Particle Fracture Research Articles

Experimental investigation on the mechanical, structural and thermal properties of Cu–ZrO2 nanocomposites hybridized by graphene nanoplatelets

Hybrid Cu–ZrO2/GNPs nanocomposites were successfully produced using powder metallurgy technique. The effect of GNPs mass fraction, 0, 0.5, 1 and 1.5%, on the mechanical and electrical properties of the produced hybrid nanocomposite was investigated while maintaining ZrO2 mass fraction constant at 5%. High-energy ball milling was applied for mixing powders followed by compaction and sintering. The morphological analysis of the produced powder showed acceleration of Cu particles fracture during ball milling with the addition of GNPs up to 0.5% with noticeable reduction of agglomeration size. Moreover, the crystallite size of Cu–5%ZrO2/0.5%GNPs hybrid nanocomposites revealed smaller crystallite size, 142 nm, compared to 300 nm for Cu–5%ZrO2 nanocomposite. Additionally, the hybrid nanocomposite with 0.5% GNPs shows homogeneous distribution of both reinforcement phases in the sintered samples. The compressive strength increased with the GNPs content and reached 504.6 MPa at 0.5%, 31% higher than the Cu-5%ZO2. The thermal conductivity had the maximum value at 0.5 wt%GNPs and reached 345 W/m k. The results provide efficient manufacturing process for high strength and good conductivity hybrid nanocomposites, which is applicable in many structural applications such as heat exchange purposes.

Synthesis and characterization of brass–AlN composites synthesized by ball milling

Abstract Mechanical alloying is a powder processing technique in which repeated cold welding and fracturing of powder particles was done in high energy ball mill to produce a homogenous material. In this work, Brass matrix composites with different weight percentages of aluminium nitride (AlN) was synthesized through MA. The necessary amount of powders was milled to capitulate different compositions such as Brass-0 wt.% AlN, Brass-4 wt.% AlN, Brass-8 wt.% AlN and Brass- 12 wt.% AlN composites. The SEM and EDAX tests were conducted on the milled composite powders to investigate about their characterization. The SEM analysis established the homogeneous sharing of AlN in the Brass matrix. The green compacts were prepared and were sintered using electric muffle furnace under controlled atmosphere for a time period of 3 hr. The SEM images of the sintered composite samples ensured the uniform distribution of AlN in the matrix exclusive of pores. The outcome exposed that the adding together of AlN with the Brass matrix improved the mechanical properties of the brass matrix composites

Study of the effect of mechanical alloying on the structure of Ni-Mn-Sn Heusler alloy

The formation process of nanocrystalline Ni-Mn-Sn Heusler alloy was investigated using mechanical alloying route. Powder samples of this alloy were fabricated using high milling energy technology of planetary ball mill in an argon atmosphere. The effects of selected milling time (0 hr, 5 hr, 10 hr and 15 hr) on the crystallite size, lattice strain, morphology and chemical composition of as-milled powder samples were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) attached with energy-dispersive Xray spectroscopy (EDX). Thermal behavior of the samples was analyzed by differential scanning caloorimetry (DSC). Results indicated that the formation of single phase Ni2MnSn Heusler alloy was obtained after 15 hr of milling through the balance between particle coalescence and fracture accompanied by uniform grain refinement. The optimum milling time resulted from the proper selection of milling parameters. Compositional analysis of 15 hr asmilled sample revealed stoichiometric Heusler composition (X2YZ) of Ni-Mn-Sn alloy with no impurities. The subsequent heating of the powder particles in DSC showed crystallization of Ni-Mn-Sn alloy. The obtained results provide an understanding of the fabrication of Ni-Mn based Heusler alloy powders by mechanical alloying technique by using laboratory scale ball mill with the aim to bring out structural and thermal aspects of the alloy.

