Single Particle Compression Tests Research Articles

Revealling pore microstructure impacts on the compressive strength of porous proppant based on finite and discrete element method

Ceramic spheres, typically with a particle diameter of less than 0.8 mm, are frequently utilized as a critical proppant material in hydraulic fracturing for petroleum and natural gas extraction. Porous ceramic spheres with artificial inherent pores are an important type of lightweight proppant, enabling their transport to distant fracture extremities and enhancing fracture conductivity. However, the focus frequently gravitates towards the low-density advantage, often overlooking the pore geometry impacts on compressive strength by traditional strength evaluation. This paper numerically bypasses such limitations by using a combined finite and discrete element method (FDEM) considering experimental results. The mesh size of the model undergoes validation, followed by the calibration of cohesive element parameters via the single particle compression test. The stimulation elucidates that proppants with a smaller pore size (40 µm) manifest crack propagation evolution at a more rapid pace in comparison to their larger-pore counterparts, though the influence of pore diameter on overall strength is subtle. The inception of pores not only alters the trajectory of crack progression but also, with an increase in porosity, leads to a discernible decline in proppant compressive strength. Intriguingly, upon crossing a porosity threshold of 10 %, the decrement in strength becomes more gradual. A denser congregation of pores accelerates crack propagation, undermining proppant robustness, suggesting that under analogous conditions, hollow proppants might not match the strength of their porous counterparts. This exploration elucidates the underlying mechanisms of proppant failure from a microstructural perspective, furnishing pivotal insights that may guide future refinements in the architectural design of porous proppant.

DEM breakage calibration for single particle fracture of maize kernels under a particle replacement approach

The Discrete Element Method (DEM) has become increasingly popular for simulating breakage operations and grinding equipment performance. Two main breakage approaches can be found in literature: bonded particle models and particle replacement models. This work is focused on fitting the parameters of a DEM particle replacement breakage model for maize, implemented in software Rocky DEM. Once all required experimental and calibration procedures were developed for maize specific DEM properties and parameters, single particle compression tests were carried out to fit the parameters of the breakage model, which was extensively analyzed for validating its capability of representing the material. Maize properties showed to be in agreement with literature sources. Compression tests simulated in DEM led to the same results as their experimental counterparts, validating the model’s capability of representing maize breakage. These results are the basis for further simulation of a full milling process in a hammer mill.

Particle Breakage Effect on Compression Behavior of Realistic Granular Assembly

A numerical investigation of the effect of particle breakage on the one-dimensional compression behavior of a realistic granular assembly was carried out using the discrete-element method. The morphologies of sands were obtained using X-ray microcomputed tomography. Sand assemblies were generated in terms of the statistical distribution of sphericity from real sands. The results of single-particle compression tests showed that particle shape significantly affects crushing strength. Particle breakage had a significant influence on compressive deformation, as demonstrated by comparing breakable assemblies with unbreakable ones. The strong force distribution became broader, and the proportion of weak force increased with particle breakability. Looser samples underwent much more particle breakage than did denser samples. It was found that breakage dissipation was a small fraction of energy input compared with frictional dissipation. An excellent hyperbolic relationship between relative breakage and energy input was found, which was independent of initial void ratio.

Effect of particle characteristics stress on the mechanical properties of cement mortar with coral sand

The coral sand is widely used as a construction material in the world. The mechanical behavior of cement mortar made by coral sand would be quite different from that made by the Leighton Buzzard sand (LBS) due to the inherent properties of coral sand, such as large void ratio, irregular shape and particle breakage. The effect of particle size on the particle crushing stress and influence on the mechanical behavior of cement mortar are examined in this study. A series of single particle compression tests of coral sand particles were carried out. The results revealed that the characteristic stress of single particle for both coral sand and LBS decreased with the increasing of particle sizes. The exponent relationship between the average crushing characteristic stress and particle size was proposed. The crushing stresses of single particles were in a wide range which varied from 0.99 MPa to 38.25 MPa and 10.98 MPa to 89.41 MPa for coral sand and LBS, respectively. The uncertainly of the crushing stress for single particles was analyzed and considered as Gaussian distribution. A probability density function of characteristic crushing strengths for both coral sand and LBS particles were derived and further verified with experimental results. Finally, the cement mortar specimens with five different types of particle size distributions of coral sands were prepared and tested to investigate the effects of the particle characteristic stress on the compressive strength of the cement specimen. An exponent relationship between the compressive strength and the particle crushing strength was derived and proposed which could helpful for the concrete mix proportion design with coral sands.

