Interfacial Characterization of Metal Wire Inlays for 3D Printed FDM Parts 15 is no standard available for determining the maximum pressure limit for this type of specimen. Therefore, to obtain the pressure at which the leakage happens for different geometries, specimens were fabricated and tested using polycarbonate as the polymer, and copper wires as the metal fibers. Specimen Fabrication: To fabricate specimens, an off-the-shelf polymer 3D printer was customized to embed metal fibers over the polymer layers with a proprietary metal fiber print head, shown in Figure 3. To facilitate the visualization of the metal wire/polymer matrix failure (i.e. leakage), clear polycarbonate was chosen as the polymer and copper as the metal. The coupons as printer were found to be leaking near the metal-polymer interface. To avoid this leakage, the composite was dip-coated in a commercially procured 3d print sealer, an epoxy-hardener mixture, and cured in an oven at 50 ◦C for 24 hours. A post-curing regimen was followed where the cured coupons were kept in an oven at 90◦C for 2 hours and allowed to cool in the oven slowly to minimize residual stresses. Fig. 3 (left) A 3D FDM printer customized at UMD for metal wire inlay using (right) a proprietary metal fiber print head. Two different types of cross-media coupons were tested for failure. All coupons had the same geometrical parameters except for wall thickness. The vertical and horizontal pitches were maintained the same in all coupons. The geometrical parameters of the cross-media coupons are mentioned in Table 1. Table 1 Geometrical parameters of the cross-media coupons All coupons after the post-curing were tested for leakage at 50 PSI using a bubble test. Only the coupons that passed the bubble test were used for failure characterization. For failure characterization, a pressure decay method was used. The schematic of the experimental setup is shown in Figure 4. To pressurize the coupon, an Additel 925 hydraulic pressure test pump was used. Once the unit under test (UUT) reaches the required pressure, the needle valve is closed to shutoff the UUT from the pump and allow for pressure decay. To record the pressure in the coupon a pressure gauge is connected between the valve and the UUT. A DAQ was connected to the pressure gauge to collect the pressure data every second to monitor the pressure decay.
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