Technical specifications tell one story about a material’s capabilities. Real-world applications tell another—often more compelling—story about how those specifications translate into solved engineering problems and competitive advantages. ROHACELL® and ROHACRYL® foams from Evonik have accumulated an impressive track record across industries ranging from commercial aviation to competitive sailing. Examining specific projects reveals patterns in how engineers leverage these materials’ unique properties to achieve results that alternative approaches simply couldn’t deliver.
The following case studies represent a cross-section of applications where PMI and acrylic foam cores proved decisive. Each project faced distinct constraints—weight budgets, thermal environments, production volumes, regulatory requirements—and each demonstrates how tailored foam selection enables design solutions that balance competing demands in ways conventional materials cannot.
Aerospace: Next-Generation Radome Development
When a major aerospace systems integrator began developing a new radome design for commercial aircraft, the electromagnetic transparency requirements were exacting. Radar and communication signals needed to pass through the structure with minimal attenuation or distortion—any degradation in signal quality would compromise safety-critical systems. The structural demands were equally challenging: the radome would face aerodynamic loads, bird strike risks, and thermal cycling from ground-level temperatures to high-altitude cold.
The engineering team selected ROHACELL® HF specifically for its extremely low dielectric constants and favorable transmission properties in the high-frequency region. Unlike alternative foam cores, ROHACELL® HF wouldn’t interfere with the sensitive antenna systems housed within the radome. The extremely fine cell structure delivered additional benefits:
- Minimal resin uptake during the prepreg layup process preserved the electromagnetic properties by preventing excessive resin accumulation in the core
- Consistent cell distribution across large panels eliminated localized variations that could create signal anomalies
- The foam’s thermoformability allowed the complex double-curvature geometry without machining from solid blocks, reducing material waste and production time
Processing occurred via autoclave cure at temperatures reaching 130°C with pressures up to 0.3 MPa—conditions well within ROHACELL® HF’s processing envelope. The finished radomes met all electromagnetic transmission specifications while achieving a 15% weight reduction compared to the previous-generation design they replaced. That weight savings, distributed across a fleet of commercial aircraft, translates into substantial fuel savings over the service life of each radome.
Helicopter Rotor Blade Optimization
Rotor blade design represents one of the most demanding applications in composite engineering. The blades experience extreme centrifugal loads, complex aerodynamic forces, and fatigue cycling measured in millions of load reversals over their service life. Any core material used in rotor blade construction must maintain its mechanical properties under these conditions while contributing to the blade’s overall stiffness-to-weight optimization.
A helicopter manufacturer’s advanced development program selected ROHACELL® WF for both main and tail rotor blade applications. The choice reflected ROHACELL® WF’s status as the first choice for aeronautic and aerospace applications, backed by qualification to MIL and CMS specifications that simplified the certification pathway. The blade design exploited several key properties:
- Outstanding compressive creep resistance ensured dimensional stability under the sustained centrifugal loading that rotor blades experience during operation
- Excellent dynamic strength accommodated the high-cycle fatigue environment inherent to rotorcraft applications
- The foam’s ability to be precisely machined allowed complex internal spar geometries that optimized the blade’s mass distribution for reduced vibration
The resulting blades demonstrated improved fatigue life in qualification testing, contributing to extended maintenance intervals and reduced lifecycle costs for operators. The manufacturer has since expanded ROHACELL® WF usage to fuselage panel applications, where the material’s strength-to-weight ratio and thermal stability proved equally advantageous.
Wind Energy: 80-Meter Blade Manufacturing
Wind turbine blade lengths have increased dramatically as the industry pursues greater energy capture efficiency. An 80-meter blade—now common in utility-scale installations—presents manufacturing challenges that simply didn’t exist when blades measured 40 meters. The sheer material volumes involved, combined with pressure to reduce per-blade costs, demand core materials that balance performance with economic viability at production scale.
