Macro-mechanical Behavior Research Articles

Dynamic impact constitutive relation of 6008-T6 aluminum alloy based on dislocation density and second-phase particle strengthening effects

To investigate the mechanical properties and constitutive relationship of 6008-T6 aluminum alloy under dynamic impact loading, dynamic impact and microscopic experiments were conducted on 6008-T6 aluminum alloy. The results demonstrated that 6008-T6 aluminum alloy exhibits strain hardening effects. As the loading strain rates increased, the grains became more refined, whereas the dislocation density and number of second-phase particles (mainly Mg2Si) increased. Several dislocations interacted with each other, thereby preventing further dislocation movement and improving the material's strength. The precipitation of second-phase particles impeded the motion of dislocations and increased the flow stress of the material. A constitutive model of dynamic impacts was developed based on the evolution of dislocation density and reinforcing effects of second-phase particles. Furthermore, based on the isotropic assumption, the damage evolution equation of 6008-T6 aluminum alloy was obtained by introducing the energy release rate. By combining the dynamic constitutive model of materials under dynamic impact compression conditions, the dynamic constitutive model of materials was obtained under dynamic impact tensile conditions. Moreover, the rationality of the model was confirmed by comparing the model's data with experimental data. In this study, we examined the macro mechanical response, microstructure, and dynamic mechanical behavior of the 6008-T6 aluminum alloy under dynamic impact conditions, which can serve as a theoretical basis and analytical tool for the structural design and safety evaluation of high-speed trains.

Investigation on the Propagation Mechanisms of a Hydraulic Fracture in Glutenite Reservoirs Using DEM

The geometry heterogeneity induced by embedded gravel can cause severe stress heterogeneity and strength heterogeneity in glutenite reservoirs, and subsequently affect the initiation and propagation of hydraulic fractures. Since the discrete element method (DEM) can accurately describe the inter-particle interactions, the macromechanical behavior of glutenite specimen can be preciously represented by DEM. Therefore, the initiation and propagation mechanisms of hydraulic fractures were investigated using a coupling seepage-DEM approach, the terminal fracture morphologies of hydraulic fractures were determined, and the effects of stress differences, permeability, and gravel strength were studied. The results show that the initiation and propagation of hydraulic fractures are significantly influenced by embedded gravel. In addition, the stress heterogeneity and strength heterogeneity induced by the gravel embedded near the wellbore increase local initiation points, causing a complicated fracture network nearby. Moreover, due to the effect of local stress heterogeneity, gravel strength, and energy concentration near the fracture tip, four interactions of attraction, deflection, penetration, and termination between propagating fractures and encountering gravel were observed.

Nonlinear Matrix Ferroelectric Composites on Construction Quality and Safety Measures

With the continuous emergence of concrete construction projects such as long-span bridges, high-rise buildings, nuclear power plants, and offshore platforms, researchers at home and abroad have made great progress in construction quality and safety measures in recent years. Construction quality is the main factor affecting the appearance and function of the building. Compared with traditional building construction materials, it has indeed made great improvements in organization and performance. For example, for nonlinear matrix ferroelectric composites, this functional material can better solve the problem of poor compatibility between general composites and concrete structural materials. It is not sensitive to humidity and can work in a concrete environment for a long time. These materials are indeed popular in building construction, various materials complement each other in performance and produce a synergistic effect so that the comprehensive performance of composite materials is better than the original composition materials and meets various high-quality requirements. But some properties are still not very clear. Therefore, this study mainly studies the influence laws of viscoelasticity, elastic viscoplasticity, and macro mechanical behavior of nonlinear matrix ferroelectric composites. Through theoretical analysis and experiments, it is concluded that the change of effective stress relaxation stiffness of nonlinear matrix ferroelectric composites tends to be stable with the increase of time, and the effective stress relaxation stiffness of composites increases with the increase of age volume fraction at t = 0 s.

