Simulations Of Compression Tests Research Articles

Micromechanical Analysis of Force Transport in Wet Granular Soils

This study investigated the mechanical behavior of a wet granular soil at low moisture content in which isolated pendular water bridges (menisci) at the interface of the solid particles give rise to capillary forces in addition to existing interparticle contact forces. We derived a single effective stress tensor encapsulating evolving liquid bridges, packing, interfaces, and water saturation. Apart from the fact that the stress due to contact forces is dependent on the fabric, we found that the so‐called suction (capillary) stress arising from liquid bridges is inevitably direction dependent, i.e., anisotropic. The latter is at odds with the common belief that capillary stress is isotropic. We demonstrate that capillary stress is a function of the distribution of liquid bridges, degree of saturation, as well as particle packing, and thus provide an adequate effective stress definition to describe both the constitutive behavior and strength of unsaturated media. We conducted discrete element modeling simulations of triaxial compression tests of pendular‐state granular samples at different matric suctions to verify the anisotropic nature of the capillary stress and resulting strength contributions to validate the proposed effective stress equation.

Uniaxial Compression Test and FEM Simulation for GH4145 Superalloy at Room Temperature

In this paper, uniaxial compression testsfor GH4145 superalloywere conducted on Gleeble-3800 at room temperature and 60°C with strain rates ranging from 0.5s-1 to 10s-1. No cracks were observed in all the specimens deformed from 10% to 70%, indicating that the GH4145 superalloy possesses great ductility under room temperature. The flow stress of GH4145 superalloywas not sensitive to strain rate deformed around room temperature and it decreased slightly with the temperature increasing. Dynamic recovery during deformation will start to balance the effect of work hardening when the true strain was arisen up to 0.4. Good agreement between the calculated and simulated temperature and strain shows that calculation method is accurate enough for the prediction.

Cockcroft-Latham Ductile Fracture Criteria for Non Ferrous Materials

The determination of ductile fracture criteria as well as friction coefficient, stress-strain curves, constants for Hollomon's equation and a material workability based on analytical methods as a forming limit diagram, a normalized Cockcroft-Latham criteria (nCL)) ring and compression tests for two materials based on aluminum and copper alloys were carried out. A calculation of nCL criteria on the basis of a compression test and numerical simulations was made. The critical values nCL criteria resulting from compression test were determined. Prediction of nCL criteria by numerical simulations were confirmed by laboratory compression tests. The values obtained from numerical simulations and compression tests for both materials show a good coincidence in results.

Development of a three-dimensional model for a 135° compression test with biological dental posts

The authors developed a model of a three-dimensional compression test at 135° of a maxillary canine tooth endodontically treated with human and bovine dentin posts and validated it with data from literature. A three-dimensional model of a canine tooth treated endodontically was built with composite resin, cement and periodontal ligament. Simulations of compression tests were performed to validate the force–time curves and then analyze the stress distributions along the tooth. These simulations were designed to show how the use of biological posts can create stresses in places where, if there are fractures, it is possible for the dental surgeon to fix the tooth with a new post, avoiding more radical treatments, such as tooth extraction and dental implant. The simulation was successfully validated with the values of contact force within the standard deviation of that of the mechanical tests. The stresses that occurred along the tooth during the tests were concentrated around the core, crown and root in the cervical region, areas favorable to fracture repair. The work could validate the mechanical tests and make a deeper analysis of the stresses that occur during the experiments. Furthermore, bovine dentin posts show favorable results as a possible material for root retention.

