Skip to content

Small Overlap, Big Challenge

My colleague, Giuseppe Resta, Manager, Global Automotive at Altair Engineering submitted the following blog post.

The Insurance Institute for Highway Safety (IIHS) just released its first results for its new small overlap frontal crash test. Despite the fact that the initial test group consisted of mid-sized luxury and near-luxury sedans, equipped with some of the best safety features available, only three of 11 achieved a good or acceptable rating.  In the test (commonly called SORB, Small Overlap Rigid Barrier), just 25 percent of a vehicle’s front end on the driver side impacts a 5-foot-tall rigid barrier at 40 mph.  It mimics an impact with a pole, tree or another vehicle that, according to the IIHS, as of 2009 represented a quarter of the frontal crashes resulting fatal or serious injury to front occupants.

The poor results indicate that most of the vehicles are just not designed with the SORB load case in mind, but carmakers will quickly address the issue through modifications to both the crumple zone geometry and the occupant restraint systems. Traditional crash absorbing structures are completely bypassed during the event, exposing the vehicle safety structure to bigger deformation and the occupant to stronger deceleration. The Volvo S60 mitigates this by introducing a new active frame rail to engage the barrier directly and by other reinforcements in the A-Pillar and key cross members. The front airbag and safety belt need to be tuned also to this new test dynamic and any uncontrolled movement of the steering column must be suppressed. At this year’s HTC in Detroit Ford’s Bhimaraddi Alavandi showed during his presentation, Semi-Rigid Occupant Simulation Using RADIOSS , how the curtain and torso airbags, historically conceived to deploy only for traditional side impacts, will play an active role in the new 25 percent offset frontal crashes.

SORB events are particularly severe focusing large loads on the car’s outer edges resulting in severe deformation and tearing off or detaching parts. To drive new designs with CAE, material modeling with failure rupture and strain limits is very important for both parts and welding. This can increase computation time, but RADIOSS performance related improvements such as AMS can be used to keep run times under control. No doubt the IIHS will continue to add additional testing regimes to reflect the crash modes. Keeping passengers safe with variations in impact dynamic, speed and even passenger position will require increased application of HPC and design robustness.