Mechanical behaviour of coarse, lightweight, recycled and natural aggregates for concrete

In this study the application of the single-particle compression test is discussed as an alternative method for the mechanical characterisation of coarse aggregates generally employed in concrete manufacturing. This leads to an estimation of the tensile strength and fracture energy of the aggregate particles. A wide range of aggregate types is considered. In particular, the mechanical responses of crushed limestone and river gravel are compared with expanded clay, recycled concrete and clay brick aggregates. In addition, physical properties are assessed experimentally and correlated to the aggregates' mechanical performance. Despite the high data scatter presented, the results demonstrate the ability of the proposed approach to accurately determine fracture energy and strength histories using single-particle compression. Overall, the porosity governs the mechanical behaviour of particles. Moreover, direct relationships between mechanical and physical properties yield consistent and expected results that validate the methodology.

Quaternary Layered Li[Ni0.89Co0.05Mn0.05Al0.01]O2 (NCMA) Cathode for High-Energy Density Lithium-Ion Batteries

Li[Ni1-x-y CoxAl z ]O2 (NCA) and Li[Ni1-x-y Co x Mn y ]O2 (NCM) cathodes have been the archetypes of current high-energy density cathodes for Li-ion batteries. A hybrid of NCA and NCM cathodes, a quaternary system consisting of Li[Ni0.89Co0.05Mn0.05Al0.01]O2 (NCMA) was benchmarked against NCM and NCA with similar Ni contents. The quaternary NCMA cathode delivered a capacity of 228 mAh g-1 and outperformed the benchmarking cathodes in long-term cycling stability (85% after 1000 cycles). The reduction in the volume change during deintercalation and the enhanced intrinsic mechanical strength confirmed by the single particle compression test suppressed the microcrack nucleation and propagation. Microcrack suppression was important because microcracks serve as channels for electrolyte infiltration and lead to the subsequent surface degradation of internal surfaces. The proposed NCMA cathode provides extra cycling stability which is essential for electric vehicles, which require a long battery life and improvs the thermal stability of the cathode, which contributes to a safer battery. Myung et al. ACS Energy Lett. 2017, 2, 196-223.Kim et al. Energy Environ. Sci. 2018, 11, 1271-1279.Yoon et al. Electrochem. Soc. 2015, 162, A2483-A2489.Kim et al. ACS Energy Lett. 2017, 2, 1848-1854.

Use of acoustic emission to evaluate the micro-mechanical behavior of sands in single particle compression tests

Particle breakage has been recognized as a crucial factor affecting the mechanical behavior of stressed granular assemblages. To understand such underlying micro-mechanical behavior, Acoustic Emission (AE) technique that is capable of continuously diagnosing the deterioration and failure process of stressed materials was employed into single particle compression tests on silica sands. Regardless of different particle sizes, the fracturing process could be highly featured by AE characteristics, in which AE hit rate and peak frequency characteristics were analyzed to evaluate the intensity and mode of micro-mechanical behaviors, respectively. “Early warning omens” regarding the impending failure of the stressed particle is revealed in terms of the initiation and rapid increase of high-frequency AE components, as well as the rapid increase of AE hit rate. The effect of “prehistory of failure” on the stressed particle is sensitively featured by the highly emitted AE events after the catastrophic failure. Furthermore, a frequency-based method is suggested to distinguish different modes of micro-mechanical behaviors associated with particle readjustment, asperity abrasion, and microcracking. Further employment of the present result is expected to continuously evaluate the intensity and mode of particle interactions in stressed granular assemblages.

On the breakage function for constructing the fragment replacement modes

The fragment replacement method (FRM), a particle breakage simulation method, is often used in discrete element simulations to investigate the particle breakage effect on the mechanical behavior of granular materials. The fragment size distribution of the fragment replacement mode of FRM, which is generally generated based on the fragmentation characteristics of single particles after uniaxial compression, affects the breakage process and the mechanical behavior of the particle assembly. However, existing fragment replacement modes are seldom generated based on experimental data analysis. To capture the fragmentation process and investigate the breakage function for the construction of the fragment replacement mode, 60 numerical single particle compression tests were implemented by DEM. The bonded-particle model was applied to generate the crushable rock particles. The numerical simulations were qualitatively validated by experimental results, and the fragment size of broken single particles was analyzed. The fractal dimension was used to describe the fragmentation degree of single particles after compression. The fragmentation degree was random, and the fractal dimensions of the 60 tests at the same loading displacement fit the Weibull distribution well. The characteristic fractal dimension increased with increasing loading displacement, indicating that the fragmentation of single particles is a gradual process. According to the overall breakage function of the 60 tests at the first bulk breakage, a two-stage distribution model with 4 parameters was proposed and validated by the numerical and experimental results. The various fracture patterns of a single particle at the first bulk breakage under compression tests were well captured by the two-stage distribution model. Finally, an initial application strategy using the two-stage distribution model to construct fragment replacement modes was discussed and presented.

