Public defence in Mechanical Engineering, M.Sc Anastasia Markou

Title of the thesis: Tailoring Mechanical Properties of Planar Lattice Materials: Mass redistribution, Hybridization, and Novel Topologies 

Thesis defender: Anastasia Markou
Opponent: Prof. Mahmoud Mousavi, Uppsala University, Sweden
Custos: Prof. Luc St-Pierre,Aalto University School of Engineering

Tailoring Mechanical Properties of Planar Lattice Materials: Mass redistribution, Hybridization, and Novel Topologies 

The demand for lighter, more efficient materials is growing—especially in sectors like transportation, where weight reduction helps lower emissions. Cellular solids, with their porous, lattice-like structures, offer a unique combination of low weight and high strength. Thanks to advances in additive manufacturing, these materials can now be produced with complex architectures, enabling tailored mechanical properties for specific engineering needs.

This doctoral thesis investigates how the mechanical behavior of planar lattice materials can be tailored through design. The work focuses on three strategies: i) redistributing material within the structure (mass redistribution), ii) combining different types of lattice cells (hybridization), and iii) introducing entirely new geometrical designs (novel topologies). The goal is to gain fine control over key mechanical properties such as stiffness, strength, and failure behavior—without increasing material usage.

The first part of the study introduces a novel design parameter called the thickness ratio, which controls the relative thickness of different struts in the lattice. This parameter allows for significant tuning of directional stiffness and strength while keeping the overall material density unchanged. For instance, carefully adjusting the thickness ratio in triangular and hexagonal lattices resulted in up to 3.8 times greater compressive strength in one direction, while also allowing for controlled anisotropy.

The second part, investigates hybrid lattices that combine stiff triangular cells with flexible hexagonal ones. Symmetric hybrids showed high strength and stiffness near the transition from bending- to stretching-dominated behavior, while random hybrids offered broader mechanical versatility.

The third part of the thesis explored a class of lesser-known structures called demi-regular lattices. These geometries offer isotropic stiffness similar to triangular lattices but significantly improved resistance to elastic buckling—up to 42% higher. This makes them particularly promising for ultra-lightweight applications where stability under load is critical.

Combining analytical models, simulations (FEM), and experiments on 3D-printed polymer samples, this work provides a comprehensive framework for designing high-performance lattice materials, advancing future engineering solutions.

Keywords: Lattice materials, Mechanical properties, Theoretical analysis, Finite Element Analysis (FEA), Mechanical testing, Demi-regular lattices

Thesis available for public display 10 days prior to the defence at Aaltodoc. 

Contact information: 
Name: Anastasia Markou 
Email: anastasia.markou@aalto.fi 
LinkedIn: www.linkedin.com/in/anastasia-markou