The finite element-based approaches to predict compression-after-impact (CAI) performance of carbon fiber reinforced polymer (CFRP) subject to a low-velocity impact rely on assumptions about compressive failure mechanisms within the barely visible impact damage (BVID). Comprehensive evaluations of finite element (FE) models concerning accuracy, efficiency, and validity with respect to experimental tests are limited. This study explores several finite element-based approaches developed in ABAQUS Explicit to predict the residual strength and related compressive failure mechanisms of multidirectional CFRP laminates. Drop-weight impact experiments followed by CAI tests employing 3D Digital Image Correlation (DIC) were used to validate our FE models by comparing strength, failure strain, and out-of-plane displacements. This paper evaluates four FE modeling strategies for simulating CAI behavior. Two FE modelling methods were developed that employ a conventional two-step approach to compute CAI response which includes both impact and subsequent compression loading simulations. One of these models includes a novel distal intralaminar cohesive zone (DICZ) to better simulate backside damage during impact. To reduce computation time, we also considered two additional parametric models that both incorporate a simplified impact damage zone including a circular delaminated interfaces and a through-hole. We found that the parametric model with circular delaminated zone is able to predict the residual strength of similarly impact-damaged composites with better computational efficiency and reasonable accuracy, making it suitable for quick estimations where operational safety is a priority. Our findings present FE modeling guidelines for accurately predicting CAI behaviors of composites to aid in structural design.

This study correlated the thermally induced distortion of large-format additive manufacturing (LFAM) printed composite structures to the alignment of reinforcing fibers. During LFAM material extrusion, shear forces near the nozzle wall align reinforcing fibers in the print direction (x-axis). This produces a complex microstructure comprised of a “shell” of highly aligned fiber near the outer edge of the bead and a “core” of randomly oriented fiber in the center. Given the inherent anisotropy of high aspect ratio reinforcing fiber materials, the orientation of these fibers dictates thermomechanical response of the LFAM part as it is heated to elevated temperatures. Understanding the extent and cause of this distortion is crucial for applications such as autoclave composite tooling such that resulting parts can maintain proper dimensional tolerance. This study characterized the microstructure of LFAM parts using microscopy, method of ellipses, extreme small-angle x-ray scattering (ESAXS), and micro-computed tomography scanning. These results were compared for type, quantity, and cost of data. While microstructural data from each technique agreed overall, ESAXS emerged as a viable option to characterize LFAM microstructure at much lower costs without sacrificing through-thickness measurement. Digital image correlation (DIC) was used to measure thermomechanical response of the LFAM part and correlate the spatial variation of thermomechanical data to varied microstructure. Results showed higher y-direction expansion occurred near bead edges where fiber was highly oriented in the x-direction. Findings from this work can better address the knowledge gap in compensation modeling so that LFAM tooling can maintain correct dimensions during thermal cycling.

In service, barely visible impact damage (BVID) occurring in carbon fiber-reinforced polymer (CFRP) composites may not only occur in a single point, but often occurs in multiple locations. While there has been a strong interest toward multiple BVID occurring in CFRPs, research on the relationship between damage mechanisms due to multiple BVIDs and in-plane mechanical performance of CFRP is limited. This paper provides an experimental study on the multiple impact behavior of quasi-isotropic CFRP laminates and their post-multiple impact performance when subjected to tension-tension fatigue loadings. CFRP laminates were subjected to 6 J impacts at multiple locations oriented as: (1) longitudinal—in line with the loading direction, (2) transverse—perpendicular to the loading direction, (3) oblique—at 45° to the loading direction. The global response for each impact was recorded, and the interaction of damage between two impact points was evaluated using X-ray micro-computed tomography (X-CT) with advanced computational segmentation techniques. Post-impacted CFRP laminates were then subjected to fatigue loadings, and the residual modulus degradation and fatigue damage growth were investigated. Our study demonstrates that CFRP with oblique orientation multiple impacts failed earlier than the other configurations due to the interaction between impact-induced damage between impact-induced oblique cracks and edge delamination.