Quaternary Layered Ni-Rich NCMA Cathode for Lithium-Ion Batteries

Li[Ni1–x–yCoxAly]O2 (NCA) and Li[Ni1–x–yCoxMny]O2 (NCM) cathodes have been the archetypes of current high-energy-density cathodes for Li-ion batteries. A hybrid of NCA and NCM cathodes, a quaternary system consisting of Li[Ni0.89Co0.05Mn0.05Al0.01]O2 (NCMA) was benchmarked against NCM and NCA with similar Ni contents. The quaternary NCMA cathode delivered a capacity of 228 mAh g–1 and outperformed the benchmarking cathodes in long-term cycling stability (85% after 1000 cycles). The reduction in the volume change during deintercalation and the enhanced intrinsic mechanical strength confirmed by the single-particle compression test suppressed the microcrack nucleation and propagation. Microcrack suppression was important because microcracks serve as channels for electrolyte infiltration and lead to subsequent surface degradation of internal surfaces. The proposed NCMA cathode provides extra cycling stability, which is essential for electric vehicles, which require a long battery life and improves the therma...

Characterization of agro-waste resources for potential use as proppant in hydraulic fracturing

Utilization of deformable substrates as proppant with sparse distributing for Hydraulic Fracturing (HF) is contributed to the improvement of fracture conductivity. Agro-waste resources, specifically shells of tropical plants such as coconut shell and palm kernel shell are two environmentally friendly and potential renewable resources that can be utilized as propping agents in HF. Nevertheless, they are not yet widely studied as such. Given this lack of particular technical and reliable data, their conversion into proppant cannot be designed with confidence as it happens with other studied biomass feedstock such as walnut-hull. This paper includes a study on the experimental characteristics of two agro-wastes or biomasses, coconut shell and palm kernel shell, as possible resources as proppants in HF. The main characteristics envisaged are particle size distribution, roundness and sphericity, density, specific gravity, bulk density, turbidity, crush resistance, single particle compression test, and fracture conductivity. The results obtained from the analyses are compared to the commonly known walnut-hull particles. These biomasses show promising results and meet some of established API/ISO standards. This paper is intended to provide technical information on the characteristics of new agro-wastes resources and to emphasize their major strengths; that have not been highlighted in the literature. These results are of key importance for the consequent development of high-strength composite proppants. Recommendations are also proposed for future improvement in increasing the quality of the results.

Contact properties determination of macroscopic fine disperse glass particles via compression tests in normal direction

The paper describes the deformation behavior of spherical, dry and non-porous particles during a single particle compression test in normal direction. Therefore a compression tester was built. Industrial used soda lime glass particles with two macroscopic fine disperse sizes (d1,50,3=284.30μmand d2,50,3=513.20μm) were applied as model material to investigate the micromechanical contact behavior. In order to influence the elastic-plastic contact properties of particles, the surfaces were altered with chemical modification by means of silanization.The determination of various micromechanical contact properties (e.g. adhesion force, modulus of elasticity and contact stiffness) was carried out model-based with the contact model ‘stiff particles with soft contacts’ by means of a back-calculation.It could be shown that the model-based determination of material properties was a good alternative compared to the comprehensive tensile tests and pull-off force measurements.In addition to the gained normal force-displacement data in normal direction, the friction limits for tangential loading and rolling with the load-dependent adhesion force were model-based determined.

Comparing particle breakage in an uniaxial confined compression test to single particle crush tests—model and experimental results

The correlation between single particle breakage parameters and the behavior of particulate beds under compression is a subject that has attracted much interest in the field of particulate solids. This knowledge can assist in simplifying the design of various units for handling and conveying of particulate solids and can be used in computer simulations (DEM) to shorten the computational time. In addition, it is convenient to compress a particulate bed in order to obtain the single particle strength distribution. The current work deals with the development of a mathematical model, correlating the ratio of broken particles in a confined bed compression to single particle strength. The model is based on Jansenn's axial-stress model for a particulate bed, single particle strength distribution and force distribution in a granular media. The developed model not only allows us to predict the ratio of broken particles during uniaxial compression but also allows us to determinate the single particle strength distribution by conducting two uniaxial confined compression tests. Narrow fractions of GNP, zirconium and sodium chloride (NaCl) in the size range of 2–5mm were tested using two rigid cylinders of 25mm and 45mm in diameter, with varying compressive forces and bulk heights. The single particle strength parameters were taken from single particle compression tests performed in the laboratory. The developed model shows good agreement with the experimental results within a certain range of the particulate bed geometry and compressive loads.

