scholarly journals Stick-Slip Dynamics in Fiber Bundle Models with Variable Stiffness and Slip Number

2021 ◽  
Vol 9 ◽  
Author(s):  
Zoltán Halász ◽  
Imre Kállai ◽  
Ferenc Kun
Keyword(s):  
Fiber Bundle ◽  
Mechanical Response ◽  
Permanent Deformation ◽  
Variable Stiffness ◽  
Plastic Behavior ◽  
Stick Slip ◽  
Maximum Deformation ◽  
Local Material ◽  
Macro Scale ◽  
Analytic Expressions

We present an extension of fiber bundle models to describe the mechanical response of systems which undergo a sequence of stick-slip cycles taking into account the changing stiffness and the fluctuating number of slip events of local material elements. After completing all stick-slip cycles allowed, fibers can either ultimately break or can keep their final stiffness leading to softening or hardening of the bundle, respectively. Under the assumption of global load sharing we derive analytic expressions for the constitutive response of the bundle with both quenched and annealed disorder of the failure thresholds where consecutive slips occur. Our calculations revealed that on the macro-scale the bundle exhibits a plastic behavior, which gets more pronounced when fibers undergo a higher number of stick-slip cycles with a gradually degrading stiffness. Releasing the load a permanent deformation remains, which increases monotonically for hardening bundles with the maximum deformation reached before unloading starts, however, in the softening case a non-monotonous behavior is obtained. We found that the macroscopic response of hardening bundles is more sensitive to fluctuations of the number of stick-slip cycles allowed than of the softening ones. The quenched and annealed disorder of failure thresholds gives rise to the same qualitative macro-scale behavior, however, the plastic response is found to be stronger in the annealed case.

Modeling and Simulation of the Mechanical Response of Martensitic Shape Memory Alloys

2011 ◽  
Author(s):  
Wael Zaki
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Evolution Equations ◽  
Mechanical Response ◽  
Permanent Deformation ◽  
Strain Tensor ◽  
Crystalline Lattice ◽  
Tangent Stiffness Matrix ◽  
Maximum Deformation ◽  
Martensite Reorientation

The process of detwinning of martensite in shape memory alloys involves the deformation of the crystalline lattice of the material by twin boundary motion. The amount of maximum deformation that can be achieved this way is known to saturate at some point, beyond which further loading will eventually lead to permanent deformation of the material. We present an algorithm for the simulation of martensite reorientation in shape memory materials subjected to multiaxial loading that may exceed the saturation threshold. If the applied load is still nonproportional beyond this threshold, the reorientation strain tensor may continue to evolve while its magnitude remains constant. Such evolution can be simulated using a simple strain-based criterion. The complete process of martensite reorientation can thus be modeled using a set of two yield functions, the first of which is stress-based and governs the detwinning process prior to saturation, and the second is strain-based and governs the reorientation of variants at maximum equivalent reorientation strain. The model is implemented in a numerical analysis code. For this purpose, the evolution equations are solved implicitly using a Newton-Raphson scheme and the tangent stiffness matrix of the material is determined using a combination of analytical and numerical techniques.

Interface Engineering of CNT/Polymer Nanocomposites With Tunable Damping Properties

2018 ◽  
Author(s):  
Michela Talò ◽  
Giulia Lanzara ◽  
Maryam Karimzadeh ◽  
Walter Lacarbonara
Keyword(s):  
Load Transfer ◽  
Mechanical Response ◽  
Material Design ◽  
Tensile Tests ◽  
Nanocomposite Films ◽  
Damping Capacity ◽  
Interfacial Region ◽  
Material Damping ◽  
Stick Slip ◽  
Multi Walled Carbon Nanotubes