Correlating the microstructural architecture and macrostructural behaviour of the brain

The computational simulation of pathological conditions and surgical procedures, for example the removal of cancerous tissue, can contribute crucially to the future of medicine. Especially for brain surgery, these methods can be important, as the ultra-soft tissue controls vital functions of the body. However, the microstructural interactions and their effects on macroscopic material properties remain incompletely understood. Therefore, we investigated the mechanical behaviour of brain tissue under three different deformation modes, axial tension, compression, and semi-confined compression, in different anatomical regions, and for varying axon orientation. In addition, we characterised the underlying microstructure in terms of myelin, cells, glial cells and neuron area fraction, and density. The correlation of these quantities with the material parameters of the anisotropic Ogden model reveals a decrease in shear modulus with increasing myelin area fraction. Strikingly, the tensile shear modulus correlates positively with cell and neuronal area fraction (Spearman’s correlation coefficient of rs=0.40 and rs=0.33), whereas the compressive shear modulus decreases with increasing glial cell area (rs=−0.33). Our study finds that tissue non-linearity significantly depends on the myelin area fraction (rs=0.47), cell density (rs=0.41) and glial cell area (rs=0.49). Our results provide an important step towards understanding the micromechanical load transfer that leads to the non-linear macromechanical behaviour of the brain. Statement of significanceWithin this article, we investigate the mechanical behaviour of brain tissue under three different deformation modes, in different anatomical regions, and for varying axon orientation. Further, we characterise the underlying microstructure in terms of various constituents. The correlation of these quantities with the material parameters of the anisotropic Ogden model reveals a decrease in shear modulus with increasing myelin area fraction. Strikingly, the tensile shear modulus correlates positively with cell and neuronal area fraction, whereas the compressive shear modulus decreases with increasing glial cell area. Our study finds that tissue non-linearity significantly depends on the myelin area fraction, cell density, and glial cell area. Our results provide an important step towards understanding the micromechanical load transfer that leads to the non-linear macromechanical behaviour of the brain.

Inversion Method of the Young’s Modulus Field and Poisson’s Ratio Field for Rock and Its Test Application

As one typical heterogeneous material, the heterogeneity of rock micro parameters has an important effect on its macro mechanical behavior. The study of the heterogeneity of micro parameters is more important to reveal the root cause of deformation and failure. However, as a typical heterogeneous material, the current testing and inversion method is not suitable for micro parameters measurement for the rock. Aiming at obtaining the distribution of micro Young’s modulus and micro Poisson’s ratio of the rock, based on the digital image correlation method (DIC) and finite element method (FEM), this paper proposed a parameter field inversion method, namely the DF-PF inversion method. Its inversion accuracy is verified using numerical simulation and laboratory uniaxial compression test. Considering the influences of heterogeneity, stress state and dimension difference, the average inversion error of Young’s modulus field and Poisson’s ratio field are below 10%, and the proportion of elements with an error of less than 15% accounts for more than 86% in the whole specimen model. Compared with the conventional measuring method, the error of macro Young’s modulus and macro Poisson’s ratio calculated by the DF-PF inversion method is less than 2.8% and 9.07%, respectively. Based on the statistical analysis of Young’s modulus field and Poisson’s ratio field, the parameter homogeneity and quantitative function relation between the micro parameter and the principal strain can also be obtained in laboratory tests. The DF-PF inversion method provides a new effective method of testing Young’s modulus field and Poisson’s ratio field of the rocks under complex stress states.

