Fracture Of Composites Research Articles

木材パルプ／バイオプラスチック積層複合材料の表面処理による力学特性の改善

In this study, wood-pulp／bio-based poly (butylene succinate) (Bio-PBS) laminated composites were made by using papermaking techniques. Wood-pulp fibers were treated with 3-aminopropyltrimethoxysilane (APTMS) and poly (vinyl alcohol) (PVA) to improve the interfacial adhesion between the wood-pulp fibers and Bio-PBS. Wood-pulp fibers without being processed (PF), wood-pulp fibers treated by APTMS (PF-Si), and wood-pulp fibers treated by both APTMS and PVA (PF-Si/PVA) were converted to sheets by the papermaking technique. Those sheets and Bio-PBS films were used to make wood-pulp/Bio-PBS laminated composites by hotpressing and cut into test pieces. Tensile testing and the heat distortion temperature measurements were conducted with those samples. As a result, the tensile strength of composites was close in value to that expected by the Reuss model when the volume fraction of wood-pulp was 12％ and 24％. Furthermore, the tensile strength of composites containing PF-Si/PVA was higher than that of composites containing PF and PF-Si. The heat distortion temperature of the composites was higher than that of Bio-PBS, although the effects of surface treatment on the heat distortion temperature were not confirmed. Microscopy observations of composite fractures indicated that the surface treatment of wood-pulp fibers enhanced interfacial adhesion between the woodpulp fibers and Bio-PBS.

Ionic Liquids Facilitate the Dispersion of Branched Polyethylenimine Grafted ZIF-8 for Reinforced Epoxy Composites.

Metal-organic frameworks (MOFs) have been previously shown as an emerging modified class of epoxy resin. In this work, we report a simple strategy for preventing zeolitic imidazolate framework (ZIF-8) nanoparticles from agglomerating in epoxy resin (EP). Branched polyethylenimine grafted ZIF-8 in ionic liquid (BPEI-ZIF-8) nanofluid with good dispersion was prepared successfully using an ionic liquid as both the dispersant and curing agent. Results indicated that the thermogravimetric curve of the composite material had no noticeable change with increasing BPEI-ZIF-8/IL content. The glass transition temperature (Tg) of the epoxy composite was reduced with the addition of BPEI-ZIF-8/IL. The addition of 2 wt% BPEI-ZIF-8/IL into EP effectively improved the flexural strength to about 21.7%, and the inclusion of 0.5 wt% of BPEI-ZIF-8/IL EP composites increased the impact strength by about 83% compared to pure EP. The effect of adding BPEI-ZIF-8/IL on the Tg of epoxy resin was explored, and its toughening mechanism was analyzed in combination with SEM images showing fractures in the EP composites. Moreover, the damping and dielectric properties of the composites were improved by adding BPEI-ZIF-8/IL.

Effect of silane coupling agent and concentration on fracture toughness and water sorption behaviour of fibre-reinforced dental composites.

