In sequence of our discussion on small cars, I raised a question in my last articles, what happens with the occupants, if the BIW of small car #smart is designed as a hard nut shell?
https://lnkd.in/dXiN8zA9
To answer this, we shall recall some of our basic physics fundamentals learnt in class 12th physics.
Let’s take an example of a car collision with a truck. There are some basic assumptions here..
1.      Mass of the both drivers are same and i.e. “md”
2.      Mass of the truck is M and mass of the car is m. The M > m.
3.      The both vehicles are travelling with same speed (v) opposite to each other.
As both moving bodies are colliding so we apply a Newton’s third law-
Thus both the vehicles are applying same force on each other and that is F.
So                       F (truck) = F (car)   ——— eq(1)
The collision time is Δt . This must be same for both the vehicles.
We can multiply both the side of eq(1) with Δt.
So                     F(truck) . Δt = F (car) . Δt  ————eq(2)
The above eq(2) is called the impulse. The impulse is equal to change in momentum.
So                    M. [Δv (truck)] = m. [Δ v (car)]       —–eq (3)
To balance the above equation (3), the change in velocity of car Δv(car) must be greater than change in velocity of Δv(truck).
So                  [Δv (car)] > [Δv (truck)]           ———- eq (4)
If we multiply both side of the equation (4) with the mass of driver (md) then we get-
                     (md) . [Δv (car)] > (md). [Δv (truck)]  —eq (5)
So we can see from equation (5) clearly that change in momentum of the car driver is more than change in momentum of the truck driver. Thus car driver will be experiencing more force.
This exactly happens in the high stiffness car body, The driver of the high stiffness car body will be experiencing more force than the deformable car structure (with bonnet car).
Actually the hard nut shell car body is not deforming at all, so the change in momentum of the car will be more. Thus driver will be experiencing more force. This could be more challenging, if this hard nutshell collide with a rigid structure. That we have already seen with a test video in my last post.
In this case the restraint system has to work more efficiently to minimize the high force experiencing by the occupants. That’s why the design of the #smart car and minimizing the injury values of occupants were the big challenge for Mercedes-Benz AG
This small baby explains well the engineering and basic physics.
So a stiff car body with unoptimized restraint system is not safe and can never achieve a 5star ratings. Hope the things are clear now.
Wish all of you a happy and prosperous happy new year 2023.
Stay tuned with some more new post….
Automotive Research Association of India (ARAI) SAEINDIA ICAT-International Centre for Automotive Technology