Understanding Of Micromechanics Research Articles

Mechanical responses and fracturing behaviors of coal under complex normal and shear stresses, Part II: Numerical study using DEM

This work presents particle-based numerical simulations on coal pillars in a coal mine based underground water reservoir (CMUWR). We aim to replicate the stress–strain characteristics and present the acoustic emission behavior of the coal under complex dynamic stress paths. The study reveals failure characteristics of coal exposed to monotonic/cyclic shear load under constant/cyclic normal loads. Based on the evolution of stress-time-dependent bond diameter implemented in particle model, different damage paths are established for dry and water-immersed samples under two loading frequencies. Furthermore, the numerical Gutenberg–Richter’s b-value was calculated from the released energy emanating from bond failure, and this work presents the evolution of numerical Gutenberg–Richter’s b-value. The numerical simulation contributes to a micromechanical understanding of the failure mechanisms of coal under water-immersion and cyclic stress, providing valuable insights for strength prediction of CMUWR.

Microscopic Description of Basal Stress Generated by Granular Free‐Surface Flows

AbstractGeophysical flows grow in volume and impact potential by eroding and entraining bed material during movement, posing potential risks to human lives and facilities downstream. This granular process is controlled by the basal stress and its fluctuations at the flow‐bed interface. Therefore, it is essential to provide physical insights into the basal stresses generated by granular flows for hazard risk management. In this study, we conduct a series of DEM simulations of channelized granular free‐surface flows to gain a micromechanical understanding of particle‐bed interactions. Basal normal and shear stresses are recorded and analyzed quantitatively through three statistical metrics: time‐averaged mean value, maximum value, and standard deviation. The relationship of these quantities with the bulk and basal flow properties and the micromechanical quantities that control stress fluctuations are discussed. Results show that the basal stress exhibits a distinct transition from a dense to dilute flow regime at a critical Savage number of 0.1, coinciding with the transition of stress‐generating and transmission mechanisms from being friction‐dominated to collision‐dominated. Maximum basal normal and shear stresses scale with the particle‐bed impact velocities in the form of a power law relation. Stress fluctuations scale with the granular temperature, revealing its dependence on random particle motions. A unified scaling law is proposed to link the standard deviation of basal stresses with the free particle volume, covering a wide range of flow regimes from dense to dilute flow.

Molecular-level characterization of changes in the mechanical properties of wood in response to thermal treatment

Thermal treatment can improve the dimensional stability of wood, but it also decreases wood’s toughness, or increases its brittleness. In this paper, combining FTIR spectroscopy and mechanical analysis were used to monitor wood molecular straining and deepen the micromechanical understanding of thermally-treated wood. The degradation of hemicellulose increased as the thermal treatment temperature increase, and the 220 °C treatment also led to cellulose microfibrils reorientation. The results of static tension FTIR spectra of thermally-treated wood indicated that the absorption peak of cellulose glycosidic bond underwent a substantial bandshift to lower wave numbers as the tensile strain increase, but the characteristic peak position of the lignin was no obvious change during stretching. For the 160–200 °C treated samples, the bandshift ratios of cellulose C–O–C glycosidic bond increased upon increasing the temperature; Furthermore, the intensities of the two split peaks of cellulose at 1169 cm−1 and 1435 cm−1 in 0° polarization dynamic FTIR spectra decreased upon increasing the treatment temperature, indicating the elastic-like response of cellulose for thermally-treated wood decrease. For the 220 °C treated sample, the bandshift ratio of cellulose glycosidic bond decreased compared with other thermal treatment samples, but the intensities of the two split peaks of cellulose increased again. Those results indicated that the shear slipping between cellulose microfibrils decrease and microfibrils reorientation due to hemicellulose degradation after thermal treatment may cause the toughness of the thermally-treated wood decrease, or the brittleness increase.Graphical abstract

Effect of Fibre Types on the Tensile Behaviour of Engineered Cementitious Composites

Engineered cementitious composite (ECC) is a group of ultra-ductile fibre-reinforced cementitious composites, characterised by high ductility and moderate content of short discontinuous fibre. The unique tensile strain-hardening behaviour of ECC results from a deliberate design based on the understanding of micromechanics between fibre, matrix, and fibre–matrix interface. To investigate the effect of fibre properties on the tensile behaviour of ECCs is, therefore, the key to understanding the composite mechanical behaviour of ECCs. This paper presents a study on the fibre-bridging behaviour and composite mechanical properties of ECCs with three types of fibres, including oil-coated polyvinyl alcohol (PVA) fibre, untreated PVA fibre, and polypropylene (PP) fibre. The experimental result reveals that various fibres with different properties result in difference in the fibre-bridging behaviour and composite mechanical properties of ECCs. The difference in the composite mechanical properties of ECCs with different fibres was interpreted by analysing the fibre-bridging behaviour.