Nanostructured merwinite bioceramic coating on Mg alloy deposited by electrophoretic deposition

Magnesium (Mg) alloys have recently attracted much attention as degradable metallic implants for bone fracture healing. A biodegradable osteosynthetic implant material will remove the need for the implant removal surgery after the bone healing process. However, the high corrosion rate of the Mg alloys in the body fluid has prevented their clinical application as implants. In the present study, a nanostructured merwinite (Ca3MgSi2O8) bioceramic coating was prepared on AZ91 Mg alloy in order to improve its corrosion resistance, bioactivity, mechanical stability and cytocompatibility. The coating was deposited by electrophoretic deposition assisted micro arc oxidation. The phase composition and the surface morphology of the samples were characterized by X-ray diffraction and electron microscopy. The corrosion, bioactivity and mechanical behavior of the samples were investigated by electrochemical measurements, immersion into simulated body fluid (SBF) and compression tests. The cytocompatibility of the samples was evaluated by a cell culture test. The results showed that the nanostructured merwinite coating not only improved the corrosion resistance, but also enhanced the bioactivity, mechanical stability and cytocompatibility of the AZ91 Mg alloy.

A Modified SPH Method for Dynamic Failure Simulation of Heterogeneous Material

A modified smoothed particle hydrodynamics (SPH) method is applied to simulate the failure process of heterogeneous materials. An elastoplastic damage model based on an extension form of the unified twin shear strength (UTSS) criterion is adopted. Polycrystalline modeling is introduced to generate the artificial microstructure of specimen for the dynamic simulation of Brazilian splitting test and uniaxial compression test. The strain rate effect on the predicted dynamic tensile and compressive strength is discussed. The final failure patterns and the dynamic strength increments demonstrate good agreements with experimental results. It is illustrated that the polycrystalline modeling approach combined with the SPH method is promising to simulate more complex failure process of heterogeneous materials.

Validation of stress magnetic resonance imaging of the canine stifle joint with and without an intact cranial cruciate ligament

To validate use of stress MRI for evaluation of stifle joints of dogs with an intact or deficient cranial cruciate ligament (CrCL). 10 cadaveric stifle joints from 10 dogs. A custom-made limb-holding device and a pulley system linked to a paw plate were used to apply axial compression across the stifle joint and induce cranial tibial translation with the joint in various degrees of flexion. By use of sagittal proton density-weighted MRI, CrCL-intact and deficient stifle joints were evaluated under conditions of loading stress simulating the tibial compression test or the cranial drawer test. Medial and lateral femorotibial subluxation following CrCL transection measured under a simulated tibial compression test and a cranial drawer test were compared. By use of tibial compression test MRI, the mean ± SD cranial tibial translations in the medial and lateral compartments were 9.6 ± 3.7 mm and 10 ± 4.1 mm, respectively. By use of cranial drawer test MRI, the mean ± SD cranial tibial translations in the medial and lateral compartments were 8.3 ± 3.3 mm and 9.5 ± 3.5 mm, respectively. No significant difference in femorotibial subluxation was found between stress MRI techniques. Femorotibial subluxation elicited by use of the cranial drawer test was greater in the lateral than in the medial compartment. Both stress techniques induced stifle joint subluxation following CrCL transection that was measurable by use of MRI, suggesting that both methods may be further evaluated for clinical use.

Viscosity estimation of semi-solid alloys based on thermal simulation compression tests

Abstract In this paper, according to the thermal simulation compression test data, relationships for flow stress, temperature, strain rate and strain of semi-solid ZL201 alloy were studied through multiple regressions, and the constitutive equation of the alloy was established. The relationship between apparent viscosity and the shear rate was also researched. The results indicated that the maximum stress increased as strain rates increased at a constant temperature. The peak stress was clearly affected by deformation temperature, strain rate and strain. The plateau stress showed the same characteristics as the peak stress. In general, it increased slightly with increasing of the deformation temperature, except at high strain rates. The relationship between apparent viscosity and the shear rate was in accordance with the power law. The results provided a technological reference for the study of semi-solid die-casting numerical simulation of semi-solid ZL201 alloy parts. The viscosity of other semi-solid alloys could be calculated, as in the case of viscosity estimation of semi-solid ZL201 alloy.

