i3 (I01) [Official] The BMW i3 Official Thread

[Sayyaaf]

^lol, for real race tracks, sure. But for the tight autocross tracks on a parking lot, 911s with it's rear weight bias, not so great. For AX you need a light nimble car with good turn in and traction of slow corners. Not too powerful, because you probably never exceed 50 mph on most tracks. An i3 with low center of gravity, short wheel base, gobs of torque from slow speeds will do awesome. I really believe it will really humble a lot of sports cars at AX.

Yeah I saw that. Clios and megans beating gt3 and even EVOs at times. I see your proposition right there

 

[Sunny]

An i3 battery cell and a module. 8 of these modules make the battery pack.

 

[Centurion]

^^
That's neat, that a faulty cell can be swapped out individually.

 

[Sunny]

Tesla on the other hand uses large number (~7000) of smaller commercial cells (Panasonic 18650) for it's battery modules.

The advantage I guess is cheaper and more compact, but on the other hand the large number of cells apparently also increases the chances of "field failure".

 

[Cashmere]

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[Rainer271]

BMW i3 gets only a four star rating in Euro NCAP crash tests [videos]


Weak chest protection
The 2014 BMW i3 managed to obtain only a four star rating in Euro NCAP’s crash tests.

Euro NCAP says the frugal electric/hybrid premium city car offered "weak" chest protection in more severe pole side impact tests. In addition, the front seats and head restraints provided "marginal protection" against whiplash in a rear-end collision.

Euro NCAP is also criticizing the BMW i3 for its lack of a standard rear seatbelt reminder. Moreover, the organization isn't too fond of the i3's speed limiter that uses sign recognition to inform the driver about the speed limit. In terms of pedestrian protection, the i3 provided poor results at the base of the windscreen and along the stiff windscreen pillars.

It's not all that bad since the BMW i3 offers good protection in case of a frontal impact and was able to score maximum points in child protection when the car was equipped with the BMW-recommended rear-facing seats. However, parents will have some issues handling their child in and out of the car because of the suicide doors (which BMW likes to mention as "coach doors.")

More details are provided by Euro NCAP in the attached press release.

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Link: http://www.worldcarfans.com/113112766782/bmw-i3-gets-only-a-four-star-rating-in-euro-ncap-crash

 

[klier]

 

[jack]

Autozeitung.de says that the car was tested with the new 2013 assessment rules. You can t really compare it to previous evaluations.

 

[Centurion]

Indeed. At first I was unimpressed by the side impact test that uses an oversized broom, but then I saw the side of the car get slammed by a huge pillar but held up despite not having a B-Pillar. Good stuff! The structural integrity of the passenger cell appears to be very high grade. Do you even need a roll cage to go racing in that car?

 

[LaArtist]

BMW are expected to fix the issues..especially the poor whiplash protection..

 

[DJRaze99]

So Tourneo Connect Ford achieved a definitely more better result even new principles won't justify assessing it. After i3 I expected the good result...

 

[Mr Robert]

I really like this car, and I would too have lauched it to the public wearing my lederhosen.

 

[Giannis]

I wonder how the carbon based structure handles energy dissipation, lingering cracks and what-not.

CFRP as a material has a very high modulus of elasticity (Young's modulus) and great deformability. The material needs to remain elastic though, as CFRP is a very brittle material and when the first crack develops, instantly you get your car cut in half.

There's another factor to consider, which is debonding. Carbon fibers have a tremendous strength, but the various parts that are not made from a single mold need to be properly bonded together (there's a huge advantage in choosing a monocoque chassis, when using CFRP material!!!).

Bottom line, CFRP handles energy dissipation by utilizing its high modulus of elasticity (σ=E*ε, where σ is the stress, ε is the strain, and E is the modulus of elasticity. A high E means that you get the same stress with less strain - compared to other materials - basic mechanics) while remaining elastic.

Steel on the other hand, does have a much better deformability, but after a certain point (yield) the material is no more elastic, it goes into its plastic region, meaning that after the external force (or deformation) is removed, the material won't return in its original shape. So, steel absorbs energy by permanently deforming. CFRP can deform less than steel, but all this deformation is elastic. Also, its strength (in terms of stress) is many times higher than conventional steel, or even those new high strength steels used by the auto industry.