Influences of strain rate, Al concentration and grain heterogeneity on mechanical behavior of CoNiFeAlxCu1-x high-entropy alloys: a molecular dynamics simulation

High-entropy alloys (HEAs) with a heterogeneous grain structure have been revealed to possess excellent combination of strength and toughness. However, the atomic-level deformation mechanisms of the heterogeneous HEAs were not reported yet. In this work, physical models were constructed based on the experimental observation and atomic simulations are performed to investigate the tensile behavior of face centered cubic (FCC) heterogeneous CoNiFeAl x Cu 1-x HEAs at different strain rates (5 × 10 7 –1 × 10 10 s −1 ), Al concentration (x = 0.1, 0.2, 0.3 and 0.4) and degrees of grain heterogeneity. Result analysis reveals the multiple deformation mechanisms including dislocation motion, diffusion from grain interior to grain boundary and stacking faults (SFs) as well as their interaction. The strain rates seriously influence the body centered cubic (BCC) transformation from FCC in the large grains. Besides, with the reduction of Al concentration, the value of stable stacking fault energy (SFE) raises, while the tensile yield stress increases. Finally, increasing the large grain size (D G ) of the heterogeneous grain structure improved the plasticity due to the combination of enhanced FCC to BCC phase transformation and high uniform ductility of large grains. This work provides a micromechanical understanding for designing the excellent mechanical property of HEAs by optimizing material structure parameters of heterogeneous grain structure HEAs.

PLATYMATCH – A particle-matching algorithm for the analysis of platy particle kinematics using X-ray Computed Tomography

Particle scale mechanisms influence the mechanical behaviour of geomaterials. A better understanding of soil micromechanics will help develop more accurate constitutive models and, by extension, safer and more economic geotechnical design. Sand-grained soils have been widely studied at the particle scale using X-ray Computed tomography and this has revealed important micromechanical behaviour of sands. Clays are least understood and studied at the particle scale. As technology rapidly progresses, to understand clay kinematics, a particle kinematic algorithm to match plate shaped (platy) particles will be required. Current algorithms developed for the matching of quartz and carbonate sand particles may not be suitable, since particle attributes that are strong discriminators of round particles may be less unique on platy particles, due to their extremely small c-axis and the reduced image resolution associated with their smaller size. This study presents, particle tracking of kaolin sample using mica markers and provides a platy soil particle matching algorithm for evaluating platy particle kinematics. After testing a range of alternative particle attributes, it was observed that a combination of particle major axis length, intermediate axis length, and perimeter was a good discriminant of the platy mica particles studied. On this basis, we developed PLATYMATCH, an optimised platy particle matching algorithm that considers a minimised combined normalised error of unique particle attributes within a defined search volume space. The algorithm was implemented such that particle attributes were compared in parallel, rather than sequentially, to avoid filtering out a potential particle match based on a single non-unique attribute. PLATYMATCH was then successfully validated using a compressed mica soil sample.

Layer-specific arterial micromechanics and microstructure: Influences of age, anatomical location, and processing technique

The importance of matrix micromechanics is increasingly recognized in cardiovascular research due to the intimate role they play in local vascular cell physiology. However, variations in micromechanics among arterial layers (i.e. intima, media, adventitia), as well as dependency on local matrix composition and/or structure, anatomical location or developmental stage remain largely unknown. This study determined layer-specific stiffness in elastic arteries, including the main pulmonary artery, ascending aorta, and carotid artery using atomic force indentation. To compare stiffness with age and frozen processing techniques, neonatal and adult pulmonary arteries were tested, while fresh (vibratomed) and frozen (cryotomed) tissues were tested from the adult aorta. Results revealed that the mean compressive modulus varied among the intima, sub-luminal media, inner-middle media, and adventitia layers in the range of 1–10 kPa for adult arteries. Adult samples, when compared to neonatal pulmonary arteries, exhibited increased stiffness in all layers except adventitia. Compared to freshly isolated samples, frozen preparation yielded small stiffness increases in each layer to varied degrees, thus inaccurately representing physiological stiffness. To interpret micromechanics measurements, composition and structure analyses of structural matrix proteins were conducted with histology and multiphoton imaging modalities including second harmonic generation and two-photon fluorescence. Composition analysis of matrix protein area density demonstrated that decrease in the elastin-to-collagen and/or glycosaminoglycan-to-collagen ratios corresponded to stiffness increases in identical layers among different types of arteries. However, composition analysis was insufficient to interpret stiffness variations between layers which had dissimilar microstructure. Detailed microstructure analyses may contribute to more complete understanding of arterial micromechanics.