Modeling the micromechanical behaviors of Zircaloy-2 alloy under large deformation

The orientation distribution of grains (so-called texture) and its evolution almost decisively govern the in-service performance of a polycrystalline material, especially for materials with low crystallographic symmetry. As an important nuclear material, zirconium and its alloys have a hexagonal-close-packed (hcp) crystallographic structure and multiple plastic deformation mechanisms. Among them, deformation twinning, reorienting the basal poles 85.22°, could result in an abrupt and drastic change in the texture. As simulation plays a more and more important role in the design, manufacturing, and service of an end-product, a reliable twinning model is essential for zirconium alloys. Two twinning models, namely the Twinning and De-twinning (TDT) and Predominant Twin Reorientation (PTR) models, were implemented in an Elastic Viscoplastic Self-consistent (EVPSC) framework with the thermal effect accounted for. The EVPSC-TDT and EVPSC-PTR models were applied to study the deformation behavior of a Zircaloy-2 slab under different strain paths. A predictive capability of the two twinning models was assessed by both the macro-mechanical behavior of stress-strain response and Lankford coefficient and the micro-mechanical behavior of texture evolution in terms of both pole figure and texture coefficient. It was found that the TDT model exhibits superior performance to the PTR model, especially in predicting texture development.

Mechanical response and damage mechanism of 2D woven SiCf/SiC ceramic matrix composites under tension-shear coupling load

The macroscopic mechanical behavior and coupling damage mechanism of 2D woven SiCf/SiC ceramic matrix composites (CMC) prepared by chemical vapor infiltration (CVI) process under tension-shear coupling load were experimentally analyzed. At macroscale, the uniaxial tension, uniaxial shear and off-axis tension tests were completed and the results were compared. The tensile modulus and proportional limit have no significant difference with the increase of off-axis angle, while failure strength decreases by 22.3% compared the 45° tensile (165.4 MPa) with the 0° tensile (212.8 MPa). Based on the strain-difference analysis, the coupling damage effect of SiCf/SiC-CMC was characterized. At microscale, the main damage types of SiCf/SiC-CMC during loading were analyzed by scanning electron microscope (SEM), and the corresponding laws between micro damage development and macro mechanical behavior under different loading conditions were revealed by cluster analysis of acoustic emission (AE) signals. The test results show that the micro damage caused by tensile and shear stress components promote each other. The macro mechanical behavior of SiCf/SiC-CMC under complex loading is controlled by basic micro damage forms such as matrix cracking, interface debonding and fiber fracture. The tension-shear coupling load affects the evolution process of the basic damage forms, and then change the macro properties of SiCf/SiC-CMC.

Quantitative relationships between the mineral composition and macro mechanical behaviors of granite under different temperatures: Insights from mesostructure-based DEM investigations

Since the nuclear waste releases heat during the decay process, the mechanical behaviors of granites adjacent to the nuclear waste repository are inevitably impacted by the discrepancies in the thermal expansion characteristics of composite minerals. In this study, a mesostructure-based model (MSBM) was first proposed to characterize the thermal behaviors of varying minerals and cementation interfaces with consideration of the aperture-dependent weakening effects of pre-existing micro-cracks on mineral properties. Based on the MSBM, nine sets of numerical models with different mineral compositions were generated to explore the relationship between the mineral composition and the macro mechanical behaviors of granite at the temperatures of 25–250 °C. The meso-mechanisms behind the varied macro mechanical behaviors were comprehensively analyzed. The results indicate that the macro mechanical properties, i.e., the uniaxial compressive stress (UCS) and elastic modulus (E) are dependent on the combined effects of the different thermal expansion characteristics of minerals and the different thermoelastic behaviors of the crystalline interfaces, especially the quartz-biotite and quartz-feldspar mineral boundaries. Finally, an evaluation system aiming to quantify the effects of mineral composition and temperature on the mechanical behaviors of granite was proposed. Principal minerals such as quartz and feldspar strongly influence the UCS and E of the rock at different temperatures, and the influence of feldspar on UCS becomes more pronounced with increasing the temperature. Biotite has little influence on the change in elastic modulus with temperature, while the contribution of biotite to UCS varies with the temperature.

A Numerical Measurement Method for Dynamic Granular Materials Based on Computer Vision.

