Geometry Method for Localization Analysis in Gradient-Dependent J2 Plasticity

2006 ◽  
Vol 73 (6) ◽  
pp. 1026-1030 ◽  
Author(s):  
G. Etse ◽  
S. M. Vrech
Keyword(s):  
Failure Modes ◽  
Characteristic Length ◽  
Critical Value ◽  
Elastoplastic Model ◽  
Geometrical Method ◽  
Localization Analysis ◽  
Classical Plasticity ◽  
Discontinuous Bifurcation ◽  
Geometry Method ◽  
Localization Condition

In this work the geometrical method for the assessment of discontinuous bifurcation conditions is extended to encompass gradient-dependent plasticity. To this end, the gradient-dependent localization condition is cast in the form of an elliptical envelope condition in the coordinates of Mohr. The results in this work demonstrate the capability of thermodynamically consistent gradient-dependent elastoplastic model formulations to suppress the localized failure modes of the classical plasticity that take place when the hardening/softening modulus H¯ equals the critical value for localization H¯c, provided the characteristic length l remains positive.

scholarly journals Cracking Behaviors and Mechanical Properties of Rock-Like Specimens with Two Unparallel Flaws under Conventional Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Chenghua Xu ◽  
Liuyang Li ◽  
Yong Liu
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Critical Value ◽  
Tensile Failure ◽  
Rock Bridge ◽  
Bridge Length

Flaws existing in rock masses are generally unparallel and under three-dimensional stress; however, the mechanical and cracking behaviors of the specimens with two unparallel flaws under triaxial compression have been rarely studied. Therefore, this study conducted comprehensive research on the cracking and coalescence behavior and mechanical properties of specimens with two unparallel flaws under triaxial compression. Triaxial compressive tests were conducted under different confining pressures on rock-like specimens with two preexisting flaws but varying flaw geometries (with respect to the inclination angle of the two unparallel flaws, rock bridge length, and rock bridge inclination angle). Six crack types and eleven coalescence types in the bridge region were observed, and three types of failure modes (tensile failure, shear failure, and tensile-shear failure) were observed in experiments. Test results show that bridge length and bridge inclination angle have an effect on the coalescence pattern, but the influence of bridge inclination angle is larger than that of the bridge length. When the confining pressure is low, coalescence patterns and failure modes of the specimens are greatly affected by flaw geometry, but when confining pressure rose to a certain level, the influence of confining pressure is larger than the effect of flaw geometry. The peak strength of the specimens is affected by flaw geometry and confining pressure. There is a critical value for the bridge length. If the bridge length is larger than the critical value, peak strengths of the samples almost keep constant as the bridge length increases. In addition, as the bridge inclination angle increases, there is an increase in the probability of tensile cracks occurring, and with an increase in the confining pressure, the probability of the occurrence of shear cracks increases.

Vacuum solutions for a twisted scalar field

1978 ◽  
Vol 363 (1715) ◽  
pp. 581-596 ◽  
Keyword(s):  
Scalar Field ◽  
Ground State ◽  
Characteristic Length ◽  
Scalar Fields ◽  
Finite Energy ◽  
Critical Value ◽  
Dimensional Model ◽  
Translational Invariance ◽  
Spontaneous Breakdown ◽  
Vacuum Solutions

The properties of the ground state of a classical self-interacting twisted scalar field on a two-dimensional Einstein cylinder are discussed. In parti­cular there is a spontaneous breakdown of the spatial translational invariance of the twisted ground state as a characteristic length increases across a critical value. Similar properties are shown to hold in a four­-dimensional model. Finally, it is shown that there exist four-dimensional models which do not have any finite-energy twisted scalar fields.

Failure of Composites with Discontinuous Fabric Preform under Bending

2011 ◽  
Vol 462-463 ◽  
pp. 698-703
Author(s):  
Thanh Trung Do ◽  
Dong Joo Lee
Keyword(s):  
Bonding Strength ◽  
Failure Modes ◽  
Failure Mechanisms ◽  
Critical Value ◽  
Fiber Content ◽  
Interfacial Bonding ◽  
Failure Strength ◽  
Three Point Bending ◽  
Potential Strength ◽  
Interfacial Bonding Strength

During the fabric preform and/or mold closure processes of the resin transfer molded composites (RTMCs), the discontinuous fabric patterns such as wrinkling and overlapping can be occurred and influenced the failure strength. It is found that the composites with discontinuous fabric preform had two failure mechanisms as functions of fabric ply number and discontinuous fabric length under the three-point bending. First, the failure modes can be related to the bend strengths that were controlled by the interfacial bonding strength depending on the discontinuous fabric length. Second, the failures were controlled by the potential strength of fabric when the discontinuous length reached the critical value. Moreover, the experimentally measured results of the normal and discontinuous preform models under bending were compared to examine the safety conditions as functions of fiber content and other factors.