In this work, the arising of stick-slip dissipation as well as the global mechanical response of carbon nanotube (CNT) nanocomposite films are tailored by exploiting a three-phase nanocomposite. The three phases are represented by the CNTs, a polymer coating localized on the CNTs surface and a hosting matrix. In particular, a polystyrene (PS) layer coats multi-walled carbon nanotubes (MWNTs) that are randomly dispersed in a polyimide (PI) matrix. The coating phase is strongly bonded to the CNTs outer sidewalls ensuring the effectiveness of the load transfer mechanism and reducing the material damping capacity. The coating phase can be thermally-activated to modify, and in particular, decrease the CNT-matrix interfacial shear strength (ISS) thus facilitating the stick-slip onset in the nanocomposite. The ISS decrease finds its roots in a partial degradation of the coating phase and, in particular, in the formation of voids. By weakening the CNT/polymer interfacial region, a significant enhancement in the material damping capacity is observed. An extensive experimental campaign consisting of monotonic and cyclic tensile tests proved the effectiveness of this novel multi-phase material design.

scholarly journals Computation of history-dependent mechanical damage of axonal fiber tracts in the brain: towards tracking sub-concussive and occupational damage to the brain

2018 ◽  
Author(s):  
Jesse I. Gerber ◽  
Harsha T. Garimella ◽  
Reuben H. Kraft
Keyword(s):  
Fiber Bundle ◽  
Brain Injuries ◽  
Mechanical Response ◽  
Head Injuries ◽  
Mechanical Damage ◽  
Tissue Level ◽  
Internal Damage ◽  
Damage Models ◽  
Axonal Fiber ◽  
The Brain

ABSTRACTFinite element models are frequently used to simulate traumatic brain injuries. However, current models are unable to capture the progressive damage caused by repeated head trauma. In this work, we propose a method for computing the history-dependent mechanical damage of axonal fiber bundle tracts in the brain. Through the introduction of multiple damage models, we provide the ability to link consecutive head impact simulations, so that potential injury to the brain can be tracked over time. In addition, internal damage variables are used to degrade the mechanical response of each axonal fiber bundle element. As a result, the stiffness of the aggregate tissue decreases as damage evolves. To counteract this degenerative process, we have also introduced a preliminary healing model that reverses the accumulated damage, based on a user-specified healing duration. Using two detailed examples, we demonstrate that damage produces a significant decrease in fiber stress, which ultimately propagates to the tissue level and produces a measurable decrease in overall stiffness. These results suggest that damage modeling has the potential to enhance current brain simulation techniques and lead to new insights, especially in the study of repetitive head injuries.

scholarly journals COMPRESSION OF ECAPED TITANIUM MICRO-PILLARS FOR TWO PRINCIPAL ORIENTATIONS

2020 ◽  
Vol 27 ◽  
pp. 1-5
Author(s):  
David Vokoun ◽  
Jan Maňák ◽  
Karel Tesař ◽  
Stanislav Habr
Keyword(s):  
Room Temperature ◽  
Focused Ion Beam ◽  
Mechanical Response ◽  
Thermomechanical Processing ◽  
Ion Beam ◽  
Orientation Dependence ◽  
Material Strength ◽  
Angular Pressing ◽  
Macro Scale ◽  
Micro Pillars

The thermomechanical processing by equal-channel angular pressing (ECAP) is used for certain metals and alloys in order to make their structure fine and to increase material strength. In the previous study done at our institute, grade 2 titanium was successfully processed using four consecutive route A passes via a 90 ° ECAP die with high backpressure at room temperature. Orientation dependence of compressive and tensile loading of ECAPed titanium samples was demonstrated at macro-scale. However, scarce attention has been paid so far to the mechanical behavior of ECAPed titanium samples at micro-scale. In the present study, compression experiments on titanium micropillars, fabricated using focused ion beam, are carried out for two main directions in respect to preceding ECAP pressing (insert and extrusion directions). The purpose of this study is to discuss the orientation dependence of mechanical response during compression of the as-ECAPed titanium micro-pillars.

scholarly journals Anisotropic Mechanical Response and Strain Localization of a Metallic Glassy-Fiber-Reinforced Polyethylene Terephthalate Fabric

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5619
Author(s):  
Jie Li ◽  
Bo Huang ◽  
Jun Shen ◽  
Jun Yi ◽  
Yandong Jia ◽  
...  
Keyword(s):  
Polyethylene Terephthalate ◽  
Strain Localization ◽  
Fiber Bundle ◽  
Mechanical Response ◽  
Materials Science ◽  
Image Correlation ◽  
Woven Fabric ◽  
Dominant Factor ◽  
Fracture Mechanisms ◽  
Young’S Moduli