This study presents a finite element analysis (FEA)-based numerical homogenization method for evaluating the effective thermo-mechanical properties of a large-area additively manufactured particulate-filled composite using realistic periodic representative volume elements (RVEs) generated from reconstructed X-ray µ-CT image scans of a 3D-printed bead. The numerical results of the predicted effective properties, including the elastic stiffness, coefficient of thermal expansion (CTE) and thermal conductivity, were benchmarked with the Mori–Tanaka–Benveniste analytical estimates, which were found to be comparable. Initial sensitivity analysis using a single region of interest (ROI) extracted from the bead’s volume was performed to determine a suitable RVE size. The impact of inherent micro-porosities on the resulting composite material’s behavior was also quantified in the current investigation and was shown to reduce the composite’s effective properties. Using a suitable RVE size, the effect of anisotropy due to spatial variation in the microstructure across the bead specimen on the computed composite’s effective properties was also assessed. The results show that the regions closer to the exposed surface of the print bead with highly aligned and densely packed fiber particulates have superior properties as compared to inner regions with a more randomly oriented and less densely packed fibrous microstructure.

Laminated polymer composites are used extensively in the automotive and aerospace industries due to their high stiffness and strength-to-weight ratios. Although these composites have become a key enabler in engineering design, this material system is prone to developing out-of-plane wrinkles in its internal layers during layup and/or resin curing, which may severely degrade critical material properties, such as elastic modulus and strength. As the fibers within the composite structure take on internal waviness patterns, the distance between layers may change depending on the profile of the wrinkle, which affects local elastic properties due to the resulting spatially varying non-uniform fiber volume fraction. The aim of this work is to investigate how this phenomenon affects the homogenized properties of a wrinkled composite layup. Our approach uses the Rule of Mixtures, Chamis, Halpin-Tsai, Bridging, and Vignoli-Savi-Pacheco-Kalamkarov micromechanics models to estimate laminate orthotropic elastic properties from its constituents via modifications to Takeda's analytical homogenization procedure. The goal is to quantify the change in homogenized elastic properties as the local volume fraction varies due to waviness within a laminated composite panel, ultimately increasing safety and reliability for vehicles and other applications that may employ laminated composites.

The orientation of fibers in short discontinuous fiber reinforced polymer composites is a critical factor in determining final mechanical and thermal properties. Tensor-based models of fiber orientation are common but require difficult-to-obtain model parameters and are limited by assumptions. Direct fiber simulations (DFS) models individually simulate fibers and their interactions with each other and the surrounding fluid. The motion of fibers simulated in DFS is determined by interaction models which require proper calibration to accurately simulate a given fiber material system. An automated generalized method of parameter selection for DFS using surrogate model-based optimization is developed for short fiber polymer composites processing. A DFS model is presented and subjected to the calibration for fibers with a 15.64 aspect ratio at a volume fraction of 8% in simple shear flow. To demonstrate the process, this system is calibrated using Jeffery's Orbit, a theoretical pARD tensor model, and an experimentally obtained orientation distribution function. The calibrated DFS model results are shown to agree well with targeted fiber behavior and provide unique insight into the contact mechanics of fiber interaction. Further, a DFS model calibrated to experimental results is used to obtain orientation tensor model parameters from simple physical experiments and demonstrate enhanced insight available from the data-rich simulations. Results appearing here illustrate the advantages realized through the use of commercially available discrete element software for simulating short fiber composite suspensions.

Fiber orientation is an important descriptor of the microstructure for short fiber polymer composite materials where accurate and efficient prediction of the orientation state is crucial when evaluating the bulk thermo-mechanical response of the material. Macroscopic fiber orientation models employ the moment-tensor form in representing the fiber orientation state, and they all require a closure approximation for the higher-order orientation tensors. In addition, various models have more recently been developed to account for rotary diffusion due to fiber-fiber and fiber-matrix interactions which can now more accurately simulate the experimentally observed slow fiber kinematics in polymer composite processing. It is common to use explicit numerical initial value problem-ordinary differential equation (IVP-ODE) solvers such as the 4th- and 5th-order Dormand Prince Runge–Kutta (RK45) method to predict the transient and steady-state fiber orientation response. Here, we propose a computationally efficient method based on the Newton-Raphson (NR) iterative technique for determining steady state orientation tensor values by evaluating exact derivatives of the moment-tensor evolution equation with respect to the independent components of the orientation tensor. We consider various existing macroscopic-fiber orientation models and several closure approximations to ensure the robustness and reliability of the method. The performance and stability of the approach for obtaining physical solutions in various homogeneous flow fields is demonstrated through several examples. Validation of our orientation tensor exact derivatives is performed by benchmarking with results of finite difference techniques. Overall, our results show that the proposed NR method accurately predicts the steady state orientation for all tensor models, closure approximations and flow types considered in this paper and was relatively faster compared to the RK45 method. The NR convergence and stability behavior was seen to be sensitive to the initial orientation tensor guess value, the fiber orientation tensor model type and complexity, the flow type and extension to shear rate ratio.