Results and analytical simulation of axial and diagonal compression tests on reinforced concrete panels cast with wood blocks system

This paper deals with the mechanical behavior of r.c. panels produced via the building technology of Large lightly reinforced concrete walls–wood blocks system (LLRCW–WBS). The results of axial and diagonal compression tests conducted on panels produced with this system are presented. The theoretical and numerical analyses carried out in order to reproduce the mechanical behavior of the panels, evaluate their stress-strain states and their elastic-plastic behavior are then described. The theoretical analyses are performed on the basis of an improvement in the methodology as set out in European guidelines. The results of the theoretical and numerical models are compared with those obtained from experimentation reaching a good correspondence. The defined models may be used in the design of structures made of LLRCW–WBS.

Theoretical and numerical investigations of single arm dislocation source controlled plastic flow in FCC micropillars

The ‘dislocation source’ controlled plastic behaviors in submicron single crystals, which differ significantly from macroscopic plastic flow, are widely observed in recent in situ TEM tests. In this paper, single arm source (SAS) controlled plastic flow in the micropillars with diameter ranging from 200 to 800nm is extensively investigated by a statistically based theoretical model and three dimensional discrete dislocation dynamic (3D DDD) method. First, by 3D DDD simulations of micropillar compression test, some specific features of submicron plastic flow are obtained: (1) Intermittent strain burst is directly controlled by the operation and shutdown of SAS; (2) Strain hardening is virtually absent due to continuous operation of stable SAS and weak dislocation interactions; (3) The initially high dislocation density finally reaches a stable value after a sharp decrease. And meanwhile, it is found that stable SAS length also reaches a constant value which only depends on the pillar diameter. Then by modifying the conventional dislocation density evolution equation and strain hardening model to consider the SAS operation mechanism, a theoretical model is developed to quantitatively describe the submicron plastic behavior. Here the evolution of SAS length is decided by a statistical model. Once the pillar diameter and initial dislocation density are given, the stress–strain curve, dislocation density, SAS length, and the stable flow stress can all be predicted by this theoretical model and match well with the experimental data and 3D DDD simulation results.

On the Reconstruction Method of Ceramic Foam Structures and the Methodology of Young Modulus Determination

Abstract In the present paper a finite element model was used to investigate the mechanical properties such as Young’s modulus of open-cell ceramic foam. Finite element discretization was derived from real foam specimen by computer tomography images. The generated 3D geometry of the ceramic foam was used to simulate deformation process under compression. The own numerical procedure was developed to control finite element mesh density by changing the element size. Several numerical simulations of compression test have been carried out using commercial finite element code ABAQUS. The size of the ceramic specimen and the density of finite element mesh were examined. The influence of type and size of finite element on the value of Young’s modulus was studied, as well. The obtained numerical results have been compared with the results of experimental investigations carried out by Ortega [11]. It is shown that numerical results are in close agreement with experiment. It appears also that the dependency of Young’s modulus of ceramic foam on density of finite element mesh cannot be ignored.

Investigation into macroscopic and microscopic behaviors of bonded sands using distinct element method

This paper presents an investigation into the inter-particle bonding effects on the mechanical behaviors of structured sands using the distinct element method (DEM) incorporating measured inter-particle mechanical behaviors. The inter-particle mechanical behaviors are first studied by testing on idealized bonded granules under designed loading paths, which demonstrates a linear pre-failure force–displacement relationship and normal force-dependent shear strength of bonded particles. Then a modified contact model is proposed by employing different force–displacement laws for pre-failure and post-failure bonded particles, in which a failure criterion is introduced to describe the inter-particle debonding. The third part deals with the DEM numerical simulation of isotropic and biaxial compression tests to investigate the bonding effects on the mechanical behaviors of bonded sands, where the proposed model has been verified capable of capturing the main mechanical behaviors of bonded sands. In addition, the investigation into the microscopic responses quantitatively figures out the effects of inter-particle cementation on the mechanical behaviors and the loss of soil structure.