This paper presents the effect of silane treatment of S-2 Glass fibres on the fracture toughness and water sorption/solubility behaviour of fibre-reinforced flowable dental composites. The effect of epoxy- and methacrylate-based silane coupling agents (SCAs) on the mechanical strength and hydrolytic properties were investigated. The concentration of the selected SCAs on the mechanical and physical properties were investigated. The influence of molecular structure and concentration in the interfacial adhesion at the fibre-matrix interfaces was also studied. Short S-2 Glass fibres of 250µm in length and 5µm in diameter were etched with acid to remove any impurities and roughen the surface. The acid-etched fibres were silane treated with 3MPS, 3GPS, and 8MOTS at different concentrations by weight (%). The silane-treated fibres were incorporated at 5 % into the dental resin mixture. Untreated fibres were added at 5 % to the dental resin mixture and served as the control group. The physical properties such as water sorption, solubility, and desorption along with mechanical properties such as fracture toughness and total fracture work of the fibre-reinforced dental composites grafted with the above-mentioned SCAs were evaluated. The surface morphology of the fractured surface was studied and analysed. The fracture toughness tests showed that the dental composites grafted with optimum weight per cent (wt. %) concentration of the SCA had a better stress intensity factor (KIC) when compared to the 2.0wt. % and 3.0wt. % concentration. The KIC value of dental composites grafted with untreated surface etched glass fibres was less than the KIC values of dental composites grafted with optimum concentrations of 3MPS, 3GPS, and 8MOTS by 81.6 %, 38.6 %, and 110.5 %, respectively. A similar trend was found while investigating the total work of fracture of the dental composites, between optimum concentration, 2.0wt. % and 3.0wt. % concentration of respective SCA. The increase in silane concentration also led to an increase in the water sorption/solubility characteristics. The absorption of water was most severe in the fibre-reinforced dental composites without silane treatment (32.9µg/mm3). The ANOVA results showed that the fibre-reinforced dental composites grafted with 8MOTS at optimum concentration showed an increase in fracture toughness when compared to optimum concentrations of 3GPS and 3MPS by 51.9 % and 15.9 %, respectively. The enhanced mechanical and physical characteristics are due to the increased adhesion between the fibre and silane achieved from the optimum wt. % concentration of 8MOTS. Similarly, dental composites grafted with 8MOTS at optimum concentration showed a decrease in water sorption characteristics when compared to optimum concentrations of 3GPS and 3MPS by 18.2 % and 0.6 %, respectively. The decreased water sorption characteristics at the optimum concentration of 8MOTS could be due to the reduced availability of reactive hydroxyl groups and the hydrophobic characteristics of 8MOTS. Silane coupling agents (SCAs) are important components of dental composites. The type and concentration of SCA have a significant effect on material properties. The current study focuses on understanding the effects of different SCAs and wt. % concentrations on the interfacial fracture behaviour and the influence of different SCAs on the water sorption and solubility behaviour of S-2 Glass fibre-reinforced flowable dental composites.

A Study on Fracture Propagation Law of CO2 Composite Fracturing in Shale Reservoir

Background: In recent years, CO2 composite fracturing technology has been widely used in unconventional reservoirs. Compared to conventional hydraulic fracturing, CO2 fracturing can create complex fractures, replenish formation energy and reduce oil flow resistance. For shale oil reservoirs with natural fractures, CO2 composite fracturing can not only give full play to the advantages of complex fracture networks created by CO2 but also make use of water-based fracturing fluid to create long fractures with high conductivity. Methods: Based on fracture fluid flow, stress interference, natural fracture description, and CO2 phase change equation, a CO2 composite fracture propagation model was established in this paper to simulate the effects of fracturing fluid type, CO2 proportion, construction scale, natural fracture development, fracturing fluid injection rate and other factors on the propagation morphology of CO2 injection fracture network in shale oil reservoirs. Results: The results show that the water-based fracturing fluid is beneficial to the formation of long main fractures, but the overall complexity of the fracture network and the effective stimulated volume of the fracture network are significantly lower than that of CO2 fracturing. The application of the appropriate proportion of CO2 composite fracturing fluid can give full play to the comprehensive advantages of CO2 and water-based fracturing fluid and realize the full stimulation of the reservoir. CO2 fracturing in shale oil reservoirs with low principal stress difference and high natural fracture development extent can communicate natural fractures in a large range and form a complex fracture network. For shale oil reservoirs with natural fractures, a high fracturing fluid injection rate can significantly improve the complexity of the fracture network. Conclusion: The CO2 composite fracturing technology is applied to horizontal wells in X shale reservoir, and the production after fracturing is significantly higher than that of offset wells, which can be applied in the same type of reservoir and has broad application prospects.