Recent Advances in Simulating Failure Evolution with the Material Point Method

2015 ◽  
Vol 784 ◽  
pp. 193-199
Author(s):  
Zhen Chen ◽  
Xiong Zhang
Keyword(s):  
Failure Modes ◽  
Computational Cost ◽  
Material Point Method ◽  
Material Point ◽  
Point Method ◽  
Damage Models ◽  
Recent Advances ◽  
Failure Evolution ◽  
Discontinuous Bifurcation ◽  
Multi Phase

To predict a complete process of failure evolution, discontinuous bifurcation analysis has been performed to link elastoplasticity and damage models with decohesion models. To simulate multi-phase interactions involving failure evolution, the Material Point Method (MPM) has been developed to discretize localized large deformations and the transition from continuous to discontinuous failure modes. In a recent study for the Sandia National Laboratories (SNL) challenge, the decohesion modeling is improved by making the failure mode adjustable and by replacing the critical normal and tangential decohesion strengths with the tensile and shear peak strengths, in order to predict the cracking path in a complex configuration with the least computational cost,. It is found that there is a transition between different failure modes along the cracking path, which depends on the stress distribution around the path due to the nonlocal nature of failure evolution. Representative examples will be used to demonstrate the recent advances in simulating failure evolution with the MPM.

The Ultimate Strength of Cylindrical Liquid Storage Tanks Under Earthquakes: Elasto-Plastic Dynamic Analysis With FSI of Buckling Failure Modes

2009 ◽  
Author(s):  
Akira Mikami ◽  
Yuji Sato ◽  
Akihito Otani ◽  
Kosuke Iwamoto ◽  
Toru Iijima
Keyword(s):  
Failure Modes ◽  
Fem Simulation ◽  
Plasticity Theory ◽  
Hydraulic Pressure ◽  
Storage Tanks ◽  
Buckling Modes ◽  
Liquid Storage ◽  
Classical Plasticity ◽  
Shear Buckling ◽  
Buckling Failure

The objective of this study is to simulate the shaking test of a condensate storage tank (CST). In this test, the typical failure mode was an elephant-foot bulge (EFB) or a shear buckling. It is difficult to reproduce such buckling modes. However, at last, an analytical model which describes those modes with enough accuracy was achieved. The comparison between simulation results and experiments is explained. Acoustic theory and classical plasticity theory were used in the FEM simulation. The phase and magnitude of the response acceleration and hydraulic pressure obtained from the FEM simulation are well corresponded to those from the experiments. In addition, asymmetrical distribution of maximum and minimum hydraulic pressure is described.

scholarly journals Near-critical 2D percolation with heavy-tailed impurities, forest fires and frozen percolation

2021 ◽  
Author(s):  
Jacob van den Berg ◽  
Pierre Nolin
Keyword(s):  
Forest Fires ◽  
Characteristic Length ◽  
Critical Time ◽  
Critical Value ◽  
Critical Percolation ◽  
Infinite Cluster ◽  
Physics Literature ◽  
Heavy Tailed ◽  
Frozen Percolation ◽  
The Impact

AbstractWe introduce a new percolation model on planar lattices. First, impurities (“holes”) are removed independently from the lattice. On the remaining part, we then consider site percolation with some parameter p close to the critical value $$p_c$$ p c . The mentioned impurities are not only microscopic, but allowed to be mesoscopic (“heavy-tailed”, in some sense). For technical reasons (the proofs of our results use quite precise bounds on critical exponents in Bernoulli percolation), our study focuses on the triangular lattice. We determine explicitly the range of parameters in the distribution of impurities for which the connectivity properties of percolation remain of the same order as without impurities, for distances below a certain characteristic length. This generalizes a celebrated result by Kesten for classical near-critical percolation (which can be viewed as critical percolation with single-site impurities). New challenges arise from the potentially large impurities. This generalization, which is also of independent interest, turns out to be crucial to study models of forest fires (or epidemics). In these models, all vertices are initially vacant, and then become occupied at rate 1. If an occupied vertex is hit by lightning, which occurs at a very small rate $$\zeta $$ ζ , its entire occupied cluster burns immediately, so that all its vertices become vacant. Our results for percolation with impurities are instrumental in analyzing the behavior of these forest fire models near and beyond the critical time (i.e. the time after which, in a forest without fires, an infinite cluster of trees emerges). In particular, we prove (so far, for the case when burnt trees do not recover) the existence of a sequence of “exceptional scales” (functions of $$\zeta $$ ζ ). For forests on boxes with such side lengths, the impact of fires does not vanish in the limit as $$\zeta \searrow 0$$ ζ ↘ 0 . This surprising behavior, related to the non-monotonicity of these processes, was not predicted in the physics literature.

