3M, Matrix Engineering Consultants Collaborate to Enhance Performance of Chassis Bolted Joints

The vehicle electrification trend means chassis designs are evolving. The increasing number of vehicle variants on a modular architecture can present challenges of how to handle the differences in weight and loading dynamics while utilizing the same or similar carry-over chassis designs. In a new white paper, 3M and Matrix Engineering Consultants demonstrate how the shear capacity of critical bolted connections can be enhanced by using 3MTM Friction Shims. Florian Grimm, Global Technical Lead at 3M Friction Solutions, and Jon Ness, Principal Engineer at Matrix Engineering Consultants, discussed their findings with SAE’s Automotive Engineering magazine.

September 1, 2022

Jon Ness, Principal Engineer at Matrix Engineering Consultants

Automotive Engineering: Why is it important for OEM design engineers to care about bolted joints?

Jon Ness: Although they appear to be relatively simple structures, bolted joints actually play a critical role in the structural integrity and reliability of an automobile. In the automobile application, weight and costs are both critical constraints, even though the joints are highly loaded dynamically. The key to achieving high reliability in dynamically loaded shear joints is to prevent the joints from slipping under all loading conditions. So, that is why engineers need to pay attention to bolted joints.

Automotive Engineering: Bolted joints in vehicles aren’t uncommon. Why is your new study relevant?

Florian Grimm: The number of vehicle variants for a model is increasing — and especially in battery electric vehicles, there are multiple models using the same chassis or ‘skateboard’ design. These variants can present challenges of how to handle differences in weight and loading dynamics while utilizing the same or similar carryover chassis design.

One solution can be to increase the shear capacity of the critical bolted connections. This can either be done by increasing the clamp load in the joint using a stronger bolt or increasing the friction coefficient at the joint interface; 3MTM Friction Shims are an effective way of increasing the friction coefficient with minimal impact to the design as they are very, very thin, nickel-coated steel substrates with partially embedded diamonds. When you place them between two components in a bolted connection, the diamonds bite into each surface to create a microform fit — and that leads to much higher friction within this connection.

Automotive Engineering: Your new white paper takes a deeper dive into the performance of shear loaded bolted joints using finite element analysis?

Jon Ness: Yes — it is common practice to model these joints using finite element analysis, especially in situations where the load path for the joint is unclear or where perhaps the slip behavior of the joint under the load must be modeled accurately. This paper includes a case study of a typical automotive-chassis strut bolted joint, where we took the CAD model and converted it into the finite element model where the strut was loaded in shear. And we completed multiple iterations of the finite element model, where we varied bolt sizes in one case and we ran it with and without a 3MTM Friction Shim. And as expected, the analysis revealed only an incremental increase in the shear capacity due to changing the bolt size — say from M10 to M12 — but using a 3MTM Friction Shim increased a friction coefficient and order of magnitude.

Automotive Engineering: When do you find that that sort of increase in performance is needed — particularly in an existing design?

Florian Grimm, 3M Global Technical Lead, Friction Solutions.

Florian Grimm: Shims are proven customizable solution that have been used in a variety of different applications across the vehicle. While they have commonly been used in engine applications for over 20 years, there’s even more need with electrified powertrains. As we mentioned before, cars are getting heavier due to additional batteries, and examples are chassis applications in subframe or suspension parts, steering components or e-motor and battery mounts.

The white paper detailing the collaboration between 3M and Matrix Engineering Consultants can be downloaded at 3M.com/connections. Watch the full interview with Florian and Jon here.