Adaptive isogeometric analysis–based phase-field modeling of interfacial fracture in piezoelectric composites

This paper implements an adaptive phase-field model to investigate the interfacial fracture in transversely isotropic piezoelectric composites under different electromechanical loadings using an isogeometric framework based on polynomial splines over hierarchical T-meshes (PHT-splines). The model introduces the interface and crack phase-field parameters to regularize the sharp interface and crack topologies, respectively and the regularized energy terms are incorporated corresponding to crack and interface evading the need for line integration along them. It also modifies the energy functional to scrutinize the interaction between interfacial damage and crack propagation in piezocomposites and thus is capable of capturing the fracture patterns including interfacial debonding, matrix cracking and their interactions under different electric fields. An adaptive mesh refinement scheme using PHT-splines is implemented to efficiently resolve for interface and crack phase-fields and track the complex crack propagation paths without any ad hoc criteria. The efficacy and robustness of the proposed model are demonstrated using a set of examples simulating the electromechanical fracture in piezoelectric composites. Moreover, different fracture mechanisms in composite materials including the crack nucleation, interfacial debonding, matrix cracking, crack propagation and coalescence are found to be precisely captured using the present modeling technique.

Evaluation of the Impact Strength and Morphology Properties of Musa Acuminata Fiber Composite/CaCo3 Powder

Banana stem (Musa Acuminata, MA) fiber is a free agricultural waste obtained after harvesting the fruit. When compared to synthetic fibers, banana fiber has significant weaknesses in composite production, such as low interfacial bond strength between the fiber and the matrix. The purpose of this research is to improve the impact strength of banana stem fiber composites by adding CaCO3 powder. The hot press technique is used to create composites. In the production of polyester composites, woven MA and CaCO3 stem fibers are prepared. An impact testing machine and a scanning electron microscope were used to investigate the effect on morphological properties and impact strength. The study's findings revealed that a polyester composite containing 10% banana stem fiber and 25% CaCO3 had the highest impact strength of 45.27 KJ/m2, which was associated with strong adhesion between the CaCO3-fiber and the polyester matrix. Fiber pullout, matrix cracking, and fiber debonding were all observed in the composite fracture morphology. The resulting composite properties could be used to replace palm fiber/fiber glass composites.

Characteristics of Epoxy Composites Containing Carbon Nanotubes/Graphene Mixtures.

The paper considers the development of fillers representing mixtures of carbon nanotubes and graphene materials (graphene oxide and graphene nanoplatelets) in different mass ratios to modify epoxy resin. The graphene type and content effect on the dispersed phase particle effective sizes-both in aqueous suspensions and the resin-was analyzed. Hybrid particles were characterized by Raman spectroscopy and electron microscopy. The composites containing 0.15-1.00 wt.% CNTs/GO and CNTs/GNPs were thermogravimetrically analyzed, and their mechanical characteristics were determined. SEM images of the composite fracture surfaces were acquired. Optimal dispersions containing 75-100 nm particles were obtained at the CNTs:GO mass ratio of 1:4. It was shown that the CNTs can be located between the GO layers and on the GNP surface. The samples containing up to 0.2 wt.% CNTs/GO (at 1:1 and 1:4 ratios) were stable when heated in air up to 300 °C. For 0.15-0.20 wt.% CNTs/GO (at 1:1 ratio), the tensile strength and modulus of the composite increased by 84-88 and 40%, respectively. The increase in the strength characteristics was found to occur due to the interaction of the filler layered structure with the polymer matrix. The obtained composites can be used as structural materials in different fields of engineering.

Composite interlaminar fracture toughness imparted by electrospun PPO veils and interleaf particles: A mechanistical comparison

Thermoset composite toughening by interleaf materials receives increasing attention as requirements for high toughness become essential for primary structures. Here, polyphenylene oxide (PPO) electrospun veils were used for carbon fiber epoxy composite interleaf toughening. Their Mode I, Mode II interlaminar fracture toughness (GIC and GIIC) were measured as a function of veil loading levels. 10 wt% veil loading rendered the best toughening performance, reached to 530 J/m2 and 1400 J/m2 in GIC and GIIC, respectively, and it yielded further increase of 140% and 30% compared to the corresponding PPO particles. Scanning electron microscopy (SEM) and 3-D laser microscopic imaging analysis (3D-LMIA) on fracture surfaces revealed energy absorbing mechanisms such as bridging and plastic deformation. The continuous network structure imparted by the veils accounted for the additional toughening mechanisms, i.e. the deformation, breakage and pull-out of PPO fibers, that were responsible for the outstanding fracture toughness.