In-situ and ex-situ microtensile testing of individual struts of Al foams and Ni/Al hybrid foams

Metal foams are cellular materials, offering a strong structure-property relationship. Their global properties are strongly connected to the local micromechanical properties of the struts and to the microstructure of the foams. The mechanical properties of individual struts differ widely from the bulk matrix material as a result of differences in solidification conditions and the surface-to-volume ratio. A robust micromechanical understanding and knowledge of micromaterial parameters is essential to design components made of foams e.g. supported by numerical simulations. However, up to now, micromechanical charaterisation of individual struts is very challenging but an emerging field of research.The present contribution deals with the microstructural and micromechanical characterisation of individual struts of open-cell aluminium foams and Ni/Al hybrid foams. The crystallographic texture is investigated by electron backscatter diffraction. Microtensile testing is performed on individual struts to determine real micromechanical material properties by ex-situ testing using a specially developed device and a digital image correlation method. Furthermore, in-situ microtensile tests using scanning electron microscopy are conducted for high-resolution investigation of the micromechanical deformation and damage mechanism occuring under loading of individual struts. The experimentally determined Young's modulus of the nickel coating is compared with theoretical calculations based on the grain orientation data.

Transformation induced softening and plasticity in high entropy alloys

Nanostructured high-entropy alloys (HEAs) with excellent properties have recently attracted extensive attention from both academia and industry in recent years. However, as a consequence of the resolution limitations of existing experimental techniques, the effects of dynamical microstructure on the strength-and-plasticity properties in nanoscale HEAs is still not well understood. Here we report the kinetics of strain induced phase transformation from face-centered cubic to body-centered cubic (fcc→bcc) in the single-crystal and nanocrystalline HEA investigated by molecular dynamics simulations. The fcc→bcc phase transformation in HEA occurs when the critical stress induced by severe lattice distortion combined with high local strain effect exceeds the stress required for the nucleation of bcc phase in the matrix. In addition, the emergence of this phase transformation is dominated by strain rate and initial orientation, where maintaining high strength in nanocrystalline HEA is achieved without the sacrifice of ductility attributable to the strain-induced fcc→bcc transformation. Interestingly, owing to the structural dissipation and strain relaxation by the volume expansion, the phase transformation agreeing with N-W relationship could convert the stress state from tensile to compressive in single-crystal HEA. Therefore, the evolution of microstructures and fcc→bcc phase fractions is studied to provide a micromechanical understanding of phase transformation induced plasticity responsible for the combination of high strength and high ductility.

Experimental Investigation of Particle Agglomeration Effects on Slurry Settling in Viscous Fluid

This paper presents fundamental analysis and micromechanical understanding of dense slurry behavior during settling in narrow smooth and rough slots. Particularly, this study seeks to contribute toward better understanding of dynamics of particle–particle and particle–wall interactions in viscous fluids using simple experiments. The findings of this study are applicable in a wide variety of problems, for example sediment transport, flow and transport of slurry in pipes, and industrial applications. However, the results interpretation focuses on better understanding of proppant flow and transport in narrow fractures. A sequence of experiments image frames captured by video camera is analyzed with particle image velocimetry (GeoPIV). The measurements include vertical velocities and displacement vectors of singular and agglomerated particles and larger area of formed slurry. Results present novel insights into the formation and effects of agglomerates on general slurry settling, and are supplemented with a comparison with previously published theoretical and empirical relationships. This work also emphasizes a role of particle–particle interactions in promoting agglomeration in viscous fluid. Particularly, a thin layer of viscous fluid between approaching particles dissipates particle kinetic energy due to lubrication effect. Lubrication effect is more pronounced when particles are constrained between two narrow walls and interact frequently with each other. Fluid tends to flow around agglomerated particles, and agglomerates remain stable for prolonged time periods gravitationally moving downward. The relative amount and size of agglomerated affects general settling of the slurry. It was found that fluid viscosity due to lubrication effect promotes agglomeration, and therefore, the overall slurry settling relatively increases at higher fluid viscosities. The results of the presented work have impact on various industrial and engineering processes, such as proppant flow and transport in hydraulic fractures, sand production in oil reservoirs, piping failure of dams and scour of foundation bridges.

