w******x
发帖数: 4396 | |
f********m
发帖数: 8397 | 2 我没根据，胡猜的。
nano是自己设计的，整体上考虑了安全性。
landwind的原型isuzu的那个能在美国卖，安全性应该也不差，但是江铃拿掉了很多东
西，或者材料上以次充好，结果车身强度大为降低。
是不是因为nano车本身轻crash test也很站便宜。
帝国主义亡我之心不死，crash test作弊！哈哈 |
w******x
发帖数: 4396 | 3 话说回来，tata原来就是个搞钢铁买卖的，估计这方面恐怕比国内好些厂家强不少。
【在 f********m 的大作中提到】
: 我没根据，胡猜的。
: nano是自己设计的，整体上考虑了安全性。
: landwind的原型isuzu的那个能在美国卖，安全性应该也不差，但是江铃拿掉了很多东
: 西，或者材料上以次充好，结果车身强度大为降低。
: 是不是因为nano车本身轻crash test也很站便宜。
: 帝国主义亡我之心不死，crash test作弊！哈哈
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k*****a
发帖数: 823 | 4 但是nano也轻多了，同等速度要吸收的能量小很多啊。那个isuzu原型在美国卖的时候
已经有撞墙试验了？ |
f********m
发帖数: 8397 | 5 有了，1997 isuzu rodeo
【在 k*****a 的大作中提到】
: 但是nano也轻多了，同等速度要吸收的能量小很多啊。那个isuzu原型在美国卖的时候
: 已经有撞墙试验了？
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w******x
发帖数: 4396 | 6
on the flip side, when the chassis becomes lighter and smaller it's also
more difficult for it to withstand the same impact.
moreover smaller cars don't have much crumple zone, so the safety cage
pretty much take all the impact.
【在 k*****a 的大作中提到】
: 但是nano也轻多了，同等速度要吸收的能量小很多啊。那个isuzu原型在美国卖的时候
: 已经有撞墙试验了？
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c*********r
发帖数: 19468 | 7
different classes don't have "the same impact" during the crash test
【在 w******x 的大作中提到】
:
: on the flip side, when the chassis becomes lighter and smaller it's also
: more difficult for it to withstand the same impact.
: moreover smaller cars don't have much crumple zone, so the safety cage
: pretty much take all the impact.
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w******x
发帖数: 4396 | 8 you didn't get the point. kushana only pointed out the reduced impact on
smaller cars. my point was there's also reduced capacity to withstand impact
on smaller cars.
【在 c*********r 的大作中提到】
:
: different classes don't have "the same impact" during the crash test
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c*********r
发帖数: 19468 | 9 so, we can't compare cars directly if they're not in the same class for
crash testes,
right?
impact
【在 w******x 的大作中提到】
: you didn't get the point. kushana only pointed out the reduced impact on
: smaller cars. my point was there's also reduced capacity to withstand impact
: on smaller cars.
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w******x
发帖数: 4396 | 10 stop repeating the obvious. i'm not comparing cars. i'm comparing the R&D of
two different companies. the capability of producing chassis that can
withstand the impact of its own mass moving at 35mph is a pretty good
indicator of the R&D level.
【在 c*********r 的大作中提到】
: so, we can't compare cars directly if they're not in the same class for
: crash testes,
: right?
:
: impact
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p*********e
发帖数: 32207 | 11 in this case, the smaller, the easier. size-wize.
There is a physics law behind this but i'm so sorry i can't recall the
term.
of
【在 w******x 的大作中提到】
: stop repeating the obvious. i'm not comparing cars. i'm comparing the R&D of
: two different companies. the capability of producing chassis that can
: withstand the impact of its own mass moving at 35mph is a pretty good
: indicator of the R&D level.
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p*********e
发帖数: 32207 | 12 however one thing i can recall. Not 100% sure this can explain my previous
point
Let's compare two chassis with exactly the same material and design,
and only difference lies that the former one is one half of the other
in length.
