[Nalin1]

A massive independent investigative exercise is required to ascertain the exact cause of this accident. And even after that there are bound to be disagreements depending on which side of the fence you are on.

Any surprises at all that Tata's team concludes their investigation with a statement that this is a 'driver error'?

Thank God that there were no casualties on any side.

[risham]

From what I gather form this discussion, all bhp-ians are in agreement that an independent investigation is required.

1. How to get it. Is there any provision where a customer or a body like ARAI can demand an investigation? Can a criminal case be filed against TATA for endangering the lives of occupants and when the case goes to trial, independent investigators be demanded? A member with a more legal background can suggest.

2. Can it be that TATA realises there is a metallurgy problem in the Vehicle and is quietly working on rectifying it without admitting to the deficiency? Can we know if after the incident TATA has changed the design/vendor of the part under scanner? It may be indirect evidence against TATA.

Just my thoughts.

The very fact that four occupants were wearing seat belts proves how safety concious they were. So to blame them without evidence is plain wrong in my opinion.

[Turbohead]

Originally Posted by saurabh2711

Have been a regular traveler on the road where this accident took place. Though completely paved, it is bumpy. Lot of tractors ply on this road. Very much possible that rock was left on the road after being used as support to change a tyre or provide a support to a vehicle.

Referring to the observation Point#1 (Heavy Impact found over Rear Axle Tube & Rear RHS Shock Absorber): Is their a possibility that only the rear part which broke off had hit a rock (but front missed it); while swerving for some reasons? The impact may have ripped apart the parts. I am only guessing that car the car fully loaded (in terms of weight - Five passengers on a long trip).

.

Makes perfect sense!

1) If the axle broke close to the LHS wheel on a right handed corner, due to inertia, the vehicle should have rolled over to the left side of the road and not on to the right side. The only way it can land on the right side is due to an external impact, like a rock, as you mentioned. An impact on the LHS wheel due to a rock can only provide the moment to make the vehicle roll on to the right side in a right handed corner
A vehicle on a right handed corner leans to the left and not to the right.

2) The picture of the axle shows that there was a crack before hand and that it was already rusted. That's typical mild steel property to rust like that when exposed to the elements for several weeks. The rest of the piece seems like it was torn away. Expected.

3) 65kmph on such a corner is pretty low. That's regular city speed! There has to be an external impact to roll, that to towards the opposite side.

4) Coming back to the axle, such cracks can occur only due to a defect or an external impact. I'm assuming it was due to a previous impact considering point 1. The ride comfort of Tata's may tempt you to run over obstacles,I guess.

I guess I'll go with Tata's statement. There has to be an external impact to roll on to the right in a right hander. But I guess I'll never know!

[Sutripta]

Any pictures/ statements on the condition of the tyre and rim which broke off?

Regards
Sutripta

[Carpainter]

Any post accident investigation from the manufacturers side is bound to be biased and this one is no exception to that. Cases like these need to have an independent expert investigation to find out the real truth. But from a layman's point of view, the bend was not sharp and 65kmph is not an excessive speed so to have a car topple over multiple times, even if there was an error from the driver, that would break an axle is very unlikely. Only a neutral investigation can bring out the truth.

[sandeepmohan]

I am curious about TATA's point of something that may have struck the rear twist beam. You can't rule this out though it has to be something really strong to dislodge the beam. Then again, it should have struck something up front before the rear.

This is the other problem of driving at night or at an odd hour on our highways. Having done it a few times, to be honest, avoid it as much as you can. You can have the brightest of lights and the best brakes but there is no way to steer yourself out of danger when a obstacle is noticed too late. You may not even notice it at times. This could have very well been the case here.

[dark.knight]

As far as Tata having the rights to defend their product and quality goes, one can make out their angle within the first 2-3 points they make in their defence :

1) Its obvious that the turn is not a "sharp" "90 degree bend" at all.. 45 degrees is about right, exaggeration by 100%

2) Poor visibility, no street light - no bearing on this case where the axle has split. One cannot say that the cause for a sharp, sudden turn leading to an axle breakage and subsequent wheel dislodgement was caused by no lighting.