Investigation of fused deposition modeling parameters on mechanical properties and characterization of ABS/carbon fiber composites

The effect of parameters of acrylonitrile butadiene styrene composites reinforced with carbon fabricated by fused deposition modeling was studied in this work. Parameters like infill density, raster angle, layer thickness, and printing parameters are varied and their influence on mechanical properties was analyzed experimentally. Experiments were planned by the design of experiments technique and mathematical equations were generated to analyze the impact of these parameters. ANOVA is involved to ensure the validity of the mathematical equations. The mechanism of the fractured samples was studied using scanning electron microscopy. The tensile strength of ABS/carbon fiber composites ranges from 21.74 to 28.09 N/mm2, while the flexural strength ranges from 2.62 to 3.14 N/mm2 and the impact strength ranges from 3.66 to 5.19 kJ/m2. The fracture of composites is characterized by cavities, infill gaps, bonding, dimples, tearing debonding of fiber, crack, delamination, shearing, crack, and fiber protrusion. The nature of failure varied from ductile to brittle depending upon the change in process parameters.

Simultaneously tuning interfacial and interlaminar properties of glass fiber fabric/epoxy laminated composites via modifying fibers with graphene oxide

A series of graphene oxide (GO) with various oxidation degrees were synthesized in this work and then grafted onto the surface of glass fiber fabric (GFf), and subsequently a resin infusion process was engaged in the fabrication of GFf/epoxy laminated composites. Interlaminar and interfacial properties as well as interlaminar microstructure of laminated composites were investigated in detail. Results showed that various oxygen-containing functional groups on the GO surface due to oxidation degrees endowed GO with different dispersion states in composites and strengthening/toughening efficiency, thus greatly influenced composites’ interlaminar and interfacial adhesion. Also, the desorption and diffusion of GO from the fiber surface into matrix-enriched interlaminar region during the resin infusion process were evidenced. Making use of a moderate weight ratio of oxidation agent (KMnO4)/graphite (2:1), the optimal oxidation degree of GO was achieved for reinforcing fiber/matrix interface and matrix-enriched interlaminar regions. Under this case, the interlaminar shear strength and work of fracture of resultant composites were raised by 28.2% and 138.3%, respectively; storage moduli in glass regions and at the beginning of rubbery regions were enhanced by 22.3% and 104.5%, respectively; the significantly fiber/matrix interfacial adhesion and glass-transition temperature were obtained, compared with those of the control sample. This work provides a guiding strategy for optimizing strength and toughness of fiber-reinforced composites by regulating GO oxidation degrees.

Effect of the Welding Thermal Cycle on the Microstructure and Mechanical Properties of TiC Cermet HAZ Using the Gleeble Simulator

The effect of heat input on the microstructure and mechanical properties of TiC cermet in MIG welding has been comprehensively investigated by Gleeble simulation. The microstructure, phase composition and shear fracture of TiC cermet were examined by OM (optical microscopy), SEM (scanning electron microscope), TEM (transmission electron microscope) and XRD (X-ray diffraction) analyses. The results show that the heat input has a significant effect on the properties of TiC cermet. With TiC particles and the austenite bonding phase remaining the same, the heat input can effectively improve the toughness of the bonding phase and the structural strength from 219.9 HV0.01 to 380.5 HV0.01 and from 469 MPa to 684 MPa, respectively, as the dislocation density increases while the heat input increases. When the heat input is 3.4 KJ/cm, the shear strength reaches the peak at 684 MPa, with the increase in heat input, the secondary fragmentation of TiC particles increases, and the crack propagation leads to a significant decrease in material strength.

