphasizes on the methodology and the high-throughput tools that were developed and used in this study, as such elements are growing in importance in the current context of intensive global research for new materials, especially in the CCAs field.

Comparison of toughening mechanisms in natural silk-reinforced composites with three epoxy resin matrices

Natural silk fibre can reinforce the polymer matrix for composites with improved toughness and impact strength. However, the optimum selection of matrices for the mechanical performance of silk fibre reinforced plastics (SFRPs) is still unclear, especially with respect to toughness. Here Bombyx mori silk is applied to reinforce three epoxy resin matrices with various crosslinking structures. The epoxy resin from bisphenol-A epoxy and aliphatic diamine precursors that is the most ductile and the toughest leads to the SFRPs with the highest tensile breaking energy (14.1 MJ·m−3) and impact strength (110 kJ·m−2). Examination of the toughening mechanisms in these composites, which haveeither a brittle or ductile matrix, indicated the predominance of crack propagation and fibre pull-out to increase specific energy dissipation during the fracture processes. The rationale for this study is to provide guidelines for the design of matrices in SFRPs with optimal toughness, by identifying the salient toughening mechanisms in these tough and ductile fibre-reinforced composites.

Effect of laser welding on microstructure and mechanical behaviour of dual phase 600 steel sheets

Dual Phase steels are one of the most used advanced high-strength materials in the industry, due to its combination of a ductile ferritic matrix and disperse hard martensite islands, which provide outstanding mechanical properties for components to be cold stamped. This work investigated fiber laser welding applicability in Dual Phase 600 1.6 mm thick steel sheets, evaluating potential welding impacts on properties of the material for industrial applications. A first set of bead-on-plate welds was generated to define best parameters for subsequent tests. A second set was prepared, consisting of butt joints welded in the optimized condition. Weld microstructure was characterized as 100% martensitic at fusion zone (FZ), with growing fractions of ferrite at Heat Affected Zone (HAZ) as one moves away from fusion line. Hardness is around 60% higher at FZ than at BM, being maximum at supercritical HAZ due to its highly refined microstructure and HAZ softening was not observed. Tensile and Erichsen cupping tests presented similar strength results between welded and non-welded specimens, with slight ductility reduction. Finally, numeric simulations based on Finite Element Analysis were carried out to estimate temperature evolution, phase proportions, residual stresses and distortion levels, achieving excellent agreement with experimental results.

Simulation of ductile crack propagation in metal matrix composites ‐ Comparison with cyclic experiments

AbstractThe efficient operation of mechanized tunnel drilling machines is strongly determined by the wear resistance of the applied mining tools. Especially in chisels, but also partly in cutting disks, metal matrix composites are used. Their wear mechanism is dominated by surface spalling, i.e. subcritical crack propagation through the material's microstructure, mainly consisting of a ductile metal matrix and carbide inclusions. Since this process is primarily governed by the morphology of the microstructure and the mechanical behavior of the individual phases, simulations at the microscale enable the design of improved materials. In this contribution, a method for the modeling of this process is presented. The approach is based on the eigenerosion framework introduced in [1] and an algorithmic scheme for large strains is given, which extends the small strain implementation in [2]. For the phases at the microscale, the finite strain plasticity formulation [3] is applied. Examples according to [4] are shown in order to demonstrate the mesh independence of the framework for ductile crack propagation. Furthermore, simulations are carried out on the microscale by applying the Finite Cell Method [5] on metal matrix composite microstructures. Here, a specific cell arrangement is constructed which minimizes the required number of cells for a given microstructure morphology. Additionally, an experimental setup for the validation of the eigenerosion framework on the microscale is presented. By evaluating the results of these simulations, failure of the material can be investigated on a microscopic level and improvements of the material morphology regarding wear can be realized.

Nanoprecipitate-Strengthened High-Entropy Alloys.

