Simulated Compression Research Articles

Multiscale finite element analysis model of needle-punched carbon/carbon composites

The mechanical properties of matrix, fiber bundle, and chopped fiber felt are evaluated by means of micromechanical analysis. An equivalent matrix model composed of matrix and chopped fiber felt material is established, which together with fiber bundle is used as the basic component of single cell. Based on the mesostructural characteristics of NP C/C composites, the local structure is divided into five typical unit cells to characterize the five representative microstructures of NP C/C composites, and the mechanical properties of the five typical unit cells are calculated, respectively. According to the true distribution of needle holes, the five typical unit cells are arranged to form a representative volume element model of NP C/C composites. The Cai–Wu failure criterion is used to determine the failure of the five typical unit cells model, and the periodic boundary condition is applied to the tension and compression simulation of the NP C/C composites, the progressive damage law of the model is analyzed. The results show that the prediction of mechanical properties of the composites under unidirectional tensile load and unidirectional compression load are in good agreement with the experimental data.

Simulation of attenuation and compression in beam quality measurement of high power laser

Simulation of attenuation and compression in beam quality measurement of high power laser

3D printing for Growth Adaptive Medical Devices: an alternative approach for craniosynostosis

An adaptive medical device is a piece of equipment designed to adjust or respond to changes in a patient’s condition or environment. The use of 3D printing technology for the development of adaptive medical devices has opened up new possibilities for customization, efficiency, and accessibility in healthcare. Sagittal craniosynostosis is a birth defect that arises due to a premature fusion of the sagittal suture in infants. This disease causes a misshapen skull and a rise of intracranial pressure that can lead to cognitive impairments. At six months of age, the preferred technique for craniosynostosis is an open vault remodeling surgery, an extremely invasive procedure with severe blood loss for the patient and significant postoperative pain. In this context, growth adaptive cranial plates, that can be tuned depending on the patient to achieve the desired skull shape through the deformation of the structure, can be a valid alternative. Cellular and lattice structures offer tailorable mechanical properties in relation to the designed geometry. Specifically, the geometry of cellular materials can be modified in relation to the final mechanical requirements. In this study, the predictability of the deformation of a PLA structure composed by honeycomb unit cells was studied performing compression simulations. The geometry was then modified, simulations and compression tests were then repeated in order to find an equation that could describe the relation between the internal angle of the honeycomb and the relative Poisson ratio. This relation can be further exploited for the production of customized adaptive devices for the treatment of sagittal craniosynostosis.

牛粪压缩和应力松弛特性及其本构模型构建研究

In order to study the mechanical properties of compression and stress relaxation of manure under drainage conditions, the experiment was carried out with cattle manure as the object, and the constitutive models were improved to describe the stress-strain curves of compression and stress relaxation. The defined constitutive model was determined by parameter identification, and the influence laws of moisture content and filling mass on the compression and relaxation process were investigated. The results show that the improved Nishihara model and the five-component generalized Maxwell model can better describe the compression and stress relaxation properties of cattle manure, and the coefficients of determination of the parameters of the fitted intrinsic model are all greater than 0.9, with high fitting accuracy. The compression process was divided into three stages: exhaust, drainage, and viscoelastic-plastic deformation. The stress decay rate tended to change quickly and then slowly, and there was a negative correlation between the compressed mass, moisture content, and stress decay rate. Duncan's mean comparisons revealed that the differences in elastic modulus between different moisture content / compressed mass groups in the parameters of the cattle manure compression principal model were all significant (P<0.05). The differences in elastic modulus and coefficient of viscous attenuation between different moisture content groups in the parameters of the stress relaxation model were all significant. The study's results can provide the theoretical basis for the study and simulation of CM's compression and dewatering mechanism and provide support for the solid-liquid separator for livestock and poultry manure.

A high-performance design of tubular lattice structure having zero Poisson’s ratio

In this work, novel zero Poisson’s ratio (ZPR) tubular lattice structures, named as strut-reinforced semi-reentrant honeycomb (SR-SRH), were designed. Finite element simulations of quasi-static compression were conducted, and Design of Experiments (DoE) technique was used to study the effects of geometric parameters of the tubular lattices on the mechanical properties. One of the proposed designs of SR-SRH tubular lattices (SR-SRH-1) exhibited remarkably higher ZPR strain limit and energy absorption ability compared to previously studied ZPR tubular lattices. Another design (SR-SRH-2) demonstrated excellent compressive strength and elastic modulus. These 3D-printed structures were tested under quasi-static compression to corroborate the numerical simulations.

