scholarly journals DEM Modeling of Crushable Grain Material under Different Loading Conditions

2021 ◽  
Author(s):  
M. Amine Benmebarek ◽  
Majid Movahedi Rad
Keyword(s):  
Coordination Number ◽  
Contact Area ◽  
Particle Model ◽  
Displacement Curve ◽  
Loading Conditions ◽  
Large Area ◽  
Bonded Particle Model ◽  
Grain Crushing ◽  
Particle Strength ◽  
Force Displacement

This paper deals with the effect of contact conditions on the crushing mechanisms and the strength of granular materials. The computation of crushable grain material under different loading conditions is performed using 3D model of discrete element method (DEM). The crushable macro-grain is generated from a large number of identical spherical micro-grains which are connected according to the bonded particle model. First, the parameters of the proposed DEM model are calibrated to match the force-displacement curve obtained from Brazilian Tests performed on cylinders made of artificially crushable material. The damage profile right at the point when the force-displacement curve reaches its maximum is seen to replicate the same crack patterns observed in Brazilian test experiments. Then, parametric investigations are performed by varying the coordination number, the contact location distribution, and the contact area. The results show that these parameters play a significant role in determining the critical contact force and fracture mechanism of crushable particles compared to a traditional macro-grain crushing test. Increasing distribution and coordination number of the macro-grain increases particle strength when large area contact is permitted. However, for linear contact area, the effect of increasing coordination number on particle strength is marginal.

On the Nonlinear Snap-Through of Arch-Shaped Clamped–Clamped Bistable Beams

2019 ◽  
Vol 87 (2) ◽  
Author(s):  
Jian Zhao ◽  
Jian Zhang ◽  
K. W. Wang ◽  
Kai Cheng ◽  
Hongxi Wang ◽  
...  
Keyword(s):  
Displacement Curve ◽  
Loading Conditions ◽  
Curved Beams ◽  
Buckling Mode ◽  
Strongly Coupled ◽  
Deformation Behaviors ◽  
And Control ◽  
Force Displacement ◽  
Element Theory ◽  
Cubic Function

Abstract Bistable compliant elements offer excellent advantages in many applications ranging from high precision sensing to energy harvesting. The essential nonlinear mechanics of such elements are strongly coupled with their buckling mode, geometric parameters, and loading conditions. The force–displacement plot of bistable curved beams could contain a displacement limit point, which cannot be well modeled by the commonly used smooth cubic function and would cause operational problems due to incorrect predictions of the bistability. In this technical brief, the nonlinear bistable mechanics of a compliant curved beam with both ends fixed is analyzed based on the large deflection finite element theory. By using the multistep displacement loading method, the deformation behaviors and their transition from symmetric to asymmetric modes are numerically studied, which provides insights into the force–displacement curve and the multiple snapping pathways. Furthermore, the influences of the structure parameters on bistable mechanics are analyzed, and a quality factor for identifying the occurrence of displacement limit points is introduced for different loading conditions. Finally, a method for achieving a single smooth snapping pathway is proposed, providing a theoretical basis to the design and control of the bistable compliant structures.

scholarly journals Study on improvement of prefolded energy absorption device to constant resistance and its mechanical properties

2021 ◽  
Vol 104 (3) ◽  
pp. 003685042110368
Author(s):  
Dong An ◽  
Jiaqi Song ◽  
Hailiang Xu ◽  
Jingzong Zhang ◽  
Yimin Song ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Energy Absorption ◽  
Compression Test ◽  
Side Wall ◽  
Concave Side ◽  
Displacement Curve ◽  
Static Compression ◽  
Constant Resistance ◽  
The Impact ◽  
Force Displacement

When the rock burst occurs, energy absorption support is an important method to solve the impact failure. To achieve constant resistance performance of energy absorption device, as an important component of the support, the mechanical properties of one kind of prefolded tube is analyzed by quasi-static compression test. The deformation process of compression test is simulated by ABAQUS and plastic strain nephogram of the numerical model are studied. It is found that the main factors affecting the fluctuation of force-displacement curve is the stiffness of concave side wall. The original tube is improved to constant resistance by changing the side wall. The friction coefficient affects the folding order and form of the energy absorbing device. Lifting the concave side wall stiffness can improve the overall stiffness of energy absorption device and slow down the falling section of force-displacement curve. It is always squeezed by adjacent convex side wall in the process of folding, with large plastic deformation. Compared with the original one, the improved prefolded tube designed in this paper can keep the maximum bearing capacity ( Pmax), increase the total energy absorption ( E), improve the specific energy absorption (SEA), and decrease the variance ( S2) of force-displacement curve.

scholarly journals Young’s Modulus of Polycrystalline Titania Microspheres Determined by In Situ Nanoindentation and Finite Element Modeling

