Search

Material extrusion (MEX) is a popular additive manufacturing (AM) method that can process a wide range of feedstock materials, most commonly in filament form. Currently, there is no standardized testing method for filament tensile properties, and researchers resort to 3D-printed dog-bone specimens, which necessarily include the effects of the printing process. In this study, the impact of the strain measurement device, knife-edge type, gage length, testing speed, and oven treatment on filament tensile properties was explored using an off-the-shelf fixture. It was observed that an extensometer with blunt knife edges, a filament gage length of 165 mm, and a 6.35 mm/min (0.25 in./min) testing speed could accurately evaluate the tensile properties of acrylonitrile butadiene styrene (ABS) filaments. In addition, an optimized raster path, 3D printing design, and process parameters were used to manufacture dog bone tensile specimens according to ASTM D638-22 from the same ABS filament spool. The tensile properties of the filaments were validated using the results of 3D-printed dog-bone specimens. Young's modulus, stress at yield, and stress at break for the optimum filament test set (2.20 GPa, 43.9 MPa, and 39.1 MPa) were very similar to those of the 3D-printed specimens (2.26 GPa, 44.9 MPa, and 37.3 MPa). The optimum filament tensile testing parameters determined in this study for ABS can be used for the initial test setup for other filament materials to provide baseline values that can serve as the foundation for AM process development.

Fused filament fabrication (FFF) 3D printing was used to fabricate continuous wire polymer composite (CWPC) heat flux sensors; the integrated wires acted as resistive sensing elements. Sensor configurations consisting of polylactic acid (PLA) with copper wire (Cu), PLA with nickel (Ni) wire, and thermoplastic polyurethane (TPU) with Cu wire were investigated. For each composition, samples with different numbers of layers were 3D printed to investigate the effect of sensor thickness on performance. Element spacing, polymer conductivity, and wire temperature coefficient of resistances were quantified. Performance testing of the 3D-printed CWPC as a heat flux sensor showed promising results for all compositions and demonstrated their ability to be used as heat flux sensors for low temperature and low heat flux applications. Measurement errors were less than 17% for all configurations and less than 10% for 2-layer samples at the higher heat fluxes. A case study demonstrated the use of a 3D-printed flexible CWPC heat flux sensor to estimate heat loss from an insulated system with good accuracy. This sensor fabrication approach can potentially be employed in a wide range of applications because it allows for custom geometries and can use different types of polymers and sensing elements.

3D printing, especially fused filament fabrication, presents a potentially attractive manufacturing technique for thermal applications such as polymer heat exchangers due to the ability to create complex internal geometries which can be used to enhance convective heat transfer. Recently, commercial and modified open-source printers have utilized continuous fibers such as carbon fiber to create continuous fiber reinforced polymer composites (FRPCs) which enhance the mechanical properties of the printed products. This continuous filler network can also serve to improve thermal conductivity. In this study, the effective thermal conductivity of 3D-printed FRPCs is characterized using a steady-state, modified, guarded hot plate apparatus. The effect of the fiber direction and volume fraction on the effective thermal conductivity of the 3D-printed composites was characterized experimentally and modeled analytically using series and parallel models. Thermal conductivities of up to 2.97 W/mK were measured for samples in which the fibers were aligned with the direction of heat flow. Measured values were in good agreement with analytical model predictions. The importance of fiber conductivity on overall performance of the FRPCs was further demonstrated using a handlaid-up, pitch-based carbon fiber sample which exhibited an effective thermal conductivity of 23.6 W/mK.

Braided composites consist of yarns that are interwoven to produce a braided structure. Braided composites can be manufactured in a number of different configurations including: Diamond (1/1), Regular (2/2) and Hercules (3/3) braiding patterns. Braid patterns are classified by the number of yarns which pass over and under each other. Currently, few software tools are available for the design and manufacture of braided composites. Additionally, mathematical models that exist for braided composites require specialized knowledge. The goal of Braid CAM is to provide an easy to use tool for the design and manufacture of braided composites. Availability of programs like Braid CAM will help to increase the implementation of braided composites for engineering design applications. Keywords: Braided composites, Analytical model, Elastic properties, Composite materials

Material extrusion additive manufacturing (MEAM), a sub-branch of three-dimensional (3D) printing is growing in popularity. Test specimens were 3D-printed using commercial polylactic acid (PLA) filament, and PLA filament reinforced with short-carbon fibers (PLA/CF). As-printed specimens and specimens that were annealed at three different temperatures, then subjected to tensile testing. The internal microstructures of the samples were also examined. The effects of the short-carbon fiber fillers on the mechanical properties of 3D-printed PLA were investigated, and the effects of the annealing process on polymer crystallinity and mechanical properties. The annealing process was shown to increase the crystallinity of both sample groups, though no statistically significant effect of annealing on mechanical properties was observed. The tensile properties of the PLA and PLA/CF filaments showed that the addition of carbon fibers to the PLA filament led to a significant increase in elastic modulus of the MEAM samples.

This study presents the electromechanical properties of three-dimensional (3D) printed unidirectional continuous wire polymer composite (CWPC) to study the correlation of the elastic mechanical deformation and the electrical resistance under uniaxial loading conditions. Two kinds of wires were used for this study: copper (Cu) and nichrome (NiCr). 3D printing was utilized due to its flexibility in design and structure for different applications. From mechanical testing, the NiCr CWPCs demonstrated an increase of 13.5% and 54% in ultimate tensile strength and Young’s modulus, respectively, compared to pure 3D printed Poly(lactic acid) while the Cu CWPC did not exhibit significant improvement in the mechanical properties. A direct linear relationship was observed between the applied tensile strain and the measured electrical resistance for both Cu and NiCr CWPCs indicating the ability of these 3D printed structures to be used as a sensor to measure stress/strain in the real time. In addition, the sensitivity of both composites in terms of gauge factor, representing the relative change in the electrical resistance with the tensile strain of the material, were found to be 1.17 ± 0.06 and 1.13 ± 0.07 for Cu and NiCr CWPCs, respectively. This sensitivity was compared with a simple analytical model and showed a good agreement with the experimental results. Finally, the reliability of these CWPCs was evaluated by conducting a cyclic loading test within their elastic ranges. The results of this work will enable the manufacture of integrated sensors within 3D printed components with improved mechanical properties and increased functionality. [ABSTRACT FROM AUTHOR]

The effect of short fiber reinforcements on the mechanical properties of cement has been examined using a splitting tensile - digital image correlation (DIC) measurement method. Three short fiber reinforcement materials have been used in this study: fiberglass, nylon, and polypropylene. The method outlined provides a simple experimental setup that can be used to evaluate the ultimate tensile strength of brittle materials as well as measure the full field strain across the surface of the splitting tensile test cylindrical specimen. Since the DIC measurement technique is a contact free measurement this method can be used to assess sample failure.