Study of the effect of dual-phase transformation on the processing map of Al0.9FeCoNiCr high-entropy alloys under peak stress conditions

ABSTRACT Single-pass thermal compression simulation experiments were performed on a dual-phase Al0.9FeCoNiCr high-entropy alloy at strain rates of 1–0.001 s−1, temperatures of 850–1050°C (true strain of 0.916). According to a model of the dynamic DMM processing map proposed by Prasad et al, the hot-deformation behaviour of the alloy was analysed. The flow-instability regions were obtained as follows: temperature 850–1040°C with a strain rate 1–0.1 s−1 and 850–900°C with a strain rate of 1–0.001 s−1. The microstructure was obtained by EBSD characterisation. It was found that under certain strain-rate conditions, the FCC phase in the dual-phase Al0.9FeCoNiCr high-entropy alloy did not change significantly at low temperatures but increased significantly when the temperature was over 1000°C. The hot-working properties of the alloy are affected when the FCC phase exceeds 80%.

A progressive damage model associated with dynamic fracture toughness and IFF criterion with a fast search algorithm of fracture angle

This paper presents a quick search algorithm of the fracture angle of inter-fiber fracture (IFF) criterion and a progressive damage model considering the dynamic fracture toughness effect. The fracture angle determination of the IFF criterion is necessary and time-consuming, which has limited its practicality. Therefore, to accurately calculate stress exposure factors under various combinations of stress states, a highly efficient algorithm is needed. In this paper, a novel algorithm using stress tractions on the fracture plane and the golden section search (GSS) is promoted. Through a series of simulation tests, this novel algorithm has been proven to be exact and efficient compared with other two common algorithms, which saves an average of 63.2 % and 28.1 % of the time in 1 million calculations and 2 h 2 min 4 sec and 39 min 2 sec in simulations. Additionally, fracture toughness, which controls material damage evolution process, also has strain-rate effect like elastic modulus and strength. Hence, a new progressive damage model considering the dynamic fracture toughness effect is proposed. The results of dynamic compression and ballistic impact tests and simulations demonstrate the fidelity of the novel damage model.

Meso-scale deformation and strength mobilization mechanisms of EPS composite soil

Expanded polystyrene (EPS) composite soil is composed of two solid constituents (cemented soil and EPS beads), which together with the inter-constituent interfaces form a unique mesoscopic structure. The macroscopic behavior of EPS composite soil has been widely investigated so far, but the focus has seldom been put on the meso-scale mechanisms behind the macroscopic deformation features and strength mobilization processes. In this study, systematic experiments and refined numerical simulations are utilized to examine the meso-scale mechanical responses of EPS composite soil under triaxial compression to reveal the associated mechanisms. Here, meso-scale is a scale smaller than a sample scale but larger than an EPS bead scale. First, the mechanical behavior of cemented soil, EPS material and their interface is obtained in experiments; their constitutive models are formulated, and the model parameters are calibrated based on experimental results. Then, experiments and refined numerical simulations of triaxial compression on EPS composite soil are performed. It is found that the rich macroscopic mechanical behavior of EPS composite soil has a mechanical source (contrast in mechanical behavior between EPS and cemented soil) and a geometric source (non-uniform distribution of EPS beads). The mechanical source leads to highly non-uniform stress and strain distributions within an EPS composite soil. The geometric source causes strain localization in zones with local concentration of EPS beads, leading to three macroscopic deformation modes, i.e., overall shear localization, local lateral expansion, and overall uniform expansion. In strength mobilization, cemented soil matrix first mobilizes its strength because it takes most of the load and contributes much to deformation at the early stage of triaxial compression. EPS beads are later progressively involved in the overall load bearing and deformation of the EPS composite soil sample. EPS beads make more contribution to stress than to strain due to its soft nature.

Ultrahigh Strength and Plasticity Mechanisms of Si and SiC Nanoparticles Revealed by First-Principles Molecular Dynamics.

It is now well established that materials are stronger when their dimensions are reduced to the submicron scale. However, what happens at dimensions such as a few tens of nanometers or lower remains largely unknown, with conflicting reports on strength or plasticity mechanisms. Here, we combined first-principles molecular dynamics and classical force fields to investigate the mechanical properties of 1-2nm Si and SiC nanoparticles. These compression simulations unambiguously reveal that the strength continues to increase down to such sizes, and that in these systems the theoretical bulk strength can be reached or even exceeded in some cases. Most of the nanoparticles yield by amorphization at strains greater than 20%, with no evidence of the β-tin phase for Si. Original and unexpected mechanisms are also identified, such as the homogeneous formation of a dislocation loop embryo for the ⟨111⟩ compression of SiC nanoparticles, and an elastic softening for the ⟨001⟩ compression of Si nanoparticles.