2014 ◽  
Vol 2014 ◽  
pp. 1-5 ◽  
Author(s):  
Peida Hao ◽  
Yanping Liu ◽  
Yuanming Du ◽  
Yuefei Zhang
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Young’S Modulus ◽  
Young's Modulus ◽  
Deformation Mechanisms ◽  
Displacement Curve ◽  
Element Simulation ◽  
Nanoindentation Experiment ◽  
Force Displacement

In situ nanoindentation was employed to probe the mechanical properties of individual polycrystalline titania (TiO2) microspheres. The force-displacement curves captured by a hybrid scanning electron microscope/scanning probe microscope (SEM/SPM) system were analyzed based on Hertz’s theory of contact mechanics. However, the deformation mechanisms of the nano/microspheres in the nanoindentation tests are not very clear. Finite element simulation was employed to investigate the deformation of spheres at the nanoscale under the pressure of an AFM tip. Then a revised method for the calculation of Young’s modulus of the microspheres was presented based on the deformation mechanisms of the spheres and Hertz’s theory. Meanwhile, a new force-displacement curve was reproduced by finite element simulation with the new calculation, and it was compared with the curve obtained by the nanoindentation experiment. The results of the comparison show that utilization of this revised model produces more accurate results. The calculated results showed that Young’s modulus of a polycrystalline TiO2microsphere was approximately 30% larger than that of the bulk counterpart.

Can indentation technique measure unique elastoplastic properties?

2009 ◽  
Vol 24 (3) ◽  
pp. 784-800 ◽  
Author(s):  
Ling Liu ◽  
Nagahisa Ogasawara ◽  
Norimasa Chiba ◽  
Xi Chen
Keyword(s):  
Critical Strain ◽  
Indentation Test ◽  
Strain Curve ◽  
Spherical Indentation ◽  
Plastic Behavior ◽  
Displacement Curve ◽  
Application Range ◽  
Indentation Technique ◽  
Elastoplastic Properties ◽  
Force Displacement

Indentation is widely used to extract material elastoplastic properties from measured force-displacement curves. Many previous studies argued or implied that such a measurement is unique and the whole material stress-strain curve can be measured. Here we show that first, for a given indenter geometry, the indentation test cannot effectively probe material plastic behavior beyond a critical strain, and thus the solution of the reverse analysis of the indentation force-displacement curve is nonunique beyond such a critical strain. Secondly, even within the critical strain, pairs of mystical materials can exist that have essentially identical indentation responses (with differences below the resolution of published indentation techniques) even when the indenter angle is varied over a large range. Thus, fundamental elastoplastic behaviors, such as the yield stress and work hardening properties (functions), cannot be uniquely determined from the force-displacement curves of indentation analyses (including both plural sharp indentation and deep spherical indentation). Explicit algorithms of deriving the mystical materials are established, and we qualitatively correlate the sharp and spherical indentation analyses through the use of critical strain. The theoretical study in this paper addresses important questions of the application range, limitations, and uniqueness of the indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material constitutive properties.

Crack Propagation Experiments on Flip Chip Solder Joints

1998 ◽  
Vol 515 ◽  
Author(s):  
S. Wiese ◽  
F. Feustel ◽  
S. Rzepka ◽  
E. Meusel
Keyword(s):  
Crack Propagation ◽  
Flip Chip ◽  
Solder Joints ◽  
Shear Loading ◽  
Displacement Curve ◽  
In Situ Experiments ◽  
Propagation Experiment ◽  
Crack Propagation Experiment ◽  
Number Of Cycles ◽  
Force Displacement

ABSTRACTThe paper presents crack propagation experiments on real flip chip specimens applied to reversible shear loading. Two specially designed micro testers will be introduced. The first tester provides very precise measurements of the force displacement hysteresis. The achieved resolutions have been I mN for force and 20 nm for displacement. The second micro tester works similar to the first one, but is designed for in-situ experiments inside the SEM. Since it needs to be very small in size it reaches only resolutions of 10 mN and 100nm, which is sufficient to achieve equivalence to the first tester. A cyclic triangular strain wave is used as load profile for the crack propagation experiment. The experiment was done with both machines applying equivalent specimens and load. The force displacement curve was recorded using the first micro mechanical tester. From those hysteresis, the force amplitude has been determined for every cycle. All force amplitudes are plotted versus the number of cycles in order to quantify the crack length. With the second tester, images were taken at every 10th … 100th cycle in order to locate the crack propagation. Finally both results have been linked together for a combined quatitive and spatial description of the crack propagation in flip chip solder joints.

