Car Crash

Introduction:

1886 was the year when the first car came into this world. Throughout the years the world of cars has grown immensely. Cars have become faster, stronger, better, safer, and fuel-efficient over the period. Cars have become a basic necessity of life these days. And almost every person around us has a car as means of transport.

With newer models of cars coming out each year we have heard the statement from people around us that “Cars these days are not like the old ones” or “Old cars were much stronger and better than the new ones” and to some extent they are right. Old cars were stronger than the new ones but were they safe? To that, we say NO old cars were not safe than the cars made today.

According to the stats the death rate per 100 million miles of cars driven has improved by 92% that is in 1992 it was calculated that 18.65 deaths occurred per 100 million miles of cars driven. Today this figure is calculated at 1.46 death per 100 million miles of cars driven. So, it means that cars being tougher in the old days was highly unsafe whereas the safety of vehicles has improved over the time period.

But what has changed over time? Although many revolutions come in the automobile industry two major changes play an important role in the improvement of the overall safety of cars. These changes are:

• Introduction to Monocoque chassis
• Strength gradient with the crumple zone

Introduction to Monocoque chassis:

 

 

 

 

 

 

Monocoque chassis as the name suggests are the chassis in which the frame is built inside the body. The word monocoque is a French word that consists of two words Mono means “Single” and Coque means “Shell” which means monocoque chassis are “single shell chassis” cars. A monocoque is a shell around the car made by using both chassis as the frame in a single construction.

Monocoque chassis was first introduced in 1962 and an aluminum alloy monocoque chassis was used in formula 1 car in lotus 25. It is a structural system in which loads are supported by an object’s external skin. In principle, it is like an eggshell. The formed sheet metal is ultimately welded together with the structure pieces to strengthen the body that will bear all the tensile, bending, and torsion forces applied to the body.

Advantages of Monocoque chassis:

• It’s safer than both the other chassis due to its cage-like structure
• It is easy to repair
• It has superior torsional rigidity.

Strength gradient with crumple zone:

Along with the monocoque chassis, the car body structure was reengineered with a clever gradient of the strength of materials. It has basically divided the car into 3 major sections.

The front section of the car: Usually consists of light metal and thin sheets.

Center section: This is also called the cage. It is highly reinforced with metal in two or more layers with high thicknesses.

Rear section of car: Usually has lighter than cage metal but higher than front end metal.

These engineering design modifications were made so that the metal absorbs most of the impact from the accident. Such areas are called crumple zone. Every metal in the crumple zone gets bent, every plastic broken and every rubber piece pancaked as if the car wants to break itself apart. But this only happens till the impact goes to the cage section. If the impact reaches the cage section, the high-strength steel stops the impact from getting inside as it is highly reinforced from multilayered metal.

Breaking the car structure according to strength:

• Exterior parts: Fenders, bumpers, sheet metal:

Most of the exterior parts are made up of very thin metal, plastic, or aluminum. These parts do not play a very high role in absorbing the impact during an accident rather they are more for scrapes, fender benders, etc.

• Front end interior part: Radiator support, Bumper reinforcement.

Front end interior parts are in sea green color. These parts are meant for medium size accidents where the passenger does not get hurt but most likely the airbags may go off. These parts do not have a high absorption capability hence this material on impact will break and bend fairly easily. Usually, these parts are made up of aluminum or mild steel.

• Front Frame: engine mounting transmission mounting:

The front frame parts are in blue and white color. These are meant for bad accidents. In these accidents, the passenger may get hurt. Airbags are likely to go off. The impact comes to the frame after damaging the bumper, bumper support, hood, and radiator support so some of the impacts till it reaches the frame are absorbed. The metal in the front frame is highly strong as it is made up of high-strength steel and is rarely replaceable as it is welded together.

• Cages are: front pillar, center pillar, rear pillar, roof

The cage parts are red and yellow in color. These are meant for the worst of the worst accidents. If the impact reaches this area then the passenger has a possibility of really getting hurt, paralyzed, or even killed. In such impacts, all the airbags will go off. A safety cage comes into play when all the other things have failed. Hence the steel in the cage is made very thick. These are made up of high-strength steel and are welded together in multiple layers.

But why were the old cars so unsafe?

Most of the old cars were made completely of high-strength steel. Making the body tough and strong was the reason for most casualties. It can be explained with a simple scenario where physics will come into play.

Let’s say you have a rigid block against your chest. Your weight is around 80Kg and running at 40km/hr. you struct into a wall and your velocity go to 0km/hr. in 0.8 sec then the force exerted on your chest can be calculated using the formula

impulse = change in momentum.

This formula is used to understand the physics of collision. In this formula:

F*T (Impulse) =M*ΔV (Change in momentum)

Putting in the values we get.

F*(0.8/3600) = 80* (40-0)

F*0.000222 = 3200

F= 3200/0.000222

F=14414.41 KN of force exerted on your chest.

Note: This is a tentative calculation.

Now let’s suppose you have a rubber or a material that compresses against your chest. Now after striking the wall you reach 0km/hr. in 2sec.

F* (2/3600) = 3200

F= 5765.76 KN of force exerted in your chest.

Now you see the difference. The solid material transfers all the force of impact to your chest while in the second scenario the rubber or compression material absorbs the force.

This is the same with old cars. They don’t compress but transfer all the force to the passenger’s body while the new cars self-destruct themselves but absorb most of the impact keeping the passengers safe. This is why the old cars are very unsafe as compared to the new cars.

Crumble zones are the reasons why we can extend the time of impact transfer, thus spreading out the deceleration more. If the car crushes and acts like a sponge, it will make the deceleration less quick and more gradual. If the whole car was made of high-strength steel like the old cars, it would stop almost as soon as it gets into an impact. No crumbling, no reducing the quickness, no extending time. It will be a very rugged and rough experience, likely leading to bad injuries and even death.