Multicomponent high‐entropy alloys (HEAs) can be tuned to a simple phase with some unique alloy characteristics. HEAs with body‐centered‐cubic (BCC) or hexagonal‐close‐packed (HCP) structures are proven to possess high strength and hardness but low ductility. The faced‐centered‐cubic (FCC) HEAs present considerable ductility, excellent corrosion and radiation resistance. However, their strengths are relatively low. Therefore, the strategy of strengthening the ductile FCC matrix phase is usually adopted to design HEAs with excellent performance. Among various strengthening methods, precipitation strengthening plays a dazzling role since the characteristics of multiple principal elements and slow diffusion effect of elements in HEAs provide a chance to form fine and stable nanoscale precipitates, pushing the strengths of the alloys to new high levels. This paper summarizes and review the recent progress in nanoprecipitate‐strengthened HEAs and their strengthening mechanisms. The alloy‐design strategies and control of the nanoscale precipitates in HEAs are highlighted. The future works on the related aspects are outlined.

Abrasive wear behavior of TiC-strengthened eutectic high chromium cast iron composites

The present research on high chromium cast irons (HCCIs) strengthened with TiC particles was motivated by a need to improve the abrasive wear resistance of materials for mining equipment such as board hammers and liners. The effect of TiC content and heat treatment on the wear properties of eutectic HCCIs was investigated by combining the three-body abrasive wear and micro-scratch tests. The experimental results show that the wear rate of the as-cast HCCIs decreases from 8.0 to 5.1 cm3/cm·10−8 as the volume fraction of TiC increases to 9.8%. The superior wear resistance of TiC-reinforced HCCIs was originated from the synergic contributions of ductile austenitic matrix and high volume fraction of carbides. However, the heat treatment reduces the hardness and wear resistance of the HCCIs with high TiC content due to the high volume fraction of brittle carbide phases and the low ductility of martensite matrix.

Development & Fabrication of AL-3Mg Based SiC & Gr. Hybrid Metal Matrix Composite by Stir Casting Method

The congregation of ceramic particulates in Aluminum hybrid metal matrix composites induces a greater significance in marine and automotive engineering applications because of its strength to weight ratio, good anti-corrosive properties, and high-temperature resistance. The research work focuses on the fabrication of hybrid metal matrix composite with influences of hard ceramic particulates like silicon carbide and dispersoid of graphite in Al-3Mg matrix material, and tribology behavior routed through the liquid metallurgical vortex method. The characterizations of conglomerate like, tensile properties, hardness, compression tests were investigated. The wear resistance increases with assorted graphite compositions. Microstructural examination shows the dispersoids of graphite and silicon carbides are uniformly distributed. The test results of Al-3Mg conglomerates reveal that tensile and hardness properties were enhanced with the addition of Gr. & SiC, as silicon carbide being a harder constituent mixed with a ductile matrix.

Statistics-based numerical study of the fatigue damage evolution in the microstructures of WC-Co hardmetals

In industrial applications, hardmetal tools are often exposed to fatigue loads. This paper proposes a micromechanics-based numerical approach for evaluating the fatigue performance of WC-Co hardmetals. Because the mechanical response of the material is sensitive to the coexisting toughening and damage mechanisms of the ductile binder matrix, this study employed a Chaboche model to precisely present the kinematic hardening behavior and describe the material plasticity of the binder phase. The progressive fracture in the microstructure is modeled by an implicit damage mechanics model implemented in the commercial solver Abaqus/Standard. The numerical study successfully simulated different stages of the fatigue failure process by modeling the damage behavior in the microstructure and reproducing the compromising roles of the ductile binder under the fatigue regime. In addition, the study also emphasizes the need to view fatigue behavior from a statistical perspective owing to the high level of microstructure heterogeneity. By studying the cyclic responses of 50 representative volume element models converted from real scanning electron microscope images, the study revealed how the microstructural characteristics of the hardmetal interact with the imposed external loading and how these two factors jointly determine the load-bearing capacity of the material.

