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Flavio Stochino's picture

A simplified model for railway catenary wire dynamics

In this paper, a simplified analytic model for the dynamic behaviour of railway catenary wire is presented. The model is discussed and validated with the help of numerical results obtained by a finite element code, for the case of a typical Italian railway installation. The simplified model is convenient from the computational point of view and is useful for sensitivity analysis. Some parametric studies have been developed by considering as free parameters the velocity and the distance of the train pantographs and looking at their effect on catenary dynamics.

karelmatous's picture

Google Maps/Earth Computer Graphics Algorithms for Model Reduction in Mechanics of Materials

We present an innovative image-based modeling technique, based on Google Earth like algorithms, to effectively resolve intricate material morphology and address the computational complexity associated with heterogeneous materials. This sharp volumetric billboard algorithm stems from a volumetric billboard method, a multi-resolution modeling strategy in computer graphics. In this work, we enhance volumetric billboards through a sharpening filter to reconstruct the statistical information of heterogeneous systems.

Any helpful information about 2 & 3 surface models

Does anyone have any helpful information (Organised governing equations & subroutine files) about Two & Three surface models which are developed by Shen & Goto respectively? 

PhD Positions in Polymer Composites (Mechanical Engineering at University of Maine)

There are two open positions starting in the fall of 2017 for PhD students interested in analysis and design optimization of polymer composite materials and structures subject to impact and shock loading conditions. A master's degree in Mechanical Engineering or a closely related field is required. Students will have an opportunity to work closely with the faculty in mechical engineering and researchers at Advanced Structures and Composites Center at UMaine.

 

The positions are restricted to individuals with US citizenship or permanent residency.

MRC - Bruno Boley 90th Anniversary Issue

In memory of Prof. Bruno Boley, Founding Editor-in-Chief of Mechanics Research Communications (MRC), we made the Special Issue, published in MRC in September 2015, freely available until 13 June 2017.

To read it, go to http://www.sciencedirect.com/science/journal/00936413/68

 

oliver oreilly's picture

Textbook on Modeling Nonlinear Problems in the Mechanics of Strings and Rods

My latest textbook, O. M. O’Reilly, Modeling Nonlinear Problems in the Mechanics of Strings and Rods, has just been published by Springer Verlag. The electronic version of this book is available (for free if your university's library has a subscription) on this website:

 

http://www.springer.com/us/book/9783319505961

 

Shuze Zhu's picture

Compressible, Dense, Three-Dimensional Holey Graphene Monolithic Architecture

We demonstrated outstanding compressibility of holey graphene nanosheets, which is impossible for pristine graphene. Holey graphene powder can be easily compressed into dense and strong monoliths with different shapes at room temperature without using any solvents or binders. 

ACS Nano, Article ASAP, http://pubs.acs.org/doi/abs/10.1021/acsnano.7b00227

 

qing.peng's picture

The normal-auxeticity mechanical phase transition in graphene

When a solid object is stretched, in general, it shrinks transversely. However, the abnormal ones are auxetic, which exhibit lateral expansion, or negative Poisson ratio. While graphene is a paradigm 2D material, surprisingly, graphene converts from normal to auxetic at certain strains. Here, we show via molecular dynamics simulations that the normal-auxeticity mechanical phase transition only occurs in uniaxial tension along the armchair direction or the nearest neighbor direction. Such a characteristic persists at temperatures up to 2400 K.

ahmedettaf's picture

Localization and instability in sheared granular materials: Role of friction and vibration

Shear banding and stick-slip instabilities have been long observed in sheared granular materials. Yet, their microscopic underpinnings, interdependencies and variability under different loading conditions have not been fully explored. Here, we use a non-equilibrium thermodynamics model, the Shear Transformation Zone theory, to investigate the dynamics of strain localization and its connection to stability of sliding in sheared, dry, granular materials. We consider frictional and frictionless grains as well as presence and absence of acoustic vibrations.

Bin Liu's picture

Objective Fracture Parameters and a Paradox for Interface Cracks

Due to the oscillatory singular stress field around a crack tip, interface fracture has some peculiar features. This paper is focused on two of them. One can be reflected by a proposed paradox that geometrically similar structures with interface cracks under similar loadings may have different failure behaviors. The other one is that the existing fracture parameters of the oscillatory singular stress field, such as a complex stress intensity factor, exhibit some nonobjectivity because their phase angle depends on an arbitrarily chosen length.

