BRANDED CONTENT: Reinventing BEV Rocker Structures With a Hybrid Approach

As battery electric vehicles evolve, their body structures face a new set of engineering challenges. The rocker—the structural member running along the lower side of the vehicle—is particularly important. It must contribute to occupant protection and crash energy management while accommodating the packaging demands of a battery-electric platform. Henkel has developed a hybrid structural solution for BEV rocker reinforcement that combines advanced high-strength steel (AHSS), a fibre-reinforced polymer (FRP) insert and expandable structural foam. The objective is straightforward: deliver the crash performance of a highly engineered structural component while reducing weight, complexity and cost.

A hybrid structure designed around load management. At the heart of the concept is an AHSS rocker cavity, typically manufactured in a hat-profile geometry. The steel section provides the primary structural load path, delivering the mechanical strength and geometric foundation required for the rocker assembly.

Inside this cavity sits a specially engineered Henkel FRP insert, which acts as a secondary energy-absorption element. Rather than simply adding material to increase strength, the FRP component uses an optimised rib architecture designed to provide directional stiffness and controlled load distribution. This enables the structure to respond more effectively to crash loads while maintaining compatibility with different rocker geometries and vehicle platforms. 

Structural Foam Completes the System 

The third element is Henkel TEROSON EP14XX expandable structural foam. The foam expands within the structural cavity, helping transfer loads between the individual components while supporting the integrity of the assembly during a crash. The result is a multi-material structural system in which steel, FRP and structural foam perform complementary functions rather than acting as independent components. 

Engineering for BEV Crash Performance

The concept was validated using a simplified rocker substructure incorporating floor and cross-member sections. Henkel benchmarked the hybrid solution against a three-chamber aluminium extrusion, using a dynamic high-speed impact test. The objective was to determine whether the hybrid architecture could deliver comparable structural and crash performance without imposing a weight penalty.

The results are significant. According to testing, the hybrid system achieved peak force and intrusion performance comparable with the conventional aluminium solution, demonstrating its ability to manage crash energy while maintaining structural integrity. Importantly, this performance was achieved without increasing weight.

Up to 20% Cost Reduction
Performance is only one part of the equation for automotive manufacturers. As BEV platforms become increasingly cost-sensitive, the ability to manufacture structural components economically is becoming just as important as their crash performance. Henkel's analysis indicates that the hybrid rocker concept can deliver up to 20% cost reduction compared with traditional aluminium extrusion designs.

This potentially makes the technology particularly attractive for high-volume EV platforms, where even relatively small savings in structural-component cost can have a significant impact on overall vehicle economics.

From Material Supplier to Structural Technology Partner
The significance of the Henkel concept goes beyond a new rocker reinforcement. It illustrates a broader shift taking place in automotive body engineering: materials and joining technologies are increasingly being engineered as part of the structure itself.

Instead of treating adhesives, foams and composite inserts simply as joining or reinforcement materials, the hybrid approach integrates them into the vehicle's load-management architecture. For BEV manufacturers, this opens up the possibility of designing structural components around the complementary characteristics of different materials:

• AHSS provides primary structural strength.
• FRP contributes lightweight stiffness and energy absorption.
• Expandable structural foam supports load transfer and structural integrity.
• The combined architecture enables engineers to optimise crash performance, weight and cost simultaneously.

The Bigger Opportunity
The rocker is just one example of where this philosophy could be applied. As EV manufacturers seek to reduce mass, improve crashworthiness and lower manufacturing costs, multi-material structural design is likely to become increasingly important.

Henkel's BEV rocker reinforcement demonstrates how combining conventional steel architecture with composite reinforcement and engineered structural foam can create a solution that is not simply lighter or stronger—but optimised around the complete performance requirements of an electric vehicle.