A multiscale tensile failure model for double network elastomer composites

Double network elastomer is a class of molecular composites consisting of a brittle filler network and a ductile matrix network. Upon deformation, progressive scission of the filler network dissipates strain energy while the matrix network resists the micro defect propagation, thus enhancing both stiffness and toughness of the composites. Over the past few years, several types of constitutive models have been developed to capture the nonlinear stress-strain relation of double network elastomers, most of which were formulated by taking consideration of network interaction, chain scission and damage evolution. In parallel, despite the abundant macroscopic experiments and microscopic characterizations on the multiscale failure mechanism of double network elastomers, a theoretical prediction for the ultimate strength of the composites is yet to be built up. In this paper, we develop a multiscale model which describes the deformation and tensile failure of double network elastomer composites at the same time. The progressive damage at molecular level is captured by the stretch-induced scission of randomly distributed polymer chains; the propagation of chain-scission-induced defects at microscale is modeled with analogy to cavitation; finally, the macroscopic necking failure is predicted by tracking the stress softening phenomenon. Our model is validated through the comparison between theoretical calculations and experiments, as well as the predictions and analysis of empirical design principles for double network elastomer composites.

Effect of Laser Welding on Microstructure and Mechanical Behaviour of Dual Phase 600 Steel Sheets

Dual Phase steels are one of the most used advanced high-strength materials in the industry, due to its combination of a ductile ferritic matrix and disperse hard martensite islands, which provide outstanding mechanical properties for components to be cold stamped. This work investigated fiber laser welding applicability in Dual Phase 600 1.6 mm thick steel sheets, evaluating potential welding impacts on properties of the material for industrial applications. A first set of bead-on-plate welds was generated to define best parameters for subsequent tests. A second set was prepared, consisting of butt joints welded in the optimized condition. Weld microstructure was characterized as 100% martensitic at fusion zone (FZ), with growing fractions of ferrite at Heat Affected Zone (HAZ) as one moves away from fusion line. Hardness is around 60% higher at FZ than at BM, being maximum at supercritical HAZ due to its highly refined microstructure and HAZ softening was not observed. Tensile and Erichsen cupping tests presented similar strength results between welded and non-welded specimens, with slight ductility reduction. Finally, numeric simulations based on Finite Element Analysis were carried out to estimate temperature evolution, phase proportions, residual stresses and distortion levels, achieving excellent agreement with experimental results.

Refractory high entropy alloy with ductile intermetallic B2 matrix / hard bcc particles and exceptional strain hardening capacity

In this study, a new Nb30Mo30Hf20Co20 (at. %) refractory high entropy alloy (RHEA) comprising an intermetallic (Hf, Co)-rich B2 matrix and disordered (Nb, Mo)-rich bcc particles was introduced. The B2 matrix showed relatively high dislocation mobility, which, coupled with its continuity, allowed bridging and blunting of the cracks formed in the hard bcc particles during plastic deformation. The complex deformation behavior of the constitutive phases resulted in extraordinary high strain hardening capacity at 22–600 °C, exceeding single- and multi-phase RHEAs, together with the high strength. Our work endows new opportunities to develop high-performance alloys for high-temperature applications.

Static recrystallized annealing treatment-induced strength-ductility trade-off in cold-rolled Co36Fe36Cr18Ni10 multi-principal alloy

Multi-component alloys are recrystallized with various heterogeneous microstructures to regulate their main properties. However, the production of conventionally structured alloys with high strength and superior ductility is exigent because ductility is typically deteriorated by strength enhancement. The microstructure features of alloys determine their mechanical properties. In this work, a new multi-component Co 36 Fe 36 Cr 18 Ni 10 alloy is developed. The alloy was prepared by arc melting and solidified in a Cu mold with a single face-centered cubic phase that provides an outstanding ductile matrix. The mechanical properties and microstructures were systematically investigated through tensile tests, electron backscatter diffraction, and transmission electron microscopy. The as-cast alloy was cold-rolled at 90% reduction and subsequently annealed at 700, 800, and 900 °C. The texture evolution formed numerous fine grains with stacking faults, dislocations, and nanoscale annealed twins in their interior, effectively improving the mechanical properties of the alloy. In single-phase alloys, the twins dominated the matrix and the efficiency of grain refinement achieved by annealing at 700 °C afforded strength improvement. The strength and ductility trade-off is attributed to a microstructure that combines incompletely recrystallized and recrystallized grain regions, forming a heterogeneous microstructure whose performance dimensions span from the submicron to the nanoscale. The microstructure of the fabricated multicomponent alloy was created by large-deformation cold rolling followed by low-temperature annealing treatment. The results show that heterogeneous designs can be effectively achieved by implementing simple low-temperature annealing processes with reduced energy consumption. This strategy provides a means for developing new generation structural materials with high strength and ductility. • The Co 36 Fe 36 Cr 18 Ni 10 alloy exhibits a beneficial combination of strength and ductility when annealed at 700°C. • Stacking faults, dislocation entanglement and nanotwins interactions are effective way to strengthen FCC structure alloys. • Low SFE promotes annealed twins formation and LAGB is the nucleation site for strain-induced martensitic phase transitions.