3) A car can topple also with 3 wheels, 1 missing from the opposite side or even the same side as the topple, it all depends on velocity.

Not saying that Tata is all wrong, the defending points of the customer may have an equal amount of loopholes as well, but only facts can produce facts.. rest are only passing the buck or changing the nature of reality.

[--gKrish--]

I do not know how many of us have noticed the marks on the failed axle. In the case of fatigue failure, striations occur and crack initiation will be from the centre of the those concentric lines. If the axle failed due to sudden action of force, (like when something hits the axle) brittle or shear fracture occurs and necking would be observed at region where the shaft failed (not seen here at least from the pics). Why I think it is a fatigue fracture is that the bands (though not so dense to completely confirm fatigue failure) are at the same point where crack seems to have propagated. So the breaking point load of the axle must have come down some time ago and it failed during the turn.


Deducing from photographs without inspecting the subject matter in person without proper instruments is a stupid idea which I just did ( My Metallurgy and materials science grades aren't good either)

[Surya-TJet]

Looking at the photos of the wheel end which seems to be ripped off, I have one alternate theory for this:

There could have been some metallurgical fatigue in the car since production (maybe manufacturing defect) - This could have had a weakening of that region in the wheel end over the usage of 7000+ km.

This is a top end vehicle with ABS + EBD & Corner Stability Control [CSC]. CSC works by selectively braking each individual wheel as determined by the software. Anyone who has experience of slamming the brakes in an emergency situation in a ABS equipped vehicle will be aware of tire scrubbing sounds from the particular wheel end where the ABS is working (by modulating / pulsating the brake force repeatedly to avoid wheel lockup).

Since the car was taking a right turn, the left side wheels (both front & rear) would be at a higher rotational velocity than the right side wheels. When the CSC ECU detects this, it will automatically assume that the car is tending to oversteer and hence will try to automatically apply braking force on the left side wheels.

At this juncture, due to the combined factors of braking force and lateral force at the rear left wheel (which could have been subject to fatigue exerted from 7000+ km use of a metallurgically defective wheel end), it could have led to shearing off of the wheel end, thereby ripping the wheel off completely from the RTB assembly. This would have caused the car to topple on towards its' left - but since rear wheel is missing, the car would have spun 180 degrees and rolled over to its' right into the ditch multiple times and landed into a final spot in the opposite direction of traffic flow.

I could be entirely wrong. This is just my hypothesis based on my limited understanding from the evidence posted here in Team-BHP.

Hope it adds some value to the OP and the forum.

Cheers & Safe Driving

[feluda86]

The amount of rust on the broken axle seem too high for a car this new. Experts will be able to throw more light on this. I am not really convinced by TATA's method of investigation though - how could they have come to a conclusion without structural and metallurgical examination of the failed part (as pointed out by forum members). A rather interesting case we have here! Do we have any update on what actions are being taken by the user against TATA if any?

Off-topic:
Recently the number of reports on build quality of TATA vehicles (post accident) is on the rise. First was a case of a toppled test drive Nexon vehicle, then a toppled Tigor with a family in it, then a vlogger posting about how TATA build quality saved him on his Pune-Mumbai trip and then this! Some of these, if not all seem to be an orchestrated move by TATA to build an image. To add to that all of them seem to have similar headlines.

Links to some of the reports that have recently surfaced:

https://www.drivespark.com/off-beat/...ty-024759.html

https://www.cartoq.com/massive-tata-...upants-unhurt/

https://www.rushlane.com/tata-nexon-...-12250589.html

[virage]

Originally Posted by Turbohead

Makes perfect sense!

