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How crash testing changed car design

How crash testing changed car design
Tristan Honeywill

Back in the 1980s, cars didn’t have to pass the same safety tests as today. The front impact protection was tested just by crashing the car into a solid wall. It looks spectacular but it’s not a good guide to what happens when two cars collide.

1991-Ford-Fiesta-crashes-against-a-solid-wall-at-TRLThe tests were a bad influence in fact. To do well, carmakers placed very rigid structures at the front of the vehicle, but did not reinforce the passenger compartment. Crashing against a wall, all the force concentrated on the car’s front end structure, which collapsed as designed. Here’s a 1991 Ford Fiesta hitting a wall. It looks OK, right?

In real life, when the cars hit other cars they just punched holes in each other. For anything softer than solid concrete, the crash structure was just too stiff. Something had to give and the passenger compartments were forced to collapse instead. Limbs were lost and people died.

The introduction of standard legal tests using deformable barriers in the 1990s was a turning point for car design. These small honeycomb barriers surprised some manufacturers. Many arrived at the first crash tests expecting their cars just to obliterate the barriers. Instead they saw their vehicles twisted weirdly out of shape.

 

How do the barriers work?

Cellbond_side_impact_barrierJust like hitting another vehicle, the barrier dampens the big initial contact. The stresses then spread more evenly throughout the car. The way the car then collapses is much more like what happens in the real world.

That’s why legislators have made the deformable barrier test at 56km/h (35mph) the basis for minimum crash safety standards. However, it’s worth remembering that a barrier crash test at 56km/h actually simulates a slightly slower real-world crash involving two cars. There’s no absolute figure, but it’s probably more like 50km/h (30mph).

 

Why does Euro NCAP crash test at 64km/h?

The most common types of crash that result in deaths and serious injuries occur with slightly higher impact speeds. This is what prompted Euro NCAP to start crash testing cars at 64km/h (40mph). This additional bit of speed produces a lot of extra energy in the crash – to calculate how much, you square the speed and multiply it by half the mass. Going two times faster means there’s four times as much kinetic energy involved.

To score well in an NCAP 64km/h test, car designers developed crash structures that worked with the rest of the vehicle. As a result, new cars now have heavily reinforced passenger compartments and well-engineered seatbelts and airbags. Cars with five-star ratings significantly reduce the risk of serious injury for the people inside.

 

Not convinced?

Take a look at what happens when a 1987 Ford Sierra crashes into a modern, much smaller Fiesta. The voiceover is in German, but watch how the Fiesta’s passenger compartment stays intact while the much heavier and longer Sierra collapses. That’s what more than 20 years of crash testing against deformable barriers has taught car designers.

Comments

  1. That’s all very well and the Fiesta/Sierra test doesn’t surprise me; but surely the tests that need to be done are the expensive one’s where we put different sizes (classes) of cars into each other on small overlap or std. offset.I think if we put the Fiesta against a Galaxy or an S-Max the outcome would be quite different. That’s when the extra weight (approx 300-500kg extra) of the similarly modern but heavier and higher front-ended Galaxy/S-Max would be quite telling. It’s simple physics after all….

    • Agreed. I’d love to see more compatibility testing. Not sure it’s the way to drive real world advances in safety though. Wouldn’t it be easier and more effective to push autonomous emergency braking systems? Simpler to prevent big cars from hitting little cars than to sort out the consequences after impact.

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