In a more graphical interpretation:

where with red is the stress - strain diagram for CFRP, green is for steel. The area under each line equals the dissipated energy.

 

[Sunny]

Wow, awesome post @Giannis. Thanks.

 

[LaArtist]

CFRP as a material has a very high modulus of elasticity (Young's modulus) and great deformability. The material needs to remain elastic though, as CFRP is a very brittle material and when the first crack develops, instantly you get your car cut in half.

There's another factor to consider, which is debonding. Carbon fibers have a tremendous strength, but the various parts that are not made from a single mold need to be properly bonded together (there's a huge advantage in choosing a monocoque chassis, when using CFRP material!!!).

Bottom line, CFRP handles energy dissipation by utilizing its high modulus of elasticity (σ=E*ε, where σ is the stress, ε is the strain, and E is the modulus of elasticity. A high E means that you get the same stress with less strain - compared to other materials - basic mechanics) while remaining elastic.

Steel on the other hand, does have a much better deformability, but after a certain point (yield) the material is no more elastic, it goes into its plastic region, meaning that after the external force (or deformation) is removed, the material won't return in its original shape. So, steel absorbs energy by permanently deforming. CFRP can deform less than steel, but all this deformation is elastic. Also, its strength (in terms of stress) is many times higher than conventional steel, or even those new high strength steels used by the auto industry.

In a more graphical interpretation:

where with red is the stress - strain diagram for CFRP, green is for steel. The area under each line equals the dissipated energy.

Love that post!

 

[Giannis]

And another few things, just mentioning some numbers for the sake of comparison:

1. The slope of both diagrams equals the stiffness of the material, or the modulus of elasticity. Conventional steel used here (Greece, a country with very high seismicity, requiring very high strength and deformation capacity steel) in construction has a characteristic (*) modulus of elasticity of 200-210GPa. For CFRP used for retrofitting structures, E=225 GPa.

2. The conventional reinforcement bars steel that we use here, called B500c, has a characteristic strength of 500 MPa. For CFRP it's about 3000 MPa.

3. In terms of strain, you can easily calculate the yield strain of steel:

εy=(fy/SafetyFactor)/E and is typically around 0.0025.

Rebars' steel ultimate strain is about 0.02. When it comes to CFRP, the material doesn't yield - it remains elastic all the way to failure, which comes around 0.01, half the value of steel. When using CFRP in structures, though, we only use 40% of that strain, up to 0.004 for a variety of reasons, one being compatibility with concrete (concrete fails at 0.0035) and safety. CFRP is very brittle and once it starts cracking, the whole retrofit will crack and you can easily have a whole beam falling on your head - this has actually happened!

(*) Characteristic strength is defined as the strength value which is smaller than the 95% of the required (by code/law) tests carried. So, if you test 100 rebars, you take as characteristic strength the one that is the number 95, when you arrange your results from greater to smaller.

-> Note that the σ-ε (stress - strain) diagram for CFRP is one straight line. That is elastic behavior. For steel it consists of two lines, the second being horizontal. This is plastic behavior. The horizontal line means that the material will take more deformation, while not increasing the resistance it provides. It reaches it's ultimate strength, yet still continues to deform. It holds its maximum resistance (strength), and continues to deform. That's the main mechanism that steel dissipates energy and this tremendous deformability is the main reason why reinforced concrete structures are so popular. If designed properly, it's the safest type of structure. So, if you remove the applied load or deformation, while steel has reached its plastic region, it won't return to a zero deformation, but it will work like this: (notice the arrows)

CFRP will just return to its original state.

Be sure that the chassis of both the i3 and i8 are way over designed. For obvious safety reasons.

In terms of safety stiffness, though, you can't say the same. Because this doesn't really depend on the material, but on the way the chassis is designed. And using smaller cross-sections (due to the much higher strength of the material) certainly doesn't help.



PS. I'll ban anyone that calls my handwriting girly

 

[LaArtist]

^lol i was just about to say that..damn you write very clear and nice for man

 

[Giannis]

From the frontpage article: http://www.germancarforum.com/bmw-i3-gets-four-starts-in-euroncap-crash-tests

 

[Sunny]

 

[mini_cooper4]

WOW that Renault looks like a modern Mercedes! I like it!