Laboratory visualization of supercritical CO2 fracturing in tight sandstone using digital image correlation method

Hydraulic fracturing is a crucial technology for reservoir stimulation in unconventional reservoirs. Conventional water-based fracturing has several potential issues of environmental pollution and waste of water resources. Anhydrous fracturing fluids, such as supercritical CO2 (SC–CO2), are now utilized for fracturing in recently years. However, the fundamental mechanism of fracture initiation and propagation during SC-CO2 fracturing has not been fully understood. A tri-axial fracturing visualization equipment is developed in this work, which can conduct fracturing experiments under reservoir conditions (150 °C and 50 MPa). The injection pressure, fracture propagation and strain field of the entire hydraulic fracturing procedure can be quantitatively monitored using a high-speed camera and digital image correlation (DIC) technology. Results demonstrate that low-viscosity fluids (SC–CO2) tend to induce micro-fractures, mainly generating mode I-II composite fractures. However, relatively high-viscosity fluids (Liquid-CO2) tend to form a simple pattern, mainly mode I fractures. SC-CO2 shows strong diffusivity and can easily diffuse into micro-fractures. As a result of the increased pore pressures in the rock around the wellbore, SC-CO2 fracturing has a breakdown pressure that is 22% lower than L-CO2 fracturing. The fracture initiation time of SC-CO2 fracturing is about 34% later than that of L-CO2 fracturing. An equivalent strain difference coefficient is proposed and indicates that the strain concentration effect of SC-CO2 fracturing is more obvious than L-CO2 fracturing. Meanwhile, the DIC measured full-field displacement field indicates that the fracture width produced by SC-CO2 is 1.31 mm, which is narrower than that produced by L-CO2 of 1.58 mm. This experiment shows that the DIC method can provide an intuitive, accurate, and effective method for quantifying fracture characteristics. The results can provide an empirical reference for further analysis of the fracturing mechanism.

Evaluation of properties of hybrid laminated composites with different fiber layers based on Coir/Al2O3 reinforced composites for structural application

Hybrid composites produced using natural and synthetic fibers are sustainable alternative materials for different structural applications. Therefore, this study aimed to incorporate coir fiber, E-glass, synthetic fabric, and rubber sheet into epoxy matrix by adding alumina filler to the coir composite. The hand layup method was used to manufacture a hybrid laminates composite of coir/E-glass/synthetic fabric/rubber sheet with different stacking sequences. The tensile, flexural, impact, hardness properties, water absorption, and thickness swelling of the products were evaluated. Scanning electron microscopy was used to study the morphology of the fractured surfaces. The results showed that the hybridization fiber and filler can enhance the tensile properties of the products up to 280% as well as improve the water absorption performance and thickness swelling to 78%. The flexural properties decreased after the incorporation of the fiber layer to the coir/alumina composite. An increase was also observed in the flexural and impact properties after the synthetic fabric was replaced with a rubber sheet. This study revealed that the incorporation of fibers layers into a coir composite led to higher hardness resistance. Furthermore, SEM image and macroscopic fractography showed fiber breakage on the matrix, a brittle fracture of composites, and delamination failure between the rubber sheet and matrix during the bending test. Based on the results, coir/E-glass/synthetic fabric/rubber sheet hybrid composites with different layering sequences were appropriate for various structures applications.

Tuning microstructure and mechanical and wear resistance of ZrNbTiMo refractory high-entropy alloy films via sputtering power

Introduction: Recently, great efforts have been dedicated to tailoring the microstructure of the RHEA films to further optimize the performance of the films. However, there is still a lack of in-depth study on their wear mechanism and microstructure evolution.Methods: In this work, the novel ZrNbTiMo RHEA films were prepared by DC magnetron sputtering and splicing target techniques. The effects of sputtering power on the microstructure, hardness, toughness, and wear resistance of ZrNbTiMo RHEA films were investigated in detail.Results: The ZrNbTiMo films possess the nanocomposite structure, the bcc nanocrystal is wrapped in an amorphous phase. The wear resistance of the film is expected to be improved by finding an appropriate ratio between the amorphous phase and the nanocrystal phase. The nanocrystal structure ensures the high hardness (6.547 ∼ 7.560 GPa) of the ZrNbTiMo film. In addition, the nanocrystals hinder crack propagation, this toughness mechanism effectively improves the toughness of the film. The ZrNbTiMo film prepared at 150 W possesses excellent mechanical properties, hardness of 7.240 GPa and toughness of 0.437 ± 0.040 MPa × m1/2, exhibits better wear resistance (wear rate: 5.223 × 10−7 mm3/N m).Discussion: The wear resistance of ZrNbTiMo film is controlled by both hardness and toughness. The nanocomposite structure makes the ZrNbTiMo films possess a composite fracture which could improve the toughness of the ZrNbTiMo film. The wear-resistant ZrNbTiMo RHEA films with wear rates of the order of 10−6 mm3/N m have been prepared by tuning the sputtering power, this film can be used as a potential candidate for wear-resistant coatings.