Impact of Particle Size Distribution for Variable Mixing Time on Mechanical Properties and Microstructural Evaluation of Al-Cu/B4C Composite

Abstract In the present work the combined effects of particle size and distribution on the mechanical properties of the 20vol.% B4C particle reinforced Al–Cu alloy composites by powder metallurgy is investigated. The aim of this work was to evaluate the effect of mixing time (5h, 15h and 25h) and particle size (23µm and 67µm) of B4C particles on the metallurgical and mechanical properties. It has been found that small ratio between matrix/reinforcement particles sizes resulted in more uniform distribution in the matrix. The particles distributed more uniformly in the matrix with increasing in mixing time. The results also showed that homogenous distribution of the B4C particles resulted in higher hardness, ultimate tensile strength, yield strength and elongation. Fracture surface observations showed that the dominant fracture mechanism of the composites with small B4C particle size (23µm) is ductile fracture of the matrix, accompanied by the “pull-out” of the particles from the matrix, which is attributed to positive effect of reinforcement particles in resistance to the movement of dislocations while the dominant fracture mechanism of the composites with large B4C particle size (67µm) is ductile fracture of the matrix, accompanied by the B4C particle fracture

Experimental Study on Mechanical Properties of Prefabricated Single‐Cracked Red Sandstone under Uniaxial Compression

This paper aims at the phenomenon of the fractured rock column in underground engineering which is prone to collapse when subjected to ground pressure. Uniaxial compression test and particle flow code (PFC2D) are used to analyze the influence of crack dip angle on the mechanical properties, crack propagation, and the failure mode of red sandstone. From the results, it is observed that the stress–strain curve of the precracked red sandstone can be divided into five stages, and there is a critical stress value in the stage of accelerated crack propagation and unstable fracture of the rock sample. Further, the peak strength, maximum strain, and the elastic modulus of the precracked red sandstone increase with the increase of crack dip angle, and the ultimate failure mode of rock sample changes from the “ladder” type failure to slope uneven failure. Furthermore, from PFC2D simulation, it is found that the tensile microcracks contribute more towards the failure of rock samples than the shear cracks. The contact force chain is very weak at the places where the precracks and macroshear planes are formed. This indicates that the original contact force is weakened due to particle fracture. Therefore, the bearing capacity of the precracked rock samples decreases with the increase in load. From the simulation results, it is found that the displacement at the shear plane of the rock sample is large, and the shear dilatation occurs. With the increase in load, the specimen falls off and is ejected. This is due to the weakening of the contact force between the internal particles. Thereafter, it fractures to produce microcracks, which gradually converge, thus providing a prerequisite for the transformation of elastic strain energy into kinetic energy.

Evolution of particle damage of sand during axial compression via arrested tests

A series of axial loading and unloading compression tests was conducted on siliceous and calcareous sand, using a modified oedometer apparatus. Samples were prepared using aspect ratios of 6:1 and 1:1 (diameter:height) and loaded at uniform axial strain rates of 0.01 and 10%/s. Compression was arrested at various strains up to 30%, after which the size distribution of the sand particles was determined using a dynamic particle size analyzer capable of identifying particle shapes and sizes in the 10–3000 µm range. Samples responded slightly stiffer and experienced more crushing in the 1:1 aspect ratio tests. For silica sand, significant reduction in grain size was observed beyond 10% strain, with modest rate dependency observed. Faster breakage and greater rate sensitivity were seen in the softer coral sand, where particle breakage was observed to start at 5% strain. Strain-hardening behavior and hysteresis were observed in the stress–strain behavior and correlated with the size reduction observed in the arrested tests. In addition, it was noticed that smaller particles break more than larger particles. Both sands exhibited fractal particle evolution, i.e., when particles fracture, daughter particles preserve a similar sphericity to that of the parent material.

