EAGER: Stereolithography-based Multi-material Additive Manufacturing of Particle-reinforced Composite Lattices to Achieve Tunable Negative-Thermal-Expansions

University Of Southern California, Los Angeles CA

Investigators

Abstract

Solid materials usually expand when heated. This property may induce severe thermal mismatch problems in a wide range of engineering settings. It is highly desirable to manufacture materials with nearly-zero or negative thermal expansions that can mitigate the thermal mismatch. One promising approach is to harness the geometrical interactions within composite lattice structures composed of constituents of distinctive thermal expansion coefficients. However, it is difficult to fabricate 3D composite lattices with multiple distinctive components and highly sophisticated geometries. This EArly-concept Grant for Exploratory Research (EAGER) award supports fundamental research on a stereolithography-based multi-material additive manufacturing process that can make 3D particle-reinforced composite lattices with tunable negative thermal-expansions. Research results will benefit a number of applications where thermal stress should be carefully managed, including bridge joints, microchip devices, adhesive fillers, dental fillings, and high precision optical or mechanical devices that experience variable temperatures. In the stereolithography-based multi-material additive manufacturing process, two types of photoresins (with and without particle reinforcement) are procured layer by layer to form two types of photoresin beams alternately. When experiencing rising temperature, the two types of beams with different thermal expansion coefficients interact with each other to induce an overall negative-thermal-expansion of the composite lattice. The first research objective is to establish the relationships between the photocuring depth of the particle-reinforced photoresins and manufacturing parameters (light intensity, photoexposure time, particle type, and particle volume fraction). To achieve this objective, a frontal photopolymerization model will be developed to elucidate the transition from liquid to solid of reinforced-photoresins under ultraviolet radiation. It will be used to predict photocuring depth as a function of manufacturing parameters. Some model predictions will be compared against with photocuring experiments with varied light intensity (5-100 W/m^2), photoexposure time (0.5-300 s), particle type (copper, silica, iron, and alumina), and particle volume fraction (0-10 percent). The second research objective is to understand the effects of lattice geometric parameters (reinforced beam length, angle between reinforced and unreinforced beams) and particle volume fraction on the negative-thermal-expansion of the composite lattices. To achieve this objective, an analytical thermoelastic model will be constructed to describe the thermal-induced geometrical interactions between photoresin beams within the composite lattices. Based on the model, the negative thermal expansion of the composite lattices will be analytically predicted for different values of lattice geometric parameters and particle volume fraction. Thermal expansion experiments on manufactured composite lattices will be conducted in a thermal chamber with temperature control. Reinforced beam length will be varied from 2 to 2.8 mm, beam angle from 60 to 90 degrees, and particle volume fraction from 2 percent to 10 percent. The negative-thermal-expansion of the composite lattices will be measured from image sequences taken by a digital camera during the temperature variation.