Numerical Simulation of the Coalescence Behavior of Intermittent Structures with Fissures

To further study the failure behavior of the rock-like materials containing intermittent fissures subjected to uniaxial compression, 3D printing technology was adopted to manufacture specimens with prefabricated kinked and straight fissures (K-S fissure). The order of average peak strength was −45° > −90° > +90° > +45°. The influence of different parameters, including the effective length and inclination angle of branch fissure, on the coalescence pattern was discussed. Results showed that two failure modes were observed: Model I represented tensile-shear composite failure in the rock bridge area, while Model II showed non-coalescence occurring. The effective length parameter presented a relatively larger influence than the inclination angle on the failure behavior. Additionally, Model I was discovered to tend to occur in the rock bridge region when the branch fissure turned anticlockwise. Based on numerical simulation using the Realistic Failure Process Analysis (RFPA2D), a quick damage criterion approach was proposed to estimate the coalescence behavior in the rock bridge, which was beneficial to determine coalescence pattern and failure behavior. Based on the curve fitted by the simulation, the coalescence pattern of cracks initiated from pre-existing intermittent fissures occurs in the tensile-shear composite fracture pattern, while non-coalescence occurs in the rock bridge below the curve.

Formulation and evaluation of a new multi-functional fracturing fluid system with oil viscosity reduction, rock wettability alteration and interfacial modification

Low permeability heavy oil reservoir has the characteristics of poor physical properties and poor oil mobility, and its primary production is very limited.Based on the synergistic mechanism, the multi-functional composite fracturing fluid system HC-5 was constructed in this study, which combines fracturing, viscosity reduction, wettability change, and interface modification. Taking a low permeability heavy oil block in Changqing Oilfield as an example, the oil recovery of the new multifunctional composite fracturing fluid system was evaluated. The results show that the viscosity reduction should not be used as a single evaluation index for enhanced oil recovery in heavy oil reservoirs, and the improvement degree of the water–oil mobility ratio is more significant.Wettability reversal can change capillary resistance into displacing force and affect the influence of interfacial tension.The interfacial tension is not the smaller the better, the contribution of reducing interfacial tension to enhancing oil recovery has decreased after reaching a low value (10−2 mN/m), even lower than the contribution of mobility ratio, so it is not recommended to blindly pursue extremely low interfacial tension and the synergistic effects of various reasons should be played to obtain the best result.In addition, by adding polymer, the viscoelasticity can be used to increase the microscopic pull force and expand the macroscopic sweep volume. The field test of 10 volumetric fracturing wells provides that the fracturing fluid system can significantly increase the primary production of the well by 20–25%.

Effect of strain rate on fractography texture descriptor of AA6063/(Si3N4)x/(Cu(NO3)2)y (x=12%, y = 2–6%)composite after multiple ECAP passes: second order statistical texture analysis conjunction with regression analysis

The tensile strength of the ECAP processed composite of AA6063/(Si3N4)x/(Cu(NO3)2)y (x=12%, y=2-6%) at various strain rates from 0.0001 to 1s-1 with an increment of 10 was examined in relation to the seven-fracture image texture descriptor through void features such as void size and distribution. In order to measure the matrices of voids on the fracture surface created through the coalescence of void results to enhance the material hardening as strain rate increases, the second order statistical texture analysis has been used. With respect to the rising strain rate, it was observed that the composite fracture image feature parameter correlation, homogeneity improved by 6 %, and 20.74% for AA6063/12%Si3N4/6%Cu(NO3)2 after I passes as compared to AA6063/12% Si3N4 after III pass. The contrast was reduced by around 58.643% when reinforcement went from a single reinforcement of 12% Si3N4 with I Pass to a composite of two reinforcements (Si3N4, Cu(NO3)2) that had 6% Cu(NO3)2 with I Pass. After three passes on AA6063/12%Si3N4/2%Cu(NO3)2, the maximum entropy was seen due to the material's increased plastic deformation, which led to an uneven particle distribution. As strain rate and copper nitrate percentage grew from 0 to 6 percent, the tensile strength of the composite improved by 34.69%. To assess the importance of fracture image features in relation to tensile strength with respect to strain rate, a regression model was developed. In order to get information about the fracture studies from fractography, the contrast with varying strain rate was nevertheless the aspect, which had the greatest influence.