Effect of copper content on the tensile elongation of Al–Cu–Mn–Zr alloys: Experiments and finite element simulations

Microstructures of cast aluminum alloys used in automotive engine applications often consist of intermetallic particles that can impact the tensile elongation of these alloys. Here, we investigate the effect of intermetallic grain boundary particles on tensile elongation by fabricating a series of alloys with Cu content varying between 6.0 - 9.0 wt% in cast Al–Cu–Mn–Zr (ACMZ) type compositions. The tensile elongation of as-aged ACMZ alloys decreases monotonically with increase in Cu content. While the microstructure within the grains and yield stress of the alloy remains invariant with Cu content, the decrease in tensile elongation correlates well with increase in the size and volume fraction of grain boundary particles. Microstructural observations are combined with finite element simulations to explain the trend in tensile elongation with changing Cu content. Crack initiation is found to occur by brittle fracture of the grain boundary particles. Increase in particle size promotes crack initiation by reduction in size dependent particle fracture strength. Lower inter-particle spacing at higher particle volume fraction further facilitates crack initiation by increasing stress within the particles caused by the interaction between stress fields of neighboring particles. Increase in particle volume fraction also accelerates crack propagation through the formation of macro shear zones in the microstructure. The increase in Cu content of cast ACMZ alloys, therefore, decreases tensile elongation by promoting both crack initiation and crack propagation.

Effect of Rare Earth Element Content on High Cycle Fatigue Property of Titanium Alloys

High cycle fatigue (HCF) properties for high temperature titanium alloys without and with different content of rare earth element Y have been tested at ambient temperature at a frequency of 100Hz or so and a load ratio R of 0.1, and the effect of Y on fatigue fracture behavior was also analyzed. The results indicated that the HCF strength for the alloys increases with the increment of rare earth element content, and the strength of the two alloys with Y are lower than that of the alloy without Y. Compared with the alloy without Y, the strength for the two alloys with Y decreases 11.2% and 17.4%, respectively. The particle size for rare earth oxide dispersely precipitated from the matrix alloy varies from several hundred nanometer to several micrometer. The crack initiations for the alloys are related to the fracture of rare earth oxide particles.

Structural, mechanical and tribological properties of Cu–ZrO2/GNPs hybrid nanocomposites

Hybrid Cu–ZrO2/GNPs nanocomposites were successfully produced using powder metallurgy technique. The effect of GNPs mass fraction, 0, 0.5, 1 and 1.5%, on mechanical and tribological properties of the produced hybrid nanocomposite was studied while maintaining ZrO2 mass fraction constant at 5%. High energy ball milling was applied for mixing powders and compaction and sintering were applied for consolidation. The morphological analysis of the produced powder showed acceleration of Cu particles fracture during ball milling with the addition of GNPs up to 0.5% with noticeable reduction of agglomeration size. Moreover, the crystallite size of Cu–5%ZrO2/0.5%GNPs hybrid nanocomposites revealed smaller crystallite size, 142 nm, compared to 300 nm for Cu–5%ZrO2 nanocomposite. Additionally, the hybrid nanocomposite with 0.5% GNPs shows homogeneous distribution of both reinforcement phases in the sintered samples. This improved nano and micro structure of Cu–5%ZrO2/0.5%GNPs nanocomposites revealed higher hardness, 169.3 HV, compared to 65.5 HV for Cu–5%ZrO2 nanocomposite. The wear rate is decreased in this composite while it increased with increasing GNPs content more than 0.5%. The coefficient of friction is decreased as well for this hybrid nanocomposite and remain constant with increasing GNPs content more than 0.5%.

Plastic deformation and fracture behaviors in particle-reinforced aluminum composites: A numerical approach using an enhanced finite element model

A microstructure-based comprehensive finite element model, which incorporated the deformation/fracture of the matrix alloy, fracture of the particle and decohesion of interface, was built to predict the effects of particle size and shape on the plastic deformation and fracture behaviors in particle-reinforced metal matrix composites. The effect of particle size on the yield strength and work hardening rate of the matrix alloy was demonstrated. When the particle diameter is <10 µm, the fracture of the matrix alloy near the interface dominates the failure mechanism of the composite, whereas changed to particle fracture with particle diameter >10 µm. A cohesive zone model was also included in order to predict interfacial failure behavior. It was noted that SiC/Al interface exhibits a high interfacial bonding strength and the interfacial decohesion was caused by crack propagation from the particle to the interface. The simulation results are in good agreement with the experiment tensile test results in the SiCp/6061Al composite.