Granular materials are widespread in nature and human production, and their macro-mechanical behavior is significantly affected by granule movement. The development of computer vision has brought some new ideas for measuring the numerical information (including the amount of translation, the rotation angle, velocity, acceleration, etc.) of dynamic granular materials. In this paper, we propose a numerical measurement method for dynamic granular materials based on computer vision. Firstly, an improved video instance segmentation (VIS) network is introduced to perform end-to-end multi-task learning, and its temporal feature fusion module and tracking head with long-sequence external memory can improve the problems of poor video data quality and high similarity in appearance of granular materials, respectively. Secondly, the numerical information can be extracted through a series of post-processing steps. Finally, the effectiveness of the measurement method is verified by comparing the numerical measurement results with the real values. The experimental results indicate that our improved VIS obtains an average precision (AP) of 76.6, the relative errors and standard deviations are maintained at a low level, and this method can effectively be used to measure the numerical information of dynamic granular materials. This study provides an intelligent proposal for the task of measuring numerical information of dynamic granular materials, which is of great significance for studying the spatial distribution, motion mode and macro-mechanical behavior of granular materials.

Real-Time Measurement of Mechanical Behavior of Granite During Heating–Cooling Cycle: A Mineralogical Perspective

Changes in mechanical properties of rocks at high temperatures are significant to various scientific and engineering problems, such as efficient exploration in enhanced geothermal systems (EGS) and rock mass stability in radioactive waste disposal. However, a comprehensive understanding of changes in rock mechanical behaviors at high temperatures and corresponding mechanisms, especially granites, remains unclear, which calls for the examination of micromechanical properties of the constituent minerals. This work investigates four representative minerals in granites, including quartz, plagioclase, amphibole, and biotite. The micromechanical properties of these minerals in the heating–cooling cycle were characterized in real time by using the nanoindentation technique. The morphology of samples was observed not only under real-time cyclic heating–cooling conditions, but also after thermal treatment. Subsequently, changes in structure of the minerals at elevated temperatures based on X-ray diffraction (XRD) were studied. Thermogravimetric analysis coupled with Fourier’s transform infrared spectroscopy (TG-FTIR) was performed to examine physio-chemical alterations of minerals at high temperatures. The experimental results revealed that the reduced modulus and hardness of quartz decreased during heating and subsequently increased during cooling. During the heating–cooling cycle, the hardness of plagioclase varied similarly to that of quartz, but its reduced modulus increased up to approximately 300,^{circ }hbox {C} followed by a decrease during heating. Unlike the net decrease of modulus of quartz after exposure to the heating–cooling cycle, feldspar showed a net increase of modulus. The micromechanical properties of biotite were found to rise significantly during heating, followed by a decrease during cooling. XRD results suggested the alteration of mineral structure, including spacing of lattice planes, crystallinity, and phase transitions, which controlled the above changes in mechanical behaviors of quartz, amphibole, and plagioclase. However, the aperture of open cracks along the cleavage in biotite determined its micromechanical properties during heating and cooling. Thermally-induced microcracks were observed during heating; whereas, closure of pre-existing cracks and initiation of microcracks were found during cooling. The real-time measured micromechanical properties of minerals could relate to the macromechanical behaviors of rocks under heating–cooling conditions based on thermally-induced microcracks.

The weakening of inter-particle friction and its effect on mechanical behaviors of granular soils

This paper describes a numerical study examining the effect of weakening of inter-particle friction on granular soil responses. A bi-linear friction weakening model is proposed to describe the reduction of inter-particle friction with the increase of contact normal force. Through a series of drained triaxial loading tests from 3D DEM simulations, it is observed that the influence of friction weakening is quite limited on macro-mechanical behaviors for granular packing under a low confining stress. With the increase of confining stress, the influence of friction weakening gradually becomes significant. Samples embedded with friction weakening model exhibit relative lower peak strength and less dilatancy, compared with samples with constant inter-particle friction. From micromechanical perspective, samples embedded with friction weakening model has lower particle friction, which in turn lead to higher contact sliding ratio and lower tangential contact force for the packing. Higher sliding ratio implies more particle movement and less dilatancy of the packing. The lower tangential contact force at the microscale matches well with the lower peak strength at the macroscale. At critical state, the strength for samples with different friction models is concisely explained by analyzing the critical void ratio and tangential contact force distribution.