The strength(ability to resisting stress) for a given material is
proportional
to 1-dimension, or length(think about the definition of Young's modulus),
and the mass is proportional to volume or length^3, and so is the kinetic
energy (1/2*mass*velocity^2).
Which means
【在 w******x 的大作中提到】
: stop repeating the obvious. i'm not comparing cars. i'm comparing the R&D of
: two different companies. the capability of producing chassis that can
: withstand the impact of its own mass moving at 35mph is a pretty good
: indicator of the R&D level.
|
c*********r
发帖数: 19468 | 13 靠，印度造个几千美元的nano，crash test水平就比江铃什么的好
r u sure u r not comparing cars?
just kidding:-)
of
【在 w******x 的大作中提到】
: stop repeating the obvious. i'm not comparing cars. i'm comparing the R&D of
: two different companies. the capability of producing chassis that can
: withstand the impact of its own mass moving at 35mph is a pretty good
: indicator of the R&D level.
|
D*****I
发帖数: 8268 | 14 that's natural law.
that's why there are more rats & roaches than elephants
【在 p*********e 的大作中提到】
: however one thing i can recall. Not 100% sure this can explain my previous
: point
: Let's compare two chassis with exactly the same material and design,
: and only difference lies that the former one is one half of the other
: in length.
: The strength(ability to resisting stress) for a given material is
: proportional
: to 1-dimension, or length(think about the definition of Young's modulus),
: and the mass is proportional to volume or length^3, and so is the kinetic
: energy (1/2*mass*velocity^2).
|
w******x
发帖数: 4396 | 15 i think it's a matter of the scale of the load. in the event of a crash, you
are no longer only dealing with reversible deformation characterized by the
young's modulus. a lot of the deformation is plastic. you are dealing with
more of a lattice of springs than a lattice of rigid tubes. the more
material you have to distribute the energy over, the easier for the
structure to retain its original shape (more reversible deformation, less
plastic). and it's the ability to retain shape that you are l
【在 p*********e 的大作中提到】
: however one thing i can recall. Not 100% sure this can explain my previous
: point
: Let's compare two chassis with exactly the same material and design,
: and only difference lies that the former one is one half of the other
: in length.
: The strength(ability to resisting stress) for a given material is
: proportional
: to 1-dimension, or length(think about the definition of Young's modulus),
: and the mass is proportional to volume or length^3, and so is the kinetic
: energy (1/2*mass*velocity^2).
|
p*********e
发帖数: 32207 | 16 or we can treat the problem like this
overall crashing performance = reversible deformation plus non-reversible
ones.
With the same model mentioned before, even if the latter doesn't change
for both structures (suppose the ability of absorbing kinetic energy is
proportional to the total volume/mass of the structure in an non-reversible
deformation), the former part, which at least works for the bearly unchanged
saftty cage (if it does remain unchange), still gives the smaller structure
an edge,
【在 w******x 的大作中提到】
: i think it's a matter of the scale of the load. in the event of a crash, you
: are no longer only dealing with reversible deformation characterized by the
: young's modulus. a lot of the deformation is plastic. you are dealing with
: more of a lattice of springs than a lattice of rigid tubes. the more
: material you have to distribute the energy over, the easier for the
: structure to retain its original shape (more reversible deformation, less
: plastic). and it's the ability to retain shape that you are l
|
w******x
发帖数: 4396 | 17 no. crash performance == plastic deformation. all the crash tests only look
at the result of non-reversible deformation.
so a larger structure is actually advantageous. it can reversibly deform a
small amount to absorb a large amount of energy, before the remainder of the
energy force it into plastic deformation.
a smaller structure, on the other hand, might be more rigid, in the sense
that for a given load at one point that doesn't exceed elastic limit, it
deforms less. but at the same time it
【在 p*********e 的大作中提到】
: or we can treat the problem like this
: overall crashing performance = reversible deformation plus non-reversible
: ones.