1) If the axle broke close to the LHS wheel on a right handed corner, due to inertia, the vehicle should have rolled over to the left side of the road and not on to the right side. The only way it can land on the right side is due to an external impact, like a rock, as you mentioned. An impact on the LHS wheel due to a rock can only provide the moment to make the vehicle roll on to the right side in a right handed corner
A vehicle on a right handed corner leans to the left and not to the right.

I would really wait for an independent investigator to study the fatigue pattern. This is not your standard mild steel, its most probably a specific alloy subjected to a heat treatment process. Everything from impurities in the metal to a botched fitting can lead to a failure. The chances of this happening are not astronomically low as manufactures would have you believe.

I am not taking sides here, but a rock that is capable of taking out the axle of a car must have a fair amount of mass and hardness. I am not saying its impossible but the driver would have to miss this fairly beefy chunk of rock, visually and then front wheels would have to miss it so as to allow only the rear wheel to impact it. Even then, isn't the wheel supposed to stay on?. I have personally driven cars over solid concrete speed breakers (these things have aggregate mixed in they are basically immovable ) at quite high speeds and came out with just an unbalanced wheel.

Coming to the case at hand, again I am only theorizing:
Driver takes a right hand turn, somewhere in the turn the forces on the car are directed downward and outward on the left side of the car, now due to some reason axle is week and shears. I would like to remind you the car and the wheel are still moving together, i.e. the relative motion between the car and wheel is very small. Now the front wheels keep the car along curve. Recall the direction of the forces i mentioned, it would simply pull the wheel off the car. This explains why there are no scuff marks on the wheel arches. And all this drama is registered by our occupants as a noise from the rear wheel.

I would like to point out that all this is happening within a second or a maximum of three seconds . Now our driver in our three wheel car notices the imbalance cause by this unintentional weight shedding. Instinct kicks in and he automatically counter steers to keep the car in control. If the driver turns the steering to the left in the right hand corner to keep it stable, the direction of forces invert. Now the car spins anti clockwise to the left and the side of the car without the wheel will act like an anchor, mind you the car still has forward momentum, which causes the car to flip along the direction of force which happens to be the right side of the vehicle which continues to roll over and land on the right side of the road in the opposite direction.

Again, it would be highly unethical to jump to conclusions, I am merely countering one narrative for the want of evidence.


On a side note, four of the passengers were wearing seat belts. A reminder that these things really do work.

[aniketi]

Disclaimer - I am not taking anybody's side here, just expressing my view as a third party.

I think its not a car's fault. If Axle breaks, car like Tigor is very difficult to toggle at speed of 60-70 KMPH only. It's a very stable car. As it was 5:15 AM, there is a possibility of driver loosing control due to sleep. There is also possibility of car has gone over any stone or something else which has damaged the Axle (& silencer too as per report) and that time driver would have not realized the same due to low visibility. After going over, car would have lost control and toggled.

[LoneRidder]

Originally Posted by Jaggu

The corrosion on the face of the broken part is worrisome to a layman like me. If it was a fresh cut, shouldn't it be shiny metal like at the edge?

The axle are made of carbon steel and quite normal to look rusty and one of the strongest. A fresh cut may not give shiny finish as 'normal' steel.

Without taking sides, one can loose control of the vehicle even at much lower speeds, irrespective of how long he has been driving and has experience.

[Jaggu]

Originally Posted by LoneRidder

The axle are made of carbon steel and quite normal to look rusty and one of the strongest. A fresh cut may not give shiny finish as 'normal' steel.

Ok agreed but doesn't the cross section look little too pitted for a break, especially the way in which the color changes from end to center? Again i am no metallurgy expert, just clearing doubts

[LoneRidder]

Originally Posted by Jaggu

Ok agreed but doesn't the cross section look little too pitted for a break, especially the way in which the color changes from end to center? Again i am no metallurgy expert, just clearing dobts

Oh, I am also not a metallurgy guy But with my limited experience with few Mahindra Jeeps and Maruti Cars it is common for the more exposed part to be looking more rusty. Again, not all parts, but the typical strong parts that are not painted/coated.