Effects of bedding planes on progressive failure of shales under uniaxial compression: Insights from acoustic emission characteristics

It is believed that the bedding plane is one of controlling factors in progressive failure of shales and its characterization is of great significance in the gas shale engineering. However, it is often difficult to directly capture and visualize the progressive failure process of shales in practice. Although the microseismic method is feasible and economical to overcome this problem, to date, the effect of bedding plane on progressive failure of shales is still not fully clarified by this method. Here, we use the bonded-particle model (BPM) embedded with moment tensor algorithm to explore the progressive failure process and acoustic emission (AE) characteristics of shales under uniaxial compression. The macro mechanical behaviors such as stress-strain response and failure modes of shales were well reproduced by BPM. Meanwhile, AE characteristics were systematically monitored and analyzed during the progressive failure process. Then, the failure type dependent on layer orientation was determined by the moment tensor decomposition. And bedding-orientation-controlled crack stress thresholds as well as the degree of progressive failure could be captured by the AE cumulative number and hits. It was found that b-value in post-peak stage was susceptive to layer orientation and could be used as the indicator of the fracture complexity. Also, proportion of shear AE sources have a good consistence with fracture complexity, which suggests that shear failures favor the complex fracture formation. Our study provided a new insight into effects of bedding planes on progressive failure of shales from the viewpoint of AE characteristics.

A virtual laboratory based on full-field crystal plasticity simulation to characterize the multiscale mechanical properties of AHSS

In this work, we proposed a virtual laboratory based on full-field crystal plasticity (CP) simulation to track plastic anisotropy and to calibrate yield functions for multiphase metals. The virtual laboratory, minimally, only requires easily accessible EBSD data for constructing the highly-resolved microstructural representative volume element and macroscopic flow stress data for identifying the micromechanical parameters of constituent phases. An inverse simulation method based on a global optimization scheme was developed to identify the CP parameters, and a nonlinear least-squares method was employed to calibrate yield functions. Mechanical tests of advanced high strength steel sheet under various loading conditions were conducted to validate the virtual laboratory. Three well-known yield functions, the quadratic Hill48 and non-quadratic Yld91 and Yld2004-18p yield functions, were selected as the validation benchmarks. All the studied functions, calibrated by numerous stress points of arbitrary loading conditions, successfully captured both the deformation and strength anisotropies. The full-field CP modeling correlated well the microscopic deformation mechanism and plastic heterogeneity with the macromechanical behavior of the sheet. The proposed virtual laboratory, which is readily extended with physically based CP models, could be a versatile tool to explore and predict the mechanical property and plastic anisotropy of advanced multiphase materials.

Mechanical responses of grain-based models considering different crystallographic spatial distributions to simulate heterogeneous rocks under loading

Grain-based models (GBM) are widely used to reproduce the heterogeneous characteristics of natural rocks at the grain size level. To incorporate the spatial distribution of the constituent minerals into the GBM, the digital image processing (DIP) technique and the random distribution of property (RDP) method are frequently adopted. However, an analysis of the differences, advantages and disadvantages of the named two popular methods in simulating the mechanical response of rocks under loading has so far not been undertaken. This study considers Brazilian and uniaxial compression tests using DIP and RDP models, showing distinct differences in stress-deformation behavior (especially tensile strength) and final failure patterns. Fracture initiation , accumulation, propagation, and the corresponding stress-deformation behavior of polycrystalline rocks are sensitive to the crystallographic spatial distribution and the micro-strength parameters of mineral contacts. The clustering of mineral grains tends to induce more significant local stresses while the stress fluctuations in RDP models are more widely distributed and isolated, leading to different microcracking behavior furtherly affected by the superimposed effect of heterogeneous contact properties. Therefore, it is essential to use DIP methods to model heterogeneous rocks if the grain-scale mechanical behavior is of interest. If a heterogeneous model is used to study the overall macro-mechanical behavior of rocks, using the RDP method may be appropriate with the advantage of reduced effort for model set-up.