Multidirectional laminated composites are essential for load-bearing structures, especially under frequent impact loading. While existing modeling techniques simulate various impact damage modes, our understanding of the underlying mechanisms, specifically the initiation and progression of intralaminar distal cracks and interlaminar delamination, needs improvement. Validating these mechanisms is crucial for enhancing modeling accuracy and expediting the design process. In this work, we propose a three-dimensional finite element modeling (3D FEM) approach aimed at elucidating the impact damage mechanisms in multidirectional carbon fiber reinforced polymer (CFRP). Our model incorporates cohesive zone models (CZM) to simulate the behavior of intralaminar cracks at distal points and assess their impact on interlaminar delamination at ply interfaces. Using high-resolution pulse-echo ultrasonic testing (UT) and an advanced algorithm, we provide a detailed layer-by-layer quantification of impact damage. Our modeling strategy effectively predicts both intralaminar and interlaminar damage modes across various laminate configurations and thicknesses, yielding results that align with experimental data. The strategy can be a significant step forward in understanding the low-velocity impact damage in composite laminates. By enabling visualization of through-thickness damage, the strategy may enhance the safety and efficiency of composite structures.

Large-Area Additive Manufacturing (LAAM) has seen increased application in manufacturing meter-scale, polymeric composite structural parts, especially for tooling and fixturing. Unfortunately, LAAM introduces manufacturing-induced defects in printed composites, e.g., intrabead microvoids and poor interbead adhesion that are not otherwise seen when traditional manufacturing methods are used, causing degradation of mechanical and fracture properties. In this paper, the fracture behavior of neat acrylonitrile butadiene styrene (ABS) and short carbon fiber-reinforced ABS (CF/ABS) fabricated by LAAM is compared and analyzed by evaluating their energy release rate GIc and fracture mechanisms. A double cantilever beam with doublers (DCB-D) test for single-bead, double-bead, and multiple-bead configurations is developed by incorporating rigid doublers to reduce the compressive failure at the crack tip, allowing for the measurement of crack propagation. A new data reduction method for these configurations is derived to remove the doubler effect from the GIc calculation, producing 'pure' intrabead and interbead GIc values. We show that CF/ABS is more damage tolerant than ABS at the intrabead level, but less damage tolerant than ABS at the interbead level. The development of plastic ligaments in ABS helps dissipate additional strain energy, improving the overall energy release rate. The experimental fracture test approach developed here is expected to provide mechanistic insight into their damage tolerance capability, accelerating the qualification process of LAAM-produced polymer and polymer composites.

Fiber orientation is an important descriptor of the microstructure for short fiber polymer composite materials where accurate and efficient prediction of the orientation state is crucial when evaluating the bulk thermo-mechanical response of the material. Recent macroscopic fiber orientation models have employed the moment-tensor form in representing the fiber orientation state which all require a closure approximation for the higher order orientation tensors. In addition, various models have been developed to account for rotary diffusion due to fiber-fiber and fiber-matrix interactions which can now more accurately simulate the experimentally observed slow fiber kinematics in polymer composite processing. Traditionally explicit numerical IVP-ODE transient solvers like the 4th order Runge-Kutta method have been used to predict the steady-state fiber orientation state. Here we propose a computationally efficient method based on the Newton-Raphson iterative technique for determining steady state orientation tensor values by evaluating the exact derivatives of the moment-tensor evolution equation with respect to the independent components of the orientation tensor. We consider various existing macroscopic fiber orientation models and several closure ap-proximations to ensure the robustness and reliability of the method. The performance and stability of the approach for obtaining physical solutions in various homogeneous flow fields is demonstrated through several examples. Validation of the obtained exact derivatives of the orientation tensor is performed by benchmarking with results of finite difference techniques

