scholarly journals Fracture of Elastomeric Materials by Crosslink Failure

2018 ◽  
Vol 85 (8) ◽  
Author(s):  
Yunwei Mao ◽  
Lallit Anand
Keyword(s):  
Free Energy ◽  
Failure Mode ◽  
Chain Scission ◽  
Progressive Damage ◽  
Central Feature ◽  
Single Chain ◽  
Elastomeric Material ◽  
Damage And Fracture ◽  
Elastomeric Materials ◽  
Covalent Crosslinks

If an elastomeric material is subjected to sufficiently large deformations, it eventually fractures. There are two typical micromechanisms of failure in such materials: chain scission and crosslink failure. The chain scission failure mode is mainly observed in polymers with strong covalent crosslinks, while the crosslink failure mode is observed in polymers with weak crosslinks. In two recent papers, we have proposed a theory for progressive damage and rupture of polymers with strong covalent crosslinks. In this paper, we extend our previous framework and formulate a theory for modeling failure of elastomeric materials with weak crosslinks. We first introduce a model for the deformation of a single chain with weak crosslinks at each of its two ends using statistical mechanics arguments, and then upscale the model from a single chain to the continuum level for a polymer network. Finally, we introduce a damage variable to describe the progressive damage and failure of polymer networks. A central feature of our theory is the recognition that the free energy of elastomers is not entirely entropic in nature; there is also an energetic contribution from the deformation of the backbone bonds in a chain and/or the crosslinks. For polymers with weak crosslinks, this energetic contribution is mainly from the deformation of the crosslinks. It is this energetic part of the free energy which is the driving force for progressive damage and fracture of elastomeric materials. Moreover, we show that for elastomeric materials in which fracture occurs by crosslink stretching and scission, the classical Lake–Thomas scaling—that the toughness Gc of an elastomeric material is proportional to 1/G0, with G0=NkBϑ the ground-state shear modulus of the material—does not hold. A new scaling is proposed, and some important consequences of this scaling are remarked upon.

Finite elasticity of elastomeric materials

2020 ◽  
pp. 637-654
Author(s):  
Lallit Anand ◽  
Sanjay Govindjee
Keyword(s):  
Free Energy ◽  
Constitutive Relations ◽  
Finite Elasticity ◽  
Energy Functions ◽  
Slightly Compressible ◽  
Elastomeric Materials ◽  
Volumetric Response

This chapter presents several technologically important constitutive relations for elastomeric materials. In particular, the Neo-Hookean, Mooney-Rivlin, Ogden, Arruda-Boyce, and Gent free energy functions are discussed in the context of incompressible response. Extensions to the slightly compressible case are also detailed, this includes a presentation of a number of possible volumetric response relations and their properties.

Gun Liner Emplacement Using Elastomeric Materials

2010 ◽  
Author(s):  
Robert H. Carter ◽  
David M. Gray
Keyword(s):  
Refractory Metal ◽  
Outer Diameter ◽  
Elastomeric Material ◽  
Elastomeric Materials ◽  
Residual Internal Stress ◽  
Inner Diameter ◽  
Bond Strengths ◽  
Frictional Bond ◽  
Load Frame ◽  
Metal Liner

The development of a process to emplace a refractory metal liner inside a gun tube is described. The process consists of filling the liner with an elastomeric material and then slipping this arrangement into the gun tube whose inner diameter is close to the outer diameter of the liner. The ends of the liner are plugged with plastic disks and pressure is applied to the elastomeric material by a load frame. This pressure can produce a residual internal stress within the steel gun tube that produces a frictional bond between the liner and gun tube. Initial efforts have resulted in bond strengths over 3 ksi (21 MPa). In addition, by tailoring the degree of lubrication between the elastomeric material and the liner, a graded autofrettage can be produced in the steel gun tube.