On the mechanical behavior of rubber springs for high speed rail vehicles

There are many engineering design problems that call for rubber components as the best solution. Vulcanized rubber has found its way into all sorts of devices, from the universal automobile pneumatic tire to the ubiquitous compliant bushing. Some high-speed rail vehicle suspensions make use of rubber, not only in the air spring itself, but also in the auxiliary spring. The mechanical characteristics of this component influence vehicle dynamics and, therefore, accurate spring models with which to conduct dynamic analysis would make for powerful design tools. Nevertheless, the mechanical behavior of rubber defies simple modeling on account of stress relaxation, creep, set, viscosity, internal friction, and nonlinear stress–strain relations. Despite the advances in the micromechanical understanding of these phenomena, as well as in the macroscopic modeling of rubber spring behavior, there is ample room for refinement, and this is precisely the goal of this paper. The mechanical behavior of a particular rubber spring for high speed rail vehicles has been characterized. The results reveal the necessary components of the model, and suggest the appropriate procedure for parameter extraction. Our model proposal consists of three elements in parallel: a nonlinear elastic spring; a “soft friction” element; and a Maxwell viscous component. The characterization procedure takes into account both stress relaxation and nonlinear elasticity. The proposed model accurately reproduces experimental results and may then be used with confidence in any type of numerical simulation. Nevertheless, for this statement to be true, the problem of “numerical softening” potentially induced by soft friction models should be resolved. The paper will show that a trailing moving average filter, seamlessly tied to the model, wipes out the softening effect.

A coupled CFD-DEM approach to model particle-fluid mixture transport between two parallel plates to improve understanding of proppant micromechanics in hydraulic fractures

Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) was used in this paper to model particle-liquid mixture transport between two parallel plates to improve the understanding of proppant micromechanics in a hydraulic fracture. The linear spring-dashpot model was used to model contact behavior between the particles in DEM code, and the interaction between the particles and fluid was coupled in the CFD code in terms of volumetric porosity and coupling force. The flow patterns and particle transport mechanisms were investigated based on which four developmental stages were divided from the beginning of injection to the formation of the final particle bank. The results show that when particles are transported in a thin fluid, they will quickly settle out of the fluid and accumulate at the bottom forming a particle dune. As the dune height increases, the flow stream is gradually hindered by the dune, and then the injected particles are vertically lifted and settle at the front of the dune. When the equilibrium height of the dune is reached, the dune develops to a bank, and then the particles injected later overshoot the bank and settle at the back side of the bank. The dune shape is significantly influenced by the erosion caused by the transported particles and flowing fluid, and the flow patterns of three-layers and two-layers are observed in different stages. Three particle transport mechanisms of settlement, fluidization and suspension, previously presented in early experimental studies, are observed in the CFD-DEM simulations. A new important transport mechanism of vorticity is also observed, which can control the motion direction of the injected particles during earlier and later injection stages.

Image-based numerical simulation of the local cyclic deformation behavior around cast pore in steel

The local cyclic stress/strain responses around an actual, irregular pore in cast Hadfield steel under fatigue loading are investigated numerically, and compared with those around a spherical and an ellipsoidal pore. The actual pore-containing model takes into account the real shape of the pore imaged via high-resolution synchrotron X-ray computed tomography and combines both isotropic hardening and Bauschinger effects by using the Chaboche's material model, which enables to realistically simulate the cyclic deformation behaviors around actual pore. The results show that the stress and strain energy density concentration factors (Kσ and KE) around either an actual irregular pore or an idealized pore increase while the strain concentration factor (Kε) decreases slightly with increasing the number of fatigue cycles. However, all the three parameters, Kσ, Kε and KE, around an actual pore are always several times larger than those around an idealized pore, whatever the number of fatigue cycles. It is suggested that the fatigue properties of cast pore-containing materials cannot be realistically evaluated with any idealized pore models. The feasibility of the methodology presented highlights the potential of its application in the micromechanical understanding of fatigue damage phenomena in cast pore-containing materials.

