Computer crash tests

Crash tests may come across as an outdated evaluation method, but they do save lives. However, the real breakthrough in greater passive safety for vehicles was achieved with crash simulations on computers. TECOSIM began assisting vehicle manufacturers with such simulations when it was formed as a start-up 25 years ago. Today, the company performs all types of simulations on a large scale, delivering precise predictions on how a structure will behave in an emergency.

The first Mercedes-Benz crash test of 10 September 1959 (Image: Mercedes-Benz).

It is 10 September 1959. The United States and the Soviet Union are fighting for supremacy in the Space Race, Fidel Castro has taken power in Cuba and the first small car in the Mini range has just come onto the market in the UK. A group of engineers are standing next to a new test set-up in an open field in the Mercedes-Benz Sindelfingen works in South Germany. A test vehicle which dices with death is the focal point of attention. In front is a solid barrier made of used press dies. There is a cable between the vehicle and barrier, part of a towing system which the Mercedes testers have borrowed from glider pilots at HFT Stuttgart, the city's technical university. But the towing system is not launching any aircraft today; instead, it is catapulting the test vehicle along a direct collision path. The vehicle takes full frontal impact.

Beginning of a new era

The first crash test in Sindelfingen marks the beginning of a new era. The focus of development work shifts to passive safety for the first time after being previously limited to analyses of accidents in the field. There were almost 14,000 deaths in 843,412 accidents when traffic volumes were still pretty low back in 1959. This means that every 60th road accident resulted in a death. In 2015, 3,475 people died in some 2.5 million accidents in Germany, meaning "just" 1 in 720 accidents resulted in death. Every death is tragic, of course, yet the figures show that the decades of hard work by engineers has paid off: it saves lives. "From a technical perspective, a solution has been found for the key issues of passive safety," says Mark Gevers, General Manager at TECOSIM's Cologne location. Involved with crash simulation for decades, the expert adds: "A decisive factor in this advance is the development of CAE, computer-aided engineering, which has allowed systematic accident simulation and analysis on computers since the 1990s."

However, physical crash tests prevail initially. "Passive safety was a privilege limited to luxury class vehicles for many years and was used to provide differentiation from the competition," reports Gevers. Manufacturers which occupy this segment primarily include Mercedes-Benz and Volvo. Initially, the opinion prevails that vehicle bodies should be as rigid as possible to provide the greatest possible occupant safety. However, crash tests show that such vehicle bodies survive accidents largely intact, but the kinetic energy is channelled to the occupants, leading to serious injuries. Consequently, design engineers develop car bodies with a high-strength passenger safety cell and crumple zones at the front and rear, such as the car body for the Mercedes W 111 with its popular fintails.

The diagram uses virtual crash testing to illustrate the development of computer-aided engineering over the last 25 years

"Democratisation" is extended to the mass market segment

Numerical crash simulation has its origins in the 1980s. Individual auto-manufacturers begin to use the finite element method (FEM) to calculate vehicle parts such as longitudinal beams. In doing so, they use FEM to dismantle the model concerned into a specific number of simply shaped partial bodies. However, computer capacities are limited, meaning that it is only possible to recalculate real crash tests at a low resolution to validate the procedure used. Numerical crash simulation does not become prevalent until parallel multi-processor computers emerge and development departments are widely equipped with desktop computers in the early nineties. CAE software such as Pam-Crash, LS-Dyna, Radioss and Abaqus become established tools.

Crash simulation thus enables passive safety measures to be developed and evaluated without expensive, complex physical crash tests for the first time. Safety is now no longer reserved just for luxury class motors – "democratisation" is extended to the mass market segment. It is also time for service providers to come to the fore: in 1992, Ulrich Rusche founded TECOSIM as a company in his Rüsselsheim living room with three computers and a small team of CAE engineers. Just one year later, TECOSIM calculates frontal impact behaviour in a new generation of Fiestas for Ford. This represents a first milestone in integrating CAE into development departments at major automotive manufacturers since the results from the calculation are confirmed in real crash tests. "At that time, Ford was a "fast follower" which sought to bring technologies to the wider public with the aid of simulation procedures," explains Gevers. Other manufacturers soon follow with TECOSIM calculating crash characteristics for a new platform for Opel's European model Omega in 1994.

This was seen as a breakthrough at the time, but is now regarded as just the beginning since the resolution with which developers work today is about 240 times greater than in the mid-1990s. In simulated crash tests, the numerous distortions which emerge during deformation need to be calculated. This allows engineers to find out what effect the kinetic energy from a collision has on the vehicle body structure. In 1992, the model for complete vehicle crash consisted of about 25,000 elements. Today, some six million elements are calculated in a crash simulation. This is only possible, because computing capacity has permanently increased over the last 25 years and software tools have become increasingly more powerful. Despite the significantly higher number of calculation elements, a calculation procedure now takes just 15 hours instead of the previous 150. It is not only thanks to individual processors experiencing an exponential increase in power, but also calculations being performed in clusters on several computers.

Computer crash tests have allowed systematic accident simulation and analysis on software since the nineties (Image: TECOSIM TEC|BENCH)

Laws and regulations

How essential numerical simulation has become for passive safety is not only shown by the fact that far fewer occupants are injured in accidents nowadays. There are also increasingly more laws and regulations, such as those by the Euro NCAP Organisation, which vehicle manufacturers must observe when new vehicles and model ranges are approved. In 1992, there were fewer than ten such regulations; today, there are more than 50 worldwide, covering all aspects, from frontal and side impact through to rear collision and roof crush. The number of real crash tests has increased marginally in the same period. Whereas, in 1992, there were some 100 tests for each type approval, today about 100 to 150 are required, primarily because they are mandatory under legislation. "Simulations are so reliable today that an approval procedure based entirely on crash simulations is almost upon us," affirms Gevers.

With or without real crash tests, numerical simulation has become standard practice in the development of passive safety concepts. "Today, simulation is a matter of course to some extent, but that does not mean that it is any less important," stresses Gevers. The figures speak for themselves. When TECOSIM was established back in 1992, around 250 crash simulations formed part of a new vehicle's design process. Today, there are about 25,000, a hundred times as many. Crash testing demonstrates that it would be hard to imagine automotive development without CAE, all the more so because of new requirements for active safety whether this is for assisted and automated driving or new, electrified vehicle concepts. The development which began back on the field in Sindelfingen continues apace.