scholarly journals Hans Adolf Krebs, 25 August 1900 - 22 November 1981

1984 ◽  
Vol 30 ◽  
pp. 351-385 ◽  
Keyword(s):  
Free Energy ◽  
Krebs Cycle ◽  
Intermediary Metabolism ◽  
Central Feature ◽  
Chemical Substances ◽  
Otto Warburg ◽  
Biographical Memoir

Hans Adolf Krebs died in Oxford on 22 November 1981, at the age of 81 and only two weeks after leaving his beloved laboratory for treatment, in hospital, of what he believed was a trivial gastric upset. With his death ended an era of research into intermediary metabolism and its regulation, of which Krebs had been a pioneer, that he had brought to fruition, and to the central feature of which—‘the Krebs Cycle’—his name will surely always be attached. In his Biographical Memoir [111] of his own teacher, Otto Warburg, Hans quoted from the preface of G. N. Lewis & M. Randall’s (1923) Thermodynamics and the free energy of chemical substances . There, the edifice of science was likened to a cathedral built by the efforts of many workers but of only a few architects: Hans believed that Warburg was one of those few. Indubitably, Hans Krebs was another.

Optimizing Ceramic Matrix Composite Interlaminar Fracture Toughness (Mode I) Wedge Test

2016 ◽  
Author(s):  
Frank Abdi ◽  
Saber DorMohammadi ◽  
Jalees Ahmad ◽  
Cody Godines ◽  
Gregory N. Morscher ◽  
...  
Keyword(s):  
Finite Element ◽  
Fracture Energy ◽  
Crack Growth ◽  
Failure Mode ◽  
Mixed Mode ◽  
Crack Growth Resistance ◽  
Mode I ◽  
Multi Scale ◽  
Fracture Evolution ◽  
Damage And Fracture

ASTM test standards for CMC’s Crack Growth Resistance (CGR) may exhibit a zig-zag (wavy) crack path pattern, and fiber bridging. The experimental parameters that may contribute to the difficulty can be summarized as: specimen width and thickness, interface coating thickness, mixed mode failure evolution, and interlaminar defects. Modes I crack growth resistances, GI were analytically determined at ambient temperature using wedge test, a modified double cantilever beam (DCB). Several Finite Element (FE) based Multi-scale modeling potential techniques were investigated: a) Multi-scale progressive failure analysis (MS-PFA); b) Virtual Crack Closure Technique (VCCT). Advantages and disadvantages of each were identified. The final modeling algorithm recommended was an integrated damage and fracture evolution methodology using combined MS-PFA and VCCT. The material tested in this study was a slurry-cast melt-infiltrated SiC/SiC composite with Tyranno ZMI fibers (Ube Industries, Kyoto, Japan) and a BN interphase. The fiber architecture consisted of eight plies of balanced 2-D woven five-harness satin. The total fiber volume fraction was about 30% with half of the fibers in the 0° direction and half in the 90° direction. All specimens had a nominal thickness of 4 mm. An alumina wedge with 18° head angle (2α) was used. In this method, a splitting force is created by inserting a vertically-moving wedge in a notch causing the arms to separate and forcing an interlaminar crack at the sharpest end of the notch The MS-PFA numerical model predicted the damage and fracture evolution and utilized the GENOA UMAT (User Material Subroutine) for Damage and FEM (Finite Element Model) stress intensity and LEFM (Linear elastic Fracture Model), Cohesive Model for Fracture. The analysis results (Fracture energy vs. crack length, Fracture energy vs. load, Fracture energy vs. crack opening displacement) matched the Mode I coupon tests and revealed the following key findings. Mode I-Wedge specimen exhibits: 1) failure mode is due to interlaminar tension (ILT) only in the interface section and a zig-zag pattern observed; 2) VCCT crack growth resistance is well matched to the test data; and 3) failure mode is a mixed mode behavior of Interlaminar tension (ILT) to interlaminar shear (ILS). The final Wedge test specimen configuration optimization includes the sensitivity of design parameters to CGR: a) wedge contact coefficient of friction; b) lever arms thickness, and c) inclined head angle, distance between the initial crack and wedge tip.