Determination of elastic properties of particles using single particle compression test

The current work concerns determining elastic properties of particles when employing single particle uniaxial compression tests. These properties are essential for numerical computations using DEM simulations. Five different particulate materials were tested. Three crystalline materials: dead sea salt, potash and green zirconium spheres. Also, two amorphous materials: GNP and glass spheres. The yield point, elastic contact stiffness and effective modulus of elasticity were determined by characterizing the force–displacement experimental curve. Statistical analysis showed that for some materials the effective modulus of elasticity depends on particle size. Finally, a mathematical model was established that describes the distribution of the effective modulus of elasticity and its dependence on the particle size for salt.

Compressive Characterization of Single Porous SiC Hollow Particles

Silicon carbide hollow spheres are compression tested to understand their energy absorption characteristics. Two types of particles having tap densities of 440 kg/m3 and 790 kg/m3 (referred to as S1 and S2, respectively) were tested in the present study. The process used to fabricate the hollow spheres leads to porosity in the walls, which affects the mechanical properties of the hollow spheres. The porosity in the walls helps in obtaining mechanical bonding between the matrix material and the particle when such particles are used as fillers in composites. The single-particle compression test results show that the S1 and S2 particles had fracture energies of 0.38 × 10−3 J and 3.18 × 10−3 J, respectively. The modulus and fracture energy of the particles were found to increase with increasing diameter. However, the increasing trend shows variations because the wall thickness can vary as an independent parameter. Hollow particle fillers are used in polymer and metal matrices to develop porous composites called syntactic foams. The experimentally measured properties of these particles can be used in theoretical models to design syntactic foams with the desired set of properties for a given application.

Relationship between single and bulk mechanical properties for zeolite ZSM5 spray-dried particles

In this work typical mechanical properties for a catalyst support material, ZSM5 (a spray-dried granular zeolite), have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy (SEM), confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Carr index. This was confirmed by bulk measurements of the particle–particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical properties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test.

The mechanics of rigid irregular particles subject to uniaxial compression

Single-particle compression tests, in which an individual sand grain is vertically compressed between two rigid horizontal platens, are often used in particle-scale soil mechanics studies. They are useful index tests to examine the susceptibility of a given sand to particle breakage; they provide information for calibration of particulate discrete-element models that capture crushing; and they can give information on size–strength relationships. The test is conceptually simple, but the response of an irregular particle in these compression tests is not straightforward. During compression the particle can rotate. Both horizontal and vertical forces are induced at the particle–platen contacts, and so there may be frictional sliding at the contact points at the same time as, or prior to, compression of the bulk particle. Asperities can yield, changing the particle geometry. The variation in the response mechanism during compression leads to a load–deformation response that is not always easy to interpret. This paper describes two relatively simple analytical studies of an irregular particle in a particle compression test. The susceptibility of the particle to rotation under the applied compressive force is shown to depend on the particle geometry and the particle–platen friction. The rotation of the particle is shown to induce a kinematic degradation or reduction in the effective stiffness of the system, and the system stiffness depends on the particle size. Frictional sliding at the contact points will also cause a reduction in stiffness. These observations may have implications not only for the test itself, but also for the response of irregular particles participating in the strong force chains in stressed granular materials.

Temperature Effect on Breakage Behavior of Cement Clinker by Compression

This paper describes the temperature effect on breakage behavior of cement clinker by single particle compression test. Portland cement clinker nodules, with mean diameter of 22 mm, were chosen as the test specimens. They were treated with heating to the temperatures of 300°C and 1000°C or cooling to -20°C and -88°C, respectively. The breakage behaviors were compared with the untreated nodules. The compression force-displacement profiles show that the treated nodules are easier to be broken because of the micro-cracks. Scanning electron microscope images illustrate that the clinker microstructures were changed after heating or cooling treatments. However, the main components are still the same according to the examination of X-ray diffraction. Comparing the heating with the cooling processes, it is more possible to use the waste heat of clinker sintering stage to reheat the clinker nodules, and these new reheating circuits may improve the energy efficiency of comminution.

Breakage behaviour of spherical granulates by compression

This paper describes the deformation and breakage behaviour of granulates in single particle compression test. Three industrial spherical granulates— γ - Al 2 O 3 , the synthetic zeolite Köstrolith ® and sodium benzoate ( C 6 H 5 COONa ) were used as model materials to study the mechanical behaviour from elastic to plastic range. The elastic compression behaviour of granulates is described by means of force-displacement curves, by application of Hertz–Huber contact theory and continuum mechanics. An elastic–plastic contact model was proposed to describe the deformation behaviour of elastic–plastic granules. The effects of granulate size and stressing velocity on the breakage force and contact stiffness during elastic and elastic–plastic displacement are examined. It is shown that the zeolite granulates with elastic–plastic behaviour have viscous properties as well. Breakage mechanisms of granulates during elastic, elastic–plastic and plastic deformation are also explained. The breakage probability is approximated by Weibull distribution function. The behaviour of the granulate during compression under the repeated loading–unloading conditions was investigated.