This study investigated the thermomechanical behavior of 4D-printed polylactic acid (PLA), focusing on its response to varying temperatures and strain rates in a wide range below the glass transition temperature (T_g). The material was characterized using tension, compression, and dynamic mechanical thermal analysis (DMTA), confirming PLA’s strong dependency on strain rate and temperature. The glass transition temperature of 4D-printed PLA was determined to be 65 °C using a thermal analysis (DMTA). The elastic modulus changed from 1045.7 MPa in the glassy phase to 1.2 MPa in the rubber phase, showing the great shape memory potential of 4D-printed PLA. The filament tension tests revealed that the material’s yield stress strongly depended on the strain rate at room temperature, with values ranging from 56 MPa to 43 MPA as the strain rate decreased. Using a commercial FDM Ultimaker printer, cylindrical compression samples were 3D-printed and then characterized under thermo-mechanical conditions. Thermo-mechanical compression tests were conducted at strain rates ranging from 0.0001 s⁻¹ to 0.1 s⁻¹ and at temperatures below the glass transition temperature (T_g) at 25, 37, and 50 °C. The conducted experimental tests showed that the material had distinct yield stress, strain softening, and strain hardening at very large deformations. Clear strain rate dependence was observed, particularly at quasi-static rates, with the temperature and strain rate significantly influencing PLA’s mechanical properties, including yield stress. Yield stress values varied from 110 MPa at room temperature with a strain rate of 0.1 s⁻¹ to 42 MPa at 50 °C with a strain rate of 0.0001 s⁻¹. This study also included thermo-mechanical adiabatic tests, which revealed that higher strain rates of 0.01 s⁻¹ and 0.1 s⁻¹ led to self-heating due to non-dissipated generated heat. This internal heating caused additional softening at higher strain rates and lower stress values. Thermal imaging revealed temperature increases of 15 °C and 18 °C for strain rates of 0.01 s⁻¹ and 0.1 s⁻¹, respectively.

The plate heat exchanger (PHE) is a component that provides heat to be transferred from hot water to domestic cold water without mixing them with high efficiency. Over the lifetime of the PHE, cyclic pressures act on the brazing points and the plates, and this may lead to fatigue failure. The fatigue behaviour of the PHE, designed using copper-brazed 316L stainless steel, was investigated in this study. First, the fatigue tests under the load ratio R = 0.1 were performed on the Vibrophore 100 testing machine to obtain the S-N curve of the analysed brazed joint. Based on the obtained experimental results, an appropriate material model of the analysed brazed joint has been created, which was validated with numerical calculation in the framework of a program code Ansys. A validated material model was then used for the subsequent numerical analysis of PHE. In order to carry out a numerical calculation using the finite element method (FEM), a three-dimensional model of the heat exchanger was created based on the previous scanning of PHE-geometry. Thereafter, the geometry was parameterised, which allowed us to perform parametric simulations (monitoring different responses depending on the input geometry). Numerical simulations were carried out in the framework of the Ansys 2023-R1 software, whereby the obtained results were analysed, and the responses were appropriately characterised according to previously determined load cases.

This study investigates the thermomechanical response of polylactic acid (PLA) specimens fabricated by fused filament fabrication (FFF) at two nozzle temperatures (190°C and 230°C), while mechanical testing was performed at three temperatures (20°C, 30°C, and 40°C) below the glass transition temperature ( T _g ). Quasi‐static uniaxial tensile and compression tests were conducted to characterize the mechanical response under these thermal conditions. The experimental results showed that increasing nozzle temperature improved tensile stiffness and strength. The highest tensile and compressive properties were obtained for specimens printed at 230°C and tested at 20°C, with tensile modulus and tensile strength of 3573 MPa and 54 MPa, and compressive modulus and compressive strength of 1343 MPa and 71 MPa, respectively, indicating anisotropic mechanical behavior. In addition, dynamic mechanical thermal analysis (DMTA) was also performed to evaluate the viscoelastic response and determine T _g , including a comparison with injection‐molded PLA. To establish a reliable predictive framework for thermomechanical behavior, experimental measurements were used to calibrate the ANSYS‐Three Network Model (TNM). The resulting numerical simulations of the tensile and compression tests demonstrated good agreement with the experimental results, confirming the capability of the model to predict the thermomechanical response of polylactic acid fabricated by fused filament fabrication.

This study presents a predictive manufacturing framework for customizing the biomechanical response of a 3D printed ergonomic armrest based on relaxed Voronoi metamaterials. A double curved armrest geometry was combined with parametric lattice generation, stereolithography printing in BioMed Elastic 50A resin, uniaxial compression testing of cylindrical lattice specimens, and homogenized finite element simulations using a CT derived forearm model under 15, 30, and 45 N loading. The results showed that both cell size and ligament thickness strongly affected compressive behavior, with smaller cells and thicker ligaments producing higher stiffness and earlier densification. Among the uniform configurations selected for simulation, the E-9-1.5 lattice provided the most balanced response, maintaining contact pressure below about 70 kPa up to 45 N, whereas the stiffer E-7-1.5 configuration exceeded 160 kPa and the E-7-1 configuration surpassed 100 kPa at higher load. Based on these findings, a functionally graded Voronoi concept was developed to combine a more compliant central zone with a stiffer peripheral support region while preserving conformity to the complex armrest boundary. Overall, the results show that relaxed Voronoi lattices offer a computationally efficient route toward anatomically conforming and mechanically tunable cushioning interfaces.