Phase-Field Model for the Simulation of Brittle-Anisotropic and Ductile Crack Propagation in Composite Materials.

In this work, a small-strain phase-field model is presented, which is able to predict crack propagation in systems with anisotropic brittle and ductile constituents. To model the anisotropic brittle crack propagation, an anisotropic critical energy release rate is used. The brittle constituents behave linear-elastically in a transversely isotropic manner. Ductile crack growth is realised by a special crack degradation function, depending on the accumulated plastic strain, which is calculated by following the -plasticity theory. The mechanical jump conditions are applied in solid-solid phase transition regions. The influence of the relevant model parameters on a crack propagating through a planar brittle-ductile interface, and furthermore a crack developing in a domain with a single anisotropic brittle ellipsoid, embedded in a ductile matrix, is investigated. We demonstrate that important properties concerning the mechanical behaviour of grey cast iron, such as the favoured growth of cracks along the graphite lamellae and the tension–compression load asymmetry of the stress–strain response, are covered by the model. The behaviour is analysed on the basis of a simulation domain consisting of three differently oriented elliptical inclusions, embedded in a ductile matrix, which is subjected to tensile and compressive load. The material parameters used correspond to graphite lamellae and pearlite.

Reinforced Composite Polymer in Automotive Industry : A Review

Modern era is witnessing tremendous move on in discipline of Science and technology. Near has been provocation of notice in Reinforced Composite Polymer (RPC’s) in a range of regime of technology. Broad study is want of hour in line of work of composite fibers anticipated to innovation of new technology and necessitate of advance accomplishment from open material. RPC’s are emerging environment pleasant materials as they container be recycled thermally without posing any menace to environment and originates from renewable sources. They have become a viable alternatives to existing employed carbon fibers polymers having disastrous effect on environment and having limited workability as well as cumbersome disposal. RPC’s have remarkable properties of impact toughness and Fatigue Strength. This is due to their partial brittle structure comprising of ductile and tough matrix interfolded with strong as well as brittle binder. RPC’s have encompassed almost every sphere of automobile industry and are widely used in interior parts, bonnets design and fabrication of accessories as well as in providing insulation platform in automobiles.

Effect of ZrB2 addition on microstructure evolution and mechanical properties of 93 wt.% tungsten heavy alloys

In this study, 93 wt.% tungsten heavy alloys reinforced with highly uniform and dispersed ZrO2 particles were successfully manufactured by powder metallurgy method. In order to fabricate fine-grained tungsten heavy alloys with outstanding performances, ultrafine 93W-4.9Ni-2.1Fe composite powder fabricated using a two-step reduction approach was selected as raw material. Microstructure and mechanical properties were experimentally examined to investigate the influence of ZrB2 addition. Meanwhile, transmission electron microscope and energy spectral analysis identified that ZrO2 particles were generated through the reaction between ZrB2 and oxygen from the grain boundaries. The ultimate tensile strength, elongation, and hardness of 93W-0.75ZrB2 alloys could reach to 963 ± 16 MPa, 18.4 ± 1.3% and 387.6 ± 4.4 HV, respectively, benefitted from the combination of fine-grained strengthening and oxide dispersion strengthening mechanisms. The W grains without observable texture were homogeneously distributed in the γ matrix phase based on electron back-scattered diffraction analysis. Moreover, it was determined that the main fracture types of 93W-ZrB2 alloys were W grain cleavage failure and ductile matrix rupture, closely related to the ZrB2 content in alloys. The current work provided a possible method for purifying the boundaries and enhancing the strength and elongation of W-Ni-Fe alloys simultaneously.

