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DAMAGe AND FAILURe OF MATERIALS UNDER EXTREME CONDITIONS

hello:

I attach a flyer for the coming CISM course in Udine.

All welcome

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Materials Science and Engineering C

Checking upon the status of a submitted paper that has been with the journal for 2 weeks, we received the following response.

I will let you judge.....

 

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Ballistic penetration and fragmentation of brittle targets

The attached, to appear in I.J. Impact Engng., is an attempt to simplify such very complex calculations using an incubation time concept for defects coalescence, in the spirit of Tuler and Butcher and others.

By comparing the calculations and the experiments, it seems that the approach works nicely, produces realistic results, and most of all does not necessitate complex models with too many parameters of very sophisticated FE formulations.

 

Enjoy

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the Taylor-Quinney coefficient may depend on the loading mode....

A systematic comparison of dynamic tension, compression and shear....The TQ factor is not necessarily the same for different loading modes, emphasizing the role of the deformation micromechanisms.

 

https://authors.elsevier.com/a/1VMDY57ZjlaZD

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Dynamic crushing of a multi-columnar structure

Experiment realized by Daniel Levy (DFL-technion). We use a Kirana ultra high speed camera and the framing rate is 500,000/second.

https://www.youtube.com/watch?v=LNWh9JDDepY&feature=youtu.be

 

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Adiabatic shear-Dynamic recrystallization-Softening

The attached results address the extent to which the presence of a nanograined, dynamically recrystallized phase may soften a material (in that case Ti6Al4V), causing ultimately failure by shear localization.

Comments welcome.

D. Rittel

 

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Dynamic fracture of transparent ceramic

Captured at 7.5 and 8 million fps with a Kirana camera. This is a one point impact test used to determine the dynamic flexural strength. Courtesy of Dvir Blumer and Eden Promushkin, the Dynamic Fracture Laboratory, Technion, Haifa, Israel.

https://www.youtube.com/watch?v=mhce_sEyk60&feature=youtu.be

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About adiabatic shear failure.....

Not too long ago, we identified dynamic recrystallization (DRX) as a potentially softening factor leading to the formation of adiabatic shear bands. However, the exact nature and the extent of the softening effect till remained to be assessed. The link to our new paper provides additional information on this issue.

http://www.nature.com/articles/srep37226

(the paper is also attached)

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A new concept of fast vessel

When one introduces hydrodynamic concept together with protective polyurea coating into the design of fast planning boats, this is the result. Enjoy!

https://www.youtube.com/watch?v=P4_CSaDYMVQ&feature=youtu.be

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phd position H2020 Marie Slodowska Curie ITN/ETN program

We are offering a PhD position to start this coming september at technion, Haifa, Israel, as advertised in the attached file.

To qualify, the candidates should hold an M.Sc. with thesis in mechanical/materials engineering and have passed the GRE with a grade of 85% or more.

The research will be experimental and numerical in character.

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phd position H2020 Marie Slodowska Curie ITN/ETN program

We are offering a PhD position within the franework of OUTCOME consortium (see attached).

The subject of the reserach is adiabatic shear banding of metallic alloys subjected to impact loading and the reserach will combine experimental and numerical work.

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PhD position in D. Rittel's group - OUTCOME collaborative project - ITN-ETN

We are looking for a highly motivated individual with a strong background in materials science and mechanics, to sudy dynamic shear failure of metallic materials. Experience with numerical modeling required. Previous exposure to experimental work will be considered as an advantage.

Additional information can be found in the atatched description of the planned research.

Contact email:  merittel@technion.ac.il

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ICEM 17 - Dynamic behavior of metals under impact and blast

The attached is an invitation to submit your work to the session Prof. P.Chen (BIT) and I are coorganizing at ICEM 17.
We hope to see you there!

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Dental implants: facts one should know

The sad news is that a large percentage of implants contain cracks which have the potential of causing fracture after fatigue growth. This is the outcome of the present study in which a 100 implants were examined, all apparently intact, having been extracted for various reasons, most likely biological but definitely not mechanical.