Nanolaminate transformation-induced plasticity–twinning-induced plasticity steel with dynamic strain partitioning and enhanced damage resistance

Conventional martensitic steels have limited ductility due to insufficient microstructural strain-hardening and damage resistance mechanisms. It was recently demonstrated that the ductility and toughness of martensitic steels can be improved without sacrificing the strength, via partial reversion of the martensite back to austenite. These improvements were attributed to the presence of the transformation-induced plasticity (TRIP) effect of the austenite phase, and the precipitation hardening (maraging) effect in the martensitic matrix. However, a full micromechanical understanding of this ductilizing effect requires a systematic investigation of the interplay between the two phases, with regards to the underlying deformation and damage micromechanisms. For this purpose, in this work, a Fe–9Mn–3Ni–1.4Al–0.01C (mass%) medium-Mn TRIP maraging steel is produced and heat-treated under different reversion conditions to introduce well-controlled variations in the austenite–martensite nanolaminate microstructure. Uniaxial tension and impact tests are carried out and the microstructure is characterized using scanning and transmission electron microscopy based techniques and post mortem synchrotron X-ray diffraction analysis. The results reveal that (i) the strain partitioning between austenite and martensite is governed by a highly dynamical interplay of dislocation slip, deformation-induced phase transformation (i.e. causing the TRIP effect) and mechanical twinning (i.e. causing the twinning-induced plasticity effect); and (ii) the nanolaminate microstructure morphology leads to enhanced damage resistance. The presence of both effects results in enhanced strain-hardening capacity and damage resistance, and hence the enhanced ductility.

Micro-poro-elasticity of baghdadite-based bone tissue engineering scaffolds: a unifying approach based on ultrasonics, nanoindentation, and homogenization theory.

Microstructure-elasticity relations for bone tissue engineering scaffolds are key to rational biomaterial design. As a contribution thereto, we here report comprehensive length measuring, weighing, and ultrasonic tests at 0.1MHz frequency, on porous baghdadite (Ca3ZrSi2O9) scaffolds. The resulting porosity-stiffness relations further confirm a formerly detected, micromechanically explained, general relationship for a great variety of different polycrystals, which also allows for estimating the zero-porosity case, i.e. Young modulus and Poisson ratio of pure (dense) baghdadite. These estimates were impressively confirmed by a physically and statistically independent nanoindentation campaign comprising some 1750 indents. Consequently, we can present a remarkably complete picture of porous baghdadite elasticity across a wide range of porosities, and, thanks to the micromechanical understanding, reaching out beyond classical elasticity, towards poroelastic properties, quantifying the effect of pore pressure on the material system behavior.

Kinematic description of crystal plasticity in the finite kinematic framework: A micromechanical understanding of F=FeFp

The plastic component of the deformation gradient plays a central role in finite kinematic models of plasticity. However, its characterization has been the source of extended debates in the literature and many important issues still remain unresolved. Some examples are the micromechanical understanding of F=FeFp with multiple active slip systems, the uniqueness of the decomposition, or the characterization of the plastic deformation without reference to the so-called intermediate configuration. In this paper, we shed some light to these issues via a two-dimensional kinematic analysis of the plastic deformation induced by discrete slip surfaces and the corresponding dislocation structures. In particular, we supply definitions for the elastic and plastic components of the deformation gradient as a function of the active slip systems without any a priori assumption on the decomposition of the total deformation gradient. These definitions are explicitly and uniquely given from the microstructure and do not make use of any unrealizable intermediate configuration. The analysis starts from a semi-continuous mathematical description of the deformation at the microscale, where the displacements are considered continuous everywhere in the domain except at the discrete slip surfaces, over which there is a displacement jump. At this scale, where the microstructure is resolved, the deformation is uniquely characterized from purely kinematic considerations and the elastic and plastic components of the deformation gradient can be defined based on physical arguments. These quantities are then passed to the continuous limit via homogenization, i.e. by increasing the number of slip surfaces to infinity and reducing the lattice parameter to zero. This continuum limit is computed for several illustrative examples, where the well-known multiplicative decomposition of the total deformation gradient is recovered. Additionally, by similar arguments, an expression of the dislocation density tensor is obtained as the limit of discrete dislocation densities which are well characterized within the semi-continuous model.