Finite Element Analysis and Comparison of the Machinability of SiCp/Al Composite and CNT/Al Composite

Metal matrix composites are widely used in aerospace and automotive industries due to their extraordinarily attractive physical and mechanical behavior. In order to compare the machining property of SiCp/Al composite and CNT/Al composite, the two-dimensional orthogonal cutting finite element models were developed by the finite element analysis software ABAQUS/Explicit. The comparison of SiCp/Al composite and CNT/Al composite on the basis of surface quality, sub-surface damage and edge quality was tried out in order to know the machinability of two materials. The results show that the machined surface defects such as small pits, large voids, tear of the matrix and particle breakage are commonly observed during machining of SiCp/Al composite, and the surface residual stress changes from compressive stress to tensile stress. However, there are some large holes, bulges matrix fracture and particle fracture on the machined surface of CNT/Al composite, and the residual stress is mainly compressive stress. Therefore, at the equal reinforcement effect, the machinability of CNT/Al composite is better than that of SiCp/Al composite.

Effect of Mn Addition on the Mechanical Properties of Al–12.6Si Alloy: Role of Al15(MnFe)3Si2 Intermetallic and Microstructure Modification

Effect of manganese (Mn) addition (0.0, 1.0, 2.0 and 3 wt%) on the microstructural morphology, hardness, tensile properties and fracture behaviour of the gravity cast eutectic Al–12.6Si alloy has been studied through XRD analysis, chemical analysis, optical metallography, FESEM analysis, energy dispersive spectroscopy analysis, hardness test, tensile test and quantitative phase analysis. As-cast Al–12.6Si–0.0Mn alloy has a non-uniformly distributed coarser and irregular shape primary and eutectic silicon particles inside the α-Al phase, and both the Si phase have very sharp corners. Whereas, the 1 wt% Mn added alloy has uniformly distributed fine eutectic and primary Si particles with blunt corners. Further, the addition of 1.0 wt% Mn forms very few (0.26 vol %) irregular shape Al15(MnFe)3Si2 intermetallic phase within the α-Al phase and eutectic Si phase. But, 2.0 wt% and 3 wt% Mn added alloy has an irregular shape coarse plate-like Al15(MnFe)3Si2 intermetallic phase besides the primary and eutectic Si phase. The bulk hardness of the Al–12.6Si alloy is increased with an increase in Mn concentration as the harder Al15(MnFe)3Si2 intermetallic phase forms and both the Si phase morphology modify. The microhardness of the constituent phases also varies with the change in Mn concentration in the alloy. The Mn addition improved the ultimate tensile strength, yield strength, and elongation (%) of the alloy. However, fractographs reveal that the brittle mode of fracture has been increased due to the presence of a higher volume of brittle Al15(MnFe)3Si2 intermetallic in 2.0 and 3.0% Mn alloy. On the other hand, the amount of brittle and cleavage fracture of Si particles decreased, and ductile fracture with dimples formation increased in 1.0 wt%Mn added alloy.

Experimental study on strain behavior and permeability evolution of sandstone under constant amplitude cyclic loading‐unloading

AbstractThe coupling of in situ stress, seepage, and fracture makes the strata exhibit complex strain behavior and permeability evolution under the stress path of cyclic loading‐unloading. In this study, the cyclic loading‐unloading experiments of constant amplitude axial stress of sandstone under the combination of different initial confining pressures and loading‐unloading rates are conducted. The experimental results show that the heterogeneity of sandstone, Poisson's ratio produced by adjacent loading‐unloading, and confining pressure determine the deformation characteristics of sandstone in lateral and axial directions. Sandstone can produce significant shear dilatancy at a low rate; this is because stress perturbation can activate more particle slippage and fracture structure changes. However, the fracture preferentially propagates along the end or edge of the crack with strong stress sensitivity to form a shear failure plane at high rate. The normalized permeability of sandstone decreases with an increase in the loading‐unloading rate before failure. The evolution of normalized permeability is closely related to the shear slip of fracture structure and sandstone particles. For the prevention of rock engineering disasters, the high loading‐unloading rate results in lower normalized permeability, which favors the prevention of gas‐type disasters in rocks with higher gas potential energy; however, it is not conducive to the prevention of rockburst.