scholarly journals Excellent Stability in Water of Single-Chain Nanoparticles against Chain Scission by Sonication

2018 ◽  
Vol 39 (6) ◽  
pp. 1700675 ◽  
Author(s):  
Marina González-Burgos ◽  
Edurne González ◽  
José A. Pomposo
Keyword(s):  
Chain Scission ◽  
Single Chain ◽  
Excellent Stability

Progressive damage and fracture of laminated glass beams

2010 ◽  
Vol 24 (4) ◽  
pp. 577-584 ◽  
Author(s):  
Luigi Biolzi ◽  
Sara Cattaneo ◽  
Gianpaolo Rosati
Keyword(s):  
Laminated Glass ◽  
Progressive Damage ◽  
Damage And Fracture

scholarly journals Simulation-Based Engineering of Humanized Scfv Antibody against hTNF-α

2020 ◽  
Vol 26 (1) ◽  
pp. 45-51
Author(s):  
Maryam Hamzeh-Mivehroud ◽  
Ayda Baghal Safarizad ◽  
Siavoush Dastmalchi
Keyword(s):  
Free Energy ◽  
Inflammatory Diseases ◽  
Binding Free Energy ◽  
Scfv Antibody ◽  
Single Chain ◽  
Necrosis Factor Alpha ◽  
Tnf Α ◽  
Factor Alpha ◽  
Dynamics Calculation ◽  
Mutant Forms

Background : Uncontrolled activity of tumor necrosis factor alpha (TNF-α) as pro-inflammatory cytokine has been linked with pathogenesis of autoimmune/inflammatory diseases. Therefore, modulating of TNF-α associated biological pathways is a promising strategy for alleviating of such diseases. In view of this, the use of antibody fragments such as single-chain variable fragments (scFv) in therapeutic applications has been gained much attention in terms of pharmacokinetic as well as production and therapeutic costs. Methods: In the current investigation, the previously designed and humanized hD2 antibody was modeled and docked onto the TNF-α structure. The binding free energy was predicted for the complex of hD2-TNF-α using molecular dynamics calculation followed by per-residue energy decomposition for residues of hD2. In addition in silico mutations of important amino acids at the binding site of enzyme were performed and the binding free energy was calculated for mutant forms of scFv in complex with TNF-α. Results: The analyses of the results proposed Y27F mutation in heavy chain CDR1 of hD2 scFv antibody may be considered as a promising substitution. Conclusion: The results may be used for designing new anti-TNF-α antibody with improved activity.

scholarly journals Enhanced polymer mechanical degradation through mechanochemically unveiled lactonization

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Yangju Lin ◽  
Tatiana B. Kouznetsova ◽  
Chia-Chih Chang ◽  
Stephen L. Craig
Keyword(s):  
Single Molecule ◽  
Ring Opening ◽  
Stress Transfer ◽  
Polymeric Materials ◽  
Chain Scission ◽  
Mechanical Degradation ◽  
Single Chain ◽  
Single Molecule Force Spectroscopy ◽  
Polymer Backbone ◽  
Single Polymer Chain

Abstract The mechanical degradation of polymers is typically limited to a single chain scission per triggering chain stretching event, and the loss of stress transfer that results from the scission limits the extent of degradation that can be achieved. Here, we report that the mechanically triggered ring-opening of a [4.2.0]bicyclooctene (BCOE) mechanophore sets up a delayed, force-free cascade lactonization that results in chain scission. Delayed chain scission allows many eventual scission events to be initiated within a single polymer chain. Ultrasonication of a 120 kDa BCOE copolymer mechanically remodels the polymer backbone, and subsequent lactonization slowly (~days) degrades the molecular weight to 4.4 kDa, > 10× smaller than control polymers in which lactonization is blocked. The force-coupled kinetics of ring-opening are probed by single molecule force spectroscopy, and mechanical degradation in the bulk is demonstrated. Delayed scission offers a strategy to enhanced mechanical degradation and programmed obsolescence in structural polymeric materials.

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