To address challenges such as gray elements and material overlaps, this paper extends the level set-based negative-mapping interpolation method to the multi-material proportional topology optimization of macro-scale structures in two and three dimensions. The approach utilizes an alternating active-phase algorithm to decompose M-phase problems into simplified two-phase subproblems described by level set functions. By integrating an evolutionary strategy, the method circumvents complex sensitivity calculations. A negative-mapping interpolation then removes the material overlaps at the interfaces. Numerical experiments on 2D cantilever and MBB beams and on a 3D cantilever beam demonstrate that the present method eradicates gray elements, produces smooth boundaries and ensures overlap-free material distributions at a compliance comparable to that of the classical SIMP method, lower than the SIMP value in four of the eight two-dimensional test cases and higher by 0.3%, 0.4%, 4.8% and 12.7% in the other four; the influence of the material properties, of the interface treatment and of the number of iterations on the results is also discussed.

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