Constitutive model for gas hydrate-bearing soils considering different types of hydrate morphology and prediction of strength-band

The present study proposes a new elasto-plastic constitutive model that considers different types of hydrates in pore spaces. Many triaxial compression tests on both methane hydrate-bearing soils and carbon dioxide hydrate-bearing soils have been carried out over the last few decades. It has been revealed that methane hydrate-bearing soils and carbon dioxide hydrate-bearing soils have different strength and dilatancy properties even though they have the same hydrate contents. The reason for this might be due to the different types of hydrate morphology. In this study, therefore, the effect of the hydrate morphology on the mechanical response of gas-hydrate-bearing sediments is investigated through a model analysis by taking into account the different hardening rules corresponding to each type of hydrate morphology. In order to evaluate the capability of the proposed model, it is applied to the results of past triaxial compression tests on both methane hydrate-containing and carbon dioxide hydrate-containing sand specimens. The model is found to successfully reproduce the different stress–strain relations and dilatancy behaviors, by only giving consideration to the different morphology distributions and not changing the fitting parameters. The model is then used to predict a possible range in which the maximum deviator stress can move for various hydrate morphology ratios; the range is defined as the strength-band. The predicted curve of the maximum deviator stress obtained by the constitutive model matches the empirical equations obtained from past experiments. It supports the fact that the hydrate morphology ratio changes with the total hydrate saturation. These findings will contribute to a better understanding of the relation between the microscopic structures and macro-mechanical behaviors of gas-hydrate-bearing sediments.

Influence of small particle surface asperities on macro and micro mechanical behavior of granular material

AbstractThe shape of particles can have a great impact on the mechanical behavior of granular material, which is not only limited to general shape measures such as sphericity and roundness, but also applies for small scale measures such as surface asperities. In this study, triaxial tests on 3D printed particles and DEM tests show that small surface asperities on spherical particles can contribute significantly to the peak strength and dilatancy of granular material, which cannot be reflected by simply altering the traditional contact parameters in DEM. Using polydispersed particles with artificially designed surface asperities in the form of bumps for laboratory and DEM triaxial tests, both macro and micro scale behavior of granular material are analyzed to reveal the influence of these small surface asperities. The result shows that surface asperities can change the coordination number, anisotropy, and normal contact force on the micro scale, increasing the interlocking between particles and restricting particle rotation, which leads to the increase of peak strength and dilatancy on the macro scale. Although the commonly adopted approach of introducing rolling resistance to reflect shape influence can help to enhance the simulation of stress‐strain relationship, especially for particles with relatively small artificial asperities, the micro scale influence of rolling resistance and surface asperities are found to be different as the size of the asperities increase.

A textile reinforcement method for 3D printed concrete

The reinforcement of 3D printed concrete elements has proven to be a significant challenge that needs to be addressed. However, before reinforcement can be applied, the behaviour of the consequent composite materials must first be studied. This study, therefore, investigates the macromechanical behaviour of AR glass fibre textile material as reinforcement in terms of its flexural performance, to determine whether it is a feasible solution. During this study, elements, consisting of four layers, are printed flat on the surface bed of the printer and are reinforced by a textile mesh in between subsequently printed layers. The specimens are reinforced at different locations, with different geometrical orientations as well as different filament orientations, and are then compared. The flexural performance is quantified by conducting four-point bending tests 28 days after printing. The results of the tests show that by adding this specific mesh, the average flexural strength of the elements increases significantly. Furthermore, elements with the warp yarns aligned with the printed filament have increased flexural strength. During the testing, it is also discovered that voids form underneath the textile mesh when applied between the layers and that these voids influence on the performance of the elements.

