Author(s): Erik Johansson, Sofia Andersson and Henrik Nilsson

Abstract: Roughly 18% of a passenger-car front-suspension assembly mass sits in the steering knuckle, yet conventional knuckle geometries carry material that contributes little to stiffness or strength under realistic service loads. This research applied density-based topology optimization coupled with parametric finite element analysis to reduce the mass of a forged-steel steering knuckle for a B-segment hatchback while satisfying strength constraints under four simultaneous load cases: 1.2 g braking, 0.8 g cornering, combined 1.0 g braking plus 0.6 g cornering, and 3.0 g pothole impact. The baseline knuckle weighed 3.74 kg and was modelled with second-order tetrahedral elements at a mesh density of 1.8 mm mean edge length, producing 412,600 nodes. Design variables were the pseudo-densities of elements in the permissible design domain all regions except bearing seats, bolt interfaces, and the strut-mount contact face. The Solid Isotropic Material with Penalisation (SIMP) method with a penalisation factor of 3.0 and a minimum-member-size filter of 4 mm drove the optimization over five iterations. Convergence was reached at a volume fraction of 0.637, yielding a topologically optimized concept that was smoothed into a manufacturable CAD model with a final mass of 2.83 kg a 24.3% reduction. Validation FEA on the reconstructed geometry confirmed that peak von Mises stress under the combined load case rose from 231.8 MPa (baseline) to 282.1 MPa, still 21.4% below the yield strength of the forging-grade 38MnVS6 steel (359 MPa). Fatigue life estimation using the Goodman criterion at the most stressed fillet predicted a safety factor of 1.47 against infinite life at 10? cycles, satisfying the OEM target of 1.30. The hub-mount region retained 31.4% of the total knuckle mass and was the least affected by material removal, whereas the central web which carried only 12.8% of the baseline mass saw the deepest cuts. These results show that topology optimization under multi-load-case constraints can deliver meaningful weight savings on a safety-relevant suspension component without compromising durability margins.

DOI: https://www.doi.org/10.22271/27078205.2026.v7.i2a.79

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