The presence of voids within the microstructure of short carbon fiber polymer composites produced by additive manufacturing (AM) technology are known to alter the expected material behavior that impair part performance. Previous research efforts aimed at understanding the formation mechanisms of these micro-voids during the polymer extrusion/deposition process have not kept up with the advancement of this AM technology. The present study investigates the phenomenon of micro-void nucleation at the fiber/matrix interface, especially those that form at fiber tips, by characterizing the microstructural configuration of a 13% carbon fiber filled ABS polymer composite print bead specimen using 3D X-ray micro computed tomography image acquisition and analysis. The results reveal a high level of micro-voids segregation at the ends of fibers that are relatively larger in size and less spherical as compared to micro-voids isolated within the ABS matrix. Additionally, by simulating the hydrostatic flow-field pressure distribution surrounding a single rigid ellipsoidal fibre in colloidal suspension using Jeffery's model equations, we show that the pressure drops to a critical value at the fibre tips where the micro-voids nucleation is experimentally observed to occur. The study helps to improve our understanding of the potential mechanisms that may be responsible for micro-void development within beads printed with extrusion/ deposition AM.

Short carbon fiber-reinforced polymer composites are widely used in polymer extrusion additive manufacturing (AM), including large-area additive manufacturing (LAAM), due to their enhanced mechanical properties as compared to neat polymers. However, the mechanical properties of these composites depend on microstructural characteristics, including fibers and micro-voids, which are determined during processing. In this work, the correlation between fibers and micro-voids within the microstructure of LAAM polymer composites throughout various processing stages of short carbon fiber-reinforced acrylonitrile butadiene styrene (SCF/ABS) is investigated. The processing stages considered here include the incoming pellets, a single freely extruded strand, a single regularly deposited bead, and a single regularly deposited bead pressed by a mechanical roller. A high-resolution X-ray micro-computed tomography (µCT) system is employed to characterize the microstructural features in terms of the fibers (volume fraction, fiber orientation tensor) and micro-voids (volume fraction, sphericity) in the SCF/ABS samples. The results indicate that micro-voids exist within the microstructure of the SCF/ABS composite in all four stages considered here and that the micro-void volume fraction and micro-void sphericity vary among the test samples. Moreover, the results show a considerable variation in fiber orientation and fiber volume fraction within the microstructure throughout all the stages considered; however, all the samples show the highest alignment in the extrusion/print direction. Furthermore, a correlation is identified between the fiber orientation and the micro-void volume fraction within samples from all four stages considered here. This finding suggests that fibers tend to align more in the extrusion/print direction in regions with less micro-void content.

This article presents the uncertainty of the part performance due to the estimated ply orientations of a carbon fiber laminate inspected using ultrasound inspection. Recent developments to quantify the orientation using ultrasound inspection is accurate to within +/- 2 degrees$$ \pm {2}<^>{{}<^>{\circ}} $$ for each lamina. The research presented in the current work statistically analyzes the impact this uncertainty in measurement has on the resulting expected failure envelope using two different analytical methods: (1) Monte-Carlo (MC) simulation approach extending classical laminate theory and (2) Closed form approach of Mean Value First Order Second Moment method based on derivatives of failure envelope as a function of lamina orientation. The results are validated against a commercial finite element-based MC simulation approach. The Tsai-Wu failure criteria is implemented to determine the first ply failure stresses by applying a variety of planer loads to form the failure envelope for a given layup sequence of a carbon fiber reinforced polymer laminate. In this article, using stochastic simulations, the failure envelope is no longer deterministic but is stochastic in nature and converts the reporting from a deterministic factor of safety concept to a probability of failure for a given loading state. The analysis is visualized and quantified using the cumulative-density-function (CDF), which demonstrates the similarity between the stochastic results and the classical deterministic approach. To demonstrate a possible end use of the presented statistical analysis, a study of a woven composite laminate is presented where the ply orientation is estimated using ultrasound and the resulting CDF of failure is presented.HighlightsStatistical analysis (Monte-Carlo, mean value, first order, second moment) on the ply orientation variability via ultrasound inspection.Statistical analysis of classical laminate theory and FE based Tsai-Wu failure model is developed and compared.Tsai-Wu failure envelope is quantified and visualized using cumulative density function. Using statistical analysis from the characterized ply stack orientation using an ultrasonic inspection, the uncertainty of the as manufactured failure envelope can be generated.image