Modelling Microstructural Deformation and the Failure Process of Plastic Bonded Explosives Using the Cohesive Zone Model.

A microstructure finite element method combining the cohesive zone model (CZM) is used to simulate the mechanical behavior, deformation, and failure of polymer-bonded explosive (PBX) 9501 under quasi-static loading. PBX 9501 consists of Cyclotetramethylene tetranitramine (HMX) filler particles with a random distribution packaged in a polymeric binder. The particle is treated as elastic and the binder as viscoelastic. Cohesive elements with a bilinear softening law are inserted into the particle/binder interface, the HMX particle, and the binder to study the interface’s debonding and failure evolution. Macroscopic stress–strain curves homogenized across the microstructure under tension and compression with different strain rates are basically consistent with the experimental data. The interface debonding approximately vertical to the loading direction is the primary failure mechanism under tension, while shear failure along the interfaces and particle fracture plays a significant role under compression. The effects of interface strengths and strain rates on the performance of PBX 9501 are also evaluated. The tensile and compressive strengths are dependent on the interface strength and strain rate, but the failure paths are insensitive. This model is shown to accurately predict macroscopic responses and improve our understanding of the relationship between the mechanical behavior and microstructure of PBX 9501.

Effect of stress relaxation and creep recovery on transportation in porous medium and fracture of the millimeter-scale polymer gel particles for conformance control of heterogeneous oil reservoir

To further improve the utilization of millimeter-scale polymer gel particles (PPGs) in the heterogeneous oil reservoir, it is necessary to investigate its mechanical state of transportation in porous medium and fracture. In this paper, for comparison, a non-uniform capillary and a uniform capillary are used to simply simulate the porous medium and the fracture, which is mainly applied to reveal the mechanical behavior of a PPG during transportation. Subsequently, the displacement experiments were carried out by using the heterogeneous core and the fractured cores, which is mainly applied to evaluate the influence of pore structure of the actual reservoir on the flow resistance of the PPGs and reveal the mechanical mechanism. The experiment result shows that the flow resistance in the uniform capillary of a PPG is less than that in the non-uniform capillary under the same conditions. This is because the transportation in the uniform capillary of a PPG is a process of creep recovery but the transportation in the non-uniform capillary of a PPG is a process of stress relaxation. In the actual reservoir, the transportation in the porous medium of the PPGs is a continuous process of creep recovery, but the transportation in the fracture of the PPGs is a process of stress relaxation. During transportation, the flow resistance of PPGs in the porous medium is high, but the flow resistance of PPGs in the fracture is low. However, when the PPGs transport to the end of the partially open fracture, the PPGs fill the space of the partially open fracture, which can decrease the effective size of the partially open fracture and lead to the increase of the injection pressure. Therefore, the PPGs have a better plugging effect in the porous medium and partially open fracture but have a poor plugging effect in the open fracture. For the high-water-cut oil production well with the open fracture, it is not the best choice to directly use the PPGs as the plugging agent. The conclusions can provide a theoretical guidance for the highly efficient application of gel particles for conformance control in the heterogeneous reservoir.

Micromechanical response of Al–Mg2Si composites using approximated representative volume elements (RVEs) model

Deformation behaviour, micromechanical response, and failure initiation of Al–Mg2Si composites have been investigated in terms of stress-strain flow behaviour and localization through finite element (FE) analysis. The experimental and FE analysis results have a good agreement, and the results show that the yield strength of the composites increases with an increase in Mg2Si concentration, whereas the elongation decreases. Decohesion, particle fracture, and matrix yielding are the dominated fracture mode. The reinforcing Mg2Si phase always carries a higher load than the α-Al phase. The matrix (α-Al) phase has much higher ductility than the Mg2Si phase, but the ductility of the α-Al phase decreases with an increase in Mg2Si concentration in the composite.