Antonio Papangelo's picture

A note on the pull-off force for a pattern of contacts distributed over a halfspace

ArticleinMeccanica · March 2017 --- We found a very simple formula for pull-off force for a pattern of contacts distributed over an halfspace which could be very useful in predicting the adhesive propreties of structured surfaces, as bioinspired surfaces.  

Mike Ciavarella's picture

A simple finding on variable amplitude (Gassner) fatigue SN curves obtained using Miner’s rule for unnotched or notched specimen

We provide a very simple result for a problem which has been often neglected (variable amplitude loading) in academia, but which is of paramount importance in real engineering situations, where fatigue is almost never "constant amplitude".

We found few cases where we could check this extremely simple result, but it worked very well.  We would welcome further verifications.

The paper is in press here.

Giorgio Carta's picture

A phononic band gap model for long bridges. The ‘Brabau’ bridge case

In this paper, we study the dynamic flexural behaviour of a long bridge, modelled as an infinite periodic structure. The analysis is applied to the ‘Brabau’ bridge across the river Tirso in Italy. The approach reduces to a spectral problem leading to the analytical expression of the dispersion relation, which provides the ranges of frequencies for which waves do and do not propagate. The contributions of the bridge structural elements on the dispersive properties of the structure are investigated in detail.

Why CVOL increases?

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Hello,

Abaqus VUMAT for hypoplastic law

Please, I’m investing about the hypoplastic model for granular materials to study the behavior of sand under a dynamic excitation. I try to use the UMAT – VUMAT interface, Interface between UMAT (Abaqus/Standard) and VUMAT (Abaqus/Explicit) from http://www.soilmodels.info/ node17.html website.

zichen's picture

Shape formation of helical ribbons induced by material anisotropy

Helices are ubiquitous building blocks in natural and engineered systems. Previous studies showed that helical ribbon morphology can result from anisotropic driving forces and geometric misorientation between the principal axes of the driving forces and the geometric axes. However, helical ribbon shapes induced by elastic modulus anisotropy have not been systematically examined even though most natural and engineered structures are made of composite materials with anisotropic mechanical properties.

cohesive model of Needleman was input into abaqus, but wrong???

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 I have written  vumat codes of a cohesive model of Needleman (whose paper entilted "Numerical simulations of fast crack growth in brittle solids"), and I have implemented it into ABAQUS/Explicit, but the predicted result is wrong. I don't know why. The corresponding fortran file is as follows:

      subroutine vumat(

C Read only (unmodifiable)variables -

     1  nblock, ndir, nshr, nstatev, nfieldv, nprops, lanneal,

     2  stepTime, totalTime, dt, cmname, coordMp, charLength,

     3  props, density, strainInc, relSpinInc,

Ballistic impact simulation of composite targets in AUTODYN?

In general we use Johnson-Cook model for bullet, which accounts for strain-rate effects, while for the target (Composites), the we use orthotropic constitutive model. Does it mean that strain-rate effects are not important for composites? The Johnson-Cook model cannot be readily used for composites. How does the AUTODYN considers strain rate effects for composites in ballistic impact simulations? 

UMAT for Kinematic hardening

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I just followed the code that ABAQUS presented (Copied below), but I'm getting very strange results comparing with ABAQUS GUI, what's wrong with that? 

Please help if you have experience 

 

 

      SUBROUTINE UMAT(STRESS, STATEV, DDSDDE, SSE, SPD, SCD, RPL,

     1 DDSDDT, DRPLDE, DRPLDT, STRAN, DSTRAN, TIME, DTIME, TEMP, DTEMP,

     2 PREDEF, DPRED, CMNAME, NDI, NSHR, NTENS, NSTATV, PROPS, NPROPS,

     3 COORDS, DROT, PNEWDT, CELENT, DFGRD0, DFGRD1, NOEL, NPT, LAYER,

     4 KSPT, KSTEP, KINC)

C

saberelarem's picture

On a systematic approach for cracked rotating shaft study: breathing mechanism, dynamics and instability

We present a systematic approach to deal with the modelling and analysis of the cracked rotating shafts behaviour. We begin by revisiting the problem of modelling the breathing mechanism of the crack. Here we consider an original approach based on the form we give to the energy of the system and then identify the mechanism parameters using 3D computations with unilateral contact conditions on the crack lips. A dimensionless flexibility is identified which makes the application of the approach to similar problems straightforward.

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