Simulation of Unstable Fault Slip in Granite Using a Bonded-particle Model

2002 ◽  
pp. 221-245 ◽  
Author(s):  
James F. Hazzard ◽  
David S. Collins ◽  
William S. Pettitt ◽  
R. Paul Young
Keyword(s):  
Fault Slip ◽  
Particle Model ◽  
Bonded Particle Model

scholarly journals Comparison of waveform-derived corneal stiffness and stress-strain extensometry-derived corneal stiffness using different cross-linking irradiances: an experimental study with air-puff applanation of ex vivo porcine eyes

2020 ◽  
Vol 258 (10) ◽  
pp. 2173-2184 ◽  
Author(s):  
Robert Herber ◽  
Mathew Francis ◽  
Eberhard Spoerl ◽  
Lutz E. Pillunat ◽  
Frederik Raiskup ◽  
...  
Keyword(s):  
Experimental Study ◽  
Ex Vivo ◽  
Cross Linking ◽  
Displacement Curve ◽  
Stress Strain ◽  
Strain Measurements ◽  
Deflection Amplitude ◽  
Force Displacement ◽  
Stiffening Effect ◽  
Porcine Eyes

Abstract Purpose To assess corneal stiffening of standard (S-CXL) and accelerated (A-CXL) cross-linking protocols by dynamic corneal response parameters and corneal bending stiffness (Kc[mean/linear]) derived from Corvis (CVS) Scheimpflug-based tonometry. These investigations were validated by corneal tensile stiffness (K[ts]), derived from stress-strain extensometry in ex vivo porcine eyes. Methods Seventy-two fresh-enucleated and de-epithelized porcine eyes were soaked in 0.1% riboflavin solution including 10% dextran for 10 min. The eyes were separated into four groups: controls (n = 18), S-CXL (intensity in mW/cm2*time in min; 3*30) (n = 18), A-CXL (9*10) (n = 18), and A-CXL (18*5) (n = 18), respectively. CXL was performed using CCL Vario. CVS measurements were performed on all eyes. Subsequently, corneal strips were extracted by a double-bladed scalpel and used for stress-strain measurements. K[ts] was calculated from a force-displacement curve. Mean corneal stiffness (Kc[mean]) and constant corneal stiffness (Kc[linear]) were calculated from raw CVS data. Results In CVS, biomechanical effects of cross-linking were shown to have a significantly decreased deflection amplitude as well as integrated radius, an increased IOP, and SP A1 (P < 0.05). Kc[mean]/Kc[linear] were significantly increased after CXL (P < 0.05). In the range from 2 to 6% strain, K[ts] was significantly higher in S-CXL (3*30) compared to A-CXL (9*10), A-CXL (18*5), and controls (P < 0.05). At 8% to 10% strain, all protocols induced a higher stiffness than controls (P < 0.05). Conclusion Several CVS parameters and Kc[mean] as well as Kc[linear] verify corneal stiffening effect after CXL on porcine eyes. S-CXL seems to have a higher tendency of stiffening than A-CXL protocols have, which was demonstrated by Scheimpflug-based tonometry and stress-strain extensometry.

A Reexamination of the Extraction of Material Properties Using Nanoindentation

2008 ◽  
Author(s):  
B. Poon ◽  
D. Rittel ◽  
G. Ravichandran
Keyword(s):  
Contact Area ◽  
Material Properties ◽  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Nanoindentation Test ◽  
Displacement Curve ◽  
Elastic Solids ◽  
Ratio Effect ◽  
Elastic Plastic ◽  
Tip Radius

The paper reexamines the extraction of material properties using nanoindentation for linearly elastic and elastic-plastic materials. The paper considers indentation performed using a rigid conical indenter, as follows. Linearly elastic solids: The reduction of nanoindentation test data of elastic solids is usually processed using Sneddon’s relation [1], which assumes a linearly elastic infinite half space and an infinitely sharp indenter tip. These assumptions are violated in practical indentation experiments. Since most of the research on the extraction of material properties relies heavily on numerical simulations, we used them to investigate the specimen dimensions required for it to qualify as an infinite body, and the indentation conditions for finite tip radius effect to be negligible. The outcome of this part is firstly, the definition of a “converged” 2D geometry so that additional magnification of the numerical model does not influence the load-displacement curve, and secondly, an explicit relationship between the measured load and displacement that takes into account the finite tip radius. Elastic-plastic solids: Here, the main data reduction technique was proposed by Pharr et al. [2], assuming elastic unloading of a plastic nanoindentation. We investigated the effects of finite tip radius in elastic-plastic indentations and found that the accuracy of the prediction is currently limited by the accurate determination of the projected contact area. This point will be discussed and a new experimental technique to measure the projected contact area will be proposed. The Poisson’s ratio effect in elastic-plastic indentations is found to be different from the linearly elastic case. This leads to the discussion on the applicability of the correction factor (for Poisson’s ratio effect) derived in linear elastic indentations, on elastic-plastic indentations. Finally, a technique to obtain an upper bound estimate of the yield stress for the indented elastic-plastic material (which is an exact estimation for non-hardening materials), will be presented.

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