Research and analysis of the impact of the pore structure on the mechanical properties and fracture mechanism of sandstone

Rock pore structure, including porosity, pore size, and particle size, plays a crucial role in determining rock mechanical properties. This study investigates the impact of pore structure on rock mechanical properties through laboratory experiments and numerical simulation methods on sandstones with varying porosity and pore size. The pore structure characteristics of sandstone were determined using XRD, SEM, and NMR microscopic techniques. Additionally, the influence of rock porosity on rock mechanical properties was analyzed by combining Uniaxial compression test with DIC technology, revealing the fracture mechanism caused by porosity in rocks. Numerical models were constructed to simulate sandstones with different porosities and pore diameters, followed by uniaxial compression simulation tests to explore the influence of varying pore diameters on rock mechanical properties and the fracture mechanism. The study reveals the presence of four distinct pore types in the sandstone: micropores in the matrix (0–0.002 µm), intergranular pores (0.002–0.2 µm), dissolution pores (0.2–4 µm), and fracture pores (4–30 µm). Among these, intergranular pores and dissolution pores are the predominant types, accounting for approximately 92–96% of the total pore volume in the sandstone. It is observed that an increase in porosity leads to a decrease in the mechanical strength of sandstone and an increase in Poisson's ratio while keeping the pore size constant. Similarly, when the porosity remains constant, an increase in pore size results in a decrease in the mechanical strength and an increase in Poisson's ratio. Additionally, the study also finds that as the porosity and pore diameter of sandstone increase, the area of internal equivalent stress expands, leading to a shorter crack initiation time and accelerated crack penetration speed, ultimately resulting in a decline in the mechanical properties of sandstone. Numerical simulation experiments further demonstrate that large pores exhibit higher stress concentration compared to small pores, thereby exerting a more significant influence on the mechanical properties of sandstone.

A simplified numerical simulation of uniaxial compression for polyacrylonitrile fiber reinforced permeable concrete based on CT images

For fiber reinforced permeable concrete, numerical simulation method have been applied to reduce the time consumption of physical experiments and to study the mesostructure of the material. In this paper, polyacrylonitrile fiber reinforced permeable concrete (PANFRPC) is considered to consist of aggregate, mortar (containing fibers inside), interface transition zone (ITZ) and pores in 3D mesostructure model generated from computer tomography (CT) images. For the numerical simulation of the, material properties of each component in the model are assigned according to physical experimental results. The failure curve of the mortar in PANFRPC is determined by physical test results to reflect the effect of fibers. The simulation results show that the model has similar mechanical properties to the actual specimen and can be used to simulate the elastic stage of the uniaxial compression process and predict the strength with an error of less than 15% despite the simplification of fiber. the accuracy and reliability of the model have also been verified by the distribution pattern of vertical caraks and x-shaped shear cracks from macro and meso perspectives.

A parametric study into the influence of Taylor-type scale-bridging artifacts on accuracy of multi-level crystal plasticity finite element models for Mg alloys

Meshing grain structures explicitly to incorporate microstructure dependent material behavior in modeling tools for metal forming processes and structural components is unfeasible. Grain-to-polycrystal meso-level homogenization theories are employed to embed polycrystal plasticity constitutive laws in finite element (FE) frameworks, which hence relate the meso-scale to the macro-scale response. A Taylor-type polycrystal plasticity (T-CP) theory is often used at the meso-scale within FE frameworks (T-CPFE) owing to its simplicity and computational efficiency. The theory relies on the iso-strain constraint imposed over constituent grains at each integration point. The constraint can be relaxed by spreading orientation distributions over finite elements in a mesh. This work seeks to establish an optimal number of crystal orientations to spread over integration points for accurate modeling of Mg alloys. Quasi-static and high strain-rates simulations of tension, compression, simple-shear, and plane strain deformation conditions are performed and post-processed to reveal the differences in predicted mechanical fields between T-CPFE and an explicit polycrystalline grain microstructure of an AZ31 Mg alloy. Moreover, several flow stress curves of the alloy are simulated and compared with measured data. A range of meshes with variable degree of relaxed constraints at integration points are suitably designed and used in the simulations. The performance of the six crystals per integration point is established to be an optimum in smoothing local deformation while allowing heterogenous deformation over the mesh. As such, the relaxed Taylor homogenization can provide tractable part level simulations of Mg alloys.