Effect of fiber hybridization on tensile fracture of 3D woven textile composites

3D Woven composites provide the ability to handle higher damage tolerance (Pankow et al., 2019). Hybridization of fibers is an additional method to provide improved damage tolerance (Pankow et al., 2014) . This work is the first time that the tensile response of “hybrid” 3D woven composites (H3DWC) is investigated. The hybridization showed an increase in modulus with increasing carbon fiber volume fraction ( > 30 % in general). While, the strength showed a decrease that was proportional to the carbon fiber volume fraction ( > 78% of the baseline glass). Although the carbon failed, the material remains intact as the glass fibers have not failed, maintaining 80% of the strength after failure in the warp direction. The unsymmetric samples, which have benefits for bending type loading, produced coupled behavior due to thermally induced shrinkage. Overall looking at the combination of factors from previous bending work with this new tensile work, it can clearly be seen that there is a clear tradeoff in the amount and way one would perform hybridization.

Microstructure based numerical simulation of the micromechanics and fracture in hypereutectic Al–Mg2Si composites

In the present study, both experimental and numerical examinations were performed to understand the hypereutectic Al–Mg2Si composite's microstructural morphology, mechanical properties and fracture correlation. The innovation of this research includes the micromechanics studies and failure initiation in hypereutectic Al–Mg2Si composite through the compiled induce stress, deformation plasticity and energy dissipation theory subjected to tension. Ultimate tensile strength (UTS), toughness and elongation have decreased, but the yield strength has increased up to 25% Mg2Si addition and then decreased at the composites with 30 wt% Mg2Si because the brittle fracture increases due to the presence of comparatively coarser and dendritic primary Mg2Si particles. Additionally, an increase in the microporosity with the increase in Mg2Si concentration also affects the same. Finite element analysis (FEA) was performed using the Ramberg-Osgood constitutive model and actual microstructure 2D representative volume elements model. The FEA and experimental results have a satisfactory agreement. The fractography unveils the presence of a mix-mode of fracture, i.e. the ductile and the brittle fracture of the composites. Mises and Tresca failure criteria reveal that the distribution of stress is non-homogeneous and stress is localized in the narrow eutectic and irregular Mg2Si phase region, which acts as a crack initiation site. Analysis of the stress triaxiality and equivalent plastic strain distribution shows that void initiation and growth take place during the deformation of the Al–Mg2Si composites. The plastic dissipated energy distribution in deformed RVEs interestingly consents to the von mises stress, plastic strain and stress triaxiality analysis findings.

Microindentation testing as a means of predicting lump iron ore physical properties

ABSTRACT This study utilised Vickers and Knoop microindentation testing to characterise the physical and chemical properties of a range of iron ore material types and lump ore samples. Lump ore composite microhardness (CH) and fracture toughness (CFT) correlated best with Tumble and Abrasion Indices and with Fe-total, Al2O3 and LOI contents. General trends were evident between CH/CFT and other common metallurgical indices, e.g. higher Reduction Degradation Index with lower CH. Correlations between ore group CH/CFT and the metallurgical data were generally similar, but relatively stronger, than those for the lump ores. The chemistry of mineralogical-textural sub-sets of ore groups correlated with lump ore CH/CFT. Calculating ore group CH/CFT using a textural method is therefore capable of capturing differences in ore group chemistry that relate in part to texture. A textural database of microhardness and fracture toughness can be utilised with automated optical image analysis to provide geometallurgical characterisation of iron ores.