EDAG study finds NanoSteel sheet steels can achieve up to 30% weight reduction in automotive structures
|NanoSteel body-in-white using the three grades of steel. Click to enlarge.
The NanoSteel Company released the results of an automotive light-weighting study it had commissioned from EDAG, Inc., an independent engineering firm, demonstrating the potential for the company’s Advanced High Strength Steel (AHSS) (earlier post) to enable a 30% reduction of weight in the BIW (body-in-white) structure of a baseline mass-market sedan.
EDAG used methodology in the study consistent with recent similar studies, including NHTSA’s “Light Weight Vehicle (LWV)” study in 2012, and WorldAutoSteel’s “Future Steel Vehicle” design in 2011. The NHTSA LWV study was a comprehensive redesign of the 2011 Honda Accord that met North American competitive targets for safety and other significant vehicle attributes while optimizing for weight savings. EDAG duplicated the criteria and methods used then have been duplicated in that study to investigate NanoSteel’s materials.
NanoSteel materials are designed with a combination of high strength and formability that permit complex part designs while utilizing conventional manufacturing processes. The NanoSteel sheet steels enable the use of thinner gauges of steel, which provide superior tensile and elongation properties compared to currently available steels.
When applying NanoSteel’s AHSS to the NHTSA Light Weight Vehicle design, EDAG calibrated material gauges and design parameters to ensure the vehicle met crashworthiness criteria, as well as noise, vibration and harshness (NVH) requirements. In the study, EDAG tested for torsional stiffness, bending stiffness and normal modes frequency. Additionally, EDAG tested for frontal, frontal offset, side impact, side pole, roof crush and rear impact.
NanoSteel’s three classes of AHSS (N1, N2 and N3) were used to replace crush zone parts that require high energy absorption, deep draw parts with significant complexity and structural parts such as B-pillars and cross-members where strength is paramount to protect the passenger.
N1 Grade was used for external body panels due to the need for high formability. The ability to create Class A surfaces has not yet been validated.
N2 Grade was used for front and rear crash rails and floor structure due to its high work-hardening capability, which allows for large amounts of energy absorption during a crash event.
N3 Grade was used for the roof structure and body side structure where the highest possible strength is required to maintain the integrity of the passenger compartment.
Among the findings of the study were:
NanoSteel’s three grades of sheet steel offer progressively higher strength and lower elongation, from N1 at 450/950 MPa with 35% elongation, to N2 at 450/1200 MPa with 20% elongation and N3 at 1000/1600 MPa and 12% elongation. In replacing the grades used for the LWV Body-in- White (BIW), equivalent elongation was the key feature used to determine which grades could be substituted.
Although no formability analysis was carried out in this study, NanoSteel’s sheet steel mechanical properties indicate better formability at equivalent or higher strength levels. Consequently, the majority of the LWV BIW panels were replaced with reduced-gauge NanoSteel panels. Since NanoSteel’s sheet steel has been developed to be cold formable in parts production, no hot stamping is required.
When NanoSteel’s grades were substituted for the LWV BIW steels, an incremental mass reduction of 10.5% (27 kg/60 lb) was generated versus the LWV BIW, amounting to a 30% reduction (100 kg/220 lb) from the baseline Honda Accord. This was achieved at equivalent simulated vehicle attribute performance, including crashworthiness, noise, vibration and harshness. In this study, there was no redesign of the automotive architecture from the LWV. Assuming the architecture was optimized for the attributes of these new materials, geometries would be adjusted and additional weight reduction could likely be attained.
The light-weighting findings from the study demonstrate how the high strength and elongation of NanoSteel’s sheet steels can provide automakers with the ability to use thinner gauges of stronger steels in a significant number of assemblies and parts to reduce weight while increasing the fuel efficiency of mass market vehicles, the company suggested.
In August 2012, General Motors Ventures LLC announced an investment in NanoSteel Company.