K 2007 Trade press conference
July 3 and 4, 2007 in Frankenthal, Germany
5000 hours in hot oil and then struck by stones
Impact simulation on aged plastic
Presentation by Thomas Hohenstein,
Applications Development, Engineering Plastics, Automotive,
Power Train,
BASF Aktiengesellschaft, Ludwigshafen, Germany
The significance of computers in the development of plastic parts has grown considerably, not least thanks to the efforts by BASF.The technique of Integrative Simulation has recently also been utilized to configure crash-relevant and safety-relevant plastic components that perform their duty under the engine hood. In a parallel development, BASF has considerably expanded the material data available for selected materials and refined the mathematical description of the material behavior. These new insights make it possible to realistically simulate, analyze and also optimize the behavior of components that have been in contact with oil for years or that have aged in hot air. One example is oil pans made of the glass-fiber-reinforced polyamide Ultramid® A3HG7 Q17 which, after a long operating time, are struck by stones or, in case of repairs being made to the engine, are placed roughly onto the floor of the workshop.
Stone impact under the engine hood
The statutory regulations for pedestrian protection stipulate that even components installed under the engine hood have to absorb energy, that is to say, fail in a controlled manner, in case of impact with a person’s head. For this reason, air filter systems, for instance, have been developed with weakened points that collapse in case of a crash, thus reducing the acceleration of the head. However, through a combination of material know-how and mathematical simulation, even parts in the engine compartment such as oil pans, which do not have anything to do with pedestrian safety, can be optimized in terms of their short-term dynamic (i.e. impact) properties. Motor-oil or transmission-oil pans made of plastic have to be able to withstand damage caused by stones – a special kind of impact – or, for instance, striking the edge of a curb or being placed onto the floor roughly after being dismantled. Leakage must not occur in any of these stress cases.Components that carry fuel such as fuel filters can also benefit from optimized simulation methods since they can then be configured – with less need for prototypes – in such a way that no flammable medium can escape if they are damaged.
Hot-oil contact, high-speed measurement and integration into the simulation
The mathematical modeling of impact fromstones in the area of the power train poses two special challenges in comparison to crash simulation involving the car body: the loads are not distributed over a wide area but rather, are very localized as well as highly dynamic. Atthe same time the ageing of the plastic after exposure to hot oil or air has to be taken into account. Solutions have now been found for both of these issues:Some time ago, BASF conducted accelerated tensile tests as well as a sophisticated, automatic optical determination of measured values; it then ascertained the plastic-specific behavior at crash-typical strain rates of 102/s, took the material models derived from the obtained data and integrated them into familiar simulation tools. This approach has already been successfully employed several times.
Even though these very capable instruments can account for strain rates and fiber orientation as well as for parameters such as temperature and material moisture, up to now they had not been able to ascertain the ageing effects on the plastic. Now, however, with a great deal of effort, BASF has succeeded in integrating plastic ageing almost completely into its material models. In order for these models to be based on realistic data, comprehensive batteries of measurements have been and continue to be carried out on Ultramid® samples that were kept in hot oil at a temperature of up to 160°C [320°F] for up to 5,000 hours or that were aged in hot air.Since 1,000 hours correspond to a car’s being driven for about 100,000 kilometers, 5,000 hours of contact with oil by far exceed the estimated service life of an automobile. This ensures greater reliability for the configuration and also allows conclusions to be drawn about especially long-lasting applications such as those typically encountered in the realm of utility vehicles or stationary diesel engines.
Good correlation between reality and model
The high-speed measurement of material characteristic values on these test specimens thus yields all of the prerequisites for using a computer in order to test and optimize the stressability of aged engine components prior to building more complex prototypes. By constantly comparing simulations and calculations, and by continuously refining the material models, BASF has now attained a good correlation between the calculations and the test results.The example of an oil pan made of Ultramid® A3HG7 Q17 serves to demonstrate the computer-assisted impact simulation of an engine component. This material, which has been characterized in great detail, stands out for its improved mechanical properties which are safeguarded by correspondingly narrow specifications.A direct comparison between the actual impact by a projectile, which represents a stone striking the outer wall, and the simulation of this event in the computer clearly reveals the benefits of the method.
The support provided by BASF enables users to quickly and economically develop such components that are exposed to abrupt loads. This is the first time that ageing in media such as air or oil has been taken into consideration for the mathematical optimization of selected materials. In the case of stones, for example, ribs can be configured in such a manner that they sufficiently protect the pan against being destroyed while still remaining intact themselves. As an alternative, it could be advisable to configure the ribs as so-called sacrifice ribs. They consume the kinetic energy of a striking projectile and are partially destroyed in the process. The pan containing the oil, however, remains unaffected.
Thanks to Ultramid® A3HG7 Q17, which has been specifically optimized for oil pan applications, as well as the associated simulation methods, it has now become possible to predict and systematically influence the behavior of components following highly dynamic stress such as that caused by stones, a free fall or a crash. This leads to completely new fields of application such as, for example, automotive oil pans, which up to now did not seem feasible in plastic. In the coming years, interesting components will go into serial production, components that did not seem possible a short while ago.
Photo: BASF, 2007
The technique of Integrative Simulation, which was developed by BASF and is particularly well-suited to predict crash behavior, has recently also been utilized to configure crash-relevant and safety-relevant plastic components – such as oil pans – that perform their duty under the engine hood. As a result, BASF can realistically simulate the behavior of components that have been in contact with hot oil for years or that have aged in hot air. Ribs or so-called sacrifice ribs can be manufactured in order to protect these plastic transmission-oil and engine-oil pans as well as their hot, flammable contents from the effects of stones. They consume the energy of the stone at the time of the impact, are partially destroyed as a result and thus protect the oil pan, which remains intact.