Mesoscale study on the mechanical properties and energy absorption characteristics of aluminum foam-filled CFRP tubes under axial compression

This study investigates the axial compression mechanics and energy absorption characteristics of aluminum foam-filled carbon fiber-reinforced polymer (CFRP) tubes from both experimental and simulation perspectives. Quasi-static compression experiments of aluminum foam specimens, single CFRP tubes and aluminum foam-filled CFRP tubes are carried out. Based on the experimental results, compression simulations are conducted to investigate the structural deformation and the energy absorption characteristics of aluminum foam-filled CFRP tubes at the mesoscale. The effects of structural parameters on the compression mechanics and energy absorption characteristics of aluminum foam-filled CFRP tubes are explored.

Lessons learned from matching 3D DEM and experiments at macro, meso and fabric scales for triaxial compression tests on lentils

A series of discrete element method (DEM) triaxial compression simulations on specimens of an anisometric granular material starting from distinct initial fabric anisotropy states are conducted and compared with physical experiments on lentils at different scales, assisted by operando X-ray tomography measurements. A quantitative reproduction of the group of experimental results is achieved by appropriate idealization and determination of particle shape, boundary conditions, contact parameters, and initial state. The reliability of DEM in quantitative representation of macro scale stress–strain response, meso scale strain localization, and micro scale fabric anisotropy evolution is thus comprehensively validated against measurements from physical experiments, which is a step forward from comparisons only at the macro or particle kinematics level. Several key factors that govern realistic DEM simulations are also identified. The friction coefficient between particles during specimen generation, particle shape, and specimen preparation method can significantly affect the initial state of DEM specimens. Differences in initial state at macro and micro scales and boundary conditions can strongly influence the stress–strain response. However, the evolution of fabric anisotropy appears to be insensitive to changes in initial state and boundary conditions.

DAMAGE ACCUMULATION IN THE V95\3% TIC METALMATRIX COMPOSITE DURING DEFORMATION AT HIGH TEMPERATURES

Damage accumulation in a dispersion-strengthened metal matrix composite was studied at deformation temperatures ranging between 300 and 500°C. The composite has the V95 alloy matrix (the Russian analogue of the 7075 alloy) reinforced by titanium carbide (TiC) particles in a volume content of 3%. The composite was made by ex-situ liquid-phase technology. Damage calculation is based on the data of the evolution of the elastic modulus value obtained by the instrumented microindentation technique. It has been experimentally found that, under compression at the macroscale, the composite has the best plasticity at a temperature of 400°C. The plasticproperties at a deformation temperature of 500°C are significantly lower than at 300 and 400°C. ranging from 300 to 500°C and strain rates ranging between 0.1 and 10 s-1. The paper presents experimental dependences between flow stress and strain for temperatures ranging from 300 to 500°C and strain rates ranging between 0.1 and 10 s-1. Based on these data, finite element simulation of specimen compression was carried out, which makes it possible to describe the influence of loading conditions on the evolution of the stress state characterized by the Lode-Nadai coefficient mσ and the σ/T ratio, where σ is mean normal stress and T is tangential stress intensity.

Investigation into the Influence of Stress Conditions on the Permeability Characteristics of Weakly Cemented Sandstone

This study, conducted in the geological context of the Yixin coalfield, systematically performed indoor mechanical tests to analyze the impact of different stress conditions on the permeability of weakly cemented sandstone. The results were used to establish numerical simulations of permeability curves, revealing the following key findings. (1) After saturation, weakly cemented sandstone transitions from brittle to plastic failure. Numerical simulations closely matched experimental results, ensuring the accuracy of subsequent permeability simulations using the Hoek–Brown method. (2) Indoor permeability experiments identified a unique “√” shaped permeability curve for weakly cemented sandstone, differing from traditional sandstone. Numerical simulations confirmed this pattern and provided a basis for modeling weakly cemented strata under varying confining pressures. (3) The mesoscopic analysis of numerical simulation shows that that confining pressure limits the expansion of microcracks, while pore pressure causes cracks to develop from high- to low-pressure areas. Increasing pore pressure gradually raises permeability, and elevated confining pressure initially reduces, then increases permeability. (4) A damage parameter “D” was introduced to monitor fractures during compression simulations, showing that with increasing confining pressure, the damage parameter decreases and then sharply increases. Hydraulic pressure differentials directly correlated with the damage. This comprehensive study enhances our understanding of weakly cemented sandstone’s hydrological behavior under varying stress conditions and parameters.

Effect of the loading condition on the statistics of crackling noise accompanying the failure of porous rocks.