: With the same model mentioned before, even if the latter doesn't change
: for both structures (suppose the ability of absorbing kinetic energy is
: proportional to the total volume/mass of the structure in an non-reversible
: deformation), the former part, which at least works for the bearly unchanged
: saftty cage (if it does remain unchange), still gives the smaller structure
: an edge,
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w******x
发帖数: 4396 | 18 remember that if you have a spring half as long and you stretch it the same amount, the force (or stress) is doubled. simplistically, a smaller structure therefore cannot deform as much before parts of it go into plastic deformation.
you can get yourself a copy of solidworks and the like and try the finite element package. |
p*********e
发帖数: 32207 | 19 question:
What's the rough relationship between non-reversible deformation and size?
also, that's not a problem a smaller structure has a lower capability
in absorbing kinetic energy. What we are comparing is small vs large.
As long as the drop in crash performance is slower than that of the kinetic
energy with a smaller structure, we have a winner. That's why I am asking
the above question.
Plus, as i recall from the crash test video, the collision between the car
and the barrier is not complet
【在 w******x 的大作中提到】
: no. crash performance == plastic deformation. all the crash tests only look
: at the result of non-reversible deformation.
: so a larger structure is actually advantageous. it can reversibly deform a
: small amount to absorb a large amount of energy, before the remainder of the
: energy force it into plastic deformation.
: a smaller structure, on the other hand, might be more rigid, in the sense
: that for a given load at one point that doesn't exceed elastic limit, it
: deforms less. but at the same time it
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p*********e
发帖数: 32207 | 20 here's the problem. by doing this you suggests the smaller car will face
the same impact, however it does not. The kinetic energy is proportional to
the mass of the structure (given both cars are tested at the same collision
speed).
same amount, the force (or stress) is doubled. simplistically, a smaller
structure therefore cannot deform as much before parts of it go into plastic
deformation.
element package.
【在 w******x 的大作中提到】
: remember that if you have a spring half as long and you stretch it the same amount, the force (or stress) is doubled. simplistically, a smaller structure therefore cannot deform as much before parts of it go into plastic deformation.
: you can get yourself a copy of solidworks and the like and try the finite element package.
|
|
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w******x
发帖数: 4396 | 21 i didn't assume same impact. i compared on the ground of local displacement.
when you have a structure rather than a simple solid cylinder, half as much
KE doesn't translate into "half as much force at all places" or "half as
much displacement at all places".
if you really like to think of structures like solid cylinders, good for you
.
to
collision
plastic
【在 p*********e 的大作中提到】
: here's the problem. by doing this you suggests the smaller car will face
: the same impact, however it does not. The kinetic energy is proportional to
: the mass of the structure (given both cars are tested at the same collision
: speed).
:
: same amount, the force (or stress) is doubled. simplistically, a smaller
: structure therefore cannot deform as much before parts of it go into plastic
: deformation.
: element package.
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p*********e
发帖数: 32207 | 22 if you don't, why you apply the same spring displacement(thus the same force)
to a same(materially speaking) spring with half the leength?
Yes it won't translate to "half as much ...",
but i'd say it's closer to half than to whole.
displacement.
much
you
【在 w******x 的大作中提到】
: i didn't assume same impact. i compared on the ground of local displacement.
: when you have a structure rather than a simple solid cylinder, half as much
: KE doesn't translate into "half as much force at all places" or "half as
: much displacement at all places".
: if you really like to think of structures like solid cylinders, good for you
: .
:
: to
: collision
: plastic
|
w******x
发帖数: 4396 | 23
force)
let me ask you two questions, college physics 101 style:
1) throughout the crush of crumple zone, is the force exerted by the crumple
zone on the safety cage determined by total vehicle weight?
2) at the point of total crush of the crumple zone, which of the two safety
cages have more displacement (assuming they behaves like springs and one is
twice the length of the other)? and which of the two safety cages have
absorbed more energy?
【在 p*********e 的大作中提到】
: if you don't, why you apply the same spring displacement(thus the same force)
: to a same(materially speaking) spring with half the leength?
: Yes it won't translate to "half as much ...",
: but i'd say it's closer to half than to whole.
:
: displacement.