A leading blade manufacturer restructured their core material strategy around ROHACRYL® SW for new blade programs. The decision reflected multiple factors aligning favorably. The foam’s recyclable structural formulation addressed increasingly stringent sustainability requirements from wind farm developers and regulators. Mechanical properties, particularly the shear modulus reaching 47 MPa, provided adequate stiffness for spar cap and shear web applications where structural demands are most intense.
The resin uptake characteristics proved particularly significant at blade scale. With surface areas measured in hundreds of square meters per blade, the difference between 250 g/m² resin uptake and the 400-500 g/m² typical of some competing materials represented meaningful weight and cost implications. Across annual production volumes measured in thousands of blades, those per-blade savings accumulated into substantial competitive advantage.
ROHACRYL® SW’s 120°C thermal stability also enabled process optimization. The manufacturer implemented higher-temperature cure profiles that reduced cycle times without risking core degradation. The throughput improvement allowed them to meet growing order volumes without proportional capacity expansion—a significant capital efficiency gain in an industry characterized by high facility investment.
Automotive: Structural Battery Enclosure
Electric vehicle development has created new composite applications that didn’t exist a decade ago. Battery enclosures must protect cells from external impact, contain thermal events, and contribute to overall vehicle structure—all while minimizing weight that would otherwise reduce driving range. A European automotive OEM partnered with their tier-one supplier to develop a next-generation battery enclosure using sandwich composite construction.
The application demanded core material that could withstand the thermal environment near battery cells, which generate significant heat during charging and discharge cycles. ROHACRYL® SW’s 120°C thermal stability provided necessary margin above expected operating temperatures. The closed-cell structure delivered additional benefits specific to battery applications:
- Inherent thermal insulation properties contributed to battery thermal management
- The foam remained dimensionally stable through the thermal cycling that battery enclosures experience over vehicle life
- CNC machinability allowed integration of mounting features and cable routing channels directly into the core material
- Recyclability aligned with automotive end-of-life vehicle regulations in European markets
The resulting enclosure achieved target weight specifications while passing all structural and safety qualification tests. Production-scale manufacturing using vacuum infusion proved economically viable, validating ROHACRYL® for high-volume automotive applications where cost sensitivity is intense.
Medical Imaging: X-Ray Equipment Tables
Medical imaging equipment presents unusual material requirements. X-ray tables must support patient weight while remaining essentially transparent to radiation—any material that attenuates or scatters the X-ray beam degrades image quality and potentially increases patient radiation exposure. Traditional materials forced compromises between structural capability and radiographic transparency.
ROHACELL® HF found application in X-ray table construction specifically for its exceptional performance in electronic-medical devices. The foam’s extremely low density combined with minimal beam attenuation allowed table designs that met structural requirements without compromising image quality. The fine cell structure ensured uniform material properties across the table surface, eliminating the risk of localized density variations that could create imaging artifacts.
Processing flexibility allowed manufacturers to produce complex table geometries through thermoforming, reducing the machining operations and material waste associated with alternative approaches. The resulting tables demonstrated measurable improvements in image quality compared to designs using conventional materials, while maintaining full structural qualification under relevant medical device standards.
Lessons Across Applications
These case studies share common threads despite spanning vastly different industries. In each instance, engineers exploited specific ROHACELL® or ROHACRYL® properties to solve problems that couldn’t be addressed through conventional material selection. The ability to tailor cell sizes for specific processing methods appeared repeatedly as a decisive factor—enabling optimization for prepreg, infusion, or RTM processes depending on application requirements.
The economic dimension proved equally consistent. None of these applications selected foam core materials purely on performance criteria. Each balanced capability against cost, production volume requirements, and process integration considerations. ROHACELL® grades addressed applications where premium performance justified premium pricing, while ROHACRYL® opened opportunities in cost-sensitive, high-volume contexts where legacy PMI pricing would have been prohibitive.
Perhaps most significantly, these projects demonstrate that advanced foam core materials have matured beyond aerospace specialty applications into mainstream industrial use. The combination of thermal stability, mechanical properties, and processing versatility now available enables sandwich composite construction in applications where it simply wasn’t practical a generation ago. That expansion continues as engineers in additional industries discover how these materials can transform their design possibilities.