We test the hypothesis that loading conditions affect the statistical features of crackling noise accompanying the failure of porous rocks by performing discrete element simulations of the tensile failure of model rocks and comparing the results to those of compressive simulations of the same samples. Cylindrical samples are constructed by sedimenting randomly sized spherical particles connected by beam elements representing the cementation of granules. Under a slowly increasing external tensile load, the cohesive contacts between particles break in bursts whose size fluctuates over a broad range. Close to failure breaking avalanches are found to localize on a highly stressed region where the catastrophic avalanche is triggered and the specimen breaks apart along a spanning crack. The fracture plane has a random position and orientation falling most likely close to the centre of the specimen perpendicular to the load direction. In spite of the strongly different strengths, degrees of 'brittleness' and spatial structure of damage of tensile and compressive failure of model rocks, our calculations revealed that the size, energy and duration of avalanches, and the waiting time between consecutive events all obey scale-free statistics with power law exponents which agree within their error bars in the two loading cases.

Effect of Mineral Grain and Hydrate Layered Distribution Characteristics on the Mechanical Properties of Hydrate-Bearing Sediments

The mechanical characteristics of gas hydrate-bearing sediments (HBS) are important for evaluating reservoir stability. The interbedded formation of HBS is common in target mining reservoirs. Existing studies on the triaxial mechanical properties of HBS are primarily based on homogeneous and isotropic samples. Therefore, the stress–strain law of the target mining reservoirs cannot be predicted accurately. In this study, a series of sediment models with interlayers of coarse and fine mineral grains were established based on the PFC3D code, and the influence of the layered distribution characteristics of sediment particles and hydrates on the macroscopic mechanical behaviour of the reservoir was comprehensively analysed. The triaxial compression simulation results indicate that the peak strength, deformation modulus, and cohesion of the layered HBS are significantly lower than those of the homogeneous model. The deformation modulus of the reservoir is mainly affected by the fine-grained layer without hydrates. When the coarse and fine grains correspond to different mineral components, the two minerals are heterogeneous in terms of their micromechanical parameters, which can further reduce the macroscopic mechanical parameters of the HBS. In addition, the layered distribution of hydrate results in significant anisotropy of the reservoir. This study constitutes a reference regarding the control mechanism of gas hydrate reservoir strength.

Shaping Micro-Bunched Electron Beams for Compact X-ray Free-Electron Lasers with Transverse Gradient Undulators

Laser-modulator-based micro-bunching of electron beams has been applied to many novel operating modes of X-ray free-electron lasers from harmonic generation to attosecond pulse production. Recently, it was also identified as a key enabling technology for the production of a compact XFEL driven by a relatively low-energy beam. In traditional laser modulator schemes with low-energy and high-current bunches, collective effects limit the possible working points that can be employed, and thus it is difficult to achieve optimal XFEL performance. We propose to utilize transverse longitudinal coupling in a transverse gradient undulator (TGU) to shape micro-bunched electron beams so as to optimize their performance in a compact X-ray free-electron laser. We show that a TGU added to a conventional laser modulator stage enables much more flexibility in the design, allowing one to generate longer micro-bunches less subject to slippage effects and even lower the slice emittance of the micro-bunches. We present a theoretical analysis of laser-based micro-bunching with an added TGU, simulation of compression with collective effects in such systems, and finally XFEL simulations demonstrating the gains in peak power enabled by the TGU. Although we focus on the application to compact XFELs, what we propose is a general phase space manipulation that may find utility in other applications as well.

Dynamic strength characteristics of fractured rock mass

Fractures play crucial role in the behavior of rock masses, yet the understanding of their natural distribution and impact on dynamic characteristics remain unclear. Here the effect of “natural” fractures on the dynamic impact strength of rock mass was investigated using numerical specimens with fractures prepared using the Split Hopkinson Pressure Bar (SHPB) model. These fractures were generated through biaxial compression simulation. Various axial stress levels and confining pressures replicated diverse natural rock fracture distributions. To capture the anisotropic distribution of fractures in natural rock and the randomness of impact direction, impact from 0°, 90°, 180° and 270° directions were imposed. The biaxial loading simulation showed that fracture increases with higher loading stress, and rapidly expands in the post-peak stress stage, with ∨ or ∧ shaped slip plane depending on confining pressure. The impact strength of the fractured specimen decreases as the number of prefabricated fractures increases, following a two-stage pattern, i.e., rapidly decrease with small number of fractures and gradually decrease with high number of fractures. Pre-existing fractures aligning with the impact direction provide stronger resistance compared with fractures deviated, and their location and distribution significantly affect the stress transmission. The impact from other directions has different stress transmission routes related to the fracture and macroscopic surface distribution. Importantly, a specimen’s loading history shapes its internal fracture distribution, thereby affecting its resistance to impact stress. This research provides invaluable insights into the role and mechanics of fractures in rock masses, thus enhancing our understanding of rock dynamics and potentially informing more effective geotechnical engineering practices.