Editor | On 13, Oct 2019

Darrell Mann

We head to the Motor City for our patent of the month this month, to a trio of inventors at Ford. Their strengthening-member patent, US10,279, 842, was granted on 7 May. Here’s what the trio has to say about the problem being addressed:

It is desirable, for vehicle strengthening members, to maximize impact energy absorption and bending resistance while minimizing mass per unit length of the strengthening member. Impact energy absorption may be maximized, for example, by assuring that the strengthening member compacts substantially along a longitudinal axis of the strengthening member upon experiencing an impact along this axis. Such longitudinal compaction may be referred to as a stable axial crush of the strengthening member.

When a compressive force is exerted on a strengthening member, for example, by a force due to a front impact load on a vehicle’s front rail or other strengthening member in the engine compartment, the strengthening member can crush in a longitudinal direction to absorb the energy of the collision. In addition, when a bending force is exerted on a strengthening member, for example, by a force due to a side impact load on a vehicle’s front side sill, B-pillar or other strengthening member, the strengthening member can bend to absorb the energy of the collision.

Conventional strengthening members rely on increasing the thickness and hardness of side and/or corner portions to improve crush strength. However, such increased thickness and hardness increases weight of the strengthening member and reduces manufacturing feasibility. It may be desirable to provide a strengthening assembly configured to achieve the same or similar strength increase as provided by the thickened sides and/or corners, while minimizing mass per unit length of the member, and maintaining a high manufacturing feasibility.

Which looks something like this when mapped on to the Contradiction Matrix:

When we see a list of Inventive Principle recommendations like this, it should give us a pretty strong clue that the answer lies primarily within the realms of geometry – Asymmetry (Principle 4), Another Dimension (17) and Local Quality – and that’s pretty much what the inventors’ solution comprises. At first sight, the solution, in fact, is all about geometry, and more specifically the cross-sectional profile, where we see evidence of all three Principles:

Of particular interest, I think is the combination of ‘internal’ and ‘external’ folds, and ‘acute’ and ‘obtuse’ angles. Looking at the presence of Principle 19, Periodic Action amongst the list of recommended solution strategies, I also wonder whether the buckling that eventually takes place in all structures when subject to enough longitudinal compression load is being controlled by the new geometry better than it is in other cross-sectional profiles. Buckling, in other words, doesn’t happen in a linear fashion, it happens through periodic phases of collapse followed by consolidation. Looking at the collapsed images at the beginning of the article, it looks as though these periods of collapse-and-consolidation are constrained by the geometry to occur more often and thus in a more controlled fashion. There’s nothing to this effect in the invention disclosure description. What that description does say, however, is something inventors want to see with all their designs: unexpected non-linear benefits:

…the strengthening member having a twenty-eight-cornered cross section could sustain a much higher crushing force for a given resulting crushing distance as compared with the square, hexagonal, circular, octagonal, and twelve-cornered cross sections. Specifically, the twenty-eight-cornered cross section in accordance with the present teachings achieved about a 145% increase in averaged crush force and/or crash energy absorption as compared with the octagon. A person having ordinary skill in the art would have expected that a strengthening member with four lobes and four protrusions in accordance with the present disclosure would have performed similarly to a strengthening member with a corrugated cross section, which is known to have relatively poor energy absorption and undesirably open in a flower-like fashion when crushed, as evidenced by, for example, the strengthening members with corrugated cross sections shown in U.S. Pat. No. 8,459,726, which is hereby incorporated by reference. Accordingly, the substantially increased energy absorption provided by the strengthening member with a twenty-eight cornered was an unexpected result.

My only doubt beyond this lovely result is how come 28-cornered is the absolute best configuration? I think TRIZ tells us that there are still plenty of degrees of freedom to evolve the design that haven’t as yet been exploited. Consider that your lateral-thinking exercise for the month… what else could/should be done to further increase the energy-absorption-thickness(/weight) ratio?

Meanwhile, let’s not take anything away from the Ford team. What they’ve hit upon looks like it has the potential to chop a significant amount of weight out of, not just automotive, but structures across a range of different domains.