An insight into the role of the grain boundary in plastic deformation by means of a bicrystalline pillar compression test and atomistic simulation

A combination of experimental and molecular dynamics (MD) simulations is used to investigate the interaction of dislocations with a selected grain boundary (GB) in bicrystalline pillars (BCPs) with component crystals oriented for single slip and multiple slip. As a reference, single-crystalline pillars with the same orientations are also tested and compared with the BCPs. Orientations identical to the experiments are used to generate models in MD simulations. Further, electron backscatter diffraction (EBSD) measurements on the cross-section of the pillars are performed to investigate the crystal lattice rotation in correlation with the excess dislocation density. A clear change in mechanical behavior of the BCP was observed when the size of the component crystals reduced below 1μm. The EBSD analyses of these small BCPs showed an increase in the misorientation in the vicinity of the GB. MD simulation provided atomistic insights into the dislocation nucleation process and the BCPs’ interaction with the GB. On the basis of these observations, it is concluded that in BCPs smaller than 1μm the dislocation–GB interaction plays a more crucial role than the dislocation–dislocation interaction.

Mechanical behavior of FCC single crystals at finite temperatures in the presence of point defects

Molecular dynamics simulations have been performed to study the effect of temperature and the presence of various types of point defects on the mechanical response of copper. Nanoindentation and uniaxial tests have been modeled to compare different loading conditions. Anisotropy effects have been also added to the study by applying the uniaxial load in various crystallographic orientations. The yield stress in all cases decreases with increased temperature for both perfect crystals and crystals with point defects. However, the temperature sensitivity of the yield stress is significantly lowered by the presence of defects in simulated nanoindentation and compression tests, while the combined effect of point defects and elevated temperature on the yield in tension is less than in the other loading conditions. The deformation mechanism which causes this effect is described, and points towards possible explanations for previously observed variations in nanomechancial testing between common experimental methods.

Microscopic contact model of lunar regolith for high efficiency discrete element analyses

The grains of lunar regolith are characterized with rough surfaces, angular shapes and mutual adhesions due to short-range interactions. These features control the macroscopic mechanical behavior of lunar regolith but have not been completely captured by contact models in previous Discrete Element Method (DEM) analyses. In this paper, a simplified two-dimensional microscopic contact model is proposed for high efficiency DEM analyses of lunar regolith. The model consists of three components in the normal, tangential and rolling directions respectively, plus two new parameters. A shape parameter is used to control the rolling resistance ability at the contact area between two particles to capture the features of grain shape and interlocking. The second parameter, micro-separation, which denotes the nominal minimum distance between the molecules of the two contacting particles, is introduced to account for van der Waals force as the major component of the short-range interactions that contribute to the adhesion of regolith grains in lunar environment conditions. The novel model has been implemented in a two-dimensional DEM code for numerical simulations of biaxial compression tests on lunar regolith. The effects of interparticle friction, grain shape, lunar environment conditions and void ratio on the strength of lunar regolith were numerically investigated. The results show that soils in the simulated lunar environment exhibit greater strength and more apparent strain-softening and shear dilatancy than on the Earth. The proposed model can capture the main features of the mechanical behavior of lunar regolith (apparent cohesion and high peak friction angle) and a wide range of strength indices can be obtained by the contact model.

Computational modeling of the crushing behavior of SKYDEX® material using homogenized material laws

As a novel light weight protective material, SKYDEX® pad consists of layers of periodic twin-hemispherical microstructures made of gray thermoplastic polyurethane. During the crash/blast event, a large amount of kinetic energy can be dissipated in the collapse of microstructures. To characterize the mechanical properties of such material, two types of experimentation, namely, uniaxial compressions (at strain rates of 0.01s−1 to 300s−1) and drop tests (from three different heights) were conducted. Based on test results, numerical models were developed using three homogenized foam-type material laws (MAT_26, MAT_83, and MAT_163) in the LS-DYNA software without building individual cells. Corresponding parametric values were determined based on the compression testing data. The simulation results were evaluated using experimental results from both types of experiment, and then quantified using a gross correlation index (GCI). Calculated results indicate that in the simulation of compression tests, MAT_163 made the best prediction; while in the simulation of drop tests, MAT_83 and MAT_163 demonstrated the same performance. But considering less material constants required and more straightforward parameter calibration, MAT_163 is considered the best among the three material types studied. It is also concluded that in the current scenarios, local deformation observed in the drop tests can be predicted accurately without conducting shear tests.