: much
: you
|
p*********e
发帖数: 32207 | 24
crumple
assuming both cars are traveling at the same speed, the kinetic energy
and the momentum are solely determined by the mass. And given the impact
time
are the same, the force generated by the impact, in the case of complete
non-elastic collision(final speed zero, means delta V is the same),
is solely determined by the mass.
is that enough?
safety
is
definitely the one with larger size. BUT, at the same time, it has more
energy to absorb.
【在 w******x 的大作中提到】
:
: force)
: let me ask you two questions, college physics 101 style:
: 1) throughout the crush of crumple zone, is the force exerted by the crumple
: zone on the safety cage determined by total vehicle weight?
: 2) at the point of total crush of the crumple zone, which of the two safety
: cages have more displacement (assuming they behaves like springs and one is
: twice the length of the other)? and which of the two safety cages have
: absorbed more energy?
|
w******x
发帖数: 4396 | 25 1) fail. the force is not determined by the total vehicle weight. it's
determined by the crumple zone itself. in other words, how crumple zone
crumples determines how much force (at any time during the crush) it exerts
back onto the safety cage.
2) assume there's no plastic deformation of the safety cage, the amount of
energy stored in the larger car safety cage is about twice as much as the
smaller car.
【在 p*********e 的大作中提到】
:
: crumple
: assuming both cars are traveling at the same speed, the kinetic energy
: and the momentum are solely determined by the mass. And given the impact
: time
: are the same, the force generated by the impact, in the case of complete
: non-elastic collision(final speed zero, means delta V is the same),
: is solely determined by the mass.
: is that enough?
: safety
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p*********e
发帖数: 32207 | 26 sorry i messed up question 1. thought it's the force between
the front of the vehicle and the barrier.
But even considering the force from the crumple zone to the safety cage,
mass of the entire vehicle (through the kinetic energy and momentum)
still plays an important role in determining the aformentioned force.
It makes significant difference when the crumple zone received twice
as much impact(in terms of energy).
for 2)
if your definition for the larger car remains the same as my OP, i.e.,
tw
【在 w******x 的大作中提到】
: 1) fail. the force is not determined by the total vehicle weight. it's
: determined by the crumple zone itself. in other words, how crumple zone
: crumples determines how much force (at any time during the crush) it exerts
: back onto the safety cage.
: 2) assume there's no plastic deformation of the safety cage, the amount of
: energy stored in the larger car safety cage is about twice as much as the
: smaller car.
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w******x
发帖数: 4396 | 27 1) no. it's entirely up to the crumple zone--it's designed to crumple in the
desired manner. think about it.
2) i assumed a car twice as long with other dimensions the same. width and
height really don't vary that much. do you know any car that's twice as wide
AND twice as high as the tata (or any other modern car)?
also weight of the car does not scale like that. look it up.
【在 p*********e 的大作中提到】
: sorry i messed up question 1. thought it's the force between
: the front of the vehicle and the barrier.
: But even considering the force from the crumple zone to the safety cage,
: mass of the entire vehicle (through the kinetic energy and momentum)
: still plays an important role in determining the aformentioned force.
: It makes significant difference when the crumple zone received twice
: as much impact(in terms of energy).
: for 2)
: if your definition for the larger car remains the same as my OP, i.e.,
: tw
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p*********e
发帖数: 32207 | 28
the
let's do it this way. will the "force" be the same when the car is traveling
at 1.414* speed (so the kinetic energy is twice, as in the twice-as-heavy
car)? How about at 2* speed when the momentum is comparable?
if not, why are you so sure "it's entirely up to the crumple zone"?
wide
i assumed you were following my scenario and thus obeying the definition,
sorry i misunderstood it.
【在 w******x 的大作中提到】
: 1) no. it's entirely up to the crumple zone--it's designed to crumple in the
: desired manner. think about it.
: 2) i assumed a car twice as long with other dimensions the same. width and
: height really don't vary that much. do you know any car that's twice as wide
: AND twice as high as the tata (or any other modern car)?
: also weight of the car does not scale like that. look it up.
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