Effects of Migrating Cell-Induced Matrix Reorganization on 3D Cancer Cell Migration

The migration of cells is fundamental to a number of physiological/pathological processes, ranging from embryonic development, tissue regeneration to cancer metastasis. Current research on cell migration is largely based on simplified in vitro models that assume a homogeneous microenvironment and overlook the modification of extracellular matrix (ECM) by the cells. To address this shortcoming, we developed a nested three-dimensional (3D) collagen hydrogel model mimicking the connective tissue confronted by highly malignant breast cancer cells, MDA-MB-231. Strikingly, our findings revealed two distinct cell migration patterns: a rapid and directionally persistent collective migration of the leader cells and a more randomized migration in the regions that have previously been significantly modified by cells. The cell-induced modifications, which typically include clustering and alignment of fibers, effectively segmented the matrix into smaller sub-regions. Our results suggest that in an elastic 3D matrix, the presence of adjacent cells that have modified the matrix may in fact become physical hurdle to a migrating cell. Furthermore, our study emphasizes the need for a micromechanical understanding in the context of cancer invasion that allows for cell-induced modification of ECM and a heterogeneous cell migration.

Micro- and Macromechanics of Hopper Discharge of Ultrafine Cohesive Powder

Abstract Typical flow problems, like arching or bridging, of ultrafine cohesive powders are caused by undesired particle adhesion, poor flowability and large compressibility and intensified by poor permeability. Thus, the physical understanding of micromechanics of ultrafine particle flow and permeation is very essential to design properly the product quality and to improve the process performance in particle technology.A force balance at a homogenously assumed, dynamic bridge is formulated at the hopper outlet that includes the dead weight, inertia, wall and drag forces. The permeation resistance is calculated as sum of a microscopic flow-around resistance of single particles plus the macroscopic bed resistance of the moving cohesive powder bridge. The resulting differential equation is shown for turbulent flow-through conditions of air. The first integration gives analytical discharge velocity-time function, steady-state discharge velocity and the characteristic discharge time of incipient (accelerated) flow. The second integration results in analytical height-time and velocity-height functions, discharge and residence times. This method results in physically consistent, analytical models that are comfortable to handle and easy to prove. The steady-state discharge velocity is compared with measurements of full-scale silos at Coperion and Zeppelin companies. This publication describes the results of a closed collaboration between university and industry. The practical objective of the project was to solve the serious discharge problems of ultrafine, compressible, hardly permeable, cohesive powders by applying mechanical vibrations during their gravitational flow.

Three-dimensional characterisation and modelling of small fatigue corner cracks in high strength Al-alloys

The growth of fatigue cracks at small length scales is known to be influenced by a variety of factors, including local microstructure, varying stress states and crack shape. High resolution computed tomography allows for sub-micron resolution imaging of failure processes in small test coupons undergoing in situ cyclic loading, providing detailed three-dimensional (3D) assessment of propagation processes across the entire crack front (surface and depth). In this work fatigue crack growth has been examined in an advanced Direct Chill (DC) cast aluminium alloy, along with a fine grained powder-metallurgy alloy. The latter is identified as a model material, offering considerably simpler microscopic crack paths than the DC cast alloy, and hence a means of separating bulk mechanical effects (such as stress state variations across a crack front and plasticity induced closure) from microstructural effects (such as crystallographic deflection and roughness induced crack closure). Crack growth has been studied in both materials under both constant amplitude (CA) and single peak overload (OL) conditions. Experimental results are presented in the present paper, particularly in relation to micromechanical understanding of failure. A modelling approach based on those results, and some typical results, is also presented.

Micromechanical modeling of the microbond test to quantify the interfacial properties of fiber-reinforced composites

The present study has focused on achieving a micromechanical understanding of the microbond test, which involves pulling a fiber out of a bead of matrix (i.e. droplet) through a knife-edge, in order to quantify the interfacial fracture properties of fiber-reinforced composites. According to the microbond test results for carbon-fiber and epoxy-resin system, matrix cracking occurred during the fiber pullout, in addition to the debonding at the fiber–matrix interface. Therefore, in evaluating the fracture properties of the fiber–matrix interface, we should pay attention to the coupling effects of matrix failure and interfacial debonding on the test results. Then, we discuss how to best extract the interfacial properties while excluding the influence of matrix plasticity and cracking, using numerical simulations. The key mechanism demonstrated here is that the pullout force, in the cases where the influence of matrix cracking is negligible, appears as the upper limit among the experimental data of the pullout force for a constant initial embedded length of the fiber in the matrix. For this reason, the upper-limit data all over the range of embedded fiber length in experiments can be reasonably evaluated by the simulation focusing on the debonding process with matrix plasticity. This evaluation technique is effective as a way of extracting interfacial properties appropriately from microbond test results.