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railway disaster road

  • Thread starter Thread starter AlbertoC
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AlbertoC

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from what I heard he gave a cart.
someone to more precise news? What actually broke up?
I express my sympathy for the victims and their families.
tree
 
I have already seen a very similar fracture, it was a tree turned from bar and had yielded for fatigue composed cut-tortion. I would think that wheel worked badly for a long time, for example with the gripped bushing.

That's crazy.
 
I agree, perhaps for abnormal effort due to the support bearing in the avary.
alternatively, but always of fatigue it is, I would propend more for a break triggered by a superficial clique, strangely (????) not detected to ultrasound to the production of the axis.

In any case the rust story is a joke.
just take a ride in a train station and better still in a freight stop to find tons, rust.
 
from photo n°2 placed as a hunter, it is appreciated how the cedimento took place of crash when the residual resistant section was insufficient. to be noticed how smooth and clean the surfaces adjacent to the fracture, the clique, when it left, widened sit down and the mutual disapproval of the surfaces left them in that state.
the action of fatigue must never be neglected, in this case, who was responsible for carrying out controls and maintenance should be hanged.
tree
 
AlbertoC said:
from photo n°2 placed as a hunter, it is appreciated how the cedimento took place of crash when the residual resistant section was insufficient. to be noticed how smooth and clean the surfaces adjacent to the fracture, the clique, when it left, widened sit down and the mutual disapproval of the surfaces left them in that state.
the action of fatigue must never be neglected, in this case, who was responsible for carrying out controls and maintenance should be hanged.
tree
Click to expand...
photo n°1
 
Meccbell said:
I agree, perhaps for abnormal effort due to the support bearing in the avary.
alternatively, but always of fatigue it is, I would propend more for a break triggered by a superficial clique, strangely (????) not detected to ultrasound to the production of the axis.

In any case the rust story is a joke.
just take a ride in a train station and better still in a freight stop to find tons, rust.
Click to expand...
Well, come on, it's the classic approximation of the journalist talking about topics he doesn't know. Fortunately, a photo speaks more than a thousand words to the eye of people who know a little.
Even somewhere you find it written that the wrinkled fracture area is the victim of rust, while the shiny one is the one that gave birth to schianto (s.i.c.).
 
Meccbell said:
I agree, perhaps for abnormal effort due to the support bearing in the avary.
alternatively, but always of fatigue it is, I would propend more for a break triggered by a superficial clique, strangely (????) not detected to ultrasound to the production of the axis.

In any case the rust story is a joke.
just take a ride in a train station and better still in a freight stop to find tons, rust.
Click to expand...
I don't think it's bearing fault, a gripped bearing generates the destruction of the boccola-support group well before reaching those fracture values for fatigue.

Besides rust, well, rust, at the university, they taught me that rust can inject the micro-rust from which the clique starts. In fact, the fatigued parts are often subject to superficial treatments that reduce their wrinkle (pallining, polishing, etc.). even a slight surface tempering can be useful. the formation of martensitein fact causes an increase in volume that puts in the compression state the area subject to treatment. compression makes the opening of the rats more difficult for obvious reasons.
 
cacciatorino said:
Besides rust, well, rust, at the university, they taught me that rust can inject the micro-rust from which the clique starts.
Click to expand...
Undeniable reasoning if the sizing is done pulling everything to the bone.
but if it is done also taking into account a certain "denseness" of the particular for external events (which may be both corrosion, and any indentation due, for example, to foreign bodies on the tracks), then the corrosion clique has no way to propagate more than much, as the scorriment of the superficial layers due to the yields remain under the propagation limit.
 
Now, you have to explain it to me!
I do not understand anything (premium) but in the newspapers and tg showed a round sock consumed by the wrinkles that resulted in the failure of a mechanical component. the surrender then caused the overthrow of the first car....! I understood correctly?
but the question is: how is it possible?
 
incasinata said:
Now, you have to explain it to me!
I do not understand anything (premium) but in the newspapers and tg showed a round sock consumed by the wrinkles that resulted in the failure of a mechanical component. the surrender then caused the overthrow of the first car....! I understood correctly?
but the question is: how is it possible?
Click to expand...
Actually, it's not that good. the weight of the car is rested on the wheel axis, as well as when you go with the bike, the strength of the leg is discharged on the pedal pin and from that on the chain and then the wheel.

Then, it happens that you go and go the pin you crack a little, and at every turn that makes the wheel the crack widens of a billionth billionth of centth of millimeter. turn after round, the crack becomes so big that the resistant section of the pin (that not yet cracked) is no longer able to hold the weight and therefore breaks.
Unlike what you read in the newspaper, the cracked part is the one you see glossy, while instead the wrinkled-granular part was the one that finally raised white flag. The reason for the polish is that the two faces of the aprte cracked at each wheel turn make a small relative movement back and forth so they polish each other.
It's the phenomenon of fatigue, which is perhaps unknown to civilian designers, but it's a real curse for machine makers.
the slot usually starts from super-ificial imperfections: a bit granulous welding, a carving due to a shock, a mechanical processing not quite fine and too rough.