Optimizing the mechanical properties of composites through microstructural design has been a long-standing issue in materials science. In this study, we reinforced a typical polymer, i.e., polyethylene-terephthalate-woven fabric, with a type of Fe-based metallic glassy fiber (MGF) with an extremely large Young’s moduli. The MGF-reinforced fabrics, with three different fiber bundle orientations (0°, 45°, and 90°), were investigated by in situ electron-microscopy mechanical testing techniques in conjunction with a digital image correlation (DIC) technique. The fabrics exhibited a pronounced anisotropic mechanical response, and the associated characteristics were verified to depend on the fiber bundle orientation relative to the external load. Furthermore, localized strains near the intersections of the fiber bundles were found to be much higher than the global strain. It is confirmed that the restriction from warp to weft is the dominant factor influencing strain localization during deformation. Our results are enlightening for understanding the fracture mechanisms of composites.

Computational Design and Analysis of Nitinol-Based Arch Wedge Support

2018 ◽  
Author(s):  
Tyler Stranburg ◽  
Yucheng Liu ◽  
Harish Chander ◽  
Adam Knight
Keyword(s):  
Boundary Conditions ◽  
Mechanical Response ◽  
Computational Study ◽  
Experimental Testing ◽  
Permanent Deformation ◽  
Computational Design ◽  
Element Analysis ◽  
Human Movements ◽  
First Time ◽  
Human Motions

A nitinol-based arch wedge support (AWS) was designed using computational approach. Finite element analysis (FEA) was performed to on this design to assess the influence of loading, boundary conditions, and thickness on the mechanical response of the computer-aid design (CAD) model. Five loading conditions caused by different human movements, two boundary conditions, and three thicknesses are involved in this computational study. FEA results showed that the presented AWS design can resist forces caused by different human motions without generating any permanent deformation. The study features the first time to design and evaluate a thin-walled nitinol AWS model. The results of this study form the background of prototyping and experimental testing of the design in the next phase.

Thin Film Fracture During Nanoindentation of Hard Film – Soft Substrate Systems

2001 ◽  
Vol 695 ◽  
Author(s):  
M. Pang ◽  
K.D. Weaver ◽  
D.F. Bahr
Keyword(s):  
Mechanical Response ◽  
Film Formation ◽  
Permanent Deformation ◽  
Dislocation Nucleation ◽  
Titanium Oxides ◽  
Soft Substrate ◽  
Aluminum Oxides ◽  
Anodic Titanium Oxide ◽  
Formation Conditions ◽  
Film Cracking

ABSTRACTNanoindentation testing of hard film – soft substrate systems can exhibit permanent deformation prior to a yield excursion, indicating that the occurrence of this sudden discontinuity is predominantly controlled by the hard film cracking rather than dislocation nucleation and multiplication. In a previous paper, a model was developed to predict the mechanical response prior to hard film fracture. In the current study a this model, which superimposes large deflection of the hard film and plastic deformation of the substrate the model, is further refined by testing a variety of materials with different film formation conditions. The tested materials include anodic titanium oxide on titanium, thermal aluminum oxide on aluminum and sputtered tungsten films on aluminum. The film fracture strength of titanium oxides on titanium is estimated as 15 GPa and that of aluminum oxides on aluminum is around 10 GPa. In the case of vacuum sputtered tungsten film on aluminum, the tungsten layer is likely plastically deformed. The strain at film fracture is roughly estimated to be 3.4%.