Homogenization of anisotropic elastoplastic behaviors of a porous polycrystal with interface effects

SUMMARYThis paper is devoted to develop a theoretical framework to predict the macroscopic transversely isotropic elastoplastic behavior of clay‐like material, which is viewed as a porous polycrystal. We consider evolutions of two local plastic mechanisms of grains and interface simultaneously, for which a Schmid criterion is used for the strength of sheet‐like grains and a Tresca criterion for the strength of interfaces between particles. By adapting the standard incremental method, we propose firstly a classic self‐consistent model, which does not consider the effect of interface, then a generalized self‐consistent model in which the solid phase is represented by laminated (or isotropic) spherical grains surrounded by interfaces. Comparisons of numerical predictions between these two methods are performed and have demonstrated the validity of the generalized self‐consistent model taking account of interface effects. Numerical simulations of uniaxial compression tests have shown that the macroscopic elastoplastic behavior of polycrystalline (clay‐like) material can be successfully predicted by the way of considering the two local plastic mechanisms at microscopic scale. Copyright © 2013 John Wiley & Sons, Ltd.

DEM simulation on the one-dimensional compression behavior of various shaped crushable granular materials

In order to investigate the effects of particle shape on the compression behavior of granular materials, a series of simulations was conducted using a two-dimensional discrete element method employing moment springs. Fracturable granular assemblies were constructed from particles of the same shape and size. The range of possible particle shapes includes disk, ellipse and hexagon, with different aspect ratios. Simulations of single particle crushing tests on elliptical particles showed that crushing could be classified into three types: cleavage destruction, bending fracture and edge abrasion, depending on the manner of compression. A series of simulations of one-dimensional compression tests was then conducted on six types of crushable particle assemblies; the three types of crushing mentioned above were also observed, but their rates of occurrence depended on the particle shape. Cleavage destruction was mainly observed with circular and elliptical particles; bending fracture was observed only with elongated particles; edge abrasion was frequently observed with angular particles. Despite the difference in crushing type, all samples, when subjected to intense compression, converged to a critical grading with unique void ratio, grain size distribution and aspect ratio, with a similar distribution of number of contact points.

승용차용 알루미늄 듀오타입 LPG 탱크의 형상 및 두께 최적설계

In this study, to develop a light weight duo type aluminum LPG tank in stead of a conventional steel tank optimization technology is used. Two types of optimization method are carried out for internal compression test simulation of a LPG tank. The first is the thickness only optimization of LPG tank components. The second is the thickness and shape optimization. For the case of the thickness only optimization the weight reduction rate of an optimized tank compare to that of the initial design is 42%. Also 48% weight reduction was achieved for the case of the thickness and shape optimization.

Effect of Particle Shape on Mechanical Behaviors of Rocks: A Numerical Study Using Clumped Particle Model

Since rocks are aggregates of mineral particles, the effect of mineral microstructure on macroscopic mechanical behaviors of rocks is inneglectable. Rock samples of four different particle shapes are established in this study based on clumped particle model, and a sphericity index is used to quantify particle shape. Model parameters for simulation in PFC are obtained by triaxial compression test of quartz sandstone, and simulation of triaxial compression test is then conducted on four rock samples with different particle shapes. It is seen from the results that stress thresholds of rock samples such as crack initiation stress, crack damage stress, and peak stress decrease with the increasing of the sphericity index. The increase of sphericity leads to a drop of elastic modulus and a rise in Poisson ratio, while the decreasing sphericity usually results in the increase of cohesion and internal friction angle. Based on volume change of rock samples during simulation of triaxial compression test, variation of dilation angle with plastic strain is also studied.