Investigating the effect of heat treatment on the fracture toughness of a hot extruded Al–Ti composite produced by powder metallurgy route

An Al-5 wt% Ti composite was fabricated via powder metallurgy technique and hot extrusion. The produced composite samples were heat-treated subsequently at 600 °C for various time durations of 0, 4 and 10 h to achieve different volume fractions of the intermetallic Al3Ti phase. Pure aluminum sample was produced as a benchmark specimen to be compared to the composite samples. SEM studies were used to investigate the microstructure of the composite samples, and it was revealed that core-shell structured particles were formed in the composite heat-treated for 4 h. Triple point bending test was performed on the single edge notched beam specimens of the heat-treated Al-5 wt% Ti composite and the pure aluminum sample to investigate the bending strength and the fracture toughness. Two different methods of Kee and the fracture energy were implemented to evaluate the toughness of the Al-5 wt% Ti composites and the pure aluminum sample; the results indicated raising the heat treatment duration caused the fracture toughness (Kee) of the composite samples to decline, and the same trend was observed for the initiation and propagation fracture energies as well. By increasing the heat treatment time from 0 to 10 h, the fracture toughness of the composite dropped from 20.1 MPa m to 10.2 MPa m, while the pure aluminum sample had the greatest value of 25.6 MPa m. The SEM images of the fractured surface of the composite samples elucidated the effect of heating time on the fracture mechanism of the composites; the governing fracture mechanism changed from particle fracture for the composite heat-treated for 4 h to the particle decohesion for the one heat-treated for 10 h.

3D ex-situ and in-situ X-ray CT process studies in particle technology – A perspective

X-ray computed tomography (XCT) has seen significant development in scan time and spatial resolution over the last decades. It is now increasingly used in the field of particle technology including ex-situ and in-situ applications to study time-lapse processes. This is due to its non-destructive principle giving 3D information on the inner structure and composition of specimens.This article shortly summarizes the field of XCT focusing on terms relevant for particle technology. It also gives a brief outlook on promising directions of development, which may significantly improve XCT. Using different examples from bulk solids handling, flow in porous structures and filtration, the monitoring of concentration differences and the fracture of particles, the application of XCT in particle technology is shown and its perspective is discussed.

The mechanical response of a α2(Ti3Al) + γ(TiAl)-submicron grained Al2O3 cermet under dynamic compression: Modeling and experiment

Novel experimental data, obtained using an advanced digital image correlation technique coupled to ultra-high-speed photography, have been used to develop and validate a microstructure-dependent constitutive model for a α2(Ti3Al) + γ(TiAl)-submicron grained Al2O3 cermet. Utilizing experimental characterization for important simulation inputs (e.g., microstructural features size, constituent stiffness), the numerical model makes use of a variational form of the Gurson model, based on the nonlinear homogenization approach, to account for the experimentally observed deformation features in this composite (e.g., void deformation and growth, particle fracture). By considering the variability in microstructural features (e.g., particle shape, size, and aspect ratio), as well as densely packed ceramic particles, the proposed model is evaluated by comparing the numerical responses to experimental results for quasi-static and dynamic stress-strain behavior of the material. The results show that the proposed approach is able to reasonably predict the mechanical response and deformation of the microstructure. Once validated, the model is expanded for studying the predominant damage mechanisms in this material, as well as determining important mechanical response features such as transitional strain rates, flow stress hardening, extensive flow softening, and energy absorbing efficiency of the material as a function of void and particle volume fraction under high strain rate loading. The totality of this work opens promising avenues for qualitative (damage micromechanisms) and quantitative (stress-strain curves) understanding of ceramic-metal composites under various loading conditions, and offer insights for designing and optimizing cermet microstructures.

Revealing the fatigue crack initiation mechanism of a TiB2-reinforced steel matrix composite

The initiation of fatigue cracks in a TiB2-reinforced high-modulus, low-density steel was revealed by in-situ scanning electron microscopy for the first time. The results show that the superior interfacial strength between the TiB2particles and the matrix prevents the initiation of micro-cracks at the interfaces. Fatigue micro-cracks are mainly induced by the brittle fracture of small eutectic TiB2 particles, while the coalescence of these micro-cracks plays the major role in the fatigue failure. This failure mechanism is essentially different from the static tensile failure mode in which the large primary TiB2 particles are the main source of fracture failure.