Material extrusion (MEX) additive manufacturing has successfully fabricated assembly-free structures composed of different materials processed in the same manufacturing cycle. Materials with different mechanical properties can be employed for the fabrication of bio-inspired structures (i.e., stiff materials connected to soft materials), which are appealing for many fields, such as bio-medical and soft robotics. In the present paper, process parameters and 3D printing strategies are presented to improve the interfacial adhesion between carbon fiber-reinforced nylon (CFPA) and thermoplastic polyurethane (TPU), which are extruded in the same manufacturing cycle using a multi-material MEX setup. To achieve our goal, a double cantilever beam (DCB) test was used to evaluate the mode I fracture toughness. The results show that the application of a heating gun (assembled near the nozzle) provides a statistically significant increase in mean fracture toughness energy from 12.3 kJ/m2 to 33.4 kJ/m2. The underlying mechanism driving this finding was further investigated by quantifying porosity at the multi-material interface using an X-ray computed tomography (CT) system, in addition to quantifying thermal history. The results show that using both bead ironing and the hot air gun during the printing process leads to a reduction of 24% in the average void volume fraction. The findings from the DCB test and X-ray CT analysis agree well with the polymer healing theory, in which an increased thermal history led to an increased fracture toughness at the multi-material interface. Moreover, this study considers the thermal history of each printed layer to correlate the measured debonding energy with results obtained using the reptation theory.

The process-structure-property relationship in Large Area Additive Manufacturing (LAAM) technology is an ongoing area of research as the inherent microstructural properties (chiefly fibers and voids) affect the performance of printed parts. Unfortunately, we currently lack adequate understanding of micro void nucleation and evolution during the LAAM and fused deposition modelling (FDM) processes. Modeling of the polymer melt flow during the extrusion process is important in understanding the underlying microstructural formation and associated properties of the print, that determines the part performance in service conditions. In this paper we compute fiber-induced local pressure fluctuations which may promote void formation in the bead’s microstructure. On a macro-scale, we determine flow fields of a purely viscous, Newtonian planar polymer deposition flow through a LAAM nozzle which are utilized on a micro-scale model where we simulate the evolution of a single ellipsoidal fiber along streamlines obtained from the macro-model. On the micro-scale, we determine instantaneous values of the translational and rotational velocities of the rigid ellipsoidal fiber that satisfies a balance of hydrodynamic forces and couples on the fiber’s surface based on a Newton Raphson algorithm and we track the fiber’s motion along the flow path via an explicit numerical iterative algorithm. Model verification is achieved by benchmarking results with solutions from well-known Jeffery’s equation of motion of a particle in homogeneous simple shear flow. We account for rotary diffusivity due to short-range fiber-fiber interaction in the FEA simulation by determining an effective fluid domain size representative of the interaction coefficient of the melt flow through a correlation analysis that yields an equivalent steady state orientation based on the Advani-Tucker equation. We also consider different possible motions of the fiber along individual LAAM flow paths from a given set of random initial fiber conditions to determine pressure bounds on the fiber surface along each streamline. For improved computational efficiency, calculations are carried out with respect to the fiber’s local coordinate axes to overcome the rigor of adaptive remeshing during the quasi-transient analysis. Results show low pressure extremes near the fiber’s surface which varies across the printed bead as well as through its thickness. Discussion is provided to gain insight into the effect of low-pressure extremes on micro void formation, particularly at the nozzle exit and during die swell/expansion.

Fusion-based Material Extrusion (MEX) Additive Manufacturing (AM) processes have been extensively used for the fabrication of smart structures with embedded sensors, proving to have several benefits such as reduction in cost, manufacturing time, and assembly. A major issue negatively affecting 3D printed sensors is related to their poor electrical conductivity, as well as inconsistent electrical performance, which leads to electrical power losses amongst other issues. In the present paper, a set of process parameters (ironing, printing temperature, and infill overlap) has been analyzed by performing a Design of Experiment (DoE) factorial plan to minimize the electrical resistance. The best process parameters configuration involves a remarkable reduction of electrical resistance of 47.9%, as well as an improvement of mechanical properties of 31.9% (ultimate tensile strength), 25.8% (elongation at break) and 28.14% (flexural stress). The microstructure of the obtained results has also been analyzed by employing a high-resolution, X-ray Computed Tomography (X-Ray CT) system showing a reduction of intralayer voids of 19.5%. This work demonstrates a clear correlation between process parameters and the corresponding electrical properties, mechanical properties, and internal microstructure. In the present research, it has been shown that i) it is possible to significantly improve the overall 3D printed sensors performance by process parameter selection, and ii) small changes in the microstructure lead to remarkable improvements in electrical and mechanical performance.