Thermodynamic modeling of stress–strain behavior of saturated sand considering temperature effect

Based on the thermodynamic process of granular matter, considering the influence of temperature on energy dissipation at the mesoscopic level, a thermodynamic constitutive model, which can describe the thermal properties of saturated sand, is proposed in this paper. The model adopts the idea of double entropy theory, which introduces the concept of granular entropy to reflect the energy dissipation at the mesoscopic level. The energy dissipative structure composition and the related migration coefficient relationships are determined theoretically. Combined with the thermodynamic differential equation and the conservation and entropy increase equations, the thermodynamic identity is established; then, the mathematical expression of effective stress, plastic deformation, and granular temperature motion including the temperature effect are deduced accordingly. The relationship between the mesoscopic energy dissipation process caused by temperature change and macro-mechanical behavior is established by means of migration coefficient relationships and the energy function model. In addition, the dilatancy equation considering the state parameters is combined with the model parameters, so the stress–strain behavior of saturated sand considering the temperature effect can be described. The ability of the model to describe the thermal properties of saturated sand is verified by comparing the simulation results with the heating-induced volume change and triaxial undrained shear test results.

A grain texture model to investigate effects of grain shape and orientation on macro-mechanical behavior of crystalline rock

Grain texture characteristics play vital roles in modulating the anisotropy, strength, and ductility of crystalline rock . Grain textures (shape, size, orientation and heterogeneity) are a key parameter controlling response but are challenging to incorporate in a quantitative manner. We propose and incorporate a grain texture model (GTM) into granular mechanics modeling by the distinct element method (DEM). This model seeds then grows individual non-spherical grain clusters that honor the granular and intergranular textures of granites . The model is applied to “virtually sinter” Lac du Bonnet granite and represent the pre-through post-peak evolution of damage and deformation. The model is able to capture all significant features of this macroscopic mechanical evolution of damage through failure. With an increase in confining pressures, a transition from brittle to ductile response occurs in the post peak stage and the fitted Hoek-Brown strength envelopes for peak strength and crack-initiation stress in these numerical experiments are consistent with physical observations. An increase in aspect ratio of individual grains slightly increases the UCS/TS ratio, whereas an increase in dip angle decreases the UCS/TS ratio. Parametric studies varying the proportion of minerals and the form of contact groups with various grain shapes and orientations allow the systematic evaluation of controls of grain texture on the evolving macroscale strength and deformability . An increase in grain aspect ratio increases the proportion of inter-grain contacts. A change in dip of the grain long-axis does not change the balance of either the mineral groups or the contact groups but significantly influences the number of inter-grain tensile cracks and the resulting UCS/TS ratio.

Effect of Microstructure on Micro-Mechanical Properties of Composite Solid Propellant.

This study was aimed at determining the effect of microstructure on the macro-mechanical behavior of a composite solid propellant. The microstructure model of a composite solid propellant was generated using molecular dynamics algorithm. The correlation of how microstructural mechanical properties and the effect of initial interface defects in propellant act on the macro-mechanics were studied. Results of this study showed that the mechanical properties of propellant rely heavily on its mesoscopic structure. The grain filling volume fraction mainly influences the propellant initial modulus, the higher the volume fraction, the higher initial modulus. Additionally, it was found that the ratio of particles influences the tensile strength and breaking elongation rate of the propellant. The big particles could also improve the initial modulus of a propellant, but decrease its tensile strength and breaking elongation rate. Furthermore, the initial defects lowered the uniaxial tensile modulus, tensile strength, and the relaxation modulus of propellant, but did not affect the relaxation behavior of the propellant.