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| Saab Takes Safety Inspiration from Real Life
Crash tests and real life accident data are used to improve vehicles
“We never forget that we are protecting real people, not just dummies in a laboratory,” says Per Lenhoff as he explains how the team at Saab’s Crash Safety Center are primarily concerned with what actually happens on the road under real-life conditions when it is a person, instead of a dummy, who is behind the wheel or in the passenger seat. Unlike a standard laboratory crash test, each road accident is a unique event because of the almost limitless number of variations in the speed, point, angle or type of impact. The fact that Saab cars are frequently placed at the top of major consumer crash tests published in Europe and the US, as well as Swedish and US surveys of road accident injury claims, demonstrates the effectiveness of their work. In its real-life safety philosophy Saab, almost literally, tries to cover all the angles by studying the outcome of thousands of road accidents involving Saab cars. This work has led, for example, to the use of front and rear crumple zones that are designed to deform in a controlled manner under varying points or angles of impact. Real-life has also demonstrated the effectiveness of Saab's 'pendulum' B-pillar design in handling side impact forces. And it has inspired the development of Saab Active Head Restraints (SAHR), an industry first in helping to prevent neck injury following a rear-end impact. Real-life experience also forms the basis of the crash simulation and testing work carried out by the Safety Center team at Saab's technical development center in Trollhättan, Sweden. They perform many tough tests based on common, real-life accidents that do not figure in consumer crash tests. For example, car-to-car crashes with both vehicles in motion at closing speeds of up to 120 kph; ‘under-ride’ frontal impacts, where a car shoots under the rear of a truck; glancing ‘sideswipe’ impacts, where there is very little time for airbags or seatbelts to be deployed, and roll-overs, which may happen following a collision. Learning and applying the lessons of real-life involves three main areas of activity: accident investigations, crash simulation and crash testing. Each team responsible for the design of a structural safety element or an in-car restraint system will be composed of colleagues working in these areas. In this way, real-life knowledge is shared as widely as possible and embedded in the whole process of safety engineering. Accident Investigations Saab's interest in safety goes right back to the company's roots as an aircraft manufacturer. It is routine practice to ensure the safety of test pilots and their aircraft by investigating accidents, so it was instinctive for engineers in the fledging Saab car division to do likewise. In fact, records show the first road accident investigation involving a Saab car was carried out before commercial production had even begun. Today, the database at the Saab Safety Center holds details of about 6100 real-life accidents involving Saab cars, mainly on Swedish roads. Information can relate to the extent of occupant injury, as well as the performance of structures and safety restraints. “This work is entirely confidential within the department. We are not interested in apportioning blame or finding out who was at fault,” explains Lenhoff. “We focus purely on examining how the car's safety systems have performed in helping to prevent injury so that we can increase our knowledge and understanding.” The safety team work closely with Swedish insurance companies, who usually notify them of about 50 accidents a week. The majority of these cases involve relatively minor incidents but about one or two cases per week are followed up by a full investigation. This involves reference to police reports of the circumstances, a detailed examination of the vehicle and usually a subsequent visit to the accident scene. Where appropriate, occupants may also be interviewed. Here the team-use the services of two medical experts, specializing in trauma and orthopedics, who assist in gaining access to medical records and analyzing injuries. “It is rather like fitting a puzzle together,” says Lenhoff. “When we have assembled all the data, we try to find out exactly how injuries were caused and how the car safety systems functioned.” Whilst most of this work is done in Sweden, members of the crash safety team are prepared to travel almost anywhere in the world in order to increase their knowledge of real-life accidents. “We now have a very large database,” adds Lenhoff. “So we are quite selective in choosing to examine only those cases that will add to our fund of knowledge.” Lessons learned from accident investigations are fed back into the design of future models and, just as important, may lead also to detail improvements in current products. The work also provides the terms of reference for Saab's extensive program of crash simulation and testing. Crash Simulation Advances in CAD (Computer Aided Design) and Finite Element Method (FEM) make it possible to create extremely sophisticated and accurate 'virtual' crashes. About 1,500 simulations are carried out at the Saab Crash Safety Center every year, each one requiring massive computing capacity. The work is now so complex that a real-life collision, which is over in a split second, may take the computer 12 or even 24 hours to reproduce. The crash safety team-liaise closely with their colleagues in design and structural engineering, working with X-ray images that are often composed of 1.2 million tiny cells, each covering details of the car and its components, including the virtual dummies. The data is so detailed, and the calculations so sophisticated, that laboratory testing proves simulations can now function with 90-95 per cent accuracy. Crash simulations are used primarily in product development, allowing engineers and designers to test the effectiveness and compatibility of components, features or systems in the car. These virtual crashes allow the safety team to enact and analyze more impacts, more quickly and more efficiently than they can through physical testing alone. During the development of a new product, for example, it is no longer necessary to conduct crash tests for first or second generation prototypes before validation testing with a third or final prototype. “This is an area of our work which has developed a great deal over the last 10 years and will continue to become more sophisticated,” says Lenhoff. “We can explore the absolute limits through simulation, finding out how deformation structures or restraint systems work in precise detail. “We are now so confident in the results that our crash testing is really just a means of physically verifying what we already know. These days there are very few surprises when we go into the laboratory.” Crash Testing Although there may be few surprises in store for Lenhoff and his team when they carry out crash tests, the sheer scale of their work would probably raise an eyebrow or two. For example, during the development of the latest Saab 9-3 product range no less than 75 different crash configurations were evaluated, only 15 of which were legally required. Many permutations of frontal, side and rear impacts at different speeds and angles are involved, including roll-overs. Apart from using sleds with barriers and poles in the laboratory to replicate collisions with other vehicles and fixed objects, moving car-to-car, and even car-to-truck, impacts are staged. These are severe examinations of crashworthiness that go far beyond the demands of any statutory or consumer crash test standard. But, like all the other tests, they are based on what actually happens in real-life, irrespective of whether the authorities deem them necessary. To satisfy the requirements of real-life, simulation work and crash testing is used to perfect the design of metal joints that are resistant to tearing, as well as those body structures that deform in a controlled and predictable way under varying conditions. As a result, the front structure of a Saab car incorporates three interconnected load paths, behind a broad front beam, that help absorb and dissipate as much crash energy as possible, safeguarding an extremely strong central passenger compartment. Inside this safety cell, the car's interior restraint systems - seatbelts and airbags - must function effectively in helping to minimize potential injury, irrespective of an occupant's age, size or seating location. Even in side impacts, where there is limited scope for a deformation 'buffer', crash testing has helped in the development of a B-pillar (the central post between the doors in the side of the car) that acts as a protective 'pendulum'. This is designed to bend inwards at the bottom, deflecting forces down towards the floor and away from the passenger compartment. “For occupant protection, we focus on the most common areas, such as the risk of neck and head injury,” adds Lenhoff. “From real-life we also know that people are human and will not necessarily do what is best. That's why we have put a lot of effort into having quite a persistent automatic warning system inside the car if the front occupants are not using their seatbelts. And we have in-car safety advice cards, similar to those found in passenger aircraft, to encourage occupants to use such things as seatbelts, head restraints or child seats properly. “At the end of the day, people must use the roads responsibly and do everything possible to avoid getting involved in an accident. But, for whatever reason, if they do become involved in a crash, our job is to help minimize the consequences. Winning awards is recognition of our work, but it is not why we do it.” |
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