It seems that the whole field of dental implants, which is growing very fast, needs a serious mechanical re-assessment, from the design stage all the way up to surface roughening.

Comments are welcome

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Prof. Yaakov Benveniste, Tel Aviv University

It is with great sorrow that I heard that our colleague from tel Aviv University, Prof. Y. Benveniste passed away recently. This is a great loss for the Israeli Mechanics Community in particular and for the community in general. I am sure he will be remembered as an exceptional scientist and a very modest and kind person.

He will be missed.

To his family, I adress my sincere condolences

D. Rittel

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An interesting paper

I came across this very instructive article, so I decided to share it here. 

Enjoy!

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Dynamic necking can avoid notches

Following an earlier post on dynamic necking of tensile bars, we show in the attached paper (to appear in JMPS) that the presence of deep notches in the specimen does not necessarily dictate the location of the neck. Various material parameters are identified and modeled numerically, to assess their respective influence. Strain-rate sensitivity is identified as an important factor. Stated simply, given the fact that local strain rates in a notch are significantly higher than in the rest of the bar, the notch will harden to an extent that it transfers the load elsewhere in the specimen. 

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Surface preparation of dental implants

It is commonly admitted that "rough" surfaces promote osseo-integration of dental implants. Numerous studies emphasize an optimal Ra parameter for this purpose. One very common way to achieve that state is the so-called "grit blasting" process whereby tiny ceramic (alumina) particles are shot on the implant's surface.

Up to here for the basic story.

It has also been noted in other instances that surface blasting may not be entirely beneficial and it should be controlled, in terms of blasting pressure, particle size and shape. 

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Dental implants can fail......

Contrary to the common naive feeling of clinical dentists, it so happens that dental implants can also fracture. This is a very unpleasant event which necessitates a surgical extraction procedure. So far, the most part of reserach on dental implants has been emphasizing biological failures and biocompatibility related issues. Mechanical aspects of implant design have been touched upon and a lot of work has been done on the surface condition of the implants to allow optimal osseo-integration. Those are all central clinical issues.

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Experiments with porous materials

The additive manufacturing technology, among its many advantages, allows us to manufacture solids with controlled enclosed porosity. To the best of my knowledge, this was not doable with conventional machining technologies, but now this is done. In the attached document, the interested reader will find experimental results (both static and dynamic) describing the influence of the porosity on the specimen's performance. We show that while the volume fraction is indeed an important parameter, aas expected, the spatial arrangement of the voids is also of prime importance.

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Dynamic neck formation can "ignore" a deep grove in a tensile specimen.....

In this movie taken at 1 Mfps using our new Kirana camera (courtesy Y. Rotbaum), one can see a dynamic tension test of a grroved specimen in a tensile Hopkinson bar. The groove is relatively sharp and 10% of the diameter in depth.

It so happens that the dynamic neck inception occurs outside the notch area, in other words a strong geometrical flaw does not dictate the failure locus. We have performed over a hundred of such experiments. This is a very interesting and challenging observation.... 

 

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What happens when an engineer submits a paper to a physics journal

I believe many of us went through that kind of ostracism. Now, I will provide a concrete argument. This is the reply we received when we responded our paper was indeed of interest to the Physics community, which was first raised as an issue by the editor. We provided a very detailed explanation.

So when they run out of valuable arguments, all they can produce is this pathetic statement below.

The question is more fundamental. Why do we, as mechanicians always welcome papers from physicists, while the reciprocal is far from being obvious?

 

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Ultra high speed imaging of impact fracture

Here are some movies of impact fracture of various test cases, recorded at up to 5Mfps using the new Kirana camera. The sensor is not the final one yet, but the results are promising. Wedge loaded PMMA plates with holes reveal very nice crack branching (somewhat analogous to fireworks). My students Y. Rotbaum and A. Godinger who performed to test cases thought that Haendel "lascia chio pianga" is appropriate. I don't take a stance on that!

Enjoy:

 

https://www.youtube.com/watch?v=ERhvhWogysw 

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