Consider that these breaks generally have a very slow progression, so it is usually possible to notice it in time making regular inspection visits, which probably in this case were omitted or at least performed superficially.
 
they did not do the visits, these things are planned and there are suitable tools; in the welding of the civil constructions the x-rays are used. There was also a "warning" the other week, with a reservoir of hydrofluoric acid, which for a miracle did not have serious consequences, other than gpl, also touched a passenger train. same dynamic.
 
In your opinion, after this disaster, will things improve? ! ?
in addition to the trains, because they do not control the tir that do not always circulate in the only highways.
Hi.
 
I believe that the knowledge is already there, to avoid these things, and perhaps also the norms (which I do not know, in the railway sector, but I imagine they know well what fatigue is...).
the problem remains in the quality of controls, on which you could open an endless speech, including tir, planes, and more...
 
typical phenomenon of breakage for fretting-fatigue generated by flexo-torsional action. the area subject to breakage is particularly critical due to the fitting with the wheel and due to the calettamento on the bearing support.
observing the distribution of the beach lines due to the propagation of the clique and in particular the relationship between the propagation section and the last resistant section is observed how this last one is very reduced, an index of excellent breaking load of the material used. In short, the material has resisted until the last while with a resistant section that looks to be 1/4 of the total section.
from the investigations it turns out that in the last maintenance of March several axes were replaced, apparently however using axes "second hand".
and here arises the doubt that probably the calettamento of the end of the axis on the bearing support was excessively forced, or however not performed optimally, favoring the phenomenon of fretting.
periodic controls and replacements are performed precisely because fatigue is a phenomenon that, if they seem strange, is not completely solved.
Of course, if used spare parts are used...no comment.
regarding the superficial oxidation speech (rust), in the incident under examination has negligible influence.
 
I am curious to compare these beautiful technically motivated opinions with what they will tell us officially.

from the website lastampa.it.

"... not by chance the axis section at the breakpoint has two shades: smooth metal, evident sign of an instantaneous and recent trauma, and a rusty part, that oxygen had time to oxidize. a pre-existing vice, that is. ...
 
stefanobruno said:
I am curious to compare these beautiful technically motivated opinions with what they will tell us officially.

from the website lastampa.it.
"... not by chance the axis section at the breakpoint has two shades: smooth metal, evident sign of an instantaneous and recent trauma, and a rusty part, that oxygen had time to oxidize. a pre-existing vice, that is. ...
Click to expand...
:eek:eek: oh jesus!
 
then, at least among us, we all agree with the fact that the smooth part is the fracture zone for fatigue and the rough one is the last crash for "surcharge" (it was no longer there).
on superficial oxidation (extended obviously only to the open area that could be in contact with the air) I think that only with in-depth investigations can be defined how long the clique was: However, there will be so many hypotheses that will make the results vain (some years ago I wanted to understand how long a clique was present on a chain mesh that had crashed hard: Unfortunately, after a week from the event all the surface of breakage was so oxidized to make impossible any investigation. It is true that we were in a port and that the brackish air is tremendous, but a train that makes up and down for Italy often passes near a coast and therefore good night).
As regards ndt controls, I would leave rx investigations (on a board they do not give better results than ut). similarly the ut made axially are not reliable to verify a superficial microcrych (the echo of the defect hides in the echoes of rebound from the surface), it would be necessary to disassemble the piece and to use cylindrical angular probes, but at this point, with a disassembled axis, for the supeficie you have much more reliability from a magnetic control with powders (which allows you to see also the subsuperficidal defects) or even penetrating defects. considering the staff of the company that carried out the controls (although it seems that by contract in the particular case they should not be executed), I cannot understand how 150 people can control and maintain on 2000 tanks a year (only to disassemble the covers of an axial that traveled for Europe put a couple of hours of work, then clean it and prepare the surfaces, then do the controls, then put it back in maintenance, make yourself a little calculation of the time it takes).
with regard to the relationship between the final area of breakage and the overall one, although in nose it seems that it is sufficiently low to give a good safety coefficient, I would not draw fast conclusions (which factor of intensification of the efforts we have in those variations of section? ).
we see before recovering the official conclusions of the assigned experts (they should be public, if someone can find them, it would be good for them to spread them to all).
Finally, the more above hunter has broken that for civil designers fatigue is an unknown thing: I found myself checking out projects made by civilians who did not consider it, even with very high voltages (well beyond 21 n/mm2, to understand). It is rarely part of their cultural baggage, as well as for me any crack in the wall is always a source of extreme fear, even if it turns out to be just a crack of paint.
Good day to all
 

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