Structure and mechanical behavior of Big Area Additive Manufacturing (BAAM) materials

Abstract

Purpose This paper aims to investigate the deposited structure and mechanical performance of printed materials obtained during initial development of the Big Area Additive Manufacturing (BAAM) system at Oak Ridge National Laboratory. Issues unique to large-scale polymer deposition are identified and presented to reduce the learning curve for the development of similar systems. Design/methodology/approach Although the BAAM’s individual extruded bead is 10-20× larger (∼9 mm) than the typical small-scale systems, the overall characteristics of the deposited material are very similar. This study relates the structure of BAAM materials to the material composition, deposition parameters and resulting mechanical performance. Findings Materials investigated during initial trials are suitable for stiffness-limited applications. The strength of printed materials can be significantly reduced by voids and imperfect fusion between layers. Deposited material was found to have voids between adjacent beads and micro-porosity within a given bead. Failure generally occurs at interfaces between adjacent beads and successive layers, indicating imperfect contact area and polymer fusion. Practical implications The incorporation of second-phase reinforcement in printed materials can significantly improve stiffness but can result in notable anisotropy that needs to be accounted for in the design of BAAM-printed structures. Originality/value This initial evaluation of BAAM-deposited structures and mechanical performance will guide the current research effort for improving interlaminar strength and process control.

Prediction of the Fiber Orientation State and the Resulting Structural and Thermal Properties of Fiber Reinforced Additive Manufactured Composites Fabricated Using the Big Area Additive Manufacturing Process

“…In mathematical terms, this can be expressed as E 1 = σ 11 /(u 1 /w o ), where E 1 is the bulk, effective, longitudinal Young's modulus, σ 11 is the reaction stress on the left side of the sample, u 1 is the average displacement of the entire left side of the sample in the x 1 direction, and w o is the original x 1 dimension of the sample. Solving this equation yields a Young's modulus at the end of the bead of E 1 = 6.82 GPa for the IRD model with C I = 10 −2 , not too dissimilar from those results provided in Duty et al [3] for a similar system. A similar procedure can be done using the stiffness tensor values at the nozzle exit and this yields a Young's modulus of E 2 = 7.10 GPa at the nozzle exit for the IRD model with C I = 10 −2 .…”

“…The Young's modulus, CTE, Poisson's ratio, and density of the carbon fiber were taken to be 230 GPa, −2.6 × 10 −6 (mm/mm)/ • C, 0.2, and 1700 kg/m 3 , respectively. The weight fraction was taken to be 13% to match that of the composite system studied in Duty et al [3] for a carbon fiber reinforced FFF bead with similar bead deposition geometry to that considered here. The shape of the fiber was taken into account using a geometric aspect ratio of 20, within the range of the carbon fiber reinforcement in [3].…”

“…This work seeks to quantify the intra-layer structural and thermal performance of the deposited bead. The inter-layer performance is another significant consideration, and there are a variety of authors who have presented methods to improve the inter-layer bonding strength such as tamping (see e.g., [2,3]), infrared preheating (see e.g., [4]), and plasma treating (see e.g., [5]). …”

Rheology Effects on Predicted Fiber Orientation and Elastic Properties in Large Scale Polymer Composite Additive Manufacturing

“…Our material stiffness predictions agree remarkably well with test data appearing in the literature. Duty et al [4] measured the Young's modulus of a 13 per cent carbon fiber reinforced ABS printed bead, reporting a mean value of 7.24 GPa and standard deviation of 0.59 GPa. Our predictions of the elastic modulus for the same material system shown as E 22 in Table 4 are in good agreement with these previously published experimental results.…”

“…To achieve a relatively high dimensional accuracy and superior mechanical performances in large-scale parts, carbon fiber filled polymers are employed. Duty et al show that adding short carbon fibers into the neat Acrylonitrile Butadiene Styrene (ABS) polymer yields a composite with improved elastic properties, especially along the printing direction, and less distortion in the printed part following the bead deposition process of the BAAM system [3,4].…”