A mechanochromic donor-acceptor torsional spring

Mechanochromic polymers are intriguing materials that allow to sense force of specimens under load. Most mechanochromic systems rely on covalent bond scission and hence are two-state systems with optically distinct “on” and “off” states where correlating force with wavelength is usually not possible. Translating force of different magnitude with gradually different wavelength of absorption or emission would open up new possibilities to map and understand force distributions in polymeric materials. Here, we present a mechanochromic donor-acceptor (DA) torsional spring that undergoes force-induced planarization during uniaxial elongation leading to red-shifted absorption and emission spectra. The DA spring is based on ortho-substituted diketopyrrolopyrrole (o-DPP). Covalent incorporation of o-DPP into a rigid yet ductile polyphenylene matrix allows to transduce sufficiently large stress to the DA spring. The mechanically induced deflection from equilibrium geometry of the DA spring is theoretically predicted, in agreement with experiments, and is fully reversible upon stress release.

Effect of low-temperature tempering on confined precipitation and mechanical properties of carburised steels

Surface-carburised steels are widely used in gears and bearings. The mechanical properties of the surface layers are crucial to improve contact fatigue and anti-wear performance. In this study, the effect of low-temperature tempering on confined precipitation and mechanical properties across surface layers in a high-alloy carburising steel (18Cr2Ni4W) were investigated. The steel was tempered at 240 °C with different tempering durations. Microstructure changes, including confined precipitation, and local mechanical properties were analysed layer-by-layer. During tempering, the morphology and size of martensite remained unchanged while confined precipitation occurred in martensitic matrix; coherent ε phase precipitates formed after 1.5 h, they then transformed to less coherent η phase within 3 h and subsequently evolved to non-coherent θ phase after 3 h of tempering. After tempering for 1.5 h, the strength and ductility of the surface layers reach a maximum value, and elongation of the surface layers with high carbon content is comparable to that of the core with low carbon content. It is revealed that the coherent ε precipitates are mainly responsible for the increase in strength; whilst ductility of the martensitic matrix increases due to a reduced carbon concentration, avoiding tempering brittleness. The results are valuable to the optimisation of surface properties of carburised steels using lower temperature tempering.

Mitigating the impact of the static and cyclic loading on loose coastal saturated sands utilizing a waterproof and super-fast curing polymer

According to the dramatic increase in construction near loose coastal saturated soils, stabilizing these soils due to saturation conditions has always faced challenges. The main purpose of this investigation is to assess the static and dynamic performance of saturated sand stabilized with polyvinyl acetate powder - as a newly introduced source of polymers which besides helping vegetation grow, owing to its numerous features such as anti-acid, and most importantly waterproof properties and super-fast curing, is superior to its rival, traditional liquid polyvinyl acetate. This paper Analyzes the dynamic properties of soil stabilized based on the results of tensile test crack pattern, microscopic observations of matrix texture, and elasticity modulus of hysteresis loops. Lack of significant change in the strength of samples in saturated and dry conditions indicated waterproofness of polyvinyl acetate powder and revealed a significant rise in the compressive and tensile strength of saturated specimens up to 6% of the polymer. Also, an exponential correlation of unconfined compressive strength (UCS) with direct tensile strength (DTS) was found by data fitting. Also, evaporation tests showed a 7% reduction in evaporation rate with 6% polymer, which can confirm this polymer as a suitable option for improving vegetation. Shear modulus and damping ratio also increased and decreased up to 2% of the polymer, respectively, and by increasing the polymer beyond the 2%, dynamic properties were changed due to the zigzag crack pattern and consequently more ductility of the soil matrix, reduction of elasticity modulus, and increasing the thickness of polymer membranes between soil particles. Ultimately, the research results confirmed polyvinyl acetate powder's efficiency, especially with these tiny amounts, as a potential method for controlling saturated grounds.