Recycled PET Composites Reinforced with Stainless Steel Lattice Structures Made by AM

Polyethylene terephthalate (PET) recycling is one of the most important environmental issues, assuring a cleaner environment and reducing the carbon footprint of technological products, taking into account the quantities used year by year. The recycling possibilities depend on the quality of the collected material and on the targeted product. Current research aims to increase recycling quantities by putting together recycled PET in an innovative way as a filler for the additive manufactured metallic lattice structure. Starting from the structures mentioned above, a new range of composite materials was created: IPC (interpenetrating phase composites), materials with a complex architecture in which a solid phase, the reinforcement, is uniquely combined with the other phase, heated to the temperature of melting. The lattice structure was modeled by the intersection of two rings using Solid Works, which generates the lattice structure, which was further produced by an additive manufacturing technique from 316L stainless steel. The compressive strength shows low values for recycled PET, of about 26 MPa, while the stainless-steel lattice structure has about 47 MPa. Recycled PET molding into the lattice structure increases its compressive strength at 53 MPa. The Young's moduli are influenced by the recycled PET reinforcement by an increase from about 1400 MPa for the bare lattice structure to about 1750 MPa for the reinforced structure. This sustains the idea that recycled PET improves the composite elastic behavior due to its superior Young's modulus of about 1570 MPa, acting synergically with the stainless-steel lattice structure. The morphology was investigated with SEM microscopy, revealing the binding ability of recycled PET to the 316L surface, assuring a coherent composite. The failure was also investigated using SEM microscopy, revealing that the microstructural unevenness may act as a local tensor, which promotes the interfacial failure within local de-laminations that weakens the composite, which finally breaks.

A New Uniaxial Tensile Model for Foam Metal/Epoxy Interpenetrated Phase Composites

Foam metal/epoxy interpenetrating phase composite is a new type of composite material with interpenetrating continuity in composition, which exhibits different intrinsic relationships under different stress states in tension and compression, and it is necessary to study the intrinsic relationships in the tensile state in depth. A mesoscopic damage-based tensile intrinsic model is developed, and the elasto-plastic tensile intrinsic equations of the representative volume element are derived based on small deformation theory and total strain theory, as well as the assumptions of equal stress and equal strain. The tensile strengths of nickel-iron foam/epoxy interpenetrated phase composites in three different sizes and their constituent phases were measured, and it was shown in the results that the composite of three-dimensional network interpenetration with high-strength foam metal and epoxy resin formed a weak surface inside the material, and did not significantly improve the tensile strength of the composites. The tensile instantonal equations and damage instantonal equations of nickel-iron foam/epoxy interpenetrated phase composites were predicted by the method of inversion, and the applicability and high accuracy of the tensile intrinsic model were verified in comparison with the measured results.

The Influence of the Microstructure of Ceramic-Elastomer Composites on Their Energy Absorption Capability

The paper presents the experimental results of static and dynamic compressive tests conducted on ceramic-elastomer composites. The alumina ceramic preforms were fabricated by the four-step method: ceramic mixture preparation, consolidation under pressure, presintering, and sintering under pressure, respectively. To obtain ceramic preforms with a similar volume fraction of open pores, but with different pore sizes, alumina powder with different particle size and a ceramic binder were used, as well as pore-forming agents that were evenly distributed throughout the volume of the molding mass. The composites were obtained using vacuum pressure infiltration of porous alumina ceramic by urea-urethane elastomer in liquid form. As a result, the obtained composites were characterized by two phases that interpenetrated three-dimensionally and topologically throughout the microstructure. The microstructure of the ceramic preforms was revealed by X-ray tomography, which indicated that the alumina preforms had similar porosity of approximately 40% vol. but different pore diameter in the range of 6 to 34 µm. After composite fabrication, image analysis was carried out. Due to the microstructure of the ceramic preforms, the composites differed in the specific surface fraction of the interphase boundaries (S_v). The highest value of the S_v parameter was achieved for composite fabricated by infiltration method of using ceramic preform with the smallest pore size. Static and dynamic tests were carried out using different strain rate: 1.4·10⁻³, 7·10⁻², 1.4·10⁻¹, and 3·10³ s⁻¹. Compressive strength, stress at plateau zone, and absorbed energy were determined. It was found that the ceramic-elastomer composites’ ability to absorb energy depended on the specific surface fraction of the interphase boundaries and achieved a value between 15.3 MJ/m³ in static test and 51.1 MJ/m³ for dynamic strain rate.

Uniaxial Compression Mechanical Properties of Foam Nickel/Iron-Epoxy Interpenetrating Phase Composites

The damage process and failure mechanisms were analyzed by a series of quasi-static compressive experiments of seven materials including pure epoxy (EP), three different PPI (pores per linear inch) foam nickel-iron, and three different PPI foam nickel/iron-epoxy interpenetrating phase composites (IPC). Plotting the stress-strain curves of different materials, their change rules are discussed, then the effective elastic modulus and yield limit of the materials are provided, and the energy absorption properties of different materials are analyzed by the stress-strain curves. It was found that the effective elastic modulus and specific stiffness of the three IPC materials were higher than pure foam nickel-iron. The brittleness of epoxy can be obviously changed by selecting a suitable PPI foam nickel-iron composited with it. The unit volume energy absorption rate of foam nickel/iron-epoxy was significantly higher than pure epoxy and pure foam nickel-iron. It was also found that the energy absorption rate decreased with the increase in PPI. The stress relaxation rate decreased first and then increased with the increase in PPI. The creep behavior of the three composites was obvious in the creep elastic stage, and the creep rate increased with the increase in PPI. The creep rate decreased with the increase in PPI in the creep transition stage.