Characteristics of Dynamic Loading Obtained From Braced Piping Support Under Sinusoidal Shaking Condition

2020 ◽  
Author(s):  
Ryuya Shimazu ◽  
Ichiro Tamura ◽  
Shinichi Matsuura ◽  
Michiya Sakai ◽  
Yohei Ono
Keyword(s):  
Time History ◽  
Maximum Force ◽  
Plastic Behavior ◽  
Deformation Diagram ◽  
Restoring Force ◽  
Maximum Deformation ◽  
Elastic Plastic ◽  
Vibration Tests ◽  
Input Wave

Abstract Loads applied to structures by means of vibration can be classified into load-controlled and displacement-controlled loads. The realistic elastic-plastic behavior of structures subjected to seismic loads is not fully understood, and the classification of the load applied to structures by means of earthquakes is unclear. The failure mode differs depending on the load classification, and thus clarifying the classification of the load applied to the structure is useful for designing the structure. This study clarified the realistic load classification of structures under an elastic-plastic response. Vibration tests were conducted using sinusoidal waves as inputs, and the elastic-plastic behavior of the piping supports undergoing buckling or fatigue failure was obtained. The maximum restoring force and the maximum deformation relationship were obtained from the envelope of the time history data of the test results. In addition, it was shown that the classification of the load could be determined from the maximum force-deformation diagram, even in cases involving buckling and fatigue. In the maximum force-deformation diagram, when the change in the ratio of dynamic restoring force to static restoring force is small, a load-controlled load is applied to the structure because the restoring force of the structure follows the change in the input wave. By contrast, when the change in the ratio of dynamic response displacement to static displacement is small, a displacement-controlled load is applied to the structure because the response displacement of the structure follows the change in the input wave.

scholarly journals Dependence of the permanent deformation of red blood cell membranes on spectrin dimer-tetramer equilibrium: implication for permanent membrane deformation of irreversibly sickled cells

Blood ◽  
1993 ◽  
Vol 81 (2) ◽  
pp. 522-528 ◽  
Author(s):  
SC Liu ◽  
LH Derick ◽  
J Palek
Keyword(s):  
Temperature Dependence ◽  
Permanent Deformation ◽  
Membrane Skeleton ◽  
Irreversible Deformation ◽  
Cell Deformation ◽  
Plastic Behavior ◽  
Exact Nature ◽  
Skeletal Rearrangement ◽  
Prolonged Incubation

Abstract Red blood cells (RBCs) in sickle cell anemia, transformed into a sickled shape by prolonged deoxygenation, or normal RBCs deformed by a prolonged micropipette aspiration become permanently stabilized in their abnormal shape. This semisolid plastic behavior is thought to involve an irreversible reorganization of the membrane skeleton, but the exact nature of this skeletal rearrangement is not known. In this study, we first asked whether the irreversible deformation is associated with a permanent stretching of the skeletal network, and then whether it is due to a rearrangement of skeletal components involving a disruption of pre-existing protein associations and the subsequent reassociation of new protein contacts. Having found no ultrastructural evidence of stretching of the skeletal lattice in membranes derived from permanently deformed RBCs, we addressed the possibility of reorganization of the proteins of the membrane skeleton. We examined the temperature dependence of irreversible cell deformation to see if it correlated with the known temperature dependence of spectrin tetramers to dimer dissociation and reassociation. Testing the shape irreversibility of both deoxygenated reversibly sickled cells and Nucleopore-aspirated normal cells, we found that both types of cells became permanently deformed when the prolonged incubation of applied force or deoxygenation was performed at 37 degrees C, the temperature at which spectrin tetramers were free to dissociate and reassociate. In contrast, both types of cells were able to regain their original discocytic shape if the prolonged incubation was performed at the lower temperature: at less than 13 degrees C instead of 37 degrees C. Furthermore, normal RBCs were incubated with inosine and pyruvate to elevate intracellular 2,3-diphosphoglycerate, the polyanion shown to destabilize spectrin-actin-protein 4.1 association. This did not result in a promotion of irreversible deformation of these cells. We conclude that the irreversible cell deformation observed at physiologic temperature is associated with a skeletal rearrangement through dissociation of spectrin tetramers to dimers and a subsequent reassociation of dimers to tetramers in the new (deformed) configuration. These findings may explain a permanent stabilization of irreversibly sickled cells in their abnormal shape in vivo.

scholarly journals Fiber bundle model with stick-slip dynamics

2009 ◽  
Vol 80 (2) ◽  
Author(s):  
Zoltán Halász ◽  
Ferenc Kun
Keyword(s):  
Fiber Bundle ◽  
Stick Slip ◽  
Fiber Bundle Model
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