The flow-induced fibre orientation formed during polymer extrusions causes the composite to exhibit non-homogeneous thermal-mechanical behaviours during Large Area extrusion-deposition Additive Manufacturing (LAAM) processes. This study numerically evaluates the fibre orientation state of a 20 wt.% short carbon fibre reinforced polyethylenimine fabricated by LAAM. The fibre orientation state of the solidified deposited bead is determined by a fully coupled flow/orientation simulation approach. The material properties of deposited composites are computed by assuming that the deposited bead has heterogeneous regions with varying local fibre orientation states. A finite element simulation is performed to model the LAAM process of a thin-wall structure, where the predicted inhomogeneous material properties are employed. Computed results show notable differences between simulations performed by employing homogenous properties and those obtained using heterogeneous properties. The bead-direction tensile stress contours computed under the heterogeneous assumption are comparable to experimental data in the literature, supporting our numerical approach.

Short fiber polymer composites are used in extrusion-deposition Large Area Additive Manufacturing (LAAM) to improve mechanical and thermal properties of printed parts. Unfortunately, the presence of fibers produces micro-voids within bead fiber suspension microstructure during processing which is not well understood. This paper investigates low pressure extremes on the surface of fibers suspended in the melt flow that may promote micro-void formation within the bead microstructure using a multiscale computational approach. A macro-scale model is used to calculate the flow field of a purely viscous Newtonian planar polymer deposition flow through a LAAM nozzle. Then a micro-model simulates fiber kinematics and the evolution of its surface pressure as it travels along streamlines via a custom single fiber finite element analysis which accounts for near field fiber-fiber interactions in the simulation. Minimum pressure extremes that appear just outside the nozzle provide new insight into potential micro-void formation within LAAM printed beads.

The structural integrity of adhesive joints used in the attachment of laminated composite panels has received considerable attention over the past few decades. Of particular concern and the topic of this paper is the effect that a nonuniform bond line thickness has on the load carrying capacity of a bonded joint. To this end, carbon fiber adherends were joined in a single lap joint configuration using a two-part epoxy adhesive. The joints were initially fabricated and tested with various uniform bond line thickness in a single lap joint configuration to establish a benchmark. Bonded single lap joints with linearly varying bond line thickness were then investigated. A finite element study was performed to predict bond strength of the uniform and linearly varying bond lines using the Critical Zone method. The failure strength of the uniform bond line thickness specimens was found to decrease with an increase in the bond line thickness. In the case of linearly varying bond line thickness specimens, the bond strength decreased as the bond thickness at one end of the bonded joint overlap deviated from its intended value. The finite element model using the Critical Zone method was able to predict the failure strength of the joints in both uniform and linearly varying bond thickness configurations. The reduction in failure strength was attributed to an increase in the stresses in the adherend ply adjacent to the bond line as determined through the finite element stress analysis.

Short carbon fiber-reinforced composite materials produced by large-area additive manufacturing (LAAM) are attractive due to their lightweight, favorable mechanical properties, multifunctional applications, and low manufacturing costs. However, the physical and mechanical properties of short carbon-fiber-reinforced composites 3D printed via LAAM systems remain below expectations due in part to the void formation within the bead microstructure. This study aimed to assess void characteristics including volume fraction and sphericity within the microstructure of 13 wt% short carbon fiber acrylonitrile butadiene styrene (SCF/ABS). Our study evaluated SCF/ABS as a pellet, a single freely extruded strand, a regularly deposited single bead, and a single bead manufactured with a roller during the printing process using a high-resolution 3D micro-computed tomography (µCT) system. Micro voids were shown to exist within the microstructure of the SCF/ABS pellet and tended to become more prevalent in a single freely extruded strand which showed the highest void volume fraction among all the samples studied. Results also showed that deposition on the print bed reduced the void volume fraction and applying a roller during the printing process caused a further reduction in the void volume fraction. This study also reports the void’s shape within the microstructure in terms of sphericity which indicated that SCF/ABS single freely extruded strands had the highest mean void sphericity (voids tend to be more spherical). Moreover, this study evaluated the effect of printing process parameters, including nozzle temperature, extrusion speed and nozzle height above the printing table on the void volume fraction and sphericity within the microstructure of regularly deposited single beads.