Scanning Electron Microscopy in Hybrid Microelectronics

1976 ◽  
Vol 34 ◽  
pp. 456-457
Author(s):  
S. Khadpe ◽  
R. Faryniak
Keyword(s):  
Integrated Circuits ◽  
Thick Film ◽  
Integrated Circuit ◽  
Failure Modes ◽  
Three Dimensional ◽  
Circuit Components ◽  
Hybrid Microcircuit ◽  
Electrical Connections ◽  
Scanning Electron

The Scanning Electron Microscope (SEM) is an important tool in Thick Film Hybrid Microcircuits Manufacturing because of its large depth of focus and three dimensional capability. This paper discusses some of the important areas in which the SEM is used to monitor process control and component failure modes during the various stages of manufacture of a typical hybrid microcircuit.Figure 1 shows a thick film hybrid microcircuit used in a Motorola Paging Receiver. The circuit consists of thick film resistors and conductors screened and fired on a ceramic (aluminum oxide) substrate. Two integrated circuit dice are bonded to the conductors by means of conductive epoxy and electrical connections from each integrated circuit to the substrate are made by ultrasonically bonding 1 mil aluminum wires from the die pads to appropriate conductor pads on the substrate. In addition to the integrated circuits and the resistors, the circuit includes seven chip capacitors soldered onto the substrate. Some of the important considerations involved in the selection and reliability aspects of the hybrid circuit components are: (a) the quality of the substrate; (b) the surface structure of the thick film conductors; (c) the metallization characteristics of the integrated circuit; and (d) the quality of the wire bond interconnections.

Food-Evoked Changes in Humans

2010 ◽  
Vol 24 (1) ◽  
pp. 25-32 ◽  
Author(s):  
Peter Walla ◽  
Maria Richter ◽  
Stella Färber ◽  
Ulrich Leodolter ◽  
Herbert Bauer
Keyword(s):  
Food Intake ◽  
Startle Response ◽  
Brain Activity ◽  
Soft Drink ◽  
Ice Cream ◽  
Response Amplitude ◽  
Response Modulation ◽  
Motivational States ◽  
Localization Analysis ◽  
Study Participants

Two experiments investigate effects related to food intake in humans. In Experiment 1, we measured startle response modulation while study participants ate ice cream, yoghurt, and chocolate. Statistical analysis revealed that ice cream intake resulted in the most robust startle inhibition compared to no food. Contrasting females and males, we found significant differences related to the conditions yoghurt and chocolate. In females, chocolate elicited the lowest response amplitude followed by yoghurt and ice cream. In males, chocolate produced the highest startle response amplitude even higher than eating nothing, whereas ice cream produced the lowest. Assuming that high response amplitudes reflect aversive motivation while low response amplitudes reflect appetitive motivational states, it is interpreted that eating ice cream is associated with the most appetitive state given the alternatives of chocolate and yoghurt across gender. However, in females alone eating chocolate, and in males alone eating ice cream, led to the most appetitive state. Experiment 2 was conducted to describe food intake-related brain activity by means of source localization analysis applied to electroencephalography data (EEG). Ice cream, yoghurt, a soft drink, and water were compared. Brain activity in rostral portions of the superior frontal gyrus was found in all conditions. No localization differences between conditions occurred. While EEG was found to be insensitive, startle response modulation seems to be a reliable method to objectively quantify motivational states related to the intake of different foods.

Identification of the characteristic length scale for fatigue cracking in fretting contacts

1998 ◽  
Vol 08 (PR8) ◽  
pp. Pr8-159-Pr8-166 ◽  
Author(s):  
S. Fouvry ◽  
Ph. Kapsa ◽  
F. Sidoroff ◽  
L. Vincent
Keyword(s):  
Characteristic Length ◽  
Fatigue Cracking ◽  
Length Scale ◽  
Characteristic Length Scale
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