When we think about efficiency, we think about all the different regulations, restrictions and requirements the modern vehicle has to adhere to and how we can manage what we have and make it better, optimize every little detail and try to maximize the car's potential to the fullest. That means introducing new structural parts, material science and engineering excellence to existing and future vehicle concepts and optimizing potential areas accordingly. Every small improvement and detail counts and can become a massive factor in efficiency, whereby we talk about up to 50 percent of potential weight savings for multiple parts in the vehicle while maintaining the structural integrity, safety and improving the performance and efficiency of the entire concept, all in one stop.
Ambitious approach
In the light of these constraints, Henkel and RLE International have undertaken a collaborative study targeted at reducing the weight of closures, fenders, pillars, bumpers etc. by 10 to 15 percent without compromising stiffness and crash performance in line with standard automotive crash scenarios. The ambitious approach is based on the extensive replacement of common all-metal (steel) components by hybrid designs with rigid local reinforcement patches using high-performance structural foam.
The structural foam behind the concept
The structural foam used in the hybrid designs is an epoxy-based Teroson® EP material from Henkel that delivers high strength and stiffness at extremely low weight. The non-cured injected foam is resistant to normal automotive washing and phosphating solutions as well as to electro-dip coating. It cures within 15 minutes when passing through the e-coat oven. The current material technology features a commercially available grade (EP 1450) with extensive approvals from automakers worldwide. Typical properties are listed in Table I.
Several OEMs are already using the material in various lightweight hybrid structural parts, replacing traditional steel reinforcements. Further grades are in the pipeline and are being developed with a focus on lowering the cured foam density, increasing the foam expansion beyond 100 percent and reducing the required curing time.
Table I: Properties of Teroson® EP structural foam (based on typical test results)
Uncured |
|
|---|---|
| Colour | grey |
| Consistency | solid |
| Density at delivery | aprox. 1.3g/cm3 |
| Solids Content | > 99% |
| (3h, 105°C) | |
Cured |
|
| Recommended curing conditions: | |
| mini: | 15 min 155°C (keep) |
| maxi: | 15 min 195 °C (keep) |
| Density after expansion | approx. 0.6 g/cm3 |
| Expansion | >100% |
| Compression test | |
| Compressive strength | > 10 MPa |
| Compressive modulus | > 450 Mpa |
| Lap shear strength | |
| Substrates | galvanized steel |
| Bonding Area | 20 x 25 mm |
| Layer thickness | 2 mm |
| Strength | >2 MPa |
| Glass transition | >100°C |
| temperature range | |
| (Tg) DMTA (40Hz, 2K/min | |
| Corosion resistance | |
| Salt spray test | no corrosion, no loss of adhesion |
| (35°C, salt solution 5%, 500 hours) | |
| Corrosion test (VDA 621-415) | no corrosion, no loss of adhesion |
| Water absorption | <0.5% weight increase |
| (24 h, 98% humidity, 40°C) | |
| In service temperature | -30 to 80°C |